Nitric oxide production in the perifornical-lateral hypothalamic area and its influences on the modulation of perifornical-lateral hypothalamic area neurons

Abstract

The perifornical-lateral hypothalamic area (PF-LHA) is a major wake-promoting structure. It predominantly contains neurons that are active during behavioral and cortical activation. PF-LHA stimulation produces arousal and PF-LHA lesions produce somnolence. Nitric oxide (NO) is a gaseous neurotransmitter that has been implicated in the regulation of multiple pathological and physiological processes including the regulation of sleep. NO levels are higher in the cortex and in the basal forebrain (BF) during arousal. In this study we determined whether NO levels increase in the PF-LHA during prolonged arousal and whether increased NO modulates the discharge activity of PF-LHA neurons. Experiments were conducted during lights-on phase between 8.00 – 20.00h (lights-on at 8.00h). First, we quantified levels of NO metabolites, NO2− and NO3− (collectively called NOx−) in the microdialysis dialysates collected from the PF-LHA during baseline (undisturbed rats), 6h of sleep deprivation (SD), and recovery after SD. We further determined the effects of a NO donor, NOC-18, on the discharge activity of PF-LHA neurons in urethane-anesthetized rats. Overall, SD significantly affected NOx− production in the PF-LHA (one way repeated measures ANOVA, F=7.827, p=0.004). The levels of NOx− increased progressively in animals that were subjected to prolonged arousal as compared to the undisturbed predominantly sleeping animals and decreased during the recovery period. Local application of NOC-18 significantly suppressed the discharge of PF-LHA neurons including a majority of stimulus-on neurons or neurons exhibiting activation during EEG desynchronization. The findings of this study suggest that in the PF-LHA, NO production is elevated during prolonged waking and that NO exerts predominantly inhibitory effects on PF-LHA neurons, especially on those neurons that are active during cortical activation. These findings are consistent with a hypothesis that NO in the PF-LHA plays a role in sleep regulation by inhibiting its neurons.

Sleep deprivation under sustained hypoxia protects against oxidative stress

“…NO is the only endogenous source of brain nitrates and nitrites, since dietary nitrates and nitrites do not cross the blood brain barrier [37]. Increased NO levels, assessed by changes in total nitrite levels, have been observed in the perifornical lateral hypothalamus (PFLH) [38] the basal forebrain (BF), the frontal cortex (CC), but not the cingulate cortex [39] with sleep deprivation (SD). NO levels in the BF gradually increased during the first 3h of SD, while NO levels in the FC increased only after 5h of SD [39].…”

Control of Sleep and Wakefulness

“…Similarly, in vivo, the effects of NO donors on BF neurons were found to be dose-dependent, with lower doses favoring excitation and higher doses leading to more inhibition (662, 663). Similar mechanisms may also be active in the perifornical lateral hypothalamus (661). …”

Activation of the Ventrolateral Preoptic Neurons Projecting to the Perifornical-Hypothalamic Area Promotes Sleep: DREADD Activation in Wild-Type Rats

“…The details of the surgical procedures have been described previously [ 31 ]. Briefly, under surgical anesthesia (100 mg/Kg ketamine + 15 mg/Kg xylazine; maintenance with isoflurane) and under aseptic conditions, two holes (~1 mm diameter), one above the VLPO and another above the PF-HA, were drilled ipsilaterally into the skull.…”