<p> Exposure to prolonged chronic stress induces heightened vulnerability to anxiety, depression, and a lot of mood disorders. Dysfunction of the medial prefrontal cortex (mPFC) in the brain has been linked to the cognitive and emotional deficiency induced by long-term stress exposure. Chronic stress-induced depression (CSID), therefore, is an imperative mental disorder. If treated improperly, upcoming psychiatric disorders, such as major depressive disorders (MDD), anxiety, and even post-traumatic stress disorder (PTSD) caused by lasting sensitivity to recurring sensors, will eventually tear the patient to shreds<sup>[<a href="#ref1">1</a>]</sup>. According to the World Health Organization (WHO), depression is already becoming the leading cause of disability around the world. It even haunts more than 264 million people worldwide<sup>[<a href="#ref2">2</a>]</sup>. However, it is only the tip of the iceberg.</p>
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<p> Exposure to prolonged chronic stress induces heightened vulnerability to anxiety, depression, and a lot of mood disorders. Dysfunction of the medial prefrontal cortex (mPFC) in the brain has been linked to the cognitive and emotional deficiency induced by long-term stress exposure. Chronic stress-induced depression (CSID), therefore, is an imperative mental disorder. If treated improperly, upcoming psychiatric disorders, such as major depressive disorders (MDD), anxiety, and even post-traumatic stress disorder (PTSD) caused by lasting sensitivity to recurring sensors, will eventually tear the patient to shreds<sup>[<a href="#ref1">1</a>]</sup>. According to the World Health Organization (WHO), depression is already becoming the leading cause of disability around the world. It even haunts more than <b>264 million</b> people worldwide<sup>[<a href="#ref2">2</a>]</sup>. However, it is only the tip of the iceberg.</p>
<p> Depression is a complex disease. Deficits of neurotransmitters, genetic inheritance, and dysregulation of the hypothalamus-pituitary-adrenal axis (HPA axis), etc, widely account for depression. Nevertheless, the nature of this disorder has recently been reconceptualized as dysregulation of the gut-brain axis. Mounting scientific evidence indicates that gut-modifying agents could regulate intestinal function and health, which is widely composed of activated immune-inflammatory substances and oxidative stress (OS)<sup>[<a href="#ref1">3</a>]</sup>. Those pathways mentioned above will be further discussed in the following sections.</p>
<p> Depression is a complex disease. Deficits of neurotransmitters, genetic inheritance, and dysregulation of the hypothalamus-pituitary-adrenal axis (HPA axis), etc, widely account for depression. Nevertheless, the nature of this disorder has recently been reconceptualized as dysregulation of the gut-brain axis. Mounting scientific evidence indicates that gut-modifying agents could regulate intestinal function and health, which is widely composed of activated immune-inflammatory substances and oxidative stress (OS)<sup>[<a href="#ref1">3</a>]</sup>. Those pathways mentioned above will be further discussed in the following sections.</p>
<h3>Immune-inflammatory Pathway in Depression</h3>
<h3>Immune-inflammatory Pathway in Depression</h3>