Stress is commonly viewed as the brain’s response to a demand or a challenge. These stimuli are referred to as stressors and can be real or perceived. Not all stress is bad, as it is needed for survival and to be kept out of harm’s way. However, stress can have a negative impact on an individual’s health as it can affect a body’s ability to function and can also lead to psychiatric disorders.
Psychiatric disorders greatly disturb your thinking, moods and behaviour on a daily basis. Anhedonia is a critical feature of neuropsychiatric disorders and is described as the inability to experience pleasure. This was later redefined as an impairment to the pleasure mechanism of wanting, liking and learning. The term anhedonia comes from the two approaches of happiness, which are the eudemonic and hedonic approach. The hedonic approach is a concept that considered the pursuit of pleasure and the avoidance of pain to be the main path to happiness. What are the effects of stress?
Stress-related psychiatric disorders include major depressive disorder and general anxiety disorder. Stress causes cortisol production, in humans, to increase as a result of the hypothalamus being stimulated; this is then modulated by feedback loops when it binds to types of corticoid receptors. Compared with healthy individuals, depressed patients often have enlarged adrenal glands, as well as increased levels of cortisol. Healthy adults have a corticosteroid receptor agonist called dexamethasone, which causes reduction of the hormone cortisol. This is not the case for depressed patients as they have high levels of cortisol, indicating there is an impairment in the negative feedback mechanism.
Chronic stress is known to impair not only hippocampal-dependent cognitive function but also enhances amygdala-dependent unlearned fear and fear conditioning. This enables an individual to learn to predict danger rapidly. However, it can become a problem if they continue to display fear responses where there is no danger. These are characteristics of anxiety disorders.
Corticotropin-releasing factor (CRF) is a neuropeptide that stimulates cortisol to be released. CRF is released into the amygdala, which has high concentrations of CRF receptors, that are activated when CRF binds to it. Studies show long term exposure to CRF in adult mice, reduces the number of thin dendritic spines; this meant the number of excitatory synapses also decreased. Exposure to CRF can enhance memory; however, if the exposure is endured over a long period of time, like chronic stress, it can have detrimental effects on memory. Studies were also conducted to see the correlation between cortisol, one of the hormones released when feeling stressed, and memory. Healthy participants received cortisol or a placebo and were tested on verbal, spatial, explicit and implicit memory. Results showed that cortisol affected verbal, spatial and explicit memory but had no effect on implicit memory. This supported the notion that stress-induced cortisol blocked memory retrieval and showed that the activity of the hippocampus also decreased. However, the acute stress response expresses that it can enhance the memory of emotional items twenty-four hours after cortisol was given to the patients. This revealed that amygdala was activated in response to emotional items.
Chronic stress, which causes an increase of cortisol, has shown to result in a decrease of dendritic branches of neurones, the number of neurones and changes to the shape of synaptic terminals. It also prevents neurogenesis of neurones from stem cells in the dentate gyrus area of the hippocampus. Severe stress can suppress the immune system by causing a decrease of activity of cytotoxic T lymphocytes, which are responsible for killing foreign and abnormal cells.
Factors like acute and chronic stress can also increase the risk of drug addiction, which is another type of chronic neuropsychiatric disorder. Drug addiction is described as the intake of drugs of abuse and the loss of control over this consumption, despite the negative consequences it has to the individual. The hypothalamic pituitary adrenal (HPA) axis, which is the main system that responds to stress, as well as the amygdala and other brain systems all interact with the brain’s reward circuit that is involved with addictive behaviours. Excessive activation of the neural reward system leads to dysfunction and over activation of the brain’s stress response, this then leads to an increase in the reward threshold. The mesocorticolimbic system is the neurocircuitry associated with addiction, and repeated exposure to drugs leads to changes to this system, making them more vulnerable to develop addiction and relapse. As mentioned before stress causes the secretion of CRF; this stimulates the release of adrenocorticotropic hormone (ACTH) into the bloodstream. Studies have identified stress as one of the main risk factors for developing an addiction and have found high levels of CRF and ACTH within individuals who are dependent on drugs.
Stress is normal, and everyone experiences it in their lifetime. However, depending on the intensity and duration of experiencing stress, it can have both positive and negative effects on an individual. Both acute and chronic stress has a strong correlation with psychiatric disorders and can affect a person’s health significantly. It is essential to understand that stress is not the only factor that can lead to disorders like anxiety, depression and addiction, as several other factors can also lead to psychiatric disorders.
