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thermal POA stimulation induced sleep (McGinty and Szymusiak, 2001). There is a population in the anterior hypothalamus that shows increased metabolic activities during sleep. Many sleep-promoting substances act in the POA. These neurons are concentrated in the ventrolateral POA (VLPO) and produce the inhibitory amino acid, γ-amino butyric acid (GABA), and the inhibitory neuropeptide, galanin. At sleep onset, these neurons become active and inhibit ascending arousal systems of the brain stem, posterior hypothalamus, and basal forebrain (Fig. 1). In addition, the numbers of c-Fos/GAD double-labeled neurons increased following sleep, compared with waking, in dorsal and lateral POA sites, as well as in the rostral median preoptic nucleus (MnPN) and VLPO (Szymusiak and McGinty, 2008; Suntsova et al., 2009). Sleep-active neurons were found throughout the lateral POA and in the adjacent basal forebrain. Therefore, most of the available evidence suggests that sleep-active neurons are distributed in the median, dorsal, and ventrolateral POA as well as in the adjacent basal forebrain (Szymusiak et al., 2001). Neurotransmitters/ neuromodulators responsible for maintaining wakefulness include norepinephrine (NE), dopamine (DA), serotonin (5HT), acetylcholine (ACh), excitatory amino acids, hypocretin (orexin), and histamine, while those responsible for inducing sleep are GABA, adenosine, glycine and melatonin (Mendelson, 2001; Monti and Jantos, 2004) (Table 1). There are descending pathways from the VLPO to neuronal populations Review Biomol Ther 19(3), 274-281 (2011) DOI: 10.4062/biomolther.2011.19.3.274 Copyright © 2011 The Korean Society of Applied Pharmacology *Corresponding Authors E-mail: [email protected] Tel: +82-43-261-2827, Fax: +82-43-261-2827 Received Apr 15, 2011 Revised Jul 4, 2011 Accepted Jul 4, 2011 pISSN: 1976-9148 eISSN: 2005-4483 Open Access www.biomolther.org