Effects of acetylcholine antagonist injection into the prefrontal cortex on the progress of lever-press extinction in rats.

To determine the relationship between cholinergic modulation within the rat medial prefrontal cortex (mPFC) and the progress of lever-press extinction, we conducted an experiment in which muscarinic and nicotinic acetylcholine (ACh) receptor antagonists were microinjected into the mPFC. The muscarinic antagonist injected immediately before the initial extinction training did not affect the progress of extinction during the training (no within-session effect), but disrupted a second re-training session the next day (across-session effect). By contrast, the nicotinic antagonist disrupted the progress of extinction both within and across training sessions. These results confirm that ACh in the mPFC modulates lever-press extinction and suggest that nicotinic and muscarinic receptors are involved in short- and long-term memory processes.