Paradoxically, stimulation of 5-HT 1B receptors (5-HT 1B Rs) enhances sensitivity to the reinforcing effects of cocaine but attenuates incentive motivation for cocaine as measured using the extinction/ reinstatement model. We revisited this issue by examining the effects of a 5-HT 1B R agonist, CP94253, on cocaine reinforcement and cocaine-primed reinstatement, predicting that CP94253would enhance cocaine-seeking behavior reinstated by a low priming dose, similar to its effect on cocaine reinforcement. Rats were trained to self-administer cocaine (0.75 mg/kg, i.v.) paired with light and tone cues. For reinstatement experiments, they then underwent daily extinction training to reduce cocaine-seeking behavior (operant responses without cocaine reinforcement). Next, they were pre-treated with CP94253 (3-10 mg/kg, s.c.) and either tested for cocaine-primed (10 or 2.5 mg/kg, i.p.) or cue-elicited reinstatement of extinguished cocaine-seeking behavior. For reinforcement, effects of CP94253 (5.6 mg/kg) across a range of self-administered cocaine doses (0-1.5 mg/kg, i.v.) were examined. Cocaine dose-dependently reinstated cocaine-seeking behavior, but contrary to our prediction, CP94253 reduced reinstatement with both priming doses. Similarly, CP94253 reduced cue-elicited reinstatement. In contrast, CP94253 shifted the self-administration dose-effect curve leftward, consistent with enhanced cocaine reinforcement. When saline was substituted for cocaine, CP94253 reduced response rates (i.e. cocaine-seeking behavior). In subsequent control experiments, CP94253 decreased open-arm exploration in an elevated plus-maze suggesting an anxiogenic effect, but had no effect on locomotion or sucrose reinforcement. These results provide strong evidence that stimulation of 5-HT 1B Rs produces opposite effects on cocaine reinforcement and cocaine-seeking behavior, and further suggest that 5-HT 1B Rs may be a novel target for developing medications for cocaine dependence.

Ultrasonic vocalizations in the 50 kHz range (50 kHz USVs) are emitted by rodents upon activation of positive affective states and appear to be a direct measure of internal emotional and motivational urges to seek rewarding stimuli such as drugs of abuse. Since these behavioral responses do not rely on training for expression, they can be viewed as a “spontaneous” measure of affective state. The goal of the present study was to monitor spontaneous USVs throughout a widely-used cocaine self-administration and reinstatement model of addiction and relapse. To gain insight into the changes in affective state across the different phases of a standard self-administration experiment, we measured 50 kHz USVs in rats during cocaine self-administration and reinstatement, and compared these to sucrose self-administration and reinstatement. During cocaine self-administration, the number of 50 kHz USVs increased over acquisition of self-administration and decreased during extinction. Furthermore, the number of USVs on the first day of acquisition in the cocaine experiment was positively correlated with how rapidly cocaine self-administration was acquired. These findings suggest that the initial affective response to cocaine may be a sensitive predictor of the motivational efficacy of rewarding stimuli and therefore the susceptibility to acquire self-administration of cocaine. Cue-and cocaine-induced reinstatement elevated 50 kHz USVs above extinction levels. Rats trained for sucrose self-administration showed no elevation in USVs during acquisition when USVs were considered over the entire 2 hr session, but they did show an elevation in USVs during acquisition when considered over only the first 5 min of the session. As with cocaine-induced reinstatement, sucrose-induced reinstatement produced significantly more USVs compared to the prior extinction day. Taken together, USVs may serve as a sensitive and dynamic noninvasive measure that spontaneously (i.e. without any formal reinforcement contingencies) quantifies the extent to which positive affect is elicited by rewards such as drugs of abuse.

Background The paraventricular thalamus (PVT) is rapidly becoming recognized as part of the addiction circuitry. In addition to its strong anatomical connection to most of the brain regions underlying addiction, such as the nucleus accumbens, prefrontal cortex, amygdala, and hippocampus, the PVT has recently been shown to contribute to cocaine sensitization and reinstatement. In the present study we examined the role of the PVT in the expression of cocaine conditioned place preference (CPP). Methods We tested the impact of PVT inactivation by baclofen/muscimol (bac-mus) microinjection on the expression of cocaine-induced CPP in rats. Rats were implanted with guide cannulae into the PVT. Bac-mus (GABAB-GABAA agonists) or saline was injected into the PVT prior to CPP testing. Results Inactivation of the PVT by bac-mus prevented the expression of CPP, while placements outside the PVT did not affect CPP. Intra-PVT injections of bac-mus did not affect locomotor activity during the session. Conclusions In the present study we contribute to the growing body of research supporting a role for the PVT in addiction by demonstrating that the PVT is necessary for the expression of cocaine CPP.

This study investigated the effects of the AMPA/Kainate receptor antagonist, NBQX, on cueelicited cocaine-seeking behavior and concomitant changes in Fos protein expression. After cocaine self-administration training, rats underwent 24 days of abstinence during which they were exposed daily either to the self-administration environment with response-contingent cues previously paired with cocaine infusions available (Extinction group) or to an alternate environment (No Extinction group). Subsequently, rats were tested for cocaine-seeking behavior (i.e., operant responses without cocaine reinforcement) elicited by the cocaine-associated cues after pretreatment with either vehicle or NBQX (10 mg/kg, IP). NBQX markedly attenuated cueelicited cocaine-seeking behavior relative to vehicle pretreatment in the No Extinction group and also decreased cue-elicited Fos protein expression in a region-specific manner in the anterior cingulate and orbitofrontal cortices, basolateral amygdala, nucleus accumbens core, and dorsal caudate-putamen, suggesting involvement of AMPA glutamate systems in specific subregions of the neuronal circuitry activated by cocaine cues.

Cocaine-associated cues can elicit incentive motivational effects that drive cocaine-seeking behavior and contribute to relapse. The extinction/reinstatement model is commonly used to measure these effects in animals. This study examined the influence of training and testing schedules of reinforcement on cue-elicited reinstatement. Lever presses during training resulted in cues and cocaine (0.75 mg/kg/IV) on either continuous or partial reinforcement schedules [fixed ratio (FR) 1 or 11, variable ratio (VR) 5 or 11]. Animals then underwent extinction training, followed by a test for cue-elicited reinstatement of extinguished cocaine-seeking behavior by response-contingent cue presentations on either a continuous (FR 1) or a partial reinforcement schedule (FR 11). Partial reinforcement during training resulted in higher response rates during cue-elicited reinstatement relative to continuous reinforcement. In contrast, delivery of cues on a continuous reinforcement schedule during testing yielded higher response rates relative to delivery on a partial reinforcement schedule. Finally, the shift from a partial to a continuous reinforcement schedule across training and testing phases did not alter response rates. These findings provide important information for choosing parameters for reinstatement of drug-seeking behavior that would allow the most sensitive method to detect changes in response rate after an experimental manipulation.

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