The effect of pentobarbital on serotonin content and turnover in six discrete areas of rat brain

Male Sprague Dawley rats (150-200 gm) were injected with pentobarbital sodium (50 mg/kg, i.p.) and were sacrificed 5, 15, 30 or 60 min later. Serotonin (5HT) content was significantly elevated (P<0.001) in the midbrain and thalamus at 5, 15 and 30 min after pentobarbital, but the 5HT content returned to control levels by 60 min. No significant change in 5HT content was noted in the medulla pons, cerebral cortex, striatum or cerebellum. Prolonging the anesthesia to two hours with a supplemental injection of pentobarbital (30 mg/kg) at 60 min resulted in a significant increase (P<0.01) in 5HT content in all brain areas except the cerebellum and striatum. If the anesthesia was prolonged to three hours with supplemental doses of pentobarbital (25 mg/kg) given at 60 and 120 min, 5HT content was elevated in all brain areas except the cerebellum; and, in addition, 5HT turnover, measured by the accumulation of 5 hydroxyindoleacetic acid following probenecid (200 mg/kg), was significantly decreased (P<0.025) in all brain areas except the midbrain and striatum. The observed increase in 5HT content and the decrease in 5HT turnover following the administration of pentobarbital may result from a decrease in impulse activity in serotonergic fibers in discrete regions of the rat brain.