Associative learning is necessary for airborne pheromones to activate sexual arousal-linked brain areas of female rats.

In rodents, urine-borne male pheromones include volatile organic compounds (VOCs) and major urinary proteins (MUPs). In mice, the attraction of females to male odor is reportedly acquired through associative learning with MUPs in some studies. Here, we found that VOC and MUP sex pheromones were differentiated in rats at around 8 weeks of age and that females separated from males at weaning showed no preference for male urine odor after sexual maturity. Olfactory preferences could be gained in females after repeated experience of VOC pheromones alone as well as male urine or a blend of synthetic VOC pheromones and recombinant MUPs. However, differences in acquired olfactory preferences for male urine were further revealed by neuro-immuno-histochemical studies. The blend exhibited neural activation in the main olfactory system (MOS), accessory system (AOS), and the ventromedial hypothalamus (VMH), indicating sexual arousal, whereas the VOC alone only caused neural activation of MOS. We suggest that olfactory preference is generated through repeated experience of either VOCs or a blend of VOCs and MUPs, but the neural activations related to sexual arousal have to be acquired through associative learning with MUPs in female rats. Significance statement: When adult female rats were separated from males before maturity, they lost their attraction to male urine odor. Female preference to volatiles in male urine could be gained by repeated experience of volatile and protein pheromones. Brain regions related to sexual arousal were activated by male urine in females with experience of VOCs together with MUPs but not in those experienced with VOCs alone. Associative learning between VOC and MUP pheromones is necessary for male urine odor-induced FOS responses in the key regions for sexual arousal/excitement in female rats. [ABSTRACT FROM AUTHOR]