Ultrastructure of 6-aminonicotinamide (6-AN)-induced lesions in the central nervous system of rats. III. Alterations of the spinal gray matter lesion with aging.

Following a single i.p. injection of 6-AN (10 mg/kg), the anterior horn cells of 20- and 25-month-old rats increased more in size and recovered slower from chromatolytic changes than those of 3-month-old rats. Neurofilamentous hyperplasia of the perikarya was more prominent in aged rats; proliferated neurofilaments were arranged in thick parallel bundles. In the acute stage, reactive and degenerative changes of glial and mesenchymal elements were more conspicuous in 3-month-old rats; however, they disappeared by day 14 with prominent proliferation of hypertrophic astrocytes. The older rats showed less intensity and slower progression of these changes; sponginess and swelling of the astrocytic cytoplasm were still observed at day 14. Our results suggest that these age-dependent changes in the response to neurotoxins are not only induced on the neuron without mitotic phenomena after birth, but also on neuroglial cells. Furthermore, an alteration or reduction in the support of the neuron augments its intensified and delayed susceptibility to neurotoxins.