Tongue blade neuromuscular junction defects in old F344 rats.

Tongue-muscle associated behaviours (swallow, speech) are impaired in the elderly. In the Fischer 344 (F344) rat model of aging, hypoglossal motor neurons (MNs) and intrinsic tongue muscle weakness and atrophy are evident. Here we evaluated young (6-months) and old (24-months-old) F344 rat longitudinal muscles for neuromuscular junction (NMJ) innervation. In 140 µm free floating sections, presynaptic components were labelled with synaptophysin and neurofilament. Postsynaptic acetylcholine receptors were labelled with α-Bungarotoxin. NMJs were imaged using confocal microscopy with presynaptic invasion of the postsynaptic endplate quantified. We found marked denervation of female and male tongue NMJs in old age. Our findings are consistent with the significant role that tongue dysfunction has in aged tongue muscle dysfunction and hypoglossal MN death.