Fig. 1.

The effects of hypocapnia and hypercapnia on the spontaneous firing rate and input resistance in locus coeruleus (LC) neurons. A: traces of membrane potential (Vm) vs. time showing action potential frequency. Compared with control (5% CO₂), firing rate went down in 2.5% CO₂. B: compared with control, firing rate increased in 10% CO₂. C: compared with control, firing rate increased in 15% CO₂. D: relationship between the CO₂ and the change in firing rate induced by different levels of CO₂ in LC neurons. The response is presented as the percentage of change of firing rate in altered CO₂ vs. control (5% CO₂). Symbols represent the mean changes in firing rate ± SE. Note the large effect of CO₂ on firing rate between 2.5 and 10% but the plateau of firing rate above 10% CO₂. The % change in firing rates at various levels of CO₂ were significant at *P < 0.05, **P < 0.01, or ***P < 0.001. E: effect of CO₂ on input resistance (Rin). The response is plotted as paired data for Rin at 5% CO₂ vs. 2.5%, 10%, or 15% CO₂. Each pair shows the response of Rin for a given neuron in response to the indicated change of CO₂. Rin is significantly different from the values at 5% CO₂ at either *P < 0.05 or ***P < 0.001 based on paired t-tests.