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) paral ysis altered the passive membrane properties of rat tibial motoneurones. Im pulse activity along the sciatic nerve was blocked for 4 weeks using TTX de livered by an osmotic minipump to a Silastic cuff placed around the nerve. That portion of the sample exhibiting the 20% slowest After-hyperpolarizati on (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 (presum ptive fast motoneurons), in which an increased AHPd, in fact, was found. Th e results thus support the hypothesis that retrograde signals from inactive slow and fast muscle fibers have different effects on their innervating mo toneurones. (C) 2000 Published by Elsevier Science Ireland Ltd.