Vomeronasal Organ Removal Blocks Pheromonal Induction of Estrus in Gray Short-Tailed Opossums (Monodelphis Domestica)1

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.

Changes in the Epithelium of the Vaginal Complex during the Estrous Cycle of the Marsupial <i>Monodelphis domestica</i>

“…Monodelphis belongs to the family Didelphidae; it has achieved an increasing importance for biomedical research and is easily kept under laboratory conditions [Fadem et al, 1982;Fadem, 1985;Fadem and Rayve, 1985;Baggott et al, 1987;Philips and Fadem, 1987;Adam et al, 1988;Baker et al, 1990;VandeBerg, 1990;Olson and Winfrey, 1991;Falconnier and Kress, 1992;Selwood and VandeBerg, 1992;Harder et al,1993;Taggart et al, 1993;Jackson and Harder, 1996;Harder and Jackson, 1999;Jackson and Harder, 2000].…”

Ultrastructural Changes in the Uterine Luminal and Glandular Epithelium during the Oestrous Cycle of the Marsupial <i>Monodelphis domestica</i> (Grey Short-Tailed Opossum)

“…M. domestica is native to southeast Brazil, where it is nocturnal and terrestrial or semiarboreal [Harder and Jackson, 1999]. Monodelphis breeds all year round, and the oestrous cycle is induced by male pheromones [Fadem, 1985[Fadem, , 1989Fadem and Rayve, 1985;Jackson and Harder, 1996]. The female shows no oestrous cycle when isolated from males [Stonerook and Harder, 1992;Harder et al, 1993;Harder and Jackson, 1999;Jackson and Harder, 2000].…”

Vomeronasal organ and its associated structures in the opossumMonodelphis domestica

“…At least 7 different types of scent marking behaviors have been identified for this species and the animals spend a substantial amount of their time sniffing and nuzzling odorous objects in their environment (Fadem and Cole, 1985;Poran et al, 1993b). The vomeronasal system in the opossum is involved in conspecific communication (Poran et al, 1993b;Poran and Genter, 1995) and reproduction (Jackson and Harder, 1996). Recently, Poran et al (1993a) described a unique stereotypical chemosensory investigative behavior that was termed ''nuzzling.''…”