6-cyano-7-nitroquinoxaline-2-3-dione and biotinamide

Previous studies have reported subsets of medullary raphé neurons that are either stimulated or inhibited by CO2/pH in vitro, in situ, and in vivo. We tested the hypothesis that medullary raphé CO2-inhibited neurons are GABAergic. Extracellular recordings in unanesthetized juvenile in situ rat preparations showed reversible hypercapnia-induced suppression of 19% (63/323) of medullary raphé neurons, and this suppression persisted after antagonism of NMDA, AMPA/kainate, and GABAA receptors. We stained a subset of CO2-inhibited cells and found that most (11/12) had glutamic acid decarboxylase 67 immunoreactivity (GAD67-ir). These data indicate that the majority of acidosis-inhibited medullary raphé neurons are GABAergic, and that their chemosensitivity is independent of major fast synaptic inputs. Thus, CO2-sensitive GABAergic neurons may play a role in central CO2/pH chemoreception.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Animals, Newborn; Bicuculline; Biotin; Carbon Dioxide; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; GABA Antagonists; GABAergic Neurons; gamma-Aminobutyric Acid; Glutamate Decarboxylase; In Vitro Techniques; Male; Midbrain Raphe Nuclei; Patch-Clamp Techniques; Piperazines; Rats; Rats, Sprague-Dawley; Tryptophan Hydroxylase