Proper brain development is based on the orchestration of key neurodevelopmental processes (KNDP), including the for­mation and function of neural networks. If at least one KNDP is affected by a chemical, an adverse outcome is expected. To enable a higher testing throughput than the guideline animal experiments, a developmental neurotoxicity (DNT) in vitro testing battery (DNT IVB) comprising a variety of assays that model several KNDPs was set up. Gap analysis revealed the need for a human-based assay to assess neural network formation and function (NNF). Therefore, we established the human NNF (hNNF) assay. A co-culture comprised of human induced pluripotent stem cell (hiPSC)-derived excitatory and inhibitory neurons as well as primary human astroglia was differentiated for 35 days on microelectrode arrays (MEA), and spontaneous electrical activity, together with cytotoxicity, was assessed on a weekly basis after washout of the compounds 24 h prior to measurements. In addition to the characterization of the test system, the assay was challenged with 28 com­pounds, mainly pesticides, identifying their DNT potential by evaluating specific spike-, burst-, and network parameters. This approach confirmed the suitability of the assay for screening environmental chemicals. Comparison of benchmark con­centrations (BMC) with an NNF in vitro assay (rNNF) based on primary rat cortical cells revealed differences in sensitivity. Together with the successful implementation of hNNF data into a postulated stressor-specific adverse outcome pathway (AOP) network associated with a plausible molecular initiating event for deltamethrin, this study suggests the hNNF assay as a useful complement to the DNT IVB.

Background: Modulation of pathological neural circuit activity in the brain with a minimum of com-plications is an area of intense interest. Objective: The goal of the study was to alter neurons' physiological states without apparent damage of cellular integrity using stereotactic radiosurgery (SRS). Methods: We treated a 7.5 mm-diameter target on the visual cortex of Goeurottingen minipigs with doses of 40, 60, 80, and 100 Gy. Six months post-irradiation, the pigs were implanted with a 9 mm-wide, eight-shank multi-electrode probe, which spanned the radiation focus as well as the low-exposure neighboring areas. Results: Doses of 40 Gy led to an increase of spontaneous firing rate, six months post-irradiation, while doses of 60 Gy and greater were associated with a decrease. Subjecting the animals to visual stimuli resulted in typical visual evoked potentials (VEP). At 40 Gy, a significant reduction of the P1 peak time, indicative of higher network excitability was observed. At 80 Gy, P1 peak time was not affected, while a minor reduction at 60 Gy was seen. No distance-dependent effects on spontaneous firing rate, or on VEP were observed. Post-mortem histology revealed no evidence of necrosis at doses below 60 Gy. In an in vitro assay comprising of iPS-derived human neuron-astrocyte co-cultures, we found a higher vulnerability of inhibitory neurons than excitatory neurons with respect to radiation, which might provide the cellular mechanism of the disinhibitory effect observed in vivo. Conclusion: We provide initial evidence for a rather circuit-wide, long-lasting disinhibitory effect of low sub-ablative doses of SRS. (c) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Human iPSC-derived in vitro neural co-culture systems have been used increasingly in drug discovery for neurological and neurodegenerative disorders. Here we describe the development of iPSC-derived platforms of AD that can be used to screen for preclinical targets and drug candidates. The foundation of these platforms utilizes a proprietary method for the generation of pure populations of NGN2-based excitatory and ASCL1/DLX2 inhibitory neurons. Transgenic overexpression of tau isoforms leads to prion-like tau spreading that can be used to screen for compounds to mitigate tau propagation. Using this platform, we investigated how tau overexpression leads to neuron-neuron tau transmission, alters neuron electrophysiology as assessed by MEA, and leads to the accumulation of key neuropathological tau biomarkers. In addition, we have developed co-culture platforms that facilitate examination of the role of neuroinflammation on the development of key neuropathological hallmarks of AD. This platform can be used in conjunction with isogenic iPSCs to interrogate the mechanism by which genetic risk factors confer increased or decreased AD risk. Taken together, these phenotypic assays demonstrate the utility of NeuCyte platforms that can be applied to high-throughput drug screening efforts for AD.