Name: full-circle cauterization of limbal vascular plexus for surgically induced glaucoma in rodents
Uploaded: 2022-02-15T14:00:00
Description: Watch this Scientific Journal Video about Full-Circle Cauterization of Limbal Vascular Plexus for Surgically Induced Glaucoma in Rodents at JoVE.com

We acknowledge our laboratory technicians Jos&#233;; Nilson dos Santos, Daianne Mandarino Torres, Jos&#233; Francisco Tib&#250;rcio, Gildo Brito de Souza, and Luciano Cavalcante Ferreira. This research was funded by FAPERJ, CNPq, and CAPES.

All procedures were performed in compliance with the Statement for the Use of Animals in Ophthalmic and Visual Research from the Association for Research in Vision and Ophthalmology (ARVO) and approved by the Ethics Committee on the Use of Animals in Scientific Experimentation from the Health Sciences Center, Federal University of Rio de Janeiro (protocol 083/17). In the present work, Lister Hooded rats of both genders were used, aged 2-3 months and weighing 180-320 g. However, the procedure can be adapted in different r...

<ol>
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Limbal plexus cauterization (LPC) is a novel post-trabecular model with the advantage that it targets easily accessible vascular structures not requiring conjunctival or tenon dissection17,28. Differently from the vortex veins cauterization model, a renowned OHT model based on the surgical impairment to choroid venous drainage, venous congestion is not expected to influence IOP rise in the LPC model, as limbal veins are situated upstream in aqueous humor outflow....

Medical literature understands glaucoma as a heterogeneous group of optic neuropathies characterized by progressive degeneration of retinal ganglion cells (RGCs), dendrites, soma, and axons, resulting in structural cupping (excavation) of the optic disc and functional deterioration of the optic nerve, leading to amaurosis in uncontrolled cases by interrupting the transmission of visual information from the eye to the brain1. Glaucoma is currently the most common cause of irreversible blindness worldwide, predicted to reach approximately 111.8 million people in 20402, thus deeply affecting patients&#39; quality of life (QoL) and leading to significant socioeconomic concerns3.
Elevated intraocular pressure (IOP) is one of the most important and the only modifiable risk factor for the development and progression of glaucoma. Among the multiple types of glaucoma, all, except for normal tension glaucoma (NTG), are associated with elevated IOP at some time in the clinical history of the disease. Despite remarkable clinical and surgical advances to target IOP and slow down or stop disease progression, patients still lose sight due to glaucoma4,5. Therefore, a thorough understanding of the complex and multifactorial pathophysiology of this disease is imperative for the development of more effective treatments, especially to provide neuroprotection to RGCs.
Among a variety of experimental approaches for the understanding of disease mechanisms, animal models based on ocular hypertension (OHT) most closely resemble human glaucoma. Rodent models are particularly useful as they are&#160;low-cost, are easy to handle,&#160;can be genetically manipulated, have a short lifespan, and present ocular anatomical and physiological features comparable to humans, such as aqueous humor production and drainage6,7,8,9,10,11,12,13. Currently used models include sclerosis of the trabecular meshwork following injection of hypertonic saline into episcleral veins14, intracameral injection of microbeads15&#160;or viscoelastic substances16, cauterization of vortex veins17, photocoagulation of the trabecular meshwork with argon laser18, circumlimbal suture19, and use of a transgenic model of age-related OHT (DBA/2J mice)8. However, invasiveness, post-operative opacification of the cornea, anterior segment disruption, extensive learning curves, expensive equipment, and highly variable postoperative IOPs, are among few of the reported pitfalls associated with the current models, making the development of an alternative model of OHT a demand to overcome these problems20,21,22.
The present protocol formalizes a novel surgical procedure to induce OHT as a proxy to glaucoma, based on limbal plexus cauterization (LPC) in rodents23. This is an easy, reproducible, accessible, and non-invasive model that provides high efficiency and low variability of IOP elevation, associated with a uniquely high rate of full clinical recovery, therefore providing in vivo functional evaluation in a reduced number of animals used in each experiment. The surgery technique induces subacute OHT with a gradual return to baseline levels in a few days, which models the hypertensive attack seen in acute angle-closure glaucoma. Moreover, the IOP recovery in the model is followed by continuous glaucomatous neurodegeneration, which is useful for future mechanistic studies of the secondary degeneration of RGCs, which occurs in several cases of human glaucoma despite adequate control of IOP.

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			<td>Acetone</td>
			<td>Isofar</td>
			<td>201</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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		<tr>
			<td>Active electrode for electroretinography</td>
			<td>Hansol Medical Co</td>
			<td>-</td>
			<td>Stainless steel needle 0.25 mm &#215; 15 mm</td>
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			<td>Anestalcon</td>
			<td>Novartis Bioci&#234;ncias S/A</td>
			<td>MS-1.0068.1087</td>
			<td>Proxymetacaine hydrochloride 0.5%</td>
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			<td>Calcium chloride</td>
			<td>Vetec</td>
			<td>560</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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			<td>Cautery Low Temp Fine Tip 10/bx</td>
			<td>Bovie Medical Corporation</td>
			<td>AA00</td>
			<td>Low-temperature ophthalmic cautery</td>
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			<td>Syntec do Brasil Ltda</td>
			<td>000200-3-000003</td>
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			<td>DAKO</td>
			<td>Dako North America</td>
			<td>S3023</td>
			<td>Antifade mounting medium</td>
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			<td>DAPI</td>
			<td>Thermo Fisher Scientific</td>
			<td>28718-90-3</td>
			<td>diamidino-2-phenylindole; blue fluorescent nuclear counterstain; emission at 452&#177;3 nm</td>
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			<td>Ecofilm</td>
			<td>Crist&#225;lia Produtos Qu&#237;micos Farmac&#234;uticos Ltda</td>
			<td>MS-1.0298.0487</td>
			<td>Carmellose sodium 0.5%</td>
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			<td>EPON Resin</td>
			<td>Polysciences, Inc.</td>
			<td>-</td>
			<td>Epoxy resin used for electron microscopy, composed of a mixture of four reagents: Poly/Bed 812 Resin (CAT#08791); DDSA - Dodecenylsuccinic Anhydride (CAT#00563); NMA - Nadic Methyl Anhydride (CAT#00886); DMP-30 - 2,4,6-tris(dimethylaminomethyl)phenol (CAT#00553)</td>
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			<td>Glutaraldehyde</td>
			<td>Electron Microscopy Sciences</td>
			<td>16110</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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			<td>Hyabak</td>
			<td>Uni&#227;o Qu&#237;mica Farmac&#234;utica Nacional S/A</td>
			<td>MS-8042140002</td>
			<td>Sodium hyaluronate 0.15%</td>
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			<td>Icare Tonolab</td>
			<td>Icare Finland Oy</td>
			<td>TV02 (model number)</td>
			<td>Rebound handheld tonometer</td>
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			<td>IgG donkey anti-mouse antibody + Alexa Fluor 555</td>
			<td>Thermo Fisher Scientific</td>
			<td>A31570</td>
			<td>Secondary antibody solution</td>
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			<td>LCD monitor 23 inches</td>
			<td>Samsung Electronics Co. Ltd.</td>
			<td>S23B550</td>
			<td>Model LS23B550, for electroretinogram recording</td>
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			<td>LSM 510 Meta</td>
			<td>Carl Zeiss</td>
			<td>-</td>
			<td>Confocal epifluorescence microscope</td>
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			<td>Maxiflox</td>
			<td>Crist&#225;lia Produtos Qu&#237;micos Farmac&#234;uticos Ltda</td>
			<td>MS-1.0298.0489</td>
			<td>Ciprofloxacin 3.5 mg/g</td>
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			<td>MEB-9400K</td>
			<td>Nihon Kohden Corporation</td>
			<td>-</td>
			<td>System for electroretinogram recording</td>
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			<td>monoclonal IgG1 mouse anti-Brn3a</td>
			<td>MilliporeSigma</td>
			<td>MAB-1585</td>
			<td>Brn3a primary antibody solution</td>
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			<td>Neuropack Manager v08.33</td>
			<td>Nihon Kohden Corporation</td>
			<td>-</td>
			<td>Software for electroretinogram signal processing</td>
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			<td>Optomotry</td>
			<td>CerebralMechanics</td>
			<td>-</td>
			<td>System for optomotor response analysis</td>
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			<td>Osmium tetroxide</td>
			<td>Electron Microscopy Sciences</td>
			<td>19100</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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			<td>Potassium ferrocyanide</td>
			<td>Electron Microscopy Sciences</td>
			<td>20150</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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			<td>Reference and ground electrodes for electroretinography</td>
			<td>Chalgren Enterprises</td>
			<td>110-63</td>
			<td>Stainless steel needles 0.4 mm &#215; 37 mm</td>
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			<td>Sodium cacodylate buffer</td>
			<td>Electron Microscopy Sciences</td>
			<td>12300</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
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		<tr>
			<td>Ster MD</td>
			<td>Uni&#227;o Qu&#237;mica Farmac&#234;utica Nacional S/A</td>
			<td>MS-1.0497.1287</td>
			<td>Prednisolone acetate 0.12%</td>
		</tr>
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			<td>Terolac</td>
			<td>Crist&#225;lia Produtos Qu&#237;micos Farmac&#234;uticos Ltda</td>
			<td>MS-1.0497.1286</td>
			<td>Ketorolac trometamol 0.5%</td>
		</tr>
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			<td>Terramicina</td>
			<td>Laborat&#243;rios Pfizer Ltda</td>
			<td>MS-1.0216.0024</td>
			<td>Oxytetracycline hydrochloride 30 mg/g + polymyxin B 10,000 U/g</td>
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			<td>Tono-Pen XL</td>
			<td>Reichert Technologies</td>
			<td>230635</td>
			<td>Digital applanation handheld tonometer</td>
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			<td>TO-PRO-3</td>
			<td>Thermo Fisher Scientific</td>
			<td>T3605</td>
			<td>Far red-fluorescent nuclear counterstain; emission at 661 nm</td>
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			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>9036-19-5</td>
			<td>Non-ionic surfactant</td>
		</tr>
		<tr>
			<td>Uranyl acetate</td>
			<td>Electron Microscopy Sciences</td>
			<td>22400</td>
			<td>Used for electron microscopy tissue preparation (step 5)</td>
		</tr>
		<tr>
			<td>Xilazin</td>
			<td>Syntec do Brasil Ltda</td>
			<td>7899</td>
			<td>Xylazine hydrochloride 2%</td>
		</tr>
		<tr>
			<td></td>
			<td>Carl Zeiss</td>
			<td>-</td>
			<td>Stereo microscope for surgery and retinal dissection</td>
		</tr>
	</tbody>
</table>

full-circle cauterization of limbal vascular plexus for surgically induced glaucoma in rodents

Glaucoma, the second leading cause of blindness worldwide, is a heterogeneous group of ocular disorders characterized by structural damage to the optic nerve and retinal ganglion cell (RGC) degeneration, resulting in visual dysfunction by interrupting the transmission of visual information from the eye to the brain. Elevated intraocular pressure is the most important risk factor; thus, several models of ocular hypertension have been developed in rodents by either genetic or experimental approaches to investigate the causes and effects of the disease. Among those, some limitations have been reported such as surgical invasiveness, inadequate functional assessment, requirement of extensive training, and highly variable extension of retinal damage. The present work characterizes a simple, low-cost, and efficient method to induce ocular hypertension in rodents, based on low-temperature, full-circle cauterization of the limbal vascular plexus, a major component of aqueous humor drainage. The new model provides a technically easy, noninvasive, and reproducible subacute ocular hypertension, associated with progressive RGC and optic nerve degeneration, and a unique post-operative clinical recovery rate that allows in vivo functional studies by both electrophysiological and behavioral methods.

The quantitative variables are expressed as mean &#177; standard error of the mean (SEM). Except for the comparison of IOP dynamics between OHT and control groups (Figure 1F), statistical analysis was performed using two-way ANOVA followed by Sidak&#39;s multiple comparisons test. A p-value &#60; 0.05 was considered statistically significant.
Figure 1 illustrates surgical steps of the full-circle limbal plexus cauterization (LPC) mode...

Watch this Scientific Journal Video about Full-Circle Cauterization of Limbal Vascular Plexus for Surgically Induced Glaucoma in Rodents at JoVE.com

Full-Circle Cauterization of Limbal Vascular Plexus for Surgically Induced Glaucoma in Rodents

The goal of this protocol is to characterize a novel model of glaucomatous neurodegeneration based on 360&#176; thermic cauterization of limbal vascular plexus, inducing subacute ocular hypertension.

Glaucoma, the second leading cause of blindness worldwide, is a heterogeneous group of ocular disorders characterized by structural damage to the optic ...

We developed a simple method to induce robust and progressive glaucoma degeneration based on temporary intraocular pressure elevation. This represents a unique opportunity to study key points of glaucoma pathophysiology. This is an easy-learning, non-invasive, low-cost, and highly-reproducible model that enables in vivo function analysis and short-term experimental designs using a reduced number of animals for each experiment.The retina and optic nerve are assessable parts of the central nervous system, so modeling the progressive impairment of these structures can provide valuable insights into other neurodegenerative disorders. To measure baseline intraocular pressure, or IOP, of both experimental and contralateral control eyes, place the anesthetized rat in a ventral decubitus position on the bench top, such that the corneal surface is easily accessible to the tip of the tonometer. Position the tonometer tip such that it slightly touches the central corneal zone perpendicularly.Then, acquire the measurement by pressing the measurement button. Next, place the rat in a slight lateral decubitus position under a stereo microscope and inspect the experimental eye at 40 times magnification. During the procedure, keep the contralateral control eye lubricated by instilling a drop of carmellose sodium or sodium hyaluronate.Next, using curved forceps, gently push the experimental eyeball forward to expose the vasculature surrounding 360 degrees of the limbus. Then, with the other hand, using a low-temperature ophthalmic cautery, gently cauterize the vessels all around the cornea. Be careful not to cauterize the corneal periphery.Confirm the success of the surgical procedure by observing the emergence of small circular marks of cauterization on the scleral limbus, the obliteration of limbal vasculature, and pupil dilation in the operated eye. After the surgery, check the immediate postoperative IOP in both eyes as demonstrated earlier. Then, apply a drop of ophthalmic prednisolone acetate to the anterior surface of the experimental eye.After 40 seconds, replace it with an ophthalmic antibiotic ointment. Apply a daily clinical follow-up of the experimental eye with topical medications composed of a non-steroidal anti-inflammatory drug and antibiotic ointment. For optomotor response analysis, place the rat for habituation on a platform built with four computer monitors in a quadrangle.Maintain the red cross-hair cursor on the video frame between the eyes of the freely moving rat, as it indicates the center of the virtual cylinder. Observe the optomotor response consisting of a reflexive tracking of the rat head and neck elicited by the rotating gradings. Initially, introduce a stimulus with low spatial frequency, then increase the frequency progressively until tracking movement is not noticed.To record the pattern electroretinogram, after anesthetizing the rat, carefully insert the active electrode at the temporal periphery of the cornea. Additionally, insert the reference electrode into the subcutaneous tissue of the ipsilateral temporal canthus and the ground electrode into one of the hind limbs. Then position the rat 20 centimeters from the stimulus screen, monitor the signal baseline, and start the acquisition by pressing the Analysis button on the acquisition system.After isolating the retinas, transfer them into a 24-well culture plate containing one-milliliter PBS, keeping the inner retina facing up. Permeabilize the tissue by washing with a 0.5%non-ionic surfactant diluted in PBS. Then, incubate the tissue and blocking solution for one hour at room temperature with gentle shaking.During the incubation, prepare Brn-3a primary antibody solution and store at four degree Celsius. After tissue blocking, incubate the retinas in 200 microliters of primary antibody solution at four degrees Celsius for 72 hours with gentle shaking. Next, wash the tissue with PBS.Incubate the tissue in 200 microliters of the secondary antibody solution for two hours at room temperature and then with nuclear counter stain solution for 10 minutes for fluorescent nuclei staining. After three PBS washes, transfer the retina onto a glass microscope slide using two small brushes maintaining the vitreous side up. Position the dorsal retinal quadrant up on the microscope slide.Finally, apply 200 microliters of antifade mounting medium on a glass cover slip and place it onto the flat mounted retina for microscopic analysis. Under a confocal epifluorescence microscope, using a 40 times magnifying objective, examine the flat mounts to estimate retinal ganglion cells. After eyeball enucleation, remove the proximal segment of the intraorbital portion of the optic nerve, including part of the intraocular portion.Then, immediately place the samples into vials or tubes containing 200 to 300 microliters of cold fixative. After two hours, wash the tissue with cold 100 micromolar sodium cacodylate buffer. Then, post-fixate the tissue for one hour in 1%osmium tetroxide and five nanomolar calcium chloride at four degrees Celsius under gentle shaking.After three washes with cold sodium cacodylate buffer, wash the optic nerve fragments with cold distilled water before incubating overnight and 1%urinal acetate at four degrees Celsius. The following day, after three washes with water, progressively dehydrate the tissue in increasing acetone concentrations. Then, perform three rounds of embedding and epoxy resin acetone solutions before embedding the tissue in pure epoxy resin for 24 hours.The next day, remove the samples from the specimen carrier and transfer them to embedding molds for 48 hours at 60 degrees Celsius. After polymerization, use an ultra microtome to cut transversal semi-thin sections of the optic nerve fragments. Then, collect and transfer the sections onto a microscope glass slide.Stain the sections with toluidine blue and image them using an optic microscope at 100 times magnification. For ultra structural analysis, perform ultra thin cross-sections and collect them on a copper grid. Then, stain the sections with urinal acetate and lead citrate for transmission electron microscopic examination.Full-circle cauterization induced IOP elevation immediately after surgery compared to control eyes. The peak for postoperative IOP was observed on day one and decreased gradually to the baseline levels on day six. Further, retinal function was evaluated both behaviorally and electrophysiologically using optomotor reflex and pattern electroretinogram, respectively.After the surgery, both parameters showed two distinct phases of impairment:ocular hypertension acute phase on day three and a secondary degeneration phase on day 30. Compared to control optic nerves, axonal counts and semi-thin transversal optic nerve sections decreased progressively after surgery. Transmission electron micrographs of optic nerves from the control eye demonstrated densely-packed myelinated fibers separated by thin glial cell processes and evident axonal microtubules and neurofilaments.In contrast, after three days of ocular hypertension, a few degenerated fibers, cytoplasmic vacuolation in glial cell processes, and condensed chromatin in glial cell nuclei were observed. After seven days, there was an increase in degenerated axonal fibers and hypertonic glial cell processes. And after 14 days, more disarrangement of the optic nerve fibers associated with the invasion of glial cell processes among the axons were observed.Furthermore, the density of retinal ganglion cells decreased with time mainly in the dorsal and temporal retinal quadrants. While performing this procedure, try to gently touch limbal vessels with a cautery tip, sparing the cord periphery and ensuring continuous cauterization marks are observed all around the scleral limbus. Following this procedure, a variety of methods can be applied, such as functional biochemical and immunohistochemical evaluation of eye structures and other methods that may acknowledge on glaucoma physiopathology.

full-circle-cauterization-limbal-vascular-plexus-for-surgically

Research

JoVE Journal

Neuroscience

Preparing Undercut Model of Posttraumatic Epileptogenesis in Rodents

Partially isolated cortex ("undercut") is an animal model of posttraumatic epileptogenesis. The surgical procedure involves cutting through the sensorimotor cortex and the underneath white matter (undercut) so that a specific region of the cerebral cortex is largely isolated from the neighboring cortex and subcortical regions1-3. After a latency of two or more weeks following the surgery, epileptiform discharges can be recorded in brain slices from rodents1; and electrical or behavior seizures can be observed in vivo from other species such as cat and monkey4-6. This well established animal model is efficient to generate and mimics several important characteristics of traumatic brain injury. However, it is technically challenging attempting to make precise cortical lesions in the small rodent brain with a free hand. Based on the procedure initially established in Dr. David Prince's lab at the Stanford University1, here we present an improved technique to perform a surgery for the preparation of this model in mice and rats. We demonstrate how to make a simple surgical device and use it to gain a better control of cutting depth and angle to generate more precise and consistent results. The device is easy to make, and the procedure is quick to learn. The generation of this animal model provides an efficient system for study on the mechanisms of posttraumatic epileptogenesis.

Partially isolated cortex (&#x201C;undercut&#x201D;) is an efficient animal model of posttraumatic epileptogenesis. Here we demonstrate how to make a novel surgical device and use it to make more precise and consistent lesions to generate this model.

Partially isolated cortex ("undercut") is an animal model of posttraumatic epileptogenesis. The surgical procedure involves cutting through the ...

Whole Animal Perfusion Fixation for Rodents

The goal of fixation is to rapidly and uniformly preserve tissue in a life-like state. While placing tissue directly in fixative works well for small pieces of tissue, larger specimens like the intact brain pose a problem for immersion fixation because the fixative does not reach all regions of the tissue at the same rate 5,7. Often, changes in response to hypoxia begin before the tissue can be preserved 12. The advantage of directly perfusing fixative through the circulatory system is that the chemical can quickly reach every corner of the organism using the natural vascular network. In order to utilize the circulatory system most effectively, care must be taken to match physiological pressures 3. It is important to note that physiological pressures are dependent on the species used. Techniques for perfusion fixation vary depending on the tissue to be fixed and how the tissue will be processed following fixation. In this video, we describe a low-cost, rapid, controlled and uniform fixation procedure using 4% paraformaldehyde perfused via the vascular system: through the heart of the rat to obtain the best possible preservation of the brain for immunohistochemistry. The main advantage of this technique (vs. gravity-fed systems) is that the circulatory system is utilized most effectively.

Here we describe a low-cost, rapid, controlled and uniform fixation procedure using 4% paraformaldehyde perfused via the vascular system: through the heart of the rat to obtain the best possible preservation of the brain.

The goal of fixation is to rapidly and uniformly preserve tissue in a life-like state. While placing tissue directly in fixative works well for small ...

Large-scale Recording of Neurons by Movable Silicon Probes in Behaving Rodents

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of neurons and circuits requires methods with the spatial selectivity and temporal resolution appropriate for mechanistic analysis of neural ensembles in the behaving animal, i.e. recording of representatively large samples of isolated single neurons. Ensemble monitoring of neuronal activity has progressed remarkably in the past decade in both small and large-brained animals, including human subjects1-11. Multiple-site recording with silicon-based devices are particularly effective because of their scalability, small volume and geometric design.
Here, we describe methods for recording multiple single neurons and local field potential in behaving rodents, using commercially available micro-machined silicon probes with custom-made accessory components. There are two basic options for interfacing silicon probes to preamplifiers: printed circuit boards and flexible cables. Probe supplying companies (<a href="http://www.neuronexustech.com/" >http://www.neuronexustech.com/</a>; <a href="http://www.sbmicrosystems.com/">http://www.sbmicrosystems.com/</a>; <a href="http://www.acreo.se/">http://www.acreo.se/</a>) usually provide the bonding service and deliver probes bonded to printed circuit boards or flexible cables. Here, we describe the implantation of a 4-shank, 32-site probe attached to flexible polyimide cable, and mounted on a movable microdrive. Each step of the probe preparation, microdrive construction and surgery is illustrated so that the end user can easily replicate the process.

We describe methods for large-scale recording of multiple single units and local field potential in behaving rodents with silicon probes. Drive fabrication, probe attachment to the drive and probe implantation processes are illustrated in sufficient details for easy replication.

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of ...

A Low Cost Setup for Behavioral Audiometry in Rodents

In auditory animal research it is crucial to have precise information about basic hearing parameters of the animal subjects that are involved in the experiments. Such parameters may be physiological response characteristics of the auditory pathway, e.g. via brainstem audiometry (BERA). But these methods allow only indirect and uncertain extrapolations about the auditory percept that corresponds to these physiological parameters. To assess the perceptual level of hearing, behavioral methods have to be used. A potential problem with the use of behavioral methods for the description of perception in animal models is the fact that most of these methods involve some kind of learning paradigm before the subjects can be behaviorally tested, e.g. animals may have to learn to press a lever in response to a sound. As these learning paradigms change perception itself 1,2 they consequently will influence any result about perception obtained with these methods and therefore have to be interpreted with caution. Exceptions are paradigms that make use of reflex responses, because here no learning paradigms have to be carried out prior to perceptual testing. One such reflex response is the acoustic startle response (ASR) that can highly reproducibly be elicited with unexpected loud sounds in na&iuml;ve animals. This ASR in turn can be influenced by preceding sounds depending on the perceptibility of this preceding stimulus: Sounds well above hearing threshold will completely inhibit the amplitude of the ASR; sounds close to threshold will only slightly inhibit the ASR. This phenomenon is called pre-pulse inhibition (PPI) 3,4, and the amount of PPI on the ASR gradually depends on the perceptibility of the pre-pulse. PPI of the ASR is therefore well suited to determine behavioral audiograms in na&iuml;ve, non-trained animals, to determine hearing impairments or even to detect possible subjective tinnitus percepts in these animals. In this paper we demonstrate the use of this method in a rodent model (cf. also ref. 5), the Mongolian gerbil (Meriones unguiculatus), which is a well know model species for startle response research within the normal human hearing range (e.g. 6).

A fast and inexpensive method for the behavioral determination of hearing parameters like hearing thresholds, hearing impairments or phantom perceptions (subjective tinnitus) is described. It uses pre-pulse inhibition of the acoustic startle response and can be easily implemented in a personal computer using a programmable AD/DA-converter and a piezo sensor.

In auditory animal research it is crucial to have precise information about basic hearing parameters of the animal subjects that are involved in the ...

Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day1-5. Nocturnal rodents, including rats, hamsters, and mice, are active during the night and relatively inactive during the day. Many other behavioral and physiological measures also exhibit daily rhythms, but in rodents, running-wheel activity serves as a particularly reliable and convenient measure of the output of the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus. In general, through a process called entrainment, the daily pattern of running-wheel activity will naturally align with the environmental light-dark cycle (LD cycle; e.g. 12 hr-light:12 hr-dark). However circadian rhythms are endogenously generated patterns in behavior that exhibit a ~24 hr period, and persist in constant darkness. Thus, in the absence of an LD cycle, the recording and analysis of running-wheel activity can be used to determine the subjective time-of-day. Because these rhythms are directed by the circadian clock the subjective time-of-day is referred to as the circadian time (CT). In contrast, when an LD cycle is present, the time-of-day that is determined by the environmental LD cycle is called the zeitgeber time (ZT).
Although circadian rhythms in running-wheel activity are typically linked to the SCN clock6-8, circadian oscillators in many other regions of the brain and body9-14 could also be involved in the regulation of daily activity rhythms. For instance, daily rhythms in food-anticipatory activity do not require the SCN15,16 and instead, are correlated with changes in the activity of extra-SCN oscillators17-20. Thus, running-wheel activity recordings can provide important behavioral information not only about the output of the master SCN clock, but also on the activity of extra-SCN oscillators. Below we describe the equipment and methods used to record, analyze and display circadian locomotor activity rhythms in laboratory rodents.

Circadian rhythms in voluntary wheel-running activity in mammals are tightly coupled to the molecular oscillations of a master clock in the brain. As such, these daily rhythms in behavior can be used to study the influence of genetic, pharmacological, and environmental factors on the functioning of this circadian clock.

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day1-5. Nocturnal rodents, ...

Deep Brain Stimulation with Simultaneous fMRI in Rodents

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) to image rodents with simultaneous DBS. DBS fMRI presents a number of technical challenges, including accuracy of electrode implantation, MR artifacts created by the electrode, choice of anesthesia and paralytic to minimize any neuronal effects while simultaneously eliminating animal motion, and maintenance of physiological parameters, deviation from which can confound the BOLD signal.&#160;Our laboratory has developed a set of procedures that are capable of overcoming most of these possible issues. For electrical stimulation, a homemade tungsten bipolar microelectrode is used, inserted stereotactically at the stimulation site in the anesthetized subject. In preparation for imaging, rodents are fixed on a plastic headpiece and transferred to the magnet bore. For sedation and paralysis during scanning, a cocktail of dexmedetomidine and pancuronium is continuously infused, along with a minimal dose of isoflurane; this preparation minimizes the BOLD ceiling effect of volatile anesthetics. In this example experiment, stimulation of the subthalamic nucleus (STN) produces BOLD responses which are observed primarily in ipsilateral cortical regions, centered in motor cortex. Simultaneous DBS and fMRI allows the unambiguous modulation of neural circuits dependent on stimulation location and stimulation parameters, and permits observation of neuronal modulations free of regional bias. This technique may be used to explore the downstream effects of modulating neural circuitry at nearly any brain region, with implications for both experimental and clinical DBS.

This protocol describes a standard method for simultaneous functional magnetic resonance imaging and deep brain stimulation in the rodent. The combined use of these experimental tools allows for the exploration of global downstream activity in response to electrical stimulation at virtually any brain target.

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for ...

Quantification of Cerebral Vascular Architecture using Two-photon Microscopy in a Mouse Model of HIV-induced Neuroinflammation

Human Immunodeficiency Virus 1 (HIV-1) infection frequently results in HIV-1 Associated Neurocognitive Disorders (HAND), and is characterized by a chronic neuroinflammatory state within the central nervous system (CNS), thought to be driven principally by virally-mediated activation of microglia and brain resident macrophages. HIV-1 infection is also accompanied by changes in cerebrovascular blood flow (CBF), raising the possibility that HIV-associated chronic neuroinflammation may lead to changes in CBF and/or in cerebral vascular architecture. To address this question, we have used a mouse model for HIV-induced neuroinflammation, and we have tested whether long-term exposure to this inflammatory environment may damage brain vasculature and result in rarefaction of capillary networks. In this paper we describe a method to quantify changes in cortical capillary density in a mouse model of neuroinflammatory disease (HIV-1 Tat transgenic mice). This generalizable approach employs in vivo two-photon imaging of cortical capillaries through a thin-skull cortical window, as well as ex vivo two-photon imaging of cortical capillaries in mouse brain sections. These procedures produce images and z-stack files of capillary networks, respectively, which can be then subjected to quantitative analysis in order to assess changes in cerebral vascular architecture.

This paper describes a method by which the vascular architecture in the brain can be quantified using in vivo and ex vivo two-photon microscopy.

Human Immunodeficiency Virus 1 (HIV-1) infection frequently results in HIV-1 Associated Neurocognitive Disorders (HAND), and is characterized by a chronic ...

Cannula Implantation into the Cisterna Magna of Rodents

Cisterna magna cannulation (CMc) is a straightforward procedure that enables direct access to the cerebrospinal fluid (CSF) without operative damage to the skull or the brain parenchyma. In anesthetized rodents, the exposure of the dura mater by blunt dissection of the neck muscles allows the insertion of a cannula into the cisterna magna (CM). The cannula, composed either by a fine beveled needle or borosilicate capillary, is attached via a polyethylene (PE) tube to a syringe. Using a syringe pump, molecules can then be injected at controlled rates directly into the CM, which is continuous with the subarachnoid space. From the subarachnoid space, we can trace CSF fluxes by convective flow into the perivascular space around penetrating arterioles, where solute exchange with the interstitial fluid (ISF) occurs. CMc can be performed for acute injections immediately following the surgery, or for chronic implantation, with later injection in anesthetized or awake, freely moving rodents. Quantitation of tracer distribution in the brain parenchyma can be performed by epifluorescence, 2-photon microscopy, and magnetic resonance imaging (MRI), depending on the physico-chemical properties of the injected molecules. Thus, CMc in conjunction with various imaging techniques offers a powerful tool for assessment of the glymphatic system and CSF dynamics and function. Furthermore, CMc can be utilized as a conduit for fast, brain-wide delivery of signaling molecules and metabolic substrates that could not otherwise cross the blood brain barrier (BBB).

Here we describe a protocol to perform cisterna magna cannulation (CMc), a minimally invasive way to deliver tracers, substrates and signaling molecules into the cerebrospinal fluid (CSF). Combined with different imaging modalities, CMc enables glymphatic system and CSF dynamics assessment, as well as brain-wide delivery of various compounds.

Cisterna magna cannulation (CMc) is a straightforward procedure that enables direct access to the cerebrospinal fluid (CSF) without operative damage to ...

Intracranial Pharmacotherapy and Pain Assays in Rodents

Pain is a salient sensory experience with affective and cognitive dimensions. However, central mechanisms for pain remain poorly understood, hindering the development of effective therapeutics. Intracranial pharmacology presents an important tool for understanding the molecular and cellular mechanisms of pain in the brain, as well as for novel treatments. Here we present a protocol that integrates intracranial pharmacology with pain behavior testing. Specifically, we show how to infuse analgesic drugs into a select brain region, which may be responsible for pain modulation. Furthermore, to determine the effect of the candidate drug in the central nerve system, pain assays are performed after intracranial treatment. Our results demonstrate that intracranial administration of analgesic drugs in a targeted region can provide relief of pain in rodents. Thus, our protocol successfully demonstrates that intracranial pharmacology, combined with pain behavior testing, can be a powerful tool for the study of pain mechanisms in the brain.

Here we present a protocol to perform intracranial pharmacological experiments followed by pain behavior assays in rodents. This protocol allows researchers to deliver molecular and cellular targets in the brain, for pharmacologic agents in the treatment of pain.

Pain is a salient sensory experience with affective and cognitive dimensions. However, central mechanisms for pain remain poorly understood, hindering the ...

The Power of Interstimulus Interval for the Assessment of Temporal Processing in Rodents

Temporal processing deficits have been implicated as a potential elemental dimension of higher-level cognitive processes, commonly observed in neurocognitive disorders. Despite the popularization of prepulse inhibition (PPI) in recent years, many current protocols promote using a percent of control measure, thereby precluding the assessment of temporal processing. The present study used cross-modal PPI and gap prepulse inhibition (gap-PPI) to demonstrate the benefits of employing a range of interstimulus intervals (ISIs) to delineate effects of sensory modality, psychostimulant exposure, and age. Assessment of sensory modality, psychostimulant exposure, and age reveals the utility of an approach varying the interstimulus interval (ISI) to establish the shape of the ISI function, including increases (sharper curve inflections) or decreases (flattening of the response amplitude curve) in startle amplitude. Additionally, shifts in peak response inhibition, suggestive of a differential sensitivity to the manipulation of ISI, are often revealed. Thus, the systematic manipulation of ISI affords a critical opportunity to evaluate temporal processing, which may reveal the underlying neural mechanisms involved in neurocognitive disorders.

Temporal processing, a preattentive process, may underlie deficits in higher-level cognitive processes, including attention, commonly observed in neurocognitive disorders. Using prepulse inhibition as an exemplar paradigm, we present a protocol for manipulating interstimulus interval (ISI) to establish the shape of the ISI function to provide an assessment of temporal processing.