Determination of Endogenous Acetylcholine Release in Freely Moving Rats by Transstriatal Dialysis Coupled to a Radioenzymatic Assay: Effect of Drugs

Abstract

The technique of intracerebral dialysis in combination with a sensitive and specific radioenzymatic method was used for recovery and quantification of endogenous extracellular acetylcholine from the striata of freely moving rats. A thin dialysis tube was inserted transversally through the caudate nuclei, and the tube was perfused with Ringer solution, pH 6.1, at a constant rate of 2 μl min⁻¹. The perfusates were collected at 10-min intervals. In the presence of 1 and 10 μM physostigmine, acetylcholine release was 4.5 ± 0.02 and 7.3 ± 0.3 pmol/10 min, respectively (not corrected for recovery). The latter concentration of the acetylcholinesterase inhibitor was used in all experiments. Under basal conditions, acetylcholine output was stable over at least 4 h. A depolarizing K⁺ concentration produced a sharp, reversible 87% increase in acetylcholine output. Both the basal and K⁺-stimulated release were Ca²⁺ dependent. The choline uptake inhibitor hemicholinium-3 (20 μg intracerebroventricularly) reduced striatal acetylcholine output to 35% of the basal value within 90 min. Scopolamine (0.34 mg/kg s.c.) provoked a sharp enhancement of acetylcholine release of ∼63% over basal values, whereas oxotremorine (0.53 mg/kg i.p.) transiently reduced acetylcholine release by 54%. These results indicate the physiological and pharmacological suitability of transstriatal dialysis for monitoring endogenous acetylcholine release.