What neurotransmitter changes are commonly associated with Major Depressive Disorder?

The correct response highlights the common neurochemical alterations found in individuals with Major Depressive Disorder (MDD). Research has consistently demonstrated that MDD is associated with decreased levels of neurotransmitters such as dopamine, serotonin, and norepinephrine. These neurotransmitters play crucial roles in regulating mood, affect, and emotional well-being.

Decreased serotonin levels, for instance, are often linked to feelings of sadness and anhedonia (loss of interest), which are core symptoms of depression. Similarly, low levels of norepinephrine have been associated with feelings of fatigue and lack of motivation. Dopamine, meanwhile, is crucial for the brain's reward pathways and its reduced levels can contribute to the inability to experience pleasure, commonly seen in depressive states.

Conversely, increased levels of these neurotransmitters or solely elevated levels of norepinephrine do not align with the established understanding of MDD, which reflects why the other options do not accurately represent the typical neurochemical profile associated with the disorder. Additionally, decreased cortisol levels are not characteristic of MDD; in fact, individuals with major depression often show elevated levels of cortisol, indicating dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis.