Spontaneous and carbachol-evoked in vivo secretion of acetylcholinesterase from the hippocampus of the rat.

Spontaneous and evoked secretion of acetylcholinesterase from the hippocampus in vivo has been demonstrated by the use of push-pull cannulae. Local perfusion with 10(?5)M carbachol evoked an increase of 104% in acetylcholinesterase release with no accompanying change in butyrylcholinesterase or lactic dehydrogenase. Local or systemic atropine sulphate blocked the carbachol-evoked increase in acetylcholinesterase release, whilst gallamine had no effect. Local perfusion of ?-aminobutyric acid (10(?4)M) also blocked the carbachol-evoked release of acetylcholinesterase but had no effect on the spontaneous release. It is concluded that a soluble form of acetylcholinesterase is secreted from the hippocampus in response to stimulation of muscarinic receptors; this secretion can be influenced by ?-aminobutyric acid, which is present in interneurones in the hippocampus.