In situ microwave fixation provides an instantaneous snapshot of the brain metabolome

Brain glucose metabolism is highly heterogeneous among brain regions and continues postmortem. In particular, we demonstrate exhaustion of glycogen and glucose and an increase in lactate production during conventional rapid brain resection and preservation by liquid nitrogen. In contrast, we show that these postmortem changes are not observed with simultaneous animal sacrifice and in situ fixation with focused, high-power microwave. We further employ microwave fixation to define 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 brain regions, evidenced by reduced 13C enrichment into glycogen, glycolysis, and the tricarboxylic acid (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 for more accurate studies of brain metabolism in rodent models. [Display omitted] •Direct in situ fixation of rodent brain by high-powered, focused microwave•Microwave fixation preserves glycogen and glycolytic metabolites•Glucose hypometabolism demonstrated type 1 diabetes mellitus mouse model brains•Decreased enzyme levels observed in the same T1DM mouse model Brain metabolism directly connects to brain physiology and neuronal function, but challenges remain to capturing an accurate snapshot of the physiological brain metabolome in healthy and diseased rodent models. One challenge is that brain metabolism does not cease at the moment of animal sacrifice, and in conventional protocols, there is typically a delay between animal sacrifice and surgical isolation of the tissue for snap freezing and/or fixation, during which time postmortem conditions such as hypoxia may start to influence the pools of metabolites in the sample. To overcome this barrier, we employed high-power, focused microwave for the simultaneous euthanasia and fixation of mouse brain tissue in situ to preserve metabolite pools prior to surgical removal and dissection of brain regions. Juras et al. demonstrate the use of a high-power, focused microwave for the simultaneous euthanasia and fixation of mouse brain to preserve metabolite pools prior to surgical dissection and metabolomic studies. They apply this approach to characterize brain glucose metabolism in a mouse model of type 1 diabetes mellitus.