A study of NADPH-diaphorase positive septohippocampal neurons in rat.

Retrograde transport of fluorescent tracers and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical techniques were combined in a study of septohippocampal projections in the rat. The dorsal (DH) and ventral (VH) hippocampus were simultaneously injected with different tracers (Fast Blue or Fluoro-Gold). Histochemical procedures revealed many NADPH-d positive cells located in the medial septum and the horizontal limb of the diagonal band. In the medial septum, NADPH-d positive neurons were mostly located lateral to the midline region and some of these were double-labeled by the tracer injected into the VH. Also, NADPH-d positive cells were found in the horizontal diagonal band and some of these were double-labeled following injections into the DH. No fluorescence/NADPH-d double-labeled neurons were observed in other structures known to project to the hippocampus.