Major Depressive disorder (MDD) is a disease that affects many adolescents and adults globally; according to the NIMH (National Institute of Mental Health) 6.7 percent of adults as well as 3.3 percent of adolescents 13 to 18 years old in the United States will experience MDD. Characterized by feelings of hopelessness, guilt, fatigue and often thoughts of suicide, this disease can be harder to classify than other (Johnson et al. 2011)more physical) diseases. The resurgence rate of MDD is 50 percent, so a “cure” could still only be temporary. Research in the field of MDD has majorly focused on specific proteins to find to actual cause of MDD.
It had been discovered around 1960 that a certain protein was associated with MDD, an enzyme called monoamine oxidase A and B (MAO A and MAO B). These enzymes are responsible for helping reactions in the brain that break down neurotransmitters. Of the neurotransmitters that are broken down, serotonin and dopamine are shown to be broken down by MAO A; both of these neurotransmitters are shown to be important in regulating mood (Duncan et al. 2012). Recent work in the field has tried to figure out how MAO A works and what other proteins affect MAO A. Studies such as Figure 1 (Johnson et al. 2011) show us that there is an increase in MAO A as well as a decrease in proteins that regulate MAO A such as, for example, a repressor protein called R1; this protein stops MAO A from functioning. Since there is more degradation of serotonin by more MAO A and less R1 to stop MAO A from working, there is less serotonin and dopamine to regulate mood. This is the predominant theory of mechanism for MDD in research today, and new drugs are being developed to target the above mentioned proteins specifically. Other theories of mechanism for the disease center around the neurotransmitters themselves and how their receptors are the cause of MDD (Hvenegaard et al. 2012, Peng et al. 2012). As shown in Figure 2 (McCord 2003), neurotransmitters such as serotonin or dopamine bind to a receptor to initiate a response in an adjacent neuron to stimulate activity in that neuron; when the receptor is either damaged or not working this response doesn’t work and can cause MDD symptoms. Researchers are also creating drugs to help these receptors interact with the neurotransmitters or to stimulate the receptor itself. Only by studying all mechanisms of MDD and investigating all treatment options can we be closer to treating this disease.