From the article:
The Mount Sinai research team sought to understand why women, once they try cocaine, are much more likely than men to become addicted. While the overall rate of addiction is higher in males, previous research has shown that when females have the opportunity to try cocaine and other drugs, they are more likely than men to continue use and they transition to full addiction significantly faster than their male counterparts. Addiction investigators have also uncovered that women are more likely to use cocaine at an earlier age, take the drug in larger quantities, and have greater difficulty remaining abstinent compared to men. Additionally, women report that when estrogen levels are rising during their menstrual cycles, they experience a greater “high” from cocaine administration.
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The research team found that estrogen affects the quantity of dopamine released by neurons in response to cocaine, as well as how long the dopamine stays in the synapse between brain cells. Both actions increase the pleasurable effects of cocaine, and each was significantly bolstered as estrogen levels increased in the female mice. Both male and female mice linked pleasure/reward to where it occurred in their cages, spending more time on the side of their cage that was previously paired with cocaine. Female mice did so to a greater extent, indicating enhanced reward to cocaine use.
“The mice quickly learned that a particular environment is linked to drugs, and we demonstrated that when these mice, especially females at the height of their estrous cycle, were put into that environment, it stimulated a dopamine reward signal even without cocaine use,” Dr. Calipari says. “It is the same kind of strong, learned response that we know happens in humans.”
Researchers surmise that the evolutionary mechanism underlying the link between estrogen and the reward pathway is pleasure from seeking a mate and having sex, actions which promote the survival of the species. Another evolutionary hypothesis is that heightened estrogen could promote food seeking, via effects on dopamine signaling, to ensure females are healthy enough to carry offspring.