Role of GABA within the nucleus tractus solitarii in the hypoxic ventilatory decline of awake rats

The purpose of this study was to examine our hypothesis that gamma -aminobu tyric acid (GABA) in the nucleus tractus solitarii (NTS) may be related to the hypoxic ventilatory decline (HVD) and that chemoreceptor stimulation wa s essential to activate this mechanism. We used unanesthetized, freely movi ng rats in this study. An in vivo microdialysis technique was used to measu re the extracellular GABA concentration ([ GABA](o)), and an in vivo microi njection technique was used to examine the effects of the GABA agonists and antagonists on the ventilation during hypoxia. The GABA agonists injected into the NTS attenuated the ventilation during hypoxia. By hypoxic exposure , [GABA](o) was increased during the HVD. However, by carotid body denervat ion (CBD), this GABA increase was abolished. Although GABA antagonists micr oinjected into the NTS during the HVD phase significantly increased the dep ressed ventilation, this effect on the ventilation was abolished by CBD. Th ese results suggest that the GABA in the NTS has a pivotal role in the HVD and that this mechanism is not activated without chemoreceptor stimulation.