Sites of major nuclei that regulate arousal and respiration. (a) A sagittal diagram of a human brain with cholinergic nuclei (green), monoaminergic nuclei (dark blue), GABAergic and galanergic nuclei (red), orexin nuclei (pink), and the respiratory nuclei (light blue). (b) Sites of major respiratory and motor relay nuclei in the pons and medulla. Abbreviations: 5HT, serotonin; ACh, acetylcholine; DA, dopamine; DRG, dorsal respiratory group; GABA, gamma aminobutyric acid; Gal, galanin; His, histamine; LC, locus coeruleus; LDT, laterodorsal tegmental area; LH, lateral hypothalamus; NE, norepinephrine; POA, preoptic area; PPT, pedunculopontine tegmental area; TMN, tuberomamillary nucleus; VAG, ventral periaquaductal gray; VRG, ventral respiratory group.