Name: a protocol for measuring cue reactivity in a rat model of cocaine use disorder
Uploaded: 2018-06-18T12:30:00
Description: Watch this Scientific Journal Video about A Protocol for Measuring Cue Reactivity in a Rat Model of Cocaine Use Disorder at JoVE.com

All behavioral testing was performed in the University of Texas Medical Branch (UTMB) Rodent In Vivo Assessment (RIVA) Core, directed by Dr. Kelly Dineley and housed within the Center for Addiction Research, directed by Dr. Kathryn Cunningham. Support for this work came from the Peter F. McManus Charitable Trust, National Institute of Environmental Health Sciences Center for Environmental Toxicology at UTMB (T32ES007254), Institute for Translational Sciences at UTMB (UL1TR001439), Mitchell Center for Neurodegenerative Diseases, and Center for Addiction Research at UTMB (DA007287, DA070087, and pilot study funds).

All animal manipulations are carried out in accordance with the Guide for the Care and Use of Laboratory Animals (2011) and with approval from the Institutional Animal Care and Use Committee.
1. Animals
<ol>
	<li>Acclimate male Sprague Dawley rats approximately 8-9 weeks of age (250-260 g) for a minimum of seven days in a colony room maintained at 21-23 &#176;C and 45-50% humidity on a 12 h light-dark cycle (lights on 6:00-18:00 h).</li>
	<li>House rats two/cage and handle daily thr...

Exposure to drug-paired cues and physiological changes in response to these cues16 are associated with relapse,11,16 and the cocaine cue reactivity test employed above contingently presents cocaine-paired cues in the absence of drug; thus, drug-seeking behavior in the form of previously-active lever presses&#160;serves as a measure of relapse vulnerability. The cue reactivity protocol described herein is a preclinical means by which relaps...

Cocaine use disorder (CUD) follows a trajectory of repetitive self-administration during which previously neutral stimuli gain incentive value1. Cue reactivity is the sensitivity to cues previously linked with the drug-taking experience, and it plays a prominent role in human craving2,3,4,5. The risk of progression to CUD, as well as relapse during abstinence, is thought to be higher for individuals who express high sensitivity to drug-associated cues6,7. Both environmental contexts (e.g., people, buildings, music genres) and discrete drug-associated stimuli (e.g., paraphernalia) become associated with the cocaine reward; exposure to these cues can trigger changes in peripheral physiology (e.g., heart rate, skin temperature, and skin resistance), brain plasticity, and brain functional connectivity2,8,9,10. In other words, re-exposure to cocaine-associated cues activates limbic corticostriatal circuits to evoke conditioned physiological and subjective responses that drive appetitive approach (drug-seeking) behavior11,12,13,14,15.
Cue reactivity measured with functional brain imaging analyses is predictive of relapse vulnerability in subjects with CUD16. Cue reactivity measurements in rodent models serve as a surrogate measure for relapse risk and can be exploited for translational studies. Thus, a pharmacotherapy that decreases cue reactivity in rodents may be carried forward as a relapse-prevention treatment in human clinical trials. Preclinical models with the necessary translational merit and predictive validity are especially important since there are currently no FDA-approved pharmacotherapies for CUD17.
The rodent self-administration procedure is the gold standard, translational model with predictive validity for human drug-taking18 and critically important to understanding the molecular and physiological processes underlying CUD. Response-independent delivery of cocaine results in distinct behavioral, molecular, and neurochemical effects relative to response-dependent cocaine exposure; e.g., response-independent cocaine delivery evokes significantly higher mortality19. Furthermore, the neurochemical consequences of abstinence from response-dependent cocaine self-administration are distinct from those triggered by abstinence from response-independent cocaine delivery20,21. Thus, CUD models based upon response-dependent delivery of cocaine are superior translational models when assessing cue reactivity and associated mechanisms of action.
In the protocol outlined below, cocaine is delivered intravenously through an indwelling intra-jugular catheter. However, alternative methods to self-administer drug via oral and inhalation routes have been developed. Importantly, rodents control delivery of the drug, analogous humans, through operant responses. Therefore, there is high concordance between drugs self-administered by rodents and humans22. The preclinical drug self-administration procedure below employs lever pressing, reinforced by drug delivery, to motivate response rates higher than vehicle control. Drug-seeking behavior is trained by pairing originally &#34;neutral&#34; cues (e.g., a stimulus light or tone and the contextual environment in which cocaine self-administration occurs) with cocaine infusion; these cues become conditioned reinforcers (for review:&#160;Cunningham &#38; Anastasio, 201423). Subsequent re-exposure to cocaine-associated cues triggers drug-seeking behavior in rodents (i.e., attempts to deliver cocaine through pressing on the previously-active lever) as well as craving and relapse in CUD subjects24,25,26,27.
Typically, preclinical rodent studies of drug-seeking behavior following cocaine self-administration utilize extinction training and/or drug reinstatement conducted within the drug-associated environment28,29,30,31,32. Presses on the previously-active lever, in the absence of drug and/or cue delivery, typically constitute the measure of reinstatement following extinction33,34,35. On the contrary, cue reactivity drug-seeking behavior is assessed following forced abstinence without prior extinction training28,36,37,38,39.
Outcome measures and experimental variables have been carefully chosen and validated to dissect different aspects of the neurobiology of drug-seeking and relapse-like behavior, and it is well-established that neuroadaptations differ between models with and without extinction training 40,41,42,43. Furthermore, from a translational perspective, rodent extinction training is not mirrored in clinical settings for CUD since drug-related cues include mood states, places, and people44; the unique combination of these cues are likely not available in a clinical environment45,46,47. Thus, the rodent model described herein acts as a better parallel to the human condition than many of the models currently available.
The following describes a validated cocaine self-administration training, forced abstinence and cue reactivity test protocol for rats. Briefly, rats are implanted with intra-jugular catheters, trained to self-administer cocaine or saline via &#39;active&#39; lever press, and receipt of the cocaine or saline stimulus is paired with discrete light and sound cues which serve as conditioned reinforcers. Following 14 days of cocaine self-administration, rats are subjected to 30 days of forced abstinence and a subsequent 60-min cue reactivity test in which lever pressing is measured. The cue reactivity test is a surrogate measure for cocaine relapse vulnerability in humans.

<table>
	<tbody>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Catheter Tubing: 0.50mm ID x 0.94mm OD x 0.2mm width</td>
			<td>Fisher Scientific, Hampton, NH, USA</td>
			<td>11-189-15A</td>
			<td>1/experiment</td>
		</tr>
		<tr>
			<td>Cue Light</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>ENV-229M</td>
			<td>2/operant chamber</td>
		</tr>
		<tr>
			<td>Guide Cannulae (22 gauge, pedestal size-8mm, cut length 11 mm, 5 mm above the pedestal)</td>
			<td>Plastics One, Roanoke, VA, USA</td>
			<td>8IC313G5UPXC</td>
			<td>1/rat</td>
		</tr>
		<tr>
			<td>House Light</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>ENV-227M</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>Infusion Pump</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>PHM-100</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>Levers</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>ENV-110M</td>
			<td>2/operant chamber</td>
		</tr>
		<tr>
			<td>Liquid Swivels</td>
			<td>Instech, Plymouth Meeting, PA, USA</td>
			<td>375/22</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>MED-PC Package with Infusion Pump Software</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>SOF-735 (infusions software SOF-700RA-10 version 1.04)</td>
			<td>1</td>
		</tr>
		<tr>
			<td>Metal Spring Leash</td>
			<td>Plastics One, Roanoke, VA, USA</td>
			<td>C313CS/SPC</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>Needle (23g, 1 in)</td>
			<td>Becton Dickinson, Franklin Lakes, NJ, USA</td>
			<td>305193</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>Nitex Mesh (6/6 woven mesh sheet, 12&#34;x12&#34;, 500 microns thick, 38% Open Area)</td>
			<td>Amazon, Seattle, WA, USA</td>
			<td>CMN-0500-C, B000FMUNE6</td>
			<td>~1 sheet/100 rats</td>
		</tr>
		<tr>
			<td>PCI Interface Package</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>DIG-700P2-R2, MED-SYST-16</td>
			<td>1/16 operant chambers</td>
		</tr>
		<tr>
			<td>Power Supply for Interface Modules</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>SG-6510D</td>
			<td>1/16 operant chambers</td>
		</tr>
		<tr>
			<td>Sound-attenuating Cubicle</td>
			<td>Med-Associates Inc. St. Albans, VT, USA</td>
			<td>ENV-018V</td>
			<td>1/operant chamber</td>
		</tr>
		<tr>
			<td>Syringes, 10 mL Luer-Lok&#8482; tip</td>
			<td>Fisher Scientific, Hampton, NH, USA</td>
			<td>14-827-52</td>
			<td>1 case/experiment (1/operant chamber)</td>
		</tr>
		<tr>
			<td>Tygon Tubing for flushes: 0.51mmID x 1.52mmOD 0.51mm thick x 152.4m</td>
			<td>Fisher Scientific, Hampton, NH, USA</td>
			<td>14-170-15B</td>
			<td>1/experiment</td>
		</tr>
		<tr>
			<td>Chemicals</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Acepromazine (10mg/mL)</td>
			<td>Henry Schein (Animal Health), Melville, NY, USA</td>
			<td>003845</td>
			<td>~0.5mg/rat*</td>
		</tr>
		<tr>
			<td>Acraweld Repair Resin</td>
			<td>Henry Schein (Dental), Melville, NY, USA</td>
			<td>1013959</td>
			<td>1/experiment</td>
		</tr>
		<tr>
			<td>Altalube (ophthalmic ointment)</td>
			<td>Henry Schein (Dental), Melville, NY, USA</td>
			<td>6050059</td>
			<td>1/experiment</td>
		</tr>
		<tr>
			<td>Cocaine</td>
			<td>NIDA North Bethesda, MD, USA</td>
			<td>N/A</td>
			<td>~350mgs/rat for whole experiment*; requires DEA License</td>
		</tr>
		<tr>
			<td>Heparin (10,000 USP units/10 mL)</td>
			<td>SAGENT Pharmaceuticals, Schaumburg, IL, USA</td>
			<td>NDC 25021-400-10</td>
			<td>1/experiment (~21 units/rat*)</td>
		</tr>
		<tr>
			<td>Jet Liquid</td>
			<td>Henry Schein (Dental), Melville, NY, USA</td>
			<td>1256401</td>
			<td>1/experiment</td>
		</tr>
		<tr>
			<td>Ketamine (100mg/mL, 10mL)</td>
			<td>Henry Schein (Dental), Melville, NY, USA</td>
			<td>1049007</td>
			<td>~15mg/rat*; requieres DEA license</td>
		</tr>
		<tr>
			<td>Methohexital Sodium (Brevital&#174;, 500 mg/50 mL)</td>
			<td>Patterson Dental, Saint Paul, MN, USA</td>
			<td>043-5461</td>
			<td>1/experiment; requires DEA License</td>
		</tr>
		<tr>
			<td>Saline (0.9%, USP)</td>
			<td>Baxter, Deerfield, IL, USA</td>
			<td>2B1307</td>
			<td>1 case/experiment</td>
		</tr>
		<tr>
			<td>Streptokinase from &#946;-hemolytic Streptococcus (Lancefield Group C) &#8805;3,000 units/mg</td>
			<td>Sigma Aldrich, St. Louis, MO, USA</td>
			<td>S3134-250KU</td>
			<td>1 vial/experiment (~1.5mg/rat/experiment*)</td>
		</tr>
		<tr>
			<td>Ticarcillin Disodium Salt</td>
			<td>Fisher Scientific, Hampton, NH, USA</td>
			<td>50-213-695</td>
			<td>~4 vials/exeriment or purchase the 25g vial cat.# 50-489-093 (~150mg/rat/experiment*)</td>
		</tr>
		<tr>
			<td>Xylazine (100mg/mL)</td>
			<td>Henry Schein (Animal Health), Melville, NY, USA</td>
			<td>033198</td>
			<td>~3mg/rat*</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>*Assumes rat age is that described in the protocol, rats self-administer for 14 days, and flushes occur for 21 days.</td>
		</tr>
	</tbody>
</table>

a protocol for measuring cue reactivity in a rat model of cocaine use disorder

Cocaine use disorder (CUD) follows a trajectory of repetitive self-administration during which previously neutral stimuli gain incentive value. Cue reactivity, the sensitivity to cues previously linked with the drug-taking experience, plays a prominent role in human craving during abstinence. Cue reactivity can be assessed as the attentional orientation toward drug-associated cues that is measurable as appetitive approach behavior in both preclinical and human studies. Herein describes an assessment of cue reactivity in rats trained to self-administer cocaine. Cocaine self-administration is paired with the presentation of discrete cues that act as conditioned reinforcers (i.e., house light, stimulus light, infusion pump sounds). Following a period of abstinence, lever presses in the cocaine self-administration context accompanied by the discrete cues previously paired with cocaine infusion are measured as cue reactivity. This model is useful to explore neurobiological mechanisms underlying cue reactivity processes as well as to assess pharmacotherapies to suppress cue reactivity and therefore, modify relapse vulnerability. Advantages of the model include its translational relevance, and its face and predictive validities.&#160;The primary limitation of the model is that the cue reactivity task can only be performed infrequently and must only be used in short duration (e.g., 1 hour), otherwise rats will begin to extinguish the pairing of the discrete cues with the cocaine stimulus. The model is extendable to any positively reinforcing stimulus paired with discrete cues; though particularly applicable to drugs of abuse, this model may hold future applications in fields such as obesity, where palatable food rewards can act as positively reinforcing stimuli.

Results of a cocaine self-administration and abstinence experiment followed by a cue reactivity test from a previously published study57 are shown in Figure 1. The study timeline is depicted in Figure 1A.
Rats individually transition from FR1 to FR5 as they meet criteria. As operant conditioning proceeds in the cocaine-administering group, rats g...

Watch this Scientific Journal Video about A Protocol for Measuring Cue Reactivity in a Rat Model of Cocaine Use Disorder at JoVE.com

A Protocol for Measuring Cue Reactivity in a Rat Model of Cocaine Use Disorder

Cue reactivity is conceptualized as sensitivity to cues linked with drug-taking experiences that contribute to craving and relapse in abstinent humans. Cue reactivity is modeled in rats by measuring attentional orientation toward drug-associated cues that results in appetitive approach behavior in a cue reactivity test following self-administration and forced abstinence.

Cocaine use disorder (CUD) follows a trajectory of repetitive self-administration during which previously neutral stimuli gain incentive value. Cue ...

In this protocol, cue reactivity measures an animal's motivation to seek cocaine following absence from cocaine self-administration. Cue reactivity occurs when the rat is re-exposed to the context and cues previously associated with intravenous cocaine delivery. Cue reactivity is a measure for relapse risk.The cue reactivity protocol described here is a pre-clinical means to test relapse modifying pharmacotherapies as well as investigate genetic and environmental factors that contribute to relapse risk. This is an operant task for drug-seeking behavior that aligns with many properties of human drug taking and relapse. Optimization of key parameters such as cocaine dose, delivery volume, and infusion duration have been made to establish phase validity and translational productive power.For this protocol, use male Sprague Dawley rats that are roughly eight to nine weeks old which have been acclimated to the colony room for at least seven days. During the acclimation period, house the rats in pairs and handle them daily throughout the study. Provide unlimited access to food in their home cages throughout all phases of the study.Implant jugular vein catheters using the method outlined by Kmiotek and collaborators in their JoVE video, then randomly assign the rats to saline or cocaine treatment groups. For training, program schedules for cocaine self-administration as described in the text protocol. Equip the training chambers with two retractable response levers, a stimulus light above each response lever, and a house light opposite the levers.Deliver cocaine or saline from syringe infusion pumps outside of the cubicle. Use 23 gauge needles attached to the syringes and polyethylene tubing encased in a metal spring leash attached to the rat's catheters. Cocaine or saline is delivered after an active lever press, but not after inactive lever press.Change the solutions daily. Use freshly made cocaine dilutions in sterile 0.9%sodium chloride tailored to each rat's weight. Load at least eight milliliters of solution into each rat's syringe.Begin with training the rats on an FR1 schedule of reinforcement and progress to an FR5 schedule after three straight days of seven infusions per hour with less than 10%variability in the total number of infusions per session. It is imperative to analyze self-administration behavior data on a daily basis to determine when to advance an animal to FR5 and to check for loss of catheter patency. One of the most critical steps of the protocol is to monitor self-administration during the first 14 days of training to ensure the animal self-administer normally.If self-administration dramatically decreases, the rat's catheter has likely lost patency. At the start of a session, check that there are no bubbles in the syringe. Attach the syringe to the polyethylene tubing and insert it into the infusion pump.Carefully adjust the syringe so that the solution is evenly and completely distributed in the polyethylene tubing. Next, connect the rats to the delivery system and place them into their respective standard operant conditioning chambers housed in ventilated sound-attenuating cubicles with fans. Consistency throughout the experiment is vital.Always place a rat into the same chamber and keep the active lever on the same side within that chamber. Over 14 daily 180-minute sessions, the rats have free access to the levers and will readily learn which lever provides stimulation provided the system is working. Each trigger of the active lever on a fixed ratio schedule of one releases 0.1 milliliters of solution over six seconds and simultaneously illuminates the cage light and the stimulus light above the active lever.There is a one-second delay before solution is released. Following each cocaine or saline delivery, the stimulus light and infusion pump are deactivated for 20 seconds during which the house light remains on and pressing the lever does nothing but is recorded. When the light goes off, the lever is reactivated.Any triggering of the inactive lever produces no scheduled consequences. At the end of that 180-minute session, use slow careful movements to remove the potentially aggressive rat from the chamber. Then flush its catheter.Between sessions, carefully clean the chambers. Wipe down every surface with a 70%ethanol solution. At the end of the training sessions, put the rats into forced abstinence for 30 days with no access to the operant chamber.Continue to handle the rats on a daily basis and monitor the general health. After the long abstinence period, allow the rats 60 minutes in the operant chamber immediately followed by brain harvesting. For this session, run the cue reactivity scheduled program.Stagger the session start times to allow time to harvest brains between sessions. Importantly, operate the pump without the syringe attached so the auditory cue of the pump is still a part of the stimulus without the substance delivery. Begin this session as usual with the rat in the self-administration chamber in which it was trained.In this test, when the active lever that previously delivered cocaine or saline is pressed, only the cues are delivered on an FR1 schedule. The inactive lever still does nothing. Record all the cue presentations, previously active lever presses and inactive lever presses as well as the latency to first lever press.Using the described protocol, a study was conducted and rats were individually transitioned from FR1 to FR5 as they met criteria. In the cocaine-administering group, rats gradually increased number of infusions until they reached criterion, then they were transitioned from FR1 to FR5. Multiple output measures were gathered from the cocaine cue reactivity test.For example, rats which previously self-administered cocaine pressed the previously active lever much more than rats which self-administered saline. Another important output measure is latency to first level press. When a change in this is observed, the animal may be physically stressed or have decreased motivation for cocaine self-administration.Locomotor behavior tasks can be used to assess changes in physical health and differentiate motor impairment from motivational changes. After watching this video, you should have a good understanding of how to train rats to self-administer a drug, maintain catheter patency during self-administration, and assess cue reactivity to drug-associated cues following abstinence as a measure of relapse risk. While attempting this procedure, it's important to remember to carefully program the software, properly handle the animals, and regularly flush intravenous catheters.Following this procedure, one can assess the cellular and molecular mechanisms that drive cocaine cue reactivity as well as test potential pharmacotherapuetics that modify cocaine cue reactivity.

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Research

JoVE Journal

Neuroscience

A Procedure for Studying the Footshock-Induced Reinstatement of Cocaine Seeking in Laboratory Rats

The most insidious aspect of drug addiction is the high propensity for relapse. Animal models of relapse, known as reinstatement procedures, have been used extensively to study the neurobiology and phenomenology of relapse to drug use. Although procedural variations have emerged over the past several decades, the most conventional reinstatement procedures are based on the drug self-administration (SA) model. In this model, an animal is trained to perform an operant response to obtain drug. Subsequently, the behavior is extinguished by withholding response-contingent reinforcement. Reinstatement of drug seeking is then triggered by a discrete event, such as an injection of the training drug, re-exposure to drug-associated cues, or exposure to a stressor 1.
Reinstatement procedures were originally developed to study the ability of acute non-contingent exposure to the training drug to reinstate drug seeking in rats and monkeys 1, 2. Reinstatement procedures have since been modified to study the role of environmental stimuli, including drug-associated cues and exposure to various forms of stress, in relapse to drug seeking 1, 3, 4.
Over the past 15 years, a major focus of the reinstatement literature has been on the role of stress in drug relapse. One of the most commonly used forms of stress for studying this relationship is acute exposures to mild, intermittent, electric footshocks. The ability of footshock stress to induce reinstatement of drug seeking was originally demonstrated by Shaham and colleagues (1995) in rats with a history of intravenous heroin SA5. Subsequently, the effect was generalized to rats with histories of intravenous cocaine, methamphetamine, and nicotine SA, as well as oral ethanol SA 3, 6.
Although footshock-induced reinstatement of drug seeking can be achieved reliably and robustly, it is an effect that tends to be sensitive to certain parametrical variables. These include the arrangement of extinction and reinstatement test sessions, the intensity and duration of footshock stress, and the presence of drug-associated cues during extinction and testing for reinstatement. Here we present a protocol for footshock-induced reinstatement of cocaine seeking that we have used with consistent success to study the relationship between stress and cocaine seeking.

Animal models of relapse, known as reinstatement procedures, have been used extensively to study the role of stress in relapse to drug seeking. Here, we report on a method for inducing the reinstatement of cocaine seeking in laboratory rats via acute exposures to mild, intermittent electric footshock.

The most insidious aspect of drug addiction is the high propensity for relapse.  Animal models of relapse, known as reinstatement procedures, have been ...

Isolation and Culture of Rat Embryonic Neural Cells: A Quick Protocol

We are describing a quick method to dissociate and culture hippocampal or cortical neurons from E15-17 rat embryos. The procedure can be applied successfully to the isolation of mouse and human primary neurons and neural progenitors. Dissociated neurons are maintained in serum-free medium up to several weeks. These cultures can be used for nucleofection, immunocytochemistry, nucleic acids preparation, as well as electrophysiology. Older neuronal cultures can also be transfected with a good efficiency rate by lentiviral transduction and, less efficiently, with calcium phosphate or lipid-based methods such as lipofectamine.

We describe a rapid methodology to isolate and culture hippocampal and cortical neurons from rodent embryos. This protocol allows us to perform experiments in which nearly pure neuronal cultures are required.

We are describing a quick method to dissociate and culture hippocampal or cortical neurons from E15-17 rat embryos. The procedure can be applied ...

Trypsin Digest Protocol to Analyze the Retinal Vasculature of a Mouse Model

Trypsin digest is the gold standard method to analyze the retinal vasculature 1-5. It allows visualization of the entire network of complex three-dimensional retinal blood vessels and capillaries by creating a two-dimensional flat-mount of the interconnected vascular channels after digestion of the non-vascular components of the retina. This allows one to study various pathologic vascular changes, such as microaneurysms, capillary degeneration, and abnormal endothelial to pericyte ratios. However, the method is technically challenging, especially in mice, which have become the most widely available animal model to study the retina because of the ease of genetic manipulations 6,7. In the mouse eye, it is particularly difficult to completely remove the non-vascular components while maintaining the overall architecture of the retinal blood vessels. To date, there is a dearth of literature that describes the trypsin digest technique in detail in the mouse. This manuscript provides a detailed step-by-step methodology of the trypsin digest in mouse retina, while also providing tips on troubleshooting difficult steps.

Trypsin digest is one of the most commonly used methods to analyze retinal vasculature. This manuscript describes the method in detail, including key alterations to optimize the technique and remove the non-vascular tissue while preserving the overall architecture of the vessels.

Trypsin digest is the gold standard method to analyze the retinal vasculature 1-5. It allows visualization of the entire network of complex ...

Use of a Caspase Multiplexing Assay to Determine Apoptosis in a Hypothalamic Cell Model

The ability to multiplex assays in studies of complex cellular mechanisms eliminates the need for repetitive experiments, provides internal controls, and decreases waste in costs and reagents. Here we describe optimization of a multiplex assay to assess apoptosis following a palmitic acid (PA) challenge in an in vitro hypothalamic model, using both fluorescent and luminescent based assays to measure viable cell counts and caspase-3/7 activity in a 96-well microtiter plate format. Following PA challenge, viable cells were determined by a resazurin-based fluorescent assay. Caspase-3/7 activity was then determined using a luminogenic substrate, DEVD, and normalized to cell number. This multiplexing assay is a useful technique for determining change in caspase activity following an apoptotic stimulus, such as saturated fatty acid challenge. The saturated fatty acid PA can increase hypothalamic oxidative stress and apoptosis, indicating the potential importance of assays such as that described here in studying the relationship between saturated fatty acids and neuronal function.

Multiplex assays can provide beneficial information for basic cellular mechanisms&#160;and eliminate waste of reagents and unnecessary repetitive experiments. We describe here a multiplex caspase-3/7 activity assay, using fluorescent- and luminescent-based methods, to determine cell viability in an in vitro hypothalamic model following oxidative challenge with palmitic acid.

The ability to multiplex assays in studies of complex cellular mechanisms eliminates the need for repetitive experiments, provides internal controls, and ...

Measuring Progressive Neurological Disability in a Mouse Model of Multiple Sclerosis

After intracerebral infection with the Theiler's Murine Encephalomyelitis Virus (TMEV), susceptible SJL mice develop a chronic-progressive demyelinating disease, with clinical features similar to the progressive forms of multiple sclerosis (MS). The mice show progressive disability with loss of motor and sensory functions, which can be assessed with multiple apparatuses and protocols. Among them, the Rotarod performance test is a very common behavioral test, its advantage being that it provides objective measurements, but it is often used assuming that it is straightforward and simple. In contrast to visual scoring systems used in some models of MS, which are highly subjective, the Rotarod test generates an objective, measurable, continuous variable (i.e., length of time), allowing almost perfect inter-rater concordances. However, inter-laboratory reliability is only achieved if the various testing parameters are replicated. In this manuscript, recommendations of specific testing parameters, such as size, speed, and acceleration of the rod; amount of training given to the animals; and data processing, are presented for the Rotarod test.

An optimized testing protocol is presented in this paper for the Rotarod performance test, used for measuring progressive neurological disability in TMEV-infected mice.

After intracerebral infection with the Theiler's Murine Encephalomyelitis Virus (TMEV), susceptible SJL mice develop a chronic-progressive demyelinating ...

The Use of Trace Eyeblink Classical Conditioning to Assess Hippocampal Dysfunction in a Rat Model of Fetal Alcohol Spectrum Disorders

Neonatal rats were administered a relatively high concentration of ethyl alcohol (11.9% v/v) during postnatal days 4-9, a time when the fetal brain undergoes rapid organizational change and is similar to accelerated brain changes that occur during the third trimester in humans. This model of fetal alcohol spectrum disorders (FASDs) produces severe brain damage, mimicking the amount and pattern of binge-drinking that occurs in some pregnant alcoholic mothers. We describe the use of trace eyeblink classical conditioning (ECC), a higher-order variant of associative learning, to assess long-term hippocampal dysfunction that is typically seen in alcohol-exposed adult offspring. At 90 days of age, rodents were surgically prepared with recording and stimulating electrodes, which measured electromyographic (EMG) blink activity from the left eyelid muscle and delivered mild shock posterior to the left eye, respectively. After a 5 day recovery period, they underwent 6 sessions of trace ECC to determine associative learning differences between alcohol-exposed and control rats. Trace ECC is one of many possible ECC procedures that can be easily modified using the same equipment and software, so that different neural systems can be assessed. ECC procedures in general, can be used as diagnostic tools for detecting neural pathology in different brain systems and different conditions that insult the brain.

Trace eyeblink classical conditioning (ECC) was used to assess hippocampal-dependent associative learning in adult rats that were administered a high concentration (11.9% v/v) of alcohol during early neonatal brain development. In general, ECC procedures are sound diagnostic tools for detecting brain dysfunction across many psychological and biomedical settings.

Neonatal rats were administered a relatively high concentration of ethyl alcohol (11.9% v/v) during postnatal days 4-9, a time when the fetal brain ...

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the ...

Online Transcranial Magnetic Stimulation Protocol for Measuring Cortical Physiology Associated with Response Inhibition

We describe the development of a reproducible, child-friendly motor response inhibition task suitable for online Transcranial Magnetic Stimulation (TMS) characterization of primary motor cortex (M1) excitability and inhibition. Motor response inhibition prevents unwanted actions and is abnormal in several neuropsychiatric conditions. TMS is a non-invasive technology that can quantify M1 excitability and inhibition using single- and paired-pulse protocols and can be precisely timed to study cortical physiology with high temporal resolution. We modified the original Slater-Hammel (S-H) stop signal task to create a &#34;racecar&#34; version with TMS pulses time-locked to intra-trial events. This task is self-paced, with each trial initiating after a button push to move the racecar towards the 800 ms target. GO trials require a finger-lift to stop the racecar just before this target. Interspersed randomly are STOP trials (25%) during which the dynamically adjusted stop signal prompts subjects to prevent finger-lift. For GO trials, TMS pulses were delivered at 650 ms after trial onset; whereas, for STOP trials, the TMS pulses occurred 150 ms after the stop signal. The timings of the TMS pulses were decided based on electroencephalography (EEG) studies showing event-related changes in these time ranges during stop signal tasks. This task was studied in 3 blocks at two study sites (n=38) and we recorded behavioral performance and event-related motor-evoked potentials (MEP). Regression modelling was used to analyze MEP amplitudes using age as a covariate with multiple independent variables (sex, study site, block, TMS pulse condition [single- vs. paired-pulse], trial condition [GO, successful STOP, failed STOP]). The analysis showed that TMS pulse condition (p&#60;0.0001) and its interaction with trial condition (p=0.009) were significant. Future applications for this online S-H/TMS paradigm include the addition of simultaneous EEG acquisition to measure TMS-evoked EEG potentials. A potential limitation is that in children, the TMS pulse sound could&#160;affect behavioral task performance.

We describe an experimental procedure to quantify excitability and inhibition of primary motor cortex during a motor response inhibition task by using Transcranial Magnetic Stimulation throughout the course of a Stop Signal Task.

We describe the development of a reproducible, child-friendly motor response inhibition task suitable for online Transcranial Magnetic Stimulation (TMS) ...

A Hydrophobic Tissue Clearing Method for Rat Brain Tissue

Hydrophobic tissue clearing methods are easily adjustable, fast, and low-cost procedures that allows for the study of a molecule of interest in unaltered tissue samples. Traditional immunolabeling procedures require cutting the sample into thin sections, which restricts the ability to label and examine intact structures. However, if brain tissue can remain intact during processing, structures and circuits can remain intact for the analysis. Previously established clearing methods take significant time to completely clear the tissue, and the harsh chemicals can often damage sensitive antibodies. The iDISCO method quickly and completely clears tissue, is compatible with many antibodies, and requires no special lab equipment. This technique was initially validated for the use in mice tissue, but the current protocol adapts this method to image hemispheres of control and transgenic rat brains. In addition to this, the present protocol also makes several adjustments to preexisting protocol to provide clearer images with less background staining. Antibodies for Iba-1 and tyrosine hydroxylase were validated in the HIV-1 transgenic rat and in F344/N control rats using the present hydrophobic tissue clearing method. The brain is an interwoven network, where structures work together more often than separately of one another. Analyzing the brain as a whole system as opposed to a combination of individual pieces is the greatest benefit of this whole brain clearing method.

Here we present a hydrophobic tissue clearing method that allows for the viewing of target molecules as part of intact brain structures. This technique has now been validated for F344/N control and HIV-1 transgenic rats of both sexes.

Hydrophobic tissue clearing methods are easily adjustable, fast, and low-cost procedures that allows for the study of a molecule of interest in unaltered ...

Applying the RatWalker System for Gait Analysis in a Genetic Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder caused by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta. Gait abnormalities, including decreased arm swing, slower walking speed, and shorter steps are common in PD patients and appear early in the course of disease. Thus, the quantification of motor patterns in animal models of PD will be important for phenotypic characterization during disease course and upon therapeutic treatment. Most cases of PD are idiopathic; however, the identification of hereditary forms of PD uncovered gene mutations and variants, such as loss-of-function mutations in Pink1 and Parkin, two proteins involved in mitochondrial quality control that could be harnessed to create animal models. While mice are resistant to neurodegeneration upon loss of Pink1 and Parkin (single and combined deletion), in rats, Pink1 but not Parkin deficiency leads to nigral DA neuron loss and motor impairment. Here, we report the utility of FTIR imaging to uncover gait changes in freely walking young (2 months of age) male rats with combined loss of Pink1 and Parkin prior to the development of gross visually apparent motor abnormality as these rats age (observed at 4-6 months), characterized by hindlimb dragging as previously reported in Pink1 knockout (KO) rats.

Applying the RatWalker System for Gait Analysis in a Genetic Rat Model of Parkinson&#039;s Disease

Here we describe the RatWalker system, built by redesigning the MouseWalker apparatus to accommodate for the increased size and weight of rats. This system uses frustrated total internal reflection (FTIR), high-speed video capture, and open-access analysis software to track and quantify gait parameters.