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

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.

The transition of medication overuse status by acute medication categories in episodic or chronic migraine patients to non-overuse status after receiving anti-CGRP monoclonal antibodies: a systematic review and meta-analysis of phase 3 randomized control trial

OBJECTIVE

The objective of this systematic review and meta-analysis was to determine whether patients with episodic (EM) or chronic migraine (CM), who were treated with anti-CGRP antibodies, showed a reversal from medication overuse (MO) or medication overuse headache (MOH) status at their baseline to non-overuse status. Furthermore, this study aimed to establish which acute headache medication (AHM) categories responded more effectively to anti-CGRP antibodies.

METHODS

A systematic search was conducted in the PubMed database for relevant studies from January 2013 to September 2023. We included phase three randomized controlled trials to examine the role of anti-CGRP antibodies in patients with EM or CM and their MO status. A meta-analysis was conducted to find the association between anti-CGRP antibodies and the number of EM and CM patients with MO or MOH at baseline that reverted to non-MO status or below the MOH threshold.

RESULTS

The initial search yielded a total of 345 studies. After removing duplicates and screening with inclusion criteria, 5 studies fulfilled our conditions. Each study reviewed the response to changes in the MO status of patients after receiving anti-CGRP antibodies, including eptinezumab, fremanezumab, galcanezumab, and erenumab, compared to placebo. Our study analyzed three AHM categories: triptans, simple analgesics, and multiple drugs. The overall relative risk (RR) was 1.44 (95% CI, 1.31 to 1.59; p < 0.001). The RRs for triptans, simple analgesics, and multi-drug groups were 1.71 (95% CI, 1.53 to 1.91; p < 0.001), 1.10 (95% CI, 0.83 to 1.47; p = 0.5), and 1.29 (95%CI 1.14 to 1.46; p < 0.001) respectively.

CONCLUSION

The meta-analysis has shown that anti-CGRP antibodies were statistically significant in transitioning from MO or MOH status to non-MO status or below the MOH threshold (RR = 1.44) for all included studies and all AHM categories except for simple analgesics. Patients from the triptan group had the highest RR of 1.71 with a p-value < 0.001, while the simple analgesics group had an RR of 1.10, however, with a p-value > 0.05. Interestingly, this analysis can be interpreted as that anti-CGRP antibodies might not be effective in reducing simple analgesics use in EM or CM patients. Further studies are needed to investigate these matters.

D2 dopamine receptor-mediated mechanisms of dopaminergic system modulation in in vivo and in vitro experimental models of migraine

The dopaminergic system is implicated in the pathophysiology of migraine. However, the underlying mechanisms remain unclear. We explored the effects and mechanisms of dopaminergic system modulation in the in vivo and in vitro rat models of migraine. Dopaminergic agonist apomorphine, D2 receptor antagonists metoclopramide and haloperidol and 5-HT3 receptor antagonist ondansetron alone and together were tested in nitroglycerin-induced migraine model, in vivo. Likewise, the combinations of drugs were also tested on basal calcitonin gene-related peptide (CGRP) release in vitro hemiskull preparations. Mechanical allodynia was tested by von Frey filaments. CGRP concentrations in trigeminovascular structures and in vitro superfusates and c-Fos levels in the brainstem were determined by enzyme-linked immunosorbent assay. Meningeal mast cells were evaluated with toluidine blue staining. Apomorphine further enhanced nitroglycerin-induced mechanical allodynia, brainstem c-fos expression, trigeminal ganglion and brainstem CGRP concentrations and meningeal mast cell degranulation, in vivo. Haloperidol completely antagonised all apomorphine-induced effects and also alleviated changes induced by nitroglycerin without apomorphine. Metoclopramide and ondansetron partially attenuated apomorphine- or nitroglycerin-induced effects. A combination of haloperidol and ondansetron decreased basal CGRP release, in vitro, whereas the other administrations were ineffective. Apomorphine-mediated dopaminergic activation exacerbated nitroglycerin-stimulated nociceptive reactions by further enhancing c-fos expression, CGRP release and mast cell degranulation in strategical structures associated with migraine pain. Metoclopramide partially attenuated the effects of apomorphine, most likely because it is also a 5-HT3 receptor antagonist. Haloperidol with pure D2 receptor antagonism feature appears to be more effective than metoclopramide in reducing migraine-related parameters in dopaminergic activation- and/or NTG-induced migraine-like conditions.

Potent dual MAGL/FAAH inhibitor AKU-005 engages endocannabinoids to diminish meningeal nociception implicated in migraine pain

BACKGROUND

Engaging the endocannabinoid system through inhibition of monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), degrading endocannabinoids (endoCBs) 2-arachidonoylglycerol (2-AG) and anandamide (AEA), was proposed as a promising approach to ameliorate migraine pain. However, the activity of MAGL and FAAH and action of endoCB on spiking activity of meningeal afferents, from which migraine pain originates, has not been explored thus far. Therefore, we here explored the analgesic effects of endoCB enhancement in rat and human meningeal tissues.

METHODS

Both MAGL and FAAH activity and local 2-AG and AEA levels were measured by activity-based protein profiling (ABPP) and LC-MS/MS, respectively, in rat meninges obtained from hemiskulls of P38-P40 Wistar rats and human meninges from elderly patients undergoing non-migraine related neurosurgery. The action on endoCBs upon administration of novel dual MAGL/FAAH inhibitor AKU-005 on meningeal afferents excitability was tested by investigating paired KCl-induced spiking and validation with local (co-)application of either AEA or 2-AG. Finally, the specific TRPV1 agonist capsaicin and blocker capsazepine were tested.

RESULTS

The basal level of 2-AG exceeded that of AEA in rat and human meninges. KCl-induced depolarization doubled the level of AEA. AKU-005 slightly increased spontaneous spiking activity whereas the dual MAGL/FAAH inhibitor significantly decreased excitation of nerve fibres induced by KCl. Similar inhibitory effects on meningeal afferents were observed with local applications of 2-AG or AEA. The action of AKU-005 was reversed by CB1 antagonist AM-251, implying CB1 receptor involvement in the anti-nociceptive effect. The inhibitory action of AEA was also reversed by AM-251, but not with the TRPV1 antagonist capsazepine. Data cluster analysis revealed that both AKU-005 and AEA largely increased long-term depression-like meningeal spiking activity upon paired KCl-induced spiking.

CONCLUSIONS

In the meninges, high anti-nociceptive 2-AG levels can tonically counteract meningeal signalling, whereas AEA can be engaged on demand by local depolarization. AEA-mediated anti-nociceptive effects through CB1 receptors have therapeutic potential. Together with previously detected MAGL activity in trigeminal ganglia, dual MAGL/FAAH inhibitor AKU-005 appears promising as migraine treatment.

Biomarkers of Migraine: An Integrated Evaluation of Preclinical and Clinical Findings

In recent years, numerous efforts have been made to identify reliable biomarkers useful in migraine diagnosis and progression or associated with the response to a specific treatment. The purpose of this review is to summarize the alleged diagnostic and therapeutic migraine biomarkers found in biofluids and to discuss their role in the pathogenesis of the disease. We included the most informative data from clinical or preclinical studies, with a particular emphasis on calcitonin gene-related peptide (CGRP), cytokines, endocannabinoids, and other biomolecules, the majority of which are related to the inflammatory aspects and mechanisms of migraine, as well as other actors that play a role in the disease. The potential issues affecting biomarker analysis are also discussed, such as how to deal with bias and confounding data. CGRP and other biological factors associated with the trigeminovascular system may offer intriguing and novel precision medicine opportunities, although the biological stability of the samples used, as well as the effects of the confounding role of age, gender, diet, and metabolic factors should be considered.

Esculetin alleviates pentylenetetrazole-induced seizures, cognitive impairment and pro-inflammatory cytokines and suppresses penicillin-induced epileptiform activity in rats

AIMS

To investigate the effects of different doses of esculetin on epileptiform activity, behavioral seizures, memory impairment, and cortical and hippocampal NF-κB, as a mediator of pro-inflammatory gene induction, and pro-inflammatory cytokines in penicillin- and pentylenetetrazole(PTZ)-induced seizure models in rats.

MAIN METHODS

Different doses of esculetin (5, 10, and 20 mg/kg), and diazepam (5 mg/kg) as a positive control, were tested in penicillin- and pentylenetetrazole(PTZ)-induced seizure models. In the PTZ model, cognitive function, behavioral seizures, and cortical and hippocampal pro-inflammatory biomarkers and survival factor was evaluated. In the penicillin model, the frequency and amplitude of electrophysiological epileptiform activity were assessed.

KEY FINDINGS

In the PTZ model, the 10 mg/kg esculetin displayed anticonvulsant effects by extending onset-times of myoclonic-jerk and generalized tonic-clonic seizure, and by diminishing seizure severity and duration of generalized tonic-clonic seizure. It also ameliorated PTZ-induced cognitive impairment, and cortical and hippocampal activin-A, IL-1β, IL-6 and NF-κB levels. In the penicillin model, the 10 mg/kg esculetin decreased the frequency of spikes without changing the amplitude of spikes. As a positive-control, diazepam reversed all changes induced by both PTZ and penicillin.

SIGNIFICANCE

Esculetin exhibits anticonvulsant and memory-improving effects by alleviating the behavioral and electrophysiological characteristics of epileptic seizures. Additionally, esculetin exerts anti-neuroinflammatory actions in the PTZ-induced seizures model. Thus, esculetin may be a multi-targeted promising agent with anticonvulsant and anti-neuroinflammatory effects in the treatment of epilepsy.

UK medical cannabis registry: assessment of clinical outcomes in patients with headache disorders

OBJECTIVES

Headache disorders are a common cause of disability and reduced health-related quality of life globally. Growing evidence supports the use of cannabis-based medicinal products (CBMPs) for chronic pain; however, a paucity of research specifically focuses on CBMPs' efficacy and safety in headache disorders. This study aims to assess changes in validated patient-reported outcome measures (PROMs) in patients with headaches prescribed CBMPs and investigate the clinical safety in this population.

METHODS

A case series of the UK Medical Cannabis Registry was conducted. Primary outcomes were changes from baseline in PROMs (Headache Impact Test-6 (HIT-6), Migraine Disability Assessment (MIDAS), EQ-5D-5L, Generalized Anxiety Disorder-7 (GAD-7) questionnaire and Single-Item Sleep Quality Scale (SQS)) at 1-, 3-, and 6-months follow-up. P-values <0.050 were deemed statistically significant.

RESULTS

Ninety-seven patients were identified for inclusion. Improvements in HIT-6, MIDAS, EQ-5D-5L and SQS were observed at 1-, 3-, and 6-months (p < 0.005) follow-up. GAD-7 improved at 1- and 3-months (p < 0.050). Seventeen (17.5%) patients experienced a total of 113 (116.5%) adverse events.

CONCLUSION

Improvements in headache/migraine-specific PROMs and general health-related quality of life were associated with the initiation of CBMPs in patients with headache disorders. Cautious interpretation of results is necessary, and randomized control trials are required to ascertain causality.

Preclinical Studies of Posttraumatic Headache and the Potential Therapeutics

Posttraumatic headache (PTH) attributed to traumatic brain injury (TBI) is a secondary headache developed within 7 days after head injury, and in a substantial number of patients PTH becomes chronic and lasts for more than 3 months. Current medications are almost entirely relied on the treatment of primary headache such as migraine, due to its migraine-like phenotype and the limited understanding on the PTH pathogenic mechanisms. To this end, increasing preclinical studies have been conducted in the last decade. We focus in this review on the trigeminovascular system from the animal studies since it provides the primary nociceptive sensory afferents innervating the head and face region, and the pathological changes in the trigeminal pathway are thought to play a key role in the development of PTH. In addition to the pathologies, PTH-like behaviors induced by TBI and further exacerbated by nitroglycerin, a general headache inducer through vasodilation are reviewed. We will overview the current pharmacotherapies including calcitonin gene-related peptide (CGRP) monoclonal antibody and sumatriptan in the PTH animal models. Given that modulation of the endocannabinoid (eCB) system has been well-documented in the treatment of migraine and TBI, the therapeutic potential of eCB in PTH will also be discussed.

The effects of certain TRP channels and voltage-gated KCNQ/Kv7 channel opener retigabine on calcitonin gene-related peptide release in the trigeminovascular system

BACKGROUND

Calcitonin gene-related peptide release in trigeminovascular system is a pivotal component of neurogenic inflammation underlying migraine pathophysiology. Transient receptor potential channels and voltage-gated KCNQ/Kv7 potassium channels expressed throughout trigeminovascular system are important targets for modulation of calcitonin gene-related peptide release. We investigated the effects of certain transient receptor potential (TRP) channels the vanilloid 1 and 4 (TRPV1 and TRPV4), the ankyrin 1 (TRPA1), and metastatin type 8 (TRPM8), and voltage-gated potassium channel (Kv7) opener retigabine on calcitonin gene-related peptide release from peripheral (dura mater and trigeminal ganglion) and central (trigeminal nucleus caudalis) trigeminal components of rats.

METHODS

The experiments were carried out using well-established in-vitro preparations (hemiskull, trigeminal ganglion and trigeminal nucleus caudalis) from male Wistar rats. Agonists and antagonists of TRPV1, TRPV4, TRPA1 and TRPM8 channels, and also retigabine were tested on the in-vitro release of calcitonin gene-related peptide. Calcitonin gene-related peptide concentrations were measured using enzyme-linked immunosorbent assay.

RESULTS

Agonists of these transient receptor potential channels induced calcitonin gene-related peptide release from hemiskull, trigeminal ganglion and trigeminal nucleus caudalis, respectively. The transient receptor potential channels-induced calcitonin gene-related peptide releases were blocked by their specific antagonists and reduced by retigabine. Retigabine also decreased basal calcitonin gene-related peptide releases in all preparations.

CONCLUSION

Our findings suggest that favorable antagonists of these transient receptor potential channels, or Kv7 channel opener retigabine may be effective in migraine therapy by inhibiting neurogenic inflammation that requires calcitonin gene-related peptide release.

Inhibiting Endocannabinoid Hydrolysis as Emerging Analgesic Strategy Targeting a Spectrum of Ion Channels Implicated in Migraine Pain

Migraine is a disabling neurovascular disorder characterized by severe pain with still limited efficient treatments. Endocannabinoids, the endogenous painkillers, emerged, alternative to plant cannabis, as promising analgesics against migraine pain. In this thematic review, we discuss how inhibition of the main endocannabinoid-degrading enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), could raise the level of endocannabinoids (endoCBs) such as 2-AG and anandamide in order to alleviate migraine pain. We describe here: (i) migraine pain signaling pathways, which could serve as specific targets for antinociception; (ii) a divergent distribution of MAGL and FAAH activities in the key regions of the PNS and CNS implicated in migraine pain signaling; (iii) a complexity of anti-nociceptive effects of endoCBs mediated by cannabinoid receptors and through a direct modulation of ion channels in nociceptive neurons; and (iv) the spectrum of emerging potent MAGL and FAAH inhibitors which efficiently increase endoCBs levels. The specific distribution and homeostasis of endoCBs in the main regions of the nociceptive system and their generation ‘on demand’, along with recent availability of MAGL and FAAH inhibitors suggest new perspectives for endoCBs-mediated analgesia in migraine pain.

Inhibition of Nociception in a Preclinical Episodic Migraine Model by Dietary Supplementation of Grape Seed Extract Involves Activation of Endocannabinoid Receptors

Migraine is associated with peripheral and central sensitization of the trigeminal system and dysfunction of descending pain modulation pathways. Recently, dietary inclusion of grape seed extract (GSE) was shown to inhibit mechanical nociception in a preclinical model of chronic temporomandibular joint disorder, a condition often comorbid with migraine, with the antinociceptive effect mediated, in part, by activation of 5-HT3/7 and GABAB receptors. This study further investigated the mechanisms by which GSE inhibits mechanical nociception in a preclinical model of episodic migraine. Hyperalgesic priming of female and male Sprague Dawley rats was induced by three consecutive daily two-hour episodes of restraint stress. Seven days after the final restraint stress, rats were exposed to pungent odors from an oil extract that contains the compound umbellulone, which stimulates CGRP release and induces migraine-like pain. Some animals received dietary supplementation of GSE in their drinking water beginning one week prior to restraint stress. Changes in mechanical sensitivity in the orofacial region and hindpaw were determined using von Frey filaments. To investigate the role of the endocannabinoid receptors in the effect of GSE, some animals were injected intracisternally with the CB1 antagonist AM 251 or the CB2 antagonist AM 630 prior to odor inhalation. Changes in CGRP expression in the spinal trigeminal nucleus (STN) in response to stress, odor and GSE supplementation were studied using immunohistochemistry. Exposure of stress-primed animals to the odor caused a significant increase in the average number of withdrawal responses to mechanical stimulation in both the orofacial region and hindpaw, and the effect was significantly suppressed by daily supplementation with GSE. The anti-nociceptive effect of GSE was inhibited by intracisternal administration of antagonists of CB1 and CB2 receptors. GSE supplementation inhibited odor-mediated stimulation of CGRP expression in the STN in sensitized animals. These results demonstrate that GSE supplementation inhibits trigeminal pain signaling in an injury-free model of migraine-like pain via activation of endocannabinoid receptors and repression of CGRP expression centrally. Hence, we propose that GSE may be beneficial as a complementary migraine therapeutic.

IL-17 crosses the blood-brain barrier to trigger neuroinflammation: a novel mechanism in nitroglycerin-induced chronic migraine

Background

Chronic migraine places a disabling burden on patients, which is extensively modeled by the nitroglycerin (NTG)-treated animal model. Although the NF-κB pathway is involved in an increase in CGRP levels and activation of the trigeminal system in the NTG model, the relationship between NTG and neuroinflammation remains unclear. This study aimed to optimize a chronic NTG rat model with hyperalgesia and the ethological capacity for estimating migraine therapies and to further explore the underlying mechanism of NTG-induced migraine.

Methods

Rats were administered different doses of NTG s.c. daily or every 2 d; 30 min and 2 h later, the mechanical threshold was tested. After 9 d, the rats were injected with EB or Cy5.5 for the permeability assay. The other animals were sacrificed, and then, brainstem and caudal trigeminal ganglion were removed to test CGRP, c-Fos and NOS activity; Cytokines levels in the tissue and serum were measured by ELISA; and NF-κB pathway and blood–brain barrier (BBB)-related indicators were analyzed using western blotting. Immunohistochemistry was performed to observe microglial polarization and IL-17A⁺ T cell migration in the medulla oblongata.

Results

NTG (10 mg/kg, s.c., every 2 d for a total of 5 injections) was the optimal condition, resulting in progressive hyperalgesia and migraine behavior. TNC neuroinflammation with increases in cytokines, CGRP and c-Fos and activation of the NF-κB pathway was observed, and these changes were alleviated by ibuprofen. Furthermore, NTG administration increased BBB permeability by altering the levels functional proteins (RAGE, LRP1, AQP4 and MFSD2A) and structural proteins (ZO-1, Occludin and VE-cadherin-2) to increase peripheral IL-17A permeation into the medulla oblongata, activating microglia and neuroinflammation, and eventually causing hyperalgesia and migraine attack.

Conclusions

This study confirmed that NTG (10 mg/kg, s.c., every 2 d for a total of 5 injections) was the optimal condition to provoke migraine, resulting in mechanical hyperalgesia and observable migraine-like behavior. Furthermore, IL-17A crossed the blood–brain barrier into the medulla oblongata, triggering TNC activation through microglia-mediated neuroinflammation. This process was a novel mechanism in NTG-induced chronic migraine, suggesting that IL-17A might be a novel target in the treatment of migraine.

Emodin Interferes With Nitroglycerin-Induced Migraine in Rats Through CGMP-PKG Pathway

The purpose of this research was to explore the effect and mechanism of emodin in interfering with nitroglycerin-induced migraine rats. We carried out behavioral research within 2 h post-nitroglycerin (NTG) injection, and blood samples were collected through the abdominal aorta for measurements of nitric oxide (NO), calcitonin gene-related peptide (CGRP), substance P (SP), tumor necrosis factor (TNF-α) and cyclic guanosine monophosphate (cGMP) levels. Immunohistochemistry was adopted to detect the activation of c-Fos immunoreactive neurons in brain tissues. The number and integrated optical density (IOD) of c-Fos positive cells were measured using Image-Pro Plus. Western blotting was applied to detect the levels of PKG protein in rat brain tissues. The results showed that emodin can alleviate the pain response of migraine rats and significantly reduce the levels of NO, CGRP, SP, TNF-α and cGMP in migraine rats. In addition, emodin can significantly reduce the number of c-Fos positive cells and the IOD value. Moreover, the expression of PKG protein was significantly inhibited by emodin. Therefore, it is inferred that emodin can relieve migraine induced by NTG through the cGMP-PKG pathway, and can be used as a potential botanical medicine for the treatment of migraine.

Dual Inhibition of FAAH and MAGL Counteracts Migraine-like Pain and Behavior in an Animal Model of Migraine

The endocannabinoid system exerts an important role in pain processing and modulation. Modulation of the system with hydrolase inhibitors of anandamide (AEA) or 2-arachidonyl glycerol (2-AG) has proved effective in reducing migraine-like features in animal models of migraine. Here, we investigated the effect of dual inhibition of the AEA and 2-AG catabolic pathways in the nitroglycerin-based animal model of migraine. The dual inhibitor JZL195 was administered to rats 2 h after nitroglycerin or vehicle injection. Rats were then exposed to the open field test and the orofacial formalin test. At the end of the tests, they were sacrificed to evaluate calcitonin gene-related peptide (CGRP) serum levels and gene expression of CGRP and cytokines in the cervical spinal cord and the trigeminal ganglion. The dual inhibitor significantly reduced the nitroglycerin-induced trigeminal hyperalgesia and pain-associated behavior, possibly via cannabinoid 1 receptors-mediated action, but it did not change the hypomotility and the anxiety behaviors induced by nitroglycerin. The decreased hyperalgesia was associated with a reduction in CGRP and cytokine gene expression levels in central and peripheral structures and reduced CGRP serum levels. These data suggest an antinociceptive synergy of the endocannabinoid action in peripheral and central sites, confirming that this system participates in reduction of cephalic pain signals.

Voluntary Forelimbs Exercise Reduces Immobilization-Induced Mechanical Hyperalgesia in the Rat Hind Paw

Voluntary exercise is sufficient to protect against neuropathic pain. However, it is unclear whether voluntary exercise reduces immobilization-induced hyperalgesia. We examined the effect of voluntary forelimb exercise on immobilized-induced hyperalgesia in hind paws of rats. Wistar rats were randomly divided into the (1) both hind limbs immobilized group (IM group), (2) immobilization and exercise with nonimmobilized fore limbs group (EX group), and (3) control group. In the IM and EX groups, the bilateral ankle joints of each rat were immobilized in full plantar flexion with a plaster cast for eight weeks. In the EX group, voluntary exercise using nonimmobilized forelimbs in the running wheel was administered during the immobilization period, while hind limbs were kept immobilized (60 min/day, 5 days/week). Mechanical hyperalgesia in the hind paw was measured using a digital von Frey device every week. To investigate the abnormality of primary sensory neurons and central sensitization, the number of calcitonin gene-related peptide-positive cells in the dorsal root ganglion and the expression level of calcitonin gene-related peptide in the spinal dorsal horn were analyzed by immunohistochemical staining. Immobilization-induced mechanical hyperalgesia was inhibited in the EX group compared to the IM group at three weeks after immobilization. In the EX group, the number of calcitonin gene-related peptide-positive cells in the dorsal root ganglion and the expression level of calcitonin gene-related peptide were significantly decreased compared to those in the IM group. Our results therefore suggest that voluntary forelimb exercise during hind limb immobilization partially reduces immobilization-induced hyperalgesia by suppressing that the plastic changes of the primary sensory nerves that excessively transmit pain and increased responsiveness of nociceptive neurons in the spinal dorsal horn.

Oral cannabinoid preparations for the treatment of chronic migraine: a retrospective study

OBJECTIVE

To explore the effectiveness and safety of 3 oral cannabinoid preparations (FM2®, Bedrocan® and Bediol®) in the treatment of chronic migraine.

DESIGN

Retrospective, cohort study.

SUBJECTS

Patients with chronic migraine who received FM2®, Bedrocan® or Bediol® daily for the off-label treatment of their headache, up to 6 months.

METHODS

The number of migraine days per month, pain intensity, the number of acute medications taken per month, the number of days per month when the patient took at least one acute medication, and adverse events were recorded at baseline, 3 months, and 6 months after the start of treatment with oral cannabinoid preparations.

RESULTS

The number of migraine days didn't change significantly after the 3rd and the 6th month when compared to baseline (P = 0.1182). The pain intensity (P = 0.0004), the acute medication consumption (P = 0.0006) and the number of days per month in which patients took, at least, one acute medication, (P = 0.0004) significantly decreased when compared to the baseline. No significant differences were found between patients who were still taking a preventive treatment for chronic migraine and those who weren't (all P > 0.05). Different oral cannabinoid preparations displayed similar effectiveness (all P > 0.05). The AEs were mostly mild and occurred in the 43.75% of patients.

CONCLUSIONS

Oral cannabinoid preparations may have a role in reducing pain intensity and acute medication intake in patients with chronic migraine, but the magnitude of the effect seems modest; further studies are needed.

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.

Mast cell activation ameliorates pentylenetetrazole-induced seizures in rats: The potential role for serotonin

Neuroinflammation plays a key role in the pathogenesis of epilepsy, but the underlying mechanisms are not well understood. Mast cells are multifunctional immune cells that are also activated by stress. The effects of activated mast cells on epileptogenesis are not yet known. This study investigated the effects and mechanisms of compound 48/80-stimulated mast cell activation on pentylenetetrazole-induced epileptic seizures in rats. Male Wistar rats were separated into seven groups (n = 12). Group-1(NS+PTZ) received intraperitoneal saline solution, while groups 2(C-48/80+PTZ-1), 3(C-48/80+PTZ-2), and 4(C-48/80+PTZ-3) received compound-48/80 at doses of 0.5, 1, and 2 mg/kg, respectively, 30 min before 45 mg/kg pentylenetetrazole administration. Similarly, Group-5(Cr+C-48/80+PTZ) received 10 mg/kg cromolyn plus 2 mg/kg compound-48/80 before pentylenetetrazole, and Group-6(MC Dep+C-48/80+PTZ) was exposed to a mast cell-depletion process, and then received 2 mg/kg compound-48/80. Group-7(5-HT+PTZ) received 10 mg/kg serotonin. Seizure stages were evaluated using Racine's scale. Compound-48/80 at 2 mg/kg induced anticonvulsive effects against pentylenetetrazole-induced seizures by extending onset-times of both myoclonic-jerk and generalized tonic-clonic seizures (p = 0.0001), and by shortening the duration of generalized tonic-clonic seizure (p = 0.008). These effects were reversed by cromolyn (p = 0.0001). These effects were not observed in mast cell-depleted rats. Similarly to compound 48/80, serotonin also exhibited anticonvulsive effects against seizures (p < 0.05). Compound 48/80 acts as an anticonvulsant by activating mast cells in a dose-dependent manner. The anticonvulsive effects of mast cell activation may be mediated by serotonin. Mast cell activation may therefore provide protective activity against seizures under appropriate circumstances.

Effects of estrogen and progesterone on the neurogenic inflammatory neuropeptides: implications for gender differences in migraine

Neurogenic inflammation including calcitonin gene-related peptide (CGRP) and substance-P (SP) release plays a pivotal role in migraine pathogenesis. Prevalence of migraine is ~ 3 folds higher in women than in men, but its underlying mechanisms remained unclear. We investigated the effects of female sex hormones estrogen and progesterone on CGRP and SP in in-vivo and ex-vivo in rats of both sexes. For in-vivo experiments, male, female and ovariectomized rats were separated into four groups (n = 7) as control, estrogen, progesterone and estrogen + progesterone, respectively. Groups received daily intraperitoneal vehicle, 17β-estradiol, progesterone and 17β-estradiol + progesterone for 5 days, respectively. For ex-vivo experiments in both sexes, isolated trigeminal ganglia and hemiskull preparations were divided into four groups (n = 6 or 8), respectively, as in-vivo groups, and administered the same test substances. CGRP and SP contents in plasma and superfusates were determined using ELISA. In in-vivo experiments, 17β-estradiol decreased CGRP levels in males and SP levels in ovariectomized rats. Progesterone increased both CGRP and SP levels in females. Their combination decreased both CGRP and SP levels in males, and only SP levels in ovariectomized rats. In ex-vivo experiments, 17β-estradiol reduced CGRP release in males and SP release in females in trigeminal ganglia. While progesterone increased CGRP release in trigeminal ganglia, it reduced SP release from hemiskulls in both sexes. Their combination restored progesterone-mediated changes in neuropeptides releases in both trigeminal ganglia and hemiskulls in both sexes. Estrogen alleviates neurogenic inflammation through modulation of CGRP and SP release. Progesterone has dual effects on these neuropeptides in different sites associated with migraine pain.