AMINO-ACIDS AND AMMONIA IN THE CEREBRAL-CORTEX, THE CORPUS STRIATUM AND THE BRAIN-STEM OF THE MOUSE PRIOR TO THE ONSET AND AFTER A SEIZURE-INDUCED BY HYPERBARIC-OXYGEN

The contents of amino acids (AA) and ammonia (NH3) were measured in co rpus striatum, brain stem and cerebral cortex of two strains of mice e xposed to hyperbaric oxygen (HBO). Mice of the HBO-sensitive strain (C D1) were exposed to 600 kPa O-2 for 24 min versus 90 min for mice of t he normal C57 strain, so that 50% of the mice in both strains develope d a generalized convulsion, In the cortex of exposed but unconvulsed ( EXUN) C57 mice, the contents of taurine, glutamine and NH3 increased w hile that of GABA decreased when compared to control mice. In the CD1 mice, NH3 content was increased while that of Asp decreased. After a c onvulsion, NH3 was increased in both strains, the AA contents returned to normal in C57 but Asp remained low in CD1 mice. Somewhat similar c hanges occurred in the striatum except that NH3 levels were less affec ted while GABA ones were significantly decreased in the CD1 mice expos ed to HBO, whether convulsed or not. In the EXUN brain stem, Asp and G lu contents decreased. These decreases were greater in C57 on a percen tage basis than in CD1 mice. GABA content was decreased in the C57 str ain. After a convulsion, Asp and Glu levels remained low and NH3 accum ulated in CD1 whereas in C57 only the Glu level was decreased. The cor tical and striatal changes may indicate a lesser GABA supply in C57 st rain and some Asp release in CD1 strain. In the brain stem of both str ains, Asp and Glu release is possible in addition to GABA in C57 strai n. These data suggest that the excitatory AA, especially Asp, were mor e involved in the hyperoxic convulsion in the HBO-susceptible CD1 than is GABA. The greatest changes in CD1 as compared to C57 may be due to the faster production of brain lipid peroxides in the former strain.