Acute and chronic effects of pentobarbital on 5-hydroxytryptamine in mouse brain

1. 1. The influence of acute and chronic administration of pentobarbital on the brain 5-hydroxytryptamine systems was investigated in mice. 2. 2. Treatment of the animals with sodium pentobarbital, 75 mg/kg, i.p., resulted in an increase of 5-hydroxytryptamine and a decrease of 5-hydroxyindoleacetic acid levels. 3. 3. Acute pentobarbital treatment also caused the reduction of 5-hydroxytryptamine turnover without an equivalent decrease in 5-hydroxytryptamine synthesis. However, the 5-hydroxytryptamine synthesis was significantly decreased in animals which have developed tolerance to pentobarbital. 4. 4. The pretreatment of animals with p{combining macron below}-chlorophenylalanine attenuated the development of tolerance to pentobarbital without altering the response of the animal to acute administration pentobarbital. 5. 5. On the other hand, no significant change was observed in 5-hydroxytryptamine systems in pentobarbital-withdrawal groups. 6. 6. These results strongly suggest that functional states of brain serotonergic systems may be involved in barbiturate action.