Electroporation of neurons and growth cones in Aplysia californica

Evaluation of dicloran phototoxicity using primary cardiomyocyte culture from Crassostrea virginica

Dicloran is a commonly used fungicide throughout the Southern and Western United States. Runoff of dicloran from agriculture systems to nearby waterbodies can accumulate in the organisms that inhabit those areas. Although severe damage of dicloran to ecological systems has not been reported, its toxicity has been modified by photodegradation. The objective of this study is to assess the changes of dicloran toxicities during photo exposure using a reliable in vitro biological model. In the present investigation, the photodegradation of dicloran in vitro showed over 90% of dicloran was degraded within 24h of UV exposure in water. Two major intermediate degradation products, 2-chloro-1,4-benzoquinone (CBQ) and 1,4-benzoquinone (BQ), were detected upon UV exposure of dicloran; however, they were rapidly degraded via photolysis. To estimate the impact of the phototoxicity of dicloran to aquatic organisms, we developed an in vitro cell culture system using the C. virginica cardiomyoctes (CvCMs) which were isolated from heart tissues and formed beating cell clusters. The CvCM clusters were treated with irradiated dicloran or the two intermediate standards, CBQ and BQ, and they showed up to 41% decrease in beating rates compared to control cell clusters. Expression levels of selected genes: def, hsp70, and cam, were upregulated in response to stimulations of UV irradiated dicloran and the two standard intermediates. The four-hour irradiated dicloran also resulted in more significant inhibition in the proliferation and small cardioactive peptide β production of CvCMs than other treatment. Tested solutions of photolyzed dicloran showed elevated toxicities opposed to the standard intermediates, CBQ and BQ, suggesting additive toxicity of these dicloran products or toxicity due to other unidentified degradation products. Results of this study supported our hypothesis that the degradation of dicloran caused by photo irradiation results in an elevated toxicity which can be evaluated by the in vitro CvCM model.

Plasma membrane depolarization and permeabilization due to electric pulses in cell lines of different excitability

In electroporation-based medical treatments, excitable tissues are treated, either intentionally (irreversible electroporation of brain cancer, gene electrotransfer or ablation of the heart muscle, gene electrotransfer of skeletal muscles), or unintentionally (excitable tissues near the target area). We investigated how excitable and non-excitable cells respond to electric pulses, and if electroporation could be an effective treatment of the tumours of the central nervous system. For three non-excitable and one excitable cell line, we determined a strength-duration curve for a single pulse of 10ns-10ms. The threshold for depolarization decreased with longer pulses and was higher for excitable cells. We modelled the response with the Lapicque curve and the Hodgkin-Huxley model. At 1μs a plateau of excitability was reached which could explain why high-frequency irreversible electroporation (H-FIRE) electroporates but does not excite cells. We exposed cells to standard electrochemotherapy parameters (8×100μs pulses, 1Hz, different voltages). Cells behaved similarly which indicates that electroporation most probably occurs at the level of lipid bilayer, independently of the voltage-gated channels. These results could be used for optimization of electric pulses to achieve maximal permeabilization and minimal excitation/pain sensation. In the future, it should be established whether the in vitro depolarization correlates to nerve/muscle stimulation and pain sensation in vivo.

Optimization of single-cell electroporation protocol for forced gene expression in primary neuronal cultures

The development and function of the central nervous system (CNS) are realized through interactions between many neurons. To investigate cellular and molecular mechanisms of the development and function of the CNS, it is thus crucial to be able to manipulate the gene expression of single neurons in a complex cell population. We recently developed a technique for gene silencing by introducing small interfering RNA into single neurons in primary CNS cultures using single-cell electroporation. However, we had not succeeded in forced gene expression by introducing expression plasmids using single-cell electroporation. In the present study, we optimized the experimental conditions to enable the forced expression of green fluorescent protein (GFP) in cultured cerebellar Purkinje neurons using single-cell electroporation. We succeeded in strong GFP expression in Purkinje neurons by increasing the inside diameter of micropipettes or by making the size of the original plasmid smaller by digestion and cyclizing it by ligation. Strong GFP expression in Purkinje neurons electroporated under the optimal conditions continued to be observed for more than 25 days after electroporation. Thus, this technique could be used for forced gene expression in single neurons to investigate cellular and molecular mechanisms of the development, function, and disease of the CNS.

Dendritic differentiation of cerebellar Purkinje cells is promoted by ryanodine receptors expressed by Purkinje and granule cells

Cerebellar Purkinje cells have the most elaborate dendritic trees among neurons in the brain. We examined the roles of ryanodine receptor (RyR), an intracellular Ca(2+) release channel, in the dendrite formation of Purkinje cells using cerebellar cell cultures. In the cerebellum, Purkinje cells express RyR1 and RyR2, whereas granule cells express RyR2. When ryanodine (10 µM), a blocker of RyR, was added to the culture medium, the elongation and branching of Purkinje cell dendrites were markedly inhibited. When we transferred small interfering RNA (siRNA) against RyR1 into Purkinje cells using single-cell electroporation, dendritic branching but not elongation of the electroporated Purkinje cells was inhibited. On the other hand, transfection of RyR2 siRNA into granule cells also inhibited dendritic branching of Purkinje cells. Furthermore, ryanodine reduced the levels of brain-derived neurotrophic factor (BDNF) in the culture medium. The ryanodine-induced inhibition of dendritic differentiation was partially rescued when BDNF was exogenously added to the culture medium in addition to ryanodine. Overall, these results suggest that RyRs expressed by both Purkinje and granule cells play important roles in promoting the dendritic differentiation of Purkinje cells and that RyR2 expressed by granule cells is involved in the secretion of BDNF from granule cells.

Molluscan cells in culture: primary cell cultures and cell lines

In vitro cell culture systems from molluscs have significantly contributed to our basic understanding of complex physiological processes occurring within or between tissue-specific cells, yielding information unattainable using intact animal models. In vitro cultures of neuronal cells from gastropods show how simplified cell models can inform our understanding of complex networks in intact organisms. Primary cell cultures from marine and freshwater bivalve and gastropod species are used as biomonitors for environmental contaminants, as models for gene transfer technologies, and for studies of innate immunity and neoplastic disease. Despite efforts to isolate proliferative cell lines from molluscs, the snail Biomphalaria glabrata Say, 1818 embryonic (Bge) cell line is the only existing cell line originating from any molluscan species. Taking an organ systems approach, this review summarizes efforts to establish molluscan cell cultures and describes the varied applications of primary cell cultures in research. Because of the unique status of the Bge cell line, an account is presented of the establishment of this cell line, and of how these cells have contributed to our understanding of snail host-parasite interactions. Finally, we detail the difficulties commonly encountered in efforts to establish cell lines from molluscs and discuss how these difficulties might be overcome.

High-throughput single-cell manipulation in brain tissue

The complexity of neurons and neuronal circuits in brain tissue requires the genetic manipulation, labeling, and tracking of single cells. However, current methods for manipulating cells in brain tissue are limited to either bulk techniques, lacking single-cell accuracy, or manual methods that provide single-cell accuracy but at significantly lower throughputs and repeatability. Here, we demonstrate high-throughput, efficient, reliable, and combinatorial delivery of multiple genetic vectors and reagents into targeted cells within the same tissue sample with single-cell accuracy. Our system automatically loads nanoliter-scale volumes of reagents into a micropipette from multiwell plates, targets and transfects single cells in brain tissues using a robust electroporation technique, and finally preps the micropipette by automated cleaning for repeating the transfection cycle. We demonstrate multi-colored labeling of adjacent cells, both in organotypic and acute slices, and transfection of plasmids encoding different protein isoforms into neurons within the same brain tissue for analysis of their effects on linear dendritic spine density. Our platform could also be used to rapidly deliver, both ex vivo and in vivo, a variety of genetic vectors, including optogenetic and cell-type specific agents, as well as fast-acting reagents such as labeling dyes, calcium sensors, and voltage sensors to manipulate and track neuronal circuit activity at single-cell resolution.

Single-cell electroporation in Xenopus

Single-cell electroporation (SCE) is a versatile technique for delivering electrically charged macromolecules including DNA, RNA, synthetic oligonucleotides, peptides, dyes, and drugs to individual cells within intact tissues. Here, we describe methods for in vivo-targeted electroporation of single tectal neurons within the albino Xenopus laevis tadpole. Focal electroporation is achieved using a pipette electrode filled with a solution of the delivery molecules and with a tip diameter much smaller than the width of the target cell. The small tip allows for localization of an electric field, which restricts pore formation to only the individual cell in direct contact with the tip. Thus, the small tip permits focal delivery of the charged molecules within the pipette into individual cells. Factors affecting the efficiency of SCE, as well as various applications of this technique, are discussed. Particular focus is directed toward combining SCE with in vivo two-photon microscopy for three-dimensional (3D) imaging of neuron growth and cell-autonomous effects of altered protein function.

Long-term gene-silencing effects of siRNA introduced by single-cell electroporation into postmitotic CNS neurons

To explore how long the gene-silencing effects of siRNA introduced into postmitotic neurons continue, we transferred siRNA against GFP into GFP-expressing Purkinje and Golgi cells in cerebellar cell cultures by single-cell electroporation. The temporal changes in the intensity of GFP fluorescence in the same electroporated cells were monitored in real time using GFP imaging. Under standard conditions, GFP fluorescence was reduced to under one-tenth of the initial levels 4-7 days after electroporation. Such effects continued at least up to 14 days after electroporation. The effects of siRNAs against endogenous genes also continued for the same period. Thus, this method could be an effective tool for silencing gene expression for a long period in postmitotic neurons.

Identifiable cells in the crustacean stomatogastric ganglion

Neural circuits rely on slight physiological differences between the component cells for proper function. When any circuit is analyzed, it is important to characterize the features that distinguish one cell type from another. This review describes the methods used to identify the neurons of the crustacean stomatogastric ganglion.

Single neuron electroporation in manipulating and measuring the central nervous system

The development and application of single neuron electroporation largely advanced the use of traditional genetics in investigations of the central nervous system. This quick and accurate manipulation of the brain at individual neuron level allowed the gain and loss of functional analyses of different genes and/or proteins. This manuscript reviewed the development of the technique and discussed some technical aspects in practical manipulations. Then the manuscript summarized the potential applications with this technique. Last but not least, the technique showed prospective future when combined with other modern methods in neuroscience research.

PRODUCTION OF NITRIC OXIDE WITHIN THE APLYSIA CALIFORNICA NERVOUS SYSTEM

Nitric oxide (NO), an intercellular signaling molecule, helps coordinate neuronal network activity. Here we examine NO generation in the Aplysia central nervous system using 4,5-diaminofluorescein diacetate (DAF-2 DA), a fluorescent reagent that forms 4,5-diaminofluorescein triazole (DAF-2T) upon reaction with NO. Recognizing that other fluorescence products are formed within the biochemically complex intracellular environment, we validate the observed fluorescence as being from DAF-2T; using both capillary electrophoresis and mass spectrometry we confirm that DAF-2T is formed from tissues and cells exposed to DAF-2 DA. We observe three distinct subcellular distributions of fluorescence in neurons exposed to DAF-2 DA. The first shows uniform fluorescence inside the cell, with these cells being among previously confirmed NOS-positive regions in the Aplysia cerebral ganglion. The second, seen inside buccal neurons, exhibits point sources of fluorescence, 1.5 ± 0.7 µm in diameter. Interestingly, the number of fluorescence puncta increases when the tissue is preincubated with the NOS substrate L-arginine, and they disappear when cells are preexposed to the NOS inhibitor L-NAME, demonstrating that the fluorescence is connected to NOS-dependent NO production. The third distribution type, seen in the R2 neuron, also exhibits fluorescent puncta, but only on the cell surface. Fluorescence is also observed in the terminals of cultured bag cell neurons loaded with DAF-2 DA. Surprisingly, fluorescence at the R2 surface and bag cell neuron terminals is not modulated by L-arginine or L-NAME, suggesting it has a source distinct from the buccal and cerebral ganglion DAF 2T-positive tissues.

Molluscan memory of injury: evolutionary insights into chronic pain and neurological disorders

Molluscan preparations have yielded seminal discoveries in neuroscience, but the experimental advantages of this group have not, until now, been complemented by adequate molecular or genomic information for comparisons to genetically defined model organisms in other phyla. The recent sequencing of the transcriptome and genome of Aplysia californica, however, will enable extensive comparative studies at the molecular level. Among other benefits, this will bring the power of individually identifiable and manipulable neurons to bear upon questions of cellular function for evolutionarily conserved genes associated with clinically important neural dysfunction. Because of the slower rate of gene evolution in this molluscan lineage, more homologs of genes associated with human disease are present in Aplysia than in leading model organisms from Arthropoda (Drosophila) or Nematoda (Caenorhabditis elegans). Research has hardly begun in molluscs on the cellular functions of gene products that in humans are associated with neurological diseases. On the other hand, much is known about molecular and cellular mechanisms of long-term neuronal plasticity. Persistent nociceptive sensitization of nociceptors in Aplysia displays many functional similarities to alterations in mammalian nociceptors associated with the clinical problem of chronic pain. Moreover, in Aplysia and mammals the same cell signaling pathways trigger persistent enhancement of excitability and synaptic transmission following noxious stimulation, and these highly conserved pathways are also used to induce memory traces in neural circuits of diverse species. This functional and molecular overlap in distantly related lineages and neuronal types supports the proposal that fundamental plasticity mechanisms important for memory, chronic pain, and other lasting alterations evolved from adaptive responses to peripheral injury in the earliest neurons. Molluscan preparations should become increasingly useful for comparative studies across phyla that can provide insight into cellular functions of clinically important genes.

Transfer of small interfering RNA by single-cell electroporation in cerebellar cell cultures

RNA interference (RNAi) is a powerful means to investigate functions of genes involved in neuronal differentiation and degeneration. In contrast to widely used methods for introducing small interfering RNA (siRNA) into cells, recently developed single-cell electroporation has enabled transfer of siRNA into single and identified cells. To explore the availability of single-cell electroporation of siRNA in detail, we introduced siRNA against green fluorescent protein (GFP) into GFP-expressing Golgi and Purkinje cells in cerebellar cell cultures by single-cell electroporation using micropipettes. The temporal changes in the intensity of GFP fluorescence in the same electroporated cells were monitored in real-time up to 4 days after electroporation. Several parameters, including tip diameter and resistance of micropipettes, concentrations of siRNA and a fluorescent dye marker, voltage and time of pulses, were optimized to maximize both the efficacy of RNAi and the viability of the electroporated cells. Under the optimal conditions, transfer of GFP siRNA significantly reduced GFP fluorescence in the electroporated cells, whereas that of negative control siRNA had no effects. GFP siRNA was more efficient in Purkinje cells than in Golgi cells. The electroporated Purkinje cells were normal in their morphology, including elaborated dendrites. Thus, the single-cell electroporation of siRNA could be a simple but effective tool for silencing gene expression in individual cells in neuronal primary cultures. In addition, both gene-silencing and off-target effects of siRNA introduced by this method may differ between neuronal cell types, and the parameters of single-cell electroporation should be optimized in each cell type.

Single-cell electroporation of adult sensory neurons for gene screening with RNA interference mechanism

RNA interference appears as a technique of choice to identify gene candidate or to evaluate gene function. To date, a main problem is to achieve high transfection efficiencies on native cells such as adult neurons. In addition, transfection on organ or mass culture does not allow to approach the cellular diversity. Dorsal root ganglia are composed with several cell types to convey somato-sensory sensations. Single-cell electroporation is the most recent method of transfection that allows the introduction into cells, not only dyes or drugs, but also large molecules such plasmid DNA expression constructs. In the present study, the application of the RNA interference technique with the use of single-cell electroporation was evaluated in primary culture of adult sensory neurons. With the use of fluorescent dextran as a co-transfectant, we first determined the non-specific siRNA concentration leading to cell death. Efficacy of siRNA at the non-toxic concentration was demonstrated at the protein level by extinction of GFP fluorescence in actin-GFP neurons and by the inhibition of the intracellular Cl- concentration increase following activation of the membrane co-transporter Na+-K+-2Cl- in regenerating axotomized sensory neurons. Altogether, these data show that delivery of siRNAs by single-cell electroporation leads to the induction of functional RNA interference.

In vivo single-cell electroporation for transfer of DNA and macromolecules

Single-cell electroporation allows transfection of plasmid DNA or macromolecules into individual living cells using modified patch electrodes and common electrophysiological equipment. This protocol is optimized for rapid in vivo electroporation of Xenopus laevis tadpole brains with DNA, dextrans, morpholinos and combinations thereof. Experienced users can electroporate roughly 40 tadpoles per hour. The technique can be adapted for use with other charged transfer materials and in other systems and tissues where cells can be targeted with a micropipette. Under visual guidance, an electrode filled with transfer material is placed in a cell body-rich area of the tadpole brain and a train of voltage pulses applied, which electroporates a nearby cell. We show examples of successfully electroporated single cells, instances of common problems and troubleshooting suggestions. Single-cell electroporation is an affordable method to fluorescently label and genetically manipulate individual cells. This powerful technique enables observation of single cells in an otherwise normal environment.

Electroporation: an arsenal of application

Electroporation is a way to induce nanometersized membrane pore for exogenous substances delivery into cytoplasm using an artificial electric field. Now it was widely used for molecules transfer especially in molecular experiments and genetic aspects. In recent years, modern electroporation on the embryo was developed, whose most important point is that it adopts low energy and rectangular pulse that could obtain high transfection efficiency and low damage to the embryo. This paper reviewed on the pool of application: from lab works to human clinical treatments.

Calcium indicator loading of neurons using single-cell electroporation

Studies of subcellular Ca(2+) signaling rely on methods for labeling cells with fluorescent Ca(2+) indicator dyes. In this study, we demonstrate the use of single-cell electroporation for Ca(2+) indicator loading of individual neurons and small neuronal networks in rat neocortex in vitro and in vivo. Brief voltage pulses were delivered through glass pipettes positioned close to target cells. This approach resulted in reliable and rapid (within seconds) loading of somata and subsequent complete labeling of dendritic and axonal arborizations. By using simultaneous whole-cell recordings in brain slices, we directly addressed the effect of electroporation on neurons. Cell viability was high (about 85%) with recovery from the membrane permeabilization occurring within a minute. Electrical properties of recovered cells were indistinguishable before and after electroporation. In addition, Ca(2+) transients with normal appearance could be evoked in dendrites, spines, and axonal boutons of electroporated cells. Using negative-stains of somata, targeted single-cell electroporation was equally applicable in vivo. We conclude that electroporation is a simple approach that permits Ca(2+) indicator loading of multiple cells with low background staining within a short amount of time, which makes it especially well suited for functional imaging of subcellular Ca(2+) dynamics in small neuronal networks.