Loss of neurons from the retrofacial nucleus of the mouse in extreme old age.

The retrofacial nucleus, a general visceral efferent component of the vagal nuclei, was examined using quantitative histological techniques in young adult (6 months) and elderly (25, 28 and 31 months) mice. Neuron number remained constant between 6 months (206 +/- 2) and 25 months (209 +/- 4) and thereafter declined rapidly at 28 (181 +/- 11) and 31 months (157 +/- 4). Neuronal nuclear diameter (mean 11.0 microns) did not vary significantly with age. Neurons of the retrofacial nucleus lost Nissl substance with age and lipofuscin accumulation was marked in the perikaryon and dendrites.