Medical marijuana has been used to treat conditions such as epilepsy, nausea, pain and anxiety, and the use of it is now legal in numerous states. The primary difference between medical marijuana and recreational marijuana is in the levels of cannabidiol (CBD, higher in medical marijuana) and tetrahydrocannabinol (THC, higher in recreational marijuana). The primary psychoactive ingredient in recreational marijuana is delta 9-tetrahydrocannabinol (Δ9-THC), which has been shown to alter behavioral and locomotor responses in zebrafish embryos. Previously, we examined the effects of exposure of zebrafish embryos to Δ9-THC and found a higher death rate and shorter embryos with curved spines at the higher levels (1.25-2.5 µg/ml) of Δ9-THC compared to control embryos. Another psychoactive compound in cannabis is Δ8-THC, but because it is less potent than Δ9-THC (~50%), it is often considered “safe.” Use of Δ8-THC has risen greatly in the last few years due to the legalization of hemp-derived Δ8-THC through the 2018 US Farm Bill despite little research into its developmental effects. In this study, we compared the effects of Δ9-THC with those of Δ8-THC. Embryos were randomly divided into groups receiving 0, 0.15, 0.3, 0.6, 1.25, 2.5 and 5 µg/ml of either compound. Since stock THC solutions were in methanol, we also included a methanol-only control. Embryos were measured for length and observed for spinal curvature on day three post fertilization (3 dpf) but were kept until 5 dpf to allow further development. We monitored embryos daily to record the number dead and/or hatched. At 5 dpf, we anesthetized the embryos, fixed them in 4% paraformaldehyde and stored them in 100% methanol at 20° C for morphologic assessment of jaw structure using alcian blue staining of cartilage. Though we have yet to fully analyze the data, we are finding similar effects with Δ8-THC as with Δ9-THC: increased death rate and shorter embryos with axial curvatures. These data suggest that though Δ8-THC is legal it should not be considered safe during development.


YHC Undergraduate Research Initiative

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