Fig. 3.

CO₂ response of LC neurons. A: whole cell current clamp was made in a WT LC neuron in the brain stem slice. At baseline (5% CO₂), the LC neuron fired spontaneously with basal firing rate 3.8 Hz (A₁). Firing activity increased to 5.3 Hz when the cell was exposed to 6.5% CO₂ (A₂). A3: the instant frequency plot showed a clear increase in firing rate during 6.5% CO₂ exposure. B: a representative recording from a Mecp2^−/Y neuron. B1: in an LC neuron from a Mecp2^−/Y mouse, baseline firing activity was 2.2 Hz. B₂: the firing activity changed barely to 2.3 Hz in response to 6.5% CO₂. B₃: the instant frequency plot of the cell indicated a subtle increase in firing rate during hypercapnia. C and D: neuronal firing activity increased in response to 6.5 and 8% CO₂. Such a cellular response to 6.5% CO₂ was significantly reduced in LC neurons of Mecp2^−/Y mice than in the WT. E and F: hypercapnia caused significant increases in input resistance (R_m). The effect was much smaller in Mecp2^−/Y neurons than in the WT. G and H: membrane potential (V_m) response to hypercapnia. 6.5% CO₂ caused clear depolarization in only WT, whereas depolarization with 8% CO₂ was found in both WT and Mecp2^−/Y cells (paired t-test) Significant difference: *P < 0.05; **P < 0.01. Data were obtained from 36 WT and 21 Mecp2^−/Y LC neurons.