Fig. 4.

Effects of continuous current injections on the driving potentials during scratching. Continuous depolarizing (A) and hyperpolarizing (B) current injections in LGS4 motoneurons kept the membrane potential at −42 and −91 mV, respectively. In the absence of bias current, the membrane potential was approximately −63 mV. From topto bottom, the traces show the membrane potential (top trace), the current injection (second trace), and ENGs from the MG and TA muscle nerves (bottom two traces). In addition to the continuous current injections, short current pulses (+1.5 nA, 5 msec) were given to measure the changes in input resistance (small vertical bars on top of the current injection trace). A few seconds after the membrane potential stabilized, fictive scratching was induced. Aa,Bb, The series of events that occurred around the induction time (portions of the traces enclosed indotted rectangles) displayed on a larger scale. The fluctuations in the membrane potential trajectory during the transition between rest and motor activity (step-like, reversed hyperpolarization in B) was not uncommon. It is presumably attributable to the lack of fine control over the stimulus used to induce scratching (applied manually). Note that the fluctuation recorded intracellularly was also seen in the population response from the antagonist motoneuron pool (TA ENG).