High perfusate PO2 impairs thermosensitivity of hypothalamic thermosensitive neurons in slice preparations

The thermosensitivity of neurons in the preoptic area (POA) of guinea pigs was examined in slice preparations during perfusion with artificial cerebrospinal fluid (ACSF) gassed with 95% O2/5% CO2 (95% O2-ACSF) or 21% O2/5% CO2/74% N2 (21% O2-ACSF). Perfusate PO2, PCO2, and pH of 95% O2-ACSF measured in the incubation chamber were, respectively, 402.9 mmHg, 39.1 mmHg, and 7.38; those of 21% O2-ACSF were 154.0 mmHg, 33.1 mmHg, and 7.41. All the thermosensitive neurons (n = 6) originally identified during perfusion with 95% O2-ACSF also exhibited their thermosensitivity when examined again in 21% O2-ACSF. However, 63% of the thermosensitive neurons (n = 8) originally identified with 21% O2-ACSF lost their thermosensitivity in 95% O2-ACSF. The addition of superoxide dismutase to 95% O2-ACSF prevented the loss of thermosensitivity in 88% of the neurons (n = 8). These results suggest that oxygen toxicity due to free radical formation may account for the impairment of neuronal thermosensitivity in 95% O2-ACSF.