Stress is a common physiological challenge faced by all human beings. Stress results from prolonged exposure to cortisol hormone that is produced by suprarenal glands. When this hormone is released, it discourages the generation of new cells (neurogenesis) that replaces nerve cells in the hippocampus. Hippocampal neurons are responsible for regulating emotions, thoughts and the creation of new memories. Researchers have established the genetic mechanism that occurs in the brain to trigger stress or prolonged trauma. Scientists have shown that people with depression have brain tissues that show activation of particular genetic transcription. The transcription factor acts like a “switch” that provokes the genes to be turned on or off. During a depression, TF turns off five genes responsible for the normal formation of synaptic connections in the brain that controls emotions and cognition. These brain units are responsible for a normal emotional response in human beings.
Glucocorticoids release a stress hormone that affects the hippocampus nerve cells and prefrontal neurons. Glucocorticoids are hormones released after the amygdala nerve cells are activated by stimuli from the brain. The activation neurons send a signal to the hypothalamic tissues that release glucocorticoids hormones such as cortisol. According to Lajtha, Baker, Dunn, and Holt (2007) cortisol hormone are regarded as a stress hormone since it prepares the brain to sustain a fight or respond to an attack (p. 582). Cortisol affects hippocampal nerve cells and prefrontal neurons by disrupting normal communication between the genes that aid neuronal connections.
Recent studies have shown that stress hormone causes hippocampal neurons to retract while it precipitates amygdala neurons to expand. Stress provokes hippocampal-dependent memory to decrease when exposed to cortisol for a long period of time. Stress also causes over-excitability of nerve cells that are regulated via adrenal steroids (Siegel, Sapru, & Siegel, 2006). Mental pressure induces prefrontal cortex interruption that is characterized by the enlargement of dendrite and atrophied dendrites. The expansion of these dendrite cause disruption of cognitive flexibility that causes aging. Severe depression can also affect the replacement and generation (neurogenesis) of neurons in the dentate gyrus. Replacement of human brain nerve cells ensues in the subventricular zone. This region is responsible for the generation of new neurons for the olfactory bulbs. Reproduced units are located in the area where neurogenesis takes place. The new nerve cells are then extended to the CA3 region of the hippocampal cells (Melanie, 2012). Stress hormone causes the amygdala to produce large amounts of somatropin (growth hormone); however, it is dependent on the presence of ghrelin (hunger hormone). Ghrelin is mostly synthesized in the stomach and sometimes in the hypothalamus.
During depression or trauma, the hypothalamic hormones (corticotropin hormone) are elevated. The long-term elevation of these hormones induces the release of glucocorticoids such as cortisol from the adrenal glands. Studies have shown that long-term exposure to cortisol interferes with the proper communication between neurons of the hippocampal and amygdala units. Stress also discourages the generation of new cells (neurogenesis) that replace neurons in the hippocampal cells (The Rockefeller University, 2015).
Neurogenesis is a complex process, which begins with the migration and differentiation of newly-formed cells and ends with the formation of a new functional neuron that is integrated into the neural network. Neurogenesis occurs in the subventricular units of the olfactory system. Cortisol is released from the hypothalamic adrenal cells. Long-term exposure to cortisol interferes with brain nerve cells by causing them to shrink. This interference affects the ability of neurons to send information through the dendrites.
Studies have shown that subjects diagnosed with PTSD have decreased hippocampal cells in comparison to those without. Cortisol hormone is responsible for the shrinking of the hippocampal volume that controls the formation of new neurons in the brain cells, and it may lead to depression.
In order to counter chronic stress, it is advised to exercise regularly. Daily exercise can improve the performance of cognitive tasks. Studies have shown that exercise leads to increased BDNF, which is responsible for strengthening brain cells and also enhancing neuronal connections. It is also believed that exercise promotes neurogenesis of brain cells in the hippocampal cells.
References
Lajtha, A., Baker, G., Dunn, S., & Holt, A. (2007). Handbook of neurochemistry and molecular neurobiology. New York, N.Y.: Springer.
Melanie, G. (2012). How to Prevent Stress from Shrinking Your Brain. Web.
Siegel, A., Sapru, H., & Siegel, H. (2006). Essential neuroscience. Philadelphia, Pa.: Lippincott Williams & Wilkins.
The Rockefeller University. (2015). Stress affects on structure and function of the hippocampus. Web.