A horseradish peroxidase labeling technique for correlation of motoneuron metabolic activity with muscle fiber types.

Modifications in the tetramethylbenzidine technique by Mesulam et al. (1980) for demonstration of retrogradely transported horseradish peroxidase (HRP) in alpha-motoneurons have been made. The methodology was designed to permit use of quantitative enzyme histochemical techniques on sections serial to those used for demonstration of HRP. Injections of HRP into different muscles on contralateral limbs, each of which are composed almost exclusively of one muscle fiber type, have allowed us to determine relative enzyme activities in the motoneurons innervating specific muscle fiber types. The modifications should be useful to others using HRP as a peripheral or central nervous system tracer since significant time and chemical costs are saved, the slide-mounted sections are easier to handle, and the sensitivity is superior to currently available methods.