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

Exploring the synergistic effects of chuanxiong rhizoma and Cyperi rhizoma in eliciting a rapid anti-migraine action based on pharmacodynamics and pharmacokinetics

ETHNOPHARMACOLOGICAL RELEVANCE

Herb-herb combination has been used to maximize the therapeutic efficacy in the theory of traditional Chinese medicine. Chuanxiong rhizoma (called Chuanxiong in Chinese, CX) and Cyperi rhizoma (called Xiangfu in Chinese, XF) have been used alone or in combination (CRCR) to treat migraine dating back to Eastern Jin Dynasty (AD317) of China. But no data demonstrate the possible necessities or advantages of combining CX and XF for migraine.

AIM OF THE STUDY

This study explores the combination mechanism based on pharmacodynamics and pharmacokinetics.

MATERIALS AND METHODS

A nitroglycerin-induced acute migraine model in rats was used to evaluate the anti-migraine effects of CRCR and the individual herbs using behavior, real time polymerase chain reaction and Western blot experiments. The absorption characteristics of active components involved in the anti-migraine action were analyzed by UPLC-MS/MS.

RESULTS

CX and CRCR significantly reversed the abnormal levels of vasoactive substances (5-HT, CGRP, MMP-2 and MMP-9) to normal levels, but XF did not. XF and CRCR significantly decreased the pro-inflammatory cytokines (IL-1β, IL-6, and TNF-a), and increased the anti-inflammatory cytokines (IL-4 and IL-10). CRCR significantly decreased the mRNA expression levels of c-fos, iNos and nNos, and the corresponding protein expression levels of c-Fos, iNOS, and nNOS. CRCR inhibited NOS/NO pathway by downregulating the expression levels of NOS and NO. Furthermore, CRCR significantly increased the intestinal absorption rate and amount, and changed the pharmacokinetic parameters of active components in comparison with the individual herbs.

CONCLUSIONS

CX had an advantage in regulating vasoactive substances, and XF focused on regulating inflammatory cytokines. CRCR is more effective in treating migraine than the individual herbs by depending on the synergistic action of CX and XF. This research provided some critical evidences on synergistic action between herb-herb interactions, and revealed the potential advantages of herb-herb combination in traditional Chinese medicine.

Novel insight into atogepant mechanisms of action in migraine prevention

Recently, we showed that while atogepant-a small-molecule calcitonin gene-related peptide (CGRP) receptor antagonist-does not fully prevent activation of meningeal nociceptors, it significantly reduces a cortical spreading depression (CSD)-induced early response probability in C fibres and late response probability in Aδ fibres. The current study investigates atogepant effect on CSD-induced activation and sensitization of high threshold (HT) and wide dynamic range (WDR) central dura-sensitive trigeminovascular neurons. In anaesthetized male rats, single-unit recordings were used to assess effects of atogepant (5 mg/kg) versus vehicle on CSD-induced activation and sensitization of HT and WDR trigeminovascular neurons. Single cell analysis of atogepant pretreatment effects on CSD-induced activation and sensitization of central trigeminovascular neurons in the spinal trigeminal nucleus revealed the ability of this small molecule CGRP receptor antagonist to prevent activation and sensitization of nearly all HT neurons (8/10 versus 1/10 activated neurons in the control versus treated groups, P = 0.005). In contrast, atogepant pretreatment effects on CSD-induced activation and sensitization of WDR neurons revealed an overall inability to prevent their activation (7/10 versus 5/10 activated neurons in the control versus treated groups, P = 0.64). Unexpectedly however, in spite of atogepant's inability to prevent activation of WDR neurons, it prevented their sensitization (as reflected their responses to mechanical stimulation of the facial receptive field before and after the CSD). Atogepant' ability to prevent activation and sensitization of HT neurons is attributed to its preferential inhibitory effects on thinly myelinated Aδ fibres. Atogepant's inability to prevent activation of WDR neurons is attributed to its lesser inhibitory effects on the unmyelinated C fibres. Molecular and physiological processes that govern neuronal activation versus sensitization can explain how reduction in CGRP-mediated slow but not glutamate-mediated fast synaptic transmission between central branches of meningeal nociceptors and nociceptive neurons in the spinal trigeminal nucleus can prevent their sensitization but not activation.

Meningeal mast cell-mediated mechanisms of cholinergic system modulation in neurogenic inflammation underlying the pathophysiology of migraine

Growing evidence indicates that the parasympathetic system is implicated in migraine headache. However, the cholinergic mechanisms in the pathophysiology of migraine remain unclear. We investigated the effects and mechanisms of cholinergic modulation and a mast cell stabilizer cromolyn in the nitroglycerin-induced in vivo migraine model and in vitro hemiskull preparations in rats. Effects of cholinergic agents (acetylcholinesterase inhibitor neostigmine, or acetylcholine, and muscarinic antagonist atropine) and mast cell stabilizer cromolyn or their combinations were tested in the in vivo and in vitro experiments. The mechanical hyperalgesia was assessed by von Frey hairs. Calcitonin gene-related peptide (CGRP) and C-fos levels were measured by enzyme-linked immunosorbent assay. Degranulation and count of meningeal mast cells were determined by toluidine-blue staining. Neostigmine augmented the nitroglycerin-induced mechanical hyperalgesia, trigeminal ganglion CGRP levels, brainstem CGRP, and C-fos levels, as well as degranulation of mast cells in vivo. Atropine inhibited neostigmine-induced additional increases in CGRP levels in trigeminal ganglion and brainstem while it failed to do this in the mechanical hyperalgesia, C-fos levels, and the mast cell degranulation. However, all systemic effects of neostigmine were abolished by cromolyn. The cholinergic agents or cromolyn did not alter basal release of CGRP, in vitro, but cromolyn alleviated the CGRP-inducing effect of capsaicin while atropine failed to do it. These results ensure for a first time direct evidence that endogenous acetylcholine contributes to migraine pathology mainly by activating meningeal mast cells while muscarinic receptors are involved in CGRP release from trigeminal ganglion and brainstem, without excluding the possible role of nicotinic cholinergic receptors.

Migraine headache pathophysiology

In both episodic and chronic migraine, headache is the most disabling symptom that requires medical care. The migraine headache is the most well-studied symptom of migraine pathophysiology. The trigeminal system and the central processing of sensory information transmitted by the trigeminal system are of considerable importance in the pathophysiology of migraine headache. Glutamate is the main neurotransmitter that drives activation of the ascending trigeminal and trigeminothalamic pathways. The neuropeptide, calcitonin gene-related peptide (CGRP) that is released by the trigeminal system, plays a crucial role in the neurobiology of headache. Peripheral and central sensitizations associated with trigeminal sensory processing are neurobiologic states that contribute to both the development of headache during a migraine attack and the maintenance of chronic migraine.

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

Calcitonin-gene-related peptide (CGRP) plays a key role in migraine pathophysiology and more specifically in the mechanisms underlying peripheral and central sensitization. Here, we explored the interaction of CGRP with other pain mediators relevant for neuronal sensitization in an animal model of chronic migraine. Male Sprague-Dawley rats were exposed to nitroglycerin (NTG, 5 mg/kg, i.p.) or vehicle co-administered with the CGRP receptor antagonist 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), behavioral test and ex vivo analysis were performed. Olcegepant attenuated NTG-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 transient receptor potential ankyrin channels in the medulla-pons area, cervical spinal cord, and trigeminal ganglia. Similarly, olcegepant reduced the NTG-induced increase in CGRP and inflammatory cytokines in serum. The findings show that the activation of the CGRP pathway in a migraine animal model was associated to the persistent activation of inflammatory pathways, which was paralleled by a condition of hyperalgesia. These molecular events are relevant for informing us about the mechanisms underlying chronic migraine.

The Anti-CGRP Antibody Fremanezumab Lowers CGRP Release from Rat Dura Mater and Meningeal Blood Flow

Monoclonal antibodies directed against the neuropeptide calcitonin gene-related peptide (CGRP) belong to a new generation of therapeutics that are effective in the prevention of migraine. CGRP, a potent vasodilator, is strongly implicated in the pathophysiology of migraine, but its role remains to be fully elucidated. The hemisected rat head preparation and laser Doppler flowmetry were used to examine the effects on CGRP release from the dura mater and meningeal blood flow of the subcutaneously injected anti-CGRP monoclonal antibody fremanezumab at 30 mg/kg, when compared to an isotype control antibody. Some rats were administered glycerol trinitrate (GTN) intraperitoneally to produce a migraine-like sensitized state. When compared to the control antibody, the fremanezumab injection was followed by reduced basal and capsaicin-evoked CGRP release from day 3 up to 30 days. The difference was enhanced after 4 h of GTN application. The samples from the female rats showed a higher CGRP release compared to that of the males. The increases in meningeal blood flow induced by acrolein (100 µM) and capsaicin (100 nM) were reduced 13–20 days after the fremanezumab injection, and the direct vasoconstrictor effect of high capsaicin (10 µM) was intensified. In conclusion, fremanezumab lowers the CGRP release and lasts up to four weeks, thereby lowering the CGRP-dependent meningeal blood flow. The antibody may not only prevent the released CGRP from binding but may also influence the CGRP release stimulated by noxious agents relevant for the generation of migraine pain.

CURRENT PERSPECTIVES ON MITOCHONDRIAL DYSFUNCTION IN MIGRAINE

Mitochondria is an autonomous organelle that plays a crucial role in the metabolic aspects of a cell. Cortical Spreading Depression (CSD) and fluctuations in the cerebral blood flow have for long been mechanisms underlying migraine. It is a neurovascular disorder with a unilateral manifestation of disturbing, throbbing and pulsating head pain. Migraine affects 2.6 and 21.7% of the general population and is the major cause of partial disability in the age group 15-49. Higher mutation rates, imbalance in concentration of physiologically relevant molecules, oxidative stress biomarkers have been the main themes of discussion in determining the role of mitochondrial disability in migraine. The correlation of migraine with other disorders like hemiplegic migraine, MELAS, TTH, CVS, ischemic stroke and hypertension has helped in the assessment of the physiological and morphogenetic basis of migraine. Here, we have reviewed the different nuances of mitochondrial dysfunction and migraine. The different mtDNA polymorphisms that can affect the generation and transmission of nerve impulse has been highlighted and supported with research findings. In addition to this, the genetic basis of migraine pathogenesis as a consequence of mutations in nuclear DNA that can in turn affect the synthesis of defective mitochondrial proteins is discussed along with a brief overview of epigenetic profile. This review gives an overview of the pathophysiology of migraine and explores mitochondrial dysfunction as a potential underlying mechanism. Also, therapeutic supplements for managing migraine have been discussed at different junctures in this paper.

CGRP Administration Into the Cerebellum Evokes Light Aversion, Tactile Hypersensitivity, and Nociceptive Squint in Mice

The neuropeptide calcitonin gene-related peptide (CGRP) is a major player in migraine pathophysiology. Previous preclinical studies demonstrated that intracerebroventricular administration of CGRP caused migraine-like behaviors in mice, but the sites of action in the brain remain unidentified. The cerebellum has the most CGRP binding sites in the central nervous system and is increasingly recognized as both a sensory and motor integration center. The objective of this study was to test whether the cerebellum, particularly the medial cerebellar nuclei (MN), might be a site of CGRP action. In this study, CGRP was directly injected into the right MN of C57BL/6J mice via a cannula. A battery of tests was done to assess preclinical behaviors that are surrogates of migraine-like symptoms. CGRP caused light aversion measured as decreased time in the light zone even with dim light. The mice also spent more time resting in the dark zone, but not the light, along with decreased rearing and transitions between zones. These behaviors were similar for both sexes. Moreover, significant responses to CGRP were seen in the open field assay, von Frey test, and automated squint assay, indicating anxiety, tactile hypersensitivity, and spontaneous pain, respectively. Interestingly, CGRP injection caused significant anxiety and spontaneous pain responses only in female mice, and a more robust tactile hypersensitivity in female mice. No detectable effect of CGRP on gait was observed in either sex. These results suggest that CGRP injection in the MN causes light aversion accompanied by increased anxiety, tactile hypersensitivity, and spontaneous pain. A caveat is that we cannot exclude contributions from other cerebellar regions in addition to the MN due to diffusion of the injected peptide. These results reveal the cerebellum as a new site of CGRP actions that may contribute to migraine-like hypersensitivity.

Atogepant - an orally-administered CGRP antagonist - attenuates activation of meningeal nociceptors by CSD

BACKGROUND

This study investigated the mechanism of action of atogepant, a small-molecule CGRP receptor antagonist recently approved for the preventive treatment of episodic migraine, by assessing its effect on activation of mechanosensitive C- and Aδ-meningeal nociceptors following cortical spreading depression.

METHODS

Single-unit recordings of trigeminal ganglion neurons (32 Aδ and 20 C-fibers) innervating the dura was used to document effects of orally administered atogepant (5 mg/kg) or vehicle on cortical spreading depression-induced activation in anesthetized male rats.

RESULTS

Bayesian analysis of time effects found that atogepant did not completely prevent the activation of nociceptors at the tested dose, but it significantly reduced response amplitude and probability of response in both the C- and the Aδ-fibers at different time intervals following cortical spreading depression induction. For C-fibers, the reduction in responses was significant in the early phase (first hour), but not delayed phase of activation, whereas in Aδ-fibers, significant reduction in activation was apparent in the delayed phase (second and third hours) but not early phase of activation.

CONCLUSIONS

These findings identify differences between the actions of atogepant, a small molecule CGRP antagonist (partially inhibiting both Aδ and C-fibers) and those found previously for fremanezumab, a CGRP-targeted antibody (inhibiting Aδ fibers only) and onabotulinumtoxinA (inhibiting C-fibers only)- suggesting that these agents differ in their mechanisms for the preventive treatment of migraine.

Calcitonin gene-related peptide-induced hemodynamic changes in migraine with and without aura

OBJECTIVES

Exogenous calcitonin gene-related peptide (eCGRP) can induce CGRP-induced headaches (CGRP-IH) and aura in migraine with aura (MA). This implies a common pathophysiological mechanism of trigeminovascular sensitization (TVS) in migraine headaches and aura. The aim was to assess hemodynamic changes in cerebral circulation induced by eCGRP. We predicted that cerebral hemodynamic changes may differ between migraine without aura (MO) and MA.

MATERIALS AND METHODS

We included twenty participants with migraine, of whom 15 (75%) had MO, and 5 (25%) had MA. An intravenous infusion of eCGRP was administered. Polymodal recording of mean arterial velocity in MCA (vm MCA) and PCA (vm PCA), end-tidal carbon dioxide partial pressure (Et-CO₂ ), mean arterial pressure (MAP), and heart rate (HR) was employed using transcranial Doppler sonography (TCD). The parameters were determined at different time points with single responses vm MCA_tot , vm PCA_tot , Et-CO_2tot , MAP_tot , and HR_tot .

RESULTS

The CGRP-IH appeared in five participants with MA (100%) and in 11 participants with MO (73.3%) (p = .530). The difference of changes in vm MCA_tot (p = .014) and vm PCA_tot (p = .004) was significant, whereas in Et-CO_2tot (p = .658), MAP_tot (p = .392), and HR_tot (p = .686), it appeared to be non-significant. We found significant associations between vm MCA_tot and MA (p = .023; OR = 0.88; 95%C.I. 0.78-0.98), and vm PCA_tot and MA (p = .018; OR = 0.85; 95%C.I. 0.74-0.97).

CONCLUSIONS

Cerebral hemodynamics differs between MO and MA, indicating a pronounced vasodilatation and TVS in MA, which could induce aura.

CGRP and CGRP-receptor as targets of migraine therapy: Brain Prize-2021

BACKGROUND

Migraine is a highly prevalent primary headache with an unclear pathomechanism. During the last 40 years numerous hypotheses have arisen, among them the theory of the trigeminovascular system is the primary one. It serves as a skeleton in successful preclinical studies and in the development of effective therapeutic options for migraine headache.

OBJECTIVE

The Brain Prize (awarded annually by the Lundbeck Foundation) is the most prestigious tribute in neuroscience. The winners in 2021 were Lars Edvinsson, Peter Goadsby, Michael Moskowitz and Jes Olesen. They are the fathers of the migraine pathomechanism which led to revolutionary new treatments. This review summarizes their landmark findings.

METHODS

Data related to this topic were reviewed from PubMed records published between 1979 and May 2021. Searches were based on preclinical and clinical studies in the covered field. The findings were listed in chronological order. From a therapeutic perspective, only randomized controlled trials and meta-analysis were discussed.

RESULTS

The calcitonin gene-related peptide-related pathogenesis of migraine is based on the activation of the trigeminovascular system. The therapeutic triad for migraine is triptans, gepants and calcitonin gene-related peptide-targeted monoclonal antibodies.

CONCLUSION

In the past 40 years, the systematic work of leading headache scientists has resulted in robust theoretical and therapeutic knowledge in the preclinical and clinical study of migraine.

CGRP-dependent signalling pathways involved in mouse models of GTN- cilostazol- and levcromakalim-induced migraine

BACKGROUND

Knowledge of exact signalling events during migraine attacks is lacking. Various substances are known to trigger migraine attacks in patients and calcitonin gene-related peptide antagonising drugs are effective against migraine pain. Here, we investigated the signalling pathways involved in three different mouse models of provoked migraine and relate them to calcitonin gene-related peptide and other migraine-relevant targets.

METHODS

In vivo mouse models of glyceryl trinitrate-, cilostazol- and levcromakalim-induced migraine were applied utilising tactile sensitivity to von Frey filaments as measuring readout. Signalling pathways involved in the three models were dissected by use of specific knockout mice and chemical inhibitors. In vivo results were supported by ex vivo wire myograph experiments measuring arterial dilatory responses and ex vivo calcitonin gene-related peptide release from trigeminal ganglion and trigeminal nucleus caudalis from mice.

RESULTS

Glyceryl trinitrate-induced hypersensitivity was dependent on both prostaglandins and transient receptor potential cation channel, subfamily A, member 1, whereas cilostazol- and levcromakalim-induced hypersensitivity were independent of both. All three migraine triggers activated calcitonin gene-related peptide signalling, as both receptor antagonism and antibody neutralisation of calcitonin gene-related peptide were effective inhibitors of hypersensitivity in all three models. Stimulation of trigeminal ganglia and brain stem tissue samples with cilostazol and levcromakalim did not result in release of calcitonin gene-related peptide, and vasodilation following levcromakalim stimulation was independent of CGRP receptor antagonism.

CONCLUSION

The mouse models of glyceryl trinitrate-, cilostazol- and levcromakalim- induced migraine all involve calcitonin gene-related peptide signalling in a complex interplay between different cell/tissue types. These models are useful in the study of migraine mechanisms.

Selective targeting of peripheral cannabinoid receptors prevents behavioral symptoms and sensitization of trigeminal neurons in mouse models of migraine and medication overuse headache

ABSTRACT

Migraine affects ∼15% of the world's population greatly diminishing their quality of life. Current preventative treatments are effective in only a subset of migraine patients, and although cannabinoids seem beneficial in alleviating migraine symptoms, central nervous system side effects limit their widespread use. We developed peripherally restricted cannabinoids (PRCBs) that relieve chronic pain symptoms of cancer and neuropathies, without appreciable central nervous system side effects or tolerance development. Here, we determined PRCB effectiveness in alleviating hypersensitivity symptoms in mouse models of migraine and medication overuse headache. Long-term glyceryl trinitrate (GTN, 10 mg/kg) administration led to increased sensitivity to mechanical stimuli and increased expression of phosphorylated protein kinase A, neuronal nitric oxide synthase, and transient receptor potential ankyrin 1 proteins in trigeminal ganglia. Peripherally restricted cannabinoid pretreatment, but not posttreatment, prevented behavioral and biochemical correlates of GTN-induced sensitization. Low pH-activated and allyl isothiocyanate-activated currents in acutely isolated trigeminal neurons were reversibly attenuated by PRCB application. Long-term GTN treatment significantly enhanced these currents. Long-term sumatriptan treatment also led to the development of allodynia to mechanical and cold stimuli that was slowly reversible after sumatriptan discontinuation. Subsequent challenge with a previously ineffective low-dose GTN (0.1-0.3 mg/kg) revealed latent behavioral sensitization and increased expression of phosphorylated protein kinase A, neuronal nitric oxide synthase, and transient receptor potential ankyrin 1 proteins in trigeminal ganglia. Peripherally restricted cannabinoid pretreatment prevented all behavioral and biochemical correlates of allodynia and latent sensitization. Importantly, long-term PRCB treatment alone did not produce any behavioral or biochemical signs of sensitization. These data validate peripheral cannabinoid receptors as potential therapeutic targets in migraine and medication overuse headache.

Differential actions of indomethacin: clinical relevance in headache

ABSTRACT

Nonsteroidal anti-inflammatory drugs, cyclooxygenase inhibitors, are used routinely in the treatment of primary headache disorders. Indomethacin is unique in its use in the diagnosis and treatment of hemicrania continua and paroxysmal hemicrania. The mechanism of this specific action is not fully understood, although an interaction with nitric oxide (NO) signaling pathways has been suggested. Trigeminovascular neurons were activated by dural electrical stimulation, systemic administration of an NO donor, or local microiontophoresis of L-glutamate. Using electrophysiological techniques, we subsequently recorded the activation of trigeminovascular neurons and their responses to intravenous indomethacin, naproxen, and ibuprofen. Administration of indomethacin (5 mg·kg-1), ibuprofen (30 mg·kg-1), or naproxen (30 mg·kg-1) inhibited dural-evoked firing within the trigeminocervical complex with different temporal profiles. Similarly, both indomethacin and naproxen inhibited L-glutamate-evoked cell firing suggesting a common action. By contrast, only indomethacin was able to inhibit NO-induced firing. The differences in profile of effect of indomethacin may be fundamental to its ability to treat paroxysmal hemicrania and hemicrania continua. The data implicate NO-related signaling as a potential therapeutic approach to these disorders.

Pharmacokinetic comparative study of GAS with different concentration of tetramethylpyrazine and ferulic acid on liver-yang hyperactivity migraine model by blood-brain microdialysis method

Gastrodia elata and Ligusticum chuanxiong are used to treat primary headaches for many years. Gastrodin (GAS) and tetramethylpyrazine (TMP)/ferulic acid (FA) are the main active ingredients of Gastrodia elata and Ligusticum chuanxiong, respectively. Previous studies demonstrated the pharmacokinetics of GAS, TMP, and FA in the blood and brain interstitial fluids (BIF) in healthy animals but not in animal model with liver-yang hyperactivity migraine. Hence, this study examined the pharmacokinetics of GAS after its oral administration in the presence of different concentrations of TMP and FA in animals with liver-yang migraine hyperactivity. In the control group, GAS was administrated without TMP and FA. Pharmacokinetic parameters were determined using the blood-brain microdialysis in combination with the high-performance liquid chromatography method. Results revealed that the maximum drug concentrations (C_max) in the serum, area under curve (AUC), and mean residence time (MRT) of GAS decreased in normal animals, whereas C_max increased significantly in model animals. These findings indicate that varying concentrations of TMP and FA play an important role in the pharmacokinetics of GAS in both normal and migraine model animals, validating the utility of the ancient formulation.

Neurotransmitter and neuropeptide regulation of mast cell function: a systematic review

The existence of the neural control of mast cell functions has long been proposed. Mast cells (MCs) are localized in association with the peripheral nervous system (PNS) and the brain, where they are closely aligned, anatomically and functionally, with neurons and neuronal processes throughout the body. They express receptors for and are regulated by various neurotransmitters, neuropeptides, and other neuromodulators. Consequently, modulation provided by these neurotransmitters and neuromodulators allows neural control of MC functions and involvement in the pathogenesis of mast cell–related disease states. Recently, the roles of individual neurotransmitters and neuropeptides in regulating mast cell actions have been investigated extensively. This review offers a systematic review of recent advances in our understanding of the contributions of neurotransmitters and neuropeptides to mast cell activation and the pathological implications of this regulation on mast cell–related disease states, though the full extent to which such control influences health and disease is still unclear, and a complete understanding of the mechanisms underlying the control is lacking. Future validation of animal and in vitro models also is needed, which incorporates the integration of microenvironment-specific influences and the complex, multifaceted cross-talk between mast cells and various neural signals. Moreover, new biological agents directed against neurotransmitter receptors on mast cells that can be used for therapeutic intervention need to be more specific, which will reduce their ability to support inflammatory responses and enhance their potential roles in protecting against mast cell–related pathogenesis.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Receptor mechanisms mediating the anti-neuroinflammatory effects of endocannabinoid system modulation in a rat model of migraine

Calcitonin gene-related peptide (CGRP), substance P and dural mast cells are main contributors in neurogenic inflammation underlying migraine pathophysiology. Modulation of endocannabinoid system attenuates migraine pain, but its mechanisms of action remain unclear. We investigated receptor mechanisms mediating anti-neuroinflammatory effects of endocannabinoid system modulation in in vivo migraine model and ex vivo hemiskull preparations in rats. To induce acute model of migraine, a single dose of nitroglycerin was intraperitoneally administered to male rats. Moreover, isolated ex vivo rat hemiskulls were prepared to study CGRP and substance P release from meningeal trigeminal afferents. We used methanandamide (cannabinoid agonist), rimonabant (cannabinoid receptor-1 CB1 antagonist), SR144528 (CB2 antagonist) and capsazepine (transient receptor potential vanilloid-1 TRPV1 antagonist) to explore effects of endocannabinoid system modulation on the neurogenic inflammation, and possible involvement of CB1, CB2 and TRPV1 receptors during endocannabinoid effects. Methanandamide attenuated nitroglycerin-induced CGRP increments in in vivo plasma, trigeminal ganglia and brainstem and also in ex vivo hemiskull preparations. Methanandamide also alleviated enhanced number and degranulation of dural mast cells induced by nitroglycerin. Rimonabant, but not capsazepine or SR144528, reversed the attenuating effects of methanandamide on CGRP release in both in vivo and ex vivo experiments. Additionally, SR144528, but not rimonabant or capsazepine, reversed the attenuating effects of methanandamide on dural mast cells. However, neither nitroglycerin nor methanandamide changed substance P levels in both in vivo and ex vivo experiments. Methanandamide modulates CGRP release in migraine-related structures via CB1 receptors and inhibits the degranulation of dural mast cells through CB2 receptors. Selective ligands targeting CB1 and CB2 receptors may provide novel and effective treatment strategies against migraine.

Tibetan medicine Ru-yi-Zhen-bao Pills exhibits anti-migraine effect through mediating PAG anti-nociceptive channel

ETHNOPHARMACOLOGICAL RELEVANCE

Migraine is a disabling neurovascular disorder, which increases risk of cardiovascular events and is a social burden worldwide. The present first-line anti-migraine medications can cause overwhelming side-effects, of which one includes the onset of cardiovascular disease. As one of the marketed Tibetan drugs, Ru-yi-Zhen-bao Pills (RYZBP) have been clinically used to treat cardiovascular disorders and as anti-migraine medication. However, there is currently no research exploring the anti-migraine actions of RYZBP.

AIM OF THE STUDY

The current research was designed to assess the anti-migraine roles of RYZBP and explore the underlying mechanisms in a nitroglycerin (NTG)-induced migraine rat model trial.

MATERIALS AND METHODS

120 rats were randomly divided into the following six groups of 20 rats each: normal control group, model control group, positive control group, and RYZBP high/medium/low-dose groups (Ru-yi-Zhen-bao Pills; TH 1.00 g/kg, TM 0.50 g/kg and TL 0.25 g/kg). All rats were administered intragastrically for 7 consecutive days, which were subcutaneously injected with the NTG (10 mg/kg) after the last gavage (except in the normal control group). 3min after NTG treatment, 30 rats (5 rats from each group) were anesthetized and devoted to electroencephalogram(EEG) testing, which was used to evaluate the analgesic effect of RYZBP. One hour after NTG treatment, the rest of the 90 rats (15 rats from each group) were anesthetized and midbrain tissue sample was dissected. The dissection was then washed with physiological saline and collected. The histopathological changes in the periaqueductal gray(PAG) of 5 tissue samples were determined by aematoxylin-eosin (H&E) staining, as well as an estimation of substance P (SP) and neurokinin 1 receptor (NK1R) expression through immunohistochemically staining(IHC). Another 5 midbrain preparations were carried out to evaluate calcitonin gene-related peptide (CGRP), proenkephalin (PENK), SP, and cholecystokinin (CCK) expressions by real-time quantitative polymerase chain reaction (RT-qPCR). The rest of the 5 brainstem tissues were then used to measure CCK, CGRP, and opioid peptide receptor (DORR) levels by western blotting(WB).

RESULTS

In the EEG test, RYZBP (TM 0.50 g / kg) treatment transformed the EEG pain-wave of the NTG-induced migraine model rats in different time period. In the mechanism assay, compared with the model control group, RYZBP pretreatment reduced inflammatory cell infiltration, fibrosis and vacuolation of neuronal cells of PAG tissue seen by HE staining. IHC experiments further showed that RYZBPTM up-regulated SP expression levels and enhanced NK1R levels in the NTG-induced migraine rats (P < 0.05). Therapeutic administration of RYZBP also increased PENK mRNA expression and DORR protein level. Both RT-qPCR and western blotting trials indicated that RYZBP treatment significantly decreased CCK and CGRP expression levels (P < 0.01 or P < 0.05) in the NTG-induced migraine rats.

CONCLUSIONS

RYZBP has the potential to be an effective anti-migraine treatment through suppressing the EEG pain-wave, increasing the levels of SP, PENK, DORR and reducing expression of CCK and CGRP. Mediating the PAG anti-nociceptive channel and inhibiting central sensitization were the two potential mechanisms, which offers further evidence for clinical therapy.

Insulin-like growth factor-1 inhibits spreading depression-induced trigeminal calcitonin gene related peptide, oxidative stress & neuronal activation in rat

Migraineurs can show brain hyperexcitability and oxidative stress that may promote headache. Since hyperexcitability can enhance oxidative stress which promotes hyperexcitability, ending this feed-back loop may reduce migraine. Neocortical spreading depression, an animal model of migraine begins with hyperexcitability and triggers oxidative stress in the neocortical area involved and in the trigeminal system, which is important to pain pathway nociceptive activation in migraine. Additionally, oxidative stress causes increased trigeminal ganglion calcitonin gene-related peptide release and oxidative stress can reduce spreading depression threshold. Insulin-like growth factor-1 significantly protects against spreading depression in vitro by reducing oxidative stress and it is effective against spreading depression after intranasal delivery to animals. Here, we used adult male rats and extend this work to study the trigeminal system where insulin-like growth factor-1 receptors are highly expressed. Recurrent neocortical spreading depression significantly increased surrogate markers of trigeminal activation - immunostaining for trigeminal ganglion oxidative stress, calcitonin gene related peptide levels and c-fos in the trigeminocervical complex versus sham. These effects were significantly reduced by intranasal delivery of insulin-like growth factor-1 a day before recurrent neocortical spreading depression. Furthermore, intranasal treatment with insulin-like growth factor-1 significantly reduced naïve levels of trigeminal ganglion calcitonin gene related peptide versus sham with no impact on blood glucose levels. Intranasal delivery of insulin-like growth factor-1 not only mitigates neocortical spreading depression, a cause of migraine hyperexcitability modeled in animals, but also when neocortical spreading depression is triggered by supra-threshold stimuli, insulin-like growth factor-1 effectively reduces nociceptive activation in the trigeminal system.

Microglia P2X4R-BDNF signalling contributes to central sensitization in a recurrent nitroglycerin-induced chronic migraine model

Background

According to our previous study, microglia P2X4 receptors (P2X4Rs) play a pivotal role in the central sensitization of chronic migraine (CM). However, the molecular mechanism that underlies the crosstalk between microglia P2X4Rs and neurons of the trigeminal nucleus caudalis (TNC) is not fully understood. Therefore, the aim of this study is to examine the exact P2X4Rs signalling pathway in the development of central sensitization in a CM animal model.

Methods

We used an animal model with recurrent intermittent administration of nitroglycerin (NTG), which closely mimics CM. NTG-induced basal mechanical and thermal hypersensitivity were evaluated using a von Frey filament test and an increasing-temperature hot plate apparatus (IITC). We detected P2X4Rs, brain-derived neurotrophic factor (BDNF) and phosphorylated p38 mitogen-activated protein kinase (p-p38-MAPK) expression profiles in the TNC. We investigated the effects of a P2X4R inhibitor (5-BDBD) and an agonist (IVM) on NTG-induced hyperalgesia and neurochemical changes as well as on the expression of p-p38-MAPK and BDNF. We also detected the effects of a tropomyosin-related kinase B (TrkB) inhibitor (ANA-12) on the CM animal model in vivo. Then, we evaluated the effect of 5-BDBD and SB203580 (a p38-MAPK inhibitors) on the release and synthesis of BDNF in BV2 microglia cells treated with 50 μM adenosine triphosphate (ATP).

Results

Chronic intermittent administration of NTG resulted in chronic mechanical and thermal hyperalgesia, accompanied by the upregulation of P2X4Rs and BDNF expression. 5-BDBD or ANA-12 prevented hyperalgesia induced by NTG, which was associated with a significant inhibition of the NTG-induced increase in phosphorylated extracellular regulated protein kinases (p-ERK) and calcitonin gene related peptide (CGRP) release in the TNC. Repeated administration of IVM produced sustained hyperalgesia and significantly increased the levels of p-ERK and CGRP release in the TNC. Activating P2X4Rs with ATP triggered BDNF release and increased BDNF synthesis in BV2 microglia, and these results were then reduced by 5-BDBD or SB203580.

Conclusions

Our results indicated that the P2X4R contributes to the central sensitization of CM by releasing BDNF and promoting TNC neuronal hyper-excitability. Blocking microglia P2X4R-BDNF signalling may have an effect on the prevention of migraine chronification.

Auricular Electrical Stimulation Alleviates Headache through CGRP/COX-2/TRPV1/TRPA1 Signaling Pathways in a Nitroglycerin-Induced Migraine Rat Model

The study aimed to investigate effect of auricular electrical stimulation (ES) on migraine. Migraine was induced in rats by intraperitoneal administration of nitroglycerin (NTG, 10 mg/kg) three times. Auricular ES pretreatment was performed for five consecutive days. Migraine behaviors were observed by a video recording. Auricular ES pretreatment could reverse the decrease of the total time spent on exploratory (2619.0 ± 113.0 s vs 1581.7 ± 217.6 s, p=0.0029) and locomotor behaviors (271.3 ± 21.4 s vs 114.3 ± 19.7 s, p=0.0135) and also could reverse the increase of the total time spent on resting (19.0 ± 10.6 s vs 154.3 ± 46.5 s, p=0.0398) and grooming (369.9 ± 66.8 s vs 1302.0 ± 244.5 s, p=0.0324) behaviors. Auricular ES pretreatment could increase the frequency of rearing behaviors (38.0 ± 1.8 vs 7.7 ± 3.5, p < 0.0001) and total distance traveled (1372.0 ± 157.9 cm vs 285.3 ± 85.6 cm, p < 0.0001) and also could increase the percentage of inner zone time (6.0 ± 1.6% vs 0.4 ± 0.2%, p=0.0472). The CGRP, COX-2, TRPV1, and TRPA1 immunoreactive cells in the trigeminal ganglion increased in the NTG group compared with the control group (all p < 0.0001); this increase could, however, be reduced by auricular ES pretreatment (27.8 ± 2.6 vs 63.0 ± 4.2, p < 0.0001; 21.7 ± 1.2 vs 61.8 ± 4.0, p < 0.0001; 24.3 ± 1.0 vs 36.5 ± 1.7, p=0.0003; and 20.7 ± 1.9 vs 90.8 ± 6.5, p < 0.0001, respectively). Therefore, we suggest that auricular ES pretreatment is beneficial for the treatment of migraine and this effect is partly related to CGRP/COX-2/TRPV1/TRPA1 signaling pathways.

The Neuromodulatory Effects of ω-3 Fatty Acids and Nano-Curcumin on the COX-2/ iNOS Network in Migraines: A Clinical Trial Study from Gene Expression to Clinical Symptoms

Background:

Migraine is a common neuroinflammatory disorder characterized by recurrent attacks of pain. Human and experimental models of migraine studies have demonstrated the role played by COX-2/ iNOS in migraine’s neuroinflammatory pathogenesis. COX-2 and iNOS are closely linked and both contribute to inflammation and neurogenic pain in the central nervous system. Omega- 3 fatty acids and curcumin, an active polyphenol of turmeric, have anti-inflammatory and neuroprotective effects through several mechanisms, including the suppression of COX-2 and iNOS gene expression, as well as their serum levels. The aim of the present study is to evaluate the nutrigenomic effects of ω-3 fatty acids, nano-curcumin, and a combination of the two, on neuroinflammation and clinical symptoms in migraine patients.

Methods:

This study reports the results of a clinical trial over a 2-month period, involving 74 episodic migraine patients who received ω-3 fatty acids, nano-curcumin, a combination of them, or a placebo. At the start and end of the study, the expression of COX-2/iNOS (in peripheral mononuclear blood cells isolated from patients) and COX-2/iNOS serum levels were measured, using real-time PCR and ELISA respectively. The frequency, severity and duration of pain attacks were also recorded.

Results:

The results of the present trial showed that ω-3 fatty acids and nano-curcumin can reinforce each other’s effects in the downregulation of COX-2/iNOS mRNA, as well as reduce their serum levels. In addition, the combination of ω-3 and nano-curcumin significantly reduced the frequency, severity and duration of headaches (P<0.05).

Conclusion:

These findings indicate that combination therapy of ω-3 fatty acids and nano-curcumin can be considered as a promising new approach in migraine prevention.

Mast Cells in Gut and Brain and Their Potential Role as an Emerging Therapeutic Target for Neural Diseases

The mast cells (MCs) are the leader cells of inflammation. They are well known for their involvement on allergic reactions through degranulation and release of vasoactive, inflammatory, and nociceptive mediators. Upon encountering potential danger signal, MCs are true sensors of the environment, the first to respond in rapid and selective manner. The MC activates the algic response and modulates the evolution of nociceptive pain, typical of acute inflammation, to neuropathic pain, typical not only of chronic inflammation but also of the dysregulation of the pain system. Yet, MC may contribute to modulate intensity of the associated depressive and anxiogenic component on the neuronal and microglial biological front. Chronic inflammation is a common mediator of these co-morbidities. In parallel to the removal of the etiological factors of tissue damage, the modulation of MC hyperactivity and the reduction of the release of inflammatory factors may constitute a new frontier of pharmacological intervention aimed at preventing the chronicity of inflammation, the evolution of pain, and also the worsening of the depression and anxiogenic state associated with it. So, identifying specific molecules able to modify MC activity may be an important therapeutic tool. Various preclinical evidences suggest that the intestinal microbiota contributes substantially to mood and behavioral disorders. In humans, conditions of the microbiota have been linked to stress, anxiety, depression, and pain. MC is likely the crucial neuroimmune connecting between these components. In this review, the involvement of MCs in pain, stress, and depression is reviewed. We focus on the MC as target that may be mediating stress and mood disorders via microbiota-gut-brain axis.

TRPA1/NOX in the soma of trigeminal ganglion neurons mediates migraine-related pain of glyceryl trinitrate in mice

Glyceryl trinitrate is administered as a provocative test for migraine pain. Glyceryl trinitrate causes prolonged mechanical allodynia in rodents, which temporally correlates with delayed glyceryl trinitrate-evoked migraine attacks in patients. However, the underlying mechanism of the allodynia evoked by glyceryl trinitrate is unknown. The proalgesic transient receptor potential ankyrin 1 (TRPA1) channel, expressed by trigeminal nociceptors, is sensitive to oxidative stress and is targeted by nitric oxide or its by-products. Herein, we explored the role of TRPA1 in glyceryl trinitrate-evoked allodynia. Systemic administration of glyceryl trinitrate elicited in the mouse periorbital area an early and transient vasodilatation and a delayed and prolonged mechanical allodynia. The systemic, intrathecal or local administration of selective enzyme inhibitors revealed that nitric oxide, liberated from the parent drug by aldehyde dehydrogenase 2 (ALDH2), initiates but does not maintain allodynia. The central and the final phases of allodynia were respectively associated with generation of reactive oxygen and carbonyl species within the trigeminal ganglion. Allodynia was absent in TRPA1-deficient mice and was reversed by TRPA1 antagonists. Knockdown of neuronal TRPA1 by intrathecally administered antisense oligonucleotide and selective deletion of TRPA1 from sensory neurons in Advillin-Cre; Trpa1^fl/fl mice revealed that nitric oxide-dependent oxidative and carbonylic stress generation is due to TRPA1 stimulation, and resultant NADPH oxidase 1 (NOX1) and NOX2 activation in the soma of trigeminal ganglion neurons. Early periorbital vasodilatation evoked by glyceryl trinitrate was attenuated by ALDH2 inhibition but was unaffected by TRPA1 blockade. Antagonists of the calcitonin gene-related peptide receptor did not affect the vasodilatation but partially inhibited allodynia. Thus, although both periorbital allodynia and vasodilatation evoked by glyceryl trinitrate are initiated by nitric oxide, they are temporally and mechanistically distinct. While vasodilatation is due to a direct nitric oxide action in the vascular smooth muscle, allodynia is a neuronal phenomenon mediated by TRPA1 activation and ensuing oxidative stress. The autocrine pathway, sustained by TRPA1 and NOX1/2 within neuronal cell bodies of trigeminal ganglia, may sensitize meningeal nociceptors and second order trigeminal neurons to elicit periorbital allodynia, and could be of relevance for migraine-like headaches evoked by glyceryl trinitrate in humans.

Anti-Migraine Effect of the Herbal Combination of Chuanxiong Rhizoma and Cyperi Rhizoma and UPLC-MS/MS Method for the Simultaneous Quantification of the Active Constituents in Rat Serum and Cerebral Cortex

Chuanxiong Rhizoma and Cyperi Rhizoma (CRCR), an ancient and classic formula comprised of Chuanxiong Rhizoma and Cyperi Rhizoma in a weight ratio of 1:2, has long been used for curing migraine. This study aimed to explore their anti-migraine effect and active constituents. A nitroglycerin (NTG)-induced migraine model in rats was established to evaluate pharmacological effects. Cerebral blood flow was detected by a laser Doppler perfusion monitor. The levels of endothelin-1 (ET-1), γ-aminobutyric acid (GABA), nitric oxide synthase (NOS), nitric oxide (NO), 5-hydroxytryptamine (5-HT), 5-hydoxyindoleacetic acid (5-HIAA), calcitonin gene-related peptide (CGRP) and β-endorphin (β-EP) were quantified with enzyme-linked immunosorbent assay. CGRP and c-Fos mRNA expression were quantified with quantitative real-time polymerase chain reaction. A UPLC-MS/MS method was developed and validated for the simultaneous quantification of active constituents in rat serum and cerebral cortex. CRCR significantly increased cerebral blood flow, decreased the levels of ET-1, GABA and NOS, and increased the levels of 5-HT, 5-HIAA and β-EP in NTG-induced migraine rats. CGRP levels and CGRP mRNA expression, as well as c-Fos mRNA expression in the brainstem were markedly down-regulated with the treatment of CRCR. After oral administration of CRCR, ferulic acid (FA), senkyunolide A (SA), 3-n-butylphthalide (NBP), Z-ligustilide (LIG), Z-3-butylidenephthalide (BDPH), cyperotundone (CYT), nookatone (NKT) and α-cyperone (CYP) were qualified in rat serum and cerebral cortex. The above results suggested that CRCR showed powerfully therapeutic effects on migraine via increasing the cerebral blood flow, decreasing the expression of CGRP and c-Fos mRNA, and regulating the releasing of ET-1, GABA, NOS, 5-HT, 5-HIAA, CGRP and β-EP in the serum and brainstem, consequently relieving neurogenic inflammation. The active constituents in CRCR for treating migraine were FA, SA, NBP, LIG, BDPH, CYT, NKT and CYP. These findings contributed for the further use of CRCR as a combinational and complementary phytomedicine for migraine treatment.

CGRP and the Trigeminal System in Migraine

OBJECTIVE

The goal of this narrative review is to provide an overview of migraine pathophysiology, with an emphasis on the role of calcitonin gene-related peptide (CGRP) within the context of the trigeminovascular system.

BACKGROUND

Migraine is a prevalent and disabling neurological disease that is characterized in part by intense, throbbing, and unilateral headaches. Despite recent advances in understanding its pathophysiology, migraine still represents an unmet medical need, as it is often underrecognized and undertreated. Although CGRP has been known to play a pivotal role in migraine for the last 2 decades, this has now received more interest spurred by the early clinical successes of drugs that block CGRP signaling in the trigeminovascular system.

DESIGN

This narrative review presents an update on the role of CGRP within the trigeminovascular system. PubMed searches were used to find recent (ie, 2016 to November 2018) published articles presenting new study results. Review articles are also included not as primary references but to bring these to the attention of the reader. Original research is referenced in describing the core of the narrative, and review articles are used to support ancillary points.

RESULTS

The trigeminal ganglion neurons provide the connection between the periphery, stemming from the interface between the primary afferent fibers of the trigeminal ganglion and the meningeal vasculature and the central terminals in the trigeminal nucleus caudalis. The neuropeptide CGRP is abundant in trigeminal ganglion neurons, and is released from the peripheral nerve and central nerve terminals as well as being secreted within the trigeminal ganglion. Release of CGRP from the peripheral terminals initiates a cascade of events that include increased synthesis of nitric oxide and sensitization of the trigeminal nerves. Secreted CGRP in the trigeminal ganglion interacts with adjacent neurons and satellite glial cells to perpetuate peripheral sensitization, and can drive central sensitization of the second-order neurons. A shift in central sensitization from activity-dependent to activity-independent central sensitization may indicate a mechanism driving the progression of episodic migraine to chronic migraine. The pathophysiology of cluster headache is much more obscure than that of migraine, but emerging evidence suggests that it may also involve hypersensitivity of the trigeminovascular system. Ongoing clinical studies with therapies targeted at CGRP will provide additional, valuable insights into the pathophysiology of this disorder.

CONCLUSIONS

CGRP plays an essential role in the pathophysiology of migraine. Treatments that interfere with the functioning of CGRP in the peripheral trigeminal system are effective against migraine. Blocking sensitization of the trigeminal nerve by attenuating CGRP activity in the periphery may be sufficient to block a migraine attack. Additionally, the potential exists that this therapeutic strategy may also alleviate cluster headache as well.

Shared Fate of Meningeal Mast Cells and Sensory Neurons in Migraine

Migraine is a primary headache disorder which has complex neurogenic pathophysiological mechanisms still requiring full elucidation. The sensory nerves and meningeal mast cell couplings in the migraine target tissue are very effective interfaces between the central nervous system and the immune system. These couplings fall into three categories: intimacy, cross-talk and a shared fate. Acting as the immediate call-center of the neuroimmune system, mast cells play fundamental roles in migraine pathophysiology. Considerable evidence shows that neuroinflammation in the meninges is the key element resulting in the sensitization of trigeminal nociceptors. The successive events such as neuropeptide release, vasodilation, plasma protein extravasation, and mast cell degranulation that form the basic characteristics of the inflammation are believed to occur in this persistent pain state. In this regard, mast cells and sensory neurons represent both the target and source of the neuropeptides that play autocrine, paracrine, and neuro-endocrine roles during this inflammatory process. This review intends to contribute to a better understanding of the meningeal mast cell and sensory neuron bi-directional interactions from molecular, cellular, functional points of view. Considering the fact that mast cells play a sine qua non role in expanding the opportunities for targeted new migraine therapies, it is of crucial importance to explore these multi-faceted interactions.

Long-Term Depression Induced by Optogenetically Driven Nociceptive Inputs to Trigeminal Nucleus Caudalis or Headache Triggers

The peripheral trigeminovascular pathway mediates orofacial and craniofacial pain and projects centrally to the brainstem trigeminal nucleus caudalis (TNc). Sensitization of this pathway is involved in many pain conditions, but little is known about synaptic plasticity at its first central synapse. We have taken advantage of optogenetics to investigate plasticity selectively evoked at synapses of nociceptive primary afferents onto TNc neurons. Based on immunolabeling in the trigeminal ganglia, TRPV1-lineage neurons comprise primarily peptidergic and nonpeptidergic nociceptors. Optical stimulation of channelrhodopsin-expressing axons in the TRPV1/ChR2 mouse in TNc slices thus allowed us to activate a nociceptor-enriched subset of primary afferents. We recorded from lamina I/II neurons in acutely prepared transverse TNc slices, and alternately stimulated two independent afferent pathways, one with light-activated nociceptive afferents and the other with electrically-activated inputs. Low-frequency optical stimulation induced robust long-term depression (LTD) of optically-evoked EPSCs, but not of electrically-evoked EPSCs in the same neurons. Blocking NMDA receptors or nitric oxide synthase strongly attenuated LTD, whereas a cannabinoid receptor 1 antagonist had no effect. The neuropeptide PACAP-38 or the nitric oxide donors nitroglycerin or sodium nitroprusside are pharmacologic triggers of human headache. Bath application of any of these three compounds also persistently depressed optically-evoked EPSCs. Together, our data show that LTD of nociceptive afferent synapses on trigeminal nucleus neurons is elicited when the afferents are activated at frequencies consistent with the development of central sensitization of the trigeminovascular pathway.SIGNIFICANCE STATEMENT Animal models suggest that sensitization of trigeminovascular afferents plays a major role in craniofacial pain syndromes including primary headaches and trigeminal neuralgia, yet little is known about synaptic transmission and plasticity in the brainstem trigeminal nucleus caudalis (TNc). Here we used optogenetics to selectively drive a nociceptor-enriched population of trigeminal afferents while recording from superficial laminae neurons in the TNc. Low-frequency optical stimulation evoked robust long-term depression at TRPV1/ChR2 synapses. Moreover, application of three different headache trigger drugs also depressed TRPV1/ChR2 synapses. Synaptic depression at these primary afferent synapses may represent a newly identified mechanism contributing to central sensitization during headache.

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.

Neurogenic inflammation and its role in migraine

The etiology of migraine pain involves sensitized meningeal afferents that densely innervate the dural vasculature. These afferents, with their cell bodies located in the trigeminal ganglion, project to the nucleus caudalis, which in turn transmits signals to higher brain centers. Factors such as chronic stress, diet, hormonal fluctuations, or events like cortical spreading depression can generate a state of "sterile inflammation" in the intracranial meninges resulting in the sensitization and activation of trigeminal meningeal nociceptors. This sterile inflammatory phenotype also referred to as neurogenic inflammation is characterized by the release of neuropeptides (such as substance P, calcitonin gene related peptide) from the trigeminal innervation. This release leads to vasodilation, plasma extravasation secondary to capillary leakage, edema, and mast cell degranulation. Although neurogenic inflammation has been observed and extensively studied in peripheral tissues, its role has been primarily investigated in the genesis and maintenance of migraine pain. While some aspects of neurogenic inflammation has been disregarded in the occurrence of migraine pain, targeted analysis of factors have opened up the possibilities of a dialogue between the neurons and immune cells in driving such a sterile neuroinflammatory state in migraine pathophysiology.

Endocannabinoid System and Migraine Pain: An Update

The trigeminovascular system (TS) activation and the vasoactive release from trigeminal endings, in proximity of the meningeal vessels, are considered two of the main effector mechanisms of migraine attacks. Several other structures and mediators are involved, however, both upstream and alongside the TS. Among these, the endocannabinoid system (ES) has recently attracted considerable attention. Experimental and clinical data suggest indeed a link between dysregulation of this signaling complex and migraine headache. Clinical observations, in particular, show that the levels of anandamide (AEA)—one of the two primary endocannabinoid lipids—are reduced in cerebrospinal fluid and plasma of patients with chronic migraine (CM), and that this reduction is associated with pain facilitation in the spinal cord. AEA is produced on demand during inflammatory conditions and exerts most of its effects by acting on cannabinoid (CB) receptors. AEA is rapidly degraded by fatty acid amide hydrolase (FAAH) enzyme and its levels can be modulated in the peripheral and central nervous system (CNS) by FAAH inhibitors. Inhibition of AEA degradation via FAAH is a promising therapeutic target for migraine pain, since it is presumably associated to an increased availability of the endocannabinoid, specifically at the site where its formation is stimulated (e.g., trigeminal ganglion and/or meninges), thus prolonging its action.

Salmon calcitonin ameliorates migraine pain through modulation of CGRP release and dural mast cell degranulation in rats

The exact mechanism of migraine pathophysiology still remains unclear due to the complex nature of migraine pain. Salmon calcitonin (SC) exhibits antinociceptive effects in the treatment of various pain conditions. In this study, we explored the mechanisms underlying the analgesic effect of salmon calcitonin on migrane pain using glyceryltrinitrate (GTN)-induced model of migraine and ex vivo meningeal preparations in rats. Rats were intraperitoneally administered saline, GTN (10 mg/kg), vehicle, saline + GTN, SC (50 μg/kg) + GTN, and SC alone. Also, ex vivo meningeal preparations were applied topically 100 μmol/L GTN, 50 μmol/L SC, and SC + GTN. Calcitonin gene-related peptide (CGRP) contents of plasma, trigeminal neurons and superfusates were measured using enzyme-immunoassays. Dural mast cells were stained with toluidine blue. c-fos neuronal activity in trigeminal nucleus caudalis (TNC) sections were determined by immunohistochemical staining. The results showed that GTN triggered the increase in CGRP levels in plasma, trigeminal ganglion neurons and ex vivo meningeal preparations. Likewise, GTN-induced c-fos expression in TNC. In in vivo experiments, GTN caused dural mast cell degranulation, but similar effects were not seen in ex vivo experiments. Salmon calcitonin administration ameliorated GTN-induced migraine pain by reversing the increases induced by GTN. Our findings suggested that salmon calcitonin could alleviate the migraine-like pain by modulating CGRP release at different levels including the generation and conduction sites of migraine pain and mast cell behaviour in the dura mater. Therefore salmon calcitonin may be a new therapeutic choice in migraine pain relief.

Pathways of CGRP Release from Primary Sensory Neurons

The benefit reported in a variety of clinical trials by a series of small molecule antagonists for the calcitonin gene-related peptide (CGRP) receptor, or four monoclonal antibodies against the neuropeptide or its receptor, has underscored the release of CGRP from terminals of primary sensory neurons, including trigeminal neurons, as one of the major mechanisms of migraine headaches. A large variety of excitatory ion channels and receptors have been reported to elicit CGRP release, thus proposing these agonists as migraine-provoking agents. On the other side, activators of inhibitory channels and receptors may be regarded as potential antimigraine agents. The knowledge of the intracellular pathways underlying the exocytotic process that results in CGRP secretion or its inhibition is, therefore, of importance for understanding how migraine pain originates and how to treat the disease.

Soluble guanylyl cyclase is a critical regulator of migraine-associated pain

Background Nitric oxide (NO) has been heavily implicated in migraine. Nitroglycerin is a prototypic NO-donor, and triggers migraine in humans. However, nitroglycerin also induces oxidative/nitrosative stress and is a source of peroxynitrite - factors previously linked with migraine etiology. Soluble guanylyl cyclase (sGC) is the high affinity NO receptor in the body, and the aim of this study was to identify the precise role of sGC in acute and chronic migraine. Methods We developed a novel brain-bioavailable sGC stimulator (VL-102), and tested its hyperalgesic properties in mice. We also determined the effect of VL-102 on c-fos and calcitonin gene related peptide (CGRP) immunoreactivity within the trigeminovascular complex. In addition, we also tested the known sGC inhibitor, ODQ, within the chronic nitroglycerin migraine model. Results VL-102-evoked acute and chronic mechanical cephalic and hind-paw allodynia in a dose-dependent manner, which was blocked by the migraine medications sumatriptan, propranolol, and topiramate. In addition, VL-102 also increased c-fos and CGRP expressing cells within the trigeminovascular complex. Importantly, ODQ completely inhibited acute and chronic hyperalgesia induced by nitroglycerin. ODQ also blocked hyperalgesia already established by chronic nitroglycerin, implicating this pathway in migraine chronicity. Conclusions These results indicate that nitroglycerin causes migraine-related pain through stimulation of the sGC pathway, and that super-activation of this receptor may be an important component for the maintenance of chronic migraine. This work opens the possibility for negative sGC modulators as novel migraine therapies.

Recurrent administration of the nitric oxide donor, isosorbide dinitrate, induces a persistent cephalic cutaneous hypersensitivity: A model for migraine progression

Background

A subgroup of migraineurs experience an increase in attack frequency leading to chronic migraine.

Methods

We assessed in rats the roles of dose and repeat administration of systemic isosorbide dinitrate (ISDN), a nitric oxide donor, on the occurrence and development of cephalic/face and extracephalic/hindpaw mechanical allodynia as a surrogate of migraine pain, and the effect of acute systemic sumatriptan and olcegepant and chronic systemic propranolol on these behavioral changes.

Results

A single high (H-ISDN) but not low (L-ISDN) dose of ISDN induces a reversible cephalic and extracephalic mechanical allodynia. However, with repeat administration, L-ISDN produces reversible cephalic but never extracephalic allodynia, whereas H-ISDN induces cephalic and extracephalic allodynia that are both potentiated. H-ISDN-induced cephalic allodynia thus gains persistency. Sumatriptan and olcegepant block single H-ISDN-induced behavioral changes, but only olcegepant reduces these acute changes when potentiated by repeat administration. Neither sumatriptan nor olcegepant prevent chronic cephalic hypersensitivity. Conversely, propranolol blocks repeat H-ISDN-induced chronic, but not acute, behavioral changes.

Conclusions

Repeated ISDN administration appears to be a naturalistic rat model for migraine progression, suitable for screening acute and preventive migraine therapies. It suggests frequent and severe migraine attacks associated with allodynia may be a risk factor for disease progression.

Animal models of pain and migraine in drug discovery

Preclinical research activities in relation to pain typically involve the 'holy trinity' of nociceptive, inflammatory and neuropathic pain for purposes of target validation and defining target product profiles of novel analgesic compounds. For some reason it seems that headache or migraine are rarely considered as additional entities to explore. Frontline medications used in the treatment of, for example, inflammatory pain, neuropathic pain and migraine (NSAIDs versus pregabalin/duloxetine versus triptans) reveal distinct differences in pathophysiology that partially explain this approach. Nevertheless, for many patients enduring chronic pain, regardless of aetiology, high unmet needs remain. By focusing more on commonalities shared between neuropathic pain and headache disorders such as migraine, drug discovery efforts could be spread more efficiently across a larger indication area. Here, some of the most commonly used models and methods employed within 'pain and migraine' drug development will be presented. Recent advances within these disciplines suggest that, with the addition of a few extra carefully chosen ancillary models and/or endpoints, the relative value in terms of resources used, reciprocal flow of information and net worth of a 'typical' package could be increased substantially for the pain and migraine fields.

Effects of kynurenic acid analogue 1 (KYNA-A1) in nitroglycerin-induced hyperalgesia: Targets and anti-migraine mechanisms

Background Trigeminal sensitization represents a major mechanism underlying migraine attacks and their recurrence. Nitroglycerin (NTG) administration provokes spontaneous migraine-like headaches and in rat, an increased sensitivity to the formalin test. Kynurenic acid (KYNA), an endogenous regulator of glutamate activity and its analogues attenuate NTG-induced neuronal activation in the nucleus trigeminalis caudalis (NTC). The anti-hyperalgesic effect of KYNA analogue 1 (KYNA-A1) was investigated on animal models specific for migraine pain. Aim Rats made hyperalgesic by NTG administration underwent the plantar or orofacial formalin tests. The effect of KYNA-A1 was evaluated in terms of nocifensive behavior and of neuronal nitric oxide synthase (nNOS), calcitonin gene-related peptide (CGRP) and cytokines expression in areas involved in trigeminal nociception. Results KYNA-A1 abolished NTG-induced hyperalgesia in both pain models; NTG alone or associated to formalin injection induced an increased mRNA expression of CGRP, nNOS and cytokines in the trigeminal ganglia and central areas, which was reduced by KYNA-A1. Additionally, NTG caused a significant increase in nNOS immunoreactivity in the NTC, which was prevented by KYNA-A1. Conclusion Glutamate activity is likely involved in mediating hyperalgesia in an animal model specific for migraine. Its inhibition by means of a KYNA analogue modulates nNOS, CGRP and cytokines expression at peripheral and central levels.

Understanding migraine: Potential role of neurogenic inflammation

Neurogenic inflammation, a well-defined pathophysiologial process is characterized by the release of potent vasoactive neuropeptides, predominantly calcitonin gene-related peptide (CGRP), substance P (SP), and neurokinin A from activated peripheral nociceptive sensory nerve terminals (usually C and A delta-fibers). These peptides lead to a cascade of inflammatory tissue responses including arteriolar vasodilation, plasma protein extravasation, and degranulation of mast cells in their peripheral target tissue. Neurogenic inflammatory processes have long been implicated as a possible mechanism involved in the pathophysiology of various human diseases of the nervous system, respiratory system, gastrointestinal tract, urogenital tract, and skin. The recent development of several innovative experimental migraine models has provided evidence suggestive of the involvement of neuropeptides (SP, neurokinin A, and CGRP) in migraine headache. Antidromic stimulation of nociceptive fibers of the trigeminal nerve resulted in a neurogenic inflammatory response with marked increase in plasma protein extravasation from dural blood vessels by the release of various sensory neuropeptides. Several clinically effective abortive antimigraine medications, such as ergots and triptans, have been shown to attenuate the release of neuropeptide and neurogenic plasma protein extravasation. These findings provide support for the validity of using animal models to investigate mechanisms of neurogenic inflammation in migraine. These also further strengthen the notion of migraine being a neuroinflammatory disease. In the clinical context, there is a paucity of knowledge and awareness among physicians regarding the role of neurogenic inflammation in migraine. Improved understanding of the molecular biology, pharmacology, and pathophysiology of neurogenic inflammation may provide the practitioner the context-specific feedback to identify the novel and most effective therapeutic approach to treatment. With this objective, the present review summarizes the evidence supporting the involvement of neurogenic inflammation and neuropeptides in the pathophysiology and pharmacology of migraine headache as well as its potential significance in better tailoring therapeutic interventions in migraine or other neurological disorders. In addition, we have briefly highlighted the pathophysiological role of neurogenic inflammation in various other neurological disorders.

RNA Sequencing of Trigeminal Ganglia in Rattus Norvegicus after Glyceryl Trinitrate Infusion with Relevance to Migraine

INTRODUCTION

Infusion of glyceryl trinitrate (GTN), a donor of nitric oxide, induces immediate headache in humans that in migraineurs is followed by a delayed migraine attack. In order to achieve increased knowledge of mechanisms activated during GTN-infusion this present study aims to investigate transcriptional responses to GTN-infusion in the rat trigeminal ganglia.

METHODS

Rats were infused with GTN or vehicle and trigeminal ganglia were isolated either 30 or 90 minutes post infusion. RNA sequencing was used to investigate transcriptomic changes in response to the treatment. Furthermore, we developed a novel method for Gene Set Analysis Of Variance (GSANOVA) to identify gene sets associated with transcriptional changes across time.

RESULTS

15 genes displayed significant changes in transcription levels in response to GTN-infusion. Ten of these genes showed either sustained up- or down-regulation in the 90-minute period after infusion. The GSANOVA analysis demonstrate enrichment of pathways pointing towards an increase in immune response, signal transduction, and neuroplasticity in response to GTN-infusion. Future functional in-depth studies of these mechanisms are expected to increase our understanding of migraine pathogenesis.

Prevention of stress- or nitric oxide donor-induced medication overuse headache by a calcitonin gene-related peptide antibody in rodents

Objective The objective of this study was the determination of the role of calcitonin gene-related peptide (CGRP) in the induction of medication overuse headache (MOH)-related migraine in an injury-free preclinical model. Methods Rats were primed by a 7-day period of exposure to acute migraine therapies including sumatriptan and morphine. After an additional 14-day drug-free period, rats were exposed to putative migraine triggers including bright light stress (BLS) or nitric oxide (NO) donor in the presence or absence of TEV48125, a fully humanized CGRP antibody. Cutaneous allodynia (CA) was used as an outcome measure and CGRP blood and cerebrospinal fluid (CSF) levels were measured. Results BLS and NO donor challenge evoked delayed, long-lasting CA selectively in rats that were previously treated with sumatriptan or morphine. BLS produced a significant increase in CGRP in the plasma, but not CSF, in animals that were previously exposed to sumatriptan compared to saline controls. TEV48125 did not modify baseline tactile thresholds or produce behavioral side effects, but significantly inhibited both BLS- and NO donor-induced CA in animals that were previously primed with sumatriptan or morphine; an isotype control protein that does not bind CGRP had no effect. Interpretation These data suggest that acute migraine medications may promote MOH in susceptible individuals through CGRP-dependent mechanisms and that anti-CGRP antibodies may be a useful clinical strategy for the treatment of MOH.

Brain natriuretic peptide constitutively downregulates P2X3 receptors by controlling their phosphorylation state and membrane localization

BACKGROUND

ATP-gated P2X3 receptors are important transducers of nociceptive stimuli and are almost exclusively expressed by sensory ganglion neurons. In mouse trigeminal ganglion (TG), P2X3 receptor function is unexpectedly enhanced by pharmacological block of natriuretic peptide receptor-A (NPR-A), outlining a potential inhibitory role of endogenous natriuretic peptides in nociception mediated by P2X3 receptors. Lack of change in P2X3 protein expression indicates a complex modulation whose mechanisms for downregulating P2X3 receptor function remain unclear.

RESULTS

To clarify this process in mouse TG cultures, we suppressed NPR-A signaling with either siRNA of the endogenous agonist BNP, or the NPR-A blocker anantin. Thus, we investigated changes in P2X3 receptor distribution in the lipid raft membrane compartment, their phosphorylation state, as well as their function with patch clamping. Delayed onset of P2X3 desensitization was one mechanism for the anantin-induced enhancement of P2X3 activity. Anantin application caused preferential P2X3 receptor redistribution to the lipid raft compartment and decreased P2X3 serine phosphorylation, two phenomena that were not interdependent. An inhibitor of cGMP-dependent protein kinase and siRNA-mediated knockdown of BNP mimicked the effect of anantin.

CONCLUSIONS

We demonstrated that in mouse trigeminal neurons endogenous BNP acts on NPR-A receptors to determine constitutive depression of P2X3 receptor function. Tonic inhibition of P2X3 receptor activity by BNP/NPR-A/PKG pathways occurs via two distinct mechanisms: P2X3 serine phosphorylation and receptor redistribution to non-raft membrane compartments. This novel mechanism of receptor control might be a target for future studies aiming at decreasing dysregulated P2X3 receptor activity in chronic pain.

Utility of different outcome measures for the nitroglycerin model of migraine in mice

INTRODUCTION

Majority of the work for establishing nitroglycerin (NTG)-induced migraine models in animals was done in rats, though recently some studies in mice were also reported. Different special formulations of NTG were investigated in various studies; however, NTG treated groups were often compared to simple saline treated control groups. The aim of the present studies was to critically assess the utility of a panel of potential outcome measures in mice by revisiting previous findings and investigating endpoints that have not been tested in mice yet.

METHODS

We investigated two NTG formulations, Nitrolingual and Nitro Pohl, at an intraperitoneal dose of 10mg/kg, in comparison with relevant vehicle controls, and evaluated the following outcome measures: light aversive behaviour, cranial blood perfusion by laser Doppler imaging, number of c-Fos- and neuronal nitrogen monoxide synthase (nNOS)-immunoreactive neurons in the trigeminal nucleus caudalis (TNC) and trigeminal ganglia, thermal hyperalgesia and tactile allodynia of the hind paw and orofacial pain hypersensitivity.

RESULTS

We could not confirm previous reports of significant NTG-induced changes in light aversion and cranial blood perfusion of mice but we observed considerable effects elicited by the vehicle of Nitrolingual. In contrast, the vehicle of Nitro Pohl was apparently inert. Increased c-Fos expression in the TNC, thermal hyperalgesia, tactile allodynia and orofacial hypersensitivity were apparently good endpoints in mice that were increased by NTG-administration. The NTG-induced increase in c-Fos expression was prevented by topiramate but not by sumatriptan treatment. However, the NTG-induced orofacial hypersensitivity was dose dependently attenuated by sumatriptan.

DISCUSSION

Our results pointed to utilisable NTG formulations and outcome measures for NTG-induced migraine models in mice. Pending further cross-validation with positive and negative control drugs in these mouse models and in the human NTG models of migraine, these tests might be valuable translational research tools for development of new anti-migraine drugs.

Neuronal Nitric Oxide Synthase (nNOS, NOS1) rs693534 and rs7977109 Variants and Risk for Migraine

BACKGROUND/OBJECTIVES

Many biochemical, pharmacological, neuropathological, and experimental data suggest a possible role of nitric oxide in the pathogenesis of migraine. We investigated the possible association between functional single nucleotide polymorphisms (SNPs) in the neuronal nitric oxide synthase gene (NOS1 or nNOS; chromosome 12q24.22) and the risk for migraine.

METHODS

We studied the frequency of the of rs7977109 and rs693534 genotypes and allelic variants in 197 patients with migraine and 308 healthy controls using a TaqMan-based qPCR assay. As a secondary analysis, we studied the possible influence of gender, age at onset of migraine, positive family history of migraine, and presence or absence of aura on the genotypes frequency.

RESULTS

The frequencies of rs7977109 and rs693534 genotypes and allelic variants were not associated with the risk for migraine with OR for minor alleles = 0.94 (95% CI 0.72-1.23) and = 0.88 (0.68-1.15), respectively, and the lack of association was not influenced by gender, age at onset of migraine, positive family history of migraine, and presence or absence of aura.

CONCLUSION

NOS1 rs7977109 and rs693534 genotypes and allelic variants are not associated with the risk for migraine in Caucasian Spanish people.

Evaluation of ADMA-DDAH-NOS axis in specific brain areas following nitroglycerin administration: study in an animal model of migraine

BACKGROUND

Nitric oxide (NO) is known to play a key role in migraine pathogenesis, but modulation of NO synthesis has failed so far to show efficacy in migraine treatment. Asymmetric dimethylarginine (ADMA) is a NO synthase (NOS) inhibitor, whose levels are regulated by dimethylarginine dimethylaminohydrolase (DDAH). Systemic administration of nitroglycerin (or glyceryl trinitrate, GTN) is a NO donor that consistently induces spontaneous-like headache attacks in migraneurs. GTN administration induces an increase in neuronal NOS (nNOS) that is simultaneous with a hyperalgesic condition. GTN administration has been used for years as an experimental animal model of migraine. In order to gain further insights in the precise mechanisms involved in the relationships between NO synthesis and migraine, we analyzed changes induced by GTN administration in ADMA levels, DDHA-1 mRNA expression and the expression of neuronal and endothelial NOS (nNOS and eNOS) in the brain. We also evaluated ADMA levels in the serum.

METHODS

Male Sprague-Dawley rats were injected with GTN (10 mg/kg, i.p.) or vehicle and sacrificed 4 h later. Brain areas known to be activated by GTN administration were dissected out and utilized for the evaluation of nNOS and eNOS expression by means of western blotting. Cerebral and serum ADMA levels were measured by means of ELISA immunoassay. Cerebral DDAH-1 mRNA expression was measured by means of RT-PCR. Comparisons between experimental groups were performed using the Mann Whitney test.

RESULTS

ADMA levels and nNOS expression increased in the hypothalamus and medulla following GTN administration. Conversely, a significant decrease in DDAH-1 mRNA expression was observed in the same areas. By contrast, no significant change was reported in eNOS expression. GTN administration did not induce any significant change in serum levels of ADMA.

CONCLUSION

The present data suggest that ADMA accumulates in the brain after GTN administration via the inhibition of DDAH-1. This latter may represent a compensatory response to the excessive local availability of NO, released directly by GTN or synthetized by nNOS. These findings prompt an additional mediator (ADMA) in the modulation of NO axis following GTN administration and offer new insights in the pathophysiology of migraine.