Differences between the rat lines have also been found when assessing the efficacy of pharmacological treatments to reduce ethanol intake. Maccioni et al. (in press) conducted an in-depth study examining baclofen, a GABA-B agonist, and GS39783, a positive allosteric modulator of the GABA-B receptor, on ethanol self-administration across three of the high alcohol-consuming rat lines (AA, P and sP). The first observation was that operant self-administration of ethanol differed among the lines, such that the order of magnitude was P>sP>AA. Moreover, the order of breakpoint for ethanol self-administration among the rat lines was also P>sP>AA. Baclofen’s efficacy in decreasing ethanol intake differed across the rat lines, when the rats were placed on a fixed-ratio operant schedule; such that 1.7 and 3 mg/kg doses were effective in P rats, whereas only the 3 mg/kg dose was effective in sP and AA rats. In addition, baclofen’s efficacy in decreasing ethanol intake differed across the rat lines, when the rats were placed on a progressive-ratio operant schedule; such that 1.7 and 3 mg/kg doses were effective in P and sP rats, whereas only
