BDNF-stimulated intracellular signalling mechanisms underlie exercise-induced improvement in spatial memory in the male Wistar rat.

Exercise-induced improvements in learning are associated with neurotrophic and neurogenic changes in the dentate gyrus, but the intracellular signalling mechanisms that may mediate these improvements remain unknown. In the current study we investigate the effects of one week of forced exercise on spatial memory and analyse in parallel BDNF-stimulated signalling pathways in cells of the dentate gyrus. Additionally, we test whether a single intracerebroventricular (i.c.v.) injection of BDNF can mimic the observed cognitive and signalling changes. Male Wistar rats were assigned to exercised and sedentary groups and tested in a spatial task post-exercise. Tissue from the dentate gyrus was assessed for expression and release of BDNF, and for changes in expression and activation of TrkB, ERK and synapsin-1. In a separate set of experiments, male Wistar rats received a single i.c.v. injection of BDNF and were then tested in the same spatial learning task. Exercised and BDNF-treated (but not control) rats could successfully complete an object displacement task that tests spatial learning. Exercised rats and BDNF-treated rats displayed increases BDNF expression and ERK1 activation, while exercised rats showed increases in cell division, stimulated BDNF release, TrkB activation, and synapsin-1 expression in the dentate gyrus. We conclude that exercise-induced increases in BDNF in the dentate gyrus are sufficient to cause improvements in spatial memory by activating signalling cascades that enhance synaptic transmission in the hippocampus.