Exercise improves object recognition memory and induces BDNF expression and cell proliferation in cognitively enriched rats

Exercise and environmental enrichment are behavioural interventions that have been shown to improve learning and increase neurogenesis in rodents, possibly via neurotrophin-mediated mechanisms. However, many enrichment protocols incorporate exercise, which can itself be viewed as a source of cognitive stimulation in animals housed in standard laboratory conditions. In this experiment we investigate the effect of each intervention separately and in combination on object recognition memory, and analyse associated changes in the dentate gyrus: specifically, in BDNF expression and cell division. We show that both exercise and enrichment improve object recognition memory, but that BDNF mRNA expression and cell proliferation in the dentate gyrus of the hippocampus increase only in exercised rats. These results are in general agreement with recent studies suggesting that the exercise component is the major neurogenic and neurotrophic stimulus in environmental enrichment protocols. We add to the expanding literature several novel aspects including the finding that enrichment in the absence of exercise can improve object recognition memory, probably via mechanisms that are independent of BDNF upregulation and neurogenesis in the dentate gyrus.

► One week of forced moderate exercise and three weeks of environmental enrichment improve object recognition memory in adult rats.
► Exercise and environmental enrichment have an additive effect on task performance in a novel object recognition test.
► Exercise, but not enrichment, increases the number of dividing cells in the dentate gyrus of the hippocampus of adult rats.
► Exercise, but not enrichment, increases brain-derived neurotrophic factor mRNA in the dentate gyrus of adult rats.