Effects of peripheral chemo- and baro-receptor denervation on responses of preoptic thermosensitive neurons to inspired CO₂

The purpose of this study was to see if the responses of thermosensitive neurons in the preoptic (PO) area to inspired CO₂ seen in spontaneously ventilated rats were indirectly driven by reflexive changes in respiration and circulation. In urethanized, paralyzed, and artificially ventilated (AV) rats, the effects of 10% CO₂ inhalation on PO thermosensitive neurons were examined by regression of neuronal activity on PO temperature. The experiments were made in intact rats and in rats whose peripheral chemo- and baro-receptors were denervated (AVD). In both AV and AVD rats, the slope of the regression line decreased significantly (P<0.05) during CO₂ inhalation in half of the warmsensitive neurons studied (64.3% in AV rats, 41.7% in AVD rats). Peripheral chemo- and baro-receptors thus do not appear to be responsible for decreased thermosensitivities of warm-sensitive neurons during CO₂ inhalation. The tendency for activities of warm-sensitive neurons to increase progressively at lower T_po was seen during CO₂ inhalation in both AV and AVD rat. However, the average differences in mean firing rate between 10% CO₂ and air inhalations were 2-3 imp/s greater at any T_po in AV rats than in AVD rats. In AVD rats, warm-sensitive neurons were rather inhibited by CO₂ at higher T_po. Excitation of warm-sensitive neurons during CO₂ inhalation in AV rats, which was independent of T_po, was considered to be caused by the signals from peripheral receptors.