A comparison of age-related changes in neuron number in the dorsal motor nucleus of the vagus and the nucleus ambiguus of the mouse.

The numbers of preganglionic parasympathetic neurons in the dorsal motor nucleus of the vagus and of branchiomotor neurons in the nucleus ambiguus were estimated in mice aged 6, 15, 25, 28 and 31 months. The number of preganglionic neurons fell from 1318 at 6 months to 820 at 31 months with neuron number remaining stable until after 25 months. The number of branchiomotor neurons in the nucleus amgiguus fell from 587 at 6 months to 351 at 31 months, the significant decline in number beginning after 15 months. The retrofacial nucleus, or compact formation of the nucleus ambiguus, did not lose neurons until after 25 months whereas significant neuron loss from the remainder of the nucleus began after 15 months.