Dietary restriction inhibits spatial learning ability and hippocampal cell proliferation in rats

We investigated the effect of dietary restriction on spatial learning ability and hippocampal cell proliferation in adult rats using two spatial learning tasks and immunohistochemical staining with 5-bromo-2'-deoxyuridine (BrdU). Sixteen rats were divided into restricted or ad lib feeding groups at 70 days of age, and were trained in the delayed-matching-to-place (DMTP) task (a working memory task) from 93 days of age, and then the Morris water maze task (a reference memory task). Dietary restriction had no effect on the DMTP task with 30 s delay and on the water maze task. However, in the DMTP task with 30 min delay, restricted rats performed significantly more poorly than ad lib rats. Quantitative analysis of hippocampal cell proliferation revealed that the density of newborn cells in restricted rats was significantly lower than that in ad lib rats. These results suggest that a loss of proliferating capacity in the hippocampus may be a candidate for an anatomical and biological basis for the cognitive decline caused by dietary restriction.