[
International Worm Meeting,
2007]
The thermal avoidance response in C. elegans has been described as a retraction of the animals body and/or a directional change in locomotion in response to a 33 C heat stimulus. The genetic and molecular basis of this behavior is not fully understood. This report presents data on the effects of morphine on the thermal avoidance response in C. elegans. Wild type C .elegans N2 were grown on Nematode growth Agar (NGA) plates. The animals were allowed to reach adult stage (L4), collected from the plates using M9 washing buffer and exposed to 10-5 M morphine for 30 minutes, and with 10-4 M Naloxone or 10-4 M CTOP. The animals were then exposed to a 33 C heat stimulus directly in front of their anterior end and their response was recorded. The experiments were done blindly so that the operator didnt know what treatment was being done. At least three replicates of 250 to 300 worms were counted for each experiment. 76.46 % of the control worms exhibited a Class I response and 7.37 % showed a class IV response. The percentage of class I of the morphine exposed group decreased to 46.56 % whereas 17.83 % exhibited a Class IV response (P=0.04). As expected, Naloxone blocked the analgesic effect of morphine, 77.25% of the worms exhibited a Class I response. CTOP also blocked the response. Animals treated with 10-4 M L-NAME prior to the morphine treatment, while they had a 10% decrease in class I behavior, they were not significantly different from the controls. Nevertheless, when this group was compared to the morphine treated animals the differences were not significant. Summarizing, morphine significantly decreases the percentage of animals that display a class I thermal avoidance response. This effect was fully reversed by naloxone, an opioid receptor blocker and by CTOP a mu opioid receptor antagonist. L-NAME barely reversed the morphine effect (p=0.09) suggesting that while the analgesic effect may be mediated by nitric oxide it is not as potent as that observed in other animals. C. elegans doesnt appear to have a mu opioid receptor in its genome. A number of orphan genes appear to be homologous to the opioid receptor family in the human genome. These results are consistent with previous data reported for the parasitic nematode Ascaris suum.