Endogenous GABA in the commissural subnucleus of the NTS inhibits the carotid chemoreceptor reflex via GABA_A receptors in rats

Summary.

Using urethane-chloralose anesthetized rats, we investigated which GABA receptor is responsible for the action of endogenous GABA on the carotid chemoreceptor reflex in the commissural subnucleus of the nucleus tractus solitarius (commNTS). Microinjection of the selective GABA uptake inhibitor nipecotic acid (40 nmol) into the commNTS attenuated the increases in respiration (respiratory movement and rate) and the elevation in arterial blood pressure elicited by carotid chemoreceptor stimulation. These effects were completely antagonized by premicroinjection of the GABA_A antagonist bicuculline (20 pmol), but not of the GABA_B antagonist 2-OH-saclofen (400 pmol), into the same site. These findings suggest that endogenous GABA mainly acts on GABA_A receptors, and inhibits the chemoreceptor reflex in the commNTS in rats.