RWTH Researchers Pioneer Description of Mammals’ Pheromone Sensing Mechanisms
Animals communicate via pheromones. These mysterious signal substances are released in various bodily fluids and automatically trigger fixed behavioral patterns in the “recipient.” Depending on the pheromone, these involuntary behaviors range from aggression to mating behavior. We have long known that pheromones are detected by a separate sensory organ – the vomeronasal organ. However, it was still unclear how the pheromones enter the vomeronasal organ. Researchers at RWTH led by Christoph Hamacher and Prof. Dr. Marc Spehr have now discovered how this mechanism works.
The vomeronasal organ has puzzled scientists since its discovery in 1815. The sensory organ is a blind-ending, fluid-filled tube of nerve cells on the roof of the mouth of most mammals. The organ opens into the oral or nasal cavity through a narrow passage. For example, if a dog “sniffs out” the scent mark of another dog on a tree, the vomeronasal organ comes into play. This olfactory sense organ is used to exchange information about ranking, sex, state of health, or even whether a female is in heat. But how do the signaling substances excreted in minute concentrations in urine, sweat, saliva, or other bodily secretions reach the inside of the vomeronasal organ?
A research group from the Chemosensation Laboratory at RWTH has now shown that dense muscle tissue is also present in the vomeronasal organ in addition to the sensory nerve cells. When the muscle contracts, the fluid-filled cavity inside the organ expands, creating a massive negative pressure at the opening. In this way, signal substances from the environment are sucked into the vomeronasal organ like a vacuum cleaner. The muscular pumping movements are triggered by adrenaline pulses, which lead to the filling and emptying of the organ. Short, sudden fluctuations in muscle calcium levels play a decisive role here. Using a new imaging method (so-called optical coherence tomography), which until now has mainly been used to diagnose eye diseases, Christoph Hamacher and Prof. Dr. Marc Spehr and their team were able to see inside the sensory organ during the pumping process and observe the fluid movements in the vomeronasal organ. In mice, exchanging around 100 nanoliters (less than one-millionth of a liter) is sufficient to transmit all relevant pheromone information from the sending to the receiving animal.