Biochemical quantification of total brain glycogen concentration in rats under different glycemic states

All ¹³C NMR studies of brain glycogen to date relied on observing the incorporation of ¹³C label into glycogen, and thus interpretation was potentially affected by changes in ¹³C label turnover rates. The goal of this study was to quantify total brain glycogen concentration under conditions of hypoglycemia or normoglycemia using biochemical methods. Rats were sacrificed using a focused microwave fixation device. The results showed that metabolism of brain glycogen was Glc- and insulin-sensitive and that insulin-induced hypoglycemia promoted a gradual glycogenolysis. Moreover, we show that there are very mild effects of isoflurane and α-chloralose anesthesia on brain glycogen concentration. Altogether these results show that total brain glycogen serves as a substantial source of glucosyl units during insulin-induced moderate hypoglycemia and therefore may be neuroprotective. Finally we also conclude that previous interpretation of ¹³C NMR spectroscopy data accurately reflected the changes in total brain glycogen content.