Essence of Alpha Male

Abstract

Pheromones are chemicals involved in mating and reproduction. In rodents, these chemicals are detected by the vomeronasal organ, which humans lack, and by the olfactory system. Mate-specific pheromone memories play an important role in female rodent reproduction. Two parts of the brain that undergo neurogenesis in the adult are the olfactory bulb (the new neurons originate in the subventricular zone) and the dentate gyrus of the hippocampus. In rodents, neurogenesis in the olfactory bulb is stimulated by mating or pregnancy. Neurogenesis in the hippocampus is stimulated by running, enriched environments, or learning. Mak et al . found that pheromones in the urine of dominant, but not subordinate or castrated, male mice stimulated the neurogenesis of both the olfactory bulb and the dentate gyrus in female mice. Furthermore, females exposed to dominant-male pheromones and then presented with both a dominant and a subordinate male spent more time sniffing the dominant male's compartment, indicating preference for the dominant male. This pheromone-induced male preference was lost if the female mice were deficient in the prolactin receptor (PRLR) or if neurogenesis was blocked by injection of cytosine arabinoside. It is known that male pheromones trigger surges in luteinizing hormone (LH) and prolactin (PRL) in the female mice. Mak et al . detected PRLR in the subventricular zone (the source of the new olfactory bulb neurons) and detected the LH receptor in both the subventricular zone and the dentate gyrus. Injection of low doses of LH stimulated neurogenesis in the dentate gyrus, whereas injection of PRL stimulated neurogenesis in the subventricular zone. Male pheromones failed to stimulate subventricular zone neurogenesis in the female mice deficient for the PRL receptor, and neurogenesis in the dentate gyrus was absent in the mice deficient for the LH receptor. These results raise the question of whether male pheromones contribute to human mate selection, and undoubtedly the perfume industry will be keenly interested in whether they can create the "dominant-male fragrance" (see commentary by DiRocco and Xia). G. K. Mak, E. K. Enwere, C. Gregg, T. Pakarainen, M. Poutanen, I. Huhtaniemi, S. Weiss, Male pheromone-stimulated neurogenesis in the adult female brain: Possible role in mating behavior. Nat. Neurosci. 10 , 1003-1011 (2007). [PubMed] D. P. DiRocco, Z. Xia, Alpha males win again. Nat. Neurosci. 10 , 938-940 (2007). [PubMed]