37. Histogenesis of Heterotopic Gray Matter in the Brain of the Mouse Prenatal Exposed to X-Ray Irradiation

Xue-Zhi Sun, Sentaro Takahashi, Yoshihisa Kubota, Hiroshi Sato, Chun Cui*, Rui Zhang* and Yoshihiro Fukui*
(*Univ. of Tokushima, School of Medicine)

Keywords: cerebral cortex, pregnancy, X-rays

Histogenesis of heterotopic gray matter in the brain of the mouse prenatally exposed to X-ray irradiation at embryonic day 13 (E13) was studied immunohistochemically. Bromodeoxyuridine (BrdU) as a marker to label the migrating position of neuroblasts generated at various embryonic stages showed that no "inside-out" pattern of neuronal migration occurred in the heterotopic cell mass similar to that seen in the laminated cortex. Further results in which midkind (MK) immunoreactive radial glial fibers did not appear in the heterotopic cell mass demonstrated that heterotopia formed in the absence of radial glia system. Different types of cells (pyramidal and nonpyramidal neurons) in the heterotopic cell mass were identified with immunoreactivity for anti-parvalbumin and anti-calbindin D-28K antibodies in addition to current histological methods. Two major types of neurons were mixed together with random distribution in the heterotopic cell mass. This finding indicates that irradiation might have no selective effects on the precursors of pyramidal and nonpyramidal neurons. Moreover, anti-glial fibrillary acidic protein (GFAP) immunostaining showed that numerous astrocytes were present in the heterotopic cell mass. The fact that astrocytes appeared in the heterotopia without the transition from classic radial glial cells to astrocytes suggests that astrocytes might be generated directly from a separate astroglial precursor.