Hormone of paternal love
Japanese scientists have found a mechanism for "switching" the brain of males
Maria Azarova, Naked Science
A team of Japanese neuroscientists from the Center for the Study of Biosystem Dynamics at the Institute of Physico-Chemical Research (RIKEN) found out that due to the peptide "hormone of love" — oxytocin — male mice radically change the attitude towards cubs. As noted in a study published in the journal Neuron (Inada et al., Plasticity of neural connections underlying oxytocin-mediated parental behaviors of male mice), the same mechanism can act in humans.
The adult brain has neuroplasticity, which allows you to change behavior in accordance with the specific requirements of life. So, inexperienced animals rarely take care of children of their own kind, because such behavior can become a heavy burden and reduce their fitness: for example, an adult male mouse, who has never had a relationship with females, often attacks and even kills cubs, but can turn into a loving father after the birth of his own child.
Despite a lot of research, the neural mechanisms that cause changes in behavior are poorly understood. The main way by which the brain achieves neuroplasticity is considered to be a change in the strength of synaptic connections between neurons. But it is difficult to determine exactly which neurons or their types form synapses that undergo changes as a result of an event. To get answers to these questions, it is necessary to accurately determine the location and type of nerve cells whose synaptic connections change. This became the goal of the authors of the new work, and such a decisive life "turn" was forced fatherhood.
As previous studies have shown, injections of oxytocin produced by neurons in the paraventricular nucleus of the hypothalamus generate concern in virgin female rodents. On the contrary, the loss of the function of oxytocin or its receptor demonstrates only insignificant maternal caring behavior. In addition, scientists suggest that the action of this hormone may contribute to the beginning of caring, but to a lesser extent — its maintenance.
However, unlike the experiments with females, the function of oxytocin in the male brain and the associated caring behavior of fathers were mostly overlooked. And Japanese researchers have for the first time identified the crucial role of oxytocin-producing hypothalamic neurons in neuroplasticity in male mice when they become parents.
"While women experience many physiological and endocrinological changes in the body when becoming mothers, any neuroendocrinological changes in men were considered subtle or absent. But we found out that oxytocin, a hormone associated with childbirth and lactation, has a strong effect on male mice," said Kazunari Miyamichi, lead author of the study.
Experiments on mice have demonstrated that the forced activation of oxytocin-producing neurons provokes a complete set of characteristics of parental behavior in males, first suppressing their habitual tendency to infanticide — infanticide. "We have shown that activation of oxytocin-producing neurons modulates the activity of several different types of nerve cells: infanticidal PeFA Ucn3+ neurons are suppressed, while parental MPNm Calcr+ neurons are activated when virgin male mice meet with cubs," the scientists write.
They admit that such a function of oxytocin is also present in humans, since there is a correlation between the level of this "love hormone" in the father's blood and the intensity of his interactions with the child. By the way, unlike females, males' concern for the child completely disappeared in the absence of the action of oxytocin or prolactin.
Another unexpected discovery was the plasticity of neural connections in the hypothalamus itself. "It was believed that the functions of the hypothalamus are mediated by programmed neural circuits that never change. Our work is one of the few that demonstrated the functional and structural plasticity of the hypothalamus," the scientists concluded.
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