ΔFosB is induced uniquely by chronic cocaine exposure and persists for several weeks after drug cessation due to the unusual stability of the protein (Nestler, 2008). Increasing evidence supports the view that this induction of ΔFosB increases rewarding responses to, and incentive motivation for, cocaine (Colby et al., 2003; Hiroi et al., 1997; Kelz et al., 1999; McClung and Nestler, 2003; Nestler, 2008). In contrast, CREB activity is induced in response to acute or chronic cocaine administration and serves a homeostatic role by reducing sensitivity to drug reward and mediating negative emotional symptoms during drug withdrawal (Carlezon et al., 2005).
