Gamma-Aminobutyric Acid Metabolism and Radiation-Induced Seizures
ARMED FORCES RADIOBIOLOGY RESEARCH INST BETHESDA MD
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Miniature swine convulsed spontaneously within 30 seconds after a 10, 000-rad dose of 30 MeV electrons was delivered to the brain. The seizures ended 2 to 5 minutes later. Since alterations in gamma-aminobutyric acid GABA metabolism occur in and may be an underlying cause of a variety of convulsive disorders, regional brain concentrations of GABA and activities of L-glutamic acid decarboxylase E.C.126.96.36.199 GAD were determined in control and irradiated miniature swine. The hypothalamus and midbrain had the highest GABA concentration and GAD activity, followed, in decreasing order of GABA concentration, by the caudate nucleus, thalamus, hippocampus, cerebral cortex and cerebellum. At four minutes after irradiation, GABA concentrations did not change significantly in any brain region examined the largest apparent change was a decline from 2.31 plus or minus .13 to 2.04 plus or minus .11 micromoles g wet weight in the thalamus. Concurrently, GAD activity in the thalamus increased significantly from 238 plus or minus 7 to 315 plus or minus 29 micromolesh per g protein.