We investigated the possible involvement of prejunctional iGluR5 kainate receptors on CGRP release from trigeminal afferents. Experimental approach: We used neurogenic dural vasodilatation, which involves reproducible vasodilatation in response to CGRP release after electrical stimulation of the dura mater surrounding the middle meningeal artery. meningeal artery. The effects of the specific Ononin iGluR5 receptor antagonist UBP 302 and agonist (S)-(-)-5-iodowillardiine were investigated on neurogenic and CGRP-induced dural vasodilatation in rats, by using intravital microscopy. Key results: Administration of 10 and 20 mgkg?1 of iodowillardiine inhibited electrically induced dural vessel dilatation, an effect blocked by pretreatment with 50 mgkg?1 UBP 302. Administration of the iGluR5 receptor antagonist UBP 302 alone had no significant NIK effect. CGRP (1 mgkg?1)-induced dural vasodilatation was not inhibited by the iGluR5 receptor agonist iodowillardiine. Conclusions and implications: This study demonstrates that activation of the Ononin iGluR5 kainate receptors with the selective agonist iodowillardiine is able to inhibit neurogenic dural vasodilatation probably by inhibition of prejunctional release of CGRP from trigeminal afferents. Taken together with recent clinical studies the data reinforce CGRP mechanisms in primary headaches and demonstrate a novel role for kainate receptor modulation of trigeminovascular activation. (Mitsikostas expression after activation of structures involved in nociceptive pathways (Mitsikostas expression in an animal model of trigeminovascular nociceptive processing (Mitsikostas < 0.05 level. Drugs and materials Pentobarbital sodium salt was obtained from Sigma Chemical (Poole, Dorset, UK). The delivery of anaesthetic and experimental drugs was via different femoral catheters. In the experiments where more than one drug was given intravenously, the line was always flushed with saline prior to administration. Both iodowillardiine and UBP 302 (Tocris Cookson Inc., Bristol, UK) were dissolved in saline (pH 8). In control experiments equal volumes of vehicle only were administered. CGRP (rat; Tocris Cookson Inc.) was initially dissolved in distilled water, aliquoted and frozen. Subsequent dilutions were made in 0.9% saline before injection at a dose of 1 1 gkg?1. All drugs were made fresh on the morning of an experiment and administered in volumes ranging from 0.1 to 0.5 mL. The homeothermic blanket (TC-1000 Temperature Controller) was from CWE Inc. (Ardmore, PA, USA); small rodent ventilator (model 683), Harvard Apparatus Ltd. (Edenbridge, Kent, UK); the CO2 monitor (Capstar-100), CWE Inc. (Ardmore, PA, USA); CED spike2v5 software, CED (Cambridge, UK); intravital microscope (Microvision MV2100), Finlay Microvision (Warwickshire, UK); video dimension analyser, Living Systems Instrumentation (Burlington,VT, USA); bipolar stimulating electrode (NE 200X), Clarke Electromedical Instruments (Pangbourne, UK); Grass stimulator S88, Grass Instruments (Quincy, MA, USA). Results Baseline blood pressure and respiratory values were within normal limits for all animals included in the analysis. Visualized branches of the middle meningeal artery through the closed cranial window with diameter ranging from 90 to 140 m were studied. Electrical stimulation (50C150 A) of the cranial window produced control responses in the range of 50C180% increase in dural blood vessel diameter (< 0.005; Figure 1; Table 1) and 20 mgkg?1 (< 0.001; Figure 1; Table 1). At both doses iodowillardiine produced its maximal effect after 15 min, and responses were not fully recovered 90 min after drug administration. Iodowillardiine at 20 mgkg?1 inhibited NDV by 50% (< 0.005; < 0.05) from Ononin the neurogenic dilatation recorded at 90 min after iodowillardiine treatment, indicating that the vessel was still responding. None of the three doses had any effect on the vessel diameter at rest, and after each neurogenic dilatation following iodowillardiine administration vessel diameter returned to levels recorded at rest. Control vehicle injections demonstrated no significant effect (Figure 1). Ononin Neither control vehicle nor iodowillardiine at all three doses had any effects on blood pressure. Table 1 Effects of intravenous injection of iodowillardiine (10 mgkg?1), iodowillardiine (20 mgkg?1), UBP 302 (50 mgkg?1), co-administration of 10 mgkg?1 iodowillardiine and 50 mgkg?1 UBP 302 and control vehicle on neurogenic dural vasodilatation < 0.05 compared with control responses. Open in a separate window Figure 1 Effect of intravenous administration of iodowillardiine (5, 10 and 20 mgkg?1) on neurogenic vasodilatation. Following control responses to electrical stimulation, rats were injected with iodowillardiine at 5 (< 0.05 significance compared with the control response. #< 0.05 significance.