Changes in the phosphorylation of neurofilament proteins in facial motoneurons following various types of nerve lesion.

This report defines the conditions for changes in the phosphorylation state of neurofilaments (NF) after facial nerve lesions. In adult control rats, few phosphorylated neurofilament (pNF) epitopes were stained (using SMI 31 antibodies) in a small subpopulation of facial motoneurons. After various types of mechanical lesion (nerve transection with and without attaching a metal clip to the proximal nerve trunk, nerve crush, combined trigeminal and facial nerve lesions) of the right facial nerve, pNF immunoreactivity transiently increased in most cell bodies of facial motoneurons on the operated side. This pNF 'reaction' started within 2 days after the operation and persisted up to 2 weeks but remained longer in those animals in which axonal regeneration had been prevented or delayed by attaching a metal clip to the proximal nerve stump. After botulinum toxin application into facial muscles (i.e. inhibition of synaptic transmission at motoric endplates) there was no increase in the amount of pNF after 4 and 10 days, but it appeared in facial nuclei 4 weeks after injection on both, the treated and the untreated side, i.e. during functional restitution. Selectively transecting the 'vibrissal part' of the trigeminal nerve induced no obvious changes in the pNF immunoreactivity in facial motoneurons, but a combined trigeminal-facial lesion did. Labeling nonphosphorylated epitopes (using SMI 32 antibodies) showed a slight decrease in immunoreactivity in the neuropil of the facial nucleus 15 days after nerve transection and fixing a metal clip on the proximal nerve stump.