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In previous experiments, it was shown that rat atrial natriuretic peptide (rANP1-28) is able to increase the passive avoidance latency in a dose-dependent manner in the learning and consolidation phase (3). In order to clarify whether ANP has a direct action on this behavioral paradigm, or whether the action is mediated by neurotransmitters, rats were pretreated with different receptor blockers. The selected doses of the different receptor blockers could themselves not influence the behavioral paradigms. Haloperidol or atropine blocked the action of ANP on the consolidation of the passive avoidance response. Phenoxybenzamine, propranolol, methysergide, bicuculline and naloxone were ineffective. The data suggest that dopaminergic and cholinergic mediations are involved in the action of ANP on the passive avoidance response.

Different doses of rat atrial natriuretic peptide (rANP1-28) were tested as regards the extinction of active avoidance behavior following its injection into the lateral brain ventricle in rats. ANP delayed extinction of the active avoidance reflex in a dose-dependent manner. When the animals were pretreated with different receptor blockers in doses which themselves had no action on the extinction of active avoidance behavior, the action of ANP on this paradigm was completely blocked by haloperidol and atropine, whereas phenoxybenzamine/propranolol, naloxone, bicuculline and methysergide were ineffective. The data suggest that ANP delays the extinction of active avoidance behavior, and that cholinergic and dopaminergic transmitter systems might be involved in this action.