Fig. 1.
NaV1.6 is present at heminodes and sensory terminals of primary endings of rat muscle spindle. A: Low-magnification of a rat soleus muscle spindle labeled for NF-H (green) and NaV1.6 (red). Boxes 1 through 3 show Ia afferent supplying innervation to three different sensory terminals that form part of the primary ending. A1a and A1b: high magnification of the first order branch shown in box 1. Arrowheads show strong NaV1.6 IR at the heminode, determined by the myelin termination (labeled with MBP in A1b). NaV1.6 was also present in sensory ending originating from this branch (labeled with NF-H in A1a) and in portions of the preterminal axons (green arrows in A1b). A1c and A1d: higher magnification of NaV1.6 IR at this heminode. B and C: Ia afferent branches shown in boxes 2 and 3 in A. The original stack used to create the image in A was optically sliced to provide a clear view of these two branches. At high magnification, NaV1.6 IR is clearly seen at the heminode and sensory endings supplied by the first-order branches shown in box 2 (arrowheads in B2a and B2b) and the first-order branch shown in box 3 (arrowheads in C3a and C3b). D: NaV1.6 IR was also strong in the areas immediately surrounding the cell nuclei of the intrafusal muscle fibers (labeled with DAPI, blue), particularly those located at the end of the equatorial regions of the fibers (arrowheads). E1 and E2: NaV1.6 IR in nodes of Ranvier of a preterminal soleus nerve branch labeled with MBP and NF-H. F1 and F2: a rat muscle spindle labeled with NF-H and NaV1.6 blocking peptide. NaV1.6 IR was almost completely eliminated by the blocking peptide.