Axotomy-induced alterations in the synthesis and transport of neurofilaments and microtubules in dorsal root ganglion cells

Abstract

Changes in the synthesis and axonal transport of neurofilament (NF) proteins and tubulin were examined after various selective axotomies of adult rat DRG cells. For axonal transport studies, DRGs were labeled by microinjection of 35S-methionine 14 d after axonal injuries, and nerves were retrieved 7 or 14 d after labeling. Slowly transported proteins were examined by quantitative PAGE/fluorography. After distal peripheral nerve crush (50-55 mm from the DRG), the cytoskeleton that entered undamaged regions of peripheral branch DRG axons by slow axonal transport differed from normal, while the cytoskeleton that entered dorsal root axons did not. Specifically, smaller-than-normal ratios of labeled NF protein/tubulin were transported in peripheral DRG axons after distal peripheral nerve crush. This change was almost entirely due to a selective decrease in the output of labeled NF proteins rather than to an increase in the amount of tubulin transported with NF proteins. Since the efficiency of axonal regeneration is known to be lower after cut injury than after nerve crush, we compared the effect of cut versus crush axotomy of peripheral DRG axons on cytoskeletal protein output. A more substantial reduction in the labeled NF/tubulin transport resulted in peripheral DRG axons if the distal sciatic nerve was cut rather than crushed but, even under these axotomy conditions, the labeled NF/tubulin ratios in dorsal root axons were not reduced. Peripheral cut axotomy did result in a lag in the advance of the labeling peak of the NF/microtubule protein wave in dorsal root axons, suggesting either that these proteins were delayed in exiting the cell body or that a slowing of the rate of their transport occurred. Pulse-labeling DRGs in vitro using 35S-methionine, and analysis of labeled proteins by 2-dimensional PAGE-fluorography demonstrated that the incorporation of radioactivity into NF proteins was significantly reduced, while the labeling of tubulins was unchanged 14 d after distal peripheral axotomy. In contrast to the results of peripheral axotomy, dorsal root crushes made close to the DRG (2-3 mm) or considerably distal (at the CNS entry zone 28-30 mm from the DRG) did not produce detectable changes in the amount of labeled NF or tubulin transport in central or peripheral branch axons. These findings indicate that the down-regulation of NF production/output that is exhibited at 14 d after peripheral branch axotomy is not present after central branch injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of the Plasminogen Activator System Accompanies Peripheral Nerve Regeneration after Sciatic Nerve Crush

“…One of the most noted changes is a decrease in the production and anterograde transportation of NFP (Greenberg and Lasek, 1988;Oblinger and Lasek, 1988). Consequently, axonal continuity and transport are disrupted by the crush, and the portion distal to the lesion is no longer supplied with NFP.…”

Recovery of Neurofilament Expression Selectively in Regenerating Reticulospinal Neurons

“…In goldfish, the expression of mRNA for the NF ON-1 increased during optic nerve regeneration (Tesser et al, 1986;Glasgow et al, 1994). On the other hand, NF mRNA, protein synthesis, and transport are reduced in mammalian peripheral (Hoffman et al, 1985;Goldstein et al, 1988;Oblinger and Lasek, 1988) and central neurons (Mikucki and Oblinger, 1991;Tetzlaff et al, 1991;Hoffman et al, 1993;McKerracher et al, 1993a) after axotomy. The changes are reversed in peripheral neurons only after regenerating axons reach their targets (Hoffman et al, 1985;Hoffman and Cleveland, 1988;Muma et al, 1990;Wong and Oblinger, 1990b), and they persist if regeneration is prevented (Tetzlaff et al, 1988;Jiang et al, 1994).…”

Short-term axotomy-induced changes in the rat lumbar dorsal root ganglia: An immunohistochemical study.

“…13) have a wide range of size, and also the small and intermediate ones were altered in the second week after axotomy. Following axotomy the synthesis, axonal transport of NFP, and the expression of mRNA of NFP decrease (13,14,22,23,35), and the NFP accumulated in the neurons suggest that, as least for NFP, the transport is blocked at the level of cell body (27). In addition, it is probable that the enhanced perikaryal phosphorylation of NFP represents part of the chromatolytic response to axonal injury (11,17), but we have not seen signs of chromatolysis in the NFP IR neuronal somata.…”