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 da ily ethanol intake in the homecage as criteria for selective breeding. Usin g these lines, behavioral and neural factors that may underlie the genetic basis for the control of ethanol consumption have been examined. In this pa per, we report data from eight of these selected lines: the Alcohol-Preferr ing (P) and Alcohol-Nonpreferring (NP), the Alcohol-Accepting (AA) and Alco hol-Nonaccepting (ANA), and the High Alcohol Drinking (HAD1 and HAD2) and L ow Alcohol Drinking (LAD1 and LADS) rats. Ali lines were tested using opera nt procedures and the same protocols for both the ethanol self-administrati on initiation and measurement of continuous-access ethanol consumption. Dur ing continuous access, the animals were housed in operant chambers with acc ess 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 c onnected to a drinkometer circuit Under these procedures, both similarities and differences among the selected lines on continuous-access operant etha nol intake were observed. For example, overall total homecage ethanol drink ing was similar for the AA and both HAD lines. When examined in the operant continuous-access situation, however, the AA rats displayed a different co nsumption pattern, compared with the HAD lines. Data suggest that the frequ ency of drinking bouts was a primary factor in the phenotypic homecage sele ction of the preferring lines that was revealed by the use of the continuou s-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 oper ant 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 im pact ethanol consumption.