ACTIVE AND PASSIVE-AVOIDANCE LEARNING IN RATS NEONATALLY TREATED WITHINTRAVENTRICULAR 6-HYDROXYDOPAMINE

To clarify the behavioral characteristics of rats neonatally treated w ith 6-hydroxydopamine (6-OHDA), their performance on 4 aversive learni ng tasks, 3 active (shuttle, one-way, and rearing) avoidance tasks and one passive (step-through) avoidance task, was examined. On days 2 an d 4 after birth, each rat of F344/Du strain received bilateral intrave ntricular injections of 6-OHDA (35 mu g x 2) or vehicle solution follo wing desmethylimipramine (20 mg/kg, s.c.) pretreatment. From day 90, e ach rat was trained in one of the 4 avoidance tasks. 6-OHDA-treated ra ts showed significantly less avoidance responses in the shuttle and th e one-way avoidance tasks, but their performance on the rearing and th e step-through passive avoidance tasks was not significantly different from that of control rats. The differential impairment of avoidance s uggests that 6-OHDA treatment does not cause a general learning defici t, but facilitates rearing and/or jumping responses in aversive situat ions, which results in inappropriate escape responses.