Labeling of motoneurons supplying the cutaneous maximus muscle in the rat, following injection of the triceps brachii muscle with horseradish peroxidase

Abstract

Injection of the triceps brachii muscle of the rat with horseradish peroxidase (HRP) led to labeling of motoneurons in the dorsolateral and ventral aspects of the ventral grey horn of the brachial spinal cord. Ventral, labeled neurons were absent, however, in rats in which the motor branches of the radial nerve to triceps were exposed to HRP. Cutting the radial nerve, prior to the injection of the triceps, did not diminish this ventral labeling, whereas cutting both the radial nerve and the nerves to the cutaneous maximus muscle before injection completely eliminated it. Leakage or diffusion of HRP from the triceps and its subsequent uptake by damaged fibers of the cutaneous maximus muscle was the most likely cause of the labeling of the ventrally located motoneurons.