Topography of basal glucose utilization in the hippocampus determined with [1- 14C]glucose and [6- 14C]glucose

Abstract

The activity of the pentose phosphate shunt was assessed under basal conditions in subregions of the hippocampus by measuring the uptake and retention of [1- 14C]glucose and [6- 14C]glucose and their 14C-labelled metabolites. The relative and absolute retention of carbon-14 from each of the two compounds was nearly identical in all regions examined. For each compound, the highest accumulation of 14C occurred in the granule cell layer of the dentate gyrus and in the pyramidal cell layer. Relatively high retention of radioactivity was also found in the molecular layer of dentate gyrus and in the stratum lacunosum-moleculare. The stratum radiatum and stratum oriens contained the lowest levels of radioactivity among hippocampal regions. The equal retention of radioactivity from [1- 14C]glucose and [6- 14C]glucose implies that pentose phosphate shunt activity is very low throughout the hippocampus under the conditions of this study. The uptake and retention of radioactivity was evaluated in different hippocampal regions 10 or 30 min following intravenous injection of [1- 14C]glucose. Although there was significantly more radioactivity at 30 min than at 10 min, the same topographic pattern of radioactivity within the hippocampus was observed in rats after both survival periods, indicating that an equal fraction of the [1- 14C]glucose utilized in different hippocampal regions is oxidized to 14CO 2 under these conditions. Most regions of high glucose utilization in the hippocampus determined with [1- 14C]glucose and [6- 14C]glucose correspond to regions of intense histochemical staining for cytochrome oxidase reported in the literature. In regions that exhibit low cytochrome oxidase activity and high [1- 14C]glucose utilization, high nicotinamide adenine dinucleotide phosphate-diaphorase activity is present and high amino acid uptake occurs. These observations suggest that measurement of the uptake and retention of radioactivity from [1- 14C]glucose and [6- 14C]glucose provides an index of glucose utilized for biosynthetic mechanisms as well as for energy transducing processes.