Administration of x-rays (4000 I) to lumbar spinal cords of three-dayold rats caused a loss of neuroglia with an inhibition of myelinogenesis, neuronal damage and necrosis. In contrast, the loss of neuroglia following administration of 2000 r is temporary, with myelinogenesis occurring later than normal. Preliminary observations suggested that differences in vascular responses to these two amounts of x-rays might account for these differing fates of the spinal cords; therefore, this investigation was designed to study further the reactions of the intramedullary vessels.Rats, irradiated when three days of age, were killed 1 to 27 days later. Some were killed by perfusion with Monolite Fast Blue BNVSA Paste, a substance retained in the vessels and readily visualized on microscopic examination. The remaining rats were decapitated, and spinal cords were stained by Gomori's method for alkaline phosphatase. The earliest consistent alteration, a decreased number of vessels, was noted seven days following irradiation with either dose. Rats receiving 4000 r had marked losses of blood vessels, vasodilatation and necrosis by 15 days post-irradiation; whereas, a decreased number of vessels was the only change noted in rats irradiated with 2000 I. Alterations in rats receiving 4000 r remained the same or became more severe throughout the study; spinal cords in rats receiving 2000 r returned to normal. These vascular alterations correlate well with the changes in other spinal cord components described previously by this investigator.Ionizing radiation affects the immature spinal cord in a manner that is dose dependent (Gilmore, '63b, '65, '66; Rodgers, '65). When 2000 r or 4000 r of soft x-rays are administered to a 5 mm length of spinal cord in three-day-old rats, there is a loss of neuroglia within two days following irradiation and a consequent state of hypo-or a-myelination (Gilmore, '63b, '66; Rodgers, '65). These changes are found in all animals of both groups during the first eleven days following irradiation. After this time, however, the status of the irradiated areas is markedly different in the two groups. In the animals receiving 2000 r the neuroglia are restored, and delayed myelinogenesis takes place, so that by one month following irradiation, the spinal cords appear to be normal (Gilmore, '66). In contrast, when 4000 r of x-rays are administered the changes are quite different in that necrosis develops in many spinal cords by three weeks post-irradiation (Gilmore and Arrington, '67). Preliminary observations of vascular alterations in a few rats studied by Gilmore and Arrington ('67) showed that hemorrhages and vasodilatation begin to appear approximately two ANAT. REC., 163: 89-100.weeks following irradiation. These findings suggest that the vasculature can influence the manner in which the spinal cord reponds after exposure to ionizing radiation and these differing alterations in spinal cord parenchyma may reflect differences in the type and severity of vascular changes. It would seem reasonable to ...
