The action of pituitary adenylate cyclase activating polypeptide (PACAP) on passive avoidance learning. The role of transmitters.

In the present study, the action of PACAP 38 on one-way passive avoidance learning was investigated. PACAP-38 was administered into the lateral brain ventricle and the latency of the passive avoidance response was measured 24 h later. In order to study the possible roles of various neurotransmitters in mediating the action of PACAP on the consolidation of passive avoidance learning, the animals were pre-treated with receptor blockers in doses that per se proved to be ineffective. PACAP facilitated the learning, the consolidation of learning and the retrieval of the passive avoidance response. The following receptor blockers attenuated the action of PACAP on this consolidation: haloperidol, phenoxybenzamine, propranolol and methysergide. An antagonist of PACAP 38, PACAP 6-38, and also nitro-L-arginine (the latter blocks the enzyme nitric oxide synthase) thereby inhibiting the formation of NO from L-arginine, completely blocked the action of PACAP 38 on consolidation. The following receptor blockers were ineffective: naloxone, bicuculline and atropine. The presented data suggest that PACAP 38 is able to improve the learning and memory processes in a passive avoidance paradigm. In this action, the PACAP 38 receptor and NO are important mediators. Dopaminergic, alpha- and beta-adrenergic mediation and serotonin receptors modified the action of PACAP 38, but they are probably not of great importance.