Female odors stimulate CART neurons in the ventral premammillary nucleus of male rats

Olfactory information is known to influence both male and female sexual behavior. Chemosensory compounds known as pheromones activate distinct brain pathways, inducing innate and stereotyped behaviors, as well as hormonal changes. Studies have shown that female odors induce Fos expression in various brain nuclei of conspecific males, including the ventral premammillary nucleus (PMV). Although poorly investigated, previous studies have suggested that the PMV plays a role in aggressive and sexual behavior. In this study, we used Fos protein expression as a marker for neurons responsive to female odors in sexual inexperienced male rats exposed to soiled bedding. We observed that female odors induced intense Fos immunoreactivity throughout the PMV. Most of these neurons also express cocaine- and amphetamine-regulated transcript (CART) immunoreactivity. In addition, we used in situ hybridization and observed that, following exposure to female odors, CART mRNA increased only in the ventral PMV. Our results suggest that female odors stimulate CART production in the PMV of inexperienced males. Considering that the PMV CART neurons also express the leptin receptor, as well as the fact that they project to areas related to reproduction, we hypothesize that PMV CART neurons integrate nutritional and environmental (olfactory) information, being apt to modulate male reproductive behavior.