Modification by sulpiride, pimozide, or domperidone of apomorphine's effects on learning in hypoxic rats.

The study of apomorphine's interaction with three dopaminergic antagonists (domperidone, sulpiride and pimozide) is an attempt to characterize the dopaminergic receptors involved in the dopaminergic agonist-induced protection against hypobaric hypoxia. Apomorphine (1 mg X kg-1 but not 0.01 mg X kg-1) reduced total performance (avoidance + escape responses); this effect was antagonised by domperidone and pimozide--not by sulpiride--and appeared to have a peripheral origin. Apomorphine (0.01 and 1 mg X kg-1) increased the avoidance performance during hypoxia. This antihypoxic protection was not suppressed by domperidone, confirming its central origin, but was antagonised both by sulpiride and pimozide. The receptors involved in the anti-hypoxic protective effect appear therefore to be cerebral D4 receptors, according to the classification of Seeman.