European Headache Federation recommendations for neurologists managing giant cell arteritis

BACKGROUND AND AIM

Giant cell arteritis (GCA) remains a medical emergency because of the risk of sudden irreversible sight loss and rarely stroke along with other complications. Because headache is one of the cardinal symptoms of cranial GCA, neurologists need to be up to date with the advances in investigation and management of this condition. The aim of this document by the European Headache Federation (EHF) is to provide an evidence-based and expert-based recommendations on GCA.

METHODS

The working group identified relevant questions, performed systematic literature review and assessed the quality of available evidence, and wrote recommendations. Where there was not a high level of evidence, the multidisciplinary (neurology, ophthalmology and rheumatology) group recommended best practice based on their clinical experience.

RESULTS

Across Europe, fast track pathways and the utility of advanced imaging techniques are helping to reduce diagnostic delay and uncertainty, with improved clinical outcomes for patients. GCA is treated with high dose glucocorticoids (GC) as a first line agent however long-term GC toxicity is one of the key concerns for clinicians and patients. The first phase 2 and phase 3 randomised controlled trials of Tocilizumab, an IL-6 receptor antagonist, have been published. It is now been approved as the first ever licensed drug to be used in GCA.

CONCLUSION

The present article will outline recent advances made in the diagnosis and management of GCA.

Aids to management of headache disorders in primary care (2nd edition) : on behalf of the European Headache Federation and Lifting The Burden: the Global Campaign against Headache

The Aids to Management are a product of the Global Campaign against Headache, a worldwide programme of action conducted in official relations with the World Health Organization. Developed in partnership with the European Headache Federation, they update the first edition published 11 years ago.The common headache disorders (migraine, tension-type headache and medication-overuse headache) are major causes of ill health. They should be managed in primary care, firstly because their management is generally not difficult, and secondly because they are so common. These Aids to Management, with the European principles of management of headache disorders in primary care as the core of their content, combine educational materials with practical management aids. They are supplemented by translation protocols, to ensure that translations are unchanged in meaning from the English-language originals.The Aids to Management may be individually downloaded and, as is the case for all products of the Global Campaign against Headache, are available without restriction for non-commercial use.

Headache service quality: the role of specialized headache centres within structured headache services, and suggested standards and criteria as centres of excellence

In joint initiatives, the European Headache Federation and Lifting The Burden have described a model of structured headache services (with their basis in primary care), defined service quality in this context, and developed practical methods for its evaluation.Here, in a continuation of the service quality evaluation programme, we set out ten suggested role- and performance-defining standards for specialized headache centres operating as an integral component of these services. Verifiable criteria for evaluation accompany each standard. The purposes are five-fold: (i) to inspire and promote, or stimulate the establishment of, specialized headache centres as centres of excellence; (ii) to define the role of such centres within optimally structured and organized national headache services; (iii) to set out criteria by which such centres may be recognized as exemplary in their fulfilment of this role; (iv) to provide the basis for, and to initiate and motivate, collaboration and networking between such centres both nationally and internationally; (v) ultimately to improve the delivery and quality of health care for headache.

European Headache Federation consensus on technical investigation for primary headache disorders

The diagnosis of primary headache disorders is clinical and based on the diagnostic criteria of the International Headache Society (ICHD-3-beta). However several brain conditions may mimic primary headache disorders and laboratory investigation may be needed. This necessity occurs when the treating physician doubts for the primary origin of headache. Features that represent a warning for a possible underlying disorder causing the headache are new onset headache, change in previously stable headache pattern, headache that abruptly reaches the peak level, headache that changes with posture, headache awakening the patient, or precipitated by physical activity or Valsalva manoeuvre, first onset of headache ≥50 years of age, neurological symptoms or signs, trauma, fever, seizures, history of malignancy, history of HIV or active infections, and prior history of stroke or intracranial bleeding. All national headache societies and the European Headache Alliance invited to review and comment the consensus before the final draft. The consensus recommends brain MRI for the case of migraine with aura that persists on one side or in brainstem aura. Persistent aura without infarction and migrainous infarction require brain MRI, MRA and MRV. Brain MRI with detailed study of the pituitary area and cavernous sinus, is recommended for all TACs. For primary cough headache, exercise headache, headache associated with sexual activity, thunderclap headache and hypnic headache apart from brain MRI additional tests may be required. Because there is little and no good evidence the committee constructed a consensus based on the opinion of experts, and should be treated as imperfect.

Nociception-specific blink reflex: pharmacology in healthy volunteers

BACKGROUND

The physiology and pharmacology of activation or perception of activation of pain-coding trigeminovascular afferents in humans is fundamental to understanding the biology of headache and developing new treatments.

METHODS

The blink reflex was elicited using a concentric electrode and recorded in four separate sessions, at baseline and two minutes after administration of ramped doses of diazepam (final dose 0.07 mg/kg), fentanyl (final dose 1.11 μg/kg), ketamine (final dose 0.084 mg/kg) and 0.9 % saline solution. The AUC (area under the curve, μV*ms) and the latency (ms) of the ipsi- and contralateral R2 component of the blink reflex were calculated by PC-based offline analysis. Immediately after each block of blink reflex recordings certain psychometric parameters were assessed.

RESULTS

There was an effect due to DRUG on the ipsilateral (F 3,60 = 7.3, P < 0.001) AUC as well as on the contralateral (F 3,60 = 6.02, P < 0.001) AUC across the study. A significant decrement in comparison to placebo was observed only for diazepam, affecting the ipsilateral AUC. The scores of alertness, calmness, contentedness, reaction time and precision were not affected by the DRUG across the sessions.

CONCLUSION

Previous studies suggest central, rather than peripheral changes in nociceptive trigeminal transmission in migraine. This study demonstrates a robust effect of benzodiazepine receptor modulation of the nociception specific blink reflex (nBR) without any μ-opiate or glutamate NMDA receptor component. The nociception specific blink reflex offers a reproducible, quantifiable method of assessment of trigeminal nociceptive system in humans that can be used to dissect pharmacology relevant to primary headache disorders.

Cyclic vomiting syndrome: case report and short review of the literature

Cyclic vomiting syndrome (CVS) is a functional disorder that is considered to be a manifestation of migraine diathesis. It is characterized by stereotypical episodes of severe nausea and vomiting lasting several hours or days, with return to baseline health between episodes. CVS is still an insufficiently known syndrome among physicians, and is therefore often misdiagnosed. Treatment focuses on the different phases of CVS, with interepisodic prophylaxis, abortive therapy in the prodromal phase of CVS, and supportive care during an acute vomiting episode. Anti-migraine medications have been effectively used for prophylaxis in many patients. We report a case of CVS successfully treated with flunarizine, a non-selective calcium antagonist.

[Self-medication of regular headache: a community pharmacy-based survey in Belgium]

AIM

This observational community pharmacy-based study aimed to investigate headache characteristics and medication use of persons with regular headache presenting for self-medication.

METHODS

Participants (n=1205) completed ii) a questionnaire to assess current headache medication and previous physician diagnosis, (ii) the ID Migraine Screener [ID-M] and (iii) the MIDAS questionnaire.

RESULTS

Forty-four % of the study population (n=528) did not have a physician diagnosis of their headache, and 225 of them (225/528, 42.6%) were found to be ID-M positive. The most commonly used acute headache drugs were paracetamol (used by 62% of the study population), NSAIDs (39%) and combination analgesics (36%). Only 12% of patients physician-diagnosed with migraine used prophylactic migraine medication, and 25% used triptans. About 24% of our sample (n=292) chronically overused acute medication, which was combination analgesic overuse (n=166), simple analgesic overuse (n=130), triptan overuse (n=19), ergot overuse (n=6) and opioid overuse (n=51). Only 14.5% was ever advised to limit intake frequency of acute headache treatments.

CONCLUSIONS

This study identified underdiagnosis of migraine, low use of migraine prophylaxis and triptans, and high prevalence of medication overuse among subjects seeking self-medication for regular headache. Community pharmacists have a strategic position in education and referral of these self-medicating headache patients.

Self-medication of regular headache: a community pharmacy-based survey

BACKGROUND

This observational community pharmacy-based study aimed to investigate headache characteristics and medication use of persons with regular headache presenting for self-medication.

METHODS

Participants (n = 1205) completed (i) a questionnaire to assess current headache medication and previous physician diagnosis, (ii) the ID Migraine Screener (ID-M), and (iii) the Migraine Disability Assessment questionnaire.

RESULTS

Forty-four percentage of the study population (n = 528) did not have a physician diagnosis of their headache, and 225 of them (225/528, 42.6%) were found to be ID-M positive. The most commonly used acute headache drugs were paracetamol (used by 62% of the study population), NSAIDs (39%), and combination analgesics (36%). Only 12% of patients physician-diagnosed with migraine used prophylactic migraine medication, and 25% used triptans. About 24% of our sample (n = 292) chronically overused acute medication, which was combination analgesic overuse (n = 166), simple analgesic overuse (n = 130), triptan overuse (n = 19), ergot overuse (n = 6), and opioid overuse (n = 5). Only 14.5% was ever advised to limit intake frequency of acute headache treatments.

CONCLUSIONS

This study identified underdiagnosis of migraine, low use of migraine prophylaxis and triptans, and high prevalence of medication overuse amongst subjects seeking self-medication for regular headache. Community pharmacists have a strategic position in education and referral of these self-medicating headache patients.

Saccade behaviour in migraine patients

BACKGROUND

Voxel-based morphometry studies in migraine patients showed significant grey matter volume reduction in regions involved in the control of saccadic eye movements. We hypothesized that these changes would be reflected in dysfunctional saccadic behaviour.

METHODS

Saccades were recorded by infrared oculography using three different paradigms (pro-saccade with gap, pro-saccade overlap and anti-saccade with gap). We compared the results for migraine patients (n = 80) with those for controls (n = 87).

RESULTS

No significant differences were found between migraine patients with (n = 46) and without (n = 34) aura. Migraine patients showed a saccadic behaviour that differed from controls in three respects. In migraine patients, the latencies in the pro-saccade with gap paradigm were borderline significantly longer. Moreover, in both the pro-saccade with gap and the pro-saccade overlap paradigm we observed a larger intra-individual variation of the latency in migraine patients. However, the biggest difference was that the patients who received migraine prophylactic therapy made significantly more anti-saccade errors in the anti-saccade with gap paradigm, suggesting that inhibitory saccade control is impaired in migraine patients depending on the severity of the migraine.

CONCLUSION

We suggest a deficient inhibitory control, reflecting an executive dysfunction in the dorsolateral prefrontal cortex or a dysfunction in the cingulate cortex, is present in migraine patients.

Phenotype of patients responsive to occipital nerve stimulation for refractory head pain

Occipital nerve stimulation (ONS) has been employed off-label for medically refractory head pain. Identification of specific headache diagnoses responding to this modality of treatment is required. Forty-four patients with medically refractory head pain and treated with ONS were invited to participate in a retrospective study including a clinical interview and, if necessary, an indomethacin test to establish the headache phenotype according to the International Classification of Headache Disorders, 2nd edn (ICHD-II). We gathered data from questionnaires before implantation, at 1 month after implantation, and at long-term follow-up. Twenty-six patients consented and were phenotyped. At 1 month follow-up and at long-term follow-up a significant decrease in all pain parameters was noted, as well as in analgesic use. Quality of sleep and quality of life improved. Patient satisfaction was generally high as 80% of patients had ≥ 50% pain relief at long-term follow-up. The overall complication rate was low, but revisions were frequent. After phenotyping, two main groups emerged: eight patients had 'Migraine without aura' (ICHD-II 1.1) and eight patients 'Constant pain caused by compression, irritation or distortion of cranial nerves or upper cervical roots by structural lesions' (ICHD-II 13.12). Overuse of symptomatic acute headache treatments was associated with less favourable long-term outcome in migraine patients. We conclude that careful clinical phenotyping may help in defining subgroups of patients with medically refractory headache that are more likely to respond to ONS. The data suggest medication overuse should be managed appropriately when considering ONS in migraine. A controlled prospective study for ONS in ICHD-II 13.12 is warranted.

Diagnostic and therapeutic trajectory of cluster headache patients in Flanders

OBJECTIVE

A fraction of cluster headache (CH) patients face diagnostic delay, misdiagnosis, undertreatment and mismanagement. Specific data for Flanders are warranted.

METHODS

Data on CH characteristics, diagnostic process and treatment history were gathered using a self-administered questionnaire with 90 items in CH patients that presented to 4 neurology outpatient clinics.

RESULTS

Data for 85 patients (77 men) with a mean age of 44 years (range 23-69) were analysed. 79% suffered from episodic CH and 21% from chronic CH. A mean diagnostic delay of 44 months was reported. 31% of patients had to wait more than 4 years for the CH diagnosis. 52% of patients consulted at least 3 physicians prior to CH diagnosis. Most common misdiagnoses were migraine (45%), sinusitis (23%), tooth/jaw problems (23%), tension-type headache (16%) and trigeminal neuralgia (16%). A significant percentage of patients had never received access to injectable sumatriptan (26%) or oxygen (31%). Most prescribed preventative drugs after the CH diagnosis were verapamil (82%), lithium (35%), methysergide (31%) and topiramate (22%). Despite the CH diagnosis, ineffective preventatives were still used in some, including propranolol (12%), amitriptyline (9%) and carbamazepine (12%). 31% of patients had undergone invasive therapy prior to CH diagnosis, including dental procedures (21%) and sinus surgery (10%).

CONCLUSION

Despite the obvious methodological limitations of this study, the need for better medical education on CH is evident to optimize CH management in Flanders.

Unilateral photophobia or phonophobia in migraine compared with trigeminal autonomic cephalalgias

Our objective was to compare the presence of self-reported unilateral photophobia or phonophobia, or both, during headache attacks comparing patients with trigeminal autonomic cephalalgias (TACs)--including cluster headache, short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) and paroxysmal hemicrania--or hemicrania continua, and other headache types. We conducted a prospective study in patients attending a referral out-patient clinic over 5 months and those admitted for an intramuscular indomethacin test. Two hundred and six patients were included. In episodic migraine patients, two of 54 (4%) reported unilateral photophobia or phonophobia, or both. In chronic migraine patients, six of 48 (13%) complained of unilateral photophobia or phonophobia, or both, whereas none of the 24 patients with medication-overuse headache reported these unilateral symptoms, although these patients all had clinical symptoms suggesting the diagnosis of migraine. Only three of 22 patients (14%) suffering from new daily persistent headache (NDPH) experienced unilateral photophobia or phonophobia. In chronic cluster headache 10 of 21 patients (48%) had unilateral photophobia or phonophobia, or both, and this symptom appeared in four of five patients (80%) with episodic cluster headache. Unilateral photophobia or phonophobia, or both, were reported by six of 11 patients (55%) with hemicrania continua, five of nine (56%) with SUNCT, and four of six (67%) with chronic paroxysmal hemicrania. Unilateral phonophobia or photophobia, or both, are more frequent in TACs and hemicrania continua than in migraine and NDPH. The presence of these unilateral symptoms may be clinically useful in the differential diagnosis of primary headaches.

Medication-overuse headache in patients with cluster headache

OBJECTIVE

Medication-overuse headache (MOH) in cluster headache (CH) patients is incompletely described, perhaps because of the relatively low prevalence of CH.

METHODS

The authors describe a retrospective series of 17 patients (13 men, 4 women) with CH who developed MOH in association with overuse of a wide range of monotherapies or varying combinations of simple analgesics (n = 9), caffeine (n = 1), opioids (n = 10), ergotamine (n = 3), and triptans (n = 14). The series includes both episodic (n = 7) and chronic (n = 10) CH patients.

RESULTS

A specific triptan-overuse headache diagnosis was made in 3 patients, an opioid-overuse headache diagnosis was made in 1 patient, and an ergotamine-overuse headache diagnosis was made in 1 patient. In approximately half of the patients (n = 8), the MOH phenotype was a bilateral, dull, and featureless daily headache. In the other 9 patients, the MOH was characterized by at least one associated feature, most commonly nausea (n = 6), exacerbation with head movement (n = 5), or throbbing character of the pain (n = 5). The common denominator in 15 patients was a personal or family history, or both, of migraine. The 2 other patients gave a family history of unspecified headaches. Medication withdrawal was attempted and successful in 13 patients.

CONCLUSIONS

Medication-overuse headache is a previously underrecognized and treatable problem associated with cluster headache (CH). CH patients should be carefully monitored, especially those with a personal or family history of migraine.

Cerebral blood flow and oxygen metabolism in symptomatic internal carotid artery occlusion by (traumatic) cervical artery dissection

The present study investigates whether cerebral infarction resulting from internal carotid artery occlusion by cervical dissection is due to emboli, released from a superimposed luminal thrombus, or is due to haemodynamic failure and hypoperfusion. Ten patients with a history of stroke and with a visible cerebral infarct on computed tomographic scan, due to cervical dissection and thrombosis of the internal carotid artery, were studied with positron emission tomography in order to assess the regional cerebral blood flow (rCBF), the regional cerebral metabolic rate of oxygen (rCMRO2) and the regional oxygen extraction fraction (rOEF) in different regions of the brain. rCBF and rCMRO2 were only decreased in the infarct area but not in the peri-infarct zone or elsewhere in the brain. As rOEF was not increased in the affected cerebral hemisphere, the present study suggests artery-to-artery embolism rather than a haemodynamic event as the cause of the stroke. Use of anticoagulants thus appears to be the appropriate treatment in the acute stage.

Cerebral bloodflow and oxygen metabolism in borderzone and territorial infarcts due to symptomatic carotid artery occlusion

It remains controversial whether borderzone infarcts are due to compromised cerebral perfusion and whether territorial infarcts are caused by artery-to-artery emboli in case of occlusion of the internal carotid artery. The present positron emission tomography study compares with normal controls, the average regional cerebral bloodflow (rCBF), regional oxygen extraction fraction (rOEF) and regional cerebral metabolic rate for oxygen (rCMRO(2)) in the infarct area, the peri-infarct zone, the remaining homolateral hemisphere and in the contralateral hemisphere of 10 patients with borderzone and 17 patients with territorial infarcts, due to internal carotid artery occlusion by atherosclerosis and by cervical dissection. The steady-state technique with oxygen-15 was used. A nearly significant increase of rOEF with lowered rCBF and rCMRO(2) was observed in the peri-infarct zone of patients with territorial infarcts. In patients with borderzone infarcts rCMRO(2) was decreased in the peri-infarct zone, in the remaining homolateral hemisphere and in the contralateral hemisphere without changes in rCBF and rOEF. The present study finds no arguments that impaired cerebral perfusion is a more frequent cause of borderzone than of territorial infarcts.

The prognostic significance of changes in lesion size of established cerebral infarcts on computed tomography of the brain

BACKGROUND

As a second part of our prospective study, we assessed the size of the infarct lesion on computed tomography (CT) of the brain at two fixed time points after stroke in order to investigate its influence on the clinical outcome.

METHODS

From 220 consecutive stroke patients, admitted within 24 h after onset with symptoms lasting more than 24 h, we selected 150 displaying an anterior circulation infarct or syndrome. All included patients had CT scans without contrast enhancement on day 3 (+/- 8 h) and on day 10 (+/- 8 h) after stroke onset. The size of the X-ray hypoattenuation zone was determined by superimposing the CT slices on digital cerebral vascular maps, on which the contours of the infarct area were delineated. The lesion size was expressed as the fraction of the total surface area of these digital cerebral maps. The patients were divided into four groups according to their degree of disability at 3 months on the modified Rankin (R) scale as follows : R 0-1, R 2-3, R 4-5, R 6.

RESULTS

There was a clear association between lesion size on CT, on day 3 and on day 10, and the clinical outcome. Lesion size decreased between day 3 and day 10 in the groups R 0-1 and R 2-3, remained unchanged in the group R 4-5 and further increased in group R 6.

CONCLUSION

Lesion size on CT is a significant predictor of stroke outcome. It decreases from day 3 to day 10 in patients with no or low disability at 3 months, but increases in those who do not survive their stroke.

A pure sensorimotor stroke due to cervical vertebral artery occlusion

We reviewed the case history of a 45 year-old women, who presented a pure right sensorimotor stroke, due to a left paramedial medullary infarct as result of a left cervical vertebral artery occlusion. The unusual location of the infarct could be explained by the combination of an anatomical variant of the left branch of the anterior spinal artery and the presence of a deep cervical artery, issued from the costo-cervical trunck. This collateral circulation allowed that the lateral and upper medulla was not infarcted.

The cellular basis of neurovascular metabolic coupling

Functional brain imaging studies, such as positron emission tomography and functional nuclear magnetic resonance imaging, are based on the regional increases in cerebral blood flow, glucose consumption and oxygen consumption that are associated with regional increases in neuronal activity. The cellular basis of the signals that are measured is however incompletely understood at present. An increasingly important role for astrocytes in neurovascular metabolic coupling is being described, which was already suggested over 100 years ago as astrocytes are a structural link between endothelial cells of brain capillaries and neurons. Recent data have provided evidence for a role of the astrocytic intracellular sodium concentration in driving astrocytic glycolysis that may provide neurons with lactate as an energy substrate during activation. We have previously described intracellular sodium changes in astrocytes that are associated with astrocytic intercellular calcium waves. These intercellular calcium waves have been demonstrated both in astrocytes in culture as well as in brain slices. In this paper a new hypothesis concerning a role for astrocytic intercellular calcium waves in brain energy metabolism is formulated.

Astrocyte-endothelial cell calcium signals conveyed by two signalling pathways

Astrocytes and endothelial cells are in close contact with each other at the blood-brain barrier, where important molecular transports take place. Despite these key morphological and functional properties, little is known regarding the dynamic signalling processes that occur between these two cell types. We investigated astrocyte-endothelial cell calcium signalling mechanisms in a coculture model prepared from primary rat cortical astrocytes and ECV304 cells. We used flash photolysis of caged inositol-trisphosphate (IP3) and gentle mechanical stimulation to trigger astrocyte-endothelial cell calcium signals and to investigate the underlying propagation mechanisms. Photolytically releasing IP3 in a single cell triggered increases in cytoplasmic calcium concentration that propagated between astrocytes and endothelial cells in either direction. These propagating calcium signals did not cross cell-free zones and were not affected by fast superfusion or by the purinergic inhibitors apyrase and suramin, indicating that they are communicated through an intracellular pathway in conjunction with gap junctions. Electrophysiological experiments confirmed a low degree of astrocyte-endothelial cell electrical cell-to-cell coupling. Mechanical stimulation of a single cell also triggered astrocyte-endothelial cell calcium signals but, in contrast to the former triggering mode, these signals crossed cell-free zones and were significantly inhibited by apyrase, thus indicating the involvement of an extracellular and purinergic messenger. Astrocyte-endothelial cell calcium signalling also occurred in cocultures prepared with astrocytes and primary rat brain capillary endothelial cells. We conclude that astrocytes and endothelial cells can exchange fast-acting calcium signals (time scale of seconds) that can be communicated through an intracellular/gap junctional pathway and an extracellular purinergic pathway.

Intercellular calcium waves in HeLa cells expressing GFP-labeled connexin 43, 32, or 26

This study was undertaken to obtain direct evidence for the involvement of gap junctions in the propagation of intercellular Ca(2+) waves. Gap junction-deficient HeLa cells were transfected with plasmids encoding for green fluorescent protein (GFP) fused to the cytoplasmic carboxyl termini of connexin 43 (Cx43), 32 (Cx32), or 26 (Cx26). The subsequently expressed GFP-labeled gap junctions rendered the cells dye- and electrically coupled and were detected at the plasma membranes at points of contact between adjacent cells. To correlate the distribution of gap junctions with the changes in [Ca(2+)](i) associated with Ca(2+) waves and the distribution of the endoplasmic reticulum (ER), cells were loaded with fluorescent Ca(2+)-sensitive (fluo-3 and fura-2) and ER membrane (ER-Tracker) dyes. Digital high-speed microscopy was used to collect a series of image slices from which the three-dimensional distribution of the gap junctions and ER were reconstructed. Subsequently, intercellular Ca(2+) waves were induced in these cells by mechanical stimulation with or without extracellular apyrase, an ATP-degrading enzyme. In untransfected HeLa cells and in the absence of apyrase, cell-to-cell propagating [Ca(2+)](i) changes were characterized by initiating Ca(2+) puffs associated with the perinuclear ER. By contrast, in Cx-GFP-transfected cells and in the presence of apyrase, [Ca(2+)](i) changes were propagated without initiating perinuclear Ca(2+) puffs and were communicated between cells at the sites of the Cx-GFP gap junctions. The efficiency of Cx expression determined the extent of Ca(2+) wave propagation. These results demonstrate that intercellular Ca(2+) waves may be propagated simultaneously via an extracellular pathway and an intracellular pathway through gap junctions and that one form of communication may mask the other.

ATP-dependent astrocyte-endothelial calcium signaling following mechanical damage to a single astrocyte in astrocyte-endothelial co-cultures

In the brain, endfeet of perivascular astrocytes make close contact with capillary endothelial cells that form the blood-brain barrier. The aim of the present work was to investigate whether and how calcium signals can be communicated from astrocytes to endothelial cells following acute mechanical cell damage. The experiments were performed on astrocyte-endothelial co-cultures prepared from primary rat brain astrocytes and an endothelial cell line (ECV304). A single astrocyte was acutely damaged by mechanical stimulation of sufficient strength with a micropipette, and the resulting cytoplasmic calcium changes were monitored using fura-2 and digital calcium imaging. Mechanical damage to a single astrocyte triggered a large intercellular calcium wave that propagated to surrounding astrocytes and also to even remotely located (several hundred micrometers) endothelial cells. Astrocyte-endothelial calcium waves induced by mechanical cell damage were largely deflected by fast superfusion, were able to cross a cell-free lane, were dose-dependently inhibited by suramin, a P2-purinoceptor blocker, and were largely reduced in size in the presence of the ATP-degrading enzyme apyrase. Our results indicate that mechanical damage to a single astrocyte can produce far reaching calcium signals that are propagated by the release of a calcium mobilizing P2-purinergic agonist and that can be communicated to endothelial cells. As endothelial cytoplasmic calcium is an important factor in the regulation of blood-brain barrier permeability and transport, mechanical cell damage-induced astrocyte-endothelial calcium signals are hypothesized to play a role in the initiation of brain edema and the stimulation of brain glucose uptake.

Ionic changes accompanying astrocytic intercellular calcium waves triggered by mechanical cell damaging stimulation

Mechanically poking or damaging a single cell within a confluent astrocyte culture produces the so-called intercellular calcium (Ca(2+)) waves, that is, cell-to-cell propagating changes of intracellular free Ca(2+). We were interested whether intercellular Ca(2+) waves are also associated with changes in other intra- or extracellular ions. To that purpose, we investigated spatiotemporal changes of intracellular Ca(2+) (Ca(i)2+), sodium (Na(i)+) and protons (H(i)+) in primary cultures of rat cortical astrocytes using microfluorescence imaging with fura-2, SBFI and BCECF, respectively; changes of extracellular potassium (K(e)+) were monitored with K(+)-sensitive microelectrodes. Mechanical damage to a single cell by stimulation with a piezo-electrically driven micropipette initiated intercellular Ca(2+) waves that propagated to about 160 microm away from the stimulation point. Na(i)(+) increases could be detected in cells located 2-3 cell diameters from the stimulated cell, acidification was observed 1-2 cell diameters away and Ke(+) increases were measured up to 75 microm away. Kinetic analysis suggests that the Na(i)(+) and H(i)(+) changes occur after, and thus secondary to the Ca(i)(2+) changes. In contrast, K(e)(+) changes occurred very fast, even before the Ca(i)(2+) changes, but their propagation speed was too fast to implicate them as a trigger of Ca(i)(2+) changes. As Na(i)(+) is an important regulator of glycolysis in astrocytes, we hypothesize that astrocytic Na(i)(+) changes in cells located remotely from a damaged cell might be a signal that activates glycolysis thereby producing more lactate that is transferred to the neurons and increases their energy potential to survive the inflicted damage.

Chemically, mechanically, and hyperosmolarity-induced calcium responses of rat cortical capillary endothelial cells in culture

The purpose of the present work was to characterize calcium responses of brain-capillary endothelial cells (BCEC), the cells forming the blood-brain barrier, to chemical, hyperosmolar and mechanical stimulation. Confluent BCEC cultures were grown from capillary fragments isolated from rat cerebral cortex. Intracellular free calcium ([Ca2+]i) was measured using fura-2 and digital imaging. Our experiments show large endothelial calcium responses to substance P and ATP, up to a peak value of approximately 1000 and 600 nM, respectively, and these responses were observed in 2/3 of the cells. Calcium responses to bradykinin, histamine, and hyperosmolar sucrose or mannitol were smaller, attaining a peak in the range 180-340 nM, and were observed in a smaller fraction of the cells. No calcium responses were observed to high-potassium, L-glutamate, serotonin, carbachol, noradrenaline, and nitric-oxide donors. Consecutive superfusion of the cultures with ATP, bradykinin, and histamine showed that cells with a certain response pattern were spatially grouped; the response pattern itself varied widely between experiments. Mechanical stimulation of a single cell caused a calcium response in the stimulated cell in primary cultures and triggered an intercellularly propagating calcium wave in passaged cultures. Given the important effect of endothelial [Ca2+]i on blood-brain barrier permeability and transport, we conclude that substance P and ATP are potential modulators of blood-brain barrier function. Hyperosmolarity-induced blood-brain barrier opening is probably not mediated through endothelial [Ca2+]i.

Inositol-trisphosphate-dependent intercellular calcium signaling in and between astrocytes and endothelial cells

Interactions between astrocytes and endothelial cells are believed to play an important role in the control of blood-brain barrier permeability and transport. Astrocytes and endothelial cells respond to a variety of stimuli with an increase of intracellular free calcium ([Ca2+]i) that is propagated to adjacent cells as an intercellular Ca2+ wave. We hypothesized that intercellular Ca2+ signaling also occurs between astrocytes and endothelial cells, and we investigated this possibility in co-cultures of primary astrocytes and an endothelial cell line using caged messengers. Intercellular Ca2+ waves, induced by mechanical stimulation of a single cell, propagated from astrocytes to endothelial cells and vice versa. Intercellular Ca2+ waves could also be induced by flash photolysis of pressure-injected caged inositol trisphosphate (IP3) and also by applying the flash to remote noninjected cells. Ca2+ waves induced by flash photolysis propagated from endothelial cells to astrocytes but not from astrocytes to endothelial cells even though caged IP3 diffused between the two cell types. Flash photolysis of caged Ca2+ (NP-EGTA) resulted in an increase of [Ca2+]i but did not initiate an intercellular Ca2+ wave. We conclude that an increase of IP3 in a single cell is sufficient to initiate an intercellular Ca2+ wave that is propagated by the diffusion of IP3 to neighboring cells and that can be communicated between astrocytes and endothelial cells in co-culture. By contrast, Ca2+ diffusion via gap junctions does not appear to be sufficient to propagate an intercellular Ca2+ wave. We suggest that intercellular Ca2+ waves may play a role in astrocyte-endothelial interactions at the blood-brain barrier.