The nucleus ambiguus contains motor neurons (MNs) innervating the muscles of the larynx, pharynx and oesophagus. Many of the motor units these muscles are comprised of are fast fatigueable units — highly vulnerable to neurodegeneration. Loss of the MNs or damage to the nerves innervating the muscles of the larynx, pharynx and oesophagus may impair swallow, vocalization and/or respiratory functions. Of particular importance, human patients with deficits in swallow are at risk of sequelae such as aspiration pneumonia and malnutrition. In aged male Fischer 344-Brown Norway crosses, age-associated loss of nucleus ambiguus MNs contributes to vocalisation deficits. Here, we use female and male Fischer 344 (F344) at young (6-months old) and old (24-months old) to evaluate swallow function and nucleus ambiguus MN survival. Swallow function was evaluated under anesthesia by delivering an 0.3 mL bolus of water to the base of the tongue and videoing the number of subsequent swallows. A pressure catheter was inserted into the oesophagus to evaluate the incidence and duration of wallow-associated apneas and the magnitude of the schluckatmung in 30 s following bolus delivery. Following functional evaluations, rats were euthanized, perfused with paraformaldehyde and brainstem tissue cryopreserved, sectioned and stained with Nissl to stereologically evaluate the number of nucleus ambiguus MNs. In old age, we observed an ~30% reduction in the number of swallows per delivery of the water bolus and an increased incidence and duration of swallow apnea. Schluckatmung was not affected by age. The number of nucleus ambiguus MNs was reduced by ~20% in old F344 rats, with MN size unaffected. We propose that swallow evaluations are a robust readout of oropharyngeal behaviour, with deficits concomitant with MN death. These findings are similar to age-associated weakness in other skeletal muscle being related to MN death. It is likely that the mechanisms underpinning fast fatigue motor unit MN death in brainstem and spinal pools are similar. This research was funded by HL166204. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.