Formation of oedema in transected rat sciatic nerve. A microgravimetric study.

The formation of oedema in peripheral nerves was studied in rats at intervals varying from 6 h to 14 days after transection of the right sciatic nerve. Samples were removed proximal and distal to the injury, and the degree of oedema was determined by a microgravimetric method and by measurements of the water content and of the fascicular area. Distal to the lesion, decreased density values indicating the presence of oedema were observed in samples examined after a survival period of 6 h-14 days. The water content and fascicular area were both increased in samples taken 24 h after injury. Fourteen days postinjury the water content had increased further. Proximal to the lesion, the water content and the fascicular area were increased in samples examined after a survival period of 24 h. Fourteen days after the injury, the increase in water content was even more pronounced. No changes were detected with the microgravimetric technique 6 and 24 h after the injury. Unexpectedly, animals surviving 14 days showed increased density values. The microgravimetric technique used is a valuable adjunctive method for quantitation of peripheral nerve oedema in the acute phase after a traumatic nerve injury. Later on, loss of axons and of myelin components, together with regenerative phenomena, influence the density values obtained. Quantitative methods for studying chronic peripheral nerve oedema should, therefore, be supplemented with other techniques.