Figure 5

Sodium channel (NaCh) clusters are present in unmyelinated fibers and some lack associations with Schwann cells. A. Confocal micrograph showing NaCh (red), N52 (green), and myelin basic protein (MBP; blue) staining relationships. Clusters of NaChs are seen in fibers with and without myelin. The inserts represent enlargements of a typical disc-like nodal NaCh cluster on a myelinated fiber (left) and a torpedo-like NaCh cluster in an unmyelinated axon with N52 that lacks MBP (right). B. Confocal micrograph showing NaCh (red), caspr (green), and DAPI (blue) staining relationships. Clusters of NaChs are seen at typical caspr-identified nodal sites and at sites that lack caspr. The inserts are enlargements of a typical nodal NaCh cluster flanked by caspr staining (right) and a torpedo-like NaCh cluster on an axon that lacks caspr (left). C and D. Single confocal micrographs showing NaCh (red), caspr (green), MBP (purple), and DAPI (blue) staining relationships. The inserts represent enlargements of a typical nodal NaCh cluster flanked by caspr in a myelinated fiber (C) and a torpedo-like NaCh cluster in an axon that lacks both MBP and caspr (D). The DAPI-identified nucleus associated with the myelinated fiber appears oval (C, white arrow), whereas the nucleus associated with the nerve fiber that lacks both MBP and caspr appears flattened (D, white arrowhead). The unmyelinated fiber also shows a broad distribution of NaChs in areas beyond the torpedo-like NaCh cluster (D, black arrow). E. Single confocal image showing NaCh (red), S-100 (green), and neurofilament heavy (NFH; blue) staining relationships. Clusters of NaChs can be observed on some NFH-positive nerve fibers that lack S-100 staining (E, white-outlined arrowheads). S-100 staining can be found in the cytoplasm of Schwann cells wrapping around the axons (E, Asterisk). Scale bar, 20 μm.