Muscarinic autoreceptor regulates acetylcholine release in rat hippocampus: in vitro evidence

Abstract

Release of ³H-ACh from isolated nerve endings of rat hippocampus was evoked by incubation in Krebs-Ringer's buffer containing 25 or 35 mM potassium. The release was Ca²⁺-dependent and could be inhibited by Mg²⁺ (20 mM). The muscarinic antagonist, atropine (10^-10–10^-6 M), enhanced ³H-ACh-release. The muscarinic agonist, carbachol (10^-5–10^-3 M) inhibited ³H-ACh release via interaction with muscarinic receptors: this effect could be blocked by atropine (10^-6 M). The presence of the feed-back regulation of ³H-ACh release in a cell-free preparation provides further evidence that the presynaptic regulation is exerted by muscarinic autoreceptors localized on the cholinergic nerve ending itself. The feed back inhibition of the ³H-ACh release does not require the presence of intact neurons or neuronal loops as tetrodotoxin (2.5. 10^-6 M) does not affect the above results.