Cortical spreading depression causes and coincides with tissue hypoxia

Aquaporin-4 regulates extracellular space volume dynamics during high-frequency synaptic stimulation: a gene deletion study in mouse hippocampus

Little is known about the physiological roles of aquaporin-4 (AQP4) in the central nervous system. AQP4 water channels are concentrated in endfeet membranes of astrocytes but also localize to the fine astrocytic processes that abut central synapses. Based on its pattern of expression, we predicted that AQP4 could be involved in controlling water fluxes and changes in extracellular space (ECS) volume that are associated with activation of excitatory pathways. Here, we show that deletion of Aqp4 accentuated the shrinkage of the ECS that occurred in the mouse hippocampal CA1 region during activation of Schaffer collateral/commissural fibers. This effect was found in the stratum radiatum (where perisynaptic astrocytic processes abound) but not in the pyramidal cell layer (where astrocytic processes constitute but a minor volume fraction). For both genotypes the ECS shrinkage was most pronounced in the pyramidal cell layer. Our data attribute a physiological role to AQP4 and indicate that this water channel regulates extracellular volume dynamics in the mammalian brain.

Is there a role for vagus nerve stimulation therapy as a treatment of traumatic brain injury?

This paper aims to review the current literature on vagus nerve stimulation (VNS) use in animal models of traumatic brain injury (TBI) and explore its potential role in treatment of human TBI. A MEDLINE search yielded four primary papers from the same group that demonstrated VNS mediated improvement following fluid percussion models of TBI in rats, seen as motor and cognitive improvements, reduction of cortical oedema and neuroprotective effects. The underlying mechanisms are elusive and authors attribute these to attenuation of post traumatic seizures, a noradrenergic mechanism and as yet undetermined mechanisms. Reviewing and elaborating on these ideas, we speculate other potential mechanisms including attenuation of peri-infarct depolarisations, attenuation of glutamate mediated excitotoxicity, stabilisation of intracranial pressure, enhancement of synaptic plasticity, upregulation of endogenous neurogenesis and anti-inflammatory effects may have a role. Although this data unequivocally shows that VNS improves outcome from TBI in animal models, it remains to be determined if these findings translate clinically. Further studies are warranted.

Vascular, electrophysiological, and metabolic consequences of cortical spreading depression in a mouse model of simulated neurosurgical conditions

OBJECTIVES

Cortical spreading depression (CSD) is a metabolically taxing wave of cellular depolarization that propagates slowly across the brain. Though CSD is known to occur after brain injury in humans, it is unknown if CSD occurs during neurosurgical procedures. This study evaluates CSD in a mouse model of simulated neurosurgical conditions.

METHODS

Mice were intubated and ventilated, maintained at ~37°C, an arterial line placed to monitor mean arterial pressure and maintain pCO(2) ~30 mmHg. Mice were given simulated neuroanesthesia (fentanyl, propofol, and isofluorane). Burrholes and craniotomies were made to record the response to cortical bipolar cauterization. Separate sets of experiments (three animals each) examined electrocorticographic (ECoG) activity, optical measures of blood volume and vascular diameters (540 nm absorbance), and autofluorescence attributed to NADH (750 nm, two-photon excitation).

RESULTS

Ipsilateral cauterization invariably resulted in a propagating CSD wave identified by slow DC potential shifts (2·8±0·2 mm/minute, n = 6) and suppression of ECoG activity (range 0·5-7·3 minutes, n = 10). Each CSD was associated with an initial arteriolar constriction and decreased blood volume, followed by a longer-lasting vasodilation and increased blood volume. Tissue oxygenation, assessed indirectly by NADH imaging, was consistent with demand on oxidative metabolism following each CSD. Repetitive SDs resulted in loss of tissue autofluorescence, suggestive of tissue compromise.

CONCLUSIONS

CSD is consistently elicited by simulated neurosurgical stimuli under simulated intraoperative conditions in mice. These events caused ECoG depression, transient vasoconstriction, and metabolic demand that propagated from the manipulation site. It is likely that CSD occurs during neurosurgery and may contribute to surgical brain injuries otherwise poorly explained.

Role of HCN channels in neuronal hyperexcitability after subarachnoid hemorrhage in rats

Disruption of ionic homeostasis and neuronal hyperexcitability contribute to early brain injury after subarachnoid hemorrhage (SAH). The hyperpolarization-activated/cyclic nucleotide (HCN)-gated channels play critical role in the regulation of neuronal excitability in hippocampus CA1 region and neocortex, in which the abnormal neuronal activities are more readily provoked. This study was to investigate the interactions between HCN channels and hyperneuronal activity after experimental SAH. The present results from whole-cell recordings in rat brain slices indicated that (1) perfusion of hemoglobin (Hb)-containing artificial CSF produced neuronal hyperexcitability and inhibited HCN currents in CA1 pyramidal neurons, (2) nitric oxide/Spermine (NO/Sp), a controlled releaser of nitric oxide, attenuated neuronal excitability and enhanced HCN currents in CA1 pyramidal neurons, while L-nitroarginine (L-NNA), an inhibitor of nitric oxide synthase, reduced the HCN currents; and (3) the inhibitory action of Hb on HCN currents was reversed by application of NO/Sp, which also reduced neuronal hyperexcitability; conversely, L-NNA enhanced inhibitory action of Hb on HCN currents. Additionally, Hb perfusion scavenged the production of nitric oxide and decreased the expression of HCN1 subunits in CA1 region. In the rat SAH model, the expression of HCN1, both at mRNA and protein level, decreased in hippocampus CA1 region at 24 h and more pronounced at 72 h after SAH. These observations demonstrated a reduction of HCN channels expression after SAH and Hb reduced HCN currents in hippocampus CA1 pyramidal neurons. Inhibition of HCN channels by Hb may be a novel pathway for inducing the hyperneuronal excitability after SAH.

Cortical spreading depression impairs oxygen delivery and metabolism in mice

Cortical spreading depression (CSD) is associated with severe hypoperfusion in mice. Using minimally invasive multimodal optical imaging, we show that severe flow reductions during and after spreading depression are associated with a steep decline in cerebral metabolic rate of oxygen. Concurrent severe hemoglobin desaturation suggests that the oxygen metabolism becomes at least in part supply limited, and the decrease in cortical blood volume implicates vasoconstriction as the mechanism. In support of oxygen supply-demand mismatch, cortical nicotinamide adenine dinucleotide (NADH) fluorescence increases during spreading depression for at least 5 minutes, particularly away from parenchymal arterioles. However, modeling of tissue oxygen delivery shows that cerebral metabolic rate of oxygen drops more than predicted by a purely supply-limited model, raising the possibility of a concurrent reduction in oxygen demand during spreading depression. Importantly, a subsequent spreading depression triggered within 15 minutes evokes a monophasic flow increase superimposed on the oligemic baseline, which markedly differs from the response to the preceding spreading depression triggered in naive cortex. Altogether, these data suggest that CSD is associated with long-lasting oxygen supply-demand mismatch linked to severe vasoconstriction in mice.

Optical coherence microscopy for deep tissue imaging of the cerebral cortex with intrinsic contrast

In vivo optical microscopic imaging techniques have recently emerged as important tools for the study of neurobiological development and pathophysiology. In particular, two-photon microscopy has proved to be a robust and highly flexible method for in vivo imaging in highly scattering tissue. However, two-photon imaging typically requires extrinsic dyes or contrast agents, and imaging depths are limited to a few hundred microns. Here we demonstrate Optical Coherence Microscopy (OCM) for in vivo imaging of neuronal cell bodies and cortical myelination up to depths of ~1.3 mm in the rat neocortex. Imaging does not require the administration of exogenous dyes or contrast agents, and is achieved through intrinsic scattering contrast and image processing alone. Furthermore, using OCM we demonstrate in vivo, quantitative measurements of optical properties (index of refraction and attenuation coefficient) in the cortex, and correlate these properties with laminar cellular architecture determined from the images. Lastly, we show that OCM enables direct visualization of cellular changes during cell depolarization and may therefore provide novel optical markers of cell viability.

White matter lesions progression in migraine with aura: a clinical and MRI longitudinal study

OBJECTIVE

To prospectively evaluate longitudinal changes in white matter lesions (WMLs) in migraineurs with aura, by magnetic resonance imaging (MRI), and to correlate WMLs modifications with patients' clinical characteristics.

METHODS

Forty-one consecutive migraineurs with aura were followed for a mean time of 33.2 months. Patients underwent MRI at baseline and follow-up and were evaluated for cerebrovascular risk factors. Presence of WMLs on MRI was assessed by two neuroradiologists.

RESULTS

WMLs were present in 26 subjects (63.4%) at baseline MRI. At follow-up a total of 8 patients had new WMLs (19.5%). There was a significant correlation between aura duration and number of new WMLs, and between the number of migraine attacks with aura and new WMLs.

CONCLUSIONS

Our study demonstrates that in migraine with aura WMLs number can progress over time and suggests an association between aura features and WMLs progression. Studies with a higher number of patients are required to confirm these findings.

Spreading depolarization, a pathophysiological mechanism of stroke and migraine aura

Spreading depolarization is a mechanism of abrupt, massive ion translocation between intraneuronal and extracellular space that entails cytotoxic edema in the brain’s gray matter. It is observed in patients as a large change of the slow electrical potential. Dependent on the energy status of the tissue, spreading depolarization is either preceded by nonspreading silencing due to neuronal hyperpolarization or accompanied by spreading silencing of electrical brain activity due to a depolarization block. Nonspreading silencing seems to translate into the initial clinical symptoms of ischemic stroke and spreading silencing translates into migraine aura. Direct electrophysiological evidence exists that spreading depolarization occurs in abundance in aneurysmal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage and traumatic brain injury. Indirect evidence suggests its occurrence during migraine aura. In animals, spreading depolarizations facilitate neuronal death when they invade metabolically compromised tissue, whereas they are relatively innocuous in healthy tissue. Therapies targeting spreading depolarization may potentially treat these neurological conditions.

Critical state of energy metabolism in brain slices: the principal role of oxygen delivery and energy substrates in shaping neuronal activity

The interactive vasculo-neuro-glial system controlling energy supply in the brain is absent in vitro where energy provision is determined by experimental conditions. Despite the fact that neuronal activity is extremely energy demanding, little has been reported on the state of energy metabolism in submerged brain slices. Without this information, the arbitrarily chosen oxygenation and metabolic provisions make questionable the efficient oxidative metabolism in slices. We show that in mouse hippocampal slices (postnatal day 19–44), evoked neuronal discharges, spontaneous network activity (initiated by 4-aminopyridine), and synaptic stimulation-induced NAD(P)H autofluorescence depend strongly on the oxygen availability. Only the rate of perfusion as high as ~15 ml/min (95% O₂) provided appropriate oxygenation of a slice. Lower oxygenation resulted in the decrease of both local field potentials and spontaneous network activity as well as in significant modulation of short-term synaptic plasticity. The reduced oxygen supply considerably inhibited the oxidation phase of NAD(P)H signaling indicating that the changes in neuronal activity were paralleled by the decrease in aerobic energy metabolism. Interestingly, the dependence of neuronal activity on oxygen tension was clearly shifted toward considerably larger pO₂ values in slices when compared to in vivo conditions. With sufficient pO₂ provided by a high perfusion rate, partial substitution of glucose in ACSF for β-hydroxybutyrate, pyruvate, or lactate enhanced both oxidative metabolism and synaptic function. This suggests that the high pO₂ in brain slices is compulsory for maintaining oxidative metabolism, and glucose alone is not sufficient in fulfilling energy requirements during neuronal activity. Altogether, our results demonstrate that energy metabolism determines the functional state of neuronal network, highlighting the need for the adequate metabolic support to be insured in the in vitro experiments.

Glial Hsp70 protects K+ homeostasis in the Drosophila brain during repetitive anoxic depolarization

Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na(+)/K(+)-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K(+) homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K(+)] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.

Cortical excitation and inhibition following focal traumatic brain injury

Cortical compression can be a significant problem in many types of brain injuries, such as brain trauma, localized brain edema, hematoma, focal cerebral ischemia, or brain tumors. Mechanical and cellular alterations can result in global changes in excitation and inhibition on the neuronal network level even in the absence of histologically significant cell injury, often manifesting clinically as seizures. Despite the importance and prevalence of this problem, however, the precise electrophysiological effects of brain injury have not been well characterized. In this study, the changes in electrophysiology were characterized following sustained cortical compression using large-scale, multielectrode measurement of multiunit activity in primary somatosensory cortex in a sensory-evoked, in vivo animal model. Immediately following the initiation of injury at a distal site, there was a period of suppression of the evoked response in the rat somatosensory cortex, followed by hyper-excitability that was accompanied by an increase in the spatial extent of cortical activation. Paired-pulse tactile stimulation revealed a dramatic shift in the excitatory/inhibitory dynamics, suggesting a longer term hyperexcitability of the cortical circuit following the initial suppression that could be linked to the disruption of one or more inhibitory mechanisms of the thalamocortical circuit. Together, our results showed that the use of a sensory-evoked response provided a robust and repeatable functional marker of the evolution of the consequences of mild injury, serving as an important step toward in vivo quantification of alterations in excitation and inhibition in the cortex in the setting of traumatic brain injury.

Migraine- and dystonia-related disease-mutations of Na+/K+-ATPases: relevance of behavioral studies in mice to disease symptoms and neurological manifestations in humans

The two autosomal dominantly inherited neurological diseases: familial hemiplegic migraine type 2 (FHM2) and familial rapid-onset of dystonia-parkinsonism (Familial RDP) are caused by in vivo mutations of specific alpha subunits of the sodium-potassium pump (Na(+)/K(+)-ATPase). Intriguingly, patients with classical FHM2 and RDP symptoms additionally suffer from other manifestations, such as epilepsy/seizures and developmental disabilities. Recent studies of FHM2 and RDP mouse models provide valuable tools for dissecting the vital roles of the Na(+)/K(+)-ATPases, and we discuss their relevance to the complex patient symptoms and manifestations. Thus, it is interesting that mouse models targeting a specific α-isoform cause different, although still comparable, phenotypes consistent with classical symptoms and other manifestations observed in FHM2 and RDP patients. This review highlights that use of mouse models have broad potentials for future research concerning migraine and dystonia-related diseases, which will contribute towards understanding the, yet unknown, pathophysiologies.

Chronic daily cortical spreading depressions suppress spreading depression susceptibility

BACKGROUND

Migraine is a disabling chronic episodic disorder. Attack frequency progressively increases in some patients. Incremental cortical excitability has been implicated as a mechanism underlying progression. Cortical spreading depression (CSD) is the electrophysiological event underlying migraine aura, and a headache trigger. We hypothesized that CSD events during frequent migraine attacks condition the cortex to increase the susceptibility to further attacks.

METHODS

A single daily CSD was induced for 1 or 2 weeks in mouse frontal cortex; contralateral hemisphere served as sham control. At the end of CSD conditioning, occipital CSD susceptibility was determined by measuring the frequency of CSDs evoked by topical KCl application.

RESULTS

Sham hemispheres developed 8.4 ± 0.3 CSDs/hour, and did not significantly differ from naïve controls without prior cranial surgery (9.3 ± 0.4 CSDs/hour). After 2 but not 1 week of daily CSD conditioning, CSD frequency (4.9 ± 0.3 CSDs/hour) as well as the duration and propagation speed were reduced significantly in the conditioned hemispheres. Histopathological examination revealed marked reactive astrocytosis without neuronal injury throughout the conditioned cortex after 2 weeks, temporally associated with CSD susceptibility.

CONCLUSIONS

These data do not support the hypothesis that frequent migraine attacks predispose the brain to further attacks by enhancing tissue susceptibility to CSD.

Two-photon microscopy of cortical NADH fluorescence intensity changes: correcting contamination from the hemodynamic response

Quantification of nicotinamide adenine dinucleotide (NADH) changes during functional brain activation and pathological conditions provides critical insight into brain metabolism. Of the different imaging modalities, two-photon laser scanning microscopy (TPLSM) is becoming an important tool for cellular-resolution measurements of NADH changes associated with cellular metabolic changes. However, NADH fluorescence emission is strongly absorbed by hemoglobin. As a result, in vivo measurements are significantly affected by the hemodynamics associated with physiological and pathophysiological manipulations. We model NADH fluorescence excitation and emission in TPLSM imaging based on precise maps of cerebral microvasculature. The effects of hemoglobin optical absorption and optical scattering from red blood cells, changes in blood volume and hemoglobin oxygen saturation, vessel size, and location with respect to imaging location are explored. A simple technique for correcting the measured NADH fluorescence intensity changes is provided, with the utilization of a parallel measurement of a physiologically inert fluorophore. The model is applied to TPLSM measurements of NADH fluorescence intensity changes in rat somatosensory cortex during mild hypoxia and hyperoxia. The general approach of the correction algorithm can be extended to other TPLSM measurements, where changes in the optical properties of the tissue confound physiological measurements, such as the detection of calcium dynamics.

Acute CO2-independent vasodilatation of penetrating and pre-capillary arterioles in mouse cerebral parenchyma upon hypoxia revealed by a thinned-skull window method

AIM

Investigating spatio-temporal relationship between regional metabolic changes and microvascular responses in hypoxic brain is critical for unravelling local O(2) -sensing mechanisms. However, no reliable method to examine the relationship has been available because of inherent disadvantages associated with use of a conventional cranial window preparation. We aimed to devise a method to solve the problem.

METHODS

Anaesthetized mice were equipped with either a conventional cranial window with craniotomy or a thinned-skull preparation. Mice were mechanically ventilated to avoid hypercapnia and exposed to systemic isobaric hypoxia for 30 min. Using two-photon laser scanning microscopy, nicotinamide adenine dinucleotide, reduced form (NADH) autofluorescence and diameter changes in penetrating and pre-capillary arterioles within the parenchyma were visualized to examine their temporal alterations.

RESULTS

With the conventional cranial window preparation, marked vertical displacement of the tissue occurred through oedema within 30 s after inducing hypoxia. With a thinned-skull preparation, however, such hypoxia-induced displacement was diminished, enabling us to examine acute spatio-temporal changes in diameters of penetrating and pre-capillary arterioles and NADH autofluorescence. Vasodilatation of these microvessels was evoked within 1 min after hypoxia, and sustained during the entire observation period despite the absence of hypercapnia. This event coincided with parenchymal NADH elevation, but the onset and peak dilatory responses of the penetrating arterioles preceded the local metabolic response of the parenchyma.

CONCLUSION

Observation of hypoxia-exposed brain by the thinned-skull preparation combined with two-photon intra-vital microscopy revealed rapid vasodilatory responses in penetrating arterioles preceding parenchymal NADH elevation, suggesting the presence of acute hypoxia-sensing mechanisms involving specific segments of cortical arterioles within the neurovascular unit.

Oxygen therapy improves energy metabolism in focal cerebral ischemia

Oxygen therapy (OT) with hyperbaric oxygen (HBO) or normobaric hyperoxia (NBO) improves the oxygenation of penumbral tissue in experimental ischemic stroke. However, whether this results in the improvement of energy metabolism is unclear. We investigated the effect of both OTs on tissue acidosis and on ATP production. Beginning 25 min after filament middle cerebral artery occlusion (MCAO), mice breathed either air, 100% O₂ (NBO), or 100% O₂ at 3 ata (HBO) for 60 min. Regional tissue pH was measured using the umbelliferone fluorescence. Regional ATP concentration was depicted by substrate-specific bioluminescence. Severity of ischemia did not differ among groups in laser-Doppler flowmetry. Both NBO (70.1±14.0 mm³) and, more effectively, HBO (57.2±11.9 mm³) significantly reduced volume of tissue acidosis compared to air (89.4±4.0 mm³), p<0.05). Topographically, acidosis was less pronounced in the medial striatum and in the cortical ischemic border areas. This resulted in significantly smaller volumes of ATP depletion (77.8±7.7 mm³ in air, 61.4±15.2 mm³ in NBO and 51.2±14.4 mm³ in HBO; p<0.05). In conclusion, OT significantly improves energy metabolism in the border zones of focal cerebral ischemia which are the areas protected by OT in this model.

Cyclosporine A, FK506, and NIM811 ameliorate prolonged CBF reduction and impaired neurovascular coupling after cortical spreading depression

Cortical spreading depression (CSD) is associated with mitochondrial depolarization, increasing intracellular Ca(2+), and the release of free fatty acids, which favor opening of the mitochondrial permeability transition pore (mPTP) and activation of calcineurin (CaN). Here, we test the hypothesis that cyclosporine A (CsA), which blocks both mPTP and CaN, ameliorates the persistent reduction of cerebral blood flow (CBF), impaired vascular reactivity, and a persistent rise in the cerebral metabolic rate of oxygen (CMRO(2)) following CSD. In addition to CsA, we used the specific mPTP blocker NIM811 and the specific CaN blocker FK506. Cortical spreading depression was induced in rat frontal cortex. Electrocortical activity was recorded by glass microelectrodes, CBF by laser Doppler flowmetry, and tissue oxygen tension with polarographic microelectrodes. Electrocortical activity, basal CBF, CMRO(2), and neurovascular and neurometabolic coupling were unaffected by all three drugs under control conditions. NIM811 augmented the rise in CBF observed during CSD. Cyclosporine A and FK506 ameliorated the persistent decrease in CBF after CSD. All three drugs prevented disruption of neurovascular coupling after CSD; the rise in CMRO(2) was unchanged. Our data suggest that blockade of mPTP formation and CaN activation may prevent persistent CBF reduction and vascular dysfunction after CSD.

Migraine pathophysiology

SUMMARY Our understanding of migraine pathophysiology is a work in progress, largely because of the absence of any identifiable cephalic pathology. There are currently two main theories on the genesis of migraine pain. One hypothesizes that the origin is in the periphery, requiring the activation of primary afferent nociceptive neurons that innervate cephalic tissue. The other theorizes that the origin of migraine pain is in the CNS, as a result of abnormal processing of sensory signals, rather than the activation of nociceptors. After briefly reviewing the clinical presentation and diagnosis of migraine, this article focuses on explaining the traditional and current theories of migraine pathogenesis.

Simultaneous monitoring of intracellular pH changes and hemodynamic response during cortical spreading depression by fluorescence-corrected multimodal optical imaging

Cortical spreading depression (CSD) plays an important role in trauma, migraine and ischemia. CSD could induce pronounced hemodynamic changes and the disturbance of pH homeostasis which has been postulated to contribute to cell death following ischemia. In this study, we described a fluorescence-corrected multimodal optical imaging system to simultaneously monitor CSD associated intracellular pH (pH(i)) changes and hemodynamic response including hemoglobin concentrations and cerebral blood flow (CBF). CSD was elicited by application of KCl on rat cortex and direct current (DC) potential was recorded as a typical characteristic of CSD. The pH(i) shift was mapped by neutral red (NR) fluorescence which was excited at 516-556 nm and emitted at 625 nm. The changes in hemoglobin concentrations were determined by dual-wavelength optical intrinsic signal imaging (OISI) at 550 nm and 625 nm. Integration of fluorescence imaging and dual-wavelength OISI was achieved by a time-sharing camera equipped with a liquid crystal tunable filter (LCTF). CBF was visualized by laser speckle contrast imaging (LSCI) through a separate camera. Besides, based on the dual-wavelength optical intrinsic signals (OISs) obtained from our system, NR fluorescence was corrected according to our method of fluorescence correction. We found that a transient intracellular acidification followed by a small alkalization occurred during CSD. After CSD, there was a prolonged intracellular acidification and the recovery of pH(i) from CSD took much longer time than those of hemodynamic response. Our results suggested that the new multimodal optical imaging system had the potential to advance our knowledge of CSD and might work as a useful tool to exploit neurovascular coupling under physiological and pathological conditions.

High intracranial pressure effects on cerebral cortical microvascular flow in rats

To manage patients with high intracranial pressure (ICP), clinicians need to know the critical cerebral perfusion pressure (CPP) required to maintain cerebral blood flow (CBF). Historically, the critical CPP obtained by decreasing mean arterial pressure (MAP) to lower CPP was 60 mm Hg, which fell to 30 mm Hg when CPP was reduced by increasing ICP. We examined whether this decrease in critical CPP was due to a pathological shift from capillary (CAP) to high-velocity microvessel flow or thoroughfare channel (TFC) shunt flow. Cortical microvessel red blood cell velocity and NADH fluorescence were measured by in vivo two-photon laser scanning microscopy in rats at CPP of 70, 50, and 30 mm Hg by increasing ICP or decreasing MAP. Water content was measured by wet/dry weight, and cortical perfusion by laser Doppler flux. Reduction of CPP by raising ICP increased TFC shunt flow from 30.4±2.3% to 51.2±5.2% (mean±SEM, p<0.001), NADH increased by 20.3±6.8% and 58.1±8.2% (p<0.01), and brain water content from 72.9±0.47% to 77.8±2.42% (p<0.01). Decreasing CPP by MAP decreased TFC shunt flow with a smaller rise in NADH and no edema. Doppler flux decreased less with increasing ICP than decreasing MAP. The decrease seen in the critical CPP with increased ICP is likely due to a redistribution of microvascular flow from capillary to microvascular shunt flow or TFC shunt flow, resulting in a pathologically elevated CBF associated with tissue hypoxia and brain edema, characteristic of non-nutritive shunt flow.

The role of spreading depression, spreading depolarization and spreading ischemia in neurological disease

The term spreading depolarization describes a wave in the gray matter of the central nervous system characterized by swelling of neurons, distortion of dendritic spines, a large change of the slow electrical potential and silencing of brain electrical activity (spreading depression). In the clinic, unequivocal electrophysiological evidence now exists that spreading depolarizations occur abundantly in individuals with aneurismal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage or traumatic brain injury. Spreading depolarization is induced experimentally by various noxious conditions including chemicals such as potassium, glutamate, inhibitors of the sodium pump, status epilepticus, hypoxia, hypoglycemia and ischemia, but it can can also invade healthy, naive tissue. Resistance vessels respond to it with tone alterations, causing either transient hyperperfusion (physiological hemodynamic response) in healthy tissue or severe hypoperfusion (inverse hemodynamic response, or spreading ischemia) in tissue at risk for progressive damage, which contributes to lesion progression. Therapies that target spreading depolarization or the inverse hemodynamic response may potentially treat these neurological conditions.

Oscillating neuro-capillary coupling during cortical spreading depression as observed by tracking of FITC-labeled RBCs in single capillaries

Coupling between capillary red blood cell (RBC) movements and neuronal dysfunction during cortical spreading depression (CSD) was examined in rats by employing a high-speed camera laser-scanning confocal fluorescence microscope system in conjunction with our Matlab domain software (KEIO-IS2). Following microinjection of K(+) onto the surface of the brain, changes in electroencephalogram (EEG), DC potential and tissue optical density were all compatible with the occurrence of a transient spreading neuronal depression. RBC flow in single capillaries was not stationary. Unpredictable redistribution of RBCs at branches of capillaries was commonly observed, even though no change in diameter was apparent at the reported site of the capillary sphincter and no change of arteriolar-venule pressure difference was detected. There appeared to be a slow morphological change of astroglial endfeet. When local neurons were stunned transiently by K(+) injection, the velocity and oscillation frequency of RBCs flowing in nearby capillaries started to decrease. The flow in such capillaries was rectified, losing oscillatory components. Sluggish floating movements of RBCs in pertinent capillaries were visualized, with occasional full stops. When CSD subsided, RBC movements recovered to the original state. We postulate that neuronal depolarization blocks oscillatory signaling to local capillaries via low-shear plasma viscosity increases in the capillary channels, and a complex interaction between the RBC surface and the buffy coat on the capillary wall surface increases the capillary flow resistance. Then, when CSD subsides and oscillatory neuronal function is recovered, the normal physiological conditions are restored.

Simultaneous monitoring of tissue PO2 and NADH fluorescence during synaptic stimulation and spreading depression reveals a transient dissociation between oxygen utilization and mitochondrial redox state in rat hippocampal slices

Nicotinamide adenine dinucleotide (NADH) imaging can be used to monitor neuronal activation and ascertain mitochondrial dysfunction, for example during hypoxia. During neuronal stimulation in vitro, NADH normally becomes more oxidized, indicating enhanced oxygen utilization. A subsequent NADH overshoot during activation or on recovery remains controversial and reflects either increased metabolic activity or limited oxygen availability. Tissue P(2) measurements, obtained simultaneously with NADH imaging in area CA1 in hippocampal slices, reveal that during prolonged train stimulation (ST) in 95% O(2), a persistent NADH oxidation is coupled with increased metabolic demand and oxygen utilization, for the duration of the stimulation. However, under conditions of either decreased oxygen supply (ST-50% O(2)) or enhanced metabolic demand (K(+)-induced spreading depression (K(+)-SD) 95% O(2)) the NADH oxidation is brief and the redox balance shifts early toward reduction, leading to a prolonged NADH overshoot. Yet, oxygen utilization remains elevated and is correlated with metabolic demand. Under these conditions, it appears that the rate of NAD(+) reduction may transiently exceed oxidation, to maintain an adequate oxygen flux and ATP production. In contrast, during SD in 50% O(2), the oxygen levels dropped to a point at which oxidative metabolism in the electron transport chain is limited and the rate of utilization declined.

Light-scattering signal may indicate critical time zone to rescue brain tissue after hypoxia

A light-scattering signal, which is sensitive to cellular/subcellular structural integrity, is a potential indicator of brain tissue viability because metabolic energy is used in part to maintain the structure of cells. We previously observed a unique triphasic scattering change (TSC) at a certain time after oxygen/glucose deprivation for blood-free rat brains; TSC almost coincided with the cerebral adenosine triphosphate (ATP) depletion. We examine whether such TSC can be observed in the presence of blood in vivo, for which transcranial diffuse reflectance measurement is performed for rat brains during hypoxia induced by nitrogen gas inhalation. At a certain time after hypoxia, diffuse reflectance intensity in the near-infrared region changes in three phases, which is shown by spectroscopic analysis to be due to scattering change in the tissue. During hypoxia, rats are reoxygenated at various time points. When the oxygen supply is started before TSC, all rats survive, whereas no rats survive when the oxygen supply is started after TSC. Survival is probabilistic when the oxygen supply is started during TSC, indicating that the period of TSC can be regarded as a critical time zone for rescuing the brain. The results demonstrate that light scattering signal can be an indicator of brain tissue reversibility.

Protection of flunarizine on cerebral mitochondria injury induced by cortical spreading depression under hypoxic conditions

A rat cortical spreading depression (CSD) model was established to explore whether cerebral mitochondria injury was induced by CSD under both normoxic and hypoxic conditions and whether flunarizine had a protective effect on cerebral mitochondria. SD rats, which were divided into seven groups, received treatment as follows: no intervention (control Group I); 1 M NaCl injections (Group II); 1 M KCl injections (Group III); intraperitoneal flunarizine (3 mg/kg) 30 min before KCl injections (Group IV); 14% O(2) inhalation before NaCl injections (Group V); 14% O(2) inhalation followed by KCl injections (Group VI); 14% O(2) inhalation and intraperitoneal flunarizine followed by KCl injections (Group VII). Following treatment, brains were removed for the analysis of mitochondria transmembrane potential (MMP) and oxidative respiratory function after recording the number, amplitude and duration of CSD. The duration of CSD was significantly longer in Group VI than that in Group III. The number and duration of CSD in Group VII was significantly lower than that in Group VI. MMP in Group VI was significantly lower than that in Group III, and MMP in Group VII was significantly higher than that in Group VI. State 4 respiration in Group VI was significantly higher than that in Group III, and state 3 respiration in Group VII was significantly higher than that in Group VI. Respiration control of rate in Group VII was also significantly higher than that in Group VI. Thus, we concluded that aggravated cerebral mitochondria injury might be attributed to CSD under hypoxic conditions. Flunarizine can alleviate such cerebral mitochondria injury under both normoxic and hypoxic conditions.

Two-photon NADH imaging exposes boundaries of oxygen diffusion in cortical vascular supply regions

Oxygen transport imposes a possible constraint on the brain's ability to sustain variable metabolic demands, but oxygen diffusion in the cerebral cortex has not yet been observed directly. We show that concurrent two-photon fluorescence imaging of endogenous nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation exposes well-defined boundaries of tissue oxygen diffusion in the mouse cortex. The NADH fluorescence increases rapidly over a narrow, very low pO(2) range with a p(50) of 3.4 ± 0.6 mm Hg, thereby establishing a nearly binary reporter of significant, metabolically limiting hypoxia. The transient cortical tissue boundaries of NADH fluorescence exhibit remarkably delineated geometrical patterns, which define the limits of tissue oxygen diffusion from the cortical microcirculation and bear a striking resemblance to the ideal Krogh tissue cylinder. The visualization of microvessels and their regional contribution to oxygen delivery establishes penetrating arterioles as major oxygen sources in addition to the capillary network and confirms the existence of cortical oxygen fields with steep microregional oxygen gradients. Thus, two-photon NADH imaging can be applied to expose vascular supply regions and to localize functionally relevant microregional cortical hypoxia with micrometer spatial resolution.

Clinical relevance of cortical spreading depression in neurological disorders: migraine, malignant stroke, subarachnoid and intracranial hemorrhage, and traumatic brain injury

Cortical spreading depression (CSD) and depolarization waves are associated with dramatic failure of brain ion homeostasis, efflux of excitatory amino acids from nerve cells, increased energy metabolism and changes in cerebral blood flow (CBF). There is strong clinical and experimental evidence to suggest that CSD is involved in the mechanism of migraine, stroke, subarachnoid hemorrhage and traumatic brain injury. The implications of these findings are widespread and suggest that intrinsic brain mechanisms have the potential to worsen the outcome of cerebrovascular episodes or brain trauma. The consequences of these intrinsic mechanisms are intimately linked to the composition of the brain extracellular microenvironment and to the level of brain perfusion and in consequence brain energy supply. This paper summarizes the evidence provided by novel invasive techniques, which implicates CSD as a pathophysiological mechanism for this group of acute neurological disorders. The findings have implications for monitoring and treatment of patients with acute brain disorders in the intensive care unit. Drawing on the large body of experimental findings from animal studies of CSD obtained during decades we suggest treatment strategies, which may be used to prevent or attenuate secondary neuronal damage in acutely injured human brain cortex caused by depolarization waves.

Automated and quantitative image analysis of ischemic dendritic blebbing using in vivo 2-photon microscopy data

Ischemia induces a 'blebbing' of dendrites, a structural alteration where dendrites take on a 'beads on a string' appearance. We developed a toolkit program, BlebQuant, for quantitative automated bleb analysis to chart the morphology of dendrites labeled with GFP/YFP under normal conditions and after ischemia-induced damage. In vivo 2-photon data from mouse layer 5 neurons with apical dendritic tufts extending to the cortical surface were examined before, during, and after global ischemia. To quantify changes in dendritic structure, we used morphometric tools that exploit characteristic features of blebbing, distinguished as localized regions of spherical or ellipsoid swellings. By comparing acquired images during ischemia and reperfusion to a pre-ischemia reference image, our automated approach detected blebs based on defined eccentricity and area thresholds and quantified the percentage of blebbed dendrites based on a block-selection method. Our results indicate that the automated morphometric indices we employ yield results that correlate with manual assessment. The automated approach permits rapid and effective analysis of dendritic structure and may facilitate the study of ischemic dendritic damage.

Unilateral cortical spreading depression affects sleep need and induces molecular and electrophysiological signs of synaptic potentiation in vivo

Cortical spreading depression (CSD) is an electrophysiological phenomenon first described by Leao in 1944 as a suppression of spontaneous electroencephalographic activity, traveling across the cerebral cortex. In vitro studies suggest that CSD may induce synaptic potentiation. One recent study also found that CSD is followed by a non-rapid eye movement (NREM) sleep duration increase, suggesting an increased need for sleep. Recent experiments in animals and humans show that the occurrence of synaptic potentiation increases subsequent sleep need as measured by larger slow wave activity (SWA) during NREM sleep, prompting the question whether CSD can affect NREM SWA. Here, we find that, in freely moving rats, local CSD induction increases corticocortical evoked responses and strongly induces brain derived neurotrophic factor (BDNF) in the affected cortical hemisphere but not in the contralateral one, consistent with synaptic potentiation in vivo. Moreover, for several hours after CSD, large slow waves occur in the affected hemisphere during rapid eye movement sleep and quiet waking but disappear during active exploration. Finally, we find that CSD increases NREM sleep duration and SWA, the latter specifically in the affected hemisphere. These effects are consistent with an increase in synaptic strength triggered by CSD, although nonphysiological phenomena associated with CSD may also play a role.

Glial and neuronal control of brain blood flow

Blood flow in the brain is regulated by neurons and astrocytes. Knowledge of how these cells control blood flow is crucial for understanding how neural computation is powered, for interpreting functional imaging scans of brains, and for developing treatments for neurological disorders. It is now recognized that neurotransmitter-mediated signalling has a key role in regulating cerebral blood flow, that much of this control is mediated by astrocytes, that oxygen modulates blood flow regulation, and that blood flow may be controlled by capillaries as well as by arterioles. These conceptual shifts in our understanding of cerebral blood flow control have important implications for the development of new therapeutic approaches.

Local hemodynamics dictate long-term dendritic plasticity in peri-infarct cortex

Changes in dendritic spine turnover are a major mechanism of experience-dependent plasticity in the adult neocortex. Dendritic spine plasticity may also contribute to functional recovery after stroke, but in that setting its expression may be complicated by alterations in local tissue perfusion, especially around the infarct. Using adult Thy-1 GFP-M mice, we simultaneously recorded long-term spine dynamics in apical dendrites from layer 5 pyramidal cells and blood flow from surrounding capillaries with in vivo two-photon microscopy in peri-infarct cortex before and after unilateral middle cerebral artery occlusion. Blood flow in peri-infarct cortex decreased significantly immediately after stroke and improved gradually over time, in a distance-dependent manner from the epicenter of the infarct. However, local tissue perfusion was never fully restored even after a 3 month recovery period. On average, surviving layer 5 pyramidal neurons experienced a ∼20% decrease in spine density acutely after stroke but eventually recovered. The dynamics of this improvement were different depending on the degree of tissue perfusion acutely after arterial occlusion. Cells in ischemic areas closer to the infarct returned to normal spine density levels slowly by retaining spines, while cells in more remote regions with preserved blood flow recovered faster by adding more spines, eventually surpassing baseline spine density by 15%. Our data suggest that maintaining tissue perfusion in the area surrounding the infarct could hasten or augment synaptic plasticity and functional recovery after stroke.

Hyperperfusion syndrome after clipping an unruptured cerebral aneurysm: two case reports

A 68-year-old woman presented with severe headache 9 days after undergoing successful clipping of a right middle cerebral artery aneurysm. Postoperative imaging revealed increased perfusion and diffuse edema in the right frontotemporal cortex. A 57-year-old woman exhibited perseveration soon after undergoing successful clipping of an anterior communicating artery aneurysm. Postoperative imaging studies revealed increased perfusion and diffuse edema in the left frontal and insular cortex. The symptoms and diffuse edema gradually resolved in both patients. These two cases of hyperperfusion syndrome occurred in a series of 190 patients treated by clipping of unruptured cerebral aneurysms. Hyperperfusion syndrome is a rare complication following aneurysm surgery, especially surgery for unruptured cerebral aneurysms without temporary clipping.

Two-photon high-resolution measurement of partial pressure of oxygen in cerebral vasculature and tissue

Measurements of oxygen partial pressure (pO(2)) with high temporal and spatial resolution in three dimensions is crucial for understanding oxygen delivery and consumption in normal and diseased brain. Among existing pO(2) measurement methods, phosphorescence quenching is optimally suited for the task. However, previous attempts to couple phosphorescence with two-photon laser scanning microscopy have faced substantial difficulties because of extremely low two-photon absorption cross-sections of conventional phosphorescent probes. Here we report to our knowledge the first practical in vivo two-photon high-resolution pO(2) measurements in small rodents' cortical microvasculature and tissue, made possible by combining an optimized imaging system with a two-photon-enhanced phosphorescent nanoprobe. The method features a measurement depth of up to 250 microm, sub-second temporal resolution and requires low probe concentration. The properties of the probe allowed for direct high-resolution measurement of cortical extravascular (tissue) pO(2), opening many possibilities for functional metabolic brain studies.

Headache and cardiovascular disease: old symptoms, new proposals

Evidence of a link between headache symptoms and cardiovascular disease has rapidly grown in recent years and it is of utmost importance for the cardiologist and neurologist to be aware of this intimate connection. A brief overview of different cardiovascular diseases (namely hypertension, stroke, coronary heart disease, patent foramen ovale, atrial septal defects, atrial septal aneurisms, mitral valve prolapse, and aortic and carotid disease) that may be related to headache is presented in this article. Proposed pathophysiological mechanisms for this association and landmark studies are reviewed and discussed.

Photochemically initiated intracellular astrocytic calcium waves in living mice using two-photon uncaging of IP(3)

We have developed a caged IP(3) analogue for two-photon photolysis in living animals. This probe is a cell permeable version and was coloaded with a fluorescent Ca(2+) dye into astrocytes in layer 1 of the somatosensory cortex of anesthetized mice. Two-photon irradiation of single cells at 720 nm produced rapid and robust increases in intracellular Ca(2+) concentrations monitored using two-photon microscopy at 950 nm. The photoevoked intracellular Ca(2+) waves were similar in magnitude to intrinsic signals in wild type mice. These waves did not propagate to other cells beyond the targeted astrocyte. In contrast, we observed intercellular astrocytic Ca(2+) waves in two mouse models of familial Alzheimer's disease. These data suggest that Alzheimer's might perturb gliotransmission but not IP(3) signaling per se in mouse models of the disease.

Neurite beading is sufficient to decrease the apparent diffusion coefficient after ischemic stroke

Diffusion-weighted MRI (DWI) is a sensitive and reliable marker of cerebral ischemia. Within minutes of an ischemic event in the brain, the microscopic motion of water molecules measured with DWI, termed the apparent diffusion coefficient (ADC), decreases within the infarcted region. However, although the change is related to cell swelling, the precise pathological mechanism remains elusive. We show that focal enlargement and constriction, or beading, in axons and dendrites are sufficient to substantially decrease ADC. We first derived a biophysical model of neurite beading, and we show that the beaded morphology allows a larger volume to be encompassed within an equivalent surface area and is, therefore, a consequence of osmotic imbalance after ischemia. The DWI experiment simulated within the model revealed that intracellular ADC decreased by 79% in beaded neurites compared with the unbeaded form. To validate the model experimentally, excised rat sciatic nerves were subjected to stretching, which induced beading but did not cause a bulk shift of water into the axon (i.e., swelling). Beading-induced changes in cell-membrane morphology were sufficient to significantly hinder water mobility and thereby decrease ADC, and the experimental measurements were in excellent agreement with the simulated values. This is a demonstration that neurite beading accurately captures the diffusion changes measured in vivo. The results significantly advance the specificity of DWI in ischemia and other acute neurological injuries and will greatly aid the development of treatment strategies to monitor and repair damaged brain in both clinical and experimental settings.

Experimental and preliminary clinical evidence of an ischemic zone with prolonged negative DC shifts surrounded by a normally perfused tissue belt with persistent electrocorticographic depression

In human cortex it has been suggested that the tissue at risk is indicated by clusters of spreading depolarizations (SDs) with persistent depression of high-frequency electrocorticographic (ECoG) activity. We here characterized this zone in the ET-1 model in rats using direct current (DC)-ECoG recordings. Topical application of the vasoconstrictor endothelin-1 (ET-1) induces focal ischemia in a concentration-dependent manner restricted to a region exposed by a cranial window, while a healthy cortex can be studied at a second naïve window. SDs originate in the ET-1-exposed cortex and invade the surrounding tissue. Necrosis is restricted to the ET-1-exposed cortex. In this study, we discovered that persistent depression occurred in both ET-1-exposed and surrounding cortex during SD clusters. However, the ET-1-exposed cortex showed longer-lasting negative DC shifts and limited high-frequency ECoG recovery after the cluster. DC-ECoG recordings of SD clusters with persistent depression from patients with aneurysmal subarachnoid hemorrhage were then analyzed for comparison. Limited ECoG recovery was associated with significantly longer-lasting negative DC shifts in a similar manner to the experimental model. These preliminary results suggest that the ischemic zone in rat and human cortex is surrounded by a normally perfused belt with persistently reduced synaptic activity during the acute injury phase.

Coma in response to environmental stress in the locust: a model for cortical spreading depression

Spreading depression (SD) is an interesting and important phenomenon due to its role in mammalian pathologies such as migraine, seizures, and stroke. Until recently investigations of the mechanisms involved in SD have mostly utilized mammalian cortical tissue, however we have discovered that SD-like events occur in the CNS of an invertebrate model, Locusta migratoria. Locusts enter comas in response to stress during which neural and muscular systems shut down until the stress is removed, and this is believed to be an adaptive strategy to survive extreme environmental conditions. During stress-induced comas SD-like events occur in the locust metathoracic ganglion (MTG) that closely resemble cortical SD (CSD) in many respects, including mechanism of induction, extracellular potassium ion changes, and propagation in areas equivalent to mammalian grey matter. In this review we describe the generation of comas and the associated SD-like events in the locust, provide a description of the similarities to CSD, and show how they can be manipulated both by stress preconditioning and pharmacologically. We also suggest that locust SD-like events are adaptive by conserving energy and preventing cellular damage, and we provide a model for the mechanism of SD onset and recovery in the locust nervous system.

Recurrent spontaneous spreading depolarizations facilitate acute dendritic injury in the ischemic penumbra

Spontaneous spreading depolarizations (SDs) occur in the penumbra surrounding ischemic core. These SDs, often referred to as peri-infarct depolarizations, cause vasoconstriction and recruitment of the penumbra into the ischemic core in the critical first hours after focal ischemic stroke; however, the real-time spatiotemporal dynamics of SD-induced injury to synaptic circuitry in the penumbra remain unknown. A modified cortical photothrombosis model was used to produce a square-shaped lesion surrounding a penumbra-like "area at risk" in middle cerebral artery territory of mouse somatosensory cortex. Lesioning resulted in recurrent spontaneous SDs. In vivo two-photon microscopy of green fluorescent protein-expressing neurons in this penumbra-like area at risk revealed that SDs were temporally correlated with rapid (<6 s) dendritic beading. Dendrites quickly (<3 min) recovered between SDs to near-control morphology until the occurrence of SD-induced terminal dendritic injury, signifying acute synaptic damage. SDs are characterized by a breakdown of ion homeostasis that can be recovered by ion pumps if the energy supply is adequate. Indeed, the likelihood of rapid dendritic recovery between SDs was correlated with the presence of nearby flowing blood vessels, but the presence of such vessels was not always sufficient for rapid dendritic recovery, suggesting that energy needs for recovery exceeded energy supply of compromised blood flow. We propose that metabolic stress resulting from recurring SDs facilitates acute injury at the level of dendrites and dendritic spines in metabolically compromised tissue, expediting penumbral recruitment into the ischemic core.

Can homeostatic plasticity in deafferented primary auditory cortex lead to travelling waves of excitation?

Travelling waves of activity in neural circuits have been proposed as a mechanism underlying a variety of neurological disorders, including epileptic seizures, migraine auras and brain injury. The highly influential Wilson-Cowan cortical model describes the dynamics of a network of excitatory and inhibitory neurons. The Wilson-Cowan equations predict travelling waves of activity in rate-based models that have sufficiently reduced levels of lateral inhibition. Travelling waves of excitation may play a role in functional changes in the auditory cortex after hearing loss. We propose that down-regulation of lateral inhibition may be induced in deafferented cortex via homeostatic plasticity mechanisms. We use the Wilson-Cowan equations to construct a spiking model of the primary auditory cortex that includes a novel, mathematically formalized description of homeostatic plasticity. In our model, the homeostatic mechanisms respond to hearing loss by reducing inhibition and increasing excitation, producing conditions under which travelling waves of excitation can emerge. However, our model predicts that the presence of spontaneous activity prevents the development of long-range travelling waves of excitation. Rather, our simulations show short-duration excitatory waves that cancel each other out. We also describe changes in spontaneous firing, synchrony and tuning after simulated hearing loss. With the exception of shifts in characteristic frequency, changes after hearing loss were qualitatively the same as empirical findings. Finally, we discuss possible applications to tinnitus, the perception of sound without an external stimulus.

Dynamic metabolic response to multiple spreading depolarizations in patients with acute brain injury: an online microdialysis study

Spreading depolarizations (SDs) occur spontaneously with high incidence in patients with acute brain injury. They can be detected by subdural electrocorticographic recordings. We here characterize the dynamic metabolic response to these events. A microdialysis catheter was inserted into perilesional cortical tissue adjacent to a strip for electrocorticography following craniotomy in 10 patients. The microdialysis catheter was connected to an online microdialysis assay measuring glucose and lactate concentrations every 30 to 60 secs. Spontaneously occurring SDs systematically caused a reduction in dialysate glucose by -32.0 micromol/L (range: -92.3 to -18.4 micromol/L, n=90) and increase in lactate by +23.1 micromol/L (range: +5.5 to +93.6 micromol/L, n=49). The changes were sustained at 20 mins after the SD events and highly significant using an area under the curve analysis (P<0.0001). Multiple and frequent SDs led to a progressive stepwise depletion of brain glucose. Hence, SD events cause a massive energy imbalance and their frequent occurrence leads to a local insufficiency of glucose supply. Such a failure would compromise cellular repolarization and hence tissue viability. The findings offer a new mechanism to account for otherwise unexplained instances of depletion of brain microdialysate glucose.

An update on the blood vessel in migraine

PURPOSE OF REVIEW

The cranial blood vessel is considered an integral player in the pathophysiology of migraine, but its perceived role has been subject to much discussion and controversy over the years. We will discuss the evolution in our scientific understanding of cranial blood vessels (primarily arteries) in migraine.

RECENT FINDINGS

Recent developments have clarified the role of cranial blood vessels in the trigemino-vascular system and in cortical spreading depression. An underlying theme is the intimate relation between vascular activity and neural function, and we will emphasize the various roles of the blood vessel that go beyond delivering blood. We conclude that migraine cannot be understood, either from a research or clinical point of view, without an understanding of the vascular derangements that accompany it.

SUMMARY

Migraine is accompanied by significant derangements in vascular function that may represent important targets for investigation and treatment.