Distribution of sodium and potassium channels as well as myelin associated glycoprotein (MAG) during the early stages of Wallerian degeneration.

The distribution of sodium and potassium channel proteins and the myelin associated glycoprotein (MAG) was studied by immunofluorescence during the early stages of Wallerian degeneration. Routine electron microscopy was also performed in order to investigate the success of the lesion in producing degeneration and also to evaluate the integrity of the axolemma and cytoskeleton. Sural nerves from Sprague-Dawley rats were submitted to surgical crush and analyzed after 30, 36 and 48 h. The preparations were observed by light microscopy and the amount of labeled and unlabeled sites was quantified using a computer linked microscope. The number of sodium and potassium labeled nodes was dramatically reduced 30 h after crushing. However, a small number of labeled nodes was still present even after 48 h. These remaining nodal channel proteins are probably responsible for the maintenance of the nerve's electrical activity during the first 4 days of Wallerian degeneration. Ultrastructural analyses of longitudinal sections revealed areas of intact axolemma in the presence of a partially or completely disrupted cytoskeleton. These results are in disagreement with the generally accepted view that axolemma and cytoskeleton disruption occur simultaneously in the peripheral nervous system. Our results also concern the mechanism underlying the disappearance of these channel proteins during the degeneration of the peripheral nerve fibres, since in this pathology the axons are affected before myelin and Schwann cells become affected.