2 TYPES OF CONGENITAL HYDROCEPHALUS INDUCED IN RATS BY X-IRRADIATION INUTERO - ELECTRON-MICROSCOPIC STUDY ON THE TELENCEPHALIC WALL

Abstract

Stage-specific incidences of congenital hydrocephalus induced by X-irradiation of pregnant rats showed a bimodal distribution. At a dose level of 200 R, 100% hydrocephalic offspring were obtained at embryonic days 11 and 14. When pregnant rats were subjected to 200 R X-irradiation at embryonic day 11, numerous ventricular cells of the telencephalic wall of the embryo became necrotic during the 1st 2 h post-irradiation, but the paraventricular cell-to-cell interconnections made up of zonulae adherents were less affected. Mitosis occurred in the surviving paraventricular surface cells throughout subsequent development. The full-term fetus exhibited little change in the cytoarchitectural arrangement of neural cells and neuropils, though it was only about 1/2 the thickness of the untreated control. After 200 R X-irradiation at embryonic day 14, most of the ventricular cells became necrotic within 6 h. The paraventricular cell-to-cell interconnections were completely destroyed and never repaired in subsequent development. Mitosis took place either freely in cell clusters, or in rosettes which formed randomly in the telencephalic wall between 48 and 72 h post-irradiation. The resulting telencephalic wall of the full-term fetus was also about 1/2 the thickness of the control. In the outer part of the tissue, the cortical plate made up of differentiating neuroblasts was hypoplastic, but the inner half was filled with numerous heterotopic masses of pleomorphic cells and bundles of primitive axons. The ependymal layer at the paraventricular surface was never formed. Whether the paraventricular zonulae adherents were destroyed or not by X-irradiation was considered an important factor determining the subsequent cytoarchitectural organization of the telencephalic wall.