Neurotoxin
A
neurotoxin is a
toxin that acts specifically on nerve cells –
neurons – usually by interacting with
membrane proteins and
ion channels. Many of the
venoms and other toxins that organisms use in defense against
vertebrates are neurotoxins. A common effect is paralysis, which sets in extremely rapidly. Examples of neurotoxins include
tetrodotoxin,
batrachotoxin and components of the venom in
bees,
scorpions,
spiders and
snakes.
Toxins ingested from
the environment are described as
exogenous and include
gases (eg
carbon monoxide), metals (such as
mercury),
liquids (
ethanol) and an endless list of
solids.When exogenous toxins are ingested, the effect on neurons is largely dependent on dosage. Thus
ethanol (alcohol) is inebriating in low doses, only producing mild neurotoxicity. Prolonged exposure to "safe" alcohol levels slowly weakens and kills neurons.
Neurotoxicity also occurs from substances produced within the body -
endogenous neurotoxins. A prime example of a neurotoxin in the brain is
glutamate, which is paradoxically also a primary
neurotransmitter. When the glutamate concentration around a neuron reaches a critical point the neuron kills itself by a process called
apoptosis. This whole process is called
excitotoxicity, so named because glutamate normally acts as an excitatory neurotransmitter at lower levels.
A potent neurotoxin such as
batrachotoxin affects the nervous system by causing
depolarization of nerve and muscle fibres due to increased
sodium ion permeability of the excitable
cell membrane.
*
neurotoxic*
teratogenesis, many birth defects are essentially caused by neurotoxicity in developing neurons
