Muscarinic modulation of acetylcholine release from slices of guinea pig nucleus basalis magnocellularis

Determination of acetylcholine by on-line microdialysis coupled with pre- and post-microbore column enzyme reactors with electrochemical detection

A sensitive procedure consisting of a pre- and post-microbore column reactor sequence of a LC-electrochemical detection system coupled with on-line microdialysis system is described in the present study to measure endogenous acetylcholine concentration in freely moving rats. The pre-column packed, with immobilized choline oxidase and catalase, was used to remove choline, whereas the post-column, packed with immobilized acetylcholine oxidase and choline oxidase, was used to measure acetylcholine selectively. The detection limit of acetylcholine oxidase and choline oxidase, was used to measure acetylcholine selectively. The detection limit of acetylcholine was found to be 5 fmol/microliter (50 fmol/10 microliters). The usefulness of the described methodology was evaluated by examining the change in the striatal acetylcholine concentration of freely moving rats after physostigmine (0.5 mg/kg, s.c.) administration.

Muscarinic receptor modulation of acetylcholine release from rat cerebral cortex and hippocampus

An attempt to identify the muscarinic receptor subtypes involved in presynaptic modulation of acetylcholine (ACh) release from cortical and hippocampal slices was made by means of several muscarinic antagonists. Cortical and hippocampal slices prepared from adult rats were superfused with Krebs solution containing physostigmine; ACh content of the superfusate at rest and after electrical stimulation (1 Hz) was quantified by high performance liquid chromatography. The antagonists were added to the Krebs at the concentration of 1 microM. ACh release at rest was enhanced only in the cortex by (+/-)-5,11-dihydro-11-([(2-[2-[(dipropylamino)methyl]-1- piperidinyl)ethyl)amino]carbonyl)-6H-pyrido[2,3-b](1,4)- benzodiazepine-6-one (AFDX384), an M2/M4 selective antagonist. The evoked ACh release from the cerebral cortex was significantly increased by AFDX384, methoctramine, pirenzepine, M2/M4, M2 and M1 selective antagonists, respectively, and scopolamine. This finding suggests that M1, M2 and M4 presynaptic receptor subtypes could regulate evoked ACh release in the cortex. In hippocampal slices, the evoked ACh release was enhanced by AFDX384, pirenzepine and scopolamine but not by methoctramine. In this region ACh release seems therefore regulated only by M1 and M4 receptor subtypes. The M3 antagonist (+/-)-p-fluorohexahydro-sila-difenidol hydrochloride did not affect ACh release.