Time course of decline of radiolabeled acetylcholine formed following intracerebroventricular administration of tritiated choline: Effects of oxotremorine and scopolamine

Rats were injected intracerebroventricularly with 5 Ci of methyl-³H]choline. The time course of decline of the rediolabeled acetylcholine (ACh) formed was estimated in the ispilateral cerebral cortex and striatum. The ³H]ACh levels declined biphasically from the cerebral tissue. The initial decline proceeded rapidly, after which labeled ACh declined more slowly. Scopolamine (1 mg/kg, i.v.) caused a significant increase in the rat of ³H]ACh disappearance, which can be interpreted as an enhancement of ACh release. By contrast, oxotremorine (0.8 mg/kg, i.v.) markedly reduced the ³H]ACh disappearance. The results show that drug-induced changes in cholinergic neuronal activities can be estimated from the disappearance of radioactive ACh after labeling the endogenous transmitter through intracerebroventricular administration of labeled choline.