CALCITONIN-GENE-RELATED PEPTIDE-LIKE IMMUNOREACTIVITY, IN BOTULINUM TOXIN-PARALYZED RAT MUSCLES

Changes in calcitonin gene-related peptide-like immunoreactivity (CGRP -LI) at the motor endplates of botulinum toxin-paralysed rat muscles w ere investigated using immunohistochemistry. One day following toxin i njection, a dramatic increase in CGRP-LI was detected at the motor end plates and within preterminal axons of the soleus and gastrocnemius mu scles. The upregulation of CGRP-LI persisted throughout the period dur ing which muscle fibres were paralysed and new neuromuscular junctions were being formed by the growing sprouts. Decline of CGRP-LI at the m otor endplates coincided with clinical recovery. Both up- and down-reg ulation of CGRP-LI took place earlier in the soleus than in the gastro cnemius muscle. Up-regulation of CGRP-LI was also detected in a subpop ulation of motor axons in the sciatic nerves and in the spinal motor n eurons innervating the paralysed muscles. These results indicate that levels of CGRP are regulated, at least partly, by changes in the targe t innervation. They also suggest an important role for CGRP in the reg enerative processes following muscle paralysis.