hypobaric hypoxia: central catecholamine levels and cortical PO2 and avoidance response in rats treated with apomorphine.

The learning of a conditioned avoidance response, the catecholamine levels in some cerebral structures, and the evolution of the cortical PO2, were studied under hypobaric hypoxia (300 torr) and under normoxia, in rats treated or not with apomorphine, at the dose of 1 or 10 mg/kg i.p. Apomorphine at 1 mg/kg improves the learning capacity and stabilises the cerebral catecholamine levels under hypoxia; no modification of the evolution of the cortical PO2 during hypoxia was observed between control rats and rats treated with this dose of apomorphine. Apomorphine at 10 mg/kg totally inhibits learning under normoxia or hypoxia. It is therefore possible to suppose that the antihypoxic protective mechanism of low-dose apomorphine is due to a stabilization of the levels of both dopamine and noradrenaline during hypoxia, but not to an increase in the cerebral oxygen availability. These data suggest the clinical possibility of using other dopaminergic stimulating agents for their eventual antihypoxic properties.