In the aerodigestive system (ventilation, swallow, speech and airway defense manoeuvres), age-related neuromotor declines contribute to the increased risk of aspiration pneumonia, a leading cause of mortality in the elderly. In the Fischer 344 (F344) rat model, we and others have identified that brainstem hypoglossal motor neuron (MN) degenerations and death contribute to motor dyscoordination and tongue muscle weakness, respectively. In F344 rats, both MNs and striated muscle exhibit morphological and functional deficits of mitochondria in aging, consistent with elderly human post mortem results. However, to date the dendritic and axonal compartments have been relatively ignored. In young (6-months old; n=6 rats) and old (24-months-old; n=6 rats) female and male F344 hypoglossal motor axons were assessed using serial block face scanning electron microscopy (SDFEM). Within myelinated hypoglossal motor axons and hypoglossal MN dendrites, mitochondrial volume density and morphology (mitochondrial CSA, form factor and aspect ratios) were assessed. In old age, mitochondrial volume density was reduced in dendrites and, surprisingly, increased in axons. Mitochondrial fragmentation (reduced CSA, form factors and aspect ratios was apparent in dendrites. In axons, old age mitochondria were larger, but more simplistic. We interpret these dendritic findings to be consistent with altered neural network function in old age. In the axons, excessive mitochondria may physically impair the anterograde and retrograde transit along the axons. Our results suggest that a more nuanced compartment-specific evaluation of mitochondrial structure and function is required to fully elucidate the pathophysiology underlying age-related neuromotor dysfunction. Funding for this research was provided by National Institutes of Health (NIH) grant AG086136 (MJF). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Searles et al. (Fri,) studied this question.