Metabolic and perfusion responses to acute hypoglycemia in the rat cortex: A non-invasive magnetic resonance approach

Hypoglycemia is critical condition during diabetic treatment that involves intensive insulin therapy, and it may impair brain function. We aimed to compare cortical responses of three hypoglycemic phases and the restoration of glycemia to control levels after a severe episode in rats using non-invasive perfusion magnetic resonance (MR) imaging and localized H-1 MR spectroscopy. Under light alpha-chloralose anesthesia, cortical blood flow (cCBF) was 42 +/- 3 ml/100 g/min at euglycemia ( 5 mM plasma glucose), was not altered at mild hypoglycemia I (42 +/- 4 ml/100 g/min, 2-3.5 mM), increased to 60 +/- 8 ml/100 g/min under moderate hypoglycemia II (1-2 mM) and amplified to 190 +/- 35 ml/100 g/min at severe hypoglycemia III (< 1 mM). H-1 MRS revealed metabolic changes at hypoglycemia I without any perfusion alteration. At hypoglycemia III, glutamine and glutamate decreased, whereas aspartate increased. When animals subsequently regained glycemic control, not all metabolites returned to their control levels, for example, glutamine. Meanwhile, ascorbate was increased with amplified hypoglycemic severity, whereas glutathione was reduced; these compounds did not return to normal levels upon the restoration of glycemia. Our study is the first to report cCBF and neurochemical changes in cortex upon five glycemic stages. The cortical responses of different hypoglycemic phases would explain variable neuronal damages after hypoglycemia and might help identify the degrees of hypoglycemic insults and further improve alternative therapies.