VOMERONASAL ORGAN REMOVAL BLOCKS PHEROMONAL INDUCTION OF ESTRUS IN GRAY SHORT-TAILED OPOSSUMS (MONODELPHIS-DOMESTICA)

Estrus is induced in female gray short-tailed opossums (Monodelphis do mestica) by exposure to male chemical signals (pheromones). Isolated f emales remain anestrous, but direct exposure to a male or his scent-ma rked cage induces estrus within 4-6 days. The objective of this study was to investigate the importance of the vomeronasal organ in detectio n of and response to estrus-inducing pheromones. The vomeronasal organ was surgically removed through the palate from 8 females (VNX); 5 fem ales (SHAM) underwent sham surgeries in which the vomeronasal organ wa s exposed but not removed. After a 10-day recovery period, females wer e placed into male scent-marked cages. Body weight and urogenital sinu s cytology were monitored throughout the experiment. All females were anesthetized and perfused with 4% paraformaldehyde 12-13 days after in itial pheromone exposure. Vomeronasal organ ablation was evaluated his tologically in decalcified snouts. In addition, deafferentation of the accessory olfactory bulb was confirmed by use of a lectin stain speci fic for the vomeronasal nerve and the glomerular layer of the bulb. Al l females classified as completely VNX (n = 5) remained anestrous thro ughout the pheromonal exposure. Incompletely VNX females (n = 2) and a ll SHAM animals exhibited estrus within 7 days of pheromone stimulatio n. At perfusion, the mean uterine weight (280.71 +/- 95.6 mg/85 g BW) of SHAM females was greater (p < 0.05) than that of unresponsive, VNX females (133.33 +/- 31.14 mg/85 g). This study demonstrates that the v omeronasal organ is an essential component for transduction of male ph eromones required for induction of estrus in a marsupial species.