Blockade or stimulation of D1 dopamine receptors attenuates cue reinstatement of extinguished cocaine-seeking behavior in rats

RATIONALE

D(1) dopamine receptor antagonists and agonists attenuate cocaine reinstatement of cocaine-seeking behavior (i.e., responding in the absence of cocaine reinforcement).

OBJECTIVES

The present study investigated the effects of a D(1) antagonist (SCH-23390), partial agonist (SKF-38393), and full agonist (SKF-81297) on reinstatement of cocaine-seeking behavior elicited by presentation of cocaine-paired cues.

METHODS

Rats that had been trained to self-administer cocaine with a light/tone stimulus complex paired with each infusion underwent extinction across days. After responding diminished, rats were given response-contingent access to the cocaine-paired stimulus complex. The effects of SCH-23390 (0-10.0 microg/kg), SKF-38393 (0-3.0 mg/kg), and SKF-81297 (0-3.0 mg/kg) on cue reinstatement of cocaine-seeking behavior were examined. The ability of the two D(1) agonists to independently reinstate cocaine-seeking behavior and the effects of SKF-81297 on cocaine reinstatement were also examined. To investigate the possibility of behavioral interference, the effects of SKF-38393 and SKF-81297 on grooming and stereotypy were assessed.

RESULTS

SCH-23390 and SKF-81297, but not SKF-38393, attenuated cue reinstatement. However, while SKF-81297 dose-dependently increased response latency, SCH-23390 did not. SKF-81297 also independently reinstated responding at the two lowest doses tested while SKF-38393 had no effect. Furthermore, SKF-81297 decreased cocaine reinstatement and increased response latency only at the highest dose. Finally, stereotypy was observed at all doses of SKF-81297 that also decreased responding, although the patterns of changes in these behaviors did not completely correspond.

CONCLUSIONS

While the antagonist and full agonist produced similar effects on cocaine-seeking behavior, only the agonist increased response latency, suggesting that different processes mediate the effects of these drugs.

Role of the prelimbic subregion of the medial prefrontal cortex in acquisition, extinction, and reinstatement of cocaine-conditioned place preference

Previous research suggests that the prelimbic subregion of the medial prefrontal cortex (mPFC) is necessary for acquisition of cocaine-conditioned place preference (CPP). Recently, it has been shown that extinguished cocaine-CPP can be reinstated by cocaine priming injections, and that this effect reflects the incentive motivational effects of the cocaine prime. To determine whether the prelimbic cortex is necessary for cocaine-reinstated CPP, rats received bilateral infusions of quinolinic acid (lesion group) or vehicle (sham group) into the prelimbic cortex and were later tested for acquisition, extinction, and reinstatement of cocaine-CPP. Both sham and lesion rats exhibited robust CPP established by systemic injections of cocaine (15 mg/kg, i.p.) following either one or three drug-environment pairings. Following repeated exposure to the cocaine- and saline-paired environments, sham and lesion rats showed similar rates of extinction of cocaine-CPP. In contrast, reinstatement of cocaine-CPP by cocaine priming injections (5 and 10 mg/kg, i.p.) was attenuated in rats with prelimbic cortex lesions relative to sham controls. This finding suggests that the prelimbic cortex is involved in the incentive motivational effects of cocaine priming.

Effects of SCH-23390 infused into the amygdala or adjacent cortex and basal ganglia on cocaine seeking and self-administration in rats

Amygdala D1 receptors have been implicated in the motivating effects of cocaine-conditioned cues and cocaine itself, but the specific nucleus involved is unclear. Thus, we infused the D1 antagonist, SCH-23390, into the rostral basolateral amygdala (rBLA), caudal basolateral amygdala (cBLA), or central amygdala (CEA), and tested its effects on self-administration of cocaine, as well as reinstatement of extinguished cocaine-seeking behavior by cocaine-conditioned cues or cocaine itself. Two anatomical controls, the posterior regions of basal ganglia (BG) and somatosensory/insular cortices (CTX), were also examined. Cocaine self-administration was increased and cue and cocaine reinstatement were decreased by SCH-23390 infusion into every region when examined across the hour test session, with the exception that cBLA infusion did not alter cocaine reinstatement. In the first 20 min of the session, when SCH-23390 was more localized in the target sites, self-administration was increased by infusion into the CEA, cBLA, BG, and CTX, with lesser increases in the rBLA. Cocaine reinstatement was attenuated during the first 20 min only by infusion into the CEA, rBLA, and CTX. Cue reinstatement was not reliably observed in the first 20 min, but there was a trend for attenuation by infusion into the cBLA, and surprisingly, significant attenuations in the BG and CTX. The findings suggest that D1 receptors in subregions of the amygdala play differential roles in the reinforcing/motivational effects of cocaine, while the cue reinstatement effects are less clear. Further research is needed to examine the novel findings that neighboring regions of the BG and CTX may play a role in motivation for cocaine.

Passive exposure to a contextual discriminative stimulus reinstates cocaine-seeking behavior in rats

A significant problem in treating cocaine dependence is craving-induced relapse elicited by inadvertent (i.e., passive) exposure to cocaine-paired stimuli. Extinction/reinstatement of cocaine-seeking behavior in animals has been used to investigate this phenomenon. Most studies using this model have examined reinstatement by response-contingent exposure to discrete cocaine-paired stimuli. The present study expanded this research by examining passive (i.e., not contingent upon an operant response) exposure to a contextual cocaine-paired stimulus to better model craving elicited by inadvertent exposure to cocaine-associated environmental stimuli. Rats underwent daily cocaine and saline self-administration sessions that were identical to each other except for a discriminative stimulus (scented bedding) signaling cocaine availability (S+) or nonavailability (S-). Subsequently, they were placed into the self-administration chambers in the presence of neutral bedding. Reinforcement was not available and cocaine-seeking behavior (i.e., nonreinforced operant responses) was extinguished across days. Rats were then reintroduced to the S+ and S- stimuli. Presentation of the S+, but not the S-, elicited significant reinstatement of cocaine-seeking behavior. The results demonstrate that passive exposure to a contextual discriminative stimulus reinstates extinguished cocaine-seeking behavior. Furthermore, we suggest that reinstatement of cocaine-seeking behavior by passive exposure to cocaine-paired stimuli may provide a model of craving-induced relapse elicited by inadvertent exposure to a cocaine-associated environment.

D1-receptor drugs and cocaine-seeking behavior: investigation of receptor mediation and behavioral disruption in rats

RATIONALE

Dopamine D1-receptor antagonists and agonists both attenuate cocaine-seeking behavior (i.e., operant responding in the absence of cocaine reinforcement) elicited by a cocaine prime or cocaine-paired stimuli. It remains unclear whether these effects are D1-receptor mediated.

OBJECTIVES

The present study tested whether a D1 antagonist (SCH-23390) would reverse the attenuating effects of a D1 agonist (SKF-81297) on cocaine-seeking behavior and whether behavioral disruption is involved in these effects.

METHODS

Rats trained to press a lever for cocaine reinforcement with light and tone cues paired with each infusion underwent daily extinction sessions during which responding had no scheduled consequences (i.e., neither cocaine nor the cocaine-paired stimulus complex was available). After responding diminished, the effects of the D1 antagonist on the dose-response functions of the D1 agonist for reinstatement of cocaine-seeking behavior by response-contingent cue presentations or cocaine priming were examined. A separate experiment assessed the effects of the agonist on the dose-response function of the antagonist for cue reinstatement. Stereotyped behavior and activity were also measured during each test session.

RESULTS

The attenuating effects of SKF-81297 on cocaine-seeking behavior during cocaine-primed reinstatement were reversed by co-administration of SCH-23390. However, no evidence for reversal of the attenuation during cue reinstatement was found even though agonist-induced stereotypy and antagonist-induced hypoactivity were reversed by co-administration of the two drugs during the same test session.

CONCLUSIONS

The findings suggest that the attenuating effects of D1-receptor drugs on cocaine-seeking behavior during cocaine reinstatement are mediated by dopamine D1 receptors; however, it remains unclear whether the effects of these drugs on cocaine-seeking behavior during cue reinstatement are D1-receptor mediated. Nevertheless, it is evident that the attenuation of cocaine-seeking behavior by these drugs is not simply due to behavioral disruption.

Stimulation of dopamine D2/D3 but not D1 receptors in the central amygdala decreases cocaine-seeking behavior

Alterations in dopamine output within the various subnuclei of the amygdala have previously been implicated in cocaine reinforcement, as well as cocaine-seeking behavior. To elucidate the potential for increased stimulation of D1- and D2-like receptors (D1Rs and D2Rs, respectively) specifically in the central nucleus of the amygdala (CeA) to modulate cue- and cocaine-elicited reinstatement of cocaine-seeking behavior, we infused either the D1R agonist, SKF-38393 (0-4.0 microg/side) or the D2R agonist, 7-OH-DPAT (0-4.0 microg/side) into the CeA immediately prior to tests for cue and cocaine-primed reinstatement. We also examined the effects of 7-OH-DPAT on cocaine self-administration as a positive behavioral control. 7-OH-DPAT decreased cue-and cocaine-primed reinstatement, and reduced the number of cocaine infusions obtained during self-administration; SKF-38393 produced no discernable effects. The results suggest that enhanced stimulation of D2Rs, but not D1Rs, in the CeA is sufficient to inhibit expression of the incentive motivational effects of cocaine priming and cocaine-paired cues. Together with previous findings that D1R blockade attenuates reinstatement of cocaine-seeking behavior, the results suggest that D1R stimulation may be necessary, but not sufficient, to modulate the incentive motivational effects of cues and cocaine priming.