Fig. 1.

Effects of H⁺ and CO₂ on orexin and nonorexin cells of the LH. Current-clamp whole-cell recordings with K-gluconate intracellular solution. To monitor membrane conductance, cells were injected with periodic hyperpolarizing current pulses. The size of the resulting downward voltage deflections is inversely proportional to membrane conductance. (A) Effect of CO₂-induced changes in pH_e on an orexin neuron. Firing rate was 0.8 ± 0.3 Hz in 5% CO₂ and 3.7 ± 0.4 Hz in 10% CO₂ (n = 5; P < 0.01, two-tailed t test). (B) Effect of Hepes-buffered changes in pH_e on an orexin neuron. Firing rate was 4 ± 0.6 Hz at pH 6.9 and 0.5 ± 0.2 Hz at pH 7.4 (n = 15; P < 0.001, two-tailed t test). (C) No effect of changes in pH_e on firing of a nonorexin neuron.