Abstract

The hypothalamo-pituitary-adrenal (HPA) axis is involved in all aspects of cocaine self-administration. Corticosterone seems to be crucial for the acquisition of drug use since self-administration does not occur unless this stress hormone is increased above a critical reward threshold. Increasing circulating levels of corticosterone also augments sensitivity to low doses of cocaine, possibly from a sensitization-associated phenomenon involving dopamine, suggesting that exposure to stress can increase individual vulnerability to cocaine. Drugs affecting the synthesis and/or secretion of corticosterone decrease ongoing, low-dose cocaine self-administration. When higher doses falling on the descending limb of the cocaine dose-response curve are self-administered, plasma corticosterone can still reach this reward threshold even when synthesis is inhibited and drug intake is not affected. Corticotropin-releasing hormone (CRH) seems to play a more prominent role in the maintenance of cocaine self-administration and may even be involved in the incentive motivation for the drug. Corticosterone and CRH are also critical for the stress- and cue-induced reinstatement of extinguished cocaine-seeking behavior. Therefore, cocaine self-administration may represent an attempt to seek out specific sensations, with the internal state produced being very similar to that perceived by individuals who engage in risky, thrill-seeking behavior. During abstinence, exposure to stressors or cocaine-associated cues can stimulate the HPA axis to remind the individual about the effects of cocaine, thus producing craving and promoting relapse. Stress reduction, either alone or in combination with pharmacotherapies targeting the HPA axis may prove beneficial in reducing cravings and promoting abstinence in individuals seeking treatment for cocaine addiction.