BEHAVIORAL-EFFECTS OF SELECTIVE AND NONSELECTIVE DOPAMINE AGONISTS ONYOUNG-RATS AFTER IRREVERSIBLE ANTAGONISM OF D(1) AND OR D(2) RECEPTORS

In general, preweanling and adult rats respond similarly when challeng ed with competitive dopamine (DA) agonists or antagonists. In contrast , results using a noncompetitive antagonist suggest that the D, and D2 receptor systems of preweanling and adult rats differ in some critica l way. To further assess this phenomenon, the behavioral effects of ir reversible receptor blockade were assessed across 8 days in NPA (a non selective DA agonist), quinpirole (a D2 agonist), or SKF 38393 (a D1 a gonist) treated 17-day-old rat pups. The irreversible antagonist N-eth oxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) did not block the loc omotor activity and rearing of NPA- or quinpirole-treated rat pups, no r did EEDQ reduce SKF 38393-induced grooming. Moreover, pretreatment w ith EEDQ appeared to potentiate the normal increases in locomotor acti vity and rearing produced by NPA, but only when D2 receptors were not protected by a previous injection of sulpiride (a D2 antagonist). Take n together, these results are consistent with the presence of large re serves of D1 and D2 receptors in the preweanling rat pup.