It is obvious that persistent stress can affect our behavior, resulting in issues like sadness, a loss of interest in activities that used to make us happy, and even PTSD. Researchers now have proof that persistent stress causes a subpopulation of neurons in the bow-shaped region of the brain to become hyperactive.
These kinds of behavioral issues arise when these POMC neurons are overly active, and when researchers lower their activity, it lowers the behaviors, they report in the journal Molecular Psychiatry.
A group of neurons known as the proopiomelanocortin, or POMC, neurons were studied in the hypothalamus, which is important for processes like hormone release and regulation of hunger, thirst, mood, sex drive, and sleep, in response to 10 days of persistent, unpredictable stress. The effects of chronic unpredictable stress, which in this case comprised social isolation, extended wet bedding in a tilted cage, and constraint, are frequently studied in animal models.
According to corresponding author Xin-Yun Lu, MD, PhD, chair of the MCG Department of Neuroscience and Regenerative Medicine and Georgia Research Alliance Eminent Scholar in Translational Neuroscience, they discovered that stressors increased spontaneous firing of these POMC neurons in male and female mice. Anhedonia, or the seeming inability to experience pleasure, and behavioral despair, which is essentially depression, also appeared when scientists immediately triggered the neurons as opposed to allowing stress to boost their firing.
In humans, signs of anhedonia may include a lack of libido and a cessation of interaction with close friends. Mice lose some of their usual enthusiasm for sugar water, and male mice who typically enjoy sniffing females' urine when they are in heat do the same. These forms of stress-related behavioral alterations were lessened in both sexes when the MCG researchers blocked the neurons' firing, on the other hand.
According to the findings, POMC neurons "both essential and sufficient" to increase vulnerability to stress and their increased firing is a cause of the behavioral changes that follow, such as depression. According to Lu, stress actually blatantly lowered the inhibitory inputs to POMC neurons. The POMC neurons are located in the hypothalamus' arcuate nucleus, or ARC, a bow-shaped brain area that is previously recognized as being crucial to how chronic stress impacts behavior.
Another population of neurons known as AgRP neurons, which are crucial for resilience to chronic stress and depression, also reside in this area, according to research published by Lu and her team in Molecular Psychiatry in early 2021. Lu's lab found that when under constant stress, AgRP activation decreases along with behavioral modifications like anhedonia, and that the behaviors improved when the neurons were activated. Her team was especially interested in understanding how persistent stress affected POMC neurons.
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