Is there a common biological basis for reinforcement from alcohol and other drugs?

Vulnerability to substance abuse is an important emerging issue. A critical aspect of this phenomenon is the degree to which individuals who abuse one substance are likely to abuse other substances, alone or in combination with each other. The extent to which several distinct drugs will come to serve as positive reinforcers within genetically defined subjects defines their commonality. Questions in this area are directed at determining whether reinforcement from and abuse of alcohol and other drugs define variations within a single behavioral phenomenon, or whether reinforcement and abuse must be individually defined for each substance involved. Findings related to this commonality issue are now emerging from the areas of pharmacogenetics and operant drug self-administration. Previous studies have shown that ethanol can be readily established as a positive reinforcer in LEWIS rats, as well as C57BL/6J mice. In low ethanol preferring F344 rats, ethanol maintains significant but low levels of responding. Ethanol does not maintain lever pressing behavior in BALB/cJ mice, and is avoided in DBA/2J mice. Initial findings reported in this paper show that these genotypic patterns of reinforcement from ethanol appear to correlate highly with patterns of reinforcement from cocaine and opiates. From these findings it is concluded that (1) there exist important genetic determinants of drug reinforced behavior; and (2) drug seeking behaviors maintained by ethanol, cocaine and opiates may have at least some common biological determinants.