Hyperactivity in neonatally dopamine-lesioned rats requires residual activity in mesolimbic dopamine neurons

Neonatal destruction of mesencephalic dopamine (DA) neurons in rats through administration of 6-hydroxydopamine (6-OHDA; 75 micrograms IC) leads to locomotor hyperactivity at adulthood. Treatment with the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (H44/68; 250 mg/kg) was shown to reduce the motor activity of neonatally 6-OHDA-lesioned rats to activity levels similar to controls. In both animal groups, DA and metabolite tissue levels decreased after the H44/68 treatment. However, the extent of the H44/68-induced DA decrease was less pronounced in the 6-OHDA-lesioned animals, with no change at all in the dorsal striatum. These results imply that residual activity in mesolimbic DA neurons is required for maintaining the hyperactivity seen after neonatal 6-OHDA lesions, and that this hyperactivity is apparently mediated by postsynaptic alterations.