Rat-induced disruption of early pregnancy in mice and its prevention by the stud male.

Recently inseminated mice exhibited a high rate of pregnancy failure following exposure to male rats irrespective of whether they were housed in direct physical contact with the rat or not. Pregnancy disruption was also seen in mice which were housed on male rat-soiled bedding. By contrast, inseminated mice housed with female rats or on bedding soiled by female rats showed a significantly lower rate of pregnancy failure. The presence of the stud male prevented the pregnancy failure in mice induced by exposure to male rats or male rat-soiled bedding. This protective effect of the stud male on pregnancy in rat-exposed mice is analogous to the protective effect of the stud male on pregnancy in conspecific novel male-exposed mice and in mice subjected to nutritional stress. Hence the possibility that the protective effect of the stud male on pregnancy in male rat-exposed mice is due to the stimulation of luteotrophic activity by the stud male-originating olfactory cues cannot be ruled out. However, it is not clear whether the pregnancy failure in newly inseminated mice induced by exposure to rats is the result of a general stress or is mediated through rat-originating chemosignals acting interspecifically.

Nutritional stress-induced implantation failure in laboratory mice: inhibition by continuous illumination.

The implantation failure in newly inseminated mice induced by food deprivation for 48 hr, beginning at 0900 hrs on day 4 post coitum, was prevented by simultaneous exposure to light continuously for 48 or 36 hr. Food-deprived females that were exposed to continuous light for 36 hr showed a significant increase in fetal resorption as compared with food-deprived females exposed to continuous light for 48 hr. Since failure of hypophysial prolactin release appears to be the primary endocrine cause of the inanition-induced implantation failure, the results suggest that exposure to continuous light protects implantation in food-deprived females by stimulating luteotrophic activity.

Bromocriptine-induced implantation failure in mice: failure of the stud male to protect pregnancy.

The presence of the stud male failed to prevent implantation failure in newly inseminated females induced by administration of bromocriptine. This is in contrast with the ability of the stud male to prevent implantation failure in females induced by alien male exposure, and nutritional stress. Since bromocriptine is a potent inhibitor of hypophysial prolactin release by virtue of its stimulatory effect on hypothalamic dopaminergic activity, the results suggest that the stud male-originating luteotrophic stimulus is incapable of overriding the dopaminergic activity in bromocriptine-treated females.

Protective effect of ectopic pituitary graft on nutritional stress-induced implantation failure in mice.

Implantation failure in newly inseminated mice induced by food deprivation was prevented by the presence of an ectopic pituitary graft. Since a pituitary graft in an ectopic site is known to secrete prolactin continuously, it is suggested that suppression of implantation failure in pituitary-grafted females is due to the luteotrophic support provided by the graft. The results provide supportive evidence for the view that depression of hypophysial prolactin is the primary endocrine cause of the nutritional stress-induced implantation failure in mice.

Stud male-induced protection of implantation in food-deprived mice: masking effect of an artificial scent on pheromonal odour.

In contrast to unscented stud males, stud males anointed with a commercial perfume failed to protect implantation in food-deprived females. It is suggested that the failure of perfumed stud males to protect pregnancy in their coital partners is due to the masking effect of the perfume on the stud male-originating olfactory cue which stimulates luteotrophic activity in females. The results are also consistent with the view that the newly inseminated female mouse identifies the stud male as an individual through a pheromonal cue and this is involved in the protective effect on implantation in the food-deprived female.

Failure of familiar males to prevent alien male-induced implantation block (the Bruce effect) in laboratory mice.

Implantation failure in newly inseminated females induced by exposure to alien males (the Bruce effect) was significantly reduced when the females were housed with the stud male. By contrast, newly inseminated females housed with a familiar male during exposure to alien males exhibited a high rate of implantation failure. The results suggest that the protective effect of the stud male on implantation is not because of the familiarity of the female with his odour cues. The results are consistent with the view that the newly inseminated female mouse identifies her coital partner as an individual because she becomes 'imprinted' with his odour during the pericopulatory period.