Exploratory activity and conditioned avoidance acquisition after early postnatal 6-Hydroxydopamine administration

Newborn rats were treated with 3 injections of 6-hydroxydopamine (6-OHDA) either subcutaneously (s. c.) or intracerebrally (i. cer.).General motor activity, exploratory activities (crossing and rearing) and acquisition of conditioned avoidance response (CAR) in shuttle-box were tested in the course of the 9th postnatal week. 50 μg/g s. c. 6-OHDA injected daily during the first 3 postnatal days led to a moderate decrease in rearing but was ineffective on other behavioural parameters. A dose of 100 μg i. cer. (20, 30, 50 μg on days 2, 4, 6 resp.) resulted in a considerable reduction in both rearing and acquisition of CAR, while 200 μg i. cer. 6-OHDA (40, 60, 100 μg on days 2, 4, 6) induced a marked impairment in rearing and acquisition of CAR, and a less pronounced decrease in crossing activity. No significant change was found in general motor activity. Increasing doses of 6-OHDA led to an 80-90% depletion in brain catecholamines and induced a content-related behavioural suppression in rearing and conditioned avoidance responding in particular. It is concluded that intracerebral administration of 6-OHDA into neonatal rats almost completely prevents the development of central catecholaminergic neuronal systems, and concomitantly the capability of acquiring conditioned avoidance behaviour, while reducing exploratory behaviour.