The Journal of Neuroscience, August 1, 2002, 22(15):6388-6393
Peripheral Group II Metabotropic Glutamate Receptors
(mGluR2/3) Regulate Prostaglandin E2-Mediated
Sensitization of Capsaicin Responses and Thermal Nociception
Dongni
Yang1 and
Robert
W.
Gereau IV1, 2
1 Department of Molecular Physiology and Biophysics and
2 Division of Neuroscience, Baylor College of Medicine,
Houston, Texas 77030
Previous studies have shown that group II metabotropic glutamate
receptors (mGluRs) are present on the peripheral terminals of primary
sensory neurons, suggesting that they might be involved in nociception.
In this study, we investigated the modulation of
nociception by peripheral group II mGluRs and the molecular basis of
this modulation. Subcutaneous injection of a group II mGluR agonist,
2R,4R
4-aminopyrrolidine-2,4-dicarboxylate (APDC), did not alter
thermal sensitivity but blocked prostaglandin E2 (PGE2)-induced thermal hyperalgesia. This effect was
blocked by (2s)-2-amino-2-[(1s,2s)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid, a selective group II mGluR antagonist. In cultured primary sensory neurons, APDC blocked PGE2-induced
potentiation of capsaicin responses, which was abolished when neurons
were pretreated with pertussis toxin. Similar potentiating effects induced by forskolin but not 8-bromo-cAMP were also blocked by the
activation of group II mGluRs. These results indicate that peripheral
group II mGluRs act via inhibition of adenylyl cyclase to reverse the
sensitization of capsaicin receptors and the thermal hyperalgesia
induced by PGE2, and suggest that peripheral group II mGluRs might be targeted for therapeutic intervention in
inflammatory pain states.
Key words:
capsaicin; DRG; mGluR; VR1; pain; phosphorylation; PKA; prostanoid; PGE2; inflammation; cAMP
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