BDNF mRNA was quantified relative to placebo (A–C), and baseline (D and E). No differences were seen at 3 hours and 72 hours of morphine exposure (A). Precipitated withdrawal elevated BDNF mRNA expression (B), while seven days of abstinence reduced BDNF mRNA expression (C). BDNF mRNA expression was also decreased following 72 hours of morphine exposure compared to baseline (D). There were no differences in the placebo groups compared to baseline (E). Data indicate mean ± SEM. * P < 0.05 vs. placebo; # P < 0.05 vs. baseline by Student’s t-test. Baseline data: BL (n=8); placebo: 3 H (n=6), 72 H (n=6), PWD (n=5–6), SWD (n=5–6), 7D (n=6), 7D+FS (n=6); 3 H (n=6); morphine: 3 H (n=6), 72 H (n=7), PWD (n=7), SWD (n=5), 7D (n=5), 7D+FS (n=6).