SPINAL PROJECTION NEURONS TO THE LATERODORSAL PONTINE TEGMENTAL NUCLEUS - RELATIONSHIP TO PREGANGLIONIC NEURONS AND NITRIC-OXIDE SYNTHASE

The region of the rat sacral parasympathetic nucleus (SPN) contains di stinct subpopulations of neurons that project supraspinally or are pre ganglionic neurons. Some preganglionic neurons in the SPN serve as the motor outflow for urinary bladder contraction; other neurons in the S PN project to regions of the rostral pens that subserve micturition re flexes. Previous studies utilizing immunohistochemistry or staining fo r nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) hav e demonstrated that numerous neurons in the SPN contain nitric oxide s ynthase (NOS), the enzyme for nitric oxide synthesis. Thus, the object ives of this study were to determine 1) the distribution of neurons in the region of the SPN that project to the laterodorsal tegmentum (LDT ) of the pons, 2) whether spinal neurons projecting to a peripheral au tonomic ganglion also project to the LDT, and 3) whether NOS or NADPH- d is present in LDT projection neurons. Preganglionic neurons were ide ntified by injecting the retrograde tracer fluorogold (FG) into the ma jor pelvic ganglion (MPG). Supraspinally projecting neurons were ident ified by injecting the retrograde tracer fast blue (FB) into the LDT. Numerous FB-labeled neurons were present in the ipsi- and contralatera l SPN and were immediately dorsal to FG-labeled preganglionic neurons. Neurons containing both tracers were not observed. Approximately 20% of preganglionic neurons, but no LDT projection neurons, were reactive for NOS and NADPH-d. These data suggest that the region of the SPN is a site for distinct subpopulations of neurons that project to the LDT and to the MPG and that NOS is contained in some preganglionic neuron s, but is not a marker for LDT projection neurons. (C) 1995 Wiley-Liss , Inc.