Mood Disorders

• Description of mood disorders
• The bipolar spectrum
• Can unipolar depression be distinguished from bipolar depression?
• Are mood disorders progressive?
• Neurotransmitters and circuits in mood disorders
• Noradrenergic neurons
• Monoamine interactions: NE regulation of 5HT release
• Monoamine interactions: 5HT regulation of NE and DA release
• The monoamine hypothesis of depression
• The monoamine hypothesis, monoamine receptors, and gene expression
• Symptoms and circuits in depression
• Symptoms and circuits in mania
• Genes and neuroimaging in mood disorders
• Summary

Mood Disorders

This chapter discusses disorders characterized by abnormalities of mood: namely, depression, mania, or both. Included are descriptions of a wide variety of mood disorders that occur over a broad clinical spectrum. Also included is an analysis of how abnormalities in regulation of the trimonoaminergic neurotransmitter system – comprising the three monoamine neurotransmitters norepinephrine (NE; also called noradrenaline, or NA), dopamine (DA), and serotonin (also called 5-hydroxytryptamine, or 5HT) – are hypothesized to explain the biological basis of mood disorders. The approach taken here is to deconstruct each mood disorder into its component symptoms, followed by matching each symptom to hypothetically malfunctioning brain circuits, each regulated by one or more of the neurotransmitters within the trimonoaminergic neurotransmitter system. The genetic regulation and neuroimaging of these hypothetically malfunctioning brain circuits are also briefly mentioned. The discussion of symptoms and circuits in this chapter is intended to set the stage for understanding the pharmacological concepts underlying the mechanisms of action and use of antidepressants and mood-stabilizing drugs reviewed in the following two chapters (Chapters 12 and 13).

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FIGURE 11-1 Mood chart. Disorders of mood can be mapped on a mood chart to track the course of illness, identify phase of illness, and aid in differential diagnosis. As shown in this chart, mood can range from mania at the top, to hypomania, to euthymia (normal mood) in the middle, and to dysthymia and depression at the bottom.

Clinical descriptions and criteria for the diagnosis of disorders of mood are mentioned only in passing. The reader should consult standard reference sources for this material. Here we discuss how the discovery of various neurotransmitters and brain circuits has influenced the understanding of symptoms in mood disorders. The goal of this chapter is to outline current ideas about the clinical and biological aspects of mood disorders in order to prepare the reader to understand the various treatments for these disorders discussed in later chapters.