characterized by muscle rigidity, hyperthermia (fever), myoclonus (brief lightning-like
muscle twitches), and rapid changes in the patient’s mental status.
4.5.4 Serotonin Receptors: Postsynaptic Drug Effects4.5.4.1 Physiological Effects of Serotonin
The postsynaptic physiological effects of serotonin are varied and widespread. The
administration of serotonin leads to powerful smooth-muscle effects in the cardiovascu-
lar and gastrointestinal systems. Vasodilation and hypotension may result, partly
through central effects, if the serotonin concentration in the CNS is increased by admin-
istration of the serotonin precursor 5-hydroxytryptophan. Unlike serotonin, this precur-
sor can cross the blood–brain barrier. Intestinal mobility is also influenced by serotonin.
Serotonin has an effect on the hypothalamic control of pituitary function (see chapter 5),
in central thermoregulation (attributed to the 5-HT1Areceptor), and in pain perception
(probably the 5-HT 3 receptor), where increased serotonergic function potentiates opiate
analgesia. The administration of 5-HT reuptake inhibitors like fluoxetine increases the
anorectic effect of 5-hydroxytryptamine and induces a selective suppression of non-
protein caloric intake in rats. The involvement of serotonin in endogenous psychiatric
depression has been mentioned.
Another controversial but exciting area of research is the potential role of serotonin
in sleep. 5-Hydroxytryptamine may trigger slow-wave sleep (non-REM sleep), whereas
the muscarinic AChR and NE are involved in REM sleep (rapid-eye-movement sleep,
paradoxical sleep, dream sleep). In addition to the aminergic regulation of sleep, recent
research has identified several other presumed sleep factors: delta-sleep-inducing
peptide, sleep-promoting substance, interleukin-1, and muramyl peptides.
4.5.4.2 Serotonergic Agonists
The serotonergic agonists constitute a limited group of compounds, initially including
serotonin (4.109) itself, bufotenin (4.117), a natural product found in plants as well
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