Organotypic Hippocampal Slice Cultures: A Model System to Study Basic Cellular and Molecular Mechanisms of Neuronal Cell Death, Neuroprotection, and Synaptic Plasticity

Slack K+ channels limit kainic acid-induced seizure severity in mice by modulating neuronal excitability and firing

Mutations of the Na+-activated K+ channel Slack (KCNT1) are associated with terrible epilepsy syndromes that already begin in infancy. Here we report increased severity of acute kainic acid-induced seizures in adult and juvenile Slack knockout mice (Slack-/-) in vivo. Fittingly, we find exacerbation of cell death following kainic acid exposure in organotypic hippocampal slices as well as dissociated hippocampal cultures from Slack-/- in vitro. Furthermore, in cultured Slack-/- neurons, kainic acid-triggered Ca2+ influx and K+ efflux as well as depolarization-induced tetrodotoxin-sensitive inward currents are higher compared to the respective controls. This apparent changes in ion homeostasis could possibly explain altered action potential kinetics of Slack-/- neurons: steeper rise slope, decreased threshold, and duration of afterhyperpolarization, which ultimately lead to higher action potential frequencies during kainic acid application or injection of depolarizing currents. Based on our data, we propose Slack as crucial gatekeeper of neuronal excitability to acutely limit seizure severity.

Perivascular invasion of primary human glioblastoma cells in organotypic human brain slices: human cells migrating in human brain

INTRODUCTION

Glioblastoma (GBM) is an aggressive primary brain cancer. Lack of effective therapy is related to its highly invasive nature. GBM invasion has been studied with reductionist systems that do not fully recapitulate the cytoarchitecture of the brain. We describe a human-derived brain organotypic model to study the migratory properties of GBM IDH-wild type ex vivo.

METHODS

Non-tumor brain samples were obtained from patients undergoing surgery (n = 7). Organotypic brain slices were prepared, and green fluorescent protein (GFP)-labeled primary human GBM IDH-wild type cells (GBM276, GBM612, GBM965) were placed on the organotypic slice. Migration was evaluated via microscopy and immunohistochemistry.

RESULTS

After placement, cells migrated towards blood vessels; initially migrating with limited directionality, sending processes in different directions, and increasing their speed upon contact with the vessel. Once merged, migration speed decreased and continued to decrease with time (p < 0.001). After perivascular localization, migration is limited along the blood vessels in both directions. The percentage of cells that contact blood vessels and then continue to migrate along the vessel was 92.5% (- 3.9/ + 2.9)% while the percentage of cells that migrate along the blood vessel and leave was 7.5% (- 2.9/ + 3.9) (95% CI, Clopper-Pearson (exact); n = 256 cells from six organotypic cultures); these percentages are significantly different from the random (50%) null hypothesis (z = 13.6; p < 10-7). Further, cells increase their speed in response to a decrease in oxygen tension from atmospheric normoxia (20% O2) to anoxia (1% O2) (p = 0.033).

CONCLUSION

Human organotypic models can accurately study cell migration ex vivo. GBM IDH-wild type cells migrate toward the perivascular space in blood vessels and their migratory parameters change once they contact vascular structures and under hypoxic conditions. This model allows the evaluation of GBM invasion, considering the human brain microenvironment when cells are removed from their native niche after surgery.

The N-Formyl Peptide Receptor 2 (FPR2) Agonist MR-39 Improves Ex Vivo and In Vivo Amyloid Beta (1-42)-Induced Neuroinflammation in Mouse Models of Alzheimer's Disease

The major histopathological hallmarks of Alzheimer's disease (AD) include β-amyloid (Aβ) plaques, neurofibrillary tangles, and neuronal loss. Aβ 1-42 (Aβ_1-42) has been shown to induce neurotoxicity and secretion of proinflammatory mediators that potentiate neurotoxicity. Proinflammatory and neurotoxic activities of Aβ_1-42 were shown to be mediated by interactions with several cell surface receptors, including the chemotactic G protein-coupled N-formyl peptide receptor 2 (FPR2). The present study investigated the impact of a new FPR2 agonist, MR-39, on the neuroinflammatory response in ex vivo and in vivo models of AD. To address this question, organotypic hippocampal cultures from wild-type (WT) and FPR2-deficient mice (knockout, KO, FPR2^-/-) were treated with fibrillary Aβ_1-42, and the effect of the new FPR2 agonist MR-39 on the release of pro- and anti-inflammatory cytokines was assessed. Similarly, APP/PS1 double-transgenic AD mice were treated for 20 weeks with MR-39, and immunohistological staining was performed to assess neuronal loss, gliosis, and Aβ load in the hippocampus and cortex. The data indicated that MR-39 was able to reduce the Aβ_1-42-induced release of proinflammatory cytokines and to improve the release of anti-inflammatory cytokines in mouse hippocampal organotypic cultures. The observed effect was apparently related to the inhibition of the MyD88/TRAF6/NFкB signaling pathway and a decrease in NLRP3 inflammasome activation. Administration of MR-39 to APP/PS1 mice improved neuronal survival and decreased microglial cell density and plaque load.These results suggest that FPR2 may be a promising target for alleviating the inflammatory process associated with AD and that MR-39 may be a useful therapeutic agent for AD.

Slice Culture Modeling of CNS Viral Infection

The complexity of the central nervous system (CNS) is not recapitulated in cell culture models. Thin slicing and subsequent culture of CNS tissue has become a valued means to study neuronal and glial biology within the context of the physiologically relevant tissue milieu. Modern membrane-interface slice culturing methodology allows for straightforward access to both CNS tissue and feeding medium, enabling experimental manipulations and analyses that would otherwise be impossible in vivo. CNS slices can be successfully maintained in culture for up to several weeks for investigation of evolving pathology and long-term intervention in models of chronic neurologic disease.Herein, membrane-interface slice culture models for studying viral encephalitis and myelitis are detailed, with emphasis on the use of these models for investigation of pathogenesis and evaluation of novel treatment strategies. We describe techniques to (1) generate brain and spinal cord slices from rodent donors, (2) virally infect slices, (3) monitor viral replication, (4) assess virally induced injury/apoptosis, (5) characterize "CNS-specific" cytokine production, and, (6) treat slices with cytokines/pharmaceuticals. Although our focus is on CNS viral infection, we anticipate that the described methods can be adapted to address a wide range of investigations within the fields of neuropathology, neuroimmunology, and neuropharmacology.

Novel arylidene malonate derivative, KM-34, showed neuroprotective effects on in vitro and in vivo models of ischemia/reperfusion

Cerebral ischemia constitutes the most frequent type of cerebrovascular disease. The reduction of blood supply to the brain initiates the ischemic cascade starting from ionic imbalance to subsequent glutamate excitotoxicity, neuroinflammation and oxidative stress, eventually causing neuronal death. Previously, the authors have demonstrated the in vitro cytoprotective and antioxidant effects of a new arylidene malonate derivative, KM-34, against oxidizing agents like hydrogen peroxide, glutamate or Fe3+/ascorbate. Here, we examined for the first time the neuroprotective effect of KM-34 on ischemia/reperfusion models. In vitro, treatment with 10 and 50 μM KM-34 reduced the cellular death (propidium iodide incorporation) induced by oxygen glucose deprivation (OGD) in rat organotypic hippocampal slices cultures. In vivo, stroke was induced in male Wistar rats through middle cerebral artery occlusion (MCAO), followed by 23 h of reperfusion. KM-34 was orally administered 105 min after MCAO onset. We noticed that 1 mg/kg KM-34 reduced infarct volume and neurological score, and increased the latency to fall in the Hanging Wire test compared to vehicle-treated ischemic animals. While ischemic and sham-operated groups showed similar horizontal locomotor activity, vertical counts decreased after MCAO, suggesting that vertical movements are more sensitive to the ischemic injury. Treatment with KM-34 also alleviated the mitochondrial impairment (ROS generation, swelling and membrane potential dissipation) induced by transient MCAO but not significant alterations were found in oxidative stress parameters. Overall, the study provides preclinical evidences confirming the neuroprotective effects of a novel synthetic molecule and paved the way for future investigations regarding its therapeutic potential against brain ischemia/reperfusion injury.

In-depth quantitative proteomic characterization of organotypic hippocampal slice culture reveals sex-specific differences in biochemical pathways

Sex differences in the brain of mammals range from neuroarchitecture through cognition to cellular metabolism. The hippocampus, a structure mostly associated with learning and memory, presents high vulnerability to neurodegeneration and aging. Therefore, we explored basal sex-related differences in the proteome of organotypic hippocampal slice culture, a major in vitro model for studying the cellular and molecular mechanisms related to neurodegenerative disorders. Results suggest a greater prevalence of astrocytic metabolism in females and significant neuronal metabolism in males. The preference for glucose use in glycolysis, pentose phosphate pathway and glycogen metabolism in females and high abundance of mitochondrial respiration subunits in males support this idea. An overall upregulation of lipid metabolism was observed in females. Upregulation of proteins responsible for neuronal glutamate and GABA synthesis, along with synaptic associated proteins, were observed in males. In general, the significant spectrum of pathways known to predominate in neurons or astrocytes, together with the well-known neuronal and glial markers observed, revealed sex-specific metabolic differences in the hippocampus. TEM qualitative analysis might indicate a greater presence of mitochondria at CA1 synapses in females. These findings are crucial to a better understanding of how sex chromosomes can influence the physiology of cultured hippocampal slices and allow us to gain insights into distinct responses of males and females on neurological diseases that present a sex-biased incidence.

General Overview of Neuronal Cell Culture

In this introductory chapter, we provide a general overview of neuronal cell culture. This is a rapidly evolving area of research and we provide an outline and contextual framework for the different chapters of this book. These chapters have all been contributed by scientists actively working in the field who are currently using state-of-the-art techniques to advance our understanding of the molecular and cellular biology of the central nervous system. Each chapter provides detailed descriptions and experimental protocols for a variety of techniques ranging in scope from basic neuronal cell line culturing to advanced and specialized methods.

Genetically Encoded Tools for Research of Cell Signaling and Metabolism under Brain Hypoxia

Hypoxia is characterized by low oxygen content in the tissues. The central nervous system (CNS) is highly vulnerable to a lack of oxygen. Prolonged hypoxia leads to the death of brain cells, which underlies the development of many pathological conditions. Despite the relevance of the topic, different approaches used to study the molecular mechanisms of hypoxia have many limitations. One promising lead is the use of various genetically encoded tools that allow for the observation of intracellular parameters in living systems. In the first part of this review, we provide the classification of oxygen/hypoxia reporters as well as describe other genetically encoded reporters for various metabolic and redox parameters that could be implemented in hypoxia studies. In the second part, we discuss the advantages and disadvantages of the primary hypoxia model systems and highlight inspiring examples of research in which these experimental settings were combined with genetically encoded reporters.

PSD-95 Serine 73 phosphorylation is not required for induction of NMDA-LTD

PSD-95 is a major scaffolding protein of the post-synaptic density (PSD) of a glutamatergic synapse. PSD-95, via interactions with stargazin, anchors AMPA receptors at the synapse and regulates AMPAR currents. The expression of PSD-95 is regulated during synaptic plasticity. It is, however, unknown whether this regulation is required for induction of functional plasticity of glutamatergic synapses. Here, we show that NMDA-induced long-term depression of synaptic transmission (NMDA-LTD) is accompanied by downregulation of PSD-95 protein levels. Using pharmacologic and molecular manipulations, we further demonstrate that the NMDA-induced downregulation of PSD-95 depends on the activation of CaMKII and CaMKII-driven phosphorylation of PSD-95 serine 73. Surprisingly, neither CaMKII activity nor CaMKII-dependent phosphorylation of PSD-95 serine 73 are required for the expression of NMDA-LTD. These results support the hypothesis that synaptic plasticity of AMPARs may occur without dynamic regulation of PSD-95 protein levels.

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signalling

Amyloid beta peptides (Aβ) proteins play a key role in vascular pathology in Alzheimer’s Disease (AD) including impairment of the blood–brain barrier and aberrant angiogenesis. Although previous work has demonstrated a pro-angiogenic role of Aβ, the exact mechanisms by which amyloid precursor protein (APP) processing and endothelial angiogenic signalling cascades interact in AD remain a largely unsolved problem. Here, we report that increased endothelial sprouting in human-APP transgenic mouse (TgCRND8) tissue is dependent on β-secretase (BACE1) processing of APP. Higher levels of Aβ processing in TgCRND8 tissue coincides with decreased NOTCH3/JAG1 signalling, overproduction of endothelial filopodia and increased numbers of vascular pericytes. Using a novel in vitro approach to study sprouting angiogenesis in TgCRND8 organotypic brain slice cultures (OBSCs), we find that BACE1 inhibition normalises excessive endothelial filopodia formation and restores NOTCH3 signalling. These data present the first evidence for the potential of BACE1 inhibition as an effective therapeutic target for aberrant angiogenesis in AD.

The neuroprotective role of microglial cells against amyloid beta-mediated toxicity in organotypic hippocampal slice cultures

During Alzheimer's disease (AD) progression, microglial cells play complex roles and have potentially detrimental as well as beneficial effects. The use of appropriate model systems is essential for characterizing and understanding the roles of microglia in AD pathology. Here, we used organotypic hippocampal slice cultures (OHSCs) to investigate the impact of microglia on amyloid beta (Aβ)-mediated toxicity. Neurons in OHSCs containing microglia were not vulnerable to cell death after 7 days of repeated treatment with Aβ_1-42 oligomer-enriched preparations. However, when clodronate was used to remove microglia, treatment with Aβ_1-42 resulted in significant neuronal death. Further investigations indicated signs of endoplasmic reticulum stress and caspase activation after Aβ_1-42 challenge only when microglia were absent. Interestingly, microglia provided protection without displaying any classic signs of activation, such as an amoeboid morphology or the release of pro-inflammatory mediators (e.g., IL-6, TNF-α, NO). Furthermore, depleting microglia or inhibiting microglial uptake mechanisms resulted in significant more Aβ deposition compared to that observed in OHSCs containing functional microglia, suggesting that microglia efficiently cleared Aβ. Because inhibiting microglial uptake increased neuronal cell death, the ability of microglia to engulf Aβ is thought to contribute to its protective properties. Our study argues for a beneficial role of functional ramified microglia whereby they act against the accumulation of neurotoxic forms of Aβ and support neuronal resilience in an in situ model of AD pathology.

Organotypic slice culture based on in ovo electroporation for chicken embryonic central nervous system

Organotypic slice culture is a living cell research technique which blends features of both in vivo and in vitro techniques. While organotypic brain slice culture techniques have been well established in rodents, there are few reports on the study of organotypic slice culture, especially of the central nervous system (CNS), in chicken embryos. We established a combined in ovo electroporation and organotypic slice culture method to study exogenous genes functions in the CNS during chicken embryo development. We performed in ovo electroporation in the spinal cord or optic tectum prior to slice culture. When embryonic development reached a specific stage, green fluorescent protein (GFP)-positive embryos were selected and fluorescent expression sites were cut under stereo fluorescence microscopy. Selected tissues were embedded in 4% agar. Tissues were sectioned on a vibratory microtome and 300 μm thick sections were mounted on a membrane of millicell cell culture insert. The insert was placed in a 30-mm culture dish and 1 ml of slice culture media was added. We show that during serum-free medium culture, the slice loses its original structure and propensity to be strictly regulated, which are the characteristics of the CNS. However, after adding serum, the histological structure of cultured-tissue slices was able to be well maintained and neuronal axons were significantly longer than that those of serum-free medium cultured-tissue slices. As the structure of a complete single neuron can be observed from a slice culture, this is a suitable way of studying single neuronal dynamics. As such, we present an effective method to study axon formation and migration of single neurons in vitro.

FRET-based imaging of intracellular ATP in organotypic brain slices

Active neurons require a substantial amount of adenosine triphosphate (ATP) to re-establish ion gradients degraded by ion flux across their plasma membranes. Despite this fact, neurons, in contrast to astrocytes, do not contain any significant stores of energy substrates. Recent work has provided evidence for a neuro-metabolic coupling between both cell types, in which increased glycolysis and lactate production in astrocytes support neuronal metabolism. Here, we established the cell type-specific expression of the Förster resonance energy transfer (FRET) based nanosensor ATeam1.03^YEMK ("Ateam") for dynamic measurement of changes in intracellular ATP levels in organotypic brain tissue slices. To this end, adeno-associated viral vectors coding for Ateam, driven by either the synapsin- or glial fibrillary acidic protein (GFAP) promoter were employed for specific transduction of neurons or astrocytes, respectively. Chemical ischemia, induced by perfusion of tissue slices with metabolic inhibitors of cellular glycolysis and mitochondrial respiration, resulted in a rapid decrease in the cellular Ateam signal to a new, low level, indicating nominal depletion of intracellular ATP. Increasing the extracellular potassium concentration to 8 mM, thereby mimicking the release of potassium from active neurons, did not alter ATP levels in neurons. It, however, caused in an increase in ATP levels in astrocytes, a result which was confirmed in acutely isolated tissue slices. In summary, our results demonstrate that organotypic cultured slices are a reliable tool for FRET-based dynamic imaging of ATP in neurons and astrocytes. They moreover provide evidence for an increased ATP synthesis in astrocytes, but not neurons, during periods of elevated extracellular potassium concentrations.

Low-Intensity Ultrasound Decreases Ischemia-Induced Edema by Inhibiting N-Methyl-d-Aspartic Acid Receptors

Background: We have previously shown that low-intensity ultrasound (LIUS), a noninvasive mechanical stimulus, inhibits brain edema formation induced by oxygen and glucose deprivation (OGD) or treatment with glutamate, a mediator of OGD-induced edema, in acute rat hippocampal slice model in vitro. Methods: In this study, we treated the rat hippocampal slices with N-methyl-d-aspartic acid (NMDA) or (S)-3,5-dihydroxyphenylglycine (DHPG) to determine whether these different glutamate receptor agonists induce edema. The hippocampal slices were then either sonicated with LIUS or treated with N-methyl-d-aspartic acid receptor (NMDAR) antagonists, namely, MK-801 and ketamine, and observed their effects on edema formation. Results: We observed that treatment with NMDA, an agonist of ionotropic glutamate receptors, induced brain edema at similar degrees compared with that induced by OGD. However, treatment with DHPG, an agonist of metabotropic glutamate receptors, did not significantly induce brain edema. Treatment with the NMDAR antagonists MK-801 or ketamine efficiently prevented brain edema formation by both OGD and NMDA in a concentration-dependent manner. N-Methyl-d-aspartic acid-induced brain edema was alleviated by LIUS in an intensity-dependent manner when ultrasound was administered at 30, 50, or 100 mW/cm2 for 20 minutes before the induction of the edema. Furthermore, LIUS reduced OGD- and NMDA-induced phosphorylation of NMDARs at Y1325. Conclusion: These results suggest that LIUS can inhibit OGD- or NMDA-induced NMDAR activation by preventing NMDAR phosphorylation, thereby reducing a subsequent brain edema formation. The mechanisms by which LIUS inhibits NMDAR phosphorylation need further investigation.

Parvalbumin expression and gamma oscillation occurrence increase over time in a neurodevelopmental model of NMDA receptor dysfunction

Dysfunction of the N-methyl-d-aspartate receptor (NMDAR) is thought to play a role in the pathophysiology of neurodevelopmental diseases like schizophrenia. To study the effects of NMDAR dysfunction on synaptic transmission and network oscillations, we used hippocampal tissue of NMDAR subunit GluN2A knockout (KO) mice. Field excitatory postsynaptic potentials were recorded in acute hippocampal slices of adult animals. Synaptic transmission was impaired in GluN2A KO slices compared to wild-type (WT) slices. Further, to investigate whether NMDAR dysfunction would alter neurodevelopment in vitro, we used organotypic hippocampal slice cultures of WT and GluN2A KO mice. Immunostaining performed with cultures kept two, seven, 14, 25 days in vitro (DIV) revealed an increasing expression of parvalbumin (PV) over time. As a functional readout, oscillatory activity induced by the cholinergic agonist carbachol was recorded in cultures kept seven, 13, and 26 DIV using microelectrode arrays. Initial analysis focused on the occurrence of delta, theta, beta and gamma oscillations over genotype, DIV and hippocampal area (CA1, CA3, dentate gyrus (DG)). In a follow-up analysis, we studied the peak frequency and the peak power of each of the four oscillation bands per condition. The occurrence of gamma oscillations displayed an increase by DIV similar to the PV immunostaining. Unlike gamma occurrence, delta, theta, and beta occurrence did not change over time in culture. The peak frequency and peak power in the different bands of the oscillations were not different in slices of WT and GluN2A KO mice. However, the level of PV expression was lower in GluN2A KO compared to WT mice. Given the role of PV-containing fast-spiking basket cells in generation of oscillations and the decreased PV expression in subjects with schizophrenia, the study of gamma oscillations in organotypic hippocampal slices represents a potentially valuable tool for the characterization of novel therapeutic drugs.

Ex vivo model of epilepsy in organotypic slices-a new tool for drug screening

BACKGROUND

Epilepsy is a prevalent neurological disorder worldwide. It is characterized by an enduring predisposition to generate seizures and its development is accompanied by alterations in many cellular processes. Organotypic slice cultures represent a multicellular environment with the potential to assess biological mechanisms, and they are used as a starting point for refining molecules for in vivo studies. Here, we investigated organotypic slice cultures as a model of epilepsy.

METHODS

We assessed, by electrophysiological recordings, the spontaneous activity of organotypic slices maintained under different culture protocols. Moreover, we evaluated, through molecular-based approaches, neurogenesis, neuronal death, gliosis, expression of proinflammatory cytokines, and activation of NLRP3 inflammasome (nucleotide-binding, leucine-rich repeat, pyrin domain) as biomarkers of neuroinflammation.

RESULTS

We demonstrated that organotypic slices, maintained under a serum deprivation culture protocol, develop epileptic-like activity. Furthermore, throughout a comparative study with slices that do not depict any epileptiform activity, slices with epileptiform activity were found to display significant differences in terms of inflammation-related features, such as (1) increased neuronal death, with higher incidence in CA1 pyramidal neurons of the hippocampus; (2) activation of astrocytes and microglia, assessed through western blot and immunohistochemistry; (3) upregulation of proinflammatory cytokines, specifically interleukin-1β (IL-1β), interleukin-6, and tumor necrosis factor α, revealed by qPCR; and (4) enhanced expression of NLRP3, assessed by western blot, together with increased NLRP3 activation, showed by IL-1β quantification.

CONCLUSIONS

Thus, organotypic slice cultures gradually deprived of serum mimic the epileptic-like activity, as well as the inflammatory events associated with in vivo epilepsy. This system can be considered a new tool to explore the interplay between neuroinflammation and epilepsy and to screen potential drug candidates, within the inflammatory cascades, to reduce/halt epileptogenesis.

Long-Term Culture of Organotypic Hippocampal Slice from Old 3xTg-AD Mouse: An ex vivo Model of Alzheimer's Disease

OBJECTIVE

Conventional methods for organotypic hippocampal tissue slice culture (OHSC) have shown several disadvantages or limitations regarding age of animals used, duration of culture and difficulty using neurodegenerative models. Therefore, we tried to establish OHSC from old 3xTg-Alzheimer's disease (AD) mice for longer period (over 4 weeks) and to validate utility of this system as a valid platform for translational neuroscience of AD.

METHODS

OHSC was performed with old 3xTg-AD mice (12-14 months), old wild type mice (12-14 months) and young 3xTg-AD mice (2-4 months) using serum-free medium for 4 weeks. Hippocampal structure was evaluated by 4', 6-diamidino-2-phenylindole (DAPI) intensity and neuronal metabolism was measured by Alamarblue assay. Pathologic characteristics of AD were also investigated; β-amyloid levels by ELISA, amyloid plaque deposition by Thioflavin-S staining, and glial activation by immunohistochemistry.

RESULTS

Following 4-week culture in serum-free media, hippocampal cells and layers were well preserved in cultured slices from old AD mice as was in those from young AD and old wild type mice. On the contrary, excessive regression of total visible cells was observed in conventional serum-containing medium regardless of genotype of mice. In parallel with this well preserved structure, major pathologic characteristics of AD were also well manifested in hippocampal slices from old AD mice.

CONCLUSION

Our findings suggest that long-term OHSC from old 3xTg-AD mouse can serve as a promising ex vivo system for studies on pathophysiology of AD, especially with the minimum number of sacrifice of experimental animals.

Organotypic Hippocampal Slice Cultures As a Model to Study Neuroprotection and Invasiveness of Tumor Cells

In organotypic hippocampal slice cultures (OHSC), the morphological and functional characteristics of both neurons and glial cells are well preserved. This model is suitable for addressing different research questions that involve studies on neuroprotection, electrophysiological experiments on neurons, neuronal networks or tumor invasion. The hippocampal architecture and neuronal activity in multisynaptic circuits are well conserved in OHSC, even though the slicing procedure itself initially lesions and leads to formation of a glial scar. The scar formation alters presumably the mechanical properties and diffusive behavior of small molecules, etc. Slices allow the monitoring of time dependent processes after brain injury without animal surgery, and studies on interactions between various brain-derived cell types, namely astrocytes, microglia and neurons under both physiological and pathological conditions. An ambivalent aspect of this model is the absence of blood flow and immune blood cells. During the progression of the neuronal injury, migrating immune cells from the blood play an important role. As those cells are missing in slices, the intrinsic processes in the culture may be observed without external interference. Moreover, in OHSC the composition of the medium-external environment is precisely controlled. A further advantage of this method is the lower number of sacrificed animals compared to standard preparations. Several OHSC can be obtained from one animal making simultaneous studies with multiple treatments in one animal possible. For these reasons, OHSC are well suited to analyze the effects of new protective therapeutics after tissue damage or during tumor invasion. The protocol presented here describes a preparation method of OHSC that allows generating highly reproducible, well preserved slices that can be used for a variety of experimental research, like neuroprotection or tumor invasion studies.

Synaptophysin depletion and intraneuronal Aβ in organotypic hippocampal slice cultures from huAPP transgenic mice

Background

To date, there are no effective disease-modifying treatments for Alzheimer’s disease (AD). In order to develop new therapeutics for stages where they are most likely to be effective, it is important to identify the first pathological alterations in the disease cascade. Changes in Aβ concentration have long been reported as one of the first steps, but understanding the source, and earliest consequences, of pathology requires a model system that represents all major CNS cell types, is amenable to repeated observation and sampling, and can be readily manipulated. In this regard, long term organotypic hippocampal slice cultures (OHSCs) from neonatal amyloid mice offer an excellent compromise between in vivo and primary culture studies, largely retaining the cellular composition and neuronal architecture of the in vivo hippocampus, but with the in vitro advantages of accessibility to live imaging, sampling and intervention.

Results

Here, we report the development and characterisation of progressive pathological changes in an organotypic model from TgCRND8 mice. Aβ_1-40 and Aβ_1-42 rise progressively in transgenic slice culture medium and stabilise when regular feeding balances continued production. In contrast, intraneuronal Aβ continues to accumulate in close correlation with a specific decline in presynaptic proteins and puncta. Plaque pathology is not evident even when Aβ_1-42 is increased by pharmacological manipulation (using calpain inhibitor 1), indicating that soluble Aβ species, or other APP processing products, are sufficient to cause the initial synaptic changes.

Conclusions

Organotypic brain slices from TgCRND8 mice represent an important new system for understanding mechanisms of Aβ generation, release and progressive toxicity. The pathology observed in these cultures will allow for rapid assessment of disease modifying compounds in a system amenable to manipulation and observation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0110-7) contains supplementary material, which is available to authorized users.

Carbon Monoxide Releasing Molecule-A1 (CORM-A1) Improves Neurogenesis: Increase of Neuronal Differentiation Yield by Preventing Cell Death

Cerebral ischemia and neurodegenerative diseases lead to impairment or death of neurons in the central nervous system. Stem cell based therapies are promising strategies currently under investigation. Carbon monoxide (CO) is an endogenous product of heme degradation by heme oxygenase (HO) activity. Administration of CO at low concentrations produces several beneficial effects in distinct tissues, namely anti-apoptotic and anti-inflammatory. Herein the CO role on modulation of neuronal differentiation was assessed. Three different models with increasing complexity were used: human neuroblastoma SH-S5Y5 cell line, human teratocarcinoma NT2 cell line and organotypic hippocampal slice cultures (OHSC). Cell lines were differentiated into post-mitotic neurons by treatment with retinoic acid (RA) supplemented with CO-releasing molecule A1 (CORM-A1). CORM-A1 positively modulated neuronal differentiation, since it increased final neuronal production and enhanced the expression of specific neuronal genes: Nestin, Tuj1 and MAP2. Furthermore, during neuronal differentiation process, there was an increase in proliferative cell number (ki67 mRNA expressing cells) and a decrease in cell death (lower propidium iodide (PI) uptake, limitation of caspase-3 activation and higher Bcl-2 expressing cells). CO supplementation did not increase the expression of RA receptors. In the case of SH-S5Y5 model, small amounts of reactive oxygen species (ROS) generation emerges as important signaling molecules during CO-promoted neuronal differentiation. CO's improvement of neuronal differentiation yield was validated using OHSC as ex vivo model. CORM-A1 treatment of OHSC promoted higher levels of cells expressing the neuronal marker Tuj1. Still, CORM-A1 increased cell proliferation assessed by ki67 expression and also prevented cell death, which was followed by increased Bcl-2 expression, decreased levels of active caspase-3 and PI uptake. Likewise, ROS signaling emerged as key factors in CO's increasing number of differentiated neurons in OHSC. In conclusion, CO's increasing number of differentiated neurons is a novel biological role disclosed herein. CO improves neuronal yield due to its capacity to reduce cell death, promoting an increase in proliferative population. However, one cannot disregard a direct CO's effect on specific cellular processes of neuronal differentiation. Further studies are needed to evaluate how CO can potentially modulate cell mechanisms involved in neuronal differentiation. In summary, CO appears as a promising therapeutic molecule to stimulate endogenous neurogenesis or to improve in vitro neuronal production for cell therapy strategies.

Neuroprotective effects of 3-O-demethylswertipunicoside against MPTP-induced Parkinson's disease in vivo and its antioxidant properties in vitro

3-O-demethylswertipunicoside (3-ODS) has been reported to protect dopaminergic neurons against neurotoxicity induced by 1-methyl-4-phenylpyridinium (MPP(+)) in PC12 cells. Here, we investigate the neuroprotective effects in vivo and antioxidant activities in vitro of 3-ODS. In the 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-treated mouse model of Parkinson's disease (PD), 3-ODS dose-dependently improved motor coordination (as shown by rotarod test), increased the contents of dopamine (DA) and its metabolites in the striatum, and increased the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra (SN). In addition, 3-ODS also increased the spine density in hippocampal CA1 neurons. In antioxidant assays, 3-ODS showed a strong capacity in scavenging hydroxyl radical, superoxide anion and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical in a concentration-dependent manner. Taken together, we conclude that 3-ODS attenuates the PD-related motor deficits mainly through its neuroprotective effects, growth-promoting effects on spine density, and its antioxidant activities.

Neuroprotection by JM-20 against oxygen-glucose deprivation in rat hippocampal slices: Involvement of the Akt/GSK-3β pathway

Cerebral ischemia is the third most common cause of death and a major cause of disability worldwide. Beyond a shortage of essential metabolites, ischemia triggers many interconnected pathophysiological events, including excitotoxicity, oxidative stress, inflammation and apoptosis. Here, we investigated the neuroprotective mechanisms of JM-20, a novel synthetic molecule, focusing on the phosphoinositide-3-kinase (PI3K)/Akt survival pathway and glial cell response as potential targets of JM-20. For this purpose, we used organotypic hippocampal slice cultures exposed to oxygen-glucose deprivation (OGD) to achieve ischemic/reperfusion damage in vitro. Treatment with JM-20 at 0.1 and 10 μM reduced PI incorporation (indicative of cell death) after OGD. OGD decreased the phosphorylation of Akt (pro-survival) and GSK 3β (pro-apoptotic), resulting in respective inhibition and activation of these proteins. Treatment with JM20 prevented the reduced phosphorylation of these proteins after OGD, representing a shift from pro-apoptotic to pro-survival signaling. The OGD-induced activation of caspase-3 was also attenuated by JM-20 treatment at 10 μM. Moreover, in cultures treated with JM-20 and exposed to OGD conditioning, we observed a decrease in activated microglia, as well as a decrease in interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α release into the culture medium, while the level of the anti-inflammatory IL-10 increased. GFAP immunostaining and IB4 labeling showed that JM-20 treatment significantly augmented GFAP immunoreactivity after OGD, when compared with cultures exposed to OGD only, suggesting the activation of astroglial cells. Our results confirm that JM-20 has a strong neuroprotective effect against ischemic injury and suggest that the mechanisms involved in this effect may include the modulation of reactive astrogliosis, as well as neuroinflammation and the anti-apoptotic cell signaling pathway.

Ultrastructural investigation of microcalcification and the role of oxygen-glucose deprivation in cultured rat hippocampal slices

Intracellular calcium accumulation is associated with cell death in several neuropathological disorders including brain ischemia, but the exact mechanisms of calcification need to be clarified. We used organotypic hippocampal slice culture - cultures subjected to oxygen-glucose deprivation (OGD) mimicking the in vivo situation to investigate the events underlying ectopic calcification. Alizarin red staining indicating calcium deposition was observed in the cornu ammonis (CA)1 and dentate gyrus regions in control hippocampal slices despite no specific labeling for cell death markers. Electron microscopy using the osmium/potassium dichromate method revealed scattered degenerated cells throughout the normally appearing CA1 region. They contained electron-dense precipitates within mitochondria, and electron probe microanalysis confirmed that they were calcifying mitochondria. Selective calcium deposition was noted within, but not beyond, mitochondria in these mineralized cells. They showed ultrastructural features of non-necrotic, non-apoptotic cell death and retained their compact ultrastructure, even after the majority of mitochondria were calcified. Unexpectedly, no intracellular calcification was noted in necrotic CA1 pyramidal cells after OGD, and there was no progression of calcification in OGD-lesioned slices. In addition, mineralized cells in both control and OGD-lesioned slices were closely associated with or completely engulfed by astrocytes but not microglia. These astrocytes were laden with heterogeneous cytoplasmic inclusions that appeared to be related with their phagocytic activity. These data demonstrate that microcalcification specifically associated with mitochondria might lead to a novel type of cell death and suggest that astrocytes may be involved in the phagocytosis of these mineralized cells and possibly in the regulation of ectopic calcification.

Neuroplasticity of A-type potassium channel complexes induced by chronic alcohol exposure enhances dendritic calcium transients in hippocampus

RATIONALE

Chronic alcohol-induced cognitive impairments and maladaptive plasticity of glutamatergic synapses are well-documented. However, it is unknown if prolonged alcohol exposure affects dendritic signaling that may underlie hippocampal dysfunction in alcoholics. Back-propagation of action potentials (bAPs) into apical dendrites of hippocampal neurons provides distance-dependent signals that modulate dendritic and synaptic plasticity. The amplitude of bAPs decreases with distance from the soma that is thought to reflect an increase in the density of Kv4.2 channels toward distal dendrites.

OBJECTIVE

The aim of this study was to quantify changes in hippocampal Kv4.2 channel function and expression using electrophysiology, Ca(2+) imaging, and western blot analyses in a well-characterized in vitro model of chronic alcohol exposure.

RESULTS

Chronic alcohol exposure significantly decreased expression of Kv4.2 channels and KChIP3 in hippocampus. This reduction was associated with an attenuation of macroscopic A-type K(+) currents in CA1 neurons. Chronic alcohol exposure increased bAP-evoked Ca(2+) transients in the distal apical dendrites of CA1 pyramidal neurons. The enhanced bAP-evoked Ca(2+) transients induced by chronic alcohol exposure were not related to synaptic targeting of N-methyl-D-aspartate (NMDA) receptors or morphological adaptations in apical dendritic arborization.

CONCLUSIONS

These data suggest that chronic alcohol-induced decreases in Kv4.2 channel function possibly mediated by a downregulation of KChIP3 drive the elevated bAP-associated Ca(2+) transients in distal apical dendrites. Alcohol-induced enhancement of bAPs may affect metaplasticity and signal integration in apical dendrites of hippocampal neurons leading to alterations in hippocampal function.

Neuroprotective effects of mild hypoxia in organotypic hippocampal slice cultures

Purpose

The aim of this study was to investigate the potential effects of mild hypoxia in the mature and immature brain.

Methods

We prepared organotypic slice cultures of the hippocampus and used hippocampal tissue cultures at 7 and 14 days in vitro (DIV) to represent the immature and mature brain, respectively. Tissue cultures were exposed to 10% oxygen for 60 minutes. Twenty-four hours after this hypoxic insult, propidium iodide fluorescence images were obtained, and the damaged areas in the cornu ammonis 1 (CA1), CA3, and dentate gyrus (DG) were measured using image analysis.

Results

In the 7-DIV group compared to control tissue, hypoxia-exposed tissue showed decreased damage in two regions (CA1: 5.59%±2.99% vs. 4.80%±1.37%, P=0.900; DG: 33.88%±12.53% vs. 15.98%±2.37%, P=0.166), but this decrease was not statistically significant. In the 14-DIV group, hypoxia-exposed tissue showed decreased damage compared to control tissues; this decrease was not significant in the CA3 (24.51%±6.05% vs. 18.31%±3.28%, P=0.373) or DG (15.72%±3.47% vs. 9.91%±2.11%, P=0.134), but was significant in the CA1 (50.91%±5.90% vs. 32.30%±3.34%, P=0.004).

Conclusion

Although only CA1 tissues cultured for 14 DIV showed significantly less damage after exposure to hypoxia, the other tissues examined in this study showed a tendency towards less damage after hypoxic exposure. Therefore, mild hypoxia might play a protective role in the brain.

Novel hybrid DHPM-fatty acids: synthesis and activity against glioma cell growth in vitro

We described the first synthesis of fatty acid 3,4-dihydropyrimidinones (DHPM-fatty acids) using the Biginelli multicomponent reaction. Antiproliferative activity on two glioma cell lines (C6 rat and U-138-MG human) was also reported. The novel DHPM-fatty acids reduced glioma cell viability relative to temozolomide. Hybrid oxo-monastrol-palmitic acid was the most potent, reducing U-138-MG human cell viability by ca. 50% at 10 μM. In addition, the DHPM-fatty acids showed a large safety range to neural cells, represented by the organotypic hippocampal culture. These results suggest that the increased lipophilicity of DHPM-fatty acids offer a promising approach to overcoming resistance to chemotherapy and may play an important role in the development of new antitumor drugs.

Effects of blast overpressure on neurons and glial cells in rat organotypic hippocampal slice cultures

Due to recent involvement in military conflicts, and an increase in the use of explosives, there has been an escalation in the incidence of blast-induced traumatic brain injury (bTBI) among US military personnel. Having a better understanding of the cellular and molecular cascade of events in bTBI is prerequisite for the development of an effective therapy that currently is unavailable. The present study utilized organotypic hippocampal slice cultures (OHCs) exposed to blast overpressures of 150 kPa (low) and 280 kPa (high) as an in vitro bTBI model. Using this model, we further characterized the cellular effects of the blast injury. Blast-evoked cell death was visualized by a propidium iodide (PI) uptake assay as early as 2 h post-injury. Quantification of PI staining in the cornu Ammonis 1 and 3 (CA1 and CA3) and the dentate gyrus regions of the hippocampus at 2, 24, 48, and 72 h following blast exposure revealed significant time dependent effects. OHCs exposed to 150 kPa demonstrated a slow increase in cell death plateauing between 24 and 48 h, while OHCs from the high-blast group exhibited a rapid increase in cell death already at 2 h, peaking at ~24 h post-injury. Measurements of lactate dehydrogenase release into the culture medium also revealed a significant increase in cell lysis in both low- and high-blast groups compared to sham controls. OHCs were fixed at 72 h post-injury and immunostained for markers against neurons, astrocytes, and microglia. Labeling OHCs with PI, neuronal, and glial markers revealed that the blast-evoked extensive neuronal death and to a lesser extent loss of glial cells. Furthermore, our data demonstrated activation of astrocytes and microglial cells in low- and high-blasted OHCs, which reached a statistically significant difference in the high-blast group. These data confirmed that our in vitro bTBI model is a useful tool for studying cellular and molecular changes after blast exposure.

The blood-brain barrier as a target in traumatic brain injury treatment

Traumatic brain injury (TBI) is one of the most frequent causes of death in the young population. Several clinical trials have unsuccessfully focused on direct neuroprotective therapies. Recently immunotherapeutic strategies shifted into focus of translational research in acute CNS diseases. Cross-talk between activated microglia and blood-brain barrier (BBB) could initiate opening of the BBB and subsequent recruitment of systemic immune cells and mediators into the brain. Stabilization of the BBB after TBI could be a promising strategy to limit neuronal inflammation, secondary brain damage and acute neurodegeneration. This review provides an overview on the pathophysiology of TBI and brain edema formation including definitions and classification of TBI, current clinical treatment strategies, as well as current understanding on the underlying cellular processes. A summary of in vivo and in vitro models to study different aspects of TBI is presented. Three mechanisms proposed for stabilization of the BBB, myosin light chain kinases, glucocorticoid receptors and peroxisome proliferator-activated receptors are reviewed for their influence on barrier-integrity and outcome after TBI. In conclusion, the BBB is recommended as a promising target for the treatment of traumatic brain injury, and it is suggested that a combination of BBB stabilization and neuroprotectants may improve therapeutic success.

Paeonol attenuates inflammation-mediated neurotoxicity and microglial activation

Chronic activation of microglial cells endangers neuronal survival through the release of various proinflammatory and neurotoxic factors. The root of Paeonia lactiflora Pall has been considered useful for the treatment of various disorders in traditional oriental medicine. Paeonol, found in the root of Paeonia lactiflora Pall, has a wide range of pharmacological functions, including anti-oxidative, anti-inflammatory and neuroprotective activities. The objective of this study was to examine the efficacy of paeonol in the repression of inflammation-induced neurotoxicity and microglial cell activation. Organotypic hippocampal slice cultures and primary microglial cells from rat brain were stimulated with bacterial lipopolysaccharide. Paeonol pretreatment was performed for 30 minutes prior to lipopolysaccharide addition. Cell viability and nitrite (the production of nitric oxide), tumor necrosis factor-alpha and interleukin-1beta products were measured after lipopolysaccharide treatment. In organotypic hippocampal slice cultures, paeonol blocked lipopolysaccharide-related hippocampal cell death and inhibited the release of nitrite and interleukin-1beta. Paeonol was effective in inhibiting nitric oxide release from primary microglial cells. It also reduced the lipopolysaccharide-stimulated release of tumor necrosis factor-alpha and interleukin-1β from microglial cells. Paeonol possesses neuroprotective activity in a model of inflammation-induced neurotoxicity and reduces the release of neurotoxic and proinflammatory factors in activated microglial cells.

Electroosmotic perfusion of tissue: sampling the extracellular space and quantitative assessment of membrane-bound enzyme activity in organotypic hippocampal slice cultures

This review covers recent advances in sampling fluid from the extracellular space of brain tissue by electroosmosis (EO). Two techniques, EO sampling with a single fused-silica capillary and EO push-pull perfusion, have been developed. These tools were used to investigate the function of membrane-bound enzymes with outward-facing active sites, or ectoenzymes, in modulating the activity of the neuropeptides leu-enkephalin and galanin in organotypic-hippocampal-slice cultures (OHSCs). In addition, the approach was used to determine the endogenous concentration of a thiol, cysteamine, in OHSCs. We have also investigated the degradation of coenzyme A in the extracellular space. The approach provides information on ectoenzyme activity, including Michaelis constants, in tissue, which, as far as we are aware, has not been done before. On the basis of computational evidence, EO push-pull perfusion can distinguish ectoenzyme activity with a ~100 μm spatial resolution, which is important for studies of enzyme kinetics in adjacent regions of the rat hippocampus.

Microglial cells in organotypic cultures of developing and adult mouse retina and their relationship with cell death

Organotypic cultures of retinal explants allow the detailed analysis of microglial cells in a cellular microenvironment similar to that in the in situ retina, with the advantage of easy experimental manipulation. However, the in vitro culture causes changes in the retinal cytoarchitecture and induces a microglial response that may influence the results of these manipulations. The purpose of this study was to analyze the influence of the retinal age on changes in retinal cytoarchitecture, cell viability and death, and microglial phenotype and distribution throughout the in vitro culture of developing and adult retina explants. Explants from developing (3 and 10 postnatal days, P3 and P10) and adult (P60) mouse retinas were cultured for up to 10 days in vitro (div). Dead or dying cells were recognized by TUNEL staining, cell viability was determined by flow cytometry, and the numbers and distribution patterns of microglial cells were studied by flow cytometry and immunocytochemistry, respectively. The retinal cytoarchitecture was better preserved at prolonged culture times (10 div) in P10 retina explants than in P3 or adult explants. Particular patterns of cell viability and death were observed at each age: in general, explants from developing retinas showed higher cell viability and lower density of TUNEL-positive profiles versus adult retinas. The proportion of microglial cells relative to the whole population of retinal cells was higher in explants fixed immediately after their dissection (i.e., non-cultured) from adult retinas than in those from developing retinas. This proportion was always higher in non-cultured explants than in explants at 10 div, suggesting the death of some microglial cells during the culture. Activation of microglial cells, as revealed by their phenotypical appearance, was observed in both developing and adult retina explants from the beginning of the culture. Immunofluorescence with the anti-CD68 antibody showed that some activated microglial cells were CD68-positive but others were CD68-negative. Flow cytometry using CD68-labeling revealed that the percentage of CD68-positive microglial cells was much higher in developing than in adult retina explants, despite the activation of microglia in both types of explants, indicating that CD68-labeling was more closely related to the maturity degree of microglia than to their activation. Some swollen activated microglial cells entered the outer nuclear layer in developing and adult cultured retinal explants, whereas this layer was devoid of microglia in non-cultured explants. There was no apparent correlation between the distribution of microglia and that of TUNEL-labeled profiles. However, some swollen activated microglial cells in the outer and inner nuclear layers engulfed clusters of cell nuclei that were negative or weakly positive for TUNEL. This engulfment activity of microglia mimicked that observed in degenerative pathologies of the retina. We conclude that organotypic cultures from developing retinas show a higher rate of cell viability and better preservation of the normal cytoarchitecture in comparison to those obtained from adult retinas. In addition, the features of microglial response in cultured retinal explants show them to be a useful model for studying interactions between microglial cells and degenerating neurons in retinal diseases.

Ventral tegmental area/substantia nigra and prefrontal cortex rodent organotypic brain slices as an integrated model to study the cellular changes induced by oxygen/glucose deprivation and reperfusion: effect of neuroprotective agents

Unveiling the roles of distinct cell types in brain response to insults is a partially unsolved challenge and a key issue for new neuroreparative approaches. In vivo models are not able to dissect the contribution of residential microglia and infiltrating blood-borne monocytes/macrophages, which are fundamentally undistinguishable; conversely, cultured cells lack original tissue anatomical and functional complexity, which profoundly alters reactivity. Here, we tested whether rodent organotypic co-cultures from mesencephalic ventral tegmental area/substantia nigra and prefrontal cortex (VTA/SN-PFC) represent a suitable model to study changes induced by oxygen/glucose deprivation and reperfusion (OGD/R). OGD/R induced cytotoxicity to both VTA/SN and PFC slices, with higher VTA/SN susceptibility. Neurons were highly affected, with astrocytes and oligodendrocytes undergoing very mild damage. Marked reactive astrogliosis was also evident. Notably, OGD/R triggered the activation of CD68-expressing microglia and increased expression of Ym1 and Arg1, two markers of "alternatively" activated beneficial microglia. Treatment with two well-known neuroprotective drugs, the anticonvulsant agent valproic acid and the purinergic P2-antagonist PPADS, prevented neuronal damage. Thus, VTA/SN-PFC cultures are an integrated model to investigate OGD/R-induced effects on distinct cells and easily screen neuroprotective agents. The model is particularly adequate to dissect the microglia phenotypic shift in the lack of a functional vascular compartment.

Susceptibility of rat hippocampal neurons to hypothermia during development

Purpose

This study evaluated the extent of damage due to hypothermia in the mature and immature brain.

Methods

Hippocampal tissue cultures at 7 and 14 days in vitro (DIV) were used to represent the immature and mature brain, respectively. The cultures were exposed at 25℃ for 0, 10, 30, and 60 minutes (n=30 in each subgroup). Propidium iodide fluorescent images were captured 24 and 48 hours after hypothermic injury. Damaged areas of the cornu ammonis 1 (CA1), CA3, and dentate gyrus (DG) were measured using image analysis.

Results

At 7 DIV, the tissues exposed to cold injury for 60 minutes showed increased damage in CA1 (P<0.001) and CA3 (P=0.005) compared to the control group at 48 hours. Increased damage to DG was observed at 24 (P=0.008) and 48 hours (P=0.011). The 14 DIV tissues did not demonstrate any significant differences compared with the control group, except for the tissues exposed for 30 minutes in which DG showed less damage at 48 hours than the control group (P=0.048). In tissues at 7 DIV, CA1 (P=0.040) and DG (P=0.013) showed differences in the duration of cold exposure.

Conclusion

The immature brain is more vulnerable to hypothermic injury than the mature brain.

Lesion-induced alterations in astrocyte glutamate transporter expression and function in the hippocampus

Astrocytes express the sodium-dependent glutamate transporters GLAST and GLT-1, which are critical to maintain low extracellular glutamate concentrations. Here, we analyzed changes in their expression and function following a mechanical lesion in the CA1 area of organotypic hippocampal slices. 6-7 days after lesion, a glial scar had formed along the injury site, containing strongly activated astrocytes with increased GFAP and S100 β immunoreactivity, enlarged somata, and reduced capability for uptake of SR101. Astrocytes in the scar's periphery were swollen as well, but showed only moderate upregulation of GFAP and S100 β and efficiently took up SR101. In the scar, clusters of GLT-1 and GLAST immunoreactivity colocalized with GFAP-positive fibers. Apart from these, GLT-1 immunoreactivity declined with increasing distance from the scar, whereas GLAST expression appeared largely uniform. Sodium imaging in reactive astrocytes indicated that glutamate uptake was strongly reduced in the scar but maintained in the periphery. Our results thus show that moderately reactive astrocytes in the lesion periphery maintain overall glutamate transporter expression and function. Strongly reactive astrocytes in the scar, however, display clusters of GLAST and GLT-1 immunoreactivity together with reduced glutamate transport activity. This reduction might contribute to increased extracellular glutamate concentrations and promote excitotoxic cell damage at the lesion site.

Two cell circuits of oriented adult hippocampal neurons on self-assembled monolayers for use in the study of neuronal communication in a defined system

In this study, we demonstrate the directed formation of small circuits of electrically active, synaptically connected neurons derived from the hippocampus of adult rats through the use of engineered chemically modified culture surfaces that orient the polarity of the neuronal processes. Although synaptogenesis, synaptic communication, synaptic plasticity, and brain disease pathophysiology can be studied using brain slice or dissociated embryonic neuronal culture systems, the complex elements found in neuronal synapses makes specific studies difficult in these random cultures. The study of synaptic transmission in mature adult neurons and factors affecting synaptic transmission are generally studied in organotypic cultures, in brain slices, or in vivo. However, engineered neuronal networks would allow these studies to be performed instead on simple functional neuronal circuits derived from adult brain tissue. Photolithographic patterned self-assembled monolayers (SAMs) were used to create the two-cell "bidirectional polarity" circuit patterns. This pattern consisted of a cell permissive SAM, N-1[3-(trimethoxysilyl)propyl] diethylenetriamine (DETA), and was composed of two 25 μm somal adhesion sites connected with 5 μm lines acting as surface cues for guided axonal and dendritic regeneration. Surrounding the DETA pattern was a background of a non-cell-permissive poly(ethylene glycol) (PEG) SAM. Adult hippocampal neurons were first cultured on coverslips coated with DETA monolayers and were later passaged onto the PEG-DETA bidirectional polarity patterns in serum-free medium. These neurons followed surface cues, attaching and regenerating only along the DETA substrate to form small engineered neuronal circuits. These circuits were stable for more than 21 days in vitro (DIV), during which synaptic connectivity was evaluated using basic electrophysiological methods.

Early phase of plasticity-related gene regulation and SRF dependent transcription in the hippocampus

Hippocampal organotypic cultures are a highly reliable in vitro model for studying neuroplasticity: in this paper, we analyze the early phase of the transcriptional response induced by a 20 µM gabazine treatment (GabT), a GABA-Ar antagonist, by using Affymetrix oligonucleotide microarray, RT-PCR based time-course and chromatin-immuno-precipitation. The transcriptome profiling revealed that the pool of genes up-regulated by GabT, besides being strongly related to the regulation of growth and synaptic transmission, is also endowed with neuro-protective and pro-survival properties. By using RT-PCR, we quantified a time-course of the transient expression for 33 of the highest up-regulated genes, with an average sampling rate of 10 minutes and covering the time interval [10∶90] minutes. The cluster analysis of the time-course disclosed the existence of three different dynamical patterns, one of which proved, in a statistical analysis based on results from previous works, to be significantly related with SRF-dependent regulation (p-value<0.05). The chromatin immunoprecipitation (chip) assay confirmed the rich presence of working CArG boxes in the genes belonging to the latter dynamical pattern and therefore validated the statistical analysis. Furthermore, an in silico analysis of the promoters revealed the presence of additional conserved CArG boxes upstream of the genes Nr4a1 and Rgs2. The chip assay confirmed a significant SRF signal in the Nr4a1 CArG box but not in the Rgs2 CArG box.

Electroosmotic push-pull perfusion: description and application to qualitative analysis of the hydrolysis of exogenous galanin in organotypic hippocampal slice cultures

We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed for the products of the enzymatic degradation of the peptide substrate. The driving force for perfusion is an electric field. The fused silica capillaries used as "push" and "pull" or "source" and "collection" capillaries have a ζ-potential that is negative and greater in magnitude than the tissue's ζ-potential. Thus, depending on the magnitudes of particular dimensions, the electroosmotic flow in the capillaries augments the fluid velocity in the tissue. The flow rate is not directly measured; however, we determine it using a finite-element approach. We have determined the collection efficiency of the system using an all d-amino acid internal standard. The flow rates are low, in the nL/min range, and adjustable by controlling the current or voltage in the system. The collection efficiency of the d-amino acid peptide internal standard is variable, increasing with increased current and thus electroosmotic flow rate. The collection efficiency can be rationalized in the context of a Peclet number. Electroosmotic push-pull perfusion of the neuropeptide galanin (gal1-29) through the extracellular space of an organotypic hippocampal culture results in its hydrolysis by ectopeptidase reactions occurring in the extracellular space. The products of hydrolysis were identified by MALDI-MS. Experiments at two levels of current (8-12 μA and 19-40 μA) show that the probability of seeing hydrolysis products (apparently from aminopeptidases) is greater in the Cornu Ammonis area 3 (CA3) than in the Cornu Ammonis area 1 (CA1) in the higher current experiments. In the lower current experiments, shorter peptide products of aminopeptidases (gal13-29 to gal20-19) are seen with greater frequency in CA3 than in CA1 but there is no statistically significant difference for longer peptides (gal3-29 to gal12-29).

Paeoniflorin, a monoterpene glycoside, attenuates lipopolysaccharide-induced neuronal injury and brain microglial inflammatory response

Chronic activation of microglial cells endangers neuronal survival through the release of various proinflammatory and neurotoxic factors. Paeoniflorin (PF), a water-soluble monoterpene glycoside found in the root of Paeonia lactiflora Pall, has a wide range of pharmacological functions, such as anti-oxidant, anti-inflammatory, and anti-cancer effects. Neuroprotective potential of PF has also been demonstrated in animal models of neuropathologies. Here, we have examined the efficacy of PF in the repression of inflammation-induced neurotoxicity and microglial inflammatory response. In organotypic hippocampal slice cultures, PF significantly blocked lipopolysaccharide (LPS)-induced hippocampal cell death and productions of nitric oxide (NO) and interleukin (IL)-1β. PF also inhibited the LPS-stimulated productions of NO, tumor necrosis factor-α, and IL-1β from primary microglial cells. These results suggest that PF possesses neuroprotective activity by reducing the production of proinflammatory factors from activated microglial cells.

Repetitive magnetic stimulation induces functional and structural plasticity of excitatory postsynapses in mouse organotypic hippocampal slice cultures

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that can alter cortical excitability in human subjects for hours beyond the stimulation period. It thus has potential as a therapeutic tool in neuropsychiatric disorders associated with alterations in cortical excitability. However, rTMS-induced neural plasticity remains insufficiently understood at the cellular level. To learn more about the effects of repetitive magnetic stimulation (rMS), we established an in vitro model of rMS using mouse organotypic entorhino-hippocampal slice cultures. We assessed the outcome of a high-frequency (10 Hz) rMS protocol on functional and structural properties of excitatory synapses in mature hippocampal CA1 pyramidal neurons. Whole-cell patch-clamp recordings, immunohistochemistry, and time-lapse imaging techniques revealed that rMS induces a long-lasting increase in glutamatergic synaptic strength, which is accompanied by structural remodeling of dendritic spines. The effects of rMS on spine size were predominantly seen in small spines, suggesting differential effects of rMS on subpopulations of spines. Furthermore, our data indicate that rMS-induced postsynaptic changes depend on the NMDA receptor-mediated accumulation of GluA1-containing AMPA receptors. These results provide first experimental evidence that rMS induces coordinated functional and structural plasticity of excitatory postsynapses, which is consistent with a long-term potentiation of synaptic transmission.

Slice culture modeling of central nervous system (CNS) viral infection

The complexity of the central nervous system (CNS) is not recapitulated in cell culture models. Thin slicing and subsequent culture of CNS tissue has become a valued means to study neuronal and glial biology within the context of the physiologically relevant tissue milieu. Modern membrane-interface slice culturing methodology allows straightforward access to both CNS tissue and feeding medium, enabling experimental manipulations and analyses that would otherwise be impossible in vivo. CNS slices can be successfully maintained in culture for up to several weeks for investigation of evolving pathology and long-term intervention in models of chronic neurologic disease.Herein, membrane-interface slice culture models for studying viral encephalitis and myelitis are detailed, with emphasis on the use of these models for investigation of pathogenesis and evaluation of novel treatment strategies. We describe techniques to (1) generate brain and spinal cord slices from rodent donors, (2) virally infect slices, (3) assess virally induced injury/apoptosis, (4) characterize "CNS-specific" cytokine production, and (5) treat slices with cytokines/pharmaceuticals. Although our focus is on CNS viral infection, we anticipate that the described methods can be adapted to address a wide range of investigations within the fields of neuropathology, neuroimmunology, and neuropharmacology.

General overview of neuronal cell culture

In this introductory chapter, we provide a general overview of neuronal cell culture. This is a rapidly evolving area of research and we provide an outline and contextual framework for the different chapters of this book. These chapters were all contributed by scientists actively working in the field who are currently using state-of-the-art techniques to advance our understanding of the molecular and cellular biology of the central nervous system. Each chapter provides detailed descriptions and experimental protocols for a variety of techniques ranging in scope from basic neuronal cell line culturing to advanced and specialized methods.

Indomethacin-loaded lipid-core nanocapsules reduce the damage triggered by Aβ1-42 in Alzheimer's disease models

Neuroinflammation, characterized by the accumulation of activated microglia and reactive astrocytes, is believed to modulate the development and/or progression of Alzheimer’s disease (AD). Epidemiological studies suggesting that nonsteroidal anti-inflammatory drugs decrease the risk of developing AD have encouraged further studies elucidating the role of inflammation in AD. Nanoparticles have become an important focus of neurotherapeutic research because they are an especially effective form of drug delivery. Here, we investigate the potential protective effect of indomethacin-loaded lipid-core nanocapsules (IndOH-LNCs) against cell damage and neuroinflammation induced by amyloid beta (Aβ)1-42 in AD models. Our results show that IndOH-LNCs attenuated Aβ-induced cell death and were able to block the neuroinflammation triggered by Aβ1-42 in organotypic hippocampal cultures. Additionally, IndOH-LNC treatment was able to increase interleukin-10 release and decrease glial activation and c-jun N-terminal kinase phosphorylation. As a model of Aβ-induced neurotoxicity in vivo, animals received a single intracerebroventricular injection of Aβ1-42 (1 nmol/site), and 1 day after Aβ1-42 infusion, they were administered either free IndOH or IndOH-LNCs (1 mg/kg, intraperitoneally) for 14 days. Only the treatment with IndOH-LNCs significantly attenuated the impairment of this behavior triggered by intracerebroventricular injection of Aβ1-42. Further, treatment with IndOH-LNCs was able to block the decreased synaptophysin levels induced by Aβ1-42 and suppress glial and microglial activation. These findings might be explained by the increase of IndOH concentration in brain tissue attained using drug-loaded lipid-core NCs. All these findings support the idea that blockage of neuroinflammation triggered by Aβ is involved in the neuroprotective effects of IndOH-LNCs. These data provide strong evidence that IndOH-LNC treatment may represent a promising approach for treating AD.

15-deoxy-Δ¹²,¹⁴ -prostaglandin J₂ inhibits human immunodeficiency virus-1 tat-induced monocyte chemoattractant protein-1/CCL2 production by blocking the extracellular signal-regulated kinase-1/2 signaling pathway independently of peroxisome proliferator-activated receptor-γ and heme oxygenase-1 in rat hippocampal slices

Human immunodeficiency virus (HIV)-induced inflammation, and its consequences within the central nervous system (CNS), must be countered by multiple pharmacologic agents, and 15-deoxy-Δ(12,14) -prostaglandin J(2) (15d-PGJ2) may hold promise in the treatment of pathologies associated with this inflammatory response. 15d-PGJ2 can repress the inflammatory response by means of peroxisome proliferator-activated receptor-γ (PPARγ)-dependent and -independent mechanisms. However, its precise role and antiinflammatory mechanism in the hippocampus remain poorly understood. In the present study, rat hippocampal slices were stimulated with full-length HIV-1 Tat protein to investigate the role of 15d-PGJ2 8in the hippocampal inflammatory response. Pretreatment of slices with 15d-PGJ2 markedly reduced Tat-induced monocyte chemoattractant protein-1 (MCP-1/CCL2) production. Interestingly, the PPARγ antagonist GW9662 did not inhibit action of 15d-PGJ2, confirming the latter's PPARγ-independent mechanism of mediating antiinflammatory effects. Despite 15d-PGJ2's increasing the expression of heme oxygenase-1 (HO-1), its action was not abrogated by the HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX), nor was it recapitulated by HO-1 inducers such as cobalt protoporphyrin (CoPP). Moreover, short interfering RNA (siRNA)-directed knockdown of HO-1 did not abolish the antiinflammatory action of 15d-PGJ2 against Tat-induced MCP-1 production in human microglia-like THP-1 cells. Conversely, 15d-PGJ2 suppressed Tat-induced ERK1/2 activation, decreasing MCP-1 production upon Tat stimulation. The NADPH oxidase inhibitors DPI and apocynin also abrogated Tat-stimulated ERK1/2 activation, reducing MCP-1 production. Collectively, these data demonstrate that the antiinflammatory effects of 15d-PGJ2 on the hippocampus are exerted through inhibition of Tat-mediated ERK1/2 activation, coupled with that of a redox-sensitive pathway, independent of PPARγ and HO-1.