The hormonal control of birth behavior in the gray short-tailed opossum (Monodelphis domestica)

In all major groups of Australian marsupials, prostaglandin F2 alpha (PGF) or oxytocin injection initiates birth behavior in adult females, adult male s and pouch young. Because inhibitors of PGF synthesis block this initiatio n, oxytocin may activate birth behavior via the stimulation of PGF synthesi s. In this study, the role of PGF and oxytocin in the activation of birth b ehavior was examined in an American marsupial, the gray short-tailed opossu m (Monodelphis domestica). Adult male and female gray opossums were given P GF, oxytocin, or saline (control) before behavioral observation. On the nex t day, the animals in the oxytocin group were injected with the PGF inhibit or flunixin meglumide (Finadyne, Schering Corp., U.S.A.) before oxytocin re injection and behavioral observation. Both males and females showed birth b ehavior in response to PGF but only females responded to oxytocin. There wa s no significant difference in the latency of response of females to oxytoc in alone versus response to oxytocin after receipt of the PGF inhibitor. Th ese results suggest that, in contrast to Australian species, in this Americ an marsupial, oxytocin initiates birth behavior only in females and does no t operate via stimulation of prostaglandin secretion. (C) 2000 Academic Pre ss.