Sensitivity of guinea‐pig hippocampal granule cell field potentials to hexoses in vitro: an effect on cell excitability?

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Abstract
Evoked granule cell field potentials and levels of tissue metabolites in superfused guinea-pig hippocampal slices were studied in the presence of low glucose and an alternative glycolytic substrate (D-fructose). The effects of glucose analogs (5-thio-D-glucose, 2-deoxy-D-glucose or 3-O-methyl-D-glucose) in the presence of glucose were also tested. Concentrations of glucose or fructose in excess of 2 mM and 10 mM, respectively, were required to maintain normal evoked activity. 5-Thioglucose (15 mM) in the presence of 5 mM-glucose decreased the amplitude of the population spike by 60% with little effect on population excitatory postsynaptic potential (EPSP). Tissue levels of phosphocreatine and ATP were essentially unchanged under all conditions tested, with the exception of 10 mM-fructose. The decrease in rates of lactate efflux from superfused tissue during and after superfusion with 3-O-methylglucose, 2-deoxyglucose or 5-thioglucose was positively correlated with the extent of attenuation of field potentials. Analysis of the relationship between population spike amplitude and rates of rise of EPSP, under conditions where field potentials were attenuated, showed that the population spike was always more sensitive to metabolic perturbation than was the EPSP, thus indicating an effect on cell excitability. Some aspect of non-oxidative glucose metabolism is apparently important in maintaining this granule cell excitability.