In Situ Microwave Fixation to Define the Terminal Rodent Brain Metabolome

The brain metabolome directly connects to brain physiology and neuronal function. Brain glucose metabolism is highly heterogeneous among brain regions and continues postmortem. Therefore, challenges remain to capture an accurate snapshot of the physiological brain metabolome in healthy and diseased rodent models. To overcome this barrier, we employ a high-power focused microwave for the simultaneous euthanasia and fixation of mouse brain tissue to preserve metabolite pools prior to surgical removal and dissection of brain regions. We demonstrate exhaustion of glycogen and glucose and increase in lactate production during conventional rapid brain resection prior to preservation by liquid nitrogen that is not observed with microwave fixation. Next, microwave fixation was employed to define the impact of brain glucose metabolism in the mouse model of streptozotocin-induced type 1 diabetes. Using both total pool and isotope tracing analyses, we identified global glucose hypometabolism in multiple regions of the mouse brain, evidenced by reduced 13C enrichment into glycogen, glycolysis, and the TCA cycle. Reduced glucose metabolism correlated with a marked decrease in GLUT2 expression and several metabolic enzymes in unique brain regions. In conclusion, our study supports the incorporation of microwave fixation to study terminal brain metabolism in rodent models.