Establishment of a long-term spiral ganglion neuron culture with reduced glial cell number: Effects of AraC on cell composition and neurons

Cytarabine prevents neuronal damage by enhancing AMPK to stimulate PINK1 / Parkin-involved mitophagy in Parkinson's disease model

Parkinson's disease (PD) is a common age-related neurodegenerative disorder, which may be largely due to the mitochondrial dysfunction and impaired mitophagy. Thus, it is of great importance to seek novel therapeutic strategies for PD targeting mitochondrial function and mitophagy. Cytarabine is a marine-derived antimetabolite used in the treatment of acute leukemia, which is also used in the study of the nervous system. In this study, we found that cytarabine pretreatment significantly inhibited the apoptosis and necrosis in the ROT-induced SH-SY5Y cell PD model and reduced the oxidative stress, as evidenced by the reduced MDA levels and the increased levels of SOD, GSH, and total antioxidant capacity. Cytarabine can also enhance mitochondrial vitality, improve mitochondrial respiratory function, and preserve mitochondrial morphology. Cytarabine also enhanced the expression of the mitophagy-related proteins PINK1, Parkin, VDAC1, and DJ-1, and its actions can be reversed by treatment with AMPK inhibitor - Compound C (CC), suggesting that AMPK activation may be involved in cytarabine-enhanced mitophagy. Furthermore, cytarabine can also ameliorate the motor symptoms in the MPTP-induced PD-like mice model, and attenuate the neuropathy in the substantia nigra (SN) of PD mice, while Compound C antagonized cytarabine's beneficial effects. In summary, marine-derived compound cytarabine could resist neurological damage both in vitro and in vivo by activating AMPK to increase PINK1/Parkin-induced mitophagy, serving as a promising disease modulator for treating neurodegenerative disease.

TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype.

METHODS

We cultured sexed hippocampal neurons from ERα+/+ and ERα-/- mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions.

RESULTS

Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα+/+ neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX.

CONCLUSIONS

OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cell survival preferentially in female hippocampal neurons. The sex-dependent neuroprotective actions of 7,8-DHF were blocked by either ANA-12 or by T pre-treatment. These results are consistent with a model for a female-specific neuroprotective pathway in hippocampal neurons in response to hypoxia. The pathway is activated by 7,8-DHF, mediated by TrkB phosphorylation, dependent on ERα and blocked by pre-exposure to T.

The DDHD2-STXBP1 interaction mediates long-term memory via generation of saturated free fatty acids

The phospholipid and free fatty acid (FFA) composition of neuronal membranes plays a crucial role in learning and memory, but the mechanisms through which neuronal activity affects the brain's lipid landscape remain largely unexplored. The levels of saturated FFAs, particularly of myristic acid (C14:0), strongly increase during neuronal stimulation and memory acquisition, suggesting the involvement of phospholipase A1 (PLA1) activity in synaptic plasticity. Here, we show that genetic ablation of the PLA1 isoform DDHD2 in mice dramatically reduces saturated FFA responses to memory acquisition across the brain. Furthermore, DDHD2 loss also decreases memory performance in reward-based learning and spatial memory models prior to the development of neuromuscular deficits that mirror human spastic paraplegia. Via pulldown-mass spectrometry analyses, we find that DDHD2 binds to the key synaptic protein STXBP1. Using STXBP1/2 knockout neurosecretory cells and a haploinsufficient STXBP1+/- mouse model of human early infantile encephalopathy associated with intellectual disability and motor dysfunction, we show that STXBP1 controls targeting of DDHD2 to the plasma membrane and generation of saturated FFAs in the brain. These findings suggest key roles for DDHD2 and STXBP1 in lipid metabolism and in the processes of synaptic plasticity, learning, and memory.

Ganglioglioma cells potentiate neuronal network synchronicity and elicit burst discharges via released factors

Gangliogliomas (GGs) represent the most frequent glioneuronal tumor entity associated with chronic recurrent seizures; rare anaplastic GGs variants retain the glioneuronal character. So far, key mechanisms triggering chronic hyperexcitability in the peritumoral area are unresolved. Based on a recent mouse model for anaplastic GG (BRAFV600E, mTOR activation and Trp53KO) we here assessed the influence of GG-secreted factors on non-neoplastic cells in-vitro. We generated conditioned medium (CM) from primary GG cell cultures to developing primary cortical neurons cultured on multielectrode-arrays and assessed their electrical activity in comparison to neurons incubated with naïve and neuronal CMs. Our results showed that the GG CM, while not affecting the mean firing rates of networks, strongly accelerated the formation of functional networks as indicated increased synchrony of firing and burst activity. Washing out the GG CM did not reverse these effects indicating an irreversible effect on the neuronal network. Mass spectrometry analysis of GG CM detected several enriched proteins associated with neurogenesis as well as gliogenesis, including Gap43, App, Apoe, S100a8, Tnc and Sod1. Concomitantly, immunocytochemical analysis of the neuronal cultures exposed to GG CM revealed abundant astrocytes suggesting that the GG-secreted factors induce astroglial proliferation. Pharmacological inhibition of astrocyte proliferation only partially reversed the accelerated network maturation in neuronal cultures exposed to GG CM indicating that the GG CM exerts a direct effect on the neuronal component. Taken together, we demonstrate that GG-derived paracrine signaling alone is sufficient to induce accelerated neuronal network development accompanied by astrocytic proliferation. Perspectively, a deeper understanding of factors involved may serve as the basis for future therapeutic approaches.

Auditory Hair Cells and Spiral Ganglion Neurons Regenerate Synapses with Refined Release Properties In Vitro

Ribbon synapses between inner hair cells (IHCs) and type I spiral ganglion neurons (SGNs) in the inner ear are damaged by noise trauma and with aging, causing 'synaptopathy 'and hearing loss. Co-cultures of neonatal denervated organs of Corti and newly introduced SGNs have been developed to find strategies for improving IHC synapse regeneration, but evidence of the physiological normality of regenerated synapses is missing. This study utilizes IHC optogenetic stimulation and SGN recordings, showing that newly formed IHC synapses are indeed functional, exhibiting glutamatergic excitatory postsynaptic currents. When older organs of Corti were plated, synaptic activity probed by deconvolution, showed more mature release properties, closer to the highly specialized mode of IHC synaptic transmission that is crucial for coding the sound signal. This newly developed functional assessment of regenerated IHC synapses provides a powerful tool for testing approaches to improve synapse regeneration.

"Of mice and men": the relevance of Cometin and Erythropoietin origin for its effects on murine spiral ganglion neuron survival and neurite outgrowth in vitro

Neurotrophic factors (NTF) play key roles in the survival of neurons, making them promising candidates for therapy of neurodegenerative diseases. In the case of the inner ear, sensorineural hearing loss (SNHL) is characterized over time by a degeneration of the primary auditory neurons, the spiral ganglion neurons (SGN). It is well known that selected NTF can protect SGN from degeneration, which positively influences the outcome of cochlear implants, the treatment of choice for patients with profound to severe SNHL. However, the outcome of studies investigating protective effects of NTF on auditory neurons are in some cases of high variability. We hypothesize that the factor origin may be one aspect that affects the neuroprotective potential. The aim of this study was to investigate the neuroprotective potential of human and mouse Erythropoietin (EPO) and Cometin on rat SGN. SGN were isolated from neonatal rats (P 2-5) and cultured in serum-free medium. EPO and Cometin of mouse and human origin were added in concentrations of 0.1, 1, and 10 ng/mL and 0.1, 1, and 10 μg/mL, respectively. The SGN survival rate and morphology, and the neurite outgrowth were determined and compared to negative (no additives) and positive (brain-derived neurotrophic factor, BDNF) controls. A neuroprotective effect of 10 μg/mL human Cometin comparable to that obtained with BDNF was observed in the SGN-culture. In contrast, mouse Cometin was ineffective. A similar influence of 10 μg/mL human and mouse and 1 μg/mL human Cometin on the length of regenerated neurites compared to BDNF was also detected. No other Cometin-conditions, and none of the EPO-conditions tested had neuroprotective or neuritogenic effects or influenced the neuronal morphology of the SGN. The neuroprotective effect of 10 μg/mL human Cometin on SGN indicates it is a potentially interesting protein for the supportive treatment of inner ear disorders. The finding that mouse Cometin had no effect on the SGN in the parallel-performed experiments underlines the importance of species origin of molecules being screened for therapeutic purpose.

Differentiating PC12 cells to evaluate neurite densities through live-cell imaging

Although PC12 cells are a valuable tool in neuroscience research, previously published PC12 cell differentiation techniques fail to consider the variability in differentiation rates between different PC12 cell strains and clonal variants. Here, we present a comprehensive protocol to differentiate PC12 cells into equivalent neurite densities through live-cell imaging for morphological, immunocytochemical, and biochemical analyses. We detail steps on optimized substrate coating, plating techniques, culture media, validation steps, and quantification techniques.

A fully automated primary neuron purification system using continuous centrifugal microfluidics

Progress in neurological research has experienced bottlenecks owing to the limited availability of purified primary neurons. Since neuronal cells are non-proliferative, it is necessary to obtain purified neurons from animal models or human patients for experimental work. However, currently available methods for purifying primary neurons are time-consuming (taking approximately 1 week), and suffer from insufficient viability and purity. Here, we report a method for rapid enrichment of neurons from the mouse embryonic dorsal root ganglion (DRG), using a fully-automated continuous centrifugal microfluidics (CCM) based neuron purification disc (NPD). Non-neuronal cells were removed via negative depletion by combining density gradient centrifugation and immunomagnetic separation. The CCM-NPD platform enables effective isolation of intact neurons within 13 min, which is approximately 800 times faster than the conventional chemical purification method. Furthermore, the neurons purified using the CCM-NPD platform showed better neurite growth, along with higher viability (93.5%) and purity (97.0%) after 1 week of culture, compared to the chemical purification method. Therefore, the proposed automated and rapid system yields purified DRG neurons with high viability and purity, while avoiding the use of harsh chemicals. We believe this system will significantly mitigate the shortage of purified primary neurons and advance neurological research.

Palmitic acid control of ciliogenesis modulates insulin signaling in hypothalamic neurons through an autophagy-dependent mechanism

Palmitic acid (PA) is significantly increased in the hypothalamus of mice, when fed chronically with a high-fat diet (HFD). PA impairs insulin signaling in hypothalamic neurons, by a mechanism dependent on autophagy, a process of lysosomal-mediated degradation of cytoplasmic material. In addition, previous work shows a crosstalk between autophagy and the primary cilium (hereafter cilium), an antenna-like structure on the cell surface that acts as a signaling platform for the cell. Ciliopathies, human diseases characterized by cilia dysfunction, manifest, type 2 diabetes, among other features, suggesting a role of the cilium in insulin signaling. Cilium depletion in hypothalamic pro-opiomelanocortin (POMC) neurons triggers obesity and insulin resistance in mice, the same phenotype as mice deficient in autophagy in POMC neurons. Here we investigated the effect of chronic consumption of HFD on cilia; and our results indicate that chronic feeding with HFD reduces the percentage of cilia in hypothalamic POMC neurons. This effect may be due to an increased amount of PA, as treatment with this saturated fatty acid in vitro reduces the percentage of ciliated cells and cilia length in hypothalamic neurons. Importantly, the same effect of cilia depletion was obtained following chemical and genetic inhibition of autophagy, indicating autophagy is required for ciliogenesis. We further demonstrate a role for the cilium in insulin sensitivity, as cilium loss in hypothalamic neuronal cells disrupts insulin signaling and insulin-dependent glucose uptake, an effect that correlates with the ciliary localization of the insulin receptor (IR). Consistently, increased percentage of ciliated hypothalamic neuronal cells promotes insulin signaling, even when cells are exposed to PA. Altogether, our results indicate that, in hypothalamic neurons, impairment of autophagy, either by PA exposure, chemical or genetic manipulation, cause cilia loss that impairs insulin sensitivity.

Inhibition of intracellular proton-sensitive Ca2+-permeable TRPV3 channels protects against ischemic brain injury

Ischemic brain stroke is pathologically characterized by tissue acidosis, sustained calcium entry and progressive cell death. Previous studies focusing on antagonizing N-methyl-d-aspartate (NMDA) receptors have failed to translate any clinical benefits, suggesting a non-NMDA mechanism involved in the sustained injury after stroke. Here, we report that inhibition of intracellular proton-sensitive Ca²⁺-permeable transient receptor potential vanilloid 3 (TRPV3) channel protects against cerebral ischemia/reperfusion (I/R) injury. TRPV3 expression is upregulated in mice subjected to cerebral I/R injury. Silencing of TRPV3 reduces intrinsic neuronal excitability, excitatory synaptic transmissions, and also attenuates cerebral I/R injury in mouse model of transient middle cerebral artery occlusion (tMCAO). Conversely, overexpressing or re-expressing TRPV3 increases neuronal excitability, excitatory synaptic transmissions and aggravates cerebral I/R injury. Furthermore, specific inhibition of TRPV3 by natural forsythoside B decreases neural excitability and attenuates cerebral I/R injury. Taken together, our findings for the first time reveal a causative role of neuronal TRPV3 channel in progressive cell death after stroke, and blocking overactive TRPV3 channel may provide therapeutic potential for ischemic brain injury.

Intrinsic mechanical sensitivity of mammalian auditory neurons as a contributor to sound-driven neural activity

Mechanosensation – by which mechanical stimuli are converted into a neuronal signal – is the basis for the sensory systems of hearing, balance, and touch. Mechanosensation is unmatched in speed and its diverse range of sensitivities, reaching its highest temporal limits with the sense of hearing; however, hair cells (HCs) and the auditory nerve (AN) serve as obligatory bottlenecks for sounds to engage the brain. Like other sensory neurons, auditory neurons use the canonical pathway for neurotransmission and millisecond-duration action potentials (APs). How the auditory system utilizes the relatively slow transmission mechanisms to achieve ultrafast speed, and high audio-frequency hearing remains an enigma. Here, we address this paradox and report that the mouse, and chinchilla, AN are mechanically sensitive, and minute mechanical displacement profoundly affects its response properties. Sound-mimicking sinusoidal mechanical and electrical current stimuli affect phase-locked responses. In a phase-dependent manner, the two stimuli can also evoke suppressive responses. We propose that mechanical sensitivity interacts with synaptic responses to shape responses in the AN, including frequency tuning and temporal phase locking. Combining neurotransmission and mechanical sensation to control spike patterns gives the mammalian AN a secondary receptor role, an emerging theme in primary neuronal functions.

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.

Optimized culture of retinal ganglion cells and amacrine cells from adult mice

Cell culture is widely utilized to study the cellular and molecular biology of different neuronal cell populations. Current techniques to study enriched neurons in vitro are primarily limited to embryonic/neonatal animals and induced pluripotent stem cells (iPSCs). Although the use of these cultures is valuable, the accessibility of purified primary adult neuronal cultures would allow for improved assessment of certain neurological diseases and pathways at the cellular level. Using a modified 7-step immunopanning technique to isolate for retinal ganglion cells (RGCs) and amacrine cells (ACs) from adult mouse retinas, we have successfully developed a model of neuronal culture that maintains for at least one week. Isolations of Thy1.2⁺ cells are enriched for RGCs, with the isolation cell yield being congruent to the theoretical yield of RGCs in a mouse retina. ACs of two different populations (CD15⁺ and CD57⁺) can also be isolated. The populations of these three adult neurons in culture are healthy, with neurite outgrowths in some cases greater than 500μm in length. Optimization of culture conditions for RGCs and CD15⁺ cells revealed that neuronal survival and the likelihood of neurite outgrowth respond inversely to different culture media. Serially diluted concentrations of puromycin decreased cultured adult RGCs in a dose-dependent manner, demonstrating the potential usefulness of these adult neuronal cultures in screening assays. This novel culture system can be used to model in vivo neuronal behaviors. Studies can now be expanded in conjunction with other methodologies to study the neurobiology of function, aging, and diseases.

Deficiency of anti-inflammatory cytokine IL-4 leads to neural hyperexcitability and aggravates cerebral ischemia-reperfusion injury

Systematic administration of anti-inflammatory cytokine interleukin 4 (IL-4) has been shown to improve recovery after cerebral ischemic stroke. However, whether IL-4 affects neuronal excitability and how IL-4 improves ischemic injury remain largely unknown. Here we report the neuroprotective role of endogenous IL-4 in focal cerebral ischemia–reperfusion (I/R) injury. In multi-electrode array (MEA) recordings, IL-4 reduces spontaneous firings and network activities of mouse primary cortical neurons. IL-4 mRNA and protein expressions are upregulated after I/R injury. Genetic deletion of Il-4 gene aggravates I/R injury in vivo and exacerbates oxygen-glucose deprivation (OGD) injury in cortical neurons. Conversely, supplemental IL-4 protects Il-4^−/− cortical neurons against OGD injury. Mechanistically, cortical pyramidal and stellate neurons common for ischemic penumbra after I/R injury exhibit intrinsic hyperexcitability and enhanced excitatory synaptic transmissions in Il-4^−/− mice. Furthermore, upregulation of Nav1.1 channel, and downregulations of KCa3.1 channel and α6 subunit of GABA_A receptors are detected in the cortical tissues and primary cortical neurons from Il-4^−/− mice. Taken together, our findings demonstrate that IL-4 deficiency results in neural hyperexcitability and aggravates I/R injury, thus activation of IL-4 signaling may protect the brain against the development of permanent damage and help recover from ischemic injury after stroke.

A Co-Culture Method to Study Neurite Outgrowth in Response to Dental Pulp Paracrine Signals

Tooth innervation allows teeth to sense pressure, temperature and inflammation, all of which are crucial to the use and maintenance of the tooth organ. Without sensory innervation, daily oral activities would cause irreparable damage. Despite its importance, the roles of innervation in tooth development and maintenance have been largely overlooked. Several studies have demonstrated that DP cells secrete extracellular matrix proteins and paracrine signals to attract and guide TG axons into and throughout the tooth. However, few studies have provided detailed insight into the crosstalk between the DP mesenchyme and neuronal afferents. To address this gap in knowledge, researchers have begun to utilize co-cultures and a variety of techniques to investigate these interactions. Here, we demonstrate the multiple steps involved in co-culturing primary DP cells with TG neurons dispersed on an overlying transwell filter with large diameter pores to allow axonal growth through the pores. Primary DP cells with the gene of interest flanked by loxP sites were utilized to facilitate gene deletion using an Adenovirus-Cre-GFP recombinase system. Using TG neurons from the Thy1-YFP mouse allowed for precise afferent imaging, with expression well above background levels by confocal microscopy. The DP responses can be investigated via protein or RNA collection and analysis, or alternatively, through immunofluorescent staining of DP cells plated on removable glass coverslips. Media can be analyzed using techniques such as proteomic analyses, although this will require albumin depletion due to the presence of fetal bovine serum in the media. This protocol provides a simple method that can be manipulated to study the morphological, genetic, and cytoskeletal responses of TG neurons and DP cells in response to the controlled environment of a co-culture assay.

Guided growth with aligned neurites in adult spiral ganglion neurons cultured in vitro on silicon micro-pillar substrates

OBJECTIVE

Assessment of the relationship between the topographical organization of silicon micro-pillar surfaces (MPS) on guidance and neural alignment of adult spiral ganglion neurons (SGN) and use of the otosurgical approach as an alternative for the extraction and isolation of SGNs from adult guinea pigs.

APPROACH

SGNs from adult guinea pigs were isolated using conventional and otosurgical approach for in vitro cell culturing on MPS of various micro-pillar widths (1-5.6 µm) and spacing (0.6-15 µm). Cell cultures were compared morphologically with neuronal cultures on control glass coverslips.

MAIN RESULTS

We found enhanced SGN in vitro cultures in MPS areas with small and intermediate inter-pillar spacing (from 0.6 µm to 3.2 µm) as well as in MPS areas with wider pillars (from 1.8 µm to 4 µm) compared to MPS flat zones and control glass coverslips. Scanning electron microscopy (SEM) images highlighted how neurites of SGNs follow straight lines by growing on top and between micro-pillars. Only micro-pillars with small and intermediate pillar spacings favor neurite alignment along preferred angles (30°, 90°, and 150°), while pillars with wider spacing produced less aligned neurites. We found propensity of adult SGNs grown on MPSs to attain more bipolar and multipolar morphologies. Additionally, we observed reduced interaction between neuronal and glial cells compared to control glass coverslips. Finally, we found that the otosurgical approach was more beneficial for SGN survival on glass coverslips and MPS flat surfaces than the conventional method.

SIGNIFICANCE

MPS with specific architecture supports the guided growth of adult SGNs in vitro and controls adult SGN development and behavior.

Decellularized equine carotid artery layers as matrix for regenerated neurites of spiral ganglion neurons

Today’s best solution in compensating for sensorineural hearing loss is the cochlear implant, which electrically stimulates the spiral ganglion neurons in the inner ear. An optimum hearing impression is not ensured due to, among other reasons, a remaining anatomical gap between the spiral ganglion neurons and the implant electrodes. The gap could be bridged via pharmacologically triggered neurite growth toward the electrodes if biomaterials for neurite guidance could be provided. For this, we investigated the suitability of decellularized tissue. We compared three different layers (tunica adventitia, tunica media, and tunica intima) of decellularized equine carotid arteries in a preliminary approach. Rat spiral ganglia explants were cultured on decellularized equine carotid artery layers and neurite sprouting was assessed quantitatively. Generally, neurite outgrowth was possible and it was most prominent on the intima (in average 83 neurites per spiral ganglia explants, followed by the adventitia (62 neurites) and the lowest growth on the media (20 neurites). Thus, decellularized equine carotid arteries showed promising effects on neurite regeneration and can be developed further as efficient biomaterials for neural implants in hearing research.

An integrated cell isolation and purification method for rat dorsal root ganglion neurons

Objective

Neurobiology studies are increasingly focused on the dorsal root ganglion (DRG), which plays an important role in neuropathic pain. Existing DRG neuron primary culture methods have considerable limitations, including challenging cell isolation and poor cell yield, which cause difficulty in signaling pathway studies. The present study aimed to establish an integrated primary culture method for DRG neurons.

Methods

DRGs were obtained from fetal rats by microdissection, and then dissociated with trypsin. The dissociated neurons were treated with 5-fluorouracil to promote growth of neurons from the isolated cells. Then, reverse transcription polymerase chain reaction and immunofluorescence assays were used to identify and purify DRG neurons.

Results

Isolated DRGs were successfully dissociated and showed robust growth as individual DRG neurons in neurobasal medium. Both mRNA and protein assays confirmed that DRG neurons expressed neurofilament-200 and neuron-specific enolase.

Conclusions

Highly purified, stable DRG neurons could be easily harvested and grown for extended periods by using this integrated cell isolation and purification method, which may help to elucidate the mechanisms underlying neuropathic pain.

Influence of In Vitro Electrical Stimulation on Survival of Spiral Ganglion Neurons

Patients scheduled for cochlear implantation often retain residual hearing in the low frequencies. Unfortunately, some patients lose their residual hearing following implantation and the reasons for this are not well understood. Evidence suggests that electrotoxicity could be one of the factors responsible for this late adverse effect. Therefore, the aim of this study was to investigate the survival of spiral ganglion neurons (SGN) subjected to in vitro electrical stimulation (ES). A stimulation setup was developed to provide defined electrical fields at given points of the chamber. SGN isolated from Sprague Dawley rats (P3-4) were dissociated and cultured in the chamber for 24 h prior to biphasic, pulsed electrical field exposure for another 24 h. The current varied in the range of 0 to 2 mA and the pulse width from 10 to 400 μs. Neurite growth and survival were evaluated with respect to the charge density at the position of the cells. Non-exposed SGN cultures served as control. Charge densities below 2.2 μC·cm^-2·phase^-1 appeared to have no effect on SGN survival and neurite outgrowth. Charge densities above 4.9 μC·cm^-2·phase^-1 were detrimental to almost all cells in culture. After fitting results to a sigmoidal dose response curve, a LD₅₀ of 2.9 μC·cm^-2·phase^-1 was calculated. This screening regarding survival and outgrowth of SGN provides parameters that could be used to further investigate the effect of ES on SGN and to develop possible protection strategies, which could potentially rescue residual hearing in the implanted patients.

Advantageous environment of micro-patterned, high-density complementary metal-oxide-semiconductor electrode array for spiral ganglion neurons cultured in vitro

This study investigated micro-patterned, high-density complementary metal–oxide–semiconductor (CMOS) electrode array to be used as biologically permissive environment for organization, guidance and electrical stimulation of spiral ganglion neurons (SGN). SGNs extracted and isolated from cochleae of P5-P7 rat pups and adult guinea pigs were cultured 1, 4 and 7 days in vitro on glass coverslips (control) and CMOS electrode array. The cultures were analyzed visually and immunohistochemically for SGN presence, outgrowth, neurite alignment, neurite length, neurite asymmetry as well as the contact of a neuronal soma and neurites with the micro-electrodes. Our findings indicate that topographical environment of CMOS chip with micro-patterned pillars enhanced growth, survival, morphology, neural orientation and alignment of SGNs in vitro compared to control. Smaller spacing (0.8–1.6 µm) between protruding pillars on CMOS led SGNs to develop structured and guided neurites oriented along three topographical axes separated by 60°. We found morphological basis for positioning of the micro-electrodes on the chip that was appropriate for direct contact of SGNs with them. This configuration allowed CMOS electrode array to electrically stimulate the SGN whose responses were observed with live Fluo 4 calcium imaging.

Hyper-SUMOylation of K+ Channels in Sudden Unexplained Death in Epilepsy: Isolation and Primary Culture of Dissociated Hippocampal Neurons from Newborn Mice for Subcellular Localization

The physiological characteristics of rat and murine hippocampal neurons are widely studied, especially because of the involvement of the hippocampus in learning, memory, and neurological functions. Primary cultures of hippocampal neurons are commonly used to discover cellular and molecular mechanisms in neurobiology. By isolating and culturing individual hippocampal neurons, neuroscientists are able to investigate the activity of neurons at the individual cell and single synapse level, and to analyze properties related to cellular structure, cellular trafficking, and individual protein subcellular localization or protein-protein interaction using a variety of biochemical techniques. Conclusions addressed from such research are critical for testing theories related to memory, learning, and neurological functions. Here, we will describe how to isolate and culture primary hippocampal cells from newborn mice. The hippocampus may be isolated from newborn mice in as short as 2 min, and the cell cultures can be maintained for up to 2 weeks, and then ready for investigation of subcellular localization of K⁺ channel proteins and interaction with SUMO-specific protease 2 (SENP2). The protocol provides a fast and efficient technique for the culture of neuronal cells from mouce hippocampal tissue, and will ensure the immunocytochemistry detection of subcellular localization or protein-protein interactions in neurological research.

Endothelial Nitric Oxide Synthase Is Present in Dendritic Spines of Neurons in Primary Cultures

Nitric oxide exerts important regulatory functions in various brain processes. Its synthesis in neurons has been most commonly ascribed to the neuronal nitric oxide synthase (nNOS) isoform. However, the endothelial isoform (eNOS), which is significantly associated with caveolae in different cell types, has been implicated in synaptic plasticity and is enriched in the dendrites of CA1 hippocampal neurons. Using high resolution microscopy and co-distribution analysis of eNOS with synaptic and raft proteins, we now show for the first time in primary cortical and hippocampal neuronal cultures, virtually devoid of endothelial cells, that eNOS is present in neurons and is localized in dendritic spines. Moreover, eNOS is present in a postsynaptic density-enriched biochemical fraction isolated from these neuronal cultures. In addition, qPCR analysis reveals that both the nNOS as well as the eNOS transcripts are present in neuronal cultures. Moreover, eNOS inhibition in cortical cells has a negative impact on cell survival after excitotoxic stimulation with N-methyl-D-aspartate (NMDA). Consistent with previous results that indicated nitric oxide production in response to the neurotrophin BDNF, we could detect eNOS in immunoprecipitates of the BDNF receptor TrkB while nNOS could not be detected. Taken together, our results show that eNOS is located at excitatory synapses where it could represent a source for NO production and thus, the contribution of eNOS-derived nitric oxide to the regulation of neuronal survival and function deserves further investigations.

Bone morphogenetic protein 4 promotes the survival and preserves the structure of flow-sorted Bhlhb5+ cochlear spiral ganglion neurons in vitro

SGNs are the primary auditory neurons, and damage or loss of SGNs leads to sensorineural hearing loss. BMP4 is a growth factor that belongs to the TGF-β superfamily and has been shown to play a key role during development, but little is known about its effect on postnatal cochlear SGNs in mice. In this study, we used the P3 Bhlhb5-cre/tdTomato transgenic mouse model and FACS to isolate a pure population of Bhlhb5+ SGNs. We found that BMP4 significantly promoted SGN survival after 7 days of culture. We observed fewer apoptotic cells and decreased expression of pro-apoptotic marker genes after BMP4 treatment. We also found that BMP4 promoted monopolar neurite outgrowth of isolated SGNs, and high concentrations of BMP4 preserved the number and the length of neurites in the explant culture of the modiolus harboring the SGNs. We showed that high concentration of BMP4 enhanced neurite growth as determined by the higher average number of filopodia and the larger area of the growth cone. Finally, we found that high concentrations of BMP4 significantly elevated the synapse density of SGNs in explant culture. Thus, our findings suggest that BMP4 has the potential to promote the survival and preserve the structure of SGNs.