No abstract

There is a greater prevalence of cigarette smoking among cocaine‐dependent individuals and hyperactive children treated with stimulants (e.g., methylphenidate, MP). However, little is known about the neurochemical basis of the interaction between nicotine and cocaine or MP. It is thought that the reinforcing effects of cocaine and MP are due partly to increases in synaptic DA in the nucleus accumbens (NAc). These measurable increases are secondary to the blockade of the DA transporter. In contrast, nicotine stimulates acetylcholine receptors located presynaptically on dopaminergic projections from the ventral tegmental area (VTA) to the NAc and increases DA transmission. Here we investigate the effects of nicotine on NAc DA in animals simultaneously injected with cocaine or MP. Coadministration of nicotine (0.4 mg/kg s.c.) and cocaine (10 mg/kg i.p.) or MP (5 mg/kg i.p.) increased the extracellular NAc DA levels in an additive manner, while coadministration of nicotine (0.4 mg/kg s.c.) and a higher dose of cocaine (20 mg/kg) or MP (10 mg/kg) clearly produced a synergistic elevation in NAc DA. These findings suggest that the degree of DA transporter (DAT) occupancy contributes to the synergistic interaction between nicotine and cocaine or MP. Synapse 38:432–437, 2000. © 2000 Wiley‐Liss, Inc.

No abstract

We determined the effect of the selective dopamine D3 receptor antagonist SB-277011A on reactivation of conditioned place preference (CPP) to cocaine elicited by priming injections of cocaine or exposure to food deprivation stress (21 h) in male Sprague-Dawley rats. Animals paired with the cocaine-associated chamber displayed a robust and consistent CPP response. This CPP was extinguished after repeated pairings of the conditioned stimuli (cocaine-paired chamber contextual cues) in the absence of the unconditioned stimulus (cocaine). Twenty-four hours later, the administration of 5 mg kg(-1) i.p. of cocaine (immediately before the test) or exposure to 21 h of food deprivation reactivated the expression of the cocaine-induced CPP. In contrast, administration of 1 ml kg(-1) i.p. of vehicle did not reactivate the CPP response. Administration of the selective dopamine D3 receptor antagonist SB-277011A (3-24 mg kg(-1) i.p.) 30 min before cocaine administration on the test day produced a significant attenuation of CPP reactivation. Reactivation of the CPP response produced by food deprivation was also significantly attenuated by SB-277011A (6 or 12 mg kg(-1) i.p.) given 30 min before the test session. SB-277011A (12 or 24 mg kg(-1) i.p.) did not itself produce reactivation of the CPP response. Overall, these results suggest that the reactivation of the incentive value of drug-associated cues by cocaine or food deprivation is attenuated by selective antagonism of D3 receptors.