Behavioral effects of cannabinoids on zebrafish larvae

Cannabinoids are natural or synthetic compounds related chemically to Δ⁹-THC, the principle psychotropic constituent of the hemp plant, Cannabis sativa L. Here, we examine the effects of the cannabinoids Δ⁹-THC, WIN 55,212–2 and CP 55,940, and the cannabinoid antagonist (Am 251). Exposures were either acute (1–12h exposure at 108 hour post fertilization [hpf]); or chronic (96h exposure starting at 24 hpf. Wild type zebrafish embryos (3,250, including controls), were cultured individually in 250µl defined buffer in 96-well plates. Geometric range-finding was used to determine the experimental concentrations At day 5, behavioural analysis (visual motor response test) was carried out in which movement of individual larvae was analysed using automated video-tracking. With acute exposure, embryos showed a biphasic response to the dark challenge with Δ⁹-THC, WIN55, 212–2 and CP55,940. This response consisted of stimulation of locomotor activity at low concentrations, suppression at high doses. With the antagonist AM251 alone, the locomotor activity was suppressed at high concentrations. With chronic exposure, embryos habituated to the effects of all three cannabinoids when assayed with the dark challenge phase. Furthermore, the excitation was ameliorated when antagonist was co-administered with the cannabinoid. We conclude that cannabinoids have similar effects in zebrafish and mammals. In particular, the acute exposure response resembles behavioural effects reported for adult rodents.