Rewarding social experiences are associated with the release of factors that may serve to protect against elevated glucocorticoids and actually promote neuronal growth. Among these are neuropeptides, such as endogenous opioids and oxytocin and the neuromodulator dopamine. Some evidence suggests that each of these factors is capable of stimulating the production of new neurons in the hippocampus (Morton et al., 2009; Höglinger et al., 2004; Winner et al., 2009; Lloyd et al., 2010; Koehl et al., 2008; Persson et al., 2003). It is also possible that neurotrophic factors play a role in buffering the brain from the suppressive actions of elevated glucocorticoids. For example, brain-derived neurotrophic factor (BDNF) is increased following running (Ying et al., 2005). BDNF is a factor in survival of new neurons (Sairanen et al., 2005), and blocking BDNF decreases differentiation of new neurons in the adult mouse dentate gyrus (Taliaz et al., 2010). BDNF is required for enriched environment-induced increases in cell proliferation in adult mice (Rossi et al., 2006). Vascular endothelial growth factor (VEGF) administration also increases cell proliferation in the dentate gyrus of the
