The distribution and characterization of NADPH-d/NOS-IR neurons in the ratcuneate nucleus

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemi stry and nitric oxide synthase (NOS) immunohistochemistry have been used to characterize the nitric oxide (NO)-containing neurons in the rat cuneate n ucleus. The present results showed that NADPH-d-positive/NOS-immunoreactive (-IR) neurons were distributed in the entire rostrocaudal extent of the nu cleus. In the caudal region (approximately 1-2 mm caudal to the obex), NADP H-d/NOS-IR neurons were aggregated along the dorsal area of the nucleus not ably in the lateral aspect. When traced rostrally, labeled neurons were pro gressively reduced and the cells were randomly distributed. The labeled neu rons varied from round, ovoid to spindle-shaped with a mean profile area of about 140.1 +/-1.7 mum(2) (n=720). They made up 7-10% of the neuronal popu lation in the cuneate nucleus. By immunoelectron microscopy, the immunoreac tion product was deposited throughout the cytoplasm extending from the soma to the proximal and distal dendrites. Results of NADPH-d staining parallel ed that of NOS immunohistochemistry. Furthermore, NADPH-d reactivity and NO S-IR were colocalized in the same neurons following double labeling. Using NADPH-d histochemistry along with anti-gamma -aminobutyric acid (GABA) and -glycine postembedding immunolabeling for identification of GABA- and glyci ne-IR neurons, respectively, about 33% of the NADPH-d-positive neurons cont ained both GABA and glycine, 26% of them contained only glycine, while 41% of them showed neither GABA nor glycine labeling. Cuneothalamic neurons (CT Ns) were identified by injecting the retrograde tracer Fluorogold (FG) into the ventrobasal complex of the thalamus. Numerous FG-labeled neurons were present in the contralateral cuneate nucleus, but none were reactive for NA DPH-d. The present results suggest that approximately 60% of the NADPH-d/NO S-IR neurons in the cuneate nucleus are interneurons containing GABA and/or glycine. (C) 2001 Elsevier Science B.V. All rights reserved.