Nodulus-uvula depressor response: central GABA-mediated inhibition of alpha-adrenergic outflow.
Electrical stimulation of a lateral region of the cerebellar nodulus-uvula transition zone in anesthetized albino rabbits decreases mean arterial blood pressure in direct proportion to stimulus intensity. The hypotension has an abrupt onset and is phasic; heart rate is unaffected. Neural pathways that might mediate the depressor response were studied using autonomic-blocking agents. Pretreatment with 2 mg/kg iv of either propranolol HCl or atropine methyl nitrate did not alter the onset or duration of the hypotensive response. However, pretreatment with 2 mg/kg iv phentolamine HCl abolished the depressor response, and 7 mg.kg-1.min-1 iv tetraethylammonium infusion decreased the response by more than 50%. Ipsilateral injections of 200 ng bicuculline methiodide into an area immediately dorsal to the superior cerebellar peduncle or the dorsal aspect of the superior vestibular nucleus reversibly attenuated the nodulus-uvula evoked depression. Anterograde horseradish peroxidase-wheat germ agglutinin (HRP-WGA) transport experiments revealed that both these regions receive direct inputs from the nodulus-uvula. These data suggest that hypotensive events elicited by lateral nodulus-uvula stimuli represent a central, alpha-aminobutyric acid-mediated, phasic inhibition of vasomotor drive mediated through autonomic ganglia to alpha-adrenoreceptors in the vasculature.
Henry
R T
RT
Department of Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Connor
J D
JD
Balaban
C D
CD
D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology*; D001370:Axonal Transport; D001640:Bicuculline / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects*; D002525:Cerebellar Cortex / Q000502:physiology; D002531:Cerebellum / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects*; D006735:Horseradish Peroxidase; D010646:Phentolamine / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D011817:Rabbits; D012016:Reference Values; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D001286:Atropine Derivatives; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins; D005680:gamma-Aminobutyric Acid; C006649:methylatropine; D011433:Propranolol; D006735:Horseradish Peroxidase; D001640:Bicuculline; D010646:Phentolamine