c-Fos expression during the modulation of sexual behavior by an alarm pheromone

We previously demonstrated that an alarm pheromone released by male Wistar rats evokes several physiological and behavioral responses in other rats. In addition to these responses, the alarm pheromone increased the number of mounts needed for an ejaculation and decreased the hit rate (number of intromissions/sum of the mounts and intromissions). These effects were blocked by pretreatment by a corticotropin releasing hormone (CRH) receptor antagonist. However, the neural mechanisms underlying the modulation of sexual behavior by this pheromone remain unknown. In this study, we measured c-Fos expression in 22 brain sites in pheromone-exposed male rats 60 min after their first ejaculation. The paraventricular nucleus was double-stained for c-Fos and CRH to determine which neurons were activated by the pheromone. The alarm pheromone increased the number of mounts, decreased the hit rate, and increased the number of cells double-labeled for c-Fos and CRH in the paraventricular nucleus. These results indicate that the alarm pheromone is a stressor. Pheromone-exposed rats also showed significantly increased c-Fos expression in the anterior division medial group, anterior division lateral group, and posterior division of the bed nucleus of the stria terminalis, the anterior part of the medial and the basolateral region of the amygdala, and the nucleus paragigantocellularis. Based on these results and previous findings, we propose that the alarm pheromone modifies sexual behavior by inducing CRH release that indirectly activates the nucleus paragigantocellularis.