The effect of environmental enrichment on amphetamine-stimulated locomotor activity, dopamine synthesis and dopamine release.

In two separate experiments, rats were raised in either an enriched condition (EC) or impoverished condition (IC) from 21 to 60 days of age. Experiment 1 assessed amphetamine-stimulated locomotor activity and in vivo dopamine (DA) synthesis and metabolism in the nucleus accumbens (NA) and striatum (Str). In Experiment 2, amphetamine-stimulated DA release in the NA and Str was assessed in vitro. The results showed that EC rats have lower basal levels of locomotor activity than IC rats. However, in the presence of amphetamine, EC rats showed a greater increase in locomotion over IC when compared to their own controls. Concomitant with this behavioral difference, EC rats also showed an enhanced neurochemical response to amphetamine in vivo. That is, relative to IC rats, amphetamine produced a greater synthesis of DA in the Str of EC rats, as well as a greater metabolism of DA in the NA of EC rats. In the in vitro DA release experiment, EC rats had a lower concentration of tissue DA than IC. However, in contrast to the in vivo experiment, there were no significant differences between EC and IC rats in amphetamine-stimulated release of DA in vitro in either the Str or NA. The failure of amphetamine to produce differential neurochemical effects in EC and IC rats in vitro may be because this experiment eliminated either pharmacokinetic effects or neurochemical differences in brain regions outside the NA and Str.