This research was supported in part by an NSF EPSCoR Research Infrastructure grant to Clemson University (1632881). In addition, this research was supported in part by the Civitan International Research Center, Birmingham, AL. The authors gratefully acknowledge the use of the services and facilities of the University of Alabama at Birmingham Small Animal Imaging Shared Facility Grant [NIH P30 CA013148]. The authors acknowledge Rajiv Chopra for his support and guidance.

All experimental procedures were done in accordance with UAB Institutional Animal Care and Use Committee (IACUC) guidelines.
1. Focused ultrasound driving equipment setup
<ol>
	<li>Use 50 Ohm coaxial BNC cables to connect (1) the input of the ultrasound transducer to the output of the RF amplifier and (2) the input of the RF amplifier to the output of the function generator.</li>
	<li>Set the function generator mode to a sinusoid burst once per second with a 1% duty cycle.
	<ol>
		<li>For the damped 1 MHz low-power immersion transducer with a 0.8 inch focal distance used with a 50 dB RF amplifier, set the starting settings to: 1 MHz sine wave, 1 V peak to peak, 10k cycle, 1 s interval (or period).</li>
		<li>For the air backed, 1.1 MHz high-power transducer, set the initial settings to: 1.1 MHz sine wave, 50 mV peak to peak, 11k cycles, 1 s interval. 
		&#8203;NOTE: Do not operate the transducers unless they are submerged. Do not place a hand or other body part at the ultrasound focus or touch the transducer face while it is operating.</li>
	</ol>
	</li>
</ol>
2. Focused ultrasound benchtop setup
<ol>
	<li>3D-print the stereotaxic frame and the stereotactic frame holder.</li>
	<li>Connect the transducer to the XYZ positioner using a clamp holding a PVC pipe (Figure 1a). Bolt the clamp onto the X-axis slide and lock with a wing nut.
	<ol>
		<li>If using the high-power ultrasound transducer, attach it to the PVC pipe using a matched pair of magnets. Ensure that one magnet has a hole and the other has a matching protrusion. Cap the bottom of the PVC pipe and attach one of the magnets to it using epoxy (see Figure 1b).</li>
		<li>Attach the second magnet to the top center of the high-power ultrasound transducer using epoxy. Make sure it is at the very center of the transducer (Figure 1c).</li>
	</ol>
	</li>
	<li>If using the high-power ultrasound transducer, make a pointer for nulling the XYZ positioner. The tip of this pointer indicates the location in space of the center of the transducer focus when the ultrasound transducer is attached to the XYZ positioner. Make a pointer out of an 18 G needle cut to be the length of the focal distance of the transducer plus the thickness of the transducer (Figure 1d).
	<ol>
		<li>Apply epoxy to a third magnet (this magnet also pairs with the PVC cap magnet) and attach it to the top of the pointer. The pointer will then be able to attach to the magnet on the PVC pipe for XYZ nulling (Figure 1d).</li>
	</ol>
	</li>
	<li>If using the low-power immersion transducer, 3D-print the file for the pointer and the mounting clip.
	<ol>
		<li>Attach the low-power immersion transducer to the PVC pipe by clipping the mounting clip onto to the PVC pipe and insert the transducer into the ring (Figure 1f).</li>
	</ol>
	</li>
	<li>Make a water bath by gluing together pieces cut from acrylic sheet that will be able to rest on top of the animal&#8217;s head above the stereotactic frame (Figure 1e).
	<ol>
		<li>Cut an opening in the bottom of the bath that is about the size of the animal&#8217;s head. Cover the hole in the water bath with a polyimide tape. 
		NOTE: Care must be taken to ensure that water does not leak around the polyimide tape as it can wet the rat&#8217;s fur and cause hypothermia.</li>
	</ol>
	</li>
	<li>Make an MRI fiducial by filling a 4 mm diameter thin-shelled plastic or glass sphere with an MRI visible fluid (e.g., Vitamin E oil) and seal it. Place it in the MRI fiducial holder on the right side of the 3D-printed stereotaxic frame (Figure 2a).</li>
	<li>Firmly secure the 3D-printed frame holder to the XYZ positioner at a good location for animal positioning. Slide the tab on the rostral end of the frame holder into the matching channel on the Y-axis rail and securing with set screws (Figure 1h, red arrows).</li>
	<li>For driving the XYZ positioner, install the USB to serial converter onto a computer by following the manufacturer&#8217;s directions and plug in the converter. Install the runtime environment and motor controller software onto the PC.
	<ol>
		<li>Ensure that the proper serial port is selected in the software by selecting the USB to serial converter in the port selection dropdown control on the front panel of the controller software. Connect the USB to serial converter to the stepper motor controller box using a 9-pin serial crossover cable (e.g., RS232 null modem cable).</li>
		<li>Run the controller software to test that the stepper motors can be driven under software control. This step may require the assistance of local IT support.</li>
	</ol>
	</li>
</ol>
3. Intracranial targeting procedure
NOTE: Male Sprague Dawley rats weighing 250-350 g were used for these experiments. Animals had free access to water and rat chow, and were maintained on a 12:12 h light:dark cycle.
<ol>
	<li>Put the animal under anesthesia (3% isoflurane with oxygen) and check for the lack of response to the toe pinch. Then insert the catheter as described below.
	<ol>
		<li>Warm the tail with a lamp to make is easier to hit the vein. Be careful not to overheat the animal or to burn the tail.</li>
		<li>Once the animal is asleep (does not respond to a toe pinch), insert the 24 G tail vein catheter that will be used to deliver microbubbles, Evans blue dye (EBD), gadobutrol MRI contrast if using MRI, and the experimental agent of interest. Once the vein is hit, blood will fill the sheath, slowly remove the inner needle while pushing the sheath further into the vein. 
		NOTE: See a guide like Stuart and Schroeder33 if doing the rat tail vein injections for the first time.</li>
		<li>If there is no blood flow, slowly move the catheter sheath out of the vein to test that the needle may have poked through the vein. If blood flows when the catheter is pulled back slightly, then first poke went through the vein and the catheter placement will need to be restarted at another location on the tail that is rostral to the previous location.</li>
	</ol>
	</li>
	<li>Fill the catheter plug with saline and screw the catheter plug into the end of the catheter port as soon as the port has filled with blood. Carefully wrap the lab tape around the catheter and the tail to keep it in place. Start with a small piece at the top and work in the caudal direction, leaving the very end of the catheter plug exposed.</li>
	<li>Plug the anesthesia line onto the anesthesia connector on the stereotaxic frame (Figure 2a) and fix the animals head into the frame by placing the mouth onto the bite bar and by guiding the ear bars into both ear canals, then tighten the set screws. Make sure the animals head is secure and level.</li>
	<li>Move the animal into the MRI bed and connect the anesthesia line to the nose cone. In this protocol a 9.4 T small bore animal MRI was used.</li>
	<li>Collect coronal and axial T2-weighted images that capture the whole brain as well as the MRI fiducial (Figure 2b) for coordinate measurements. Provide the local MRI physicist or tech the following information so that they can build the MRI protocol.
	<ol>
		<li>For coronal images (Figure 2b top), use the following parameters: number of images: 27, width: 62.2 mm, height: 62.2 mm, depth: 37.97 mm, Voxel size: 0.24 x 0.24 x 1.41 mm3.</li>
		<li>For axial images (Figure 2b bottom), use the following parameters: number of images: 13, Width: 61.47 mm, Height: 53.81 mm, Depth: 16.7 mm, Voxel size: 0.41 x 0.21 x 1.29 mm3. 
		NOTE: It is not necessary to have these exact parameters as long as the coronal in plane resolution is close to 0.25 mm and the images cover the whole brain and fiducial.</li>
	</ol>
	</li>
	<li>Collect coordinate measurements from the above images by recording the distance from the MRI fiducial to the brain region that will be targeted with FUS.
	<ol>
		<li>At the scanner, on the coronal images collected in step 3.5, find the image in which the fiducial is the largest, indicating the center of the fiducial. Record the distance from the top of the fiducial to the brain region of interest in mm (the MRI software will have a scale or point measurement tool, consult local MRI tech or physicist on how to do this) in both the medial/lateral direction and in the dorsal ventral direction (Figure 2b, top).</li>
		<li>At the scanner, on the axial images collected in step 3.5, find the image that shows the very top of the fiducial and measure the distance from the center of the fiducial to the target brain region in both the dorsal/ventral direction and in the medial/lateral direction (Figure 2b, bottom).</li>
		<li>Compare the two medial/lateral measurements and if they are different use the average. These coordinate measurements will be used later in step 4.3 for guiding the FUS focal point to the target brain region with the XYZ positioner.</li>
	</ol>
	</li>
	<li>Collect MRI prescan images. Compare these images to the images collected after FUS BBB opening (Figure 4). T1-weighted images will later be used to visualize BBB opening, T2-weighted images will later be used to ensure no tissue damage has occurred following FUS treatment34.
	<ol>
		<li>For T1-weighted axial images, use the following parameters: width: 30 mm, height: 51.2 mm, depth: 3.0 mm, voxel size: 0.23 x 0.2 x 0.23 mm3, number of images: 13.</li>
		<li>For T2-weighted axial images, use the following parameters: width: 30 mm, height: 51.2 mm, depth: 2.6 mm, voxel size: 0.2 x 0.2 x 0.2 mm3, number of images: 13.</li>
		<li>For T1-weighted coronal images, use the following parameters: width: 30 mm, height: 30 mm, depth: 27 mm, voxel size: 0.16 x 0.16 x 1 mm3, number of images: 27.</li>
		<li>For T2-weighted coronal images, use the following parameters: width: 30 mm, height: 30 mm, depth: 27 mm, voxel size: 0.12 x 0.12 x 1 mm3, number of images: 27. 
		NOTE: As in step 3.5, these imaging parameters need not be exactly the same as listed. These images have a smaller FOV and higher resolution than the ones collected in step 3.5.</li>
	</ol>
	</li>
	<li>Keeping the animal in the stereotaxic frame, quickly transport the animal from the MRI bed to the benchtop FUS setup. Ensure that the animal remain asleep for the transfer under the effect of anesthesia.</li>
	<li>For longer transfer times, use a box for transfer that is large enough to fit the animal and the frame. With the anesthesia plug still attached, place the animal and frame inside the box and allow the excess isoflurane to fill the box for a few minutes. Unplug the anesthesia line and quickly transfer.</li>
</ol>
4. Focused ultrasound procedure
<ol>
	<li>Upon arriving to the FUS benchtop setup, immediately plug the anesthesia line into the nose cone and continue to run 1.5-3% isoflurane with oxygen. Do this as quickly as possible to avoid the animal waking up.</li>
	<li>Slide the frame into the frame holder and snap it into place firmly. Use clippers to shave the animal&#8217;s head. Brush away excess hair and apply hair remover cream to the scalp. Let sit for 3 min and wipe away with water and gauze.</li>
	<li>If MRI is not available for targeting, use a standard (not 3D-printed) stereotactic frame to null the pointer position to bregma by touching the pointer tip to bregma (a scalp incision will be needed for this) and nulling the software or recording the coordinates. Move the XYZ carriage up by 50 mm by clicking the up 50 button in the software and swapping the pointer for the transducer. Based on a rat brain atlas as described previously35, move to the desired brain coordinates using the stepping buttons in the software. If using this method instead of MRI, skip down to section 4.6.</li>
	<li>If using MRI guidance, attach the pointer and move the pointer to the location of the MRI fiducial (Figure 1d,g). Position the pointer at the very top and center of the MRI fiducial (a small hole in the top of the fiducial holder is provided for pointing). Click the null position button which is the point from which all distances in the MRI image were calculated.</li>
	<li>Remove the pointer and move the positioner to the medial/lateral coordinates and the rostral/caudal coordinates. Raise the positioner up by pressing the up 50 button to allow for the placement of the water bath and ultrasound gel. If the top of the Z-axis travel is reached, the nulling location will be invalidated. The dorsal/ventral coordinate will be set after the transducer is added.</li>
	<li>Apply ultrasound gel to the animal&#8217;s scalp and place the water bath over the animal with the polyimide tape window pressed onto the gel. Make sure that there are no air bubbles in the ultrasound gel.</li>
	<li>Fill the water bath with degassed water.</li>
	<li>If using the high-power transducer, lower the positioner so that the magnet is just above the water. Attach the transducer to the positioner by carefully lowering the transducer into the water at an angle to prevent air bubbles from getting trapped underneath the face and connect the magnets.</li>
	<li>If using the low-power immersion transducer, lower the positioner into the water just above the transducer clip. Then clip the transducer in place by slowly lowering it into the water at an angle to prevent air bubbles from getting trapped underneath the face. 
	NOTE: A transparent bath is helpful when looking under the transducer face for bubbles.</li>
	<li>Lower the positioner to the dorsal/ventral coordinate.</li>
	<li>Turn on the RF power amp.</li>
	<li>Inject 1 mL/kg of 3% Evans blue dye (EBD) by sticking the needle tip into the catheter plug and injecting. Allow it to circulate for 5 min.</li>
	<li>Activate the microbubbles by shaking them violently with the with the bubble shaker.
	<ol>
		<li>Prepare 5x the dose of 30 &#181;L/kg of microbubbles (bubble conc. 1.2 x 1010/mL) in 0.2 mL of saline to account for the 2 FUS treatments and the tubing in the 18 G winged infusion set. For example, if the rat weighs 200 g, then fill the syringe containing 18 G needle tip with 30 &#181;L of microbubbles in 1 mL of saline. 
		NOTE: Make sure to use 18 G needle tips for both up taking and injecting with the winged infusion set.</li>
		<li>Invert the syringe several times to get a uniform distribution of microbubbles. Then attach and fill the winged infusion set. Position the syringe on the infusion pump and set the infusion pump to deliver 0.2 mL at a rate of 6 mL/h. This will provide slow infusion of the microbubbles over the 2-min FUS exposure.</li>
		<li>Insert the winged needle into the catheter plug.</li>
	</ol>
	</li>
	<li>First, run the infusion pump, wait 3 s and start the FUS treatment by pressing the output enable button on the function generator (labeled &#8220;on&#8221; on the function generator in the Table of Materials). Repeat these two times per region with 5 min in between to allow the microbubbles to clear.
	<ol>
		<li>Press the on button again on the function generator to stop the FUS treatment when the infusion pump stops at 2 min.</li>
		<li>Wait for 5 min for the microbubbles to clear. Then start the infusion and the second FUS treatment.</li>
		<li>Immediately after the second FUS treatment, inject gadobutrol contrast (if using MRI) and the agent of interest, for example, viral particles. Total delivered volume of all agents should not exceed 5 mL/kg. 
		NOTE: The timing of delivery (e.g., before or after FUS BBB opening) of the agent of interest may differ depending on the agent used.</li>
	</ol>
	</li>
	<li>Turn off the RF power amp and immediately transport animal back to the MRI.</li>
</ol>
5. MRI confirmation of BBB opening
<ol>
	<li>If MRI is not available, skip to section 6 and use EBD expression for confirmation of BBB opening.</li>
	<li>Place the animal back onto the MRI bed at the exact same location as in step 3.7 and plug in the anesthesia line.</li>
	<li>Collect the MRI post scans with the same imaging parameters used in step 3.7 to visualize gadobutrol MRI enhancement in the region of BBB opening (Figure 3b,e).</li>
</ol>
6. Perfusion and tissue collection
<ol>
	<li>Perfuse the animal with cold 4% formalin until the blood runs completely clear.</li>
	<li>Remove the brain and place in 4% formalin or PFA at 4 &#176;C overnight. Next, place brain in 30% sucrose solution until the brain sinks (about 2-3 days). Finally, flash freeze in liquid nitrogen or on dry ice and store at -80&#176;C until cryosectioning.</li>
	<li>Freeze the brain in OCT and take cryosections.</li>
	<li>Fix and coverslip sections for fluorescence microscopy. EBD excitation peaks at 470 and 540 nm and emission peaks at 680 nm. Coverslip with DAPI mounting medium in order to visualize overall cellular morphology.</li>
</ol>

The authors have nothing to disclose.

Here we described a benchtop approach to microbubble assisted FUS BBB opening with alternative approaches including, two different transducers and methods for intracranial targeting with and without MRI guidance. Currently, in order to establish MRI-guided FUS BBB opening in the lab, there is the option to purchase excellent ready-to use devices that provide highly standardized and reproducible results with user-friendly interfaces. However, many labs are not prepared for the cost of such instruments. Therefore, the main goal of this protocol is to provide a starting point that any lab could establish in order to build their expertise in the technique.
FUS BBB opening is now a widely used technique and it is often the case that different groups utilize a variety of agents and anesthetics, each of which can affect the degree of BBB opening and extravasation. Importantly, the particular anesthetic used can affect the magnitude of BBB opening so it is important to consider this when executing this protocol38. Here, the anesthetic isoflurane is used because animals can be maintained under isoflurane for the length of the protocol and levels of isoflurane gas can be easily adjusted based on the animal&#8217;s respiration rate and heart rate. In addition, we delivered isoflurane with oxygen because it was more accessible than medical air; however, medical air may allow more extensive BBB opening39. Some MRI contrast agents are more appropriate for this protocol than others. For example, in our hands, gadoteridol produced no contrast enhancement even when EBD leakage was clearly present in tissue postmortem. Microbubble formulation is also important. Here we use perflutren lipid microspheres. Other microbubble formulations such as perflutren protein-type A microbubbles are readily available, but the type of microbubble used will affect the results15.
Controls of function generators can vary quite a bit, so refer to the manual for instructions on how to enter the settings listed in step 1. The appropriate command voltage (V peak to peak on the function generator) depends strongly on the transducer properties, RF amplifier gain, RF amplifier to transducer matching, the age and size of the animal, the microbubble type and concentration, and the desired treatment effect. The peak to peak V will need to be determined by trial and error. Start with the settings suggested in step 1 and determine the effect histologically. If there is tissue damage, lower the peak to peak V by 10% and try again. Likewise, if there is no BBBO then raise the peak to peak V by 10% and try again. Setting too high of a V can damage the low power immersion transducer. This will be apparent as a cracking or distortion of the transducer face. The manufacturing lead times on transducers can be long, so when starting, we suggest purchasing more than one transducer as a backup. Ultrasound transducers can also damage amplifiers if they are improperly matched. For simplicity and reliability, we suggest using a rugged power amplifier that can drive complex loads (such as the RF power amplifier in the materials table). Note that while the high-power transducer comes with a matching circuit, the low power immersion transducer does not. The suggested RF amplifier can handle the reflected power from the poorly matched transducer, but some amplifiers may be damaged in this configuration. Also, if step 2.7 proves problematic after installing the driver and software, double check that the proper serial port is selected in the software. Next try a different serial cable. If that fails, then seek local IT support.
From experience, it will take practice and multiple adjustments to achieve tight accuracy in brain region targeting. This can be seen in the differences of targeting between the early experiments (Figure 3) and the most recent experiments (Figure 5). We began the experiments using a classic stereotaxic frame and we include it as an option here if there is no access to a 3D printer or if there is no access to rodent MRI. However, MRI-guidance with MRI fiducials and the 3D printable frame provided (or of a custom design) is the ideal method. First, it accounts for individual differences between animals by gathering coordinates within the animal rather than relying on an averaged rat brain atlas. In addition, the use of MRI allows confirmation of FUS location targeting in vivo rather than relying on postmortem EBD expression. This is important when delivering agents that may require more than 24 hours to take effect such as AAVs (Figure 5). Lastly, the frame holder provided allows returning the animal back to the same position after MRI to fix any targeting errors or to repeat FUS after insufficient BBB opening without having to redo the coordinates. The portable 3D-printed stereotaxic frame can be used in any MRI with a clear bore of 200 mm or wider.
Depending on the blood vessel distribution in the target location, skull thickness40, the presence of ventricles, and other factors the degree of BBB opening can vary. For this reason, we provide a method for repeated targeting with the frame and frame holder. Accuracy of targeting depends critically on keeping the transducer focus at a consistent location with respect to the targeting pointer. The tip of this pointer should indicate the location in space of the center of the transducer focus when the transducer is attached to the XYZ positioner. The magnets allow the pointer and transducer to be easily swapped while maintaining this colocalization. The hole and protrusion in the magnets should match as precisely as possible. Any variability in this connection reduces the repeatability of the FUS focus targeting. However, there will be a spatial offset between the pointer tip and the ultrasound focus. Once it is confirmed that the offset is consistent, it can be corrected by using the MR images to calculate the difference in mm of the resulting BBB opening location (location of MRI contrast) and the intended target location. This difference can then be factored into the null location. Accuracy and repeatability also benefit greatly from using the same ultrasound frequency and using rats of a similar size and age in a given set of experiments. Ultrasound attenuation by the rat brain and rat skull varies with frequency and skull size and skull thickness varies with age. The skull is also a small cavity with respect to the ultrasound pulse and the incident ultrasound interacts with reflections inside the skull to produce a complex sound field that is dependent on the tissue, skull, frequency and the position of the transducer40.
As stated elsewhere, this protocol is intended to provide a low investment alternative to excellent MRI compatible commercial solutions that already available for purchase. There are important limitations that result from keeping the cost low. There are also limitations inherent to the technique given physics and the current state of the art. Remarkably, despite these limitations, and as shown in the representative results, we can achieve consistent delivery of dyes, particles, and viruses to the hippocampus of rats with submillimeter accuracy. The most important limitations are that (1) the shape of the FUS focus depends on the intervening tissue and especially the shape and thickness of the skull{...}. The need to remove the animal from the MRI to perform the FUS treatment prevents real-time feedback on the localization and intensity of the FUS focus. Without this real-time feedback several experiments need to be done to confirm setting for each combination of targeting location. Once the settings are &#8220;dialed in&#8221;, we have found good repeatability. (2) The XYZ positioning and fiducial system as constructed, while precise, does not provide accuracy in the coordinate frame of the positioner from experiment to experiment. The relative locations of the XYZ home, the rodent&#8217;s skull, and the frame can move relative to each other from experiment to experiment. This is obviated by using an MRI image for targeting, a targeting pointer and fiducial with known location in space relative to the FUS focus, ensuring the MRI coordinate system is parallel to the XYZ positioner system, by doing test treatments prior to the set of real treatments and by doing the entire procedure within one session so that the animal does not need to be repositioned into the frame. Note that, because only one fiducial is used, frame rotations are not correctable, so it is critical to ensure the frame is level with respect to the MRI bed and bore. In summary, the pointer location does not indicate the true FUS focus, but we have found the offset is consistent for a given brain location provided the skull does not rotate relative to the ultrasound transducer. Also note that consistent timing of gadobutrol delivery relative to the BBB opening and the imaging is crucial for consistent results especially if MRI contrast change is used as a proxy for the amount of BBB opening (see 36).
We first began FUS BBB opening in the lab with the low-power immersion transducer described above. We found that it is an affordable option for getting started with this technique. Most importantly, adaptation of this protocol can provide a noninvasive alternative to intracranial stereotaxic surgery and preclinical research performed with this technique can be considered highly translational due to the current use of transcranial FUS in humans30,32,41. Once established in a lab, this technique can be used as a noninvasive alternative to stereotaxic surgery. Thus, transforming a strictly investigative tool into a highly translational tool. Our lab will use this technique for the MRI guided, localized delivery of viruses and nanoparticles to develop novel, non-invasive neuromodulation techniques that can be used in freely behaving awake rodents and non-human primates. The current work focuses on Designer Drugs Exclusively Designed for Designer Receptors (DREADDs) and the sensitization of neurons to low doses of high energy particles such as x-rays. The lab is also working on a new version of this protocol that can be performed in a human 3 T scanner to eliminate the need to move the animal during the treatment and to allow real-time targeting feedback.

Despite the many discoveries in basic neuroscience, the number of emerging treatments for neurodevelopmental and neurodegenerative disorders remains relatively limited1,2. A deeper understanding of the genes, molecules and cellular circuitry involved in neurological disorders has suggested promising treatments unrealizable in humans with current techniques3. Effective treatments are often limited by the need to be brain penetrable and site-specific4,5,6,7,8. However, existing methods of localized drug delivery to specific brain regions (e.g., delivery via injection or cannula) are invasive and require an opening to be made in the skull9. The invasiveness of this surgery prevents the routine use of localized delivery into the human brain. Additionally, tissue damage and the resulting inflammatory responses are ubiquitous confounds for basic and preclinical studies that rely on intracerebral injection10. The ability to noninvasively deliver agents across the blood brain barrier (BBB) and target them to specific brain regions could have a tremendous impact on treatments for neurological disorders, while simultaneously providing a powerful investigational tool for preclinical research.
One method of targeted transport across the BBB with minimal tissue damage is transcranial focused ultrasound (FUS) together with microbubbles to focally and transiently open the BBB11,12,13,14,15,16. FUS BBB opening has gained recent attention for the treatment of neurodegenerative disorders, stroke and glioma by localizing therapeutics to target brain regions such as neurotrophic factors17,18,19, gene therapies20,21,22, antibodies23, neurotransmitters24, and nanoparticles25,26,27,28,29. With its wide range of applications and its noninvasive nature30,31, FUS BBB opening is an ideal alternative to routine stereotaxic intracranial injections. Furthermore, due to its current use in humans30,32, preclinical investigations using this technique can be considered highly translational. However, FUS BBB opening has yet to be a widely established technique in basic science and preclinical research due to lack of accessibility. Therefore, we provide a detailed protocol for a benchtop approach to FUS BBB opening as a starting point for labs interested in establishing this technique.
These studies were conducted with either a high-power air backed FUS specific ultrasound transducer or a low power damped focused ultrasonic immersion transducer. The transducers were driven by an RF power amplifier designed for reactive loads and a standard benchtop function generator. Details for these items can be found in the Table of Materials.

<table><tbody><tr><td>Bubble shaker</td><td>Lantheus Medical Imaging</td><td>VMIX</td><td>VIALMIX, actiation device used to activate Definity microbubbles</td></tr><tr><td>Catheter plug/ Injection cap</td><td>SAI infusion technologies</td><td>Part Number: IC</td><td>Catheter plug/ Injection cap</td></tr><tr><td>Evans blue dye</td><td>Sigma</td><td>E2129-10G</td><td>Evans blue dye</td></tr><tr><td>Function generator</td><td>Tektronix</td><td>AFG3022B</td><td>Dual channel, 250MS/s, 25MHz</td></tr><tr><td>FUS transducer, 1.1MHz</td><td>FUS Instruments</td><td>TX-110</td><td>1 MHz MRI-compatible spherically focused ultrasound transducer with a hydrophone</td></tr><tr><td>Heating pad for Mice and Rats</td><td>Kent Scientific</td><td>PS-03</td><td>Heating pad- PhysioSuite for Mice and Rats</td></tr><tr><td>Infusion pump</td><td>KD Scientific</td><td>780100</td><td>KDS 100 Legacy Single Syringe Infusion Pump</td></tr><tr><td>Kapton tape</td><td>Gizmo Dorks</td><td>https://www.amazon.com/dp/B01N1GGKRC/&lt;br/&gt; ref=cm_sw_em_r_mt_dp_U_GbR7Db56HKD91</td><td>Gizmo Dorks Kapton Tape (Polyimide) for 3D Printers and Printing, 8 x 8 inches, 10 Sheets per Pack</td></tr><tr><td>Low power immersion transducer, 1MHz</td><td>Olympus</td><td>V303-SU</td><td>Immersion Transducer, 1 MHz, 0.50 in. Element Diameter, Standard Case Style, Straight UHF Connector, F=0.80IN PTF</td></tr><tr><td>Magnet sets</td><td>WINOMO</td><td>https://www.amazon.com/dp/B01DJZQJBG/&lt;br/&gt; ref=cm_sw_em_r_mt_dp_U_JYQ7DbM32E5QC</td><td>WINOMO 15mm Sew In Magnetic Bag Clasps for Sewing Scrapbooking - 10 Sets</td></tr><tr><td>RF amplifier</td><td>E&amp;amp;I</td><td>A075</td><td>75W</td></tr><tr><td>Tail vein catheter</td><td>BD</td><td>382512/ Fisher Item: NC1228513</td><td>24g BD Insyte Autoguard shielded IV catheters (non-winged)</td></tr><tr><td>Ultrasound contrast microbubbles</td><td>Lantheus Medical Imaging</td><td>DE4, DE16</td><td>DEFINITY (Perflutren Lipid Microsphere)</td></tr><tr><td>Ultrasound gel</td><td>Aquasonic</td><td>https://www.amazon.com/dp/B07FPQDM4F/&lt;br/&gt; ref=cm_sw_em_r_mt_dp_U_D6Q7Db3J9QP7P</td><td>Ultrasound Gel Aquasonic 100 Transmission 1 Liter Squeeze Bottle</td></tr><tr><td>Winged infusion sets, 22ga.</td><td>Fisher Healthcare</td><td>22-258087</td><td>Terumo Surflo Winged Infusion Sets</td></tr><tr><td>motor controller software</td><td>N/A</td><td>N/A</td><td>custom software written in LabView for controlling the Velmex motor controller</td></tr><tr><td>runtime environment for the motor controller software</td><td>National Instruments</td><td>LabView runtime engine version 2017 or better</td><td>https://www.ni.com/en-us/support/downloads/software-products/download.labview.html</td></tr><tr><td>3 axis Linear stage actuator (XYZ positioner)</td><td>Velmex</td><td></td><td></td></tr><tr><td>bolts</td><td>Velmex</td><td>MB-1</td><td>BiSlide Bolt 1/4-20x3/4&quot; Socket cap screw (10 pack), Qty:3</td></tr><tr><td>motor controller</td><td>Velmex</td><td>VXM-3</td><td>Control,3 axis programmable stepping motor control, Qty:1</td></tr><tr><td>mounting cleats</td><td>Velmex</td><td>MC-2</td><td>Cleat, 2 hole BiSlide, Qty:6</td></tr><tr><td>mounting cleats</td><td>Velmex</td><td>MC-2</td><td>Cleat, 2 hole BiSlide, Qty:2</td></tr><tr><td>usb to serial converter</td><td>Velmex</td><td>VXM-USB-RS232</td><td>USB to RS232 Serial Communication Cable 10ft, Qty:1</td></tr><tr><td>x-axis linear stage</td><td>Velmex</td><td>MN10-0100-M02-21</td><td>BiSlide, travel=10 inch, 2 mm/rev, limits, NEMA 23, Qty:1</td></tr><tr><td>x-axis stepper motor</td><td>Velmex</td><td>PK266-03A-P1</td><td>Vexta Type 23T2, Single Shaft Stepper Motor, Qty:1</td></tr><tr><td>y-axis linear stage</td><td>Velmex</td><td>MN10-0100-M02-21</td><td>BiSlide, travel=10 inch, 2 mm/rev, limits, NEMA 23, Qty:1</td></tr><tr><td>y-axis stepper motor</td><td>Velmex</td><td>PK266-03A-P1</td><td>Vexta Type 23T2, Single Shaft Stepper Motor, Qty:1</td></tr><tr><td>z-axis damper</td><td>Velmex</td><td>D6CL-6.3F</td><td>D6CL Damper for Type 23 Double Shaft Stepper Motor, Qty:1</td></tr><tr><td>z-axis linear stage</td><td>Velmex</td><td>MN10-0100-M02-21</td><td>BiSlide, travel=10 inch, 2 mm/rev, limits, NEMA 23, Qty:1</td></tr><tr><td>z-axis stepper motor</td><td>Velmex</td><td>PK266-03B-P2</td><td>Vexta Type 23T2, Double Shaft Stepper Motor, Qty:1</td></tr><tr><td>3D printable files</td><td></td><td></td><td></td></tr><tr><td>Immersion transducer mount and pointer</td><td></td><td></td><td>https://www.tinkercad.com/things/cRgTthGXSRq</td></tr><tr><td>Stereotaxic frame</td><td></td><td></td><td>https://www.tinkercad.com/things/ilynoQcdqlH</td></tr><tr><td>Stereotaxic frame holder</td><td></td><td></td><td>https://www.tinkercad.com/things/aZNgqhBOHAX</td></tr><tr><td>9.4T small bore animal MRI</td><td>Bruker</td><td>Bruker BioSpec 94/20</td><td>ParaVision version 5.1</td></tr><tr><td>AAV9-hsyn-GFP</td><td>Addgene</td><td></td><td></td></tr><tr><td>Cream hair remover</td><td>Church &amp;amp; Dwight</td><td></td><td>Nair cream</td></tr><tr><td>gadobutrol MRI contrast agent</td><td>Bayer</td><td></td><td>Gadavist (Gadobutrol, 1mM/mL)</td></tr><tr><td>Stereotactic frame</td><td>Stoelting</td><td>#51500</td><td>not MRI compatible</td></tr><tr><td>turnkey FUS delivery device</td><td>FUS Instruments</td><td>RK-300</td><td>ready to use MRI compatible FUS for rodents</td></tr></tbody></table>

a benchtop approach to the location specific blood brain barrier opening using focused ultrasound in a rat model

Stereotaxic surgery is the gold standard for localized drug and gene delivery to the rodent brain. This technique has many advantages over systemic delivery including precise localization to a target brain region and reduction of off target side effects. However, stereotaxic surgery is highly invasive which limits its translational efficacy, requires long recovery times, and provides challenges when targeting multiple brain regions. Focused ultrasound (FUS) can be used in combination with circulating microbubbles to transiently open the blood brain barrier (BBB) in millimeter sized regions. This allows intracranial localization of systemically delivered agents that cannot normally cross the BBB. This technique provides a noninvasive alternative to stereotaxic surgery. However, to date this technique has yet to be widely adopted in neuroscience laboratories due to the limited access to equipment and standardized methods. The overall goal of this protocol is to provide a benchtop approach to FUS BBB opening (BBBO) that is affordable and reproducible and can therefore be easily adopted by any laboratory.

Here, we demonstrate that focused ultrasound with microbubbles can induce localized BBB opening using the parameters specified above with both the low-power immersion transducer (Figure 3) and the FUS transducer (Figure 4). First, in early experiments, the low-power immersion transducer was targeted to one brain hemisphere either anterior (Figure 3b) or medial (Figure 3a). Animals were then sacrificed 2 hours later with perfusion (Figure 3a) or without perfusion (Figure 3b) and 10 &#181;m frozen brain sections were collected. FUS BBB opening was evident by EBD autofluorescence (excitation: 470 and 540 nm, emission: 680 nm) in the target hemisphere (white arrows Figure 3a and 3b).
We have found it best to perfuse the animals for clear visualization of BBB opening with EBD autofluorescence. However, BBB opening can still be visualized without clearing the blood vessels (Figure 3b). Cellular uptake and clearance of EBD following BBB opening begins as soon as 30 minutes after BBB opening and increases over 24 hours37. For evaluation of BBB opening with EBD autofluorescence, it is best to sacrifice the animal between 15 minutes and 3 hours of BBB opening. Though ultimately, the time of sacrifice will depend on the agent that was delivered. For example, in an AAV study, 3 weeks post BBB opening and AAV delivery (Figure 5c) may be appropriate.
In later experiments, the FUS transducer was targeted to either the hippocampus (Figure 4a-c) or the anterior cingulate cortex (ACC) (Figure 4 d-f) and in addition to EBD, the MRI contrast agent gadobutrol (0.1 mL/kg) was IV injected to verify targeted opening of the BBB in vivo. Figure 4b,e show enhanced MRI contrast where the gadobutrol contrast has entered the tissue 1 hour after BBB opening and contrast agent injection. This contrast change is evident when comparing to the MRI prescans taken before the FUS procedure (Figure 4a,d). Animals were then sacrificed by perfusion 1.5 hours after BBB opening and 10 &#956;m cryosections were collected. EBD autofluorescence is evident in FUS targeted regions further indicating location of BBB opening (Figure 4c,f). This figure highlights how MRI contrast can sometimes be difficult to see (as in the difference between Figure 4b and Figure 4e); therefore, it is helpful to confirm BBB opening with visualization of EBD autofluorescence as in the fluorescence micrograph in Figure 4f.
To assess whether this technique could be used for the targeted gene delivery AAV9-hsyn-GFP and gadobutrol contrast were injected IV (titer: 1.32 x 1014 GC/mL, 0.05 mL/kg) immediately after BBB opening in the hippocampus. The animal was then MR imaged 30 minutes after BBB opening and sacrificed 3 weeks later by perfusion. 10 &#956;m cryosections were collected for fluorescent imaging of GFP expression. BBB opening was evident by gadobutrol contrast in the target hippocampus (Figure 5a,b). In addition, gene delivery was confirmed by GFP expression in the target hippocampus evident by green fluorescence (Figure 5c). Note that at this time point EBD has cleared out and is only evident in the ventricles (Figure 5c).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61113/61113fig1.jpg" /> 
Figure 1: FUS benchtop setup. (a) FUS setup including the XYZ positioner, a 30 mm diameter PVC pipe for attachment of the transducer, the 3D-printed stereotaxic frame, and the infusion pump. (b) The end of the PVC pipe is capped, and a magnet is attached to it with epoxy. (c) Another matching magnet is attached to the top center of the high-power transducer with epoxy. (d) In addition, another matching magnet is attached to the pointer for nulling the positioner at the top and center of the MRI fiducial. (e) The pointer is eventually replaced with the high-power transducer and a water bath is coupled to the animal&#8217;s head with ultrasound gel. (f) The low-power immersion transducer can be attached to the PVC pipe with the 3D-printed transducer clip. (g) For positioning, the transducer is replaced with the 3D-printed pointer and the positioner is nulled at the top and center of the MRI fiducial. (h) The stationary 3D-printed frame holder allows for the animal to be returned to the same position after MRI if multiple FUS treatments are needed. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61113/61113fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61113/61113fig2.jpg" /> 
Figure 2: Stereotaxic frame with MRI fiducial for MRI-guided coordinates. (a) Animals are first positioned in a 3D-printed stereotaxic frame equipped with an MRI fiducial. (b) The frame is then placed inside the MRI bed and distance from the fiducial (dotted circle) to the target brain region is measured using both coronal images for the dorsal/ventral (D/V) measurements and axial images for the rostral/caudal (R/C) measurements, medial/lateral (M/L) measurement can be collected from both axes. Animals are kept in the frame and transferred to the FUS station where a pointer is used to null the XYZ positioner at the location of the fiducial. The pointer is then replaced with the transducer and which can then be moved based on the coordinates collected. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61113/61113fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61113/61113fig3.jpg" /> 
Figure 3: Evans blue dye (EBD) confirms FUS BBB opening both with and without perfusion. (a) Micrograph of a 10 &#181;m brain section 2 hours after FUS BBB opening with the low-power immersion transducer targeted to the medial left hemisphere. This is a representative image of an animal that was perfused with 4% buffered formalin prior to tissue collection. BBB opening is evident by EBD red autofluorescence (arrow). (b) Micrograph of a 10 &#181;m brain section 2 hours after FUS BBB opening targeted to the anterior left hemisphere. This is a representative image of an animal who was not perfused prior to tissue collection therefore, EBD remains in the blood vessels. BBB opening is evident where EBD has leaked out of the blood vessels (arrow). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61113/61113fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61113/61113fig4.jpg" /> 
Figure 4: FUS BBB opening confirmed with Gadobutrol MRI contrast and EBD expression. MR images before (a and d) and after (b and e) BBB opening. gadobutrol contrast enhancement confirms location of BBB opening in vivo (b and e, arrows). (c) 10 &#956;m brain section showing further confirmation of BBB opening with EBD autofluorescence (red) in the hippocampus (blue DAPI nuclear stain). Scale bar; 500 &#181;m. (f) Micrograph of a 10 &#181;m brain section following BBB opening in the anterior cingulate cortex evident by EBD red autofluorescence (arrow). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61113/61113fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61113/61113fig5.jpg" /> 
Figure 5: Localized delivery of AAV9-hsyn-GFP to the hippocampus via FUS BBB opening. MRI confirmation of BBB opening with MRI contrast agent, MRI contrast (arrows) in both coronal (a) and axial (b) T1-weighted images. (c) histological confirmation of GFP expression in the FUS targeted hippocampus (green) 3 weeks after FUS BBB opening and AAV9-hsyn-GFP IV injection. Blue indicates DAPI nuclear stain for overall cellular morphology. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61113/61113fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Benchtop Approach to the Location Specific Blood Brain Barrier Opening using Focused Ultrasound in a Rat Model at JoVE.com

A Benchtop Approach to the Location Specific Blood Brain Barrier Opening using Focused Ultrasound in a Rat Model

Focused ultrasound with microbubble agents can open the blood brain barrier focally and transiently. This technique has been used to deliver a wide range of agents across the blood brain barrier. This article provides a detailed protocol for the localized delivery to the rodent brain with or without MRI guidance.

Stereotaxic surgery is the gold standard for localized drug and gene delivery to the rodent brain. This technique has many advantages over systemic ...

a-benchtop-approach-to-location-specific-blood-brain-barrier-opening

Nanyang Technological University

Research

JoVE Journal

Neuroscience

4.5K Views.  University of Alabama at Birmingham. Focused ultrasound with microbubble agents can open the blood brain barrier focally and transiently. This technique has been used to deliver a wide range of agents across the blood brain barrier. This article provides a detailed protocol for the localized delivery to the rodent brain with or without MRI guidance.

Video: A Benchtop Approach to the Location Specific Blood Brain Barrier Opening using Focused Ultrasound in a Rat Model

MRI-guided Disruption of the Blood-brain Barrier using Transcranial Focused Ultrasound in a Rat Model

Focused ultrasound (FUS) disruption of the blood-brain barrier (BBB) is an increasingly investigated technique for circumventing the BBB1-5. The BBB is a significant obstacle to pharmaceutical treatments of brain disorders as it limits the passage of molecules from the vasculature into the brain tissue to molecules less than approximately 500 Da in size6. FUS induced BBB disruption (BBBD) is temporary and reversible4 and has an advantage over chemical means of inducing BBBD by being highly localized. FUS induced BBBD provides a means for investigating the effects of a wide range of therapeutic agents on the brain, which would not otherwise be deliverable to the tissue in sufficient concentration. While a wide range of ultrasound parameters have proven successful at disrupting the BBB2,5,7, there are several critical steps in the experimental procedure to ensure successful disruption with accurate targeting. This protocol outlines how to achieve MRI-guided FUS induced BBBD in a rat model, with a focus on the critical animal preparation and microbubble handling steps of the experiment.

Microbubble-mediated focused ultrasound disruption of the blood-brain barrier (BBB) is a promising technique for non-invasive targeted drug delivery in the brain1-3. This protocol outlines the experimental procedure for MRI-guided transcranial BBB disruption in a rat model.

Focused ultrasound (FUS) disruption of the blood-brain barrier (BBB) is an increasingly investigated technique for circumventing the BBB1-5. The BBB is a ...

Medicine

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

Stereotaxic Surgery for Excitotoxic Lesion of Specific Brain Areas in the Adult Rat

Many behavioral functions in mammals, including rodents and humans, are mediated principally by discrete brain regions. A common method for discerning the function of various brain regions for behavior or other experimental outcomes is to implement a localized ablation of function. In humans, patient populations with localized brain lesions are often studied for deficits, in hopes of revealing the underlying function of the damaged area. In rodents, one can experimentally induce lesions of specific brain regions.
Lesion can be accomplished in several ways. Electrolytic lesions can cause localized damage but will damage a variety of cell types as well as traversing fibers from other brain regions that happen to be near the lesion site. Inducible genetic techniques using cell-type specific promoters may also enable site-specific targeting. These techniques are complex and not always practical depending on the target brain area. Excitotoxic lesion using stereotaxic surgery, by contrast, is one of the most reliable and practical methods of lesioning excitatory neurons without damaging local glial cells or traversing fibers.
Here, we present a protocol for stereotaxic infusion of the excitotoxin, N-methyl-D-aspartate (NMDA), into the basolateral amygdala complex. Using anatomical indications, we apply stereotaxic coordinates to determine the location of our target brain region and lower an injection needle in place just above the target. We then infuse our excitotoxin into the brain, resulting in excitotoxic death of nearby neurons. While our experimental subject of choice is a rat, the same methods can be applied to other mammals, with the appropriate adjustments in equipment and coordinates.
This method can be used on a variety of brain regions, including the basolateral amygdala1-6, other amygdala nuclei6, 7, hippocampus8, entorhinal cortex9 and prefrontal cortex10. It can also be used to infuse biological compounds such as viral vectors1, 11. The basic stereotaxic technique could also be adapted for implantation of more permanent osmotic pumps, allowing more prolonged exposure to a compound of interest.

Targeted ablation of specific brain region(s) by infusion of an excitotoxin using stereotaxic coordinates is described. This technique could also be adapted for infusion of other chemicals into the rat brain.

Many behavioral functions in mammals, including rodents and humans, are mediated principally by discrete brain regions. A common method for discerning the ...

Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant cell type in the brain, neurons are the most widely studied of these cell types given their direct role in impacting behaviors. Other cell types in the brain also impact neuronal function and behavior via the signaling molecules they produce. Neuroscientists must understand the interactions between the cell types in the brain to better understand how these interactions impact neural function and disease. To date, the most common method of analyzing protein or gene expression utilizes the homogenization of whole tissue samples, usually with blood, and without regard for cell type. This approach is an informative approach for examining general changes in gene or protein expression that may influence neural function and behavior; however, this method of analysis does not lend itself to a greater understanding of cell-type-specific gene expression and the effect of cell-to-cell communication on neural function. Analysis of behavioral epigenetics has been an area of growing focus which examines how modifications of the deoxyribonucleic acid (DNA) structure impact long-term gene expression and behavior; however, this information may only be relevant if analyzed in a cell-type-specific manner given the differential lineage and thus epigenetic markers that may be present on certain genes of individual neural cell types. The Fluorescence Activated Cell Sorting (FACS) technique described below provides a simple and effective way to isolate individual neural cells for the subsequent analysis of gene expression, protein expression, or epigenetic modifications of DNA. This technique can also be modified to isolate more specific neural cell types in the brain for subsequent cell-type-specific analysis.

The goal of this protocol is to use the fluorescence activated cell sorting (FACS) technique to sort specific types of neural cells for subsequent analysis of cell-type-specific gene expression, epigenetic markers, and or protein expression.

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant ...

An In Vivo Assessment of Blood-Brain Barrier Disruption in a Rat Model of Ischemic Stroke

Ischemic stroke leads to vasogenic cerebral edema and subsequent primary brain injury, which is mediated through destruction of the blood-brain barrier (BBB). Rats with induced ischemic stroke were established and used as in vivo models to investigate the functional integrity of the BBB. Spectrophotometric detection of Evans blue (EB) in the brain samples with ischemic injury could provide reliable justification for the research and development of novel therapeutic modalities. This method generates reproducible results, and is applicable in any laboratory without a need for special equipment. Here, we present a visualized and technical guideline on the detection of the extravasation of EB following induction of ischemic stroke in rats.

An In Vivo Assessment of Blood-Brain Barrier Disruption in a Rat Model of Ischemic Stroke

The overall goal of this procedure is to provide a highly reproducible technique for in vivo assessment of the blood-brain barrier disruption in rat models of ischemic stroke.

Ischemic stroke leads to vasogenic cerebral edema and subsequent primary brain injury, which is mediated through destruction of the blood-brain barrier ...

Disruption of the Blood-Spinal Cord Barrier Using Low-Intensity Focused Ultrasound in a Rat Model

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise neuromodulatory technology. Although LIFU-mediated blood-brain barrier (BBB) opening has been explored in detail, no standardized technique for blood-spinal cord barrier (BSCB) opening has been established to date. Therefore, this protocol presents a method for successful BSCB disruption using LIFU sonication in a rat model, including descriptions of animal preparation, microbubble administration, target selection&#160;and localization, as well as BSCB disruption visualization and confirmation. The approach reported here is particularly useful for researchers who need a fast and cost-effective method to test and confirm target localization and precise BSCB disruption in a small animal model with a focused ultrasound transducer, evaluate the BSCB efficacy of sonication parameters, or explore applications for LIFU at the spinal cord, such as drug delivery, immunomodulation, and neuromodulation. Optimizing this protocol for individual use is recommended, especially for advancing future preclinical, clinical, and translational work.

Disruption of the blood-spinal cord barrier (BSCB) can be successfully achieved with the intravenous administration of microbubbles and the application of low-intensity focused ultrasound (LIFU). This protocol details the opening of the BSCB using LIFU in a rodent model, including equipment setup, microbubble injection, target localization, and BSCB disruption visualization.

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise ...

Bioengineering

A High-Throughput Image-Guided Stereotactic Neuronavigation and Focused Ultrasound System for Blood-Brain Barrier Opening in Rodents

The blood-brain barrier (BBB) has been a major hurdle for the treatment of various brain diseases. Endothelial cells, connected by tight junctions, form a physiological barrier preventing large molecules (&#62;500 Da) from entering the brain tissue. Microbubble-mediated focused ultrasound (FUS) can be used to induce a transient local BBB opening, allowing larger drugs to enter the brain parenchyma.
In addition to large-scale clinical devices for clinical translation, preclinical research for therapy response assessment of drug candidates requires dedicated small animal ultrasound setups for targeted BBB opening. Preferably, these systems allow high-throughput workflows with both high-spatial precision as well as integrated cavitation monitoring, while still being cost effective in both initial investment and running costs.
Here, we present a bioluminescence and X-ray guided stereotactic small animal FUS system that is based on commercially available components and fulfills the aforementioned requirements. A particular emphasis has been placed on a high degree of automation facilitating the challenges typically encountered in high-volume preclinical drug evaluation studies. Examples of these challenges are the need for standardization in order to ensure data reproducibility, reduce intra-group variability, reduce sample size and thus comply with ethical requirements and decrease unnecessary workload. The proposed BBB system has been validated in the scope of BBB opening facilitated drug delivery trials on patient-derived xenograft models of glioblastoma multiforme and diffuse midline glioma.

The blood-brain barrier (BBB) can be temporarily disrupted with microbubble-mediated focused ultrasound (FUS). Here, we describe a step-by-step protocol for high-throughput BBB opening in vivo using a modular FUS system accessible for non-ultrasound experts.

The blood-brain barrier (BBB) has been a major hurdle for the treatment of various brain diseases. Endothelial cells, connected by tight junctions, form a ...

Focused Ultrasound Induced Blood-Brain Barrier Opening for Targeting Brain Structures and Evaluating Chemogenetic Neuromodulation

Acoustically Targeted Chemogenetics (ATAC) allows for the noninvasive control of specific neural circuits. ATAC achieves such control through a combination of focused ultrasound (FUS) induced blood-brain barrier opening (FUS-BBBO), gene delivery with adeno-associated viral (AAV) vectors, and activation of cellular signaling with engineered, chemogenetic, protein receptors and their cognate ligands. With ATAC, it is possible to transduce both large and small brain regions with millimeter precision using a single noninvasive ultrasound application. This transduction can later allow for a long-term, noninvasive, device-free neuromodulation in freely moving animals using a drug. Since FUS-BBBO, AAVs, and chemogenetics have been used in multiple animals, ATAC should also be scalable for the use in other animal species. This paper expands upon a previously published protocol and outlines how to optimize the gene delivery with FUS-BBBO to small brain regions with MRI-guidance but without a need for a complicated MRI-compatible FUS device. The protocol, also, describes the design of mouse targeting and restraint components that can be 3D-printed by any lab and can be easily modified for different species or custom equipment. To aid reproducibility, the protocol describes in detail how the microbubbles, AAVs, and venipuncture were used in ATAC development. Finally, an example data is shown to guide the preliminary investigations of studies utilizing ATAC.

This protocol delineates steps necessary for the gene delivery through focused ultrasound blood brain barrier (BBB) opening, evaluation of the resulting gene expression, and measurement of neuromodulation activity of chemogenetic receptors through histological tests.

Acoustically Targeted Chemogenetics (ATAC) allows for the noninvasive control of specific neural circuits. ATAC achieves such control through a ...

Enhancing Drug Delivery to the Brain: MRI-Guided Ultrasound Techniques in Rats

Monitoring Blood-Brain Barrier Opening in Rats with a Preclinical Focused Ultrasound System

The brain has a highly selective semipermeable blood barrier, termed the blood-brain barrier (BBB), which prevents the delivery of therapeutic macromolecular agents to the brain. The integration of MR-guided low-intensity pulsed focused ultrasound (FUS) with microbubble pre-injection is a promising technique for non-invasive and non-toxic BBB modulation. MRI can offer superior soft-tissue contrast and various quantitative assessments, such as vascular permeability, perfusion, and the spatial-temporal distribution of MRI contrast agents. Notably, contrast-enhanced MRI techniques with gadolinium-based MR contrast agents have been shown to be the gold standard for detecting BBB openings. This study outlines a comprehensive methodology involving MRI protocols and animal procedures for monitoring BBB opening in a rat model. The rat model provides the added benefit of jugular vein catheter utilization, which facilitates rapid medication administration. A stereotactic-guided preclinical FUS transducer facilitates the refinement and streamlining of animal procedures and MRI protocols. The resulting methods are characterized by reproducibility and simplicity, eliminating the need for specialized surgical expertise. This research endeavors to contribute to the optimization of preclinical procedures with rat models and encourage further investigation into the modulation of the BBB to enhance therapeutic interventions in neurological disorders.

This study describes a combined magnetic resonance imaging (MRI) and low-intensity pulsed focused ultrasound (FUS) protocol, utilizing living rats with jugular vein catheterization to monitor blood-brain barrier (BBB) opening.

The brain has a highly selective semipermeable blood barrier, termed the blood-brain barrier (BBB), which prevents the delivery of therapeutic ...

Focus Ultrasound Based Microbubble Mediated Blood-Brain Barrier Opening: A Technique to Create Localized Transient Openings in Blood-Brain Barrier of Mouse by Sonoporation

Source: Haumann, R. et al. <a href="https://www-jove-com.remotexs.ntu.edu.sg/video/61269" target="_blank">A High-Throughput Image-Guided Stereotactic Neuronavigation and Focused Ultrasound System for Blood-Brain Barrier Opening in Rodents.</a> J. Vis. Exp. (2020)
This video describes a method of temporarily disrupting the blood-brain barrier (BBB) by creating transient openings using microbubble-mediated focused ultrasound (FUS). These transient local BBB openings can eventually be used to deliver larger-sized drug molecules directly into the brain parenchyma.

Source: Haumann, R. et al. A High-Throughput Image-Guided Stereotactic Neuronavigation and Focused Ultrasound System for Blood-Brain Barrier Opening in ...

A Benchtop Approach to the Location Specific Blood Brain Barrier Opening using Focused Ultrasound in a Rat Model

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Monitoring Blood-Brain Barrier Opening in Rats with a Preclinical Focused Ultrasound System

Focus Ultrasound Based Microbubble Mediated Blood-Brain Barrier Opening: A Technique to Create Localized Transient Openings in Blood-Brain Barrier of Mouse by Sonoporation