Cardiovascular effects of GABA system activating drugs injected into the caudal ventrolateral medulla of the rat.
Drugs activating GABAergic systems were microinjected into the caudal ventrolateral medulla of the rat and effects on blood pressure and heart rate were investigated. In urethane-anesthetized rats, a dose-dependent increase in blood pressure and heart rate was induced by unilateral injections of GABA (30-300 ng) into the caudal ventrolateral medulla. Unilateral injections of the GABA receptor agonist muscimol (1-10 ng) and baclofen (0.1-10 ng) into the brainstem area also increased both the cardiovascular parameters. The GABA uptake inhibitors nipecotic acid (1-3 micrograms) and L-2,4-diaminobutyric acid (1 microgram), and the GABA-T inhibitor gamma-acetylenic GABA (1-3 micrograms) injected unilaterally into the brainstem area also produced hypertension and tachycardia. Bilateral microinjections of nipecotic acid (0.3 microgram) into the area potentiated the pressor and tachycardiac responses to carotid artery occlusion in pentobarbital-anesthetized rats. Lesioning of the rat nucleus tractus solitarii did not alter the GABA content in the lesioned side of the caudal ventrolateral medulla. The data provide further evidence that endogenous GABAergic mechanisms in the rat caudal ventrolateral medulla are involved in the regulation of blood pressure. It seems unlikely that the GABAergic mechanisms originate mainly from neurons in the nucleus tractus solitarii.
Kihara
M
M
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
Kubo
T
T
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002339:Carotid Arteries / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007267:Injections; D008297:Male; D008526:Medulla Oblongata; D008845:Microinjections; D051381:Rats; D011919:Rats, Inbred Strains; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D005680:gamma-Aminobutyric Acid