Abstract
The accessory olfactory system (AOS) guides behaviours that are important for survival and reproduction, but understanding of AOS function is limited by a lack of identified natural ligands. Here we report that mouse faeces are a robust source of AOS chemosignals and identify bile acids as a class of natural AOS ligands. Single-unit electrophysiological recordings from accessory olfactory bulb neurons in ex vivo preparations show that AOS neurons are strongly and selectively activated by peripheral stimulation with mouse faecal extracts. Faecal extracts contain several unconjugated bile acids that cause concentration-dependent neuronal activity in the AOS. Many AOS neurons respond selectively to bile acids that are variably excreted in male and female mouse faeces, and others respond to bile acids absent in mouse faeces. These results identify faeces as a natural source of AOS information, and suggest that bile acids may be mammalian pheromones and kairomones.
Highlights
The accessory olfactory system (AOS) guides behaviours that are important for survival and reproduction, but understanding of AOS function is limited by a lack of identified natural ligands
AOS sensory signalling begins in the vomeronasal organ (VNO), where vomeronasal sensory neurons (VSNs) detect ligands through the expression of just one or two G protein-coupled vomeronasal receptors (VRs)[23,24,25,26,27] or formyl peptide receptors[11,12]
The most prominent active components of mouse faeces are bile acids and AOS neurons discriminate between bile acids that vary with sex and species
Summary
The accessory olfactory system (AOS) guides behaviours that are important for survival and reproduction, but understanding of AOS function is limited by a lack of identified natural ligands. We delivered dilute BALB/cJ female faecal extract to the VNO of ex vivo preparations from male B6D2F1/J mice while making single-unit electrophysiological recordings from downstream AOB MCs (Fig. 1a,b). 21.4% of AOB MCs responded selectively to 300-fold diluted BALB/cJ female faeces, nearly equivalent to the selective activation by 100-fold diluted BALB/cJ female urine (24.7%; 89 cells from 56 animals Fig. 1g,h).
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