In previous experiments, it was observed that rat atrial natriuretic peptide-(1-28) (ANP-(1-28)) participated in fear-induced learning and memory processes via dopaminergic and cholinergic mediation. Since cage-climbinh behavior is described as a simple test for studying dopaminergic activity in the central nervous system, a systematic study was carried out with ANP-(1-28) in order to confirm or to exclude the possible involvement of dopamine in the ANP-induced action in the brain. The present study demonstrates that ANP-(1-28) facilitated cage-climbing behavior in mice in a dose-dependent manner. When combined with apomorphine, the peptide potentiated the effect of the dopamine agonist. The effect of ANP-(1-28) in combination with apomorphine could be antagonized by a selected dose of haloperidol. These data suggest that ANP might be regarded as a dopamine agonist-modulating agent and that a dopaminergic mechanism is a possible mode of action of ANP in the fear-induced learning studied earlier.
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