KLEMENHAGEN, K.C.*; RAND, M.S.: An Investigation of Opioid Involvement in the Modulation of Reproductive Behavior in the Whiptail Lizard Cnemidophorus velox

The role of endogenous opioids in reproductive behavior has been studied in a variety of mammalian species. Additionally, amphibian locomotory behavior can be modulated by administration of the general opioid antagonist naloxone. The investigation of the opioid system in reptiles has largely focused on the location and synthesis of central opioid peptides; however, the behavioral effects of opioids have not been fully addressed. We are interested in the possible role of opioids in reproductive behaviors of the whiptail lizard, Cnemidophorus velox. The reproductive behavior of Cnemidophorus involves a well-characterized copulatory position called the “doughnut.” In this position, the male stretches his body into an arc above the female and closes his jaw tightly on her midsection. During the doughnut, the bitefrom the male appears to immobilize the female, allowing the copulatory position to be maintained for several minutes. We hypothesized that endogenous opioids mediate this temporary immobility, thus allowing the female to sustain the copulatory position. We predicted that administration of a general opioid receptor antagonist (naloxone) to the female would block the immobility response to the doughnut position. The administration of high (10mg/kg body weight) and low (1mg/kg body weight) doses of naloxone did not significantly affect female receptivity, the duration of the copulatory position, or the amount of locomotory activity compared to saline controls. Because the peak response of naloxone in many species is between 10-30 minutes post-injection, we plan to investigate and report the effects of naltrexone, a longer-lasting general opioid antagonist, on the same behaviors.