of adult rodents can be regulated by the levels of circulating glucocorticoids. Since glucocorticoid injections produce similar effects on adult neurogenesis as stress, it is likely that the stress-induced increases in glucocorticoid levels are responsible for the stress-induced decreases in adult neurogenesis. Indeed, inhibitory effects of fox odor exposure on cell proliferation can be blocked by preventing the stress-induced rise in glucocorticoids (Tanapat et al., 2001). It remains unknown, however, whether these effects are mediated directly via actions of adrenal steroids on progenitor cells or whether they occur indirectly through some unknown factor.
