Estrous odors and sexually conditioned neutral odors activate separate neural pathways in the male rat.

Olfactory stimuli play important roles in sexual behavior. Previous studies have demonstrated that both estrous odors and initially neutral odors paired with copulation influence the sexual behavior of male rats. The present study examines the pattern of neural activation as revealed by Fos immunoreactivity (Fos-IR) following exposure to bedding scented with either a neutral odor (almond) paired previously with copulation, estrous odors or no odor. Following exposure to estrous odors Fos-IR increased in the accessory olfactory bulb, medial amygdala, medial bed nucleus of the stria terminalis, medial preoptic area, ventromedial hypothalamus, ventral tegmental area, and both the nucleus accumbens core and shell. Conversely, following exposure to the sexually conditioned odor Fos-IR increased in the piriform cortex, basolateral amygdala, nucleus accumbens core, and the anterior portion of the lateral hypothalamic area. In addition, following exposure to almond odor Fos-IR increased in the main olfactory bulb independent of its pairing with copulation. These patterns of Fos-IR following exposure to estrous or sexually conditioned odors were not influenced by either the addition or omission of the other type of odor. These findings demonstrate that estrous and sexually conditioned odors are processed by distinct neural pathways and converge in the nucleus accumbens core, suggesting that this structure has a unique role in processing sexual stimuli of both pheromonal and olfactory natures.