According to the Autism and Developmental Disabilities Monitoring Network, about 1 in 59 children have been identified with autism spectrum disorder. The new estimate represents a 15% increase in prevalence nationally from 1 in 68 children two years ago.

This disorder is reported to occur in all racial, ethnic, and socioeconomic groups and is about four times more common among boys than among girls. From 2006-2008, about 1 in 6 children in the United States had a developmental disability, ranging from mild disabilities such as speech and language impairments to serious developmental disabilities, such as intellectual disabilities, cerebral palsy, and autism.

Autism is a complex neurodevelopmental disorder. Although many causes have been proposed, the cause is still questionable and ultimately unknown.

However, a recent study shows a potential link between autistic-like behavior in adult mice and exposure to a common antidepressant in the womb. One of the most commonly prescribed antidepressants is fluoxetine (Prozac), a serotonin reuptake inhibitor.

Fluoxetine can cross the placenta and is also detected in breast milk. According to Associate Professor Hyunsoo Shawn Je, from the Duke-NUS Neuroscience and Behavioural Disorders Program, a causal relationship between antidepressant exposure during pregnancy and children with autism and attention deficit disorder has not been pinpointed in studies so far.

The researchers investigated adult mice born to mothers treated with fluoxetine over a 15-day time period, which corresponds to the second trimester in humans, compared with those born to mothers given normal saline. They noted specific differences in behavior.

For example, the unexposed mice normally explored all three arms of a Y-shaped maze over a 10-minute time period and, over the courses of multiple arm entries, mice usually enter a less recently visited arm, while the fluoxetine-exposed ones were less inclined to explore the unvisited arm.

In the second experiment, the mice were introduced to two juvenile mice, one after the other. When the second new mouse was introduced, mice that were not exposed to fluoxetine were more likely to only sniff the newly introduced mouse, recognizing that they had already met the first mouse. But the fluoxetine-exposed group sniffed both mice, indicating that they had impaired social recognition.

Next, the team examined nerve signal transmission in the prefrontal cortex, which moderates social behavior.

They found impaired transmission caused by an overactive serotonin receptor. Treating fluoxetine-exposed mice with a compound that blocks the receptor alleviated their behavioral problems and improved their working memory.

Next, the researchers want to examine autistic children born to mothers treated with antidepressants using positron emission tomography scans. If the scans also show enhanced serotonin receptor activity in the same area of the brain, the team plans to test whether serotonin receptor blockers can normalize their behaviors.