Il fluido lacrimale delle femmine inibisce il comportamento aggressivo nei topi maschi

Abstract In many animals, different social behaviors, such as aggression and sexual behavior, are governed by chemical signals, called pheromones, which are emitted by animals of the same species and acting through the vomeronasal system. Pheromones are contained in various bodies fluids such as urine, saliva, vaginal fluids and tears. The data in the literature show that the tears of the male mouse represent a great pheromone source capable of modulating different social behaviors, such as increasing aggression among males and receptive behavior in the female. At the moment are unknown the behavioral effects caused by the female’s tear; so I studied the influence of this fluid on the aggressive behaviors in males. For this reason, the tear fluid of the females was brushed on the dorsal, facial and ano-genital region of a male intruder during an intermale- aggression test. The results show that tears of females are able to inhibit aggression, stimulating sexual behavior and investigation. The female estrogen cycle doesn’t influence the production of the inhibitory molecules, however the ovaries are important for the secretion of these lacrimal substances. Preliminary attempts to characterize the nature of inhibitory molecules show that these substances are of low molecular weight, which are not volatile and difficult to dialyzed. The non-volatile nature of the lacrimal molecules suggests an involvement of the vomeronasal system for the perception of these substances. For this reason, I evaluated the projection of the vomeronasal organ to brain regions which involved in aggressive behavior by exposing residents to the tear fluid of both sexes. My results show a high neuronal activation of the medial amygdala (MeA) resulting from male and female tears stimulation; however, it has not been possible to identify subdivisions of amygdala differentially active following sex-specific stimuli. Significant differences, however, have been highlighted at the level of the venterolateral area of the venteromedial hypothalamus (VMHvl), a sub-nucleus that plays a central role in the genesis of aggressive behavior. Residents exposed to female lacrimal fluid exhibit partial inactivation of neuronal cells at VMHVL level when compared with residents exposed to male tear fluid. In addition, it was interesting to note that tear fluid of females causes inactivation of the dorso-medial nucleus of the hypothalamus (DMH) a center of regulation of neuroendocrine, cardiovascular and physiological stress responses. Instead, the tear fluid of female, activates another cerebral area, called the lateral habenula generally involved in regulating the valence of violent behavior. In conclusion, the study demonstrates how the tear fluid of females plays a central role in modulation of aggressive behavior of male mice. This is done by the activation of inhibitory and excitatory neuronal circuits that stimulate aggression and motivation.