title: Endogenous presynaptic nitric oxide supports an anterograde signaling in the central nervous system.
abstract: The source size and density determine the extent of nitric oxide (NO) diffusion which critically influences NO signaling. In the brain, NO released from postsynaptic somas following NMDA-mediated activation of neuronal nitric oxide synthase (nNOS) retrogradely affects smaller presynaptic targets. By contrast, in guinea pig trigeminal motor nucleus (TMN), NO is produced presynaptically by tiny and disperse nNOS-containing terminals that innervate large nNOS-negative motoneurons expressing the soluble guanylyl-cyclase (sGC); consequently, it is uncertain whether endogenous NO supports an anterograde signaling between pre-motor terminals and postsynaptic trigeminal motoneurons. In retrogradely labeled motoneurons, we indirectly monitored NO using triazolofluorescein (DAF-2T) fluorescence, and evaluated sGC activity by confocal cGMP immunofluorescence. Multiple fibers stimulation enhanced NO content and cGMP immunofluorescence into numerous nNOS-negative motoneurons; NOS inhibitors prevented depolarization-induced effects, whereas NO donors mimicked them. Enhance of cGMP immunofluorescence required extracellular Ca(2+), a nNOS-physiological activator, and was prevented by inhibiting sGC, silencing neuronal activity or impeding NO diffusion. In conclusion, NO released presynaptically from multiple cooperative tiny fibers attains concentrations sufficient to activate sGC in many motoneurons despite of the low source/target size ratio and source dispersion; thus, endogenous NO is an effective anterograde neuromodulator. By adjusting nNOS activation, presynaptic Ca(2+) might modulate the NO diffusion field in the TMN.
authors.affiliation: Departamento de Fisiología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay. afernan@fmed.edu.uy
authors.forename: Adriana
authors.initials: A
authors.lastname: Fernández-Alvarez
authors.forename: Leonel
authors.initials: L
authors.lastname: Gómez-Sena
authors.forename: María Gabriela
authors.initials: MG
authors.lastname: Fabbiani
authors.forename: Ruben
authors.initials: R
authors.lastname: Budelli
authors.forename: Verónica
authors.initials: V
authors.lastname: Abudara
mesh_terms: D000818:Animals; D001933:Brain Stem / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology; D002490:Central Nervous System / Q000166:cytology / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology; D055724:Electrophysiological Phenomena; D004789:Enzyme Activation / Q000502:physiology; D019793:Fluorescein; D005456:Fluorescent Dyes; D006162:Guanylate Cyclase / Q000378:metabolism; D006168:Guinea Pigs; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000502:physiology; D009412:Nerve Fibers / Q000502:physiology; D009569:Nitric Oxide / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D017661:Receptors, Presynaptic / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D014276:Trigeminal Nerve / Q000502:physiology
chemical_list: C414689:4,5-diaminofluorescein diacetate; D005456:Fluorescent Dyes; D017661:Receptors, Presynaptic; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D019793:Fluorescein