Ultrastructural changes in the cerebellum of experimental hypothyroidism (cretinism)

: We examined the cerebellum of the rats being the experimental hypothyroidism (cretinism) on the 20th day, 35th day and 60th day by the light and electron microscope. The remarkable findings were observed to the experimental group on the 20th day. The maturational states of this group correspond to that of the 16th day of the control group. On the other hand, the remarkable pathological findings were not observed on the 35th and 60th day of the experimental group. According to the findings of the experimental rats on the 20th day, the changes of the cells were the retention of the external granule cells and the maturational changes of the internal granule cells. We recognized the retardation of the maturational timing and a disagreement of the maturational rate of the internal granule cells. The lamellar bodies being the disturbance of the mitochondrial cristae were observed. About the white matter, the myelinated nerve fibers were a small quantity in number, and the deficiency of the myelin synthesis, the maturational disturbance of oligoglia were seen. In the several axons, the lamellar bodies and the honeycomb like structures were seen. It is concluded that the maturational disturbance of the internal granule cells are due to the disturbance of the secondary protein synthesis by the hypothyroid state and the degeneration of the mitocondria. The deficiency of the myelin synthesis is related to the maturational disturbance of oligoglia.