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  • 1
    Keywords: Medicine ; Neurosciences ; Ophthalmology ; Neurobiology ; Biomedicine ; Neurosciences ; Ophthalmology ; Neurobiology ; Springer eBooks
    Description / Table of Contents: 1. Introduction -- 2. Fundamental Retinal Circuitry for Circadian Rhythms -- 3. Circadian photoreception: from phototransduction to behaviour -- 4. Role of Melatonin and Dopamine in the Regulation of Retinal Circadian Rhythms -- 5. Circadian Organization of the Vertebrate Retina -- 6. Rhythmicity of the Retinal Pigment Epithelium -- 7. Retinal Circadian Rhythms in Mammals Revealed Using Electroretinography -- 8. Circadian Clock and Light Induced Retinal Damage -- 9. Circadian Rhythms and Vision in Zebrafish -- 10. Circadian Modulation of the Limulus Eye for Day and Night Vision -- 11. Molluscan Ocular Pacemakers: Lessons Learned. ℗ ℗ ℗ ℗ ℗ ℗ ℗ ℗ ℗
    Abstract: The retina plays a critical role in the organization of the circadian system by synchronizing the braiń€™s central clock with the external day through transduction of the daily light/dark cycle.℗ However, the substantial variation in luminance imposed on the retina between day and night also poses a challenge to its role as a sensory tissue ́€“ how is it possible to faithfully encode the enormous dynamic range of luminance that can exceed 10 orders of magnitude? The Retina and Circadian Rhythms summarizes the knowledge accumulated over the last 30 years about the organization of the retinal circadian clock in many different species, concentrating on the roles that this circadian system plays in retinal function. About the Series: The Springer Series in Vision Research is a comprehensive update and overview of cutting edge vision research, exploring, in depth, current breakthroughs at a conceptual level. It details the whole visual system, from molecular processes to anatomy, physiology and behavior and covers both invertebrate and vertebrate organisms from terrestrial and aquatic habitats. Each book in the Series is aimed at all individuals with interests in vision including advanced graduate students, post-doctoral researchers, established vision scientists and clinical investigators.The series editors are N. Justin Marshall, Queensland Brain Institute, The University of Queensland, Australia and Shaun P. Collin, Neuroecology Group within the School of Animal Biology and the Oceans Institute at the University of Western Australia
    Pages: VIII, 238 p. 50 illus., 33 illus. in color. : online resource.
    ISBN: 9781461496137
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  • 2
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Neurons of the mammalian suprachiasmatic nucleus (SCN) generate self-sustained rhythms of action potential frequency having a period of approximately 24 h. It is generally believed that cell autonomous circadian oscillation of a network of biological clock genes drives the circadian rhythm in neuronal firing rate through as yet unspecified effects on the neuronal membrane. While it is clear that cyclic gene expression continues in constant darkness, previous studies have not examined which specific membrane properties of SCN neurons continue to oscillate in constant conditions. Here, we demonstrate that SCN neurons exhibit robust rhythms in resting membrane potential and input resistance in constant darkness. Furthermore, application of the K+ channel blocker tetraethylammonium revealed a rhythm in K+ current amplitude that persists in constant darkness and underlies the rhythm in membrane potential.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The isolatedBulla eye expresses a circadian rhythm in optic nerve impulse frequency. In an effort to learn more about the organization of theBulla retina and, specifically, about the organization of retinal elements involved in the circadian pacemaker system, we have recorded both intracellularly and extracellularly from retinal cells, as well as examined thick sections and scanning electron micrographs of the eye. We report that: 1. TheBulla retina contains approximately 1000 large photoreceptors with distinct villousbearing distal segments which form a layer around a solid lens. There is also a population of approximately 100 neurons which surround a neuropil at the base of the retina. 2. Electrical activity in the optic nerve consists of large compound action potentials and lower amplitude activity. Compound action potentials occur spontaneously in darkness and both types of optic nerve activities can be induced by light pulses. 3. Intracellular recording from the photoreceptor layer reveals four types of responses: (a) cells which depolarize in response to a light pulse and then transiently hyperpolarize before returning to resting levels, (b) cells which depolarize and then return to resting levels without a hyperpolarization, (c) spontaneously active cells which transiently hyperpolarize and then depolarize during a light pulse and (d) cells which depolarize upon illumination with the production of action potentials. 4. Intracellular recording from cells at the base of the retina reveals neurons which are spontaneously active and fire action potentials in exact synchrony with compound impulses in the optic nerve. These basal retinal neurons are electrically coupled to one another and are responsible for the compound optic nerve impulse. 5. We find that the most common type of photoreceptors (R-type) are electrically coupled to one another but we find no evidence that these photoreceptors make contact with basal retinal neurons. 6. Localized illumination of retinal layers with miniature light guides reveals that the photoreceptor layer is responsible for light-induced low amplitude optic nerve impulses. In constrast, the light-induced compound action potential response is generated by light sensitive neurons at the retinal base. 7. The photoreceptor layer exerts an inhibitory effect on basal retinal neurons. Illumination of the photoreceptor layer leads to a hyperpolarization in basal retinal neuron membrane potential. We think it is likely that this inhibition is mediated by a particular class of retinal cells, similar to H-type cells in theAplysia retina. 8. An explicit model for the organization of theBulla retina is proposed.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have used chronic, or long-term, intracellular recording combined with simultaneous extracellular recording of optic nerve activity to examine the neurophysiological basis of circadian rhythmicity in theBulla eye. We report that: 1. Continuous intracellular recordings from R-type photoreceptors were maintained for up to 28 h. These recordings reveal that in constant conditions R-type cells do not exhibit rhythms in membrane potential which correlate with the circadian rhythm in compound action potential frequency expressed by the eye. 2. Continuous intracellular recordings from basal retinal neurons were maintained for up to 74 h. These recordings reveal that in constant conditions basal retinal neurons exhibit clear circadian rhythms in membrane potential and action potential frequency which are synchronized with the circadian rhythm in compound action potential frequency. Action potentials in individual basal retinal neurons correlate one-for-one with the compound action potentials in the optic nerve over the entire circadian cycle. The basal retinal neurons depolarize during the active phase of the compound action potential rhythm (projected day), relative to their membrane potential during the inactive phase of the rhythm (projected night). 3. The phase relationship between the rhythm in basal retinal neuron membrane potential and action potential frequency is such that the rise in membrane potential from its most hyperpolarized point precedes, or is synchronous with, the increase in action potential frequency observed near projected dawn. This suggests that the membrane potential rhythm drives the circadian rhythm in impulse frequency. 4. The quantitative relationship between basal retinal neuron membrane potential and action potential frequency is not linear, and varies predictably with circadian phase. Following the interval of peak impulse frequency the rate of impulse production declines more rapidly than does the membrane potential. Also, the impulse frequency at a given membrane potential is lower during the falling phase of the circadian cycle than during the rising phase. 5. In conclusion, we find that the basal retinal neurons are at minimum a pacemaker output pathway, and are likely the circadian pacemaker itself. We find no role for the R-type photoreceptor in the generation of circadian rhythmicity by theBulla eye.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The isolatedBulla eye expresses a circadian rhythm in optic nerve impulse frequency. In an effort to determine the anatomical location of the circadian pacemaking system within the retina we surgically reduced the eye. We report that: 1. The approximately 1000 large photoreceptors which form a cell layer immediately surrounding the lens, are not required for the expression of a circadian rhythm. Eyes which are surgically reduced so that only the basal retinal neuron population remains, continue to express a circadian rhythm indistinguishable in period to intact eyes. 2. The photoreceptor layer is also not required for light-induced phase shifts of the ocular rhythm. Retinal fragments containing only basal retinal neurons can be phase advanced or delayed by 6 h light pulses provided at the appropriate circadian phase. 3. Of the approximately 100 basal retinal neurons in theBulla eye, only a small proportion are required for the expression of a circadian rhythm in optic nerve frequency. Ocular fragments with as few as 6 basal retinal neuron somata remain rhythmic, and exhibit a free-running period indistinguishable from intact eyes. 4. Intact basal retinal somata are required for the expression of a circadian rhythm in optic nerve impulse frequency. Retinal fragments consisting of an optic nerve with a small amount of neuropil region produce spontaneous action potentials without evidence for a circadian modulation. 5. An explicit model for the organization of the circadian pacemaker system in theBulla retina is proposed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 161 (1987), S. 335-346 
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In an effort to understand the cellular basis of entrainment of circadian oscillators we have studied the role of membrane potential changes in the neurons which comprise the ocular circadian pacemaker ofBulla gouldiana in mediating phase shifts of the ocular circadian rhythm. We report that: 1. Intracellular recording was used to measure directly the effects of the phase shifting agents light, serotonin, and 8-bromo-cAMP on the membrane potential of the basal retinal neurons. We found that light pulses evoke a transient depolarization followed by a smaller sustained depolarization. Application of serotonin produced a biphasic response; a transient depolarization followed by a sustained hyperpolarization. Application of a membrane permeable analog of the intracellular second messenger cAMP, 8-bromo-cAMP, elicited sustained hyperpolarization, and occasionally a weak phasic depolarization. 2. Changing the membrane potential of the basal retinal neurons directly and selectively with intracellularly injected current phase shifts the ocular circadian rhythm. Both depolarizing and hyperpolarizing current can shift the phase of the circadian oscillator. Depolarizing current mimics the phase shifting action of light, while hyperpolarizing current produces phase shifts which are transposed approximately 180° in circadian time to depolarization. 3. Altering BRN membrane potential with ionic treatments, depolarizing with elevated K+ seawater or hyperpolarizing with lowered Na+ seawater, produces phase shifts similar to current injection. 4. The light-induced depolarization of the basal retinal neurons is necessary for phase shifts by light. Suppressing the light-induced depolarization with injected current inhibits light-induced phase shifts. 5. The ability of membrane potential changes to shift oscillator phase is dependent on extracellular calcium. Reducing extracellular free Ca++ from 10 mM to 1.3×10−7 M inhibits light-induced phase shifts without blocking the photic response of the BRNs. The results indicate that changes in the membrane potential of the pacemaker neurons play a critical role in phase shifting the circadian rhythm, and imply that a voltage-dependent and calcium-dependent process, possibly Ca++ influx, shifts oscillator phase in response to light.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 161 (1987), S. 347-354 
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have used intracellular recording to directly measure the effects of three experimental agents, light, elevated potassium seawater, and lowered sodium seawater on the membrane potential of the putative circadian pacemaker neurons of theBulla eye. These agents were subsequently tested for effects on the free running period of the circadian pacemaker. We report that: 1. When applied to the eye, light and elevated potassium seawater depolarized the putative pacemaker neurons, while lowered sodium seawater hyperpolarized them. The membrane potential changes induced by these agents are sustained for at least one hour, suggesting that they produce persistent changes in the average membrane potential of the putative pacemaker neurons. 2. The amplitude of the membrane potential response to the depolarizing agents varies with the phase of the circadian cycle. Depolarizations induced by light and elevated potassium seawater are twice as large during the subjective night than they are during the subjective day. No significant difference was found in the response to lowered sodium seawater at different phases. 3. Continuous application of each of these agents caused a lengthening of the free running period of theBulla eye. Constant light increased the period by 0.9 h, while the other depolarizing treatment (elevated potassium seawater) increased the free running period by 0.6 h. Both treatments increased the mean peak impulse frequency of treated eyes. The hyperpolarizing treatment also increased the period of the ocular pacemaker (+0.8 h), but had little effect on peak impulse frequency. 4. Simultaneous chronic application of a depolarizing period lengthening treatment (constant light) and a hyperpolarizing period lengthening treatment (lowered sodium seawater) resulted in cancellation of their effects on freerunning period. 5. In conclusion, we find that continuous application of agents which change the membrane potential of the putative circadian pacemaker neurons lengthens the free running period of theBulla ocular circadian pacemaker. We have previously reported that transient changes in membrane potential shift the phase of theBulla ocular rhythm. Thus membrane potential can influence two fundamental properties of theBulla circadian oscillator suggesting that it is an important element of the circadian oscillator mechanism.
    Type of Medium: Electronic Resource
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