Current opinion in pharmacology
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Curr Opin Pharmacol · Feb 2006
ReviewGlutamate-based therapeutic approaches: NR2B receptor antagonists.
Over the past decade, there have been major advances in our understanding of the role of glutamate and N-methyl-d-aspartate (NMDA) receptors in several disorders of the central nervous system, including stroke, Parkinson's disease, Huntington's disease and chronic/neuropathic pain. In particular, NR2B subunit-containing NMDA receptors have been the focus of intense study from both a physiological and a pharmacological perspective, with several pharmaceutical companies developing NR2B subtype-selective antagonists for several glutamate-mediated diseases. ⋯ Anatomical, biochemical and pharmacological studies over the past five years have greatly added to our understanding of the role of NR2B subunit-containing NMDA receptors in chronic and neuropathic pain states, and have shown that NR2B-mediated analgesic effects might be supra- rather than intra-spinally mediated, and that phosphorylation of the NR2B subunit could be responsible for the initiation and maintenance of the central sensitization seen in neuropathic pain states. These data will hopefully provide the impetus for development of novel compounds that use multiple approaches to modulate the activity of NR2B subunit-containing NMDA receptors, thus bringing to fruition the promise of therapeutic efficacy utilizing this approach.
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Memantine is a clinically useful drug in many neurological disorders, including Alzheimer's disease. The principal mechanism of action of memantine is believed to be the blockade of current flow through channels of N-methyl-d-aspartate (NMDA) receptors--a glutamate receptor subfamily broadly involved in brain function. ⋯ These potentially important differences between memantine and ketamine include effects on gating of blocked channels and binding of memantine to two sites on NMDA receptors. Because modulation of NMDA receptor activity can increase or decrease excitability of neuronal circuits, subtle differences in the mechanisms of action of NMDA receptor antagonists can strongly impact on their clinical effects.
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Gabapentin and pregabalin are structurally related compounds with recognized efficacy in the treatment of both epilepsy and neuropathic pain. The pharmacological mechanisms by which these agents exert their clinical effects have, until recently, remained unclear. The interaction of gabapentin and pregabalin with conventional antiepileptic and analgesic drug targets is likely to be modest, at best, and has been largely dismissed in favour of a selective inhibitory effect on voltage-gated calcium channels containing the alpha2delta-1 subunit. This mechanism is consistently observed in both rodent- and human-based experimental paradigms and may be sufficiently robust to account for much of the clinical activity of these compounds.