(Ehlers et al. 1992). In sP rats, higher levels of serum corticosterone have been reported, compared with sNP rats, suggesting differences in HPA activity (Bano et al. 1998). An examination of the data from selected mouse lines revealed that WSP and WSR mice had similar corticosterone response to acute alcohol injections (D. A. Finn, personal communication). In addition, when exposed to alcohol vapor and tested at the time of withdrawal, both selected lines had equivalent elevations of corticosterone (Beckley et al. 2008;Tanchuck et al. 2009). Differences in opioid receptor levels between the selectively bred high and low alcohol-consuming rat lines have been reported (AA vs. ANA: (De Waele et al. 1995;Soini et al. 1998;Soini et al. 1999); P vs. NP: (McBride et al. 1998); HAD-1 vs. LAD-1: (Learn et al. 2001); sP vs. sNP: (Fadda et al. 1999). However, interpretation is difficult given that: (a) different brain regions were assessed and/or found to display line differences; (b) differences in direction 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
