Shapes and Roles of Glial Cells

Oligodendrocyte

The Oligodendrocyte is the analog of the Schwann cell in the central nervous system. The oligodendrocyte, however, differs in structure. Where the Schwann cells wrap individually around the axons, each forming a separate myelin sheath, the oligodendrocyte sends out multiple paddle-shaped extensions. Each of these extensions wraps around the axon membrane to form a separate sheath. A single oligodendrocyte creates several sheaths. Each sheath is approximately 1 mm in length, and each node of Ranvier is approximately 1-2 micrometers (1 micrometer = 1/1,000th of a millimeter) in length.

Advanced

The ability of axons to regenerate following injury is determined for the most part by the glial environment. As noted, the myelinating Schwann cells of the peripheral nervous system promote regeneration and remyelination, whereas the oligodendrocytes of the central nervous system (CNS) lack these capabilities (Parent, 1996). The lack of this mechanism in the CNS has captured the imagination and energy of neuroscientists interested in neuronal repair. These scientists have been attracted by the possibility of transplanting Schwann cells to injured regions of the CNS to allow for regrowth and remyelination (Stichel, Hermanns, Lausberg & Muller, 1999; Xu, Zhang, Li, Aebischer & Bunge, 1999). More recently, the possibility of a better approach to this problem has emerged. It has been known for considerable time that glial cells supporting neurons of the olfactory system (sense of smell) are capable of forming myelin sheaths and, in addition, support axon regeneration (Williams-Hogarth, et al., 2000). In fact, the phylogenetically old, olfactory neurons (unlike other CNS neurons) recycle on a regular basis. Attempts to enhance the regeneration of CNS axons via transplantation of olfactory glial cells suggest that this method is more effective than transplantation of Schwann cells (Franklin & Barnett, 1997; Gudino-Cabrera, et al., 2000; Imaizumi, Lankford & Kocsis, 2000). The use of olfactory glial cells may provide an advantage because this cell type is indigenous to the CNS.

References

Franklin, R.J.M. & Barnett, S.C. (1997). Do olfactory glia have advantages over schwann cells for CNS repair? Journal of Neuroscience Research, 50, 665-672.

Gudino-Cabrera, G., Pastor, A.M., de la Cruz, R.R., Delgado-Garcia, J.M. & Nieto-Sampedro, M. (2000). Limits to the capacity of transplants of olfactory glia to promote axonal regrowth in the CNS. Neuroreport, 11(3), 467-471.

Imaizumi, T., Lankford, K.L. & Kocsis, J.D. (2000). Transplantation of olfactory ensheathing cells or Schwann cells restores rapid and secure conduction across the transected spinal cord. Brain Research, 854(1-2), 70-78.

Parent, A. (1996). Carpenter's human neuroanatomy (9th ed.). London: Williams & Wilkins.

Stichel, C.C., Hermanns, S., Lausberg, F. & Muller, H.W. (1999). Effects of schwann cell suspension grafts on axon regeneration in subacute and chronic CNS traumatic injuries. Glia, 28(2), 156-165.

Williams-Hogarth, L.C., Puche, A.C., Torrey, C., Cai, X., Song, I., Kolodkin, A.L., Shipley, M.T. & Ronnett, G.V. (2000). Expression of semaphorins in developing and regenerating olfactory epithelium. Journal of Comparative Neurology, 423(4), 565-578.

Xu, X.M., Zhang, S.X., Li, H., Aebischer, P. & Bunge, M.B. (1999). Regrowth of axons into the distal spinal cord through a Schwann-cell-seeded mini-channel implanted into hemisected adult rat spinal cord. European Journal of Neuroscience, 11(5), 1723-1740.