TIME-DEPENDENT RETENTION DEFICITS INDUCED BY POST-TRAINING INJECTIONS OF ATROPINE INTO THE CAUDATE-NUCLEUS

Rats were trained on a 1-trial passive avoidance task, and retention of the task was measured 24 h later. Atropine was injected bilaterally into the anterior caudate nuclei (ACN) of rats from independent groups at one of several intervals after training. Application of atropine 2 min after training produced a lack of retention of passive avoidance. An intermediate degree of impairment was seen when the treatment was given 3 min, 45 s after the learning experience, and interference with retention was still noted when an interval of 7 min, 30 s was studied. No deficits were observed in groups of animals injected with atropine 15 or 30 min after training. Rats injected with atropine into the parietal cortex 2 min after training showed only a minimal reduction of retention, and a group injected with saline solution into the ACN performed as well as non-treated animals. Evidently, there is a time-dependent process that mediates the retention of passive avoidance, and this process requires the activation of cholinergic synapses within the anterior caudate nucleus.