Animals were treated in vivo with either saline, nicotine (18 mg/kg/day), or undergoing 24h withdrawal (WD) from nicotine. Hippocampal tissues from treated animals were used in qPCR or Western blot experiments to evaluate mRNA or protein levels. As shown, chronic treatment with nicotine or 24hWD does not alter neuregulin 1 (NRG1) (A) mRNA or (D) protein levels in the hippocampus. In contrast, mRNA (B) and protein (E) levels of ErbB4 are increased following chronic treatment with nicotine and/or during 24hWD. Additionally, mRNA levels of the CREB target neuregulin 3 are increased following chronic nicotine treatment and 24hWD (C). Furthermore, protein levels of NRG3 (F) are increased following 24hWD in wildtype (WT), but not CREB mutant, mice. Representative blots are shown below each panel. *, p<0.05; **, p<0.01. A–C: N=6–11; D–F: 6–10.