The function of serotonin is exerted upon its interaction with specific receptors. Several serotonin receptors have been cloned and are identified as 5HT 1 , 5HT 2 , 5HT 3 , 5HT 4 , 5HT 5 , 5HT 6 , and 5HT 7 . 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 Cβ (PLCβ). The 5HT 3 class of receptors are ion channels, referred to as ionotropic receptors.