2000 年 77 巻 5 号 p. 181-188
The effects of prenatal X-irradiation on hypoglossal (XII) nucleus were investigated in the rat. Pregnant animals were exposed to a single whole body X-irradiation on day 11 and 16 of gestation at a does of 1.3 Gy. The offspring were killed at 7-14 days of age for the histological and immunohistochemical observations. Nissl staining revealed no significant changes of XII motoneurons in these experimental animals. In the control case it was of interest that expression of glial fibrillary acidic protein-immunoreactivity (GFAP-IR) is largely confined to the dorsomedial region including the XII nucleus at the level caudal to the obex. Exposure of X-irradiation on day 16 of gestation led to similar expression of GFAP-IR in the nucleus at the same level. However, exposure on day 11 of gestation apparently led to strong expression of GFAP-IR in the XII nucleus at the level caudal to the obex and the expression was observed to extend rostrally. The GFAP-IR cells showed hypertrophy of cell bodies and longer cytoplasmic processes. Horseradish peroxidase (HRP) injection into the tip of the tongue including the intrinsic muscles resulted in retrograde labeling in the ventromedial portion of the XII nucleus bilaterally from +0.30 to -1.25 mm. The present study would indicate that motoneurons of the XII nucleus supplying mainly the intrinsic and partly the extrinsic tongue muscles are more sensitive to X-ray exposure before the formation of the XII nucleus.
