Functional characterization of GABA(A) receptor-mediated modulation of cortical neuron network activity in microelectrode array recordings

The numerous γ-aminobutyric acid type A receptor (GABA(A)R) subtypes are differentially expressed and mediate distinct functions at neuronal level. In this study we have investigated GABA(A)R-mediated modulation of the spontaneous activity patterns of primary neuronal networks from murine frontal cortex by characterizing the effects induced by a wide selection of pharmacological tools at a plethora of activity parameters in microelectrode array (MEA) recordings. The basic characteristics of the primary cortical neurons used in the recordings were studied in some detail, and the expression levels of various GABA(A)R subunits were investigated by western blotting and RT-qPCR. In the MEA recordings, the pan-GABA(A)R agonist muscimol and the GABA(B)R agonist baclofen were observed to mediate phenotypically distinct changes in cortical network activity. Selective augmentation of αβγ GABA(A)R signaling by diazepam and of δ-containing GABA(A)R (δ-GABA(A)R) signaling by DS1 produced pronounced changes in the majority of the activity parameters, both drugs mediating similar patterns of activity changes as muscimol. The apparent importance of δ-GABA(A)R signaling for network activity was largely corroborated by the effects induced by the functionally selective δ-GABA(A)R agonists THIP and Thio-THIP, whereas the δ-GABA(A)R selective potentiator DS2 only mediated modest effects on network activity, even when co-applied with low THIP concentrations. Interestingly, diazepam exhibited dramatically right-shifted concentration-response relationships at many of the activity parameters when co-applied with a trace concentration of DS1 compared to when applied alone. In contrast, the potencies and efficacies displayed by DS1 at the networks were not substantially altered by the concomitant presence of diazepam. In conclusion, the holistic nature of the information extractable from the MEA recordings offers interesting insights into the contributions of various GABA(A)R subtypes/subgroups to cortical network activity and the putative functional interplay between these receptors in these neurons.