Early Exposure to THC Alters M-Cell Development in Zebrafish Embryos

Abstract

Cannabis is one of the most commonly used illicit recreational drugs that is often taken for medicinal purposes. The psychoactive ingredient in cannabis is Δ9-Tetrahydrocannabinol (Δ9-THC, hereafter referred to as THC), which is an agonist at the endocannabinoid receptors CB1R and CB2R. Here, we exposed zebrafish embryos to THC during the gastrulation phase to determine the long-term effects during development. We specifically focused on reticulospinal neurons known as the Mauthner cells (M-cell) that are involved in escape response movements. The M- cells are born during gastrulation, thus allowing us to examine neuronal morphology of neurons born during the time of exposure. After the exposure, embryos were allowed to develop normally and were examined at two days post-fertilization for M-cell morphology and escape responses. THC treated embryos exhibited subtle alterations in M-cell axon diameter and small changes in escape response dynamics to touch. Because escape responses were altered, we also examined muscle fiber development. The fluorescent labelling of red and white muscle fibers showed that while muscles were largely intact, the fibers were slightly disorganized with subtle but significant changes in the pattern of expression of nicotinic acetylcholine receptors. However, there were no overt changes in the expression of nicotinic receptor subunit mRNA ascertained by qPCR. Embryos were allowed to further develop until 5 dpf, when they were examined for overall levels of movement. Animals exposed to THC during gastrulation exhibited reduced activity compared with vehicle controls. Together, these findings indicate that zebrafish exposed to THC during the gastrula phase exhibit small changes in neuronal and muscle morphology that may impact behavior and locomotion.

Medium-throughput zebrafish optogenetic platform identifies deficits in subsequent neural activity following brief early exposure to cannabidiol and Δ9-tetrahydrocannabinol

“…Set-up was similar as described above. Following the experiment, larvae were stained with anti-RMO44 (Thermo Fisher Scientific, Waltham, MA, USA) and imaged using a Zeiss LSM 710 confocal microscope (Oberkochen, Germany) as described elsewhere 76 .…”

A critical review on the detection, occurrence, fate, toxicity, and removal of cannabinoids in the water system and the environment

“…Furthermore, locomotion studies also showed that the number of C-start escape responses to sound stimuli for THC and CBD exposed zebrafish larvae was severely reduced ( Ahmed et al 2018 ). Exposure to THC (6 mg L -1 ) for 5.25 to 10.75 hours post fertilization affected the zebrafish embryos’ mircofold cell axon diameter and their escape response dynamics to touch ( Amin et al 2020 ). Zebrafish muscle fibers had small but significant changes in the pattern of expression of nicotinic acetylcholine receptors and were slightly disorganized even though the muscles were largely intact ( Amin et al 2020 ).…”

“…Exposure to THC (6 mg L -1 ) for 5.25 to 10.75 hours post fertilization affected the zebrafish embryos’ mircofold cell axon diameter and their escape response dynamics to touch ( Amin et al 2020 ). Zebrafish muscle fibers had small but significant changes in the pattern of expression of nicotinic acetylcholine receptors and were slightly disorganized even though the muscles were largely intact ( Amin et al 2020 ). However, qPCR results showed no obvious changes in the expression of mRNA of the nicotinic receptor subunit ( Amin et al 2020 ).…”

“…Zebrafish muscle fibers had small but significant changes in the pattern of expression of nicotinic acetylcholine receptors and were slightly disorganized even though the muscles were largely intact ( Amin et al 2020 ). However, qPCR results showed no obvious changes in the expression of mRNA of the nicotinic receptor subunit ( Amin et al 2020 ). While adverse effect on the zebrafish was observed after exposure to THC and CBD, high concentrations of THC (6 mg L -1 ) or CBD (3 mg L -1 ) used in both experiments are not likely to occur in natural water systems.…”

Marijuana and Opioid Use during Pregnancy: Using Zebrafish to Gain Understanding of Congenital Anomalies Caused by Drug Exposure during Development

“…Cannabinoid treatment altered synaptic activity at neuromuscular junctions (NMJs) and altered nicotinic acetylcholine receptor expression at NMJs [ 83 ]. Exposure to 6 mg/L THC during gastrulation, from 5.25 to 10.75 hpf slightly altered the axon diameter of Mauthner cells (M-cell), the neurons born during gastrulation and which are involved in escape response movements [ 85 ]. The muscle fibers of those larvae were slightly disorganized with subtle but significant changes in nicotinic acetylcholine receptor expression patterns [ 85 ].…”