Increased activity in the form of endurance training increases calcitonin gene-related peptide content in lumbar motoneuron cell bodies and in sciatic nerve in the rat

The relative content of calcitonin gene-related peptide in lumbar motoneuron cell bodies (semi-quantitative immunohistochemistry) and sciatic nerve was examined in rats who had previously undergone a 16-week period of endurance training on a motor-driven treadmill. Soleus motoneurons were identified in the spinal cord by their fluorescence following injection of FluoroGold into the muscle one week before killing. In sedentary rats, calcitonin gene-related peptide was detectable in 76-90% of motoneurons, with no difference in the proportions of negative cells, or in the mean staining intensity of positive cells, between soleus and neighbouring (presumptive fast hindlimb muscle) unlabelled motoneurons. In endurance-trained rats, the estimated content of calcitonin gene-related peptide was significantly increased (90%) in cell bodies of soleus and neighbouring motoneurons, with no training-induced alterations in the proportions of calcitonin gene-related peptide-positive cells in either sample. The content of the neuropeptide was also significantly higher (37%) in sciatic nerve of endurance-trained rats. Relative accumulation of calcitonin gene-related peptide proximal to a sciatic nerve ligature applied 4 h before, however, was unchanged. The increases in calcitonin gene-related peptide in motoneuron cell bodies and sciatic nerve axons following endurance training may indicate an up-regulation of the synthesis, transport and terminal release of this neuropeptide, which could play a significant role in other morphological and functional adaptations which are known to occur at the neuromuscular junction following this chronic change in activity level. (C) 1999 IBRO. Published by Elsevier Science Ltd.