CHARACTERISTICS OF THE DOPAMINE RECEPTORS INVOLVED IN THE ANORECTIC EFFECTS OF APOMORPHINE IN MICE

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Abstract
Summary—In food‐deprived mice apomorphine injected SC induced a brief (15–30 min) dose‐dependent (30– 150 μg/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 μg/kg SC) was antagonized by sulpiride (ID50= 8.6 mg/kg) and by haloperidol (ID50= 66 μg/kg) but domperidone was ineffective (250 μg/kg). Mice submitted to a semi‐chronic (6 d) blockade of dopamine receptors by haloperidol or injected intracerebroventricularly with 125 μg 6‐hydroxydopamine 21 d before testing failed to develop a hypersensitivity to the anorectic effect of apomorphine (60 μg/kg).Although a single apomorphine injection (5 mg/kg) induced tolerance to the hypothermic effect of a second apomorphine injection of 150 μg/kg, it did not modify the anorectic effect. Repeated apomorphine injection (5times5 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 (5times5 mg/kg).