Brain stem serotonin depletion and Ponto-Geniculo-Occipital wave activity in the cat treated with reserpine

In the first part of this study the time course of depletion of serotonin (5 HT) was determined in several regions of the brain following treatment with reserpine (0.75 mg kg , i.p.). The results were compared with the temporal course of ponto-geniculo-occipital wave activity (PGO Res) induced by similar drug treatment. These experiments revealed a good correlation between the initial decrease in 5 HT throughout the brain and the appearance of PGO Res. During recovery, however, 5 HT levels remained low at the time when regulation of PGO wave activity began to return to normal. In the second part of this study, the effect upon PGO wave activity of infusions of reserpine into the ventricular and subarachnoid spaces was investigated. Infusions of reserpine phosphate (250 μg) into the fourth ventricle caused changes in wave activity similar to those induced by systemic administration of the drug. In contrast, infusions into several different regions of the subarachnoid space caused only minor changes in PGO wave activity. 5 HT levels, measured at that time when PGO Res appeared following infusion of reserpine into the fourth ventricle, were significantly depressed only in the pons. These results are consistent with the hypothesis that monoaminergic neurons exert a tonic inhibitory influence at the brain stem level which serves to regulate or gate REM-type PGO waves.