Inhibition of acetylcholine outflow from guinea-pig cerebral cortex following locus coeruleus stimulation.

Experiments were performed in unanaesthetized guinea-pigs in order to obtain direct evidence that the noradrenergic projections from locus coeruleus (L.C.) to cerebral cortex inhibit the acetylcholine (ACh) release. The animals were provided with left and right epidural cups, to collect outflowing ACh and with a stimulating electrode, positioned in the left L.C. The electrical stimulation of L.C. caused a significant reduction of ACh outflow from both parietal areas. This effect was abolished, reduced or prevented by phentolamine, phenoxybenzamine or reserpine plus alpha-mt pretreatment, hence showing to be alpha-mediated.