Depression describes a medical condition characterized by persistent feelings of sadness or hopelessness that interfere with daily activities in life. Although many factors contribute to the onset of depression, it involves biological changes in the brain and the levels of neurotransmitters, naturally occurring chemicals in the brain. Depression affects more than 20 million people in the United States, according to MedLine Plus, and many can benefit from treatment with anti-depressants. Doctors classify anti-depressant medications based on how they work and which chemicals in the brain they influence.
Selective Serotonin Reuptake Inhibitors
Serotonin, a neurotransmitter found in the gastrointestinal tract and the central nervous system, contributes to feelings of well-being. Medications classified as selective serotonin reuptake inhibitors, SSRIs, block the nerve cells in the brain from reabsorbing serotonin, therefore increasing the levels in the brain. By increasing the amount of serotonin in the brain, SSRIs enhance the nerves ability to transmit electrical signals which improves mood. Examples of SSRIs include fluoxetine, paroxetine and sertraline.
Serotonin and Norepinephrine Reuptake Inhibitors
Norepinephrine acts as both a hormone and a neurotransmitter in the body. In the brain, norepinephrine activates alertness and arousal and stimulates the reward system---the brain structures that control behavior by inducing pleasurable effects. Medications, such as duloxetine, venlafaxine and desvenlafaxine, inhibit the nerve cells in the brain from reabsorbing both serotonin and norepinephrine therefore increasing levels of both neurochemicals in the brain.
Tricyclic Antidepressants
The third major type of neurotransmitter in the brain, dopamine, functions in maintaining mood, stimulating the reward system and aiding in cognition, movement, memory, learning and attention. Tricyclic antidepressants, a group of older medications including amitriptyline and imipramine, work by blocking the reabsorption of serotonin and norepinephrine and to a lesser extent dopamine, according to MayoClinic.com. In addition tricyclic antidepressants block other types of cells in the brain, which increases the incidence of unwanted side effects with this classification of medications.
Monoamine Oxidase Inhibitors
The brain contains an enzyme known as monoamine oxidase that functions to break down the chemicals serotonin, norepinephrine and dopamine. Medications classified as monoamine oxidase inhibitors prevent monoamine oxidase from breaking down the neurotransmitters, therefore increasing the levels of all three in the brain allowing them to elevate mood. Although this class of medications, which includes tranylcypromine and phenelzine can effectively treat depression, because of the number of dangerous side effects associated with these drugs, doctors recommend taking them only after other types of treatments have failed.
Role of Glutamate
Glutamate, an amino acid used to build proteins, also functions as a neurotransmitter in the brain. Because too much or too little glutamate in the brain can cause harm, glutamate regulation is essential according to the Center for Molecular Biology and Neuroscience. Glutamate found outside of cells can have toxic effect in certain areas of the brain and therefore contribute to anxiety and depression. Antidepressant medications increase the effects of the receptors needed to keep glutamate sensitivity of cells in check, therefore protecting the nerve cells from the effects of glutamate.
