CO2-sensitive medullary neurons

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Abstract
Bioelectric activity of CO2-sensitive, ventrolateral medullary neurons (VLN(CS)) in organotypic cultures from the obex level of newborn rats was tested during changes of the intracellular pH (pHi) measured in BCECF-AM loaded cultures. Hypercapnia (pCO2 80-100 mmHg) reduced pHi by 0.15 +/- 0.06 units and stimulated neuronal discharges. Replacement of CO2/HCO3- in the bath by HEPES (26 mM, pH 7.4) for 10 min acidified pHi (0.07 +/- 0.03 units) and also excited VLN(CS). Ammonium chloride (10 mM, 1 min) initially alkalized (0.1 +/- 0.04) and thereafter acidified pHi (0.06 +/- 0.03), while the extracellular pH was first acidified and then alkalized. This resulted in neuronal discharge which were first suppressed and then accelerated. The findings strongly suggest that intracellular rather than extracellular acidification activates CO2-sensitive neurons.