The changes of extra-cellular amino acid neurotransmitter content in rat hippocampus after whole brain irradiation

Objective: To investigate the change in content of amino acid neurotransmitters in hippocampus of the irradiated rat brain, its relationship with radiation dose and the time course. Methods: The whole brain of SD rats was irradiated with single dose of 5, 15 or 30 Gy by 4 MeV electrons. The extra-cellular fluid in rat hippocampus was extracted by microdialysis in vivo, in which the contents of glutamic acid (Glu), aspartic acid (Asp). γ-aminobutyric acid (GABA), and glycine (Gly) were measured by high performance liquid chromatography, and the data were analyzed by the Student's test. Results: The contents of amino acid neurotransmitters in un-irradiated and anaesthetized control rats were: Glu, 289-317 μmol/L; Asp, 47-54 μmol/L; GABA, 85-113 μmol/L and Gly, 185-203 μmol/L. By comparison to the control group ,the contents of Glu and Asp increased significantly at one week and one month after 30 Gy irradiation, and one month after 15 Gy irradiation. But there were no obvious differences in amino acid concentration in all other groups. Conclusion: The increase of Glu and Asp in the hippocampus of hight dose-irradiated rat brain suggests a possible association between the excitatory amino acid neurotransmitter hypothesis and the pathogenic process of radiation-injured brain. (author)