Nitric oxide synthase, calcitonin gene-related peptide and NK-1 receptor mechanisms are involved in GTN-induced neuronal activation.

ABSTRACT

BACKGROUND AND AIM: Infusion of glyceryltrinitrate (GTN), a nitric oxide (NO) donor, in awake, freely moving rats closely mimics a universally accepted human model of migraine and responds to sumatriptan treatment. Here we analyse the effect of nitric oxide synthase (NOS) and calcitonin gene-related peptide (CGRP) systems on the GTN-induced neuronal activation in this model. MATERIALS AND METHODS: The femoral vein was catheterised in rats and GTN was infused (4 µg/kg/min, for 20 minutes, intravenously). Immunohistochemistry was performed to analyse Fos, nNOS and CGRP and Western blot for measuring nNOS protein expression. The effect of olcegepant, L-nitro-arginine methyl ester (L-NAME) and neurokinin (NK)-1 receptor antagonist L-733060 were analysed on Fos activation. RESULTS: GTN-treated rats showed a significant increase of nNOS and CGRP in dura mater and CGRP in the trigeminal nucleus caudalis (TNC). Upregulation of Fos was observed in TNC four hours after the infusion. This activation was inhibited by pre-treatment with olcegepant. Pre-treatment with L-NAME and L-733060 also significantly inhibited GTN induced Fos expression. CONCLUSION: The present study indicates that blockers of CGRP, NOS and NK-1 receptors all inhibit GTN induced Fos activation. These findings also predict that pre-treatment with olcegepant may be a better option than post-treatment to study its inhibitory effect in GTN migraine models.