Arousal systems sleep-active neuron

Some arousal-related neurotransmitters, including noradrenaline, serotonin, and acetylcholine, feed back to inhibit POA sleep-active neurons. This aspect of the system has been reviewed previously (McGinty Szymusiak, 2000 Saper et al., 2001). Therefore, once sleep-active neurons are activated, arousal-related neurons are inhibited, and inhibitory control of sleep-active neurons by arousal systems is reduced. In this way, sleep onset is facilitated. That is, the mutually inhibitory systems can switch more quickly from wake to sleep, and back. These mutually inhibitory interactions also promote stability of both waking and sleep. 

Sleep-related VLPO neurons exhibit increased discharge within NREM during recovery sleep after deprivation, and their discharge rates were correlated with the amount of SWA within sleep episodes (Szymusiak et al., 1998). Thus, VLPO-type sleep-active neurons may directly control the SW content of the NREM EEG, presumably by suppressing arousal systems. 

Immunohistochemical and electrophysiological studies of the hypothalamic preoptic area (POA), which plays a major role in sleep promotion, have identified a subset of sleep-active ventrolateral POA (VLPO) neurons (Sherin et al. 1996 Szymusiak et al. 1998). A tightly clustered group of VLPO neurons appears to promote non-REM sleep, by suppression of the histaminergic arousal system, which... 

With this in mind, the search for molecular markers that define populations of neurons in areas important for arousal is clearly warranted. In this chapter we describe the identification of four peptidergic systems that modulate different aspects of the sleep-wakefulness cycle. The success of this strategy demonstrates the need for new markers of neuronal cell types, which may define populations of neurons critical for our understanding of cortical activity and sleep. 

---