Information about Neurotransmitter
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Chemical structure of D-aspartic acid, a common amino acid neurotransmitter.
- It is synthesized endogenously, that is, within the presynaptic neuron;
- It is available in sufficient quantity in the presynaptic neuron to exert an effect on the postsynaptic neuron;
- Externally administered, it must mimic the endogenously-released substance; and
- A biochemical mechanism for inactivation must be present.
Types of neurotransmitters
There are many different ways to classify neurotransmitters. Often, dividing them into amino acids, peptides, and monoamines is sufficient for many purposes.Some more precise divisions are as follows:
- Around 10 "small-molecule neurotransmitters" are known:
- acetylcholine
- monoamines (epinephrine E, norepinephrine NE, dopamine DA, serotonin 5-HT, and melatonin)
- 3 or 4 amino acids, depending on exact definition used: (primarily glutamic acid, GABA, aspartic acid & glycine)
- Purines, (Adenosine, ATP, GTP and their derivatives)
- Fatty acids are also receiving attention as the potential endogenous cannabinoid.
- Over 50 neuroactive peptides (vasopressin, somatostatin, neurotensin, etc.) have been found, among them hormones such as LH or insulin that have specific local actions in addition to their long-range signalling properties.
- Single ions, such as synaptically-released zinc, are also considered neurotransmitters by some.
Effects
Some examples of neurotransmitter action:- Acetylcholine - voluntary movement of the muscles
- Norepinephrine - wakefulness or arousal
- Dopamine - voluntary movement and motivation, "wanting"
- Serotonin - memory, emotions, wakefulness, sleep and temperature regulation
- GABA (gamma aminobutyric acid) - inhibition of motor neurons
- Glycine - spinal reflexes and motor behaviour
- Neuromodulators - sensory transmission-especially pain
Mechanism of action
Within the cells, small-molecule neurotransmitters are usually packaged in vesicles. When an action potential reaches the cell body, the rapid depolarization causes calcium ion (Ca2) channels to open. Calcium then stimulates the transport of vesicles to the synaptic membrane and their release at synaptic boutons - a form of exocytosis. These neurotransmitters are released in quanta, whereby a single quantum consists of a vesicle containing possibly thousands of neurotransmitters[1].The neurotransmitters then diffuse across the synaptic cleft to bind to densely and geometrically arranged receptors. The receptors are broadly classified into ionotropic and metabotropic receptors. Ionotropic receptors are ligand-gated ion channels that open or close through neurotransmitter binding. Metabotropic receptors, which can have a diverse range of effects on a cell, transduct the signal by secondary messenger systems, or G-proteins.
Neuroactive peptides are made in the neuron's soma and are transported through the axon to the synapse. They are usually packaged into dense-core vesicles and are released through a similar, but metabolically distinct, form of exocytosis used for small-molecule synaptic vesicles.
Post-synaptic effect
A neurotransmitter's effect is determined by its receptor. For example, GABA can act on both rapid or slow inhibitory receptors (the GABA-A and GABA-B receptor respectively). Many other neurotransmitters, however, may have excitatory or inhibitory actions depending on which receptor they bind to.Neurotransmitters may cause either excitatory or inhibitory post-synaptic potentials. That is, they may help the initiation of a nerve impulse in the receiving neuron, or they may discourage such an impulse by modifying the local membrane voltage potential. In the central nervous system, combined input from several synapses is usually required to trigger an action potential. Glutamate is the most prominent of excitatory transmitters; GABA and glycine are well-known inhibitory neurotransmitters.
Many neurotransmitters are removed from the synaptic cleft by neurotransmitter transporters in a process called reuptake (or often simply 'uptake'). Without reuptake, the molecules might continue to stimulate or inhibit the firing of the postsynaptic neuron. Another mechanism for removal of a neurotransmitter is digestion by an enzyme. For example, at cholinergic synapses (where acetylcholine is the neurotransmitter), the enzyme acetylcholinesterase breaks down the acetylcholine. Neuroactive peptides are often removed from the cleft by diffusion, and eventually broken down by proteases.
Specifications
While some neurotransmitters (glutamate, GABA, glycine) are used very generally throughout the central nervous system, others can have more specific effects, such as on the autonomic nervous system, by both pathways in the sympathetic nervous system and the parasympathetic nervous system, and the action of others are regulated by distinct classes of nerve clusters which can be arranged in familiar pathways around the brain. For example, Serotonin is released specifically by cells in the brainstem, in an area called the raphe nuclei, but travels around the brain along the medial forebrain bundle activating the cortex, hippocampus, thalamus, hypothalamus and cerebellum. Also, it is released in the Caudal serotonin nuclei, so as to have effect on the spinal cord. In the peripherial nervous system (such as in the gut wall) serotonin regulates vascular tone. Dopamine classically modulates two systems: the brain's reward mechanism, and movement control.Neurotransmitters that have these types of specific actions are often targeted by drugs.
- Cocaine, for example, blocks the reuptake of dopamine, leaving these neurotransmitters in the synaptic gap longer.
- Prozac is a selective serotonin reuptake inhibitor (SSRI), hence potentiating the effect of naturally released serotonin.
- AMPT prevents the conversion of tyrosine to L-DOPA, the precursor to dopamine; reserpine prevents dopamine storage within vesicles; and deprenyl inhibits monoamine oxidase (MAO)-B and thus increases dopamine levels.
Diseases may affect specific neurotransmitter pathways. For example, Parkinson's disease is at least in part related to failure of dopaminergic cells in deep-brain nuclei, for example the substantia nigra. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success.
Common neurotransmitters
See also
References
1. ^ J. Del Castillo and B. Katz, "The effect of magnesium on the activity of motor nerve endings", 124:553-559
External links
- Molecular Expressions Photo Gallery: The Neurotransmitter Collection
- Brain Neurotransmitters
- Endogenous Neuroactive Extracellular Signal Transducers
- MeSH Neurotransmitter
Cell physiology: cell signaling | |
|---|---|
| Key concepts | Ligand - Cell signaling networks - Signal transduction - Apoptosis - Second messenger system (Ca2+ signaling, Lipid signaling) |
| Processes | Paracrine - Autocrine - Juxtacrine - Neurotransmitters - Endocrine (Neuroendocrine) |
| Types of proteins | Receptor (Transmembrane, Intracellular) - Transcription factor (General, Preinitiation complex, TFIID, TFIIH) - Adaptor protein |
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions.
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synapse. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical impulses into chemical signals.]]
Chemical synapses
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Chemical synapses
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Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
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synapse. Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical impulses into chemical signals.]]
Chemical synapses
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Chemical synapses
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Biochemistry is the study of the chemical processes in living organisms.[1] The word "biochemistry" comes from the Greek word βιοχημεία biochēmeia, which means "the chemistry of life.
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Zinc (IPA: /ˈzɪŋk/, from German: Zink) is a chemical element in the periodic table that has the symbol Zn and atomic number 30.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or 'catabolic', which is the opposite.
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amino acid is a molecule that contains both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent.
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Peptides (from the Greek πεπτίδια, "small digestibles") are short polymers formed from the linking, in a defined order, of α-amino acids.
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Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group that is connected to an aromatic ring by a two-carbon chain (-CH2-CH2-).
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The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. It is a chemical transmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms including humans.
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Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group that is connected to an aromatic ring by a two-carbon chain (-CH2-CH2-).
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Epinephrine (INN) (IPA: [ˌɛpɪˈnɛfrən]) or adrenaline (European Pharmacopoeia and BAN) (IPA: [əˈdrɛnələn]
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Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. The natural stereoisomer is L -(−)-(R)-norepinephrine.
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Dopamine is a hormone and neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In chemical structure, it is a phenethylamine.
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Serotonin (pronounced IPA: /ˌsɛrəˈtoʊnən/) (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and
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Melatonin, 5-methoxy-N-acetyltryptamine, is a hormone found in all living creatures from algae[1] to humans, at levels that vary in a diurnal cycle.
Many biological effects of melatonin are produced through activation of melatonin receptors,[2]
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Many biological effects of melatonin are produced through activation of melatonin receptors,[2]
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Glutamic acid or glutamate (abbreviated as Glu or E; Glx or Z represents either glutamic acid or glutamine), is the protonated form of glutamate (the anion). Glutamate is one of the 20 proteinogenic amino acids.
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Gamma-aminobutyric acid (usually abbreviated to GABA) is an inhibitory neurotransmitter found in the nervous systems of widely divergent species. It is the chief inhibitory neurotransmitter in the central nervous system and also in the retina.
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Aspartic acid or aspartate (abbreviated as Asp or D; Asx or B represent either aspartic acid or asparagine)[1] is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CO2H.
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For the plant, see .
Glycine (abbreviated as Gly or G)[1] is the organic compound with the formula HO2CCH2NH2.
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Purine (1) is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines make up one of the two groups of nitrogenous bases. Pyrimidines make up the other group.
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Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism.
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Guanosine-5'-triphosphate (GTP) is a purine nucleotide. Its main role is as substrate for the synthesis of RNA during transcription. Its structure is similar to that of the guanine nucleotide, the only difference being that there are two extra phosphate groups added on.
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Arginine vasopressin (AVP), also known as argipressin or antidiuretic hormone (ADH), is a hormone found in most mammals, including humans. One of its most important roles is to regulate the body's retention of water, being released when the body is
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Somatostatin (also known as growth hormone inhibiting hormone (GHIH) or somatotropin release-inhibiting hormone (SRIF)) is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with
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