NERVE-TERMINAL SPROUTING IN BOTULINUM TYPE-A TREATED MOUSE LEVATOR AURIS LONGUS MUSCLE

The marked outgrowth of the motor nerve terminal arborization triggere d by an in vivo local injection of Clostridium botulinum type-A toxin in the mouse levator auris longus muscle was studied with morphologica l and immunochemical approaches. The increase in total nerve terminal length depended on the time elapsed after toxin administration and was due to both increased number of terminal branches and branch length a s revealed by a quantitative morphological analysis of whole mounts us ing the combined cholinesterase-silver stain. Nerve terminal sprouts i ncreased in number, length and complexity even after the functional re covery of neuromuscular transmission had occurred as revealed by elect rophysiological examination. Although we cannot exclude that transmitt er release sites from the original nerve terminal arborization may sti ll be functional after botulinum type-A toxin (BoTx-A) treatment, it i s likely that newly formed functional release sites on the sprouts pla y a major role in the functional recovery of neuromuscular transmissio n. The presence of an immunoreactivity to synaptophysin and synaptotag min-II, integral proteins of synaptic vesicles, gives support to our p revious findings suggesting that nerve terminal sprouts have the molec ular machinery For acetylcholine release. Copyright (C) 1996 Elsevier Science Ltd.