Table 1.

Nomenclature Used to Identify Various Populations and Subpopulations of Serotonin Receptors (5-HT Receptor Sub-types) [2, 5, 7]

Receptor	Structural Family	Signal Transduction	Localization	Function	Comments
5-HT1A	GPCR	Inhibition of AC	Hippocampus, Septum, Amygdala, Cortical limbic areas, Raphe nuclei	Autoreceptor	Cloned and pharmacological 5-HT1A sites.
5-HT1B	GPCR	Inhibition of AC	Basal and Trigeminal ganglia, Striatum, Frontal cortex Cerebral arteries and other vascular tissues	Autoreceptor	Rodent homologue of human 5-HT1Dβ receptors.
5-HT1D	GPCR	Inhibition of AC	Basal and Trigeminal ganglia	Unknown	Newer name: 5-HT1Bβ; a mouse homologue of human 5-HT1Dβ receptors; sites identified in binding studies using brains homogenates; 5-HT1Dα and 5-HT1Dβ (cloned human 5-HT1D subpopulations).
			Cranial blood vessels	Vasoconstriction
5-ht1E	GPCR	Inhibition of AC	Cerebral cortex, Striatum	Unknown	Newer name: 5-ht1Eβ; sites identified in binding studies using brain homogenates; 5-ht1Ea (an alternate name for cloned human 5-ht1E receptors).
5-ht1F	GPCR	Inhibition of AC	Dorsal raphe, Hippocampus, Striatum, Cerebral cortex, Thalamus, Hypothalamus	Unknown	A cloned human 5-HT1-like receptor population.
			Uterus, Mesentery	Vasoconstriction
5-HT2A (D receptor)	GPCR	Activation of PLC	Cerebral cortex, Claustrum, Basal ganglia	Neuronal excitation	Newer name: 5-HT2A; original "5-HT2" (5-HT2α) receptors
			Smooth muscle	Contraction
			Platelets	Platelet aggregation
5-HT2B	GPCR	Activation of PLC (Other unknown)	Cerebellum, Lateral septum, Hypothalamus, Medial amygdala	Unknown	Newer name: 5-HT2B; 5-HT2-like receptors in rat fundus
			Stomach fundus	Contraction
			Blood vessels	Vasodilatation
5-HT2C	GPCR	Activation of PLC	Choroid plexus	Vasodilatation	Newer name: 5-HT2C; original "5-HT1C" (5-HT2β) receptors.
5-HT3 (M receptor)	5-HT-GIC	Ligand-gated ion channel	Area postrema, Enthorinal and Frontal cortex, Hippocampus, Solitary Tract, Amygdala Peripheral pre- and post-ganglionic autonomic neurons, Sensory nervous system, Gastrointestinal tract	Neuronal excitation	An ion channel receptor.
5-HT4	GPCR	Activation of AC	Hippocampus, Colliculi, Nucleus accumbens Gastrointestinal tract, Vascular smooth muscle	Neuronal excitation	5-HT4 population originally described in functional studies; 5-HT4s (short form of cloned rat 5-HT4 receptors); 5-HT4L (long form of cloned rat 5-HT4 receptors).
5-ht5A	GPCR	Inhibition of AC	Hypothalamus, Hippocampus, Corpus callosum, Fimbria, Cerebral ventricles, Glia	Unknown	Cloned mouse, rat and human 5-ht5 or 5-ht5A-like receptors.
5-ht5B	Unknown	Unknown
5-ht6	GPCR	Activation of AC	Caudate nucleus, Striatum, Amygdala, Nucleus accumbens, Hippocampus, Cerebral cortex and Olfactory tubercle	Unknown	Cloned rat and human 5-HT receptors.
5-HT7	GPCR	Activation of AC	Cerebral cortex, Thalamic nuclei, Sensory nuclei, Substantia nigra, Hypothalamus, Raphe nuclei Vascular tissues, Smooth muscle (ileum)	Unknown	Cloned rat, mouse, guinea pig and human 5-HT receptors; original "5-HT1-like" receptors.

Legend: GPCR, G protein-coupled Receptor; 5-HT-GIC, 5-HT-gated ion channel; AC, adenylate cyclase; PLC, phospholipase C.