The term mood refers to a pervasive and sustained inner emotion that affects the person's perception of the world. In addition to being part of the conscious experience of the person, it can be observed by others. In healthy people, moods can be normal, elated, or depressed, and people generally feel that they have some degree of control of their moods. That sense of control is lost, however, in the mood disorders, which include depressive disorders and bipolar disorders. Along with schizophrenia, the mood disorders form the major psychiatric illnesses today.
In the depressive disorders (depression), the prominent features are a pervasive sadness; a loss of energy, interest, or pleasure; anxiety; irritability; disturbed sleep; and thoughts of death or suicide. Depression can occur on its own, independent of any other illness, or it can arise secondary to other medical disorders. It is associated with decreased neuronal activity and metabolism in the anterior part of the limbic system and nearby prefrontal cortex. These same brain regions show abnormalities, albeit inconsistent ones, in bipolar disorders.
The term bipolar disorders describes swings between mania and depression episodes of mania, which are characterized by an abnormally and persistently elated mood, sometimes with euphoria (that is, an exaggerated sense of well-being), racing thoughts, excessive energy, overconfidence, and irritability.
Current treatment of the mood disorders emphasizes drugs and psychotherapy. The classical antide-pressant drugs are of three types. The tricyclic antidepressant drugs such as Elavil, Desyrel, and Pamelor, interfere with serotonin and/or norepinephrine reuptake by presynaptic endings. The monoamine oxidase inhibitors interfere with the enzyme responsible for the breakdown of these same two neurotransmitters. A third class of antidepressant drugs, the serotonin-specific reuptake inhibitors (SSRIs), are the most widely used antidepressant drugs and include Prozac, Paxil, and Zoloft. As their name—SSRI—suggests, these drugs selectively inhibit serotonin reuptake by presynaptic terminals. In all three classes, the result is an increased concentration of serotonin and (except for the third class) norepinephrine in the extracellular fluid at synapses. Since the biochemical effects occur immediately but the beneficial antidepressant effects appear only after several weeks of treatment, the known biochemical effect must be only an early step in a complex, and presently unknown, sequence that leads to a therapeutic effect of these drugs.
Psychotherapy of various kinds can also be helpful in the treatment of depression. An alternative to drug therapy and psychotherapy is electroconvulsive therapy (ECT). As the name suggests, pulses of electric current are used to activate a large number of neurons in the brain simultaneously, thereby inducing a convulsion, or seizure. The patient is under anesthesia and prepared with a muscle relaxant to minimize the effects of the convulsion on the musculoskeletal system. A series of ECT treatments alters neurotrans-mitter function by causing a down-regulation of certain postsynaptic receptors. Another non-drug therapy used for the type of depression known as seasonal affective disorder (SAD) is phototherapy in which the patient is exposed to bright light for several hours per day.
A major drug used in treating patients with bipolar disorder is the chemical element, lithium, sometimes given in combination with anticonvulsant drugs. It is highly specific, normalizing both the manic and depressing moods and slowing down thinking and motor behavior without causing sedation. In addition, it decreases the severity of the swings between mania and depression that occur in the bipolar disorders. In some cases, lithium is even effective in depression not associated with manias. Lithium may interfere with the formation of members of the inositol phosphate family, thereby decreasing the postsynaptic neurons' response to neurotransmitters that utilize this signal transduction pathway (Chapter 7).
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