Fig. 10.
Light and electron microscopy of biocytin-filled complex cells with oligodendrocyte morphology in the hippocampal CA3 region. A–C, Photomicrograph (A) and camera lucida drawings (B, C; B, same cell as in A) of oligodendrocytes. The fine processes of these oligodendrocytes radiate from polygonal cell bodies, are rather more delicate than those of astrocytes, and show periodic swellings (compare with Fig. 9A–D). D, Low-power magnification of the neuropil in stratum moleculare in CA3 showing a cross-section of the oligodendrocyte cell body (arrow inA) and processes (areas 1, 2).E, Electron micrograph of a biocytin-filled oligodendrocyte’s process, which forms a myelin sheath (arrowheads) around an axon (A).F, A myelinated axon (A) without biocytin is shown for comparison. G, Electron micrograph of a myelinated axon (A) showing the connecting process of the oligodendrocyte (arrows), the external tongue process (T), and the myelin sheath (MS). H, Higher magnification of a portion of the myelin sheath (indicated area in G) demonstrating that the myelin sheath is biocytin-filled. Note the axolemma (A), the lamellae, and outer membrane (OM) of the myelin sheath. I, Higher magnification of a varicosity-like swelling (arrow) of an oligodendrocyte process (area1 in D). J, K, Longitudinal sections of myelinated axons (cell in A; area 2 in D) demonstrate biocytin-filled oligodendrocyte processes (arrows) and the surrounding myelin sheaths (arrowheads). Note the different axon diameter and thickness of the myelin sheaths of both axons.