Hippocampal neuron and synaptophysin-positive bouton number in aging C57BL/6 mice

A loss of hippocampal neurons and synapses had been considered a hallmark o f normal aging and, furthermore, to br: a substrate of age-related learning and memory deficits. Recent stereological studies in humans have shown tha t only a relatively minor neuron loss occurs with aging and that this loss is restricted to specific brain regions, including hippocampal subregions. Here, we investigate these age-related changes in C57BL/6J mice, one of thr must commonly used laboratory mouse strains. Twenty-five mice (groups at 2 , 14, and 28-31 months of age) were assessed for Morris water-maze performa nce, and modern stereological techniques were used to estimate total neuron and synaptophysin-positive bouton number in hippocampal subregions at the light microscopic level. Results revealed that performance in the water maz e was largely maintained with aging. No age-related decline was observed in number of dentate gyrus granule cells or CAI pyramidal cells. In addition, no age-related change in number of synaptophysin-positive boutons was obse rved in the molecular layer of the dentate gyrus or CAI region of hippocamp us. We observed a significant correlation between dentate gyrus synaptophys in-positive bouton number and water-maze performance. These results demonst rate that C57BL/6J mice do not exhibit major age-related deficits in spatia l learning or hippocampal structure, providing a baseline for further study of mouse brain aging. (C) 1999 Elsevier Science Inc.