Antinociceptive effects of buprenorphine in zebrafish larvae: An alternative for rodent models to study pain and nociception?

The underlying processes of nociception and pain are, despite the rodent models available, still not fully understood. One of the drawbacks of rodent model systems is the difficulty to screen compound libraries for their influence on nociception, thus slowing down the discovery of novel analgesics for clinical use.Rodent behavioural tasks have been previously adapted for larval zebrafish in our group and in the current manuscript we investigated the possibilities of zebrafish larvae as an additional model system to study nociception and pain and their underlying mechanisms.Zebrafish larvae were exposed to different concentrations of diluted acetic acid, a chemical noxious stimulus, and we measured nociceptive-specific behaviours. Cyclooxygenase-2 (cox-2), a gene known to be involved in nociception, was used as a marker for the activation of nociceptive pathways. Upon exposure to diluted acetic acid, five-day old larval zebrafish showed a concentration dependent increase in locomotor activity. This increase in locomotor activity was accompanied by a stimulus dependent increase in cox-2 mRNA expression, demonstrating that nociceptive pathways were indeed activated. Pre-treatment of the larvae with 0.1 μg/ml buprenorphine before exposure to the noxious stimulus, prevented the behavioural changes induced by the diluted acid. Further, the antinociceptive properties of buprenorphine could be reversed by co-treatment with the μ-receptor antagonist naloxone.In conclusion, our results demonstrate that larval zebrafish as young as five days, show behavioural responses upon exposure to a noxious stimulus. The magnitude of the responses is dependent on the intensity of the stimulus applied and activation of nociceptive pathways was confirmed by altered cox-2 mRNA expression. The analgesic buprenorphine has similar antinociceptive properties in this model as in higher vertebrates and mammals and is able to prevent the behavioural responses induced by the noxious stimulus. We therefore propose zebrafish larvae as a novel model system in nociception and pain related research.