The release of acetylcholine was studied in isolated cerebral cortex slices of the rat. There was no significant difference in the release between right and left sides of the cerebral cortex. Noradrenaline reduced the ouabain-stimulated release of acetylcholine and phentolamine prevented its action. The spontaneous and evoked release of acetylcholine was higher in those slices where noradrenergic input was somehow impaired: 6-hydroxydopamine pretreatment or locus coeruleus lesion ipsilaterally resulted in a higher release. Following a locus coeruleus lesion the spontaneous evoked release of acetylcholine from slices dissected from the ipsilateral side was higher in comparison to the contralateral side. Noradrenaline significantly reduced the resting release of acetylcholine only in those cases where the noradrenergic control has been previously removed. It is suggested that the release of acetylcholine is continously controlled by noradrenaline released from nerves arising from the locus coeruleus. The removal of this inhibitory system results in an increase of acetylcholine release.
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