Serotonergic is a term used to describe structures and processes in the brain and body that are affected by serotonin. Serotonin is a neurotransmitter, a certain type of chemical used to send signals in the brain. Serotonin is a monoamine neurotransmitter, meaning it has only one amino group, and it is derived from an essential amino acid called tryptophan.
Serotonin can be found throughout the brain and in other parts of the body, most notably the digestive system, where it regulates digestion and the movement of food through the gastrointestinal tract. It plays a major role in regulating mood and some studies show a link between serotonin levels and impulsive, aggressive or violent behavior. It is also implicated in some psychological disorders, most notably major depressive disorder.
Serotonergic neurons can be found in the raphe nuclei, which are located in the brain stem region. Some of these neurons communicate with the dorsal spinal cord, and this pathway is thought to play a role in pain perception. Other serotonergic neurons, found in the pons and midbrain, regulate body temperature and heartbeat.
From the raphe nuclei, serotonergic pathways spread throughout the brain. A single neuron can project to hundreds of different cells. They communicate with several brain structures, including the cerebellum, hippocampus, neocortex, and thalamus. A serotonergic receptor, the part of a neuron that receives a chemical signal from another cell, can be either inhibitory or excitatory. This means that the serotonin message the cell receives can make it either more or less likely to signal to other cells.
Low levels of serotonin are thought to be a primary cause of depression, and so many antidepressant medications increase the level or the action of serotonin in the brain. The most common type of antidepressant is called a selective serotonin reuptake inhibitor (SSRI). These medications have chemicals that bind to the neuron that releases serotonin, preventing the neuron from reabsorbing the serotonin for a short time. This increases the strength of the signal sent to a neuron, because the serotonin has more time to interact with that neuron.
SSRIs are generally thought to be very effective for major depressive disorder, and may also be beneficial for some anxiety disorders. The relationship between serotonin and depression is not fully understood, however. Although SSRIs begin to work immediately, most people suffering from depression will not see improvement from these medications for four to six weeks.