Experimental Studies On Characters And Mechanisms Of Cogntive Disorder After Brain Irradiation

Objective To identify the regulation of learning and memory ability of rats at various time points after hemispheric irradiation at different dosages; examine the sensitivity of electric stimulation; measure the amount of glutamic acid in extracellular fluid of hippocampus and investigate the possible mechanisms of cognitive disorder after brain irradiation.Methods Hemispheria of female Sprague-Dawly rats were irradiated by single dose of 4 MeV electronic ray at 0, 5, 15 or 30Gy. At each dosage, different time points were chose to do different measurements. Learning and memory ability were measured by Y-maze on day 3, 7, 30 and 90 after irradiation. The sensitivity of electric stimulation of the rats was also examined by Y-maze, but on day 3, 10 and 60 after irradiation. Finally, the amount of glutamic acid in extracellular fluid of hippocampus was measured on day 15 and 90 by microdialysis.Results Compared with controls, the learning ability of female Sprague-Dawly rats was reduced significantly on day 3 and 7 after hemispheric irradiation, and partly restored on day 30 and 60. At dosage of 15Gy and 30Gy, memory ability was reduced significantly but could be restored on day 14. Histologically, rats with 30Gy irradiation showed most significant injury, but with 15Gy dosage, the injury was less. Y-maze results showed that compared with controls, at all doses, the sensitivity of electric stimulation of these rats was impaired significantlyon day 10 and 60 after irradiation. However, at 3day time-point, only at 15Gy and 30Gy doses the electric stimulation sensitivity showed statistically significant difference from controls. Compared with the group of 5Gy dosage, the sensitivity was significant reduced on both day 3 and day 60 at 30Gy group but only on day 3 at 15Gy group. Additionally, at 30Gy group, the sensitivity was reduced significantly on day 3 compared with the rats in 15Gy group. On the other hand, at the doses of 15Gy and 30Gy, the amount of glutamic acid in extracellular fluid of irradiated side of these rats was increased significantly on day 15, compared with both control rats and the contralateral side of irradiated rats. Compared with the irradiation side of 5Gy group, glutamic acid was significantly increased in 30Gy group at day 15.Conclusions The learning and memory ability and the sensitivity of electric stimulation of female Sprague-Dawly rats were injured by hemispheric irradiation. The higher the irradiation dosage, the more severe injury was found. And they could be restored at various time points after irradiation. Importantly, the impairment caused by irradiation may be due to the sensory disorder and/or the changes of amino acid neurotransmitters in extracellular fluid of rat hippocampus, such as glutamic acid.