Alcohol dependence: a commentary on mechanisms.

The alcohol dependence syndrome includes the presence of alcohol tolerance, physical dependence and an inability to control one's alcohol intake. Studies are reviewed that implicate the mesolimbic dopaminergic systems, and the gamma-aminobutyric acid-A (GABAA) and N-methyl-D-aspartate (NMDA) receptors as mediators of various aspects of the alcohol dependence syndrome. It is suggested that alcohol-induced changes in the GABAA receptor may play a role in certain aspects of tolerance to alcohol and in altered abilities of an individual to terminate alcohol intake. Chronic alcohol-induced increases in the activity of NMDA receptors may contribute to the withdrawal signs that are the defining feature of physical dependence on alcohol. It is hypothesized that decreased mesolimbic dopaminergic function, which occurs during alcohol withdrawal, may be involved in the compulsion to initiate and maintain alcohol drinking, another aspect of the alcohol dependence syndrome. Furthermore, evidence is presented that this decreased dopaminergic function could occur secondarily to the increase in NMDA receptor function, such that the alcohol-induced increase in NMDA receptor function could underlie both the overt withdrawal signs and the compulsion to drink alcohol in the alcohol-dependent individual.