Nerve growth factor modulates the activation status and fast axonal transport of ERK 1/2 in adult nociceptive neurones

Mature dorsal root ganglion cells respond to neurotrophins, and the intrace llular signalling pathways activated by neurotrophins have been characteriz ed in vitro. We have now used immunocytochemistry and Western blots to exam ine the expression and activation of extracellular signal-regulated protein kinase-1/2 (ERK) in rat dorsal root ganglion cells in vivo, using antisera to total (tERK) and phosphorylated (pERK) forms. This has revealed a numbe r of novel findings. tERK immunoreactivity is present in most dorsal root g anglion cells but is expressed most strongly in small (nociceptive) cells a nd, surprisingly, is absent in a population of large cells that expressed t rkB or trkC but mainly lack p75(NTR) immunoreactivity. In contrast pERK is prominent in a few trkA cells and in satellite glial cells, and is further increased by NGF treatment. tERK and pERK both undergo fast anterograde and retrograde axonal transport, indicated by accumulation at a sciatic nerve ligature, and NGF reduces the level of retrograde pERK transport.