Rats exposed to antidepressants just before and after birth manifest behaviors, which mimic the symptoms of autism, according to a new study that was partially funded by the National Institute of Mental Health (NIMH).
An earlier research on the link between antidepressants and autism spawned this new U.S. study, which is done on rodents because experiments cannot be performed on pregnant women, as the baby's serotonin levels will be affected in the process of the experiment.
The brain chemical and neurotransmitter serotonin plays a pivotal role in the buildup of a baby rodent's brain, just like that of human's.
The antidepressants-autism study used selective serotonin re-uptake inhibitors or serotonin-specific reuptake inhibitor (SSRIs), which are typically used as antidepressants in the treatment of depression, anxiety disorders, and some personality disorders.
The study on rats found that serotonin balance, when disrupted in a rat's developing brain by exposure to SSRIs, causes rats to become excessively fearful when faced with new situations and fail to play normally with peers - traits that are normally seen in autistic children.
"Our findings underscore the importance of balanced serotonin levels - not too high or too low - for proper brain maturation," study researcher Rick Lin of the University of Mississippi Medical Center said in a statement.
LiveScience.com reported that Lin and his colleagues exposed male and female baby rodents to the SSRI drug called citalopram just before and after birth and examined the animals' brains and behaviors as they grew into adulthood.
Male, but not female, SSRI-exposed rat pups abnormally froze when they heard an unfamiliar tone and acted erratically upon sensing unfamiliar objects or scents. These behaviors persisted into adulthood. The male pups notably showed a non-playful behavior, which is consistent with the traits of children with autism.
Interestingly, the rodent study's findings by gender are consistent with the statistics of autism in children, which is three to four times more likely in boys than girls.
The study determined that manipulation of serotonin days before a rat is born - a period that corresponds to the third trimester in humans - disrupts the sensory-processing regions of the brain. Serotonin changes have been observed to cause aggressive and anxiety-related behaviors in rodents.
Previously, an unprecedented study aimed at finding a link between antidepressants and autism risk showed researchers that women who take Zoloft, Prozac and related mood drugs anytime before giving birth are twice as likely to deliver a child with autism.
The study, published in the Archives of General Psychiatry, says autism risk is even tripled if antidepressants were taken in the first trimester of the pregnancy.
Lisa Croen, lead author of the study and an epidemiologist in the research division of Kaiser Permanente Northern California, cautioned mothers in interpreting the study's findings, saying further studies on the subject should be done first.
"A lot of people might get a little worried about these findings and change something they're doing, which they shouldn't. It indicates to us that there's more to look at," said Dr. Croen.
LiveScience further reported that the researchers on rodents also discovered bad wiring in the structure responsible for communications between the brain's left and right hemispheres, called the corpus callosum. Neurons send their signals along extensions called axons, and in SSRI-exposed rats, those axons were deformed.
The researchers report their results online Monday (Oct. 24) in the journal Proceedings of the National Academy of Sciences.
"While one must always be cautious extrapolating from medication effects in rats to medication effects in people, these new results suggest an opportunity to study the mechanisms by which antidepressants influence brain and behavioral development," said Thomas Insel, NIMH director.
"These studies will help to balance the mental health needs of pregnant mothers with possible increased risk to their offspring," he added.
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