Characteristics of the dopamine receptors involved in the anorectic effects of apomorphine in mice.

In food-deprived mice apomorphine injected SC induced a brief (15-30 min) dose-dependent (30-150 micrograms/kg) reduction in food intake. This effect occurred in naive mice as well as in mice habituated to a food deprivation procedure. The anorectic effect of apomorphine (150 micrograms/kg SC) was antagonized by sulpiride (ID50 = 8.6 mg/kg) and by haloperidol (ID50 = 66 micrograms/kg) but domperidone was ineffective (250 micrograms/kg). Mice submitted to a semi-chronic (6 d) blockade of dopamine receptors by haloperidol or injected intracerebroventricularly with 125 micrograms 6-hydroxydopamine 21 d before testing failed to develop a hypersensitivity to the anorectic effect of apomorphine (60 micrograms/kg). Although a single apomorphine injection (5 mg/kg) induced tolerance to the hypothermic effect of a second apomorphine injection of 150 micrograms/kg, it did not modify the anorectic effect. Repeated apomorphine injection (5 x 5 mg/kg) resulted in a slight but significant reduction in apomorphine-induced anorexia. A similarly significant reduction was not observed in mice submitted to repeated injections of dexamphetamine (5 x 5 mg/kg).