Vagal nuclei in the medulla oblongata: structure and activity are maintained in aged rats

The neurones and microvessels of the dorsal motor nucleus of the vagus (DMN), the nucleus ambiguus (NA) and the nucleus tractus solitarius (NTS) of 4, 24 and 30 month male Wistar rats have been examined morphometrically and by quantitative enzyme histochemical methods (4 and 24 months only) to assess the affects of old age on the structure and activity of their neurones. DMN and NTS neuronal soma area increased whilst NA neuronal area was reduced in the aged groups; the changes in neuronal size were reflected in the density of neurones per unit area. The mean diameter and percentage area occupied by microvessels was unchanged with increased age in all three nuclei. Quantitative assessment of cytochrome oxidase and NADH-tetrazolium reductase activities in the nuclei revealed no changes in old age, indicating that old age does not affect neuronal or metabolic activity of central vagal neurones. These results compliment previous age-related studies on the vagus nerve and nodose ganglion in which little change has been reported, suggesting that the vagal system is well preserved in aged rats.