90’s, two studies were conducted that examined operant self-administration of ethanol by AA, HAD1, HAD2 and P rats, as well as their low alcohol-consuming counterparts (Files et al., 1998; Samson et al., 1998). We will only discuss the findings from the high alcohol-consuming rat lines here. One study examined operant self-administration of ethanol under continuous (24-h) access conditions (Files et al., 1998). In this study (Files et al., 1998), the order of magnitude for ethanol responses per day was HAD2>HAD1=P>AA; the order of magnitude for ethanol bouts per day was HAD2>AA=P>HAD1; the order of magnitude for ethanol g/kg/day was HAD2>HAD1>AA=P; and the order of magnitude for ethanol dipper presentations per bout was HAD1>P>HAD2>AA. These authors noted that their findings indicate that even though these rat lines may drink similar amounts of ethanol per day under home-cage access conditions; there are significant differences in the reinforcing properties of ethanol as measured by operant response number, ethanol bouts per day, total ethanol consumed and dipper presentations per bout. The second study examined continuous access home-cage drinking and operant self-administration of ethanol under limited (30-min) access conditions (Samson et al., 1998). These authors reported that during initiation of ethanol drinking in the home-cage
