Supplementary Figure 1: Distribution and molecular heterogeneity of dual-labeled interneurons in the postnatal mouse brain.

(a) Overview of CCK^BAC/dsRed:GAD67^gfp/+ mouse somatosensory cortex on postnatal day 20, revealing the distribution of CCK⁺ (magenta) and/or GAD67⁺ (green) cells in the different cortical layers (L; labeled from L1-L6a). Light pink/white color depicts co-localization. Overview image of the mouse forebrain (left) was reconstructed from tiled confocal photomicrographs using a Zeiss LSM780 laser-scanning microscope. Open rectangle indicates the location of the inset (right). Scale bars = 500 μm (left) and 200 μm (right). (b-d) Representative current-clamp recordings of CCK⁺/GAD67⁻ pyramidal cells (Exc L2/3 (b), Exc L4 (c) and Exc L5 (d)). At the left of each panel, AP responses (top) to square current pulses (bottom) are shown. Phase-plane plots of the APs rising upon 2x rheobase current injection (top right) and rheobasic APs (bottom right) are depicted for each cell type. In phase-plane plots, the first AP is red, while subsequent APs shift from warm to cool blue color. For the rheobasic AP, the y-axis between -20 mV and +30 mV was omitted to emphasize AHP and ADP characteristics (scale bars = 200 pA (vertical), 25 ms (horizontal)). (e) Cell-type-specific expression of a voltage gated K⁺ channel interacting protein (Kcnip1), a GTPase-activating protein (Chn1), a protein kinase C substrate (Nrgn), a Ca²⁺ channel subunit (Cacna2d3), a Na⁺ channel subunit (Scn3a), Purkinje cell protein 4 (Pcp4), a G protein-signaling regulator (Rgs12), serotonin receptor subtype 3a (Htr3a), reelin (Reln), a superficial layer-specific marker, calbindin D28k (Calb1), a Ca²⁺-binding protein, vasoactive intestinal polypeptide (Vip) and neuropeptide Y (Npy) in sub-classified I-type CCK⁺ interneurons (magenta) and Exc-type pyramidal cells (green).