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Internal and External Control of Instinctual Social Behaviors


In sexually reproducing animals, innate sexually dimorphic behaviors are regulated internally by gonadal steroid hormones and other cues and by sensory cues from the external world, such as pheromones.

In mice, pheromones can be sensed by either the main olfactory epithelium (MOE) or the vomeronasal organ (VNO). The relative contribution of these two chemosensory subsystems to sexually dimorphic behaviors is not adequately understood. Using mouse strains genetically engineered to lack odorant-evoked signaling in either the MOE or VNO, we investigated the interaction between these systems in male mating behavior and in several female-typical behaviors. We found that the VNO inhibits aberrant male-typical mounting behavior in both males and females.

Pheromonal control of female-typical behaviors is complex, with a different requirement for MOE and VNO input for each behavior studied. While female sexual behavior is redundantly regulated by the MOE and VNO, maternal aggression requires both sensory epithelia to be functional. Maternal care of pups requires MOE function and is redundantly controlled by VNO signaling.

While olfactory input is necessary for initiating normal male mating behavior, subsequent steps are highly stereotyped and follow a genetically controlled pattern. Preliminary analysis of wild-type male mating demonstrates that the latency to begin mating predicts the likelihood of successful completion. Taken together with the data on chemosensory control of male mating, this highlights the stereotyped nature of the mating pattern between the initiation of mounting and ejaculation as well as the importance of the first mount as the output of the choice to mate.

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