Synchronous spike patterns in differently mixed cultures of human iPSC-derived glutamatergic and GABAergic neurons

Human induced-pluripotent stem cell (hiPSC)-derived neurons develop organized neuronal networks under in vitro cultivation conditions. Here, using a multielectrode array system, we examined whether the spike patterns of hiPSC-derived neuronal populations differed in a manner that depended on the proportions of glutamatergic and gamma-aminobutyric acid (GABA)ergic neurons in the cultures. Synchronous burst firing events spanning multiple electrodes became more frequent as the number of days in culture increased. However, at all developmental stages, the event rates of synchronous burst firing, the repertoires of synchronous burst firing, and the frequencies of sporadic spikes did not differ in cultures with different glutamatergic-to-GABAergic ratios. Pharmacological blockade of GABAergic synaptic transmission increased the frequencies of spike patterns specifically in cultures with lower glutamatergic-to-GABAergic ratios. These results demonstrate that a robust homeostatic property of developing hiPSC-derived neuronal networks in culture counteracts chronically imbalanced glutamatergic and GABAergic signaling.