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Spreading depolarizations (SD) contribute to lesion progression after experimental focal cerebral ischemia while such correlation has never been shown in stroke patients. In this prospective, diagnostic study, we investigate the association of SDs and secondary infarct progression after malignant hemispheric stroke. SDs were continuously monitored for 3–9 days with electrocorticography after decompressive hemicraniectomy for malignant hemispheric stroke. To ensure valid detection and analysis of SDs, a threshold based on the electrocorticographic baseline activity was calculated to identify valid electrocorticographic recordings. Subsequently SD characteristics were analyzed in association to infarct progression based on serial MRI. Overall, 62 patients with a mean stroke volume of 289.6 ± 68 cm3 were included. Valid electrocorticographic recordings were found in 44/62 patients with a mean recording duration of 139.6 ± 26.5 hours and 52.5 ± 39.5 SDs per patient. Infarct progression of more than 5% was found in 21/44 patients. While the number of SDs was similar between patients with and without infarct progression, the SD-induced depression duration per day was significantly longer in patients with infarct progression (593.8 vs. 314.1 minutes; *p = 0.046). Therefore, infarct progression is associated with a prolonged SD-induced depression duration. Real-time analysis of electrocorticographic recordings may identify secondary stroke progression and help implementing targeted management strategies. [ABSTRACT FROM AUTHOR]

Mitochondrial function is tightly linked to morphology, and fragmentation of dendritic mitochondria during noxious conditions suggests loss of function. In the normoxic cortex, spreading depolarization (SD) is a phenomenon underlying migraine aura. It is unknown whether mitochondria structure is affected by normoxic SD. In vivo two-photon imaging followed by quantitative serial section electron microscopy (ssEM) was used to monitor dendritic mitochondria in the normoxic cortex of urethane-anesthetized mature male and female mice during and after SD initiated by focal KCl microinjection. Structural dynamics of dendrites and their mitochondria were visualized by transfecting excitatory, glutamatergic neurons of the somatosensory cortex with bicistronic AAV, which induced tdTomoto labeling in neuronal cytoplasm and mitochondria labeling with roGFP. Normoxic SD triggered rapidly reversible fragmentation of dendritic mitochondria alongside dendritic beading; however, mitochondria took significantly longer to recover. Several rounds of SD resulted in transient mitochondrial fragmentation and dendritic beading without accumulating injury, as both recovered. SsEM corroborated normoxic SD-elicited dendritic and mitochondrial swelling and transformation of the filamentous mitochondrial network into shorter, swollen tubular, and globular structures. Our results revealed normoxic SD-induced disruption of the dendritic mitochondrial structure that might impact mitochondrial bioenergetics during migraine with aura. [ABSTRACT FROM AUTHOR]

Spreading depolarization (SD) describes the near-complete depolarization of central nervous system (CNS) neural cells as a consequence of chemical, electrical, or metabolic perturbations. It is well established as the central mechanism underlying insect coma and various mammalian neurological dysfunctions. Despite significant progress in our understanding, the question remains: which cation channel, if any, generates SD in the CNS? Previously, we speculated that the sodium-potassium ATPase (NKA) might function as a large-conductance ion channel to initiate SD in insects, potentially mediated by a palytoxin (PLTX)-like endogenous activator. In the current study, we evaluate the effectiveness and properties of PLTX as an SD initiator in Locusta migratoria. Whereas bath-applied PLTX failed to ignite SD, direct injection into the neuropil triggered SD in 57% of the preparations. Notably, PLTX-induced SD onset was significantly more rapid compared with ouabain (OUA) injection and azide controls, though their electrophysiological features remained similar. Furthermore, PLTX-induced SD was recoverable and resulted in a greater frequency of repetitive SD events compared with ouabain. Surprisingly, prior PLTX treatment disrupted the onset and recovery of subsequent SD evoked by other means. PLTX injection could attenuate the amplitude and even completely inhibit the onset of azide-induced SD at higher doses. These results show that PLTX can trigger repetitive and reversible SD-like events in locusts and simultaneously interfere with anoxic SD occurrence. We suggest that the well-documented NKA pump conversion into an open nonselective cationic channel is a plausible mechanism of SD activation in the locust CNS, warranting additional investigations. NEW & NOTEWORTHY: Spreading depolarization (SD) is a critical mechanism underlying central nervous system (CNS) shutdown and injury under stress, yet the initiating ion channel remains unknown. Here, we used the marine poison palytoxin (PLTX), which converts the sodium-potassium ATPase (NKA) into an open channel, to initiate SD in intact locust CNS. We show for the first time that PLTX-induced SD is rapid and recoverable in vivo, providing support that NKA conversion to a channel may be the SD-initiating mechanism. [ABSTRACT FROM AUTHOR]

Futile reperfusion is a phenomenon of inadequate perfusion despite successful recanalization after acute ischemic stroke (AIS). It is associated with poor patient outcomes and has received increasing interest due to its clinical diagnosis becoming more common. However, the underlying mechanisms remain elusive, and experimental studies are focused on the pathological background of futile reperfusion. Our recent study has confirmed that poor primary collateralization plays a crucial role in the insufficiency of reperfusion after AIS in mice. Specifically, the absence of primary collaterals in the circle of Willis (CoW) promoted the development of spreading depolarizations (SDs) during AIS. In our experimental stroke model, the occurrence of SDs during ischemia always predicted futile reperfusion. Conversely, in mice with a complete CoW, no SDs were observed, and reperfusion was complete. Importantly, the human CoW displays variation in the primary collaterals in approximately 50% of the population. Therefore, futile reperfusion may result from SD evolution in AIS patients. Our purpose here is to emphasize the crucial role of SD in the development of futile reperfusion. We propose that adequate collateral recruitment can prevent SD occurrence, leading to improved reperfusion and AIS outcomes. [ABSTRACT FROM AUTHOR]

Abstract Background Migraine is among the most prevalent and burdensome neurological disorders in the United States based on disability-adjusted life years. Cortical spreading depolarization (SD) is the most likely electrophysiological cause of migraine aura and may be linked to trigeminal nociception. We previously demonstrated, using a minimally invasive optogenetic approach of SD induction (opto-SD), that opto-SD triggers acute periorbital mechanical allodynia that is reversed by 5HT1B/1D receptor agonists, supporting SD-induced activation of migraine-relevant trigeminal pain pathways in mice. Recent data highlight hypothalamic neural circuits in migraine, and SD may activate hypothalamic neurons. Furthermore, neuroanatomical, electrophysiological, and behavioral data suggest a homeostatic analgesic function of hypothalamic neuropeptide hormone, oxytocin. We, therefore, examined the role of hypothalamic paraventricular nucleus (PVN) and oxytocinergic (OXT) signaling in opto-SD-induced trigeminal pain behavior. Methods We induced a single opto-SD in adult male and female Thy1-ChR2-YFP transgenic mice and quantified fos immunolabeling in the PVN and supraoptic nucleus (SON) compared with sham controls. Oxytocin expression was also measured in fos-positive neurons in the PVN. Periorbital mechanical allodynia was tested after treatment with selective OXT receptor antagonist L-368,899 (5 to 25 mg/kg i.p.) or vehicle at 1, 2, and 4 h after opto-SD or sham stimulation using von Frey monofilaments. Results Opto-SD significantly increased the number of fos immunoreactive cells in the PVN and SON as compared to sham stimulation (p

Abstract Background The initiation of migraine headaches and the involvement of neuroinflammatory signaling between parenchymal and meningeal cells remain unclear. Experimental evidence suggests that a cascade of inflammatory signaling originating from neurons may extend to the meninges, thereby inducing neurogenic inflammation and headache. This review explores the role of parenchymal inflammatory signaling in migraine headaches, drawing upon recent advancements. Body Studies in rodents have demonstrated that sterile meningeal inflammation can stimulate and sensitize meningeal nociceptors, culminating in headaches. The efficacy of relatively blood-brain barrier-impermeable anti-calcitonin gene-related peptide antibodies and triptans in treating migraine attacks, both with and without aura, supports the concept of migraine pain originating in meninges. Additionally, PET studies utilizing inflammation markers have revealed meningeal inflammatory activity in patients experiencing migraine with aura, particularly over the occipital cortex generating visual auras. The parenchymal neuroinflammatory signaling involving neurons, astrocytes, and microglia, which eventually extends to the meninges, can link non-homeostatic perturbations in the insensate brain to pain-sensitive meninges. Recent experimental research has brought deeper insight into parenchymal signaling mechanisms: Neuronal pannexin-1 channels act as stress sensors, initiating the inflammatory signaling by inflammasome formation and high-mobility group box-1 release in response to transient perturbations such as cortical spreading depolarization (CSD) or synaptic metabolic insufficiency caused by transcriptional changes induced by migraine triggers like sleep deprivation and stress. After a single CSD, astrocytes respond by upregulating the transcription of proinflammatory enzymes and mediators, while microglia are involved in restoring neuronal structural integrity; however, repeated CSDs may prompt microglia to adopt a pro-inflammatory state. Transcriptional changes from pro- to anti-inflammatory within 24 h may serve to dampen the inflammatory signaling. The extensive coverage of brain surface and perivascular areas by astrocyte endfeet suggests their role as an interface for transporting inflammatory mediators to the cerebrospinal fluid to contribute to meningeal nociception. Conclusion We propose that neuronal stress induced by CSD or synaptic activity-energy mismatch may initiate a parenchymal inflammatory signaling cascade, transmitted to the meninges, thereby triggering lasting headaches characteristic of migraine, with or without aura. This neuroinflammatory interplay between parenchymal and meningeal cells points to the potential for novel targets for migraine treatment and prophylaxis.

Abstract Background Neurogenic meningeal inflammation is regarded as a key driver of migraine headache. Multiple evidence show importance of inflammatory processes in the dura mater for pain generation but contribution of the leptomeninges is less clear. We assessed effects of cortical spreading depolarization (CSD), the pathophysiological mechanism of migraine aura, on expression of inflammatory mediators in the leptomeninges. Methods A single CSD event was produced by a focal unilateral microdamage of the cortex in freely behaving rats. Three hours later intact cortical leptomeninges and parenchyma of ipsi-lesional (invaded by CSD) and sham-treated contra-lesional (unaffected by CSD) hemispheres were collected and mRNA levels of genes associated with inflammation (Il1b, Tnf, Ccl2; Cx3cl1, Zc3h12a) and endocannabinoid CB2 receptors (Cnr2) were measured using qPCR. Results Three hours after a single unilateral CSD, most inflammatory factors changed their expression levels in the leptomeninges, mainly on the side of CSD. The meninges overlying affected cortex increased mRNA expression of all proinflammatory cytokines (Il1b, Tnf, Ccl2) and anti-inflammatory factors Zc3h12a and Cx3cl1. Upregulation of proinflammatory cytokines was found in both meninges and parenchyma while anti-inflammatory markers increased only meningeal expression. Conclusion A single CSD is sufficient to produce pronounced leptomeningeal inflammation that lasts for at least three hours and involves mostly meninges overlying the cortex affected by CSD. The prolonged post-CSD inflammation of the leptomeninges can contribute to mechanisms of headache generation following aura phase of migraine attack.

Background: Migraine is among the most prevalent and burdensome neurological disorders in the United States based on disability-adjusted life years. Cortical spreading depolarization (SD) is the most likely electrophysiological cause of migraine aura and may be linked to trigeminal nociception. We previously demonstrated, using a minimally invasive optogenetic approach of SD induction (opto-SD), that opto-SD triggers acute periorbital mechanical allodynia that is reversed by 5HT1B/1D receptor agonists, supporting SD-induced activation of migraine-relevant trigeminal pain pathways in mice. Recent data highlight hypothalamic neural circuits in migraine, and SD may activate hypothalamic neurons. Furthermore, neuroanatomical, electrophysiological, and behavioral data suggest a homeostatic analgesic function of hypothalamic neuropeptide hormone, oxytocin. We, therefore, examined the role of hypothalamic paraventricular nucleus (PVN) and oxytocinergic (OXT) signaling in opto-SD-induced trigeminal pain behavior. Methods: We induced a single opto-SD in adult male and female Thy1-ChR2-YFP transgenic mice and quantified fos immunolabeling in the PVN and supraoptic nucleus (SON) compared with sham controls. Oxytocin expression was also measured in fos-positive neurons in the PVN. Periorbital mechanical allodynia was tested after treatment with selective OXT receptor antagonist L-368,899 (5 to 25 mg/kg i.p.) or vehicle at 1, 2, and 4 h after opto-SD or sham stimulation using von Frey monofilaments. Results: Opto-SD significantly increased the number of fos immunoreactive cells in the PVN and SON as compared to sham stimulation (p < 0.001, p = 0.018, respectively). A subpopulation of fos-positive neurons also stained positive for oxytocin. Opto-SD evoked periorbital mechanical allodynia 1 h after SD (p = 0.001 vs. sham), which recovered quickly within 2 h (p = 0.638). OXT receptor antagonist L-368,899 dose-dependently prolonged SD-induced periorbital allodynia (p < 0.001). L-368,899 did not affect mechanical thresholds in the absence of opto-SD. Conclusions: These data support an SD-induced activation of PVN neurons and a role for endogenous OXT in alleviating acute SD-induced trigeminal allodynia by shortening its duration. [ABSTRACT FROM AUTHOR]

Objective: We attempted to record the regional cerebral blood flow (CBF) simultaneously at various regions of the cerebral cortex and the striatum during middle cerebral artery (MCA) occlusion and to evaluate neurological deficits and infarct formation. Methods: In male C57BL/6J mice, CBF was recorded in three regions including the ipsilateral cerebral cortex and the striatum with laser Doppler flowmeters, and the origin of MCA was occluded with a monofilament suture for 15–90 min. After 48 h, neurological deficits were evaluated, and infarct was examined by triphenyltetrazolium chloride (TTC) staining. Results: CBF decrease in the striatum was approximately two‐thirds of the MCA‐dominant region of the cortex during MCA occlusion. The characteristic CBF fluctuation because of spontaneously occurred spreading depolarization observed throughout the cortex was not found in the striatum. Ischemic foci with slight lower staining to TTC were found in the ipsilateral striatum in MCA‐occluded mice for longer than 30 min (n = 54). Twenty‐nine among 64 MCA‐occluded mice exhibited neurological deficits even in the absence of apparent infarct with minimum staining to TTC in the cortex, and the severity of neurological deficits was not correlated with the size of the cortical infarct. Conclusion: Neurological deficits might be associated with the ischemic striatum rather than with cortical infarction. [ABSTRACT FROM AUTHOR]

Background: Neurogenic meningeal inflammation is regarded as a key driver of migraine headache. Multiple evidence show importance of inflammatory processes in the dura mater for pain generation but contribution of the leptomeninges is less clear. We assessed effects of cortical spreading depolarization (CSD), the pathophysiological mechanism of migraine aura, on expression of inflammatory mediators in the leptomeninges. Methods: A single CSD event was produced by a focal unilateral microdamage of the cortex in freely behaving rats. Three hours later intact cortical leptomeninges and parenchyma of ipsi-lesional (invaded by CSD) and sham-treated contra-lesional (unaffected by CSD) hemispheres were collected and mRNA levels of genes associated with inflammation (Il1b, Tnf, Ccl2; Cx3cl1, Zc3h12a) and endocannabinoid CB2 receptors (Cnr2) were measured using qPCR. Results: Three hours after a single unilateral CSD, most inflammatory factors changed their expression levels in the leptomeninges, mainly on the side of CSD. The meninges overlying affected cortex increased mRNA expression of all proinflammatory cytokines (Il1b, Tnf, Ccl2) and anti-inflammatory factors Zc3h12a and Cx3cl1. Upregulation of proinflammatory cytokines was found in both meninges and parenchyma while anti-inflammatory markers increased only meningeal expression. Conclusion: A single CSD is sufficient to produce pronounced leptomeningeal inflammation that lasts for at least three hours and involves mostly meninges overlying the cortex affected by CSD. The prolonged post-CSD inflammation of the leptomeninges can contribute to mechanisms of headache generation following aura phase of migraine attack. [ABSTRACT FROM AUTHOR]

Unexplained neurological deterioration is occasionally observed in patients with traumatic brain injuries (TBIs). We aimed to describe the clinical features of post-traumatic transient neurological dysfunction and provide new insight into its pathophysiology. We retrospectively collected data from patients with focal neurological deterioration of unknown origin during hospitalization for acute TBI for 48 consecutive months. Brain imaging, including computed tomography, diffusion-weighted imaging and perfusion-weighted imaging, and electroencephalography were conducted during the episodes. Fourteen (2.0%) patients experienced unexplained focal neurological deterioration among 713 patients who were admitted for traumatic intracranial hemorrhage during the study period. Aphasia was the predominant symptom in all patients, and hemiparesis or hemianopia was accompanied in three patients. These symptoms developed within 14 days after trauma. Structural imaging did not show any significant interval change, and electroencephalography showed persistent arrhythmic slowing in the corresponding hemisphere in most patients. Perfusion imaging revealed increased cerebral blood flow in the symptomatic hemisphere. Surgical intervention and anti-seizure medications were ineffective in abolishing the symptoms. The symptoms disappeared spontaneously after 4 h to 1 month. Transient neurological dysfunction (TND) can occur during the acute phase of TBI. Although TND may last longer than a typical transient ischemic attack or seizure, it eventually resolves regardless of treatment. Based on our observation, we postulate that this is a manifestation of spreading depolarization occurring in the injured brain, which is analogous to migraine aura. [ABSTRACT FROM AUTHOR]

The mechanisms of initiation of spreading depolarization (SD) are understudied due to a paucity of disease models with spontaneously occurring events. We here present a novel mouse model of familial hemiplegic migraine type 2 (FHM2), expressing the missense T345A-mutated α2 subunit of the Na+/K+ adenosine triphosphatase pump (Atp1a2T345A). Homozygous Atp1a2T345A mice showed regular spontaneous SDs that exhibit a diurnal rhythm and typically originate from the hippocampus. Heterozygous Atp1a2T345A mice rarely exhibited spontaneous SDs and, for electrically induced SDs, only showed an increased propagation speed, whereas homozygotes showed both increased propagation and decreased threshold. Remarkably, despite hippocampal hyperexcitability, spontaneous SDs in Atp1a2T345A mice were only rarely associated with epileptic behavior, and seizure expression during kindling was decreased. Spontaneous SDs could be prevented by modulation of persistent sodium currents. Hippocampal SDs occurred in the presence of an NMDA-receptor antagonist, but these events did not reach the cortex, suggesting that initiation and propagation of SD depend on different mechanisms in this model.

This study aimed to investigate the effects of focal brain cooling (FBC) on spreading depolarization (SD), which is associated with several neurological disorders. Although it has been studied from various aspects, no medication has been developed that can effectively control SD. As FBC can reduce neuronal damage and promote functional recovery in pathological conditions such as epilepsy, cerebral ischemia, and traumatic brain injury, it may also potentially suppress the onset and progression of SD. We created an experimental rat model of SD by administering 1 M potassium chloride (KCl) to the cortical surface. Changes in neuronal and vascular modalities were evaluated using multimodal recording, which simultaneously recorded brain temperature (BrT), wide range electrocorticogram, and two-dimensional cerebral blood flow. The rats were divided into two groups (cooling [CL] and non-cooling [NC]). Warm or cold saline was perfused on the surface of one hemisphere to maintain BrT at 37°C or 15°C in the NC and CL groups, respectively. Western blot analysis was performed to determine the effects of FBC on endothelial nitric oxide synthase (eNOS) expression. In the NC group, KCl administration triggered repetitive SDs (mean frequency = 11.57/h). In the CL group, FBC increased the duration of all KCl-induced events and gradually reduced their frequency. Additionally, eNOS expression decreased in the cooled brain regions compared to the non-cooled contralateral hemisphere. The results obtained by multimodal recording suggest that FBC suppresses SD and decreases eNOS expression. This study may contribute to developing new treatments for SD and related neurological disorders.

Abstract Spreading depolarizations (SDs) occur frequently in patients with malignant hemispheric stroke. In animal-based experiments, SDs have been shown to cause secondary neuronal damage and infarct expansion during the initial period of infarct progression. In contrast, the influence of SDs during the delayed period is not well characterized yet. Here, we analyzed the impact of SDs in the delayed phase after cerebral ischemia and the potential protective effect of ketamine. Focal ischemia was induced by distal occlusion of the left middle cerebral artery in C57BL6/J mice. 24 h after occlusion, SDs were measured using electrocorticography and laser-speckle imaging in three different study groups: control group without SD induction, SD induction with potassium chloride, and SD induction with potassium chloride and ketamine administration. Infarct progression was evaluated by sequential MRI scans. 24 h after occlusion, we observed spontaneous SDs with a rate of 0.33 SDs/hour which increased during potassium chloride application (3.37 SDs/hour). The analysis of the neurovascular coupling revealed prolonged hypoemic and hyperemic responses in this group. Stroke volume increased even 24 h after stroke onset in the SD-group. Ketamine treatment caused a lesser pronounced hypoemic response and prevented infarct growth in the delayed phase after experimental ischemia. Induction of SDs with potassium chloride was significantly associated with stroke progression even 24 h after stroke onset. Therefore, SD might be a significant contributor to delayed stroke progression. Ketamine might be a possible drug to prevent SD-induced delayed stroke progression.

Oedema occurs when higher than normal amounts of solutes and water accumulate in tissues. In brain parenchymal tissue, vasogenic oedema arises from changes in blood–brain barrier permeability, e.g. in peritumoral oedema. Cytotoxic oedema arises from excess accumulation of solutes within cells, e.g. ischaemic oedema following stroke. This type of oedema is initiated when blood flow in the affected core region falls sufficiently to deprive brain cells of the ATP needed to maintain ion gradients. As a consequence, there is: depolarization of neurons; neural uptake of Na+ and Cl− and loss of K+; neuronal swelling; astrocytic uptake of Na+, K+ and anions; swelling of astrocytes; and reduction in ISF volume by fluid uptake into neurons and astrocytes. There is increased parenchymal solute content due to metabolic osmolyte production and solute influx from CSF and blood. The greatly increased [K+]isf triggers spreading depolarizations into the surrounding penumbra increasing metabolic load leading to increased size of the ischaemic core. Water enters the parenchyma primarily from blood, some passing into astrocyte endfeet via AQP4. In the medium term, e.g. after three hours, NaCl permeability and swelling rate increase with partial opening of tight junctions between blood–brain barrier endothelial cells and opening of SUR1-TPRM4 channels. Swelling is then driven by a Donnan-like effect. Longer term, there is gross failure of the blood–brain barrier. Oedema resolution is slower than its formation. Fluids without colloid, e.g. infused mock CSF, can be reabsorbed across the blood–brain barrier by a Starling-like mechanism whereas infused serum with its colloids must be removed by even slower extravascular means. Large scale oedema can increase intracranial pressure (ICP) sufficiently to cause fatal brain herniation. The potentially lethal increase in ICP can be avoided by craniectomy or by aspiration of the osmotically active infarcted region. However, the only satisfactory treatment resulting in retention of function is restoration of blood flow, providing this can be achieved relatively quickly. One important objective of current research is to find treatments that increase the time during which reperfusion is successful. Questions still to be resolved are discussed. [ABSTRACT FROM AUTHOR]

Cortical spreading depolarization (SD) imposes a massive increase in energy demand and therefore evolves as a target for treatment following acute brain injuries. Anesthetics are empirically used to reduce energy metabolism in critical brain conditions, yet their effect on metabolism during SD remains largely unknown. We investigated oxidative metabolism during SD in brain slices from Wistar rats. Extracellular potassium ([K+]o), local field potential and partial tissue oxygen pressure (ptiO2) were measured simultaneously. The cerebral metabolic rate of oxygen (CMRO2) was calculated using a reaction-diffusion model. By that, we tested the effect of clinically relevant concentrations of isoflurane on CMRO2 during SD and modeled tissue oxygenation for different capillary pO2 values. During SD, CMRO2 increased 2.7-fold, resulting in transient hypoxia in the slice core. Isoflurane decreased CMRO2, reduced peak [K+]o, and prolonged [K+]o clearance, which indicates reduced synaptic transmission and sodium-potassium ATPase inhibition. Modeling tissue oxygenation during SD illustrates the need for increased capillary pO2 levels to prevent hypoxia. In the absence thereof, isoflurane could improve tissue oxygenation by lowering CMRO2. Therefore, isoflurane is a promising candidate for pre-clinical studies on neuronal survival in conditions involving SD. [ABSTRACT FROM AUTHOR]

This Preface introduces the Special Issue entitled, “Energy Substrates and Microbiome Govern Brain Bioenergetics and Cognitive Function with Aging”, which is comprised of manuscripts contributed by invited speakers and program/organizing committee members who participated in the 14th International Conference on Brain Energy Metabolism (ICBEM) held on October 24–27, 2022 in Santa Fe, New Mexico, USA. The conference covered the latest developments in research related to neuronal energetics, emerging roles for glycogen in higher brain functions, the impact of dietary intervention on aging, memory, and Alzheimer's disease, roles of the microbiome in gut-brain signaling, astrocyte-neuron interactions related to cognition and memory, novel roles for mitochondria and their metabolites, and metabolic neuroimaging in aging and neurodegeneration. The special issue contains 25 manuscripts on these topics plus three tributes to outstanding scientists who have made important contributions to brain energy metabolism and participated in numerous ICBEM conferences. In addition, two of the manuscripts describe important directions and the rationale for future research in many thematic areas covered by the conference. [ABSTRACT FROM AUTHOR]

Spreading depolarization (SD) is assumed to be the pathophysiological correlate of migraine aura, leading to spreading depression of activity and a long-lasting vasoconstriction known as spreading oligemia. Furthermore, cerebrovascular reactivity is reversibly impaired after SD. Here, we explored the progressive restoration of impaired neurovascular coupling to somatosensory activation during spreading oligemia. Also, we evaluated whether nimodipine treatment accelerated the recovery of impaired neurovascular coupling after SD. Male, 4–9-month-old C57BL/6 mice (n = 11) were anesthetized with isoflurane (1%–1.5%), and SD was triggered with KCl through a burr hole made at the caudal parietal bone. EEG and cerebral blood flow (CBF) were recorded minimally invasively with a silver ball electrode and transcranial laser-Doppler flowmetry, rostral to SD elicitation. The L-type voltage-gated Ca2+ channel blocker nimodipine was administered i.p. (10 mg/kg). Whisker stimulation-related evoked potentials (EVPs) and functional hyperemia were assessed under isoflurane (0.1%)–medetomidine (0.1 mg/kg i.p.) anesthesia before, and repeatedly after SD, at 15-min intervals for 75 minutes. Nimodipine accelerated the recovery of CBF from spreading oligemia (time to full recovery, 52 ± 13 vs. 70 ± 8 min, nimodipine vs. control) and exhibited a tendency to shorten the duration of the SD-related EGG depression duration. The amplitudes of EVP and functional hyperemia were markedly reduced after SD, and progressively recovered over an hour post-SD. Nimodipine exerted no impact on EVP amplitude but consistently increased the absolute level of functional hyperemia from 20 min post-CSD (93 ± 11% vs. 66 ± 13%, nimodipine vs. control). A linear, positive correlation between EVP and functional hyperemia amplitude was skewed by nimodipine. In conclusion, nimodipine facilitated CBF restoration from spreading oligemia and the recovery of functional hyperemia post-SD, which were linked to a tendency of an accelerated return of spontaneous neural activity after SD. The use of nimodipine in migraine prophylaxis is suggested to be re-visited. [ABSTRACT FROM AUTHOR]

Objective: Characterize the neurophysiological effects of mild hypothermia on stroke and spreading depolarizations (SDs) in gyrencephalic brains. Methods: Left middle cerebral arteries (MCAs) of six hypothermic and six normothermic pigs were permanently occluded (MCAo). Hypothermia began 1 h after MCAo and continued throughout the experiment. ECoG signals from both frontoparietal cortices were recorded. Five-minute ECoG epochs were collected 5 min before, at 5 min, 4, 8, 12, and 16 h after MCAo, and before, during, and after SDs. Power spectra were decomposed into fast (alpha, beta, and gamma) and slow (delta and theta) frequency bands. Results: In the vascular insulted hemisphere under normothermia, electrodes near the ischemic core exhibited power decay across all frequency bands at 5 min and the 4th hour after MCAo. The same pattern was registered in the two furthest electrodes at the 12th and 16th hour. When mild hypothermia was applied in the vascular insulted hemispheres, the power decay was generalized and seen even in electrodes with uncompromised blood flow. During SD analysis, hypothermia maintained increased delta and beta power during the three phases of SDs in the furthest electrode from the ischemic core, followed by the second furthest and third electrode in the beta band during preSD and postSD segments. However, in hypothermic conditions, the third electrode showed lower delta, theta, and alpha power. Conclusion: Mild hypothermia attenuates all frequency bands in the vascularly compromised hemisphere, irrespective of the cortical location. During SD formation, it preserves power spectra more significantly in electrodes further from the ischemic core. [ABSTRACT FROM AUTHOR]

Despite the obvious importance of temperature for brain functioning, it remains one of the least studied parameters of the brain. The temperature is determined by the balance between the release of heat during metabolism and its removal by the bloodstream, which is regulated by neurovascular coupling. Using the method of laser speckle contrast imaging and micro-diamond thermometry, we performed a long-term simultaneous recording of blood flow velocity and temperature in the brain of anesthetized animals in vivo for the first time. To study the coupling between temperature and blood flow two approaches were used: enhancing the general blood flow by intraperitoneal injection of adrenaline and enhancing neuronal activity by applying KCl solution to the brain surface. The data we obtained indicated that the temperature of the nerve tissue had a more complex dynamics compared to blood flow, which was apparently associated with direct or indirect activation of both individual neurons and neural ensembles. Studies of temperature dynamics can make a significant contribution to understanding the nature of neurovascular coupling. [ABSTRACT FROM AUTHOR]

Abstract Background Spreading depolarization (SD), underlying mechanism of migraine aura and potential activator of pain pathways, is known to elicit transient local silencing cortical activity. Sweeping across the cortex, the electrocorticographic depression is supposed to underlie spreading negative symptoms of migraine aura. Main information about the suppressive effect of SD on cortical oscillations was obtained in anesthetized animals while ictal recordings in conscious patients failed to detect EEG depression during migraine aura. Here, we investigate the suppressive effect of SD on spontaneous cortical activity in awake animals and examine whether the anesthesia modifies the SD effect. Methods Spectral and spatiotemporal characteristics of spontaneous cortical activity following a single unilateral SD elicited by amygdala pinprick were analyzed in awake freely behaving rats and after induction of urethane anesthesia. Results In wakefulness, SD transiently suppressed cortical oscillations in all frequency bands except delta. Slow delta activity did not decline its power during SD and even increased it afterwards; high-frequency gamma oscillations showed the strongest and longest depression under awake conditions. Unexpectedly, gamma power reduced not only during SD invasion the recording cortical sites but also when SD occupied distant subcortical/cortical areas. Contralateral cortex not invaded by SD also showed transient depression of gamma activity in awake animals. Introduction of general anesthesia modified the pattern of SD-induced depression: SD evoked the strongest cessation of slow delta activity, milder suppression of fast oscillations and no distant changes in gamma activity. Conclusion Slow and fast cortical oscillations differ in their vulnerability to SD influence, especially in wakefulness. In the conscious brain, SD produces stronger and spatially broader depression of fast cortical oscillations than slow ones. The frequency-specific effects of SD on cortical activity of awake brain may underlie some previously unexplained clinical features of migraine aura.

Spreading depolarization (SD) is one of the most common neuropathologic phenomena in the nervous system, relating to numerous diseases. However, real‐time monitoring the rapid chemical changes during SD to probe the molecular mechanism remains a great challenge. We develop a potentiometric dual‐channel microsensor for simultaneous monitoring of H2S and pH featuring excellent selectivity and spatiotemporal resolution. Using this microsensor we first observe real time changes of H2S and pH in the rat brain induced by SD. This changes of H2S are completely suppressed when the rat pre‐treats with aminooxyacetic acid (AOAA), a blocker to inhibit the H2S‐producing enzyme, indicating H2S fluctuation might be related to enzyme‐dependent pathway during SD and less pH‐dependent. This study provides a new perspective for studying the function of H2S and the molecular basis of SD‐associated diseases. [ABSTRACT FROM AUTHOR]

Migraine is a common and disabling neurological disorder. The headache and sensory amplifications of migraine are attributed to hyperexcitable sensory circuits, but a detailed understanding remains elusive. A mutation in casein kinase 1 delta (CK1δ) was identified in non-hemiplegic familial migraine with aura and advanced sleep phase syndrome. Mice carrying the CK1δT44A mutation were more susceptible to spreading depolarization (the phenomenon that underlies migraine aura), but mechanisms underlying this migraine-relevant phenotype were not known. We used a combination of whole-cell electrophysiology and multiphoton imaging, in vivo and in brain slices, to compare CK1δT44A mice (adult males) to their wild-type littermates. We found that despite comparable synaptic activity at rest, CK1δT44A neurons were more excitable upon repetitive stimulation than wild-type, with a reduction in presynaptic adaptation at excitatory but not inhibitory synapses. The mechanism of this adaptation deficit was a calcium-dependent enhancement of the size of the readily releasable pool of synaptic vesicles, and a resultant increase in glutamate release, in CK1δT44A compared to wild-type synapses. Consistent with this mechanism, CK1δT44A neurons showed an increase in the cumulative amplitude of excitatory post-synaptic currents, and a higher excitation-to-inhibition ratio during sustained activity compared to wild-type. At a local circuit level, action potential bursts elicited in CK1δT44A neurons triggered an increase in recurrent excitation compared to wild-type, and at a network level, CK1δT44A mice showed a longer duration of 'up state' activity, which is dependent on recurrent excitation. Finally, we demonstrated that the spreading depolarization susceptibility of CK1δT44A mice could be returned to wild-type levels with the same intervention (reduced extracellular calcium) that normalized presynaptic adaptation. Taken together, these findings show a stimulus-dependent presynaptic gain of function at glutamatergic synapses in a genetic model of migraine, that accounts for the increased spreading depolarization susceptibility and may also explain the sensory amplifications that are associated with the disease. [ABSTRACT FROM AUTHOR]

Ischemic stroke occurs abruptly causing sudden neurologic deficits, and therefore, very little is known about hemodynamic perturbations in the brain immediately after stroke onset. Here, functional ultrasound imaging was used to monitor variations in relative cerebral blood volume (rCBV) compared to baseline. rCBV levels were analyzed brain-wide and continuously at high spatiotemporal resolution (100 μm, 2 Hz) until 70mins after stroke onset in rats. We compared two stroke models, with either a permanent occlusion of the middle cerebral artery (MCAo) or a tandem occlusion of both the common carotid and middle cerebral arteries (CCAo + MCAo). We observed a typical hemodynamic pattern, including a quick drop of the rCBV after MCAo, followed by spontaneous reperfusion of several brain regions located in the vicinity of the ischemic core. The severity and location of the ischemia were variable within groups. On average, the severity of the ischemia was in good agreement with the lesion volume (24 hrs after stroke) for MCAo group, while larger for the CCAo + MCAo model. For both groups, we observed that infarcts extended to initially non-ischemic regions located rostrally to the ischemic core. These regions strongly colocalize with the origin of transient hemodynamic events associated with spreading depolarizations. [ABSTRACT FROM AUTHOR]

Abstract The role of high mobility group box 1 (HMGB1) in inflammation is well characterized in the immune system and in response to tissue injury. More recently, HMGB1 was also shown to initiate an “inflammatory signaling cascade” in the brain parenchyma after a mild and brief disturbance, such as cortical spreading depolarization (CSD), leading to headache. Despite substantial evidence implying a role for inflammatory signaling in prevalent neuropsychiatric disorders such as migraine and depression, how HMGB1 is released from healthy neurons and how inflammatory signaling is initiated in the absence of apparent cell injury are not well characterized. We triggered a single cortical spreading depolarization by optogenetic stimulation or pinprick in naïve Swiss albino or transgenic Thy1-ChR2-YFP and hGFAP-GFP adult mice. We evaluated HMGB1 release in brain tissue sections prepared from these mice by immunofluorescent labeling and immunoelectron microscopy. EzColocalization and Costes thresholding algorithms were used to assess the colocalization of small extracellular vesicles (sEVs) carrying HMGB1 with astrocyte or microglia processes. sEVs were also isolated from the brain after CSD, and neuron-derived sEVs were captured by CD171 (L1CAM). sEVs were characterized with flow cytometry, scanning electron microscopy, nanoparticle tracking analysis, and Western blotting. We found that HMGB1 is released mainly within sEVs from the soma of stressed neurons, which are taken up by surrounding astrocyte processes. This creates conditions for selective communication between neurons and astrocytes bypassing microglia, as evidenced by activation of the proinflammatory transcription factor NF-ĸB p65 in astrocytes but not in microglia. Transmission immunoelectron microscopy data illustrated that HMGB1 was incorporated into sEVs through endosomal mechanisms. In conclusion, proinflammatory mediators released within sEVs can induce cell-specific inflammatory signaling in the brain without activating transmembrane receptors on other cells and causing overt inflammation.

Abstract Familial hemiplegic migraine type-1 (FHM-1) is a form of migraine with aura caused by mutations in the P/Q-type (Cav2.1) voltage-gated calcium channel. Pregabalin, used clinically in the treatment of chronic pain and epilepsy, inhibits P/Q-type calcium channel activity and recent studies suggest that it may have potential for the treatment of migraine. Spreading Depolarization (SD) is a neurophysiological phenomenon that can occur during migraine with aura by propagating a wave of silenced neuronal function through cortex and sometimes subcortical brain structures. Here, utilizing an optogenetic stimulation technique optimized to allow for non-invasive initiation of cortical SD, we demonstrate that chronic pregabalin administration [12 mg/kg/day (s.c.)] in vivo increased the threshold for cortical spreading depolarization in transgenic mice harboring the clinically-relevant Cav2.1S218L mutation (S218L). In addition, chronic pregabalin treatment limited subcortical propagation of recurrent spreading depolarization events to the striatum and hippocampus in both wild-type and S218L mice. To examine contributing underlying mechanisms of action of chronic pregabalin, we performed whole-cell patch-clamp electrophysiology in CA1 neurons in ex vivo brain slices from mice treated with chronic pregabalin vs vehicle. In WT mice, chronic pregabalin produced a decrease in spontaneous excitatory postsynaptic current (sEPSC) amplitude with no effect on frequency. In contrast, in S218L mice chronic pregabalin produced an increase in sEPSC amplitude and decreased frequency. These electrophysiological findings suggest that in FHM-1 mice chronic pregabalin acts through both pre- and post-synaptic mechanisms in CA1 hippocampal neurons to elicit FHM-1 genotype-specific inhibitory action. The results highlight the potential of chronic pregabalin to limit recurrent SD to subcortical brain structures during pathophysiological events in both the genetically-normal and FHM-1 brain. The work further provides insights into FHM-1 pathophysiology and the potential for chronic pregabalin treatment to prevent SD in migraineurs.

Abstract Background There is increasing evidence from human and animal studies that cortical spreading depression (CSD) is the neurophysiological correlate of migraine aura and a trigger of migraine pain mechanisms. The mechanisms of initiation of CSD in the brain of migraineurs remain unknown, and the mechanisms of initiation of experimentally induced CSD in normally metabolizing brain tissue remain incompletely understood and controversial. Here, we investigated the mechanisms of CSD initiation by focal application of KCl in mouse cerebral cortex slices. Methods High KCl puffs of increasing duration up to the threshold duration eliciting a CSD were applied on layer 2/3 whilst the membrane potential of a pyramidal neuron located very close to the site of KCl application and the intrinsic optic signal were simultaneously recorded. This was done before and after the application of a specific blocker of either NMDA or AMPA glutamate receptors (NMDARs, AMPARs) or voltage-gated Ca2+ (CaV) channels. If the drug blocked CSD, stimuli up to 12–15 times the threshold were applied. Results Blocking either NMDARs with MK-801 or CaV channels with Ni2+ completely inhibited CSD initiation by both CSD threshold and largely suprathreshold KCl stimuli. Inhibiting AMPARs with NBQX was without effect on the CSD threshold and velocity. Analysis of the CSD subthreshold and threshold neuronal depolarizations in control conditions and in the presence of MK-801 or Ni2+ revealed that the mechanism underlying ignition of CSD by a threshold stimulus (and not by a just subthreshold stimulus) is the CaV-dependent activation of a threshold level of NMDARs (and/or of channels whose opening depends on the latter). The delay of several seconds with which this occurs underlies the delay of CSD initiation relative to the rapid neuronal depolarization produced by KCl. Conclusions Both NMDARs and CaV channels are necessary for CSD initiation, which is not determined by the extracellular K+ or neuronal depolarization levels per se, but requires the CaV-dependent activation of a threshold level of NMDARs. This occurs with a delay of several seconds relative to the rapid depolarization produced by the KCl stimulus. Our data give insights into potential mechanisms of CSD initiation in migraine.

ObjectiveCharacterize the neurophysiological effects of mild hypothermia on stroke and spreading depolarizations (SDs) in gyrencephalic brains.MethodsLeft middle cerebral arteries (MCAs) of six hypothermic and six normothermic pigs were permanently occluded (MCAo). Hypothermia began 1 h after MCAo and continued throughout the experiment. ECoG signals from both frontoparietal cortices were recorded. Five-minute ECoG epochs were collected 5 min before, at 5 min, 4, 8, 12, and 16 h after MCAo, and before, during, and after SDs. Power spectra were decomposed into fast (alpha, beta, and gamma) and slow (delta and theta) frequency bands.ResultsIn the vascular insulted hemisphere under normothermia, electrodes near the ischemic core exhibited power decay across all frequency bands at 5 min and the 4th hour after MCAo. The same pattern was registered in the two furthest electrodes at the 12th and 16th hour. When mild hypothermia was applied in the vascular insulted hemispheres, the power decay was generalized and seen even in electrodes with uncompromised blood flow. During SD analysis, hypothermia maintained increased delta and beta power during the three phases of SDs in the furthest electrode from the ischemic core, followed by the second furthest and third electrode in the beta band during preSD and postSD segments. However, in hypothermic conditions, the third electrode showed lower delta, theta, and alpha power.ConclusionMild hypothermia attenuates all frequency bands in the vascularly compromised hemisphere, irrespective of the cortical location. During SD formation, it preserves power spectra more significantly in electrodes further from the ischemic core.

Spreading depolarizations (SD) are slow waves of complete depolarization of brain tissue followed by neuronal silencing that may play a role in seizure termination. Even though SD was first discovered in the context of epilepsy research, the link between SD and epileptic activity remains understudied. Both seizures and SD share fundamental pathophysiological features, and recent evidence highlights the frequent occurrence of SD in experimental seizure models. Human data on co-occurring seizures and SD are limited but suggestive. This mini-review addresses possible roles of SD during epileptiform activity, shedding light on SD as a potential mechanism for terminating epileptiform activity. A common denominator for many forms of epilepsy is reactive astrogliosis, a process characterized by morphological and functional changes to astrocytes. Data suggest that SD mechanisms are potentially perturbed in reactive astrogliosis and we propose that this may affect seizure pathophysiology.

The role of high mobility group box 1 (HMGB1) in inflammation is well characterized in the immune system and in response to tissue injury. More recently, HMGB1 was also shown to initiate an "inflammatory signaling cascade" in the brain parenchyma after a mild and brief disturbance, such as cortical spreading depolarization (CSD), leading to headache. Despite substantial evidence implying a role for inflammatory signaling in prevalent neuropsychiatric disorders such as migraine and depression, how HMGB1 is released from healthy neurons and how inflammatory signaling is initiated in the absence of apparent cell injury are not well characterized. We triggered a single cortical spreading depolarization by optogenetic stimulation or pinprick in naïve Swiss albino or transgenic Thy1-ChR2-YFP and hGFAP-GFP adult mice. We evaluated HMGB1 release in brain tissue sections prepared from these mice by immunofluorescent labeling and immunoelectron microscopy. EzColocalization and Costes thresholding algorithms were used to assess the colocalization of small extracellular vesicles (sEVs) carrying HMGB1 with astrocyte or microglia processes. sEVs were also isolated from the brain after CSD, and neuron-derived sEVs were captured by CD171 (L1CAM). sEVs were characterized with flow cytometry, scanning electron microscopy, nanoparticle tracking analysis, and Western blotting. We found that HMGB1 is released mainly within sEVs from the soma of stressed neurons, which are taken up by surrounding astrocyte processes. This creates conditions for selective communication between neurons and astrocytes bypassing microglia, as evidenced by activation of the proinflammatory transcription factor NF-ĸB p65 in astrocytes but not in microglia. Transmission immunoelectron microscopy data illustrated that HMGB1 was incorporated into sEVs through endosomal mechanisms. In conclusion, proinflammatory mediators released within sEVs can induce cell-specific inflammatory signaling in the brain without activating transmembrane receptors on other cells and causing overt inflammation. [ABSTRACT FROM AUTHOR]

Background: Spreading depolarizations (SDs) can be viewed at a cellular level using calcium imaging (CI), but this approach is limited to laboratory applications and animal experiments. Optical intrinsic signal imaging (OISI), on the other hand, is amenable to clinical use and allows viewing of large cortical areas without contrast agents. A better understanding of the behavior of OISI-observed SDs under different brain conditions is needed. Methods: We performed simultaneous calcium and OISI of SDs in GCaMP6f mice. SDs propagate through the cortex as a pathological wave and trigger a neurovascular response that can be imaged with both techniques. We imaged both mechanically stimulated SDs (sSDs) in healthy brains and terminal SDs (tSDs) induced by system hypoxia and cardiopulmonary failure. Results: We observed a lag in the detection of SDs in the OISI channels compared with CI. sSDs had a faster velocity than tSDs, and tSDs had a greater initial velocity for the first 400 µm when observed with CI compared with OISI. However, both imaging methods revealed similar characteristics, including a decrease in the sSD (but not tSD) velocities as the wave moved away from the site of initial detection. CI and OISI also showed similar spatial propagation of the SD throughout the image field. Importantly, only OISI allowed regional ischemia to be detected before tSDs occurred. Conclusions: Altogether, data indicate that monitoring either neural activity or intrinsic signals with high-resolution optical imaging can be useful to assess SDs, but OISI may be a clinically applicable way to predict, and therefore possibly mitigate, hypoxic-ischemic tSDs. [ABSTRACT FROM AUTHOR]

Background: Retinal migraine is a diagnosis of exclusion and is characterized by repeated episodes of transient monocular blindness associated with migraine. We report a case of systemic lupus erythematosus with acute episodes mimicking retinal migraines. Case report: A 46-year-old woman with a history of migraine with aura since her 20s and Evans syndrome presented with episodic transient monocular blindness. Retinal migraine was considered as the cause, and migraine prophylaxis initially reduced its frequency. After 5 months, the frequency increased, with chilblain-like lupus lesions on her extremities. Laboratory testing revealed lymphopenia and hypocomplementemia, fulfilling the diagnostic criteria for systemic lupus erythematosus, which may have caused Evans syndrome and transient monocular blindness, mimicking retinal migraines. After intravenous methylprednisolone and rituximab therapy, the transient monocular blindness episodes did not recur. Conclusion: Given the clinical presentation, systemic lupus erythematosus should be considered as a cause of transient monocular blindness and should be distinguished from retinal migraine. [ABSTRACT FROM AUTHOR]

Familial hemiplegic migraine type-1 (FHM-1) is a form of migraine with aura caused by mutations in the P/Q-type (Cav2.1) voltage-gated calcium channel. Pregabalin, used clinically in the treatment of chronic pain and epilepsy, inhibits P/Q-type calcium channel activity and recent studies suggest that it may have potential for the treatment of migraine. Spreading Depolarization (SD) is a neurophysiological phenomenon that can occur during migraine with aura by propagating a wave of silenced neuronal function through cortex and sometimes subcortical brain structures. Here, utilizing an optogenetic stimulation technique optimized to allow for non-invasive initiation of cortical SD, we demonstrate that chronic pregabalin administration [12 mg/kg/day (s.c.)] in vivo increased the threshold for cortical spreading depolarization in transgenic mice harboring the clinically-relevant Cav2.1S218L mutation (S218L). In addition, chronic pregabalin treatment limited subcortical propagation of recurrent spreading depolarization events to the striatum and hippocampus in both wild-type and S218L mice. To examine contributing underlying mechanisms of action of chronic pregabalin, we performed whole-cell patch-clamp electrophysiology in CA1 neurons in ex vivo brain slices from mice treated with chronic pregabalin vs vehicle. In WT mice, chronic pregabalin produced a decrease in spontaneous excitatory postsynaptic current (sEPSC) amplitude with no effect on frequency. In contrast, in S218L mice chronic pregabalin produced an increase in sEPSC amplitude and decreased frequency. These electrophysiological findings suggest that in FHM-1 mice chronic pregabalin acts through both pre- and post-synaptic mechanisms in CA1 hippocampal neurons to elicit FHM-1 genotype-specific inhibitory action. The results highlight the potential of chronic pregabalin to limit recurrent SD to subcortical brain structures during pathophysiological events in both the genetically-normal and FHM-1 brain. The work further provides insights into FHM-1 pathophysiology and the potential for chronic pregabalin treatment to prevent SD in migraineurs. [ABSTRACT FROM AUTHOR]

Background: There is increasing evidence from human and animal studies that cortical spreading depression (CSD) is the neurophysiological correlate of migraine aura and a trigger of migraine pain mechanisms. The mechanisms of initiation of CSD in the brain of migraineurs remain unknown, and the mechanisms of initiation of experimentally induced CSD in normally metabolizing brain tissue remain incompletely understood and controversial. Here, we investigated the mechanisms of CSD initiation by focal application of KCl in mouse cerebral cortex slices. Methods: High KCl puffs of increasing duration up to the threshold duration eliciting a CSD were applied on layer 2/3 whilst the membrane potential of a pyramidal neuron located very close to the site of KCl application and the intrinsic optic signal were simultaneously recorded. This was done before and after the application of a specific blocker of either NMDA or AMPA glutamate receptors (NMDARs, AMPARs) or voltage-gated Ca2+ (CaV) channels. If the drug blocked CSD, stimuli up to 12–15 times the threshold were applied. Results: Blocking either NMDARs with MK-801 or CaV channels with Ni2+ completely inhibited CSD initiation by both CSD threshold and largely suprathreshold KCl stimuli. Inhibiting AMPARs with NBQX was without effect on the CSD threshold and velocity. Analysis of the CSD subthreshold and threshold neuronal depolarizations in control conditions and in the presence of MK-801 or Ni2+ revealed that the mechanism underlying ignition of CSD by a threshold stimulus (and not by a just subthreshold stimulus) is the CaV-dependent activation of a threshold level of NMDARs (and/or of channels whose opening depends on the latter). The delay of several seconds with which this occurs underlies the delay of CSD initiation relative to the rapid neuronal depolarization produced by KCl. Conclusions: Both NMDARs and CaV channels are necessary for CSD initiation, which is not determined by the extracellular K+ or neuronal depolarization levels per se, but requires the CaV-dependent activation of a threshold level of NMDARs. This occurs with a delay of several seconds relative to the rapid depolarization produced by the KCl stimulus. Our data give insights into potential mechanisms of CSD initiation in migraine. [ABSTRACT FROM AUTHOR]

Background: Spreading depolarization (SD) has been linked to the impairment of neurovascular coupling. However, the association between SD occurrence and cerebrovascular pressure reactivity as a surrogate of cerebral autoregulation (CA) remains unclear. Therefore, we analyzed CA using the long-pressure reactivity index (L-PRx) during SDs in patients with aneurysmal subarachnoid hemorrhage (aSAH). Methods: A retrospective study of patients with aSAH who were recruited at two centers, Heidelberg (HD) and Berlin (BE), was performed. Continuous monitoring of mean arterial pressure (MAP) and intracranial pressure (ICP) was recorded. ICP was measured using an intraparenchymal probe in HD patients and was measure in BE patients through external ventricular drainage. Electrocorticographic (ECoG) activity was continuously recorded between 3 and 13 days after hemorrhage. Autoregulation according to L-PRx was calculated as a moving linear Pearson's correlation of 20-min averages of MAP and ICP. For every identified SD, 60-min intervals of L-PRx were averaged, plotted, and analyzed depending on SD occurrence. Random L-PRx recording periods without SDs served as the control. Results: A total of 19 patients (HD n = 14, BE n = 5, mean age 50.4 years, 9 female patients) were monitored for a mean duration of 230.4 h (range 96–360, STD ± 69.6 h), during which ECoG recordings revealed a total number of 277 SDs. Of these, 184 represented a single SD, and 93 SDs presented in clusters. In HD patients, mean L-PRx values were 0.12 (95% confidence interval [CI] 0.11–0.13) during SDs and 0.07 (95% CI 0.06–0.08) during control periods (p < 0.001). Similarly, in BE patients, a higher L-PRx value of 0.11 (95% CI 0.11–0.12) was detected during SDs than that during control periods (0.08, 95% CI 0.07–0.09; p < 0.001). In a more detailed analysis, CA changes registered through an intraparenchymal probe (HD patients) revealed that clustered SD periods were characterized by signs of more severely impaired CA (L-PRx during SD in clusters: 0.23 [95% CI 0.20–0.25]; single SD: 0.09 [95% CI 0.08–0.10]; control periods: 0.07 [95% CI 0.06–0.08]; p < 0.001). This group also showed significant increases in ICP during SDs in clusters compared with single SD and control periods. Conclusions: Neuromonitoring for simultaneous assessment of cerebrovascular pressure reactivity using 20-min averages of MAP and ICP measured by L-PRx during SD events is feasible. SD occurrence was associated with significant increases in L-PRx values indicative of CA disturbances. An impaired CA was found during SD in clusters when using an intraparenchymal probe. This preliminary study validates the use of cerebrovascular reactivity indices to evaluate CA disturbances during SDs. Our results warrant further investigation in larger prospective patient cohorts. [ABSTRACT FROM AUTHOR]

Spreading depolarizations (SDs) are profound disruptions of cellular homeostasis that slowly propagate through gray matter and present an extraordinary metabolic challenge to brain tissue. Recent work has shown that SDs occur commonly in human patients in the neurointensive care setting and have established a compelling case for their importance in the pathophysiology of acute brain injury. The International Conference on Spreading Depolarizations (iCSD) held in Boca Raton, Florida, in September of 2018 included a discussion session focused on the question of "Which SDs are deleterious to brain tissue?" iCSD is attended by investigators studying various animal species including invertebrates, in vivo and in vitro preparations, diseases of acute brain injury and migraine, computational modeling, and clinical brain injury, among other topics. The discussion included general agreement on many key issues, but also revealed divergent views on some topics that are relevant to the design of clinical interventions targeting SDs. A draft summary of viewpoints offered was then written by a multidisciplinary writing group of iCSD members, based on a transcript of the session. Feedback of all discussants was then formally collated, reviewed and incorporated into the final document. It is hoped that this report will stimulate collection of data that are needed to develop a more nuanced understanding of SD in different pathophysiological states, as the field continues to move toward effective clinical interventions.

Spreading depolarizations (SDs) have been linked to infarct volume expansion following ischemic stroke. Therapeutic hypothermia provides a neuroprotective effect after ischemic stroke. This study aimed to evaluate the effect of hypothermia on the propagation of SDs and infarct volume in an ischemic swine model. Through left orbital exenteration, middle cerebral arteries were surgically occluded (MCAo) in 16 swine. Extensive craniotomy and durotomy were performed. Six hypothermic and five normothermic animals were included in the analysis. An intracranial temperature probe was placed right frontal subdural. One hour after ischemic onset, mild hypothermia was induced and eighteen hours of electrocorticographic (ECoG) and intrinsic optical signal (IOS) recordings were acquired. Postmortem, 4 mm-thick slices were stained with 2,3,5-triphenyltetrazolium chloride to estimate the infarct volume. Compared to normothermia (36.4 ± 0.4°C), hypothermia (32.3 ± 0.2°C) significantly reduced the frequency and expansion of SDs (ECoG: 3.5 ± 2.1, 73.2 ± 5.2% vs. 1.0 ± 0.7, 41.9 ± 21.8%; IOS 3.9 ± 0.4, 87.6 ± 12.0% vs. 1.4 ± 0.7, 67.7 ± 8.3%, respectively). Further, infarct volume among hypothermic animals (23.2 ± 1.8% vs. 32.4 ± 2.5%) was significantly reduced. Therapeutic hypothermia reduces infarct volume and the frequency and expansion of SDs following cerebral ischemia. [ABSTRACT FROM AUTHOR]

Ketamine merits further testing in larger studies both in the setting of raised ICP refractory to tier 1 therapy and/or as part of the baseline sedative-analgesia regimen in pediatric severe TBI. In the 1990s, several studies questioned the concerns regarding the utility of ketamine in patients with severe traumatic brain injury (TBI). Kolenda et al ([5]), and Albanèse et al ([6]), reported that continuous infusion or bolus administration of racemic ketamine was associated with improved cerebral perfusion pressure (CPP) and decreased ICP, respectively, in critically ill adults with TBI. Hartings et al ([22]) also reported a case where bolus administration of ketamine (1.5 mg/kg) eliminated spreading depolarizations in a severe TBI patient. [Extracted from the article]

Despite successful recanalization, reperfusion failure associated with poor neurological outcomes develops in half of treated stroke patients. We explore here whether spreading depolarization (SD) is a predictor of reperfusion failure. Global forebrain ischemia/reperfusion was induced in male and female C57BL/6 mice (n = 57). SD and cerebral blood flow (CBF) changes were visualized with transcranial intrinsic optical signal and laser speckle contrast imaging. To block SD, MK801 was applied (n = 26). Neurological deficit, circle of Willis (CoW) anatomy and neuronal injury were evaluated 24 hours later. SD emerged after ischemia onset in one or both hemispheres under a perfusion threshold (CBF drop to 21.1 ± 4.6 vs. 33.6 ± 4.4%, SD vs. no SD). The failure of later reperfusion (44.4 ± 12.5%) was invariably linked to previous SD. In contrast, reperfusion was adequate (98.9 ± 7.4%) in hemispheres devoid of SD. Absence of the P1 segment of the posterior cerebral artery in the CoW favored SD occurrence and reperfusion failure. SD occurrence and reperfusion failure were associated with poor neurologic function, and neuronal necrosis 24 hours after ischemia. The inhibition of SD significantly improved reperfusion. SD occurrence during ischemia impairs later reperfusion, prognosticating poor neurological outcomes. The increased likelihood of SD occurrence is predicted by inadequate collaterals. [ABSTRACT FROM AUTHOR]

Glutamate levels and lifetime in the brain extracellular space are dinamically regulated by a family of Na+- and K+-dependent glutamate transporters, which thereby control numerous brain functions and play a role in numerous neurological and psychiatric diseases. Migraine is a neurological disorder characterized by recurrent attacks of typically throbbing and unilateral headache and by a global dysfunction in multisensory processing. Familial hemiplegic migraine type 2 (FHM2) is a rare monogenic form of migraine with aura caused by loss-of-function mutations in the α2 Na/K ATPase (α2NKA). In the adult brain, this pump is expressed almost exclusively in astrocytes where it is colocalized with glutamate transporters. Knockin mouse models of FHM2 (FHM2 mice) show a reduced density of glutamate transporters in perisynaptic astrocytic processes (mirroring the reduced expression of α2NKA) and a reduced rate of glutamate clearance at cortical synapses during neuronal activity and sensory stimulation. Here we review the migraine-relevant alterations produced by the astrocytic glutamate transport dysfunction in FHM2 mice and their underlying mechanisms, in particular regarding the enhanced brain susceptibility to cortical spreading depression (the phenomenon that underlies migraine aura and can also initiate the headache mechanisms) and the enhanced algesic response to a migraine trigger. [ABSTRACT FROM AUTHOR]

Touch and other types of patient stimulation are necessary in critical care and generally presumed to be beneficial. Recent pre-clinical studies as well as randomized trials assessing early mobilization have challenged the safety of such routine practices in patients with acute neurological injury such as stroke. We sought to determine whether patient stimulation could result in spreading depolarization (SD), a dramatic pathophysiological event that likely contributes to metabolic stress and ischemic expansion in such patients. Patients undergoing surgical intervention for severe acute neurological injuries (stroke, aneurysm rupture, or trauma) were prospectively consented and enrolled in an observational study monitoring SD with implanted subdural electrodes. Subjects also underwent simultaneous video recordings (from continuous EEG monitoring) to assess for physical touch and other forms of patient stimulation (such as suctioning and positioning). The association of patient stimulation with subsequent SD was assessed. Increased frequency of patient stimulation was associated with increased risk of SD (OR = 4.39 [95%CI = 1.71–11.24]). The overall risk of SD was also increased in the 60 min following patient stimulation compared to times with no stimulation (OR = 1.19 [95%CI = 1.13–1.26]), though not all subjects demonstrated this effect individually. Positioning of the subject was the subtype of stimulation with the strongest overall effect on SD (OR = 4.92 [95%CI = 3.74–6.47]). We conclude that in patients with some acute neurological injuries, touch and other patient stimulation can induce SD (PS-SD), potentially increasing the risk of metabolic and ischemic stress. PS-SD may represent an underlying mechanism for observed increased risk of early mobilization in such patients. [ABSTRACT FROM AUTHOR]

Anoxic spreading depolarization (aSD) is a hallmark of ischemic injury in the cerebral cortex. In adults, aSD is associated with rapid and nearly complete neuronal depolarization and loss of neuronal functions. While ischemia also evokes aSD in the immature cortex, developmental aspects of neuronal behavior during aSD remain largely unknown. Here, using oxygen-glucose deprivation (OGD) ischemia model in slices of the postnatal rat somatosensory cortex, we found that immature neurons displayed much more complex behaviors: they initially moderately depolarized during aSD, then transiently repolarised (for up to tens of minutes), and only then passed to terminal depolarization. The ability to fire action potentials was maintained in neurons mildly depolarized during aSD without reaching the level of depolarization block, and these functions were regained in the majority of immature neurons during post-aSD transient repolarization. The amplitude of depolarization and the probability of depolarization block during aSD increased, whereas transient post-SD repolarization levels and duration, and associated recovery in neuronal firing decreased with age. By the end of the first postnatal month, aSD acquired an adult-like phenotype, where depolarization during aSD merged with terminal depolarization and the phase of transient recovery was lost. Thus, changes in neuronal function during aSD undergo remarkable developmental changes that may contribute to lower susceptibility of the immature neurons to ischemia. [ABSTRACT FROM AUTHOR]

Background: Delayed cerebral ischemia (DCI) is a common and serious complication of aneurysmal subarachnoid hemorrhage (aSAH). Though many clinical trials have looked at therapies for DCI and vasospasm in aSAH, along with reducing rebleeding risks, none have led to improving outcomes in this patient population. We present an up-to-date review of the pathophysiology of DCI and its association with early brain injury (EBI). Recent Findings: Recent studies have demonstrated that EBI, as opposed to delayed brain injury, is the main contributor to downstream pathophysiological mechanisms that play a role in the development of DCI. New predictive models, including advanced monitoring and neuroimaging techniques, can help detect EBI and improve the clinical management of aSAH patients. Summary: EBI, the severity of subarachnoid hemorrhage, and physiological/imaging markers can serve as indicators for potential early therapeutics in aSAH. The microcellular milieu and hemodynamic pathomechanisms should remain a focus of researchers and clinicians. With the advancement in understanding the pathophysiology of DCI, we are hopeful that we will make strides toward better outcomes for this unique patient population. [ABSTRACT FROM AUTHOR]