Ionic mechanisms of CO2 sensitivity in Phox2b neurons as the medullary central chemoreceptor

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It has been suggested that Phox2b expressing cells including pFRG/Pre-I neurons in the rostral ventrolateral medulla function as the central chemoreceptors (i.e. CO2 sensor). In the present study, we investigated neuronal mechanisms of high CO2 reception of pFRG/Pre-I neurons, using the brainstem-spinal cord preparation from newborn rats. The CO2 sensitivity of pFRG/Pre-I neurons was preserved even after blockade of Na+channels and Ca2+channels, and the membrane depolarization induced by hypercapnic stimulation was mainly due to the closing of K+channels. We also found that Phox2b-expressing cells including pFRG/Pre-I neurons in the parafacial region of the rostral ventral medulla tended to assemble around capillary blood vessels. We confirmed that TASK1,2 and 3 channels were less significantly involved in hypercapnic responses of pFRG/Pre-I neurons. Our findings demonstrate that the pFRG/Pre-I neurons possess postsynaptic mechanisms that are directly responsible to high CO2 stimulation.