Sparse postnatal labeling and quantification of superficial cortical cell synapses in the mouse neocortex

We present a strategy for measuring the density of presynaptic boutons of superficial neuronal cells in the mouse neocortex. First, we show how to sparsely label individual postmitotic cells by neonatal pial-surface electroporation. Then, we present a custom-made code that allows quantification of the density of presynaptic boutons along axonal processes. Although we applied this strategy to somatostatin-positive cells, a major population of cortical interneurons, the same approach can be adjusted to target other types of neuronal cells. For complete details on the use and execution of this protocol, please refer to Gesuita et al. (2022).¹.