Alexey Krasavin

Fetal Cannabis Exposure Stunts Mental Development in Rats

Rats exposed to cannabis vapor in the womb appear to struggle to learn switch problem-solving strategies, The Scientist reports.

The study was presented on November 4 at the annual Society for Neuroscience conference. Results were “indicative of an inability to acquire and maintain a new strategy” after exposure to cannabis in utero. Researchers indicated the study was part of a move to better understand the effects of cannabis on pregnant mothers.

Ryan McLaughlin, the study’s lead researcher, said, “As states allow more access, there has been an increase in self-reported cannabis use during pregnancy.

Most prior studies have simply injected rodents with pure THC, but that methodology has been criticized as the cannabis plant contains more than 100 other cannabinoids and compounds that can affect the mammalian body. The new study used vaporized extract which included the additional compounds.

At two months old, the rats were trained to press a lever beneath a light for a sugar reward. Once the rats learned to press the lever beneath the light, researchers changed the task, and rewards were always given when the rats pressed a specific lever, regardless of light position.

The rats who were not exposed to cannabis vapor while in the fetal stage had little trouble figuring out the change, but the rats whose mothers had consumed cannabis while pregnant showed difficulty switching to the new task. The rat pups would frequently revert to the old strategy or simply choose the wrong lever if the light wasn’t lit on either.

McLaughlin said the results do not indicate a general learning disability, but rather a specific issue with switching to new strategies.

Researchers theorize that the cannabinoid system is extremely important for early brain development. Disrupting the normal biological role of cannabinoids during development may result in different pathways in the brain. McLaughlin plans to look for differences in gene expression and protein levels in the brain to account for the difference.

Researchers were clear: further research is needed and the effects of prenatal cannabis exposure are still poorly defined.

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