Figure 5.

Continuous longitudinal ensheathment of axons in the lamprey PNS. A, Scanning electron micrograph of a longitudinally sectioned LLN of an adult lamprey. B, Higher magnification to exemplify a segment of a longitudinally sectioned axon (Ax) with two adjacent ensheathing cells (arrows pointing at E1, E2). B′, Magnification from B to highlight the cell-to-cell contact between the ensheathing cells as identified by their nuclei (N1, N2). Large arrowheads point at the adaxonal and the abaxonal surfaces of the contact between the neighboring ensheathing cells. Note the direct apposition of their plasma membranes (small arrowheads). One representative of n = 27 contacts between longitudinally adjacent ensheathing glia in one adult lamprey is shown. Note that ensheathment gaps reminiscent of mammalian nodes of Ranvier were not observed, suggesting that glial ensheathment is largely continuous along peripheral lamprey axons.