Early Differential Neurometabolite Response of Hippocampus on Exposure to Graded dose of Whole Body Radiation: An in Vivo 1H MR Spectroscopy Study

Whole body radiation exposure induced injury may occur during medical or industrial accidents as well as during terrorist radiation exposure scenario. A lot of information is available on alterations in brain function and metabolism post localised cranial irradiation; changes in brain associated with whole body radiation exposure are still limited. The present study has been conducted to assess early differential effect of low and high whole body radiation exposure on hippocampus neurometabolites using in vivo proton magnetic resonance spectroscopy (1H MRS). Hippocampal 1H MRS was carried out in controls (n = 6) and irradiated mice exposed to 3 Gy, 5 Gy, and 8 Gy of radiation (n = 6 in each group) at different time points i.e., day 0, 1, 3, 5 and 10 post irradiation at 7 T MRI system. Quantitative assessment of the neurometabolites was done using LCModel. The results revealed significant decrease in myoionisitol (mI)/creatine (tCr) and taurine (tau)/tCr in animals exposed to 5 Gy and 8 Gy dose compared to controls. In 3 Gy dose group, none of the metabolites showed significant alterations at any of the time point post irradiation as compared to controls. Overall our findings suggest differential change in hippocampal volume regulatory mechanism associated neuro-metabolites following whole body radiation exposure with maximum reduction in case of high dose group. We speculate that these alterations may be a consequence of oxidative stress, neuro inflammation or systemic inflammatory response following whole body radiation exposure.