Figure 5. Defects in motor innervation with age are specific to hindlimb muscles. (A-B) Neuromuscular fragmentation was measured on EDL (A) and biceps brachii (B) from adult, early sarcopenic or sarcopenic rats after staining for acetylcholine receptors (AchR) using fluorescently conjugat α–bungarotoxin. Representative images from each condition are shown. Scale bars represent 20μm. (C) Experimental design for retrotracer labeling studies. Motor innervation in gastrocnemius and triceps brachii was evaluated by injecting fluorogold into each muscle and quantifying its spinal cord accumulation 10 days later. (D) Number of motoneurons specifically innervating gastrocnemius and triceps brachii in adult and sarcopenic rats. For all graphs n=6-7 per group and an average of 50 NMJs were counted for each sample. * p<0.05 ** p<0.01 *** p<0.001 compared to the same category in adults, and # p<0.05 compared to the same category in early sarcopenic, using a one-way ANOVA test.