Bridging the gap: coupling single-cell oscillators in the suprachiasmatic nucleus. Nat Neurosci 8:10-12

Nature Neuroscience (Impact Factor: 16.1). 02/2005; 8(1):10-2. DOI: 10.1038/nn0105-10
Source: PubMed


Neurons in the mammalian master clock can maintain circadian rhythms in isolation, but must synchronize to function as a time-keeping system. A new study finds that gap junctions between neurons promote synchronous electrical activity and rhythmic behavior.

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Available from: Christopher S Colwell, Dec 12, 2013
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    • "In addition, nNOS knockout mice (which appear to be normally entrained to light) exhibit only moderate decreases in light-induced cFOS expression [22]. SCN neurons are single cell autonomous oscillators [23] capable of generating coherent circadian output [8] [9] [24] Among other mechanisms, neuropeptide signaling [25], Na + channelsmediated action potentials, gap junction-mediated processes [26] [27] [28] and GABAergic neurotransmission [29] [30] have been proposed to mediate cellular coupling in the SCN [27]. Two subdivisions are defined within the SCN: the VL region is located above the optic chiasm and is characterized by neurons that synthesize vasoactive intestinal polypeptide (VIP) and GRP, surrounded by the DM region which contains arginine–vasopressin and calretinin neurons [31] [32] [33]. "
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    ABSTRACT: Nocturnal light pulses induce phase shifts in circadian rhythms and activate cFos expression in the suprachiasmatic nuclei (SCN). We have studied the role of nitric oxide (NO) in the intercellular communication within the dorsal and ventral portions of the SCN in Syrian hamsters. Administration of the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide blocked photic phase advances in a dose-dependent manner and inhibited light-induced cFos-ir, without affecting light-induced circadian phase delays. These results suggest that NO may act as an intercellular messenger in the SCN, mediating light-induced phase advances.
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    ABSTRACT: Following certain patterns of electrical activity the strength of conventional chemical synapses in many areas of the mammalian brain can be subject to long-term modifications. Such modifications have been extensively characterised and are hypothesised to form the basis of learning and memory. A recent study in Science now shows that activity-dependent long-term modifications may also occur in the strength of mammalian electrical synapses. This raises the enticing possibility that electrical synapses might also contribute to neural plasticity and challenges the notion that in the mammalian CNS they are a simple mechanism for 'hardwiring' discrete neuronal populations.
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    ABSTRACT: Circadian rhythms are entrained daily by environmental photic and non-photic cues. The present review describes the anatomy and functional characteristics of the three major input pathways to the circadian clock mediating entrainment: the retino-hypothalamic tract, the geniculo-hypothalamic tract and the midbrain raphe projection.
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