A neurotransmitter receptor (also known as a neuroreceptor) is a membrane

receptor protein In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a recept ...

that is activated by a

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neu ...

. Chemicals on the outside of the cell, such as a neurotransmitter, can bump into the cell's membrane, in which there are receptors. If a neurotransmitter bumps into its corresponding receptor, they will bind and can trigger other events to occur inside the cell. Therefore, a membrane

receptor Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...

is part of the molecular machinery that allows cells to

communicate Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqu ...

with one another. A neurotransmitter receptor is a class of receptors that specifically binds with neurotransmitters as opposed to other molecules. In postsynaptic cells, neurotransmitter receptors receive signals that trigger an electrical signal, by regulating the activity of

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ...

s. The influx of ions through ion channels opened due to the binding of neurotransmitters to specific receptors can change the membrane potential of a neuron. This can result in a signal that runs along the axon (see

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells ...

) and is passed along at a synapse to another neuron and possibly on to a

neural network A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...

. On presynaptic cells, there can be receptor sites specific to the neurotransmitters released by that cell (see Autoreceptor), which provide feedback and mediate excessive neurotransmitter release from it. There are two major types of

receptors: ''ionotropic'' and ''metabotropic''. Ionotropic means that ions can pass through the receptor, whereas metabotropic means that a second messenger inside the cell relays the message (i.e. metabotropic receptors do not have channels). There are several kinds of metabotropic receptors, including

G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related p ...

s. Ionotropic receptors are also called

ligand-gated ion channels Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in res ...

and they can be activated by

s (

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...

s) like glutamate and GABA, which then allow specific ions through the membrane. Sodium ions (that are, for example, allowed passage by the

glutamate receptor Glutamate receptors are synaptic and non synaptic receptors located primarily on the membranes of neuronal and glial cells. Glutamate (the conjugate base of glutamic acid) is abundant in the human body, but particularly in the nervous system ...

) excite the post-synaptic cell, while chloride ions (that are, for example, allowed passage by the GABA receptor) inhibit the post-synaptic cell. Inhibition reduces the chance that an

will occur, while excitation increases the chance. Conversely, G-protein-coupled receptors are neither excitatory nor inhibitory. Rather, they can have a broad number of functions such as modulating the actions of excitatory and inhibitory ion channels or triggering a signalling cascade that releases calcium from stores inside the cell. Most neurotransmitters receptors are G-protein coupled.

Localization

Neurotransmitter (NT) receptors are located on the surface of

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...

al and glial

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

. 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 Goldman, B. (2010, November 17). New imaging method developed at Stanford reveals stunning details of brain connections. In Stanford medicine news center. Retrieved from https://med.stanford.edu/news/all-news/2010/11/new-imaging-method-developed-at-stanford-reveals-stunning-details-of-brain-connections.html. 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 Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in res ...

(LGICs) are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane

s that are opened or closed in response to the binding of a chemical messenger (i.e., a

), such as a

. The binding site of

endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, ...

ligands on LGICs protein complexes are normally located on a different portion of the protein (an

allosteric In biochemistry, allosteric regulation (or allosteric control) is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme's active site. The site to which the effector binds is termed the ''allosteric sit ...

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 messenger Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intercellular signals, a non-local form or cell signaling, encompassing both first m ...

s. LGICs are also different from voltage-gated ion channels (which open and close depending on

membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...

), and stretch-activated ion channels (which open and close depending on mechanical deformation of the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

Metabotropic receptors: G-protein coupled receptors

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 Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

family of transmembrane receptors that sense

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...

s outside the cell and activate inside

signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...

pathways and, ultimately, cellular responses. G protein-coupled receptors are found only in

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

s, including yeast,

choanoflagellate The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates, having a funnel shaped collar of interconne ...

s, and animals. The

ligands In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

that bind and activate these receptors include light-sensitive compounds,

odor An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...

s, pheromones,

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s, and

s, and vary in size from small molecules to

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

s to large

s. 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 Camp may refer to: Outdoor accommodation and recreation * Campsite or campground, a recreational outdoor sleeping and eating site * a temporary settlement for nomads * Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...

signal pathway and the

phosphatidylinositol Phosphatidylinositol (or Inositol Phospholipid) consists of a family of lipids as illustrated on the right, where red is x, blue is y, and black is z, in the context of independent variation, a class of the phosphatidylglycerides. In such molecul ...

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 ( G_αs, G_αi/o, G_αq/11, G_α12/13).

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

s 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

because they span the cell membrane not once, but seven times. Neurotransmitter receptors are known to become unresponsive to the type of

they receive when exposed for extended periods of time. This phenomenon is known as ligand-induced desensitization or

downregulation In the biological context of organisms' production of gene products, downregulation is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external stimulus. The complementary pr ...

Example neurotransmitter receptors

The following are some major classes of neurotransmitter receptors:ed. Kebabain, J. W. & Neumeyer, J. L. (1994). "RBI Handbook of Receptor Classification" * Adrenergic: α_1A, α_1b, α_1c, α_1d, α_2a, α_2b, α_2c, α_2d, β₁, β₂, β₃ * Cholinergic: ** Muscarinic: M1, M2, M3, M4, M5 ** Nicotinic: muscle, neuronal (α-bungarotoxin-insensitive), neuronal (α-bungarotoxin-sensitive) *

Dopaminergic Dopaminergic means "related to dopamine" (literally, "working on dopamine"), dopamine being a common neurotransmitter. Dopaminergic substances or actions increase dopamine-related activity in the brain. Dopaminergic brain pathways facilitate do ...

: D₁, D₂, D₃, D₄, D₅ *

GABAergic In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter GABA. For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A ...

: GABA_A, GABA_B1a, GABA_B1δ, GABA_B2, GABA_C * Glutamatergic: NMDA, AMPA, Kainate, mGluR₁, mGluR₂, mGluR₃, mGluR₄, mGluR₅, mGluR₆, mGluR₇ * Glycinergic: Glycine * Histaminergic: H₁, H₂, H₃ * Opioidergic: μ, δ₁, δ₂, κ * Serotonergic: 5-HT_1A, 5-HT_1B, 5-HT_1D, 5-HT_1E, 5-HT_1F, 5-HT_2A, 5-HT_2B, 5-HT_2C, 5-HT₃, 5-HT₄, 5-HT₅, 5-HT₆, 5-HT₇

Notes and references

External links

Brain Explorer

Snyder (2009) Neurotransmitters, Receptors, and Second Messengers Galore in 40 Years. Journal of Neuroscience. 29(41): 12717-12721.Snyder and Bennett (1976) Neurotransmitter Receptors in the Brain: Biochemical Identification. Annual Review of Physiology. Vol. 38: 153-175Library of Congress Authorities and Vocabularies: Neurotransmitter ReceptorsNeurotransmitter Receptors, Transporters, & Ion Channels
* {{DEFAULTSORT:Neurotransmitter Receptor Receptors Behavioural genetics he:קולטן#הקולטן העצבי