Figure 5.

The effects of sAC inhibition on the magnitude of the chemosensitive response in LC neurons from neonatal rats older than P10. The inhibition of sAC enzyme by 2-hydroxyestradiol (2HE; 10 µM ) causes an increase in the chemosensitive response. (A) A typical chemosensitive response for whole cell current clamp experiments from neonatal rats older than P10 when CO₂ is increased from 5 to 15%. The bottom trace represents the integrated firing rate (reported as Hz measured in 10 s bins). Note that 15% CO₂ causes an increase in the integrated firing rate of LC neurons that is reversible upon return to 5% CO₂. The top trace shows individual action potentials (voltage scale of 50 mV) at a faster time scale than the lower panel. The first set of action potentials is in the presence of 5% CO₂, the middle set of action potentials is in the presence of 15% CO₂ and the last set of action potentials is upon return to 5% CO₂ at the end of the lower trace. (B) The same neuron as in (A) in the presence of 2HE. Notice the significant increase in the integrated firing rate response to hypercapnia (5 to 15% CO₂) in the presence of 2HE shown in the lower trace. Just as in (A), the upper traces show individual action potentials at a faster time trace in the presence of 5% CO₂ + 2HE (left trace), 15% CO₂ +2HE (middle trace) and 5% CO₂ + 2HE again (right trace) . (C) A complete current clamp record of a whole cell patch from a LC neuron from a P14 rat. In the lower trace is the integrated firing rate for this neuron in response to 15% CO₂ in the presence and the absence of 2HE. Note that repeated bouts of hypercapnia (going from 5% to 15% CO₂) result in a similar increase in integrated firing rate. The addition of 2HE does not increase the firing rate in control conditions (5% CO₂) but leads to a substantially increased firing rate response to hypercapnia (15% CO₂) that is not easily washed off upon removal of 2HE. The upper trace is a plot of action potentials vs. time for this neuron but at a slow time scale. This does not make individual action potentials clear but highlights the entire trace. Note the large apparent hyperpolarization in response to 2HE that reverses upon washing it off. This hyperpolarization is most likely due to a change in junction potential, caused by the addition of 2HE to the superfusate; however, the inhibition of sAC does not appear to reverse.