Sodium MRI in a rat migraine model and a NEURON simulation study support a role for sodium in migraine

Effects of Nitric Oxide on the Activity of P2X and TRPV1 Receptors in Rat Meningeal Afferents of the Trigeminal Nerve

Nitric oxide is one of the endogenous molecules that play a key role in migraine. However, the interaction between NO and the main players in the nociceptive activity of the meningeal trigeminal afferents-TRPV1 and P2X3 receptors-remains unstudied. In the current project, the effects of acute and chronic NO administration on the activity of TRPV1 and P2X3 receptors in the peripheral afferents were studied using electrophysiological recording of action potentials of the trigeminal nerve in the rat hemiskull preparations. The data obtained indicate that exogenous and endogenous NO increased the activity of the trigeminal nerve independent on the inhibition of the TRPV1 and P2X3 receptors. The activity of the trigeminal nerve triggered by ATP changed neither in acute incubation in the NO donor-sodium nitroprusside (SNP) nor in the chronic nitroglycerine (NG)-induced migraine model. Moreover, the chronic NG administration did not increase in the number of degranulated mast cells in the rat meninges. At the same time, the capsaicin-induced activity of the trigeminal nerve was higher with chronic NO administration or after acute NO application, and these effects were prevented by N-ethylmaleimide. In conclusion, we suggested that NO positively modulates the activity of TRPV1 receptors by S-nitrosylation, which may contribute to the pro-nociceptive action of NO and underlie the sensitization of meningeal afferents in chronic migraine.

Association between Migraines and Prior Proton Pump Inhibitor Use: A Nested Case-Control Study Using a National Health Screening Cohort

The effect of proton pump inhibitor (PPI) use on migraine risk remains controversial. We explored the odds of migraines in relation to prior PPI use and treatment duration. Data from the Korean National Health Insurance Service-Health Screening Cohort (2002−2015) were analyzed in this nested case-control study involving 28,159 participants with incident migraines and 112,636 controls (1:4 matched by sex, age, income, and residential region). The baseline covariates were balanced by performing propensity score overlap weighting-based adjustments, and the effect of prior PPI use (past vs. current) and treatment duration (<30 and 30−365 days vs. ≥365 days) on incident migraines was evaluated using logistic regression. In past and current PPI users, prior PPI use raised the likelihood of migraines (adjusted odds ratio [95% confidence interval]: 2.56 [2.36−2.79] and 4.66 [4.29−5.06], respectively). Participants who used PPI for <30, 30−365, or ≥365 days exhibited high odds of migraines (2.49 [2.29−2.72], 4.41 [4.05−4.79], and 4.14 [3.77−4.54], respectively). Incident migraines with or without aura also increased independently of PPI use history or duration. In summary, prior PPI use, irrespective of the elapsed time since use and the duration of use, is possibly associated with incident migraines with or without aura.

Nitroglycerin as a model of migraine: Clinical and preclinical review

Migraine stands as one of the most disabling neurological conditions worldwide. It is a disorder of great challenge to study given its heterogeneous representation, cyclic nature, and complexity of neural networks involved. Despite this, clinical and preclinical research has greatly benefitted from the use of the nitric oxide donor, nitroglycerin (NTG), to model this disorder, dissect underlying mechanisms, and to facilitate the development and screening of effective therapeutics. NTG is capable of triggering a migraine attack, only in migraineurs or patients with a history of migraine and inducing migraine-like phenotypes in rodent models. It is however unclear to what extent NTG and NO, as its breakdown product, is a determinant factor in the underlying pathophysiology of migraine, and importantly, whether it really does facilitate the translation from the bench to the bedside, and vice-versa. This review provides an insight into the evidence supporting the strengths of this model, as well as its limitations, and shines a light into the possible role of NO-related mechanisms in altered molecular signalling pathways.

Hyperhomocysteinemia Increases Cortical Excitability and Aggravates Mechanical Hyperalgesia and Anxiety in a Nitroglycerine-Induced Migraine Model in Rats

Homocysteine is a sulfur-containing endogenous amino acid leading to neurotoxic effects at high concentrations. Population studies suggest an association between plasma homocysteine levels and the risk of migraine headaches. The aim of this study was to analyze the sensitivity of rats with prenatal hyperhomocysteinemia (hHCY) in respect of the development of behavioral correlates of headache and spreading cortical depolarization (CSD) in a migraine model induced by the administration of the nitric oxide (NO) donor nitroglycerin. Animals with hHCY were characterized by migraine-related symptoms such as mechanical hyperalgesia, high-level anxiety, photophobia, as well as an enhanced level of neuronal activity in the somatosensory cortex along with a lower threshold of CSD generation. Likewise, acute or chronic intermittent administration of nitroglycerin also induced the development of mechanical allodynia, photophobia and anxiety in control groups. However, these symptoms were more pronounced in rats with hHCY. Unlike hHCY, nitroglycerin administration did not affect the threshold of CSD generation, but like hHCY, increased the background neuronal activity in layers 2/3 and 4 of the cerebral cortex. The latter was more pronounced in animals with hHCY. Thus, the migraine profile associated with hHCY can be further exaggerated in conditions with enhanced levels of migraine triggering the gaseous transmitter NO. Our data are consistent with the view that high levels of plasma homocysteine can act as a risk factor for the development of migraine.

Cortical excitability in migraine: Contributions of magnetic resonance imaging

Migraine is characterized by symptoms related to cortical hyperexcitability such as photophobia, phonophobia, osmophobia and allodynia. One-third of migraineurs experience aura, whose neurophysiological substrate is thought to be cortical spreading depression (CSD). Functional magnetic resonance imaging (MRI) has shown the migraine aura to be characterized by cerebral hyperactivity/hyperperfusion followed by hypometabolism/hypoperfusion spreading along the occipital cortex with the same spatiotemporal organization as the experimentally triggered CSD. The link between migraine aura and headache remains undetermined. Neuroimaging studies have failed to show a leakage of the blood-brain barrier, which was suspected to occur during CSD and to cause the stimulation of trigeminal nociceptive receptors. However, recent studies have highlighted the involvement of neuroglial inflammation and other studies have suggested that a common central network plays a role in the link between CSD and migraine pain. Finally, MRI has made it possible to study the contribution of metabolites such as glutamic acid, γ-amino-butyric acid and sodium in the pathophysiology of hyperexcitability in migraine.

Evidence that blood-CSF barrier transport, but not inflammatory biomarkers, change in migraine, while CSF sVCAM1 associates with migraine frequency and CSF fibrinogen

Objective

Our objective is to explore whether blood–cerebrospinal fluid (CSF) barrier biomarkers differ in episodic migraine (EM) or chronic migraine (CM) from controls.

Background

Reports of blood–brain barrier and blood–cerebrospinal fluid barrier (BCSFB) disruption in migraine vary. Our hypothesis is that investigation of biomarkers associated with blood, CSF, brain, cell adhesion, and inflammation will help elucidate migraine pathophysiology.

Methods

We recruited 14 control volunteers without headache disorders and 42 individuals with EM or CM as classified using the International Classification of Headache Disorders, 3rd edition, criteria in a cross‐sectional study located at our Pasadena and Stanford headache research centers in California. Blood and lumbar CSF samples were collected once from those diagnosed with CM or those with EM during two states: during a typical migraine, before rescue therapy, with at least 6/10 level of pain (ictal); and when migraine free for at least 48 h (interictal). The average number of headaches per month over the previous year was estimated by those with EM; this enabled comparison of biomarker changes between controls and three headache frequency groups: <2 per month, 2–14 per month, and CM. Blood and CSF biomarkers were determined using antibody‐based methods.

Results

Antimigraine medication was only taken by the EM and CM groups. Compared to controls, the migraine group had significantly higher mean CSF–blood quotients of albumin (Q_alb: mean ± standard deviation (SD): 5.6 ± 2.3 vs. 4.1 ± 1.9) and fibrinogen (Q_fib mean ± SD: 1615 ± 99.0 vs. 86.1 ± 55.0). Mean CSF but not plasma soluble vascular cell adhesion molecule‐1 (sVCAM‐1) levels were significantly higher in those with more frequent migraine: (4.5 ng/mL ± 1.1 in those with <2 headache days a month; 5.5 ± 1.9 with 2–14 days a month; and 7.1 ± 2.9 in CM), while the Q_fib ratio was inversely related to headache frequency. We did not find any difference in individuals with EM or CM from controls for CSF cell count, total protein, matrix metalloproteinase‐9, soluble platelet‐derived growth factor receptor β, tumor necrosis factor‐alpha, interferon‐gamma, interleukin (IL)‐6, IL‐8, IL‐10, or C‐reactive protein.

Conclusions

The higher Q_alb and Q_fib ratios may indicate that the transport of these blood‐derived proteins is disturbed at the BCSFB in persons with migraine. These changes most likely occur at the choroid plexus epithelium, as there are no signs of typical endothelial barrier disruption. The most striking finding in this hypothesis‐generating study of migraine pathophysiology is that sVCAM‐1 levels in CSF may be a biomarker of higher frequency of migraine and CM. An effect from migraine medications cannot be excluded, but there is no known mechanism to suggest they have a role in altering the CSF biomarkers.

Regulation of CSF and Brain Tissue Sodium Levels by the Blood-CSF and Blood-Brain Barriers During Migraine

Cerebrospinal fluid (CSF) and brain tissue sodium levels increase during migraine. However, little is known regarding the underlying mechanisms of sodium homeostasis disturbance in the brain during the onset and propagation of migraine. Exploring the cause of sodium dysregulation in the brain is important, since correction of the altered sodium homeostasis could potentially treat migraine. Under the hypothesis that disturbances in sodium transport mechanisms at the blood-CSF barrier (BCSFB) and/or the blood-brain barrier (BBB) are the underlying cause of the elevated CSF and brain tissue sodium levels during migraines, we developed a mechanistic, differential equation model of a rat's brain to compare the significance of the BCSFB and the BBB in controlling CSF and brain tissue sodium levels. The model includes the ventricular system, subarachnoid space, brain tissue and blood. Sodium transport from blood to CSF across the BCSFB, and from blood to brain tissue across the BBB were modeled by influx permeability coefficients P_BCSFB and P_BBB, respectively, while sodium movement from CSF into blood across the BCSFB, and from brain tissue to blood across the BBB were modeled by efflux permeability coefficients PBCSFB′ and PBBB′, respectively. We then performed a global sensitivity analysis to investigate the sensitivity of the ventricular CSF, subarachnoid CSF and brain tissue sodium concentrations to pathophysiological variations in P_BCSFB, P_BBB, PBCSFB′ and PBBB′. Our results show that the ventricular CSF sodium concentration is highly influenced by perturbations of P_BCSFB, and to a much lesser extent by perturbations of PBCSFB′. Brain tissue and subarachnoid CSF sodium concentrations are more sensitive to pathophysiological variations of P_BBB and PBBB′ than variations of P_BCSFB and PBCSFB′ within 30 min of the onset of the perturbations. However, P_BCSFB is the most sensitive model parameter, followed by P_BBB and PBBB′, in controlling brain tissue and subarachnoid CSF sodium levels within 3 h of the perturbation onset.

Cerebral sodium (23Na) magnetic resonance imaging in patients with migraine - a case-control study

OBJECTIVE

Evaluation of MRI-derived cerebral ²³Na concentrations in patients with migraine in comparison with healthy controls.

MATERIALS AND METHODS

In this case-control study, 24 female migraine patients (mean age, 34 ± 11 years) were enrolled after evaluation of standardized questionnaires. Half (n = 12) of the cohort suffered from migraine, the other half was impaired by both migraine and tension-type headaches (TTH). The combined patient cohort was matched to 12 healthy female controls (mean age, 34 ± 11 years). All participants underwent a cerebral ²³Na-magnetic resonance imaging examination at 3.0 T, which included a T1w MP-RAGE sequence and a 3D density-adapted, radial gradient echo sequence for ²³Na imaging. Circular regions of interests were placed in predetermined anatomic regions: cerebrospinal fluid (CSF), gray and white matter, brain stem, and cerebellum. External ²³Na reference phantoms were used to calculate the total ²³Na tissue concentrations. Pearson's correlation, Kendall Tau, and Wilcoxon rank sum test were used for statistical analysis.

RESULTS

²³Na concentrations of all patients in the CSF were significantly higher than in healthy controls (p < 0.001). The CSF of both the migraine and mixed migraine/TTH group showed significantly increased sodium concentrations compared to the control group (p = 0.007 and p < 0.001). Within the patient cohort, a positive correlation between pain level and TSC in the CSF (r = 0.62) could be observed.

CONCLUSION

MRI-derived cerebral ²³Na concentrations in the CSF of migraine patients were found to be statistically significantly higher than in healthy controls.

KEY POINTS

• Cerebral sodium MRI supports the theory of ionic imbalances and may aid in the challenging pathophysiologic understanding of migraine. • Case-control study shows significantly higher sodium concentrations in cerebrospinal fluid of migraineurs. • Cerebral sodium MRI may become a non-invasive imaging tool for drugs to modulate sodium, and hence migraine, on a molecular level, and influence patient management.

Endogenous Na+, K+-ATPase inhibitors and CSF [Na+] contribute to migraine formation

There is strong evidence that neuronal hyper-excitability underlies migraine, and may or may not be preceded by cortical spreading depression. However, the mechanisms for cortical spreading depression and/or migraine are not established. Previous studies reported that cerebrospinal fluid (CSF) [Na+] is higher during migraine, and that higher extracellular [Na+] leads to hyper-excitability. We raise the hypothesis that altered choroid plexus Na+, K+-ATPase activity can cause both migraine phenomena: inhibition raises CSF [K+] and initiates cortical spreading depression, while activation raises CSF [Na+] and causes migraine. In this study, we examined levels of specific Na+, K+-ATPase inhibitors, endogenous ouabain-like compounds (EOLC), in CSF from migraineurs and controls. CSF EOLC levels were significantly lower during ictal migraine (0.4 nM +/- 0.09) than from either controls (1.8 nM +/- 0.4) or interictal migraineurs (3.1 nM +/- 1.9). Blood plasma EOLC levels were higher in migraineurs than controls, but did not differ between ictal and interictal states. In a Sprague-Dawley rat model of nitroglycerin-triggered central sensitization, we changed the concentrations of EOLC and CSF sodium, and measured aversive mechanical threshold (von Frey hairs), trigeminal nucleus caudalis activation (cFos), and CSF [Na+] (ultra-high field 23Na MRI). Animals were sensitized by three independent treatments: intraperitoneal nitroglycerin, immunodepleting EOLC from cerebral ventricles, or cerebroventricular infusion of higher CSF [Na+]. Conversely, nitroglycerin-triggered sensitization was prevented by either vascular or cerebroventricular delivery of the specific Na+, K+-ATPase inhibitor, ouabain. These results affirm our hypothesis that higher CSF [Na+] is linked to human migraine and to a rodent migraine model, and demonstrate that EOLC regulates them both. Our data suggest that altered choroid plexus Na+, K+-ATPase activity is a common source of these changes, and may be the initiating mechanism in migraine.

Dynamic sodium imaging at ultra-high field reveals progression in a preclinical migraine model

Under the hypothesis that increased extracellular sodium induces sustained neuronal excitability with the onset and progression of migraine, this study evaluates dynamic in vivo Na fluxes in the brain of a preclinical rodent analogue of migraine. Ultra-high field Na magnetic resonance imaging (MRI) at 21.1 T has demonstrated potential to quantify sodium concentrations with good spatial and temporal resolution after the onset of central sensitization. Sprague-Dawley male rats with implanted intraperitoneal lines were studied by MRI before and after an in situ injection of 10 mg/kg of nitroglycerin (NTG) vs vehicle and saline controls. Slice-selective Na images were acquired using a multislice free induction decay-based chemical shift imaging sequence with resolution of 1.1 × 1.1 × 3 mm for a 9-minute acquisition. A total of 27 repeated scans were acquired over 1 hour of baseline scanning and longitudinally up to 3 hours after injection. Increases of Na MRI signal in the brainstem, extracerebral cerebrospinal fluid, and cisterna magna were evident almost immediately after NTG injection, gaining significance from controls in 36 minutes. The cerebellum and third ventricle also showed sustained trends of increased Na, with the former gaining significance at over 2 hours after NTG injection. The data provide evidence of an early change in sodium concentration, markedly in posterior fossa cerebrospinal fluid and brainstem regions. Further study of fluctuations of sodium concentration and their modulation with treatments could help understand the dynamic features of migraine, locate a putative migraine generator, and guide development of therapeutic measures to correct the disturbance of sodium homeostasis.

Metabolic assessment of a migraine model using relaxation-enhanced 1 H spectroscopy at ultrahigh field

PURPOSE

This study evaluates biochemical imbalances in a rat model that reflects dysfunctional pathways in migraine. The high sensitivity and spectral dispersion available to 1 H MRS at 21.1 T expands metabolic profiling in this migraine model to include lactate (Lac), taurine (Tau), aspartate, and Gly-a mixture of glycine, glutamine, and glutamate.

METHODS

Sprague-Dawley male rats were administered in situ an intraperitoneal injection of nitroglycerin (NTG) to induce the migraine analogue or saline as a control. A selective relaxation-enhanced MR spectroscopy sequence was used to target upfield metabolites from a 4-mm3 voxel for 2.5 h after injection.

RESULTS

Significant increases were evident for Lac as early as 10 min after NTG injection, peaking over 50% compared with baseline and control (normalized Lac/N-acetyl aspartate with NTG = 1.54 ± 0.65 versus with saline = 0.99 ± 0.08). Tau decreased progressively in controls over 2 h after injection, but remained elevated with NTG, peaking at 105 min after injection (normalized Tau/N-acetyl aspartate with NTG = 1.10 ± 0.18 versus with saline = 0.85 ± 0.14). Total creatine under NTG showed significant decreases with time and compared with saline; Gly demonstrated temporal increases for NTG.

CONCLUSIONS

These changes indicate an altered metabolic profile in the migraine analogue consistent with early changes in neural activity and/or vasodilation consistent with progressively enhanced neuroprotection and osmoregulation. Magn Reson Med 79:1266-1275, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

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.

Roads Less Traveled: Sexual Dimorphism and Mast Cell Contributions to Migraine Pathology

Migraine is a common, little understood, and debilitating disease. It is much more prominent in women than in men (~2/3 are women) but the reasons for female preponderance are not clear. Migraineurs frequently experience severe comorbidities, such as allergies, depression, irritable bowel syndrome, and others; many of the comorbidities are more common in females. Current treatments for migraine are not gender specific, and rarely are migraine and its comorbidities considered and treated by the same specialist. Thus, migraine treatments represent a huge unmet medical need, which will only be addressed with greater understanding of its underlying pathophysiology. We discuss the current knowledge about sex differences in migraine and its comorbidities, and focus on the potential role of mast cells (MCs) in both. Sex-based differences in pain recognition and drug responses, fluid balance, and the blood–brain barrier are recognized but their impact on migraine is not well studied. Furthermore, MCs are well recognized for their prominent role in allergies but much less is known about their contributions to pain pathways in general and migraine specifically. MC-neuron bidirectional communication uniquely positions these cells as potential initiators and/or perpetuators of pain. MCs can secrete nociceptor sensitizing and activating agents, such as serotonin, prostaglandins, histamine, and proteolytic enzymes that can also activate the pain-mediating transient receptor potential vanilloid channels. MCs express receptors for both estrogen and progesterone that induce degranulation upon binding. Furthermore, environmental estrogens, such as Bisphenol A, activate MCs in preclinical models but their impact on pain pathways or migraine is understudied. We hope that this discussion will encourage scientists and physicians alike to bridge the knowledge gaps linking sex, MCs, and migraine to develop better, more comprehensive treatments for migraine patients.

Severe Headache or Migraine History is Inversely Correlated With Dietary Sodium Intake: NHANES 1999-2004

Objective

We investigated whether dietary sodium intake from respondents of a national cross‐sectional nutritional study differed by history of migraine or severe headaches.

Background

Several lines of evidence support a disruption of sodium homeostasis in migraine.

Design

Our analysis population was 8819 adults in the 1999–2004 National Health and Nutrition Examination Survey (NHANES) with reliable data on diet and headache history. We classified respondents who reported a history of migraine or severe headaches as having probable history of migraine. To reduce the diagnostic conflict from medication overuse headache, we excluded respondents who reported taking analgesic medications. Dietary sodium intake was measured using validated estimates of self‐reported total grams of daily sodium consumption and was analyzed as the residual value from the linear regression of total grams of sodium on total calories. Multivariable logistic regression that accounted for the stratified, multistage probability cluster sampling design of NHANES was used to analyze the relationship between migraine and dietary sodium.

Results

Odds of probable migraine history decreased with increasing dietary sodium intake (odds ratio = 0.93, 95% confidence interval = 0.87, 1.00, P = .0455). This relationship was maintained after adjusting for age, sex, and body mass index (BMI) with slightly reduced significance (P = .0505). In women, this inverse relationship was limited to those with lower BMI (P = .007), while in men the relationship did not differ by BMI. We likely excluded some migraineurs by omitting frequent analgesic users; however, a sensitivity analysis suggested little effect from this exclusion.

Conclusions

This study is the first evidence of an inverse relationship between migraine and dietary sodium intake. These results are consistent with altered sodium homeostasis in migraine and our hypothesis that dietary sodium may affect brain extracellular fluid sodium concentrations and neuronal excitability.

Computational modeling of peripheral pain: a commentary

This commentary is intended to find possible explanations for the low impact of computational modeling on pain research. We discuss the main strategies that have been used in building computational models for the study of pain. The analysis suggests that traditional models lack biological plausibility at some levels, they do not provide clinically relevant results, and they cannot capture the stochastic character of neural dynamics. On this basis, we provide some suggestions that may be useful in building computational models of pain with a wider range of applications.

Sodium 3D COncentration MApping (COMA 3D) using (23)Na and proton MRI

Functional changes of sodium 3D MRI signals were converted into millimolar concentration changes using an open-source fully automated MATLAB toolbox. These concentration changes are visualized via 3D sodium concentration maps, and they are overlaid over conventional 3D proton images to provide high-resolution co-registration for easy correlation of functional changes to anatomical regions. Nearly 5000/h concentration maps were generated on a personal computer (ca. 2012) using 21.1T 3D sodium MRI brain images of live rats with spatial resolution of 0.8×0.8×0.8 mm(3) and imaging matrices of 60×60×60. The produced concentration maps allowed for non-invasive quantitative measurement of in vivo sodium concentration in the normal rat brain as a functional response to migraine-like conditions. The presented work can also be applied to sodium-associated changes in migraine, cancer, and other metabolic abnormalities that can be sensed by molecular imaging. The MATLAB toolbox allows for automated image analysis of the 3D images acquired on the Bruker platform and can be extended to other imaging platforms. The resulting images are presented in a form of series of 2D slices in all three dimensions in native MATLAB and PDF formats. The following is provided: (a) MATLAB source code for image processing, (b) the detailed processing procedures, (c) description of the code and all sub-routines, (d) example data sets of initial and processed data. The toolbox can be downloaded at: http://www.vuiis.vanderbilt.edu/~truongm/COMA3D/.

Altered brainstem auditory evoked potentials in a rat central sensitization model are similar to those in migraine

Migraine symptoms often include auditory discomfort. Nitroglycerin (NTG)-triggered central sensitization (CS) provides a rodent model of migraine, but auditory brainstem pathways have not yet been studied in this example. Our objective was to examine brainstem auditory evoked potentials (BAEPs) in rat CS as a measure of possible auditory abnormalities. We used four subdermal electrodes to record horizontal (h) and vertical (v) dipole channel BAEPs before and after injection of NTG or saline. We measured the peak latencies (PLs), interpeak latencies (IPLs), and amplitudes for detectable waveforms evoked by 8, 16, or 32 kHz auditory stimulation. At 8 kHz stimulation, vertical channel positive PLs of waves 4, 5, and 6 (vP4, vP5, and vP6), and related IPLs from earlier negative or positive peaks (vN1-vP4, vN1-vP5, vN1-vP6; vP3-vP4, vP3-vP6) increased significantly 2h after NTG injection compared to the saline group. However, BAEP peak amplitudes at all frequencies, PLs and IPLs from the horizontal channel at all frequencies, and the vertical channel stimulated at 16 and 32 kHz showed no significant/consistent change. For the first time in the rat CS model, we show that BAEP PLs and IPLs ranging from putative bilateral medial superior olivary nuclei (P4) to the more rostral structures such as the medial geniculate body (P6) were prolonged 2h after NTG administration. These BAEP alterations could reflect changes in neurotransmitters and/or hypoperfusion in the midbrain. The similarity of our results with previous human studies further validates the rodent CS model for future migraine research.

Opposite reactivity of meningeal versus cortical microvessels to the nitric oxide donor glyceryl trinitrate evaluated in vivo with two-photon imaging

Vascular changes underlying headache in migraine patients induced by Glyceryl trinitrate (GTN) were previously studied with various imaging techniques. Despite the long history of medical and experimental use of GTN, its effects on the brain vasculature are still poorly understood presumably due to low spatial resolution of the imaging modalities used so far. We took advantage of the micrometer-scale vertical resolution of two-photon microscopy to differentiate between the vasodynamic effects of GTN on meningeal versus cortical vessels imaged simultaneously in anesthetized rats through either thinned skull or glass-sealed cranial window. Intermediate and small calibre vessels were visualized in vivo by imaging intravascular fluorescent dextran, and detection of blood flow direction allowed identification of individual arterioles and venules. We found that i.p.-injected GTN induced a transient constriction of meningeal arterioles, while their cortical counterparts were, in contrast, dilated. These opposing effects of GTN were restricted to arterioles, whereas the effects on venules were insignificant. Interestingly, the NO synthase inhibitor L-NAME did not affect the diameter of meningeal vessels but induced a constriction of cortical vessels. The different cellular environment in cortex versus meninges as well as distinct vessel wall anatomical features probably play crucial role in the observed phenomena. These findings highlight differential region- and vessel-type-specific effects of GTN on cranial vessels, and may implicate new vascular mechanisms of NO-mediated primary headaches.

Na,K-ATPase alpha isoforms at the blood-cerebrospinal fluid-trigeminal nerve and blood-retina interfaces in the rat

Background

Cerebrospinal fluid (CSF) sodium concentration increases during migraine attacks, and both CSF and vitreous humor sodium increase in the rat migraine model. The Na,K-ATPase is a probable source of these sodium fluxes. Since Na,K-ATPase isoforms have different locations and physiological roles, our objective was to establish which alpha isoforms are present at sites where sodium homeostasis is disrupted.

Methods

Specific Na,K-ATPase alpha isoforms were identified in rat tissues by immunohistochemistry at the blood-CSF barrier at the choroid plexus, at the blood-CSF-trigeminal barrier at the meninges, at the blood-retina barrier, and at the blood-aqueous barrier at the ciliary body. Calcitonin gene-related peptide (CGRP), occludin, or von Willibrand factor (vWF) were co-localized with Na,K-ATPase to identify trigeminal nociceptor fibers, tight junctions, and capillary endothelial cells respectively.

Results

The Na,K-ATPase alpha-2 isoform is located on capillaries and intensely at nociceptive trigeminal nerve fibers at the meningeal blood-CSF-trigeminal barrier. Alpha-1 and −3 are lightly expressed on the trigeminal nerve fibers but not at capillaries. Alpha-2 is expressed at the blood-retina barriers and, with alpha-1, at the ciliary body blood aqueous barrier. Intense apical membrane alpha-1 was associated with moderate cytoplasmic alpha-2 expression at the choroid plexus blood-CSF barrier.

Conclusion

Na,K-ATPase alpha isoforms are present at the meningeal, choroid plexus, and retinal barriers. Alpha-2 predominates at the capillary endothelial cells in the meninges and retinal ganglion cell layer.

"Headache and epilepsy"--how are they connected?

The relationship between headache and seizures is a complicated one, since these two conditions are related in numerous ways. Although the nature of this association is unclear, several plausible explanations exist: the two disorders coexist by chance; headache is part (or even the sole ictal phenomenon) of seizures or the post-ictal state; both disorders share a common underlying etiology; and epilepsy mimics the symptoms of migraine (as in benign childhood epilepsy). Seizures and headaches as well as their respective primary syndromes (epilepsy and headache/migraine) share several pathophysiological mechanisms. These mechanisms especially involve neurotransmitter and ion channel dysfunctions. Also, photosensitivity seems to play a role in the connection. In order to improve the care for patients with a clinical connection between migraine and epilepsy, it is necessary to try to understand more accurately the exact pathophysiological point of connection between these two conditions. Both experimental and clinical measures are required to better understand this relationship. The development of animal models, molecular studies defining more precise genotype/phenotype correlations, and multicenter clinical studies with revision of clinical criteria for headache/epilepsy-related disorders represent the start for planning future translational research. In this paper, we review the relationship between migraine and epilepsy in terms of epidemiology and pathophysiology with regard to translational research and clinical correlations and classification.

Sodium MRI and the assessment of irreversible tissue damage during hyper-acute stroke

Sodium MRI (sMRI) has undergone a tremendous amount of technical development during the last two decades that makes it a suitable tool for the study of human pathology in the acute setting within the constraints of a clinical environment. The salient role of the sodium ion during impaired ATP production during the course of brain ischemia makes sMRI an ideal tool for the study of ischemic tissue viability during stroke. In this paper, the current limitations of conventional MRI for the determination of tissue viability during evolving brain ischemia are discussed. This discussion is followed by a summary of the known findings about the dynamics of tissue sodium changes during brain ischemia. A mechanistic model for the explanation of these findings is presented together with the technical requirements for its investigation using clinical MRI scanners. An illustration of the salient features of the technique is also presented using a nonhuman primate model of reversible middle cerebral artery occlusion.

Extracellular sodium modulates the excitability of cultured hippocampal pyramidal cells

Recent studies demonstrated a photophobia mechanism with modulation of nociceptive, cortico-thalamic neurons by retinal ganglion cell projections; however, little is known about how their neuronal homeostasis is disrupted. Since we have found that lumbar cerebrospinal fluid (CSF) sodium increases during migraine and that cranial sodium increases in a rat migraine model, the purpose of this study was to examine the effects of extracellular sodium ([Na(+)](o)) on the intrinsic excitability of hippocampal pyramidal neurons. We monitored excitability by whole cell patch using a multiplex micropipette with a common outlet to change artificial CSF (ACSF) [Na(+)](o) at cultured neurons accurately (SD<7 mM) and rapidly (<5s) as determined by a sodium-selective micro-electrode of the same size and at the same location as a neuronal soma. Changing [Na(+)](o) in ACSF from 100 to 160 mM, choline-balanced at 310-320 mOsm, increased the action potential (AP) amplitude, decreased AP width, and augmented firing rate by 28%. These effects were reversed on returning the ACSF [Na(+)](o) to 100mM. Testing up to 180 mM [Na(+)](o) required ACSF with higher osmolarity (345-355 mOsm), at which the firing rate increased by 36% between 100 and 180 mM [Na(+)](o), with higher amplitude and narrower APs. In voltage clamp mode, the sodium and potassium currents increased significantly at higher [Na(+)](o). These results demonstrate that fluctuations in [Na(+)](o) modulate neuronal excitability by a sodium current mechanism and that excessively altered neuronal excitability may contribute to hypersensitivity symptoms.