Participation of a bulbospinal serotonergic pathway in the rat brain in clonidine-induced hypotension and bradycardia.
The effects of microinjection of clonidine (1-10 micrograms in 1 microliter) into a region adjacent to the ventrolateral surface of the medulla oblongata on cardiovascular function were assessed in urethane-anesthetized rats. Intramedullary administration of clonidine, but not saline vehicle, caused a dose-dependent decrease in both the mean arterial pressure and the heart rate. The clonidine-induced hypotension was antagonized by prior spinal transection, but not bilateral vagotomy. On the other hand, the clonidine-induced bradycardia was antagonized by prior bilateral vagotomy, but not spinal transection. Furthermore, selective destruction of the spinal 5-HT nerves, produced by bilateral spinal injection of 5,7-dihydroxytryptamine, reduced the magnitude of the vasodepressor or the bradycardiac responses to clonidine microinjected into the area near the ventrolateral surface of the medulla oblongata in rats. The data indicate that a bulbospinal serotonergic pathway is involved in development of clonidine-induced hypotension and bradycardia. The induced hypotension is brought about by a decrease in sympathetic efferent activity, whereas the induced bradycardia was due to an increase in vagal efferent activity.
Tsai
M L
ML
Department of Physiology, College of Medicine, National Cheng Kung University, Taman, Taiwan, ROC.
Lin
M T
MT
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D009434:Neural Pathways / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000097:blood / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D013268:Stimulation, Chemical; D014628:Vagotomy
D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D003000:Clonidine