American scientists have identified in the nucleus accumbens of the brain perenich voles (they’re yellow-bellied vole, Microtus ochrogaster) populations of neurons, the activity of which is observed exclusively when approaching the specimen to its long-term partner. Their activity was determined by the extent to which the relationship is strong, but not changed at the time of the communication and is not dependent on the person with whom the communication occurs. Discovered the neurons that can help to clarify how mammals form monogamous relationships, write the scientists in the Proceedings of the National Academy of Sciences.
The task of every species is to produce as many offspring. The number of offspring, in turn, depends on reproductive success, and if for females it is for the most part, we provide a comfortable pregnancy, safe childbirth and successful breastfeeding, for males the best strategy is to impregnate as many females. This is why monogamy (that is, the preference to mate with one partner for a prolonged period) in the animal world are quite rare: in one form or another monogamous about 10 percent of mammalian species, including humans.
From monogamy, however, has its advantages, including, for successful breeding: formed, the pair may work together to take care of the offspring, thereby ensuring their reproductive success is not quantitatively, but qualitatively. Monogamous relationship, however, is much more complex than the plural: in addition to the basic desire to reproduce, they also have a desire to interact with a partner for an extended period, choosing this communication among all the possible others.
Therefore, it is important to understand what is the basis of a monogamous relationship — including from the point of view of neurobiology. To examine monogamy in the laboratory, however, is not so simple: the most common model organisms (including, for example, rats and mice) still prefer to lead a polygamous lifestyle.
Is suitable for this purpose parinya voles — rodents that form pairs for life. Three years ago, with the help of them managed to figure outthat conditional love in a long-term partner is responsible for the interaction included in the reward system nucleus accumbens and prefrontal cortex. In the new work, scientists led by Zoe Donaldson (Zoe Donaldson) from the University of Colorado in boulder decided to specify factors that affect the activity of the nucleus accumbens in the formation of monogamous pairs.
The study involved 17 perenich voles: 7 males and 10 females. In the region of the nucleus accumbens in their brain, scientists have implanted a miniature microscopes, which allows to assess the activity of individual populations of neurons using calcium imaging: the generated nerve action potential is characterized by the appearance of calcium ions (Ca2+). The researchers assessed the activity of neurons in the nucleus accumbens before voles formed pairs immediately after the first mating and through 20 days after pair formation.
Over time, the relationship between a male and a female paired really strengthened: more time has passed since the first mating, the more two voles spent time with each other and not with other voles, unknown (p = 0.009). However, the activity of neurons in the nucleus accumbens during the interaction vole with a partner or with unfamiliar individuals did not differ from this, scientists concluded that the activity of the nucleus accumbens, which appears during the communication of animals does not depend on the type of relationship between them.
Next of all active neurons of the nucleus accumbens, scientists have identified the part that is activated during the approach to the other individuals and during the separation from her. The number of neurons selectively active during the approach voles to model not dependent on what individuals communicates vole, to make a pair, but grew after the pair was formed. For neurons selectively active when the distance of individuals from each other, such dependence was not observed.
After the first pairing of active neurons in the nucleus accumbens was greater when the vole closer to the partner than when it was close to unfamiliar individuals (p = 0.003) and the number of these neurons increased with time in the course of how the connection was strengthened: the number of active neurons could also predict how strong was the relationship of the two voles (how much time they spent together). In addition, neurons that were active during the approach of the individuals towards the partner, do not overlap with those activated by approaching other individuals.
The authors thus were able to clarify the role of the nucleus accumbens in the formation of a lasting monogamous relationships. Contrary to expectations, the activity of this structure does not depend on whether the individual interacts with his partner or with another, unfamiliar individual. By contrast, the nucleus accumbens, appears to be more important than the events that occur before the interaction, namely the fast approach to the partner.
The appearance of living species of monogamy and explain other factors. For example, scientists have found outthat the transition of human societies to the formation of monogamy could be a response to the proliferation of these societies sexually transmitted diseases.