Vomeronasal organ removal blocks pheromonal induction of estrus in gray short-tailed opossums (Monodelphis domestica)

Abstract

Estrus is induced in female gray short-tailed opossums (Monodelphis domestica) by exposure to male chemical signals (pheromones). Isolated females remain anestrous, but direct exposure to a male or his scent-marked cage induces estrus within 4-6 days. The objective of this study was to investigate the importance of the vomeronasal organ in detection of and response to estrus inducing pheromones. The vomeronasal organ was surgically removed through the palate from 8 females (VNX); 5 females (SHAM) underwent sham surgeries in which the vomeronasal organ was exposed but not removed. After a 10-day recovery period, females were placed into male scent marked cages. Body weight and urogenital sinus cytology were monitored throughout the experiment. All females were anesthetized and perfused with 4% paraformaldehyde 12-13 days after initial pheromone exposure. Vomeronasal organ ablation was evaluated histologically in decalcified snouts. In addition, deafferentation of the accessory olfactory bulb was confirmed by use of a lectin stain specific for the vomeronasal nerve and the glomerular layer of the bulb. All females classified as completely VNX (n = 5) remained anestrous throughout the pheromonal exposure. Incompletely VNX females (n = 2) and all SHAM animals exhibited estrus within 7 days of pheromone stimulation. 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 vomeronasal organ is an essential component for transduction of male pheromones required for induction of estrus in a marsupial species.