Telling Tails

Abstract

The N-methyl-D-aspartate (NMDA)-type glutamate receptor is one of three major classes of receptors for glutamate, the principle excitatory neurotransmitter in the central nervous system. It plays a key role in learning and in the formation of memories by acting as a "coincidence detector" that initiates changes in synaptic strength that lead to the formation of new neural networks (1). It is also an important mediator of several forms of pathological neuronal toxicity. The NMDA receptor responds at a synapse only when the presynaptic terminal releases glutamate at the same time that the postsynaptic neuron is strongly depolarized by the sum of activating influences impinging on it. In effect, it initiates the strengthening of all synapses that depolarize the same postsynaptic neuron at the same time and thus triggers formation of a new, more stable circuit. When the NMDA-receptor channel opens, it allows passage of calcium ions, as well as sodium and potassium, into the cell. The calcium ions trigger a cascade of biochemical signaling reactions catalyzed by enzymes located just underneath the postsynaptic membrane. These reactions modify other membrane channels in the synapse, ultimately leading to a change in the strength of the electrical signal produced when the synapse is activated again.

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Copyright © 2001 by the National Academy of Sciences Commentary

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