Ultrastructural study of control and acute, whole body gamma-irradiated medulla oblongata tissue

Abstract

Investigations of the ultrastructure in the medulla oblongata of non-irradiated and acute, whole body, gamma-irradiated rats were carried out. There were five groups of animals, one control and four irradiated. The irradiated groups received 1000 R, 2,000 R, 5,000 R and 10,000 R respectively. Fixation techniques were developed and/or expanded from previous techniques. Necropsy tissue fixed in veronal acetate buffered OsO₄ and a perfusion technique utilizing s-collidine buffered glutaraldehyde were employed in each group, so that an inter-fixation reference could be established. Control micrographs revealed an ultrastructural morphology similar to that reported in cerebellar and cerebral studies, with one major exception. In the s-collidine buffered, perfused animals, an unreported structure termed "concentric membrane body" was shown. This entity consisted of a tight packed membranous complex which had an internal periodicity of approximately 50 Å. These structures were often observed to be associated with synaptic membrane complexes. In the irradiated groups, neurological ultrastructural alterations were observed to be in a proportional relationship to irradiation dosage. Cytoplasmic vacuolization, mitochondrial damage, and myelin sheath abnormalities were observed. Even in the lowest dosages, concentric membrane bodies were observed forming membranous swirls, and apparently are indicators of immediate irradiation sensitivity within the tissue. Of particular importance was the observation that in no dosage level was capillary bed damage seen. In the limited views of the blood compartment, as seen in the medullary capillaries, several abnormal cells were noted. These observations indicate that capillary damage is not a major direct result of irradiation, but rather an indirect effect.