14 The role of the dopaminergic system is less well established; however, recent studies indicated that lesions of wake-active dopaminergic cells in the ventral periaqueductal gray reduce waking15 and that dopamine D1 D2, and D3 receptor agonists increase waking and reduce REM and NREM sleep.16-18 Orexin (also known as hypocretin) neurons located Inhibitors,research,lifescience,medical in the perifornical region of the lateral hypothalamus seem to play a particularly important role in selleck chemical arousal since they project not only over the entire isocortex, but also to additional arousal systems,
including the aforementioned monoaminergic and cholinergic systems.19,20 The role of orexin in arousal regulation is further exemplified with narcolepsy, a sleep disorder characterized by excessive daytime sleepiness and deficiency of the orexin system.21-23 Figure 1 Simplified representation of the various structures implicated in arousal mechanisms and their interrelationships. Light-blue boxes, activated structures; blue boxes, deactivated structures; light-blue arrows, excitatory Inhibitors,research,lifescience,medical influences; blue arrows, Inhibitors,research,lifescience,medical inhibitory … An NREM-promoting system has been evidenced in the hypothalamus (Figure 2), Electrophysiological recordings have identified GABAergic (GABA, γ-aminobutyricacid)
SWS-active neurons in a specific area, the ventrolateral preoptic nucleus (VLPO), where lesions produce insomnia in animals and humans.24 These cells also contain Inhibitors,research,lifescience,medical galanin and project to all monoaminergic systems, inhibiting activity during NREM sleep, and receive inputs from multiple brain systems that regulate arousal and autonomic and circadian functions.25 Recent research implicates adenosine in the homeostatic regulation of sleep via actions on the VLPO and
other sleep regulatory regions Inhibitors,research,lifescience,medical such as the basal forebrain.26 Adenosine functions as a natural sleeppromoting agent, accumulating during period of sustained wakefulness and decreasing during sleep; It has been shown to promote SWS through direct inhibitory effects on cholinergic neurons of the basal forebrain26 and have indirect stimulatory effects on the VLPO.27,28 to A further inhibition of wake-promoting mechanism could occur through orexinergic neurons, since a study identified Gi protein-coupled adenosine A1 receptors on this group of neurons.29 Figure 2 Simplified representation of various structures implicated in non-rapid eye movement (NREM) mechanisms and their interrelationships. Light-blue boxes, activated structures; blue boxes, deactivated structures; light-blue arrows, excitatory influences; … Regarding the circadian influence on the sleep-wake rhythm, recent studies suggested that the SCN regulates sleep-wake mechanisms through the dorsomedial hypothalamus, a key output nucleus of the SCN that inhibits VLPO and stimulates orexin-containing neurons in the lateral hypothalamus.