Sleep induced by low doses of apomorphine in rats

The effect of apomorphine on the EEG of freely moving rats was studied. Apomorphine at the dose of 1 mg/kg caused stereotypy and a marked reduction of total sleep. On the contrary, acute subcutaneous administration of apomorphine at the dose of 100 microgram/kg, or less, markedly increased the amount of total sleep (corresponding mostly to synchronized sleep). Moreover, the infusion of apomorphine (80 microgram/kg/h) for 4 h doubled the duration of slow and REM sleep. The hypnotic effect of apomorphine was prevented by neuroleptics, such as pimozide, benzperidol and L-sulpiride, at doses which, per se, did not modify the EEG of the animals. These results suggest the existence in the CNS of DA receptors mediating sleep.