Etiology of Mood Disorders: Biological and Biogenic Amine Factors

There are several etiologies of mood disorders, one of them is biological and biogenic amines factors. We will follow explanation factors of biological and biogenic amines as etiologies of mood disorders below.


Biological Factors
Many studies have reported biological abnormalities in patients with mood disorders. Until recently, the monoamine neurotransmitters norepinephrine, dopamine, serotonin, and histamine were the main focus of theories and research about the etiology of mood disorders. A progressive shift has occurred from focusing on disturbances of single neurotransmitter systems in favor of studying neurobehavioral systems, neural circuits, and more intricate neuroregulatory mechanisms. The monoaminergic systems, thus, are now viewed as broader, neuromodulary systems, and disturbances are as likely to be secondary or epiphenomenal effects as they are directly or causally related to etiology of mood disorders and pathogenesis of mood disorders.

Biogenic Amines
Of the biogenic amines, norepinephrine and serotonin are the two neurotransmitters most implicated in the pathophysiology of mood disorders. This factor thought to be etiology of mood disorders.

Norepinephrine

The correlation suggested by basic science studies between the down regulation or decreased sensitivity of β-adrenergic receptors and clinical antidepressant responses is probably the single most compelling piece of data indicating a direct role for the noradrenergic system in depression. Other evidence has also implicated the presynaptic β₂-receptors in depression, because activation of these receptors results in a decrease of the amount of norepinephrine released. Presynaptic β₂-receptors are also located on serotonergic neurons and regulate the amount of serotonin released. The clinical effectiveness of antidepressant drugs with noradrenergic effects for example, venlafaxine (Effexor) further supports a role for norepinephrine in the pathophysiology of at least some of the symptoms of depression.

Serotonin

With the huge effect that the selective serotonin reuptake inhibitors (SSRIs) for example, fluoxetine (Prozac) have made on the treatment of depression, serotonin has become the biogenic amine neurotransmitter most commonly associated with depression. The identification of multiple serotonin receptor subtypes has also increased the excitement within the research community about the development of even more specific treatments for depression. Besides that SSRIs and other serotonergic antidepressants are effective in the treatment of depression, other data indicate that serotonin is involved in the pathophysiology of depression. Depletion of serotonin may precipitate depression, and some patients with suicidal impulses have low cerebrospinal fluid (CSF) concentrations of serotonin metabolites and low concentrations of serotonin uptake sites on platelets.