Editorial: Stress Induced Neural Changes in Emotional Disorders

Abstract

Editorial on the Research Topic Stress Induced Neural Changes in Emotional Disorders Psychological processes include two equally important aspects of mental processes: cognition and emotion, emotional disorders might account for more than 90% of mental disorders. For example, major depression is a prevalent emotional disorder that affects more than 1/5 of the populations worldwide, making it one of the most prevalent health-related causes of human suffering. Moreover, it is a leading risk factor for the estimated one million deaths by suicide per year world-wide. Despite that emotion is critically important to us, emotion is one of the least studied biological phenomena of the brain, the mechanism of the emotional disorders is not clear. Thus, the treatment is not as effective as expected, which might be effective in only a subset of patients and acts slowly (1). Stress has been regarded as a critical causing factor for emotional disorders. Stress is an evolutionarily adaptive response to deal with situations that impact threat to the organism and require rapid “flight or fight” responses (2). Stress is evolutionarily important for survival and benefits to all lives, however, overwhelming stress is considered to one of the main risk factors for the development of many emotional disorders such and anxiety, depression. For example, the onset of major depression are often correlated with stressful events in earlier lives, many studies reported significant correlation between the onset of major depression and the number of traumatic events within 3 months before the onset of the disease. In addition, stress can happen very long ago, for example, early life stress can induce emotional depression in adult lives (3). This means stress can induce long term changes in the body to induce emotional disorders. The stress induced neural changes are very complicated. There is compelling evidence of a causal link between chronic stress and the sympathetic system as well as the HPA axis (hypothalamus-pituitary-adrenal axis) and emotional disorders. Stress causes elevation of corticosteroids and other stress hormones, such as CRF (corticotropic-releasing factor), the known stress hormone. HPA dysregulation may be both a causative factor and a consequence of emotional disorders. In addition to hypothalamus, the locus Coerleus (central norepinephrine) also plays an important role in stress. The major function of norepinephrine (NE) system has been known as “fight or flight,” or “fear or anger” emotions (4). As we reported before, everything around us happens in an anticipated way (expected) or not anticipated way (surprising). If it happens as expected, people feel calm; if it happens unexpected, people will feel scared or angry (5). Therefore, chronic unpredictable stresses are most often used in animal models of depression. When the animals are faced with stress, they often respond with fear or anger emotions, and “fight or flight” responses trying to get rid of these stressors. After a long term of failure to deal with these stressors, they learned the “helplessness” and try to live with these stressors sadly. We say that these animals are depressed and the depression model is set up. Furthermore, stress can induce long term changes in the endocrine systems, which in turn induce behavior changes that habitually deal with the stressful situations, thus cytokine is also regarded as a causing mechanism for depression. Lymphocytes, mast cells and other immune system cells contain adrenoreceptors that respond to the peripheral release of NE. The central NE system innervates many vital parts of the immune system- the lymph organs, spleen, thymus. It is reported that lymphocyte activity was dramatically reduced in the depressed patients. There is evidence that sympathetic nervous, immune and endocrine systems are linked. Moreover, some epigenetic changes or neural changes induced by early life stress might be involved in the emotional disorders. The expression of all receptors for previous neuromodulators, neurotransmitters, cytokines can be affected by epigenetics. These changes have been suggested to be involved in the emotional diseases. In 2017, we proposed one topic “Stress Induced Neuroplasticity and Mental Disorders” for Neural Plasticity and got 41 submissions. In 2018, we proposed one topic titled “Early life stress and depression” for Frontiers in Psychiatry and got 42 submissions. This is a fast developing topic, therefore, here we continue to propose a similar topic to collect recent studies about the mechanisms of stress inducing emotional disorders, such as phobia, depression and anxiety. In this special issue, we received 27 submissions and got 18 papers accepted. In the review paper, titled “The Locus Coeruleus- Norepinephrine System in Arousal: Unraveling Historical, Current and Future Perspectives,” the authors Ross and Van Bockstaele from Drexel University gave a detailed review about the arousal function of locus-coeruleus (LC)-NE system. They discussed technological advancements that chronologically led to our current understanding of the arousal system. The paper was reviewed by professors Leszek Kubin from University of Pennsylvania, and Shahzad Khan from Stanford University, who gave a high praise for this paper: “A strength of this review is its detailed and thorough overview of stress and arousal research.” “To cover this broad topic based on several subfields of neuroscience that, traditionally, developed along their own separate paths is an ambitious undertaking. The authors have largely succeeded in producing a text that has superior educational value.” In an experimental paper, author Yang et al. from Zhejiang University, one of most famous universities in China, identified some specific genetic targets for the diagnosis and treatment of depression. They...