Chronic stress disrupts the body’s natural balance (homeostasis) and induces a cascade of nasty events within the body’s endocrine and immune systems. In a system with normal homeostasis, each cell acts like an efficient miniature machine in which the cell happily functions because it receives the nutrients it needs to power its engines (the mitochondria), is safely protected by the cell membrane and is able to rid itself of waste.
Chronic stress causes the release of glucocorticoids from the adrenal glands. These harmful hormones disrupt the functioning of the mitochondria which impairs the working of cells especially neurons. We know that glucocorticoids (or stress hormones) result in the neuron not being able to support synaptic plasticity and the hormones slow the release of beneficial brain-derived neurotrophic factor (read my posts ‘Neuroplasticity is all about chemicals and synapses’ and ‘Neurotrophins are brain fertilizers’ for some background). The effects are most prominent in an area of the brain called the hippocampus which is critical for learning and memory. Furthermore, in animals, chronic restraint stress causes blunting of neurogenesis; the birth of new neurons in the hippocampus that seems to be important for making new memories. You can begin to see that chronic stress is going to create barriers to plasticity and recovery after a brain injury.
So how is chronic stress and depression related? Chronic stress in rodents (restraining them in a tube) consistently leads to depression-like behavior in the animals (Adlard & Cotman 2004). These animals go on to have impaired learning and memory and recent research supports the notion that chronic stress and depression also cause an increase in inflammation within the cells of the brain (Eyre & Baune 2012 Brain Behavior and Immunity 2012; Nakajima Behavioral Brain Research 2010). Inflammation damages the cell membranes and causes an accumulation of free radicals (the cells’ waste products). This is particularly hazardous to the healing brain!!
It is important to recognize that the emotional and psychological symptoms experienced in chronic stress and depression are due to altered homeostasis. It is physiological. The person’s delicate cellular balance is disrupted. Restoring this balance is important for a healthy and healing brain.
Coming up: exercise to treat depression.