Sensory Adaptation to Chemical Cues by Vomeronasal Sensory Neurons

Abstract

Sensory adaptation is a source of experience-dependent feedback that impacts responses to environmental cues. In the mammalian main olfactory system (MOS), adaptation influences sensory coding at its earliest processing stages. Sensory adaptation in the accessory olfactory system (AOS) remains incompletely explored, leaving many aspects of the phenomenon unclear. We investigated sensory adaptation in vomeronasal sensory neurons (VSNs) using a combination of in situ Ca²⁺ imaging and electrophysiology. Parallel studies revealed prominent short-term sensory adaptation in VSNs upon repeated stimulation with mouse urine and monomolecular bile acid ligands at inter-stimulus intervals (ISIs) less than 30 s. In such conditions, Ca²⁺ signals and spike rates were often reduced by more than 50%, leading to dramatically reduced chemosensory sensitivity. Short-term adaptation was reversible over the course of minutes. Population Ca²⁺ imaging experiments revealed the presence of a slower form of VSN adaptation that accumulated over dozens of stimulus presentations delivered over tens of minutes. Most VSNs showed strong adaptation, but in a substantial VSN subpopulation adaptation was diminished or absent. Investigation of same- and opposite-sex urine responses in male and female VSNs revealed that adaptation to same-sex cues occurred at ISIs up to 180 s, conditions that did not induce adaptation to opposite-sex cues. This result suggests that VSN sensory adaptation can be modulated by sensory experience. These studies comprehensively establish the presence of VSN sensory adaptation and provide a foundation for future inquiries into the molecular and cellular mechanisms of this phenomenon and its impact on mammalian behavior.

Significance Statement Peripheral sensory adaptation is an initial mechanism for experience-driven feedback in the nervous system. In the mammalian accessory olfactory system, which senses many social chemosignals, peripheral adaptation remains a subject of some debate. We investigated sensory adaptation to natural cues and monomolecular ligands in acute preparations of the vomeronasal organ, finding evidence for short- and long-term adaptation on repeated stimulation at defined intervals. We further tested whether adaptation differed to same-sex versus opposite-sex cues, finding that sensory adaptation was more prominent for same-sex cues in both males and females. These inquiries into accessory olfactory system adaptation provide a foundation for future inquiries into this phenomenon.