Psychotherapy for cocaine dependence

Effects of prior cocaine versus morphine or heroin self-administration on extinction learning driven by overexpectation versus omission of reward

BACKGROUND

Addiction is characterized by an inability to stop using drugs, despite adverse consequences. One contributing factor to this compulsive drug taking could be the impact of drug use on the ability to extinguish drug seeking after changes in expected outcomes. Here, we compared effects of cocaine, morphine, and heroin self-administration on two forms of extinction learning: standard extinction driven by reward omission and extinction driven by reward overexpectation.

METHODS

In experiment 1, we trained rats to self-administer cocaine, morphine, or sucrose for 3 hours per day (limited access). In experiment 2, we trained rats to self-administer heroin or sucrose for 12 hours per day (extended access). Three weeks later, we trained the rats to associate several cues with palatable food reward, after which we assessed extinction of the learned Pavlovian response, first by pairing two cues together in the overexpectation procedure and later by omitting the food reward.

RESULTS

Rats trained under limited access conditions to self-administer sucrose or morphine demonstrated normal extinction in response to both overexpectation and reward omission, whereas cocaine-experienced rats or rats trained to self-administer heroin under extended access conditions exhibited normal extinction in response to reward omission but failed to show extinction in response to overexpectation.

CONCLUSIONS

Here we show that cocaine and heroin can induce long-lasting deficits in the ability to extinguish reward seeking. These deficits were not observed in a standard extinction procedure but instead only affected extinction learning driven by a more complex phenomenon of overexpectation.

Cocaine-induced sensitization correlates with testosterone in male Japanese quail but not with estradiol in female Japanese quail

Research has indicated that gonadal hormones may mediate behavioral and biological responses to cocaine. Estrogen, in particular, has been shown to increase behavioral responding to cocaine in female rats relative to male rats. The current study investigated the effect of cocaine on locomotor activity and hormonal correlates in male and female Japanese quail (Coturnix japonica). In Japanese quail, circulating hormone levels can be manipulated without surgical alterations via modifying the photoperiod. Male and female quail were housed on either 8L:16D (light:dark) or 16L:8D (light:dark) cycle for 21days. Blood samples were taken prior to the beginning of the experiment and assays were performed to determine the levels of testosterone (T) and estradiol (E2). Quail were given injections of saline or cocaine (10 or 20mg/kg) once a day for 10days. Immediately after each injection, birds were placed in open field arenas and distance traveled was measured for 30min. Results showed that male quail housed under long-light conditions exhibited cocaine-induced sensitization to 10mg/kg cocaine which was correlated with the high levels of plasma T. Female quail housed under short-light conditions demonstrated sensitization to 10mg/kg cocaine, but this was not correlated with the levels of plasma E2. The current findings suggest that cocaine-induced locomotor activity was associated with T in males but not with E2 in females.