Catalepsy produced by striatal microinjections of the D1 dopamine receptor antagonist SCH 23390 in neonatal rats.

Systemic injection of the D1 dopamine receptor antagonist SCH 23390 produces catalepsy that is of lesser magnitude in neonatal than in adult rats. The present experiments were conducted in order to determine if SCH 23390 would produce catalepsy in neonatal rats following intrastriatal injection and if the ontogenetic pattern of catalepsy induced by intrastriatal SCH 23390 would be similar to the pattern observed with systemic injections. Rat pups (11 or 28 days of age) were microinjected unilaterally with SCH 23390 (0.2, 1, 5 or 10 micrograms) and tested for catalepsy using the forepaw-on-horizontal-bar test. The results demonstrated that robust catalepsy occurred at both ages following intrastriatal injection and that catalepsy induced by 5 micrograms SCH 23390 was of lesser magnitude in 11-day-olds than in 28-day-olds. A separate study assessed the distribution of [3H]SCH 23390 (5 micrograms) following intrastriatal injection in 28-day-olds. Results of the distribution study indicated that [3H]SCH 23390 was localized primarily within the striatum. Taken together, these results suggest that the striatal mechanisms for catalepsy produced by D1 receptor blockade are present, but not fully mature, in preweanling rat pups.