Juan is reviewing the effects of neurotransmitter imbalances in mental health disorders. A decrease in which neurotransmitter is most commonly associated with depression?

Choice A reason: Reduced serotonin levels are strongly associated with depression, as serotonin regulates mood, sleep, and emotional stability. Many antidepressants, such as SSRIs, work by increasing serotonin availability in the brain, supporting its role in depression. Choice B reason: Histamine is primarily involved in immune responses, wakefulness, and allergic reactions, not mood regulation. It is not commonly linked to depression, making it an incorrect choice. Choice C reason: Glutamate is an excitatory neurotransmitter involved in learning and memory. While imbalances may play a role in some psychiatric conditions, it is not the primary neurotransmitter associated with depression. Choice D reason: Norepinephrine is involved in arousal and stress responses, and its dysregulation can contribute to depression. However, serotonin is more consistently and prominently linked to the pathophysiology of depression, making it the better choice.