Neurotransmitter receptor

Neurotransmitter (NT) receptors are located on the surface of neuronal and glial cells. At a synapse, one neuron sends messages to the other neuron via neurotransmitters. Therefore, the postsynaptic neuron, the one receiving the message, clusters NT receptors at this specific place in its membrane. NT receptors can be inserted into any region of the neuron's membrane such as dendrites, axons, and the cell body. Receptors can be located in different parts of the body to act as either an inhibitor or an excitatory receptor for a specific Neurotransmitter An example of this are the receptors for the neurotransmitter Acetylcholine (ACh), one receptor is located at the neuromuscular junction in skeletal muscle to facilitate muscle contraction (excitation), while the other receptor is located in the heart to slow down heart rate (inhibitory) ==Ionotropic receptors: neurotransmitter-gated ion channels==

Ligand-gated ion channels (LGICs) are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger (i.e., a ligand), such as a neurotransmitter. The binding site of endogenous ligands on LGICs protein complexes are normally located on a different portion of the protein (an allosteric binding site) compared to where the ion conduction pore is located. The direct link between ligand binding and opening or closing of the ion channel, which is characteristic of ligand-gated ion channels, is contrasted with the indirect function of metabotropic receptors, which use second messengers. LGICs are also different from voltage-gated ion channels (which open and close depending on membrane potential), and stretch-activated ion channels (which open and close depending on mechanical deformation of the cell membrane). ==Metabotropic receptors: G-protein coupled receptors==

with its agonist G protein-coupled receptors (GPCRs), also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors (GPLR), comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. G protein-coupled receptors are found only in eukaryotes, including yeast, choanoflagellates, and animals. The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein-coupled receptors are involved in many diseases, and are also the target of approximately 30% of all modern medicinal drugs. There are two principal signal transduction pathways involving the G protein-coupled receptors: the cAMP signal pathway and the phosphatidylinositol signal pathway. When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G-protein by exchanging its bound GDP for a GTP. The G-protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type (Gαs, Gαi/o, Gαq/11, Gα12/13). ==Desensitization and neurotransmitter concentration==

Neurotransmitter receptors are subject to ligand-induced desensitization: That is, they can become unresponsive upon prolonged exposure to their neurotransmitter. Neurotransmitter receptors are present on both postsynaptic neurons and presynaptic neurons with the former being used to receive neurotransmitters and the latter for the purpose of preventing further release of a given neurotransmitter. In addition to being found in neuron cells, neurotransmitter receptors are also found in various immune and muscle tissues. Many neurotransmitter receptors are categorized as a serpentine receptor or G protein-coupled receptor because they span the cell membrane not once, but seven times. Neurotransmitter receptors are known to become unresponsive to the type of neurotransmitter they receive when exposed for extended periods of time. This phenomenon is known as ligand-induced desensitization or downregulation. ==Example neurotransmitter receptors==

The following are some major classes of neurotransmitter receptors: • Adrenergic: α1A, α1b, α1c, α1d, α2a, α2b, α2c, α2d, β1, β2, β3 • Cholinergic: • Muscarinic: M1, M2, M3, M4, M5 • Nicotinic: muscle, neuronal (α-bungarotoxin-insensitive), neuronal (α-bungarotoxin-sensitive) • Dopaminergic: D1, D2, D3, D4, D5 • GABAergic: GABAA, GABAB1a, GABAB1δ, GABAB2, GABAC • Glutamatergic: NMDA, AMPA, Kainate, mGluR1, mGluR2, mGluR3, mGluR4, mGluR5, mGluR6, mGluR7 • Glycinergic: Glycine • Histaminergic: H1, H2, H3 • Opioidergic: μ, δ1, δ2, κ • Serotonergic: 5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3, 5-HT4, 5-HT5, 5-HT6, 5-HT7 ==See also==