This work was supported by the Natural Sciences &#38; Engineering Council Discovery Program (US: RGPIN-2016-06694).

All rats are treated according to the guidelines of the Canadian Council on Animal Care. Approval for all the experimental procedures was granted by the Concordia University Animal Research Ethics Committee.
1. Animals
<ol>
	<li>Acquire Long Evans rats weighing 275-300 g (males) or 225-250 g (females). Double house rats in standard plastic cages with corncob bedding and shredded paper until surgery.</li>
	<li>Keep the rats on a reversed light-dark cycle (lights off at 9:30 AM, light on at 9:30 PM).</li>
	<li>Allow unlimited access to food and water, except during the food-deprivation test. Use regular rat chow (20.9% protein, 67.2% carbohydrates, and 11.8% fat).</li>
</ol>
2. Intravenous surgeries
<ol>
	<li>Build catheters and perform intravenous surgery as described in Sedki et al. 201317 with the following differences: 1) Use Isofluorane 2-2.5% for anesthesia, 2) Change the dose of penicillin administered during surgery to 60 000 IU/rat, via subcutaneous injection, and 3) Increase the dose of gentamicin in the mixture of heparin and gentamicin used to flush the catheters to 7.5 IU + 800 &#181;g; 0.2- 0.3 mL.</li>
	<li>Inject ketoprofen or carprofen, an anti-inflammatory analgesic, intraperitoneally or subcutaneously (5 mg/kg) immediately after surgery (before recovery from the anesthesia) and on the following 3 days. During the 2 days recovery period, give mashed food and heat (if necessary) to help with the recovery. Weigh and supervise the animals daily to check for any abrupt loss of weight or any other signs of health issues.</li>
</ol>
3. Behavioral procedure
<ol>
	<li>Operant conditioning chambers:
	<ol>
		<li>Set the operant conditioning chambers as described in Sedki et al. 201317.</li>
	</ol>
	</li>
	<li>Habituation day:
	<ol>
		<li>House the rats in the operant training chambers after recovery from surgery and allow animals to habituate to the chamber for 24 h before initiating any protocol. Keep animals housed in the operant chambers throughout the whole experiment.</li>
		<li>Do not attach the rats to the metal spring and do not initiate any experimental protocol (the cue-light, the tone, and the levers are not available during habituation day).</li>
	</ol>
	</li>
	<li>Heroin self-administration:
	<ol>
		<li>Attach the 5-up connector to the Tygon tube and the metal spring.</li>
		<li>Set up daily training sessions of 6 h of heroin self-administration (0.1 mg/kg/infusion) according to the procedure described below.</li>
		<li>Start daily training sessions on the onset of the dark phase of the reversed light cycle (around 9:30 AM in the representative results) with the extension of the seek lever (or take lever on the first 2 days; see below), as well as turning off the houselight on.</li>
		<li>Self-administration with only the take lever available under fixed-ratio 1 (FR1; 2 days)
		<ol>
			<li>Program each trial to begin with the insertion of the take lever.</li>
			<li>Once the rat presses the take lever one time (FR1), retract the take lever, turn on the cue light above the lever and tone for a 20 s timeout period, turn off the houselight, and allow the delivery of a heroin infusion (0.1 mg/kg in 0.13 mL)</li>
			<li>Program a 30 s inter-trial interval in which no cues are presented, the houselight is turned off, and the lever is retracted. For the beginning of the next trial, insert the take lever, and turn on the houselight.</li>
		</ol>
		</li>
		<li>Self-administration with seek-take chain under FR1 (5 days)
		<ol>
			<li>Program the operant training system to insert only the seek lever and turn on the houselight to signal the beginning of the session. The take lever is in a retracted state.</li>
			<li>Once the rat presses one time (FR1) on the seek lever, the program retracts the seek lever and inserts the take lever.</li>
			<li>One press on the take lever (FR1) retracts the take lever and initiates the same procedure as in step 3.3.4.2 and a 30 s inter-trial interval.</li>
			<li>Program the operant training system to insert the seek lever at the conclusion of the inter-trial interval and turn on the houselight to signal the beginning of the next trial.</li>
			<li>Program the operant training system to initiate the inter-trial interval if a rat fails to accomplish the seek-take chain during 10 min (not pressing the seek or the take lever) to represent the end of a trial and the loss of the opportunity to administer the drug.</li>
		</ol>
		</li>
		<li>Self-administration with seek-take chain under Variable Intervals (VI5, VI30, and VI60)
		<ol>
			<li>Program all steps in section 3.3.5 but introduce a variable interval of 5 (VI5) as the new schedule of reinforcement on the seek lever, instead of FR1. Allow self-administration training under the VI5 schedule for 3 days.</li>
			<li>Set up the software to allow the first press on the seek lever to activate the VI5 schedule. For the VI5 schedule, let the software to randomly select an interval time from a list of 0.1 s, 5 s, and 10 s, which results in an average of 5 s interval. The first seek lever press after the selected interval has elapsed, retracts the seek lever and extends the take lever.</li>
			<li>Follow steps 3.3.4.2, 3.3.5.4., 3.3.5.5.&#160;for take lever and end of trial instructions.</li>
			<li>Next, train rats for 5 days under VI30 schedule for the seek link, followed by 3 days under VI60 schedule.</li>
			<li>For the VI30 schedule, allow the software to randomly select a time from a list of 15 s, 30 s, and 45 s, for an average of 30 s, whereas for the VI60 schedule, the software randomly selects a time from a list of 45 s, 60 s, and 75 s.</li>
			<li>Vary the inter-trial intervals along the different schedules of reinforcement. Start the inter-trial interval at 30 s during FR1 and VI5 but gradually increase to 7 min during VI30 and VI60.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Punishment-imposed abstinence
	<ol>
		<li>Start punishment sessions with insertion of seek lever and turning the houselight on. Allow punishment sessions for 8 days, with regular supervision to guarantee that animals do not show signs of abnormal pain or any health issues.</li>
		<li>Program the operant training system so that after completing the seek link under VI60, the seek lever retracts, the houselight is turned off, and a mild footshock is administered on 30% of the completed seek links instead of insertion of the take lever. The take lever extends on the other 70% of completed seek links, as in a normal self-administration trial.</li>
		<li>Program an inter-trial interval of 7 min with all cues and houselight off before inserting the seek lever and turning the houselight on to signal the beginning of the next trial.</li>
		<li>Set the footshock intensity at 0.2 mA and increase by 0.1 mA per punishment day until 1.0 mA.</li>
		<li>After rats press the take lever (on trials when it is available), repeat step 3.3.4.2 for retraction of the lever, delivery of the heroin infusion, and presentation of cues, followed by a 7 min inter-trial interval.</li>
		<li>Start the next trial with the insertion of the seek lever and turning the houselight on.</li>
		<li>If the rat does not press any lever for 10 min, follow step 3.3.5.5.</li>
	</ol>
	</li>
	<li>Acute food deprivation (24 h)
	<ol>
		<li>On the day following the last day of punishment-imposed abstinence, divide rats into two matched groups (according to body weight and the average number of seek lever and infusions over the last 3 days of self-administration training): Food Deprived (FD) and Sated.</li>
		<li>Remove food hoppers from the chambers (around 9:30 AM) for rats that undergo food deprivation-induced relapse test and keep food hoppers for the sated group that has unlimited access to food. Provide unlimited access to water in both groups and supervise animals to guarantee that they do not show any health problems during the food deprivation period.</li>
	</ol>
	</li>
	<li>Food deprivation-induced heroin seeking tests
	<ol>
		<li>The morning after the 24 h of food deprivation, perform a 3 h heroin-seeking test, under a VI60 schedule with an inter-trial interval of 7 min with no shock or heroin infusions being delivered. Return food hoppers to the food-deprived rats after the 3 h session.</li>
		<li>On the morning after the first heroin seeking test, remove food hoppers from the chambers of the rats that were sated on the first relapse test. Allow the rats that were previously food-deprived unlimited access to food (sated condition) before and during the test.</li>
		<li>Perform another 3 h heroin seeking test on the next day (after 24 h food deprivation), as in step 3.6.1.</li>
		<li>The day after the test euthanize the rats using a carbon dioxide chamber (100% CO2 at fill rate of 30-70% of the chamber volume per minute).</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

There are two important demonstrations in this paper. First, the validation of the punishment-imposed abstinence using the seek and take chain with heroin. Second, it was demonstrated that stress-induced relapse could be observed in a punishment-imposed abstinence procedure. These are important demonstrations because (i) The punishment-induced abstinence procedure more closely mimics the human condition as it results in voluntary abstinence, i.e., not due to extinction of drug-seeking or forced removal from the drug-taki...

Relapse is the most challenging problem in the treatment of drug use1,2. However, only a handful of pharmacological treatments are approved to help avoid relapse in humans3. The opioid epidemic that North America is currently facing is a striking example of it, and it demands considering different approaches on animal models of relapse to opioids.
Acute stress has been shown to be a key trigger to relapse in humans4. One environmental stressor that is often associated with drug addiction is food deprivation. Drug users often choose to allocate resources towards obtaining drugs instead of food. Caloric deficit has been shown to be correlated with higher relapse to cigarettes5 and alcohol6 use. Due to ethical and practical issues, animal models have been developed over the last decades to facilitate research in the field. In animal models, acute food deprivation has been demonstrated to robustly reinstate extinguished heroin seeking7. Currently, most animal models of relapse are based on abstinence procedures that are either not representative of human abstinence (e.g., extinction-based models) or encompass only the small percentage of drug users that are forced to abstain due to incarceration or inpatient treatment (e.g., forced abstinence models). The main reason drug users choose to abstain is the negative consequences associated with drug-seeking and taking8. Punishment-imposed abstinence is an animal model that mimics the negative consequences associated with drug-seeking on self-imposed abstinence in humans. This model introduces an aversive stimulus, e.g., a mild footshock, with drug-seeking or taking, which leads the animal to stop taking the drug voluntarily. Another procedure that incorporates negative consequences for drug-seeking is the electrical barrier conflict model for drug abstinence and relapse9. The rat must cross an electrical barrier to perform the operant behavior linked with drug self-administration. The model was used successfully to demonstrate voluntary abstinence and relapse to psychostimulant and opioid drugs10,11. However, under the electrical barrier procedure, drug-seeking efforts are always associated with an aversive event, unlike the human condition. Moreover, drug-taking itself might overlap with the electrical footshock as the animal returns to the safe area following the infusion by crossing the barrier again.
Punishment-imposed abstinence has been used with other drugs of abuse such as cocaine12, alcohol13, methamphetamine14, remifentanil15, but it was never applied to heroin-trained animals. The model has been used to study relapse induced by priming14 and drug-associated cues16, but it was not integrated into a stress-induced relapse procedure. The procedure described here is used to demonstrate acute food deprivation-induced relapse to heroin seeking after punishment-imposed abstinence in male rats.

<table><tbody><tr><td>Anafen Injection 100 mg/mL Vial/50 mL</td><td>MERIAL Canada, Inc.</td><td>1938126</td><td>anti-inflammatory drug</td></tr><tr><td>Balance arm</td><td>Coulbourn Instruments</td><td>H29-01</td><td></td></tr><tr><td>Cannulae (22 G, 5-up)</td><td>Plastics One</td><td>C313G-5up</td><td></td></tr><tr><td>Environment connection board &amp;amp; Linc cable</td><td>Coulbourn Instruments</td><td>H03-04</td><td></td></tr><tr><td>Fixed speed infusion pump (3.3 RPM)</td><td>Coulbourn Instruments</td><td>A73-01-3.3</td><td></td></tr><tr><td>GE Marine Silicon</td><td>GE</td><td>SE-1134</td><td></td></tr><tr><td>Graphic State Notation 3</td><td>Coulbourn Instruments</td><td>GS3</td><td>Software</td></tr><tr><td>Habitest universal Linc</td><td>Coulbourn Instruments</td><td>H02-08</td><td></td></tr><tr><td>Heroin HCl</td><td>National Institute for Drug Abuse, Research Triangle Park, NC, USA</td><td></td><td></td></tr><tr><td>House light-Rat</td><td>Coulbourn Instruments</td><td>H11-01R</td><td></td></tr><tr><td>Isofluorane USP 99.9% Vial/250 mL</td><td>Fresenius Kabi Canada Ltd</td><td>2237518</td><td></td></tr><tr><td>Liquid Swivels, Plastic, 22 G</td><td>Lomir Biomedical, Inc.</td><td>RSP1</td><td></td></tr><tr><td>Rat test cage</td><td>Coulbourn Instruments</td><td>H10-11R-TC</td><td>Operant conditioning chambers</td></tr><tr><td>Retractable lever-Rat</td><td>Coulbourn Instruments</td><td>H23-17RA</td><td></td></tr><tr><td>Silastic tubing (ID 0.02, OD 0.037)</td><td>Fisher Scientific (Canada)</td><td>1118915A</td><td></td></tr><tr><td>Single high-bright cue-Rat</td><td>Coulbourn Instruments</td><td>H11-03R</td><td></td></tr><tr><td>Sound attenuation boxes</td><td>Concordia University</td><td>Home made</td><td></td></tr><tr><td>Stainless steal grid floor</td><td>Coulbourn Instruments</td><td>H10-11R-TC-SF</td><td></td></tr><tr><td>System controller 2</td><td>Coulbourn Instruments</td><td>SYS CTRL 2</td><td></td></tr><tr><td>System power base</td><td>Coulbourn Instruments</td><td>H01-01</td><td></td></tr><tr><td>Tone module 2.9 KHz</td><td>Coulbourn Instruments</td><td>H12-02R-2.9</td><td></td></tr><tr><td>Tygon tubing (ID 0.02, OD 0.060)</td><td>VWR</td><td>63018-044</td><td></td></tr></tbody></table>

a procedure to study stress-induced relapse of heroin seeking after punishment-imposed abstinence

The punishment-imposed abstinence procedure models the self-imposed abstinence that humans initiate due to the adverse consequences associated with drug-taking. This model has been implemented in experiments using different types of substances of abuse such as methamphetamine, cocaine, and alcohol. However, punishment-induced abstinence in heroin-trained animals has not been demonstrated. Furthermore, acute stress is a key trigger for relapse in humans and animal models. It was previously demonstrated that acute food deprivation robustly induced reinstatement of extinguished cocaine and heroin seeking. The procedure described here can be used to assess the effects of acute stress exposure on heroin seeking after punishment-imposed abstinence. A total of 8 rats were implanted with chronic intravenous (i.v.) catheters and trained to self-administer heroin (0.1 mg/kg/infusion) for 18 days under a seek-take chained schedule. Completing the seek link gave access to the take lever, which was paired with a heroin infusion. The seek lever was programmed with a variable interval 60 schedule of reinforcement (VI60), and the take lever was programmed with a fixed-ratio 1 reinforcement schedule (FR1). Following self-administration training, a mild foot shock was delivered on 30% of the completed seek links instead of the extension of the take lever. Footshock intensity was increased by 0.1 mA per daily session from 0.2 mA to 1.0 mA. Heroin-seeking tests were performed after 24 h of food deprivation (FD) or sated conditions. Rats under acute food deprivation condition robustly increased heroin seeking after punishment-imposed abstinence.

Male rats demonstrated an increase in seek lever presses as the schedule of reinforcement increased over the training days, and a reliable, consistent number of heroin infusions over training days (Figure 1). During punishment, rats decreased the number of seek lever presses and infusions with the increase of footshock intensity over 8 punishment days (Figure 2). Food-deprivation condition significantly increased heroin seeking after punishment-imposed abstinenc...

Watch this Scientific Journal Video about A Procedure to Study Stress-Induced Relapse of Heroin Seeking after Punishment-Imposed Abstinence at JoVE.com

A Procedure to Study Stress-Induced Relapse of Heroin Seeking after Punishment-Imposed Abstinence

A procedure that demonstrates a robust acute food deprivation-induced relapse to heroin seeking after punishment-imposed abstinence is described. A punishment-imposed abstinence model was successfully implemented using the seek and take chain schedule for heroin self-administration. Heroin-seeking tests are then performed following 24 h of food-deprivation stress.

The punishment-imposed abstinence procedure models the self-imposed abstinence that humans initiate due to the adverse consequences associated with ...

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JoVE Journal

Behavior

2.5K Views.  Concordia University. A procedure that demonstrates a robust acute food deprivation-induced relapse to heroin seeking after punishment-imposed abstinence is described. A punishment-imposed abstinence model was successfully implemented using the seek and take chain schedule for heroin self-administration. Heroin-seeking tests are then performed following 24 h of food-deprivation stress.

Video: A Procedure to Study Stress-Induced Relapse of Heroin Seeking after Punishment-Imposed Abstinence

A Procedure to Study the Effect of Prolonged Food Restriction on Heroin Seeking in Abstinent Rats

In human drug addicts, exposure to drug-associated cues or environments that were previously associated with drug taking can trigger relapse during abstinence. Moreover, various environmental challenges can exacerbate this effect, as well as increase ongoing drug intake.
The procedure we describe here highlights the impact of a common environmental challenge, food restriction, on drug craving that is expressed as an augmentation of drug seeking in abstinent rats.
Rats are implanted with chronic intravenous i.v. catheters, and then trained to press a lever for i.v. heroin over a period of 10-12 days. Following the heroin self-administration phase the rats are removed from the operant conditioning chambers and housed in the animal care facility for a period of at least 14 days. While one group is maintained under unrestricted access to food (sated group), a second group (FDR group) is exposed to a mild food restriction regimen that results in their body weights maintained at 90% of their nonrestricted body weight. On day 14 of food restriction the rats are transferred back to the drug-training environment, and a drug-seeking test is run under extinction conditions (i.e.&#160;lever presses do not result in heroin delivery).
The procedure presented here results in a highly robust augmentation of heroin seeking on test day in the food restricted rats. In addition, compared to the acute food deprivation manipulations we have used before, the current procedure is a more clinically relevant model for the impact of caloric restriction on drug seeking. Moreover, it might be closer to the human condition as the rats are not required to go through an extinction-training phase before the drug-seeking test, which is an integral component of the popular reinstatement procedure.

A procedure that allows a demonstration of robust augmentation of drug seeking in food-restricted rats is described. Following heroin self-administration training, rats go through an abstinence period, in a drug-free environment, during which they are mildly food restricted. Drug seeking is then tested in the drug-associated environment.

In human drug addicts, exposure to drug-associated cues or environments that were previously associated with drug taking can trigger relapse during ...

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.

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

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 ...

Neuroscience

A Procedure to Observe Context-induced Renewal of Pavlovian-conditioned Alcohol-seeking Behavior in Rats

Environmental contexts in which drugs of abuse are consumed can trigger craving, a subjective Pavlovian-conditioned response that can facilitate drug-seeking behavior and prompt relapse in abstinent drug users. We have developed a procedure to study the behavioral and neural processes that mediate the impact of context on alcohol-seeking behavior in rats. Following acclimation to the taste and pharmacological effects of 15% ethanol in the home cage, male Long-Evans rats receive Pavlovian discrimination training (PDT) in conditioning chambers. In each daily (Mon-Fri) PDT session, 16 trials each of two different 10 sec auditory conditioned stimuli occur. During one stimulus, the CS+, 0.2 ml of 15% ethanol is delivered into a fluid port for oral consumption. The second stimulus, the CS-, is not paired with ethanol. Across sessions, entries into the fluid port during the CS+ increase, whereas entries during the CS- stabilize at a lower level, indicating that a predictive association between the CS+ and ethanol is acquired. During PDT each chamber is equipped with a specific configuration of visual, olfactory and tactile contextual stimuli. Following PDT, extinction training is conducted in the same chamber that is now equipped with a different configuration of contextual stimuli. The CS+ and CS- are presented as before, but ethanol is withheld, which causes a gradual decline in port entries during the CS+. At test, rats are placed back into the PDT context and presented with the CS+ and CS- as before, but without ethanol. This manipulation triggers a robust and selective increase in the number of port entries made during the alcohol predictive CS+, with no change in responding during the CS-. This effect, referred to as context-induced renewal, illustrates the powerful capacity of contexts associated with alcohol consumption to stimulate alcohol-seeking behavior in response to Pavlovian alcohol cues.

A procedure to study the capacity of an alcohol associated environmental context to trigger the renewal of alcohol-seeking behavior in rats is described.

Environmental contexts in which drugs of abuse are consumed can trigger craving, a subjective Pavlovian-conditioned response that can facilitate ...

A Dual Task Procedure Combined with Rapid Serial Visual Presentation to Test Attentional Blink for Nontargets

When viewers search for targets in a rapid serial visual presentation (RSVP) stream, if two targets are presented within about 500 msec of each other, the first target may be easy to spot but the second is likely to be missed. This phenomenon of attentional blink (AB) has been widely studied to probe the temporal capacity of attention for detecting visual targets. However, with the typical procedure of AB experiments, it is not possible to examine how the processing of non-target items in RSVP may be affected by attention. This paper describes a novel dual task procedure combined with RSVP to test effects of AB for nontargets at varied stimulus onset asynchronies (SOAs). In an exemplar experiment, a target category was first displayed, followed by a sequence of 8 nouns. If one of the nouns belonged to the target category, participants would respond &#8216;yes&#8217; at the end of the sequence, otherwise participants would respond &#8216;no&#8217;. Two 2-alternative forced choice memory tasks followed the response to determine if participants remembered the words immediately before or after the target, as well as a random word from another part of the sequence. In a second exemplar experiment, the same design was used, except that 1) the memory task was counterbalanced into two groups with SOAs of either 120 or 240 msec and 2) three memory tasks followed the sequence and tested remembrance for nontarget nouns in the sequence that could be anywhere from 3 items prior the target noun position to 3 items following the target noun position. Representative results from a previously published study demonstrate that our procedure can be used to examine divergent effects of attention that not only enhance targets but also suppress nontargets. Here we show results from a representative participant that replicated the previous finding.&#160;

This paper describes a novel dual task procedure combined with Rapid Serial Visual Presentation to look at attentional blink at varied stimulus onset asynchronies. This experimental procedure differed from others in that it tested attentional blink for nontargets.

When viewers search for targets in a rapid serial visual presentation (RSVP) stream, if two targets are presented within about 500 msec of each other, the ...

A General Method for Evaluating Incubation of Sucrose Craving in Rats

For someone on a food-restricted diet, food craving in response to food-paired cues may serve as a key behavioral transition point between abstinence and relapse to food taking 1. Food craving conceptualized in this way is akin to drug craving in response to drug-paired cues. A rich literature has been developed around understanding the behavioral and neurobiological determinants of drug craving; we and others have been focusing recently on translating techniques from basic addiction research to better understand addiction-like behaviors related to food 2-4.
As done in previous studies of drug craving, we examine sucrose craving behavior by utilizing a rat model of relapse. In this model, rats self-administer either drug or food in sessions over several days. In a session, lever responding delivers the reward along with a tone+light stimulus. Craving behavior is then operationally defined as responding in a subsequent session where the reward is not available. Rats will reliably respond for the tone+light stimulus, likely due to its acquired conditioned reinforcing properties 5. This behavior is sometimes referred to as sucrose seeking or cue reactivity. In the present discussion we will use the term "sucrose craving" to subsume both of these constructs.
In the past decade, we have focused on how the length of time following reward self-administration influences reward craving. Interestingly, rats increase responding for the reward-paired cue over the course of several weeks of a period of forced-abstinence. This "incubation of craving" is observed in rats that have self-administered either food or drugs of abuse 4,6. This time-dependent increase in craving we have identified in the animal model may have great potential relevance to human drug and food addiction behaviors.
Here we present a protocol for assessing incubation of sucrose craving in rats. Variants of the procedure will be indicated where craving is assessed as responding for a discrete sucrose-paired cue following extinction of lever pressing within the sucrose self-administration context (Extinction without cues) or as responding for sucrose-paired cues in a general extinction context (Extinction with cues).

Responding for food or drug-paired cues increases over the course of a period of abstinence and this may relate to an increased susceptibility to relapse behaviors. Here we detail a procedure for evaluating this "incubation of craving" in rats that have self-administered sucrose.

For someone on a food-restricted diet, food craving in response to food-paired cues may serve as a key behavioral transition point between abstinence and ...

Reinstatement of Drug-seeking in Mice Using the Conditioned Place Preference Paradigm

The present protocol describes the Conditioned Place Preference (CPP) as a model of relapse in drug addiction. In this model, animals are first trained to acquire a conditioned place preference in a drug-paired compartment, and after the post-conditioning test, they perform several sessions to extinguish the established preference. The CPP permits the evaluation of the conditioned rewarding effects of drugs related to environmental cues. Then, the extinguished CPP can be robustly reinstated by the non-contingent administration of a priming dose of the drug, and by exposure to stressful stimuli. Both methods will be explained here. When the animal reinitiates the behavioral response, a reinstatement of the conditioned reward is considered to have taken place.
The main advantages of this protocol are that it is non-invasive, inexpensive, and simple with good validity criteria. In addition, it allows the study of different environmental manipulations, such as stress or diet, which can modulate relapse into drug seeking behaviors. However, one limitation is that if the researcher aims to explore the motivation and primary reinforcing effects of the drug, it should be complemented with self-administration procedures, as they involve operant responses of animals.

This protocol describes the Conditioned Place Preference (CPP) as a model of relapse. This procedure permits the measurement of relapse in laboratory animals, considering the impact of drug-associated environmental cues as craving and relapse in abstaining addicts is currently the focus of drug-abuse treatment programs.

The present protocol describes the Conditioned Place Preference (CPP) as a model of relapse in drug addiction. In this model, animals are first trained to ...

A Conditioned Place Preference Protocol for Measuring Incubation of Craving in Rats

A major cause of repeated relapses is a craving for the drug. Drug craving increases progressively during the abstinence period, a phenomenon termed incubation of drug craving. Here, we describe a morphine conditioned place preference (CPP) protocol for measuring the incubation of craving in rats. In this protocol, a CPP paradigm mainly employing somatosensory cues is used to establish a long-term reward memory of morphine. A three-chamber CPP box that differs in the texture of the chamber floor is constructed. First, the animals are tested for their baseline preference to the two side chambers for three consecutive days. Then, they are injected intraperitoneally with morphine/saline and put into their non-preferred/preferred chamber for 45 min. After 6 days of conditioning, their preference to the side chambers is tested for 15 min at different time points after the last conditioning session. With this paradigm, the reward memory of morphine could last for at least 18 days. To test whether the above-mentioned protocol can model increased craving, the number of entrances into the two side chambers are counted during the abstinence period. The results show that the entrances increased, suggesting that the CPP paradigm could mimic the incubation of craving. Future studies can employ this model to study neural mechanisms underlying long-term memory and incubation of craving.

Here, a morphine conditioned place preference (CPP) protocol is described to measure incubation of craving in rats.

A major cause of repeated relapses is a craving for the drug. Drug craving increases progressively during the abstinence period, a phenomenon termed ...

A Conflict Model of Reward-seeking Behavior in Male Rats

The present protocol describes a novel conflict task as a model of inhibitory control in rats. In this model, a natural rewarding stimulus (sexual stimulus) that represents a high-value reward, and the aversive stimuli (pins), are concurrently presented. The male rats have to climb or jump over the obstacle full of pins to approach and investigate the sexual partner. If the animal persists in their approaching behavior regardless of the aversive stimuli, it is considered as a maladaptive or risky reward-seeking behavior. The conflict task permits the evaluation of deficit in inhibitory control resulting from exposure to abused drug, such as morphine, or a stressful event. 
The main advantage of this model is that it provides a simple and quick way to discover the deficit in inhibitory control after exposure to opiate drugs or other stressful events. In addition to opiates, this behavioral model would also be useful for quickly discovering the inhibitory control deficits induced by other addictive drugs. However, the limitation is that the male rats' performance may be subject to exercising effects with repeated testing under this conflict task. In the future, one can hope that the individuals with the compulsive phenotype of reward-seeking behavior after exposure to opiates will be identified based on modifying this conflict model.

This conflict model is used to measure the impairment of inhibitory control after exposure to addictive drugs, or other factors that may influence inhibitory control. A sexual stimulus and an aversive obstacle are concurrently presented, thus male rats have to conquer the obstacle to approach the sexual reward.

The present protocol describes a novel conflict task as a model of inhibitory control in rats. In this model, a natural rewarding stimulus (sexual ...

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.

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 ...

Self-administration Studies

Behavioral reinforcement induced by the rewarding feelings following substance use sometimes leads to addiction, which is demonstrated by increased self-administration. Drug self-administration studies in rodents model human behavior during drug abuse. These models are useful in understanding the neurobiological behavior of addiction in order to help scientists discover new treatments for drug dependence.
This video reviews the concepts underlying self-administration studies. A general protocol of self-administration is discussed, which includes description of necessary equipment and different routes of administration commonly employed. Some modified protocols used to model more complex aspects of addiction, such as progressive ratio schedule and extinction, are also explained. Finally, experiments conducted in current addiction research labs will be examined.

Self-administration Studies: Principle and Protocol

Behavioral reinforcement induced by the rewarding feelings following substance use sometimes leads to addiction, which is demonstrated by increased ...

A Procedure to Study Stress-Induced Relapse of Heroin Seeking after Punishment-Imposed Abstinence

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A Procedure to Study the Effect of Prolonged Food Restriction on Heroin Seeking in Abstinent Rats

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

A Procedure to Observe Context-induced Renewal of Pavlovian-conditioned Alcohol-seeking Behavior in Rats

A Dual Task Procedure Combined with Rapid Serial Visual Presentation to Test Attentional Blink for Nontargets

A General Method for Evaluating Incubation of Sucrose Craving in Rats

Reinstatement of Drug-seeking in Mice Using the Conditioned Place Preference Paradigm

A Conditioned Place Preference Protocol for Measuring Incubation of Craving in Rats

A Conflict Model of Reward-seeking Behavior in Male Rats

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

Self-administration Studies