Regulation of aberrant neurofilament phosphorylation in neuronal perikarya. II. Correlation with continued axonal elongation following axotomy

Abstract

Neurofilaments (NF) are normally poorly phosphorylated in neuronal perikarya and highly phosphorylated in axons. Aberrant NF phosphorylation in the neuronal perikaryon has been demonstrated in a number of human and experimental disorders. In this study, we have asked whether expression of these phosphorylated NF (pNF) epitopes is dependent upon continued axonal regeneration following nerve transection (axotomy). This hypothesis was tested using the neurotoxic chemical acrylamide (AC) which is known to inhibit axonal regeneration following systemic administration. First, we examined whether AC acts at the level of the neuronal perikaryon to inhibit axonal elongation. Systemic, high dose intraperitoneal (IP) AC administration totalling 150 mg/kg (75 mg/kg x 2) did not impair the axotomy-induced reordering of slow axonal transport in the neuronal perikaryon. Next, we studied the ability of AC to directly prevent nerve outgrowth at the growing tips of axons. Subperineurial injection of AC (0.1 M), which in preliminary studies was found not to produce nerve fiber damage, markedly reduced the extent of nerve outgrowth when injected proximal to a nerve crush; this was shown by a reduction in the extent of radiolabeling and number of axonal sprouts in the distal stump seven days following nerve crush. Using this protocol, a 67% decrease in the number of neuronal perikarya in the L4 and L5 dorsal root ganglia demonstrating immunoreactivity to antibody 07-05 (directed against pNF epitopes) was observed in AC-injected compared to contralateral saline-injected crushed nerves. Taken together, the results indicate that inhibition of axonal regeneration in the distal stump by AC reduces aberrant NF phosphorylation in the neuronal perikaryon following axotomy.