Sex differences in behavior and expression of CGRP-related genes in a rodent model of chronic migraine

17-β-Estradiol induces spreading depression and pain behavior in alert female rats

AIMS

Test the putative contribution of 17-β-estradiol in the development of spreading depression (SD) events and head pain in awake, non-restrained rats.

MAIN METHODS

Female, Sprague-Dawley rats were intact or underwent ovariectomy followed one week later by surgery to place electrodes onto the dura to detect epidural electroencephalographic activity (dEEG). dEEG activity was recorded two days later for 12 hours after systemic administration of 17-β-estradiol (180 μg/kg, i.p.). A separate set of rats were observed for changes in exploratory, ambulatory, fine, and rearing behaviors; periorbital allodynia was also assessed.

KEY FINDINGS

A bolus of 17-β-estradiol significantly elevated serum estrogen levels, increased SD episodes over a 12-hour recording period and decreased rearing behaviors in ovariectomized rats. Pre-administration of ICI 182,780, an estrogen receptor antagonist, blocked 17-β-estradiol-evoked SD events and pain behaviors; similar results were observed when the antimigraine therapeutic sumatriptan was used.

SIGNIFICANCE

These data indicate that an estrogen receptor-mediated mechanism contributes to SD events in ovariectomized rats and pain behaviors in both ovariectomized -and intact- rats. This suggests that estrogen plays a different role in each phenomenon of migraine where intense fluctuations in concentration may influence SD susceptibility. This is the first study to relate estrogen peaks to SD development and pain behaviors in awake, freely moving female rats, establishing a framework for future preclinical migraine studies.

Gender aspects of CGRP in migraine

Background

Migraine is two to three times more prevalent in women than in men, but the mechanisms involved in this gender disparity are still poorly understood. In this respect, calcitonin gene-related peptide (CGRP) plays a key role in migraine pathophysiology and, more recently, the functional interactions between ovarian steroid hormones, CGRP and the trigeminovascular system have been recognized and studied in more detail.

Aims

To provide an overview of CGRP studies that have addressed gender differences utilizing animal and human migraine preclinical research models to highlight how the female trigeminovascular system responds differently in the presence of varying ovarian steroid hormones.

Conclusions

Gender differences are evident in migraine. Several studies indicate that fluctuations of ovarian steroid hormone (mainly estrogen) levels modulate CGRP in the trigeminovascular system during different reproductive milestones. Such interactions need to be considered when conducting future animal and human experiments, since these differences may contribute to the development of gender-specific therapies.

Cranial dural permeability of inflammatory nociceptive mediators: Potential implications for animal models of migraine

Background Application of inflammatory mediators to the cranial dura has been used as a method to activate and sensitize neurons in the meningeal sensory pathway in preclinical behavioral studies of headache mechanisms. However, the relatively high concentrations and volumes used in these studies raise the question of whether the applied agents might pass through the dura to act directly on central neurons, thus bypassing the dural afferent pathway. Methods We used a radiolabeling approach to quantify the meningeal permeability of two of the inflammatory mediators, 5-HT and PGE2, when applied to the cranial dura as part of an inflammatory mixture used in preclinical headache models. Results Both agents could be detected in samples taken four hours after dural application in the cerebrospinal fluid (CSF) and, in measurements made only for PGE2, in the central nervous system (CNS) as well. Based on our measurements, we made estimates of the CSF and CNS levels that would be attained with the higher concentrations and volumes of 5HT and PGE2 that were exogenously applied in previous pre-clinical headache studies. These estimated levels were comparable to or larger than normal endogenous levels, potentially large enough to have physiological effects. Conclusions The finding that the cranial meninges are permeable to the two tested inflammatory mediators PGE2 and 5-HT raises some uncertainty about whether the behavioral changes observed in prior pre-clinical headache studies with these as well as other agents can be attributed entirely to the activation of dural nociceptors, particularly when the agents are applied at concentrations several orders of magnitude above physiological levels.

Selective Inhibition of Trigeminovascular Neurons by Fremanezumab: A Humanized Monoclonal Anti-CGRP Antibody

A large body of evidence supports an important role for calcitonin gene-related peptide (CGRP) in migraine pathophysiology. This evidence gave rise to a global effort to develop a new generation of therapeutics that inhibit the interaction of CGRP with its receptor in migraineurs. Recently, a new class of such drugs, humanized anti-CGRP monoclonal antibodies (CGRP-mAbs), were found to be effective in reducing the frequency of migraine. The purpose of this study was to better understand how the CGRP-mAb fremanezumab (TEV-48125) modulates meningeal sensory pathways. To answer this question, we used single-unit recording to determine the effects of fremanezumab (30 mg/kg, IV) and its isotype control Ab on spontaneous and evoked activity in naive and cortical spreading depression (CSD)-sensitized trigeminovascular neurons in the spinal trigeminal nucleus of anesthetized male and female rats. The study demonstrates that, in both sexes, fremanezumab inhibited naive high-threshold (HT) neurons, but not wide-dynamic range trigeminovascular neurons, and that the inhibitory effects on the neurons were limited to their activation from the intracranial dura but not facial skin or cornea. In addition, when given sufficient time, fremanezumab prevents the activation and sensitization of HT neurons by CSD. Mechanistically, these findings suggest that HT neurons play a critical role in the initiation of the perception of headache and the development of cutaneous allodynia and central sensitization. Clinically, the findings may help to explain the therapeutic benefit of CGRP-mAb in reducing headaches of intracranial origin such as migraine with aura and why this therapeutic approach may not be effective for every migraine patient.SIGNIFICANCE STATEMENT Calcitonin gene-related peptide (CGRP) monoclonal antibodies (CGRP-mAbs) are capable of preventing migraine. However, their mechanism of action is unknown. In the current study, we show that, if given enough time, a CGRP-mAb can prevent the activation and sensitization of high-threshold (central) trigeminovascular neurons by cortical spreading depression, but not their activation from the skin or cornea, suggesting a potential explanation for selectivity to migraine headache, but not other pains, and a predominantly peripheral site of action.

Disrupted functional connectivity between the periaqueductal gray and other brain regions in a rat model of recurrent headache

Functional connectivity (FC) has been used to investigate the pathophysiology of migraine. We aimed to identify atypical FC between the periaqueductal gray (PAG) and other brain areas in rats induced by repeated meningeal nociception. The rat model was established by infusing an inflammatory soup (IS) through supradural catheters in conscious rats. Quiescent and face-grooming behaviors were observed to assess nociceptive behavior. FC analysis seeded on the PAG was performed on rats 21 days after IS infusion. The rats exhibited nociceptive behavior correlates of human behaviors associated with migraine after IS infusion. The PAG showed increased FC with the prefrontal cortex, cingulate gyrus, and motor cortex but decreased FC with the basal ganglia, dorsal lateral thalamus, internal capsule and prelimbic cortex in the rat model. The atypical FC of the PAG with brain regions in the rat model that are involved in nociception, somatosensory processing, emotional processing, and pain modulation are consistent with the clinical data from migraineurs, indicate that resting-state FC changes in migraine patients may be a consequence of headache attacks, and further validate this rat model of chronic migraine.

Tyrosine Phosphorylation of NR2B Contributes to Chronic Migraines via Increased Expression of CGRP in Rats

Tyrosine phosphorylation of NR2B (NR2B-pTyr), a subunit of the N-methyl-D-aspartate (NMDA) receptor, has been reported to develop central sensitization and persistent pain in the spine, but its effect in chronic migraines has not been examined. We hypothesized that tyrosine phosphorylation of NR2B contributes to chronic migraines (CM) through calcitonin gene-related peptide (CGRP) in rats. Ninety-four male Sprague-Dawley rats were subjected to seven inflammatory soup (IS) injections. In a subset of animals, the time course and location of NR2B tyrosine phosphorylation were detected by western blot and immunofluorescence double staining. Another set of animals were given either genistein, vehicle, or genistein and recombinant CGRP. The mechanical threshold was measured, the expressions of NR2B-pTyr, NR2B, and CGRP were quantified using western blot, and nitric oxide (NO) was measured with the nitric acid reductase method. NR2B-pTyr expression, in neurons, peaked at 24 hours after CM. Genistein improved the mechanical threshold and reduced migraine attacks 24 and 72 hours after CM. Tyrosine phosphorylation of NR2B decreased the mechanical threshold and increased migraine attacks via upregulated CGRP expression in the rat model of CM. Thus, tyrosine phosphorylation of NR2B may be a potential therapeutic target for treatment of CM.

Cilostazol induces C-fos expression in the trigeminal nucleus caudalis and behavioural changes suggestive of headache with the migraine-like feature photophobia in female rats

Introduction

Research in development of new migraine therapeutics is hindered by the lack of suitable, predictive animal models. Cilostazol provokes headache in healthy humans and migraineurs by increasing intracellular cAMP levels. We aimed to investigate whether cilostazol could provoke headache-like behaviours and c-fos expression in rats. In order to evaluate the predictive validity of the model, we examined the response to the migraine specific drug sumatriptan.

Methods

The effect of cilostazol (125 mg/kg p.o.) in female Sprague Dawley rats was evaluated on a range of spontaneous behavioural parameters, light sensitivity and mechanical sensitivity thresholds. We also measured c-fos expression in the trigeminal nucleus caudalis.

Results

Cilostazol increased light sensitivity and grooming behaviour. These manifestations were not inhibited by sumatriptan. Cilostazol also induced c-fos expression in the trigeminal nucleus caudalis. Furthermore, trigeminal – but not hind paw hyperalgesia was observed.

Conclusion

The altered behaviours are suggestive of cilostazol induced headache with migraine-like features, but not specific. The presence of head specific hyperalgesia and the c-fos response in the trigeminal nucleus caudalis imply that the model involves trigeminal nociception. The model will be useful for studying mechanisms related to the cAMP pathway in headache, but its predictive properties appear to be more limited due to the lack of response to sumatriptan.

Rizatriptan overuse promotes hyperalgesia induced by dural inflammatory stimulation in rats by modulation of the serotonin system

Clinical and preclinical studies have implicated serotonin (5-HT) and the 5-HT2A receptor (5-HT2AR) in the pathogenesis of medication-overuse headache (MOH). However, with no appropriate animal model to study this phenomenon it is difficult to differentiate the effects of chronic exposure to analgesics from the consequences of frequent headache attacks during the development of MOH. Therefore, this study used a novel animal model of MOH established by a combination of the overuse of rizatriptan (RIZ) and stimulation with dural inflammatory soup (IS) to investigate whether 5-HT and 5-HT2AR are involved in central plasticity and hyperalgesia. Similar to an IS infusion, IS-RIZ treatment induced nociception-related behaviours in Sprague-Dawley rats and increased Fos expression in the cortex and trigeminal pathway, whereas the RIZ injection alone did not. In addition, overuse of RIZ, administration of an IS stimulus, and a combination of these treatments, decreased the periorbital withdrawal threshold, with IS-RIZ treatment having the most significant effects. Both chronic RIZ exposure and recurring nociception decreased 5-HT expression, whereas IS-RIZ treatment led to decreased expression of 5-HT and upregulation of 5-HT2AR, which was positively correlated with Fos activation. These findings suggest that overuse of RIZ does not directly induce pain via the activation of nociceptive pathways but may increase hyperalgesia by influencing the pain modulation system. Furthermore, decreased 5-HT levels and upregulation of 5-HT2AR may play important roles in this system. Taken together, these findings indicate that medication overuse and frequent headache attacks can promote the neural plasticity associated with MOH.

Female sex and obesity increase photophobic behavior in mice

Migraine affects predominantly women. Furthermore, epidemiological studies suggest that obesity is a risk factor for migraine and this association is influenced by sex. However, the biological basis for this bias is unclear. To address this issue, we assessed light avoidant behavior, a surrogate of photophobia, in female C57BL/6J mice fed regular diet (RD) or high-fat diet (HFD, 60% kcal from fat). We first assessed sex differences in basal photophobia in 20-25-week-old mice and found that both obese and lean females spent significantly less time in light than their male counterparts. Next, we assessed photophobia evoked by trigeminal stimulation with intradermal capsaicin. Females at 20-25weeks of age did not display capsaicin-evoked photophobic behavior unless they had diet-induced obesity. When we tested 8-11-week-old females to determine if the diet alone could be responsible for this effect, we found that both HFD and RD 8-11-week-old females exhibit capsaicin-evoked photophobic behavior. This is in contrast to what we have previously shown in males and indicates a sex difference in the photophobic behavior of mice. Comparison of 20-25-week-old RD mice with 8-11-week-old RD mice suggests that age or age-related weight gain may contribute to capsaicin-evoked photophobic behavior in males, but not in females. These findings suggest that obesity exacerbates photophobia in both sexes, but additional work is needed to understand the sex- and age-specific mechanisms that may contribute to photophobia and trigeminal pain.

Prostaglandin E2-mediated upregulation of neuroexcitation and persistent tetrodotoxin-resistant Na(+) currents in Ah-type trigeminal ganglion neurons isolated from adult female rats

Prostaglandin-E2 (PGE2) is a very important inflammatory mediator and PGE2-mediated neuroexcitation in sex-specific distribution of Ah-type trigeminal ganglion neurons (TGNs) isolated from adult female rats is not fully addressed. The whole-cell patch-clamp experiment was performed to verify the effects of PGE2, forskolin, and GPR30-selective agonist (G-1) on action potential (AP) and tetrodotoxin-resistant (TTX-R) Na(+) currents in identified Ah-type TGNs. The results showed that the firing frequency was increased in Ah- and C-types by PGE2, which was simulated by forskolin and inhibited by Rp-cyclic adenosine monophosphate (cAMP), while G-1 mimicked this effect only in Ah-types, which was abolished by GPR30-selective antagonist (G-15). Although the amplitude of AP was increased in Ah- and C-types, increased maximal upstroke velocity was confirmed only in Ah-types, suggesting distinct alternations in current density and/or voltage-dependent property of Na(+) channels. With 1.0 μM PGE2, TTX-R Na(+) currents were upregulated without changing the current-voltage relationship and voltage-dependent activation in C-types, however, the TTX-R Na(+) current was augmented in Ah-types, peaked voltage and the voltage-dependent activation were both shifted toward hyperpolarized direction with faster slope. Intriguingly, the low-threshold persistent TTX-R component was activated from -60 mV and increased almost double at -30 mV compared with ∼30-40% increment of TTX-R component being activated at ∼-10 mV. Additionally, the change in TTX-R component of Ah-types was equivalent well with that in C-type TGNs. Taken these data together, we conclude that PGE2 modulates the neuroexcitation via cAMP-mediated upregulation of TTX-R Na(+) currents in both cell-types with hormone-dependent feature, especially persistent TTX-R Na(+) currents in sex-specific distribution of myelinated Ah-type TGNs.

Alcohol-triggered signs of migraine: An animal model

We describe an animal model where characteristics of migraine can be triggered by alcohol administration. In rats chronically implanted with a cannula overlying the transverse sinus, we applied potassium chloride (KCl) (or saline) to the meninges to sensitize trigeminovascular afferents. We assessed effects of repeated KCl application on animal behavior using conditioned place avoidance paradigm. In KCl-treated rats we discovered that alcohol injections (0.2 mg/kg), but not saline, resulted in the development of extracephalic allodynia and signs of ongoing pain.

DNA methylation of RAMP1 gene in migraine: an exploratory analysis

Background

Receptor activity modifying protein 1(RAMP1) is a key receptor subunit of calcitonin gene related peptide (CGRP) playing a critical role in migraine. But variations in RAMP1 gene have not been found to link with migraine. Still it is elusive that DNA methylation at RAMP1 promoter is associated with migraine.

Methods

A total of 51 blood DNA samples from 26 patients with migraine and 25 matched healthy controls were collected, extracted and treated with bisulfate. Subsequently DNA methylation levels at RAMP1 promoter region were measured using Sequenom Mass ARRAY systems.

Results

Among 13 detected CpG sites or units at RAMP1 promoter region, there were no significant differences between the migraine and control groups, but indicating a low methylation trend overall in migraine group (total average methylation level: 8.41 % ±1.92 % vs. 9.90 % ± 3.88 %, p = 0.197). Stratification analysis showed that methylation level at (+25, +27, +31, related to the transcription start site) CpG unit was higher in migraineurs with migraine family history compared to those without (13.92 % ± 5.97 % vs. 8.77 % ± 6.61 %, p = 0.034), and methylation level at (+89, +94, +96) CpG unit was lower in migraine female than that in healthy female (2.18 % ± 1.91 % vs. 5.85 % ± 5.41 %, p = 0.02). For female with methylation level at (+89, +94, +96) CpG unit below 3.50 %, the probability of being a migraine patient was significantly higher than those with methylation level above the threshold (OR: 7.313; 95%CI: 1.439-37.164).

Conclusions

This study provides the first evidence that DNA methylation at RAMP1 promoter might play a role in migraine. A low methylation trend overall was presented in migraine subjects, and two CpG units were observed to link with positive migraine family history and female migraine, respectively. Lower methlytion level at (+89, +94, +96) CpG unit may be a risk of migraine in females.

Animal models of chronic migraine

Many animal models of migraine have been described. Some of them have been useful in the development of new therapies. All of them have their shortcomings. Animal models of chronic migraine have been relatively less frequently described. Whether a rigid distinction between episodic and chronic migraine is useful when their underlying pathophysiology is likely to be the same and that migraine frequency probably depends on complex polygenic influences remains to be determined. Any model of chronic migraine must reflect the chronicity of the disorder and be reliable and validated with pharmacological interventions. Future animal models of chronic migraine are likely to involve recurrent activation of the trigeminal nociceptive system. Valid models would provide a means for investigating pathophysiological mechanism of the transformation from episodic to chronic migraine and may also be used to test the efficacy of potential preventive medications.

CGRP as a neuropeptide in migraine: lessons from mice

Migraine is a neurological disorder that is far more than just a bad headache. A hallmark of migraine is altered sensory perception. A likely contributor to this altered perception is the neuropeptide calcitonin gene-related peptide (CGRP). Over the past decade, CGRP has become firmly established as a key player in migraine. Although the mechanisms and sites of action by which CGRP might trigger migraine remain speculative, recent advances with mouse models provide some hints. This brief review focuses on how CGRP might act as both a central and peripheral neuromodulator to contribute to the migraine-like symptom of light aversive behaviour in mice.

Increased risk of urinary calculi in patients with migraine: a nationwide cohort study

OBJECTIVE

Whether migraine is associated with urinary calculi is an unresolved issue, although topiramate, a migraine-preventive agent, is known to contribute to this complication. This study investigates the association between migraine and the risk of urinary calculi.

METHODS

We identified a total of 147,399 patients aged ≥18 years with migraine diagnoses recorded in the Taiwan National Health Insurance Research Database between 2005 and 2009. Each patient was randomly matched with one individual without headache using propensity scores. All participants were followed from the date of enrollment until urinary calculi development, death, or the end of 2010.

RESULTS

The risk of urinary calculi was greater in the migraine than the control cohort (adjusted hazard ratio (aHR), 1.58; 95% confidence interval (CI), 1.52-1.63; p < 0.001, irrespective of the influence of topiramate. The risk was higher in younger and female patients. The magnitude of the risk was proportional to the annual frequency of clinic visits for headache (≥6 vs. <3, aHR = 1.11; 95% CI, 1.04-1.17; p = 0.002), but did not differ between migraine patients with and without aura.

CONCLUSIONS

Our study showed migraine was associated with an increased risk of urinary calculi, independent of topiramate use. A higher frequency of clinic visits was associated with a greater risk.

Behavioral effects and mechanisms of migraine pathogenesis following estradiol exposure in a multibehavioral model of migraine in rat

Migraine is one of the most common neurological disorders, leading to more than 1% of total disability reported and over 68 million visits to emergency rooms or physician's offices each year in the United States. Three times as many women as men have migraine, and while the mechanism behind this is not well understood, 17β-estradiol (estradiol) has been implicated to play a role. Studies have demonstrated that exposure to estrogen can lead to activation of inflammatory pathways, changes in sodium gated channel activity, as well as enhanced vasodilation and allodynia. Estradiol receptors are found in trigeminal nociceptors, which are involved in signaling during a migraine attack. The purpose of this study was to investigate the role of estradiol in migraine pathogenesis utilizing a multibehavioral model of migraine in rat. Animals were surgically implanted with a cannula system to induce migraine and behavior was assessed following exposure to a proestrus level of estradiol for total locomotor activity, light and noise sensitivity, evoked grooming patterns, and enhanced acoustic startle response. Results demonstrated decreased locomotor activity, increased light and noise sensitivity, altered facial grooming indicative of allodynia and enhanced acoustic startle. Further examination of tissue samples revealed increased expression of genes associated with inflammation and vasodilation. Overall, this study demonstrates exacerbation of migraine-like behaviors following exposure to estradiol and helps further explain the underlying mechanisms behind sex differences found in this common neurological disorder.

General trigeminospinal central sensitization and impaired descending pain inhibitory controls contribute to migraine progression

Migraine is a chronic disease with episodic manifestations. In a subgroup, attack frequency increases over time, leading to chronic migraine. One of the most important risk factors for migraine progression is frequency of headache attacks at baseline. Unfortunately, the actual effects of repeated activation of dural nociceptors are poorly known. We investigated the behavioral, anatomical, and electrophysiological changes induced by repeated low- and high-intensity stimulation of meningeal nociceptor by injecting an inflammatory soup in rats. Single high-intensity, but not low-intensity, stimulation produces a reversible cephalic allodynia. Upon repetition, however, low-intensity stimulation, too, induces a reversible cephalic allodynia, and high-intensity, reversible cephalic and extracephalic allodynia. Moreover, cephalic allodynia becomes, in part, persistent upon repeated high-intensity stimulation. Fos expression reveals that a single high-intensity stimulation already leads to widespread, trigeminal, and spinal central sensitization, and that such general central sensitization potentiates upon repetition. Trigeminovascular nociceptive neurons become persistently sensitized and their diffuse noxious inhibitory controls (DNIC) concomitantly impaired. Thus, compared with single stimulation, repeated dural nociceptor activation specifically leads to: 1) a gradual worsening of cutaneous hypersensitivity and general neuronal hyperexcitability and 2) spreading of cutaneous hypersensitivity superimposed on 3) persistent cephalic cutaneous hypersensitivity and trigeminal central sensitization. Such repetition-induced development of central sensitization and its consequence, cutaneous allodynia, may arise from both the general neuronal hyperexcitability that results from DNIC impairment and hyperexcitability that likely develops in trigeminal nociceptive neurons in response to their repetitive activation. These neuronal changes may in turn elevate the risk for developing chronic migraine.

Exposure to bisphenol A exacerbates migraine-like behaviors in a multibehavior model of rat migraine

Migraine is a common and debilitating neurological disorder suffered worldwide. Women experience this condition 3 times more frequently than men, with estrogen strongly implicated to play a role. Bisphenol A (BPA), a highly prevalent xenoestrogen, is known to have estrogenic activity and may have an effect in migraine onset, intensity, and duration through estrogen receptor signaling. It was hypothesized that BPA exposure exacerbates migraine symptoms through estrogen signaling and downstream activation of nociception related pathways. Utilizing a multibehavior model of migraine in ovariectomized female rats, changes in locomotion, light and sound sensitivity, grooming, and acoustic startle were examined. Furthermore, changes in the expression of genes related to estrogen (ERα, GPR30), and nociception (extracellular signal regulated kinase, ERK, sodium gated channel, Nav1.8, and fatty acid amide hydrolase, FAAH) were studied following behavioral experiments. The following results were obtained: BPA treatment significantly exacerbated migraine-like behaviors in rats. Rats exposed to BPA demonstrated decreased locomotion, exacerbated light and sound aversion, altered grooming habits, and enhanced startle reflexes. Furthermore, BPA exposure increased mRNA expression of estrogen receptors, total ERK mRNA and ERK activation, as well as Nav1.8, and FAAH mRNA, indicative of altered estrogen signaling and altered nociception. These results show that BPA, an environmentally pervasive xenoestrogen, exacerbates migraine-like behavior in a rat model and alters expression of estrogen and nociception-related genes.

Pearls and pitfalls in experimental in vivo models of headache: Conscious behavioral research

Background

Physiological studies have been determinant for the understanding of migraine pathophysiology and the screening of novel therapeutics. At present, there is no animal model that translates fully the clinical symptoms of migraine, and generally these studies are conducted on anesthetized animals.

Methodology

Pain as well as non-painful symptoms such as photophobia, need to have a conscious individual to be experienced; therefore, the new development and adaptation of behavioral assays assessing pain and other non-painful symptomatology in conscious animals represents a great opportunity for headache research and it is exciting that more and more researchers are using behavioral paradigms.

Summary

This review will describe the different behavioral models for the study of headache that are performed in non-anesthetized conscious animals. The pearls and challenges for measuring hypersensitivity in rodents such as the common tests for measuring mechanical allodynia and thermal hyperalgesia have been the landmark for the development of assays that measure hypersensitivity in the craniofacial region. Here we describe the different behavioral assays that measure hypersensitivity in the craniofacial region as well as the established behavioral models of trigeminovascular nociception and non-nociceptive migrainous symptoms.

A chronic animal model of migraine, induced by repeated meningeal nociception, characterized by a behavioral and pharmacological approach

BACKGROUND

Migraine is a chronic neurovascular disease characterized by recurrent unilateral headache, which induces incapacity. Despite all the progress that migraine research has provided, the neural mechanisms underlying the onset and maintenance of migraine attacks are poorly understood. Due to the complex characteristics of the disorder, it is difficult to develop a proper animal model that mimics all the clinical manifestations in humans.

OBJECTIVE

Taking into account the principal characteristics of the disease, the aim of this study is to develop a chronic animal model of migraine in which we can reproduce behavioral and pharmacological phenomena similar to those displayed by migraineurs.

RESULTS

Our animal model displayed behavioral and pharmacological results similar to those experienced by migraineurs. Specifically, there was a decrease in routine physical activity and an increase in resting behavior. Also, the animals exhibited a novel behavior that we called ipsilateral facial grooming behavior provoked by the meningeal nociception. Moreover, one of the drugs used as treatment for migraine reduced the manifestations previously described. Our results determine that the model mimics many of the clinical features that patients exhibit during migraine attacks. This model can contribute to further understanding of the pathophysiology and the study of novel therapeutic approaches.

Calcitonin gene-related peptide promotes the wound healing of human bronchial epithelial cells via PKC and MAPK pathways

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide derived from the calcitonin gene. CGRP is widely distributed in the central and peripheral neuronal systems. In the lung, CGRP could modulate dendritic cell function, stimulate proliferation of alveolar epithelial cells and mediate lung injury in mice. In this study, we investigated the effect of CGRP on the wound healing of human bronchial epithelial cells (HBECs) in vitro. The results showed that CGRP accelerated the recovery of wound area of monolayer HBECs in a dose-dependent manner. CGRP inhibited the lipopolysaccharide-induced apoptosis in HBECs. The percentage of S phase and G2/M phase was increased in HBECs after CGRP treatment. CGRP upregulated the expression of Ki67 in a dose-dependent manner. Some pathway inhibitors were used to investigate the signal pathway in which CGRP was involved. We found out that PKC pathway inhibitor (H-7) and MAPK pathway inhibitor (PD98059) could partially attenuate the effect of CGRP, which indicated that CGRP might promote the wound healing of HBECs via PKC and/or MAPK dependent pathway by accelerating migration and proliferation, and inhibiting apoptosis.

Effects of diet-induced obesity on motivation and pain behavior in an operant assay

Obesity has been associated with multiple chronic pain disorders, including migraine. We hypothesized that diet-induced obesity would be associated with a reduced threshold for thermal nociception in the trigeminal system. In this study, we sought to examine the effect of diet-induced obesity on facial pain behavior. Mice of two different strains were fed high-fat or regular diet (RD) and tested using a well-established operant facial pain assay. We found that the effects of diet on behavior in this assay were strain and reward dependent. Obesity-prone C57BL/6J mice fed a high-fat diet (HFD) display lower number of licks of a caloric, palatable reward (33% sweetened condensed milk or 30% sucrose) than control mice. This occurred at all temperatures, in both sexes, and was evident even before the onset of obesity. This diminished reward-seeking behavior was not observed in obesity-resistant SKH1-E (SK) mice. These findings suggest that diet and strain interact to modulate reward-seeking behavior. Furthermore, we observed a difference between diet groups in operant behavior with caloric, palatable rewards, but not with a non-caloric neutral reward (water). Importantly, we found no effect of diet-induced obesity on acute thermal nociception in the absence of inflammation or injury. This indicates that thermal sensation in the face is not affected by obesity-associated peripheral neuropathy as it occurs when studying pain behaviors in the rodent hindpaw. Future studies using this model may reveal whether obesity facilitates the development of chronic pain after injury or inflammation.

P2X3 receptor mediates ectopic mechanical allodynia with inflamed lower lip in mice

Ectopic pain in other orofacial regions develops with local inflammation in separated orofacial structures. However, the basis for the spreading of pain to adjacent orofacial areas after local inflammation is still unknown. In the present study, we determined if the P2X(3) receptor (P2X(3)R) was associated with altered mechanical sensitivity of the whisker pad skin following complete Freund's adjuvant (CFA) injection into the lower lip. Mice with local inflammation induced by CFA injection into the lower lip demonstrated significant mechanical allodynia of whisker pad skin. The mechanical allodynia was reversed by P2X(3)R antagonist, A-317491 administration into whisker pad skin. The number of P2X(3)R and calcitonin gene-related peptide (CGRP) positive trigeminal ganglion (TG) neurons that innervates the whisker pad skin and lower lip was increased after CFA injection into the lower lip. CGRP protein expression in TG ipsilateral to CFA injection was also significantly greater than that of the saline-injected mice. The present findings suggest that induced CGRP by local inflammation in the lower lip increases P2X(3)R in TG neurons, the increased P2X(3)Rs are involved in the sensitization of primary afferent neurons in the whisker pad skin. This P2X(3)R overexpression may underlie ectopic mechanical allodynia in the whisker pad skin after CFA injection into the lower lip.

Activation of TRPA1 on dural afferents: a potential mechanism of headache pain

Activation of transient receptor potential ankyrin-1 (TRPA1) on meningeal nerve endings has been suggested to contribute to environmental irritant-induced headache, but this channel may also contribute to other forms of headache, such as migraine. The preclinical studies described here examined functional expression of TRPA1 on dural afferents and investigated whether activation of TRPA1 contributes to headache-like behaviors. Whole-cell patch-clamp recordings were performed in vitro with 2 TRPA1 agonists, mustard oil (MO), and the environmental irritant umbellulone (UMB) on dural-projecting trigeminal ganglion neurons. Application of MO and UMB to dural afferents produced TRPA1-like currents in approximately 42% and 38% of cells, respectively. By means of an established in vivo behavioral model of migraine-related allodynia, dural application of MO and UMB produced robust time-related tactile facial and hind paw allodynia that was attenuated by pretreatment with the TRPA1 antagonist HC-030031. Additionally, MO or UMB were applied to the dura, and exploratory activity was monitored for 30min with an automated open-field activity chamber. Dural MO and UMB decreased the number of vertical rearing episodes and the time spent rearing in comparison to vehicle-treated animals. This change in activity was prevented in rats pretreated with HC-030031 as well as sumatriptan, a clinically effective antimigraine agent. These data indicate that TRPA1 is expressed on a substantial fraction of dural afferents, and activation of meningeal TRPA1 produces behaviors consistent with those observed in patients during migraine attacks. Further, they suggest that activation of meningeal TRPA1 via endogenous or exogenous mechanisms can lead to afferent signaling and headache.

Maternal inhibition of infant behavioral response following isolation in novel surroundings and inflammatory challenge

During isolation in a novel environment, guinea pig pups gradually begin to display passive behavior that appears to be mediated by proinflammatory activity, that is, "sickness behavior.". Administration of substances that increase proinflammatory activity [corticotropin-releasing factor (CRF), lipopolysaccharide (LPS)] prior to isolation induces passive behavior from the beginning of the isolation episode. Here, we show that reunion with the mother in the novel environment rapidly and potently suppresses the passive behavior of isolated pups (Experiment 1); inhibits the passive behavior of pups administered CRF (10 µg, subcutaneous; Experiment 2); and inhibits the passive behavior of male, though not female, pups administered LPS (250 µg/kg, intraperitoneal; Experiment 3). Together these findings suggest that the presence of the mother either recruits other processes that moderate the impact of proinflammatory processes on brain mechanisms mediating the passive response or initiates compensatory mechanisms that counter the effect of proinflammatory activity. Further, the results suggest that for physically ill animals of social species, the adaptive advantage that accrues from maintaining normal social interactions may sometimes outweigh the advantage gained by engaging in sickness behavior.

Effects of aging on blood brain barrier and matrix metalloproteases following controlled cortical impact in mice

Aging alters the ability of the brain to respond to injury. One of the major differences between the adult and aged brain is that comparable injuries lead to greater blood brain barrier disruption in the aged brain. The goals of these studies were to quantify the effects of age on BBB permeability using high field strength MRI T1 mapping and to determine whether activation of matrix metalloproteases, their inhibitors, or expression of blood brain barrier structural proteins, occludin, zonnula occludins-1 (ZO-1) and claudin-5 were altered following injury to the aged C57/BL6 mouse brain. T1 mapping studies revealed greater blood brain barrier permeability in the aged (21-24 months old) brain than in the adult (4-6 months old) following controlled cortical impact. The increased blood brain barrier permeability in the pericontusional region was confirmed with IgG immunohistochemistry. MMP-9 activity was increased following controlled cortical impact in the aged brain, and this was accompanied by increased MMP-9 gene expression. MMP-2 activity was higher in the uninjured aged brain than in the adult brain. Occludin and ZO-1 mRNA levels were unchanged following injury in either age group, but claudin-5 mRNA levels were lower in the aged than the adult brain following injury. These results demonstrate quantitative increases in blood brain barrier permeability in the aged brain following injury that are accompanied by increased MMP-9 activation and decreased blood brain barrier repair responses.