Effects of prenatal cocaine exposure on zif 268 (A) and homer 1 expression (B) in the striatum at different ages. Mean density values (mean±SEM, arbitrary units) measured across the total striatum at the middle level are shown for mice that received a saline (sal) or cocaine (coc) challenge injection at postnatal day (P) 15, P36, or P60, following prenatal exposure to saline (PSAL) or cocaine (40 mg/kg/day; PCOC40). Cocaine challenge-induced gene expression is also given in percent (%) of expression in the respective saline control (right). PCOC40 mice showed enhanced induction of zif 268 and homer 1 by the cocaine challenge at P60. * P<0.05, ** P<0.01, *** P<0.001, vs. saline control or as indicated.