Populations of distinct neurons in the hypothalamus code the states associated with threats linked to predators

The ability to detect imminent threats and execute behavior aimed at protecting oneself, such as hiding, fleeing or defending itself, is at the heart of the survival of most animal species. A region of the brain of mammals known to play a key role in the response to threats is the hypothalamus, which also regulates the release of hormones and other vital body functions.

Researchers from the California Institute of Technology (Caltech) and Howard Hughes Medical Institute recently carried out a study aimed at better understanding how a specific group of neurons of the Hypothalamus Subdivision Hypothalamus (VMHDM), which are identified by the presence of the Steroidogenic 1 (SF1) Coding of the presence of the predatory immense.

Their results, published in NeuronShow that distinct subsets of VMHDM^SF1 The neurons code several internal states which are mentioned by the imminence of predators.

“We and others in the field have studied these cells deeply in the hypothalamus for years,” said David J. Anderson, main author of the newspaper, to Medical Xpress. “Using optogenetics to turn off or on these cells, we have shown that these cells were necessary for a mouse to show fear behaviors in response to a natural predator (a rat), and that the artificial activation of the cells was sufficient to evoke the responses of fear (freezing or theft), even in the absence of a rat. However, these results did not say what the activity of these cells is normally mouse brings a mouse.

VMHDM^SF1 The cells are located near the middle of a chain of eight different brain regions, which collectively convert the detection of odors emanating from other animals into rapid and instinctive behavioral responses essential to their survival. Although previous studies have confirmed that these cells play a role in mice responses to threats related to predators, their precise role in this brain chain has not yet been elucidated.

“Does he work as” rats “neurons,” fear “neurons, or” freezing / flight “neurons? Says Anderson.” Until now, this has proven to be difficult to disentangle, because all these roles are strongly correlated. “

As part of the team’s recent study, Anderson’s student Kathy Cheung, simultaneously imagined the activity of hundreds of VMHDM^SF1 Neurons in the brain of an adult mouse before, during and after exposure to a rat. In addition, they recorded the behavior of the mouse, which was separated from the rat by a protective mesh barrier, preventing him from injuring.

“Kathy then used experimental manipulations and, with Aditya Nair, a computer student, mathematical techniques and based on AI to disentangle which aspects of the behavioral response of the mouse were most strongly associated with behavior,” said Anderson.

“This process is like aligning the sentences written in two different languages ​​with each other and trying to determine which words in a language correspond to a particular word in the other, just as they did for Egyptian hieroglyphs compared to Greek using Rosetta stone. This is how you uncheck the language of brain activity in relation to behavior.”

The experiences and calculation analyzes carried out by Cheung, Nair, Anderson and their colleagues have gathered new interesting information on the way VMHDM^SF1 The neurons support mouse responses to the threats related to predators. In particular, researchers have found that neurons do not directly code freezing and flight behaviors (that is to say the exhaust).

“Some of these neurons code the identity of the rat, while others seem to code emotional states which are mentioned in the presence of the rat,” said Anderson. “For example, there are cells which continue to shoot for a while even after the removal of the rat, and which can code a persistent feeling of fear or anxiety which maintains the alert of the mouse and vigilant.”

To their surprise, the researchers also identified a subset of VMHDM^SF1 The neurons that become active when mice enter a “safe space”, which in their experiences consisted of a shelter. Interestingly, they found that these “security” cells died as soon as a mouse had removed the head from the shelter and could therefore once again see the predator (that is to say the rat).

“Conversely, the cells that are activated by the rat are deactivated as soon as the mouse enters the refuge; then they turn back as soon as the mouse is the head,” said Anderson. “These different cells pour out perfectly with each other and can code the relative threat and security level perceived in the brain of the mouse.”

In addition to discovering the existence of VMHDM^SF1 The populations of neurons which are active while the mice feel safe and when they feel threatened by the predators, Anderson and his colleagues have identified a third subset of these cells which seems to code for the imminence of the threat, or in other words, how close the rat is at a given moment and if there is a viable evacuation path that the mouse can take.

“When the rat is relatively distant and there is room to escape, these cells are triggered at a lower level; but as the rat is getting closer and the exhaust is more difficult, these cells pull more strongly,” said Anderson. “In the first situation, the mouse freezes; in the second, he tries to jump from the cage. But these” imminence “cells are not correlated with frost and jump, but rather with the internal state which evokes these behaviors.”

The results collected by these researchers have shed light on how VMHDM^SF1 Neurons contribute to the coding of threats linked to predators. Although the experiences of the team have been carried out in mice, they could also be applicable to other mammals, including humans.

“We now want to know if the different functional subsets of the cells we have identified are molecularly distinct from each other and what other chain cells to which they” speak “to convert their activity into behavior,” added Anderson.

“We also want to know what controls the strength and length (duration) of their response to the rat. This last question is particularly important, because certain human psychiatric disorders such as the SSPT appear as unsuitable changes in the force or the length of a given type of emotional response.”

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