title: Characterization of NO-producing neurons in the rat corpus callosum.
abstract: BACKGROUND
  The aim of this study was to determine the presence and distribution of nitric oxide (NO)-producing neurons in the rat corpus callosum (cc).
  
  
  METHODS
  To investigate this aspect of cc organization we used nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal NO synthase (nNOS) immunocytochemistry.
  
  
  RESULTS
  Intense NADPH-d-positive (NADPH-d+) neurons were found along the rostrocaudal extension of the cc (sagittal sections). They were more numerous in the lateral cc and gradually decreased in the more medial regions, where they were very few or absent. The Golgi-like appearance of NADPH-d+ intracallosal neurons allowed dividing them into five morphological types: (1) bipolar; (2) fusiform; (3) round; (4) polygonal; and (5) pyramidal. The number of NADPH-d+ neurons (both hemispheres) was counted in two brains using 50-μm thick sections. In the first brain, counts involved 145 sections and neurons were 2959; in the second, 2227 neurons were counted in 130 sections. The distribution and morphology of nNOS-immunopositive (nNOSIP) neurons was identical to that of NADPH-d+neurons. Some of these neurons were observed in the cc ependymal region, where they might be in contact with cerebrospinal fluid (CSF), monitoring its composition, pH, and osmolality changes, or playing a role in regulating the synthesis and release of several peptides. The somatic, dendritic, and axonal processes of many NADPH-d+/nNOSIP neurons were closely associated with intracallosal blood vessels.
  
  
  CONCLUSIONS
  Such close relationship raises the possibility that these neurons are a major source of NO during neural activity. As NO is a potent vasodilator, these findings strongly suggest that NO-positive neurons transduce neuronal signals into vascular responses in selected cc regions, thus giving rise to hemodynamic changes detectable by neuroimaging.
authors.affiliation: Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Marche Polytechnic University Ancona, I-60020, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Barbaresi
authors.affiliation: Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Marche Polytechnic University Ancona, I-60020, Italy.
authors.forename: Mara
authors.initials: M
authors.lastname: Fabri
authors.affiliation: Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Marche Polytechnic University Ancona, I-60020, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Mensà
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D048430:Cell Shape / Q000502:physiology; D003337:Corpus Callosum / Q000166:cytology / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism; D008297:Male; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; D009252:NADPH Dehydrogenase
keywords: Colocalization; GFAP; NADPH-d; immunocytochemistry; nNOS; nitric oxide