Effect of a metabotropic glutamate receptor 5 antagonist, MPEP, on the nociceptive response induced by intrathecal injection of excitatory aminoacids, substance P, bradykinin or cytokines in mice

Metabotropic glutamate receptors (mGluRs) are expressed abundantly in the spinal cord and have been shown to play important roles in the modulation of nociceptive transmission and plasticity. In this study, the involvement of metabotropic glutamate receptor 5 (mGluR5) in the nociceptive response induced by intrathecal injection (i.t.) of excitatory aminoacids, substance P (SP), bradykinin (BK) and cytokines in mice was demonstrated. The administration of 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 10–50 nmol/site, i.t.) caused a significant inhibition in the nociceptive response induced by glutamate and trans-ACPD with maximal inhibitory effects of 36 ± 7% and 56 ± 5%, respectively. MPEP completely failed to affect the nociception induced by α-amino-3-hydroxy-5-mehtyl-4-isoxazolepropionic acid (AMPA; 135 pmol/site), kainate (110 pmol/site) and N-methyl-d-aspartate (NMDA; 450 pmol/site). MPEP also reduced the nociceptive response induced by SP (135 ng/site, i.t.), BK (0.1 µg/site), tumor necrosis factor-alpha (TNF-α; 0.1 pg/site) and interleukin-1beta (IL-1β; 1 pg/site) with maximal inhibitions of 29 ± 5%, 37 ± 5%, 83 ± 3% and 88 ± 1%, respectively. Together, these results indicate the involvement of mGluRs, more specifically of subtype-5, in the nociceptive response induced by i.t. injection of excitatory aminoacids, SP, BK and cytokines in mice.