Antagonism of CGRP Receptor: Central and Peripheral Mechanisms and Mediators in an Animal Model of Chronic Migraine

This dataset includes the findings obtained in the study aimed at investigating in more depth the interplay between the neuropeptide CGRP and the inflammatory mediators within the mechanisms of neuronal sensitization in an animal model of chronic migraine, using olcegepant as a pharmacological probe. Male Sprague-Dawley rats were exposed to nitroglycerin (NTG, 10 mg/kg, i.p.) or NTG vehicle and treated with the CGRP receptor antagonist olcegepant (1 or 2 mg/kg, i.p.) or vehicle (1 ml/kg, i.p.) 1h before the orofacial formalin test. Additionally, sets of rats received NTG (5 mg/kg, i.p.) or vehicle (equivalent volume) co-administered with olcegepant (2 mg/kg i.p.) or its vehicle every other day over a 9-day period. Twenty-four hours after the last injection of NTG (or vehicle), a first set of rats underwent the orofacial formalin test. In a second set, we evaluated the gene expression of CGRP and gene and protein expression of pro-inflammatory cytokines in specific areas involved in migraine pain. We also assessed the CGRP and cytokine levels in serum.

The in vivo and ex vivo assessments were:

1)            Pain-related behavior in the orofacial formalin test: the face rubbing was measured counting the seconds the animal spent grooming the injected area (upper lip, lateral to the nose) with the ipsilateral forepaw or hindpaw 0–6 min (Phase I) or 12–45 min (Phase II) after formalin injection (50 µl, s.c.). The observation time was divided into 15 blocks of 3 min each.

2)            mRNA expression levels: CGRP, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), transient receptor potential ankyrin 1 (TRPA1) in cervical spinal cord (CSC), medulla-pons and trigeminal ganglia (TGs). mRNA levels were measured by rt-PCR. The same RNA was used for miRNAs (Mir-34a-5p, Mir-382-5p, Mir-155-5p) extraction in the same areas. All samples were assayed in triplicate and gene expression levels were calculated according to 2−∆∆Ct = 2− (∆Ct gene − ∆Ct housekeeping gene) formula by using Ct (cycle threshold) values.

3)            Pro-inflammatory cytokines in medulla-pons, CSC and TGs were evaluated using ELISA procedure. CGRP, TNF-alpha and IL-1beta serum levels were measured using commercial ELISA kits.

Results in brief

Olcegepant attenuated nitroglycerin-induced trigeminal hyperalgesia in the second phase of the orofacial formalin test. Interestingly, it also reduced gene expression and protein levels of CGRP, pro-inflammatory cytokines, inflammatory-associated miRNAs (miR-155-5p, miR-382-5p and miR-34a-5p) and TRPA1 channels in medulla-pons area, cervical spinal cord and trigeminal ganglia. Similarly, olcegepant reduced the NTG-induced increase of CGRP and inflammatory.