Quantitative electron microscopic observations on the non-neuronal cells and lipid droplets in the posterior funiculus of the kitten after dorsal rhizotomy.

Kittens were subjected to lumbosacral dorsal rhizotomies at the age of 6-8 days postnatally. After postoperative survival times of 1-25 days the number of non-neuronal cells and lipid droplets in each cell type in the posterior funiculus at L1 were counted at the ultrastructural level. Intact control animals were analyzed in the same way. The number of astrocytes and oligodendrocytes decreased with increasing postoperative survival time in the degenerating zone. This was also the case in the white matter of control animals with increasing age of sacrifice. However, in the degenerating zone of operated animals the decrease was more extensive for oligodendrocytes starting at 5 days after surgery, and possibly also for astrocytes at 25 days postoperatively. The number of microglial cells in the degenerating zone was markedly increased 2-10 days after surgery compared to the controls. The number of non-pericytic perivascular cells seemed to be somewhat increased from 9 days after surgery, while the number of pericytes remained unchanged during the experimental period. Lipid droplets in the degenerating white matter were mainly located in microglial cells and astrocytes and only to a small extent in non-pericytic perivascular cells. These findings suggest that lipid material produced during anterograde fiber degeneration in the immature white matter is mainly metabolized in glial cells.