Fig. 1.

Whole cell recordings from locus coeruleus (LC) neurons in brain slice. A: neuronal firing activity was studied in instant-frequency histogram. The cell had a firing rate (FR) of 4 Hz at baseline with 5% CO₂. Exposure to 8% CO₂ raised the FR markedly. The peak of the FR (∼12 Hz) was reached in 1 min and then declined slightly throughout the 6-min 8% CO₂ exposure. Washout with 5% CO₂ led to almost complete recovery of the FR in 4–5 min. B: membrane potentials (V_m) and action potentials of the neuron. B₁, B₂, and B₃ were obtained from A at the arrows from left to right, respectively. The V_m of each trace is indicated by the arrows. Hypercapnia augmented the FR and depolarized the cell (B₂). The input resistance (R_m) was monitored by injecting a −0.05-nA current pulse every 20 s during the experiment and then calculated with Ohm's law, which is better seen in C with expanded displays. The R_m dropped by ∼50% during the high-CO₂ exposure (C₂). C₁ and C₃ are obtained from B₁ and B₂, respectively.