Delayed effects of prenatal low-dose irradiation in the white matter of the rat brain.
OBJECTIVE
This study is part of a general search for the anatomical bases of the severe mental retardation syndrome caused by prenatal irradiation. More specifically, it seeks reasons for the high radiosensitivity of a white matter area, the cingulum of the corpus callosum.


METHODS
Pregnant primiparous Wistar rats were exposed to X-rays at 12, 13, 14 or 15 days of gestation (E12, E13, E14 or E15) with single low doses of 180 mGy. A high dose of 500 mGy was given at E15 for a complementary study. The brains of the female offspring were collected at 1 and 3 months of age. The affinity of osmium tetroxide for the white matter was used to recognize and quantify cingulum areas in a series of coronal sections made at different positions along the antero-posterior axis of the brains.


RESULTS
A 180 mGy dose of X-rays caused an atrophy of the cingulum; the effect was particularly significant in the 1-month-old brains after an exposure at E13 or at E14, and increased in the 3-month-old animals exposed at E15. The axonal size distribution was unchanged in the 3-month-old cingulums treated with 500 mGy at E15.


CONCLUSIONS
The atrophy of the cingulum is due to a loss of axons, which are abundant in this area. As a consequence of axon loss, a reduction of the postnatal myelination enhances the volumetric decrease of the cingulum at 3 months of age.
Reyners
H
H
CEN-SCK, Unit of Radiobiology, Mol, Belgium.
Gianfelici de Reyners
E
E
Yan
J
J
De Saint-Georges
L
L
Desaintes
C
C
D000818:Animals; D001284:Atrophy; D001369:Axons / Q000473:pathology / Q000528:radiation effects; D003337:Corpus Callosum / Q000293:injuries / Q000473:pathology / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005865:Gestational Age; D006801:Humans; D008607:Intellectual Disability / Q000209:etiology / Q000473:pathology; D009186:Myelin Sheath / Q000473:pathology / Q000528:radiation effects; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D011833:Radiation Injuries, Experimental / Q000209:etiology / Q000473:pathology; D011836:Radiation Tolerance; D051381:Rats; D017208:Rats, Wistar; D013577:Syndrome