Restricted growth of Schwann cells lacking Cajal bands slows conduction in myelinated nerves

Nerve impulses are propagated at nodes of Ranvier in the myelinated nerves of vertebrates. Internodal distances have been proposed to affect the velocity of nerve impulse conduction; however, direct evidence is lacking, and the cellular mechanisms that might regulate the length of the myelinated seg...

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Published in:	Nature 2004-09, Vol.431 (7005), p.191-195
Main Authors:	Brophy, Peter J, Court, Felipe A, Sherman, Diane L, Pratt, Thomas, Garry, Emer M, Ribchester, Richard R, Cottrell, David F, Fleetwood-Walker, Susan M
Format:	Article
Language:	eng
Subjects:	Animals Axons - physiology Behavior, Animal - physiology Biological and medical sciences Cell Size Cells Cytoplasm - metabolism Fundamental and applied biological sciences. Psychology Gene Deletion Membrane Proteins - deficiency Membrane Proteins - genetics Mice Mice, Knockout Microtubules - metabolism Muscle, Skeletal - innervation Mutation Myelin Basic Protein - genetics Nerve Fibers, Myelinated - physiology Nervous system RNA, Messenger - genetics RNA, Messenger - metabolism Rodents Schwann Cells - cytology Schwann Cells - physiology Sciatic Nerve - cytology Sciatic Nerve - physiology Synaptic Transmission - physiology Vertebrates: nervous system and sense organs
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Summary:	Nerve impulses are propagated at nodes of Ranvier in the myelinated nerves of vertebrates. Internodal distances have been proposed to affect the velocity of nerve impulse conduction; however, direct evidence is lacking, and the cellular mechanisms that might regulate the length of the myelinated segments are unknown. Ramón y Cajal described longitudinal and transverse bands of cytoplasm or trabeculae in internodal Schwann cells and suggested that they had a nutritive function. Here we show that internodal growth in wild-type nerves is precisely matched to nerve extension, but disruption of the cytoplasmic bands in Periaxin-null mice impairs Schwann cell elongation during nerve growth. By contrast, myelination proceeds normally. The capacity of wild-type and mutant Schwann cells to elongate is cell-autonomous, indicating that passive stretching can account for the lengthening of the internode during limb growth. As predicted on theoretical grounds, decreased internodal distances strikingly decrease conduction velocities and so affect motor function. We propose that microtubule-based transport in the longitudinal bands of Cajal permits internodal Schwann cells to lengthen in response to axonal growth, thus ensuring rapid nerve impulse transmission.
ISSN:	0028-0836 1476-4687