Zebrafish exposed to the leading cannabinoids found in cannabis in the earliest stages of development suffer a significant drop in neural activity later in life, according to a University of Alberta study that has implications for prenatal development in humans.

Richard Kanyo, the lead author on the study and post-doctoral fellow in the Faculty of Medicine & Dentistry, said despite the popular narrative that the health benefits of cannabis are many, it turns out there is a surprisingly large knowledge gap.

Once the legalization happened, people got really excited about it and there’s a lot of bias in the media about positive effects, so we began wondering about the negative implications.”

Richard Kanyo, Study’s Lead Author

Kanyo teamed up with Declan Ali, a biological sciences researcher in the Faculty of Science, whose lab had an ongoing interest in how certain chemicals and compounds alter development in young animals “when their neurons are contacting each other and trying to communicate.”

For the study, developing zebrafish embryos were left to incubate for 10 hours in a solution containing one of the two main active cannabinoids found in cannabis–tetrahydrocannabinol (THC) or cannabidiol (CBD)–or a combination of these two compounds, immediately after fertilization.

Ali explained that 10 hours represents a period in animal development that includes a stage of development known as gastrulation, when the multiplying cells start to form multiple tissue layers. In zebrafish it happens between five and 10 hours after the egg has been fertilized; in humans it lasts about a week and occurs roughly three weeks after egg fertilization.

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.

On the fourth day of development, Kanyo looked at brain activity using cutting-edge fluorescing calcium sensors that measure calcium, which is increased in active neurons.

He found that neural activity decreased by 60 to 70 per cent in the group bathed in THC and by more than 70 per cent in the group immersed in CBD. The decrease was even more pronounced in zebrafish that developed in a solution containing both compounds

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