The spatio-temporal pattern of Wallerian degeneration in mammalian peripheral nerves

Newborn to 9-week kittens were perfused with a paraformaldehyde-glutaraldehyde solution. Thoraco-lumbar segments of the spinal cord were removed and processed for examination with the electron microscope. The results of this study indicate that, at birth, the dendrites of Clarke's nucleus have few if any neurofilaments, microtubules being the prominent component. By 3 weeks, distinctive filament ‘packets’ are visible. These ‘packets’ increase in number and complexity until 9 weeks when the arrangement appears to stabilize. Perikaryal changes are less obvious but primarily involve the maturation of the clusters of filaments and tubules which create islets of the other perikaryal organelles. As a result of these observations, it is suggested that the neurofilaments, which are seen to appear within the dendrites of Clarke's nucleus at a delayed time postnatally, serve a structural function in stabilizing the adult morphology. The microtubules, on the other hand, may contribute to the structural support of these large cells during their early development but, with the appearance of the filament component, are responsible for protein transport and particle translocation.