Panels A, C: Locomotor activity in response to OXY (D2, D4) and SAL (D3, D5) in LG/J, SM/J, and AIL mice. Panels B, D: OXY-induced locomotor sensitization in LG/J, SM/J, and AIL mice as indicated by the difference in locomotor activity between D2 and D4 (D4-D2). “*” = significant increase from D2 to D4 (Panels A, C). “#” = significantly different from LG/J (Panel A). Data are represented as the mean ± S.E.M.