Which neurotransmitter levels are thought to be decreased in depression?

In the context of depression, the levels of neurotransmitters such as serotonin and norepinephrine are believed to be decreased based on prevalent theories. Both serotonin and norepinephrine play significant roles in mood regulation. Serotonin is largely associated with feelings of well-being and happiness, while norepinephrine is involved in arousal and responsiveness to stimuli. Impairments in their synthesis, release, or receptor sensitivity can contribute to the pathophysiology of depression.

Research and clinical observations suggest that individuals with depression often exhibit dysregulation of these neurotransmitters, leading to various symptoms associated with mood disorders. This understanding forms the basis for many pharmacological treatments aimed at increasing the availability of serotonin and norepinephrine in the synaptic cleft, such as selective serotonin reuptake inhibitors (SSRIs) and norepinephrine-dopamine reuptake inhibitors (NDRIs).

The other options do not fully encompass the complexities of neurotransmitter involvement in depression. While dopamine does play a role in mood and motivation, it is not the primary focus linked to depression as serotonin and norepinephrine are. Similarly, tryptophan, being a precursor to serotonin, is important, but it is the resultant serotonin levels that are more directly associated