TIME-COURSE OF DECLINE OF RADIOLABELED ACETYLCHOLINE FORMED FOLLOWINGINTRACEREBROVENTRICULAR ADMINISTRATION OF TRITIATED CHOLINE - EFFECTSOF OXOTREMORINE AMD SCOPOLAMINE

Rats were injected intracerebroventricularly with 5 mu Ci of [methyl-H -3]choline. The time course of decline of the radiolabeled acetylcholi ne (ACh) formed was estimated in the ipsilateral cerebral cortex and s triatum. The [H-3]ACh levels declined biphasically from the cerebral t issue. The initial decline proceeded rapidly, after which labeled ACh declined more slowly. Scopolamine (1 mg/kg, i.v.) caused a significant increase in the rate of [H-3]ACh disappearance, which can be interpre ted as an enhancement of ACh release. By contrast, oxotremorine (0.8 m g/kg, i.v.) markedly reduced the [H-3]ACh disappearance. The results s how that drug-induced changes in cholinergic neuronal activities can b e estimated from the disappearance of radioactive ACh after labeling t he endogenous transmitter through intracerebroventricular administrati on of labeled choline.