Infant monkeys conceived while their mothers were naturally exposed to wildfire smoke show behavioral changes compared to animals conceived days later, according to a new study from researchers. The work is published in Nature Communications.  

The findings show the importance of timing in effects of smoke exposure on pregnancy and suggest a teratogenic, or developmental mechanism, said the senior author. 

“I think this will have an effect on future studies of exposures in pregnancy, because we’ll know when to look,” the senior author said. Existing studies of environmental exposures during pregnancy in humans are mostly retrospective, and women may not even realize they are pregnant until weeks into the first trimester, the author said.

The Camp Fire, which began Nov. 8, 2018, provided a natural experiment in smoke exposure. It blanketed the Davis area, some 100 miles away, with smoke at the peak of breeding season for rhesus macaques housed in outdoor corrals at the California National Primate Research Center.

The 89 animals conceived around that time were born about six months later. They divide between 52 animals conceived on or before Nov. 22, 2018 which were considered as “exposed” to wildfire smoke in their first trimester, and 37 conceived later which were not exposed. 

At about 3-4 months old, the young monkeys are assessed on a variety of cognitive and behavioral tests. While the number of animals conceived during the Camp Fire that were assessed was fairly small, they could be compared not only to each other (exposed vs. not exposed), but also to the historical data from hundreds of animals. 

On assessment, the smoke-exposed infants showed increases in a marker of inflammation, a reduced cortisol response to stress, memory deficits and a more passive temperament than other animals, another author said. 

“It’s a mild effect across a variety of domains of psychological function,” the author said. The effects are consistent with those found in studies of prenatal exposure to air pollution, the author said. Comparison between the groups and with animals born in other years shows that the results are not due to the timing of conception (earlier versus later in the breeding season). 

The findings suggest that some component of wildfire smoke can act as a teratogen, affecting fetal development, the senior author said. That component could be airborne hydrocarbons such as phthalates, which were found in the smoke plume from the Camp Fire. 

Unlike other mammals, the placenta of primates such as humans and rhesus macaques produces hormones that support brain development through the adrenal system, the author said. 

“Since fetal adrenal glands are the source of cortisol and other steroids for neurologic development, which determines behaviors, a scenario of a placenta-adrenal-brain axis could be the causal pathway,” the senior author said.

The authors are beginning a prospective study with women with implanted embryos as a result of in vitro fertilization, as the time of conception is exactly known if the women are incidentally exposed to wildfire smoke or other pollutants. 

https://www.nature.com/articles/s41467-022-29436-9

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