Comparison of alcohol-preferring and nonpreferring selectively bred rat lines. II. Operant self-administration in a continuous-access situation

Several rat lines have been developed using preference/nonpreference and daily ethanol intake in the homecage as criteria for selective breeding. Using these lines, behavioral and neural factors that may underlie the genetic basis for the control of ethanol consumption have been examined. In this paper, we report data from eight of these selected lines: the Alcohol-Preferring (P) and Alcohol-Nonpreferring (NP), the Alcohol-Accepting (AA) and Alcohol-Nonaccepting (ANA), and the High Alcohol Drinking (HAD1 and HAD2) and Low Alcohol Drinking (LAD1 and LADS) rats. Ali lines were tested using operant procedures and the same protocols for both the ethanol self-administration initiation and measurement of continuous-access ethanol consumption. During continuous access, the animals were housed in operant chambers with access to 10% (v/v) ethanol after responses on one lever, food pellets (45 mg) after responses on a second lever, and water in a drinking tube that was connected to a drinkometer circuit Under these procedures, both similarities and differences among the selected lines on continuous-access operant ethanol intake were observed. For example, overall total homecage ethanol drinking was similar for the AA and both HAD lines. When examined in the operant continuous-access situation, however, the AA rats displayed a different consumption pattern, compared with the HAD lines. Data suggest that the frequency of drinking bouts was a primary factor in the phenotypic homecage selection of the preferring lines that was revealed by the use of the continuous-access operant procedure. In general, data suggest that genes related to ethanol preference and intake in homecage continuous-access situations may not be identical to those related to ethanol's reinforcing function in operant continuous-access conditions. Because ethanol consumption appears to be controlled by different drinking patterns across lines, the selected lines provide for a variety of models to understand how varying genotypes can impact ethanol consumption.