Environmental enrichment attenuates locomotor sensitization, but not in vitro dopamine release, induced by amphetamine.

Rats were raised from weanling until young adulthood in either an enriched condition (EC) or isolated condition (IC). Following this, the locomotor and rewarding effects of amphetamine were determined using the conditioned place preference (CPP) paradigm. EC rats were more sensitive to the acute locomotor stimulant effect and rewarding effect of amphetamine relative to IC rats. In contrast, EC rats were less sensitive than IC rats to the locomotor sensitization effect obtained across repeated amphetamine injections. To determine the effect of environmental enrichment on alteration of brain dopamine (DA) function induced by amphetamine, the effect of amphetamine on electrically evoked release of DA and dihydroxyphenylacetic acid (DOPAC) was determined in vitro using tissue slices from the nucleus accumbens and striatum of EC and IC rats. No differences between EC and IC rats in release of DA or DOPAC were evident, suggesting that the environmentally induced difference in sensitivity to the behavioral effects of amphetamine involves a neural mechanism extrinsic to the mesolimbic and nigrostriatal terminal field regions.