The effects of chronic morphine treatment on Dcc wild-type and heterozygous mice. In these experiments littermate Dcc wild-type (C57BL/6 J) and Dcc heterozygous mice were tested using the same chronic morphine paradigm used for the inbred strain mapping experiments. Panel A: Mechanical OIH measurements; Panel B: Morphine dose–response relationships before and after chronic morphine treatment; Panel C: Physical dependence measured using naloxone-precipitated jumping behavior. For these experiments n = 11 mice per genotype. Data are displayed as mean values +/- S.E.M., *p < 0.05, **p < 0.01, ***p < 0.001.