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Volume 17, Number 13, Issue of July 1, 1997 pp. 5206-5220
Copyright ©1997 Society for Neuroscience

Recovery of Neurofilament Expression Selectively in Regenerating Reticulospinal Neurons

Received Jan. 21, 1997; revised April 11, 1997; accepted April 15, 1997.

Alan J. Jacobs, Gary P. Swain, Joseph A. Snedeker, Donald S. Pijak, Laura J. Gladstone, and Michael E. Selzer

Department of Neurology and David Mahoney Institute for Neurological Sciences, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-4283

During regeneration of lamprey spinal axons, growth cones lack filopodia and lamellipodia, contain little actin, and elongate much more slowly than do typical growth cones of embryonic neurons. Moreover, these regenerating growth cones are densely packed with neurofilaments (NFs). Therefore, after spinal hemisection the time course of changes in NF mRNA expression was correlated with the probability of regeneration for each of 18 identified pairs of reticulospinal neurons and 12 cytoarchitectonic groups of spinal projecting neurons. During the first 4 weeks after operation, NF message levels were reduced dramatically in all axotomized reticulospinal neurons, on the basis of semiquantitative in situ hybridization for the single lamprey NF subunit (NF-180). Thereafter, NF expression returned toward normal in neurons whose axons normally regenerate beyond the transection but remained depressed in poorly regenerating neurons. The recovery of NF expression in good regenerators was independent of axon growth across the lesion, because excision of a segment of spinal cord caudal to the transection site blocked regeneration but did not prevent the return of NF-180 mRNA. The early decrease in NF mRNA expression was not accompanied by a reduction in NF protein content. Thus the axotomy-induced loss of most of the axonal volume resulted in a reduced demand for NF rather than a reduction in volume-specific NF synthesis. We conclude that the secondary upregulation of NF message during axonal regeneration in the lamprey CNS may be part of an intrinsic growth program executed only in neurons with a strong propensity for regeneration.

Key words: regeneration; neurofilaments; lamprey; spinal transection; reticulospinal; Müller cells; Mauthner cells; cytoskeleton

This article has been cited by other articles:

				G. Zhang, L.-Q. Jin, J.-Y. Sul, P. G. Haydon, and M. E. Selzer Live Imaging of Regenerating Lamprey Spinal Axons Neurorehabil Neural Repair, March 1, 2005; 19(1): 46 - 57. [Abstract] [PDF]

				M.I. Shifman and M.E. Selzer Expression of the Netrin Receptor UNC-5 in Lamprey Brain: Modulation by Spinal Cord Transection Neurorehabil Neural Repair, January 1, 2000; 14(1): 49 - 58. [Abstract] [PDF]

				Y. Liu, D. Kim, B. T. Himes, S. Y. Chow, T. Schallert, M. Murray, A. Tessler, and I. Fischer Transplants of Fibroblasts Genetically Modified to Express BDNF Promote Regeneration of Adult Rat Rubrospinal Axons and Recovery of Forelimb Function J. Neurosci., June 1, 1999; 19(11): 4370 - 4387. [Abstract] [Full Text] [PDF]

				T. Becker, R. R. Bernhardt, E. Reinhard, M. F. Wullimann, E. Tongiorgi, and M. Schachner Readiness of Zebrafish Brain Neurons to Regenerate a Spinal Axon Correlates with Differential Expression of Specific Cell Recognition Molecules J. Neurosci., August 1, 1998; 18(15): 5789 - 5803. [Abstract] [Full Text] [PDF]

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