Pregnancy blocking in the vole, Microtus agrestis

Abstract

Pregnancy failed in a high proportion of newly mated Microtus agrestis females when they were exposed to a strange male between 48 and 72 hr after mating with a stud male. This effect of the strange male was testosterone dependent. Direct contact with the strange male was normally necessary, and even a single barrier of wire mesh between the female and strange male prevented the male from exerting his pregnancy-blocking effect. The results suggest that the stimuli mediating pregnancy blocking in the vole may differ from those operative in the mouse.

Involvement of the vomeronasal organ and prolactin in pheromonal induction of delayed implantation in mice

“…The immediate cause of pregnancy block is thought to be a failure of luteal function (Dominic, 1970;Milligan, 1976a) and the reason for this luteal failure has been suggested to be either an increased secretion of gonadotrophins (Hoppe & Whitten, 1972) or a suppression of prolactin (Bruce & Parkes, 1960;Milligan, 1976b). Unfortunately the evidence in support of either of these proposals is largely circumstantial.…”

“…The failure of luteal function produced by the pregnancy blocking pheromone is in turn thought to be responsible for the failure of implantation (Bruce & Parkes, 1961a;Dominic, 1970). In mice (Bruce, 1960) or voles (Milligan, 1976a) there were no obvious signs of embryos following the olfactory block to pregnancy, and their fate was not determined.…”

Evidence for a coitally induced 'mnemonic' involved in luteal function in the vole (Microtus agrestis)

“…Despite the many studies of the stimulus control of the phenomenon and its potential importance to animals in the wild (Milligan, 1979), the endocrine basis of the effect is still not understood. The primary cause of pregnancy blockage is the failure of luteal function (Dominic, 1970;MUUgan, 1976b) and the reason for this luteal failure has been variously suggested to be an increased secretion of gonadotrophins (Richmond & Conaway, 1969;Hoppe & Whitten, 1972) and/or a suppression of prolactin (Parkes & Bruce, 1961;Milligan, 1976b Worth, Charlton & MacKinnon (1973) and Milligan (1974) respectively. Females were 2-to 4-month-old virgins.…”

“…Males were breeding adults. The procedure for mating females was as described by Charlton, Milligan & Versi (1978) for Exps 1, 2 and 3 and as described by Milligan (1976a) for Exp. 4 except that females that failed to mate within 7 h of the introduction of the male in Exp.…”

Pregnancy blockage and the memory of the stud male in the vole (Microtus agrestis)

“…Pheromones in the urine are believed to be the effective stimuli mediating the response in mice (Dominic, 1966), although whether the same is true for other species is uncertain. The vole, Microtus agrestis, certainly differs from the mouse in that unrestricted contact between the female and strange male is required for the effect (Milligan, 1976a). Regardless of the cues involved, however, the different responses of the female to the stud and strange male implies that the female can remember, and therefore recognize, the stud male.…”