Drug Effects on the Release of Endogenous Acetylcholine In Vivo: Measurement by Intracerebral Dialysis and Gas Chromatography–Mass Spectrometry

Abstract

Intracerebral microdialysis was combined with a sensitive and specific gas chromatographic-mass spectrometric assay to measure the release of endogenous acetylcholine in the rat striatum in vivo. In rats anesthetized with urethane (1.2 g/kg i.p.), the levels of striatal acetylcholine dialyzed into a Ringer's perfusate were: (a) reliably measurable only in the presence of physostigmine; (b) stable at between 3 and 8 h of perfusion (30-75 pmol/20 min in the presence of 75 microM physostigmine); (c) reduced by calcium-free Ringer's solution, tetrodotoxin (0.1 microM), and vesamicol (1.0 microM); and (d) increased by elevated potassium (100 mM), atropine (3-300 microM), and haloperidol (0.75 mg/kg i.p.). In conscious unrestrained rats, the spontaneous release of striatal acetylcholine was not altered significantly following the administration of urethane. The changes in acetylcholine release observed in this study are consistent with the known actions of some drugs or ionic conditions on striatal cholinergic neurotransmission and are evident under the condition of urethane anesthesia. The present results demonstrate the sensitivity and suitability of this method for monitoring endogenous striatal acetylcholine release in vivo.

Microdialysis coupled on-line to capillary liquid chromatography with tandem mass spectrometry for monitoring acetylcholine in vivo

“…A similar decrease below basal levels after high K + aCSF perfusion was also reported by Marien and Richard (1990). The temporal resolution demonstrated in these experiments is a greater than 8-fold improvement over that previously reported for off-line fraction collection coupled to HPLC-MS (Hows et al, 2002) with the added convenience of on-line analysis.…”

The effect of the acetylcholine transport blocker vesamicol on central cholinergic pressor neurons

“…While earlier studies have demonstrated this inhibition to occur in anesthetized, in vitro or in situ preparations (see Introduction), the present experiments were performed in freely moving animals. The results also are consistent with vesamicol's ability to inhibit the release of acetylcholine (Marien and Richard, 1990). The possibility that vesamicol's ability to block the response to physostigmine is due to a postsynaptic inhibition is not likely, since (1) the drug does not interact with muscarinic receptors (Marien et al, 1987); and (2) in the present study, vesamicol did not block the pressor response to the receptor agonist, arecoline.…”

“…Despite these properties it is still uncertain whether vesamicol can inhibit the 0 1991 WILEY-LISS, INC. tonic or quanta1 release of acetylcholine from nonstimulated neurons (Michaelson et al, 1987, Searl et al, 1990Suszkiw and Manalis, 1987). One recent study employing in vivo microdialysis has demonstrated that vesamicol does inhibit the basal release of acetylcholine in brain, although this interpretation may be complicated by the use of a cholinesterase inhibitor in the dialysate (Marien and Richard, 1990). Also, it has yet to be determined whether vesamicol could lead to a reduction of brain acetylcholine levels when administered in vivo.…”

Muscarinic and nicotinic modulation of cortical acetylcholine release monitored by in vivo microdialysis in freely moving adult rats

“…Sample preparation for GC-MS analysis ACh was assayed as described earlier (Wood and Peloquin, 1982) with minor modifications (Marien and Richard, 1990). Briefly, frozen dialysates were lyophilized directly in glass reaction vials, reconstituted in 250 pl of acetonitrile, capped, heated a t 80°C for 40 min, cooled to room temperature, and dried under a gentle stream of nitrogen gas.…”