An adrenergic basis for bulbar inhibition

¹ Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana

Evidence has been obtained showing that intravenous infusion of Diebenzyline in cats anesthetized with Nembutal will consistently and completely abolish inhibition of the patellar reflex induced by direct stimulation of the bulbar reticular formation. The inhibition can always be restored by subsequent infusion of epinephrine. Parallel vasopressor effects can also be observed. Various techniques, including direct injection of Dibenzyline and epinephrine into the medulla through hollow electrodes, provided evidence that these drugs exerted depressant and enhancing effects, respectively, on the thresholds for bulbar inhibition. There appear to be regional differences in epinephrine sensitivity in the medulla. The area corresponding to the nucleus reticularis gigantocellularis appears to be more sensitive to epinephrine than surrounding reticular nuclei. The results suggest that locally released epinephrine activates the gigantocellularis nucleus which, in turn, develops a pattern of discharges leading to an inhibitory effect mediated by spinal projections. This mechanism may explain immobilization which frequently occurs in highly emotional situations.