Zebrafish exposed to THC in the earliest stages of their development saw a 70 per cent dive in neural activity later in life and the decrease, at over 70 per cent, was starker when they were immersed in CBD, the University of Alberta reports.

If the same thing happens with humans, the researchers suggest that the findings could have implications for prenatal development in humans, an article posted on the university’s website notes.

“In light of legislative changes and the widespread use of cannabis as a recreational and medicinal drug, delayed effects of cannabis upon brief exposure during embryonic development are of high interest as early pregnancies often go undetected,” states the study published this week in Scientific Reports.

The study’s lead author, Richard Kanyo, a post-doctoral fellow in the University of Alberta’s Faculty of Medicine and Dentistry, teamed with Declan Ali, a biological sciences researcher in the Faculty of Science, to learn a bit more about what exposed zebrafish could tell them about possible risks.

“The amount of drug used would be equivalent to someone consuming cannabis or the active compounds every day for two to three weeks at the very start of a pregnancy,” the researchers note in the article.

Developing zebrafish embryos were left to incubate for 10 hours in a solution containing THC, CBD or a combination of the two immediately after fertilization.

Ten hours is enough time for a zebrafish to reach a stage of development when multiplying cells start to form multiple tissue layers. In humans, the stage lasts about a week and occurs roughly three weeks after egg fertilization.

On the fourth day of development, Kanyo found neural activity was down by 60 to 70 per cent in the zebrafish bathed in THC, by more than 70 per cent in the group immersed in CBD and the “decrease was even more pronounced” for the group exposed to both compounds.

“Compared with one of the control compounds, MS222, a local anesthetic that blocks activity along nerves, the drop in neural activity on the high end of the concentrations tested was the equivalent to the drop in animals that have been anesthetized,” Kanyo points out.

Ali suggests prospective parents may want to limit exposure to the compounds as they would with nicotine and alcohol. / PHOTO BY ISTOCK / GETTY IMAGES PLUS

At higher doses, the study shows both cannabinoids could dramatically reduce neural activity and locomotor activity, the abstract states. Ali acknowledges the concentrations used in the experiment were on the high side “to make up for the fact that the compounds have to work their way through an outer egg casing to get to the embryo,” the article notes.

Five days after fertilization, “the reduction in activity compared with normally developed zebrafish was about 20 per cent for CBD and THC individually, but 80 per cent or higher when in combination,” it states.

The study was meant to explore any negative implications of cannabis use given what Kanyo regards as a “bias in the media about positive effects” that followed legalization of recreational weed.

Still, more work is needed to better understand the mechanism behind the effects on neural activity, Ali says, suggesting prospective parents may want to limit exposure to the compounds as they would with nicotine and alcohol.

Acknowledging that cannabis has had positive impacts, including with regard to pain relief and reducing seizures, Ali adds the study is trying to show that “what we’re seeing is cannabis is not all good for everyone all the time and probably should not be taken during pregnancy.”

The abstract notes that future studies are warranted “to reveal other cannabinoids and their receptors to understand the implications of cannabis consumption on fetal development.”