The effects of serotonin can be divided up according to target tissues:
- blood vessels:
- the overall effect is dependent on vessel size, distribution of receptors, and modulation of noradrenergic output
- conductance vessels tend to constrict
- transfer vessels: arterioles dilate, venules constrict and capillaries become more permeable; this favours the formation of oedema in the inflammatory response
- central nervous system:
- involved in sleep induction
- involved in vascular tone: underpin agonists use in cluster headache and migraine
- involved in mood: the basis of using selective serotonin uptake inhibitors
- facilitates firing of motorneurons
- involved in ability to differentiate sensory phenomena; reduction of its effect e.g. with the antagonist LSD, contributes to hallucinogenesis
- involved in temperature regulation in the hypothalamus
- gastrointestinal tract:
- contraction due to direct stimulation of smooth muscle and indirect inhibition of noradrenergic input
- stimulus for release includes vagus nerve and physical displacement of chromaffin cells
- free nerve endings: pain, possible role in acute inflammation
Drugs which influence the serotonergic system include methysergide, sumatriptan, ketanserin, odansetron and the serotonin selective reuptake inhibitors.