Posterior nucleus of the amygdala were responsible for the social behaviour of male mice

The cells of the posterior nucleus of the amygdala expressing the alpha estrogen receptor, regulate sexual behavior in male mice and also involved in the formation of aggressive behavior in the mice fight with each other. As stated in the article, published in the journal Nature Neuroscience, these cells are the main source of excitatory signals to preoptičeskoj medial nucleus and the ventrolateral part of the ventromedial hypothalamus responsible for sexual and aggressive behavior in males.

Through many years of research on rodents is known for several key areas of the hypothalamus, through which is implemented by the social behavior aimed at the preservation of the species. Medial preoptičeskoj core was the main area of the brain responsible for sexual behavior in male mice. Inactivation of this nucleus has suppressed sexual activity, while sex hormones and stimulation of this region of the hypothalamus led to increased arousal. As for the aggressive behavior in mice, here scientists discover the reduction in natural aggression when disconnecting the cells of the ventrolateral part of the ventromedial hypothalamus. At the same time, activation of this zone will trigger an immediate attack as the other dogs, and inanimate objects.

It was previously discoveredthat the amygdala and the nucleus of the bed end strips are the main sources for preoptičeskoj medial nucleus and the ventrolateral part of the ventromedial hypothalamus. While these structures are composed mainly of GABAergic neurons and, presumably, have a mainly inhibitory effect on the examined area of the hypothalamus.

Takashi Yamaguchi (Takashi Yamaguchi) with colleagues from Medical center of Langone new York University decided to find out whether the excitatory inputs to the medial preoptičeskoj core and ventrolateral part of the ventromedial hypothalamus is important for the formation of social behavior. Based on previous studies (attack aggression in cats if the introduction of L-glutamate in the hypothalamus or the gradual increase of glutamate in the nucleus preoptičeskoj during sexual arousal in male mice), they suggested that excitatory glutamatergic inputs to the medial hypothalamus is required for both sexual and aggressive behavior. However, it is unclear how widespread these excitatory signals.

Anatomical study has led scientists to the rear nucleus of the amygdala. A previous study of this structure (mihalakopoulou region) found a significant proportion of glutamatergic neurons, which revealed a high degree of expression of alpha-estrogen receptor (Esr1). The abundance of these receptors is observed in the hypothalamus. Since estrogen has a strong influence on social behavior, a brain area with a large number of estrogen receptors are likely to participate in shaping that behavior. Thus, the expression of the transcription factor C-Fos, a member of synaptic transmission of nerve impulses, increased in the posterior nuclei of the amygdala after an attack of aggression and sexual arousal in male mice.

Because the medial preoptičeskoj core and ventrolateral region of the ventromedial hypothalamus (VOWG) are responsible for different aspects of social behavior, scientists have suggested that the neurons of the posterior nucleus of the amygdala, which are projected on these areas are likely to be non-identical cells and play a different role in male sexual and aggressive behavior. Under fluorescent staining of neurons, the authors found that labeled cells that projected to the medial preoptičeskoj core, were abundant dorsomedial located in the front part of the posterior nucleus of the amygdala, whereas the projection VOWG were concentrated in its ventrolateral part. Almost all the neurons of the posterior nucleus of the amygdala, which are projected on the medial preoptičeskoj core, was expressed Esr1 (95.5% ± 1.1%, n = 3 animals), whereas only half of the cells associated with VAWG had Esr1 (55.6% ± 2.5%, n = 3 animals).

The researchers then examined whether the neurons of the posterior nucleus of the amygdala expressing Esr1, direct synaptic inputs in cells in the hypothalamus. They watched optogenetics caused by excitatory and inhibitory postsynaptic currents in most cells of the medial nucleus preoptičeskoj (53.1 percent). Excitatory currents were distinguished by a short delay (of 2.24 ± 0.18 milliseconds), while inhibitory currents had a significantly large delay (8,58 ± 1.21 milliseconds). These data indicate that the excitatory currents are monosynaptic, and inhibitory — polysynaptic. A similar pattern was observed with the cells of the ventrolateral region of the ventromedial hypothalamus. Overall, these results indicate that neurons of the posterior nucleus of the amygdala expressing Esr1, exert a direct excitatory and indirect inhibitory effect on the hypothalamus, which is responsible for social behavior.

Scientists discovered that the neurons of the rear of the amygdala related to the preoptičeskoj the medial nucleus showed a greater increase of Ca2+ with the appearance of the female, than the appearance of the male, as well as a higher reaction during the study, females in the study than male. The appearance and research of other males neurons of the amygdala, associated with VAWG, showed a higher response than females (all p < 0.001).

Overall, the experiment with the inhibition of cells posterior nucleus of the amygdala, associated with medial preoptičeskoj nucleus, showed that these neurons are essential for all aspects of male sexual behavior, while cells related to VAWG mainly mediate male aggression, but also play a minor role in the multilateral processes of sexual behavior. The scientists also noted that these cells have a favorable anatomic location: pass through them flows olfactory, contextual, empirical and emotional information, reaction to which can be both sexual and aggressive behavior.

At comparable volume, morphology and density of cells of the medial nucleus preoptičeskoj in females it is responsible for maternal behavior. Ventrolateral region of the ventromedial hypothalamus, which plays a fundamental role in aggressive behavior in males, females are responsible for both aggression and sexual activity. The organization of neurons in the posterior nucleus of the amygdala, relevant to behaviour, and descending contours are likely to differ from those of men. Future studies on the amygdaloid body of females, will help clarify the sexual dimorphism of social behavior.

However, it is recognized that it is not so simple in the regulation of behavior. For example, earlier we were toldthat the aggressiveness in dogs have been associated with a high level of vasopressin in the blood.

Vyacheslav Gomenyuk

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