In order to investigate the underlying neurobiology of compulsive cocaine intake, it is necessary to employ an animal model that accurately recapitulates many aspects of the compulsive cocaine seeking seen in human addicts. Loss of control over the amount of drug consumed marks the transition from controlled drug use to the compulsive drug intake that is a central feature of addiction. Periods of extended drug availability and resultant excessive drug consumption are likely a critical factor triggering the development of compulsive drug seeking in humans and a loss of control over intake.4-8 Indeed, in human drug users a sudden increase in drug availability can precipitate the transition from low to high (and increasingly uncontrolled) levels of drug use.9-11 Such “escalating” levels of drug consumption by human drug users in response to increased drug availability can be observed for most drugs of abuse.9,12,13 Animal studies utilizing the intravenous cocaine selfadministration procedure have shown that periods of extended daily access to cocaine and other addictive drugs can trigger escalating cocaine intake in rats similar to that observed in human drug users.7,11,14,15 Rodents
