The function of serotonin is exerted upon its interaction with specific receptors. Within the 5HT 1 group there are subtypes 5HT 1A , 5HT 1B , 5HT 1D , 5HT 1E , and 5HT 1F . There are three 5HT 2 subtypes, 5HT 2A , 5HT 2B , and 5HT 2C as well as two 5HT 5 subtypes, 5HT 5a and 5HT 5B . Most of these receptors are coupled to G-proteins that affect the activities of either adenylate cyclase or phospholipase C g . The 5HT 3 class of receptors are ion channels.
Some serotonin receptors are presynaptic and others postsynaptic.
The 5HT 2A receptors mediate platelet aggregation and smooth muscle contraction. The 5HT 2C receptors are suspected in control of food intake as mice lacking this gene become obese fromincreased food intake and are also subject to fatal seizures. The 5HT 3 receptors are present in the gastrointestinal tract and are related to vomiting. Also present in the gastrointestinal tract are 5HT 4 receptors where they function in secretion and peristalsis. The 5HT 6 and 5HT 7 receptors are distributed throughout the limbic system of the brain and the 5HT 6 receptors have high affinity for antidepressant drugs.