Co-existence of NADPH-diaphorase, fibroblast growth factor-2 and fibroblast growth factor receptor in spinal autonomic system suggests target-specific actions.

In the rat spinal cord, we found substantial co-existence of fibroblast growth factor-2, fibroblast growth factor receptor (type-1 or flg) immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity (a histochemical marker for neuronal nitric oxide synthase) in preganglionic autonomic cell groups of intermediate layers VI, VII and X. Anti-fibroblast growth factor-2 and anti-nitric oxide synthase binding sites were confined to the cytoplasm of reactive neurons as judged by immunogold electron microscopy. Within the major autonomic nucleus, i.e. intermediolateral column, three different populations were identified: (i) fibroblast growth factor and fibroblast growth factor receptor, (ii) fibroblast growth factor/NADPH-diaphorase and (iii) NADPH-diaphorase-only stained cell groups. Sympathoadrenal neurons were prelabelled with fluorescent tracer Fast Blue and co-stained for fibroblast growth factor-like protein and NADPH-diaphorase, suggesting heterologous diversification of neuronal phenotypes and functional organization in the spinal autonomic system. Our findings suggest intriguing roles for nitric oxide and fibroblast growth factor-2 cytokine in the preganglionic sympathetic spinal cord system: The "short-term" diffusible messenger nitric oxide may act as "tonic" and/or "phasic" signal within rostrocaudally oriented function-specific preganglionic units necessary for integrated target control. The "long-term" messenger fibroblast growth factor-2 may be involved in, for example, cytokine-dependent regulation of neuronal NADPH-diaphorase/nitric oxide synthase. Furthermore, co-existence of NADPH-diaphorase, fibroblast growth factor-2 and receptor in sympathoadrenal neurons suggest mutual target-specific regulatory functions, e.g. hormone release and blood perfusion or maintenance of phenotype and plasticity responsiveness of adrenal medullary tissue.