Histiotypic electrophysiological responses of cultured neuronal networks to ethanol

Utilizing novel TBI-on-a-chip device to link physical impacts to neurodegeneration and decipher primary and secondary injury mechanisms

While clinical observations have confirmed a link between the development of neurodegenerative diseases and traumatic brain injuries (TBI), there are currently no treatments available and the underlying mechanisms remain elusive. In response, we have developed an in vitro pendulum trauma model capable of imparting rapid acceleration injuries to neuronal networks grown on microelectrode arrays within a clinically relevant range of g forces, with real-time electrophysiological and morphological monitoring. By coupling a primary physical insult with the quantification of post-impact levels of known biochemical pathological markers, we demonstrate the capability of our system to delineate and investigate the primary and secondary injury mechanisms leading to post-impact neurodegeneration. Specifically, impact experiments reveal significant, force-dependent increases in the pro-inflammatory, oxidative stress marker acrolein at 24 h post-impact. The elevation of acrolein was augmented by escalating g force exposures (30-200 g), increasing the number of rapidly repeated impacts (4-6 s interval, 3, 5 and 10×), and by exposing impacted cells to 40 mM ethanol, a known comorbidity of TBI. The elevated levels of acrolein following multiple impacts could be reduced by increasing time-intervals between repeated hits. In addition, we show that conditioned media from maximally-impacted cultures can cause cellular acrolein elevation when introduced to non-impact, control networks, further solidifying acrolein's role as a diffusive-factor in post-TBI secondary injuries. Finally, morphological data reveals post-impact acrolein generation to be primarily confined to soma, with some emergence in cellular processes. In conclusion, this novel technology provides accurate, physical insults with a unique level of structural and temporal resolution, facilitating the investigation of post-TBI neurodegeneration.

Study on influence of external factors on the electrical excitability of PC12 quasi-neuronal networks through Voltage Threshold Measurement Method

The aim of this paper was to investigate the influence of four different external factors (acetylcholine, ethanol, temperature and lidocaine hydrochloride) on PC12 quasi-neuronal networks by multielectrode-array-based Voltage Threshold Measurement Method (VTMM). At first, VTMM was employed to measure the lowest amplitude of the voltage stimulating pulses that could just trigger the action potential from PC12 quasi-neuronal networks under normal conditions, and the amplitude was defined as the normal voltage threshold (VTh). Then the changes of the VTh of PC12 quasi-neuronal networks treated by the four external factors were tested respectively. The results showed the normal VTh of PC12 quasi-neuronal networks was 36 mV. The VTh has negative correlation with the concentration of acetylcholine and has positive correlation with the concentration of ethanol. The curves of the correlation of the VTh with temperature and the concentration of lidocaine hydrochloride were U-shaped and Λ-shaped respectively. Comparing with our earlier studies on hippocampal neuronal networks and hippocampal slices, PC12 quasi-neuronal networks not only had the same typical voltage threshold characteristic, but also had similar changes on electrical excitability when treated by the four external factors mentioned above. Therefore, the rapid-formed PC12 quasi-neuronal networks could replace neuronal networks in proper conditions, and VTMM could be used to analyze the influence of external factors on the electrical excitability of PC12 quasi-neuronal networks.

Diazepam and ethanol differently modulate neuronal activity in organotypic cortical cultures

Background

The pharmacodynamic results of diazepam and ethanol administration are similar, in that each can mediate amnestic and sedative-hypnotic effects. Although each of these molecules effectively reduce the activity of central neurons, diazepam does so through modulation of a more specific set of receptor targets (GABA_A receptors containing a γ-subunit), while alcohol is less selective in its receptor bioactivity. Our investigation focuses on divergent actions of diazepam and ethanol on the firing patterns of cultured cortical neurons.

Method

We used electrophysiological recordings from organotypic slice cultures derived from Sprague–Dawley rat neocortex. We exposed these cultures to either diazepam (15 and 30 µM, n = 7) or ethanol (30 and 60 mM, n = 11) and recorded the electrical activity at baseline and experimental conditions. For analysis, we extracted the episodes of spontaneous activity, i.e., cortical up-states. After separation of action potential and local field potential (LFP) activity, we looked at differences in the number of action potentials, in the spectral power of the LFP, as well as in the coupling between action potential and LFP phase.

Results

While both substances seem to decrease neocortical action potential firing in a not significantly different (p = 0.659, Mann–Whitney U) fashion, diazepam increases the spectral power of the up-state without significantly impacting the spectral composition, whereas ethanol does not significantly change the spectral power but the oscillatory architecture of the up-state as revealed by the Friedman test with Bonferroni correction (p < 0.05). Further, the action potential to LFP-phase coupling reveals a synchronizing effect of diazepam for a wide frequency range and a narrow-band de-synchronizing effect for ethanol (p < 0.05, Kolmogorov–Smirnov test).

Conclusion

Diazepam and ethanol, induce specific patterns of network depressant actions. Diazepam induces cortical network inhibition and increased synchronicity via gamma subunit containing GABA_A receptors. Ethanol also induces cortical network inhibition, but without an increase in synchronicity via a wider span of molecular targets.

Quantitative evaluation of extrinsic factors influencing electrical excitability in neuronal networks: Voltage Threshold Measurement Method (VTMM)

The electrical excitability of neural networks is influenced by different environmental factors. Effective and simple methods are required to objectively and quantitatively evaluate the influence of such factors, including variations in temperature and pharmaceutical dosage. The aim of this paper was to introduce ‘the voltage threshold measurement method’, which is a new method using microelectrode arrays that can quantitatively evaluate the influence of different factors on the electrical excitability of neural networks. We sought to verify the feasibility and efficacy of the method by studying the effects of acetylcholine, ethanol, and temperature on hippocampal neuronal networks and hippocampal brain slices. First, we determined the voltage of the stimulation pulse signal that elicited action potentials in the two types of neural networks under normal conditions. Second, we obtained the voltage thresholds for the two types of neural networks under different concentrations of acetylcholine, ethanol, and different temperatures. Finally, we obtained the relationship between voltage threshold and the three influential factors. Our results indicated that the normal voltage thresholds of the hippocampal neuronal network and hippocampal slice preparation were 56 and 31 mV, respectively. The voltage thresholds of the two types of neural networks were inversely proportional to acetylcholine concentration, and had an exponential dependency on ethanol concentration. The curves of the voltage threshold and the temperature of the medium for the two types of neural networks were U-shaped. The hippocampal neuronal network and hippocampal slice preparations lost their excitability when the temperature of the medium decreased below 34 and 33°C or increased above 42 and 43°C, respectively. These results demonstrate that the voltage threshold measurement method is effective and simple for examining the performance/excitability of neuronal networks.

The Effects of Acute GABA Treatment on the Functional Connectivity and Network Topology of Cortical Cultures

γ-Aminobutyric acid (GABA) is an inhibitory transmitter, acting on receptor channels to reduce neuronal excitability in matured neural systems. However, electrophysiological responses of whole neuronal ensembles to the exposure to GABA are still unclear. We used micro-electrode arrays (MEAs) to study the effects of the increasing amount of GABA on functional network of cortical neural cultures. Then the recorded data were analyzed by the cross-covariance analysis and graph theory. Results showed that after the GABA treatment, the activity parameters of firing rate, bursting rate, bursting duration and network burst frequency in neural cultures decreased as expected. In addition, the functional connectivity also decreased in similarity, network density, and the size of the largest component. However, small-worldness was not found to be influenced by the acute GABA treatment. Our results support the position that using graph theory to evaluate the functional connectivity of neural cultures may enhance understanding of the pharmacological impact of neurotransmitters on neuronal networks.

Pharmacological response sensitization in nerve cell networks exposed to the antibiotic gentamicin

Gentamicin is an aminoglycoside antibiotic that is used in clinical, organismic, and agricultural applications to combat gram-negative, aerobic bacteria. The clinical use of gentamicin is widely linked to various toxicities, but there is a void in our knowledge about the neuromodulatory or neurotoxicity effects of gentamicin. This investigation explored the electrophysiologic effects of gentamicin on GABAergic pharmacological profiles in spontaneously active neuronal networks in vitro derived from auditory cortices of E16 mouse embryos and grown on microelectrode arrays. Using the GABA_A agonist muscimol as the test substance, responses from networks to dose titrations of muscimol were compared in the presence and absence of 100µM gentamicin (the recommended concentration for cell culture conditions). Spike-rate based EC₅₀ values were generated using sigmoidal fit concentration response curves (CRCs). Exposure to 100µM gentamicin exhibited a muscimol EC₅₀±S.E.M. of 80±6nM (n=10). The EC₅₀ value obtained in the absence of gentamicin was 124±11nM (n=10). The 35% increase in potency suggests network sensitization to muscimol in the presence of gentamicin. Action potential (AP) waveform analyses of neurons exposed to gentamicin demonstrated a concentration-dependent decrease in AP amplitudes (extracellular recordings), possibly reflecting gentamicin effects on voltage-gated ion channels. These in vitro results reveal alteration of pharmacological responses by antibiotics that could have significant influence on the behavior and performance of animals.

Enhancement of Cortical Network Activity in vitro and Promotion of GABAergic Neurogenesis by Stimulation with an Electromagnetic Field with a 150 MHz Carrier Wave Pulsed with an Alternating 10 and 16 Hz Modulation

In recent years, various stimuli were identified capable of enhancing neurogenesis, a process which is dysfunctional in the senescent brain and in neurodegenerative and certain neuropsychiatric diseases. Applications of electromagnetic fields to brain tissue have been shown to affect cellular properties and their importance for therapies in medicine is recognized. In this study, differentiating murine cortical networks on multiwell microelectrode arrays were repeatedly exposed to an extremely low-electromagnetic field (ELEMF) with alternating 10 and 16 Hz frequencies piggy backed onto a 150 MHz carrier frequency. The ELEMF exposure stimulated the electrical network activity and intensified the structure of bursts. Further, the exposure to electromagnetic fields within the first 28 days in vitro of the differentiation of the network activity induced also reorganization within the burst structure. This effect was already most pronounced at 14 days in vitro after 10 days of exposure. Overall, the development of cortical activity under these conditions was accelerated. These functional electrophysiological changes were accompanied by morphological ones. The percentage of neurons in the neuron glia co-culture was increased without affecting the total number of cells, indicating an enhancement of neurogenesis. The ELEMF exposure selectively promoted the proliferation of a particular population of neurons, evidenced by the increased proportion of GABAergic neurons. The results support the initial hypothesis that this kind of ELEMF stimulation could be a treatment option for specific indications with promising potential for CNS applications, especially for degenerative diseases, such as Alzheimer’s disease and other dementias.

Establishment of a Long-Term Chick Forebrain Neuronal Culture on a Microelectrode Array Platform

The biosensor system formed by culturing primary animal neurons on a microelectrode array (MEA) platform is drawing an increasing research interest for its power as a rapid, sensitive, functional neurotoxicity assessment, as well as for many other electrophysiological related research purposes. In this paper, we established a long-term chick forebrain neuron culture (C-FBN-C) on MEAs with a more than 5 month long lifespan and up to 5 month long stability in morphology and physiological function; characterized the C-FBN-C morphologically, functionally, and developmentally; partially compared its functional features with rodent counterpart; and discussed its pros and cons as a novel biosensor system in comparison to rodent counterpart and human induced pluripotent stem cells (hiPSCs). Our results show that C-FBN-C on MEA platform 1) can be used as a biosensor of its own type in a wide spectrum of basic biomedical research; 2) is of value in comparative physiology in cross-species studies; and 3) may have potential to be used as an alternative, cost-effective approach to rodent counterpart within shared common functional domains (such as specific types of ligand-gated ion channel receptors and subtypes expressed in the cortical tissues of both species) in large-scale environmental neurotoxicant screening that would otherwise require millions of animals.

Botulinum toxin suppression of CNS network activity in vitro

The botulinum toxins are potent agents which disrupt synaptic transmission. While the standard method for BoNT detection and quantification is based on the mouse lethality assay, we have examined whether alterations in cultured neuronal network activity can be used to detect the functional effects of BoNT. Murine spinal cord and frontal cortex networks cultured on substrate integrated microelectrode arrays allowed monitoring of spontaneous spike and burst activity with exposure to BoNT serotype A (BoNT-A). Exposure to BoNT-A inhibited spike activity in cultured neuronal networks where, after a delay due to toxin internalization, the rate of activity loss depended on toxin concentration. Over a 30 hr exposure to BoNT-A, the minimum concentration detected was 2 ng/mL, a level consistent with mouse lethality studies. A small proportion of spinal cord networks, but not frontal cortex networks, showed a transient increase in spike and burst activity with exposure to BoNT-A, an effect likely due to preferential inhibition of inhibitory synapses expressed in this tissue. Lastly, prior exposure to human-derived antisera containing neutralizing antibodies prevented BoNT-A induced inhibition of network spike activity. These observations suggest that the extracellular recording from cultured neuronal networks can be used to detect and quantify functional BoNT effects.

Effects of antiepileptic drugs on hippocampal neurons coupled to micro-electrode arrays

Hippocampal networks exhibit spontaneous electrophysiological activity that can be modulated by pharmacological manipulation and can be monitored over time using Micro-Electrode Arrays (MEAs), devices composed by a glass substrate and metal electrodes. The typical mode of activity of these dissociated cultures is the network-wide bursting pattern, which, if properly chemically modulated, can recall the ictal events of the epileptic phenotypes and is well-suited to study the effects of antiepileptic compounds. In this paper, we analyzed the changes induced by Carbamazepine (CBZ) and Valproate (VPA) on mature networks of hippocampal neurons in “control” condition (i.e., in the culturing medium) and upon treatment with the pro-convulsant bicuculline (BIC). We found that, in both control and BIC—treated networks, high doses (100 μM–1 mM) of CBZ almost completely suppressed the spiking and bursting activity of hippocampal neurons. On the contrary, VPA never completely abolish the electrophysiological activity in both experimental designs. Interestingly, VPA cultures pre-treated with BIC showed dual effects. In fact, in some cultures, at low VPA concentrations (100 nM–1 μM), we observed decreased firing/bursting levels, which returned to values comparable to BIC-evoked activity at high VPA concentrations (100 μM–1 mM). In other cultures, VPA reduced BIC-evoked activity in a concentration-independent manner. In conclusion, our study demonstrates that MEA-coupled hippocampal networks are responsive to chemical manipulations and, upon proper pharmacological modulation, might provide model systems to detect acute pharmacological effects of antiepileptic drugs.

d-Methionine protects against cisplatin-induced neurotoxicity in cortical networks

Cisplatin is a platinum-based chemotherapeutic agent widely used for the treatment of various types of cancer. Patients undergoing cisplatin treatment often suffer from a condition known as "chemobrain", ototoxicity, peripheral neuropathy, weight loss, nausea, vomiting, nephrotoxicity, seizures, hearing loss and tinnitus. d-Methionine (d-Met), a sulfur-containing nucleophilic antioxidant, has been shown to prevent cisplatin-induced side effects in animals without antitumor interference. In this study, we have used an in vitro model of cortical networks (CNs), enriched in auditory cortex cells; to quantify cisplatin neurotoxicity and the protective effects of d-Met. Dissociated neurons from auditory cortices of mouse embryos were grown on microelectrode arrays with 64 transparent indium-tin oxide electrodes, which enabled continuous optical and electrophysiological monitoring of network neurons. Cisplatin at 0.10-0.25 mM induced up to a 200% increase in spontaneous spiking activity, while concentrations at or above 0.5mM caused irreversible loss of neuronal activity, accompanied by cell death. Pretreatment with d-Met, at a concentration of 1.0mM, prevented the cisplatin-induced excitation at 0.10-0.25 mM, caused sustained excitation without occurrence of cell death at 0.5mM, and delayed cell death at 0.75 mM cisplatin. l-Methionine, the optical isomer, showed lower potency and less efficacy than d-Met, was less protective against 0.1mM cisplatin, and proved ineffective at a concentration of 0.5mM cisplatin. Pre-exposure time of d-Met was associated with the protective effects at 0.1 and 0.5mM cisplatin, with longer pre-exposure times exhibiting better protection. This study quantifies as a function of concentration and time that d-Met protects central nervous system tissue from acute cisplatin toxicity.

Microfabricated electrochemical cell-based biosensors for analysis of living cells in vitro

Cellular biochemical parameters can be used to reveal the physiological and functional information of various cells. Due to demonstrated high accuracy and non-invasiveness, electrochemical detection methods have been used for cell-based investigation. When combined with improved biosensor design and advanced measurement systems, the on-line biochemical analysis of living cells in vitro has been applied for biological mechanism study, drug screening and even environmental monitoring. In recent decades, new types of miniaturized electrochemical biosensor are emerging with the development of microfabrication technology. This review aims to give an overview of the microfabricated electrochemical cell-based biosensors, such as microelectrode arrays (MEA), the electric cell-substrate impedance sensing (ECIS) technique, and the light addressable potentiometric sensor (LAPS). The details in their working principles, measurement systems, and applications in cell monitoring are covered. Driven by the need for high throughput and multi-parameter detection proposed by biomedicine, the development trends of electrochemical cell-based biosensors are also introduced, including newly developed integrated biosensors, and the application of nanotechnology and microfluidic technology.

Measurement of synchronous activity by microelectrode arrays uncovers differential effects of sublethal and lethal glutamate concentrations on cortical neurons

We grew cultures of rat cortical cells on microelectrode arrays to investigate the effects of glutamate-mediated neurotoxicity as a model of traumatic brain injury. Treatment with two different concentrations of glutamate, 175 and 250 μM, led to different outcomes. Cultures treated with 250 μM glutamate suffered a loss in overall activity that was not seen in cultures treated with 175 μM glutamate. An analysis of the changes in the synchronization of action potential firing between electrodes, however, revealed a loss of synchronization in subsets of electrode pairs treated with both the higher and lower concentrations of glutamate. We found that this loss of action potential synchronization was dependent on the initial amount of synchronization prior to injury. Finally, our data suggest that the synchronization of electrical activity as well as the susceptibility to loss of firing synchrony is independent of the distance between neurons in a network.

Feasibility Assessment of Micro-Electrode Chip Assay as a Method of Detecting Neurotoxicity in vitro

Detection and characterization of chemically induced toxic effects in the nervous system represent a challenge for the hazard assessment of chemicals. In vivo, neurotoxicological assessments exploit the fact that the activity of neurons in the central and peripheral nervous system has functional consequences. And so far, no in vitro method for evaluating the neurotoxic hazard has yet been validated and accepted for regulatory purpose. The micro-electrode array (MEA) assay consists of a culture chamber into which an integrated array of micro-electrodes is capable of measuring extracellular electrophysiology (spikes and bursts) from electro-active tissues. A wide variety of electrically excitable biological tissues may be placed onto the chips including primary cultures of nervous system tissue. Recordings from this type of in vitro cultured system are non-invasive, give label free evaluations and provide a higher throughput than conventional electrophysiological techniques. In this paper, 20 substances were tested in a blinded study for their toxicity and dose-response curves were obtained from fetal rat cortical neuronal networks coupled to MEAs. The experimental procedure consisted of evaluating the firing activity (spiking rate) and modification/reduction in response to chemical administration. Native/reference activity, 30 min of activity recording per dilution, plus the recovery points (after 24 h) were recorded. The preliminary data, using a set of chemicals with different mode-of-actions (13 known to be neurotoxic, 2 non-neuroactive and not toxic, and 5 non-neuroactive but toxic) show good predictivity (sensitivity: 0.77; specificity: 0.86; accuracy: 0.85). Thus, the MEA with a neuronal network has the potency to become an effective tool to evaluate the neurotoxicity of substances in vitro.

Development of micro-electrode array based tests for neurotoxicity: assessment of interlaboratory reproducibility with neuroactive chemicals

Neuronal assemblies within the nervous system produce electrical activity that can be recorded in terms of action potential patterns. Such patterns provide a sensitive endpoint to detect effects of a variety of chemical and physical perturbations. They are a function of synaptic changes and do not necessarily involve structural alterations. In vitro neuronal networks (NNs) grown on micro-electrode arrays (MEAs) respond to neuroactive substances as well as the in vivo brain. As such, they constitute a valuable tool for investigating changes in the electrophysiological activity of the neurons in response to chemical exposures. However, the reproducibility of NN responses to chemical exposure has not been systematically documented. To this purpose six independent laboratories (in Europe and in USA) evaluated the response to the same pharmacological compounds (Fluoxetine, Muscimol, and Verapamil) in primary neuronal cultures. Common standardization principles and acceptance criteria for the quality of the cultures have been established to compare the obtained results. These studies involved more than 100 experiments before the final conclusions have been drawn that MEA technology has a potential for standard in vitro neurotoxicity/neuropharmacology evaluation. The obtained results show good intra- and inter-laboratory reproducibility of the responses. The consistent inhibitory effects of the compounds were observed in all the laboratories with the 50% Inhibiting Concentrations (IC(50)s) ranging from: (mean ± SEM, in μM) 1.53 ± 0.17 to 5.4 ± 0.7 (n = 35) for Fluoxetine, 0.16 ± 0.03 to 0.38 ± 0.16 μM (n = 35) for Muscimol, and 2.68 ± 0.32 to 5.23 ± 1.7 (n = 32) for Verapamil. The outcome of this study indicates that the MEA approach is a robust tool leading to reproducible results. The future direction will be to extend the set of testing compounds and to propose the MEA approach as a standard screen for identification and prioritization of chemicals with neurotoxicity potential.

Application of micro-electrode arrays (MEAs) as an emerging technology for developmental neurotoxicity: evaluation of domoic acid-induced effects in primary cultures of rat cortical neurons

Due to lack of knowledge only a few industrial chemicals have been identified as developmental neurotoxicants. Current developmental neurotoxicity (DNT) guidelines (OECD and EPA) are based entirely on in vivo studies that are both time consuming and costly. Consequently, there is a high demand to develop alternative in vitro methods for initial screening to prioritize chemicals for further DNT testing. One of the most promising tools for neurotoxicity assessment is the measurement of neuronal electrical activity using micro-electrode arrays (MEAs) that provides a functional and neuronal specific endpoint that until now has been used mainly to detect acute neurotoxicity. Here, electrical activity measurements were evaluated to be a suitable endpoint for the detection of potential developmental neurotoxicants. Initially, primary cortical neurons grown on MEA chips were characterized for different cell markers over time, using immunocytochemistry. Our results show that primary cortical neurons could be a promising in vitro model for DNT testing since some of the most critical neurodevelopment processes such as progenitor cell commitment, proliferation and differentiation of astrocytes and maturation of neurons are present. To evaluate if electrical activity could be a suitable endpoint to detect chemicals with DNT effects, our model was exposed to domoic acid (DomA), a potential developmental neurotoxicant for up to 4 weeks. Long-term exposure to a low concentration (50nM) of DomA increased the basal spontaneous electrical activity as measured by spike and burst rates. Moreover, the effect induced by the GABA(A) receptor antagonist bicuculline was significantly lower in the DomA treated cultures than in the untreated ones. The MEA measurements indicate that chronic exposure to DomA changed the spontaneous electrical activity leading to the possible neuronal mal functioning. The obtained results suggest that the MEAs could be a useful tool to identify compounds with DNT potential.

Microelectrode arrays: a physiologically based neurotoxicity testing platform for the 21st century

Microelectrode arrays (MEAs) have been in use over the past decade and a half to study multiple aspects of electrically excitable cells. In particular, MEAs have been applied to explore the pharmacological and toxicological effects of numerous compounds on spontaneous activity of neuronal and cardiac cell networks. The MEA system enables simultaneous extracellular recordings from multiple sites in the network in real time, increasing spatial resolution and thereby providing a robust measure of network activity. The simultaneous gathering of action potential and field potential data over long periods of time allows the monitoring of network functions that arise from the interaction of all cellular mechanisms responsible for spatio-temporal pattern generation. In these functional, dynamic systems, physical, chemical, and pharmacological perturbations are holistically reflected by the tissue responses. Such features make MEA technology well suited for the screening of compounds of interest, and also allow scaling to high throughput systems that can record from multiple, separate cell networks simultaneously in multi-well chips or plates. This article is designed to be useful to newcomers to this technology as well as those who are currently using MEAs in their research. It explains how MEA systems operate, summarizes what systems are available, and provides a discussion of emerging mathematical schemes that can be used for a rapid classification of drug or chemical effects. Current efforts that will expand this technology to an influential, high throughput, electrophysiological approach for reliable determinations of compound toxicity are also described and a comprehensive review of toxicological publications using MEAs is provided as an appendix to this publication. Overall, this article highlights the benefits and promise of MEA technology as a high throughput, rapid screening method for toxicity testing.

Quantification of zinc toxicity using neuronal networks on microelectrode arrays

Murine neuronal networks, derived from embryonic frontal cortex (FC) tissue grown on microelectrode arrays, were used to investigate zinc toxicity at concentrations ranging from 20 to 2000 microM total zinc acetate added to the culture medium. Continual multi-channel recording of spontaneous action potential generation allowed a quantitative analysis of the temporal evolution of network spike activity generation at specific zinc acetate concentrations. Cultures responded with immediate concentration-dependent excitation lasting from 5 to 50 min and consisting of increased spiking and enhanced, coordinated bursting, followed by irreversible activity decay. The time to 50% and 90% activity loss was concentration dependent, highly reproducible, and formed linear functions in log-log plots. Above 100 microM total zinc acetate, the activity loss was associated with massive cell swelling, blebbing, and even vigorous neuronal cell lysing. Glia showed stress, but did not participate in the extensive cell swelling. Network activity loss generally preceded morphological changes. Cultures pretreated with the GABA(A) receptor antagonists bicuculline (40 microM) and picrotoxin (1mM) lacked the initial excitation phase. This suggests that zinc-induced excitation may be mediated by interfering with GABA inhibition. Partial network protection was achieved by stopping spontaneous activity with either tetrodotoxin (200 nM) or lidocaine (250 microM). However, recovery was not complete and slow deterioration of network activity continued over 6-h periods. Removal of zinc by early medium changes showed irreversible, catastrophic network failure to develop in a concentration-dependent time window between 50% and 90% activity loss.

Functional screening of traditional antidepressants with primary cortical neuronal networks grown on multielectrode neurochips

We optimized the novel technique of multielectrode neurochip recordings for the rapid and efficient screening of neuroactivity. Changes in the spontaneous activity of cultured networks of primary cortical neurons were quantified to evaluate the action of drugs on the firing dynamics of complex network activity. The multiparametric assessment of electrical activity changes caused by psychoactive herbal extracts from Hypericum, Passiflora and Valeriana, and various combinations thereof revealed a receptor-specific and concentration-dependent inhibition of the firing patterns. The spike and burst rates showed significant substance-dependent effects and significant differences in potency. The effects of specific receptor blockades on the inhibitory responses provided evidence that the herbal extracts act on gamma-amino butyric acid (GABA) and serotonin (5-HT) receptors, which are recognized targets of pharmacological antidepressant treatment. A biphasic effect, serotonergic stimulation of activity at low concentrations that is overridden by GABAergic inhibition at higher concentrations, is apparent with Hypericum alone and the triple combination of the extracts. The more potent neuroactivity of the triple combination compared to Hypericum alone and the additive effect of Passiflora and Valeriana suggest a synergy between constituent herbal extracts. The extracts and their combinations affected the set of derived activity parameters in a concomitant manner suggesting that all three constituent extracts and their combinations have largely similar modes of action. This study also demonstrates the sensitivity, selectivity and robustness of neurochip recordings for high content screening of complex mixtures of neuroactive substances and for providing multiparametric information on neuronal activity changes to assess the therapeutic potential of psychoactive substances.

Investigating neuronal activity with planar microelectrode arrays: achievements and new perspectives

Neuronal networks underlie memory storage and information processing in the human brain, and ultimately participate in what Eccles referred to as "the creation of consciousness". Moreover, as physiological dysfunctions of neurons almost always translate into serious health issues, the study of the dynamics of neuronal networks has become a major avenue of research, as well as their response to pharmacological tampering. Planar microelectrode arrays represent a unique tool to investigate such dynamics and interferences, as they allow one to observe the activity of neuronal networks spread in both space and time. We will here review the major results obtained with microelectrode arrays and give an overview of the latest technological developments in the field, including our own efforts to develop the potential of this already powerful technology.

In vitro cortical neuronal networks as a new high-sensitive system for biosensing applications

By taking advantages of the main features of the microelectrode array (MEA) technology (i.e. multisite recordings, stable and long-term coupling with the biological preparation), we analyzed the changes in activity patterns induced by applying specific substances to dissociated cortical neurons from rat-embryos (E18). Data were recorded simultaneously from 60 electrodes, and the electrophysiological behavior was investigated during the third week in vitro, both at the spike and burst level. The analysis of the electrophysiological activity modulation, by applying agonists of the ionotropic glutamate receptors at low (i.e. 0.2-1-5 microM) and high (i.e. 50-100 microM) concentrations, is presented. Preliminary results show that the dynamics of the in vitro cortical neurons is very sensitive to pharmacological manipulation of the glutamatergic transmission and the effects on the network behavior are strictly dependent from the drug concentration. In particular, the addition of a high-dose of agonist determined a global and irreversible depression of the network activity, while, in the low-concentration case, the electrophysiological behavior showed different results, depending on the type of receptor involved. From these observations, we are encouraged to think of a more engineered system, based on in vitro cortical neurons, as a novel sensitive system for drug (pre)-screening and neuropharmacological evaluations.

Pharmacological effects of the marine toxins, brevetoxin and saxitoxin, on murine frontal cortex neuronal networks

Brevetoxins and saxitoxins (STXs), which are produced by marine dinoflagellates, are very potent neurotoxins targeting separate sites of the alpha subunit of voltage-dependent sodium channels (VDSCs). An attractive approach for marine toxin detection relies on pharmacological modulation of VDSCs expressed in cells or tissues. While these function-based cellular assays exhibit the required sensitivity, they are typically slow and have limited potential use for field applications. Cultured neuronal networks grown on substrate integrated microelectrode arrays (MEAs) have emerged as a robust and sensitive approach for environmental threat detection. The present work describes the rapid effects of brevetoxin-2 (PbTx-2) and STX on embryonic murine frontal cortex neuronal networks on MEAs. Network recording parameters such as mean spike rate, burst rate, burst duration, number of spikes per burst and spike amplitude were analyzed before and after exposure to the toxins. STX produced fast and reversible inhibition of all electrophysiological parameters with IC(50)s ranging between 1.2 and 2.2nM. Although PbTx-2 also caused inhibition of most of the network electrophysiological parameters, it produced an increase in burst duration at lower concentrations (EC(50)=15+/-2 nM, n=4) followed by inhibition at higher ones (IC(50)=63+/-4 nM, n=4). Exposure of frontal cortex networks to PbTx-2 and STX also caused differential effects on spike amplitude. This work demonstrates that cultured neuronal networks not only could be used for pharmacological characterization of marine toxins but they also provide a tool with unique properties for their detection.

Unique responses of auditory cortex networks in vitro to low concentrations of quinine

The anti-malarial drug quinine has several side effects including tinnitus. The aim of the study was to determine if cultured auditory networks growing on microelectrode arrays exhibited unique dynamic states when exposed to quinine. Eight auditory cortex networks (ACN), eight frontal cortex networks (FCN), and five inferior colliculus networks (ICN) were used in this study. Response of ACNs to quinine was biphasic, with an excitatory phase followed by inhibition. FCNs and ICNs revealed only inhibitory responses. The concentrations at which the spike rate was inhibited by 50% (IC50 mean +/- SE) were 42.5 +/- 3.9, 28.7 +/- 4.8 and 23.9 +/- 2.1 microM for ACNs, FCNs, and ICNs, respectively. Quinine increased the regularity and coordination of bursting in all three tissues. The increased burst pattern regularity of ICNs coupled with the excitatory responses seen only in ACNs between 1 and 10 microM show a unique susceptibility of auditory tissues to quinine that may be related to the underlying mechanism that triggers tinnitus-like activity.

Substance identification by quantitative characterization of oscillatory activity in murine spinal cord networks on microelectrode arrays

This paper presents a novel and comprehensive method to identify substances on the basis of electrical activity and is a substantial improvement for drug screening. The spontaneous activity of primary neuronal networks is influenced by neurotransmitters, ligands, and other substances in a similar fashion as known from in vivo pharmacology. However, quantitative methods for the identification of substances through their characteristic effects on network activity states have not yet been reported. We approached this problem by creating a database including native activity and five drug-induced oscillatory activity states from extracellular multisite recordings from microelectrode arrays. The response profiles consisted of 30 activity features derived from the temporal distribution of action potentials, integrated burst properties, calculated coefficients of variation, and features of Gabor fits to autocorrelograms. The different oscillatory states were induced by blocking neurotransmitter receptors for: (i) GABA(A); (ii) glycine; (iii) GABA(A) and glycine; (iv) all major synaptic types except AMPA, and (v) all major synapses except NMDA. To test the identification capability of the six substance-specific response profiles, five blind experiments were performed. The response features from the unknown substances were compared to the database using proximity measures using the normalized Euclidian distance to each activity state. This process created six identification coefficients where the smallest correctly identified the unknown substances. Such activity profiles are expected to become substance-specific 'finger prints' that classify unique responses to known and unknown substances. It is anticipated that this kind of approach will help to quantify pharmacological responses of networks used as biosensors.