mGluR2 activation of medial amygdala input impairs vomeronasal organ-mediated behavior.

The accessory olfactory bulb normally receives chemosensory input from the vomeronasal organ. Input from accessory bulb to medial amygdala for natural pheromone-containing conspecific chemosignals activates both anterior and posterior medial amygdala and elicits or modulates reproductive and social behavior. Here, a non-specific activation of accessory olfactory bulb by infusion of mGluR2 agonist LCCG1 in male hamsters activates immediate-early gene (Fos) expression only in anterior and not posterior medial amygdala. mGluR2 stimulation concurrently with female chemosensory stimulation produces small changes in the normal chemosensory response in medial amygdala but impairs behavior normally driven by the chemosensory input. The distribution of Fos expression, with an increase in anterior but not posterior medial amygdala, is also seen with chemosensory stimulation by chemosignals from other species, socially non-relevant for hamsters, and by artificial electrical stimulation of the vomeronasal organ. We propose that the spatiotemporal pattern of amygdala input is important for eliciting normal species-specific behavior and that artificial and heterospecific stimulation fails to do so because it does not match the required pattern closely enough. Thus, modification of the pattern by addition of non-specific activation from mGluR2 agonist is sufficient to disrupt behavior normally driven by conspecific chemosensory stimulation.