The Neurobiological Mechanisms Underlying Stress and its Role in Mental Health Disorders
Introduction
Mental health disorders are among the leading causes of disease and disability worldwide with stress being a critical factor, influencing both physiological and psychological health. Dysregulated stress responses can lead to the development of mental health disorders such as major depressive disorder (MDD), post-traumatic stress disorder (PTSD), anxiety disorders, and most commonly of all, depression. Depression affects over 280 million people worldwide (World Health Organization) and costs an estimated $326 billion annually in the United States alone. (NIH) Focusing on the serotonergic (5-HT), glutamatergic, and γ-Aminobutyric acid (GABA) systems, as well as the hypothalamic-pituitary-adrenal (HPA) axis, this paper explores the neurobiological mechanisms underlying stress including stress factors, the effects of stress neurologically, and how stress affects mental health.
What Causes Stress?
Many factors can induce stress and mental health disorders such as interactions of psychological, environmental, and biological factors. Psychological factors include personal relationships or traumatic experiences. Environmental factors include external conditions and biological factors include genetic predispositions and neurochemical imbalances. Resiliency, the ability to withstand or recover from stress, determines the susceptibility to mental health disorders.
What Happens Neurologically During Stress?
A stress response is primarily mediated by two systems: the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) axis. The HPA axis is central to the body’s stress response. When exposed to a stressor, the HPA releases corticotropin-releasing hormone (CRH), stimulating the pituitary gland to secrete adrenocorticotropic hormone otherwise known as ACTH. The ATCH signals the adrenal glands to produce cortisol, a glucocorticoid responsible for energy mobilization. Chronic stress and activation of the HPA axis can lead to sustained cortisol release and elevated levels of cortisol can lead to detrimental effects on brain function such as cognitive impairment and emotional dysregulation. The SAM axis initiates a rapid response by releasing noradrenaline and adrenaline, preparing the body for a “flight or fight” reaction. Both the HPA and SAM axis work together to generate quick responses that mobilize energy, suppress the digestive system and reproductive systems, activate the immune system, and restore homeostasis.
Effects of Stress on the Brain
Many neurochemical systems and structures of the brain are impacted by stress. Some of the key neurochemical systems affected by stress include: Glutamate, Serotonin, and Dopamine levels. Chronic stress reduces serotonin levels, impairing mood regulation, reward processing, and motivation which are all symptoms present in depression and anxiety disorders. Stress also dysregulates the glutamate signaling stress which can lead to excitotoxicity, neuronal damage, and cognitive impairment. Additionally, stress can alter brain structures like: the Hippocampus; reducing its volume and impairing memory and cognitive function, the Amygdala; hyperactivating it and heightening fear and emotional responses, and the Prefrontal Cortex; impairing decision-making and emotional regulation.
How Does Stress Affect Mental Health?
Chronic stress disrupts the neurochemical balance and brain structure, increasing susceptibility to mental health disorders. Examples of mental health disorders caused by stress are Major Depressive Disorder (MDD) and Post-Traumatic Stress Disorder (PTSD). Chronic stress causes disruption in mood regulation and rewards processing as well as elevated cortisol levels and cognitive deficits can cause mental health disorders like MDD. Post-Traumatic Stress Disorder, a common stress disorder, is often caused by a stress induced amygdala hyperactivation and the suppression of the prefrontal cortex that contributes to the heightened fear responses and impaired emotional regulation present in PTSD.
Conclusion
The Neurobiological mechanisms underlying stress are intricately complex, involving the HPA and SAM axes. Dysregulated stress can lead to changes in the brain’s structure and neurochemical structures that can contribute to the development of mental health disorders such as depression, PTSD, MDD, and anxiety.
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