The effect of P2X7 antagonism on subcortical spread of optogenetically-triggered cortical spreading depression and neuroinflammation.

Migraine is a neurological disorder characterized by episodes of severe headache. Cortical spreading depression (CSD), the electrophysiological equivalent of migraine aura, results in opening of pannexin 1 megachannels that release ATP and triggers parenchymal neuroinflammatory signaling cascade in the cortex. Migraine symptoms suggesting subcortical dysfunction bring subcortical spread of CSD under the light. Here, we investigated the role of purinergic P2X7 receptors on the subcortical spread of CSD and its consequent neuroinflammation using a potent and selective P2X7R antagonist, JNJ-47965567. P2X7R antagonism had no effect on the CSD threshold and characteristics but increased the latency to hypothalamic voltage deflection following CSD suggesting that ATP acts as a mediator in the subcortical spread. P2X7R antagonism also prevented cortical and subcortical neuronal activation following CSD, revealed by bilateral decrease in c-fos positive neuron count, and halted CSD-induced neuroinflammation revealed by decreased neuronal HMGB1 release and decreased nuclear translocation of NF-kappa B-p65 in astrocytes. In conclusion, our data suggest that P2X7R plays a role in CSD-induced neuroinflammation, subcortical spread of CSD and CSD-induced neuronal activation hence can be a potential target.

The Brain, the Eating Plate, and the Gut Microbiome: Partners in Migraine Pathogenesis.

This review summarizes the relationship between diet, the gut microbiome, and migraine. Key findings reveal that certain dietary factors, such as caffeine and alcohol, can trigger migraine, while nutrients like magnesium and riboflavin may help alleviate migraine symptoms. The gut microbiome, through its influence on neuroinflammation (e.g., vagus nerve and cytokines), gut-brain signaling (e.g., gamma-aminobutyric acid), and metabolic function (e.g., short-chain fatty acids), plays a crucial role in migraine susceptibility. Migraine can also alter eating behaviors, leading to poor nutritional choices and further exacerbating the condition. Individual variability in diet and microbiome composition highlights the need for personalized dietary and prebiotic interventions. Epidemiological and clinical data support the effectiveness of tailored nutritional approaches, such as elimination diets and the inclusion of beneficial nutrients, in managing migraine. More work is needed to confirm the role of prebiotics, probiotics, and potentially fecal microbiome translation in the management of migraine. Future research should focus on large-scale studies to elucidate the underlying mechanisms of bidirectional interaction between diet and migraine and develop evidence-based clinical guidelines. Integrating dietary management, gut health optimization, and lifestyle modifications can potentially offer a holistic approach to reducing migraine frequency and severity, ultimately improving patient outcomes and quality of life.

Pericytes in the brain and heart: functional roles and response to ischemia and reperfusion.

In the last 20 years there has been a revolution in our understanding of how blood flow is regulated in many tissues. Whereas it used to be thought that essentially all blood flow control occurred at the arteriole level, it is now recognised that control of capillary blood flow by contractile pericytes plays a key role both in regulating blood flow physiologically and in reducing it in clinically-relevant pathological conditions. In this article we compare and contrast how brain and cardiac pericytes regulate cerebral and coronary blood flow, focusing mainly on the pathological events of cerebral and cardiac ischemia. The cerebral and coronary capillary beds differ dramatically in morphology, yet in both cases pericyte-mediated capillary constriction plays a key role in restricting blood flow after ischemia and possibly in other pathological conditions. We conclude with suggestions for therapeutic approaches to relaxing pericytes, which may prove useful in the long term for reducing pericyte-induced ischemia.

Unraveling the interplay of neuroinflammatory signaling between parenchymal and meningeal cells in migraine headache.

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.

FGF2 gene's antisense protein, NUDT6, plays a depressogenic role by promoting inflammation and suppressing neurogenesis without altering FGF2 signalling.

Fibroblast growth factor-2 (FGF2) is involved in the regulation of affective behaviour and shows antidepressant effects through the Akt and extracellular signal regulated kinase (ERK) 1/2 pathways. Nudix hydrolase 6 (NUDT6) protein is encoded from FGF2 gene's antisense strand and its role in the regulation of affective behaviour is unknown. Here, we overexpressed NUDT6 in the hippocampus and investigated its behavioural effects and the underlying molecular mechanisms affecting the behaviour. We showed that increasing hippocampal NUDT6 results in depression-like behaviour in rats without changing FGF2 levels or activating its downstream effectors, Akt and ERK1/2. Instead, NUDT6 acted by inducing inflammatory signalling, specifically by increasing S100 calcium binding protein A9 (S100A9) levels, activating nuclear factor-kappa B-p65 (NF-κB-p65), and elevating microglia numbers along with a reduction in neurogenesis. Our results suggest that NUDT6 could play a role in major depression by inducing a proinflammatory state. This is the first report of an antisense protein acting through a different mechanism of action than regulation of its sense protein. The opposite effects of NUDT6 and FGF2 on depression-like behaviour may serve as a mechanism to fine-tune affective behaviour. Our findings open up new venues for studying the differential regulation and functional interactions of sense and antisense proteins in neural function and behaviour, as well as in neuropsychiatric disorders. KEY POINTS: Hippocampal overexpression of nudix hydrolase 6 (NUDT6), the antisense protein of fibroblast growth factor-2 (FGF2), increases depression-like behaviour in rats. Hippocampal NUDT6 overexpression triggers a neuroinflammatory cascade by increasing S100 calcium binding proteinA9 (S100A9) expression and nuclear NF-κB-p65 translocation in neurons, in addition to microglial recruitment and activation. Hippocampal NUDT6 overexpression suppresses neurogenesis. NUDT6 exerts its actions without altering the levels or downstream signalling pathways of FGF2.

Vesicular HMGB1 release from neurons stressed with spreading depolarization enables confined inflammatory signaling to astrocytes.

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.

Cortical spreading depolarization-induced constriction of penetrating arteries can cause watershed ischemia: A potential mechanism for white matter lesions.

Periventricular white matter lesions (WMLs) are common MRI findings in migraine with aura (MA). Although hemodynamic disadvantages of vascular supply to this region create vulnerability, the pathophysiological mechanisms causing WMLs are unclear. We hypothesize that prolonged oligemia, a consequence of cortical spreading depolarization (CSD) underlying migraine aura, may lead to ischemia/hypoxia at hemodynamically vulnerable watershed zones fed by long penetrating arteries (PAs). For this, we subjected mice to KCl-triggered single or multiple CSDs. We found that post-CSD oligemia was significantly deeper at medial compared to lateral cortical areas, which induced ischemic/hypoxic changes at watershed areas between the MCA/ACA, PCA/anterior choroidal and at the tip of superficial and deep PAs, as detected by histological and MRI examination of brains 2-4 weeks after CSD. BALB-C mice, in which MCA occlusion causes large infarcts due to deficient collaterals, exhibited more profound CSD-induced oligemia and were more vulnerable compared to Swiss mice such that a single CSD was sufficient to induce ischemic lesions at the tip of PAs. In conclusion, CSD-induced prolonged oligemia has potential to cause ischemic/hypoxic injury at hemodynamically vulnerable brain areas, which may be one of the mechanisms underlying WMLs located at the tip of medullary arteries seen in MA patients.

The Effect of Inhibition of Perisynaptic Astrocyte Glycogen Utilization on Depression-Like Behavior. / Sinaptik Enerji Kaynagi Glikojenin Kullaniminin Engellenmesinin Depresyon-benzeri Davranislara Etkisi.

OBJECTIVE: Under physiological conditions, astrocytes produce lactate to meet the increased synaptic energy demand due to neuronal activity. In the light of the findings showing that this process is disrupted in the pathophysiology of major depression, the aim of this study is to investigate the effect of pharmacological inhibition of perisynaptic astrocyte glycogen utilization on anxiety-like behavior and depression-like behavior in female and male mice. METHODS: In this study, DAB (1,4-dideoxy-1,4-imino-D-arabinitol), which is an inhibitor of glycogen breaking enzyme glycogen phosphorylase, was intrahippocampally administered to 15 female and 14 male Swiss albino mice, while 15 female and 12 male Swiss albino mice received intrahippocampal saline injections. Three and five days after the injections, the anxiety-like and depression-like behaviors of the mice were assessed by locomotor activity, open-field test, light-dark box test, tail suspension test and sucrose preference test. RESULTS: Three days after injection, neither depression-like nor anxietylike significant behavioral changes were detected in the male experimental group mice compared to the control group; but an increase in locomotor activity (p=0.05) and time spent in the open-field (p=0.01) were observed on the fifth day. In evaluations of the female experimental group mice on the third and fifth days, depression-like and anxiety-like behaviors were found similar to the control group, as seen in the male mice. The only significant difference in the experimental group female mice was found in the sucrose preference test, which revealed an increased tendency to prefer sucrose (p=0.003) compared to the control group. CONCLUSION: The inhibition of glycogen use in the hippocampus by DAB did not affect anxiety-like and depression-like behaviors 3 and 5 days after injection in both female and male mice. The increase in the time spent in the open-field by male experimental group mice was associated not with anxiety, but with increase in the locomotor activity. The fact that no significant difference was observed in the light-dark box test, which is another test used to evaluate anxiety, supported this opinion. The increase seen in the sucrose preference test in female experimental group mice was not interpreted as an increase in hedonic behavior because prevention of glycogen breakdown in the hypothalamus might have homeostatically increased sugar-craving and therefore resulted in an increase in sucrose preference. Different set of tests better targeting the energy and glucose metabolism and applied at farther time points than surgery are recommended for future studies.

Cortical spreading depression can be triggered by sensory stimulation in primed wild type mouse brain: a mechanistic insight to migraine aura generation.

BACKGROUND: Unlike the spontaneously appearing aura in migraineurs, experimentally, cortical spreading depression (CSD), the neurophysiological correlate of aura is induced by non-physiological stimuli. Consequently, neural mechanisms involved in spontaneous CSD generation, which may provide insight into how migraine starts in an otherwise healthy brain, remain largely unclear. We hypothesized that CSD can be physiologically induced by sensory stimulation in primed mouse brain. METHODS: Cortex was made susceptible to CSD with partial inhibition of Na+/K+-ATPase by epidural application of a low concentration of Na+/K+-ATPase blocker ouabain, allowing longer than 30-min intervals between CSDs or by knocking-down α2 subunit of Na+/K+-ATPase, which is crucial for K+ and glutamate re-uptake, with shRNA. Stimulation-triggered CSDs and extracellular K+ changes were monitored in vivo electrophysiologically and a K+-sensitive fluoroprobe (IPG-4), respectively. RESULTS: After priming with ouabain, photic stimulation significantly increased the CSD incidence compared with non-stimulated animals (44.0 vs. 4.9%, p < 0.001). Whisker stimulation also significantly increased the CSD incidence, albeit less effectively (14.9 vs. 2.4%, p = 0.02). Knocking-down Na+/K+-ATPase (50% decrease in mRNA) lowered the CSD threshold in all mice tested with KCl but triggered CSDs in 14.3% and 16.7% of mice with photic and whisker stimulation, respectively. Confirming Na+/K+-ATPase hypofunction, extracellular K+ significantly rose during sensory stimulation after ouabain or shRNA treatment unlike controls. In line with the higher CSD susceptibility observed, K+ rise was more prominent after ouabain. To gain insight to preventive mechanisms reducing the probability of stimulus-evoked CSDs, we applied an A1-receptor antagonist (DPCPX) to the occipital cortex, because adenosine formed during stimulation from ATP can reduce CSD susceptibility. DPCPX induced spontaneous CSDs but only small-DC shifts along with suppression of EEG spikes during photic stimulation, suggesting that the inhibition co-activated with sensory stimulation could limit CSD ignition when K+ uptake was not sufficiently suppressed as with ouabain. CONCLUSIONS: Normal brain is well protected against CSD generation. For CSD to be ignited under physiological conditions, priming and predisposing factors are required as seen in migraine patients. Intense sensory stimulation has potential to trigger CSD when co-existing conditions bring extracellular K+ and glutamate concentrations over CSD-ignition threshold and stimulation-evoked inhibitory mechanisms are overcome.

Overview of extracellular vesicle characterization techniques and introduction to combined reflectance and fluorescence confocal microscopy to distinguish extracellular vesicle subpopulations.

Extracellular vesicles (EVs) are nanoparticles (30 to 1000 nm in diameter) surrounded by a lipid-bilayer which carry bioactive molecules between local and distal cells and participate in intercellular communication. Because of their small size and heterogenous nature they are challenging to characterize. Here, we discuss commonly used techniques that have been employed to yield information about EV size, concentration, mechanical properties, and protein content. These include dynamic light scattering, nanoparticle tracking analysis, flow cytometry, transmission electron microscopy, atomic force microscopy, western blotting, and optical methods including super-resolution microscopy. We also introduce an innovative technique for EV characterization which involves immobilizing EVs on a microscope slide before staining them with antibodies targeting EV proteins, then using the reflectance mode on a confocal microscope to locate the EV plane. By then switching to the microscope's fluorescence mode, immunostained EVs bearing specific proteins can be identified and the heterogeneity of an EV preparation can be determined. This approach does not require specialist equipment beyond the confocal microscopes that are available in many cell biology laboratories, and because of this, it could become a complementary approach alongside the aforementioned techniques to identify molecular heterogeneity in an EV preparation before subsequent analysis requiring specialist apparatus.

Confocal reflectance microscopy for metal and lipid nanoparticle visualization in the brain.

Aim: A requirement for nanoparticle (NP) research is visualization of particles within cells and tissues. Limitations of electron microscopy and low yields of NP fluorescent tagging warrant the identification of alternative imaging techniques. Method: Confocal reflectance microscopy (CRM) in combination with fluorescence imaging was assessed for visualizing rhodamine B-conjugated silver and fluorescein isothiocyanate-conjugated lipid core-stearylamine NP uptake in vitro and in vivo. Results: CRM successfully identified cellular uptake and blood-brain barrier penetration of NPs owing to their distinguishing refractive indices. NP-dependent reflectance signals in vitro were dose and incubation time dependent. Finally, CRM facilitated the distinction between nonspecific fluorescence signals and NPs. Conclusion: These findings demonstrate the value of CRM for NP visualization in tissues, which can be performed with a standard confocal microscope.

Nanoparticles (NPs) are extremely small materials utilized in the healthcare sector mainly for the delivery of drugs into tissues that are not easily accessible with regular pharmaceuticals. One such tissue is the brain, which has a barrier between it and the bloodstream that prevents the passage of most drugs. For NP research, the successful entry of NPs into target tissues must be demonstrated, but this is complicated by the small size and weak labeling of NPs. In this article, the authors demonstrate a low-cost, complementary microscopy technique that is readily available in most biological research laboratories and that can be used to detect and analyze the entry of different NP types into brain tissue and their uptake by brain tumor cells. These data create new opportunities for research on NP-assisted drug delivery to the central nervous system.

Contractile apparatus in CNS capillary pericytes.

Significance: Whether or not capillary pericytes contribute to blood flow regulation in the brain and retina has long been debated. This was partly caused by failure of detecting the contractile protein α -smooth muscle actin ( α -SMA) in capillary pericytes. Aim: The aim of this review is to summarize recent developments in detecting α -SMA and contractility in capillary pericytes and the relevant literature on the biology of actin filaments. Results: Evidence suggests that for visualization of the small amounts of α -SMA in downstream mid-capillary pericytes, actin depolymerization must be prevented during tissue processing. Actin filaments turnover is mainly based on de/re-polymerization rather than transcription of the monomeric form, hence, small amounts of α -SMA mRNA may evade detection by transcriptomic studies. Similarly, transgenic mice expressing fluorescent reporters under the α -SMA promoter may yield low fluorescence due to limited transcriptional activity in mid-capillary pericytes. Recent studies show that pericytes including mid-capillary ones express several actin isoforms and myosin heavy chain type 11, the partner of α -SMA in mediating contraction. Emerging evidence also suggests that actin polymerization in pericytes may have a role in regulating the tone of downstream capillaries. Conclusions: With guidance of actin biology, innovative labeling and imaging techniques can reveal the molecular machinery of contraction in pericytes.

Ion Channel Dysfunction and Neuroinflammation in Migraine and Depression.

Migraine and major depression are debilitating disorders with high lifetime prevalence rates. Interestingly these disorders are highly comorbid and show significant heritability, suggesting shared pathophysiological mechanisms. Non-homeostatic function of ion channels and neuroinflammation may be common mechanisms underlying both disorders: The excitation-inhibition balance of microcircuits and their modulation by monoaminergic systems, which depend on the expression and function of membrane located K+, Na+, and Ca+2 channels, have been reported to be disturbed in both depression and migraine. Ion channels and energy supply to synapses not only change excitability of neurons but can also mediate the induction and maintenance of inflammatory signaling implicated in the pathophysiology of both disorders. In this respect, Pannexin-1 and P2X7 large-pore ion channel receptors can induce inflammasome formation that triggers release of pro-inflammatory mediators from the cell. Here, the role of ion channels involved in the regulation of excitation-inhibition balance, synaptic energy homeostasis as well as inflammatory signaling in migraine and depression will be reviewed.

Parenchymal neuroinflammatory signaling and dural neurogenic inflammation in migraine.

BACKGROUND: Pain is generally concomitant with an inflammatory reaction at the site where the nociceptive fibers are activated. Rodent studies suggest that a sterile meningeal inflammatory signaling cascade may play a role in migraine headache as well. Experimental studies also suggest that a parenchymal inflammatory signaling cascade may report the non-homeostatic conditions in brain to the meninges to induce headache. However, how these signaling mechanisms function in patients is unclear and debated. Our aim is to discuss the role of inflammatory signaling in migraine pathophysiology in light of recent developments. BODY: Rodent studies suggest that a sterile meningeal inflammatory reaction can be initiated by release of peptides from active trigeminocervical C-fibers and stimulation of resident macrophages and dendritic/mast cells. This inflammatory reaction might be needed for sustained stimulation and sensitization of meningeal nociceptors after initial activation along with ganglionic and central mechanisms. Most migraines likely have cerebral origin as suggested by prodromal neurologic symptoms. Based on rodent studies, a parenchymal inflammatory signaling cascade has been proposed as a potential mechanism linking cortical spreading depolarization (CSD) to meningeal nociception. A recent PET/MRI study using a sensitive inflammation marker showed the presence of meningeal inflammatory activity in migraine with aura patients over the occipital cortex generating the visual aura. These studies also suggest the presence of a parenchymal inflammatory activity, supporting the experimental findings. In rodents, parenchymal inflammatory signaling has also been shown to be activated by migraine triggers such as sleep deprivation without requiring a CSD because of the resultant transcriptional changes, predisposing to inadequate synaptic energy supply during intense excitatory transmission. Thus, it may be hypothesized that neuronal stress created by either CSD or synaptic activity-energy mismatch could both initiate a parenchymal inflammatory signaling cascade, propagating to the meninges, where it is converted to a lasting headache with or without aura. CONCLUSION: Experimental studies in animals and emerging imaging findings from patients warrant further research to gain deeper insight to the complex role of inflammatory signaling in headache generation in migraine.

Widespread brain parenchymal HMGB1 and NF-κB neuroinflammatory responses upon cortical spreading depolarization in familial hemiplegic migraine type 1 mice.

Neuroinflammatory changes involving neuronal HMGB1 release and astrocytic NF-κB nuclear translocation occur following cortical spreading depolarization (CSD) in wildtype (WT) mice but it is unknown to what extent this occurs in the migraine brain. We therefore investigated in familial hemiplegic migraine type 1 (FHM1) knock-in mice, which express an intrinsic hyperexcitability phenotype, the extent of neuroinflammation without and after CSD. CSD was evoked in one hemisphere by pinprick (single CSD) or topical KCl application (multiple CSDs). Neuroinflammatory (HMGB1, NF-κB) and neuronal activation (pERK) markers were investigated by immunohistochemistry in the brains of WT and FHM1 mutant mice without and after CSD. Effects of NMDA receptor antagonism on basal and CSD-induced neuroinflammatory changes were examined by, respectively, systemically administered MK801 and ifenprodil or topical MK801 application. In FHM1 mutant mice, CSD caused enhanced neuronal HMGB1 release and astrocytic NF-κB nuclear translocation in the cortex and subcortical areas that were equally high in both hemispheres. In WT mice such effects were only pronounced in the hemisphere in which CSD was induced. Neuroinflammatory responses were associated with pERK expression indicating neuronal activation. Upon CSD, contralateral cortical and striatal HMGB1 release was reduced by topical application of MK801 in the hemisphere contralateral to the one in which CSD was induced. This study reveals that neuroinflammatory activation after CSD is widespread and extends to the contralateral hemisphere, particularly in brains of FHM1 mutant mice. Effective blockade of CSD-induced neuroinflammatory responses in the contralateral hemisphere in FHM1 mice by local NMDA receptor antagonism suggests that neuronal hyperexcitability-related neuroinflammation is relevant in migraine pathophysiology, but possibly also other neurological disorders in which spreading depolarization is involved.

Pericyte morphology and function.

The proper delivery of blood is essential for healthy neuronal function. The anatomical substrate for this precise mechanism is the neurovascular unit, which is formed by neurons, glial cells, endothelia, smooth muscle cells, and pericytes. Based on their particular location on the vessel wall, morphology, and protein expression, pericytes have been proposed as cells capable of regulating capillary blood flow. Pericytes are located around the microvessels, wrapping them with their processes. Their morphology and protein expression substantially vary along the vascular tree. Their contractibility is mediated by a unique cytoskeleton organization formed by filaments of actin that allows pericyte deformability with the consequent mechanical force transferred to the extracellular matrix for changing the diameter. Pericyte ultrastructure is characterized by large mitochondria likely to provide energy to regulate intracellular calcium concentration and fuel contraction. Accordingly, pericytes with compromised energy show a sustained intracellular calcium increase that leads to persistent microvascular constriction. Pericyte morphology is highly plastic and adapted for varying contractile capability along the microvascular tree, making pericytes ideal cells to regulate the capillary blood flow in response to local neuronal activity. Besides the vascular regulation, pericytes also play a role in the maintenance of the blood-brain/retina barrier, neovascularization and angiogenesis, and leukocyte transmigration. Here, we review the morphological and functional features of the pericytes as well as potential specific markers for the study of pericytes in the brain and retina.

KCl-induced cortical spreading depression waves more heterogeneously propagate than optogenetically-induced waves in lissencephalic brain: an analysis with optical flow tools.

Although cortical spreading depolarizations (CSD) were originally assumed to be homogeneously and concentrically propagating waves, evidence obtained first in gyrencephalic brains and later in lissencephalic brains suggested a rather non-uniform propagation, shaped heterogeneously by factors like cortical region differences, vascular anatomy, wave recurrences and refractory periods. Understanding this heterogeneity is important to better evaluate the experimental models on the mechanistics of CSD and to make appropriate clinical estimations on neurological disorders like migraine, stroke, and traumatic brain injury. This study demonstrates the application of optical flow analysis tools for systematic and objective evaluation of spatiotemporal CSD propagation patterns in anesthetized mice and compares the propagation profile in different CSD induction models. Our findings confirm the asymmetric angular CSD propagation in lissencephalic brains and suggest a strong dependency on induction-method, such that continuous potassium chloride application leads to significantly higher angular propagation variability compared to optogenetically-induced CSDs.

F-actin polymerization contributes to pericyte contractility in retinal capillaries.

Although it has been documented that central nervous system pericytes are able to contract in response to physiological, pharmacological or pathological stimuli, the underlying mechanism of pericyte contractility is incompletely understood especially in downstream pericytes that express low amounts of alpha-smooth muscle actin (α-SMA). To study whether pericyte contraction involves F-actin polymerization as in vascular smooth muscle cells, we increased retinal microvascular pericyte tonus by intravitreal injection of a vasoconstrictive agent, noradrenaline (NA). The contralateral eye of each mouse was used for vehicle injection. The retinas were rapidly extracted and fixed within 2 min after injections. Polymeric/filamentous (F-actin) and monomeric/globular (G-actin) forms of actin were labeled by fluorescently-conjugated phalloidin and deoxyribonuclease-I, respectively. We studied 108 and 83 pericytes from 6 NA- and 6 vehicle-treated retinas and, found that F/G-actin ratio, a microscopy-based index of F-actin polymerization, significantly increased in NA-treated retinas [median (IQR): 4.2 (3.1) vs. 3.5 (2.1), p = .006], suggesting a role for F-actin polymerization in pericyte contractility. Shift from G-actin monomers to polymerized F-actin was more pronounced in 5th and 6th order contracted pericytes compared to non-contracted ones [7.6 (4.7) vs. 3.2 (1.2), p < .001], possibly due to their dependence on de novo F-actin polymerization for contractile force generation because they express α-SMA in low quantities. Capillaries showing F-actin polymerization had significantly reduced diameters compared to the ones that did not exhibit increased F/G-actin ratio in pericytes [near soma / branch origin diameter; 0.67 (0.14) vs. 0.81 (0.34), p = .005]. NA-responsive capillaries generally did not show nodal constrictions but a tide-like diameter decrease, reaching a maximum near pericyte soma. These findings suggest that pericytes on high order downstream capillaries have F-actin-mediated contractile capability, which may contribute to the vascular resistance and blood flow regulation in capillary bed.

Combination of Paclitaxel and R-flurbiprofen loaded PLGA nanoparticles suppresses glioblastoma growth on systemic administration.

Malignant gliomas are highly lethal. Delivering chemotherapeutic drugs to the brain in sufficient concentration is the major limitation in their treatment due to the blood-brain barrier (BBB). Drug delivery systems may overcome this limitation and can improve the transportation through the BBB. Paclitaxel is an antimicrotubule agent with effective anticancer activity but limited BBB permeability. R-Flurbiprofen is a nonsteroidal antienflammatory drug and has potential anticancer activity. Accordingly, we designed an approach combining R-flurbiprofen and paclitaxel and positively-charged chitosan-modified poly-lactide-co-glycolic acid (PLGA) nanoparticles (NPs) and to transport them to glioma tissue. NPs were characterized and, cytotoxicity and cellular uptake studies were carried out in vitro. The in vivo efficacy of the combination and formulations were evaluated using a rat RG2 glioma tumor model. Polyethylene glycol (PEG) modified and chitosan-coated PLGA NPs demonstrated efficient cytotoxic activity and were internalized by the tumor cells in RG2 cell culture. In vivo studies showed that the chitosan-coated and PEGylated NPs loaded with paclitaxel and R-flurbiprofen exhibited significantly higher therapeutic activity against glioma. In conclusion, PLGA NPs can efficiently carry their payloads to glioma tissue and the combined use of anticancer and anti-inflammatory drugs may exert additional anti-tumor activity.

Small Vessels Are a Big Problem in Neurodegeneration and Neuroprotection.

The cerebral microcirculation holds a critical position to match the high metabolic demand by neuronal activity. Functionally, microcirculation is virtually inseparable from other nervous system cells under both physiological and pathological conditions. For successful bench-to-bedside translation of neuroprotection research, the role of microcirculation in acute and chronic neurodegenerative disorders appears to be under-recognized, which may have contributed to clinical trial failures with some neuroprotectants. Increasing data over the last decade suggest that microcirculatory impairments such as endothelial or pericyte dysfunction, morphological irregularities in capillaries or frequent dynamic stalls in blood cell flux resulting in excessive heterogeneity in capillary transit may significantly compromise tissue oxygen availability. We now know that ischemia-induced persistent abnormalities in capillary flow negatively impact restoration of reperfusion after recanalization of occluded cerebral arteries. Similarly, microcirculatory impairments can accompany or even precede neural loss in animal models of several neurodegenerative disorders including Alzheimer's disease. Macrovessels are relatively easy to evaluate with radiological or experimental imaging methods but they cannot faithfully reflect the downstream microcirculatory disturbances, which may be quite heterogeneous across the tissue at microscopic scale and/or happen fast and transiently. The complexity and size of the elements of microcirculation, therefore, require utilization of cutting-edge imaging techniques with high spatiotemporal resolution as well as multidisciplinary team effort to disclose microvascular-neurodegenerative connection and to test treatment approaches to advance the field. Developments in two photon microscopy, ultrafast ultrasound, and optical coherence tomography provide valuable experimental tools to reveal those microscopic events with high resolution. Here, we review the up-to-date advances in understanding of the primary microcirculatory abnormalities that can result in neurodegenerative processes and the combined neurovascular protection approaches that can prevent acute as well as chronic neurodegeneration.