Histology of the irradiated rat brain in the first post-irradiation year.

The histology of the brains of rats killed were studied, following various doses of 250 kV X rays. The majority of rats which were killed before 200 days showed no damage to the mid-brain and cerebral hemispheres. However, the trigeminal and facial nerves exhibited necrosis, the origin of which was probably in the central nervous tissue of the transitional region between central and peripheral nerve systems. The result of these lesions was atrophy of the masticatory muscles and a consequent difficulty in feeding. Rats surviving beyond 200 days post-irradiation exhibited focal necrosis within central white matter regions which resembled, both in form and location, those described in previous reports for rats.