Localization of large conductance calcium-activated potassium channels and their effect on calcitonin gene-related peptide release in the rat trigemino-neuronal pathway

Hypersensitivity to BKCa channel opening in persistent post-traumatic headache

BACKGROUND

Large conductance  calcium-activated potassium (BKCa) channels have been implicated in the neurobiological underpinnings of migraine. Considering the clinical similarities between migraine and persistent post-traumatic headache (PPTH), we aimed to examine whether MaxiPost (a BKCa channel opener) could induce migraine-like headache in persons with PPTH.

METHODS

This is a randomized double-blind, placebo-controlled, two-way crossover study from September 2023 to December 2023. Eligible participants were adults with PPTH after mild traumatic brain injury who reported having no personal history of migraine. The randomized participants received a single dose of either MaxiPost (0.05 mg/min) or placebo (isotonic saline) that was infused intravenously over 20 minutes. The two experiment sessions were scheduled at least one week apart to avoid potential carryover effects. The primary endpoint was the induction of migraine-like headache after MaxiPost as compared to placebo within 12 hours of drug administration. The secondary endpoint was the area under the curve (AUC) values for headache intensity scores between MaxiPost and placebo over the same 12-hour observation period.

RESULTS

Twenty-one adult participants (comprising 14 females and 7 males) with PPTH were enrolled and completed both experiment sessions. The proportion of participants who developed migraine-like headache was 11 (52%) of 21 participants after MaxiPost infusion, in contrast to four (19%) participants following placebo (P = .02). Furthermore, the median headache intensity scores, represented by AUC values, were higher following MaxiPost than after placebo (P < .001).

CONCLUSIONS

Our results indicate that BKCa channel opening can elicit migraine-like headache in persons with PPTH. Thus, pharmacologic blockade of BKCa channels might present a novel avenue for drug discovery. Additional investigations are nonetheless needed to confirm these insights and explore the therapeutic prospects of BKCa channel blockers in managing PPTH.

CLINICALTRIALS

GOV IDENTIFIER

NCT05378074.

Neurotransmission, Vasculogenesis, and Osteogenesis Activities are Altered in the Aging Temporomandibular Joint of the Senescence-Accelerated Prone 8 Mouse Model

BACKGROUND

Alterations in neurotransmission, vasculogenesis, and osteogenesis pathways that may play pivotal roles in age-related changes in the temporomandibular joint (TMJ) are poorly understood.

PURPOSE

This study aimed to measure the associations between gene and protein profiles in senescence-accelerated prone 8 (SAMP8) mice.

STUDY DESIGN

The investigators designed and used 3 groups of 2 mouse models: 1) early aging SAMP8 at 24 weeks of age and control SAMR1 at 12 and 24 weeks (each stage n = 12).

PREDICTOR/EXPOSURE/INDEPENDENT VARIABLE

The independent variable was investigated using 3 mouse models: an early aging mouse model and a control mouse model (12 and 24 weeks).

MAIN OUTCOME VARIABLE(S)

The primary outcome variables were CGRP, VEGF-A, CD31, LYVE-1, osteocalcin, osteopontin, type I and II collagen, and MMP-2. The secondary outcome variables were histological characteristics.

COVARIATES

Not applicable.

ANALYSES

The gene and protein expression profiles of neurotransmitters, vasculogenesis, and osteogenesis were identified by quantitative real-time polymerase chain reaction and dot blot analysis, respectively. The cellular localization of these events was verified by in situ hybridization and immunohistochemistry. Bivariate statistics were computed for each of the outcome variables. Statistical significance was set to a P value < .05.

RESULTS

The expression of CGRP mRNA in the bony mandibular condyle (BMC) of SAMP8 mice (SAMP8, 3.3 ± 0.39 vs SAMR1, 0.001 ± 0.0001) was high at 24 weeks of age (24 weeks) (P < .001). Higher numbers of cells positive percentage for CGRP (MF, SAMP8, 28.67 ± 1.60 vs SAMR 1, 6.36 ± 1.10; CMC, 27.5 ± 2.12 vs 9.00 ± 1.21; BMC, 31.31 ± 2.81 vs 7.85 ± 1.14) and VEGF-A (MF, 34.43 ± 2.45 vs 14.01 ± 1.28; MD, 32.69 ± 1.86 vs 8.00 ± 0.91; CMC, 36.60 ± 2.05 vs 14.19 ± 1.25 BMC 36.49 vs 12.59 ± 1.41) antibodies were found in the 24 weeks TMJ (P < .01).

CONCLUSIONS AND RELEVANCE

The neurotransmitter, vasculogenesis, and osteogenesis pathways are associated with TMJ aging in the SAMP8 mouse model. In the future, the SAMP8 mouse model may prove to be a robust model for identifying molecular and biochemical events underlying the effects of feeding, occlusal changes, and tooth loss in the aging TMJ.

Ion Channel Disturbances in Migraine Headache: Exploring the Potential Role of the Kynurenine System in the Context of the Trigeminovascular System

Migraine is a primary headache disorder, which is an enormous burden to the healthcare system. While some aspects of the pathomechanism of migraines remain unknown, the most accepted theory is that activation and sensitization of the trigeminovascular system are essential during migraine attacks. In recent decades, it has been suggested that ion channels may be important participants in the pathogenesis of migraine. Numerous ion channels are expressed in the peripheral and central nervous systems, including the trigeminovascular system, affecting neuron excitability, synaptic energy homeostasis, inflammatory signaling, and pain sensation. Dysfunction of ion channels could result in neuronal excitability and peripheral or central sensitization. This narrative review covers the current understanding of the biological mechanisms leading to activation and sensitization of the trigeminovascular pain pathway, with a focus on recent findings on ion channel activation and modulation. Furthermore, we focus on the kynurenine pathway since this system contains kynurenic acid, which is an endogenous glutamate receptor antagonist substance, and it has a role in migraine pathophysiology.

Involvement of Potassium Channel Signalling in Migraine Pathophysiology

Migraine is a primary headache disorder ranked as the leading cause of years lived with disability among individuals younger than 50 years. The aetiology of migraine is complex and might involve several molecules of different signalling pathways. Emerging evidence implicates potassium channels, predominantly ATP-sensitive potassium (KATP) channels and large (big) calcium-sensitive potassium (BKCa) channels in migraine attack initiation. Basic neuroscience revealed that stimulation of potassium channels activated and sensitized trigeminovascular neurons. Clinical trials showed that administration of potassium channel openers caused headache and migraine attack associated with dilation of cephalic arteries. The present review highlights the molecular structure and physiological function of KATP and BKCa channels, presents recent insights into the role of potassium channels in migraine pathophysiology, and discusses possible complementary effects and interdependence of potassium channels in migraine attack initiation.

Novel Therapeutic Targets for Migraine

Migraine, a primary headache disorder involving a dysfunctional trigeminal vascular system, remains a major debilitating neurological condition impacting many patients' quality of life. Despite the success of multiple new migraine therapies, not all patients achieve significant clinical benefits. The success of CGRP pathway-targeted therapy highlights the importance of translating the mechanistic understanding toward effective therapy. Ongoing research has identified multiple potential mechanisms in migraine signaling and nociception. In this narrative review, we discuss several potential emerging therapeutic targets, including pituitary adenylate cyclase-activating polypeptide (PACAP), adenosine, δ-opioid receptor (DOR), potassium channels, transient receptor potential ion channels (TRP), and acid-sensing ion channels (ASIC). A better understanding of these mechanisms facilitates the discovery of novel therapeutic targets and provides more treatment options for improved clinical care.

Global Epidemiology, Clinical Features, Diagnosis and Current Therapeutic Novelties in Migraine Therapy and their Prevention: A Narrative Review

INTRODUCTION

The current article reviews the latest information on epidemiology, clinical features, diagnosis, recent advancements in clinical management, current therapeutic novelties, and the prevention of migraines. In a narrative review, all studies as per developed MeSH terms published until February 2023, excluding those irrelevant, were identified through a PubMed literature search.

METHODS

Overall, migraine affects more than a billion people annually and is one of the most common neurological illnesses. A wide range of comorbidities is associated with migraines, including stress and sleep disturbances. To lower the worldwide burden of migraine, comprehensive efforts are required to develop and enhance migraine treatment, which is supported by informed healthcare policy. Numerous migraine therapies have been successful, but not all patients benefit from them.

RESULTS

CGRP pathway-targeted therapy demonstrates the importance of translating mechanistic understanding into effective treatment. In this review, we discuss clinical features, diagnosis, and recently approved drugs, as well as a number of potential therapeutic targets, including pituitary adenylate cyclase-activating polypeptide (PACAP), adenosine, opioid receptors, potassium channels, transient receptor potential ion channels (TRP), and acid-sensing ion channels (ASIC).

CONCLUSION

In addition to providing more treatment options for improved clinical care, a better understanding of these mechanisms facilitates the discovery of novel therapeutic targets.

The role of high-conductance calcium-activated potassium channel in headache and migraine pathophysiology

Migraine is a common, neurovascular headache disorder with a complex molecular interplay. The involvement of ion channels in the pathogenesis of migraine gathered considerable attention with the findings that different ion channels subfamilies are expressed in trigeminovascular system, the physiological substrate of migraine pain, and several ion channel openers investigated in clinical trials with diverse primary endpoints caused headache as a frequent side effect. High-conductance (big) calcium-activated potassium (BK_Ca ) channel is expressed in the cranial arteries and the trigeminal pain pathway. Recent clinical research revealed that infusion of BK_Ca channel opener MaxiPost caused vasodilation, headache and migraine attack. Thus, BK_Ca channel is involved in pathophysiological mechanisms underlying headache and migraine, and targeting BK_Ca channel presents a new potential strategy for migraine treatment.

Anatomy and Physiology of Headache

Headache disorders can produce recurrent, incapacitating pain. Migraine and cluster headache are notable for their ability to produce significant disability. The anatomy and physiology of headache disorders is fundamental to evolving treatment approaches and research priorities. Key concepts in headache mechanisms include activation and sensitization of trigeminovascular, brainstem, thalamic, and hypothalamic neurons; modulation of cortical brain regions; and activation of descending pain circuits. This review will examine the relevant anatomy of the trigeminal, brainstem, subcortical, and cortical brain regions and concepts related to the pathophysiology of migraine and cluster headache disorders.

Brain barriers and their potential role in migraine pathophysiology

Migraine is a ubiquitous neurologic disease that afflicts people of all ages. Its molecular pathogenesis involves peptides that promote intracranial vasodilation and modulate nociceptive transmission upon release from sensory afferents of cells in the trigeminal ganglion and parasympathetic efferents of cells in the sphenopalatine ganglion. Experimental data have confirmed that intravenous infusion of these vasoactive peptides induce migraine attacks in people with migraine, but it remains a point of scientific contention whether their site of action lies outside or within the central nervous system. In this context, it has been hypothesized that transient dysfunction of brain barriers before or during migraine attacks might facilitate the passage of migraine-inducing peptides into the central nervous system. Here, we review evidence suggestive of brain barrier dysfunction in migraine pathogenesis and conclude with lessons learned in order to provide directions for future research efforts.

Opening of BKCa channels causes migraine attacks: a new downstream target for the treatment of migraine

ABSTRACT

Migraine is a common and frequently disabling neurological disorder, but the initiating migraine mechanisms are still poorly understood. Potassium channel opening may cause migraine, and we therefore examined the migraine-inducing effect of MaxiPost, a large (big)-conductance calcium-activated potassium (BKCa) channel opener, on migraine induction and cephalic vasodilation in individuals with migraine. Twenty-six patients with migraine without aura were randomly allocated to receive an infusion of MaxiPost or placebo on 2 study days separated by at least 1 week. The primary endpoint was the difference in incidence of migraine attacks after MaxiPost compared with placebo. The secondary endpoints were the difference in incidence of headaches and the difference in area under the curve for headache intensity scores (0-12 hours), for middle cerebral artery blood flow velocity (VMCA) (0-2 hours), and for superficial temporal artery and radial artery diameter. Twenty-two patients completed the study. Twenty-one of 22 (95%) developed migraine attacks after MaxiPost compared with none after placebo (P < 0.0001); the difference of incidence is 95% (95% confidence interval 86%-100%). The incidence of headache over the 12-hour observation period was higher after MaxiPost day (n = 22) than after placebo (n = 7) (P < 0.0001). We found a significant increase of VMCA and superficial temporal and radial arteries' diameter. Because BKCa channel opening initiates migraine attacks, we suggest that BKCa channel blockers could be potential candidates for novel antimigraine drugs.

Excitatory Effects of Calcitonin Gene-Related Peptide (CGRP) on Superficial Sp5C Neurons in Mouse Medullary Slices

The neuromodulator calcitonin gene-related peptide (CGRP) is known to facilitate nociceptive transmission in the superficial laminae of the spinal trigeminal nucleus caudalis (Sp5C). The central effects of CGRP in the Sp5C are very likely to contribute to the activation of central nociceptive pathways leading to attacks of severe headaches like migraine. To examine the potential impacts of CGRP on laminae I/II neurons at cellular and synaptic levels, we performed whole-cell patch-clamp recordings in juvenile mouse brainstem slices. First, we tested the effect of CGRP on cell excitability, focusing on neurons with tonically firing action potentials upon depolarizing current injection. CGRP (100 nM) enhanced tonic discharges together with membrane depolarization, an excitatory effect that was significantly reduced when the fast synaptic transmissions were pharmacologically blocked. However, CGRP at 500 nM was capable of exciting the functionally isolated cells, in a nifedipine-sensitive manner, indicating its direct effect on membrane intrinsic properties. In voltage-clamped cells, 100 nM CGRP effectively increased the frequency of excitatory synaptic inputs, suggesting its preferential presynaptic effect. Both CGRP-induced changes in cell excitability and synaptic drives were prevented by the CGRP receptor inhibitor BIBN 4096BS. Our data provide evidence that CGRP increases neuronal activity in Sp5C superficial laminae by dose-dependently promoting excitatory synaptic drive and directly enhancing cell intrinsic properties. We propose that the combination of such pre- and postsynaptic actions of CGRP might underlie its facilitation in nociceptive transmission in situations like migraine with elevated CGRP levels.

Involvement of the BNP/NPR-A/BKCa pathway in rat trigeminal ganglia following chronic constriction injury

Accumulating evidence indicates that the brain natriuretic peptide (BNP) and its receptor (natriuretic peptide receptor, NPR) are widely distributed in a variety of tissues including trigeminal ganglion (TG). Furthermore, recent studies support the involvement of the BNP-NPR-A pathway in acute and chronic pain. To investigate the role of this pathway in chronic pain, an infraorbital nerve-chronic constriction injury (ION-CCI) model of trigeminal neuralgia (TN) was produced in the rat. The time course of changes in mechanical pain threshold was examined. We observed an upregulation of BNP and NPR-A and a downregulation of large-conductance Ca²⁺-activated K⁺ (BKCa) mRNA and protein in rats subjected to ION-CCI. Patch clamping experiments in vitro found that BKCa currents were significantly reduced in rats subjected to ION-CCI. BNP increased BKCa currents in ION-CCI rats. These results suggest that BNP and NPR-A might serve as endogenous pain relievers in ION-CCI rats. Modulation of the BNP/NPR-A/BKCa channel pathway in TG may be a viable strategy for the treatment of TN.NEW & NOTEWORTHY BNP has been known to activate its receptor, NPR-A, to modulate inflammatory pain. However, the potential modulatory roles of BNP in TN have not been investigated in detail. We established an ION-CCI model of TN in the rat and observed an upregulation of BNP and NPR-A and a downregulation of BKCa in rats subjected to ION-CCI. Moreover, BNP can increase BKCa currents in ION-CCI rats. Thus, BNP and NPR-A might have inhibitory effects on trigeminal neuralgia through activating the BNP/NPR-A/BKCa channel pathway.

The action of a BK channel opener

Rockman et al. in this issue of JGP describe how NS11021 opens BK channels, which make the compound a better tool to probe physiological roles and gating mechanisms of BK channels.

Opening of BKCa channels alters cerebral hemodynamic and causes headache in healthy volunteers

Introduction

Preclinical data implicate large conductance calcium-activated potassium (BKCa) channels in the pathogenesis of headache and migraine, but the exact role of these channels is still unknown. Here, we investigated whether opening of BKCa channels would cause headache and vascular effects in healthy volunteers.

Methods

In a randomized, double-blind, placebo-controlled, cross-over study, 21 healthy volunteers aged 18–39 years were randomly allocated to receive an intravenous infusion of 0.05 mg/min BKCa channel opener MaxiPost and placebo on two different days. The primary endpoints were the difference in incidence of headache and the difference in area under the curve (AUC) for headache intensity scores (0–12 hours) and for middle cerebral artery blood flow velocity (VMCA) (0–2 hours) between MaxiPost and placebo. The secondary endpoints were the differences in area under the curve for superficial temporal artery and radial artery diameter (0–2 hours) between MaxiPost and placebo.

Results

Twenty participants completed the study. Eighteen participants (90%) developed headache after MaxiPost compared with six (30%) after placebo ( p = 0.0005); the difference of incidence is 60% (95% confidence interval 36–84%). The area under the curve for headache intensity (AUC0–12 hours, p = 0.0003), for mean VMCA (AUC0–2 hours, p = 0.0001), for superficial temporal artery diameter (AUC0–2 hours, p = 0.003), and for radial artery diameter (AUC0–2 hours, p = 0.03) were significantly larger after MaxiPost compared to placebo.

Conclusion

MaxiPost caused headache and dilation in extra- and intracerebral arteries. Our findings suggest a possible role of BKCa channels in headache pathophysiology in humans. ClinicalTrials.gov, ID: NCT03887325.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

ATP sensitive potassium (KATP) channel inhibition: A promising new drug target for migraine

BACKGROUND

Recently, the adenosine triphosphate (ATP) sensitive potassium channel opener levcromakalim was shown to induce migraine attacks with a far higher incidence than any previous provoking agent such as calcitonin gene-related peptide. Here, we show efficacy of ATP sensitive potassium channel inhibitors in two validated rodent models of migraine.

METHODS

In female spontaneous trigeminal allodynic rats, the sensitivity of the frontal region of the head was tested by an electronic von Frey filament device. In mice, cutaneous hypersensitivity was induced by repeated glyceryl trinitrate or levcromakalim injections over nine days, as measured with von Frey filaments in the hindpaw. Release of calcitonin gene-related peptide from dura mater and trigeminal ganglion was studied ex vivo.

RESULTS

The ATP sensitive potassium channel inhibitor glibenclamide attenuated the spontaneous cephalic hypersensitivity in spontaneous trigeminal allodynic rats and glyceryl trinitrate-induced hypersensitivity of the hindpaw in mice. It also inhibited CGRP release from dura mater and the trigeminal ganglion isolated from spontaneous trigeminal allodynic rats. The hypersensitivity was also diminished by the structurally different ATP sensitive potassium channel inhibitor gliquidone. Mice injected with the ATP sensitive potassium channel opener levcromakalim developed a progressive hypersensitivity that was completely blocked by glibenclamide, confirming target engagement.

CONCLUSION

The results suggest that ATP sensitive potassium channel inhibitors could be novel and highly effective drugs in the treatment of migraine.

Targeting BKCa Channels in Migraine: Rationale and Perspectives

Large (big)-conductance calcium-activated potassium (BK_Ca) channels are expressed in migraine-related structures such as the cranial arteries, trigeminal ganglion and trigeminal spinal nucleus, and they play a substantial role in vascular tonus and neuronal excitability. Using synthetic BK_Ca channels openers was associated with headache as a frequent adverse effect in healthy volunteers. Additionally, BK_Ca channels are downstream molecules in migraine signalling pathways that are activated by several compounds known to provoke migraine, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP) and glyceryl trinitrate (GTN). Also, there is a high affinity and a close coupling between BK_Ca channels and ATP-sensitive potassium (K_ATP) channels, the role of which has recently been established in migraine pathophysiology. These observations raise the question as to whether direct BK_Ca channel activation can provoke migraine in migraine patients, and whether the BK_Ca channel could be a potential novel anti-migraine target. Hence, randomized and placebo-controlled clinical studies on BK_Ca channel openers or blockers in migraine patients are needed.

Molecular Determinants of BK Channel Functional Diversity and Functioning

Large-conductance Ca2+- and voltage-activated K+ (BK) channels play many physiological roles ranging from the maintenance of smooth muscle tone to hearing and neurosecretion. BK channels are tetramers in which the pore-forming α subunit is coded by a single gene ( Slowpoke, KCNMA1). In this review, we first highlight the physiological importance of this ubiquitous channel, emphasizing the role that BK channels play in different channelopathies. We next discuss the modular nature of BK channel-forming protein, in which the different modules (the voltage sensor and the Ca2+ binding sites) communicate with the pore gates allosterically. In this regard, we review in detail the allosteric models proposed to explain channel activation and how the models are related to channel structure. Considering their extremely large conductance and unique selectivity to K+, we also offer an account of how these two apparently paradoxical characteristics can be understood consistently in unison, and what we have learned about the conduction system and the activation gates using ions, blockers, and toxins. Attention is paid here to the molecular nature of the voltage sensor and the Ca2+ binding sites that are located in a gating ring of known crystal structure and constituted by four COOH termini. Despite the fact that BK channels are coded by a single gene, diversity is obtained by means of alternative splicing and modulatory β and γ subunits. We finish this review by describing how the association of the α subunit with β or with γ subunits can change the BK channel phenotype and pharmacology.

BK channel activators and their therapeutic perspectives

The large conductance calcium- and voltage-activated K⁺ channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability. Additionally, cardioprotective roles have been revealed in recent years. After a short introduction to the structure, function and regulation of BK channels, we review the small organic molecules activating BK channels and how these tool compounds have helped delineate the roles of BK channels in health and disease.

The role of large-conductance, calcium-activated potassium channels in a rat model of trigeminal neuropathic pain

BACKGROUND

Trigeminal neuralgia is a disorder of paroxysmal and severely disabling facial pain and continues to be a real therapeutic challenge. At present there are few effective drugs. Here the aim of this study was to investigate the role of BKCa channels in trigeminal neuropathic pain.

METHODS

Rats were divided into two groups: a sham and a chronic constriction injury of infraorbital branch of trigeminal nerve (ION-CCI) group. Nociceptive behavior testing, immunohistochemistry, RT-PCR, Western blotting and whole-cell patch clamp recording were used.

RESULTS

Relative to the sham group, rats with ION-CCI consistently displayed lower mechanical pain thresholds in the vibrissal pad region from day 6 to 42 after ION-CCI operation. ION-CCI induced a significant down-regulation of BKCa channels both in mRNA and protein levels in the ipsilateral trigeminal ganglion (TG), a lower threshold intensity of action potential, and decreased total BKCa currents in cultured TG neurons. TG target injection of NS1619 (20-100 µg), an opener of BKCa channels, dose-dependently increased the mechanical pain threshold, which was blocked by the BKCa channel inhibitor iberiotoxin (IbTX, 20 µg). NS1619 (10 µM) significantly increased the mean threshold intensities of action potentials in ION-CCI rats, while failing to affect those in the sham rats. The levels of phosphorylated extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinases (JNK) in TG were significantly increased after ION-CCI operation. The ERK1/2 antagonist U0126, p38 antagonist SB203580 and JNK antagonist SP600125 significantly reversed the facial mechanical allodynia in ION-CCI rats. However, the ERK1/2 antagonist U0126, p38 antagonist SB203580 but not JNK antagonist SP600125 significantly increased BKCa currents in ION-CCI TG neurons.

CONCLUSIONS

Our results indicate the important involvement of mainly ERK and p38 MAPK pathways in modulating BKCa channels in ION-CCI TG neurons. BKCa channels represent a new therapeutic target for the clinical treatment of trigeminal neuropathic pain.

PACAP-38 but not VIP induces release of CGRP from trigeminal nucleus caudalis via a receptor distinct from the PAC1 receptor

OBJECTIVE

To investigate if PACAP and VIP have an effect on CGRP release or NOS activity in the trigeminal ganglion and trigeminal nucleus caudalis and if there can be a difference in effect between PACAP and VIP on these two systems. Furthermore, we investigate if PACAP co-localize with CGRP and/or nNOS in the two tissues.

BACKGROUND

The structurally related neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide-38 (PACAP-38) partially share receptors and are both potent vasodilators. However, PACAP-38 but not VIP is an efficient inducer of migraine attacks in migraineurs. Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are two signaling molecules known to be involved in migraine.

METHODS

Rat tissue was used for all experiments. Release of CGRP induced by VIP and PACAP in dura mater, trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC) was quantified by EIA. Regulation of NOS-enzymes caused by VIP and PACAP was investigated in dura mater, TG and TNC by measuring the conversion of L-[3H]arginine to L-[3H]citrulline. Co-expression of PACAP, neuronal nitric oxide synthase (nNOS) and CGRP was explored by immunohistochemistry in TG and TNC. mRNA expression studies of VPAC1, VPAC2 and PAC1-receptors were performed by qRT-PCR.

RESULTS

PACAP-38 administered in increasing concentrations caused a concentration-dependent CGRP-release in the TNC, but not in TG. VIP was without effect in both tissues examined. The PAC1 receptor agonist maxadilan had no effect on CGRP release and the PAC1 antagonist M65 did not inhibit PACAP-38 induced CGRP release. PACAP-38 or VIP did not affect NOS activity in homogenates of TG and TNC. Quantitative PCR demonstrated the presence of VPAC1, VPAC2 and PAC1 receptors in TG and TNC. Immunohistochemistry of PACAP and CGRP showed co-expression in TG and TNC. PACAP and nNOS were co-localized in TG, but not in TNC. PACAP was found to co-localize with glutamine synthetase in TG satellite glial cells.

CONCLUSION

PACAP-38 cause release of CGRP from TNC but not from TG. We suggest that the release is not caused via activation of PAC1, VPAC1 or VPAC2 receptors. PACAP has no effect on NOS activity in TG or TNC. In TG PACAP was found in neuronal cells and in satellite glial cells. It co-localized with CGRP and nNOS in the neuronal cells. In TNC PACAP was co-localized with CGRP but not with nNOS.

Large conductance calcium-activated potassium channels: their expression and modulation of glutamate release from nerve terminals isolated from rat trigeminal caudal nucleus and cerebral cortex

Large conductance, calcium-activated potassium channels [big potassium (BK) channel] consist of a tetramer of pore-forming α-subunit and distinct accessory β-subunits (β1-4) that modify the channel's properties. In this study, we analyzed the effects of BK channel activators and blockers on glutamate and γ-aminobutyric acid (GABA) release from synaptosomes isolated from the cerebral cortices or trigeminal caudal nuclei (TCN) of rats. Real-time polymerase chain reaction was used to characterize BK channel α and β(1-4) subunit expression in the cortex and in the trigeminal ganglia (TG), whose neurons project primary terminal afferents into the TCN. Immunocytochemistry was used to localize these subunits on cortical and TCN synaptosomes. The BK channels regulating [(3)H]D-aspartate release from primary afferent nerve terminals projecting into the TCN displayed limited sensitivity to iberiotoxin, whereas those expressed on cortical synaptosomes were highly sensitive to this toxin. BK channels did not appear to be present on GABAergic nerve terminals from the TCN since [(3)H]-γ-aminobutyric acid release in this model was unaffected by BK channel activators or blockers. Gene expression studies revealed expression levels of the α subunit in the TG that were only 31.2 ± 2.1% of those found in cortical tissues. The β4 subunit was the accessory subunit expressed most abundantly in both the cortex and TG. Levels of β1 and β2 were low in both these areas although β2 expression in the TG was higher than that found in the cortex. Immunocytochemistry experiments showed that co-localization of α and β4 subunits (the accessory subunit most abundantly expressed in both brain areas) was more common in TCN synaptosomes than in cortical synaptosomes. On the basis of these findings, it is reasonable to hypothesize that BK channels expressed on glutamatergic terminals in the TCN and cortex have distinct pharmacological profiles, which probably reflect different α and β subunit combinations. Channels in the cortex seem to be composed mainly of α subunits and to a lesser degree by α and β4 subunits, whereas in the TG the α + β4 combination seems to prevail (although α and/or α + β2 channels cannot be excluded). In light of the BK channels' selective control of excitatory transmission and their pharmacological diversity, their effects on primary glutamatergic afferents projecting to TCN represent a potential target for drug therapy of migraines and other types of orofacial pain.

Phosphodiesterases 3 and 5 express activity in the trigeminal ganglion and co-localize with calcitonin gene-related peptide

Background

Understanding of the neuropathology leading to migraine pain has centered on either a vascular or neuronal origin. Sildenafil, a specific inhibitor of phosphodiesterase 5 (PDE5), induces migraine-like headache in a human headache model without concomitant artery dilation. The presence and activity of PDE3 and PDE5 is known in cerebral arteries. However, the presence in the neuronal part of the trigeminovascular pathway, i.e. the trigeminal ganglion and the possible co-localization with calcitonin gene-related peptide (CGRP), is not known.

Methods

Rat trigeminal ganglia were isolated and immunohistochemistry and in situ hybridization was applied. Evaluations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) hydrolysis were performed using scintillation proximity assays.

Results

PDE3 and PDE5 were present and active in the trigeminal ganglia. A subset of PDE3- and PDE5-positive neurons contained CGRP. In contrast to cGMP, both sildenafil and cilostazol influenced cAMP hydrolysis.

Interpretation

Sildenafil may exert its effect on the neuronal part of the migraine pain pathway. In addition to the effects on cGMP signaling, sildenafil may indirectly affect cAMP signaling in the trigeminal ganglion. This result may suggest a common cAMP-related pathway for sildenafil, cilostazol, and CGRP in eliciting migraine pain.

Calcitonin gene-related peptide receptors in rat trigeminal ganglion do not control spinal trigeminal activity

Calcitonin gene-related peptide (CGRP) is regarded as a key mediator in the generation of primary headaches. CGRP receptor antagonists reduce migraine pain in clinical trials and spinal trigeminal activity in animal experiments. The site of CGRP receptor inhibition causing these effects is debated. Activation and inhibition of CGRP receptors in the trigeminal ganglion may influence the activity of trigeminal afferents and hence of spinal trigeminal neurons. In anesthetized rats extracellular activity was recorded from neurons with meningeal afferent input in the spinal trigeminal nucleus caudalis. Mechanical stimuli were applied at regular intervals to receptive fields located in the exposed cranial dura mater. α-CGRP (10(-5) M), the CGRP receptor antagonist olcegepant (10(-3) M), or vehicle was injected through the infraorbital canal into the trigeminal ganglion. The injection of volumes caused transient discharges, but vehicle, CGRP, or olcegepant injection was not followed by significant changes in ongoing or mechanically evoked activity. In animals pretreated intravenously with the nitric oxide donor glyceryl trinitrate (GTN, 250 μg/kg) the mechanically evoked activity decreased after injection of CGRP and increased after injection of olcegepant. In conclusion, the activity of spinal trigeminal neurons with meningeal afferent input is normally not controlled by CGRP receptor activation or inhibition in the trigeminal ganglion. CGRP receptors in the trigeminal ganglion may influence neuronal activity evoked by mechanical stimulation of meningeal afferents only after pretreatment with GTN. Since it has previously been shown that olcegepant applied to the cranial dura mater is ineffective, trigeminal activity driven by meningeal afferent input is more likely to be controlled by CGRP receptors located centrally to the trigeminal ganglion.

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.