TRANSIENT REINNERVATION OF ANTAGONISTIC MUSCLES BY THE SAME MOTONEURON

When reinnervation is allowed after a sciatic nerve cut in the adult r at, motoneuron axons may branch to innervate antagonistic muscles. Thi s multiple innervation is widespread, but transient. Fourteen weeks af ter denervation isometric muscle contraction experiments and studies w ith anterograde transport of the fluorescent tracer Fast Blue showed t hat branches from the same motoneurons reached the distal part of the tibial nerve and either the soleus or the extensor digitorum longus mu scles or both muscles. Retrogradely double-labeled motoneurons were fo und after injections of different fluorescent tracers into these muscl es. Sixty-four to 88 weeks after the nerve cut, similar experiments sh owed that selective innervation was reestablished. The findings sugges t a selective mechanism for axon withdrawal in an adult mammal. (C) 19 94 Academic Press, Inc.