Chronic stress is associated with the appearance of health problems because it affects all body systems -according to the American Psychological Association- and can increase the risk of hypertension and cardiovascular diseases, and even alter beneficial intestinal bacteria. In addition, it influences our emotional well-being and the way we behave, and can contribute to the development of depression or reduce interest in things or activities that previously gave us pleasure, preventing us from enjoying life.
New research has now revealed that the origin of this physical and psychological discomfort is to be found in a group of neurons in an arc-shaped area of the brain that become hyperactivated after chronic exposure to stress. When these neurons called proopiomelanocortin, or POMC, become overactive, these types of behavioral problems occur, which decrease when scientists reduce their activity.
The study was conducted by researchers at the Medical College of Georgia at Augusta University, who looked at the hypothalamus – which plays a key role in releasing hormones and regulating hunger, thirst, mood, desire sex and sleep – the reaction of this population of POMC neurons in response to 10 days of chronic and unpredictable stress. Unpredictable chronic stress is used to study the impact of stress exposure in animal models, and in this case environmental factors such as restraint, prolonged wet bedding in a tilted cage, and social isolation were included.
Neurons that induce stress and reduce pleasure and libido
The researchers found that stressors increased the spontaneous firing of these POMC neurons in both male and female mice, said Xin-Yun Lu, MD, chair of MCG’s Department of Neuroscience and Regenerative Medicine, Georgia Research Alliance Eminent Scholar in translational neuroscience, and author of the paper, which has been published in Molecular Psychiatry.
When the scientists inhibited the firing of POMC neurons, stress-induced behavioral changes were decreased.
When these scientists directly activated neurons, rather than waiting for stress to hyperactivate them, they observed an apparent inability to feel pleasure—known as anhedonia—and behavioral despair, which is essentially depression. In people, the symptoms of anhedonia can include losing contact with good friends and a loss of libido. In the case of mice, they lose interest in the sugar water for which they have a predilection, and males, who tend to like to smell the urine of females when they are in heat, also lose some of their interest.
However, when the scientists inhibited the firing of the neurons, these types of stress-induced behavioral changes decreased in both sexes. The results of the study show that POMC neurons are “both necessary and sufficient” to increase susceptibility to stress, and that their increased activation is a factor driving resulting behavioral changes, such as depression. Indeed, stress overtly decreased inhibitory inputs in POMC neurons, Lu concludes.
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