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The blood-brain barrier (BBB) is a tightly and actively regulated vascular barrier. Answering fundamental biological and translational questions about the BBB with currently available approaches is hampered by a trade-off between accessibility and biological validity. We report an approach combining micropipette-based local perfusion of capillaries in acute brain slices with multiphoton microscopy. Micro-perfusion offers control over the luminal solution and allows application of molecules and drug delivery systems, whereas the bath solution defines the extracellular milieu in the brain parenchyma. Here we show, that this combination allows monitoring of BBB transport at the cellular level, visualization of BBB permeation of cells and molecules in real-time and resolves subcellular details of the neurovascular unit. In combination with electrophysiology, it permits comparison of drug effects on neuronal activity following luminal versus parenchymal application. We further apply micro-perfusion to the human and mouse BBB of epileptic hippocampi highlighting its utility for translational research and analysis of therapeutic strategies.

Objective Assess occurrence of the dendritic spine scaffolding protein Drebrin as a pathophysiologically relevant autoantibody target in patients with recurrent seizures and suspected encephalitis as leading symptoms. Methods Sera of 4 patients with adult onset epilepsy and suspected encephalitis of unresolved etiology and equivalent results in autoantibody screening were subjected to epitope identification. We combined a wide array of approaches, ranging from immunoblotting, immunoprecipitation, mass spectrometry, subcellular binding pattern analyses in primary neuronal cultures, and immunohistochemistry in brains of wild-type and Drebrin knockout mice to in vitro analyses of impaired synapse formation, morphology, and aberrant neuronal excitability by antibody exposure. Results In the serum of a patient with adult onset epilepsy and suspected encephalitis, a strong signal at ∼70kDa was detected by immunoblotting, for which mass spectrometry revealed Drebrin as the putative antigen. Three other patients whose sera also showed strong immunoreactivity around 70kDa on Western blotting were also anti-Drebrin-positive. Seizures, memory impairment, and increased protein content in cerebrospinal fluid occurred in anti-Drebrin-seropositive patients. Alterations in cerebral magnetic resonance imaging comprised amygdalohippocampal T2-signal increase and hippocampal sclerosis. Diagnostic biopsy revealed T-lymphocytic encephalitis in an anti-Drebrin-seropositive patient. Exposure of primary hippocampal neurons to anti-Drebrin autoantibodies resulted in aberrant synapse composition and Drebrin distribution as well as increased spike rates and the emergence of burst discharges reflecting network hyperexcitability. Interpretation Anti-Drebrin autoantibodies define a chronic syndrome of recurrent seizures and neuropsychiatric impairment as well as inflammation of limbic and occasionally cortical structures. Immunosuppressant therapies should be considered in this disorder. ANN NEUROL 2020;87:869-884.

Stable function of networks requires that synapses adapt their strength to levels of neuronal activity, and failure to do so results in cognitive disorders. How such homeostatic regulation may be implemented in mammalian synapses remains poorly understood. Here we show that the phosphorylation status of several positions of the active-zone (AZ) protein RIM1 are relevant for synaptic glutamate release. Position RIMS1045 is necessary and sufficient for expression of silencing-induced homeostatic plasticity and is kept phosphorylated by serine arginine protein kinase 2 (SRPK2). SRPK2-induced upscaling of synaptic release leads to additional RIM1 nanoclusters and docked vesicles at the AZ and is not observed in the absence of RIM1 and occluded by RIMS1045E. Our data suggest that SRPK2 and RIM1 represent a presynaptic phosphosignaling hub that is involved in the homeostatic balance of synaptic coupling of neuronal networks.

Neuro-Oncology 24(5), 741-754 (2022). doi:10.1093/neuonc/noab268, Published by Oxford Univ. Press, Oxford

Transient brain insults, including status epilepticus (SE), can trigger a period of epileptogenesis during which functional and structural reorganization of neuronal networks occurs resulting in the onset of focal epileptic seizures. In recent years, mechanisms that regulate the dynamic transcription of individual genes during epileptogenesis and thereby contribute to the development of a hyperexcitable neuronal network have been elucidated. Our own results have shown early growth response 1 (Egr1) to transiently increase expression of the T-type voltage-dependent Ca2+channel (VDCC) subunit CaV3.2, a key proepileptogenic protein. However, epileptogenesis involves complex and dynamic transcriptomic alterations; and so far, our understanding of the transcriptional control mechanism of gene regulatory networks that act in the same processes is limited. Here, we have analyzed whether Egr1 acts as a key transcriptional regulator for genes contributing to the development of hyperexcitability during epileptogenesis. We found Egr1 to drive the expression of the VDCC subunit α2δ4, which was augmented early and persistently after pilocarpine-induced SE. Furthermore, we show that increasing levels of α2δ4 in the CA1 region of the hippocampus elevate seizure susceptibility of mice by slightly decreasing local network activity. Interestingly, we also detected increased expression levels of Egr1 and α2δ4 in human hippocampal biopsies obtained from epilepsy surgery. In conclusion, Egr1 controls the abundance of the VDCC subunits CaV3.2 and α2δ4, which act synergistically in epileptogenesis, and thereby contributes to a seizure-induced “transcriptional Ca2+channelopathy.”SIGNIFICANCE STATEMENTThe onset of focal recurrent seizures often occurs after an epileptogenic process induced by transient insults to the brain. Recently, transcriptional control mechanisms for individual genes involved in converting neurons hyperexcitable have been identified, including early growth response 1 (Egr1), which activates transcription of the T-type Ca2+channel subunit CaV3.2. Here, we find Egr1 to regulate also the expression of the voltage-dependent Ca2+channel subunit α2δ4, which was augmented after pilocarpine- and kainic acid-induced status epilepticus. In addition, we observed that α2δ4 affected spontaneous network activity and the susceptibility for seizure induction. Furthermore, we detected corresponding dynamics in human biopsies from epilepsy patients. In conclusion, Egr1 orchestrates a seizure-induced “transcriptional Ca2+channelopathy” consisting of CaV3.2 and α2δ4, which act synergistically in epileptogenesis.

BackgroundDevelopmental brain tumors harboring BRAFV600E somatic mutation are diverse. Here, we describe molecular factors that determine BRAFV600E-induced tumor biology and function.MethodsIntraventricular in utero electroporation in combination with the piggyBac transposon system is employed as a tool to generate developmental brain neoplasms. In vivo tumor growth is monitored by using the infrared fluorescent protein (iRFP). Lineage inference is carried out by using the Brainbow transgene. Neural activity from tumor slices is assessed by multielectrode array. RNA sequencing is exploited to analyze the induced neoplasms at the transcriptomic level.ResultsBRAFV600E in murine neural progenitors only in concert with active PI3K/mTOR-signaling through constitutively phosphorylated Akt-kinase (pAkt) elicits benign neoplasms composed of enlarged dysmorphic neurons and neoplastic astroglia recapitulating ganglioglioma (GG). Purely glial tumors partially resembling polymorphous low-grade neuroepithelial tumors of the young (PLNTYs) emerge from BRAFV600E alone. Additional somatic Trp53-loss is sufficient to induce anaplastic GGs (aGGs) with glioneuronal clonality. Functionally, only BRAFV600E/pAkt tumors intrinsically generate substantial neuronal activity and show enhanced relay to adjacent tissue conferring high epilepsy propensity. In contrast, PLNTY- and aGG-models lack significant spike activity, which appears in line with the glial differentiation of the former and a dysfunctional tissue structure combined with reduced neuronal transcript signatures in the latter.ConclusionmTOR-signaling and Trp53-loss critically determine the biological diversity and electrical activity of BRAFV600E-induced tumors.Key pointsIUE of BRAFV600E and activation of mTOR leads to ganglioglioma (GG)-like tumors, while BRAFV600E alone give rise to PLNTY-like neoplasms.Anaplastic GGs depend on the Trp53 deletion in combination to BRAFV600E and PI3K-mTOR signaling cascade.Importance of the StudyGlioneuronal tumors are challenging with respect to biological behavior and seizure emergence. While BRAFV600E in murine neural precursors induces oligoid tumors, it requires an overactivation of PI3K/mTOR-signaling for the development of hyperexcitable gangliogliomas and additional Trp53-loss for anaplastic transformation.

The size and structure of the dendritic arbor play important roles in determining how synaptic inputs of neurons are converted to action potential output. The regulatory mechanisms governing the development of dendrites, however, are insufficiently understood. The evolutionary conserved Ste20/Hippo kinase pathway has been proposed to play an important role in regulating the formation and maintenance of dendritic architecture. A key element of this pathway, Ste20-like kinase (SLK), regulates cytoskeletal dynamics in non-neuronal cells and is strongly expressed throughout neuronal development. However, its function in neurons is unknown. We show that, during development of mouse cortical neurons, SLK has a surprisingly specific role for proper elaboration of higher, ≥ third-order dendrites both in male and in female mice. Moreover, we demonstrate that SLK is required to maintain excitation-inhibition balance. Specifically, SLK knockdown caused a selective loss of inhibitory synapses and functional inhibition after postnatal day 15, whereas excitatory neurotransmission was unaffected. Finally, we show that this mechanism may be relevant for human disease, as dysmorphic neurons within human cortical malformations revealed significant loss of SLK expression. Overall, the present data identify SLK as a key regulator of both dendritic complexity during development and inhibitory synapse maintenance. SIGNIFICANCE STATEMENT We show that dysmorphic neurons of human epileptogenic brain lesions have decreased levels of the Ste20-like kinase (SLK). Decreasing SLK expression in mouse neurons revealed that SLK has essential functions in forming the neuronal dendritic tree and in maintaining inhibitory connections with neighboring neurons.

The wiring scheme of neurons is key to the function of the brain. Neurons are structurally wired by synapses and it is a long-held view that most synapses in the CNS are sufficiently isolated to avoid cross-talk to AMPA receptors of neighboring synapses. Here we report in hippocampal brain slices that quantal glutamate release activated optical reporter proteins >1.5 µm distant to the releasing synapse. 2P-glutamate uncaging was used to quantitatively probe glutamate spread in the neuropil. Releasing ∼35000 molecules of glutamate (∼5 vesicles) at a distance of 500 nm to a spine generated an uncaging EPSC reaching ∼30% of the quantal amplitude at synaptic AMPA-Rs. The same stimulus activated ∼70% of the quantal amplitude at NMDA-Rs and still generated clear current and calcium responses when applied at >= 2 µm remote to the spine. Extracellular spread of glutamate on the sub-micrometer scale appeared cooperative and caused supra-additive activation of AMPA-Rs in a spine. These observations are not predicted by previously used models of glutamate diffusion in the neuropil. An extracellular glutamate scavenger system weakly reduced field potential responses but not the quantal amplitude, indicating that a cross-talk component regularly contributes to synaptic transmission. Our data suggest that slight synaptic crosstalk responses at AMPA receptors of ∼2-4 adjacent synapses may be common (>70 synapses for NMDA receptors). Such broadcasting of synaptic signals to very local neighborhoods could stabilize network learning performance and allow for integration of synaptic activity within the extracellular space.

SummaryThe size and structure of the dendritic arbor play important roles in determining how synaptic inputs of neurons are converted to action potential output. The regulatory mechanisms governing the development of dendrites, however, are insufficiently understood. The evolutionary conserved Ste20/Hippo kinase pathway has been proposed to play an important role in regulating the formation and maintenance of dendritic architecture. A key element of this pathway, Ste20-like kinase (SLK), regulates cytoskeletal dynamics in non-neuronal cells and is strongly expressed throughout neuronal development. However, its function in neurons is unknown. We show that during development of mouse cortical neurons, SLK has a surprisingly specific role for proper elaboration of higher, ≥ 3rd, order dendrites. Moreover, we demonstrate that SLK is required to maintain excitation-inhibition balance. Specifically, SLK knockdown caused a selective loss of inhibitory synapses and functional inhibition after postnatal day 15, while excitatory neurotransmission was unaffected. Finally, we show that this mechanism may be relevant for human disease, as dysmorphic neurons within human cortical malformations revealed significant loss of SLK expression. Overall, the present data identify SLK as a key regulator of both dendritic complexity during development and of inhibitory synapse maintenance.

Here we design and optimize a genetically encoded fluorescent indicator, iAChSnFR, for the ubiquitous neurotransmitter acetylcholine, based on a bacterial periplasmic binding protein. iAChSnFR shows large fluorescence changes, rapid rise and decay kinetics, and insensitivity to most cholinergic drugs. iAChSnFR revealed large transients in a variety of slice and in vivo preparations in mouse, fish, fly and worm. iAChSnFR will be useful for the study of acetylcholine in all animals.

To investigate the release of proinflammatory damage-associated molecular pattern molecule "high-mobility group box-1" in the serum of patients after aneurysmal subarachnoid hemorrhage and its association with cerebral vasospasm.Retrospective observational study.University hospital.Aneurysmal subarachnoid hemorrhage patients admitted within 24 hours of ictus.Standard subarachnoid hemorrhage treatment after clipping or coiling of aneurysm.We enrolled 53 aneurysmal subarachnoid hemorrhage patients from which peripheral venous blood was withdrawn on days 1, 3, 5, 7, 9, 11, and 13 and once from the controls to obtain the serum. Serum high-mobility group box-1 concentration was quantified by enzyme-linked immunosorbent assay. Serum interleukin-6 and peripheral blood leukocytes were also determined over the first 2 weeks after subarachnoid hemorrhage. Patients' data were recorded prospectively. Serum high-mobility group box-1 was significantly elevated in subarachnoid hemorrhage patients from day 1 to day 13 when compared with nonsubarachnoid hemorrhage patients (p0.05). Patients with cerebral vasospasm showed significantly higher high-mobility group box-1 starting from day 1 to day 13 when compared with patients without cerebral vasospasm. Cumulative levels of high-mobility group box-1 showed significant correlation with peripheral blood leukocytes and interleukin-6 levels (p0.05). Receiver operating characteristic curve analysis showed that serum high-mobility group box-1 level at admission may be a predictive biomarker for cerebral vasospasm with a sensitivity of 59% and a specificity of 82% at a cutoff value of 5.6 ng/mL.Serum high-mobility group box-1 is differentially elevated after subarachnoid hemorrhage. Serum high-mobility group box-1 levels were elevated early after subarachnoid hemorrhage (day 1) and remained significantly high until day 13 in patients who developed cerebral vasospasm. Our data suggest that serum high-mobility group box-1 may be a predictive biomarker for the detection of CVS.

IL-23 and IL-17 are pro-inflammatory cytokines. IL-23 is secreted by activated macrophages and dendritic cells, while IL-17 by Th17 cells. Serum IL-23 and IL-17 are known to be elevated in numerous inflammatory diseases including neurodegenerative diseases. The role of serum IL-23 and IL-17 in aneurysmal subarachnoid hemorrhage (aSAH) has still not been investigated. The present work investigates the serum IL-23 and IL-17 levels and their association with post hemorrhagic complications and clinical outcome in patients with aSAH. Methods In this study, 80 patients with aSAH (Hunt and Hess grade I-V) were prospectively recruited. We enrolled 24 control patients with lumbar spinal stenosis. Peripheral venous blood was withdrawn from controls and from aSAH patients at day 1 and day 7, allowed to clot and centrifuged to obtain serum. Enzyme linked immunoassay kits were employed to quantify the serum levels of IL-23 and IL-17 by applying 50 µL of serum samples. Post hemorrhagic complications and clinical outcome were documented prospectively from patient’s hospital record. Results Serum IL-23 and IL-17 levels were significantly elevated in aSAH patients at day 1 and day 7 (n = 80) as compared to control patients (n = 24). Further analysis after dichotomy of patients who suffered from post hemorrhagic complications including cerebral vasospasm, chronic hydrocephalus, seizures, cerebral ischemia, delayed neurological deficits showed differential correlations with different post hemorrhagic complications (Table 1). Serum IL-23 and IL-17 levels did not correlate with clinical outcome. Conclusion Serum IL-23 and IL-17 levels were elevated in patients with aSAH showing upregulation of IL-23/IL-17 inflammatory axis after aSAH. Serum IL-23 and IL-17 showed differential correlations with post hemorrhagic complications and no correlation with clinical outcome.

Here we design and optimize a genetically encoded fluorescent indicator, iAChSnFR, for the ubiquitous neurotransmitter acetylcholine, based on a bacterial periplasmic binding protein. iAChSnFR shows large fluorescence changes, rapid rise and decay kinetics, and insensitivity to most cholinergic drugs. iAChSnFR revealed large transients in a variety of slice and in vivo preparations in mouse, fish, fly and worm. iAChSnFR will be useful for the study of acetylcholine in all organisms.

Stable function of networks in the brain requires that synapses adapt their strength to levels of neuronal activity in a durable manner and failures to do so result in cognitive disorders. How such persistent and homeostatic regulation of synaptic connections may be biologically implemented in mammalian synapses remains poorly understood. Here, we have employed optical recordings of vesicle release from single synapses, super-resolution microscopy, and phosphoproteomics and reveal that the level of homeostatic regulation of transmitter release is stored in the phosphorylation state of a single serine (1045) of the central active zone organizer protein RIM1. While we also discovered other phosphosites in RIM1 with differential effects on neurotransmitter output, we only found S1045 to be necessary and sufficient for expression of silencing-induced HP. Furthermore, we show that S1045 is kept phosphorylated by regulated expression of the serine arginine protein kinase 2 (SRPK2) which binds to RIM1 and effectively targets this (and other) AZ proteins. SRPK2-induced upscaling of synaptic release involved formation of additional RIM1 nanoclusters and docked vesicles at the AZ, was not observed in the absence of RIM1 and occluded by RIMS1045E. Our data suggest that SRPK2 and RIM1 present a presynaptic phosphosignalling hub and that the spatial association of a kinase and AZ protein can achieve the persistent regulation of transmitter release required for the homeostatic balance of synaptic coupling of neuronal networks.

Summary: Synaptically released glutamate is largely cleared by glutamate transporters localized on perisynaptic astrocyte processes. Therefore, the substantial variability of astrocyte coverage of individual hippocampal synapses implies that the efficacy of local glutamate uptake and thus the spatial fidelity of synaptic transmission is synapse dependent. By visualization of sub-diffraction-limit perisynaptic astrocytic processes and adjacent postsynaptic spines, we show that, relative to their size, small spines display a stronger coverage by astroglial transporters than bigger neighboring spines. Similarly, glutamate transients evoked by synaptic stimulation are more sensitive to pharmacological inhibition of glutamate uptake at smaller spines, whose high-affinity N-methyl-D-aspartate receptors (NMDARs) are better shielded from remotely released glutamate. At small spines, glutamate-induced and NMDAR-dependent Ca2+ entry is also more strongly increased by uptake inhibition. These findings indicate that spine size inversely correlates with the efficacy of local glutamate uptake and thereby likely determines the probability of synaptic crosstalk.

NG2 expressing oligodendroglial precursor cells are ubiquitous in the central nervous system and the only cell type cycling throughout life. Previous fate mapping studies have remained inconsistent regarding the question whether NG2 cells are capable of generating certain types of neurons. Here, we use CNP-Cre mice to map the fate of a sub-population of NG2 cells assumed to be close to differentiation. When crossing these mice with the ROSA26/YFP Cre-reporter line we discovered large numbers of reporter-expressing pyramidal neurons in the piriform and dorsal cortex. In contrast, when using Z/EG reporter mice to track the fate of Cnp-expressing NG2 cells only oligodendroglial cells were found reporter positive. Using BrdU-based birth dating protocols and inducible NG2CreER:ROSA26/YFP mice we show that YFP positive neurons are generated from radial glial cells and that these radial glial cells display temporary and low level activity of certain oligodendroglial genes sufficient to recombine the Cre-inducible reporter gene in ROSA26/YFP but not in Z/EG mice. Taken together, we did not obtain evidence for generation of neurons from NG2 cells. Our results suggest that with an appropriate reporter system Cnp activity can be used to define a proliferative subpopulation of NG2 cells committed to generate oligodendrocytes. However, the strikingly different results obtained from ROSA26/YFP versus Z/EG mice demonstrate that the choice of Cre-reporter line can be of crucial importance for fate mapping studies and other applications of the Cre-lox technology. GLIA 2017;65:342-359.

Direct cytoplasmic delivery is essential for susceptible molecules as proteins and some nucleic acids to improve their therapeutic efficacy in cells. Using liposomes for their delivery proved challenging due to known uptake by endocytosis followed by partial or complete lysosomal breakdown. Thus, “fusogenic” liposomes (FL) composed of the neutral lipid dioleoylphosphatidylethanolamine (DOPE) combined with the cationic lipid 1, 2-dioleoyl-3-trimethylammoniumpropane (DOTAP) were tested in different ratios for their cell membrane fusion ability and their cytoplasmic delivery was compared to “pH-sensitive” liposomes in murine brain endothelial cells (bEnd.3). They were loaded with cargos of different molecular sizes (calcein/ enhanced green fluorescent-protein (EGFP)/ EGFP coding plasmid) and their intracellular delivery was quantitatively and qualitatively analyzed. FL composed of equimolar ratios of DOPE and DOTAP showed the most efficient cytoplasmic delivery of all cargos by fusing with the cell membranes within the first 15 min of addition. Their EGFP plasmid delivery to cells was quantified to be 58.2 ± 9.5 % of the total EGFP load and calcein delivery was measured in buffer to be 64.1 ± 4.0 % of the total calcein load, and reduced in blood to 26.1 ± 0.6 %. Thus our tested FL allowed a fast and abundant cytoplasmic delivery of cargos independent of their molecular sizes while avoiding endocytosis, although they also underwent fast fusion with erythrocytes. Seemingly, these carriers could be used as a powerful delivery tool for in-vitro purposes.

Within recent decades, the development of nanotechnology has made a significant contribution to the progress of various fields of study, including the domains of medical and pharmaceutical sciences. A substantially transformed arena within the context of the latter is the development and production of various injectable parenteral formulations. Indeed, recent decades have witnessed a rapid growth of the marketed and pipeline nanotechnology-based injectable products, which is a testimony to the remarkability of the aforementioned contribution. Adjunct to the ability of nanomaterials to deliver the incorporated payloads to many different targets of interest, nanotechnology has substantially assisted to the development of many further facets of the art. Such contributions include the enhancement of the drug solubility, development of long-acting locally and systemically injectable formulations, tuning the onset of the drug’s release through the endowment of sensitivity to various internal or external stimuli, as well as adjuvancy and immune activation, which is a desirable component for injectable vaccines and immunotherapeutic formulations. The current work seeks to provide a comprehensive review of all the abovementioned contributions, along with the most recent advances made within each domain. Furthermore, recent developments within the domains of passive and active targeting will be briefly debated.

Zusammenfassung NG2- Gliazellen repräsentieren einen häufig vorkommenden glialen Zelltyp im Gehirn, der das Proteoglykan NG2 exprimiert, dessen funktionelle Bedeutung jedoch weitgehend unklar ist. Ein Großteil dieser Zellen ist auch im erwachsenen Gehirn noch teilungsaktiv. Diese Zellen besitzen eine Vielzahl von Ionenkanalen und Transmitter-Rezeptoren, die es ihnen ermöglichen, neuronale Aktivität zu detektieren. Bemerkenswerterweise werden NG2 - Gliazellen durch glutamaterge und GABAerge Neurone synaptisch innerviert. Da die postsynaptischen glialen Strome vergleichsweise klein sind, kommt der räumlichen und zeitlichen Integration dieser Signale möglicherweise eine wichtige Rolle zu. In der weißen Hirnsubstanz differenzieren viele NG2 - Gliazellen in Oligodendrozyten , und vermutlich wird dieser Prozess über die Aktivität der Neuron-Glia -Synapsen beeinflusst. Es zeichnet sich immer deutlicher ab, dass sich die Eigenschaften der NG2 - Glia in verschiedenen Hirnregionen unterscheiden, obgleich wir die Bedeutung dieser Heterogenität noch nicht verstehen.

Although NG2 glial cells represent a frequent glial cell type in the brain, characterized by expression of the NG2 proteoglycan, the functional impact of these cells is still enigmatic. A large proportion of NG2 glia are proliferatively active throughout life. These cells express a plethora of ion channels and transmitter receptors, which enable them to detect neuronal activity. Intriguingly, NG2 glial cells receive synaptic input from glutamatergic and GABAergic neurons. Since these postsynaptic glial currents are very small, their spatial and temporal integration might play an important role. In white matter, most NG2 glial cells differentiate into oligodendrocytes and this process might be influenced through the activity of the aforementioned neuron-glia synapses. Increasing evidence suggests that the properties of NG2 glia vary across brain regions; however, the impact of this variability is not understood yet.

Single-wavelength fluorescent reporters allow visualization of specific neurotransmitters with high spatial and temporal resolution. We report variants of the glutamate sensor iGluSnFR that are functionally brighter; can detect sub-micromolar to millimolar concentrations of glutamate; and have blue, green or yellow emission profiles. These variants allow in vivo imaging where original-iGluSnFR was too dim, reveal glutamate transients at individual spine heads, and permit kilohertz imaging with inexpensive, powerful fiber lasers.

International audience; Single-wavelength fluorescent reporters allow visualization of specific neurotransmitters with high spatial and temporal resolution. We report variants of intensity-based glutamate-sensing fluorescent reporter (iGluSnFR) that are functionally brighter; detect submicromolar to millimolar amounts of glutamate; and have blue, cyan, green, or yellow emission profiles. These variants could be imaged in vivo in cases where original iGluSnFR was too dim, resolved glutamate transients in dendritic spines and axonal boutons, and allowed imaging at kilohertz rates.

Epithelial administration of low molecular weight heparin (LMWH) has proven its therapeutic efficiency in ulcerative colitis (UC) but still lacks of a sufficiently selective drug delivery system. Polymeric nanoparticles were used here not only to protect LMWH from intestinal degradation but also to provide targeted delivery to inflamed tissue in experimental colitis mice. LMWH was associated with polymethacrylate nanoparticles (NP) type A (PEMT-A) or type B (PEMT-B) of a size: 150 nm resulting in a maximum drug loading: 0.1 mg/mg. In a lipopolysaccharide-stimulated macrophages both, free LMWH and LMWH-NP have significantly reduced the cytokines secretion independently from cellular uptake. The in-vivo therapeutic efficiency was dose dependent as at low doses (100 IU/kg) only minor differences between free LMWH and LMWH-NP were found and the superiority of LMWH-NP became prominent with dose increase (500 IU/kg). Administration of LMWH-NP at 500 IU/kg has markedly improved the clinical activity as compared to LMWH while similarly pathophysiological indicators revealed increased therapeutic outcome in presence of NP compared to LMWH alone: Myeloperoxidase (Colitis control: 10 480 ± 5335, LMWH-PEMT-A NP: 1507 ± 2165, LMWH-PEMT-B NP: 382 ± 143, LMWH: 8549 ± 5021 units/g) and tumor necrosis factor: (Colitis control: 1636 ± 544, LMWH-PEMT-A NP: 511 ± 506, LMWH-PEMT-B NP: 435 ± 473, LMWH: 1110 ± 309 pg/g). Associating LMWH with NP is improving the anti-inflammatory efficiency of LMWH in-vivo by its protection against degradation in luminal environment and selective drug delivery. Such a combination holds promise for a highly specific therapy by its double selectivity towards the inflamed intestinal tissue. LMWH-PEMT NP have significantly improved the clinical activity in-vivo in comparison to free LMWH.

Depolarization of presynaptic terminals stimulates calcium influx, which evokes neurotransmitter release and activates phosphorylation-based signalling. Here, we present the first global temporal profile of presynaptic activity-dependent phospho-signalling, which includes two KCl stimulation levels and analysis of the poststimulus period. We profiled 1,917 regulated phosphopeptides and bioinformatically identified six temporal patterns of co-regulated proteins. The presynaptic proteins with large changes in phospho-status were again prominently regulated in the analysis of 7,070 activity-dependent phosphopeptides from KCl-stimulated cultured hippocampal neurons. Active zone scaffold proteins showed a high level of activity-dependent phospho-regulation that far exceeded the response from postsynaptic density scaffold proteins. Accordingly, bassoon was identified as the major target of neuronal phospho-signalling. We developed a probabilistic computational method, KinSwing, which matched protein kinase substrate motifs to regulated phosphorylation sites to reveal underlying protein kinase activity. This approach allowed us to link protein kinases to profiles of co-regulated presynaptic protein networks. Ca2+- and calmodulin-dependent protein kinase IIα (CaMKIIα) responded rapidly, scaled with stimulus strength, and had long-lasting activity. Mitogen-activated protein kinase (MAPK)/extracellular signal–regulated kinase (ERK) was the main protein kinase predicted to control a distinct and significant pattern of poststimulus up-regulation of phosphorylation. This work provides a unique resource of activity-dependent phosphorylation sites of synaptosomes and neurons, the vast majority of which have not been investigated with regard to their functional impact. This resource will enable detailed characterization of the phospho-regulated mechanisms impacting the plasticity of neurotransmitter release., Analysis of activity-dependent phosphorylation-based signalling in synaptosomes revealed six patterns of long-lasting presynaptic regulation from 1,917 phosphopeptides. The authors identified patterns most likely to be regulated by CamKII and MAPK/ERK and showed the active zone scaffold protein bassoon to be a major signalling target., Author summary Neurobiological processes are altered by linking neuronal activity to regulated changes in protein phosphorylation levels that influence protein function. Although some of the major targets of activity-dependent phospho-signalling have been identified, a large number of substrates remain unknown. Here, we have screened systematically for these substrates and extended the list from hundreds to thousands of phosphorylation sites, thereby providing a new depth of understanding. We monitored phospho-signalling for 15 min after the stimulation, which to our knowledge had not been attempted at a large scale. We focused on presynaptic protein substrates of phospho-signalling by isolating the presynaptic terminal. We also stimulated hippocampal neurons but did not monitor the poststimulus. Although the phospho-signalling is immensely complex, the findings could be simplified through data exploration. We identified distinct patterns of presynaptic phospho-regulation across the time course that may constitute co-regulated protein networks. In addition, we found a subset of proteins that had many more phosphorylation sites than the average and high-magnitude responses, implying major signalling or functional roles for these proteins. We also determined the likely protein kinases with the strongest responses to the stimulus at different times using KinSwing, a computational tool that we developed. This resource reveals a new depth of activity-dependent phospho-signalling and identifies major signalling targets, major protein kinases, and co-regulated phosphoprotein networks.

In the version of this paper originally published, important figure labels in Fig. 3d were not visible. An image layer present in the authors' original figure that included two small dashed outlines and text labels indicating ROI 1 and ROI 2, as well as a scale bar and the name of the cell label, was erroneously altered during image processing. The figure has been corrected in the HTML and PDF versions of the paper.

The large isoforms of the Rab3 interacting molecule (RIM) family, RIM1α/β and RIM2α/β, have been shown to be centrally involved in mediating presynaptic active zone function. The RIM protein family contains two additional small isoforms, RIM3γ and RIM4γ, which are composed only of the RIM-specific C-terminal C2B domain and varying N-terminal sequences and whose function remains to be elucidated. Here, we report that both, RIM3γ and RIM4γ, play an essential role for the development of neuronal arborization and of dendritic spines independent of synaptic function. γ-RIM knock-down in rat primary neuronal cultures andin vivoresulted in a drastic reduction in the complexity of neuronal arborization, affecting both axonal and dendritic outgrowth, independent of the time point of γ-RIM downregulation during dendrite development. Rescue experiments revealed that the phenotype is caused by a function common to both γ-RIMs. These findings indicate that γ-RIMs are involved in cell biological functions distinct from the regulation of synaptic vesicle exocytosis and play a role in the molecular mechanisms controlling the establishment of dendritic complexity and axonal outgrowth.

NG2 expressing oligodendroglial precursor cells are ubiquitous in the central nervous system and the only cell type cycling throughout life. Previous fate mapping studies have remained inconsistent regarding the question whether NG2 cells are capable of generating certain types of neurons. Here, we use CNP-Cre mice to map the fate of a sub-population of NG2 cells assumed to be close to differentiation. When crossing these mice with the ROSA26/YFP Cre-reporter line we discovered large numbers of reporter-expressing pyramidal neurons in the piriform and dorsal cortex. In contrast, when using Z/EG reporter mice to track the fate of Cnp-expressing NG2 cells only oligodendroglial cells were found reporter positive. Using BrdU-based birth dating protocols and inducible NG2CreER:ROSA26/YFP mice we show that YFP positive neurons are generated from radial glial cells and that these radial glial cells display temporary and low level activity of certain oligodendroglial genes sufficient to recombine the Cre-inducible reporter gene in ROSA26/YFP but not in Z/EG mice. Taken together, we did not obtain evidence for generation of neurons from NG2 cells. Our results suggest that with an appropriate reporter system Cnp activity can be used to define a proliferative subpopulation of NG2 cells committed to generate oligodendrocytes. However, the strikingly different results obtained from ROSA26/YFP versus Z/EG mice demonstrate that the choice of Cre-reporter line can be of crucial importance for fate mapping studies and other applications of the Cre-lox technology. GLIA 2017;65:342-359.

Synaptic signaling to NG2-expressing oligodendrocyte precursor cells (NG2 cells) could be key to rendering myelination of axons dependent on neuronal activity, but it has remained unclear whether NG2 glial cells integrate and respond to synaptic input. Here we show that NG2 cells perform linear integration of glutamatergic synaptic inputs and respond with increasing dendritic calcium elevations. Synaptic activity induces rapid Ca2+ signals mediated by low-voltage activated Ca2+ channels under strict inhibitory control of voltage-gated A-type K+ channels. Ca2+ signals can be global and originate throughout the cell. However, voltage-gated channels are also found in thin dendrites which act as compartmentalized processing units and generate local calcium transients. Taken together, the activity-dependent control of Ca2+ signals by A-type channels and the global versus local signaling domains make intracellular Ca2+ in NG2 cells a prime signaling molecule to transform neurotransmitter release into activity-dependent myelination. DOI: http://dx.doi.org/10.7554/eLife.16262.001

NG2-expressing glia (NG2 cells, polydendrocytes) appear in the embryonic brain, expand perinatally, and persist widely throughout the gray and white matter of the mature central nervous system. We have previously reported that NG2 cells generate oligodendrocytes in both gray and white matter and a subset of protoplasmic astrocytes in the gray matter of the ventral forebrain and spinal cord. To investigate the temporal changes in NG2 cell fate, we generated NG2creER™BAC transgenic mice, in which tamoxifen-inducible Cre is expressed in NG2 cells. Cre induction at embryonic day 16.5, postnatal day (P) 2, P30 and P60 in mice that were double transgenic for NG2creER™BAC and the Cre reporter revealed that NG2 cells in the postnatal brain generate only NG2 cells or oligodendrocytes, whereas NG2 cells in the embryonic brain generate protoplasmic astrocytes in the gray matter of the ventral forebrain in addition to oligodendrocytes and NG2 cells. Analysis of cell clusters from single NG2 cells revealed that more than 80% of the NG2 cells in the P2 brain give rise to clusters consisting exclusively of oligodendrocytes, whereas the majority of the NG2 cells in the P60 brain generate clusters that contain only NG2 cells or a mixture of oligodendrocytes and NG2 cells. Furthermore, live cell imaging of single NG2 cells from early postnatal brain slices revealed that NG2 cells initially divide symmetrically to produce two daughter NG2 cells and that differentiation into oligodendrocytes occurred after 2-3 days.

Mossy fiber long-term depression (LTD) has been shown to be triggered by either pharmacological or synaptic activation of Group II metabotropic glutamate receptors (mGluRs) whereas other studies indicate that synaptic activation of mGluRs is very limited. Therefore, we reexamined the role of Group II mGluRs for the induction of mossy fiber LTD. The complete depression of field potentials (fEPSPs) by 1 microM (2S,2'R,3'R)-2-(2',3'-Dicarboxycyclopropyl)glycine (DCG-IV) only partially reversed upon removal of the drug but fEPSPs were completely restored by the Group II antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495) (3 microM). In contrast, fEPSPs returned back to baseline within 30 min after a brief application of 0.2 microM DCG-IV suggesting that the incomplete reversal of higher concentrations may be due to a residual receptor occupancy rather than to an induction of LTD. LY341495 itself did not increase fEPSPs and also blocked the inhibition of (2S,1'S,2'S)-2-(2-carboxycyclopropyl)glycine (L-CCG-I) (20 microM) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) (10 microM) and its effect was mimicked by CPPG (50 microM). Furthermore, stimulation at 1 Hz for 15 min induced an LTD of 81% +/- 3% and 80% +/- 4% in the absence and presence of LY341495, respectively (n = 7, 5). Finally, we found that synaptic activation of Group II mGluRs during 15 min of 1-Hz stimulation only produces an inhibition of release by 8% +/- 1% (30 degrees C, n = 3). Our data suggests that pharmacological activation of Group II mGluRs is fully reversible per se and does not produce a long lasting depression and that activation of Group II mGluRs is neither necessary nor sufficient for the induction of mossy fiber LTD.

It is well established that NG2 cells throughout the young and adult brain consistently detect the release of single vesicles filled with glutamate from nearby axons. The released neurotransmitter glutamate electrically excites NG2 cells via non-NMDA (N-methyl-D-aspartic acid) glutamate receptors but the individual contribution of AMPA and kainate receptors to neuron-NG2 cell signalling, is not well understood. Here we pharmacologically block AMPA-type glutamate receptors and investigate whether hippocampal NG2 cells also express the kainate subtype of glutamate receptors and what may be their contribution to synaptic connectivity. It has been shown previously that vesicular glutamate release does not lead to a detectable activation of kainate receptors on NG2 cells. Here we report that while bath application of 250 nM–1 μM kainate does not have a major effect on NG2 cells it consistently induces a small and persistent depolarising current. This current was not mimicked by ATPA, suggesting that this current is carried by non-GluR5 containing kainate receptors. In addition to this inward current, nanomolar concentrations of kainate also produced a dramatic increase in the frequency of spontaneous GABA-A receptor-mediated synaptic currents (IPSCs) in NG2 cells. This increase in spontaneous IPSC frequency was even more pronounced on application of the GluR5-specific agonist ATPA (approximately 15-fold increase in frequency). In contrast, mono-synaptic stimulated IPSCs recorded in NG2 cells were unaffected by kainate receptor activation. Those and further experiments show that the occurrence of the high frequency of IPSCs is due to action potential firing of hippocampal interneurons caused by activation of GluR5 receptors on the somatodendritic membrane of the interneurons. Our data suggest that hippocampal kainate receptors are not only important for communication between neurons but may also play a dual and subtype-specific role for neuron–glia signalling: Firstly, extra-synaptic non-GluR5 kainate receptors in the membrane of NG2 cells are ideally suited to instruct NG2 cells on the population activity of local excitatory neurons via ambient glutamate. Secondly, based on the known importance of GluR5 receptors on hippocampal interneurons for the generation of network rhythms and based on our finding that these interneurons heavily project onto NG2 cells, it appears that synaptic activation of interneuronal GluR5 receptors triggers signalling to NG2 cells which transmits the phase and frequency of ongoing network oscillations in the developing hippocampus.

Progenitor cells expressing the proteoglycan NG2 represent approximately 5% of the total cells in the adult brain, and are found both in grey and white matter regions where they give rise to oligodendrocytes. The finding that these cells receive synaptic contacts from excitatory and inhibitory neurons has not only raised major interest in the possible roles of these synapses, but also stimulated further research on the developmental and cellular functions of NG2-expressing (NG2+) progenitors themselves in the context of neural circuit physiology. Here we review recent findings on the functional properties of the synapses on NG2+ cells in grey and white matter regions of the brain. In this review article we make an attempt to integrate current knowledge on the cellular and developmental properties of NG2+ progenitors with the functional attributes of their synapses, in order to understand the physiological relevance of neuron–NG2+ progenitor signal transmission. We propose that, although NG2+ progenitors receive synaptic contact in all brain regions where they are found, their synapses might have different developmental and functional roles, probably reflecting the distinct functions of NG2+ progenitors in the brain.

Vesicular release of neurotransmitter is the universal output signal of neurons in the brain. It is generally believed that fast transmitter release is restricted to nerve terminals that contact postsynaptic cells in the gray matter. Here we show in the rat brain that the neurotransmitter glutamate is also released at discrete sites along axons in white matter in the absence of neurons and nerve terminals. The propagation of single action potentials along axons leads to rapid vesicular release of glutamate, which is detected by ionotropic glutamate receptors on local oligodendrocyte precursor cells. Axonal release of glutamate is reliable, involves highly localized calcium microdomain signaling and is strongly calcium cooperative, similar to vesicle fusion at synapses. This axonal transmitter release represents a widespread mechanism for high-fidelity, activity-dependent signaling at the axon-glia interface in white matter.

The diffusion of calcium inside neurons is determined in part by the intracellular calcium binding species that rapidly bind to free calcium ions upon entry. It has long been known that some portion of a neuron’s intracellular calcium binding capacity must be fixed or poorly mobile, as calcium diffusion is strongly slowed in the intracellular environment relative to diffusion in cytosolic extract. The working assumption was that these immobile calcium binding sites are provided by structural proteins bound to the cytoskeleton or intracellular membranes and may thereby be relatively similar in composition and capacity across different cell types. However, recent evidence suggests that the immobile buffering capacity can vary greatly between cell types and that some mobile calcium binding proteins may alter their mobility upon binding calcium, thus blurring the line between mobile and immobile. The ways in which immobile buffering capacity might be relevant to different calcium domains within neurons has been explored primarily through modeling. In certain regimes, the presence of immobile buffers and the interaction between mobile and immobile buffers have been shown to result in complex spatiotemporal patterns of free calcium. In total, these experimental and modeling findings call for a more nuanced consideration of the local intracellular calcium microenvironment. In this review we focus on the different amounts, affinities, and mobilities of immobile calcium binding species; propose a new conceptual category of physically diffusible but functionally immobile buffers; and discuss how these buffers might interact with mobile calcium binding partners to generate characteristic calcium domains.

Hippocampal mossy fiber synapses show unique molecular features and dynamic range of plasticity. A recent paper proposed that the defining features of mossy fiber synaptic plasticity are caused by a local buildup of extracellular adenosine (Moore et al., 2003). In this study, we reassessed the role of ambient adenosine in regulating mossy fiber synaptic plasticity in mouse and rat hippocampal slices. Synaptic transmission was highly sensitive to activation of presynaptic adenosine A1receptors (A1Rs), which reduced transmitter release by >75%. However, most of A1Rs were not activated by ambient adenosine. Field potentials increased only by 20-30% when A1Rs were fully blocked with the A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (1 μm). Moreover, blocking A1Rs hardly altered paired-pulse facilitation, frequency facilitation, or posttetanic potentiation. Frequency facilitation was similar inA1R-/-mice and when measured with NMDA receptor-mediated EPSCs in CA3 pyramidal cells in the presence of DPCPX. Additional experiments suggested that the results obtained by Moore et al. (2003) can partially be explained by their usage of a submerged recording chamber and elevated divalent cation concentrations. In conclusion, a reduction of the basal release probability by ambient adenosine does not underlie presynaptic forms of plasticity at mossy fiber synapses.

Specific agonists of metabotropic glutamate receptors (mGluRs) provide powerful tools to discriminate afferent fibers originating from different presynaptic neurons. The group II mGluR agonists L-CCG-I ((2S,1'S,2'S)-2-(2-carboxycyclopropyl)glycine) and DCG-IV ((2S,2'R,3'R)-2-(2',3'-dicarboxy-cyclopropyl)glycine) are commonly used to distinguish between mossy fiber and associational-commissural (A/C) fiber input to the hippocampal CA3 region because only on the former group II mGluRs are expressed. Since previous reports indicated that L-CCG-I can activate group III mGluRs as well, we investigated whether L-CCG-I depresses A/C field potentials. L-CCG-I (10-300 microM) exhibited a significant dose-dependent and reversible reduction of A/C field potentials by 8 +/- 4% (10 microM), by 32 +/- 4% (100 microM, p0.001) and by 38 +/- 7% (300 microM, p0.05) that was accompanied by a concomitant increase in paired-pulse facilitation. Moreover, the selective group III antagonist (R,S)-alpha-methylserine-O-phosphate (MSOP; 100 microM) significantly reduced the field potential inhibition by L-CCG-I (100 microM) to 9 +/- 4% (p0.05). In contrast, DCG-IV did not affect A/C field potentials. In conclusion, the purported group II mGluR agonist L-CCG-I depresses A/C synaptic transmission by activation of group III mGluRs. For this reason, DCG-IV should be the drug of choice when aiming to discriminate between mossy fiber and A/C input to CA3 pyramidal cells.

Hybrid clamp protocols, in which a discontinuous single electrode voltage clamp (dSEVC) amplifier is switched from current to voltage clamp during the recording, are frequently used to investigate conductance changes after high frequency trains of action potentials. This technique is advantageous because it combines physiological stimulation of the cell with the possibility of analyzing the consecutive conductance changes quantitatively. In this study an improved hybrid clamp protocol, called dynamic hybrid clamp, is developed that enables the experimenter to study tail currents after single action potentials. The protocol employs real time action potential detection to assure precise timing of the mode switch and utilizes an external sample and hold amplifier to avoid voltage steps during the switch to voltage clamp. With the use of whole-cell patch clamp recordings and high switching frequencies (or =25 kHz), dSEVC can easily be started with a minimal delay (1.5 ms) after single action potentials and tail currents underlying afterhyperpolarisations (AHPs) and afterdepolarisations ensuing single spikes are clearly resolved. The dynamic hybrid clamp should also be useful for analysis of spontaneously occurring events such as intrinsic or population bursts.

Metabotropic glutamate receptors (mGluRs) control excitatory neurotransmission as inhibitory autoreceptors at many synapses throughout the CNS. Since pharmacological activation of mGluRs potently depresses excitatory transmission, anticonvulsive effects were found in a number of experimental epilepsies. However, although native rodent mGluRs and heterologously expressed human mGluRs have so far been investigated in great detail, our knowledge about native human mGluRs in situ is limited. Here we used acute human hippocampal slices prepared from hippocampi surgically removed for the treatment of temporal lobe epilepsy in order to investigate the modulation of glutamatergic transmission by human mGluRs at the perforant path-granule cell synapse. The broad spectrum mGluR agonist (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) profoundly and reversibly reduced field EPSPs (fEPSPs) with an EC50 of 30±7.4 μM. Paired-pulse depression of fEPSPs was converted into strong facilitation. The inhibition of fEPSPs by ACPD was mimicked by the specific group II mGluR agonist (2S, 2′R, 3′R)-2-(2′,3′-dicarboxycyclopropyl)glycine (DCG-IV), while the specific group I agonist (S)-3,5-dihydroxyphenylglycine (DHPG) was ineffective. The effect of ACPD was blocked by group II antagonist (2S,3S,4S)-2methyl-2-(carboxycyclopropyl)glycine (MCCG) but was not changed by coapplication of the specific group III antagonist (S)2 amino2methyl4phosphonobutanoic acid (MAP4). ACPD reduced pharmacologically isolated intracellular EPSPs in granule cells to the same extent as fEPSPs, whereas a specific group III agonist had no effect on EPSPs. Whole-cell recordings from morphologically identified granule cells revealed that DCG-IV significantly reduced the frequency of miniature EPSCs (mEPSCs) in granule cells while the mean amplitude of mEPSCs was not affected. We conclude that in human dentate gyrus mGluR2/3 can almost completely depress glutamate release by a presynaptic mechanism which acts downstream of presynaptic voltage gated calcium-entry and most likely involves a direct modulation of the release machinery.

Background: Aneurysmal subarachnoid hemorrhage (aSAH) is still a fatal and morbid disease, although bleeding aneurysms can be secured in almost all cases. Occurrence of post-SAH complications including cerebral vasospasm, delayed cerebral ischemia, hydrocephalus, epilepsy, and infections are the main determinants of clinical outcome. Hence, it is important to search for early predictors for specific post-SAH complications to treat these complications properly. Both cellular and molecular (cytokines) inflammation play a key role after aSAH during the phase of occurrence of post-SAH complications. Interleukin-6 (IL-6) is a well-known cytokine that has been extensively analyzed in cerebrospinal fluid (CSF) of patients after aSAH, but detailed studies exploring the role of systemic IL-6 in aSAH associated complications and its impact on early clinical outcome prediction are lacking. The current study aims to analyze the systemic IL-6 levels over two weeks after bleeding and its role in post-SAH complications. Methods: We recruited 80 aSAH patients prospectively who underwent peripheral venous blood withdrawal in serum gel tubes. The blood was centrifuged to harvest the serum, which was immediately frozen at −80 °C until analysis. Serum IL-6 levels were quantified using Immulite immunoassay system. Patient records including age, gender, post-SAH complications, aneurysm treatment, and clinical outcome (modified Rankin scale and Glasgow outcome scale) were retrieved to allow different subgroup analysis. Results: Serum IL-6 levels were significantly raised after aSAH compared to healthy controls over the first two weeks after hemorrhage. Serum IL-6 levels were found to be significantly elevated in aSAH patients presenting with higher Hunt and Hess grades, increasing age, and both intraventricular and intracerebral hemorrhage. Interestingly, serum IL-6 was also significantly raised in aSAH patients who developed seizures, cerebral vasospasm (CVS), and chronic hydrocephalus. IL-6 levels were sensitive to the development of infections and showed an increase in patients who developed pneumoniae. Intriguingly, we found a delayed increase in serum IL-6 in patients developing cerebral infarction. Finally, IL-6 levels were significantly higher in patients presenting with poor clinical outcome in comparison to good clinical outcome at discharge from hospital. Conclusion: Serum IL-6 levels were elevated early after aSAH and remained high over the two weeks after initial bleeding. Serum IL-6 was elevated in different aSAH associated complications, acting as a non-specific marker for post-SAH complications and an important biomarker for clinical outcome at discharge.

6-Hydroxykynurenic acid (6-HKA), a derivative of kynurenic acid (KYNA) extracted from Ginkgo biloba leaves, was tested for its putative glutamate receptor (GluR) antagonism in comparison to the scaffold substance. The patch-clamp method together with fast-application techniques were used to estimate inhibition by 6-HKA and KYNA of agonist binding at NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (NMDARs and AMPARs) of CA1 pyramidal neurones. 6-Hydroxykynurenic acid proved to be a low-affinity antagonist. When comparing with KYNA, 6-HKA was less potent at NMDARs (IC(50) = 136 versus 59 microM), but showed a higher affinity to AMPARs (K(B) = 22 versus 172 microM). The replacement of 6-HKA and KYNA by glutamate was investigated on outside-out patches. Both antagonists competitively inhibited AMPAR responses and displayed fast unbinding kinetics, but the derivative was significantly slower displaced than KYNA (tau = 1.63 versus 1.22 ms). Our findings demonstrate that 6-hydroxylation considerably changes the pharmacological profile of KYNA. Among the 6-derivatives of KYNA, 6-HKA shows the highest affinity to AMPARS: Despite its relatively low lipophily, these properties might be of clinical relevance under conditions that compromise the integrity of the blood-brain barrier. Furthermore, 6-HKA should be a useful tool to analyse glutamate-mediated synaptic responses.

We investigated the electrophysiology of morphologically identified human granule cells with conventional current-clamp recordings. Slices were prepared from 14 human epileptic sclerotic hippocampi. Granule cells appeared to have a diverse electrophysiology. Each cell was distinguished by the shape of the afterhyperpolarization following single action potentials. Two types could be discerned: type I afterhyperpolarizations were monophasic and brief (typically 10-40 ms), whilst type II afterhyperpolarizations were biphasic and long (typically 50-100 ms). The two types also differed in their repetitive firing behaviour and action potential morphology: type I cells had significantly weaker spike frequency adaptation, lower action potential amplitude and smaller action potential upstroke/downstroke ratio. Thus, the firing pattern of type I cells resembled that of rodent dentate interneurons. In contrast, the corresponding parameters of type II cells were comparable to rodent dentate granule cells. Despite the distinct firing patterns, membrane properties were not different. The two types of cells also differed in their synaptic responses to stimulation of the perforant path. At strong suprathreshold stimulation intensity, type I cells always generated multiple action potentials, whereas type II cells usually spiked once only. Slow inhibitory postsynaptic potentials were not detected in type I neurons, but were easily identified in type II neurons. Extracellular recordings of perforant path-evoked field potentials in the cell layer confirmed that the majority of granule cells showed multiple discharges even when we recorded simultaneously from a type II cell that generated one action potential only. The morphology of both types of cells was characteristic of what has been described for primate dentate granule cells. Based on comparisons with previous studies on rodent and human granule cells, we tentatively hypothesize that: (i) the majority of granule cells from sclerotic hippocampus display an hyperexcitable epileptogenic electrophysiology; (ii) there is a subset of granule cells whose electrophysiology is preserved and is more comparable to granule cells from non-epileptic hippocampus.

NG2 expressing oligodendrocyte precursor cells stand out from other types of glial cells by receiving classical synaptic contacts from many neurons. This unconventional form of signalling between neurons and glial cells enables NG2 cells to receive information about the activity of presynaptic neurons with high temporal and spatial precision and has been postulated to be involved in activity-dependent myelination. While this still unproven concept is generally compelling, how NG2 cells may integrate synaptic input has hardly been addressed to date. Here we review the biophysical characteristics of synaptic currents and membrane properties of NG2 cells and discuss their capabilities to perform complex temporal and spatial signal integration and how this may be important for activity-dependent myelination.

It has remained difficult to ascribe a specific functional role to immobile or fixed intracellular calcium buffers in central neurons because the amount of these buffers is unknown. Here, we explicitly isolated the fixed buffer fraction by prolonged whole-cell patch-clamp dialysis and quantified its buffering capacity in murine hippocampal slices using confocal calcium imaging and the “added-buffer” approach. In dentate granule cells, the calcium binding ratio (κ) after complete washout of calbindin D28k(Cb), κfixed, displayed a substantial value of ∼100. In contrast, in CA1 oriens lacunosum moleculare (OLM) interneurons, which do not contain any known calcium-binding protein(s), κfixedamounted to only ∼30. Based on these values, a theoretical analysis of dendritic spread of calcium after local entry showed that fixed buffers, in the absence of mobile species, decrease intracellular calcium mobility 100- and 30-fold in granule cells and OLM cells, respectively, and thereby strongly slow calcium signals. Although the large κfixedalone strongly delays the spread of calcium in granule cells, this value optimizes the benefits of additionally expressing the mobile calcium binding protein Cb. With such high κfixed, Cb effectively increases the propagation velocity to levels seen in OLM cells and, contrary to expectation, does not affect the peak calcium concentration close to the source but sharpens the spatial and temporal calcium gradients. The data suggest that the amount of fixed buffers determines the temporal availability of calcium for calcium-binding partners and plays a pivotal role in setting the repertoire of cellular calcium signaling regimens.

The hyperpolarization-activated cation current I(h) is an important regulator of neuronal excitability and may contribute to the properties of the dentate gyrus granule (DGG) cells, which constitute the input site of the canonical hippocampal circuit. Here, we investigated changes in I(h) in DGG cells in human temporal lobe epilepsy (TLE) and the rat pilocarpine model of TLE using the patch-clamp technique. Messenger-RNA (mRNA) expression of I(h)-conducting HCN1, 2 and 4 isoforms was determined using semi-quantitative in-situ hybridization. I(h) density was ∼1.8-fold greater in DGG cells of TLE patients with Ammon's horn sclerosis (AHS) as compared to patients without AHS. The magnitude of somatodendritic I(h) was enhanced also in DGG cells in epileptic rats, most robustly during the latent phase after status epilepticus and prior to the occurrence of spontaneous epileptic seizures. During the chronic phase, I(h) was increased ∼1.7-fold. This increase of I(h) was paralleled by an increase in HCN1 and HCN4 mRNA expression, whereas HCN2 expression was unchanged. Our data demonstrate an epilepsy-associated upregulation of I(h) likely due to increased HCN1 and HCN4 expression, which indicate plasticity of I(h) during epileptogenesis and which may contribute to a compensatory decrease in neuronal excitability of DGG cells.

The ubiquitous presynaptic metabotropic glutamate receptors (mGluRs) are generally believed to primarily inhibit synaptic transmission through blockade of Ca(2+) entry. Here, we analyzed how mGluR8 achieves a nearly complete inhibition of glutamate release at hippocampal synapses. Surprisingly, presynaptic Ca(2+) imaging and miniature excitatory postsynaptic current recordings showed that mGluR8 acts without affecting Ca(2+) entry, diffusion, and buffering. We quantitatively compared the Ca(2+) dependence of the inhibition of release by mGluR8 with the inhibition by ω-conotoxin GVIA. These calculations suggest that the inhibition produced by mGluR8 may be explained by a decrease in the apparent Ca(2+) affinity of the release sensor and, to a smaller extent, by a reduction of the maximal release rate. Upon activation of mGluR8, phasic transmitter release toward the end of a train of action potentials is greater as compared with presynaptic inhibition induced by blocking Ca(2+) entry, which is consistent with the important role of Ca(2+) in accelerating the replenishment of released vesicles. The action of mGluR8 was resistant to blockers of classical G-protein transduction pathways including inhibition of adenylate cyclase and may represent a direct effect on the release machinery. In conclusion, our data identify a mode of presynaptic inhibition which allows mGluR8 to profoundly inhibit vesicle fusion while not diminishing vesicle replenishment and which thereby differentially changes the temporal transmission properties of the inhibited synapse.

NG2-expressing oligodendrocyte precursor cells (OPCs) are ubiquitous and generate oligodendrocytes throughout the young and adult brain. Previous work has shown that virtually every NG2 cell receives synaptic input from many axons, but the meaning of this signaling is not understood. In particular, it is unclear whether neurons specifically synapse onto OPCs or whether OPCs merely trace adjacent neurotransmitter release sites and are not recognized by the presynaptic neuron. Here, we show with whole-cell recordings from distinct developmental stages of oligodendroglial cells in brain slices that synaptic input essentially disappears as soon as OPCs differentiate into premyelinating oligodendrocytes (NG2 − , DM20/PLP + , O1 + ). Uncaging experiments and tracer loading revealed that premyelinating oligodendrocytes still express a substantial number of AMPA/kainate receptors and many processes, but spontaneous and stimulated synaptic currents are mostly absent. Nevertheless, in a minority of premyelinating cells, electrical stimulation evoked small synaptic currents with an unusual behavior: their amplitude compared well with the quantal amplitude in OPCs but they occurred asynchronously and with the remarkable latency of 40–100 ms, indicating that the presynaptic release machinery has become ineffective. Mature myelinating oligodendrocytes completely lack AMPA/kainate receptors and respond to uncaging and synaptic stimulation with glutamate transporter currents. Our data show that neurons selectively synapse onto only one of several coexisting developmental stages of glial cells and thereby indicate that neurons indeed specifically signal to OPCs and are able to modulate transmitter output by regulating the local release machinery in a manner specific to the developmental stage of the postsynaptic glial cell.

Progenitor cells expressing the proteoglycan NG2 represent approximately 5% of the total cells in the adult brain, and are found both in grey and white matter regions where they give rise to oligodendrocytes. The finding that these cells receive synaptic contacts from excitatory and inhibitory neurons has not only raised major interest in the possible roles of these synapses, but also stimulated further research on the developmental and cellular functions of NG2-expressing (NG2(+)) progenitors themselves in the context of neural circuit physiology. Here we review recent findings on the functional properties of the synapses on NG2(+) cells in grey and white matter regions of the brain. In this review article we make an attempt to integrate current knowledge on the cellular and developmental properties of NG2(+) progenitors with the functional attributes of their synapses, in order to understand the physiological relevance of neuron-NG2(+) progenitor signal transmission. We propose that, although NG2(+) progenitors receive synaptic contact in all brain regions where they are found, their synapses might have different developmental and functional roles, probably reflecting the distinct functions of NG2(+) progenitors in the brain.