EXPRESSION OF IMMEDIATE-EARLY GENE PROTEINS FOLLOWING AXOTOMY AND INHIBITION OF AXONAL-TRANSPORT IN THE RAT CENTRAL-NERVOUS-SYSTEM

The expression of the immediate early gene-encoded proteins c-Jun, Jun B, Jun D, c-Fos, Fos B and Krox-24 in central neurons following transection of, or inhibition of, axonal transport in their axons was investigated in the rat using immunocytochemistry. Transection of the medial forebrain bundle, which produces an essentially complete axotomy of neurons in the ipsilateral mammillary nucleus, substantia nigra pars compacta, ventral tegmental area and parafascicularis, induced the expression of c-Jun, Jun D and, to a lesser extent, Krox-24, in these nuclei. Microinjection of colchicine into the medial forebrain bundle to chemically inhibit axonal transport similarly induced the expression of these proteins in these areas. The expression of the proteins was first evident 24 h after transection, reached a maximum at 48 h and was still present after 10 days. However, after 30 days the proteins were absent from the substantia nigra, ventral tegmentum and parafascicularis, and were still present only in the mammillary nuclei. The other immediate early genes, Jun B, c-Fos and Fos B, were never expressed above the basal levels seen in untreated rats. Transection of the corpus callosum and the hippocampal commissure, which produces only a partial axotomy of neurons in the cerebral cortex and hippocampus, respectively, did not induce the expression of any of the genes in these neurons. Microinjection of colchicine or vinblastine to produce a localized inhibition of axonal transport in the cerebral cortex, hippocampus, thalamus and cerebellum also induced the expression of c-Jun, Jun D and, again to a lesser extent, Krox-24, in neurons surrounding the injection site. In contrast to this selective expression, administration of the neuronal excitant metrazole induced the expression of all six immediate early gene proteins in central nervous system neurons.