Effects of Morphine, Physostigmine Stimulation on 5-hydroxytryptamine Cerebral Cortex of the and Raphe Nuclei Release from the Cat

1 The release of 5-hydroxytryptamine (5-HT) from the cerebral cortex and caudate nucleus of brainstem-transected cats and from the cerebral cortex of rats anaesthetized with urethane was determined by radioenzymatic and biological assay. 2 The stimulation of nucleus linearis intermedius of raphe doubles the basal 5-HT release in the caudate nucleus and increases it 3 fold in the cerebral cortex. The effects of the electrical stimulation of the raphe are potentiated by chlorimipramine. 3 Brain 5-HT release is greatly increased by morphine hydrochloride (6 mg/kg i.v.) and by physostigmine (100 jg/kg i.v.), but not by DL-DOPA (50 mg/kg i.v.). 4 It is suggested that the 5-HT releasing action of physostigmine can contribute to some of its pharmacological effects such as the analgesic effect so far attributed exclusively to its indirect cholinomimetic activity. 5 The 5-HT releasing action of physostigmine seems unrelated to its anticholinesterase activity.