Light and Electron Microscopic Observations of Pia-Arachnoid in N-Methyl-Nitrosourea-Induced Dysgenetic Hydromicrocephalic Rat Offsprings

Abstract

Pregnant rats were treated with N-methylnitrosourea (MNU), and dysgenetic hydromicrocephalic offsprings was morphologically examined at the ages of 1, 3, 12 and 27 weeks. The changes of the pia-arachnoid became more severe with advanced age, and partial destruction of the arachnoideal trabeculae was observed at 1 week of age. At 27 weeks remarkable dilation of the subarachnoid space with extremely thin arachnoid was characteristic. In the subpial parenchyma spongy degeneration accompanied with slight infiltration of mononuclear cells was seen. Ultrastructurally, the arachnoideal cells were polyhedral showing irregular interdigitation with each other at 3 weeks of age. Most of the cells had scanty chromatin in the nuclei and a large number of swollen or condensed mitochnodria, vesiculated or aqueous humor-containing rough endoplasmic reticulum (RER) and increased microfilaments in the cytoplasm. At 12 weeks, the arachnoid was extremely thin, showing short tubular RER, condensed mitochondria and some altered subcellular organelles in the cytoplasm. Changes of the pia mater and subpial parenchyma was prominent with advanced age. At 12 weeks, irregularly arranged pial cells processed marginated or decreased nuclear chromatin, condensed mitochondria and altered RER. In the subpial parenchyma the remarkable concavo-convex appearance of the basal lamina and may swollen astrocytic processes with a few macrophages were observed. From the results, it was considered that dysfunction of the arachnoid may be closely associated with pathogenesis of the MNU-induced hydrocephalus.