[Studies on distribution patterns of modulator CGRP in different motoneuron pools in rats]

Using retrograde labelling combined with calcitonin gene-related peptide (CGRP) immunocytochemistry technique, distribution patterns of the content of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) were studied in two different motoneuron (Mn) pools supplying soleus (SOL, slow-twitch muscle) and extensor digitorium longus (EDL, fast-twitch muscle) of hindlimbs in rats during development. The Mn pools were identified with a novel retrograde tracer, choleragen B subunit (CB) coupled with colloidal gold (CB-Au, 5 nm particle, prepared by ourselves), which was injected into EDL or SOL. After the silver intensification for visualizing colloidal gold particles, CGRP immunocytochemistry were processed. The CB-Au retrogradely identified Mns in each Mn pool were counted and CGRP-LI intensity of Mns was evaluated as strong, moderate, weak and negative. The double labelling revealed different distribution patterns of CGRP-LI content between SOL and EDL Mn pools during development. Comparing the level of CGRP expression between the two Mn pools, SOL Mn pool had a higher ratio of neurons lacking CGRP-LI/weak CGRP LI and a lower proportion of strongly CGRP-LI labelled ones. These results suggest that the difference in content of CGRP-LI in Mns is related to the type of muscular motor activity.