This paper was supported by CAS Key Laboratory of Mental Health, Institute of Psychology (KLMH2016K01) and Evaluation and Intervention Technology Research for Post-traumatic Stress Patients Population (JCYJ20170413170301569)

This study is approved by the International Review Board (IRB) of the Institute of Psychology, Chinese Academy of Sciences, and all experiments are conducted in accordance with the National Institutes of Health (U.S.A) Guide for Care and Use of Laboratory Animals (2011).
1. Materials and Setup for the Conflict Model
<ol>
	<li>House four rats per cage (50 cm long x 22.5 cm wide x 30 cm high) in colony rooms with controlled temperature (22&#8211;25 &#176;C) and a reversed 12 h/12 h light/dark cycle (lights on at 21:00) for at least 10 days. 
	NOTE: Male and female Sprague-Dawley rats weighing 330&#8211;400 and 230&#8211;250 g at the beginning of the experiments, respectively were used.</li>
	<li>Perform all the tests under dim lighting during the dark phase.</li>
	<li>Use the opaque cartons (37 cm long x 26 cm wide x 18 cm high) with pine wood shaving bedding to transport rats from home cages to testing rooms.</li>
	<li>Handle rats 3 min each per day for 5 days prior to beginning the experiments.</li>
	<li>Prepare 120 mL of morphine for the whole experiment. Dissolve morphine hydrochloride in 0.9% NaCl (physiological saline) at a final concentration of 20 mg/mL. Store at room temperature (RT).</li>
	<li>Prepare 10 mL of the pentobarbital sodium solution for the surgery. Dissolve pentobarbital sodium in 0.9% NaCl at a concentration of 1 g/mL. Store at 4 &#176;C.</li>
	<li>Prepare 10 mL of estradiol benzoate (EB) and 10 mL of progesterone for artificial induction of estrus. Dissolve estradiol benzoate and progesterone in sesame oil at a concentration of 0.125 mg/mL and 5 mg/mL, respectively. 
	NOTE: Incubate the oil suspension of EB or progesterone in a water bath (55&#8211;60 &#176;C) for at least 1 h and then thoroughly shake it. Ensure that EB or progesterone is dissolved completely. Store at RT.</li>
	<li>For the risky reward-seeking behavior testing, use the open-field reward-proximity chambers made of black acrylic glass. At one end of the open-field arena (85 cm long x 35 cm wide x 50 cm high) mount a wire-screen stimulus cage (15 cm long x 25 cm wide x 25 cm high). Install the board with pins on the floor about 20 cm in front of the stimulus-cage. 
	NOTE: Pins are fixed on the 34.5 cm long x 13 cm wide boards (Figure 1). The boards with three types of pins are used in turn during testing (Table 2).</li>
</ol>
2. Estrus induction in Females and Mating Screening in Males
<ol>
	<li>Bilateral ovariectomy in female rats 
	NOTE: The surgical instruments and other items used in surgery are sterile. And surgery is performed using aseptic technique.
	<ol>
		<li>Prepare surgical instruments and materials such as scalpels, surgical blades, hemostatic forceps, tweezers, ophthalmic scissors, gauze, cotton swabs, suture needles and silk sutures in advance, as well as 75% alcohol, iodine, sodium pentobarbital, 0.9% NaCl, penicillin sodium.</li>
		<li>Intraperitoneally inject pentobarbital sodium (55 mg/kg), waiting for complete anesthesia of female rats. Rats respire smoothly and do not react to tail pinch. 
		NOTE: The ovariectomy is performed only when the weight of female rat reaches at least 240 g.</li>
		<li>Place the female rat in prone position, shave off the fur on the back, and disinfect the exposed skin with iodophor. Then use a scalpel to make a middle vertical incision (about 2 cm long) on the back (1 cm below the edge of the ribcage).</li>
		<li>Pull the skin to the left side, and blunt dissect subcutaneous tissue with hemostatic forceps to expose the lumbar muscles. Cut the muscle layer (incision of 1 cm) into the abdominal cavity, till the adipose tissue is reached.</li>
		<li>Pull out the adipose tissue with bent tweezers, and locate the ovary which is a flesh-pink tissue (about 0.5 cm x 0.4 cm x 0.3 cm) surrounded by adipose tissue with the twining fallopian tube on the surface.</li>
		<li>Clamp the fallopian tube with forceps and ligate it, then cut off the ovary together with the surrounding adipose tissue.</li>
		<li>Put the residual fallopian tube and adipose tissue back into the abdominal cavity after ensuring no bleeding, and suture the muscle layer.</li>
		<li>Remove the ovary on the other side by the same procedure and then suture the skin incision.</li>
		<li>Place the rat on a heated blanket till awakening and then put it back into the home cage.</li>
		<li>After at least two weeks of recovery, use the female rats as a tool for mating screening and behavioral testing. 
		NOTE: Pay attention to the state of the female rat after surgery, and supply adequate water and food. Keep the ovariectomized rats single housed for one week and then house four per cage.</li>
	</ol>
	</li>
	<li>Induction of estrus in ovariectomized female rats
	<ol>
		<li>Handle all ovariectomized female rats three times (3 min/day) before using them for mating screening.
		<ol>
			<li>Gently pick up a rat from the transport box with the left hand and hold it in the arms for a few seconds. Then put the rat back into the box and repeat these operations for 3 min.</li>
		</ol>
		</li>
		<li>Subcutaneously inject estradiol benzoate (25 &#956;g/rat) about 48&#8211;52 h before mating screening or the conflict test.</li>
		<li>Subcutaneously inject progesterone (1 mg/rat) about 4&#8211;6 h before mating screening or the conflict test. 
		NOTE: The estrogenic hormones are injected subcutaneously on the back of the neck. Since an estrus cycle lasts for ~4&#8210;5 days, the female rats are used once a week.</li>
	</ol>
	</li>
	<li>Screening male rats for mating performance 
	NOTE: Screening is conducted under dim light during the dark phase of the light/dark cycle in the housing room.
	<ol>
		<li>Place a male rat individually into the carton (60 cm long x 50 cm wide x 40 cm high) with pine wood shaving bedding and leave it to habituate for 5 min.</li>
		<li>Introduce an estrous female rat into the carton and monitor male copulatory behaviors (by experienced observers).</li>
		<li>Put the rats back to home cages after male rats complete their first ejaculation within 30 min or do not display intromission within 15 min or ejaculation within 30 min.</li>
		<li>Assign the male rats that pass the screening (successful ejaculation for three consecutive days) randomly into different groups (such as the saline- and morphine-treated groups).</li>
	</ol>
	</li>
</ol>
3. Pretreatment in Male Rats Prior to the Conflict Test
<ol>
	<li>Binge-like morphine treatment 
	NOTE: Male rats are intraperitoneally injected with saline or morphine delivered in a binge-like regimen14 (Table 1).
	<ol>
		<li>Weigh the male rats and calculate the injection volume for each rat based on the body weight (see Table 1).</li>
		<li>Prepare syringes with morphine or saline solutions.</li>
		<li>Inject one rat at a time intraperitoneally and immediately place it gently into the home cage (4 rats/cage).</li>
		<li>After at least 6 h, give the male rats the second injection in the same way.</li>
	</ol>
	</li>
	<li>Acute stress 
	NOTE: Foot shocks are delivered prior to each conflict test in four identical chambers assembled with four shock generators and controlled by professional software installed on a computer.
	<ol>
		<li>On the day of the conflict test, take the male rats to another room different from the conflict testing room.</li>
		<li>Put the male rats into the chambers (30.5 cm long x 25.4 cm wide x 30.5 cm high) to habituate for 1 min.</li>
		<li>Set up the software program in advance. The program includes the intermittent foot shocks delivered within 10 min (0.5 mA x 0.5 s x 10 min; mean inter-shock interval 40 s, range 10&#8211;70 s).</li>
		<li>Enter animal IDs and choose whether to turn on the shock generators according to the grouping (the shock group and the control group). Then press the start button.</li>
		<li>When the stress procedure is finished, bring the rats immediately to the conflict test room in transport boxes; one rat per box.</li>
	</ol>
	</li>
</ol>
4. The Conflict Test
NOTE: The test is conducted under dim light during the dark phase of the light/dark cycle in the conflict test room.
<ol>
	<li>On the day before testing, bring all rats to the conflict test room and allow them to habituate to the open-field reward-proximity chamber (without any obstacle, Figure 1) for 15 min.</li>
	<li>On the testing day, place the male rat in the chamber allowing free exploration for 10 min (under the same condition as the day before testing).</li>
	<li>Place an estrous female rat in the stimulus-cage as an incentive and allow the male subject to freely approach and investigate the incentive rat for 5 min. 
	NOTE: The male rat is randomly exposed to an estrous female, and this female is not a familiar rat.</li>
	<li>After 5 min-free approach, move the male subject from the stimulus-cage to the other end of the arena, place an obstacle (a 14 cm-wide board thick with pins), and then start the first trial of the test. 
	NOTE: The difficulty level of obstacles is varied among trials based on the types of pins and the height of the board. The grading system is shown in Table 2.</li>
	<li>Move the male rat away from the stimulus-cage about 15&#8211;20 s after each time it surmounts the obstacle.</li>
	<li>End a trial if the male subject climbs or jumps over the obstacle 3 times within 4 min and immediately start the next trial with increasing difficulty of the obstacle.</li>
	<li>If a male subject surmounts the obstacle less than three times within 4 min, end the test and record the times it surmounts the obstacle.</li>
	<li>Bring the male rat back to the home cage and scrub the open-field chamber with 0.05% glacial acetic acid.</li>
	<li>Score each surmounting (or approaching) as per Table 2. Use the sum of the scores for all of the surmountings as a total score for a male subject in this conflict test.</li>
</ol>
5. Statistical Analysis
<ol>
	<li>Present the data as mean &#177; SEM or single data points. In case that homogeneity of variance or normal distribution of the datasets is challenged, log-transform the data sets.</li>
	<li>Analyze the effects of morphine pretreatment on reward-seeking behavior displayed on day 7 and day 17 of withdrawal (Wd7 and Wd17) using t-tests with &#8220;pretreatment&#8221; as a between-subjects factor (morphine versus saline, Figure 2).</li>
	<li>Analyze the effects of morphine pretreatment on reward-seeking behavior after repeated testing using repeated-measure&#8217;s analysis of variance (ANOVA) with &#8220;withdrawal time&#8221; (Wd7 versus Wd14) as the within-subjects factor and &#8220;pretreatment&#8221; (morphine versus saline) as a between-subjects factor.</li>
	<li>In addition, use Pearson&#8217;s correlation to analyze the correlation between the scores that male subjects acquired on days 7 and 14 of abstinence (Wd7 and Wd14, Figure 3). 
	NOTE: After the logarithmic conversion of the original data, statistical analyses are performed.</li>
	<li>Analyze the effect of acute stress on reward-seeking behavior in drug-na&#239;ve rats using t-test with stress as a between-subjects factor (shock versus control, Figure 4)</li>
</ol>

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The authors have nothing to disclose.

The inhibitory control deficits caused by drug abuse18 play a key role in promoting compulsive drug seeking/taking behaviors and relapse19,20. The conflict model presented here provides a new approach to explore the changes in inhibitory control of the individuals exposed to addictive drugs.
There are several critical steps in the protocol. First of all, the subjects (male rats) must acquire sexual experience be...

Drug addiction is a chronic brain disease which is characterized by impulsive and compulsive drug seeking and taking1. These key features of addiction have both been hypothesized to result from the impaired ability of inhibitory control2,3, i.e., failing in inhibiting the immediate pursuit of rewarding stimuli and thus developing maladaptive patterns of behavior4.
The go/no-go task and stop-signal task are the prototypical tasks used to measure the ability of response inhibition2,5. These two experimental paradigms assess one&#39;s ability to suppress actions that are inappropriate, by contrasting infrequent inhibitory responses against an implicit go baseline6,7. The response inhibition displayed in these tasks has been shown to be impaired in cocaine users8,9, opiate addicts10, and nicotine users11. Another two tasks&#8212;reversal learning and multiple choice serial reaction time tasks&#8212;also provide measurements of response inhibition/inhibitory control12,13. However, most of these paradigms performed in rodents not only require long-term training so that subjects can distinguish the response requirements represented by different signals, but also the individual differences in learning speed and learning effects may interfere with the results of subsequent inhibitory test11.
In this paper, we present a novel conflict task which can be used to measure the impairment of inhibitory control after exposure to addictive drugs. In this task, a natural rewarding stimulus (sexual stimulus) that represents a high-value reward14, and the aversive stimuli (pins) that male rats have to conquer, 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 its approaching behavior regardless of the aversive stimuli, it is considered as a maladaptive or risky reward-seeking behavior. One of the rationales for establishing this task is that it is conceptually simple and does not place heavy demands on executive processes as other tasks do. Compared to other tasks which measure response inhibition, this conflict task is based on natural behavior, and rats with normal sexual function and sexual experience can be tested directly without a learning process. Another rationale is that a conflict presented in this task between approaching the reward and avoiding the aversive stimuli (or the risk of being pricked) may have a better validity, as it mimics what occurs in addicts who often place themselves in the similar conflict but persistently pursue drug reward regardless of the risk of negative consequences in real life15.
Therefore, application of this conflict model is a quick and sensitive way to discover the deficit in inhibitory control after exposure to addictive drugs, or other factors that may influence ability of inhibitory control, such as stress. It also provides a novel behavioral strategy for investigation of neural mechanisms underlying deficits in inhibitory control. Furthermore, alternative modifications can be added onto this task. For example, altering the cost/benefit ratio by replacing the sexual stimulus with the social stimulus can reveal more behavioral significances.

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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.

To explore whether this conflict model can reveal maladaptive/risky reward-seeking behavior induced by opiates, the reward-seeking behaviors displayed by the saline- and morphine-pretreated groups were compared by t-tests after short-term (Wd7) and long-term (Wd17) withdrawal from morphine respectively (Figure 2). The results show that on both day 7 and day 17 of withdrawal, the morphine-pretreated rats showed significantly more approaching behaviors than the...

Watch this Scientific Journal Video about A Conflict Model of Reward-seeking Behavior in Male Rats at JoVE.com

A Conflict Model of Reward-seeking Behavior in Male Rats

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-conflict-model-of-reward-seeking-behavior-in-male-rats

Research

JoVE Journal

Behavior

7.4K Views.  Chinese Academy of Sciences. 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. 

Video: A Conflict Model of Reward-seeking Behavior in Male Rats

Operant Sensation Seeking in the Mouse

Operant methods are powerful behavioral tools for the study of motivated behavior. These 'self-administration' methods have been used extensively in drug addiction research due to their high construct validity. Operant studies provide researchers a tool for preclinical investigation of several aspects of the addiction process. For example, mechanisms of acute reinforcement (both drug and non-drug) can be tested using pharmacological or genetic tools to determine the ability of a molecular target to influence self-administration behavior1-6. Additionally, drug or food seeking behaviors can be studied in the absence of the primary reinforcer, and the ability of pharmacological compounds to disrupt this process is a preclinical model for discovery of molecular targets and compounds that may be useful for the treatment of addiction3,7-9. One problem with performing intravenous drug self-administration studies in the mouse is the technical difficulty of maintaining catheter patency. Attrition rates in these experiments are high and can reach 40% or higher10-15. Another general problem with drug self-administration is discerning which pharmacologically-induced effects of the reinforcer produce specific behaviors. For example, measurement of the reinforcing and neurological effects of psychostimulants can be confounded by their psychomotor effects. Operant methods using food reinforcement can avoid these pitfalls, although their utility in studying drug addiction is limited by the fact that some manipulations that alter drug self-administration have a minimal impact on food self-administration. For example, mesolimbic dopamine lesion or knockout of the D1 dopamine receptor reduce cocaine self-administration without having a significant impact on food self-administration 12,16. 
Sensory stimuli have been described for their ability to support operant responding as primary reinforcers (i.e. not conditioned reinforcers)17-22. Auditory and visual stimuli are self-administered by several species18,21,23, although surprisingly little is known about the neural mechanisms underlying this reinforcement. The operant sensation seeking (OSS) model is a robust model for obtaining sensory self-administration in the mouse, allowing the study of neural mechanisms important in sensory reinforcement24. An additional advantage of OSS is the ability to screen mutant mice for differences in operant behavior that may be relevant to addiction. We have reported that dopamine D1 receptor knockout mice, previously shown to be deficient in psychostimulant self-administration, also fail to acquire OSS24. This is a unique finding in that these mice are capable of learning an operant task when food is used as a reinforcer. While operant studies using food reinforcement can be useful in the study of general motivated behavior and the mechanisms underlying food reinforcement, as mentioned above, these studies are limited in their application to studying molecular mechanisms of drug addiction. Thus, there may be similar neural substrates mediating sensory and psychostimulant reinforcement that are distinct from food reinforcement, which would make OSS a particularly attractive model for the study of drug addiction processes. The degree of overlap between other molecular targets of OSS and drug reinforcers is unclear, but is a topic that we are currently pursuing. While some aspects of addiction such as resistance to extinction may be observed with OSS, we have found that escalation 25 is not observed in this model24. Interestingly, escalation of intake and some other aspects of addiction are observed with self-administration of sucrose26. Thus, when non-drug operant procedures are desired to study addiction-related processes, food or sensory reinforcers can be chosen to best fit the particular question being asked. 
In conclusion, both food self-administration and OSS in the mouse have the advantage of not requiring an intravenous catheter, which allows a higher throughput means to study the effects of pharmacological or genetic manipulation of neural targets involved in motivation. While operant testing using food as a reinforcer is particularly useful in the study of the regulation of food intake, OSS is particularly apt for studying reinforcement mechanisms of sensory stimuli and may have broad applicability to novelty seeking and addiction.

In this protocol we describe a method of operant learning using sensory stimuli as a reinforcer in the mouse. It requires no prior training or food restriction, and it allows the study of motivated behavior without the use of a pharmacological or natural reinforcer such as food.

Operant methods are powerful behavioral tools for the study of motivated behavior.  These 'self-administration' methods have been used extensively in drug ...

Neuroscience

Pavlovian Conditioned Approach Training in Rats

Cues that are contingently paired with unconditioned, rewarding stimuli can acquire rewarding properties themselves through a process known as the attribution of incentive salience, or the transformation of neutral stimuli into attractive, &#34;wanted&#39; stimuli capable of motivating behavior. Pavlovian conditioned approach (PCA) develops after the response-independent presentation of a conditioned stimulus (CS; e.g., a lever) that predicts the delivery of an unconditioned stimulus (US; e.g., a food pellet) and can be used to measure incentive salience. During training, three patterns of conditioned responses (CRs) can develop: sign-tracking behavior (CS-directed CR), goal-tracking behavior (US-directed CR), and an intermediate response (both CRs). Sign-trackers attribute incentive salience to reward-related cues and are more vulnerable to cue-induced reinstatement of drug-seeking as well as other addiction-related behaviors, making PCA a potentially valuable procedure for studying addiction vulnerability. Here, we describe materials and methods used to elicit PCA behavior from rats as well as analyze and interpret PCA behavior in individual experiments.

Here, we present a protocol to elicit Pavlovian conditioned approach behavior in rats. This procedure can be used to measure individual differences in the tendency to approach and attribute incentive salience to reward-related cues and investigate addiction vulnerability.

Cues that are contingently paired with unconditioned, rewarding stimuli can acquire rewarding properties themselves through a process known as the ...

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can produce a rewarding effect that strengthens action-outcome associations and reinforces future behavior directed at obtaining these foods. Increasing evidence that the rewarding effects of energy-dense foods play a profound role in overeating and the development of obesity has heightened interest in studying the genes, molecules and neural circuitry that modulate food reward1,2. The rewarding impact of different stimuli can be studied by measuring the willingness to work to obtain them, such as in operant conditioning tasks3. Operant models of food reward measure acquired and voluntary behavioral responses that are directed at obtaining food. A commonly used measure of reward strength is an operant procedure known as the progressive ratio (PR) schedule of reinforcement.4,5 In the PR task, the subject is required to make an increasing number of operant responses for each successive reward. The pioneering study of Hodos (1961) demonstrated that the number of responses made to obtain the last reward, termed the breakpoint, serves as an index of reward strength4. While operant procedures that measure changes in response rate alone cannot separate changes in reward strength from alterations in performance capacity, the breakpoint derived from the PR schedule is a well-validated measure of the rewarding effects of food. The PR task has been used extensively to assess the rewarding impact of drugs of abuse and food in rats (e.g.,6-8), but to a lesser extent in mice9. The increased use of genetically engineered mice and diet-induced obese mouse models has heightened demands for behavioral measures of food reward in mice. In the present article we detail the materials and procedures used to train mice to respond (lever-press) for a high-fat and high-sugar food pellets on a PR schedule of reinforcement. We show that breakpoint response thresholds increase following acute food deprivation and decrease with peripheral administration of the anorectic hormone leptin and thereby validate the use of this food-operant paradigm in mice.

The present report details the protocol employed to measure the rewarding effects of high-fat food in mice using a progressive ratio operant conditioning task.

Foods that are rich in fat and sugar significantly contribute to over-eating and escalating rates of obesity. The consumption of palatable foods can ...

Chronic Stress Shifts Effort-Related Choice Behavior in a Y-Maze Barrier Task in Mice

Mood disorders, including major depressive disorder, can be precipitated by chronic stress. The Y-maze barrier task is an effort-related choice test that measures motivation to expend effort and obtain reward. In mice, chronic stress exposure significantly impacts motivation to work for a higher value reward when a lesser value reward is freely available compared to unstressed mice. Here we describe the chronic corticosterone administration paradigm, which produces a shift in effortful responding in the Y-maze barrier task. In the Y-maze task, one arm contains 4 food pellets, while the other arm contains only 2 pellets. After mice learn to select the high reward arm, barriers with progressively increasing height are then introduced into the high reward arm over multiple test sessions. Unfortunately, most chronic stress paradigms (including corticosterone and social defeat) were developed in male mice and are less effective in female mice. Therefore, we also discuss chronic non-discriminatory social defeat stress (CNSDS), a stress paradigm we developed that is effective in both male and female mice. Repeating results with multiple distinct chronic stressors in male and female mice combined with increased usage of translationally relevant behavior tasks will help to advance the understanding of how chronic stress can precipitate mood disorders.

The Y-maze barrier task is a behavior test that examines motivation to expend effort for reward. Here, we discuss testing multiple well-validated chronic stressors including chronic corticosterone and social defeat stress with this behavior, as well as the novel chronic non-discriminatory social defeat stress (CNSDS), which is effective in females.

Mood disorders, including major depressive disorder, can be precipitated by chronic stress. The Y-maze barrier task is an effort-related choice test that ...

A Complex Diving-For-Food Task to Investigate Social Organization and Interactions in Rats

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include dominant-submissive relationships are common in both animal and human societies. These relationships can be affected by interactions with others and with their environment, making them difficult to analyze in a controlled study. Rather than a simple dominance hierarchy, this formation has a complicated presentation that allows rats to avoid aggression. Status can be stagnant or mutable, and results in complex societal stratifications. Here we describe a complex diving-for-food task to investigate rodent social hierarchy and behavioral interactions. This animal model may allow us to assess the relationship between a wide range of mental illnesses and social organization, as well as to study the effectiveness of therapy on social dysfunction.

This protocol describes a method of examining social hierarchy in a rat model. Rats perform a complex diving-for-food task in which they form a distinct hierarchy according to their willingness to dive underwater and swim to obtain a food pellet. This method is used to understand decision making and social relationships among highly social animals in small groups.

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include ...

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.

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 ...

Developing a Rat Model for Bipolar Disorder

Bipolar disorder is a mental health condition characterized by extreme mood swings, including periods of emotional highs (mania) and lows (depression). While the exact underlying neurobiology is not yet fully understood, imbalances in neurotransmitter systems, particularly dopamine, appear to play a central role. For this reason, manipulations of dopaminergic pathways have been used to model mania or depression in rodents. However, models that accurately represent the typical switch between these two episodes are rare, limiting face validity. In a unique model, modern techniques are used to temporarily increase dopamine D1 receptor expression, which has been implicated in the pathology of bipolar disorder. A tetracycline-inducible lentiviral construct that expresses the dopamine D1 receptor under the control of the calmodulin kinase II alpha promoter is stereotactically injected into the medial prefrontal cortex of adult rats. Dopamine D1 receptor overexpression is achieved by adding the tetracycline analog doxycycline to the animals&#39; drinking water, leading to an increase in reward-related, impulsive, and risk-taking behaviors and a decrease in anxiety. These behaviors resemble a mania-like phenotype. By removing doxycycline from the drinking water, a depressive-like phenotype, characterized by increased helplessness and anhedonia, can be induced within the same animal. This article provides a step-by-step protocol for performing the surgery, as well as procedures for inducing the bipolar disorder-like phenotype. Additionally, considerations for assessing behavioral changes associated with mania-like and depressive-like behavior are described. This promising model, which demonstrates good construct and face validity, offers a valuable tool for further investigating the pathophysiological mechanisms of bipolar disorder.

This article presents a protocol for the induction of a unique rat model of bipolar disorder that captures both mania-like and depressive-like behavior.

Bipolar disorder is a mental health condition characterized by extreme mood swings, including periods of emotional highs (mania) and lows (depression). ...

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We demonstrate a simple way to tap into the fly reward system, modify experiences related to natural reward, and use voluntary ethanol consumption as a measure for changes in reward states. The approach serves as a relevant tool to study the neurons and genes that play a role in experience-mediated changes of internal state. The protocol is composed of two discrete parts: exposing the flies to rewarding and nonrewarding experiences, and assaying voluntary ethanol consumption as a measure of the motivation to obtain a drug reward. The two parts can be used independently to induce the modulation of experience as an initial step for further downstream assays or as an independent two-choice feeding assay, respectively. The protocol does not require a complicated setup and can therefore be applied in any laboratory with basic fly culture tools.

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for inducing rewarding and nonrewarding experiences in fruit flies (Drosophila melanogaster) using voluntary ethanol consumption as a measure for changes in reward states.

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We ...

Measuring In Vivo Changes in Extracellular Neurotransmitters During Naturally Rewarding Behaviors in Female Syrian Hamsters

The ability to measure neurotransmitter release on a rapid time scale allows patterns of neurotransmission to be linked to specific behaviors or manipulations; a powerful tool in elucidating underlying mechanisms and circuitry. While the technique of microdialysis has been used for decades to measure nearly any analyte of interest in the brain, this technique is limited in temporal resolution. Alternatively, fast scan cyclic voltammetry is both temporally precise and extremely sensitive; however, because this technically difficult method relies on the electroactivity of the analyte of interest, the possibility to detect nonelectroactive substances (e.g., the neurotransmitter glutamate) is eliminated. This paper details the use of a turn-key system that combines fixed-potential amperometry and enzymatic biosensing to measure both electroactive and nonelectroactive neurotransmitters with temporal precision. The pairing of these two powerful techniques allows for the measurement of both tonic and phasic neurotransmission with relative ease, and permits recording of multiple neurotransmitters simultaneously. The aim of this manuscript is to demonstrate the process of measuring dopamine and glutamate neurotransmission in vivo using a naturally rewarding behavior (i.e., sexual behavior) in female hamsters, with the ultimate goal of displaying the technical feasibility of this assay for examining other behaviors and experimental paradigms.

Measuring In Vivo Changes in Extracellular Neurotransmitters During Naturally Rewarding Behaviors in Female Syrian Hamsters

This paper details the use of fixed-potential amperometric recordings using carbon fiber electrodes and enzymatic biosensor technology to measure the release of dopamine and glutamate with high temporal resolution during natural rewarding behavior in the female hamster.

The ability to measure neurotransmitter release on a rapid time scale allows patterns of neurotransmission to be linked to specific behaviors or ...

Adolescent Social Stress Paradigm in C57BL&#47;6 Mice for Behavioral Research

Social Defeat Stress Model for Adolescent C57BL&#47;6 Male and Female Mice

Social adversity in adolescence is prevalent and can negatively impact mental health trajectories. Modeling social stress in adolescent male and female rodents is needed to understand its effects on ongoing brain development and behavioral outcomes. The chronic social defeat stress paradigm (CSDS) has been widely used to model social stress in adult C57BL/6 male mice by leveraging on the aggressive behavior displayed by an adult male rodent to an intruder invading its territory. An advantage of this paradigm is that it allows to categorize defeated mice into resilient and susceptible groups based on their individual differences in social behavior 24 h after the last defeat session. Implementing this model in adolescent C57BL/6 mice has been challenging because adult or adolescent mice do not typically attack early adolescent male or female mice and because adolescence is a short period of life, encompassing discreet temporal windows of vulnerability. This limitation was overcome by adapting an accelerated version of the CSDS to be used for adolescent male and female mice. This 4-day stress paradigm with 2 physical attack sessions per day uses a C57BL/6 male adult to prime the CD-1 mouse for aggressiveness such that it readily attacks the male or female adolescent mouse. This model was termed accelerated social defeat stress (AcSD) for adolescent mice. Adolescent exposure to AcSD induces social avoidance 24 h later in both males and females, but only in a subset of defeated mice. This vulnerability occurs despite the number of attacks being consistent across sessions between resilient and susceptible groups. The AcSD model is short enough to allow exposure during discrete periods within adolescence, allows the segregation of mice according to the presence or absence of social avoidance behavior, and is the first model available to study social defeat stress in adolescent C57BL/6 female mice.

Author Spotlight: Understanding Adolescent Social Adversity Effects on Neurodevelopment in Mice

We developed an accelerated social defeat stress model for adolescent C57BL/6 mice, which works in both males and females and allows exposure during discrete adolescent periods. Exposure to this model induces social avoidance, but only in a subset of defeated male and female mice.

Social adversity in adolescence is prevalent and can negatively impact mental health trajectories. Modeling social stress in adolescent male and female ...

A Conflict Model of Reward-seeking Behavior in Male Rats

Summary

Explore More Videos

Operant Sensation Seeking in the Mouse

Pavlovian Conditioned Approach Training in Rats

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

Chronic Stress Shifts Effort-Related Choice Behavior in a Y-Maze Barrier Task in Mice

A Complex Diving-For-Food Task to Investigate Social Organization and Interactions in Rats

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

Developing a Rat Model for Bipolar Disorder

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

Measuring In Vivo Changes in Extracellular Neurotransmitters During Naturally Rewarding Behaviors in Female Syrian Hamsters

Social Defeat Stress Model for Adolescent C57BL/6 Male and Female Mice