title: Hypertonicity increases NO production to modulate the firing rate of magnocellular neurons of the supraoptic nucleus of rats.
abstract: Increases in plasma osmolality enhance nitric oxide (NO) levels in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and modulate the secretion of both vasopressin (VP) and oxytocin (OT). In this paper, we describe the effects of hypertonicity on the electrical properties of MNCs by focusing on the nitrergic modulation of their activity in this condition. Membrane potentials were measured using the patch clamp technique, in the presence of both glutamatergic and GABAergic neurotransmission blockers, in coronal brain slices of male Wistar rats. The recordings were first made under a control condition (295 mosm/kg H2O), then in the presence of a hypertonic stimulus (330 mosm/kg H2O) and, finally, with a hypertonic stimulus plus 500 μM L-Arginine or 100 μM N-nitro-L-Arginine methyl ester hydrochloride (L-NAME). Hypertonicity per se increased the firing frequency of the neurons. L-Arginine prevented the increase in fire frequency induced by hypertonic stimulus, and L-NAME (inhibitor of nitric oxide synthase) induced an additional increase in frequency when applied together with the hypertonic solution. Moreover, L-Arginine hyperpolarizes the resting potential and decreases the peak value of the after-hyperpolarization; both effects were blocked by L-NAME and hypertonicity and/or L-NAME reduced the time constant of the rising phase of the after-depolarization. These results demonstrate that an intrinsic nitrergic system is part of the mechanisms controlling the excitability of MNCs of the SON when the internal fluid homeostasis is disturbed.
authors.affiliation: Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Avenida Bandeirantes, 3900, 14049-900 Ribeirão Preto, SP, Brazil.
authors.forename: M P
authors.initials: MP
authors.lastname: da Silva
authors.forename: R R
authors.initials: RR
authors.lastname: Ventura
authors.forename: W A
authors.initials: WA
authors.lastname: Varanda
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D020532:Basal Nucleus of Meynert / Q000166:cytology / Q000378:metabolism*; D055724:Electrophysiological Phenomena / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006982:Hypertonic Solutions / Q000494:pharmacology; D007038:Hypotonic Solutions / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013495:Supraoptic Nucleus / Q000166:cytology / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D006982:Hypertonic Solutions; D007038:Hypotonic Solutions; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester
keywords: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; 4-amino-5-methylamino-2′,7′ diaminofluorescein-FM; 6-cyano-7-nitroquinoxaline-2,3-dione; ACSF; ADP; AHP; CNQX; DAF-FM; DMSO; EGTA; HEPES; MNCs; N-nitro-l-Arginine methyl ester hydrochloride; NADPH; NO; NOS; OT; SON; VP; after-depolarization potential; after-hyperpolarization potential; artificial cerebro spinal fluid; dimethylsulfoxide; electrophysiology; ethylene glycol tetraacetic acid; extracellular tonicity; l-NAME; magnocellular neurons; magnocellular neurosecretory cells; nicotinamide adenine dinucleotide phosphate; nitric oxide; nitric oxide synthase; oxytocin; supraoptic nucleus; vasopressin