Pheromones are chemicals that animals produce to change the behavior of another animal of the same species. Many species use these chemicals to communicate information about the location, sexual, and social status of potential partners. A team of researchers from Columbia University may have unlocked how the pheromone darcin, aids in attracting mice of the opposite sex.
The chemical, darcin, was named after Mr. Darcy, a character in Jane Austen’s Pride and Prejudice, who had a problem attracting women. But the chemical may have a different impact on female mice as a new study published in the journal Nature shows that it changed the brains of female mice, giving cells in the brain’s emotion center the power to assess sexual readiness and help in the selection of a male partner.
The chemical, also called a sex pheromone, hijacks potential partners’ brains, changing behavior and activating courtship, at least in laboratory mice models.
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Pheromones as powerful scent messages
The new study highlights the power of a single protein to change the brain and drive behavior. The team has revealed the pathway on how a group of cells in one area in the brain assimilates information from the outside world, with the animal’s internal state.
Pheromones have various types of chemicals, all of which act as powerful scent messages to warn against potential danger and alert the animal of food or prospective partners or mates. In the study, the researchers studied and traced the route the chemical darcin takes from the nose to the brain, shedding light on the mechanisms by which animals can use scents or odors to communicate.
Darcin, which was first described in 2010 by scientists at the University of Liverpool, is released from male mice in their urine to mark their territory and begin courtship signals. When females smell the chemical, they can identify the male mice and decide whether to mate with him.
It is well-known that mice use olfactory receptors in the nose to sense odors, while specialized proteins work by sending the information about a particular scent to a selected brain region for processing. However, darcin and other pheromones are processed differently, as they communicate with another olfactory system, which is found in animals like mice but not in people.
Mice have two functional noses, with the first one working like that of humans, and the second one, dubbed as the vomernasal nose, is specialized solely for perceiving pheromones.
Darcin changes brain activities
To arrive at their findings, the researchers studied the reactions of female mice on the pheromone darcin. They first exposed female mice to darcin-scented urine and assessed for their behavior. The team found that all of the female mice manifested immediate attraction to the chemical and after about 50 minutes, some females started leaving their own urinary scent markings.
When the team studied ultrasonic frequencies, they observed some of the female mice started to sing, which registered as a high-frequency sound that is too high for the human ear to hear. The behaviors manifested by female mice indicate sexual arousal.
However, they also noted that not all the female mice reacted the same way, as lactating female mice, ignored the darcin-marked locations after the sniffing of the chemical.
The scientists believe that the reaction may depend on a brain region known as the medial amygdala, which contains a group of neurons, nNOS neurons, that activated when exposed to darcin. They also found the location of the neurons in the medial amygdala as interesting, since it serves a different role from the usual processing of emotional responses.
“Our results suggest that nNOS neurons in the medial amygdala do not simply pass along information about darcin. These neurons seem to be integrating sensory information about the pheromone with the internal state of the animal, such as whether she is a lactating mother and therefore not interested in mating,” Ebru Demir, PhD., an associate research scientist in the laboratory of Nobel Laureate Richard Axel, MD, at Columbia's Mortimer B. Zuckerman Mind Brain Behavior Institute, said.
The study authors hope that the study findings provide an update on pheromones and their roles in the brain and behavior.
Demir, E., Li, K., Bobrowski-Khoury, N. et al. The pheromone darcin drives a circuit for innate and reinforced behaviours. Nature (2020). https://doi.org/10.1038/s41586-020-1967-8