D1 and D2 receptor contributions to ingestive and locomotor behavior are altered after dopamine depletions in neonatal rats

The effects of selective D1 and D2 antagonists on ingestive and locomotor behavior were studied in adult rats depleted of dopamine (DA) as neonates and their vehicle-treated controls. Blockade of either D1 or D2 receptors inhibited food intake and produced akinesia in control animals. Simultaneous administration of subthreshold doses of these antagonists produced similar behavioral deficits, indicating a synergism between the two receptor subtypes. In contrast, adults depleted of DA as neonates were unaffected by either D1 or D2 blockade. However, combined administration of these antagonists produced behavioral deficits comparable to those seen in controls. These data demonstrate that while activity within residual DA neurons remains critical for the expression of ingestive and locomotor behavior in rats depleted of DA as neonates, the precise nature of the interactions between the D1 and D2 receptor subtypes is altered after the depletion.