Astrocyte priming promotes enhanced cortical synchrony and increased network bursting in response to perinatal cytokine exposure

Introduction: In normal development, activity patterns in the embryonic and early postnatal neocortex transition from asynchronous, individual action potentials to network-wide, synchronous activity, a process termed Giant Depolarizing Potentials (GDPs). The development of synchronous cortical oscillations plays a crucial role in consolidating synaptic connectivity and forebrain maturation throughout neurodevelopment, and alterations in patterned cortical activity during neurodevelopment can induce lasting deficits in neural circuit structure and function.

Methods: We employed an in vitro neuron-astrocyte coculture model to characterize the combinatorial effects of astrocyte priming and an immune insult on the emergence of cortical synchrony during the perinatal period. This mouse model of cortical development was established by co-culturing cortical neurons isolated from E15.5 C57BL/6J embryos with primary astrocytes extracted from mouse neocortices, isolated by immunopanning, and cultured in previously-validated serum free conditions. Calcium imaging of neuronal and ensemble-level activity patterns over time was achieved using a synapsin-driven GCaMP6m reporter, and custom-built MATLAB programs were used for all computational and machine learning analyses of neuronal and network synchrony. Neurons co-cultured on naïve astrocytes provided baseline measures of activity and synchrony within neuronal ensembles.

Results: IFNγ exposure accelerated the acquisition of synchrony within ensembles co-cultured with serum-preactivated, but not naïve, astrocytes. Machine learning analyses of neuronal synchrony data identified distinct, immune exposure-dependent patterns of maturation which are sufficient to predict the immune exposure history of cells based on their signaling properties with over 90% accuracy. Combined exposure to IFNγ and primed astrocytes was also consistent with increases in the ratio of protein expression levels of chloride symporters KCC2 and NKCC1, suggestive of accelerated neuronal maturation in dual hit-challenged neuron-astrocyte co-cultures.

Conclusion : Collectively, these findings suggest that early-life inflammatory exposures can prime astrocytes to respond differently to later immune events than naïve astrocytes and identify one potential mechanism through which immune challenges can alter key neural network milestones in perinatal development.