Pathways linking the olfactory bulbs with the medial preoptic anterior hypothalamus are important for intermale aggression in mice.

Manipulations affecting olfaction, as well as bilateral lesions of the medial preoptic anterior hypothalamic (MPAH) continuum, decrease intermale aggression in mice. In the present study, unilateral removal of an olfactory bulb was combined with a contralateral lesion of the MPAH. This surgery, like bulbectomy and bilateral lesions of the MPAH, substantially decreased aggressive behavior. This surgery bilaterally destroys the ipsilateral links between the olfactory bulbs and the MPAH, and it is this disruption that presumably causes the decrease in aggression. The effect is not due to removal of an olfactory bulb combined with hypothalamic damage per se, because ipsilaterally lesioned/bulbectomized males continued to fight without decrement after surgery. These results provide compelling evidence that multisynaptic neural pathways linking the chemosensory systems of the olfactory bulbs with the rostral hypothalamus are involved in the regulation of intermale aggression in mice.