Nitric oxide (NO) has been implicated in the regulation of sleep. The perifornical-lateral hypothalamic area (PF-LHA) is a key wake-promoting region and contains neurons that are active during behavioral or cortical activation. Recently, we found higher levels of NO metabolites (NOx), an indirect measure of NO levels, in the PF-LHA during prolonged waking (SD). However, NO is highly reactive and diffuses rapidly and the NOx assay is not sensitive enough to detect rapid-changes in NO levels across spontaneous sleep-waking states. We used a novel Nafion®-modified Platinum (NF-PT) electrode for real-time detection of NO levels in the PF-LHA across sleep-wake cycles, dark-light phases, and during SD. Sprague-Dawley male rats were surgically prepared for chronic sleep-wake recording and implantation of NF-PT electrode into the PF-LHA. Electroencephalogram (EEG), electromyogram (EMG), and electrochemical current generated by NF-PT electrode were continuously acquired for 5-7days including one day with 3h of SD. In the PF-LHA, NO levels exhibited a waking>rapid eye movement (REM)>non-rapid eye movement (nonREM) sleep pattern (0.56±0.03μM>0.47±0.02μM>0.42±0.02μM; p<0.01). NO levels were also higher during the dark- as compared to the light-phase (0.53±0.03μM vs. 0.44±0.02μM; p<0.01). NO levels increased during 3h of SD as compared to undisturbed control (0.58±0.04μM vs. 0.47±0.01μM; p<0.05). The findings indicate that in the PF-LHA, NO is produced during behavioral or cortical activation. Since elevated levels of NO inhibits most of the PF-LHA neurons that are active during cortical activation, these findings support a hypothesis that NO produced in conjunction with the activation of PF-LHA neurons during waking/SD, inhibits the same neuronal population to promote sleep.
Keywords: 3,3-bis(aminoethyl)-1-hydroxy-1-oxo-1-triazene (or DETA NONOate, a NO donor); 3,4-dihydroxyphenylacetic acid; 5-HIAA; 5-hydroxyindolacetic acid; AA; ANOVA; BF; DOPAC; EEG; EMG; HCRT; MCH; N-methyl-d-aspartate; NF-PT; NMDA; NO; NO sensor; NOC-18; NOS; Nafion®-modified Platinum; Nafion®-modified Platinum electrode; PF-LHA; REM; SD; aCSF; analysis of variance; artificial cerebrospinal fluid; ascorbic acid; basal forebrain; eNOS; electroencephalography; electromyography; endothelial nitric oxide synthase; hypocretin also called orexin; iNOS; inducible nitric oxide synthase; melanin-concentrating hormone; nNOS; neuronal nitric oxide synthase; nitric oxide; nitric oxide synthase; non-rapid eye movement; nonREM; perifornical-lateral hypothalamic area; perifornical-lateral hypothalamus; rapid eye movement; sleep deprivation; sleep deprivation or prolonged waking; sleep-wakefulness.
Published by Elsevier Ltd.