Effects of axotomy on the distribution of passive electrical properties of cat motoneurones.

Abstract

Previously obtained experimental results concerning the effect of axotomy on motoneurone passive electrical properties have been re‐analysed. As shown earlier, axotomy causes an average increase of motoneurone input resistance, membrane time constant and after‐hyperpolarization duration. The present analysis suggests that the increased input resistance is related to a higher specific membrane resistivity, a decreased cell size and an altered dendritic geometry. The results also suggest that the change takes place only in neurones projecting to fast‐twitch muscle units and produces in them passive electrical properties normally exhibited only by motoneurones projecting to slow‐twitch units. Based on the notion that axotomy causes a 'dedifferentiation' of motoneurone properties, the present results might be taken to indicate that undifferentiated motoneurones are slow in character. A possible scheme in which a post‐natal differentiation of motoneurone properties may lead to muscle differentiation is discussed. © 1984 The Physiological Society