Remodeling of neuromuscular junctions in aged rat genioglossus muscle.

Speech and swallowing disorders represent a large clinical problem in elderly persons. Poor lingual control is associated with both speech and swallowing impairment. Studies of limb and laryngeal muscles suggest that age-related musculoskeletal changes may be characterized by remodeling of muscles, nerves, and their connections at neuromuscular junctions (NMJs). To evaluate dynamic remodeling of NMJ structure in the tongue as a function of aging, we studied tongues from 10 aged and 10 young rats. A fluorescent, triple-labeled, immunohistochemical technique was used with genioglossus (GG) muscle samples to allow confocal microscopic visualization of receptor clusters, nerve terminals, axons, and synaptic vesicles. Normal axon terminals and receptor clusters were easily identified in young rat GG muscles, whereas aging induced a significantly higher degree of receptor dispersal. These results suggest that NMJ remodeling is found in aged GG muscles and may underlie the progressive neuromuscular changes observed in the elderly.