Taken in the context of the negative actions of glucocorticoids on adult neurogenesis, these findings are puzzling and raise the question of whether running, enriched environment living, sexual experience and learning have a common characteristic that permits neuronal growth despite a negative hormonal milieu. In this regard, it may be relevant that all of these experiences have a hedonic component. Running, environmental enrichment, and sexual experience are rewarding to rodents. Rats form place preferences for running wheels and mating chambers (Belke & Wagner, 2005; Tenk et al., 2009) and show increased bar pressing to gain access to wheels or receptive females (Everitt et al., 1987; Hundt & Premack, 1963). Rats show anticipatory behavior towards gaining access to an enriched environment (van der Harst et al., 2003). Other types of rewarding experiences can also promote adult neurogenesis, as intercranial self-stimulation will stimulate cell proliferation in the dentate gyrus of adult rats and mice despite elevated glucocorticoid levels (Takahashi et al., 2009). The rewarding nature of these experiences may provide some clues about mechanisms that protect the brain from the negative influences of high levels of glucocorticoids.
