Ethanol reinforcement in the alcohol nonpreferring rat: initiation using behavioral techniques without food restriction.

Genetic selection of rats can markedly alter their ethanol consumption. The manner in which environmental factors interact in these genetically selected animals to influence ethanol consumption has not been thoroughly investigated. Using the alcohol-nonpreferring (NP) line of rats selectively bred at the Indiana University School of Medicine, alcohol self-administration in an operant situation was initiated using either a sucrose-fading or a secondary-conditioning procedure. These initiation procedures do not require any food or fluid restriction. Initiation was successful in 10 out of 12 NP animals, with the initiated rats self-administering ethanol at concentrations as high as 40%. Following initiation, a retest of home-cage ethanol preference found increases in ethanol acceptability. When tested in a concurrent operant situation, the initiated NP rats also chose ethanol over water. However, the NP rats had lower alcohol intakes and a different pattern of drinking over time when compared to that of nonselected Long-Evans rats. While the NP rats could be initiated to lever-press for ethanol, at no time did their intake approach that of the selected line of alcohol-preferring (P) rats. Thus, while an upward shift from the genetic baseline in ethanol preference and intake can result from the environmental initiation manipulations employed in these studies, genetic factors would appear to limit the extent to which ethanol ingestion can be increased.