Codes for depression

As a student of science and psychology, I am interested in learning about inherent biological mechanisms that are responsible for the various external experiences we go through on a daily basis. Why do people act the way they do, or why do humans feel a certain kind of way when watching a sad movie, or a funny movie or a scary movie?

Module 15.1, addresses the broad topic of Mood Disorders.

I wanted to know specifically about the chemical responsible for "depression". Why do we feel sad or down during not so happy times? What makes us feel that way? well, there are many factors that can help explain this mechanism, but in this post, I will talk mainly about the chemical imbalance in the brain.

Neurotransmitters, which are chemicals responsible for relaying most neural information from one neuron or nerve cell to the next have been helpful in explaining the case of depression.

The cause of depression, is dependent upon the volume or amount of these neurotransmitters being communicated throughout the neural pathways. If there is too much or too little then there is an imbalance or a breach to homeostatic event, which can then lead to the person feeling depressed or sad. The family of neurotransmitters that have been linked to depression are all classified in a group called monoamines which are further classified into three: 

Serotonin, Dopamine, and Norepinephrine

Low levels of monoamines cause depression in humans. One study have found that high levels of an enzyme responsible for breaking down serotonin, the Monoamine Oxidase-A (MAO-A), is significantly higher in cases of depression. 

Chemically, that is the explanation. Physiologically, the parts of the brain depression is most prevalent are: 

The Amygdala, Thalamus, Hippocampus.

Depression, once again, is experienced by the human in effect of a biological mechanism... Some argue that this is not the only cause of depression, things like the environment, and genetics also influence the occurrence of depression. However, for me chemically and biologically explained is much more satisfying. If you want to learn about the physical effects of depression, I have included an image below: 

Good luck and happy day! 

The Immune-Brain Loop and Stress

So the title might boggle you, because you did not come across that specific terminology in the text. But in fact it is just another synonym we did visit in the text: psychoneuroimmunology. I was interested in this topic because it explains a relationship between the immune system (yes) and the central nervous system. Yes, in fact, chemicals involved in fighting infection can be linked to emotional feelings like depression and other mental mechanisms.

To illustrate, first I must introduce what is called the HPA axis which stands for the hypothalamus-pituitary-adrenal cortex.

The image below depicts what happens when a stimulus of stress is introduced via externally (i.e., you experience through your sense of sight, smell, touch, etc.). It leads to a cascade of responses that involves the HPA axis. First response, through the hypothalamus, which releases CRF and so on....

Stress is a broad term. It can change its meaning and purpose if you place "stress" in a different context. Like in psychology, when we mention stress, we immediately associate it with emotions, like frustration or anger. However, in physical biology, stress means an injury. A physical trauma to the foot or finger or what have you. And the immune system is directly involved in eradicating stress to the physical aspect of your body. Levels of white blood cells (WBCs) that fight infection, such as cytokines and natural killer cells, are elevated in response to a physical stress like a cut in your bleeding finger, etc. But it has been shown that elevated levels of cytokines, are also correlated with emotional stress. One explanation is that (as shown in the table below) increased cortisol production directs its energy to increasing metabolism and therefore detracts energy synthesizing proteins. In other words, increasing the cortisol production will lead into a deprivation of normal levels of B cells, T cells, and natural killer cells, which are all WBCs found in the immune system. Having low levels of WBCs mean depression and extreme sadness.

Prolonged stress also harms the physiological aspect of the brain. In the hippocampus elevated levels of cortisol can mean toxicity that eventually leads to damage in the neurons of the hippocampus, which is responsible for maintaing stability in emotional pursuits.