Long-Term Primary Culture of Highly-Pure Rat Embryonic Hippocampal Neurons of Low-Density

A functional network of highly pure enteric neurons in a dish

The enteric nervous system (ENS) is the intrinsic nervous system that innervates the entire digestive tract and regulates major digestive functions. Recent evidence has shown that functions of the ENS critically rely on enteric neuronal connectivity; however, experimental models to decipher the underlying mechanisms are limited. Compared to the central nervous system, for which pure neuronal cultures have been developed for decades and are recognized as a reference in the field of neuroscience, an equivalent model for enteric neurons is lacking. In this study, we developed a novel model of highly pure rat embryonic enteric neurons with dense and functional synaptic networks. The methodology is simple and relatively fast. We characterized enteric neurons using immunohistochemical, morphological, and electrophysiological approaches. In particular, we demonstrated the applicability of this culture model to multi-electrode array technology as a new approach for monitoring enteric neuronal network activity. This in vitro model of highly pure enteric neurons represents a valuable new tool for better understanding the mechanisms involved in the establishment and maintenance of enteric neuron synaptic connectivity and functional networks.

Branched Chondroitin Sulfate Oligosaccharides Derived from the Sea Cucumber Acaudina molpadioides Stimulate Neurite Outgrowth

Fucosylated chondroitin sulfate (FCS) from the sea cucumber Acaudina molpadioides (FCS_Am) is the first one that was reported to be branched by disaccharide GalNAc-(α1,2)-Fuc_3S4S (15%) and sulfated Fuc (85%). Here, four size-homogenous fractions, and seven oligosaccharides, were separated from its β-eliminative depolymerized products. Detailed NMR spectroscopic and MS analyses revealed the oligomers as hexa-, hepta-, octa-, and nonasaccharide, which further confirmed the precise structure of native FCS_Am: it was composed of the CS-E-like backbone with a full content of sulfation at O-4 and O-6 of GalNAc in the disaccharide repeating unit, and the branches consisting of sulfated fucose (Fuc_4S and Fuc_2S4S) and heterodisaccharide [GalNAc-(α1,2)-Fuc_3S4S]. Pharmacologically, FCS_Am and its depolymerized derivatives, including fractions and oligosaccharides, showed potent neurite outgrowth-promoting activity in a chain length-dependent manner. A comparison of analyses among oligosaccharides revealed that the sulfate pattern of the Fuc branches, instead of the heterodisaccharide, could affect the promotion intensity. Fuc_2S4S and the saccharide length endowed the neurite outgrowth stimulation activity most.

MiR-132 down-regulates high glucose-induced β-dystroglycan degradation through Matrix Metalloproteinases-9 up-regulation in primary neurons

Cognitive dysfunction is one of the complications of diabetes. Unfortunately, there is no effective methods to block its progression currently. One of the pathophysiological mechanisms is synaptic protein damage and neuronal signal disruption because of glucose metabolism disorder. Dystroglycan protein, located in the post‐synaptic membrane of neurons, links the intracellular cytoskeleton with extracellular matrix. Abnormal expression of dystroglycan protein affects neuronal biological functions and leads to cognitive impairment. However, there are no relevant studies to observe the changes of β‐dystroglycan protein in diabetes rat brain and in primary neurons under high glucose exposure. Our data demonstrated the alterations of cognitive abilities in the diabetic rats; β‐dystroglycan protein degradation occurred in hippocampal and cortical tissues in diabetic rat brain. We further explored the mechanisms underlying of this phenomenon. When neurons are exposed to high glucose environment in long‐term period, microRNA‐132 (miR‐132) would be down‐regulated in neurons. Matrix Metalloproteinases‐9 (MMP‐9) mRNA, as a target of miR‐132, could be up‐regulated; higher expression and overlay activity of MMP‐9 protein could increase β‐DG protein degradation. In this way, β‐DG degradation may affect structure and functions among the synapses, which related to cognition decline. It may provide some theoretical basis for elucidating the molecular mechanism of diabetes‐induced cognitive dysfunction.

Modeling the mature CNS: A predictive screening platform for neurodegenerative disease drug discovery

Background:

Mature primary neuronal cultures are an important model of the nervous system, but limited scalability has been a major challenge in their use for drug discovery of neurodegenerative diseases. This work describes a method for improving scalability through the use of larger format microtiter plates while preserving culture quality.

New Method:

Here we describe a method and quality control procedures for growing embryonic day 18 rat hippocampal/cortical neuronal cultures in 384-well microtiter plates for three weeks in vitro.

Results:

We use these cultures in two assays measuring intracellular lipid vesicle trafficking and synapse density for routine screening of small molecule libraries. Together this culture system and screening platform have successfully identified therapeutics capable of improving cognitive function in transgenic models of Alzheimer’s disease that have advanced to clinical trials, validating their translational applicability.

Comparison with Existing Methods:

Our method enables the growth of healthy, mature neurons in larger format microtiter plates than in traditional primary neuronal culturing protocols, making it ideal for drug screening and mechanism of action studies.

Conclusion:

The predictive capacity of this culture system and screening platform provides a method for rapidly identifying novel disease-modifying neurodegenerative therapeutics.

Involvement of α7nAChR in the Protective Effects of Genistein Against β-Amyloid-Induced Oxidative Stress in Neurons via a PI3K/Akt/Nrf2 Pathway-Related Mechanism

Abnormal excessive production and deposition of β-amyloid (Aβ) peptides in selectively susceptible brain regions are thought to be a key pathogenic mechanism underlying Alzheimer's disease (AD), resulting in memory deficits and cognitive impairment. Genistein is a phytoestrogen with great promise for counteracting diverse Aβ-induced insults, including oxidative stress and mitochondrial dysfunction. However, the exact molecular mechanism or mechanisms underlying the neuroprotective effects of genistein against Aβ-induced insults are largely uncharacterized. To further elucidate the possible mechanism(s) underlying these protective effects, we investigated the neuroprotective effects of genistein against Aβ-induced oxidative stress mediated by orchestrating α7 nicotinic acetylcholine receptor (α7nAChR) signaling in rat primary hippocampal neurons. Genistein significantly increased cell viability, reduced the number of apoptotic cells, decreased accumulation of reactive oxygen species (ROS), decreased contents of malondialdehyde (MDA) and lactate dehydrogenase (LDH), upregulated BCL-2 expression, and suppressed Caspase-3 activity occurring after treatment with 25 μM Aβ25-35. Simultaneously, genistein markedly inhibited the decreases in α7nAChR mRNA and protein expression in cells treated with Aβ25-35. In addition, α7nAChR signaling was intimately involved in the genistein-mediated activation of phosphatidylinositol 3-kinase (PI3K)/Akt and Nrf2/keap1 signaling. Thus, α7nAChR activity together with the PI3K/Akt/Nrf2 signaling cascade likely orchestrates the molecular mechanism underlying the neuroprotective effects of genistein against Aβ-induced oxidative injury.

Paclitaxel is effective for controlling astrocyte proliferation in vitro: Implications for generating ventral mesencephalic cultures enriched with dopamine neurons

BACKGROUND

Primary embryonic ventral mesencephalic (VM) cultures are a high throughput tool for understanding and manipulating dopamine neurons, to study the mechanisms that trigger their degeneration during Parkinson's disease (PD), and to test new drugs aimed at treating the disease. Unfortunately, primary cell cultures are often quickly overwhelmed by dividing astrocytes which both obscure neuronal cells and distort the cellular composition that exists in vivo.

NEW METHOD

To develop a new in vitro system whereby astrocyte division can be readily controlled while maintaining neuronal integrity, VM cultures were treated with different doses (1.75, 3.5, 7, 14 nM) of the anti-mitotic drug paclitaxel for up to seven days in vitro. The study subsequently sought to determine the importance of astrocytes in dopamine neuron survival when challenged with an exposure to the toxin 6-hydroxydopamine (6-OHDA).

RESULTS

Optical density (O.D.) measures of GFAP expression and counts of β-III tubulin and tyrosine hydroxylase positive neurons reveals that a low dose of 3.5 nM of paclitaxel significantly reduced the density of GFAP + astrocytes in primary VM cultures, while maintaining the viability of neurons and dopamine neurons. Interestingly, a reduction of GFAP + astrocytes within primary VM cultures did not reveal any statistically significant differences in the number of dopamine neurons surviving treatment with 6-OHDA.

CONCLUSIONS

These findings detail a quick and simple method for stabilising astrocyte numbers in primary VM cultures, without affecting the viability of dopamine neurons, and suggest that astrocytes may not enhance the survival of dopamine neurons when challenged with the 6-OHDA toxin.

Live Neuron High-Content Screening Reveals Synaptotoxic Activity in Alzheimer Mouse Model Homogenates

Accurate quantification of synaptic changes is essential for understanding the molecular mechanisms of synaptogenesis, synaptic plasticity, and synaptic toxicity. Here we demonstrate a robust high-content imaging method for the assessment of synaptic changes and apply the method to brain homogenates from an Alzheimer's disease mouse model. Our method uses serial imaging of endogenous fluorescent labeled presynaptic VAMP2 and postsynaptic PSD95 in long-term cultured live primary neurons in 96 well microplates, and uses automatic image analysis to quantify the number of colocalized mature synaptic puncta for the assessment of synaptic changes in live neurons. As a control, we demonstrated that our synaptic puncta assay is at least 10-fold more sensitive to the toxic effects of glutamate than the MTT assay. Using our assay, we have compared synaptotoxic activities in size-exclusion chromatography fractioned protein samples from 3xTg-AD mouse model brain homogenates. Multiple synaptotoxic activities were found in high and low molecular weight fractions. Amyloid-beta immunodepletion alleviated some but not all of the synaptotoxic activities. Although the biochemical entities responsible for the synaptotoxic activities have yet to be determined, these proof-of-concept results demonstrate that this novel assay may have many potential mechanistic and therapeutic applications.

Oxycodone suppresses the apoptosis of hippocampal neurons induced by oxygen-glucose deprivation/recovery through caspase-dependent and caspase-independent pathways via κ- and δ-opioid receptors in rats

Cerebral ischemia/reperfusion injury (CIRI) can lead to perioperative neurocognitive disorders (PND) during clinical recanalization procedures in cerebral vessels, principally due to neuronal apoptosis in the hippocampus. Oxycodone appears to be a multiple opioid receptor agonist and exerts intrinsic antinociception activity via κ-opioid receptor (KOR). Recent evidence has revealed that activation of both δ-opioid receptor (DOR) and KOR can provide neuroprotection against CIRI in vivo and in vitro. In our study, we established an oxygen-glucose deprivation/recovery (OGD/R) model with fetal hippocampal neurons and found that oxycodone could induce CIRI tolerance in these neurons, primarily through KOR and DOR. Possible mechanisms might involve the regulatory effect of oxycodone on the MAPK-Bcl2/Bax-caspase-9-caspase-3 pathway, as well as its inhibitory effect on cellular reactive oxygen species (ROS) production and mitochondrial membrane potential activation. Taken together, our findings may indicate a potential method for the prevention and treatment of PND associated with CIRI.

Efficient generation of functional Schwann cells from adipose-derived stem cells in defined conditions

Schwann cells (SCs) are hitherto regarded as the most promising candidates for viable cell-based therapy to peripheral nervous system (PNS) injuries or degenerative diseases. However, the extreme drawbacks of transplanting autologous SCs for clinical applications still represent a significant bottleneck in neural regenerative medicine, mainly owing to the need of sacrificing a functional nerve to generate autologous SCs and the nature of slow expansion of the SCs. Thus, it is of great importance to establish an alternative cell system for the generation of sufficient SCs. Here, we demonstrated that adipose-derived stem cells (ADSCs) of rat robustly give rise to morphological, phenotypic and functional SCs using an optimized protocol. After undergoing a 3-week in vitro differentiation, almost all of treated ADSCs exhibited spindle shaped morphology similar to genuine SCs and expressed SC markers GFAP and S100. Most importantly, apart from acquisition of SC antigenic and biochemical features, the ADSC-derived SCs were functionally identical to native SCs as they possess a potential ability to form myelin, and secret nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glia-derived neurotrophic factor (GDNF). The current study may provide an ideal strategy for harvesting sufficient SCs for cell-based treatment of various peripheral nerve injuries or disorders.

Dynamic Regulation of the Adenosine Kinase Gene during Early Postnatal Brain Development and Maturation

The ubiquitous metabolic intermediary and nucleoside adenosine is a “master regulator” in all living systems. Under baseline conditions adenosine kinase (ADK) is the primary enzyme for the metabolic clearance of adenosine. By regulating the availability of adenosine, ADK is a critical upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. ADK protein exists in the two isoforms nuclear ADK-L, and cytoplasmic ADK-S, which are subject to dynamic expression changes during brain development and in response to brain injury; however, gene expression changes of the Adk gene as well as regulatory mechanisms that direct the cell-type and isoform specific expression of ADK have never been investigated. Here we analyzed potential gene regulatory mechanisms that may influence Adk expression including DNA promoter methylation, histone modifications and transcription factor binding. Our data suggest binding of transcription factor SP1 to the Adk promoter influences the regulation of Adk expression.

Two outward potassium current types are expressed during the neural differentiation of neural stem cells

The electrophysiological properties of potassium ion channels are regarded as a basic index for determining the functional differentiation of neural stem cells. In this study, neural stem cells from the hippocampus of newborn rats were induced to differentiate with neurotrophic growth factor, and the electrophysiological properties of the voltage-gated potassium ion channels were observed. Immunofluorescence staining showed that the rapidly proliferating neural stem cells formed spheres in vitro that expressed high levels of nestin. The differentiated neurons were shown to express neuron-specific enolase. Flow cytometric analysis revealed that the neural stem cells were actively dividing and the percentage of cells in the S + G2/M phase was high. However, the ratio of cells in the S + G2/M phase decreased obviously as differentiation proceeded. Whole-cell patch-clamp recordings revealed apparent changes in potassium ion currents as the neurons differentiated. The potassium ion currents consisted of one transient outward potassium ion current and one delayed rectifier potassium ion current, which were blocked by 4-aminopyridine and tetraethylammonium, respectively. The experimental findings indicate that neural stem cells from newborn rat campus could be cultured and induced to differentiate into functional neurons under defined conditions in vitro. The differentiated neurons expressed two types of outward potassium ion currents similar to those of mature neurons in vivo.

Culture of dissociated hippocampal neurons

Hippocampal neurons consist mainly of pyramidal neuron and granule cell, and dissociated hippocampal neurons are a good tool to investigate the molecular and cellular mechanism of neuronal development and neuronal degenerative disease in the central neuronal system (CNS). Here, we describe a general procedure of dissociated hippocampal neuron culture.

Comprehensive Method for Culturing Embryonic Dorsal Root Ganglion Neurons for Seahorse Extracellular Flux XF24 Analysis

Changes in mitochondrial dynamics and function contribute to progression of multiple neurodegenerative diseases including peripheral neuropathies. The Seahorse Extracellular Flux XF24 analyzer provides a comprehensive assessment of the relative state of glycolytic and aerobic metabolism in live cells making this method instrumental in assessing mitochondrial function. One of the most important steps in the analysis of mitochondrial respiration using the Seahorse XF24 analyzer is plating a uniform monolayer of firmly attached cells. However, culturing of primary dorsal root ganglion (DRG) neurons is associated with multiple challenges, including their propensity to form clumps and detach from the culture plate. This could significantly interfere with proper analysis and interpretation of data. We have tested multiple cell culture parameters including coating substrates, culture medium, XF24 microplate plastics, and plating techniques in order to optimize plating conditions. Here we describe a highly reproducible method to obtain neuron-enriched monolayers of securely attached dissociated primary embryonic (E15) rat DRG neurons suitable for analysis with the Seahorse XF24 platform.

A modified technique for culturing primary fetal rat cortical neurons

The study explored a modified primary culture system for fetal rat cortical neurons. Day E18 embryos from pregnant Sprague Dawley rats were microdissected under a stereoscope. To minimize enzymatic damage to the cultured neurons, we applied a sequential digestion protocol using papain and Dnase I. The resulting sifted cell suspension was seeded at a density of 50,000 cells per cm² onto 0.1 mg/mL L-PLL-covered vessels. After a four-hour incubation in high-glucose Dulbecco's Modified Eagle's Medium (HG-DMEM) to allow the neurons to adhere, the media was changed to neurobasal medium that was refreshed by changing half of the volume after three days followed by a complete medium change every week. The cells displayed progressively robust neurite extension, and nonneuronal-like cells could barely be detected by five days in vitro (DIV); cell growth was still substantial at 14 DIV. Neurons were identified by β-tubulin III immunofluorescence, and neuronal purity within the cultures was assessed at over 95% by both flow cytometry and by dark-field counting of β-tubulin III-positive cells. These results suggest that the protocol was successful and that the high purity of neurons in this system could be used as the basis for generating various cell models of neurological disease.

Making the case: married versus separate models of alphaherpes virus anterograde transport in axons

Alphaherpesvirus virions infect neurons and are transported in axons for long distance spread within the host nervous system. The assembly state of newly made herpesvirus particles during anterograde transport in axons is an essential question in alphaherpesvirus biology. The structure of the particle has remained both elusive and controversial for the past two decades, with conflicting evidence from EM, immunofluorescence, and live cell imaging studies. Two opposing models have been proposed-the Married and Separate Models. Under the Married Model, infectious virions are assembled in the neuronal cell body before sorting into axons and then traffic inside a transport vesicle. Conversely, the Separate Model postulates that vesicles containing viral membrane proteins are sorted into axons independent of capsids, with final assembly of mature virions occurring at a distant egress site. Recently, a complementary series of studies employing high-resolution EM and live cell fluorescence microscopy have provided evidence consistent with the Married Model, whereas other studies offer evidence supporting the Separate Model. In this review, we compare and discuss the published data and attempt to reconcile divergent findings and interpretations as they relate to these models.