Depression is a common illness. According to the World Health Organization (WHO), there is more than 264 million people are affected by depression. This being one of the problems that need to be solved as depression can lead to insomnia, present of the feeling of sadness, heart attack and more. However, in serious cases, it can lead to suicide. The feeling of sadness and emptiness can be observed in most of the patient with depression.
If depression is caused by stress and the imbalance of chemicals present in the brain, then it is closely related to the nerve cell connection and communication. To answer the hypothesis stated, different research had been done. Researchers suggest that the causes of depression are not as simple as the different levels of chemicals present in the brain. Despite this, it was a complicated process that involved the chemical secreted which work inside and outside the nerve cells, the nerve cells connection, the nerve cells' growth, and the functioning of nerve circuits.
Hippocampus is part of the limbic system responsible for the processing of long-term memory and recollection. Stress hormones had been identified as one of the caused that impairs the growth of nerve cells in this part of the brain. In one of the functional magnetic resonance imaging (fMRI) studies done, investigators studied 24 women who had a history of depression. Through the study done, it shows that the hippocampus of depressed women was 9% to 13% smaller than those who were not depressed.. In other human and animal studies, it was proved that stress changes neuronal morphology, suppresses neuronal proliferation, and reduces hippocampal volume . This study was supported by other animal studies using an antidepressant. From this study, it shows that antidepressants had spurred the growth and enhanced branching of nerve cells in the hippocampus. The generation of new neurons, strengthening of nerve cell connection had improved the exchange of information between the nerve circuit. The information changed between the nerve cells involved neurotransmitters which are the chemicals that relay on the messages from neuron to neuron. Thus, the development of neurons is important for nerve cell communication to occurs.
In nerve cell communication, neurotransmitter plays an important part in it. One of the neurotransmitters that play an important role in depression is serotonin. Serotonin had a function that helps to regulate sleep, appetite, emotion, cognitive and autonomic. A low level of serotonin can cause depression and it can lead to suicide while the high level of serotonin can produce a manic state. Manic depression illness or it was commonly known as bipolar disorder. Next, norepinephrine is another neurotransmitter that plays important roles in depression as it regulates cognition, motivation, and intellect, which are fundamental in social relationships. Besides, norepinephrine is also a stress hormone. Social dysfunction is one of the most important factors affecting the quality of life in depressed patients. Genetic studies on mice shown that mice are protected from stress-induced depression-like behaviors when it was impaired genetically engineered functional enhancement of the norepinephrine system .
From the studies done, we can conclude that stress and the imbalance of brain chemicals had an obvious impact on depression. It affects the growth of nerve cell and nerve cell communication. Cell-cell communication is important to cure depression. This is because as the neurons in the hippocampus grow and communicate the impaired recall of positive memories and increased recall of negative memories will not happen. This directly will prevent depression.