FIG. 4.

DOI increases self-sustained firing and enables very slow firing, in association with increases in the Na PIC. All recordings were done in motoneurons from acute spinal rats, with nimodipine blocking Ca PIC. A: slow triangular current ramp (bottom) elicited repetitive firing and a very small amount of self-sustained firing (middle; ΔI= 0.1 nA). Firing frequency (top) not <6 Hz (horizontal dashed line). B: from same motoneuron as in A; DOI increased Na PIC amplitude in this cell (not shown). ΔI was increased and firing occurred at <6 Hz just before derecruitment. C: different cell in DOI showing continuous firing <6 Hz with current held at threshold. Close up shown at right. Note interspike interval longer than AHP duration (open rectangle).