Release of GABA from the guinea-pig neocortex induced by electrical stimulation of the 'locus coeruleus' or by norepinephrine.

GABA release from the cortical surface was measured in freely moving guinea-pigs using collecting cups and a mass-fragmentographic method. Stimulation of the locus coeruleus caused a prolonged sedation of the animals and a 60% increase of GABA output from their cerebral cortex. Similar results were obtained after intraventricular injections of norepinephrine. Phentolamine antagonized these effects. The results suggest that the noradrenergic innervation of the cortex modulates the function of cortical GABA neurons.