Subacute combined degeneration in totally gastrectomized rats: an ultrastructural study.

Severe permanent cobalamin (Cbl) deficiency was induced in rats either by total gastrectomy (TG) or through prolonged dietary Cbl deprivation. This paper deals with an ultrastructural investigation of different parts of the central nervous system (CNS) of rats made Cbl-deficient through one of these of two procedures. In both totally gastrectomized (TGX) rats and in rats chronically fed a Cbl-deficient diet, we observed intramyelin edema, with splitting of the lamellae, and interstitial edema affecting the white matter, mainly in the spinal cord (SC). These lesions were also present in the subcortical white matter, although to a lesser degree. In both TGX-rats and in rats chronically fed a Cbl-deficient diet the pyramidal tract and the optic nerve were completely spared. Vascular lesions were never observed. Intramyelin edema and interstitial edema of the white matter account for the patchy myelopathic spongy vacuolation, which is the histological hallmark of human subacute combined degeneration and has been previously seen in SC white matter of TGX-rats. Macro- and micro-glial cells in the white matter were activated, at least as seen ultrastructurally. Interestingly enough, there were activated glial cells even in the gray matter, in which neurons showed absolutely no alterations. Chronic subcutaneous Cbl administration of TGX-rats partially repaired the CNS damage. However, the amelioration produced by this treatment was greater when Cbl was given shortly after TG than when given three and four months after TG, i.e. when the lesions have already been formed.