Fig. 4.

Stuttering in firing is not due to inactivation of sodium channels. A: shown is the firing of a motoneuron from a septic rat during a 5-s current injection. The motoneuron stops firing for ∼2 s during the middle of the current injection. B: shown on an expanded time scale are the last action potential before the pause (large arrowhead in A, on left in B) and the 1st action potential after the pause in firing (small arrowhead in A, on right in B). The 1st potential after the pause has a threshold that is 5 mV higher, a slower rate of rise and a lower peak. These differences in action potential characteristics suggest firing resumes despite sodium channel inactivation that is greater than before the pause. C: the maximum rate of rise of action potentials is plotted vs. time during the 5-s current injection. The plot is aligned with the action potential plot shown in A. The rate of action potential rise gradually decreases to a steady-state value before the pause. The rate of rise of the action potential is lowest when the motoneuron resumes firing after the pause and then gradually increases to the steady-state value before the pause in firing.