Expression of myelin basic protein in the human auditory nerve—An immunohistochemical and comparative study

(A) Image of a montage showing immunofluoresence of a fresh human auditory nerve collected at surgery in a patient with normal hearing. Patient had severe brain stem compression and was operated through a trans-cochlear route after re-routing of the facial nerve. The nerve was fixed immediately in formaldehyde at removal and cryo-sectioned at the level of the fundus. The nerve is surrounded by an endoneurium. Tubulin (Tuj-1; green); myelin basic protein (MBP; red). Nuclear staining (DAPI; blue). Scale bar is 100μm. (B) Auditory nerve shown in higher magnification. Most fibers express MBP. Only a few (2.7%) axons lack a surrounding myelin layer (arrow). Some of these may represent Ranvier nodes (upper inset; Ranvier's node in a TEM reconstruction of the human auditory nerve). Axon in lower inset (arrow) is surrounded by a thin layer of myelin.

Immunofluoresence of the human auditory nerve. (A) Lamina fibers express MBP (red) up to the level of habenula perforata. A few axons lack MBP expression. All Corti nerve fibers (arrows) lack MBP expression. (B) Schwann cells contain myelin that express MBP while their cytoplasm express S-100. There is little co-expression. (C) Schwann cells stain positive for S-100 and axons for neural marker Tuj-1. (D) Laser confocal microscopy of human spiral ganglion at one turn. (E) The SGCs stain positive for S-100 and form a communicating network (LCM). (F) Co-expression of Tuj-1 and MBP in the human spiral ganglion (mid portion). Type 1 cell somata are surrounded by SGCs that lack MBP expression.

Immunofluoresence of guinea pig spiral (A) and guinea pig trigeminal (B) ganglion. Spiral ganglion cell somata are physically separated from each other by MBP-expressing Schwann cells (insets) while the trigeminal ganglion cell somata lack MBP expression (inset a). Their cell bodies are surrounded by “satellite glia cells” (SGCs) expressing S-100 (Inset b). SGCs form a communicating network similar to the human spiral ganglion SGCs. Arrows in A show intraganglionic spiral bundle (IGSB).

Expression of myelin marker MBP in human (A) and pig (B) spiral ganglion. Human type I perikarya are surrounded by cells lacking MBP expression while pig type I cells are surrounded by cells containing a thick layer of myelin. Distribution of MBP expression at the axon hillocks varies in human (arrows).