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Bidirectional modulation of windup by NMDA receptors in the rat spinal trigeminal nucleus
Author(s) -
Woda Alain,
Blanc Olivier,
Voisin Daniel L.,
Coste Jérôme,
Molat JeanLouis,
Luccarini Philippe
Publication year - 2004
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.0953-816x.2004.03328.x
Subject(s) - nmda receptor , nociception , neuroscience , glutamate receptor , chemistry , nociceptor , long term depression , receptor , ampa receptor , biology , biochemistry
Activation of afferent nociceptive pathways is subject to activity‐dependent plasticity, which may manifest as windup, a progressive increase in the response of dorsal horn nociceptive neurons to repeated stimuli. At the cellular level, N ‐methyl‐ d ‐aspartate (NMDA) receptor activation by glutamate released from nociceptive C‐afferent terminals is currently thought to generate windup. Most of the wide dynamic range nociceptive neurons that display windup, however, do not receive direct C‐fibre input. It is thus unknown where the NMDA mechanisms for windup operate. Here, using the Sprague–Dawley rat trigeminal system as a model, we anatomically identify a subpopulation of interneurons that relay nociceptive information from the superficial dorsal horn where C‐fibres terminate, to downstream wide dynamic range nociceptive neurons. Using in vivo electrophysiological recordings, we show that at the end of this pathway, windup was reduced (24 ± 6%, n = 7) by the NMDA receptor antagonist AP‐5 (2.0 fmol) and enhanced (62 ± 19%, n = 12) by NMDA (1 nmol). In contrast, microinjections of AP‐5 (1.0 fmol) within the superficial laminae increased windup (83 ± 44%, n = 9), whereas NMDA dose dependently decreased windup ( n = 19).These results indicate that NMDA receptor function at the segmental level depends on their precise location in nociceptive neural networks. While some NMDA receptors actually amplify pain information, the new evidence for NMDA dependent inhibition of windup we show here indicates that, simultaneously, others act in the opposite direction. Working together, the two mechanisms may provide a fine tuning of gain in pain.