of effect were seen between the different sets of selected lines (e.g., for mu-opioid receptor levels, AA< or > ANA, P > NP, HAD-1 < LAD-1); as well as (c) mixed results as to the importance of the mu-versus the kappa-opioid receptor. Regarding this last point, there is evidence, from family-based studies, of a significant association between a variation in the OPRK1 (opioid receptor kappa 1) gene and a higher risk for developing alcoholism (Edenberg et al. 2008).
