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 co ndition (EC) or impoverished condition (IC) from 21 to 60 days of age. Experiment 1 assessed amphetamine-stimulated locomotor activity and i n vivo dopamine (DA) synthesis and metabolism in the nucleus accumbens (NA) and striatum (Str). In Experiment 2, amphetamine-stimulated DA r elease in the NA and Str was assessed in vitro. The results showed tha t EC rats have lower basal levels of locomotor activity than IC rats. However, in the presence of amphetamine, EC rats showed a greater incr ease in locomotion over IC when compared to their own controls. Concom itant with this behavioral difference, EC rats also showed an enhanced neurochemical response to amphetamine in vivo. That is, relative to I C rats, amphetamine produced a greater synthesis of DA in the Str of E C 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 amphe tamine-stimulated release of DA in vitro in either the Str or NA. The failure of amphetamine to produce differential neurochemical effects i n EC and IC rats in vitro may be because this experiment eliminated ei ther pharmacokinetic effects or neurochemical differences in brain reg ions outside the NA and Str.