Synaptic Zn2+ contributes to deleterious consequences of spreading depolarizations

Spreading depolarizations (SDs) are profound waves of neuroglial depolarization that can propagate repetitively through injured brain. Recent clinical work has established SD as an important contributor to expansion of acute brain injuries and have begun to extend SD studies into other neurological disorders. A critical challenge is to determine how to selectively prevent deleterious consequences of SD. In the present study, we determined whether a wave of profound Zn2+ release is a key contributor to deleterious consequences of SD, and whether this can be targeted pharmacologically. Focal KCl microinjection was used to initiate SD in the CA1 region of the hippocampus in murine brain slices. An extracellular Zn2+ chelator with rapid kinetics (ZX1) increased SD propagation rates and improved recovery of extracellular DC potential shifts. Under conditions of metabolic compromise, tissues showed sustained impairment of functional and structural recovery following a single SD. ZX1 effectively improved recovery of synaptic potentials and intrinsic optical signals in these vulnerable conditions. Fluorescence imaging and genetic deletion of a presynaptic Zn2+ transporter confirmed synaptic release as the primary contributor to extracellular accumulation and deleterious consequences of Zn2+ during SD. These results demonstrate a role for synaptic Zn2+ release in deleterious consequences of SD and show that targeted extracellular chelation could be useful for disorders where repetitive SD enlarges infarcts in injured tissues.

Vagus nerve stimulation inhibits cortical spreading depression via glutamate-dependent TrkB activation mechanism in the nucleus tractus solitarius

BACKGROUND

Vagus nerve stimulation (VNS) was recently found to inhibit cortical spreading depression (CSD), the underlying mechanism of migraine aura, through activation of the nucleus tractus solitarius (NTS), locus coeruleus (LC) and dorsal raphe nucleus (DRN). The molecular mechanisms underlying the effect of VNS on CSD in these nuclei remain to be explored. We hypothesized that VNS may activate glutamate receptor-mediated tropomyosin kinase B (TrkB) signaling in the NTS, thereby facilitating the noradrenergic and serotonergic neurotransmission to inhibit CSD.

METHODS

To investigate the role of TrkB and glutamate receptors in non-invasive VNS efficacy on CSD, a validated KCl-evoked CSD rat model coupled with intra-NTS microinjection of selective antagonists, immunoblot and immunohistochemistry was employed.

RESULTS

VNS increased TrkB phosphorylation in the NTS. Inhibition of intra-NTS TrkB abrogated the suppressive effect of VNS on CSD and CSD-induced cortical neuroinflammation. TrkB was found colocalized with glutamate receptors in NTS neurons. Inhibition of glutamate receptors in the NTS abrogated VNS-induced TrkB activation. Moreover, the blockade of TrkB in the NTS attenuated VNS-induced activation of the LC and DRN.

CONCLUSIONS

VNS induces the activation of glutamate receptor-mediated TrkB signaling in the NTS, which might modulate serotonergic and norepinephrinergic innervation to the cerebral cortex to inhibit CSD and cortical inflammation.

Spreading depolarization suppression from inter-astrocytic gap junction blockade assessed with multimodal imaging and a novel wavefront detection scheme

Spreading depolarizations (SDs) are an enigmatic and ubiquitous co-morbidity of neural dysfunction. SDs are propagating waves of local field depolarization and increased extracellular potassium. They increase the metabolic demand on brain tissue, resulting in changes in tissue blood flow, and are associated with adverse neurological consequences including stroke, epilepsy, neurotrauma, and migraine. Their occurrence is associated with poor patient prognosis through mechanisms which are only partially understood. Here we show in vivo that two (structurally dissimilar) drugs, which suppress astroglial gap junctional communication, can acutely suppress SDs. We found that mefloquine hydrochloride (MQH), administered IP, slowed the propagation of the SD potassium waveform and intermittently led to its suppression. The hemodynamic response was similarly delayed and intermittently suppressed. Furthermore, in instances where SD led to transient tissue swelling, MQH reduced observable tissue displacement. Administration of meclofenamic acid (MFA) IP was found to reduce blood flow, both proximal and distal, to the site of SD induction, preceding a large reduction in the amplitude of the SD-associated potassium wave. We introduce a novel image processing scheme for SD wavefront localization under low-contrast imaging conditions permitting full-field wavefront velocity mapping and wavefront parametrization. We found that MQH administration delayed SD wavefront's optical correlates. These two clinically used drugs, both gap junctional blockers found to distinctly suppress SDs, may be of therapeutic benefit in the various brain disorders associated with recurrent SDs.

Targeting CGRP pathways and aura: A peripheral site with a central effect

Targeting CGRP-pathways has substantially expanded our options for treating individuals with migraine. Although the efficacy of these drugs on migraine aura is yet to be fully revealed, it seems from existing studies that CGRP antagonism reduces the number of migraine auras. The present perspective summarizes the evidence linking CGRP to the migraine aura and proposes a model by which targeting the CGRP-pathways and, thus, inhibition the interaction between C- and Aδ-trigeminal fibers might reverse a possible high cortical glutamate level leading to a reduced number of migraine auras.

Canonical Transient Receptor Potential Channel 3 Contributes to Cerebral Blood Flow Changes Associated with Cortical Spreading Depression in Mice

Cortical spreading depression is a pathophysiological event shared in migraines, strokes, traumatic brain injuries, and epilepsy. It is associated with complex hemodynamic responses, which, in turn, contribute to neurological problems. In this study, we investigated the role of canonical transient receptor potential channel 3 (TRPC3) in the hemodynamic responses elicited by cortical spreading depression. Cerebral blood flow was monitored using laser speckle contrast imaging, and cortical spreading depression was triggered using three well-established experimental approaches in mice. A comparison of TRPC3 knockout mice to controls revealed that the genetic ablation of TRPC3 expression significantly altered the hemodynamic responses elicited using cortical spreading depression and promoted hyperemia consistently. Our results indicate that TRPC3 contributes to hemodynamic responses associated with cortical spreading depression and could be a novel therapeutic target for a host of neurological disorders.

A Spatial-Temporal Graph Attention Network for Automated Detection and Width Estimation of Cortical Spreading Depression Using Scalp EEG

We present an end-to-end Spatial-Temporal Graph Attention Network (STGAT) for non-invasive detection and width estimation of Cortical Spreading Depressions (CSDs) on scalp electroencephalography (EEG). Our algorithm, that we refer to as CSD Spatial-temporal graph attention network or CSD-STGAT, is trained and tested on simulated CSDs with varying width and speed ranges. Using high-density EEG, CSD-STGAT achieves less than 10.96% normalized width estimation error for narrow CSDs, with an average normalized error of 6.35%±3.08% across all widths, enabling non-invasive and automated estimation of the width of CSDs for the first time. In addition, CSD-STGAT learns the temporal and spatial features of CSDs simultaneously, which improves the "spatio-temporal tracking accuracy" (i.e., the defined detection performance metric at each electrode) of the narrow CSDs by up to 14%, compared to the state-of-the-art CSD-SpArC algorithm, with only one-tenth of the network size. CSD-STGAT achieves the best spatio-temporal tracking accuracy of 86.27%±0.53% for wide CSDs using high-density EEG, which is comparable to the performance of CSD-SpArC with less than 0.38% performance reduction. We further stitch the detections across all electrodes and over time to evaluate the "temporal accuracy". Our algorithm achieves less than 0.7% false positive rate in the simulated dataset with inter-CSD intervals ranging from 5 to 60 minutes. The lightweight architecture of CSD-STGAT paves the way towards real-time detection and parameter estimation of these waves in the brain, with significant clinical impact.

Sustained Effects of CGRP Blockade on Cortical Spreading Depolarization-Induced Alterations in Facial Heat Pain Threshold, Light Aversiveness, and Locomotive Activity in the Light Environment

A migraine is clinically characterized by repeated headache attacks that entail considerable disability. Many patients with migraines experience postdrome, the symptoms of which include tiredness and photophobia. Calcitonin gene-related peptide (GGRP) is critically implicated in migraine pathogenesis. Cortical spreading depolarization (CSD), the biological correlate of migraine aura, sensitizes the trigeminovascular system. In our previous study, CSD caused hypomotility in the light zone and tendency for photophobia at 72 h, at which time trigeminal sensitization had disappeared. We proposed that this CSD-induced disease state would be useful for exploring therapeutic strategies for migraine postdrome. In the present study, we observed that the CGRP receptor antagonist, olcegepant, prevented the hypomotility in the light zone and ameliorated light tolerability at 72 h after CSD induction. Moreover, olcegepant treatment significantly elevated the threshold for facial heat pain at 72 h after CSD. Our results raise the possibility that CGRP blockade may be efficacious in improving hypoactivity in the light environment by enhancing light tolerability during migraine postdrome. Moreover, our data suggest that the CGRP pathway may lower the facial heat pain threshold even in the absence of overt trigeminal sensitization, which provides an important clue to the potential mechanism whereby CGRP blockade confers migraine prophylaxis.

Postischemic Neuroprotection of Aminoethoxydiphenyl Borate Associates Shortening of Peri-Infarct Depolarizations

Brain stroke is a highly prevalent pathology and a main cause of disability among older adults. If not promptly treated with recanalization therapies, primary and secondary mechanisms of injury contribute to an increase in the lesion, enhancing neurological deficits. Targeting excitotoxicity and oxidative stress are very promising approaches, but only a few compounds have reached the clinic with relatively good positive outcomes. The exploration of novel targets might overcome the lack of clinical translation of previous efficient preclinical neuroprotective treatments. In this study, we examined the neuroprotective properties of 2-aminoethoxydiphenyl borate (2-APB), a molecule that interferes with intracellular calcium dynamics by the antagonization of several channels and receptors. In a permanent model of cerebral ischemia, we showed that 2-APB reduces the extent of the damage and preserves the functionality of the cortical territory, as evaluated by somatosensory evoked potentials (SSEPs). While in this permanent ischemia model, the neuroprotective effect exerted by the antioxidant scavenger cholesteronitrone F2 was associated with a reduction in reactive oxygen species (ROS) and better neuronal survival in the penumbra, 2-APB did not modify the inflammatory response or decrease the content of ROS and was mostly associated with a shortening of peri-infarct depolarizations, which translated into better cerebral blood perfusion in the penumbra. Our study highlights the potential of 2-APB to target spreading depolarization events and their associated inverse hemodynamic changes, which mainly contribute to extension of the area of lesion in cerebrovascular pathologies.

Assessment of neurovascular coupling and cortical spreading depression in mixed mouse models of atherosclerosis and Alzheimer's disease

Neurovascular coupling is a critical brain mechanism whereby changes to blood flow accompany localised neural activity. The breakdown of neurovascular coupling is linked to the development and progression of several neurological conditions including dementia. In this study, we examined cortical haemodynamics in mouse preparations that modelled Alzheimer's disease (J20-AD) and atherosclerosis (PCSK9-ATH) between 9 and 12 m of age. We report novel findings with atherosclerosis where neurovascular decline is characterised by significantly reduced blood volume, altered levels of oxyhaemoglobin and deoxyhaemoglobin, in addition to global neuroinflammation. In the comorbid mixed model (J20-PCSK9-MIX), we report a 3 x increase in hippocampal amyloid-beta plaques. A key finding was that cortical spreading depression (CSD) due to electrode insertion into the brain was worse in the diseased animals and led to a prolonged period of hypoxia. These findings suggest that systemic atherosclerosis can be detrimental to neurovascular health and that having cardiovascular comorbidities can exacerbate pre-existing Alzheimer's-related amyloid-plaques.

Inverse neurovascular coupling and associated spreading depolarization models for traumatic brain injury

The paper presents the mathematical model of cortical spreading depolarisation and its effect on inverse neurovascular coupling. The paper considers the potassium ion channels present in the neuron-astrocyte blood vascular network to access the role of potassium ions during spreading depolarisation and associated inverse neurovascular coupling. Simulation of our proposed mathematical model confirms the experimental results that an increase in concentration of potassium ions beyond 20mM in the perivascular space essentially leads to vasoconstriction and hence inverse neurovascular coupling. The propagatory nature of depolarizing potassium waves has been unraveled though our proposed mathematical model.

Development and Evaluation of a Method for Automated Detection of Spreading Depolarizations in the Injured Human Brain

BACKGROUND

Spreading depolarizations (SDs) occur in some 60% of patients receiving intensive care following severe traumatic brain injury and often occur at a higher incidence following serious subarachnoid hemorrhage and malignant hemisphere stroke (MHS); they are independently associated with worse clinical outcome. Detection of SDs to guide clinical management, as is now being advocated, currently requires continuous and skilled monitoring of the electrocorticogram (ECoG), frequently extending over many days.

METHODS

We developed and evaluated in two clinical intensive care units (ICU) a software routine capable of detecting SDs both in real time at the bedside and retrospectively and also capable of displaying patterns of their occurrence with time. We tested this prototype software in 91 data files, each of approximately 24 h, from 18 patients, and the results were compared with those of manual assessment ("ground truth") by an experienced assessor blind to the software outputs.

RESULTS

The software successfully detected SDs in real time at the bedside, including in patients with clusters of SDs. Counts of SDs by software (dependent variable) were compared with ground truth by the investigator (independent) using linear regression. The slope of the regression was 0.7855 (95% confidence interval 0.7149-0.8561); a slope value of 1.0 lies outside the 95% confidence interval of the slope, representing significant undersensitivity of 79%. R2 was 0.8415.

CONCLUSIONS

Despite significant undersensitivity, there was no additional loss of sensitivity at high SD counts, thus ensuring that dense clusters of depolarizations of particular pathogenic potential can be detected by software and depicted to clinicians in real time and also be archived.

OnabotulinumtoxinA affects cortical recovery period but not occurrence or propagation of cortical spreading depression in rats with compromised blood-brain barrier

ABSTRACT

OnabotulinumtoxinA (BoNT-A) is an Food and Drug Administration-approved, peripherally acting preventive migraine drug capable of inhibiting meningeal nociceptors. Expanding our view of how else this neurotoxin attenuates the activation of the meningeal nociceptors, we reasoned that if the stimulus that triggers the activation of the nociceptor is lessened, the magnitude and/or duration of the nociceptors' activation could diminish as well. In the current study, we further examine this possibility using electrocorticogram recording techniques, immunohistochemistry, and 2-photon microscopy. We report (1) that scalp (head) but not lumbar (back) injections of BoNT-A shorten the period of profound depression of spontaneous cortical activity that follows a pinprick-induced cortical spreading depression (CSD); (2) that neither scalp nor lumbar injections prevent the induction, occurrence, propagation, or spreading velocity of a single wave of CSD; (3) that cleaved SNAP25-one of the most convincing tools to determine the anatomical targeting of BoNT-A treatment-could easily be detected in pericranial muscles at the injection sites and in nerve fibers of the intracranial dura, but not within any cortical area affected by the CSD; (4) that the absence of cleaved SNAP25 within the cortex and pia is unrelated to whether the blood-brain barrier is intact or compromised; and (5) that BoNT-A does not alter vascular responses to CSD. To the best of our knowledge, this is the first report of peripherally applied BoNT-A's ability to alter a neuronal function along a central nervous system pathway involved in the pathophysiology of migraine.

Astrocytes mediate migraine-related intracranial meningeal mechanical hypersensitivity

ABSTRACT

The genesis of the headache phase in migraine with aura is thought to be mediated by cortical spreading depression (CSD) and the subsequent activation and sensitization of primary afferent neurons that innervate the intracranial meninges and their related large vessels. Yet, the exact mechanisms underlying this peripheral meningeal nociceptive response remain poorly understood. We investigated the relative contribution of cortical astrocytes to CSD-evoked meningeal nociception using extracellular single-unit recording of meningeal afferent activity and 2-photon imaging of cortical astrocyte calcium activity, in combination with 2 pharmacological approaches to inhibit astrocytic function. We found that fluoroacetate and l-α-aminoadipate, which inhibit astrocytes through distinct mechanisms, suppressed CSD-evoked afferent mechanical sensitization, but did not affect afferent activation. Pharmacological inhibition of astrocytic function, which ameliorated meningeal afferents' sensitization, reduced basal astrocyte calcium activity but had a minimal effect on the astrocytic calcium wave during CSD. We propose that calcium-independent signaling in cortical astrocytes plays an important role in driving the sensitization of meningeal afferents and the ensuing intracranial mechanical hypersensitivity in migraine with aura.

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.

Recurrent migraine aura-like symptoms in an elderly woman: symptomatic cortical spreading depression?

Cortical spreading depression (CSD) has been directly observed in humans with malignant stroke, traumatic brain injury and subarachnoid haemorrhage and is also considered to be the correlate of migraine aura. We report on a 76-year-old woman with new-onset episodes of headache, paraesthesia, hemiparesis and dysarthria, in whom a small cortical subarachnoid haemorrhage was diagnosed with MRI. Repeated diffusion-weighted MRI scans shortly after transient focal neurological episodes as well as diagnostic workup were normal, which makes recurrent transient ischaemic attacks unlikely. Ictal electroencephalogram recordings showed no epileptic activity. Long-term follow-up revealed a diagnosis of probable cerebral amyloid angiopathy. We propose that CSD could be a pathophysiological correlate of transient focal neurological deficits in patients with cortical bleeding.

Reversibility of excitation waves in brain and heart and the energy of interfacial water. Can reversibility be explained by it?

In this manuscript, we interpret the implications of a discovery we made in 1993 for the understanding of the spread of excitation waves in axon, central gray matter (isolated retina) and heart. We propose that the initial burst of energy dissipation in these waves measured as potentials drops, ionic activities marked changes or optical properties being mostly the effect of dissociated water becoming liquid water and be reversible due to the further on dissociation during the refractory period. We also propose experiments in order to falsify or agree with this conjecture.

Spreading depression as an innate antiseizure mechanism

Spreading depression (SD) is an intense and prolonged depolarization in the central nervous systems from insect to man. It is implicated in neurological disorders such as migraine and brain injury. Here, using an in vivo mouse model of focal neocortical seizures, we show that SD may be a fundamental defense against seizures. Seizures induced by topical 4-aminopyridine, penicillin or bicuculline, or systemic kainic acid, culminated in SDs at a variable rate. Greater seizure power and area of recruitment predicted SD. Once triggered, SD immediately suppressed the seizure. Optogenetic or KCl-induced SDs had similar antiseizure effect sustained for more than 30 min. Conversely, pharmacologically inhibiting SD occurrence during a focal seizure facilitated seizure generalization. Altogether, our data indicate that seizures trigger SD, which then terminates the seizure and prevents its generalization.

Cortical spreading depression aggravates early brain injury in a mouse model of subarachnoid hemorrhage

Cortical spreading depression (CSD) has been observed during the early phase of subarachnoid hemorrhage (SAH). However, the effect of CSD on the cerebral blood flow (CBF) and cerebral oxyhemoglobin (CHbO) during the early phase of SAH has not yet been assessed directly. We, therefore, used laser speckle imaging and optical intrinsic sinal imaging to record CBF and CHbO during CSD and cerebral cortex perfusion (CCP) at 24 hours after CSD in a mouse model of SAH. SAH was induced by blood injection into the prechiasmatic cistern. When CSD occurred, the change trend of CBF and CHbO in Sham group and SAH group was the same, but ischemia and hypoxia in SAH group was more significant. At 24 hours after SAH, the CCP of CSD group was lower than that of no CSD group, and the neurological function score of CSD group was lower. We conclude that induction of CSD further aggravates cerebral ischemia and worsens neurological dysfunction in the early stage of experimental SAH. Our study underscores the consequence of CSD in the development of early brain injury after SAH.

Astrocyte Ca2+ Waves and Subsequent Non-Synchronized Ca2+ Oscillations Coincide with Arteriole Diameter Changes in Response to Spreading Depolarization

Spreading depolarization (SD) is a wave of mass depolarization that causes profound perfusion changes in acute cerebrovascular diseases. Although the astrocyte response is secondary to the neuronal depolarization with SD, it remains to be explored how glial activity is altered after the passage of SD. Here, we describe post-SD high frequency astrocyte Ca²⁺ oscillations in the mouse somatosensory cortex. The intracellular Ca²⁺ changes of SR101 labeled astrocytes and the SD-related arteriole diameter variations were simultaneously visualized by multiphoton microscopy in anesthetized mice. Post-SD astrocyte Ca²⁺ oscillations were identified as Ca²⁺ events non-synchronized among astrocytes in the field of view. Ca²⁺ oscillations occurred minutes after the Ca²⁺ wave of SD. Furthermore, fewer astrocytes were involved in Ca²⁺ oscillations at a given time, compared to Ca²⁺ waves, engaging all astrocytes in the field of view simultaneously. Finally, our data confirm that astrocyte Ca²⁺ waves coincide with arteriolar constriction, while post-SD Ca²⁺ oscillations occur with the peak of the SD-related vasodilation. This is the first in vivo study to present the post-SD astrocyte Ca²⁺ oscillations. Our results provide novel insight into the spatio-temporal correlation between glial reactivity and cerebral arteriole diameter changes behind the SD wavefront.

Neuronal plumes initiate spreading depolarization, the electrophysiologic event driving migraine and stroke

In this issue of Neuron, Parker et al. discover neuronal plumes of glutamate release that initiate spreading depolarization, the electrophysiologic event underlying migraine. Mice with human migraine mutations express spontaneous and frequent plumes, which may explain the propensity to develop migraine attacks and the increased stroke risk in migraine-susceptible brains.

Cerebral Spreading Depression Transient Disruption of Cross-Frequency Coupling in the Rat Brain: Preliminary Observations

Normal brain function requires an integrated, simultaneous communication between brain regions in a coordinated manner. In our studies on cortical spreading depolarization (CSD) induced electrically in the rat brain while recording electrocorticography (ECoG) and delta wave activity, we found for the first time that CSD suppressed delta wave activity, which began even before the CSD was fully developed. We pursued this observation to determine whether repeated CSD suppressed delta wave activity in rats. CSD was produced by electrical stimulation of the neocortex while recording the development of CSD and changes in the coupling of low-frequency band cross coupling to four typical physiological neuronal activity frequency bands, i.e., 5-7 Hz, 8-12 Hz, 13-30 Hz, and 30-80 Hz. Band-pass filters were applied to achieve the corresponding physiological band signals. Besides the cross-frequency coupling (CFC) analysis, the distribution of delta wave density in time domain was analyzed. We calculated the delta wave density per 30 seconds but represent the density as frequency per minute. A Generalized Linear Models (GLM) was used to carry out the CFC analysis in Matlab. Because delta waves dominated the ECoG recorded, we modeled the higher-frequency amplitude envelope as a function of low-frequency phase using a spline basis. Besides the CFC analysis, we also characterized the distribution of the delta wave density in time domain. Four CFC, Theta, Alpha, Beta, and Gamma were at very small values after CSD, and after about 8 minutes, the CFC recovered to the pre-CSD level. CFC were seen to decrease before a CSD occurred at the higher-frequency bands and tended to decrease quickly. Whether the attenuated CFC by CSD has long-term consequences remains to be determined. Future studies will explore the impact of cortical CSD on CFC with deeper brain structures, including the thalamus and the caudate putamen.

Spreading Depressions and Periinfarct Spreading Depolarizations in the Context of Cortical Plasticity

Studies of cortical function-recovery require a comparison between normal and post-stroke conditions that lead to changes in cortical metaplasticity. Focal cortical stroke impairs experience-dependent plasticity in the neighboring somatosensory cortex and usually evokes periinfarct depolarizations (PiDs) - spreading depression-like waves. Experimentally induced spreading depressions (SDs) affect gene expression and some of these changes persist for at least 30 days. In this study we compare the effects of non-stroke depolarizations that impair cortical experience-dependent plasticity to the effects of stroke, by inducing experience-dependent plasticity in rats with SDs or PiDs by a month of contralateral partial whiskers deprivation. We found that whiskers' deprivation after SDs resulted in normal cortical representation enlargement suggesting that SDs and PiDs depolarization have no influence on experience-dependent plasticity cortical map reorganization. PiDs and the MMP-9, -3, -2 or COX-2 proteins, which are assumed to influence metaplasticity in rats after stroke were compared between SDs induced by high osmolarity KCl solution and the PiDs that followed cortical photothrombotic stroke (PtS). We found that none of these factors directly caused cortical post-stroke metaplasticity changes. The only significant difference between stoke and induced SD was a greater imbalance in interhemispheric activity equilibrium after stroke. The interhemispheric interactions that were modified by stroke may therefore be promising targets for future studies of post-stroke experience-dependent plasticity and of recuperation studies.

Parametric exploration of cellular swelling in a computational model of cortical spreading depression

Cortical spreading depression (CSD) is a slowly propagating wave of depolarization of brain cells, followed by temporary silenced electrical brain activity. Major structural changes during CSD are linked to neuronal and possibly glial swelling. However, basic questions still remain unanswered. In particular, there are open questions regarding whether neurons or glial cells swell more, and how the cellular swelling affects the CSD wave propagation.In this study, we computationally explore how different parameters affect the swelling of neurons and astrocytes (starshaped glial cells) during CSD and how the cell swelling alters the CSD wave spatial distribution. We apply a homogenized mathematical model that describes electrodiffusion in the intraand extracellular space, and discretize the equations using a finite element method. The simulations are run with a twocompartment (extracellular space and neurons) and a threecompartment version of the model with astrocytes added. We consider cell swelling during CSD in four scenarios: (A) incorporating aquaporin-4 channels in the astrocytic membrane, (B) increasing the neuron/astrocyte ratio to 2:1, (C) blocking and increasing the Na⁺/K⁺-ATPase rate in the astrocytic compartment, and (D) blocking the Cl^- channels in astrocytes. Our results show that increasing the water permeability in the astrocytes results in a higher astrocytic swelling and a lower neuronal swelling than in the default case. Further, elevated neuronal density increases the swelling in both neurons and astrocytes. Blocking the Na⁺/K⁺-ATPase in the astrocytes leads to an increased wave width and swelling in both compartments, which instead decreases when the pump rate is raised. Blocking the Cl^- channels in the astrocytes results in neuronal swelling, and a shrinkage in the astrocytes. Our results suggest a supporting role of astrocytes in preventing cellular swelling and CSD, as well as highlighting how dysfunctions in astrocytes might elicit CSD.

Rapid Neuronal Ultrastructure Disruption and Recovery during Spreading Depolarization-Induced Cytotoxic Edema

Two major pathogenic events that cause acute brain damage during neurologic emergencies of stroke, head trauma, and cardiac arrest are spreading depolarizing waves and the associated brain edema that course across the cortex injuring brain cells. Virtually nothing is known about how spreading depolarization (SD)-induced cytotoxic edema evolves at the ultrastructural level immediately after insult and during recovery. In vivo 2-photon imaging followed by quantitative serial section electron microscopy was used to assess synaptic circuit integrity in the neocortex of urethane-anesthetized male and female mice during and after SD evoked by transient bilateral common carotid artery occlusion. SD triggered a rapid fragmentation of dendritic mitochondria. A large increase in the density of synapses on swollen dendritic shafts implies that some dendritic spines were overwhelmed by swelling or merely retracted. The overall synaptic density was unchanged. The postsynaptic dendritic membranes remained attached to axonal boutons, providing a structural basis for the recovery of synaptic circuits. Upon immediate reperfusion, cytotoxic edema mainly subsides as affirmed by a recovery of dendritic ultrastructure. Dendritic recuperation from swelling and reversibility of mitochondrial fragmentation suggests that neurointensive care to improve tissue perfusion should be paralleled by treatments targeting mitochondrial recovery and minimizing the occurrence of SDs.

A mathematical model for persistent post-CSD vasoconstriction

Cortical spreading depression (CSD) is the propagation of a relatively slow wave in cortical brain tissue that is linked to a number of pathological conditions such as stroke and migraine. Most of the existing literature investigates the dynamics of short term phenomena such as the depolarization and repolarization of membrane potentials or large ion shifts. Here, we focus on the clinically-relevant hour-long state of neurovascular malfunction in the wake of CSDs. This dysfunctional state involves widespread vasoconstriction and a general disruption of neurovascular coupling. We demonstrate, using a mathematical model, that dissolution of calcium that has aggregated within the mitochondria of vascular smooth muscle cells can drive an hour-long disruption. We model the rate of calcium clearance as well as the dynamical implications on overall blood flow. Based on reaction stoichiometry, we quantify a possible impact of calcium phosphate dissolution on the maintenance of F0F1-ATP synthase activity.

Fremanezumab and its isotype slow propagation rate and shorten cortical recovery period but do not prevent occurrence of cortical spreading depression in rats with compromised blood-brain barrier

Most centrally acting migraine preventive drugs suppress frequency and velocity of cortical spreading depression (CSD). The purpose of the current study was to determine how the new class of peripherally acting migraine preventive drug (ie, the anti-CGRP-mAbs) affect CSD-an established animal model of migraine aura, which affects about 1/3 of people with migraine-when allowed to cross the blood-brain barrier (BBB). Using standard electrocorticogram recording techniques and rats in which the BBB was intentionally compromised, we found that when the BBB was opened, the anti-CGRP-mAb fremanezumab did not prevent the induction, occurrence, or propagation of a single wave of CSD induced by a pinprick, but that both fremanezumab and its isotype were capable of slowing down the propagation velocity of CSD and shortening the period of profound depression of spontaneous cortical activity that followed the spreading depolarization. Fremanezumab's inability to completely block the occurrence of CSD in animals in which the BBB was compromised suggests that calcitonin gene-related peptide (CGRP) may not be involved in the initiation of CSD, at least not to the extent that it can prevent its occurrence. Similarly, we cannot conclude that CGRP is involved in the propagation velocity or the neuronal silencing period (also called cortical recovery period) that follows the CSD because similar effects were observed when the isotype was used. These finding call for caution with interpretations of studies that claim to show direct central nervous system effects of CGRP-mAbs.

Celecoxib reduces cortical spreading depression-induced macrophage activation and dilatation of dural but not pial arteries in rodents: implications for mechanism of action in terminating migraine attacks

Nonsteroidal anti-inflammatory drugs, commonly known as COX-1/COX-2 inhibitors, can be effective in treating mild to moderate migraine headache. However, neither the mechanism by which these drugs act in migraine is known, nor is the specific contribution of COX-1 vs COX-2. We sought to investigate these unknowns using celecoxib, which selectively inhibits the enzymatic activity of COX-2, by determining its effects on several migraine-associated vascular and inflammatory events. Using in vivo 2-photon microscopy, we determined intraperitoneal celecoxib effects on cortical spreading depression (CSD)-induced blood vessel responses, plasma protein extravasation, and immune cell activation in the dura and pia of mice and rats. Compared to vehicle (control group), celecoxib reduced CSD-induced dilatation of dural arteries and activation of dural and pial macrophages significantly, but not dilatation or constriction of pial arteries and veins, or the occurrence of plasma protein extravasation. Collectively, these findings suggest that a mechanism by which celecoxib-mediated COX-2 inhibition might ease the intensity of migraine headache and potentially terminate an attack is by attenuating dural macrophages' activation and arterial dilatation outside the blood-brain barrier, and pial macrophages' activation inside the blood-brain barrier.

Distortion-Free Sensing of Neural Activity Using Graphene Transistors

Graphene solution-gated field-effect transistors (g-SGFETs) are promising sensing devices to transduce electrochemical potential signals in an electrolyte bath. However, distortion mechanisms in g-SGFET, which can affect signals of large amplitude or high frequency, have not been evaluated. Here, a detailed characterization and modeling of the harmonic distortion and non-ideal frequency response in g-SGFETs is presented. This accurate description of the input-output relation of the g-SGFETs allows to define the voltage- and frequency-dependent transfer functions, which can be used to correct distortions in the transduced signals. The effect of signal distortion and its subsequent calibration are shown for different types of electrophysiological signals, spanning from large amplitude and low frequency cortical spreading depression events to low amplitude and high frequency action potentials. The thorough description of the distortion mechanisms presented in this article demonstrates that g-SGFETs can be used as distortion-free signal transducers not only for neural sensing, but also for a broader range of applications in which g-SGFET sensors are used.

Direct electrophysiological evidence that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura and a review of the spreading depolarization continuum of acute neuronal mass injury

Spreading depolarization is observed as a large negative shift of the direct current potential, swelling of neuronal somas, and dendritic beading in the brain's gray matter and represents a state of a potentially reversible mass injury. Its hallmark is the abrupt, massive ion translocation between intraneuronal and extracellular compartment that causes water uptake (= cytotoxic edema) and massive glutamate release. Dependent on the tissue's energy status, spreading depolarization can co-occur with different depression or silencing patterns of spontaneous activity. In adequately supplied tissue, spreading depolarization induces spreading depression of activity. In severely ischemic tissue, nonspreading depression of activity precedes spreading depolarization. The depression pattern determines the neurological deficit which is either spreading such as in migraine aura or migraine stroke or nonspreading such as in transient ischemic attack or typical stroke. Although a clinical distinction between spreading and nonspreading focal neurological deficits is useful because they are associated with different probabilities of permanent damage, it is important to note that spreading depolarization, the neuronal injury potential, occurs in all of these conditions. Here, we first review the scientific basis of the continuum of spreading depolarizations. Second, we highlight the transition zone of the continuum from reversibility to irreversibility using clinical cases of aneurysmal subarachnoid hemorrhage and cerebral amyloid angiopathy. These illustrate how modern neuroimaging and neuromonitoring technologies increasingly bridge the gap between basic sciences and clinic. For example, we provide direct electrophysiological evidence for the first time that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura.

TRP Channels in the Focus of Trigeminal Nociceptor Sensitization Contributing to Primary Headaches

Pain in trigeminal areas is driven by nociceptive trigeminal afferents. Transduction molecules, among them the nonspecific cation channels transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1), which are activated by endogenous and exogenous ligands, are expressed by a significant population of trigeminal nociceptors innervating meningeal tissues. Many of these nociceptors also contain vasoactive neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P. Release of neuropeptides and other functional properties are frequently examined using the cell bodies of trigeminal neurons as models of their sensory endings. Pathophysiological conditions cause phosphorylation, increased expression and trafficking of transient receptor potential (TRP) channels, neuropeptides and other mediators, which accelerate activation of nociceptive pathways. Since nociceptor activation may be a significant pathophysiological mechanism involved in both peripheral and central sensitization of the trigeminal nociceptive pathway, its contribution to the pathophysiology of primary headaches is more than likely. Metabolic disorders and medication-induced painful states are frequently associated with TRP receptor activation and may increase the risk for primary headaches.

Mapping optogenetically-driven single-vessel fMRI with concurrent neuronal calcium recordings in the rat hippocampus

Extensive in vivo imaging studies investigate the hippocampal neural network function, mainly focusing on the dorsal CA1 region given its optical accessibility. Multi-modality fMRI with simultaneous hippocampal electrophysiological recording reveal broad cortical correlation patterns, but the detailed spatial hippocampal functional map remains lacking given the limited fMRI resolution. In particular, hemodynamic responses linked to specific neural activity are unclear at the single-vessel level across hippocampal vasculature, which hinders the deciphering of the hippocampal malfunction in animal models and the translation to critical neurovascular coupling (NVC) patterns for human fMRI. We simultaneously acquired optogenetically-driven neuronal Ca2+ signals with single-vessel blood-oxygen-level-dependent (BOLD) and cerebral-blood-volume (CBV)-fMRI from individual venules and arterioles. Distinct spatiotemporal patterns of hippocampal hemodynamic responses were correlated to optogenetically evoked and spreading depression-like calcium events. The calcium event-related single-vessel hemodynamic modeling revealed significantly reduced NVC efficiency upon spreading depression-like (SDL) events, providing a direct measure of the NVC function at various hippocampal states.

Encephalopathy in a Large Cohort of British Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy Patients

Background and Purpose- Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common monogenic form of stroke usually presenting with migraine with aura, lacunar infarcts, and cognitive impairment. Acute encephalopathy is a less recognized presentation of the disease. Methods- Data collected prospectively from 340 consecutively recruited symptomatic patients with diagnosis of CADASIL seen in a British National CADASIL clinic was retrospectively reviewed and original clinical records and imaging obtained. An encephalopathic event was defined as an acute event of an altered state of consciousness in a patient with CADASIL, manifesting with signs of brain dysfunction, which warranted hospital admission in the absence of any other cause. Clinical characteristics, risk factors, and outcome of encephalopathic presentations were studied. Results- A total of 35 of 340 (10.3%) participants had a history of 50 encephalopathic events which was the first hospital presentation of CADASIL in 33 (94.3%) patients. Most commonly reported features during episodes were visual hallucinations (44%), seizures (22%), and focal neurological deficits (60%).Complete recovery within 3 months was reported in 48(96%) episodes. In 62% of episodes, there was a history of migraine or migraine aura directly preceding the encephalopathy. In 2 out of 15 cases where magnetic resonance imaging during episodes was available, unilateral focal cortical swelling was seen. A past history of migraine was independently associated with encephalopathy (odds ratio=12.3 [95% CI, 1.6-93.7]; P=0.015). Conclusions- In up to 10% of CADASIL patients, a reversible encephalopathy is the first presentation leading to diagnosis. The strong association with migraine suggests a shared pathogenesis. Focal cortical swelling may be seen on magnetic resonance imaging during the acute episode.

Spreading Depolarization Waves in Neurological Diseases: A Short Review about its Pathophysiology and Clinical Relevance

Lesion growth following acutely injured brain tissue after stroke, subarachnoid hemorrhage and traumatic brain injury is an important issue and a new target area for promising therapeutic interventions. Spreading depolarization or peri-lesion depolarization waves were demonstrated as one of the significant contributors of continued lesion growth. In this short review, we discuss the pathophysiology for SD forming events and try to list findings detected in neurological disorders like migraine, stroke, subarachnoid hemorrhage and traumatic brain injury in both human as well as experimental studies. Pharmacological and non-pharmacological treatment strategies are highlighted and future directions and research limitations are discussed.

Control of Spreading Depression with Electrical Fields

Spreading depression or depolarization is a large-scale pathological brain phenomenon related to migraine, stroke, hemorrhage and traumatic brain injury. Once initiated, spreading depression propagates across gray matter extruding potassium and other active molecules, collapsing the resting membrane electro-chemical gradient of cells leading to spike inactivation and cellular swelling, and propagates independently of synaptic transmission. We demonstrate the modulation, suppression and prevention of spreading depression utilizing applied transcortical DC electric fields in brain slices, measured with intrinsic optical imaging and potassium dye epifluorescence. We experimentally observe a surface-positive electric field induced forcing of spreading depression propagation to locations in cortex deeper than the unmodulated propagation path, whereby further propagation is confined and arrested even after field termination. The opposite surface-negative electric field polarity produces an increase in propagation velocity and a confinement of the wave to more superficial layers of cortex than the unmodulated propagation path. These field polarities are of opposite sign to the polarity that blocks neuronal spiking and seizures, and are consistent with biophysical models of spreading depression. The results demonstrate the potential feasibility of electrical control and prevention of spreading depression.

Current Prophylactic Medications for Migraine and Their Potential Mechanisms of Action

A relatively high number of different medications is currently used for migraine prevention in clinical practice. Although these compounds were initially developed for other indications and differ in their mechanisms of action, some general themes can be identified from the mechanisms at play. Efficacious preventive drugs seem to either suppress excitatory nervous signaling via sodium and/or calcium receptors, facilitate GABAergic inhibition, reduce neuronal sensitization, block cortical spreading depression and/or reduce circulating levels of CGRP. We here review such mechanisms for the different compounds.

Targeted Acid-Sensing Ion Channel Therapies for Migraine

Acid-sensing ion channels (ASICs) are a family of ion channels, consisting of four members; ASIC1 to 4. These channels are sensitive to changes in pH and are expressed throughout the central and peripheral nervous systems-including brain, spinal cord, and sensory ganglia. They have been implicated in a number of neurological conditions such as stroke and cerebral ischemia, traumatic brain injury, and epilepsy, and more recently in migraine. Their expression within areas of interest in the brain in migraine, such as the hypothalamus and PAG, their demonstrated involvement in preclinical models of meningeal afferent signaling, and their role in cortical spreading depression (the electrophysiological correlate of migraine aura), has enhanced research interest into these channels as potential therapeutic targets in migraine. Migraine is a disorder with a paucity of both acute and preventive therapies available, in which at best 50% of patients respond to available medications, and these medications often have intolerable side effects. There is therefore a great need for therapeutic development for this disabling condition. This review will summarize the understanding of the structure and CNS expression of ASICs, the mechanisms for their potential role in nociception, recent work in migraine, and areas for future research and drug development.

Patient-specific computational modeling of cortical spreading depression via diffusion tensor imaging

Cortical spreading depression, a depolarization wave originating in the visual cortex and traveling towards the frontal lobe, is commonly accepted as a correlate of migraine visual aura. As of today, little is known about the mechanisms that can trigger or stop such phenomenon. However, the complex and highly individual characteristics of the brain cortex suggest that the geometry might have a significant impact in supporting or contrasting the propagation of cortical spreading depression. Accurate patient-specific computational models are fundamental to cope with the high variability in cortical geometries among individuals, but also with the conduction anisotropy induced in a given cortex by the complex neuronal organisation in the grey matter. In this paper, we integrate a distributed model for extracellular potassium concentration with patient-specific diffusivity tensors derived locally from diffusion tensor imaging data.

Dynamic diameter response of intraparenchymal penetrating arteries during cortical spreading depression and elimination of vasoreactivity to hypercapnia in anesthetized mice

Cortical spreading depression (CSD) induces marked hyperemia with a transient decrease of regional cerebral blood flow (rCBF), followed by sustained oligemia. To further understand the microcirculatory mechanisms associated with CSD, we examined the temporal changes of diameter of intraparenchymal penetrating arteries during CSD. In urethane-anesthetized mice, the diameter of single penetrating arteries at three depths was measured using two-photon microscopy during passage of repeated CSD, with continuous recordings of direct current potential and rCBF. The first CSD elicited marked constriction superimposed on the upstrokes of profound dilation throughout each depth of the penetrating artery, and the vasoreaction temporally corresponded to the change of rCBF. Second or later CSD elicited marked dilation with little or no constriction phase throughout each depth, and the vasodilation also temporally corresponded to the increase of rCBF. Furthermore, the peak dilation showed good negative correlations with basal diameter and increase of rCBF. Vasodilation induced by 5% CO2 inhalation was significantly suppressed after CSD passage at any depth as well as hyperperfusion. These results may indicate that CSD-induced rCBF changes mainly reflect the diametric changes of the intraparenchymal arteries, despite the elimination of responsiveness to hypercapnia.

Low-Frequency Intracortical Electrical Stimulation Decreases Sensorimotor Cortex Hyperexcitability in the Acute Phase of Ischemic Stroke

Ischemic stroke causes a series of complex pathophysiological events in the brain. Electrical stimulation of the brain has been considered as a novel neuroprotection intervention to save the penumbra. However, the effect on the cells' responsiveness and their ability to survive has yet to be established. The objective of the present study was to investigate the effects of low-frequency intracortical electrical stimulation (lf-ICES) applied to the ischemia-affected sensorimotor cortex immediately following ischemic stroke. Twenty male Sprague-Dawley rats were instrumented with an intracortical microelectrode array (IC MEA) and a cuff-electrode around the sciatic nerve. Photothrombosis intervention was performed within the sensorimotor cortex and the electrophysiological changes were assessed by analysis of the neural responses to stimulation of the sciatic nerve. Neuroprotection intervention consisted of eight 23 min lf-ICES blocks applied to the IC MEA during the initial 4 h following photothrombosis. Our results revealed that the area and magnitude of the sensorimotor cortex response significantly increased if ischemic stroke was allowed to progress uninterrupted, whereas this was not observed for the group of rats subjected to lf-ICES. Our findings indicate that low-frequency electrical stimulation is able to minimize hyperexcitability and may therefore be a candidate as neuroprotection intervention in the future.

Ischemia-induced spreading depolarization in the retina

Cortical spreading depolarization is a metabolically costly phenomenon that affects the brain in both health and disease. Following severe stroke, subarachnoid hemorrhage, or traumatic brain injury, cortical spreading depolarization exacerbates tissue damage and enlarges infarct volumes. It is not known, however, whether spreading depolarization also occurs in the retina in vivo. We report now that spreading depolarization episodes are generated in the in vivo rat retina following retinal vessel occlusion produced by photothrombosis. The properties of retinal spreading depolarization are similar to those of cortical spreading depolarization. Retinal spreading depolarization waves propagate at a velocity of 3.0 ± 0.1 mm/min and are associated with a negative shift in direct current potential, a transient cessation of neuronal spiking, arteriole constriction, and a decrease in tissue O2 tension. The frequency of retinal spreading depolarization generation in vivo is reduced by administration of the NMDA antagonist MK-801 and the 5-HT(1D) agonist sumatriptan. Branch retinal vein occlusion is a leading cause of vision loss from vascular disease. Our results suggest that retinal spreading depolarization could contribute to retinal damage in acute retinal ischemia and demonstrate that pharmacological agents can reduce retinal spreading depolarization frequency after retinal vessel occlusion. Blocking retinal spreading depolarization generation may represent a therapeutic strategy for preserving vision in branch retinal vein occlusion patients.

Effect of Intertrial Interval on Avoidance Learning in Rats Trained under Bilateral Spreading Depression

Groups of 10 rats were given one-way avoidance training under bilateral spreading depression (BSD) or Sham BSD (control) with ITIs of 30, 60, 120, or 240 sec.; shock side confinement was held constant at 20 sec. Results indicated BSD Ss were inferior to Sham BSD Ss; there was a significant ITI effect, the short ITIs resulting in slower learning.

How does spreading depression spread? Physiology and modeling

Spreading depression (SD) is a wave phenomenon in gray matter tissue. Locally, it is characterized by massive redistribution of ions across cell membranes. As a consequence, there is sustained membrane depolarization and tissue polarization that depress any normal electrical activity. Despite these dramatic events, SD remains difficult to observe in humans noninvasively, which, for long, has slowed advances in this field. The growing appreciation of its clinical importance in migraine and stroke is therefore consistent with an increasing need for computational methods that tackle the complexity of the problem at multiple levels. In this review, we focus on mathematical tools to investigate the question of spread and its two complementary aspects: What are the physiological mechanisms and what is the spatial extent of SD in the cortex? This review discusses two types of models used to study these two questions, namely, Hodgkin-Huxley type and generic activator-inhibitor models, and the recent advances in techniques to link them.

Large-scale mass spectrometry imaging investigation of consequences of cortical spreading depression in a transgenic mouse model of migraine

Cortical spreading depression (CSD) is the electrophysiological correlate of migraine aura. Transgenic mice carrying the R192Q missense mutation in the Cacna1a gene, which in patients causes familial hemiplegic migraine type 1 (FHM1), exhibit increased propensity to CSD. Herein, mass spectrometry imaging (MSI) was applied for the first time to an animal cohort of transgenic and wild type mice to study the biomolecular changes following CSD in the brain. Ninety-six coronal brain sections from 32 mice were analyzed by MALDI-MSI. All MSI datasets were registered to the Allen Brain Atlas reference atlas of the mouse brain so that the molecular signatures of distinct brain regions could be compared. A number of metabolites and peptides showed substantial changes in the brain associated with CSD. Among those, different mass spectral features showed significant (t-test, P < 0.05) changes in the cortex, 146 and 377 Da, and in the thalamus, 1820 and 1834 Da, of the CSD-affected hemisphere of FHM1 R192Q mice. Our findings reveal CSD- and genotype-specific molecular changes in the brain of FHM1 transgenic mice that may further our understanding about the role of CSD in migraine pathophysiology. The results also demonstrate the utility of aligning MSI datasets to a common reference atlas for large-scale MSI investigations.

Hyperperfusion counteracted by transient rapid vasoconstriction followed by long-lasting oligemia induced by cortical spreading depression in anesthetized mice

Cortical spreading depression (CSD) involves mass depolarization of neurons and glial cells accompanied with changes in regional cerebral blood flow (rCBF) and energy metabolism. To further understand the mechanisms of CBF response, we examined the temporal diametric changes in pial arteries, pial veins, and cortical capillaries. In urethane-anesthetized mice, the diameters of these vessels were measured while simultaneously recording rCBF with a laser Doppler flowmeter. We observed a considerable increase in rCBF during depolarization in CSD induced by application of KCl, accompanied by a transient dip of rCBF with marked vasoconstriction of pial arteries, which resembled the response to pin-prick-induced CSD. Arterial constriction diminished or disappeared during the second and third passages of CSD, whereas the rCBF increase was maintained without a transient dip. Long-lasting oligemia with a decrease in the reciprocal of mean transit time of injected dye and mild constriction of pial arteries was observed after several passages of the CSD wave. These results indicate that CSD-induced rCBF changes consist of initial hyperemia with a transient dip and followed by a long-lasting oligemia, partially corresponding to the diametric changes of pial arteries, and further suggest that vessels other than pial arteries, such as intracortical vessels, are involved.

Spreading depolarization-induced adenosine accumulation reflects metabolic status in vitro and in vivo

Spreading depolarization (SD), a pathologic feature of migraine, stroke and traumatic brain injury, is a propagating depolarization of neurons and glia causing profound metabolic demand. Adenosine, the low-energy metabolite of ATP, has been shown to be elevated after SD in brain slices and under conditions likely to trigger SD in vivo. The relationship between metabolic status and adenosine accumulation after SD was tested here, in brain slices and in vivo. In brain slices, metabolic impairment (assessed by nicotinamide adenine dinucleotide (phosphate) autofluorescence and O2 availability) was associated with prolonged extracellular direct current (DC) shifts indicating delayed repolarization, and increased adenosine accumulation. In vivo, adenosine accumulation was observed after SD even in otherwise healthy mice. As in brain slices, in vivo adenosine accumulation correlated with DC shift duration and increased when DC shifts were prolonged by metabolic impairment (i.e., hypoglycemia or middle cerebral artery occlusion). A striking pattern of adenosine dynamics was observed during focal ischemic stroke, with nearly all the observed adenosine signals in the periinfarct region occurring in association with SDs. These findings suggest that adenosine accumulation could serve as a biomarker of SD incidence and severity, in a range of clinical conditions.

Imaging reveals the focal area of spreading depolarizations and a variety of hemodynamic responses in a rat microembolic stroke model

Spreading depolarizations (SDs) occur in stroke, but the spatial association between SDs and the corresponding hemodynamic changes is incompletely understood. We applied multimodal imaging to visualize the focal area of selected SDs, and hemodynamic responses with SDs propagating over the ischemic cortex. The intracarotid infusion of polyethylene microspheres (d=45 to 53 μm) produced multifocal ischemia in anesthetized rats (n=7). Synchronous image sequences captured through a cranial window above the frontoparietal cortex revealed: Changes in membrane potential (voltage-sensitive (VS) dye method); cerebral blood flow (CBF; laser speckle contrast (LSC) imaging); and hemoglobin (Hb) deoxygenation (red intrinsic optical signal (IOS) at 620 to 640 nm). A total of 31 SD events were identified. The foci of five SDs were seen in the cranial window, originating where CBF was the lowest (56.9±9%), but without evident signs of infarcts. The hyperemic CBF responses to propagating SDs were coupled with three types of Hb saturation kinetics. More accentuated Hb desaturation was related to a larger decrease in CBF shortly after ischemia induction. Microsphere-induced embolization triggers SDs in the rat brain, relevant for small embolic infarcts in patients. The SD occurrence during the early phase of ischemia is not tightly associated with immediate infarct evolution. Various kinetics of Hb saturation may determine the metabolic consequences of individual SDs.

Role of cortical spreading depression in the pathophysiology of migraine

A migraine is a recurring neurological disorder characterized by unilateral, intense, and pulsatile headaches. In one-third of migraine patients, the attacks are preceded by a visual aura, such as a slowly-propagating scintillating scotoma. Migraine aura is thought to be a result of the neurovascular phenomenon of cortical spreading depression (SD), a self-propagating wave of depolarization that spreads across the cerebral cortex. Several animal experiments have demonstrated that cortical SD causes intracranial neurogenic inflammation around the meningeal blood vessels, such as plasma protein extravasation and pro-inflammatory peptide release. Cortical SD has also been reported to activate both peripheral and central trigeminal nociceptive pathways. Although several issues remain to be resolved, recent evidence suggests that cortical SD could be the initial trigger of intracranial neurogenic inflammation, which then contributes to migraine headaches via subsequent activation of trigeminal afferents.

Cortical spreading depression: origins and paths as inferred from the sequence of events during migraine aura

Patients with migraine with aura often experience a variety of visual and somatosensory phenomena and disturbances of higher cortical functions. Analysis of these alterations may provide important information about the involvement of different cortical regions in cortical spreading depression (CSD). We report five cases of migraineurs who experience unusually abundant clinical phenomena during auras. These patients were selected from a cohort of migraine with aura patients who were interviewed, using a specially designed questionnaire, to evaluate the presence of higher cortical dysfunctions. On the basis of the aura symptoms they reported, we attempted to infer the origin and the possible paths of CSD in each patient. According to their reported symptoms, CSD could begin in the primary visual cortex, in the primary somatosensory cortex or simultaneously in both, and propagate to the posterior parietal cortex, the temporal lobe and Broca's area. We believe that clinical descriptions of aura could play an important role in further investigations of the pathophysiology of migraine.

Real-time optical diagnosis of the rat brain exposed to a laser-induced shock wave: observation of spreading depolarization, vasoconstriction and hypoxemia-oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3-4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.