Lack of Age‐related Change and Exercise‐induced Plasticity in the Hypoglossal Nucleus

Abstract

Aging can result in a loss of neuronal cell bodies and a decrease in neuronal size in certain brainstem nuclei. In this study, we aimed to determine if similar changes occurred in the hypoglossal nucleus. If present, these changes might help to explain the decrease in genioglossus activity seen in elderly patients with obstructive sleep apnea (OSA). In addition to aging, we examined the effects of exercise on hypoglossal motorneurons, as previous work has shown that spinal motoneurons undergo compensatory morphological changes in response to exercise. We explored the idea that cranial motoneurons could respond in a similar manner. We hypothesized that as rats age, the number and size of hypoglossal motoneurons, as well as the number of primary dendrites associated with them would decrease. Further, it was expected that exercise would reduce the age-related changes in hypoglossal motoneurons. Hypoglossal motoneurons were retrogradely labeled with tongue injections of Cholera toxin β into the genioglossus muscle of young (9–10 months), middle-aged (24–25 months), and old (32–33 months) male F344/BN rats, as well as age-matched rats that had undergone eight weeks of tongue resistance exercise. Neurons were visualized using immunocytochemistry, light and fluorescent microscopy and were measured with ImagePro software. Preliminary results suggest that no age-associated or exercise-induced changes occur in the hypoglossal nucleus in neuronal number, size, or the number of primary dendrites. (Supported by NIH-NIA 18760 to M. Behan)