Sequential expression of JUN B, JUN D and FOS B proteins in rat spinal neurons: cascade of transcriptional operations during nociception.

Expression of the immediate-early gene encoded proteins JUN B, JUN D and FOS B was investigated by immunocytochemistry in rat L5 spinal cord up to 24 h following stimulation of hind limb somatosensory nociceptors by noxious heat or injection of formalin. In both experimental protocols, JUN B, which did not show basal expression, reached maximum expression after 2 h and thereafter slowly decreased. In contrast, the expression of JUN D, which was present before stimulation in many spinal neurons, was increased after 4 h, reached its maximum after 8 h and thereafter remained elevated. FOS B which was absent under basal conditions reached its maximum between 4 h and 8 h and thereafter declined but was still present after 24 h. All immunoreactivities were restricted to the ipsilateral dorsal horn except JUN D which was also induced in the contralateral side after 8 h. The results are discussed in respect to their meaning for transcriptional operations of JUN and FOS proteins.