Ceasing exercise induces depression-like, anxiety-like, and impaired cognitive-like behaviours and altered hippocampal gene expression

Background: Regular exercise can reduce depression-, anxiety-, and impaired cognitive-like behaviours, and upregulate hippocampal genes associated with neuroplasticity. However, the effects of ceasing exercise on depression-, anxiety-, and cognitive-like behaviours, and hippocampal gene expression remain unknown. Methods: 12-week-old C57BL/6 mice (n = 12-16/group) were randomised to six months of exercise (exercise (EXC)), four months of exercise then two months of no exercise (exercise-cessation (EC)), or no-exercise control (CONT) until aged nine months. Depression-, anxiety-, and cognitive-like behaviours were tested with the forced swim test, open field and elevated zero maze, Y-maze, and Barnes maze. The expression of 75 hippocampal genes were investigated by high-throughput quantitative polymerase chain reaction (qPCR). Results: Exercise cessation increased depression- and anxiety-like behaviours, and impaired spatial learning and cognitive flexibility compared to CONT and EXC mice. 10/75 hippocampal genes were differentially expressed in EC mice, including increased expression of neurogenesis associated genes (Ntrk1), and reduced expression of immune (Il10, Gfap) and monoamine related genes (Htr1a) compared to CONT mice. Altered expression of nine genes including increased Slc6a4 and reduced Sirt1 expression were shown in EC mice compared to EXC mice. Conclusions: Exercise cessation increased depression- and anxiety-like behaviours and impaired some cognition like behaviours with altered neurogenic, monoaminergic, and immune hippocampal gene expression consistent with the pathogenesis of depression and related anxiety described by the neurogenic, monoaminergic, and immune hypotheses of depression. Mice and humans share mammalian physiology, so these findings could be relevant to humans. These results require replication and possibly translation into high-quality pilot clinical trials.