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The effects of rat atrial natriuretic peptide (ANP 1–28) on passive avoidance behaviour were tested following its administration into the lateral brain ventricle in rats. Different doses of ANP 1–28 were administered immediately after the learning trial of passive avoidance behaviour and the effects on the consolidation of learning were tested 24 h later. ANP 1–28, in doses in the range 50–2000 ng/rat, caused a dose-dependent increase in passive avoidance latency. Selected doses (100, 200 and 500 ng/animal) were given 30 min before the learning trial. These doses lengthened the passive avoidance latency in a dose-dependent manner. When the peptide was given 30 min before the retention trial, there was no significant alteration in passive avoidance response. The data suggest that ANP 1–28 is able to facilitate the learning and consolidation of fear-motivated passive avoidance behaviour.

The effect of rat atrial natriuretic peptide (ANP 1–28 ) on the pargyline-DOPA potentiation test was studied following its administration into the lateral brain ventricle in mice. Thirty minutes after pargyline pretreatment, three doses of ANP (200, 500, or 1,000 ng/mouse) were administered simultaneously with DOPA and animals were then observed for 2 h. ANP in doses of 500 and 1,000 ng markedly enhanced the effect of DOPA. The maximum intensity of the effect was registered 30–45 min following administration of the peptide. The data suggest that ANP might be regarded as a dopaminergic-modulating agent in the CNS.