Most of the serotonin in the brain is in the brainstem, specifically in the raphe nuclei; considerable amounts also are present in areas of the hypothalamus, the lim-bic system, and the pituitary gland. Current evidence indicates that serotonin is involved in the regulation of several aspects of behavior, including sleep, pain perception, depression, sexual activity, and aggressiveness. Some of the most important antidepressant agents are believed to prevent the reuptake of serotonin (see Chapter 33). Serotonin also may be involved in temperature regulation and in the hypothalamic control of the release of pituitary hormones.
In addition to its presumed role as a neurotransmit-ter within the brain, serotonin is synthesized in the pineal gland, where it is a precursor for the synthesis of melatonin, a hormone that influences endocrine activity, presumably by an action within the hypothalamus.
The mammalian brain appears to have an abundance of sites with which serotonin interacts. Fourteen
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