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Concept
Acide kaïnique
Résumé
Kainic acid, or kainate, is an acid that naturally occurs in some seaweed. Kainic acid is a potent neuroexcitatory amino acid agonist that acts by activating receptors for glutamate, the principal excitatory neurotransmitter in the central nervous system. Glutamate is produced by the cell's metabolic processes and there are four major classifications of glutamate receptors: NMDA receptors, AMPA receptors, kainate receptors, and the metabotropic glutamate receptors. Kainic acid is an agonist for kainate receptors, a type of ionotropic glutamate receptor. Kainate receptors likely control a sodium channel that produces excitatory postsynaptic potentials (EPSPs) when glutamate binds.
Kainic acid is commonly injected into laboratory animal models to study the effects of experimental ablation. Kainic acid is a direct agonist of the glutamic kainate receptors and large doses of concentrated solutions produce immediate neuronal death by overstimulating neurons to death. Such damage and death of neurons is referred to as an excitotoxic lesion. Thus, in large, concentrated doses kainic acid can be considered a neurotoxin, and in small doses of dilute solution kainic acid will chemically stimulate neurons. In fact, kainate seems to regulate serotonergic activity in the vertebrate retina.
Electrical stimulation of designated areas of the brain are generally administered by passing an electric current through a wire that is inserted into the brain to lesion a particular area of the brain. Electrical stimulation indiscriminately destroys anything in the vicinity of the electrode tip, including neural bodies and axons of neurons passing through; therefore it is difficult to attribute the effects of the lesion to a single area. Chemical stimulation is typically administered through a cannula that is inserted into the brain via stereotactic surgery. Chemical stimulation, while more complicated than electrical stimulation, has the distinct advantage of activating cell bodies, but not nearby axons, because only cell bodies and subsequent dendrites contain glutamate receptors.
Source officielle
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