Glutamate receptor

Jun 3, 2010 8:10 PM  from Wiki on Glutamate as a Neurotransmitter.

Glutamate is the most abundant excitatory neurotransmitter in the vertebrate nervous system. At chemical synapses, glutamate is stored in vesicles. Nerve impulses trigger release of glutamate from the pre-synaptic cell. In the opposing post-synaptic cell, glutamate receptors, such as the NMDA receptor, bind glutamate and are activated. Because of its role in synaptic plasticity, glutamate is involved in cognitive functions like learning and memory in the brain[3]. The form of plasticity known as long-term potentiation takes place at glutamatergic synapses in the hippocampus, neocortex, and other parts of the brain

Wiki article on glutamate recpetor

The two primary glutamate receptors are named after agonists that bind to them with high specificity: AMPA (α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate) and NMDA (N-Methyl-D-Aspartate).[1]

Ionotropic receptors form an ion channel pore that activates when glutamate is bound.

Metabotropic glut receptors work indirectly thru G protein signaling.  Ionotropics are faster.

ionotropic receptors:  NMDA,  Kainate receptor,  AMPA.

All ionotropic glutamate receptors are ligand-gated nonselective cation channels which allow the flow of K+, Na+ and sometimes Ca2+ in response to glutamate binding. Upon binding, the agonist will stimulate direct action of the central pore of the receptor, an ion channel, allowing ion flow and causing EPSC (excitatory post-synaptic current). This current is depolarizing and, if enough glutamate receptors are activated, may trigger an action potential in the post-synaptic neuron. All produce excitatory post-synaptic current, but the speed and duration of the current is different for each type. NMDA receptors have an internal binding site for an Mg2+ ion

below  is from the Ben Best article below node.

Glutamate is the most common neurotransmitter in the brain. It is always excitatory

Possibly the most complicated of all neurotransmitter receptors is the NMDA glutamate receptor. N-Methyl-D-Aspartate is a synthetic chemical not naturally found in biological systems, but it binds specifically to the NMDA glutamate receptor (receptors are frequently named for artificial substances that bind to the receptor with higher specificity than their natural neurotransmitter ligands). The NMDA receptor is the only known receptor which is regulated both by a ligand (glutamate) and by voltage.

There are at least 5 binding sites which regulate NMDA receptor activity, ie, sites for (1) glutamate (2) glycine (3) magnesium (4) zinc and (5) a site that binds the hallucinogenic substance phencyclidine (PCP, "angel dust"). Phencyclidine can induce psychosis — an NMDA effect that is difficult to explain. NMDA receptors have a capacity for an activity-dependent increase in synaptic efficiency known as LTP (Long-Term Potentiation), which may be crucial to some forms of learning and memory.

NMDA receptors are most densely concentrated in the cerebral cortex (hippocampus, especially — particularly the CA1 region), amygdala, & basal ganglia. They are particularly vulnerable to glutamic acid excitotoxicity, ie, damaging effects due to excessive excitatory neurotransmitter release. Both aspartic acid & glutamic acid (the two amino acids having 2 carboxyl groups — the "acidic amino acids") have the capacity for destroying neurons when released in excessive amounts (although calcium seems to be more of a cause than acidity). Monosodium glutamate (MSG), a major component of soya sauce, has been shown to destroy nerve cells when fed to young animals. Insofar as glutamate does not normally cross the blood-brain barrier, it is open to question whether this is relevant to a human adult.

Glutamate receptor

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