Alcohol and Nicotine : Conditioning and Automatic Behavior

by National Institute of Health

(Page 6 of 6)

Conditioning occurs when a stimulus or cue (food) that results in a specific effect (salivation) is repeatedly paired with a previously unrelated stimulus (a certain sound). After a while, the unrelated stimulus becomes a conditioned stimulus that can evoke the same effect, even in the absence of the original stimulus. Conditioning is involved in several ways in dependence on both alcohol and nicotine. Environmental cues present during drug taking (the sight or smell of a bar) become associated with the drug effect (physiological responses to alcohol and nicotine), and conditioned responses are then seen in the absence of the drug. Such responses can be either in the opposite direction to the drug's effects, causing tolerance, or in the same direction, mimicking drug action. Drugassociated cues therefore acquire the ability to control behavior, and this effect has been suggested to be involved in relapse drug taking.

Conditioning factors that contribute to dependence on one drug may increase dependence on another drug, and it is possible that conditioning factors are involved in the cross-tolerance reported between some actions of alcohol and nicotine. Thus, an increase in locomotor activity in an environment in which mice had previously experienced nicotine was seen only in animals that had previously consumed alcohol chronically, suggesting that prior chronic alcohol intake may increase conditioned responses to nicotine.

Conditioned withdrawal - that is, the precipitation of withdrawal symptoms by environmental cues previously associated with the drug - has been reported for alcohol and for nicotine. This response can be produced at long intervals after cessation of drug use and therefore is likely to contribute to relapse drug use during abstinence.

With repeated practice, many everyday processes (getting dressed or driving a car) become so automatic that a person can carry them out rapidly, without conscious awareness or involvement of cognitive processes. Such processes form a stereotypic series of actions that is difficult to halt. It has been suggested that automatic processes contribute to the dependence process. According to this theory, repeated association of drug effects with drug-taking behavior causes incremental strengthening of the stimulus-response relationship, resulting in drug taking becoming an automatic process. Such processes may contribute particularly to nicotine dependence, because cigarette smoking involves stereotyped, ritualistic behavioral patterns (taking the cigarette out of the package and lighting it). It is difficult, however, to reconcile this theory with the occurrence of relapse drinking and smoking that continues despite the knowledge of serious health consequences and the adverse reactions on the part of family and friends, or in situations in which the drug is not easily available. In such scenarios, a person would become much more conscious of his or her behavior (to obtain a drug), and thus the behavior would no longer be automatic. Binge drinking by alcoholics also does not fit a pattern of automatic behavior. The theory also posits that during co-dependence of alcohol and nicotine, alcohol may act as a triggering cue for the automatic behavior leading to nicotine use as well as interfere with nonautomatic processing aimed at the avoidance of smoking.

The Influence of Stress

One factor common to the use of nicotine and alcohol is the influence of stress. Traumatic life events and chronic stressful experiences are associated with the development of both alcohol and nicotine dependence. Stress has also been reported to precipitate relapse drug taking and may affect conditioning. Stressful experiences result in the release of stress hormones called glucocorticoids from the adrenal glands, which are located on top of the kidneys. The primary glucocorticoid in humans is cortisol; the corresponding hormone in rodents is corticosterone. Laboratory studies have shown that corticosterone increases alcohol consumption by rodents. Furthermore, stress has been shown to reinstate operant responding for alcohol and nicotine after such behavior had been extinguished by cessation of the drug presentation. Both alcohol and nicotine increase release of glucocorticoid hormones, and this effect may contribute to their use. Corticosterone has been shown to be self-administered by rodents and therefore may itself have reinforcing properties. The effects of glucocorticoid hormones on the CNS also may be involved in sensation seeking, a currently speculative but interesting line of investigation.

Long-term changes in the control of stress hormone release have been demonstrated after stressful experiences, and these changes may also influence drugtaking behavior and the development of dependence. Stress has been found experimentally to cause sensitization to drugs and may thus increase their rewarding and/or reinforcing actions and incentive salience. It is conceivable that changes in the control of stress hormone release caused by alcohol or nicotine may be involved in co-dependence on both drugs, but more information is needed before such a link can be validated. Prolonged excess alcohol consumption has been reported to affect hormonal responses to stress and to nicotine.

Conclusions

Many factors that contribute to the initial use of both alcohol and nicotine differ for the two drugs, but some factors may be synergistic. The prolonged nature of dependence on both drugs suggests that long-term changes occur in neuronal activity and that these may be common to both drugs. Considerably more information is needed, however, about the behavioral and neurochemical interactions between the two drugs - in particular, their effects on impulsivity and sensation seeking and in relieving anxiety and depression, as well as their rewarding and reinforcing effects - before codependence can be fully understood.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.