Females find cocaine more addictive than males do

In drug addiction research, it is well established that an enhanced response to novelty can predispose certain individuals to addiction. Research has previously shown that rats, selectively bred to have an increased locomotor response to novelty, display differences in the amount of cocaine they self-administer, compared to rats bred to be less reactive. Not only do they ingest greater doses of the drug, they also exhibit enhanced impulsivity due to lowered behavioural inhibition.

An additional factor that also puts individuals at increased risk for drug abuse is gender. Trend analysis shows that, compared to men, women begin using cocaine at younger ages, become addicted to it more quickly and also suffer more intense cravings during periods of abstinence. A hormonal element to addiction has also been implicated by women reporting greater pleasure from smoking cocaine when their estradiol levels are elevated.

In support of this, researchers at the University of Michigan found that female rats, selectively bred to have higher reactivity to novelty, increase self-administration of cocaine more quickly than male rats also bred to have a heightened response level. In light of these findings, Jennifer Cummings and colleagues then investigated whether increased motivation was behind the difference in behaviour and have sought to determine the impact of sex on the motivation to self-administer cocaine.

The study, published today in Biology of Sex Differences, revealed an underlying sex difference in the desire to ingest the drug, regardless of phenotype, with females showing a greater motivation than males. Interestingly, the researchers found that male rats, bred to have a low reactivity to novelty, did not work hard for their dose of cocaine, but the equivalent female rats did.

The authors explain "This suggests that whilst this selective breeding has proved "protective" to a certain degree by reducing the motivation for cocaine, this protection is limited in females, and ultimately sex overrides behavioural phenotype in this situation."

Source: Bio Med Central