Effect of mannose, fructose and lactate on the preservation of synaptic potentials in hippocampal slices.

We investigated the effect of fructose, mannose and lactate on the preservation of synaptic transmission in the granule cell layer of guinea pig hippocampal slices during deprivation of glucose. After replacement of glucose with lactate (5 mM) or fructose (10 mM), population spikes (PS) extinguished transiently and thereafter recovered to 60-70% of the original amplitude. Replacement of glucose with mannose (10 mM) decreased the PS amplitude by 50-60% within 20 min. and was followed by recovery to 80% of the original amplitude. The levels of ATP and CrP (creatine phosphate) in fructose, mannose and lactate containing medium were maintained at 80-90% of the original levels. PS of the slices exposed to both glucose and lactate showed a similar pattern to that observed in lactate medium with deprivation of glucose. These results suggest that lactate, mannose and fructose could be metabolic substrates for energy production and are able to preserve the synaptic potentials, however, it takes 20-30 min for the functional replacement of glucose with these sugars or metabolites to occur.