[Action of PMA (phorbol myristate acetate), scopolamine, propranolol, and oxotremorine on memorization of an active or passive avoidance test].

The role of various second messengers in the learning and retention of a passive or active avoidance has been investigated in mice. Scopolamine at 3 mg/kg i.p. inhibits muscarinic M1 and M2 receptors and thus acetylcholine activation of the phosphoinositide cycle. This results in amnesia of passive avoidance but has no effect on active avoidance learning. Oxotremorine at 0.05 mg/kg i.p., whose preferential M2 muscarinic action limits acetylcholine release and also inhibits adenylate cyclase activity, causes amnesia of the retention of a passive avoidance and antagonizes the learning of an active avoidance. DL-propranolol at 40 mg/kg i.p., which inhibits cAMP formation, does not affect retention of a passive avoidance but antagonizes that of an active avoidance. Similarly, phorbol myristate acetate a 0.1 mg/kg i.p., which activates protein kinase C, has no effect on the retention of a passive avoidance but antagonizes that of an active avoidance. The results tend to show a distinct role for cAMP-dependent protein kinase, which would participate in memorization processes of an active avoidance, and for protein kinase C, which would participate in that of a passive avoidance. The authors discuss the involvement of different neurophysiological mechanisms as a function of the type of behavior, depending on whether or not it is related to the control of environmental situations.