Major Depressive Disorders: A Case Study

factors play a big role in making an individual susceptible to major depressive disorder. However, the DSM-V notes that stressful events occurring close to the onset of MDD does not entirely guarantee a correlation. (APA et al., 2013).

Neural structures/ neurotransmitters implicated
Several neural structures are implicated in MDD, particularly the medial orbital pre-frontal cortex, amygdala, hippocampus, ventromedial parts of basal ganglia, and changes in the gray matter volume. Other neural structures include the dorsomedial prefrontal cortex, supragenual anterior cingulate cortex, precuneus, ventral striatum, and the dorsomedial thalamus(Grimm, Ernst, Boesiger, Schuepback, Hell, Boeker, & Northoff, 2009). The dorsal medial prefrontal

cortex (DMPRFC) is activated when individuals with MDD experience symptoms of severity and hopelessness. In addition to activation in the DMPRFC, the ventral striatum and dorsomedial thalamus are active when individuals are asked to judge themselves based on reactions to negative stimuli (Grimm et al, 2009).
Neurotransmitters that are implicated in MDD include serotonin, dopamine, and norepinephrine. These three neurotransmitters consequently affect functioning of libido(sexual arousal), appetite, sleep, locomotion(movement), cognition(thinking), anxiety, and aggression ( Holtzeimer & Nemeroff, 2006). Individuals diagnosed with MDD have also been found to have an inconsistency with the amount of monoamine in their body; this deficiency is considered one of the prevailing theories of depression. In addition to controlling basic functions and drives, these three neurotransmitters also control excitatory and inhibitory neurotransmitter circuits (Holtzeimer et al., 2006).
Serotonin
Activation of serotonin is implicated in the hypothalamus, thalamus, hippocampus, amygdala, basal ganglia, cingulate cortex, and prefrontal cortex( Holtzeimer et al., 2006).

The receptors involved in serotonin are 5-HT pre and postsynaptic receptors. Understanding the mechanism of serotonin aids in various treatments for depression. For example, understanding the levels of cerebrospinal fluid regarding serotonin has significantly aided scientists in understanding the root cause for depression. These levels are much lower in depressed individuals, as well as depressed individuals who attempted suicide (Holtzeimer et al., 2006). In addition to lower cerebrospinal fluid metabolites of serotonin, abnormalities with serotonin binding and reduced amounts of tryptophan have also lead to an understanding of the causes of depression.
Norepinephrine
Norepinephrine is produced in the pontine locus ceruleus( Holtzeimer et al., 2006). This neurotransmitter is particularly important in mediating stress response in individuals, and is thought that norepinephrine perform crucial interactions with pre and post synaptic alpha and beta adrenergic receptors. Although it is known that norepinephrine plays an important role in depressive symptoms, further research is needed to understand the role norepinephrine plays on the body, and the mechanisms in which it elicits depressive symptoms.

Dopamine
The final of the three neurotransmitters discussed for MDD, dopamine transmission is conducted through three important pathways in the brain: the nigrostriatal pathway, mesolimbic-mesocortical pathway, and the periventricular system(Holtzeimer et al.,2006). Holtzeimer and colleagues also noted that in depressed patients, homovanillic acid(a metabolite of dopamine) was found in lesser concentrations in the cerebrospinal fluid when compared to healthy individuals. Dopamine plays one of the most important roles in the onset of depression, as dopaminergic neurons are significantly reduced in depressive individuals( Holtzeimer et al., 2006).

Treatments
A variety of treatments are used for treating individuals with MDD. Current treatments include the use of medications, such as SSRIs (selective serotonin reuptake inhibitors). The generic names for these medications are Prozac, Paxil, Zoloft, Celexa, and Lexapro. These are considered generally safer, and cause reduced side effects than anti-depressants, which may interfere with existing medications or medical conditions (Mayo Clinic, 2014). In addition to SSRIs, SNRIs( Selective and Norepinephrine Reuptake Inhibitors) may be prescribed, which may cause decreased sexual side effects( Mayo Clinic et al., 2014). Other types of medications include NDRIs(norepinephrine and dopamine reuptake inhibitors), atypical anti-depressants , tricyclic anti-depressants(anti-depressants known to cause more severe side effects than most; prescribed when SSRIs do not work), MAOIs(Monoamine Oxidase Inhibitors), anti-psychotics, and mood stabilizers.
Besides medications, psychotherapy is a popular form of depression treatment.

This involves the patient talking to a clinician about various stressors in their lives, such as environmental, work, or family related stressors. Other names for this therapy include talk therapy, or counseling. Various subtypes of psychotherapy are used, such as cognitive behavioral therapy, mindfulness techniques(in which an individual becomes aware of current behaviors, and mindfully changes them on a daily basis), and dialectic behavior therapy(where individuals write down thoughts or feelings in a journal). (Mayo Clinic et al.,

2014).
Other forms of treatment include hospitalization, ECT(electroconvulsive treatments where electric currents are passed through the brain), TMS(transcranial magnetic stimulation where a magnetic coil stimulates nerve cells), as well as lifestyle and home remedies.

Future Research
Future research in MDD currently focuses on genetic and environmental factors that may predispose individuals to placing themselves at risk for susceptibility. In addition to these factors, emphasis is also being placed on researching childhood memories and events that may be potential triggers for depression onset in adulthood. Relevant psychological, biological, social, and patterns between adolescent to adulthood is a significant consideration for current research. (Hunter, 2013).
Conclusion
Major Depressive Disorder has undergone a dramatic change throughout history, from being treated as a demonic possession by ancient cultures to a modern day mental illness that affects millions of individuals around the world annually. Many relationships have been formed through modern neuroscientific discoveries, such as the relationship between neurotransmitters and neural structures. Successful treatment approaches, such as psychotherapy, medication, and brain stimulation techniques are now being used instead of exorcisms and archaic practices. As new information emerges regarding major depressive disorder, more insight regarding genetic and behavioral relationships may be determined through the identification of patterns in individuals.