Mammalian pheromones: emerging properties and mechanisms of detection

Abstract

The concept of mammalian pheromones was established decades before the discovery of any bioactive ligands. Therefore, their molecular identity, native sources, and the meaning of their detection has been largely speculative. There has been recent success in identifying a variety of candidate mouse pheromones and other specialized odors. These discoveries reveal that mammalian pheromones come in a variety of ligand types and they are detected by sensory neurons that are pre-set to promote an array of social and survival behaviors. Importantly, recent findings show that they activate molecularly diverse sensory neurons that differ from canonical odorant detectors. These novel sensory neurons hold future promise to unlock the mystery of how their detection is hardwired to generate behavior.

Figure 1. Two classes of olfactory sensory signals; associative and specialized

Left: Associative odors do not inherently encode behavioral meaning (trial 1). Upon either positive or negative experience (trial 2) further interaction with the odor will elicit a largely predictable behavior (trial 3). Right: Specialized odors activate neural pathways that are pre-set with meaning. Upon first detection of either odors detected in a complex environment or even purified ligands will elicit behavior (trial 1). The associated behavior is largely fixed, repeated exposure does not alter its pre-set meaning (trials 2–3).

Figure 2. Sensory neurons that have been implicated in pheromone detection

The mouse VNO is composed of two major sensory neuron subtypes those expressing V1R receptors (orange) and V2R expressing cells (yellow). Both have been implicated in pheromone detection. a–e) The mouse MOE (blue) is primarily populated with canonical sensory neurons (a) which express Ors, Golf, and CNG1. These neurons are thought to generate associative olfaction. b–e) Sensory neurons expressing signaling elements that differ from canonical odorant neurons have been implicated in pheromone detection.