Modulation of Respiratory Rhythmogenesis by Chloride-Mediated Conductances during the Perinatal Period

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Abstract
Respiratory rhythmogenesis is modulated by chloride-mediated conductances via GABAAand glycine receptors. In this study, we determine the actions of chloride-mediated conductances on respiratory rhythmogenesis in perinatal rats from the time of inception of fetal inspiratory drive through to the newborn period. Data were obtained from perinatal rat models, including (1) recordings of nerve roots and neuronal population discharge from medullary slice and brainstem–spinal cordin vitropreparations, (2) gramicidin perforated-patch recordings of respiratory neurons in medullary slices, and (3) plethysmographic recordings from unanesthetized pups. The transition from excitatory to inhibitory effects on respiratory rhythmogenesis occurs at approximately embryonic day 19. By birth, GABA, glycine, and taurine all induce a hyperpolarization of the membrane potential in respiratory medullary neurons and a suppression of respiratory frequency. The age-dependant change in the actions of chloride-mediated conductances is regulated by the development of chloride cotransporters (KCC2 and NKCC1). The function of KCC2 chloride cotransporter is strongly modulated by [K+]o, which must be considered when evaluating responses observed usingin vitroperinatal preparations.