Effects of scopolamine, physostigmine and chlordiazepoxide on punished and extinguished water consumption in rats.

It has been postulated that behavioral inhibition due to punishment or extinction may be mediated by brain acetylcholine, and drugs which have disinhibitory action are thought to interact with this system. This notion was tested by comparing the effects of scopolamine, physostigmine and chlordiazepoxide on punished and extinguished water consumption. Scopolamine hydrobromide (0.3, 0.5 mg/kg, i.p.), a centrally and peripherally acting antimuscarinic agent and physostigmine sulfate, (0.3 mg/kg, i.p.), a centrally and peripherally acting acetylcholinesterase inhibitor, lowered both non-punished and punishment suppressed water intake and lick rate, whereas their quaternary analogs which primarily act in the periphery, had no significant effect at comparable dose levels. Scopolamine and physostigmine suppressed punished water consumption at lower dose levels than nonpunished intake. In contrast, chlordiazepoxide (5.0, 10.0, 20.0 mg/kg, i.p.) enhanced punished as well as non-punished water intake. In a further experiment comparing punishment and extinction suppression, scopolamine and physostigmine did not affect punished or extinguished water intake; chlordiazepoxide (5.0, 10.0, 20.0 mg/kg) reliably increased punished, but not extinguished licking on the water nozzle. These results suggest (1) that scopolamine and chlordiazepoxide do not act via a common mechanism, and (2) that punishment and extinction suppression are not a pharmacological entity.