5-HT2 receptor subtypes
5-HT receptors are found in the peripheral nervous system (PNS) as well as in the CNS. They are linked to phospholipase C, and thus stimulate IP3 formation, and exert an excitatory post-synaptic effect. The 5-HT2A subtype is functionally the most important and these receptors are abundant in the brain, particularly the cortex and hippocampus. The effects of 5-HT on smooth muscle and platelets are mediated by 5-HT2A. Some of the behavioural effects of agents such as lysergic acid diethylamide – acting as an agonist in the CNS and as an antagonist in the periphery – are also mediated at 5-HT2A receptors. Specific antagonists at these sites include ketanserin, cyproheptadine and methysergide, which is used primarily for migraine prophylaxis. The 5-HT2B and 5-HT2C subtypes have a much more limited distribution and functional role than the 5-HT2A receptors. The role of 5-HT2 receptors in normal physiological processes is a minor one, but becomes more prominent in pathological conditions, such as asthma and vascular thrombosis.
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References
Other peripheral mediators: 5-hydroxytryptamine and purines. In: Pharmacology, 4th edition. Rang HP, Dale MM and Ritter JM. Edinburgh, UK: Harcourt Publishers Ltd, 2001:164–176.