The purpose of the study was to whether motoneurons innervating the rat hindlimb muscles, soleus and plantaris active during treadmill running could be identified and quantified by use of insitu hybridization histochemistry (ISH) for c-fos. Two of Wistar rats had previously trained for two wks were used in the study. The both muscles of two Wistar rats were injected with retrograde tracer, Nuclear Yellow (NY), and then (two days later) subjected to half an hour of treadmill running test at 25 m/min. The colony of the grains showing c-fos gene expression were found within the labeled motoneurons with the NY in the motoneurons innervating both the muscle. The quantitative analysis of the grains were performed with microspectrophotometry as a criteria for active motoneurons during the running. The result showing a speed dependent increase in c-fos expression in the motoneurons for plantaris muscle is consisitent with previous finding by use of electrophysiolgical technique, suggesting that the use of ISH for c-fos should be available to examine the active motoneurons in the rat during running.
