title: Single unit activity of the suprachiasmatic nucleus and surrounding neurons during the wake-sleep cycle in mice.
abstract: The suprachiasmatic nucleus (SCN) of the mammalian hypothalamus contains a circadian clock for timing of diverse neuronal, endocrine, and behavioral rhythms, such as the cycle of sleep and wakefulness. Using extracellular single unit recordings, we have determined, for the first time, the discharge activity of individual SCN neurons during the complete wake-sleep cycle in non-anesthetized, head restrained mice. SCN neurons (n=79) were divided into three types according to their regular (type I; n=38) or irregular (type II; n=19) discharge activity throughout the wake-sleep cycle or their quiescent activity during waking and irregular discharge activity during sleep (type III; n=22). The type I and II neurons displayed a long-duration action potential, while the type III neurons displayed either a short-duration or long-duration action potential. The type I neurons discharged exclusively as single isolated spikes, whereas the type II and III neurons fired as single isolated spikes, clusters, or bursts. The type I and II neurons showed wake-active, wake/paradoxical (or rapid eye movement) sleep-active, or state-unrelated activity profiles and were, respectively, mainly located in the ventral or dorsal region of the SCN. In contrast, the type III neurons displayed sleep-active discharge profiles and were mainly located in the lateral region of the SCN. The majority of type I and II neurons tested showed an increase in discharge rate following application of light to the animal's eyes. Of the 289 extra-SCN neurons recorded, those displaying sleep-active discharge profiles were mainly located dorsal to the SCN, whereas those displaying wake-active discharge profiles were mainly located lateral or dorsolateral to the SCN. This study shows heterogeneity of mouse SCN and surrounding anterior hypothalamic neurons and suggests differences in their topographic organization and roles in mammalian circadian rhythms and the regulation of sleep and wakefulness.
authors.affiliation: Integrative Physiology of the Brain Arousal System, Lyon Neuroscience Research Center, INSERM U1028-CNRS UMR5292, School of Medicine, Claude Bernard University Lyon 1, F-69373 Lyon, France. Electronic address: sakai@univ-lyon1.fr.
authors.forename: K
authors.initials: K
authors.lastname: Sakai
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*
keywords: 3,3′-diaminobenzidine; AHA; AHPs; AVP; AW; CV; D; DAB; EEG; EMG; GABA; GAD; IMF; LA; MF; MPO; Nb; PB; PBST; PS; PSt; QW; S1 and S2; SCN; SD; SEM; SPZ; SWS; VIP; W; active waking; after-hyperpolarization; anterior hypothalamic area; arginine vasopressin; coefficient of variation of the spike interval; drowsy state; electroencephalogram; electromyogram; functional heterogeneity; gamma-aminobutyric acid; glutamate decarboxylase; instantaneous mean frequency; lateroanterior hypothalamic nucleus; light and deep slow-wave sleep, respectively; mean frequency; medial preoptic nucleus; neurobiotin; paradoxical sleep; phosphate buffer; phosphate-buffered saline containing 0.3% Triton X-100; quiet waking; single unit recording; slow-wave sleep; standard deviation; standard error of the mean; subparaventricular zone; suprachiasmatic nucleus; topographic organization; transition period from slow-wave sleep to PS; vasoactive intestinal peptide; wake/sleep cycle; wakefulness