Feeling fear is playing an important role in the survival of human beings and all other species. It is not very enjoyable feeling that for sure, but the feeling, saved and will save us from dangerous situations. So, scientists try to understand how it evolve during the evolution of all complex life forms, and how fear responses hardwired into the brain of different life forms.
For testing, what brain do, scientist try to scare innocent little mouses. And thankfully, mouses almost afraid of anything. Researchers used fox odor that knows as TMT. When a mice smell the odor it usually freezes, this response generated by an increase blood levels of stress hormones such as corticosterone and adrenocorticotropic hormone (ACTH). These hormones control by corticotropin-releasing hormone (CRH) neurons, which is located in a region called the hypothalamus.
How these neurons are getting to release these hormones?
They get their signals from multiple areas of the Olfactory Cortex – a part of the brain that processes the smell – so when this part detect anything risky, it warns the neurons right away. For seeing this process, researchers from Howard Hughes Medical Institute injected mice with a neural activity marker to see how neurons in the Olfactory Cortex response to the threat like fox odor.
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In the research which published in nature.com, the authors explain how Corticotropin-Releasing Hormone (CRH) neurons in a tiny area that is known as Amygdalo-Piriform Transition Area (AmPir) — appeared to modulate the fear responses to the odors. To understand the role of the AmPir, the scientists used a process that called chemogenetics to stimulate this part of the mice’s OC with no predator smell and found that this test caused blood levels of ACTH to increase by 7.6 times. The second time, they tried the same technique to silence the AmPir, and they found that there were no rises in stress level. In conclusion, AmPir plays a significant role in hormonal fear response to predator smells. Also, this reaction appears to be inherited rather than learned. So, as even a mice that had never been exposed to any predator smell, the animal still experienced the same stress hormone levels increase when encountering the particular odors.
