REGULATION OF MOTONEURONAL CALCITONIN-GENE-RELATED PEPTIDE (CGRP) DURING AXONAL GROWTH AND NEUROMUSCULAR SYNAPTIC PLASTICITY INDUCED BY BOTULINUM TOXIN IN RATS

The aim of this study was to examine whether changes in rat motoneuron al calcitonin gene-related peptide (CGRP) can be correlated with axona l growth and plasticity of neuromuscular synapses. Nerve terminal outg rowth was induced by local paralysis with botulinum toxin, Normal adul t soleus and tibialis anterior did not show detectable CGRP content at the motor endplates, Following botulinum toxin injection there was a progressive, transient and bimodal increase in CGRP in both motoneuron cell bodies which innervated poisoned muscles and their motor endplat es. CGRP content was moderately increased 1 day after paralysis and, a fter an initial decline, reached a peak 20 days after injection. This was followed by a gradual decrease and a return to normal levels at th e 200th day. CGRP changes in intoxicated endplates were less evident i n the tibialis anterior than in the soleus muscle. The CGRP content in motoneurons was positively correlated with the degree of intramuscula r nerve sprouting found by silver staining. In situ hybridization reve aled an increase in CGRP mRNA in spinal cord motoneurons 20 days after toxin administration. We conclude that motoneurons regulate their CGR P in situations in which peripheral synapse remodelling and plasticity occur.