Calcitonin gene-related peptide receptor blockade by olcegepant reduced mechanical allodynia induced by infraorbital nerve ligation but not that caused by sciatic nerve ligation in rats.
Previous studies showed that 5-hydroxytryptamine (5-HT)1B/1D receptor stimulation by triptans alleviates neuropathic pain caused by chronic constriction injury to the infraorbital nerve (CCI-ION) but not the sciatic nerve (CCI-SN) in rats. To assess whether such differential effects in the cephalic vs extracephalic territories is a property shared by other antimigraine drugs, we used the same models to investigate the effects of olcegepant, which has an antimigraine action mediated through calcitonin gene-related peptide (CGRP) receptor blockade. Adult male rats underwent unilateral CCI to the ION or the SN, and subsequent allodynia and/or hyperalgesia were assessed in ipsilateral vibrissal territory or hindpaw, respectively, using von Frey filaments and validated nociceptive tests. c-Fos expression was quantified by immunohistochemistry and interleukin 6 and activating transcription factor 3 (ATF3) mRNAs by real-time quantitative reverse transcriptase-polymerase chain reaction. Like naratriptan (0.1 to 0.3 mg/kg, subcutaneously), olcegepant (0.3 to 0.9 mg/kg, intravenously) markedly reduced mechanical allodynia in CCI-ION rats. In contrast, in CCI-SN rats, mechanical allodynia was completely unaffected and hyperalgesia was only marginally reduced by these drugs. A supra-additive antiallodynic effect was observed in CCI-ION rats treated with olcegepant (0.3 mg/kg intravenously) plus naratriptan (0.1 mg/kg subcutaneously), whereas this drug combination remained inactive in CCI-SN rats. Olcegepant (0.6 mg/kg, intravenously) significantly reduced the number of c-Fos immunolabeled cells in spinal nucleus of the trigeminal nerve and upregulation of ATF3 transcript (a marker of neuron injury) but not that of interleukin-6 in trigeminal ganglion of CCI-ION rats. These findings suggest that CGRP receptor blockade might be of potential interest to alleviate trigeminal neuropathic pain.
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INSERM, UMR_S894, CPN, Neuropsychopharmacologie, Paris, France
UPMC University Paris 06, Faculté de Médecine Pierre et Marie Curie, Site Pitié-Salpêtrière, UMR_S894, 91, boulevard de l’Hôpital, Paris, France
Université Paris Descartes, Centre de Psychiatrie et Neurosciences, 91 Boulevard de l’Hôpital, Paris, France
*Corresponding author at: UMR_S894 INSERM-UPMC, CPN, Faculté de Médecine Pierre et Marie Curie, Site Pitié-Salpêtrière, 91, boulevard de l’Hôpital, 75634 Paris Cedex 13, France. Tel.: +33 1 4077 9709; fax: +33 1 4077 9790.
Article history: Received 2 January 2012; Received in revised form 22 May 2012; Accepted 11 June 2012.