Changes in hippocampal cholinergic activity following learning in mice.

A short bar-press operant conditioning acquisition session with food reward on continuous reinforcement was shown to induce a decrease (13.5%) of hippocampal choline acetyltransferase activity in mice. Such an effect seems to be specific to this kind of learning since no change was observed in several control groups, including a group of mice submitted to another type of conditioning in the same apparatus. It is suggested that these enzymatic modifications might be responsible for the delayed improvement of performance observed on retention of this task.