Evaluation of multi-well microelectrode arrays for neurotoxicity screening using a chemical training set

Abstract

Microelectrode array (MEA) approaches have been proposed as a tool for detecting functional changes in electrically excitable cells, including neurons, exposed to drugs, chemicals or particles. However, conventional single well-MEA systems lack the throughput necessary for screening large numbers of uncharacterized compounds. Recently, multi-well MEA (mwMEA) formats have become available to address the need for increased throughput. The current experiments examined the effects of a training set of 30 chemicals on spontaneous activity in networks of cortical neurons grown on mwMEA plates. Each plate contained 12 wells with 64 microelectrodes/well, for a total of 768 channels. Of the 30 chemicals evaluated, 23 were known to alter neuronal function in vivo (“positives”), including 6 GABAergic and 3 glutamatergic antagonists/agonists, 4 pyrethroids, 3 metals, 2 cholinesterase inhibitors, 2 nicotinic acetylcholine receptor agonists, valproic acid, verapamil, and fluoxetine. Seven compounds expected to have no effect on neuronal function were tested as “negatives” (glyphosate, acetaminophen, salicylic acid, paraquat, saccharin, d-sorbitol and amoxicillin). Following collection of 33 min of baseline activity, chemical effects (50 µM or highest soluble concentration) were recorded for 33 min. Twenty of the positives altered the mean network spike rate by more than the 14% threshold (two standard deviations from the mean for DMSO control). The three positives without effect were bifenthrin, nicotine and imidacloprid. None of the negative compounds caused a change in activity beyond the threshold. Based on these results, the mwMEA assay has both high sensitivity (87% identification of positive compounds) and specificity (100% identification of negative compounds). These experiments demonstrate the capacity of mwMEAs to screen compounds for neurotoxic effects mediated by a broad variety of mechanisms.

Adverse Outcome Pathway on binding of agonists to ionotropic glutamate receptors in adult brain leading to excitotoxicity that mediates neuronal cell death, contributing to learning and memory impairment

“…Higher concentrations of DomA (1 and 2 μM) also significantly decrease the MFR, whereas concentrations up to 0.1 μM of DomA do not cause any effect on MFR (Hogberg et al, 2011). In primary rat cortical neurons (12-22 DIV), DomA (50 μM) has been reported to reduce MFR by more than 90% (McConnell et al, 2012).…”

“…For example it has been shown that MEA-coupled neuronal cortical networks are very sensitive to pharmacological manipulation of the excitatory ionotropic glutamatergic transmission (Frega et al, 2012). MEAs can also be applied in higher throughput platforms to facilitate screening of numerous chemical compounds (McConnell et al, 2012). Excessive excitability can be also measured directly by evaluating the level of the extracellular glutamate using the enzyme-based microelectrode arrays.…”

In vitro neurotoxic hazard characterization of different tricresyl phosphate (TCP) isomers and mixtures

“…As such, MEA recordings allow for reproducible screening of neurotoxic compounds with high sensitivity and specificity (McConnell et al, 2012;Valdivia et al, 2014;Nicolas et al, 2014). Despite the marked increase in mitochondrial activity, MEA recordings demonstrated that neuronal activity of primary cortical cultures is largely unaffected upon acute (30 min) exposure to TCP isomers, mixtures and CBDP (Figs.…”

“…Consequently, ToCP and TmCP may have different modes of action. So far, increases in MSR have been largely limited to glutamatergic agonists and GABAergic antagonists (McConnell et al, 2012;Mack et al, 2014). Since prolonged exposure to ToCP was recently reported to decrease glutamatergic signaling (Hausherr et al, 2014), it is tempting to speculate that the neurotoxicity of ToCP also involves modulation of glutamatergic receptors.…”

“…First, effects on cell viability and mitochondrial activity were assessed. Next, effects of TCPs on spontaneous neuronal electrical activity were assessed using microelectrode array (MEA) recordings as a noninvasive in vitro neurotoxicity screening method (Hogberg et al, 2011;McConnell et al, 2012;Valdivia et al, 2014;Nicolas et al, 2014). Lastly, effects on neurite outgrowth were measured as a specific, integrated measure of neurotoxicity that represents the effects of multiple underlying targets (Harrill et al, 2011).…”