Ethanol self-administration in Maudsley reactive and Maudsley nonreactive inbred rats

This study was performed to investigate ethanol self-administration in inbred Maudsley rats, which were selected for differences in stress susceptibility and which often differ in their home cage ethanol consumption. Adult, male, Maudsley reactive (MR/Har) and Maudsley nonreactive (MNRA/Har) rats were tested in a standard protocol for the sucrose-substitution procedure for the initiation of self-administration of ethanol in an operant setting. Before and after initiation for self-administration in the operant setting, rats were tested for home cage consumption of 10% (vol./vol.) ethanol in a two-bottle test for 14 consecutive days. During the sucrose-substitution procedure, MNRA/Har rats consumed more sucrose and ethanol than did MR/Har rats. In addition, MNRA/Har rats self-administered a greater amount of ethanol during a concentration manipulation with the use of a fixed ratio (FR) 4 response requirement. However, both strains self-administered low amounts of 10% ethanol (MNRA/Har, 0.15 g/kg/day; MR/Har, 0.08 g/kg/day) after concentration manipulation compared with those observed in outbred rats and alcohol-preferring rats tested under identical conditions in other studies. Both MR/Har and MNRA/Har rats markedly increased their ethanol intake in the home cage after the initiation protocol, but there was no difference between MR/Har and MNRA/Har on that measure. The failure of MR/Har rats to self-administer ethanol was inconsistent with their home cage drinking in other studies, and this is distinctly different from the self-administration pattern of high-alcohol-drinking rat lines tested in this paradigm.