ACQUISITION OF COCAINE SELF-ADMINISTRATION AFTER SOCIAL STRESS - ROLEOF ACCUMBENS DOPAMINE

Exposure to either aversive or rewarding environmental stimuli increas es extracellular dopamine (DA) concentrations in terminal areas of the mesocorticolimbic dopamine system. Furthermore, behavioral reactivity to an environmental stressor has been shown to correlate with latency to initiate self-administration of psychomotor stimulant drugs. The p resent study examined the behavioral and dopaminergic responses of rat s to social defeat stress and compared latencies to initiate cocaine s elf-administration in defeated and non-defeated rats. In vivo microdia lysis was used to examine the effects of social defeat stress on DA co ncentrations in nucleus accumbens of freely-moving rats. During the ex perimental session, dialysate and video recording samples were collect ed from previously-defeated and non-defeated ''intruder'' rats in cons ecutive phases, while (1) in the home cage, (2) when placed in the emp ty, soiled cage of a resident rat which had previously defeated them, and (3) when exposed to threat of defeat by the resident. Immediately following threat of defeat, previously-defeated and non-defeated intru ders were given the opportunity to self-administer cocaine IV. When ex posed to the olfactory cues of an aggressive resident, extracellular D A levels in nucleus accumbens increased to approximately 135% of basel ine in previously defeated rats versus 125% of baseline in non-defeate d rats. When exposed to social threat by the resident, DA levels furth er increased to 145% of baseline in previously defeated rats versus 12 0% in non-defeated rats. Previously defeated rats acquired cocaine sel f-administration in approximately half the time of non-defeated rats, consistent with the hypothesis that prior stress exposure may induce a cross-sensitization to the rewarding effects of cocaine. These result s are consistent with the idea that exposure to stress may induce chan ges in central dopaminergic activity, which may render an individual m ore vulnerable to acquiring psychomotor stimulant self-administration.