Psychoneuroimmunology of depression and its relation to the gut-brain axis

Background: Psychoneuroimmunology (PNI) or also called psychoneuroendocrinology is the study of how psychological, neural, and immunological processes interact and influence human health and behavior. It is known that psychosocial factors contribute to the development of many diseases and that the immune system plays an important role in this relationship. Likewise, immune system signals in the brain affect mood, cognitive function, and behavior. Method: Literature review through scientific sources from books and journals related to the psychoneuroimmunology of depression and its relationship with the gut-brain axis. Discussion: Several studies have shown that patients with severe mental disorders including depression are affected by various changes in the gut microbiota and increased intestinal permeability. The gut microbiota can activate the Hypothalamic-Pituitary-Adrenal (HPA) axis through some mediators that cross the blood-brain barrier and include antigens, microbes, cytokines, and prostaglandins. Some bacterias release neurotransmitters that can interact directly with the vagus nerve. Hypothalamic-Pituitary-Adrenal axis activation can influence gut microbiota and gut permeability. An imbalance in intestinal flora can reduce protective properties, and increase neurotoxins and inflammatory mediators, causing nerve damage from the synaptic cleft which causes depression. Conclusion: There is an interrelated relationship between the psychoneuroimmunology of depression and the gut-brain axis.