Depression alters stress response

Scientists have found that moderate stress, of little significance for a healthy person, causes a stronger and more lasting reaction in depression. New data will help to understand the mechanism of development of the disease and develop new methods for its diagnosis. Research article published in Metabolic Brain Disease . This work was supported by a grant from the Russian Science Foundation (RSF).     

The body of any animal reacts to stress in a similar way, mobilizing all resources: the level of stress hormones increases, respiration and heart rate increase, the level of glucose in the blood rises, from which all organs receive energy. The immune system is also preparing to fend off the danger: more pro-inflammatory cytokines are produced . These small protein molecules send messages to cells that potentially dangerous foreign substances are emerging, and trigger a protective reaction – inflammation.

The response to stress is universal, but the strength and duration of such a response (stress reactivity) depends on many factors. One of them is mental disorders, including depression. Neurophysiologists from the Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, have confirmed this by studying a rodent model of depression. Scientists have suggested that in people with depressive disorder, the psychophysiological response to stress will also differ from normal, not only externally, but also in terms of biochemical indicators: blood glucose levels, cholesterol, and others.

The study involved 33 patients aged 18 to 45 years with diagnosed depression, but without concomitant mental, neurological or hormonal disorders. The control group consisted of 43 healthy volunteers of the corresponding age. All participants performed a simple task: they had to sequentially find numbers from 1 to 25 in the Schulte table , where they are located in random order. Moreover, each participant worked with several tables in a row, and each time the problem had to be solved faster. In the second stage of the test, the experimenter changed tables every 15 seconds, and each time the search had to start over. In total, both stages took each participant 8–12 minutes. This is sufficient to induce short-term moderate stress, and the test is not medically or traumatized.

Immediately before the test and one hour after it began, each participant gave blood samples. In them, the researchers measured the levels of stress hormones, pro-inflammatory cytokines, standard metabolic parameters: levels of glucose, cholesterol, triglycerides, and so on. Separately, during the test itself, each participant was assessed for changes in heart rate.

Scientists have found differences already in the blood taken before the test. Participants with depression had higher levels of adrenocorticotropic hormone and cortisol associated with stress responses, as well as some pro-inflammatory cytokines. These findings confirmed the findings of previous studies on changes in the neuroendocrine and immune systems in depression. The scientists obtained the most important results by comparing blood counts after the test. People with depression, in contrast to the control group, had increased levels of glucose and one of the pro-inflammatory cytokines, tumor necrosis factor (TNFα). Even an hour after the start of the test, the depressed patients still continued to respond to the stress caused. This confirmed that moderate stress, of little significance for a healthy person, induces a stronger and more lasting response in depression. Such excessive psychophysiological responses occur in patients with depressive disorders and in everyday life.

“We were able to verify the results obtained in experiments with rodents in the clinic only thanks to cooperation with a team of doctors who, under the leadership of Professor Alla Hecht, conducts such research at the Scientific and Practical Center for Psychoneurology,” emphasizes one of the authors of the work, an employee of the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences Natalia Gulyaeva. – The new stress test allows you to assess the individual stress reactivity of a patient by changing specific biochemical markers in the blood. The results provide new information on the mechanisms of the pathogenesis of depression, and can also be used in the diagnosis and assessment of the effectiveness of treatment of patients. We continue to work and have already modified the stress test, making it non-invasive: now key indicators of stress reactivity can be determined not in blood, but in saliva. “

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