The major catabolic enzyme for serotonin, monoamine oxidase (MAO), is present in the endothelium of cerebral vessels. We report the effects of the intracarotid administration of serotonin on local cerebral glucose utilisation in rats following MAO inhibition with the drug clorgyline. It was found that saline, clorgyline, or serotonin alone produced no significant changes in glucose utilisation. Following the infusion of clorgyline, the administration of serotonin produced significant decreases in glucose utilisation in cortical areas of between 12 and 33% and in the caudate nucleus of 16%.
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