Nerve sprouting and endplate growth induced in normal muscle by contralateral partial denervation of rat plantaris

The incidence of motor nerve and terminal sprouting was quantitatively analyzed in normal unoperated muscles, in homologous muscles contralateral to muscles which have been partially denervated, in partially denervated muscles, and in sham-operated muscles. Muscles were studied by light microscopy after staining motor endplates by a combined silver-cholinesterase stain. In addition, the incidence of endplates containing terminal sprouts, the number of terminal branch points per endplate, and endplate size were also assessed in the various groups examined. We observed that following section of the L₄ spinal nerve, the incidence of sprouting (preterminal and intranodal) in the contralateral muscle exhibited a 2-fold increase over sham-operated controls. We also found a correlation between nerve terminal sprouting, terminal branch point number and endplate size. All of these parameters were significantly increased in the contralateral muscles as compared to the sham-operated control muscles. These findings suggest that normal muscles undergo sprouting which can be enhanced by contraleteral partial denervation. The possible underlying mechanism may be the transneuronal induction of sprouting.