title: Day- and nighttime injection of a nitric oxide synthase inhibitor elicits opposite sleep responses in rats.
abstract: Previous studies suggest that nitric oxide (NO) may play a role in sleep regulation, particularly in the homeostatic process. The present studies were undertaken to compare the sleep effects of injecting a NO synthase (NOS) inhibitor when homeostatic sleep pressure is naturally highest (light onset) or when it is at its nadir (dark onset) in rats. Sleep, electroencephalogram delta-wave activity during nonrapid eye movement sleep (NREMS), also known as slow-wave activity (SWA), and brain temperature responses to three doses of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME ; 5, 50, and 100 mg/kg) injected intraperitoneally at light or dark onset were examined in rats (n = 6 to 8). The effects of 5 mg/kg L-NAME were determined in both normal and vagotomized (VX) rats. Light onset administration of 50 mg/kg L-NAME decreased NREMS amounts and suppressed SWA and increased rapid eye movement sleep (REMS) amounts. At dark onset, L-NAME injection also dose dependently suppressed SWA; however, unlike light onset injections, both NREMS and REMS amounts were increased after all three doses. Sleep responses to 5 mg/kg L-NAME were not different in control and VX rats, suggesting that the sleep effects of L-NAME are not mediated through the activation of sensory vagal mechanisms. The present findings suggest that timing of the injection is a major determinant of the sleep responses observed after systemic L-NAME injection in rats.
authors.affiliation: Dept. of Biological Sciences, Fordham University, 441 E. Fordham Road, Bronx, NY 10458, USA.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Ribeiro
authors.forename: Levente
authors.initials: L
authors.lastname: Kapás
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D001921:Brain / Q000502:physiology; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004569:Electroencephalography; D004791:Enzyme Inhibitors / Q000008:administration & dosage* / Q000494:pharmacology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage* / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000187:drug effects* / Q000502:physiology; D012894:Sleep Stages / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester