Anxiolytic Actions of Exercise in Absence of New Neurons.

Physical exercise reduces anxiety-like behavior in adult mice. The specific mechanisms that mediate this anxiolytic effect are unclear, but adult neurogenesis in the dentate gyrus has been implicated because it is robustly increased by running and has been linked to anxiodepressive-like behavior. We therefore tested the effects of long-term wheel running on anxiety-like behavior in GFAP-TK (TK) mice, a transgenic strain with complete ablation of adult neurogenesis. Five weeks of running reduced anxiety-like behavior equally in both TK mice and wild type (WT) control mice on two tests, elevated plus-maze and novelty-suppressed feeding. WT and TK mice also had similar patterns of c-fos expression in the hippocampus following anxiety testing. Following testing on the elevated plus-maze, running reduced c-fos expression in the dorsal dentate gyrus and CA3 in both WT and TK mice. Following testing on novelty-suppressed feeding, running reduced c-fos expression throughout the dentate gyrus and CA3 in both WT and TK mice. Interestingly, following testing on a less anxiogenic version of novelty-suppressed feeding, running reduced c-fos expression only in the dorsal dentate gyrus in both WT and TK mice, supporting earlier suggestions that the dorsal hippocampus is less involved in emotional behavior than the ventral region. These results suggest that although running increases adult neurogenesis, new neurons are not involved in the decreased anxiety-like behavior or hippocampal activation produced by running.