• GABAergic neurons in the medullary raphé possess network independent chemosensitivity in situ

      Iceman, Kimberly E. (2012)
      The identity and location of central pH/CO2 sensitive chemoreceptors are not fully understood. Serotonin (5-HT) and γ-aminobutyric acid (GABA) synthesizing neurons in the medullary raphé have demonstrated intrinsic chemosensitivity in vitro. This evidence forms the basis for our "push-pull" model of raphé contributions to chemosensitivity. We have previously shown that CO2-stimulated 5-HT neurons occur in the medullary raphé in situ. Here, we test the hypothesis that the medullary raphé contains GABA synthesizing CO2-inhibited neurons that retain their chemosensitivity after pharmacological blockade of major fast synaptic inputs. To assess chemosensitivity, we record extracellular single neuron discharge during normocapnic and hypercapnic conditions within the medullary raphé of the unanesthetized juvenile rat in situ perfused decerebrate brainstem preparation. Network dependence of chemosensitivity is assessed by application of antagonists for AMPA, NMDA, glycine, and GABAa receptors that disrupt fast-synaptic network properties. Juxtacellular labeling and immunohistochemistry establish neurotransmitter phenotypes of recorded neurons. Results support independence of CO2-inhibited GABA neuron chemosensitivity from fast synaptic inputs.