The process of decompaction and myelin removal after C7 ventral root avulsion in the cat

An electron microscopical study was carried out on the ventral horn in order to investigate the microvascular changes after C7 ventral root avulsion in cats. Endothelial cells: At 2 days after avulsion the endothelial cells contained vacuoles filled with fibrous-like substances. After 14 days the endothelial phagosomes also contained myelin sheath-like and "soap-bubble" structures. Tight junctions between the endothelial cells remained present without exception. From 14 up to 90 days, intraluminal debris was observed. Edema and glia: From 2 up to 30 days after avulsion perivascular edema was noted around blood vessels and polymorphonuclear granulocytes were found mainly in the peri-endothelial space. Eight days after avulsion, the number of astrocytic processes around the blood vessels and the phagocytic activity of perivascular cells increased. Myelin sheath-like structures were encountered in phagosomes of the pericytes. After 14 days the distribution of astrocytic processes around the blood vessels had stabilized and remained so until day 90 after avulsion. In the same period the phagocytic activity decreased, and the myelin sheath-like material in the perivascular cell phagosomes gradually disappeared. The amount of microglial cells around the blood vessels showed an increase after 30 days survival and then stabilized. These results indicate transport of debris from the neuropil across the endothelial cells into the blood vessel lumen after ventral root avulsion.