Expression of neurotrophin receptors trkB and trkC and their ligands in rat adrenal gland and the intermediolateral column of the spinal cord

Neurotrophins and their trk receptors constitute major classes of signaling molecules with important actions in the developing and adult nervous syste m. With regard to the sympathoadrenal cell lineage, which gives rise to sym pathetic neurons and chromaffin cells, neurotrophin-3 (NT-3) and nerve grow th factor (NGF) are thought to influence developing sympathetic neurons. Ne urotrophin requirements of chromaffin cells of the adrenal medulla are less well understood than those for NGF. In order to provide the bases for unde rstanding of putative functions of neurotrophins for the development and ma intenance of chromaffin cells and their preganglionic innervation, in situ hybridization has been used to study the expression of brain-derived neurot rophic factor (BDNF) and NT-3, together with their cognate receptors trkB a nd trkC, in the adrenal gland and in the intermediolateral column (IML) of the spinal cord. BDNF is highly expressed in the embryonic adrenal cortex a nd later in cells of the cortical reticularis zone. Adrenal medullary chrom affin cells fail to express detectable levels of mRNAs for BDNF, NT-3, and their cognate receptors trkB and trkC. Neurons in the IML express BDNF and trkB, and low levels of NT-3 and trkC. Our data make it unlikely that BDNF and NT-3 serve as retrograde trophic factors for IML neurons but suggest ro les of BDNF and NT-3 locally within the spinal cord and possibly for sensor y nerves of the adrenal cortex.