Functional design of neural networks with different ratios of inhibitory and excitatory neurons

This study aimed to model and functionally characterize in vitro neural networks with varying excitation-inhibition (E/I) ratios by generating and analyzing dorsal telencephalic and striatal progenitor-derived neuronal cultures. By comparing structural and functional parameters, I sought to elucidate the role of GABAergic interneurons in shaping network maturation and activity dynamics. The cerebral cortex contains glutamatergic pyramidal neurons and GABAergic interneurons. While pyramidal neurons constitute the majority and form long-range projections, GABAergic interneurons exhibit local connectivity and play a crucial role in regulating network activity. To model these neuronal populations,Forebrain identity is established early in development through the inhibition of caudalizing morphogens. Using mouse embryonic stem cells (mESCs) I mimicked this process in vitro by manipulating Sonic Hedgehog (Shh) signaling. Shh inhibition (with Cyclopamine treatment) promoted the generation of dorsal telencephalic progenitors, which differentiated into glutamatergic neurons. Conversely, Shh activation (SAG treatment) led to the differentiation of ventral telencephalic progenitors, which gave rise to GABAergic interneurons. After migration, the GABAergic inhibitory interneurons integrate and form synaptic connections with glutamatergic excitatory neurons, establishing a balanced Excitation/Inhibition (E/I) ratio, which is crucial for the normal brain functioning that would otherwise cause several brain disorders such as Schizophrenia or Autism Spectrum Disorders (ASDs).To investigate neural networks with different E/I ratios and functionally characterize them during developmental maturation, I modeled two distinct populations of cells in vitro, comparing the activity of a network composed of dorsal telencephalic neurons with that of a striatal network and with networks formed by varying ratios of dorsal and ventral telencephalic neurons. This approach enabled me to investigate how the presence of GABAergic interneurons shapes the development and maturation of neuronal networks. Thus, I analyzed basic structural and functional network parameters such as synapse density, firing activity and network burst synchronization, unraveling the role of specific neurotransmitter receptors (GABA, AMPA, NMDA) in modulating network activity, burst generation and connectivity. Overall, my findings indicated that:Cortical network with low inhibitory neuron ratio develops poor synchronized network activity.Inhibition of GABA unmask intrinsic network ability to generate highly synchronized activity.Network response to single node stimulus depends on optimal inhibitory neuron ratioE/I balance affects the maturation of neuronal cultures: thus, a proper excitatory/inhibitory ratio is necessary for the development of network burst activity