Isolation rearing in rats: pre- and postsynaptic changes in striatal dopaminergic systems

Isolation rearing of rats produces a behavioral syndrome indicative of altered dopamine (DA) function in the nucleus accumbens (NAC). The present experiments extend these findings by investigating: (a) interactions between isolation rearing and repeated handling/testing on presynaptic DA function in the NAC using in vivo microdialysis: (b) the dose-response curve for the effects of d-amphetamine, and the responses elicited by high potassium, using in vivo microdialysis, and (c) postsynaptic function in isolates as indexed by DA receptor-linked cAMP production. Experiment 1 showed that both isolation rearing and repeated handling/testing had effects on monoamine function in the NAC. However, while both manipulations enhanced DA release evoked by d-amphetamine, only isolated rats had elevated basal DA levels. Opposite neurochemical changes were observed with respect to the serotonin metabolite 5-HIAA, isolates having lower, and repeatedly handled/tested animals having higher, extracellular levels. Experiment 2 provided evidence for enhanced d-amphetamine-evoked DA release in isolated animals, while potassium-evoked DA release was reduced. Experiment 3 provided evidence that the isolation rearing induced changes in presynaptic DA function were accompanied by postsynaptic changes. Specifically, the inhibitory influence of the D2 receptor on D1 receptor-stimulated cAMP production was attenuated in ventral striatal slices taken from isolates, suggesting a functional downregulation of D2 receptors.