Glutamatergic receptors regulate expression, phosphorylation and accumulation of neurofilaments in spinal cord neurons

Glutamatergic regulation of neurofilament expression, phosphorylation and a ccumulation in cultured spinal cord neurons was studied. At seven days in c ulture, 0.15% of the neurons were immunoreactive for non-phosphorylated neu rofilaments, but essentially no cells immunoreactive for phosphorylated neu rofilaments were seen. The number and size of the immunoreactive cells in c ulture corresponded well to those of rat and human spinal cord neurons in v ivo. In spinal cord cultures, sublethal, longlasting stimulation of alpha-a mino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate or metabotroph ic receptors, but not N-methyl-D-aspartate receptors, dose-dependently incr eased the number of non-phosphorylated neurofilament-immunoreactive cells, which was blocked by nifedipine, an antagonist of voltage-sensitive Ca2+ ch annels. Stimulation of kainate or all non-N-methyl-D-aspartate receptors de creased the expression of medium-molecular-weight neurofilament messenger R NA. Blockade of AMPA/kainate receptors, but not of N-methyl-D-aspartate rec eptors, increased the amount of phosphorylated neurofilament protein and th e number of phosphorylated neurofilament-immunoreactive cell bodies. The ph osphorylated neurofilament-immunoreactive cell population was different fro m the non-phosphorylated neurofilament-immunoreactive neurons, which lost t heir axonal nonphosphorylated neurofilament immunoreactivity but showed int ense cytoplasmic labeling in response to the blockade of AMPA/kainate recep tors. Immunoreactivity for phosphoserine did not change upon glutamate rece ptor stimulation and blockade. The results show that activation of AMPA/kainate receptors decreases the ex pression of neurofilament messenger RNA and neurofilament phosphorylation i n spinal cord neurons by a mechanism involving active voltage-sensitive Ca2 + channels. Blockade of these receptors seems to disturb axonal neurofilame nt transport. Because AMPA/kainate receptors mediate chronic glutamatergic death of spinal motor neurons and these receptors have been suggested to be involved in the pathogenesis of amyotrophic lateral sclerosis, the observe d alteration in neurofilament phosphorylation and distribution may contribu te to the pathogenesis of chronic motor neuron diseases. (C) 1999 IBRO. Pub lished by Elsevier Science Ltd.