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  • 1
    Electronic Resource
    Electronic Resource
    Extraocular photoreceptors can entrain the circadian oscillator in the eye ofAplysia (1974)
    Springer
    Journal of comparative physiology 89 (1974), S. 237-249 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The eye ofAplysia contains a circadian oscillator which can be entrained by cycles of white light (Jacklet, 1969b). Photoreceptors sufficient for entrainment of this oscillator reside within the eye itself (Eskin, 1971). We now report that extraocular photoreceptors can also entrain the ocular oscillator. Our evidence is: (1) Although the eye gives only a weak sensory response to red light (Fig. 2), red light cycles will entrain the ocular oscillator in an intactAplysia (Fig. 3). (2) Ocular entrainment by red light cycles, but not by white, requires that the optic nerve be intact (Fig. 4a, b); denervation of the eye allows the ocular oscillator to freerun in red light cycles (Fig. 4c). (3) The procedure of denervation does not prevent ocular entrainment by white light cycles in denervated eyes (Fig. 8). TheAplysia nervous system contains several circadian oscillators and several photoreceptors. Functional integrity of the organism requires that these elements be synchronized with one another. A neural, as opposed to hormonal, link is required for coupling the circadian oscillator in the eye to other neural sources of temporal information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696189
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  • 2
    Electronic Resource
    Electronic Resource
    Extraocular photoreceptors and oscillators can control the circadian rhythm of behavioral activity inAplysia (1973)
    Springer
    Journal of comparative physiology 84 (1973), S. 367-374 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The daily rhythm of behavioral activity inAplysia does not require the eyes as essential photoreceptors or essential driving oscillators; activity can be diurnal in lightcycles (Figs. 1, 2) and can freerun in constant darkness (Fig. 2) after the eyes have been surgically removed. The eyes, however, do play a role in modulating the activity rhythm; eye removal may change the temporal distribution of diurnal activity; reduce the punctuality of activity onsets, increase the amount of nocturnal activity, and decrease the total amount of activity (Fig. 1). These results, together with previously published ones, make it unlikely that a circadian oscillator known to reside in the eye and another one located in the abdominal ganglion are the sole sources of behavioral rhythmicity inAplysia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696349
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  • 3
    Electronic Resource
    Electronic Resource
    Cellular analysis of theBulla ocular circadian pacemaker system (1984)
    Springer
    Journal of comparative physiology 155 (1984), S. 379-385 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00610591
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  • 4
    Electronic Resource
    Electronic Resource
    Calcium channels mediate phase shifts of theBulla circadian pacemaker (1988)
    Springer
    Journal of comparative physiology 164 (1988), S. 195-206 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Light-induced phase advances of the activity rhythm of theBulla ocular circadian pacemaker are blocked when the extracellular calcium concentration is reduced with EGTA to 0.13 μM. Phase advances are also blocked in low calcium solutions without EGTA ([Ca]〈50 μM). 2. The dependence of light-induced phase delays on extracellular calcium concentration in EGTA-free seawater was determined. Phase delays are blocked at calcium concentrations below 400μ M, and reduced at concentrations of 1 mM and 3.5 mM (relative to shifts in normal ASW, [Ca] = 10 mM). Phase delays are also reduced and blocked at calcium concentrations higher than normal (60 mM and 110 mM, respectively). 3. Low calcium EGTA also blocked both phase delays and phase advances induced by pulses of depolarizing high K+ seawater. Low calcium EGTA pulses presented alone at the same times did not generate significant phase shifts. 4. The organic calcium channel antagonists verapamil, diltiazem and nitrendipine as well as the inorganic calcium channel antagonists La3+, Co2+, Cd2+, and Mn2+ were applied along with light pulses, however, the treated eyes were either phase shifted by these substances, or these substances were found to be toxic. 5. The inorganic calcium channel antagonist Ni2+ blocked both light-induced phase delays and advances at a concentration of 5 mM. Ni2+ applied alone did not generate significant phase shifts. Phase delays induced by high K+ seawater were blocked in the presence of 50 mM Ni2+ but not in 5 mM Ni2+. The light-induced CAP activity of the putative pacemaker cells was not inhibited by Ni2+, suggesting that its blocking action was probably via its known role as a calcium channel antagonist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00603950
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  • 5
    Electronic Resource
    Electronic Resource
    FMRFamide modulates the action of phase shifting agents on the ocular circadian pacemakers of Aplysia and Bulla (1992)
    Springer
    Journal of comparative physiology 170 (1992), S. 211-215 
    Details
    ISSN: 1432-1351
    Keywords: Modulation ; Mollusk ; Efferent ; Oscillator ; Retina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The eye of the marine mollusk Aplysia californica contains a photo-entrainable circadian pacemaker that drives an overt circadian rhythm of spontaneous compound action potentials in the optic nerve. Both light and serotonin are known to influence the phase of this ocular rhythm. The current study evaluated the effect of FMRFamide on both light and serotonin induced phase shifts of this rhythm. The application of FMRFamide was found to block serotonin induced phase shifts but, by itself, FMRFamide did not cause significant phase shifts. Furthermore, the effects of FMRFamide on light-induced phase shifts appeared to be phase dependent (i.e., the application of FMRFamide inhibited light-induced phase delays but actually enhanced the magnitude of phase advances). As in Aplysia, the eye of Bulla gouldiana also contains a circadian pacemaker. In Bulla, FMRFamide prevented light-induced phase advances and delays. Although FMRFamide alone generated phase dependent phase shifts, it did not cause phase shifts at the phases where it blocked the effects of light. These data demonstrate that FMRFamide can have pronounced modulatory effects on phase shifting inputs to the ocular pacemakers of both Aplysia and Bulla.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196903
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence that potassium channels mediate the effects of serotonin on the ocular circadian pacemaker of Aplysia (1992)
    Springer
    Journal of comparative physiology 171 (1992), S. 651-656 
    Details
    ISSN: 1432-1351
    Keywords: Aplysia ; barium ; circadian ; potassium channels ; serotonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The eye of the marine mollusk Aplysia californica contains a photo-entrainable circadian pacemaker that drives an overt circadian rhythm of spontaneous compound action potentials in the optic nerve. Serotonin is known to influence the phase of this ocular rhythm. The aim of the present study was to evaluate whether potassium channels are involved in effects on the ocular circadian rhythm. Our experimental approach was to study the effect of the potassium channel antagonist barium on serotonin-induced phase shifts of this rhythm. The application of barium was found to block serotonininduced phase shifts whereas barium alone did not cause significant phase shifts. The effects of barium were found to be dose dependent. In addition, barium blocked forskolin-induced phase advances but did not interfere with serotonin-induced increases in cAMP content. Finally, barium antagonized serotonin-induced suppression of compound action potential activity. These results are consistent with a model in which the application of serotonin phase shifts the ocular pacemaker by causing a membrane hyperpolarization which is mediated by a cAMP-dependent potassium conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194112
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  • 7
    Electronic Resource
    Electronic Resource
    Cellular analysis of theBulla ocular circadian pacemaker system (1984)
    Springer
    Journal of comparative physiology 155 (1984), S. 387-395 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00610592
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  • 8
    Electronic Resource
    Electronic Resource
    Cellular analysis of theBulla ocular circadian pacemaker system (1984)
    Springer
    Journal of comparative physiology 155 (1984), S. 365-378 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00610590
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  • 9
    Electronic Resource
    Electronic Resource
    TheBulla ocular circadian pacemaker (1987)
    Springer
    Journal of comparative physiology 161 (1987), S. 335-346 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00603959
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  • 10
    Electronic Resource
    Electronic Resource
    Circadian and light-induced conductance changes in putative pacemaker cells of Bulla gouldiana (1990)
    Springer
    Journal of comparative physiology 166 (1990), S. 589-595 
    Details
    ISSN: 1432-1351
    Keywords: Circadian rhythms ; Retinal rhythms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ocular circadian rhythm of compound action potential frequency in Bulla gouldiana is driven by rhythmic changes in the membrane potential of putative circadian pacemaker cells. Changes in the membrane potential of these neurons is required for light-induced phase shifts of the rhythm. We have tested the proposition that these changes in membrane potential reflect underlying changes in ionic conductances. We have found that: 1. Membrane conductance in the dark is highest during the subjective night when the cells are hyperpolarized, decreases as the cells depolarize spontaneously near projected dawn and is lowest during the subjective day. The changes in membrane potential and conductance follow a similar time course. 2. Long pulses of light delivered to eyes during their subjective night produce a characteristic response: There is initially a large, phasic depolarization accompanied by a burst of CAPs; this is followed by a repolarizing phase during which CAP activity is reduced to zero; and finally a tonic depolarization develops that is accompanied by a resumption of CAP activity at a steady rate. 3. During the subjective night, the tonic depolarization is accompanied by a decrease in conductance compared to the previous dark value. However, light pulses of similar duration delivered to eyes during their subjective day causes tonic depolarizations and increased CAP activity, but no measurable change in conductance. 4. Membrane responses to light are sensitive to agents that reduce Ca2+ flux. Light pulses during the subjective night produce a phasic depolarization, but the repolarization phase is eliminated in low Ca2+/EGTA seawater and is reduced in 5 mM Ni2+. The same treatments produce greater tonic depolarizations in response to light at night, and also block the light induced decrease in conductance. 5. These results suggest that a reduction in membrane conductance may underlie the observed membrane depolarizations at subjective dawn and in response to light at night; however, the causal relationship between these effects will require the identification of specific ion conductances that are regulated under these circumstances. Possible candidates include K+ and Cl− currents that are being reduced at dawn and in response to light. The channel is probably inactivated by Ca2+ which may enter during depolarization. The mechanisms that underlie the normal expression of rhythmicity in Bulla appear similar to those involved in the photic input pathway to the circadian pacemaker.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240008
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