Changes in electrophysiological properties of tibial motoneurones in the rat following 4 weeks of tetrodotoxin-induced paralysis.

In this study, we test the hypothesis that 4 weeks tetrodotoxin (TTX) paralysis altered the passive membrane properties of rat tibial motoneurones. Impulse activity along the sciatic nerve was blocked for 4 weeks using TTX delivered by an osmotic minipump to a Silastic cuff placed around the nerve. That portion of the sample exhibiting the 20% slowest After-hyperpolarization (AHP) decay time (AHPd), and which therefore included presumptive type S motoneurons, demonstrated responses (reduced AHPd, increased rheobase and rheobase voltage), which were not evident in the rest of the sample (presumptive fast motoneurons), in which an increased AHPd, in fact, was found. The results thus support the hypothesis that retrograde signals from inactive slow and fast muscle fibers have different effects on their innervating motoneurones.