New research presents a potential link between the use of antidepressants in pregnant mice and autistic-like behaviors in their offspring, according to a study published in the journal Molecular Brain.

One in six Americans take antidepressants or other psychiatric drugs, according to a 2017 study published in JAMA. Of them, most commonly prescribed is a serotonin reuptake inhibitor (SSR) called fluoxetine, better known by its generic name Prozac or Sarafem. Such drugs are used to treat major depression and post-traumatic stress disorder (PTSD), which can be increasingly important during pregnancy as untreated depression is associated with an increased risk of premature birth, low birth weight, and other problems for the baby notes the Mayo Clinic. However, little is known about the safety of these drugs during pregnancy other than they can cross the placenta and can be detected in breast milk. Prescribing such pharmaceuticals during pregnancy is done so by balancing its risk with potential benefits.

"Many human association studies have been conducted to investigate connections between antidepressant exposure during pregnancy and children with autism and attention deficit disorder (ADHD). But they have not been able to pinpoint a causal relationship," said study author Hyunsoo Shawn Je in a statement. 

To find out what these potential risks might be, researchers observed adult mice born to mothers who had been treated with fluoxetine over 15 days during the mice version of a human’s second trimester. They then compared these observations with the behavior of mice born to mothers who had only been given saline as a control.

Key differences in behavior were identified between the two groups, particularly in memory loss and social interactions. For starters, mice born to mothers given the saline solution normally explored three arms of a Y-shaped maze over a 10-minute timeframe and were more apt to explore arms that they hadn’t recently visited. Mice born to mothers treated with antidepressants, on the other hand, were less inclined to explore the unvisited arm. In a second experiment, mice were introduced to two juvenile mice one after the other. Saline mice were more likely to sniff the second mouse, indicating that they were aware of the fact that they had already met the first. Mice exposed to antidepressants while in the womb sniffed both introduced mice, which shows that they weren’t able to recognize that they had already met the first mouse.

Lastly, researchers looked at nerve signals in the prefrontal cortex, the part of the brain responsible for social behavior. They found impaired transmissions believed to have been caused by an overactive serotonin receptor but showed evidence of improved memory when the mice were given compounds that block receptor alleviated behavioral problems.

"The consensus among experts is that the rise in the number of people diagnosed with autism around the world is likely due to more awareness and testing rather than an increase in the prevalence of autism," said researcher Patrick Casey. "This collaborative study by our researchers offers a compelling case for a link between autism and antidepressant exposure in the womb in an animal model, and a possible mechanism that could potentially be exploited for future therapies