These co-cultures consist of GABAergic, glutamatergic, dopaminergic, serotonergic, and cholinergic neurons, as well as astrocytes and exhibit spontaneous electrical activity on micro-electrode arrays (MEA; Maestro Pro MEA assay system (Axion BioSystems)), detectable as so-called spikes. To enable the identification of single active neuronal “units” within the recording of one MEA electrode, a spike sorting algorithm is applied. By challenging the neural networks with neurotransmitter agonists and antagonists targeting glutamate, GABA and dopamine receptors, prior to the acute exposure of the test compound, the hMNR assay enables the analysis of neurotoxic MoA for unknown test compounds.
Since the nervous system is a very complex organ, it can be disrupted via a plethora of modes-of-action (MoA) involving neurotransmitter receptors and ion transporters, amongst others. In general, these MoA affect neuronal function and communication by inhibiting neurotransmitter synthesis or degradation, increasing or preventing neurotransmitter release, blocking neurotransmitter receptors, or interfering with the multiple ion channels.
While spike parameters, e.g. the mean firing rate, provide important information about general network function, their level of granularity is not particularly high. Therefore, we apply the method of spike sorting to the MEA data. Spike sorting allows the identification of single active neuronal ‘units’ within the signal of one MEA electrode using curve progression analysis. These units can be individually evaluated and thus quantified across multiple electrodes. This allows the identification of specific responses of individual neurons within the integrated neuronal activity of individual electrodes (e.g. glutamatergic units responding to glutamate and the respective antagonist AP5/NBQX).
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