Fibrillary accumulations in oligodendroglial processes of rats subjected to portocaval anastomosis

After portocaval anastomosis in rats ultrastructural changes have been observed in the inner and outer cytoplasmic tongues of the myelin sheaths and also in the paranodal cytoplasmic loops. Principally, these consist of aggregates of fibrils (4–5 nm wide) in various stages of orderly packing. Additionally, closely-packed hexagonal arrays of tubular structures (20 nm wide) were occasionally found, as well as banded and coiled arrangements. Certain minor abnormalities may be found in the large neurones of the dentate nucleus. These findings are in general conformity with the hypothesis that a disturbance to microtubular metabolism in the brain occurs in association with high plasma ammonium levels, probably due to reduction in size of the glutamate and aspartate pools in glial cells.