Effects of neonatal and adult 6-hydroxydopamine treatment on random-interval behavior

Rats were given intraventricular injections of 6-hydroxydopamine (6-HDA) or saline-ascorbate vehicle as neonates (3-days old) and as adults (49 and 51 days old). At 73 days of age, they were trained on a random interval 90-sec schedule of water reinforcement. The rats treated with 6-HDA as adults stabilized at response rates approximately twice those of vehicle-treated rats, while rats treated with 6-HDA as neonates showed response rates which were not significantly different from vehicle-treated rats; Both L-Dopa and apomorphine decreased response rates at all doses tested. There were no differences among the groups with respect to the effect of these drugs. Adult-treated rats showed greater response rate decreases following peripheral decarboxylase inhibition with Ro 4-4602. Catecholamine analyses revealed the rats treated with 6-HDA as neonates had greater depletions in the striatum and the remainder of telencephalon than adult-treated rats but an increase in brainstem norepinephrine. These findings suggest that age of treatment is an important determinant of the biochemical and behavioral effects of treatment with 6-HDA.