Effects of fructose-1,6-bisphosphate on morphological and functional neuronal integrity in rat hippocampal slices during energy deprivation

Abstract

d-Fructose-1,6-bisphosphate, a high energy glycolytic intermediate, attenuates ischemic damage in a variety of tissues, including brain. To determine whether d-fructose-1,6-bisphosphate serves as an alternate energy substrate in the CNS, rat hippocampal slices were treated with d-fructose-1,6-bisphosphate during glucose deprivation. Unlike pyruvate, an endproduct of glycolysis, 10 mM d-fructose-1,6-bisphosphate did not preserve synaptic transmission or morphological integrity of CA1 pyramidal neurons during glucose deprivation. Moreover, during glucose deprivation, 10-mM d-fructose-1,6-bisphosphate failed to maintain adenosine triphosphate levels in slices. d-Fructose-1,6-bisphosphate, however, attenuated acute neuronal degeneration produced by 200 μM iodoacetate, an inhibitor of glycolysis downstream of d-fructose-1,6-bisphosphate. Because (5 S, 10 R)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine, an antagonist of N-methyl- d-aspartate receptors, exhibited similar protection against iodoacetate damage, we examined whether (5 S, 10 R)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine and d-fructose-1,6-bisphosphate share a common neuroprotective mechanism. Indeed, d-fructose-1,6-bisphosphate diminished N-methyl- d-aspartate receptor-mediated synaptic responses and partially attenuated neuronal degeneration induced by 100-μM N-methyl- d-aspartate. Taken together, these results indicate that d-fructose-1,6-bisphosphate is unlikely to serve as an energy substrate in the hippocampus, and that neuroprotective effects of d-fructose-1,6-bisphosphate are mediated by mechanisms other than anaerobic energy supply.