Neurotoxin

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Neurotoxin

A neurotoxin is a toxin

Toxin

A toxin is a poisonous substance produced by living cells or organisms. For a toxic substance not produced by living organisms, "toxicant" is the more appropriate term, and "toxics" is an acceptable plural....
that acts specifically on nerve cells (neuron

Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
s), usually by interacting with membrane protein

Membrane protein

A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. More than half of all proteins interact with membranes....
s such as ion channel

Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cell s by allowing the flow of ions down their electrochemical gradient....
s.

Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue. Bungarotoxin

Bungarotoxin

a-bungarotoxin is one of the components of the venom of the elapid snake Taiwanese banded krait . It binds irreversibly and competitively to the acetylcholine receptor found at the neuromuscular junction, causing paralysis, respiratory failure and death in the victim....
, which is considered a neurotoxin, has its effect at the motor end plate.

of the venoms and other toxins that organisms use in defense against vertebrate

Vertebrate

Vertebrates are members of the subphylum Vertebrata, chordates with Vertebras or Vertebral columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae....
s are neurotoxins.

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Encyclopedia

A neurotoxin is a toxin

Toxin

Neuron

Membrane protein

Ion channel

Bungarotoxin

Classification and examples

Venoms

Many of the venoms and other toxins that organisms use in defense against vertebrate

Vertebrate

Bee

Bees are flying insects closely related to wasps and ants. Bees are a monophyly lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila....
s, scorpion

Scorpion

Scorpions are any arachnid of the order Scorpionida. They are members of the order Scorpiones within the class Arachnida. There are about 2,000 species of scorpions, found widely distributed south of about Latitude, except New Zealand and Antarctica....
s, pufferfish

Pufferfish

Tetraodontidae is a family of primarily marine and estuarine fish. The family includes many familiar species which are variously called puffers, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish, and toadies....
, spider

Spider

Spiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. In their bodies the usual arthropod segments are fused into two Tagma , the cephalothorax and abdomen, joined by a small, cylindrical pedicel....
s and snake

Snake

Snakes are elongate legless carnivore reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears....
s can contain many different toxins.

Channel inhibitors

Many neurotoxins act by affecting voltage-dependent ion channels:

Agent	Channel >- \| tetrodotoxin Tetrodotoxin Tetrodotoxin is a potent neurotoxin with no known antidote. Tetrodotoxin blocks action potentials in nerves by binding to the pores of the voltage-gated, fast sodium channels in neuron cell membrane.... and batrachotoxin Batrachotoxin Batrachotoxins are extremely potent cardiotoxic and neurotoxic steroids alkaloids found in certain species of frogs , Melyridae beetles, and birds ....	sodium channels \|- \| maurotoxin Maurotoxin Maurotoxin is a peptide toxin from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus, from which it was first isolated and from which the chemical gets its name.... , agitoxin Agitoxin Agitoxin is a toxin found in the venom of the scorpion Deathstalker .Agitoxin binds to the shaker gene K+ channel in Drosophila as well as to its mammalian homologue.... , charybdotoxin Charybdotoxin Charybdotoxin is a 37 amino acid neurotoxin from the venom of the scorpion Deathstalker that blocks calcium-activated potassium channels. This blockade causes hyperexcitability of the nervous system.... , margatoxin Margatoxin Margatoxin is a Kv1.3 voltage-dependent potassium channel-blocking toxic peptide found in the venom of the South American scorpion Centruroides margaritatus.... , slotoxin Slotoxin Slotoxin is a peptide from Centruroides noxius Hoffmann scorpion venom. It belongs to the short scorpion toxin superfamily.... , scyllatoxin Scyllatoxin Scyllatoxin is a toxin from the scorpion Deathstalker, which blocks small-conductance Ca2+-activated K+ channels.... and hefutoxin Hefutoxin Kappa- Hefutoxin 1 and 2 are toxins from the venom of the Asian forest black scorpion with a unique structure. It blocks the potassium channels Kv1.2 and Kv1.3 and slows the activation of Kv1.3....	potassium channel Potassium channel In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms.... s \|- \| calciseptine Calciseptine colspan="2" align=center bgcolor="#cccccc" \| 'Calciseptine' \|- \|Molecular weight \|\| 7036 \|- \| colspan=2 align=center \| \|}'Calciseptine' is a natural neurotoxin isolated from the black mamba Dendroaspis p.... , taicatoxin Taicatoxin Taicatoxin is a snake toxin that blocks voltage-dependent L-type calcium channels and SK channel. The name taicatoxin is derived from its natural source, the taipan snake, the site of its action, calcium channels, and from its function as a toxin.... and calcicludine Calcicludine Calcicludine is a protein toxin from the venom of the green mamba that inhibits high-voltage-activated calcium channels, especially L-type calcium channels....	calcium channel Calcium channel A Calcium channel is an ion channel which displays selective permeabiltiy to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels.... s

A potent neurotoxin such as batrachotoxin

Batrachotoxin

Batrachotoxins are extremely potent cardiotoxic and neurotoxic steroids alkaloids found in certain species of frogs , Melyridae beetles, and birds ....
affects the nervous system by causing depolarization

Depolarization

In biology, depolarization is a decrease in the absolute value of a cell's membrane potential. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations....
of nerve and muscle fibers due to increased sodium

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
ion

Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
permeability

Permeability (fluid)

Permeability in the earth sciences is a measure of the ability of a material to transmit fluids. It is of great importance in determining the flow characteristics of hydrocarbons in Petroleum and gas reservoirs, and of groundwater in aquifers....
of the excitable cell membrane

Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
.

A very potent neurotoxin is tetrodotoxin

Tetrodotoxin

Tetrodotoxin is a potent neurotoxin with no known antidote. Tetrodotoxin blocks action potentials in nerves by binding to the pores of the voltage-gated, fast sodium channels in neuron cell membrane....
. This chemical acts to block sodium channels

Sodium channel blocker

Sodium channel blockers are agents that impair conduction through sodium channels....
in neurons, preventing action potential

Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s. This leads to paralysis and eventually death.

Botulinum neurotoxins are the most potent natural toxins known. They are produced by various toxigenic strains of Clostridium botulinum
Clostridium botulinum

Clostridium botulinum is a Gram-positive, rod shaped bacteria that produces the neurotoxin botulin, which causes the flaccid muscular paralysis seen in botulism....
and act as metalloproteinases that enter peripheral cholinergic nerve terminals and cleave proteins that are crucial components of the neuroexocytosis apparatus, causing a persistent but reversible inhibition of neurotransmitter release resulting in flaccid muscle paralysis.

Nerve agents

A number of artificial neurotoxins, known as nerve agent

Nerve agent

Nerve agents, also referred to as nerve gases though these chemicals are liquid at room temperature, are a class of phosphorus-containing organic chemistry that disrupt the mechanism by which nerves transfer messages to organs....
s, have been developed for use as chemical weapons.

Neurotoxin sources

Exogenous

Toxins ingested from the environment

Environment (biophysical)

The biophysical environment is the symbiosis between the physics environment and the biological life forms within the environment, and include all variables that comprise the Earth's biosphere....
are described as exogenous and include gas

Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
es (such as carbon monoxide

Carbon monoxide

Carbon monoxide, with the chemical formula CO, is a colorless and odorless, tasteless, yet highly toxic gas. Its molecules consist of one carbon atom covalent bond to one oxygen atom....
), metals (such as mercury

Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
), liquid

Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
s (ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
) and numerous solids. Many neurotoxins are found in plant and animal matter found in nature; for example the neurotoxin aesculin

Aesculin

Aesculin is a glucoside that naturally occurs in the Horse-chestnut , California Buckeye and in daphnin ....
is found in the horse chestnut (Aesculus hippocastanum), and the California buckeye tree. When exogenous toxins are ingested, the effect on neuron

Neuron

Endogenous

Neurotoxicity also occurs from substances produced within the body, known as endogenous neurotoxins. An example of an endogenous neurotoxin is the primary neurotransmitter

Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
glutamate, which, when levels reach too high, can result in excitotoxicity

Excitotoxicity

Excitotoxicity is the pathological process by which neuron are damaged and killed by glutamate and similar substances. This occurs when cell surface receptor for the excitatory neurotransmitter glutamic acid such as the NMDA receptor and AMPA receptor are overactivated....
and cause neuronal death by apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
.

Neurotoxin

Classification and examples

Venoms

Channel inhibitors

Nerve agents

Neurotoxin sources

Exogenous

Endogenous

See also

External links