The researchers examined the vomeronasal organ of juvenile and adult mice at the single-cell level. They discovered a potential novel class of cells and, surprisingly, some neurons usually found in the main olfactory system. The study highlights the cellular and molecular complexities of this organ and its neuronal circuitry that could expand our understanding of how sensory information is processed in humans.

Located near the base of the nose, the vomeronasal organ has an unusual name—vomer refers to a triangular-shaped bone between the nose and mouth derived from the Latin word for the blade of a plow. Though not functional in humans, the vomeronasal organ’s sensory neurons detect pheromones and other chemical cues that provide crucial environmental information that can influence behaviors, such as finding potential mates or fleeing from predators.

Sensory neurons express receptor proteins on their surface, which are specific for different odor molecules—the human nose has around 400, the dog nose has over 1,000. Sensory neurons then send signals to other neurons for additional information processing. Typically, the sensory neuron to receptor connection follows a one-to-one rule, where each neuron displays a single receptor type, so that signals and responses can be very specific and trigger an appropriate reaction.

While vomeronasal and olfactory sensory neurons have different roles—pheromones and innate behavior versus odors and learned behavior—the team discovered potential new types of cells in the vomeronasal organ that have both kinds of receptors. These findings suggest that the main and accessory olfactory sensory systems overlap in more complex ways than previously recognized. In addition, the researchers found a co-expression of receptors, meaning a single neuron can express several different types of receptors simultaneously.

If you have ever wondered whether our four-legged friends have an extra sense, the vomeronasal organ is a likely source. And while humans lack this extra scent sensor, untangling sensory system circuitry may reveal parallels for how odors can induce our own emotions and behaviors.

Additional authors include Limei Ma, Ph.D., Ai Fang, Ph.D., Thelma Chiremba, Ph.D., Seth Malloy, Allison Scott, and Anoja Perera.

This work was funded by the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health (NIH) (awards: R01DC008003, R01DC020368) and by institutional support from the Stowers Institute of Medical Research. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.