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A new WSU study suggests pregnant mothers who smoke cannabis could be impairing their children 

click to enlarge Pregnant rats, like pregnant humans, should probably lay off the weed for their kid's sake.
  • Pregnant rats, like pregnant humans, should probably lay off the weed for their kid's sake.

A pregnant rat crouches down inside a clear box. Suddenly, a puff of vapor bursts through. The rat inhales it. Two minutes later, it happens again. And again. After one hour, the rat — having no choice in the matter — is completely high.

The rat, being a rat, probably has no idea how this will affect its offspring. Unfortunately, humans don't know very much either, which is why this rat and her baby were chosen for this study conducted by Washington State University researchers.

As a result, researchers are a little bit closer to understanding how weed impacts the brain of children exposed to cannabis in the womb — both in rats and in humans.

"There appears to be some subtle deficits with respect to domains of cognitive functioning," says Ryan McLaughlin, assistant professor in the WSU Department of Integrative Physiology and Neuroscience.

click to enlarge Ryan McLaughlin
  • Ryan McLaughlin

Essentially, that means pregnant mothers who use cannabis may be altering brain development in their children. McLaughlin presented a summary of the study earlier this month at Neuroscience 2018, the largest neuroscience conference in the world. While he stresses that the results of the study are still preliminary and have not been published in a peer-reviewed publication, the study appears to reinforce what public health officials have recommended for decades: Don't smoke while you're pregnant.

McLaughlin says it's an important area of research since perceptions of cannabis have shifted as it's been legalized in Washington and other states.

"We have an increased urgency to really understand what the long-term ramifications are," he says.

Pregnant women appear to be using weed more often — or at least they're more comfortable admitting they do. A national survey published last year indicates that marijuana use among pregnant women increased from 2.4 percent in 2002 to 3.8 percent in 2014, a 62 percent jump.

Susan Schultz, program manager for the Spokane Regional Health District's (SRHD) nurse-family partnership program, says she notices pregnant mothers are more often assuming marijuana is OK to use during their pregnancy. Most frequently it's used for nausea or anxiety.

"[They think] it wouldn't have been legalized if there was a problem with it," Schultz says.

Schultz says the message has always been not to smoke anything during pregnancy. Cannabis could lead to premature birth, cause the child to have lifelong issues paying attention or following rules, or lower a child's IQ, according to the SRHD.

But Schultz admits there's still plenty left to be learned about how pregnant mothers smoking marijuana will impact kids. In studies on children exposed to marijuana before birth, it can be difficult to isolate marijuana when mothers often use other substances as well. In fact, McLaughlin says those extraneous factors make it difficult to be certain what the effects of cannabis would be on children.

"Really, we don't know a whole lot about what the effects of cannabis alone are on the cognitive development of offspring," McLaughlin says.

That's where the rats come in. McLaughlin and the team of researchers exposed the pregnant rats to marijuana vapor to try to replicate how humans consume marijuana. The offspring of those rats were then trained to press one of two levers, coming to understand eventually that the lever near a light gave them sugar. That was an easy rule to learn for both the cannabis-exposed rat offspring and for those not exposed to cannabis.

But then the rule changed. They got sugar if they chose only the left lever, regardless of where the light was. The rat offspring who had been prenatally exposed to high levels of cannabis "showed marked deficits in their ability to shift strategies when the new rule was implemented," WSU researchers wrote.

It suggests a problem with cognitive flexibility, McLaughlin says. The rats had difficulty learning the new strategy, and it may negatively impact that cognitive flexibility in adulthood, researchers say.

The study was one of three new studies presented at the Society for Neuroscience annual meeting in early November. One, from Auburn University, found that pregnant mothers injected with a continuous dose of synthetic cannabis produced offspring that were significantly impaired in different memory tasks. Another, from the University of Maryland School of Medicine, found that rats exposed to THC in the womb also had memory impairments.

But McLaughlin notes that the experiences of rodents may not necessarily guarantee it carries over to humans.

"There's a lot of opportunity for environmental variables," he notes. "So basically what we can really say is that maybe there might be deficits that emerge long term, but we need further research to validate it." ♦

The original print version of this article was headlined "Ratted Out"

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