Repeated withdrawal from barbital as a drive for 'drug taking behavior' in rats.

Investigations were performed to determine whether the pharmacodynamic effect of barbital, the development of tolerance to or the physical dependence on the hypnotic are responsible for drug-taking behavior. Three groups of male rats, untreated, tolerant to and physically-dependent on barbital, were given free choice between 0.5% barbital solution and tap water. Drug-taking behavior was estimated according to specified criteria. Initially naive rats rejected an unsweetened barbital solution. Tolerant rats also refused the hypnotic, even after they had experienced abstinence symptoms only once. However, tolerant rats that repeatedly underwent withdrawal after an intake of more than 400 mg/kg/day of barbital did show drug taking behavior. Therefore, several experiences with pronounced abstinence symptoms seem to be necessary for initiating and sustaining barbital drug taking behavior in rats.