Voltage-gated sodium (Nav) channel distribution in the axon initial segments (AISs) in motor neurons (MNs). Quadruple immunostaining of Peripherin (A, G), ankyrin G (AnkG) (B, H), Nav1.1 (C, I) and Nav1.6 (D, J) (Nav1.1 and Nav1.6 are merged in (E, K)) showing two populations of AISs: expressing Nav1.1 in a proximal compartment complementary to Nav1.6 expression (A-F) or expressing Nav1.6 alone throughout the AIS (G-L). (F, L) The mean immunofluorescence intensity profile (shown by the line) ± SEM from n = 6 AISs is shown for AnkG, Nav1.1 and Nav1.6. For each AIS and each antibody, immunofluorescence intensities were normalized relative both to its maximum intensity along the AIS and to the length of the AIS. The beginning and the end of the AnkG+ AIS in B and H are shown (also in F and L) by blue arrowheads. The bracket indicates the proximal AIS Nav1.1 expression domain. Scale bar = 5 μm.