Rita A. Fuchs

The Role of the Dorsomedial Prefrontal Cortex, Basolateral Amygdala, and Dorsal Hippocampus in Contextual Reinstatement of Cocaine Seeking in Rats

The present study tested the hypothesis that separate neural substrates mediate cocaine relapse elicited by drug-associated contextual stimuli vs explicit conditioned stimuli (CSs) and cocaine. Specifically, we investigated the involvement of the dorsal hippocampus (DH), basolateral amygdala (BLA), and dorsomedial prefrontal cortex (dmPFC) in contextual reinstatement of cocaine-seeking behavior and the involvement of the DH in explicit CS- and cocaine-induced reinstatement. Rats were trained to self-administer cocaine in a distinct context or in the presence of CSs paired explicitly with cocaine infusions. Responding of context-trained rats was then extinguished in the previously cocaine-paired or an alternate context, whereas responding of explicit CS-trained rats was extinguished in the absence of the CSs. Subsequently, the target brain regions or anatomical control regions were functionally inactivated using tetrodotoxin (0 or 5 ng/side), and cocaine-seeking behavior (ie, nonreinforced responses) was assessed in the cocaine-paired context, in the alternate context, in the presence of the explicit CSs, or following cocaine priming (10 mg/kg, i.p.). DH inactivation abolished contextual, but failed to alter explicit CS- or cocaine-induced, reinstatement of cocaine-seeking behavior. BLA or dmPFC inactivation also abolished contextual reinstatement. Conversely, inactivation of the control brain regions failed to alter contextual reinstatement. In conclusion, the DH, BLA, and dmPFC play critical roles in contextual reinstatement. Previous findings suggest that the BLA is critical for explicit CS-induced, but not cocaine-primed, reinstatement and the dmPFC is critical for both explicit CS-induced and cocaine-primed reinstatement. Thus, distinct but partially overlapping neural substrates mediate context-induced, explicit CS-induced, and cocaine-primed reinstatement of extinguished cocaine-seeking behavior.

Different Neural Substrates Mediate Cocaine Seeking after Abstinence versus Extinction Training: A Critical Role for the Dorsolateral Caudate–Putamen

Cue-induced reinstatement of extinguished drug seeking is a preclinical model of relapse. However, relapse typically occurs after abstinence rather than explicit extinction training. We show that inactivation of the dorsolateral caudate–putamen, but not other structures previously implicated in reinstatement, attenuates cocaine seeking after abstinence. This suggests that there is limited overlap in the substrates of cocaine seeking after abstinence versus extinction, and that habit learning exerts greater control over drug seeking than regions implicated in stimulus–reward associations.

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.

Differential involvement of the core and shell subregions of the nucleus accumbens in conditioned cue-induced reinstatement of cocaine seeking in rats

RationaleThe nucleus accumbens (NAC) is theorized to be a critical element of the neural circuitry that mediates relapse to cocaine seeking. Evidence suggests that the NAC is a functionally heterogeneous structure, and the core (NACc) and shell (NACs) regions of the NAC may play a differential role in stimulus-induced motivated behavior. Thus, determination of the involvement of NAC subregions in conditioned cue-induced reinstatement of cocaine seeking is warranted.ObjectivesThe present study compared the effects of GABA agonist-induced inactivation of the NACc versus NACs on conditioned cue-induced reinstatement of cocaine seeking behavior.MethodsRats were trained to lever press for cocaine infusions (0.20xa0mg/infusion, IV) paired with presentations of a light-tone stimulus complex. Responding was then allowed to extinguish prior to reinstatement testing. Reinstatement of cocaine seeking (i.e. responses on the previously cocaine-paired lever) was measured in the presence of response-contingent presentation of the light-tone stimulus complex following microinfusion of muscimol+baclofen (Mus+Bac, 0.1/1.0xa0mM, respectively, 0.3xa0μl/side) or vehicle into the NACc or NACs. The effects of these manipulations on locomotor activity were also examined.ResultsMus+Bac-induced inactivation of the NACc abolished, whereas inactivation of the NACs failed to alter, conditioned cue-induced reinstatement of operant responding relative to vehicle pretreatment. Time course analyses of the effects of these manipulations on locomotion versus operant responding confirmed that the effects of Mus+Bac on reinstatement were not due to suppression of general activity.ConclusionsThe functional integrity of the NACc, but not the NACs, is necessary for conditioned cue-induced reinstatement of cocaine seeking behavior.

Basolateral amygdala inactivation abolishes conditioned stimulus- and heroin-induced reinstatement of extinguished heroin-seeking behavior in rats

Rationale: Drug-paired stimuli elicit drug craving and relapse in addicts and drug-seeking behavior in rats. The functional integrity of the basolateral amygdala (BLA) is necessary for reinstatement of cocaine-seeking behavior elicited by cocaine-conditioned stimuli, but not by cocaine itself. It is unclear, however, whether the BLA plays a similar role in reinstatement of heroin-seeking behavior. Objectives: To this end, we examined the effects of tetrodotoxin (TTX)-induced inactivation of the BLA on conditioned and heroin-primed reinstatement of extinguished heroin-seeking behavior. Methods: Rats were trained to press a lever for IV infusions of heroin (maintenance dose of 25xa0µg/infusion) paired with presentations of a light-tone stimulus complex during daily 3-h sessions. Responding was then allowed to extinguish prior to reinstatement testing. Reinstatement of extinguished heroin-seeking behavior (i.e. lever pressing in the absence of heroin reinforcement) was measured in the presence of response-contingent presentation of the heroin-paired stimulus complex alone and then following TTX (5xa0ng/0.5xa0µl per side) or vehicle infused into the BLA. In a separate group of rats, reinstatement was measured after saline injection (SC) and then following heroin priming (0.25xa0mg/kg, SC) with TTX or vehicle infused into the BLA. Results: Both response contingent presentation of the stimulus complex and heroin priming significantly reinstated extinguished heroin-seeking behavior, and BLA inactivation abolished the ability of the heroin-paired stimuli and of heroin priming to reinstate responding. Conclusions: These findings suggests that the BLA is a critical component of the neural circuitry that mediates conditioned and heroin-induced reinstatement of heroin-seeking behavior. Furthermore, different neural substrates may mediate drug-primed relapse to cocaine versus heroin-seeking behavior.

Drug Addiction, Relapse, and the Amygdala

Abstract: Evidence has extensively implicated the amygdala in the associative learning process for appetitive reinforcers. Recent interest has focused on the role of the amygdala in the learned associations that occur during the process of drug addiction and relapse. Using an animal model of relapse after chronic cocaine self‐administration, we found that rats reinstate extinguished lever responding for conditioned stimuli (tone + light) previously paired with cocaine or heroin (‘conditioned‐cued reinstatement’). The basolateral amygdala (BLA) complex plays a critical role in this behavior, because permanent lesions or reversible pharmacologic inactivation of the BLA attenuates conditioned‐cued reinstatement without affecting cocaine self‐administration or cocaine‐primed reinstatement. Conditioned‐cued reinstatement appears to be mediated in part by dopamine inputs to the BLA, as intra‐BLA infusion of a dopamine D1 receptor antagonist blocks reinstatement, whereas intra‐BLA infusion of amphetamine potentiates reinstatement. Furthermore, the BLA is also necessary for acquisition of associative learning with cocaine‐paired stimuli. Disruption of neural activity within the BLA by sodium channel blockade or muscarinic receptor blockade just before acquisition of stimulus‐cocaine associations blocks the ability of conditioned stimuli to elicit conditioned‐cued reinstatement after extinction. Together, these results reveal the importance of the amygdala as part of a corticolimbic circuit mediating both the acquisition and the expression of conditioning that plays a critical role in relapse to drug‐seeking behavior.

Differential Involvement of Orbitofrontal Cortex Subregions in Conditioned Cue-Induced and Cocaine-Primed Reinstatement of Cocaine Seeking in Rats

Orbitofrontal cortex (OFC) damage elicits impulsivity and perseveration, and impairments in OFC function may underlie compulsive drug seeking in cocaine users. To test this hypothesis, we assessed the effects of fiber-sparing lesions or functional inactivation of OFC subregions on cocaine seeking in rats. Rats were trained to lever press for intravenous cocaine (0.20 mg/infusion) paired with the presentations of light plus tone stimuli. Responding was then allowed to extinguish. Rats received bilateral NMDA (0.1 M) or sham lesions of the lateral OFC (lOFC) or medial OFC (mOFC) before self-administration training (experiment 1) or muscimol plus baclofen (0.1 and 1.0 mM) or vehicle infusions into the lOFC or mOFC before reinstatement testing (experiment 2). The effects of these manipulations on reinstatement of cocaine seeking (i.e., responding on the previously cocaine-paired lever) were assessed in the presence of the light plus tone stimuli or after a cocaine priming injection (10 mg/kg, i.p.). Post-training lOFC inactivation impaired conditioned cue-induced reinstatement, whereas other manipulations failed to alter this behavior. This suggests that the lOFC plays a critical role in assessing the current motivational significance of cocaine-conditioned stimuli or in using this information to guide cocaine-seeking behavior if stimulus-reward learning takes place before lOFC damage. OFC inactivation failed to alter cocaine-primed reinstatement. However, lOFC lesions augmented cocaine-primed reinstatement in a perseverative manner, whereas mOFC lesions attenuated cocaine-primed reinstatement, suggesting that prolonged cell loss in OFC subregions may modulate the propensity for cocaine seeking in a subregion-specific manner.

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

Abstractu2002The 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 (0.75u2005mg/kg per 0.1u2005ml 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 (10u2005mg/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 1u2005h, 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.