Environmental influences on the failure to drink in inbred rats with an ethanol preference

To investigate the environmental influences on the initiation of voluntary consumption of 10% ethanol (EtOH) in rats with differing genetic susceptibility to excessive EtOH consumption, Maudsley reactive (MR/Har) and nonreactive (MNRA/Har) inbred rats were observed in different types of caging environments. Singly housed male and female rats of both strains living in Observational (O) cages drank markedly less EtOH during 3 weeks of two-bottle choice than did rats living in standard-control (C) individual cages. When male rats had a preexisting moderate or heavy pattern of EtOH intake (manipulated through prior EtOH experience), moving to the O cage did not reduce EtOH intake. To investigate the nature of the above cage effect (the reduced initiation of EtOH consumption), we compared the manner in which food had been distributed (traditional food hopper in C cages versus loose distribution in O cages) independently of cage type. The results showed that MR/Har male rats that obtained food through a hopper in both O or C cages drank significantly more EtOH than rats that had food loosely distributed in the O or C cages. The results suggest that differences in the mode of food procurement and caging can play a large role in whether the phenotype for excessive EtOH intake is expressed in the acquisition of an EtOH preference in genetically vulnerable rats.