relationship between Schwann cells and endoneurial macrophages after sciatic nerve crush injury

ABSTRACT

Twenty eight male albino rats aged 6-8 weeks [weighed 300g to 350g] were used in this study Twenty animals were used for the ultrastuctural study while eight animals were used for the ferritin intravenous injection study. The animals of the ultrastuctural study were divided into two groups; the experimental group [16 rats] and the control group [4 rats]. The left sciatic nerves of the experimental rats were subjected to crush injury while the right and left sciatic nerves of the other 4 rats were used as a control.The animals of the ferritin intravenous injection study were divided into the experimental group [4 rats] and the control group [4 rats]. The left sciatic nerves of the experimental rats were subjected to crush injury. After one week, ferritin was injected intravenously through the vein of the rat tail. The control 4 rats were intravenously injected with ferritin without crush injury and used as a control group.The ultrastractural study of the crushed sciatic nerves showed that nerve fibres could be classified into three main categories. These are the regenerating, recovering and degenerating nerve fibres. The regenerating myelinated and recovering nerve fibres were surrounded by endoneurial macrophages, fibroblasts and collagen fibrils. The cytoplasm of the Schwann cells of the recovering nerve fibres contained large fat globules. They also showed increased pinocytotic vesicles in their cytoplasmic membranes and basal laminae. Macrophages sent their processes to be in close contact to the basal laminae of Schwann cells of the regenerating nerve fibres. Most of the regenerating unmyelinated nerve fibres were not surrounded by the endoneurial macrophages. Active mitosis of the Schwann cells was recorded during the first four weeks after the crush injury.Ferritin intravenous injection study showed that after crush injury, ferritin particles did not cross the cytoplasmic membrane of the Schwann cells indicating that fat cells inside them were of endogenous origin.It could be concluded that there are three types of nerve fibres after peripheral nerve crush injury. They are the regenerating, the recovering and degenerating nerve fibres. The presence of macrophages, fibroblasts and collagen bundles around the nerve fibres could be an indication to its viability. Macrophages might play a role in promoting the Schwann cells for myelin formation and possibly for active mitosis. The myelin carried by the endoneurial macrophages is probably the wasted myelin