Putting Nose into Reproduction: Influence of Nasal and Reproductive Odourant Signaling on Male Reproduction.

Odourant receptors (ORs) are not restricted only to the nose, but also occur in many other organs and tissues, including the reproductive system. In fact, ORs are the most heavily expressed in testis than in any other extra-nasal tissue. Accumulating evidence suggests that olfactory and reproductive systems are both structurally and functionally linked and that these interconnections can influence various aspects of reproduction. In this article, we first review our current understanding of these interconnections and then collate accumulated evidence on the presence of ORs in the male reproductive system and sperm cells. We then investigate the potential role of female reproductive tract odourants in sperm chemotaxis and selection. Finally, since the existing evidence especially for sperm odor sensing capability and its physiological function are controversial, we also review potential reasons for the controversy and propose some ways to resolve the debate. Collectively, we conclude that reproductive odourant signaling may play an important, although currently largely unclear role in many key processes directly related to male fertility. However, since we lack holistic understanding of the functional significance of ORs and odor sensing pathways of the male reproductive system, more empirical research is warranted.