Sleep–wake regulation and hypocretin–melatonin interaction in zebrafish

Center for Narcolepsy, Department of Psychiatry and Behavioral Sciences, Howard Hughes Medical Institute, Stanford University, Palo Alto, CA 94305, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2009; 106(51):21942-7. DOI: 10.1073/pnas.906637106
Source: PubMed


In mammals, hypocretin/orexin (HCRT) neuropeptides are important sleep-wake regulators and HCRT deficiency causes narcolepsy. In addition to fragmented wakefulness, narcoleptic mammals also display sleep fragmentation, a less understood phenotype recapitulated in the zebrafish HCRT receptor mutant (hcrtr-/-). We therefore used zebrafish to study the potential mediators of HCRT-mediated sleep consolidation. Similar to mammals, zebrafish HCRT neurons express vesicular glutamate transporters indicating conservation of the excitatory phenotype. Visualization of the entire HCRT circuit in zebrafish stably expressing hcrt:EGFP revealed parallels with established mammalian HCRT neuroanatomy, including projections to the pineal gland, where hcrtr mRNA is expressed. As pineal-produced melatonin is a major sleep-inducing hormone in zebrafish, we further studied how the HCRT and melatonin systems interact functionally. mRNA level of arylalkylamine-N-acetyltransferase (AANAT2), a key enzyme of melatonin synthesis, is reduced in hcrtr-/- pineal gland during the night. Moreover, HCRT perfusion of cultured zebrafish pineal glands induces melatonin release. Together these data indicate that HCRT can modulate melatonin production at night. Furthermore, hcrtr-/- fish are hypersensitive to melatonin, but not other hypnotic compounds. Subthreshold doses of melatonin increased the amount of sleep and consolidated sleep in hcrtr-/- fish, but not in the wild-type siblings. These results demonstrate the existence of a functional HCRT neurons-pineal gland circuit able to modulate melatonin production and sleep consolidation.

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    • "Automated methods have recently been developed in these species to track the position of individuals alone or in a group (Branson et al., 2009; Swierczek et al., 2011) and to categorize behavior (Dankert et al., 2009; Kabra et al., 2013). The zebrafish has emerged as an important vertebrate model organism for developmental biology, neurobiology, and human disease models, and is now used as a genetic model organism for the study of the mechanisms modulating complex behaviors in vertebrates such as depression and anxiety (Blaser et al., 2010; Lee et al., 2010; Cachat et al., 2011; Vermoesen et al., 2011; Zakhary et al., 2011; Ziv et al., 2013), sleep (Zhdanova et al., 2001; Appelbaum et al., 2009), or addiction (Petzold et al., 2009; Khor et al., 2011). The permeability, small size, genetic tractability , transparency, and low cost of zebrafish make them highly suitable for large-scale genetic and chemical screens (Driever et al., 1996; Granato et al., 1996; Haffter and Nusslein-Volhard, 1996). "

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    • "As such, OX innervations of other sleep-regulating brain nuclei are extensively studied. While it is well known that OX axons project throughout the dorsal spinal cord (Cutler et al., 1999; van den Pol, 1999; Appelbaum et al., 2009; de Lecea, 2010), the interaction of the central OX system with the peripheral nervous system (PNS) including the dorsal root ganglia (DRG) (Hervieu et al., 2001) has been less explored. Interestingly, several studies have shown that OXA and OR1 can modulate sensory and nociception processing (for review Chiou et al., 2010). "
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    ABSTRACT: Hypothalamic orexin/hypocretin neurons send long axonal projections through the dorsal spinal cord in lamina I-II of the dorsal horn (DH) at the interface with the peripheral nervous system (PNS). We show that in the DH OXA fibers colocalize with substance P (SP) positive afferents of dorsal root ganglia (DRG) neurons known to mediate sensory processing. Further, OR1 is expressed in p75(NTR) and SP positive DRG neurons, suggesting a potential signaling pathway between orexin and DRG neurons. Interestingly, DRG sensory neurons have a distinctive bifurcating axon where one branch innervates the periphery and the other one the spinal cord (pseudo-unipolar neurons), allowing for potential functional coupling of distinct targets. We observe that OR1 is transported selectively from DRG toward the spinal cord, while OXA is accumulated retrogradely toward the DRG. We hence report a rare situation of asymmetrical neuropeptide receptor distribution between axons projected by a single neuron. These molecular and cellular data are consistent with the role of OXA/OR1 in sensory processing, including DRG neuronal modulation, and support the potential existence of an OX/HCRT circuit between CNS and PNS.
    Frontiers in Neuroscience 02/2014; 8(8):20. DOI:10.3389/fnins.2014.00020 · 3.66 Impact Factor
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    • "All of these wake-active neurons form a circuit that maintains arousal (including cortical arousal in mammals) and, during REM, dis-facilitate motor neurons via activation of GABA-ergic interneurons (Siegel, 2000). Hypothalamic melatonin and neural peptides are highly conserved in zebrafish (Appelbaum et al., 2009; Berman et al., 2009). The transition to sleep may depend on the activation of GABA-ergic neurons in the ventrolateral preoptic area which inhibit all the wake-active monoamine-ergic and hypocretin cells (Saper et al., 2001). "
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    ABSTRACT: Zebrafish (Danio rerio) are used extensively in sleep research; both to further understanding of sleep in general and also as a model of human sleep. To date, sleep studies have been performed in larval and adult zebrafish but no efforts have been made to document the ontogeny of zebrafish sleep-wake cycles. Because sleep differs across phylogeny and ontogeny it is important to validate the use of zebrafish in elucidating the neural substrates of sleep. Here we describe the development of sleep and wake across the zebrafish lifespan and how it compares to humans. We find power-law distributions to best fit wake bout data but demonstrate that exponential distributions, previously used to describe sleep bout distributions, fail to adequately account for the data in either species. Regardless, the data reveal remarkable similarities in the ontogeny of sleep cycles in zebrafish and humans. Moreover, as seen in other organisms, zebrafish sleep levels are highest early in ontogeny and sleep and wake bouts gradually consolidate to form the adult sleep pattern. Finally, sleep percentage, bout duration, bout number, and sleep fragmentation are shown to allow for meaningful comparisons between zebrafish and human sleep.
    Frontiers in Neural Circuits 11/2013; 7:178. DOI:10.3389/fncir.2013.00178 · 3.60 Impact Factor
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