Evaluation of arterial spin labeling in the diagnosis and monitoring of myelin oligodendrocyte glycoprotein-associated cerebral cortical encephalitis.

Myelin oligodendrocyte glycoprotein (MOG)-associated disorders are inflammatory demyelinating diseases of the CNS. Cerebral cortical encephalitis (CCE) is characterized by cortical fluid-attenuated inversion recovery hyperintensity with seizures and headaches. We report two cases of MOG antibody-associated CCE (MOG-CCE) evaluated using serial MRI sequences, including arterial spin labeling (ASL), pre- and posttreatment. In both patients, ASL demonstrated hyperperfusion correlating with disease activity, which normalized following steroid therapy. Our cases highlight the usefulness of ASL in early detection, monitoring, and assessment of treatment response in MOG-CCE.

Reciprocal Interaction Between Pericytes and Macrophage in Poststroke Tissue Repair and Functional Recovery.

BACKGROUND AND PURPOSE: Poststroke tissue repair, comprised of macrophage-mediated clearance of myelin debris and pericyte-mediated fibrotic response within the infarct area, is an important process for functional recovery. Herein, we investigated the reciprocal interaction between pericytes and macrophages during poststroke repair and functional recovery. METHODS: We performed a permanent middle cerebral artery occlusion in both wild-type and pericyte-deficient PDGFRß (platelet-derived growth factor receptor ß) heterozygous knockout (Pdgfrb+/-) mice and compared histological changes and neurological functions between the 2 groups. We also examined the effects of conditioned medium harvested from cultured pericytes, or bone marrow-derived macrophages, on the functions of other cell types. RESULTS: Localization of PDGFRß-positive pericytes and F4/80-positive macrophages was temporally and spatially very similar following permanent middle cerebral artery occlusion. Intrainfarct accumulation of macrophages was significantly attenuated in Pdgfrb+/- mice. Intrainfarct pericytes expressed CCL2 (C-C motif ligand 2) and CSF1 (colony stimulating factor 1), both of which were significantly lower in Pdgfrb+/- mice. Cultured pericytes expressed Ccl2 and Csf1, both of which were significantly increased by PDGF-BB and suppressed by a PDGFRß inhibitor. Pericyte conditioned medium significantly enhanced migration and proliferation of bone marrow-derived macrophages. Poststroke clearance of myelin debris was significantly attenuated in Pdgfrb+/- mice. Pericyte conditioned medium promoted phagocytic activity in bone marrow-derived macrophages, also enhancing both STAT3 (signal transducer and activator of transcription 3) phosphorylation and expression of scavenger receptors, Msr1 and Lrp1. Macrophages processing myelin debris produced trophic factors, enhancing PDGFRß signaling in pericytes leading to the production of ECM (extracellular matrix) proteins and oligodendrogenesis. Functional recovery was significantly attenuated in Pdgfrb+/- mice, parallel with the extent of tissue repair. CONCLUSIONS: A reciprocal interaction between pericytes and macrophages is important for poststroke tissue repair and functional recovery.

Early Reperfusion After Brain Ischemia Has Beneficial Effects Beyond Rescuing Neurons.

BACKGROUND AND PURPOSE: Recent studies show that successful endovascular thrombectomy 6 to 12 hours after stroke onset enhances functional outcomes 3 months later. In this study, we investigated the effects of reperfusion after ischemia on repair processes in the ischemic areas, as well as on functional recovery, using mouse stroke models. METHODS: We examined time-dependent histological changes and functional recovery after transient middle cerebral artery occlusion of different durations, including permanent middle cerebral artery occlusion, using the CB-17 (CB-17/lcr-+/+Jcl) mouse strain, which has poor pial collateral blood flow. RESULTS: Large microtubule-associated protein 2-negative areas of neuronal death were produced in mice subjected to ≥60 minutes of ischemia followed by reperfusion on day 1, while restricted microtubule-associated protein 2-negative regions were observed in mice subjected to a 45-minute period of ischemia. A substantial reduction in microtubule-associated protein 2-negative areas was observed on day 7 in mice given early reperfusion and was associated with better functional recovery. Klüver-Barrera staining demonstrated that white matter injury on day 1 was significantly lesser in mice with reperfusion. Immunohistochemistry and electron microscopy revealed that a greater number of endothelial cells were present in the infarct areas in mice with earlier reperfusion and were associated with a more rapid recruitment of platelet-derived growth factor receptor ß-positive pericytes and subsequent intrainfarct fibrosis. Early reperfusion also resulted in a greater accumulation of glial fibrillary acidic protein-positive astrocytes in peri-infarct areas. Peri-infarct astrogliosis was attenuated in platelet-derived growth factor receptor ß heterozygous knockout mice. CONCLUSIONS: Early reperfusion after ischemia enhances the survival of endothelial cells and pericytes within ischemic areas even after the infarct is established, resulting in efficient intrainfarct fibrosis and peri-infarct astrogliosis. These effects might be associated with efficient peri-infarct reorganization and functional recovery.

Matrix metalloproteinase-9 contributes to kindled seizure development in pentylenetetrazole-treated mice by converting pro-BDNF to mature BDNF in the hippocampus.

Recurrent seizure activity has been shown to induce a variety of permanent structural changes in the brain. Matrix metalloproteinases (MMPs) function to promote neuronal plasticity, primarily through cleavage of extracellular matrix proteins. Here, we investigated the role of MMP-9 in the development of pentylenetetrazole (PTZ)-induced kindled seizure in mice. Repeated treatment with PTZ (40 mg/kg) produced kindled seizure, which was accompanied by enhanced MMP-9 activity and expression in the hippocampus. No change in MMP-9 activity was observed in the hippocampi of mice with generalized tonic seizure following single administration of PTZ (60 mg/kg). MMP-9 colocalized with the neuronal marker NeuN and the glial marker GFAP in the dentate gyrus of the kindled mouse hippocampus. Coadministration of diazepam or MK-801 with PTZ inhibited the development of kindling and the increased MMP-9 levels in the hippocampus. Marked suppression of kindled seizure progression in response to repeated PTZ treatment was observed in MMP-9((-/-)) mice compared with wild-type mice, an observation that was accompanied by decreased hippocampal levels of mature brain-derived neurotrophic factor. Microinjecting the BDNF scavenger TrkB-Fc into the right ventricle before each PTZ treatment significantly suppressed the development of kindling in wild-type mice, whereas no effect was observed in MMP-9((-/-)) mice. On the other hand, bilateral injections of pro-BDNF into the hippocampal dentate gyrus significantly enhanced kindling in wild-type mice but not MMP-9((-/-)) mice. These findings suggest that MMP-9 is involved in the progression of behavioral phenotypes in kindled mice because of conversion of pro-BDNF to mature BDNF in the hippocampus.

Neurosarcoidosis Presenting with Prominent Periventricular White-Matter Lesions during Steroid Treatment for Autoimmune Hepatitis.

A 63-year-old woman under treatment of autoimmune hepatitis presented with headache, memory loss, and somnolence. Three months before admission, the patient experienced liver inflammation relapse after prednisolone (PSL) cessation. Consequently, PSL was resumed and then tapered. Cerebrospinal fluid (CSF) examination showed lymphocytic pleocytosis with remarkably reduced glucose and elevated angiotensin-converting enzyme and soluble interleukin-2 receptor levels. Magnetic resonance imaging (MRI) revealed prominent bilateral periventricular white-matter lesions, hydrocephalus, ischemic stroke with gadolinium enhancement of frontoparietal and basilar meninges on contrast-enhanced fluid-attenuated inversion recovery. Magnetic resonance angiography (MRA) showed narrowing of the bilateral middle cerebral arteries. Based on these findings, we diagnosed the patient with neurosarcoidosis. Re-increment of PSL improved the neurological symptoms, CSF findings, and abnormalities found on MRI and MRA. This case suggests that neurosarcoidosis may occur as a complication of some autoimmune diseases during immunotherapy administration.

Pericyte-Mediated Tissue Repair through PDGFRß Promotes Peri-Infarct Astrogliosis, Oligodendrogenesis, and Functional Recovery after Acute Ischemic Stroke.

Post-stroke functional recovery can occur spontaneously during the subacute phase; however, how post-stroke fibrotic repair affects functional recovery is highly debated. Platelet-derived growth factor receptor ß (PDGFRß)-expressing pericytes are responsible for post-stroke fibrotic repair within infarct areas; therefore, we examined peri-infarct neural reorganization and functional recovery after permanent middle cerebral artery occlusion (pMCAO) using pericyte-deficient Pdgfrb+/- mice. Time-dependent reduction of infarct area sizes, i.e., repair, was significantly impaired in Pdgfrb+/- mice with recovery of cerebral blood flow (CBF) in ischemic areas attenuated by defective leptomeningeal arteriogenesis and intrainfarct angiogenesis. Peri-infarct astrogliosis, accompanied by increased STAT3 phosphorylation, was attenuated in Pdgfrb+/- mice. Pericyte-conditioned medium (PCM), particularly when treated with platelet-derived growth factor subunit B (PDGFB) homodimer (PDGF-BB; PCM/PDGF-BB), activated STAT3 and enhanced the proliferation and activity of cultured astrocytes. Although peri-infarct proliferation of oligodendrocyte (OL) precursor cells (OPCs) was induced promptly after pMCAO regardless of intrainfarct repair, OPC differentiation and remyelination were significantly attenuated in Pdgfrb+/- mice. Consistently, astrocyte-CM (ACM) promoted OPC differentiation and myelination, which were enhanced remarkably by adding PCM/PDGF-BB to the medium. Post-stroke functional recovery correlated well with the extent and process of intrainfarct repair and peri-infarct oligodendrogenesis. Overall, pericyte-mediated intrainfarct fibrotic repair through PDGFRß may promote functional recovery through enhancement of peri-infarct oligodendrogenesis as well as astrogliosis after acute ischemic stroke.

Simultaneous targeting of mitochondria and monocytes enhances neuroprotection against ischemia-reperfusion injury.

Ischemia-reperfusion injury impairs the efficacy of reperfusion therapy after ischemic stroke. Cyclophilin D (CypD)-mediated openings of mitochondrial permeability transition pore (mPTP) and subsequent monocyte-mediated inflammation are considered as major mechanisms of reperfusion injury. However, no medical therapies are currently available. Therefore, we have tested a hypothesis that simultaneous targeting of mPTP and inflammation confers substantial neuroprotection after cerebral ischemia-reperfusion. To address this point, we prepared CypD knockout mice, C-C chemokine receptor 2 (CCR2) knockout mice and CypD/CCR2 double knockout mice. These mice were subjected to 60 min transient cerebral ischemia by occluding middle cerebral arteries. Neurological deficits evaluated 3 days after reperfusion were significantly attenuated in CypD/CCR2 double knockout mice as compared to wild-type mice and other single knockout mice. Then, we have prepared polymeric nanoparticles containing cyclosporine A (CsA-NPs) and pitavastatin (Pitava-NPs), targeting mPTP opening and inflammation, respectively. Simultaneous administration of CsA-NP and Pitava-NP at the time of reperfusion also decreased infarct size and attenuated neurological deficits as compared to control nanoparticles and single administration of CsA-NPs or Pitava-NPs. These results indicate that simultaneous targeting of the mPTP opening and monocyte-mediated inflammation could be a novel strategy for better neurological outcomes in patients with ischemic stroke.

Possible promotion of neuronal differentiation in fetal rat brain neural progenitor cells after sustained exposure to static magnetism.

We have previously shown significant potentiation of Ca(2+) influx mediated by N-methyl-D-aspartate receptors, along with decreased microtubules-associated protein-2 (MAP2) expression, in hippocampal neurons cultured under static magnetism without cell death. In this study, we investigated the effects of static magnetism on the functionality of neural progenitor cells endowed to proliferate for self-replication and differentiate into neuronal, astroglial, and oligodendroglial lineages. Neural progenitor cells were isolated from embryonic rat neocortex and hippocampus, followed by culture under static magnetism at 100 mT and subsequent determination of the number of cells immunoreactive for a marker protein of particular progeny lineages. Static magnetism not only significantly decreased proliferation of neural progenitor cells without affecting cell viability, but also promoted differentiation into cells immunoreactive for MAP2 with a concomitant decrease in that for an astroglial marker, irrespective of the presence of differentiation inducers. In neural progenitors cultured under static magnetism, a significant increase was seen in mRNA expression of several activator-type proneural genes, such as Mash1, Math1, and Math3, together with decreased mRNA expression of the repressor type Hes5. These results suggest that sustained static magnetism could suppress proliferation for self-renewal and facilitate differentiation into neurons through promoted expression of activator-type proneural genes by progenitor cells in fetal rat brain.

Early initiation of a factor Xa inhibitor can attenuate tissue repair and neurorestoration after middle cerebral artery occlusion.

The timing of anti-coagulation therapy initiation after acute cardioembolic stroke remains controversial. We investigated the effects of post-stroke administration of a factor Xa inhibitor in mice, focusing on tissue repair and functional restoration outcomes. We initiated administration of rivaroxaban, a Xa inhibitor, immediately after permanent distal middle cerebral artery occlusion (pMCAO) in CB-17 mice harboring few leptomeningeal anastomoses at baseline. Rivaroxaban initiated immediately after pMCAO hindered the recovery of blood flow in ischemic areas by inhibiting leptomeningeal anastomosis development, and led to impaired restoration of neurologic functions with less extensive peri-infarct astrogliosis. Within infarct areas, angiogenesis and fibrotic responses were attenuated in rivaroxaban-fed mice. Furthermore, inflammatory responses, including the accumulation of neutrophils and monocytes/macrophages, local secretion of pro-inflammatory cytokines, and breakdown of the blood-brain barrier, were enhanced in infarct areas in mice treated immediately with rivaroxaban following pMCAO. The detrimental effects were not found when rivaroxaban was initiated after transient MCAO or on day 7 after pMCAO. Collectively, early post-stroke initiation of a factor Xa inhibitor may suppress leptomeningeal anastomosis development and blood flow recovery in ischemic areas, thereby resulting in attenuated tissue repair and functional restoration unless occluded large arteries are successfully recanalized.

Nox4 Promotes Neural Stem/Precursor Cell Proliferation and Neurogenesis in the Hippocampus and Restores Memory Function Following Trimethyltin-Induced Injury.

Reactive oxygen species (ROS) modulate the growth of neural stem/precursor cells (NS/PCs) and participate in hippocampus-associated learning and memory. However, the origin of these regulatory ROS in NS/PCs is not fully understood. In the present study, we found that Nox4, a ROS-producing NADPH oxidase family protein, is expressed in primary cultured NS/PCs and in those of the adult mouse brain. Nox inhibitors VAS 2870 and GKT137831 or Nox4 deletion attenuated bFGF-induced proliferation of cultured NS/PCs, while lentivirus-mediated Nox4 overexpression increased the production of H2O2, the phosphorylation of Akt, and the proliferation of cultured NS/PCs. Nox4 did not significantly affect the potential of cultured NS/PCs to differentiate into neurons or astrocytes. The histological and functional development of the hippocampus appeared normal in Nox4-/- mice. Although pathological and functional damages in the hippocampus induced by the neurotoxin trimethyltin were not significantly different between wild-type and Nox4-/- mice, the post-injury reactive proliferation of NS/PCs and neurogenesis in the subgranular zone (SGZ) of the dentate gyrus were significantly impaired in Nox4-/- animals. Restoration from the trimethyltin-induced impairment in recognition and spatial working memory was also significantly attenuated in Nox4-/- mice. Collectively, our findings suggest that Nox4 participates in NS/PC proliferation and neurogenesis in the hippocampus following injury, thereby helping to restore memory function.

Upregulation of Annexin A1 in Reactive Astrocytes and Its Subtle Induction in Microglia at the Boundaries of Human Brain Infarcts.

Annexin A1 (ANXA1) has multiple functions, including anti-inflammatory effects, and is thought to be neuroprotective in various pathophysiologies of the central nervous system. The importance of ANXA1 in microglia and endothelial cells in ischemic environments in the brain has been recognized, but its detailed behavior in astrocytes in the ischemic brain remains unknown. Using immunohistochemistry, we therefore assessed the altered distribution of ANXA1 in human brain infarcts using 14 autopsied samples and 18 surgical samples. Elevated expression of ANXA1 was observed in reactive astrocytes in peri-infarct regions. ANXA1 accumulated at the cell periphery and in swollen cytoplasmic processes of reactive astrocytes, as well as at the rim of vacuoles at the boundary of necrosis, and colocalized with aberrantly distributed aquaporin 4 and excitatory amino acid transporter 1. Foamy macrophages in the necrotic core also expressed abundant ANXA1, whereas resident microglia at the boundary of necrosis rarely showed intrinsic expression of ANXA1. This characteristic distribution of ANXA1 in human brain infarcts may represent the good adaptability of reactive astrocytes to ischemic damage.

Flow-injection determination of L-histidine with an immobilized histidine oxidase from Brevibacillus borstelensis KAIT-B-022 and chemiluminescence detection.

A chemiluminometric flow injection analytical system for the quantitation of L-histidine is described. Histidine oxidase (EC 1.4.3.-) from Brevibacillus borstelensis KAIT-B-022 was immobilized on tresylated poly(vinyl alcohol) beads and packed into a stainless-steel column. The hydrogen peroxide produced was detected chemiluminometrically by a flowthrough sensor containing immobilized peroxidase (EC 1.1 1.1.7). The maximum sample throughput was 10 h(-1). The calibration graph was linear from 0.05 to 5 mM; the detection limit (signal to noise ratio = 3) was 0.01 mM. The activity of immobilized histidine oxidase reduced to 65% of the initial value after 350 injections. The system was applied to the determination of L-histidine in fish meat, such as salmon, tunny, bonito, and mackerel.

Detrimental role of pericyte Nox4 in the acute phase of brain ischemia.

Pericytes are mural cells abundantly present in cerebral microvessels and play important roles, including the formation and maintenance of the blood-brain barrier. Nox4 is a major source of reactive oxygen species in cardiovascular cells and modulate cellular functions, particularly under pathological conditions. In the present study, we found that the expression of Nox4 was markedly induced in microvascular cells, including pericytes, in peri-infarct areas after middle cerebral artery occlusion stroke models in mice. The upregulation of Nox4 was greater in a permanent middle cerebral artery occlusion model compared with an ischemia/reperfusion transient middle cerebral artery occlusion model. We performed permanent middle cerebral artery occlusion on mice with Nox4 overexpression in pericytes (Tg-Nox4). Infarct volume was significantly greater with enhanced reactive oxygen species production and blood-brain barrier breakdown in peri-infarct areas in Tg-Nox4, compared with littermate controls. In cultured brain pericytes, Nox4 was significantly upregulated by hypoxia and was promptly downregulated by reoxygenation. Phosphorylation of NFκB and production of matrix metalloproteinase 9 were significantly increased in both cultured pericytes overexpressing Nox4 and in peri-infarct areas in Tg-Nox4. Collectively, Nox4 is upregulated in pericytes in peri-infarct areas after acute brain ischemia and may enhance blood-brain barrier breakdown through activation of NFκB and matrix metalloproteinase 9, thereby causing enlargement of infarct volume.

Possible involvement of basic FGF in the upregulation of PDGFRß in pericytes after ischemic stroke.

Central nervous system (CNS) pericytes have been recognized as an indispensable component of the neurovascular unit. The expression of platelet-derived growth factor receptor ß (PDGFRß) is markedly increased in CNS pericytes after brain ischemia. It has been elucidated that PDGFRß, expressed in pericytes and pericyte-derived fibroblast-like cells, plays important roles in the maintenance of the blood-brain barrier (BBB) and in the repair process in infarct areas. The aim of this study was to uncover how the PDGFRß expression is regulated in pericytes after brain ischemia. We found that basic fibroblast growth factor (bFGF), but neither hypoxia at 1% O2 nor acidification at pH 6.5, significantly upregulated the PDGFRß expression in human cultured CNS pericytes. SU5402, an inhibitor of FGF receptor (FGFR), and inhibitors of its downstream effectors Akt and Erk abolished the bFGF-induced upregulation of PDGFRß. On the other hand, acidification significantly upregulated the expression of bFGF, while hypoxia upregulated the expression of FGFR1 in the pericytes. The expression of bFGF and FGFR1 was markedly induced in the ischemic hemisphere after ischemic insult in a middle cerebral artery occlusion stroke model. Immunofluorescent double labeling demonstrated that the expression of bFGF and FGFR1 was co-localized with PDGFRß-positive cells in peri-infarct areas. Moreover, treatment with bFGF enhanced cell growth and the PDGF-BB-induced migratory activity of cultured pericytes, which were significantly suppressed by SU5402 or Sunitinib, an inhibitor of PDGFR. These data suggested that increased bFGF upregulates the expression of PDGFRß and may enhance PDGFRß-mediated pericyte functions after brain ischemia.

Involvement of platelet-derived growth factor receptor ß in fibrosis through extracellular matrix protein production after ischemic stroke.

Fibrosis is concomitant with repair processes following injuries in the central nervous system (CNS). Pericytes are considered as an origin of fibrosis-forming cells in the CNS. Here, we examined whether platelet-derived growth factor receptor ß (PDGFRß), a well-known indispensable molecule for migration, proliferation, and survival of pericytes, was involved in the production of extracellular matrix proteins, fibronectin and collagen type I, which is crucial for fibrosis after ischemic stroke. Immunohistochemistry demonstrated induction of PDGFRß expression in vascular cells of peri-infarct areas at 3-7days in a mouse stroke model. The PDGFRß-expressing cells extended from peri-infarct areas toward the ischemic core after day 7 while expressing fibronectin and collagen type I in the infarct areas. In contrast, desmin and α-smooth muscle actin, markers of pericytes, were only expressed in vascular cells. In PDGFRß heterozygous knockout mice, the expression of fibronectin and collagen type I was attenuated at both mRNA and protein levels with an enlargement of the infarct volume after ischemic stroke compared with that in wild-type littermates. In cultured brain pericytes, the expression of PDGF-B, PDGFRß, fibronectin, and collagen type I, but not desmin, was significantly increased by serum depletion (SD). The SD-induced upregulation of fibronectin and collagen type I was suppressed by SU11652, an inhibitor of PDGFRß, while PDGF-B further increased the SD-induced upregulation. In conclusion, the expression level of PDGFRß may be a crucial determinant of fibrosis after ischemic stroke. Moreover, PDGFRß signaling participates in the production of fibronectin and collagen type I after ischemic stroke.

Simultaneous determination of choline and acetylcholine based on a trienzyme chemiluminometric biosensor in a single line flow injection system.

A detector for the simultaneous determination of choline (Ch) and acetylcholine (ACh) based on a sensitive trienzyme chemiluminometric biosensor in a single line flow injection (FI) system is described. Immobilized choline oxidase (ChOx), immobilized peroxidase (POx), immobilized acetylcholinesterase, and coimmobilized ChOx/POx were packed, in turn, in a transparent ETFE tube (1 mm i.d., 75 cm) and the tube was placed in front of a photomultipier tube as a flow cell. Two-peak response was obtained by one injection of the sample solution. The first and second peaks were dependent on the concentrations of Ch and ACh, respectively. The influence of some experimental parameters such as flow rate, amounts of immobilized enzymes on the behavior of the sensor was studied in order to optimize the sensitivity, sample throughput and resolution. Calibration curves were linear at 1 - 1000 nM for Ch and 3 - 3000 nM for ACh. The sample throughput was 25/h without carryover. The FI system was applied to the simultaneous determination of Ch and ACh in rabbit brain tissue homogenates.

Simultaneous determination of D-glucose and 3-hydroxybutyrate by chemiluminescence detection with immobilized enzymes in a flow injection system.

A chemiluminometric flow-through sensor for the simultaneous determination of glucose (Glu) and 3-hydroxybutyrate (HB) in a single sample has been developed. Coimmobilized 3-hydroxybutyrate dehydrogenase/NADH oxidase/peroxidase, a support material, and coimmobilized glucose dehydrogenase/NADH oxidase/peroxidase were packed sequentially in a transparent PTFE tube. The tube was then placed in front of a photomultiplier tube as a flow cell. A two-peak recording was obtained by one injection of the sample solution. The peak heights of the first and second peaks were dependent on the concentrations of HB and Glu, respectively. The calibration graphs for HB and Glu were linear at 0.05-10 and 0.1-30 microM, respectively. The maximum sample throughput was 30 h(-1). The sensor was stable for two weeks.

Flow-through micro sensor using immobilized peroxidase with chemiluminometric FIA system for determining hydrogen peroxide.

A micromachined flow cell (overall size; 25 x 25 x 1 mm3) was designed for the fast determination of hydrogen peroxide, based on a luminol-H2O2 chemiluminescence reaction catalyzed by immobilized peroxidase (POD). The flow cell consisted of a sandwich of anisotropically etched silicon and glass chips and contained a spiral channel (20 turns, 50 cm long, 150 microm wide, 20 microm depth, channel volume 1.4 microl) and two holes (1 mm diameter). POD was covalently immobilized with 3-(trimethoxysilyl)propyldietylenetriamine and glutaraldehyde on the inner surface of the channel. The chip was placed in front of a window of a photomultiplier tube and used as a flow cell in a single-line flow-injection analysis system using a luminol solution as a carrier solution. The sample volume for one measurement was 0.2 microl. The maximal sampling rate was 315 h(-1) at a carrier solution flow rate of 10 microl min(-1). A calibration graph for H2O2 was linear for 5 nM - 5 microM; the detection limit (signal-to-noise = 3) was 1 nM (7 fg in 0.2 microl injection). The H2O2 concentration in rainwater was determined using this sensor system.