A centrifugal pathway to the mouse accessory olfactory bulb from the medial amygdala conveys gender‐specific volatile pheromonal signals

Abstract

We previously found that female mice exhibited Fos responses in the accessory olfactory bulb (AOB) after exposure to volatile opposite-, but not same-sex, urinary odours. This effect was eliminated by lesioning the main olfactory epithelium, raising the possibility that the AOB receives information about gender via centrifugal inputs originating in the main olfactory system instead of from the vomeronasal organ. We asked which main olfactory forebrain targets send axonal projections to the AOB, and whether these input neurons express Fos in response to opposite-sex urinary volatiles. Female mice received bilateral injections of the retrograde tracer, cholera toxin B (CTB), into the AOB, and were exposed to either same-or opposite-sex volatile urinary odours one week later. We found CTB-labeled cell bodies in several forebrain sites including the bed nucleus of the accessory olfactory tract, the rostral portion of the medial amygdala (MeA), and the posteromedial cortical nucleus of the amygdala. A significant increase in the percentage of CTB/Fos co-labeled cells was seen only in the MeA of female subjects exposed to male but not to female urinary volatiles. In Experiment 2, CTB-injected females were later exposed to volatile odours from male mouse urine, food, or cat urine. Again, a significant increase in the percentage of CTB/Fos co-labeled cells was seen in the MeA of females exposed to male mouse urinary volatiles but not to food or predator odours. Main olfactory -MeA -AOB signaling may motivate approach behaviour to opposite-sex pheromonal signals that ensure successful reproduction.

The Olfactory System

“…Clues as to the circuit role of the feedback connections from the medial amygdala to the AOB were found by combining retrograde tracing with c-fos labeling after exposure to odors (Martel and Baum, 2009). A significant increase in fos-positive retrogradely-labeled neurons was seen in those mice (all female) which were exposed to male mouse urine volatiles; using other odors produced little or no increase.…”

The densities of calbindin and parvalbumin, but not calretinin neurons, are sexually dimorphic in the amygdala of the guinea pig

“…Model7 pp: À 1214ðcol: fig: : NILÞ Moreover, many studies indicate that this part of the brain is also strongly involved in the integrative circuitry mediating pheromonal and reproductive functions (Baum, 2009;Kevetter and Winans, 1981;Martel and Baum, 2009;Morris et al, 2008;Segovia et al, 2006) as well as various aspects of its anatomy and physiology seem to be sexually dimorphic (Hamann, 2005;Fagergren and Hurd, 1999;King et al, 1999;Morris et al, 2008;Rollins and King, 2000;Równiak, 2013;Segovia et al, 2006;Swaab et al, 2003). An important role in the sexually dimorphic functions mediated by the amygdala and other brain structures may be played by cells which contain γ-aminobutyric acid (GABA).…”

The main and the accessory olfactory systems interact in the control of mate recognition and sexual behavior

“…In addition, it has been recently suggested that the AOB receives backward connections from several forebrain sites including the bed nucleus of the accessory olfactory tract, the rostral portion of the medial amygdala (MeA), and the posteromedial cortical nucleus of the amygdala (PMCo). When exposed to male urinary volatiles, these connections show specific activation, suggesting that main olfactory-MeA-AOB signaling may motivate approach behavior to opposite-sex pheromonal signals that ensure successful reproduction [71].…”