Although humans are animals, there are some biological mechanisms that occur in many species other than our own, and one of them, very important indeed, is the emission of pheromones.

Pheromones can be responsible for activating a wide range of behaviours and physiological processes, the most important of which is the sexual response, and it is the pheromone known as darcine that is especially important during rodent reproduction.

This pheromone is named after an attractive character of the romantic Jane Austen, which already suggests its ability to generate a chemical attraction between animals. Let’s see more in depth what this pheromone does and how it influences the brain of certain animals, such as rodents.

Darcine: pheromones and chemical love

Jane Austen, famous British writer of Romanticism, introduced us to Mr. Fitzwilliam Darcy , a handsome and rich young man who fell in love with the protagonist of Pride and Prejudice (1813), Miss Elizabeth Bennet. Although it has not yet been discovered in humans something that can give us the power of attraction of Darcy on Lizzie, it has been seen in nature a pheromone that has a similar power in rodents and has been named after this romantic hero: the Darcina.

Pheromones are airborne chemicals that can have varying effects on behavior in different animal species . They are specific and are used as a method of communication between individuals of the same species, inducing both behavioural and physiological changes.

Although no such substances have been found in humans to date, in many animals pheromones are primarily responsible for the act of reproduction, with Darwin being one of them.

The Sex Life of Mice

Although they are small animals with tiny brains, mice have a surprisingly complex sex life. As it happens with other mammals, including our species, these small mammals interpret the behavioral signals and smells emitted by other individuals of their species as a sign that they are ready, or not, for mating . It seems that darcine is a pheromone that plays a great role in this process.

When male mice urinate, in addition to marking their territory, they send a signal that they are looking for a female to mate with. In their urine is the darken, which will make the female mice aware of the availability of the male and, depending on the smell he is emitting, go for him and decide if they want to have their offspring. This act of smelling is not as simple as in our species. Animals that use pheromones have two types of noses, each one fulfilling different functions.

On the one hand, we have the nose that fulfills the same function as that of humans: to identify odors. It is through this structure that animals are able to detect the pleasant smells of food and go towards it or smelly smells like dead animals that indicate that you cannot eat their meat or that you are even close to a danger.

But it is the vomeronasal nose, which is not found in our species, that perceives pheromones, such as Darwin, and sends the signal to the brain. It is in the animal’s brain where the signal will be interpreted and a behavior will be orchestrated according to the demands of the environment. If the hormone is of the reproductive type, the animal will initiate behaviours in search of the individual that has emitted the signal that it is available for mating, as happens with mice.

Although the importance of darcin on the sexual behaviour of mice was known, it was only relatively recently that the brain mechanisms that would explain this type of behaviour were discovered, in addition to understanding the behavioural differences between available female mice and those that have just had young that are still nursing.

Brain changes

A very recent study, from this same year 2020 and carried out by Ebru Demir’s group at Columbia University, discovered the process by which the pheromone of darcine influences the brain of female mice.

As we have already seen, it is this pheromone that activates the sexual desire of the females and makes them predisposed to mating. However, not all female mice, when smelling the males’ urine, showed pro-mating behaviors. Females that had recently given birth to young and were still nursing seemed to ignore those places where the males had marked their territory.

The reason behind this fact seems to be found in the medial amygdala of the roedo brain r. Ebru Demir’s group found that in this region would be a subset of neurons, called nNOS neurons, which are activated when there is darcin floating in the air. By artificially activating this structure, the researchers saw that sexual behavior was induced, while deactivation of these neurons caused the animal to lose interest in mating.

But the nNOS neurons do not simply deal with information that has to do with darcine. These neurons are also involved in the integration of sensory information about the pheromone with the mouse’s internal state, and whether or not the mouse is breast-feeding.

The main finding of this study is that a widely held belief about pheromones has been challenged, and that pheromones induce a behavioral response that is innate and immediate. In the case of the darcin, this induces more complex behaviours , which depend on the state in which the female to whom it is directed is found, whether it is a lactating mother or a mouse in search of a male.

Bibliographic references:

  • Roberts et al., Darcin: a male pheromone that stimulates female memory and sexual attraction to an individual male’s odour BMC Biology 2010, 8:75.
  • Demir, E., Li, K., Bobrowski-Khoury, N. et al. (2020) The pheromone darcin drives a circuit for innate and reinforced behaviours.Nature https://doi.org/10.1038/s41586-020-1967-8.
  • Percy-Cunningham JE, MacDonald JA (1987). “Biology and ultrastructure of sex pheromone-producing glands.” Prestwich GD, Blomquist GJ (eds) Pheromone Biochemistry. Orlando/FL: Academic Press: 27-75.
  • Winman, A. (2004). Do perfume additives termed human pheromones warrant being termed pheromones? Physiology & Behavior 82 (4): 697-701.
  • Moncho-Bogani, J, Martínez-García, F., Novejarque, A., Lanuza, E. (2005). “Attraction to sexual pheromones and associated odorants in female mice involves activation of the reward system and basolateral amygdala. European Journal of Neuroscience. 21(8) 2186 – 2198.