Tuesday, May 22, 2012

Waking and dreaming consciousness: Neurobiological and functional considerations

  • J.A. Hobsona
  • K.J. Fristonb,
  • a Division of Sleep Medicine, Harvard Medical School, Boston, MA 02215, USA
  • b The Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, Queen Square, London WC1N 3BG, United Kingdom


This paper presents a theoretical review of rapid eye movement sleep with a special focus on pontine-geniculate-occipital waves and what they might tell us about the functional anatomy of sleep and consciousness. In particular, we review established ideas about the nature and purpose of sleep in terms of protoconsciousness and free energy minimization. By combining these theoretical perspectives, we discover answers to some fundamental questions about sleep: for example, why is homeothermy suspended during sleep? Why is sleep necessary? Why are we not surprised by our dreams? What is the role of synaptic regression in sleep? The imperatives for sleep that emerge also allow us to speculate about the functional role of PGO waves and make some empirical predictions that can, in principle, be tested using recent advances in the modeling of electrophysiological data.

Tuesday, May 15, 2012

Basic sleep mechanisms: an integrative review.

Basic sleep mechanisms: an integrative review.:

Cent Nerv Syst Agents Med Chem. 2012 Mar 1;12(1):38-54
Authors: Murillo-Rodriguez E, Arias-Carrion O, Zavala-Garcia A, Sarro-Ramirez A, Huitron-Resendiz S, Arankowsky-Sandoval G

Regulation of the sleep-waking cycle is complex and involves diverse brain circuits and molecules. On one hand, an interplay among many neuroanatomical and neurochemical systems including acetylcholine, dopamine, noradrenaline, serotonin, histamine, and hypocretin has been shown to control the waking state. On the other hand the sleep-onset is governed by the activity of sleep-promoting neurons placed in the anterior hypothalamus that utilize GABA to inhibit wake-promoting regions. Moreover, brainstem regions inhibited during wakefulness (W) and slow wave sleeps (SWS) become active during rapid eye movement (REM) sleep. Further complexity has been introduced by the recognition of sleep-promoting molecules that accumulate in the brain in prolonged W as well as the physiological role of gene expression during sleep. The sleep-wake cycle is currently undergoing intense research with many new findings leading to new paradigms concerning sleep regulation, brain organization and sleep function. This review provides a broader understanding of our present knowledge in the field of sleep research.

PMID: 22524274 [PubMed - in process]

Fat incites tanycytes to neurogenesis

Fat incites tanycytes to neurogenesis

Nature Neuroscience 15, 651 (2012). doi:10.1038/nn.3091

Authors: Marcelo O Dietrich & Tamas L Horvath

Tanycytes in the hypothalamic median eminence have now been found to form a metabolically sensitive neurogenic niche in the brain. In adult mice, tanycytes give rise to hypothalamic regulatory neurons in response to a high-fat diet.

via Nature Neuroscience - Issue - nature.com science feeds http://www.nature.com/neuro/journal/v15/n5/full/nn.3091.html

The wake-promoting effects of hypocretin-1 are attenuated in old rats.

The wake-promoting effects of hypocretin-1 are attenuated in old rats.

Neurobiol Aging. 2011 Aug;32(8):1514-27

Authors: Morairty SR, Wisor J, Silveira K, Sinko W, Kilduff TS


Disruption of sleep is a frequent complaint among elderly humans and is also evident in aged laboratory rodents. The neurobiological bases of age-related sleep/wake disruption are unknown. Given the critical role of the hypocretins in sleep/wake regulation, we sought to determine whether the wake-promoting effect of hypocretin changes with age in Wistar rats, a strain in which age-related changes in both sleep and hypocretin signaling have been reported. Intracerebroventricular infusions of hypocretin-1 (10 and 30 μg) significantly increased wake time relative to vehicle in both young (3 mos) and old (25 mos) Wistar rats. However, the magnitude and duration of the wake-promoting effects were attenuated with age. An increase of parameters associated with homeostatic sleep recovery after sleep deprivation, including non-rapid eye movement (NR) sleep time, NR delta power, the ratio of NR to rapid eye movement (REM) sleep, and NR consolidation, occurred subsequent to Hcrt-induced waking in young but not old rats. ICV infusions of hypocretin-2 (10 and 30 μg) produced fewer effects in both young and old rats. These data demonstrate that activation of a major sleep/wake regulatory pathway is attenuated in old rats.

PMID: 19781813 [PubMed - indexed for MEDLINE]

via pubmed: sleep metabolism http://www.ncbi.nlm.nih.gov/sites/entrez

Thursday, May 10, 2012

Wake, sleep and ghrelin

Impaired wake-promoting mechanisms in ghrelin receptor-deficient mice.:
Eur J Neurosci. 2012 Jan;35(2):233-43
Authors: Esposito M, Pellinen J, Kapás L, Szentirmai É

Ghrelin receptors are expressed by key components of the arousal system. Exogenous ghrelin induces behavioral activation, promotes wakefulness and stimulates eating. We hypothesized that ghrelin-sensitive mechanisms play a role in the arousal system. To test this, we investigated the responsiveness of ghrelin receptor knockout (KO) mice to two natural wake-promoting stimuli. Additionally, we assessed the integrity of their homeostatic sleep-promoting system using sleep deprivation. There was no significant difference in the spontaneous sleep-wake activity between ghrelin receptor KO and wild-type (WT) mice. WT mice mounted robust arousal responses to a novel environment and food deprivation. Wakefulness increased for 6 h after cage change accompanied by increases in body temperature and locomotor activity. Ghrelin receptor KO mice completely lacked the wake and body temperature responses to new environment. When subjected to 48 h food deprivation, WT mice showed marked increases in their waking time during the dark periods of both days. Ghrelin receptor KO mice failed to mount an arousal response on the first night and wake increases were attenuated on the second day. The responsiveness to sleep deprivation did not differ between the two genotypes. These results indicate that the ghrelin-receptive mechanisms play an essential role in the function of the arousal system but not in homeostatic sleep-promoting mechanisms.

PMID: 22211783 [PubMed - indexed for MEDLINE]