Pharmacological validation of a refined burrowing paradigm for prediction of analgesic efficacy in a rat model of sub-chronic knee joint inflammation

BACKGROUND

Burrowing is an evolutionarily conserved behaviour in rodents. This study validates a refined burrowing paradigm (requiring a reduced number of animals) in a rat model of sub-chronic knee joint inflammation and evaluates its sensitivity and specificity for analgesic drugs.

METHODS

Knee joint inflammation in rats was induced by intra-articular injection with complete Freund's adjuvant (CFA). Burrowing performance was assessed at baseline without study drugs, and in CFA-naive and CFA-injected animals following administration of the analgesic drugs naproxen, pregabalin and morphine, each at three doses, or corresponding vehicle (nine rats per dose group). The specificity of the model was evaluated by also testing the anxiogenic drug yohimbine, the stimulant drug dexamphetamine and the anxiolytic drug chlordiazepoxide in CFA-naive and CFA-injected animals. Percentage maximum possible effect (%MPE) was determined by relating the difference between post-CFA and baseline burrowing performance in each drug dose group to that in the vehicle group in each experiment.

RESULTS

Burrowing performance in the vehicle groups was decreased by 39.0-59.8% in CFA-injected animals compared with CFA-naive animals. CFA-induced reductions in burrowing performance were reversed by each of the three analgesic drugs tested. The highest %MPE was 75.2% with naproxen 50 mg/kg, 80.9% with pregabalin 10 mg/kg and 77.0% with morphine 1 mg/kg (all p < 0.05 vs. control). CFA-induced reductions in burrowing performance were not reversed by yohimbine, dexamphetamine or chlordiazepoxide.

CONCLUSIONS

This study provides pharmacological validation of a refined burrowing paradigm for analgesic efficacy that exhibits good predictive validity, with high sensitivity and specificity.

Burrowing as a non-reflex behavioural readout for analgesic action in a rat model of sub-chronic knee joint inflammation

BACKGROUND

Innate responses against spontaneous pain are proposed to improve the predictive validity of preclinical analgesia models. Therefore, development and validation of novel readouts is necessary. To investigate whether innate rodent burrowing is a useful alternative behavioural readout for assessment of analgesic efficacy, a complete Freund's adjuvant (CFA)-induced model of sub-chronic inflammation was used to compare the effects of naproxen, ibuprofen and pregabalin in weight-bearing (WB), open-field (OF) and burrowing assays.

METHODS

Male Sprague Dawley rats were injected with 150 μL of CFA (2 mg/mL) into the knee (hind leg) 3 days before testing. Naproxen, ibuprofen and pregabalin were administered at different doses 30, 90 and 60 min, respectively, before testing. WB was determined using a rat incapacitance tester; horizontal distance moved and vertical rearings were recorded in an OF; and burrowing was measured by the weight of gravel remaining in a hollow tube after 60 min.

RESULTS

CFA-induced arthritis reduced WB, OF activity and burrowing. Naproxen, pregabalin and ibuprofen treatment normalized WB; however, horizontal OF activity was not improved by any treatment; rearing behaviour was moderately reinstated by ibuprofen (100 mg/kg). In burrowing, naproxen (100 mg/kg), ibuprofen (31.6 and 100 mg/kg) and pregabalin (10 mg/kg) reversed CFA-induced deficits.

CONCLUSIONS

Burrowing performance is an alternative non-reflex readout relying on innate rodent behaviour that is affected by nociceptive behaviour and can be pharmacologically manipulated. The burrowing assay appears to be more sensitive than OF assays and is as sensitive as WB assays at distinguishing between analgesic doses and doses that impair locomotion.

Effect of baseline rheumatoid factor and anticitrullinated peptide antibody serotype on rituximab clinical response: a meta-analysis

BACKGROUND

Studies examining the relationship between serological status (rheumatoid factor and/or anticitrullinated antibody) and rituximab treatment outcome in rheumatoid arthritis (RA) have been hampered by limited numbers of seronegative patients.

OBJECTIVE

To carry out a meta-analysis of trials from the rituximab RA clinical programme to investigate this relationship further.

METHODS

This was a meta-analysis of four placebo-controlled, phase II or III clinical trials. The efficacy end point in all analyses was change from baseline in Disease Activity Score in 28 joints-erythrocyte sedimentation rate (DAS28-ESR) at 24 weeks. Assay of serotype and missing data imputation methods were consistent across all studies.

RESULTS

The population analysed comprised 2177 patients (rituximab, n=1416; placebo, n=761). Demographics and baseline disease characteristics were well balanced. When a fixed-effects meta-analysis approach was used, the overall-effect model indicated evidence of additional treatment benefit with rituximab in seropositive patients: reduction in DAS28-ESR at week 24 was on average 0.35 units (95% CI 0.12 to 0.84; n=1394) greater than in seronegative patients; this effect was not seen in placebo patients. Heterogeneity indices indicated significant uncertainty in the overall-effect model (Q=8.8, I=0.77; p=0.03 (χ(2) test)). Baseline Health Assessment Questionnaire score, pain visual analogue scale, swollen joint counts of 28 joints and race were significant contributors to this heterogeneity, with additional analysis indicating that these effects may predominate in early RA (methotrexate-naïve) populations. A dominant effect was seen in patients for whom one or more tumour necrosis factor inhibitors had failed.

CONCLUSION

Although the difference was modest, the overall-effect model indicates that seropositive patients respond better to rituximab than seronegative patients.

Neurological disease associated with Mycoplasma pneumoniae infection. PCR evidence against a direct invasive mechanism

Aims-To investigate the pathology in patients presenting with sudden onset neurological illnesses associated with Mycoplasma pneumoniae infection.Methods-M pneumoniae infection was diagnosed by a highly rigorous interpretation of serological markers initially using complement fixation, agglutination and IgM antibodies. Confirmation of the serological diagnosis was achieved using indirect immunofluorescence for IgM, IgA, and IgG. Serum and cerebrospinal fluid (CSF) samples from these patients were examined using the polymerase chain reaction to look for evidence of M pneumoniae DNA.Results-No M pneumoniae DNA was found in any serum or CSF samples. Diagnosis of M pneumoniae infection by agglutination and complement fixation antibodies was not always confirmed by indirect immunofluorescence.Conclusion-The neurological lesions in these patients do not appear to be caused by the direct invasion of M pneumoniae into the nervous system. The lesions may be an immune response to infection. Serological diagnosis of M pneumoniae continues to be a laboratory problem.

Cellular and histopathological changes in the infrapatellar fat pad in the monoiodoacetate model of osteoarthritis pain

OBJECTIVE

The infrapatellar fat pad (IPFP) has been identified as a source of anterior knee pain. Fibrosis and marked inflammatory infiltrate in the IPFP of patients with arthritis of the knee and reduction in pain post knee replacement in patients following resection of the IPFP have been observed. We have investigated changes in the IPFP of rats undergoing the monoiodoacetate (MIA) model of degenerative joint disease, a model that exhibits some histopathological similarities to osteoarthritis (OA).

METHODS

Rats were injected intra-articularly with MIA and the development of weight bearing asymmetry was followed for 21 days as compared to vehicle-injected animals. In addition, IPFPs were removed from both ipsilateral and contralateral joints. Both inflammatory infiltrate and histopathological changes were analysed.

RESULTS

MIA injection caused marked weight bearing asymmetry. Ipsilateral IPFP wet weights were significantly increased on days 1 and 3 in MIA-treated animals. MIA treatment also resulted in significant increases in IPFP total white blood cells and monocytes on days 1, 3, and 7 and neutrophils on days 1 and 3. This was supported by histopathological findings at early time points which progressed to adipocyte necrosis, IPFP fibrosis, patellar cartilage and subchondral bone necrosis with synovial hyperplasia at later timepoints.

CONCLUSIONS

The current study clearly demonstrated that marked inflammatory changes in the IPFP occur during the early stage of the MIA model of OA which may contribute to the pain observed at this early stage. The role of the IPFP in later stages of the model needs to be further explored.

The identification of differentially expressed microRNA in osteoarthritic tissue that modulate the production of TNF-alpha and MMP13

OBJECTIVE

To identify differentially expressed microRNAs (miRNAs) in human osteoarthritic (OA) cartilage and bone tissue and to determine their relevance to chondrocyte function.

METHODS

Cartilage and bone was obtained from OA patients who underwent total knee joint replacement surgery or from post-mortem patients with no previous history of OA. MiRNA expression was quantified by real-time PCR (RT-PCR). Functional pathway analysis of miRNA was performed using Ingenuity Pathway Analysis. Primary chondrocytes were isolated by collagenase digestion and transfected with miRNA mimics and miRNA inhibitors using cationic lipid. Tumour Necrosis Factor-alpha (TNF-alpha) and Matrix metalloprotease 13 (MMP13) protein levels were measured by Enzyme-Linked ImmunoSorbent Assay (ELISA).

RESULTS

In total we identified 17 miRNA that showed greater than 4-fold differential expression between OA and normal cartilage, and 30 miRNA that showed greater than 4-fold differential expression in OA bone. Functional pathway analysis of the predicted gene targets for miR-9, miR-98, which were upregulated in both OA bone and cartilage tissue, and miR-146, which was downregulated in OA cartilage, suggested that these miRNA mediate inflammatory functions and pathways. Over-expression of miR-9, miR-98 or miR-146 in isolated human chondrocytes reduced interleukin-1 beta (IL-1 beta) induced TNF-alpha production. Furthermore, inhibition and over-expression of miR-9 modulated MMP13 secretion.

CONCLUSIONS

We have identified a number of differentially expressed miRNAs in late-stage human OA cartilage and bone. Functional analysis of miR-9, miR-98 and miR-146 in primary chondrocytes suggests a role in mediating the IL-1 beta induced production of TNF-alpha. MiR-9, upregulated in OA tissue, was found to inhibit secretion of the collagen type II-targeting metalloproteinase MMP13 in isolated human chondrocytes.

Immune and inflammatory responses to stroke: good or bad?

Inflammatory and immune responses play important roles following ischaemic stroke. Inflammatory responses contribute to damage and also contribute to repair. Injury to tissue triggers an immune response. This is initiated through activation of the innate immune system. In stroke there is microglial activation. This is followed by an influx of lymphocytes and macrophages into the brain, triggered by production of pro-inflammatory cytokines. This inflammatory response contributes to further tissue injury. There is also a systemic immune response to stroke, and there is a degree of immunosuppression that may contribute to the stroke patient's risk of infection. This immunosuppressive response may also be protective, with regulatory lymphocytes producing cytokines and growth factors that are neuroprotective. The specific targets of the immune response after stroke are not known, and the details of the immune and inflammatory responses are only partly understood. The role of inflammation and immune responses after stroke is twofold. The immune system may contribute to damage after stroke, but may also contribute to repair processes. The possibility that some of the immune response after stroke may be neuroprotective is exciting and suggests that deliberate enhancement of these responses may be a therapeutic option.

Natural history of blood glucose within the first 48 hours after ischemic stroke

BACKGROUND

Despite suggestions that glucose levels rise after stroke before falling within a few hours, the natural history and determinants of this phenomenon remain unclear. We aimed to better characterize the time course of changes in glucose levels after ischemic stroke and to identify factors that affect poststroke glycemia.

METHODS

Patients with ischemic stroke without previously diagnosed diabetes had blood glucose measured at least 4-hourly until 48 hours poststroke. The relationship between baseline factors, such as the NIH Stroke Scale, and blood glucose was assessed with mixed-effects models. The behavior of glucose over time was modeled in the whole cohort, and for the cohort partitioned into two around an admission glucose of 6.0 mmol/L.

RESULTS

In the cohort of 124 patients the mean glucose was 6.6 mmol/L throughout the period of monitoring, with no change over time. Mixed-effects models identified more severe stroke and glucose-lowering therapy to be associated with higher poststroke glucose levels. When the cohort was partitioned, the mean glucose of those below 6.0 mmol/L at admission increased and the mean glucose of those above 6.0 mmol/L at admission decreased to the overall mean.

CONCLUSIONS

Mean glucose levels remain static in patients with ischemic stroke without diabetes until at least 48 hours poststroke. Serial glucose levels are higher in patients with more severe stroke. Initially high or low mean glucose recordings exhibit regression to the mean over time, a change which may merely be a statistical phenomenon without necessarily indicating resolution of abnormal glycemia.

Extensive hemispheric cerebral infarction

BACKGROUND AND PURPOSE

Patients with extensive hemispheric cerebral infarction have a high incidence of mortality and serious morbidity. Because of their poor prognosis, they warrant attention; however, in acute stroke therapy trials they do not appear to benefit from treatment. We sought to determine the clinical features, pathophysiological mechanisms, and outcome in a series of cases with radiologically defined extensive hemispheric infarction.

METHODS

Cases of extensive hemispheric infarction were ascretained retrospectively from stroke admissions during a 5-year period. Extensive hemispheric infarction was defined radiologically as infarction involving greater than 75% of the middle cerebral artery territory, with or without involvement of the adjacent anterior or posterior cerebral artery territories. Clinical, risk factor, and stroke mechanism data were compared with that of a control group of ischemic stroke patients admitted during the same period.

RESULTS

Extensive hemispheric infarction occurred in 53 of 1,440 cases of ischemic stroke (3.7%). Infarction involved the middle cerebral artery territory alone in 79% of cases, and the adjacent anterior or posterior cerebral artery territories as well as 21% of cases. A cardioembolic mechanism was likely in 58% of cases; 42% had atrial fibrillation. When compared with the control group, a cardioembolic mechanism was the only feature more frequently associated with extensive hemispheric infarction. The overall in-hospital mortality rate was 52%; 84% of those discharged from hospital required nursing home care because of severe disability.

CONCLUSION

Although uncommon, extensive hemispheric infarction is an important stroke subtype with dramatic and easily recognizable presenting clinical features, frequent cardio-embolic mechanism, an extremely poor outcome, and failure to benefit from most experimental acute stroke therapies.

Structural pathology in a rodent model of osteoarthritis is associated with neuropathic pain: increased expression of ATF-3 and pharmacological characterisation

Intra-articular injection of mono-iodoacetate (MIA) in the rat knee joint induces a histopathology with similarities to osteoarthritis (OA). Typically, a synovitis (days 1-3) is observed followed by thinning of articular cartilage and subsequent lesion of subchondral bone at days 8-14 onwards. Behaviourally, weight-bearing asymmetry is observed, which is sensitive to anti-inflammatory pharmacology at early but not later (days 14+) time points. As subchondral bone is densely innervated, an intriguing possibility is that focal bone pathology may cause neuropathy in this model. In male Wistar rats, activating transcription factor (ATF)-3-immunofluorescence was used as a marker of nerve injury in lumber (L)4 and L5 dorsal root ganglia of the ipsilateral knee. Significantly increased ATF-3-immunoreactivity following MIA treatment was measured in L5 on days 8 and 14 (P<0.05, Kruskal-Wallis and Mann-Whitney U-test), compared to saline controls. Furthermore, in an additional study animals were orally dosed vehicle (5 ml/kg), naproxen (0.3-10 mg/kg), celecoxib (1-10 mg/kg), amitriptyline (3-30 mg/kg) and gabapentin (10-100mg/kg) and evaluated for weight-bearing asymmetry on days 14, 21 and 28 post-MIA. Significant resolution of weight-bearing was observed at high and intermediate doses of amitriptyline and gabapentin at all time points (P<0.05, ANOVA, post-hoc Bonferroni's, vs pre-dose measurements). Transient and weak effects were observed with naproxen (10mg/kg) on days 14 and 28, whereas celecoxib showed no significant effects. Collectively, these data suggest that this putative model of OA is associated with an early phase neuropathy in the L5 innervation territory of the knee.

Arthritis and pain. Future targets to control osteoarthritis pain

Clinical presentation of osteoarthritis (OA) is dominated by pain during joint use and at rest. OA pain is caused by aberrant functioning of a pathologically altered nervous system with key mechanistic drivers from peripheral nerves and central pain pathways. This review focuses on symptomatic pain therapy exemplified by molecular targets that alter sensitization and hyperexcitability of the nervous system, for example, opioids and cannabinoids. We highlight opportunities for targeting inflammatory mediators and their key receptors (for example, prostanoids, kinins, cytokines and chemokines), ion channels (for example, NaV1.8, NaV1.7 and CaV2.2) and neurotrophins (for example, nerve growth factor), noting evidence that relates to their participation in OA etiology and treatment. Future neurological treatments of pain appear optimistic but will require the systematic evaluation of emerging opportunities.

Effects of care pathways on stroke care practices at regional hospitals

BACKGROUND

Our previous work identified deficiencies in stroke care practices at regional hospitals in comparison to standards suggested by published stroke care guidelines. These deficiencies might be improved by the implementation of clinical pathways. The aim of this study was to assess changes in acute stroke care practices following the implementation of stroke care pathways at four regional Queensland hospitals.

METHODS

The medical records of two cohorts of 120 patients with a discharge diagnosis of stroke or transient ischaemic attack were retrospectively audited before and after implementation of stroke care pathways to identify differences in the use of acute interventions, investigations and secondary prevention strategies.

RESULTS

Following pathway implementation there were clinically important, but not statistically significant, increases in the rates of swallow assessment, allied health assessment (significant for occupational therapy, P = 0.04) and use of deep vein thrombosis prevention strategies (also significant, P = 0.006). Fewer patients were discharged on no anti-thrombotic therapy (statistically significant in the subgroup of patients with atrial fibrillation, P = 0.02). Only 37% of the patients audited were actually enrolled on the pathway. Among this subgroup there were significant increases in the rates of swallow assessment (first 24 h, P = 0.01; any time during admission, P = 0.0001), allied health assessments (all P < 0.05), estimation of blood glucose level (P = 0.0015) and the use of deep vein thrombosis prevention strategies (P = 0.0003).

CONCLUSION

Stroke care pathways appear to improve the process of care. Whether this influences outcomes such as mortality, functional and neurological recovery, the incidence of complications, length of stay or the cost of care was beyond the scope of this study and will require further examination.

Differences in stroke care practices between regional and metropolitan hospitals

BACKGROUND

A recent audit of stroke care in major Australian metropolitan teaching hospitals showed considerable variation in care practices and uptake of evidence-based therapies. We could find no published data on stroke care practices in regional Australia.

AIM

To compare acute stroke care practices at four regional hospitals with a metropolitan teaching hospital with a stroke unit.

METHODS

The hospital medical records of 30 consecutive patients at each hospital (total 150 patients), with a discharge diagnosis of stroke, were retrospectively audited to identify differences in stroke care practices, including the use of investigations, acute interventions, and secondary prevention strategies, between the regional and metropolitan, and between smaller (less than 150 stroke admissions annually) and larger (more than 250 admissions annually) hospitals.

RESULTS

Patients treated at regional or smaller hospitals were less likely to have a computed tomography head scan within 24 h of admission, carotid duplex, echocardiography, estimations of lipids and glucose, a swallow assessment, involvement of allied health professionals or be prescribed prophylaxis against deep vein thrombosis, compared to patients treated at metropolitan or larger hospitals.

CONCLUSIONS

Significant differences in stroke care practices exist between regional/smaller and metropolitan/larger hospitals. Strategies designed to minimize variation in care practices, such as evidence-based care pathways, should be explored.

Connectionism, parallel constraint satisfaction processes, and gestalt principles: (re) introducing cognitive dynamics to social psychology

We argue that recent work in connectionist modeling, in particular the parallel constraint satisfaction processes that are central to many of these models, has great importance for understanding issues of both historical and current concern for social psychologists. We first provide a brief description of connectionist modeling, with particular emphasis on parallel constraint satisfaction processes. Second, we examine the tremendous similarities between parallel constraint satisfaction processes and the Gestalt principles that were the foundation for much of modem social psychology. We propose that parallel constraint satisfaction processes provide a computational implementation of the principles of Gestalt psychology that were central to the work of such seminal social psychologists as Asch, Festinger, Heider, and Lewin. Third, we then describe how parallel constraint satisfaction processes have been applied to three areas that were key to the beginnings of modern social psychology and remain central today: impression formation and causal reasoning, cognitive consistency (balance and cognitive dissonance), and goal-directed behavior. We conclude by discussing implications of parallel constraint satisfaction principles for a number of broader issues in social psychology, such as the dynamics of social thought and the integration of social information within the narrow time frame of social interaction.

Introduction to stroke genomics

Translation of the explosion in knowledge of acute ischemic stroke into satisfactory treatment regimens has yet to happen. At present tPA, intra-arterial prourokinase and low-molecular-weight heparin form the vanguard for therapeutic intervention, yet these treatments have a limited therapeutic window. Part of this expansion in understanding has been driven by the contribution of stroke genetics and genomics. However, despite the enormous preclinical and clinical information of receptors, enzymes, second messenger systems, and so forth, that are implicated in stroke pathophysiology, delivery of novel drug treatment has been slow. This introductory chapter discusses the multiple sources of clinical and preclinical genetic information. It will describe the importance of integrating expression information into multiple preclinical models with temporal and spatial roles in lesion pathology and, furthermore developing an understanding of function in the clinic before claiming a role in ischemic stroke. The goal of such a holistic integration of information is to increase the yield from current datasets of gene expression and ultimately to help expand the choice of treatment available to the physician and patient.

Posterior leukoencephalopathy following intrathecal chemotherapy with MRA-documented vasospasm

Posterior leukoencephalopathy syndromes have been reported with hypertension, and immunosuppressive and chemotherapy agents. Cerebral vasospasm on MR angiography (MRA) has been noted in cases due to eclampsia. The authors report a case of Balint syndrome with irreversible posterior leukoencephalopathy on MRI following intrathecal methotrexate and cytarabine. Hypertension was not present. Diffuse, reversible arterial irregularities consistent with vasospasm were present on MRA during the acute illness.

Programmable microchip monitoring of post-stroke pyrexia: effects of aspirin and paracetamol on temperature and infarct size in the rat

BACKGROUND

Recent studies have demonstrated spontaneous and prolonged hyperthermia following stroke in both humans and rodents. However, a full characterization of these pyretic changes and the effects of anti-pyretic drugs on outcome is not available.

METHODS

The aims of this study were to monitor conscious body temperature (n=10 per group) using programmable microchips for up to 24 h in rats following either permanent (p) or 90 min transient (t) middle cerebral artery occlusion (MCAO) or sham surgery, and to evaluate the relationship to hypothalamic damage. Also, the effects of anti-pyretic drug therapy on body temperature and infarct volume were evaluated in animals treated with vehicle, optimal doses of either aspirin or paracetamol (250 mg/kg i.p.) following pMCAO (n=10 per group).

RESULTS

At 1 h, body temperature significantly (P<0.01) increased to 38.6+/-0.2 degrees C following tMCAO and 38.9+/-0.1 degrees C following pMCAO compared with sham-operated animals (37.1+/-0.1 degrees C). Sustained hyperthermia (> or =38.1 degrees C) was observed for up to 24 h following pMCAO but approached baseline within 30 min (37.6+/-0.2 degrees C) following tMCAO with reperfusion. The post-stroke pyrexia was related to the degree of ischemia where hypothalamic damage was observed in (80%) of the animals undergoing pMCAO and (0%) in the tMCAO group (P<0.05). Treatment with paracetamol (250 mg/kg i.p.) significantly attenuated (P<0.05) but did not normalize core body temperature up to 2 h (38.2+/-0.4 degrees C) compared with vehicle treated animals (39.3+/-0.1 degrees C). Aspirin had no effect on temperature under these conditions. Hypothalamic damage and lesion volume were not different between animals treated with paracetamol (253.3+/-8.5 mm(3)), aspirin (264.0+/-11.6 mm(3)) or vehicle (274.4+/-8.2 mm(3)).

CONCLUSIONS

This study is the first to demonstrate the utility of programmable microchips to monitor serial changes in post-stroke hyperthermia. The sustained post-stroke pyrexia and negative effects of antipyretic treatment may be attributed to the extensive hypothalamic injury suggesting that better pharmacologic approaches to reduce body temperature should be identified and evaluated for brain protection in severe experimental stroke.

Characterisation of gene expression changes following permanent MCAO in the rat using subtractive hybridisation

Failure of several putative neuroprotectants in large multicentred clinical trials has re-focussed attention on the predictability of pre-clinical animal models of stroke. Model characterisation and relationship to heterogeneous patient sub-groups remains of paramount importance. Information gained from magnetic resonance imaging (MRI) signatures indicates that the Zea Longa model of rat middle cerebral artery occlusion may be more representative of slowly evolving infarcts. Understanding the molecular changes over several hours following cerebral ischaemia will allow detailed characterisation of the adaptive response to brain injury. Using a fully characterised model of Zea Longa middle cerebral artery occlusion we have used the representational difference analysis (RDA) subtractive hybridisation method to identify transcripts that accumulate in the ischaemic cortex. Along with a number of established ischaemia-induced gene products (including MCP-1, TIMP-1, hsp 70) we were also able to identify nine genes which have not previously been shown to accumulate following focal ischaemia (including SOCS-3, GADD45gamma, Xin).

LightCycler multiplex PCR for the laboratory diagnosis of common viral infections of the central nervous system

A conventional multiplex PCR assay that detects herpes simplex virus type 1 (HSV-1), HSV-2, varicella-zoster virus, and enteroviruses for the diagnosis of central nervous system infections was modified to be performed using the LightCycler system. The sensitivity of detection of each of the viruses using the LightCycler assay was compared to that of the conventional assay using external quality assessment material. The assays had equivalent sensitivities, but the LightCycler assay was more rapid, reduced the risk of contamination, and used an amplicon detection format that demonstrated greater discrimination than a gel electrophoresis method.

Stroke genomics: approaches to identify, validate, and understand ischemic stroke gene expression

Sequencing of the human genome is nearing completion and biologists, molecular biologists, and bioinformatics specialists have teamed up to develop global genomic technologies to help decipher the complex nature of pathophysiologic gene function. This review will focus on differential gene expression in ischemic stroke. It will discuss inheritance in the broader stroke population, how experimental models of spontaneous stroke might be applied to humans to identify chromosomal loci of increased risk and ischemic sensitivity, and also how the gene expression induced by stroke is related to the poststroke processes of brain injury, repair, and recovery. In addition, we discuss and summarise the literature of experimental stroke genomics and compare several approaches of differential gene expression analyzes. These include a comparison of representational difference analysis we have provided using an experimental stroke model that is representative of stroke evolution observed most often in man, and a summary of available data on stroke differential gene expression. Issues regarding validation of potential genes as stroke targets, the verification of message translation to protein products, the relevance of the expression of neuroprotective and neurodestructive genes and their specific timings, and the emerging problems of handling novel genes that may be discovered during differential gene expression analyses will also be addressed.

Prediction of the final infarct volume within 6 h of stroke using single photon emission computed tomography with technetium-99m hexamethylpropylene amine oxime

BACKGROUND

A simple method to predict the final infarct volume within 6 h of onset of hemispheric ischemic stroke based on the measurement of cerebral blood flow (CBF) using single photon emission computed tomography (SPECT) with techneticum-99m hexamethylpropylene amine oxime ((99m)Tc-HMPAO) was investigated in a clinical model involving patients without definite early reperfusion or clinical recovery.

METHODS

A group of 16 patients (group 1) was used to establish the methodology, which was then validated in a second group of 14 patients (group 2). The final infarct volume was defined using computed tomography (CT) performed at least 7 days after stroke. The relative CBF threshold value, expressed as a percentage of the mean contralateral hemispheric value, which most closely estimated the final infarct size on coregistered CT was established for each patient.

RESULTS

The mean threshold CBF value for group 1 was 63.7%. When this value was used to predict infarct size in group 2, a close correlation was observed between the actual and the estimated sizes (r = 0.973, p < 0.0001). This value was not time dependent.

CONCLUSIONS

If no significant early reperfusion or clinical recovery occurs, a CBF threshold value of 63.7% on (99m)Tc-HMPAO SPECT performed within 6 h of stroke onset will reliably predict the final infarct size.

Recovery efficiences on nucleic acid extraction kits as measured by quantitative LightCycler PCR

AIMS

To compare the efficiency of five nucleic acid extraction kits for processing clinical material for the diagnosis of infection.

METHODS

Five nucleic acid extraction kits for processing clinical material for the diagnosis of infection were compared for their relative efficiencies in purifying and recovering either viral DNA or RNA from serum samples. Quantitative polymerase chain reaction (PCR) assays for hepatitis B virus (HBV) DNA and hepatitis C virus (HCV) RNA were performed on the Light-Cycler instrument to determine the relative concentrations of the viral nucleic acids recovered by the various protocols.

RESULTS

Large differences between kits in recovery efficiencies were observed for HBV DNA, with those protocols using enzyme digestion in addition to chaotropic solutions performing better than those using chemical disruption alone.

CONCLUSIONS

There were large differences between the kits and it appeared that those extraction kits containing a proteolytic enzyme and carrier nucleic acid (and that are supplied RNase free) have the widest potential application in the routine microbiology laboratory.

Cortical spreading depression produces increased cGMP levels in cortex and brain stem that is inhibited by tonabersat (SB-220453) but not sumatriptan

Migraine headache is proposed to be mediated by nitric oxide (NO). Suitable mechanisms for eliciting increases in brain NO concentration in migraineurs have not yet been identified, although, animal models highlight cortical spreading depression (CSD) as a potential candidate. These studies have focused on CSD-associated NO release at highly acute time points (min-hours) and have not employed markers of NO metabolism with direct clinical application e.g. cGMP. The current study evaluated changes in plasma cGMP concentrations 3 h, 24 h and 3 days post-CSD and compared these to cortical and brainstem cGMP concentrations at 3 days. Moreover, this study also examined the effect of sumatriptan, a clinically effective antimigraine agent, and tonabersat (SB-220453) a potential novel antimigraine agent, on any observed changes in cGMP. Following pre-treatment with vehicle (n=3), sumatriptan (300 microg kg(-1) i.v, n=3) or tonabersat (SB-220453 10 mg kg(-1) i.p., n=3), CSD was evoked in anaesthetised rats by a 6-min KCl application to the parietal cortex. In the vehicle-treated group a median of eight depolarisations, were observed. Sumatriptan had no effect on the number of depolarisations, whereas tonabersat significantly reduced the number of events (median=2). No depolarisation events were observed throughout the recording period in the sham group. Following KCl application plasma cGMP concentrations were reduced up to 24 h post-CSD, but not significantly different from sham animals at 3 days. CSD in vehicle-treated animals produced a highly significant elevation in cGMP concentration in the brain stem 3 days after application of KCl. cGMP concentration increased 2.3-fold from 68+/-8 fmol/mg in sham animals (n=3) to 158+/-28 fmol/mg in the vehicle group. This increase in brain stem cGMP was abolished by tonabersat pre-treatment but not by sumatriptan.

The fate of hypoxic tissue on 18F-fluoromisonidazole positron emission tomography after ischemic stroke

We studied 24 patients up to 51 hours after ischemic stroke using 18F-fluoromisonidazole positron emission tomography to determine the fate of hypoxic tissue likely to represent the ischemic penumbra. Areas of hypoxic tissue were detected on positron emission tomography in 15 patients, and computed tomography was available in 12 patients, allowing comparison with the infarct volume to determine the proportions of the hypoxic tissue volume that infarcted and survived. The proportion of patients with hypoxic tissue and the amount of hypoxic tissue detected declined with time. On average, 45% of the total hypoxic tissue volume survived and 55% infarcted. Up to 68% (mean, 17.5%) of the infarct volume was initially hypoxic. Most of the tissue "initially affected" proceeded to infarction. We correlated hypoxic tissue volumes with neurological and functional outcome assessed using the National Institutes of Health Stroke Scale, Barthel Index, and Rankin Score. Initial stroke severity correlated significantly with the "initially affected" volume, neurological deterioration during the first week after stroke with the proportion of the "initially affected" volume that infarcted, and functional outcome with the infarct volume. Significant reductions in the size of the infarct and improved clinical outcomes might be achieved if hypoxic tissue can be rescued.

Sumatriptan modifies cortical free radical release during cortical spreading depression. A novel antimigraine action for sumatriptan?

Increases in concentration of brain NO are proposed to initiate and mediate migraine headache. Triggered by focal depolarisation, spreading depression (SD) represents a suitable mechanism for eliciting widespread release of nitric oxide. The current study examines the effect of sumatriptan, a 5-HT(1B/1D) agonist and effective antimigraine therapy, on free radical release (nitric oxide and superoxide) in SD in the simple and complex cortices of the rat and cat. Following initiation of SD, sumatriptan pretreatment (300 microg kg(-1) i.v., 15 min prior to SD) modulated all phases of nitric oxide release associated with each SD in both cats and rats. As a result, superoxide levels were observed to significantly (ANOVA, post hoc LSD) increase versus vehicle treated animals (saline 1 ml kg(-1) i.v. 15 min prior to SD) during specific phases of each SD depolarisation. Averaged over all SD depolarisations, mean peak SD nitric oxide levels per depolarisation were 0.73+/-0.23 microM (n=29) in cats, and 0.42+/-0.09 microM (n=34) in rats. Sumatriptan significantly (Students t-test, P<0.05, two tailed hypothesis, P<0.05) modulated this increase in cortical nitric oxide concentrations to 0.32+/-0.06 microM (n=25) and 0. 22+/-0.07 microM (n=37) in cats and rats. Sumatriptan appears to decrease the amplitude of nitric oxide release but enhances extracellular superoxide concentrations in both lissencephalic and gyrencephalic cortices during SD.

Repetitive cortical spreading depression in a gyrencephalic feline brain: inhibition by the novel benzoylamino-benzopyran SB-220453

Transient cortical depolarization is implicated in the pathology of migraine. SB-220453 is a potent anti-convulsant which inhibits neurogenic inflammation and cortical spreading depression (SD)-evoked nitric oxide release via a novel but unknown mechanism. This study further investigates the effects of SB-220453 on generation and propagation of repetitive SD in the anaesthetized cat. Vehicle or SB-220453 1, 3 or 10 mg/kg was administered intraperitoneally 90 min prior to induction of SD in the suprasylvian gyrus (SG). Changes in d.c. potential were recorded in the SG and the adjacent marginal gyrus (MG). In vehicle-treated animals (n = 7), a brief exposure (6 min) to KCl induced a median (25-75% range) number of five (four to six) and three (two to four) depolarizations over a duration of 55 min (32-59 min) and 51 min (34-58 min) in the SG and MG, respectively. SB-220453 produced dose-related inhibition of the number of events and period of repetitive SD activity. SB-220453 also reduced SD-induced repetitive pial vasodilatation but had no effect on resting haemodynamics. However, when SD events were observed in the presence of SB-220453, it had no effect on metabolic coupling. These results show that SB-220453 produces marked inhibition of repetitive SD in the anaesthetized cat. SB-220453 may therefore have therapeutic potential in treatment of SD-like activity in migraine.

The use of TaqMan RT-PCR assays for semiquantitative analysis of gene expression in CNS tissues and disease models

TaqMan reverse transcription polymerase chain reaction (RT-PCR) is a recently developed technique which allows the measurement of an accumulating PCR product in real time. In the present study we have validated the use of TaqMan RT-PCR for mRNA localisation studies in human and rat tissues, and for the investigation of gene expression changes in CNS animal models. In human brain, D(2) receptor mRNA was enriched in caudate nucleus and putamen, whilst in rat brain, highest levels of D(2) receptor mRNA expression were observed in striatum and nucleus accumbens, consistent with the known distribution of this receptor in basal ganglia. In a rat model of permanent middle cerebral artery occlusion (pMCAO), endogenous interleukin-1 receptor antagonist (IL-1ra) mRNA was upregulated over 30-fold at 24 h post-lesion in both striatum and cortex ipsilateral to artery occlusion. Brain-derived neurotrophic factor (BDNF) mRNA was transiently upregulated 3.7-fold at 3 h, but not at 24 h or 3 days after induction of cortical spreading depression (CSD) in rats. Our observations in these two animal models using TaqMan RT-PCR were consistent with previous reports using other techniques. In conclusion, TaqMan RT-PCR assays provide a rapid and reliable method for semi-quantitative analysis of gene expression in the nervous system.

SB-220453, a potential novel antimigraine agent, inhibits nitric oxide release following induction of cortical spreading depression in the anaesthetized cat

Profound nitric oxide release associated with cortical spreading depression (SD), has been implicated in stroke, traumatic brain injury and migraine pathophysiology. SB-220453 represents a mechanistically novel, well-tolerated class of compounds which may have therapeutic potential in the treatment of conditions associated with neuronal hyperexcitability and inflammation. The aim of the present study was to investigate the effects of SB-220453 on the nitric oxide (NO) release associated with SD in the anaesthetized cat. In vehicle treated animals, KCl application for 6 min to the cortical suface produced repeated changes in extracellular direct current field potential with associated NO release. This activity was sustained for a median duration of 55 min (25-75% range, 32-59 min) and 59 min (25-75% range, 34-59 min), respectively. SB-220453 (1, 3 and 10 mg/kg i.p.) produced a dose-related inhibition of this activity and at the highest dose tested, the median duration of changes in extracellular field potential and NO release were reduced to 4 min (25-75% range, 4-5 min) and 5 min (25-75% range, 5-5 min), respectively. No effect was observed on basal systemic haemodynamic parameters or resting cerebral laser Doppler blood flux at any of the doses of SB-220453 tested. SB-220453 therefore represents a novel compound to assess the potential benefit of inhibiting SD associated nitric oxide release in neurological disease.

No evidence of hypoxic tissue on 18F-fluoromisonidazole PET after intracerebral hemorrhage

We studied six patients after intracerebral hemorrhage (ICH) and eight controls using positron emission tomography (PET) with to determine whether a zone of tissue hypoxia, possibly representing "penumbral" tissue, exists surrounding an intracerebral hemorrhage. None of the stroke patients, studied 24 to 43 hours after symptom onset, nor any of the controls exhibited areas of tissue hypoxia on 18F-fluoromisonidazole PET images. These findings may have implications for the treatment of intracerebral hemorrhage with neuroprotective strategies.

Effects of sumatriptan on nitric oxide and superoxide balance during glyceryl trinitrate infusion in the rat. Implications for antimigraine mechanisms

Infusion of glyceryl trinitrate (GTN) into patients with migraine precipitates the onset of a migraine attack several hours after completion of the infusion. Using an infusion of GTN into anaesthetised rats, this study investigates the relationship of regional cerebral blood flux rCBF(ldf), cortical nitric oxide (NO) and cortical superoxide concentrations and the effect of sumatriptan on each variable. In saline treated animals, a 30 min infusion of GTN (2 microgram kg(-1) min(-1), i.v.) was found to markedly increase cortical rCBF(ldf) (133+/-3% of baseline) and NO concentrations (141+/-13% of baseline). Superoxide levels exhibited an inverse relationship to NO levels, decreasing below basal to 48+/-14% of baseline. It is hypothesised that high NO levels during GTN infusion may decrease the detectable superoxide due to "leeching" of the superoxide into low level peroxynitrite formation. In the presence of sumatriptan, a decrease below baseline in cortical rCBF(ldf) (82+/-5% of baseline) and NO concentration (64+/-13% of baseline) was observed throughout GTN infusion, although superoxide levels significantly increased above baseline by 105+/-14 nM (p<0.05, ANOVA post hoc LSD test). The mechanism for this action of sumatriptan is unknown but may include; modulation of cell redox state, NO scavenging or direct manipulation of superoxide release.

Plasticizers increase adhesion of the deteriogenic fungus Aureobasidium pullulans to polyvinyl chloride

Initial adhesion of fungi to plasticized polyvinyl chloride (pPVC) may determine subsequent colonization and biodeterioration processes. The deteriogenic fungus Aureobasidium pullulans was used to investigate the physicochemical nature of adhesion to both unplasticized PVC (uPVC) and pPVC containing the plasticizers dioctyl phthalate (DOP) and dioctyl adipate (DOA). A quantitative adhesion assay using image analysis identified fundamental differences in the mechanism of adhesion of A. pullulans blastospores to these substrata. Adhesion to pPVC was greater than that to uPVC by a maximum of 280% after a 4-h incubation with 10(8) blastospores ml(-1). That plasticizers enhance adhesion to PVC was confirmed by incorporating a dispersion of both DOA and DOP into the blastospore suspension. Adhesion to uPVC was increased by up to 308% in the presence of the dispersed plasticizers. Hydrophobic interactions were found to dominate adhesion to uPVC because (i) a strong positive correlation was observed between substratum hydrophobicity (measured by using a dynamic contact angle analyzer) and adhesion to a range of unplasticized polymers including uPVC, and (ii) neither the pH nor the electrolyte concentration of the suspension buffer, both of which influence electrostatic interactions, affected adhesion to uPVC. In contrast, adhesion to pPVC is principally controlled by electrostatic interactions. Enhanced adhesion to pPVC occurred despite a relative reduction of 13 degrees in the water contact angle of pPVC compared to that of uPVC. Furthermore, adhesion to pPVC was strongly dependent on both the pH and electrolyte concentration of the suspension medium, reaching maximum levels at pH 8 and with an electrolyte concentration of 10 mM NaCl. Plasticization with DOP and DOA therefore increases adhesion of A. pullulans blastospores to pPVC through an interaction mediated by electrostatic forces.

Laboratory diagnosis of common viral infections of the central nervous system by using a single multiplex PCR screening assay

A multiplex PCR assay that detects the four commonest causes of viral meningitis and encephalitis in the United Kingdom (herpes simplex virus [HSV] type 1 [HSV-1], HSV type 2 [HSV-2], varicella-zoster virus [VZV], and enteroviruses) was developed, and its sensitivity was compared with those of similar assays described previously for this application. Compared to the previous assays, this single multiplex PCR assay had higher molecular sensitivities for the detection for each of the viruses and improved utility for routine use in a diagnostic laboratory. The assay was used to test a series of 1,683 consecutive cerebrospinal fluid (CSF) samples between June 1997 and March 1998 inclusively. Viral nucleic acid was detected in 138 (8.2%) of the CSF samples, including enteroviruses in 51 samples, HSV-2 in 33 samples, VZV in 28 samples, and HSV-1 in 25 samples. Compared to the accepted relative incidence of viral etiologies, aseptic meningitis due to HSV-2 infection was high, and in adult female patients with symptoms of aseptic meningitis, HSV-2 was the virus most commonly detected in the CSF.

Identification of (-)-cis-6-acetyl-4S-(3-chloro-4-fluoro-benzoylamino)- 3,4-dihydro-2,2-dimethyl-2H-benzo[b]pyran-3S-ol as a potential antimigraine agent

Optimisation of novel cis- and trans-4-(substituted-amido)benzopyran-3-ol derivatives has led to the identification of SB-220453 20 with an in vivo pre-clinical CNS profile predictive of potential antimigraine activity.

Limiting neurological damage after stroke: a review of pharmacological treatment options

Acute ischaemic stroke is a leading cause of death and a major cause of long term disability worldwide. Effective treatments for limiting the neurological damage after stroke have proven elusive. An improved understanding of the complicated cascade of cellular events following the onset of cerebral ischaemia has led to exploration of a number of avenues for early intervention. Reperfusion of the ischaemic territory using thrombolytic drugs has shown promise in clinical trials as a method for achieving tissue salvage. Antithrombotic and antiplatelet agents have not demonstrated efficacy as acute therapies, although the early use of aspirin (acetylsalicylic acid) appears to produce a reduction in early stroke recurrence. A wide variety of drugs which interfere at various points in the ischaemic cascade, so-called 'neuroprotective agents', have also been studied, but with mixed success. Of these, antagonists of voltage-gated calcium channels, antagonists at the N-methyl-D-aspartate (NMDA) receptor and scavengers of free radicals have been most extensively studied. Despite proving effective in animal models of cerebral ischaemia, these drugs have largely failed to fulfil their promise in clinical trials. While individual compounds have proven ineffective, combinations of drugs with different mechanisms of action may yet provide the best treatment for acute ischaemic stroke.

Identifying hypoxic tissue after acute ischemic stroke using PET and 18F-fluoromisonidazole

OBJECTIVE

To show that PET with 18F-fluoromisonidazole (18F-FMISO) can detect peri-infarct hypoxic tissue in patients after ischemic stroke.

BACKGROUND

PET with (15)O-labeled oxygen and water is the only established method for identifying the ischemic penumbra in humans. We used PET with 18F-FMISO in patients after ischemic stroke to identify hypoxic but viable peri-infarct tissue likely to represent the ischemic penumbra, and to determine how long hypoxic tissues persist after stroke.

METHODS

Patients with acute hemispheric ischemic stroke were studied using PET with 18F-FMISO either within 48 hours or 6 to 11 days after stroke onset. The final infarct was defined by CT performed 6 to 11 days after stroke. Tracer uptake was assessed objectively by calculating the mean activity in the contralateral (normal) hemisphere, then identifying pixels with activity greater than 3 SDs above the mean in both hemispheres. Positive studies were those with high-activity pixels ipsilateral to the infarct.

RESULTS

Fifteen patients were studied; 13 within 48 hours of stroke, 8 at 6 to 11 days, and 6 during both time periods. Hypoxic tissue was detected in 9 of the 13 patients studied within 48 hours of stroke, generally distributed in the peripheries of the infarct and adjacent peri-infarct tissues. None of the 8 patients studied 6 to 11 days after stroke exhibited increased 18F-FMISO activity. All 6 patients studied both early and late exhibited areas of increased activity during the early but not the late study.

CONCLUSIONS

PET with 18F-FMISO can detect peri-infarct hypoxic tissue after acute ischemic stroke. The distribution of hypoxic tissue suggests that it may represent the ischemic penumbra. Hypoxic tissues do not persist to the subacute phase of stroke (6 to 11 days).

White matter medullary infarcts: acute subcortical infarction in the centrum ovale

Acute infarction confined to the territory of the white matter medullary arteries is a poorly characterised acute stroke subtype. 22 patients with infarction confined to this vascular territory on CT and/or MRI were identified from a series of 1,800 consecutive admissions to our stroke unit (1.2%) between August 1993 and March 1997. 19 patients had small infarcts (< 1.5 cm maximum diameter) and 3 large infarcts (> 1.5 cm). Small infarcts were associated with a history of smoking (69%), hypertension (58%), and hyperlipidaemia (37%), and less frequently with atrial fibrillation (21%). Significant (>50%) ipsilateral carotid stenosis (16%) was a less frequent finding in this group. Patients most commonly presented with weakness and/or sensory disturbance affecting mainly the upper limbs, but dysarthria, dysphasia, and ataxia were also seen. Large infarcts were infrequent in our series, but did not differ significantly from small infarcts with respect to clinical presentation or risk factor profiles (p > 0.05 for all comparisons). The majority of symptomatic patients with white matter medullary infarcts are associated with small (< 1.5 cm diameter) lesions and a risk factor profile consistent with small vessel disease. More data are required to elucidate the mechanism of larger (> 1.5 cm) infarcts. Because of the potential overlap between white matter medullary infarcts and internal watershed infarcts, suggested criteria for each are presented.

Nitric oxide does not mediate cerebral blood flow changes during cortical spreading depression in the anaesthetised rat

To date, the role of nitric oxide (NO) in mediation of cerebrovascular regulation during spreading depression (SD) in rats remains controversial. Studies are compromised by indirect assay of 'regional' nitric oxide synthase activity (NOS) and/or inappropriate doses of antagonists. The present study utilises direct electrochemical detection in the pia to demonstrate a local, biphasic release of NO associated with each wave of cortical depolarisation. The mean peak of SD-induced NO release was 0.35 microM, which was significantly inhibited by L-N(G)-nitroarginine methyl ester (L-NAME) pre-treatment. Changes in cerebrovascular flux remained intact following treatment with L-NAME, indicating little role for NO in mediation of rat SD blood-flux changes. Mean peak NO release was found to be lower than that observed in rat cerebral ischaemia studies (approximately 4 microM) and in SD in the cat gyrencephalic brain (approximately 0.8 microM).

Experience with diffusion-weighted imaging in an acute stroke unit

We performed diffusion-weighted MRI (DWI) on a standard 1.5-tesla MRI scanner using a high-speed stimulated echo pulse sequence (turboSTEAM) in 9 stroke patients and 9 control subjects to investigate whether this technique can be used clinically to assist in ischaemic stroke diagnosis within the time frame for potential therapy. Stroke patients underwent DWI between 3.75 h and 3 days after stroke onset. Three patients were studied on more than one occasion. DWI was normal in the 9 controls. Seven of 9 stroke patients showed areas of increased signal on DWI. DWI detected cerebral ischaemia 3.75 h after stroke onset when both CT and T2-weighted MRI were normal. In 6 DWI-positive patients studied at later times, increased signal on T2-weighted images was present at the same time. Two patients had normal CT, T2-weighted and DWI images; both made good neurological recoveries. For the routine assessment of stroke patients, DWI implemented on a standard MRI system can provide additional information of clinical value to that obtained with conventional pulse sequences. In particular it facilitates early detection of cerebral ischaemia during the first few hours after stroke.

Furosemide inhibits regenerative cortical spreading depression in anaesthetized cats

Ionic perturbations occur during cortical spreading depression (SD), a phenomenon implicated in migraine pathophysiology. We studied the effect of 0.2, 2 and 20 mg kg-1 i.v. (n=4) furosemide on cortical direct current (d.c.) potential, cerebrovascular laser Doppler flux (rCBF[LDF]), artery diameter and NO concentration in the parietal cortex of the anaesthetized cat during repetitive SD. In vehicle-treated animals (n=4), SD activity was sustained for 50+/-1.8 min. However, duration of SD activity was significantly reduced when compared to vehicle to 39+/-6.6 (n=4), 34+/-8.5 (n=4) and 27.3+/-11.3 min (n=4), at 0.2, 2 and 20 mg kg-1 i.v. furosemide respectively. It is hypothesized that the mechanism of inhibition of SD d.c. activity by furosemide may be through alterations in cortical ion buffering capacity or inhibition of cell swelling in neurones or glia. These mechanisms may represent potential novel drug targets in future migraine therapy.

The dynamics of nitric oxide release measured directly and in real time following repeated waves of cortical spreading depression in the anaesthetised cat

Cortical application of crystalline KCl in male cats anaesthetised with alpha-chloralose induced four transient negative deflections in cortical direct current (d.c.) potential. In vehicle treated animals d.c. shifts were associated with a hyperaemia and a multiphasic nitric oxide (NO) release. In these animals, the first negative shift in d.c. potential produced a significantly larger NO electrode current, when compared to subsequent cortical depolarisations. However, regional cerebrovascular laser Doppler flux (rCBF[LDF]) increases were similar for each event. In L-N(G)-nitro-L-arginine (L-NAME; 10 mg/kg i.v. infused over 30 min) treated animals, d.c. shifts were also associated with NO release following a multiphasic waveform and increase in rCBF(LDF), but were significantly attenuated when compared to controls.

Enhanced nitric oxide release during cortical spreading depression following infusion of glyceryl trinitrate in the anaesthetized cat

Intravenous infusion of glyceryl trinitrate (GTN) into migraineurs induces an immediate headache followed by migraine. We studied the effect of GTN (0.25 microgram kg-1 min-1) on local cerebrovascular laser Doppler flux (rCBFLDF), artery diameter and NO concentration (selective NO microelectrode) in the pial middle cerebral artery perfusion territory of the anaesthetized cat, at rest and during cortical spreading depression (SD). GTN infusion induced a significant increase in pial artery diameter, rCBFLDF, and NO concentration. Following termination of infusion, NO concentrations remained significantly elevated above controls for 60 min, other parameters returned to baseline within 10 min (p < 0.05, ANOVA, post hoc Dunnett's multiple comparison procedure). Two hours after termination of infusion KCl-evoked SD was initiated. GTN-treated animals exhibited significantly (p < 0.05, Kruskal-Wallis) elevated SD-induced NO release compared to controls. All other parameters remained unaffected. Our results demonstrate that GTN induces a prolonged increase in local NO concentrations and enhances SD-induced NO release.