Exposure to allergy during pregnancy linked to ADHD, autism in newborn rats

Researchers have found significant changes in the brain makeup of fetuses and newborn rats exposed to allergens before birth and signs of attention-deficit hyperactivity disorder (ADHD) and autism when they lived to adulthood.

The researchers, led by Kathryn Lenz, an assistant professor of psychology at the Ohio State University, presented their findings in the southern Californian city of San Diego at Neuroscience 2016, the annual meeting of the Society for Neuroscience.

To study the effects of allergies on offspring, the researchers sensitized female rats to ovalbumin before pregnancy. Then, 15 days into their pregnancies, the team exposed the rats to the allergen, prompting an immune response in the animals.

They analyzed whether prenatal allergen exposure changed the number and behavior of immune cells in the developing brain of offspring, explored possible changes in young rats' physical activity, anxiety-like behavior, ability to learn and sociability, and examined the density of dendritic spines in the juvenile animals' brains, finding that rats exposed to allergens before birth had higher levels of immune cells called mast cells in the brain and lower numbers of immune cells called microglia, and that animals with allergic mothers were hyperactive, but had lower levels of anxiety-like behavior.

"This is evidence that prenatal exposure to allergens alters brain development and function and that could be an underappreciated factor in the development of neurodevelopmental disorders," Lenz was quoted as saying in a news release from Ohio State.

When the researchers looked at the animals' ability to be mentally flexible, the rats born to allergic mothers had a tougher time, Lenz said. "They have to use rules to find a reward - a Cheerio in a terracotta pot - and the rules we give them keep shifting," Lenz said, explaining that in one test the treat might be in a pot covered in sandpaper and in another test it might be in a pot covered in velvet. The rats in the allergen group weren't as capable of adapting to the changing parameters of the test.

Early data from the study shows that the dendritic spines - the points of synaptic connection between cells in the frontal cortex of the animals' brains - were decreased in males with allergy exposure and increased in their female counterparts.

Though there are established links between allergies and ADHD and autism, as well as between inflammation and risk of autism, schizophrenia and ADHD, the cellular-level changes that could contribute to those connections largely remain a mystery. The new study in rats is expected to help begin to explain the link. Endit