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Objective Layer i is the most distinct and characteristic lamina of the cerebral cortex.As the neocortex develops, layer 1 populated by two basic neuronal cell types, Cajal-Retzius (C-R) cells and interneurons.Although many studies strongly showed that the neurons in layer 1 have the important roles for the neocortical development and integrating inputs from high order cortical and thalamic areas, yet the developmental neural microcircuits of layer 1 neuron remain poorly understood.Methods Here we studied the development neural microcircuits in the layer 1 using multiple patch clamp recording and neurobiotin labeling.Results From P1 to P7, we observed that electrical coupling interconnected around 14% between interneurons and 19% between C-R cells.We also found the chemical synaptic connections between layer 1 neurons were rather low around the first postnatal week; it increased dramatically around the second postnatal week.After P8, two types of interneuron characterized by action potentials, the late spike (LS) and the bursting nonadapting (bNA), were observed.Approximately 68% of the cells we recorded were LS cells which the dendrites and the very dense local axonal field were confined primarily to layer 1; 22% of the bNA cells were multipolar neurons with axons descending out of layer 1.We found that LS cells were interconnected by electrical coupling (87%), whereas electrical coupling between bNA cells was infrequent (5%).We also found that the electrical coupling mediated synchronizations of the spontaneous activities were 34.5% between LS cells and only 1% between bNA cells.In addition to the chemical synapse, we observed that bi-directional GABAergic synaptic connections were widely populated between the LS cells (57%), and only 4% between bNA cells.The chemical synaptic direction between LS cells and bNA cells was uni-direction, and was mostly from LS cells to bNA cells.Conclusion We showed the developmental microcircuits between two types of GABAergic neurons within layer 1 and can provide significant inhibitory inputs to neurons in layer 1 and to distal dendrites of pyramidal cells.