Pheromones in mice: reciprocal interaction between the nose and brain

Abstract

Blockade of pregnancy by odours from strange males^1–3 has interested considerably those that adopt a sociobiological approach to reproduction^4–6. It has been suggested that the mechanism has evolved to promote heterogeneity in the population, and that strange males in possessing the capacity to block pregnancy thereby increase their reproductive potential. However, such knowledge as we have of the territorial behaviour⁷ and social organization of mice⁸ makes this explanation less likely as resident males have such an advantage over intruders that access by strange males is probably an infrequent event. Another explanation relates pregnancy block to the effect that the male pheromones have on the female reproductive hormones in other contexts. Male pheromones can stimulate both early puberty⁹ and induction of oestrus^10–12 in grouped females by suppressing prolactin secretion. Such a response, highly appropriate in this context, would be extremely disadvantageous following fertilization, since lowering prolactin is known to prevent implantation^13,14. Thus, some mechanism must exist to offset the more general effect of the male's own pheromone on the endocrine function of his female at such times, and this, we suggest, is prevented by the noradrenergic mechanism which we describe here.