Expression of raf serine/threonine protein kinases in the cell bodies of primary sensory neurons of the adult rat.

We have used immunocytochemistry to examine the distribution of raf protein kinases in sensory neurons of the adult rat. In lumbar and trigeminal sensory ganglia, cells of all size ranges appeared to be raf immunoreactive and this was confirmed by double labeling using subpopulation specific markers. Almost all cells labeled with Griffonia simplicifolia IB4 (a small cell marker) or immunostained by using a large cell marker (RT97) showed raf immunoreactivity. These two markers label cells known to differ in their expression of neurotrophin receptors (trk). Thus raf kinases are not confined to cells expressing only certain trk subtypes. In the dorsal horn of the spinal cord, raf immunoreactivity was present in scattered neurons. However, sensory axons identified by IB4 histochemistry were devoid of raf immunostaining. Lectin-labeled nerve fibers in the cornea, lower lip and glans penis were also not immunoreactive. Ligation of the sciatic nerve did not produce any accumulation of raf immunoreactivity, confirming that raf kinases are not axonally transported to the peripheral processes of sensory neurons. Surgical dissection of the sciatic nerve caused the normal homogeneous cytoplasmic raf immunoreactivity to be replaced in some cells by a staining concentrated predominantly under the plasma membrane. One possibility is that this represents activation of raf in these cells.