This study was funded by the following grants: National Key R&#38;D Program of China (2021YFA1101200); Medical Research Project of Wenzhou (Y20170188), National Key R&#38;D Program of China (2016YFC1101200); National Natural Science Foundation of China (81770926;81800842); Key R&#38;D Program of Zhejiang Province (2018C03G2090634); and Key R&#38;D Program of Wenzhou Eye Hospital (YNZD1201902). The sponsor or funding organization had no role in the design or conduct of this research.

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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vertical,+horizontal,+and+torsional+eye+movement+responses+to+head+roll+in+the+squirrel+monkey.">Vertical, horizontal, and torsional eye movement responses to head roll in the squirrel monkey.</a> Experimental Brain Research. 104 (2), 218-226 (1995).</li><li>Porciatti, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mouse+pattern+electroretinogram.">The mouse pattern electroretinogram.</a> Documenta Ophthalmologica. 115 (3), 145-153 (2007).</li></ol>

The authors do not have any conflicts of interest to disclose.

In this study, we present a protocol of VEP, PERG, and OCT in goat and rhesus macaque. These in vivo methods can be applied in large animal models of various optic neuropathies, such as glaucoma, ischemic, or traumatic optic neuropathy and optic neuritis9.
PVEP is more stable and sensitive than FVEP17; however, it can't be elicited in goat9. As such, FVEP is performed in goat and PVEP is performed in rhesus macaque in our lab to evaluate the integrity of the retino-geniculo-cortical pathway. The mechanism underlying the observation that PERG, but not PVEP, can be induced in goat is still unclear according to our knowledge. It is possible that the optic nerve function and structure from goat might be different from human.
Since the amplitude of FVEP may be affected by pupillary size and ambient light, we dilate the pupil and place a black blanket over the goat's head during FVEP recording. It should be noticed that pupil dilation is not needed for FVEP in clinics17. Similarly, although dark adaptation is not necessary for FVEP recording in clinics, we found that a 5 min adaption to the ambient light before FVEP recording may increase intrasession repeatability in amplitude.
PERG signal is thought to originated from the RGCs and thus its amplitude could be used to estimate the function of the RGCs13,20. Compared with some special flash ERG components, such as scotopic threshold response (STR) and photopic negative response (PhNR), PERG is more sensitive to RGC dysfunction13. Potential limitations of PERG test in this study are as follows. First, ISCEV recommends using classic CRT (cathode ray tube) stimulator for PERG recording to keep mean luminance constant. However, the classic CRT stimulator is less available than liquid crystal display (LCD). Although the screen of LCD usually presents transient luminance changes during pattern reversal, potentially causing luminance artifact17, it didn't contribute to the amplitude of PERG in goat according to our previous finding: the amplitude of PERG at the spatial frequency of 12.6 cpd is usually neglectable compared with those at lower spatial frequencies9. Another limitation is that we didn't correct refractive error before PERG test for the sake of simplicity. To make up for this limitation, baseline PERG amplitude should be recorded as a reference.
Our previous study had assessed and optimized the intra- and inter session variation of VEP and PERG9. We found that compared with xylazine, isoflurane resulted in more repeatable FVEP but more variable PERG waveforms in goats9. Therefore, we used isoflurane in FVEP test and xylazine in PERG and OCT test in goats. Additionally, compared with PERG, VEP recording is potentially more variable. As such, we regularly repeat VEP recording at each light intensity or spatial frequency to check the intrasession variation. On the contrast, PERG waveforms are much more stable. Therefore, we generally do not repeat PERG recording. Although repeated recording on a different day on the same subject is generally recommended, we do not regularly repeat VEP or PERG recording on the same subject on a different day for the sake of simplicity and animal ethics. Nevertheless, FVEP and PERG recordings without inter-session repeat is sensitive enough to detect optic nerve injury according to our previous study9.
Retinal OCT imaging is a convenient, reliable and non-invasive technique to longitudinally monitor and quantify dynamic changes in the retinal structure. Compared with PERG and VEP, OCT imaging has much better intersession repeatability9. Furthermore, OCT imaging can capture and quantify all the optic nerve fiber within minutes without sampling error, offering a much cheaper and effective opportunity to examine the retinal structure than traditional histological analysis. However, the spatial resolution of current OCT imaging is still too limited to tell individual RGC soma or optic nerve fiber. Additionally, it should be noticed that a thicker GCC measured by OCT does not necessarily mean a more intact inner retina because GCC thickening may be caused by retinal edema or hemorrhage.

The optic nerve (ON), which consists of axons from the retinal ganglion cells (RGC), transmits visual signal from the retina to the brain. ON diseases, such as glaucoma, traumatic or ischemic optic neuropathy, often caused irreversible ON/RGC degeneration and devastating visual loss. Although there are currently many breakthroughs in ON regeneration and RGC protection in rodent models1,2,3,4,5,6, clinical treatments for most of the ON diseases remained essentially the same over the last half century with unsatisfactory outcome7,8. To fill the gap between basic research and clinical practice, translational studies using large animal model of ON diseases are often necessary and beneficial because of their closer anatomical similarity to humans than rodent models.
Goat and rhesus macaques are two large animal species used in our lab to model human&#39;s ON disease. The size of a goat&#39;s eyeball, ON, and the adjacent structure (orbital and nasal cavity, skull base, etc.) is similar to that of a human based on skull CT scan9. As such, goat model provides an opportunity to evaluate and refine therapeutic devices or surgical procedures prior to use in humans. The rhesus macaque, as non-human primate (NHP), has human-like unique visual system that does not exist in other species10,11. In addition, pathophysiological responses to injuries and treatments in NHP is much similar to that in humans12.
In vivo tests to assess the ON and RGC&#39;s structure and function longitudinally are important in large animal studies. Pattern electroretinogram (PERG) has been used to evaluate the RGC function. Flash visual evoked potential (FVEP) reflects the integrity of retino-geniculo-cortical pathway in the visual system. Thus, PERG combined with FVEP can reflect the ON function9,13,14 . The retinal optic coherence tomography (OCT) imaging can show the retinal structure with high temporal and spatial resolution, which enables measurement of the thickness of the retinal ganglion complex (GCC)9,15. For electrophysiological examinations in this study, monitoring vital signs (heat rate, breach rate, blood pressure) and level of oxygen saturation (SpO2) before testing are crucial since these parameters have potent impacts on ocular blood flow and thus the function of the visual system. However, we didn&#39;t monitor the vital signs when carrying out OCT retinal imaging for the sake of simplicity. According to our previous study9, the GCC thickness measured by OCT retinal imaging is quite stable, with inter-session coefficient of variation close to 3%. These in vivo tests in goat and rhesus macaque have been described in detail in our previous study9. Here we present these methods to help increase experimental transparency and reproducibility.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>47.6 x 26.8 cm monitors</td>
			<td>DELL Inc.</td>
			<td>E2216HV</td>
			<td>The visual stimuli of contrast-reversal black-white checkerboards were displayed on screens</td>
		</tr>
		<tr>
			<td>6.0 mm tracheal tube</td>
			<td>Henan Tuoren Medical Device Co., Ltd</td>
			<td>PVC 6.0</td>
			<td>ensure the airway</td>
		</tr>
		<tr>
			<td>alligator clip</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>atropine</td>
			<td>Guangdong Jieyang Longyang Animal pharmaceutical Co.,Ltd.</td>
			<td></td>
			<td>reduce bronchial secretion and protect heart from vagal nerve activation</td>
		</tr>
		<tr>
			<td>Carbomer Eye Gel</td>
			<td>Fabrik GmbH Subsidiary of Bausch &#38; Lomb</td>
			<td></td>
			<td>moisten the cornea and stabilize the recording electrodes</td>
		</tr>
		<tr>
			<td>ERG-Jet recording electrodes</td>
			<td>Roland Consult Stasche&#38;Finger GmbH</td>
			<td>2300 La Chaux-De-Fonds</td>
			<td>ERG recording</td>
		</tr>
		<tr>
			<td>eye speculum</td>
			<td>Shanghai Jinzhong Medical Device Co., Ltd</td>
			<td>ZYD020</td>
			<td>open palpebral fissure</td>
		</tr>
		<tr>
			<td>Heidelberg Spectralis OCT system</td>
			<td>Heidelberg Engineering</td>
			<td></td>
			<td>OCT system</td>
		</tr>
		<tr>
			<td>Imaging</td>
			<td></td>
			<td></td>
			<td>(https://www.heidelbergengineering.com/media/e-learning/Totara-US/files/pdf-tutorials/2238-003_Spectralis-Training-Guide.pdf)</td>
		</tr>
		<tr>
			<td>isoflurane</td>
			<td>RWD Life Science Co., Ltd</td>
			<td>R510-22</td>
			<td>isoflurane anesthesia</td>
		</tr>
		<tr>
			<td>male Saanen goats</td>
			<td>Caimu Livestock Company, country (Hangzhou, China)</td>
			<td></td>
			<td>The male Saanen goats, aged from 4 to 6 months with weight of 19&#8211;23 kg</td>
		</tr>
		<tr>
			<td>needle electrode</td>
			<td>Roland Consult Stasche&#38;Finger GmbH</td>
			<td>U51-426-G-D</td>
			<td>use for FVEP ground electrode and PERG reference electrodes</td>
		</tr>
		<tr>
			<td>periphery venous catheter intravenously</td>
			<td>BD shanghai Medical Device Co., Ltd</td>
			<td>383019</td>
			<td>intravenous access for atropine and propofol</td>
		</tr>
		<tr>
			<td>propofol</td>
			<td>Xian Lipont Enterprise Union Management Co.,Ltd.</td>
			<td></td>
			<td>induce Isoflurane anesthesia in goat</td>
		</tr>
		<tr>
			<td>Tropicamide Phenylephrine Eye Drops</td>
			<td>SANTEN OY, Japan</td>
			<td></td>
			<td>5% tropicamide and 5% phenylephrine hydrochloride</td>
		</tr>
		<tr>
			<td>visual electrophysiology device</td>
			<td>Gotec Co., Ltd</td>
			<td>GT-2008V-III</td>
			<td>use for FVEP &#38; PERG</td>
		</tr>
		<tr>
			<td>xylazine</td>
			<td>Huamu Animal Health Products Co., Ltd.</td>
			<td></td>
			<td>xylazine anesthesia: intramuscular injection of xylazine 3mg/kg</td>
		</tr>
		<tr>
			<td>zoletil50</td>
			<td>Virbac</td>
			<td></td>
			<td>induce Isoflurane anesthesia in monkey</td>
		</tr>
	</tbody>
</table>

in vivo methods to assess retinal ganglion cell and optic nerve function and structure in large animals

The optic nerve collects axons signals from the retinal ganglion cells and transmits visual signal to the brain. Large animal models of optic nerve injury are essential for translating novel therapeutic strategies from rodent models to clinical application due to their closer similarities to humans in size and anatomy. Here we describe some in vivo methods to evaluate the function and structure of the retinal ganglion cells (RGCs) and optic nerve (ON) in large animals, including visual evoked potential (VEP), pattern electroretinogram (PERG) and optical coherence tomography (OCT). Both goat and non-human primate were employed in this study. By presenting these in vivo methods step by step, we hope to increase experimental reproducibility among different labs and facilitate the usage of large animal models of optic neuropathies.

Figure 1A shows representative results of FVEP in goat. Although the waveforms in same flash intensity have relative similarity, we still recommend to examine the waveforms twice. Electromagnetic waves generated by electronic devices will interfere with the collected electrical signals, resulting in high baseline noise and poor repeatability of the waveform. Therefore, it is recommended to ensure that there are no redundant electronic devices plugged into the surrounding environment during electrophysiological examination to avoid such interference, and it is recommended to repeat at least two measurements to determine the stability and repeatability of experimental results. When patching both eyes, the waveforms are totally flat on both eyes, which shows that the waveforms are certainly generating from our flash stimulus. Figure 1B shows representative results of PERG in goat. Due to its stability and high signal, we acquire reliable waveform just by one time measurement at each spatial frequency. As the spatial frequency increases, the size of the checkerboard will gradually exceed the recognition of the goat&#39;s eyes. So we can see that at 12.7 cpd, the PVEP waveform has dropped a lot. Analogous to FVEP, the waveform disappears when we close the screen. Figure 1C shows representative results of PVEP in rhesus macaque. We repeat the measurement twice at each spatial frequency. As the spatial frequency increases, the amplitude will decrease. This is due to the fact that the spatial frequency exceeds the perception of the eye. Figure 1D shows representative results of PERG in rhesus macaque. The reason why the amplitude decreases with the spatial frequency is the same as described above. When analyzing these data, you can choose to analyze the amplitude between the peaks and troughs or the latency time of the peaks or troughs as the statistics.
Figure 2 shows the representative results of OCT in goat. The leftmost image shows a fundus photograph taken by infrared camera. Tightly to the right is a tomogram of the retina, showing the overall thickness of the retina around the ONH and the thickness of each layer. As shown in the picture, we can clearly see that goats have larger retinal blood vessels than monkeys. The green discs on the far right is a quantitative analysis of the thickness of the GCC around the ONH. G stands for general, T stands for temporal side, N stands for nasal side, S stands for superior, and I stands for inferior. The black font represents the GCC thickness measurement value in micrometers, and the green is the clinical reference measurement value for human, not as a reference for this experiment.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62879/62879fig01.jpg" /> 
Figure 1: Representative electrophysiological waveforms in goat and rhesus macaques. (A) Representative FVEP waveforms at different light intensities from an individual goat within the same anesthetic session. (B,D) Representative PERG waveforms at different spatial frequencies from an individual goat (B) or rhesus macaque (D) within the same anesthetic session. (C) Representative PVEP waveforms at different spatial frequencies from an individual rhesus macaque within the same anesthetic session. The typical implicit time of each waveform is mentioned in the Protocol section. n = 1 subject for each test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62879/62879fig01large.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/62879/62879fig02.jpg" /> 
Figure 2: OCT results. Representative retinal OCT images around the optic nerve head (left panel) and the thickness of GCC in different peripapillary regions (right panel) in goat (A) and rhesus macaque (B). n = 1 subject for each test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62879/62879fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals at JoVE.com

In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

Here we demostrate several in vivo tests (flash visual evoked potential, pattern electroretinogram and optic coherence tomography) in goat and rhesus macaque to understand the structure and function of the optic nerve and its neurons.

In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

The optic nerve collects axons signals from the retinal ganglion cells and transmits visual signal to the brain. Large animal models of optic nerve injury ...

in-vivo-methods-to-assess-retinal-ganglion-cell-optic-nerve-function

Universidad San Sebastian

Research

JoVE Journal

Neuroscience

9.8K Views.  Wenzhou Medical University. Here we demostrate several in vivo tests (flash visual evoked potential, pattern electroretinogram and optic coherence tomography) in goat and rhesus macaque to understand the structure and function of the optic nerve and its neurons.

Video: In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

Methods for Experimental Manipulations after Optic Nerve Transection in the Mammalian CNS

Retinal ganglion cells (RGCs) are CNS neurons that output visual information from the retina to the brain, via the optic nerve. The optic nerve can be accessed within the orbit of the eye and completely transected (axotomized), cutting the axons of the entire RGC population. Optic nerve transection is a reproducible model of apoptotic neuronal cell death in the adult CNS 1-4. This model is particularly attractive because the vitreous chamber of the eye acts as a capsule for drug delivery to the retina, permitting experimental manipulations via intraocular injections. The diffusion of chemicals through the vitreous fluid ensures that they act upon the entire RGC population. Viral vectors, plasmids or short interfering RNAs (siRNAs) can also be delivered to the vitreous chamber in order to infect or transfect retinal cells 5-12. The high tropism of Adeno-Associated Virus (AAV) vectors is beneficial to target RGCs, with an infection rate approaching 90% of cells near the injection site 6, 7, 13-15. Moreover, RGCs can be selectively transfected by applying siRNAs, plasmids, or viral vectors to the cut end of the optic nerve 16-19 or injecting vectors into their target the superior colliculus 10. This allows researchers to study apoptotic mechanisms in the injured neuronal population without confounding effects on other bystander neurons or surrounding glia. RGC apoptosis has a characteristic time-course whereby cell death is delayed 3-4 days postaxotomy, after which the cells rapidly degenerate. This provides a window for experimental manipulations directed against pathways involved in apoptosis. Manipulations that directly target RGCs from the transected optic nerve stump are performed at the time of axotomy, immediately after cutting the nerve. In contrast, when substances are delivered via an intraocular route, they can be injected prior to surgery or within the first 3 days after surgery, preceding the initiation of apoptosis in axotomized RGCs. In the present article, we demonstrate several methods for experimental manipulations after optic nerve transection.

Optic Nerve transection is a widely used model of adult CNS injury. This model is ideal for performing a number of experimental manipulations that target the retina globally or directly target the injured neuronal population of retinal ganglion cells.

Retinal ganglion cells (RGCs) are CNS neurons that output visual information from the retina to the brain, via the optic nerve. The optic nerve can be ...

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural connectivity form during development. In mice, retinofugal projections are arranged in a topographic manner and form eye-specific layers in the Lateral Geniculate Nucleus (dLGN) of the thalamus and the Superior Colliculus (SC). The development of these precise patterns of retinofugal projections has typically been studied by labeling populations of RGCs with fluorescent dyes and tracers, such as horseradish peroxidase1-4. However, these methods are too coarse to provide insight into developmental changes in individual RGC axonal arbor morphology that are the basis of retinotopic map formation. They also do not allow for the genetic manipulation of RGCs.
Recently, electroporation has become an effective method for providing precise spatial and temporal control for delivery of charged molecules into the retina5-11. Current retinal electroporation protocols do not allow for genetic manipulation and tracing of retinofugal projections of a single or small cluster of RGCs in postnatal mice. It has been argued that postnatal in vivo electroporation is not a viable method for transfecting RGCs since the labeling efficiency is extremely low and hence requires targeting at embryonic ages when RGC progenitors are undergoing differentiation and proliferation6. 
In this video we describe an in vivo electroporation protocol for targeted delivery of genes, shRNA, and fluorescent dextrans to murine RGCs postnatally. This technique provides a cost effective, fast and relatively easy platform for efficient screening of candidate genes involved in several aspects of neural development including axon retraction, branching, lamination, regeneration and synapse formation at various stages of circuit development. In summary we describe here a valuable tool which will provide further insights into the molecular mechanisms underlying sensory map development.

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

We demonstrate an in vivo electroporation protocol for transfecting single or small clusters of retinal ganglion cells (RGCs) and other retinal cell types in postnatal mice over a wide range of ages. The ability to label and genetically manipulate postnatal RGCs in vivo is a powerful tool for developmental studies.

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural ...

An Optic Nerve Crush Injury Murine Model to Study Retinal Ganglion Cell Survival

Injury to the optic nerve can lead to axonal degeneration, followed by a gradual death of retinal ganglion cells (RGCs), which results in irreversible vision loss. Examples of such diseases in human include traumatic optic neuropathy and optic nerve degeneration in glaucoma. It is characterized by typical changes in the optic nerve head, progressive optic nerve degeneration, and loss of retinal ganglion cells, if uncontrolled, leading to vision loss and blindness.
The optic nerve crush (ONC) injury mouse model is an important experimental disease model for traumatic optic neuropathy, glaucoma, etc. In this model, the crush injury to the optic nerve leads to gradual retinal ganglion cells apoptosis. This disease model can be used to study the general processes and mechanisms of neuronal death and survival, which is essential for the development of therapeutic measures. In addition, pharmacological and molecular approaches can be used in this model to identify and test potential therapeutic reagents to treat different types of optic neuropathy.
Here, we provide a step by step demonstration of (I) Baseline retrograde labeling of retinal ganglion cells (RGCs) at day 1, (II) Optic nerve crush injury at day 4, (III) Harvest the retinae and analyze RGC survival at day 11, and (IV) Representative result.

This protocol shows how to retrogradely label retinal ganglion cells, and how to subsequently make an optic nerve crush injury in order to analyze retinal ganglion cell survival and apoptosis. It is an experimental disease model for different types of optic neuropathy, including glaucoma.

Injury to the optic nerve can lead to axonal degeneration, followed by a gradual death of retinal ganglion cells (RGCs), which results in irreversible ...

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 ...

In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice

The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and postsynaptic projections to the visual cortex. Based on its distinct anatomical structure and convenient accessibility, it has become the favored structure for studies on neuronal survival, axonal regeneration, and synaptic plasticity. Recent advancements in MR imaging have enabled the in vivo visualization of the retino-tectal part of this projection using manganese mediated contrast enhancement (MEMRI). Here, we present a MEMRI protocol for illustration of the visual projection in mice, by which resolutions of (200 &#181;m)3 can be achieved using common 3 Tesla scanners. We demonstrate how intravitreal injection of a single dosage of 15 nmol MnCl2 leads to a saturated enhancement of the intact projection within 24 hr. With exception of the retina, changes in signal intensity are independent of coincided visual stimulation or physiological aging. We further apply this technique to longitudinally monitor axonal degeneration in response to acute optic nerve injury, a paradigm by which Mn2+ transport completely arrests at the lesion site. Conversely, active Mn2+ transport is quantitatively proportionate to the viability, number, and electrical activity of axon fibers. For such an analysis, we exemplify Mn2+ transport kinetics along the visual path in a transgenic mouse model (NF-&#954;B p50KO) displaying spontaneous atrophy of sensory, including visual, projections. In these mice, MEMRI indicates reduced but not delayed Mn2+ transport as compared to wild type mice, thus revealing signs of structural and/or functional impairments by NF-&#954;B mutations.
In summary, MEMRI conveniently bridges in vivo assays and post mortem histology for the characterization of nerve fiber integrity and activity. It is highly useful for longitudinal studies on axonal degeneration and regeneration, and investigations of mutant mice for genuine or inducible phenotypes.

In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice

This video illustrates a method, using a clinical 3 T scanner, for contrast-enhanced MR imaging of the na&#239;ve mouse visual projection and for repetitive and longitudinal in vivo studies of optic nerve degeneration associated with acute optic nerve crush injury and chronic optic nerve degeneration in knock-out mice (p50KO).

The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and ...

Imaging Serotonergic Fibers in the Mouse Spinal Cord Using the CLARITY/CUBIC Technique

Long descending fibers to the spinal cord are essential for locomotion, pain perception, and other behaviors. The fiber termination pattern in the spinal cord of the majority of these fiber systems have not been thoroughly investigated in any species. Serotonergic fibers, which project to the spinal cord, have been studied in rats and opossums on histological sections and their functional significance has been deduced based on their fiber termination pattern in the spinal cord. With the development of CLARITY and CUBIC techniques, it is possible to investigate this fiber system and its distribution in the spinal cord, which is likely to reveal previously unknown features of serotonergic supraspinal pathways. Here, we provide a detailed protocol for imaging the serotonergic fibers in the mouse spinal cord using the combined CLARITY and CUBIC techniques. The method involves perfusion of a mouse with a hydrogel solution and clarification of the tissue with a combination of clearing reagents. Spinal cord tissue was cleared in just under two weeks, and the subsequent immunofluorescent staining against serotonin was completed in less than ten days. With a multi-photon fluorescent microscope, the tissue was scanned and a 3D image was reconstructed using Osirix software.

Supraspinal projections are important for pain perception and other behaviors, and serotonergic fibers are one of these fiber systems. The present study focused on the application of the combined CLARITY/CUBIC protocol to the mouse spinal cord in order to investigate the termination of these serotonergic fibers.

Long descending fibers to the spinal cord are essential for locomotion, pain perception, and other behaviors. The fiber termination pattern in the spinal ...

In Vivo Gene Transfer to Schwann Cells in the Rodent Sciatic Nerve by Electroporation

The formation of the myelin sheath by Schwann cells (SCs) is essential for rapid conduction of nerve impulses along axons in the peripheral nervous system. SC-selective genetic manipulation in living animals is a powerful technique for studying the molecular and cellular mechanisms of SC myelination and demyelination in vivo. While knockout/knockin and transgenic mice are powerful tools for studying SC biology, these methods are costly and time consuming. Viral vector-mediated transgene introduction into the sciatic nerve is a simpler and less laborious method. However, viral methods have limitations, such as toxicity, transgene size constraints, and infectivity restricted to certain developmental stages. Here, we describe a new method that allows selective transfection of myelinating SCs in the rodent sciatic nerve using electroporation. By applying electric pulses to the sciatic nerve at the site of plasmid DNA injection, genes of interest can be easily silenced or overexpressed in SCs in both neonatal and more mature animals. Furthermore, this in vivo electroporation method allows for highly efficient simultaneous expression of multiple transgenes. Our novel technique should enable researchers to efficiently manipulate SC gene expression, and facilitate studies on SC development and function.

In Vivo Gene Transfer to Schwann Cells in the Rodent Sciatic Nerve by Electroporation

Here, we present an in vivo technique for gene transfer to Schwann cells (SCs) in the rodent sciatic nerve. This simple technique is useful for investigating signaling mechanisms involved in the development and maintenance of myelinating SCs.

The formation of the myelin sheath by Schwann cells (SCs) is essential for rapid conduction of nerve impulses along axons in the peripheral nervous ...

Single-cell RNA-Seq of Defined Subsets of Retinal Ganglion Cells

The discovery of cell type-specific markers can provide insight into cellular function and the origins of cellular heterogeneity. With a recent push for the improved understanding of neuronal diversity, it is important to identify genes whose expression defines various subpopulations of cells. The retina serves as an excellent model for the study of central nervous system diversity, as it is composed of multiple major cell types. The study of each major class of cells has yielded genetic markers that facilitate the identification of these populations. However, multiple subtypes of cells exist within each of these major retinal cell classes, and few of these subtypes have known genetic markers, although many have been characterized by morphology or function. A knowledge of genetic markers for individual retinal subtypes would allow for the study and mapping of brain targets related to specific visual functions and may also lend insight into the gene networks that maintain cellular diversity. Current avenues used to identify the genetic markers of subtypes possess drawbacks, such as the classification of cell types following sequencing. This presents a challenge for data analysis and requires rigorous validation methods to ensure that clusters contain cells of the same function. We propose a technique for identifying the morphology and functionality of a cell prior to isolation and sequencing, which will allow for the easier identification of subtype-specific markers. This technique may be extended to non-neuronal cell types, as well as to rare populations of cells with minor variations. This protocol yields excellent-quality data, as many of the libraries have provided read depths greater than 20 million reads for single cells. This methodology overcomes many of the hurdles presented by Single-cell RNA-Seq and may be suitable for researchers aiming to profile cell types in a straightforward and highly efficient manner.

Here, we present a combinatorial approach for classifying neuronal cell types prior to isolation and for the subsequent characterization of single-cell transcriptomes. This protocol optimizes the preparation of samples for successful RNA Sequencing (RNA-Seq) and describes a methodology designed specifically for the enhanced understanding of cellular diversity.

The discovery of cell type-specific markers can provide insight into cellular function and the origins of cellular heterogeneity. With a recent push for ...

Optical Coherence Tomography: Imaging Mouse Retinal Ganglion Cells In Vivo

Structural changes in the retina are common manifestations of ophthalmic diseases. Optical coherence tomography (OCT) enables their identification in vivo&#8212;rapidly, repetitively, and at a high resolution. This protocol describes OCT imaging in the mouse retina as a powerful tool to study optic neuropathies (OPN). The OCT system is an interferometry-based, non-invasive alternative to common post mortem histological assays. It provides a fast and accurate assessment of retinal thickness, allowing the possibility to track changes, such as retinal thinning or thickening. We present the imaging process and analysis with the example of the Opa1delTTAG mouse line. Three types of scans are proposed, with two quantification methods: standard and homemade calipers. The latter is best for use on the peripapillary retina during radial scans; being more precise, is preferable for analyzing thinner structures. All approaches described here are designed for retinal ganglion cells (RGC) but are easily adaptable to other cell populations. In conclusion, OCT is efficient in mouse model phenotyping and has the potential to be used for the reliable evaluation of therapeutic interventions.

Optical Coherence Tomography: Imaging Mouse Retinal Ganglion Cells In Vivo

This manuscript describes a protocol for the in vivo imaging of the mouse retina with high-resolution spectral domain optical coherence tomography (SD-OCT). It focuses on retinal ganglion cells (RGC) in the peripapillary region, with several scanning and quantifying approaches described.

Structural changes in the retina are common manifestations of ophthalmic diseases. Optical coherence tomography (OCT) enables their identification in ...

Partial Optic Nerve Transection in Rats: A Model Established with a New Operative Approach to Assess Secondary Degeneration of Retinal Ganglion Cells

Previous studies have shown that the secondary degeneration of retinal ganglion cells (RGCs) occurs commonly in glaucoma. Partial optic nerve transection is considered a useful and reproducible model. Compared with other optic nerve injury models used commonly for assessing secondary degeneration, e.g. complete optic nerve transection and optic nerve crush models, the partial optic nerve transection model is superior as it distinguishes primary from secondary degeneration in situ. Therefore, it serves as an excellent tool for evaluating secondary degeneration. This study describes a novel operative approach of partial optic nerve transection by directly accessing the area of the retrobulbar optic nerve through the orbital lateral wall of the eyeball. Moreover, we present a newly designed, low cost surgical instrument to assist with transection. As demonstrated by the representative results in distinguishing the boundary of primary and secondary injury areas, the new approach and instrument ensures high efficiency and stability of the model by providing adequate space for surgical operation. This in turn makes it easy to separate the meningeal sheath and ophthalmic vessels from the optic nerve before transection. An additional benefit is that this space-saving operative approach improves the investigators&#39; ability to administer drugs, carriers, or selective RGC tracers to the stump of the partially transected optic nerve, allowing the exploration of mechanisms behind secondary injury in RGCs, in a new way.

Secondary degeneration of retinal ganglion cells (RGCs) occurs commonly in glaucoma. This study describes an innovative operative approach for partial optic nerve transection. The use of this space-saving operative approach extends the model's application range, and allows exploration of secondary injury mechanisms in RGCs in a new way.

Previous studies have shown that the secondary degeneration of retinal ganglion cells (RGCs) occurs commonly in glaucoma. Partial optic nerve transection ...

In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

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Chapters in this video

Methods for Experimental Manipulations after Optic Nerve Transection in the Mammalian CNS

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

An Optic Nerve Crush Injury Murine Model to Study Retinal Ganglion Cell Survival

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

In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice

Imaging Serotonergic Fibers in the Mouse Spinal Cord Using the CLARITY/CUBIC Technique

In Vivo Gene Transfer to Schwann Cells in the Rodent Sciatic Nerve by Electroporation

Single-cell RNA-Seq of Defined Subsets of Retinal Ganglion Cells

Optical Coherence Tomography: Imaging Mouse Retinal Ganglion Cells In Vivo

Partial Optic Nerve Transection in Rats: A Model Established with a New Operative Approach to Assess Secondary Degeneration of Retinal Ganglion Cells