D-1 and D-2 receptor mediation of sensorimotor behavior in rats depleted of dopamine during development

The effects of selective D-1 and D-2 antagonists on sensorimotor behavior were studied in rats treated with 6-OHDA or its vehicle solution on either postnatal day 3, 20, or 35. Blockade of either D-1 or D-2 receptors induced akinesia and somatosensory neglect in adults treated with vehicle at any of the three ages. The behavioral effects of antagonists on rats with 6-OHDA-induced dopamine depletions varied as a function of the age at the time of damage. Adults depleted of DA on Day 35 exhibited behavioral deficits after either D-1 or D-2 blockade and at doses that were ineffective in controls. Adults depleted of DA on Day 20 exhibited deficits after either D-1 or D-2 blockade but were not any more sensitive than were controls. In contrast, adults depleted of DA on Day 3 were insensitive to the behavioral effects of D-1 or D-2 blockers but were impaired after the dual administration of both antagonists. Moreover, simultaneous administration of subthreshold doses of D-1 and D-2 antagonists produced behavioral deficits in controls and rats depleted on Day 3. These data demonstrate that activity within residual DA neurons remains critical for the expression of sensorimotor behavior in rats depleted of DA during development. However, the specific contribution of D-1 and D-2 receptors to these behaviors depends upon the animals' age at the time of depletion.