Selective cephalic upregulation of p-ERK, CamKII and p-CREB in response to glyceryl trinitrate infusion

Background A common characteristic of migraine-inducing substances is that they cause headache and no pain in other areas of the body. Few studies have compared pain mechanisms in the trigeminal and spinal systems and, so far, no major differences have been noted. We compared signalling molecules in the trigeminal and spinothalamic system after infusion of the migraine-provoking substance glyceryltrinitrate. Method A catheter was placed in the femoral vein of rats and one week later glyceryltrinitrate 4 µg/kg/min was infused for 20 min. Protein expression in the dura mater, trigeminal ganglion, nucleus caudalis, dorsal root ganglion and the dorsal horn of the thoracic spinal cord was analysed at different time points using western blotting and immunohistochemistry. Results Glyceryltrinitrate caused a threefold increase in expression of phosphorylated extracellular signal-regulated kinases at 30 min in the dura mater and nucleus caudalis ( P < 0.05) and at 2 h in the trigeminal ganglion with very few expressions in the dorsal root ganglion. In the nucleus caudalis, expression of phosphorylated extracellular signal-regulated kinases and Cam KII increased 2.6-fold and 3.2-fold, respectively, at 2 h after glycerytrinitrate infusion ( P < 0.01). p-CREB/ATF-1 upregulation was observed only at 30 min ( P < 0.05) in the nucleus caudalis. None of these markers showed increased expression in the regions of thoracic spinal cord dorsal horn. Conclusion The dura, trigeminal ganglion and nucleus caudalis are activated shortly after glycerytrinitrate infusion with long-lasting expression of phosphorylated extracellular signal-regulated kinases observed in the nucleus caudalis. These activations were not observed at the spinal level.

Mechanisms of glyceryl trinitrate provoked mast cell degranulation

BACKGROUND

Migraine patients develop attacks several hours after intravenous infusion of glyceryl trinitrate. Due to the short half-life of nitric oxide, this delayed migraine cannot be caused by a direct action of nitric oxide derived from glyceryl trinitrate. The involvement of meningeal inflammation and dural mast cell degranulation is supported by the effectiveness of prednisolone on glyceryl trinitrate-induced delayed headache.

METHODS

Using a newly developed rat model mimicking the human glyceryl trinitrate headache model, we have investigated the occurrence of dural mast cell degranulation after a clinically relevant dose of glyceryl trinitrate.

RESULTS

A 6-fold increase in degranulation was observed starting at 2 hours after glyceryl trinitrate infusion. Interestingly, pre-treatment with the effective anti-migraine substances L-nitro-arginine methyl ester and sumatriptan prevented glyceryl trinitrate-induced mast cell degranulation whereas the calcitonin gene-related peptide-receptor antagonist olcegepant and the substance P receptor antagonist L-733,060 did not affect mast cell degranulation. However, topical application of two different nitric oxide donors did not cause mast cell degranulation ex vivo.

CONCLUSIONS

Direct application of an exogenous nitric oxide donor on dural mast cells does not cause mast cell degranulation ex vivo. In vivo application of the nitric oxide donor glyceryl trinitrate leads to a prominent level of degranulation via a yet unknown mechanism. This effect can be completely blocked by inhibition of the endogenous nitric oxide production and by 5-HT1B/1D receptor agonists but is unaffected by calcitonin gene-related peptide and substance P receptor antagonists.

K(ATP) channel openers in the trigeminovascular system

BACKGROUND

The ATP-sensitive K(+) (K(ATP)) channel openers levcromakalim and pinacidil are vasodilators that induce headache in healthy people. The neuropeptide calcitonin gene-related peptide (CGRP) induces headache in healthy people and migraine in migraineurs, potentially through a mechanism that involves opening of vascular or neuronal K(ATP) channels and mast cell degranulation. Using rat as a model, we studied the molecular presence of K(ATP) channels in the trigeminovascular system. Furthermore, we examined whether K(ATP) channel openers stimulate the in vitro release of CGRP and whether they degranulate dural mast cells.

METHODS

mRNA and protein expression of K(ATP) channel subunits were studied in the trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC) by qPCR and western blotting. In vitro CGRP release was studied after application of levcromakalim (1 µM) and diazoxide (10 µM) to freshly isolated rat dura mater, TG and TNC. Rat dural mast cells were challenged in situ with levcromakalim (10(-5) M) to study its potential degranulation effect.

RESULTS

mRNA and protein of K(ATP) channel subunits Kir6.1, Kir6.2, SUR1 and SUR2B were identified in the TG and TNC. K(ATP) channel openers did not release or inhibit capsaicin-induced CGRP release from dura mater, TG or TNC. They did also not induce dural mast cell degranulation.

CONCLUSIONS

K(ATP) channel openers do not interact with CGRP release or mast cell degranulation. Activation of these channels in the CNS is antinociceptive and therefore cannot explain the headache induced by K(ATP) channel openers. Thus, they are likely to induce headache by interaction with extracerebral K(ATP) channels, probably the SUR2B isoforms.

Evidence for CGRP re-uptake in rat dura mater encephali

BACKGROUND AND PURPOSE

Calcitonin gene-related peptide (CGRP) is widely distributed in the trigeminovascular system and released from sensory fibres of the cranial dura mater upon noxious stimulation. Such release may be a mechanism underlying migraine headache. Based on data from guinea pig basilar artery preparations, we have here studied CGRP release and uptake in an organ preparation of the hemisected rat skull.

EXPERIMENTAL APPROACH

CGRP release from the cranial dura was quantified by a commercial enzyme-linked immunoassay. CGRP was depleted using repetitive challenges of capsaicin. After incubating the tissue with CGRP for 20 min and extensive washing, another capsaicin challenge was performed. Immunohistochemistry was used to visualize CGRP immunofluorescence in dural nerve fibres.

KEY RESULTS

Capsaicin-induced CGRP release was attenuated by the transient receptor potential vanilloid receptor type I antagonist capsazepine or by Ca(2+)-free solutions. After the CGRP-depleted preparation had been exposed to exogenous CGRP, capsaicin-induced CGRP release was increased compared to the challenge just prior to incubation. CGRP uptake was not influenced by Ca(2+)-free solutions. Olcegepant and CGRP(8-37) (CGRP receptor antagonists) did not affect uptake of CGRP. However, a monoclonal CGRP-binding antibody decreased CGRP uptake significantly. Release of CGRP after incubation was attenuated by Ca(2+)-free solutions and by capsazepine. Immunohistochemical assays indicated a weak trend towards CGRP uptake in rat dura mater.

CONCLUSION AND IMPLICATIONS

We have presented evidence for CGRP uptake in nerves and its re-release in rat dura mater. This may have implications for the pathophysiology and treatment of migraine.

Role for voltage gated calcium channels in calcitonin gene-related peptide release in the rat trigeminovascular system

Clinical and genetic studies have suggested a role for voltage gated calcium channels (VGCCs) in the pathogenesis of migraine. Release of calcitonin gene-related peptide (CGRP) from trigeminal neurons has also been implicated in migraine. The VGCCs are located presynaptically on neurons and are involved in the release of these peptides to different stimuli. We have examined the presence and importance of VGCCs in controlling the CGRP release from rat dura mater, freshly isolated trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC). Each of the four VGCCs, P/Q-, N-, and L- and T-type are abundantly found in TG and TNC relative to the dura mater and each mediates a significant fraction of high potassium concentration induced CGRP release. In dura mater, blockade of P/Q-, N- and L-type VGCCs by ω-agatoxin TK, ω-conotoxin GVIA and nimodipine at 1 μM respectively, significantly decreased the potassium induced CGRP release. In the absence of calcium ions (Ca2+) and in the presence of a cocktail of blockers, the stimulated CGRP release from dura mater was reduced almost to the same level as basal CGRP release. In the TG ω-conotoxin GVIA inhibited the potassium induced CGRP release significantly. In the absence of Ca2+ and in the presence of a cocktail of blockers the stimulated CGRP release was significantly reduced. In the TNC only the cocktail of blockers and the absence of Ca2+ could reduce the potassium induced release significantly. These results suggest that depolarization by high potassium releases CGRP, and the release is regulated by Ca2+ ions and voltage-gated calcium channels.