(Stevenson et al. 2009). Similarly stress induced IL-1β reduces neurogenesis causing depression like behavior (Koo and Duman 2008). Thus, neurogenesis reflects mood, with reduced neurogenesis associated with innate immune gene induction, drug induced negative affect and depression-like behavior. Interestingly, recovery from alcoholism is associated with improved mood and cognition, human brain enlargement and increased neurogenesis (Crews and Nixon 2009). Overall findings suggest adult hippocampal stem cells and neurogenesis provide an index of mood and negative affect that allow molecular studies on regulation of mood, both negative and positive (Crews and Nixon 2003; Koo et al. 2011) (Fig.4). These findings are consistent with drug induced depression sharing common mechanisms with endogenous depression as well as the negative affect of substance use disorder, e. g. addiction.
