c-Jun regulation in rat neonatal motoneurons postaxotomy.

Motoneurons respond to peripheral nerve transection by either regenerative or degenerative events depending on their state of maturation. Since the expression of c-Jun has been involved in the early signalling of the regenerative process that follows nerve transection in adults, we have investigated c-Jun on rat neonatal axotomized motoneurons during the period in which neuronal death is induced. Changes in levels of c-Jun protein and its mRNA were determined by means of quantitative immunocytochemistry and in situ hybridization. Three hours after nerve transection performed on postnatal day (P)3, c-Jun protein and mRNA is induced in axotomized spinal cord motoneurons, and high levels were reached between 1 and 10 days after. This response is associated with a detectable c-Jun activation by phosphorylation on serine 63. No changes were found in the levels of activating transcription factor -2. Most of dying motoneurons were not labelled by either a specific c-Jun antibody or a c-jun mRNA probe. However, dying motoneurons were specifically stained by a polyclonal anti c-Jun antibody, indicating that some c-Jun antibodies react with unknown epitopes, probably distinct from c-Jun p39, that are specifically associated with apoptosis.