Which neurotransmitter's abnormality is linked to depressive symptoms, according to the monoamine hypothesis?

The monoamine hypothesis of depression suggests that abnormalities in neurotransmitters, specifically serotonin, norepinephrine, and dopamine, contribute to the development of depressive symptoms. According to this hypothesis, a deficiency in one or more of these neurotransmitters can lead to changes in mood, anhedonia (loss of interest or pleasure), and other symptoms characteristic of depression.

Serotonin is often highlighted for its role in mood regulation and emotional response, with low levels being associated with feelings of sadness and anxiety. Similarly, norepinephrine is closely linked to arousal and alertness, and its deficiency can result in fatigue and lack of motivation, which are common in depression. Dopamine, which is involved in the brain's reward pathways, is also significant, as low dopamine levels can impact pleasure and motivation, contributing to the anhedonia observed in depressive disorders.

Given that the monoamine hypothesis encompasses all three of these neurotransmitters—serotonin, norepinephrine, and dopamine—indicating that imbalances in any of them can lead to depressive symptoms, the most comprehensive answer acknowledges the role of all three. Thus, the correct choice reflects the broad understanding of how these neurotransmitters interact in relation to mood disorders.