Figure 12.

Modulatory effect of IA on the pacemaker frequency of bulbospinal inspiratory-inhibited RVLM presympathetic neurons. Ai, Transient IA current and a sustained outward current of a pacemaker nonmodulated RVLM presympathetic neuron elicited by depolarizing voltage steps (from −80 to 60 mV) with a holding voltage either of −110 mV or −40 mV. With the off-line subtraction of the currents evoked with holding voltage of −110 and −40 mV, the IA current was isolated. Aii, Average amplitude of IA current measured at the peak values of the subtracted current showed in Ai. Aiii, Voltage-dependent inactivation was measured as the decrease in IA during a step to −30 mV after 1 s of preholding potentials from −130 to −30 mV. Bi, When the average normalized IA amplitude obtained with the voltage-dependent activation (■) and inactivation (□) protocols are plotted together (Boltzmann fitted—see Materials and Methods) as a function of the command potential, a region of overlap between −70 mV and −35 mV was observed. Bii, In current-clamp mode, the pacemaker spike discharge frequency of the inspiratory-inhibited RVLM presympathetic neuron increased after application of 4-AP (5 mm). Biii, Broadening of a pacemaker action potential and reduction of after-hyperpolarization potential in the presence of 4-AP was observed.