Opiate receptor in praying mantis: effect of morphine and naloxone

A praying mantis displays a "frightening reaction" called deimatic reaction (DR), any time that it is faced with a patterned visual stimulus that represents a potential damage for the insect. Results of the present paper show that the DR could be also elicited by an actual noxious (an electrical shock) and that this response is similar to that elicited by a potential nociceptive stimulus (a patterned visual stimulus). The DR elicited by the electric shock was used as a model for studying the analgesic effect of opiates. The mantis was placed in an apparatus that allowed us to give the insect an electrical shock and to measure the strength of its DR. During a first session the voltage threshold necessary to induce a full DR was determined, and then, the insect was injected with a certain solution. The voltage threshold was tested one, two and four hours after injection. Mantises that were injected with only distilled water showed no changes in their voltage threshold during the three tests. Injections of 300, 350 and 400 micrograms/g of morphine-HCl increased the voltage threshold in both a time-dependent and a dose related manner. A dose of 350 micrograms/g of morphine-HCl produced 50% of response inhibition after two hours of injections and is referred to as the median antinoxious dose ( AD50 ). Sixteen micrograms/g of naloxone given in conjunction with an AD50 of morphine, partially blocked the effect of morphine during the first hour and fully blocked it during the second hour. Thirty-two micrograms/g of naloxone fully blocked the morphine effect during the first and the second hour. However, more than 48 micrograms/g of naloxone alone also increased the voltage threshold in insects, similar to those described for vertebrates.