Researchers have found a neuron in male mice that allows them to detect and respond to female pheromones. Oddly, this type of neuron disappears if males are constantly exposed to female scents. The findings are in a paper just published in the journal Neuron.
Male mice generally live alone, defending their territories from other males. The only other time they interact with other mice is when mating with females. This requires them to quickly notice female mice in the area. Male mice tend to get excited when exposed to female urine but scientists weren’t sure how they detected the pheromones.
Researchers from the Washington University School of Medicine in St. Louis examined neurons in the vomeronasal organs of mice. The vomeronasal organ, also called Jacobson’s organ, is located in the nose and is part of the olfactory system. Its function is to detect chemical signals, including pheromones. The research team discovered that the male mice had a unique type of neuron not found in females. This neuronal cell type could detect epitestosterone sulfate, a sex hormone by-product.
The team also found that if males were constantly exposed to pheromones in female urine, they lost the female-detecting neurons. This changed their behavior; mice without the special neuron type lost interest in female scents. If the males were once again isolated and not exposed to female smells, the neurons showed up again. This shows that environmental conditions are responsible; it’s not an innate sex-determined cell type. The researchers even removed the testes of the male mice and the ovaries of the females. The neurons still behaved the same way, suggesting that the cell type wasn’t directly related to hormones.
These findings show that environmental factors are responsible for some sex differences in mice. Males have a special type of neuron for sensing female pheromones but the cells disappear after chronic exposure to female urine. The mice can regain the neurons once isolated from female scents. The authors speculate that this makes the mice more adaptable. If they’re constantly in contact with female pheromones, the neurons can shut down rather than overwhelm them with signals.
Xu, Pei Sabrina et al. Experience-Dependent Plasticity Drives Individual Differences in Pheromone-Sensing Neurons. Neuron (2016).