Janet L. Neisewander

Time-Dependent Changes in Cocaine-Seeking Behavior and Extracellular Dopamine Levels in the Amygdala during Cocaine Withdrawal

Cocaine and cocaine-associated cues elicit craving in addicts and reinstate cocaine-seeking behavior in rats. Craving and cocaine-seeking behavior may be mediated by withdrawal-induced changes in dopamine (DA) neurotransmission in the amygdala. To examine whether there are concomittant changes in cocaine-seeking behavior and extracellular DA levels during withdrawal, experimental rats were trained to self-administer cocaine (0.75 mg/kg IV). After 14 daily 3-hour training sessions, animals underwent either a 1-day, 1-week, or 1-month withdrawal period. Extracellular DA levels were assessed during baseline, extinction, cue reinstatement, and cocaine (15 mg/kg IP) reinstatement of cocaine-seeking behavior (i.e., defined as the difference in nonreinforced lever presses on an active minus inactive lever). Cocaine-seeking behavior became more intense during the course of cocaine withdrawal. Additionally, basal and cocaine-induced extracellular DA levels were enhanced after the 1-month withdrawal period. We suggest that the former may reflect a persistent elevation in tonic extracellular DA levels in the amygdala, whereas the latter may reflect a persistent elevation in phasic extracellular DA levels.

Dopamine Overflow in the Nucleus Accumbens during Extinction and Reinstatement of Cocaine Self-Administration Behavior

Both cocaine and cocaine-associated stimuli can reinstate extinguished self-administration behavior in animals. It has been suggested that reinstatement of drug-seeking behavior may be mediated by enhanced dopamine (DA) neurotransmission. To examine this hypothesis, DA overflow was measured in the nucleus accumbens (NAc) of rats during both extinction and cocaine-induced reinstatement of self-administration behavior. Rats were either allowed to self-administer cocaine for 3 hours daily for 14 days, or they received yoked administration of saline. A stimulus light above the lever was illuminated during drug delivery. Baseline DA overflow was measured in the NAc, using in vivo microdialysis 7 to 8 days after the last self-administration session. The rats were then placed into the operant chambers and allowed to respond in extinction for 90 minutes, during which responses resulted in presentation of the stimulus light. The rats then received a cocaine injection that reinstated self-administration behavior. Contrary to our hypothesis, cocaine-experienced animals exhibited less DA overflow in the NAc relative to controls during both extinction and reinstatement.

Effects of excitotoxic lesions of the basolateral amygdala on cocaine-seeking behavior and cocaine conditioned place preference in rats

Incentive motivation for cocaine, elicited by cocaine-associated stimuli, is thought to be involved in craving and relapse. To examine the role of the basolateral amygdala complex (BLC) in this phenomenon, we assessed the effects of post-training BLC lesions on extinction of cocaine-seeking behavior and cocaine-conditioned place preference (CPP) and the effects of pre-training BLC lesions on acquisition of cocaine-CPP. In Experiment 1, rats were first trained to self-administer cocaine and then received bilateral infusions of the excitotoxin, N-methyl-D-aspartic acid (NMDA, 0.12 M; 0.3 microl/side), or vehicle into the BLC. They were then tested repeatedly for extinction of cocaine-seeking behavior (i.e. nonreinforced responses in the presence of cocaine-paired stimuli). Subsequently, they were trained and tested for acquisition of cocaine-CPP (i.e. increased time spent in a previously cocaine-paired, relative to a saline-paired, environment). Locomotion and compartment entries were also measured. In Experiment 2, rats were first trained and tested for cocaine-CPP, and then received NMDA or vehicle infusions into the BLC. Subsequently, they were tested repeatedly for extinction of cocaine-CPP. Post-training BLC lesions retarded extinction of cocaine-seeking behavior and cocaine-CPP, whereas pre-training lesions disrupted acquisition of cocaine-CPP. These effects did not appear to be related to changes in general activity. We suggest that pre-training BLC lesions disrupted acquisition of cocaine-CPP by impairing assignment of incentive value to cocaine-paired stimuli, whereas post-training BLC lesions disrupted extinction of cocaine-conditioned behaviors by impairing the assessment of the current incentive value of cocaine-paired stimuli.

Predictive validity of the extinction/reinstatement model of drug craving

Abstract The effects of chronic desmethylimipramine (DMI) treatment on measures of incentive motivation for cocaine were assessed in order to investigate the predictive validity of the extinction/reinstatement model of drug craving. Rats were trained to respond for cocaine infusions (0.75 mg/kg per 0.1 ml IV) or received yoked-saline infusions during daily 3-h sessions. A light and tone were presented with the infusions. Following self-administration training, each group received daily injections of either saline or DMI (10 mg/kg, IP) for 21 days of withdrawal from the self-administration regimen. On days 12–21 of withdrawal, rats were allowed to respond in the absence of cocaine reinforcement (extinction phase). After reaching an extinction criterion of no responses for 1 h, the cocaine-paired stimuli were repeatedly presented to reinstate responding (reinstatement phase). In the control group, DMI treatment did not alter responding during either test phase, but increased the response latency during the extinction phase. In contrast, DMI treatment in the cocaine group decreased responding and increased the response latency during both test phases, and decreased the extinction latency during the extinction phase. Overall, the effects of DMI were consistent with a reduction of incentive motivation for cocaine, lending support for the predictive validity of the extinction/reinstatement model of drug craving.

Social Reward-Conditioned Place Preference: A Model Revealing an Interaction between Cocaine and Social Context Rewards in Rats

A recent thrust in drug abuse research is the influence of social interactions on drug effects. Therefore, the present study examined conditioned place preference (CPP) as a model for assessing interactions between drug and social rewards in adolescent rats. Parameters for establishing social reward-CPP were examined, including the number of conditioning sessions/day (1 or 2), the total number of sessions (2, 8, or 16), and the duration of sessions (10 or 30 min). Subsequently, the effects of cocaine or dextromethorphan on social reward-CPP and play behavior were examined. The results demonstrate that social reward-CPP (i.e., preference shift for an environment paired previously with a rat) was similar using either 1 or 2 conditioning sessions/day and either 10 or 30 min sessions; however, social reward-CPP increased as the number of social pairings increased. Additionally, a low dose of cocaine (2 mg/kg, IP) and a low number of social pairings (2 pairings) failed to produce CPP when examined alone, but together produced a robust CPP, demonstrating an interaction between these rewards. The non-rewarding drug, dextromethorphan (30 mg/kg, IP), failed to enhance social reward-CPP, suggesting that drug-enhanced social reward-CPP is specific to rewarding drugs. Surprisingly, there was no relationship between play behaviors and preference shift in drug-naïve animals. Furthermore, cocaine inhibited play behavior despite enhancing social reward-CPP, suggesting that aspects of social interaction other than play behavior likely contribute to social reward. The findings have important implications for understanding the influence of social context on cocaine reward during adolescence.

Novelty-induced place preference behavior in rats: Effects of opiate and dopaminergic drugs

In Experiment 1, adult male rats were given eight 30-min exposures to one of two distinct environments. Control animals received either four exposures to each environment or were not exposed to either environment. When given free-choice access to both environments simultaneously, animals spent significantly more time in the novel environment relative to the familiar environment. In these same animals, horizontal and vertical activity rates were lower in the novel environment than in the familiar environment. In Experiments 2-5, animals were assessed for novelty preference behavior under the influence of either morphine (0, 0.1, 0.3, 1.0 or 3.0 mg/kg), naltrexone (0, 0.1, 0.3 or 1.0 mg/kg), amphetamine (0, 0.1, 0.3 or 1.0 mg/kg) or haloperidol (0, 0.03, 0.1, 0.3 or 1.0 mg/kg). Haloperidol produced a dose-dependent disruption in novelty preference behavior, while all other drugs tested were without effect. Haloperidol also disrupted the novelty-induced decrease in horizontal and vertical activity rates. These results suggest that haloperidol blocks the reinforcing and locomotor-depressant effects of a novel environment in a free-choice preference test.

Differential roles of 5-HT receptor subtypes in cue and cocaine reinstatement of cocaine-seeking behavior in rats

The 5-HT indirect agonist, d-fenfluramine, attenuates cue reinstatement of extinguished cocaine-seeking behavior. To investigate the role of 5-HT receptor subtypes in this effect, we examined whether the attenuation is reversed by either a 5-HT1A, 5-HT2A/C, or 5-HT2C receptor antagonist. We also examined the effects of the antagonists alone on both cue and cocaine-primed reinstatement. Rats that had been trained to press a lever for cocaine (0.75 mg/kg/0.1 ml, i.v.) paired with light and tone cues underwent daily extinction sessions during which responding had no consequences. We then examined the effects of WAY 100635 (0–1.0 mg/kg, s.c.), ketanserin (0–10.0 mg/kg, i.p.), or SB 242,084 (0–1.0 mg/kg, i.p.) with and without d-fenfluramine (1.0 mg/kg, i.p.) pretreatment on cue reinstatement. Subsequently, we examined the effects of the antagonists on cocaine-primed (7.5 or 15.0 mg/kg, i.p.) reinstatement. The 5-HT1A antagonist, WAY 100635, failed to alter cue reinstatement, but attenuated cocaine reinstatement. Conversely, the 5-HT2A/C antagonist, ketanserin, attenuated cue reinstatement, but failed to alter cocaine reinstatement. The 5-HT2C-selective antagonist, SB 242,084, did not alter cue or cocaine reinstatement, but was the only drug that reversed the d-fenfluramine-induced attenuation of cue reinstatement. The findings suggest that stimulation of 5-HT1A receptors plays a critical role in cocaine-primed, but not cue, reinstatement. Furthermore, 5-HT2A and 5-HT2C receptors may play oppositional roles in cue reinstatement. The SB 242,084 reversal of the d-fenfluramine attenuation suggests that stimulation of 5-HT2C receptors inhibits cue reinstatement, whereas the ketanserin-induced attenuation of cue reinstatement suggests that decreased stimulation of 5-HT2A receptors inhibits this behavior.

Conditioned place preference with morphine: the effect of extinction training on the reinforcing CR.

Rats were injected with either morphine (5 mg/kg) or saline in association with one set of distinct environmental stimuli, and injected with saline in association with a different set of stimuli. After four conditioning trials, animals were given a 15-minute free-choice test to determine which stimulus environment was preferred. Animals displayed CPP as a significant increase in duration spent within the morphine-associated environment, but did not display any change in number of entries into that environment. In contrast, when extinction training was given following CPP, animals displayed a significant decrease in duration spent per entry into the morphine-associated environment, but did not display any change in total duration spent in that environment. These results suggest that assessment of the reinforcing conditioned response (CR) in the CPP model may require measurement of both duration spent in and number of entries into the drug-associated environment.

Increases in dopamine D3 receptor binding in rats receiving a cocaine challenge at various time points after cocaine self-administration: implications for cocaine-seeking behavior.

Previous research suggests that cocaine dysregulates dopamine D3 receptors. The present study examined the time course of changes in dopamine D3 receptor binding after terminating a cocaine self-administration regimen. [125I]-7-hydroxy-2-[N-propyl-N-(3′-iodo-2′-propenyl)-amino]-tetralin was used to label dopamine D3 receptors in rats that had undergone testing for cocaine-seeking behavior reinstated by a cocaine priming injection (15 mg/kg, i.p.; the behavior results have been previously published), and were killed 24 h after the test at time points that were either 2, 8, or 31–32 days after their last cocaine self-administration session. The results indicated a time-dependent increase in D3 receptor binding relative to controls that received saline yoked to the delivery of cocaine in an experimental animal. Specifically, there was no significant change in D3 receptor binding in cocaine-experienced rats killed at the 2- or 8-day time points relative to controls, but there was an increase in D3 receptor binding in the nucleus accumbens core and ventral caudate-putamen in rats killed at the 31- to 32-day time point. In a subsequent experiment, we replicated the increase in D3 receptor binding in rats that underwent a less extensive self-administration regimen, then were tested for cocaine-primed reinstatement of cocaine-seeking behavior, and then were killed 24 h later at a time point of 22 days after their last self-administration session. Furthermore, the increase in binding was attenuated by repeated 7-hydroxy-N,N-di-n-propyl-2-aminotetralin administration (1 mg/kg/day, s.c. for 14 days), a regimen that also reduces cocaine-seeking behavior in animals when tested in a nondrug state. Collectively, the findings suggest that regulatory responses of D3 receptors may be functionally related to changes in propensity for cocaine-seeking behavior.

EFFECTS OF INTRAACCUMBENS ADMINISTRATION OF SCH-23390 ON COCAINE-INDUCED LOCOMOTION AND CONDITIONED PLACE PREFERENCE

The effects of systemic (0–1.0 mg/kg) or intraaccumbens (0–1.0 μg/side) administration of SCH‐23390 on cocaine‐induced (0 or 4.2 mg/kg, IV) locomotion, sniffing, and conditioned place preference (CPP) were investigated in rats. After behavioral testing was completed, animals were injected with their respective dose of SCH‐23390 into the nucleus accumbens (NAc), followed by a systemic injection of the irreversible antagonist N‐ethoxycarbonyl‐2‐ethoxy‐1,2‐dihydroquinoline (EEDQ). Receptors occupied by intraaccumbens SCH‐23390, and therefore protected from EEDQ‐induced inactivation, were then quantified from autoradiograms of sections labeled with 3H‐SCH‐23390. Systemic administration of 0.5 and 1.0 mg/kg SCH‐23390 reversed cocaine‐induced locomotion, sniffing, and CPP, suggesting that stimulation of D1‐like receptors is necessary for these behavioral changes. Intraaccumbens administration of 1.0 μg/side SCH‐23390 reversed cocaine‐CPP, and this dose occupied D1‐like receptors primarily in the rostral pole of the NAc. Intraaccumbens administration of 0.5 μg/side SCH‐23390 reversed cocaine‐induced locomotion. However, this dose occupied a similar number of D1‐like receptors in the NAc as a lower and behaviorally ineffective dose of 0.1 μg/side, but occupied more receptors in the caudate‐putamen relative to both the 0.1 and 1.0 μg/side doses. These findings suggest that stimulation of D1‐like receptors in the NAc is necessary for cocaine‐CPP, but not for cocaine‐induced locomotion. Synapse 30:181–193, 1998.