The Involvement of Excitatory Amino Acids and their Receptors in the Spinal Processing of Nociceptive Input from the Normal and Inflamed Knee Joint in the Rat
Several studies have shown that excitatory amino acids such as L-glutamate are involved in the processing of nociceptive information in the dorsal and ventral horn of the spinal cord. Since it has become clear that excitatory amino acids activate different types of receptors on postsynaptic neurons efforts are made to identify the importance of these receptor types for the different aspects of nociceptive processing, namely (1) the mediation of nociceptive information under normal conditions and (2) the development of hyperexcitability of neurons which is seen in pathophysiological states such as injury or inflammation of the tissue and nerve lesions. Briefly, glutamate receptor subtypes include the ionotropic NMDA receptor (activated by the specific agonist N-methyl-D-aspartate), the ionotropic non-NMDA receptors (activated by the agonists alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid, AMPA, and kainate), and the metabotropic receptor activated by trans-(±)-1-amino-(1S,3R)-cyclopentane dicarboxylic acid (t-ACPD). 8,16,17,29,30,43 The NMDA receptor has gained considerable interest since it is a “conditional” receptor10 that is blocked by Mg2+ ions unless the depolarization of the neuron is sufficient to remove the block.28,29,38 When opened, NMDA receptors allow the entry of Ca2+ into the neuron.4,39 It is thought that these characteristics qualify the NMDA receptor to play a key role in processes of neuronal plasticity.
KeywordsNMDA Receptor Receptive Field Dorsal Horn Excitatory Amino Acid NMDA Antagonist
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