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Department of Clinical Neurosciences, Institute of Psychiatry, London, SE5 8AF, UK
Glutamate is the principal excitatory neurotransmitter in brain. Our
knowledge of the glutamatergic synapse has advanced enormously in the
last 10 years, primarily through application of molecular biological
techniques to the study of glutamate receptors and transporters. There
are three families of ionotropic receptors with
intrinsic cation permeable channels
[N-methyl-D-aspartate (NMDA),
-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and
kainate]. There are three groups of metabotropic, G
proteincoupled glutamate receptors (mGluR) that modify neuronal and
glial excitability through G protein subunits acting on membrane ion
channels and second messengers such as diacylglycerol and cAMP. There
are also two glial glutamate transporters and three neuronal
transporters in the brain. Glutamate is the most abundant amino acid in
the diet. There is no evidence for brain damage in humans resulting
from dietary glutamate. A kainate analog, domoate, is sometimes
ingested accidentally in blue mussels; this potent toxin causes limbic
seizures, which can lead to hippocampal and related pathology and
amnesia. Endogenous glutamate, by activating NMDA, AMPA or mGluR1
receptors, may contribute to the brain damage occurring acutely after
status epilepticus, cerebral ischemia or traumatic brain injury. It may
also contribute to chronic neurodegeneration in such disorders as
amyotrophic lateral sclerosis and Huntingtons chorea. In animal
models of cerebral ischemia and traumatic brain injury, NMDA and AMPA
receptor antagonists protect against acute brain damage and delayed
behavioral deficits. Such compounds are undergoing testing in humans,
but therapeutic efficacy has yet to be established. Other clinical
conditions that may respond to drugs acting on glutamatergic
transmission include epilepsy, amnesia, anxiety, hyperalgesia and
psychosis.
KEY WORDS: glutamate excitotoxicity domoate neuroprotection cerebral ischemia
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