Human stem cell-derived neurons establish functional inhibitory-excitatory cortical circuits in a chimeric transplantation model.

Excitation/inhibition balance is crucial to homeostatic brain function and disrupted in several neurodevelopmental and neurodegenerative diseases. Cortical inhibitory neurons derived from the medial ganglionic eminence (MGE) provide input to glutamatergic projection neurons, an essential function in neural processing. While neural grafts for stroke improve motor function following engraftment, these grafts typically contain only excitatory neurons (and glia), and little effort has been directed at understanding the role of inhibitory neurons in this context. Here, we generate a channelrhodopsin line to optogenetically control grafted human pluripotent stem cell-derived MGE interneurons in the context of a mixed inhibitory-excitatory chimeric transplantation model. We demonstrate robust differentiation toward either dorsal cortical excitatory or ventral MGE inhibitory fates. Co-grafts of inhibitory and excitatory neurons demonstrate lineage-specific maturation-predominantly excitatory CTIP2 + layer 5 projection neurons or inhibitory Calretinin + and SST+ interneurons. Co-grafts integrate and densely innervate both the graft and host tissues. We observed juxtaposition of excitatory and inhibitory fibres and synapses. Optogenetic stimulation confirmed that grafted inhibitory neurons are functionally integrated with grafted excitatory neurons, inducing inhibitory post-synaptic potentials, which were blocked with gabazine. Together, these data provide evidence of functional inhibitory-excitatory circuit reconstruction following transplantation and provide a platform for advanced cell therapies and disease modelling.