Nicotine sensitization and levels of brain-derived neurotrophic factor (BDNF) were analyzed in adolescent β-arrestin-2 knockout (βA-2 KO) and wild type (WT) mice. The β-arrestin-2 protein has been shown to be important in G-protein hydrolysis and receptor internalization. Four- to five-week-old adolescent βA-2 KO and WT C57/Bl6 mice were administered either nicotine (0.5 mg/kg free base) or saline 10 min before being placed into a locomotor arena on each of 7 (Experiment 1) or 14 (Experiment 2) consecutive days. A nicotine challenge was given 7 days after sensitization was complete. In Experiment 1, βA-2 KO mice administered nicotine or saline and WT mice administered nicotine demonstrated significant hypoactivity during early in testing, and neither WT nor βA-2 KO mice administered nicotine demonstrated sensitization. On the nicotine challenge, WT mice administered nicotine demonstrated significantly higher activity levels compared to all groups, and this same group demonstrated significantly higher levels of accumbal BDNF compared to all groups. In Experiment 2, βA-2 KO mice were again hypoactive compared to WT mice, whereas WT mice administered nicotine demonstrated significant hypoactivity during initial testing and significantly higher levels of activity compared to all other groups late in testing. On the nicotine challenge, WT mice that received nicotine demonstrated a significant increase in activity compared to all groups, and showed increased accumbal BDNF compared to all groups. These results show that the β-arrestin-2 protein is important in induction and expression of nicotine sensitization as well as nicotine's effects on accumbal BDNF. Synapse 63:510-519, 2009. © 2009 Wiley-Liss, Inc.