Axon initial segment contains both Cav2.1 (α1A; P/Q-type) and Cav2.2 (α1B; N-type) subunits. a, Immunocytochemical localization of Cav2.1, ankyrin-G (AnkG), which is prevalent in axon initial segments of cortical pyramidal cells, and DAPI, which marks nuclei in the ferret prefrontal cortex. The overlap of all three stains is shown on the right. Note that both Cav2.1 and ankyrin-G are prevalent in cortical axon initial segments, as revealed by ankyrin-G staining. b, Immunocytochemical localization of Cav2.2 and ankyrin-G demonstrating that the AIS also contains this subtype of Ca²⁺ channel protein. Cav2.2 was also prevalent in the somata and neuropil of the neocortex, causing a higher background than seen with antibodies to Cav2.1 (a). Solid arrowheads, AIS with calcium channels staining in cells; open arrowheads, cell body. Scale bar, 15 μm.