Differential effects of cholinergic blockade of anterior and posterior caudate nucleus on avoidance behaviors.

Groups of rats were trained in a one-trial passive avoidance task and then tested for retention 24 and 48 h later. They were also trained, in a single session, according to a one-way active avoidance paradigm. The effects of microinjections of atropine or of saline into the anterior caudate nucleus (CN) and of atropine into the posterior CN were assessed on these conditioned responses. Only those rats injected with atropine in the anterior CN showed a retention deficit in passive avoidance, while no effects on active avoidance became evident in any of the groups. These results suggest that cholinergic activity of the anterior CN is critically involved in memory consolidation of passive avoidance, but not in the processes mediating the acquisition of relatively simple active avoidance learning.