Reinstatement of a food-maintained operant produced by compounding discriminative stimuli

Renewal of cocaine seeking using social and nonsocial contextual stimuli

RATIONALE

Various nonsocial cues have been used as stimuli to examine the contextual control of drug seeking behavior, but little is known about the role of social stimuli.

OBJECTIVES

This study determined if renewal of cocaine seeking is differentially controlled using a context consisting of either a social peer and/or house light illumination.

METHODS

In Experiment 1, male and female rats trained to self-administer cocaine in the presence of a same-sex social peer and house light illumination (context A). Following self-administration, rats were randomly assigned to either an AAA (control) or ABA (renewal) group for extinction. For AAA rats, extinction consisted of the same context A as self-administration; for ABA rats, extinction occurred without the peer or house light (context B). Following extinction, renewal of cocaine seeking occurred by testing the peer alone, house light alone, and the peer + house light combination. Experiment 2 was conducted to ensure that the house light alone was sufficiently salient to produce renewal.

RESULTS

Both experiments showed that rats acquired cocaine self-administration and extinguished lever pressing. In Experiment 1, the ABA group renewed cocaine seeking to the peer and peer + house light, but not to the house light alone. In Experiment 2, ABA rats renewed cocaine seeking to the house light alone, indicating it was sufficiently salient to produce renewal. The AAA group did not show renewal in either experiment.

CONCLUSION

Social peers serve as powerful stimuli that can overshadow nonsocial visual stimuli in the renewal of cocaine seeking.

Inactivation of the infralimbic cortex decreases discriminative stimulus-controlled relapse to cocaine seeking in rats

Persistent susceptibility to cue-induced relapse is a cardinal feature of addiction. Discriminative stimuli (DSs) are one type of drug-associated cue that signal drug availability (DS+) or unavailability (DS-) and control drug seeking prior to relapse. We previously established a trial-based procedure in rats to isolate DSs from context, conditioned stimuli, and other drug-associated cues during cocaine self-administration and demonstrated DS-controlled cocaine seeking up to 300 abstinence days. The behavioral and neural mechanisms underlying trial-based DS-control of drug seeking have rarely been investigated. Here we show that following discrimination training in our trial-based procedure, the DS+ and DS- independently control the expression and suppression of cocaine seeking during abstinence. Using microinjections of GABA_A + GABA_B receptor agonists (muscimol + baclofen) in medial prefrontal cortex, we report that infralimbic, but not prelimbic, subregion of medial prefrontal cortex is critical to persistent DS-controlled relapse to cocaine seeking after prolonged abstinence, but not DS-guided discriminated cocaine seeking or DS-controlled cocaine self-admininstration. Finally, using ex vivo whole-cell recordings from pyramidal neurons in the medial prefrontal cortex, we demonstrate that the disruption of DS-controlled cocaine seeking following infralimbic cortex microinjections of muscimol+baclofen is likely a result of suppression of synaptic transmission in the region via a presynaptic mechanism of action.

Social reinstatement: a rat model of peer-induced relapse

BACKGROUND

An important factor that can lead to drug relapse is to re-associate with drug-using social peers, but there is little literature on the effect of social peers on relapse in animal models.

METHODS

The current study used a dual-compartment operant conditioning apparatus that allowed adult male rats to respond for cocaine in the presence of a conspecific. In experiment 1, rats were trained to self-administer cocaine in the presence of a social peer that was separated by a wire screen partition and then that peer was used as a reinstatement cue following a period of extinction. In the next experiments, rats were trained on alternating sessions to self-administer cocaine in the presence of one peer and to self-administer saline in the presence of a different peer using either a single-active lever procedure (experiment 2) or a double-active lever procedure (experiment 3). Following extinction of responding in the absence of the peers, the effect of re-exposure to the cocaine- and saline-associated peers on reinstatement of drug seeking was determined. This was tested using both single- and double-active lever procedures.

RESULTS

In experiment 1, a peer that was present throughout cocaine self-administration was able to reinstate cocaine seeking following a period of extinction. In experiments 2 and 3, drug seeking was reinstated by the cocaine-associated peer (S+), but not the saline-associated peer (S-). This discrimination occurred when using either the single-active lever procedure or double-active lever procedure.

CONCLUSION

These results indicate that a social peer can be used as a discriminative stimulus to signal cocaine availability and that re-introduction of a peer previously paired with cocaine can reinstate cocaine seeking, confirming clinical reports that peer affiliation among abstinent cocaine users is an important determinant of relapse.

Differential stimulus control of drug-seeking: multimodal reinstatement

In animal models of substance-use disorder, individuals that repeatedly self-administer drugs of abuse have long-lasting neuronal adaptations that do not occur ostensibly in control animals only exposed to natural reinforcers (e.g. food). Because any treatment for substance-use disorder will be given to individuals with drug-taking histories, adequate dissociation of the specific neurobehavioral mechanisms underlying drug reinforcement, natural reinforcement and their associated cue effects requires an experimental model that exposes individuals to both reinforcer conditions, along with their associated stimuli. Furthermore, contingent stimuli that reinforce drug seeking through second-order relationships may produce reinstatement of drug seeking through different neurobehavioral means than non-contingent exposure to stimuli that signal the availability of a drug reinforcer, effectively producing different modes of stimulus-induced reinstatement. Toward experimental isolation of the relationships mentioned, herein, we used a within-session multiple schedule of reinforcement containing both discriminative (S^D ) and conditioned (CS) stimuli to study stimulus control of drug-taking and food-taking behavior, along with how these functionally distinct cues may differentially reinstate drug-seeking and food-seeking behavior within a single animal. We demonstrate specific stimulus control over drug and food taking; furthermore, we demonstrate that the same stimulus (i.e. cue light) operating as an S^D or CS produced differential reinstatement of drug-taking and food-taking behavior. The results suggest that contingent CSs and non-contingent S^D s produce reinstatement through different neurobehavioral processes and, within-session multiple schedules, can be used to study different modes of specific stimulus control over drug and food seeking in a single animal with both drug-taking and food-taking history.

Cocaine cues retain silent traces of an excitatory history after conversion into conditioned inhibitors: 'the ghost in the addict'

The present experiment investigated the extent to which the A+/AB- conditioned inhibition procedure could counteract an excitatory drug-related conditioning history. In two groups of rats, a light stimulus was established as a signal for the absence of cocaine. For the History group, the light had previously been a discriminative stimulus (S) that occasioned cocaine self-administration and could thus be classified as a cocaine excitor. In comparison, the No-History group first encountered the light during conditioned inhibition training. During conditioned inhibition training, both groups self-administered cocaine during tone as well as during click Ss, whereas drug seeking was eliminated in click-plus-light, wherein cocaine was not available (A+/AB-). Drug seeking was essentially eliminated in both groups. Nevertheless, on a summation test the light reduced cocaine seeking occasioned by the tone S by 95% in the No-History group, but by less than 50% in the History group. This summation test result showed that the effects of a drug-related history persisted even after the light was converted into an effective conditioned inhibitor on the training baseline through the powerful A+/AB- procedure. Future research should seek procedures that produce even stronger conditioned inhibition that eliminates such residual 'silent' drug excitation, the 'ghost in the addict'.

Configurations of the interoceptive discriminative stimulus effects of ethanol and nicotine with two different exteroceptive contexts in rats: Extinction & recovery

Interoceptive states interact with exteroceptive contexts in modulating operant behavior, which is maintained by its consequences. Evaluating discriminative stimulus control by overlapping interoceptive and exteroceptive configurations (gestalts) and the contribution of each modality may be clinically important for understanding aspects of relapsing behavior (e.g., drug abuse). With rats, the current investigation used a completely counterbalanced one-manipulandum operant drug discrimination procedure that established discriminative stimulus control between nicotine (0.3mg/kg) in one exteroceptive context and EtOH (1.0g/kg) in a differing exteroceptive context. One combined interoceptive-exteroceptive condition occasioned sessions of food reinforcement (S(D)) and the other counterbalanced condition occasioned sessions of non-reinforcement (S(Δ)). Each stimulus modality contributed to discriminative control, but to lesser extents than the combined intero-exteroceptive compound configurations (Experiments 1 & 2). In Experiment 1, responding was extinguished in the interoceptive stimulus conditions alone in a neutral exteroceptive context, but then renewed by reconfiguring the drugs with the exteroceptive contexts, and reversed in the opposing exteroceptive contexts. In Experiment 2, responding was extinguished in the interoceptive and exteroceptive contexts separately. Reconfiguration of the full intero-exteroceptive compound configurations did not promote recovery. These results suggest that interoceptive and exteroceptive discriminative control can be methodologically configured in modulating operant behavior during acquisition, extinction, and recovery of behavior; however, configuring interoceptive and exteroceptive discriminative stimuli do not appear to function as unique cues that differ from each stimulus modality alone. Clinical implications are discussed.

Deepened extinction of cocaine cues

BACKGROUND

A method for reducing the power of drug cues could help in treating drug abuse and addiction. Extinction has been used, with mixed success, in such an effort. Research with non-drug cues has shown that simultaneously presenting (compounding) those cues during extinction can enhance the effectiveness of extinction. The present study investigated whether this procedure could be used to similarly deepen the extinction of cocaine cues.

METHODS

Rats were first trained to self-administer cocaine during tone, click, and light stimuli. Then, these stimuli were subjected to extinction in an initial phase where they were presented individually. In a second extinction phase, one of the auditory stimuli (counterbalanced) was compounded with the light. The other auditory stimulus continued to be presented alone. Rats were then given a week of rest in their homecages prior to testing for spontaneous recovery of cocaine seeking.

RESULTS

The cue that was compounded with the light during the second phase of extinction training occasioned less spontaneous recovery of cocaine seeking than the cue that was always presented individually during extinction. Increasing the number of compound cue extinction sessions did not produce a greater deepened extinction effect.

CONCLUSIONS

The present study showed that simultaneously presenting already-extinguished cocaine cues during additional extinction training enhanced extinction. This extends the deepened extinction effect from non-drug cues to drug cues and further confirms predictions of error-correction learning theory. Incorporating deepened extinction into extinction-based drug abuse treatments could help to reduce the power of drug cues.

Extinguished cocaine cues increase drug seeking when presented simultaneously with a non-extinguished cocaine cue

BACKGROUND

Previous research with non-drug reinforcers has shown that simultaneously presenting (compounding) an extinguished cue with another cue formerly associated with the same reinforcer can increase rates of cue-controlled behavior. The present study investigated whether an extinguished cocaine cue would energize cocaine seeking when presented simultaneously with another cocaine cue. This study also investigated whether extinction could be enhanced by subjecting an extinguished cocaine cue to further extinction after administration of reinstating injections of cocaine.

METHODS

Rats were first trained to self-administer cocaine in the presence of three different cues. Then, one of the cues was subjected to the standard extinction treatment. Another cue was subjected to a modified extinction treatment where additional extinction sessions were preceded by non-contingent cocaine injections. The third cue was not extinguished.

RESULTS

The cue subjected to standard extinction ceased to control cocaine seeking when presented alone, but significantly increased cocaine seeking when compounded with the non-extinguished cocaine cue. The cocaine cue subjected to the modified extinction treatment also significantly increased cocaine seeking occasioned by the non-extinguished cocaine cue.

CONCLUSIONS

Extending results of previous studies involving non-drug stimuli, the present study showed that extinguished cocaine cues can enhance cocaine seeking when compounded with other cocaine cues. These results illustrate the persistence of drug cues in controlling behavior despite extinction and highlight the need for developing treatments that eliminate this residual energizing capacity that survives extinction.

Extinction of goal tracking also eliminates the conditioned reinforcing effects of an appetitive conditioned stimulus

Previous studies have suggested that the effects of extinction are response-specific. The present study investigated whether an extinction treatment that eliminated goal tracking elicited by an appetitive conditioned stimulus (CS) would also eliminate the conditioned reinforcing effects of that CS. Rats were first trained on a goal-tracking procedure in which an auditory CS was paired with a food unconditioned stimulus. Animals learned to approach the location where the food was delivered. In a subsequent phase, rats in one group received extinction training that eliminated the goal-tracking elicited by the CS. Rats in the other group did not experience extinction of the food-paired CS. Then, both groups received a test for conditioned reinforcement in which leverpresses resulted in the brief presentation of the stimulus previously paired with food. This stimulus did not act as a conditioned reinforcer in the group that had been subjected to extinction training, but did serve as a conditioned reinforcer in the group that did not experience extinction. These results indicate that the effects of extinction generalize from the approach-eliciting to the conditioned reinforcing effects of an appetitive CS.

A comparison of the effects of discriminative and Pavlovian inhibitors and excitors on instrumental responding

In two experiments, the effects of Pavlovian or discriminative conditioned inhibitors on operant responding were investigated in rats. Experiment 1 found that a Pavlovian conditioned inhibitor for food suppressed food-reinforced lever pressing more than a non-differentially trained control stimulus did. Experiment 2 demonstrated that an operant discriminative inhibitor produced greater suppression of lever pressing than a Pavlovian conditioned inhibitor. Experiment 2 also found that compounding an operant discriminative stimulus (SD) for food-reinforced responding with another SD for food-reinforced responding resulted in more additive summation than when an SD was compounded with a Pavlovian conditioned excitor for food. The results of these experiments support two-factor theories that postulate that incentive and response discriminative processes summate algebraically when the processes are inhibitory or excitatory.

The habitual brain: an "adapted habit" theory of substance use disorders

Behavioral habits are essential to human and animal life. We consider the many ways that habits - which are normally adaptive - can be expressed as drug use behavior and addiction. Although habit theories of substance use disorders have been proposed (e.g., Tiffany, 1990), the behavioral science and underlying neurobiology of habit development, maintenance, and change is only now being studied. We first define "adapted habit." We then propose that the etiology of an adapted habit represents the combination of: (a) initial "capture" of a habit, (b) development of behavioral action schemata, and (c) an overlay of cognitive expectancies concerning aspects of the habit. This combination conspires to make an intractable adapted habit such as substance abuse and addiction. Many intractable habits change, including substance use disorders such as cigarette smoking. As part of a science of habits, we need a real understanding of how to change habits to avoid or minimize harm.