Multi-well microelectrode array recordings detect neuroactivity of ToxCast compounds

Spontaneous activity in neuronal cultures on microelectrode arrays (MEAs) is sensitive to effects of drugs, chemicals, and particles. Multi-well MEA (mwMEA) systems have increased throughput of MEAs, enabling their use for chemical screening. The present experiments examined a subset of EPA's ToxCast compounds for effects on spontaneous neuronal activity in primary cortical cultures using 48-well MEA plates. A first cohort of 68 compounds was selected from the ToxCast Phase I and II libraries; 37 were positive in one or more of 20 individual ToxCast Novascreen assays related to ion channels (NVS_IC), with the remainder selected based on known neuroactivity. A second cohort of 25 compounds was then tested with 20 originating from the ToxCast Phase I and II libraries (not hits in NVS_IC assays) and 5 known negatives from commercial vendors. Baseline activity (1h) was recorded prior to exposing the networks to compounds for 1h, and the weighted mean firing rate (wMFR) was determined in the absence and presence of each compound. Compounds that altered activity by greater than the weighted change of DMSO-treated wells plus 2SD were considered "hits". Of the first set of 68 compounds, 54 altered wMFR by more than the threshold, while in the second set, 13/25 compounds were hits. MEAs detected 30 of 37 (81.1%) compounds that were hits in NVS_IC assays, as well as detected known neurotoxicants that were negative in NVS_IC assays, primarily pyrethroids and GABAA receptor antagonists. Conversely, wMFR of cortical neuronal networks on MEAs was insensitive to nicotinic compounds, as only one neonicotinoid was detected by MEAs; this accounts for the bulk of non-concordant compounds between MEA and NVS_IC assays. These data demonstrate that mwMEAs can be used to screen chemicals efficiently for potential neurotoxicity, and that the results are concordant with predictions from ToxCast NVS_IC assays for interactions with ion channels.