ULTRASTRUCTURAL-CHANGES IN THE RAT SCIATIC-NERVE AFTER LOCAL HYPERTHERMIA

The rat sciatic nerve was heated over a length of 5 mm for 30 min at 43, 44 or 45-degrees-C. Morphological changes were not observed after heating at 43-degrees-C. Treatment at 44-degrees-C resulted in endoneurial oedema and mild vascular changes, such as contraction and vacuolization of endothelial cells and thickening of the media of the larger vessels. Within 1 week several demyelinated axons were observed. The first changes after heating at 45-degrees-C included oedema, blood vessel occlusion and severe endothelial cell damage. Axonal changes, e.g. the accumulation of cell organelles, appeared 8 h after treatment; 24 h after treatment most axons and myelin sheaths showed degenerative changes. Absence of blood flow in the heated area of the nerve was shown 2 h after heating at 45-degrees-C. We conclude that hyperthermic treatment directly affects endothelial cells and myelin sheaths in the rat sciatic nerve. Axons degenerate most probably as a consequence of ischaemia.