X-irradiation exencephaly.

Abstract

Exencephaly, a major congenital anomaly among mammalian fetuses, may be produced by genetic factors after thc first generation or by direct exposure of the developing embryos at certain critical stages to a variety of substances or to ionizing radiation. The mechanism, when genetically induced, is no doubt through interference with gastrulation by unbalanced chromosomal complexes, and in the embryo by direct irradiation, due to the high radiosensitivity of the transient neuroblasts. Roertgen irradiation of the embryo produces a phenocopy of the genetrically produced exencephaly. The period of greatest radiosensitivity with respect to this cerebral congenital anomaly corresponds to 16 to l8 days for the human embryo. Original data and summaries from the literature are presented from a series of studies on the effects of roentgen irradiation on the mature spermatozoa in mices the effects of irradiation on the developing mouse embryos genetic effects relating to central nervous system anomaliess the effects of exposure to ionizing radiations on the adult central nervous system, the effects of ionizing radiations on the human embryonic central nervous system, and production of animal central nervous system teratologies by both chemical means and radiation exposure. Speculations are included as to the causative factors involved in exencephaly.more » 143 references. (C.H.)« less