Respiratory Signaling of Locus Coeruleus Neurons during Hypercapnic Acidosis in the Bullfrog, Lithobates catesbeianus

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The locus coeruleus (LC) in the brainstem senses alterations in CO2/pH and influences ventilatory adjustments that restore blood gas values to starting levels in bullfrogs (Lithobates catesbeianus ). We hypothesized that neurons of the bullfrog LC are sensitive to changes in CO2/pH and that chemosensitive responses are intrinsic to individual neurons. In addition, we hypothesized putative respiratory control neurons of the bullfrog LC would be stimulated by hypercapnic acidosis within physiological ranges of PCO2/pH. 84% of LC neurons depolarized and increased firing rates during exposure to hypercapnic acidosis (HA). A pH dose response curve shows LC neurons from bullfrogs increase firing rates during physiologically relevant CO2/pH changes. With chemical synapses blocked, half of chemosensitive neurons lost sensitivity to HA; however, gap junction blockade did not alter chemosensitive responses. Intrinsically chemosensitive neurons increased input resistance during HA. These data demonstrate that majority of neurons within the bullfrog LC elicit robust firing responses during physiological ΔCO2/pH, likely enabling adjustment of acid–base balance through breathing.



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