Motherhood may dampen cocaine's effects on the brain

Having a baby may do more than just change a woman’s behavior; her brain chemistry may undergo some distinct changes as well.

New research from the University of Michigan has revealed that motherhood may dampen the effects of cocaine use – a discovery that could lead to more customized drug therapies to fight addiction.

“We know there are sex differences in the way men and women respond to drugs in the brain,” Jennifer Cummings, a research investigator at the Molecular and Behavioral Neuroscience Institute and lead author of the study, told  “We want to make sure we have gender specific treatments so we can tailor them towards men and women.”

According to Cummings, more and more research has been dedicated to studying the physiological and behavioral effects that motherhood can have on women.  Growing research has revealed that hormone changes during pregnancy can actually boost abilities such as memory and the ability to navigate.

Hoping to better understand other chemical changes the brain undergoes during pregnancy and motherhood, the researchers decided to focus on drug response patterns in mother rats versus non-mother rats.  After giving the female rats doses of cocaine, they found very clear differences in how the “pleasure centers” of their brains reacted.

“We looked at dopamine release in the brain,” Cummings said.  “One of the big things you hear about is this neurotransmitter dopamine; it produces the high that comes with taking drugs.  We wanted to see much of this dopamine is released in the ‘pleasure center’ for those who are mothers and those who are not.”

Overall the maternal animals released far less amounts of dopamine when given cocaine compared to their non-mother counterparts – meaning the drug had less of an effect on the brain.

In another experiment examining the behavior of the mother rats, all the rats were given multiple doses of cocaine.  According to Cummings, as more and more doses are given to test subjects, the researchers would expect to see the rats become increasingly active.  However, the mother rats did not increase their activity and had much weaker responses.

In order to test the animal’s desire for cocaine after receiving their first dose, the researchers designed a series of self-administration experiments.  They poked holes into the animals’ testing chamber and inserted an intravenous catheter, which would give the rats an immediate dose of cocaine if they poked their nose through the hole.  If the rats wanted another dose, they would have to poke their noses through the catheter more and more each time – making them work progressively harder to get the cocaine.  This led to some interesting findings for the researchers.

“When we made the animals work harder for the cocaine, the moms were just not as motivated to take the cocaine.  The mothers tended to fall out,” Cummings said.  “It could be that perhaps it is less reinforcing for them. However, if we applied some stress to the animals, the moms took more cocaine compared to the non-maternal animals.  So something about that stress was interacting with the maternal experience.”

The researchers did not specifically study why the interaction of motherhood and stress would have this impact.  However, they theorized that changes in hormones may play a key role.
“[During pregnancy,] there’s a huge increase in the amount of hormones to which the female is exposed; there’s an increase in progesterone in huge, huge numbers,” Cummings said.  “Then at the end, you have a huge increase in estrogen, while there are also big increases in the stress hormone corticosterone.”

“Those hormones can change the brain structurally – they can make the neurons stronger,” Cummings added.  “We also see this neuroplasticity (the ability of neurons to change) when animals are caring for offspring.  It has something to do with the reorganization of neural circuitry.”

Now that Cummings and her team have an idea as to some of the changes that may be happening in a mother’s brain, they hope to further discern the most significant variations that interfere with drug response.

“What is it we can target to better aid these drug therapies?” Cummings wondered.  According to her, the male brain and female brain are the same structures with the same reward circuitry.  “But, if we can really determine how hormones or experiences might be affecting brain function, we can really use that in terms of developing more individualized drug therapies and behavioral therapies.”

Cummings present her study at an oral presentation at the Society for Neuroscience meeting on Oct. 15.