cut-loading-useful-tool-for-examining-extent-gap-junction-tracer

Cut-loading: A Useful Tool for Examining the Extent of Gap Junction Tracer Coupling Between Retinal Neurons

In addition to chemical synaptic transmission, neurons that are connected by gap junctions can also communicate rapidly via electrical synaptic ...

Zinc is strikingly co-localized with glutamate-containing vesicles in the synaptic terminals of retinal photoreceptors, and it is thought to be co-released with glutamate onto postsynaptic neurons such as horizontal cells and bipolar cells. Here we examined exogenous zinc modulation of glutamate receptors on cultured retinal horizontal cells using patch-clamp recording and endogenous zinc effect on intact horizontal cells using intracellular recording techniques. Application of 3, 30, and 300 microM zinc reduced the whole cell peak current of response to 200 microM glutamate by 2, 30, and 56%, respectively. Zinc suppression of glutamate response persisted in the presence of 10 microM cyclothiazide (CTZ). Glutamate responses of outside-out patches were completely abolished by 30 microM 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466), and the receptor desensitization was blocked by 30 microM CTZ, indicating that receptor target for the zinc action on horizontal cells is alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproponic acid (AMPA) receptors. Zinc decreased the amplitude of outside-out patch peak current without an effect on either its 10-90% rise time or the rate of receptor desensitization. Dose-response curves for glutamate show that zinc reduced the maximal current evoked by glutamate and increased EC(50) from 50 +/- 3 to 70 +/- 6 microM without changing the Hill coefficient. Chelation of endogenous zinc with 1 mM Ca-EDTA depolarized horizontal cells in the intact retina by 3 mV, consistent with relief of the partial glutamate receptor inhibition by zinc. Overall, the results describe a unimodal form of zinc modulation of AMPA-type glutamate receptor responses not previously described in native neuronal preparations and a novel role for endogenous zinc in modulating neurotransmission.

Suppression by zinc of AMPA receptor-mediated synaptic transmission in the retina.

Die Unterdr&#xFC;ckung von Zink von AMPA-Rezeptor-vermittelten synaptischen Transmission in der Netzhaut.

A circadian (24-hour) clock regulates the light responses of fish cone horizontal cells, second order neurones in the retina that receive synaptic contact from cones and not from rods. Due to the action of the clock, cone horizontal cells are driven by cones in the day, but primarily driven by rods at night. We show here that dopamine, a retinal neurotransmitter, acts as a clock signal for the day by increasing cone input and decreasing rod input to cone horizontal cells. The amount of endogenous dopamine released from in vitro retinae was greater during the subjective day than the subjective night. Application of dopamine or quinpirole, a dopamine D(2)-like agonist, during the subjective night increased cone input and eliminated rod input to the cells, a state usually observed during the subjective day. In contrast, application of spiperone, a D(2)-like antagonist, or forskolin, an activator of adenylyl cyclase, during the subjective day reduced cone input and increased rod input. SCH23390, a D(1) antagonist, had no effect. Application of R(p)-cAMPS, an inhibitor of cAMP-dependent protein kinase, or octanol, an alcohol that uncouples gap junctions, during the night increased cone input and decreased rod input. Because D(2)-like receptors are on photoreceptor cells, but not horizontal cells, the results suggest that the clock-induced increase in dopamine release during the day activates D(2)-like receptors on photoreceptor cells. The resultant decrease in intracellular cyclic AMP and protein kinase A activation then mediates the increase in cone input and decrease in rod input.

Dopamine mediates circadian clock regulation of rod and cone input to fish retinal horizontal cells.

Dopamin vermittelt circadianen Uhr Regulation der St&#xE4;bchen und Zapfen der Netzhaut Eingang horizontale Zellen angeln.

Although many biochemical, morphological and physiological processes in the vertebrate retina are controlled by a circadian (24 h) clock, the location of the clock and how the clock alters retinal function are unclear. For instance, several observations have suggested that dopamine, a retinal neuromodulator, may play an important role in retinal rhythmicity but the link between dopamine and a clock located within or outside the retina remains to be established. We found that endogenous dopamine release from isolated goldfish retinae cultured in continuous darkness for 56 h clearly exhibited a circadian rhythm with high values during the subjective day. The continuous presence of melatonin (1 nM) in the culture medium abolished the circadian rhythm of dopamine release and kept values constantly low and equal to the night-time values. The selective melatonin antagonist luzindole (1 microM) also abolished the dopamine rhythm but the values were high and equal to the daytime values. Melatonin application during the late subjective day introduced rod input and reduced cone input to fish cone horizontal cells, a state usually observed during the subjective night. In contrast, luzindole application during the subjective night decreased rod input and increased cone input. Prior application of dopamine or spiperone, a selective dopamine D(2)-like antagonist, blocked the above effects of melatonin and luzindole, respectively. These findings indicate that a circadian clock in the vertebrate retina regulates dopamine release by the activation of melatonin receptors and that endogenous melatonin modulates rod and cone pathways through dopamine-mediated D(2)-like receptor activation.

A circadian clock in the fish retina regulates dopamine release via activation of melatonin receptors.

Eine innere Uhr im Fisch Netzhaut regelt die Freisetzung von Dopamin &#xFC;ber die Aktivierung von Melatonin-Rezeptoren.

The ability of directionally selective (DS) retinal ganglion cells to respond selectively to stimulus motion in one direction is a classic unresolved example of computation in a local neural circuit. Recent evidence indicates that DS responses occur first in the retina in the dendrites of starburst amacrine cells (interneurons presynaptic to the ganglion cells). We report that the directional responses of starburst-cell dendrites and DS ganglion cells are highly sensitive to the polarity of the transmembrane chloride gradient. Reducing the transmembrane chloride gradient by ion substitution or by blocking the K-Cl cotransporter resulted in the starburst cells responding equally to light moving in opposite directions. Conversely, increasing the chloride gradient by blocking the Na-K-Cl cotransporter eliminated responses to light moving in either direction. Moreover, in each case, blocking the chloride cotransporters or reducing the transmembrane chloride gradient eliminated the directional responses of DS ganglion cells in a manner opposite that of the starburst cells. These results indicate that chloride cotransporters play a key role in the generation of direction selectivity and that the directional responses of starburst cells and DS ganglion cells are exquisitely sensitive to the chloride equilibrium potential. The findings further suggest that the directional responses of DS ganglion cells are mediated in part by the directional release of gamma-aminobutyric acid from starburst dendrites and that the asymmetric distribution of the two cotransporters along starburst-cell dendrites mediates direction selectivity. A model of direction selectivity in the retina that incorporates these and other findings is discussed.

Cation--chloride cotransporters mediate neural computation in the retina.

Kationen - Chlorid Cotransporter vermitteln Neural Computation in der Netzhaut.

The extracellular pH of living tissue in the retina and elsewhere in the brain is lower than the pH of the surrounding milieu. We have shown that the pH gradient between the in vitro retina and the superfusion solution is regulated by a circadian (24-h) clock so that it is smaller in the subjective day than in the subjective night. We show here that the circadian changes in retinal pH result from a clock-mediated change in the generation of H+ that accompanies energy production. To demonstrate this, we suppressed energy metabolism and recorded the resultant reduction in the pH difference between the retina and superfusate. The magnitude of the reduction in the pH gradient correlated with the extent of energy metabolism suppression. We also examined whether the circadian-induced increase in acid production during the subjective night results from an increase in energy metabolism or from the selective activation of glycolysis compared with oxidative phosphorylation. We found that the selective suppression of either oxidative phosphorylation or glycolysis had almost identical effects on the dynamics and extent of H+ production during the subjective day and night. Thus the proportion of glycolysis and oxidative phosphorylation is maintained the same regardless of circadian time, and the pH difference between the tissue and superfusion solution can therefore be used to evaluate total energy production. We conclude that circadian clock regulation of retinal pH reflects circadian regulation of retinal energy metabolism.

Retinal pH reflects retinal energy metabolism in the day and night.

Retinal pH-Wert spiegelt retinalen Energiestoffwechsels in der Tag und Nacht.

Although the purine adenosine acts as an extracellular neuromodulator in the mammalian CNS in both normal and pathological conditions and regulates sleep, the regulation of extracellular adenosine in the day and night is incompletely understood. To determine how extracellular adenosine is regulated, rabbit neural retinas were maintained by superfusion at different times of the regular light/dark and circadian cycles. The adenosine level in the superfusate, representing adenosine overflow from the retinas, and the adenosine level in retinal homogenates, representing adenosine content, were measured using HPLC with fluorescence detection in the absence or presence of blockers of adenosine transport and/or extracellular adenosine synthesis. We report that darkness, compared with illumination, increases the level of extracellular adenosine, and that a circadian clock also increases extracellular adenosine at night. In addition, we show that the darkness-evoked increase in the level of extracellular adenosine results primarily from an increase in the conversion of extracellular ATP into adenosine, but that the clock-induced increase at night results primarily from an increase in the accumulation of intracellular adenosine. We also show that a slightly hypoxic state increases adenosine content and overflow to an extent similar to that of the clock. Our findings demonstrate that the extracellular level of adenosine in the mammalian retina is differentially regulated by a circadian clock and the lighting conditions and is maximal at night under dark-adapted conditions. We conclude that adenosine is a neuromodulator involved in both circadian clock and dark-adaptive processes in the vertebrate retina.

A circadian clock and light/dark adaptation differentially regulate adenosine in the mammalian retina.

Eine innere Uhr und Hell / Dunkel-Anpassung der unterschiedlichen Regulierbarkeit in der S&#xE4;uger-Retina Adenosin.

One of the fundamental principles of neuroscience is that direct electrical interactions between neurons are not possible without specialized electrical contacts, gap junctions, because the transmembrane resistance of neurons is typically much higher than the resistance of the adjacent extracellular space. However it has been proposed that in the retina direct electrical interactions between cones and second-order neurons occur due to the specific morphology of the cone synaptic terminal. This electrical mechanism could potentially explain the phenomenon of "negative feedback" from horizontal cells to cones and the recent finding that the tips of horizontal cell dendrites contain hemichannels has rekindled interest in the idea. We quantitatively evaluated the possibility that hemichannels and/or glutamate channels mediate electrical feedback from horizontal cells to cones. The calculations show that it is unlikely that an electrical mechanism plays a significant functional role because 1) the necessity of preserving adequate cone-to-horizontal-cell synaptic transmission limits the extracellular space resistance and the horizontal-cell dendritic transmembrane resistances to values at which the effectiveness of electrical feedback is very low and its electrical effect on the cone presynaptic membrane is negligible, 2) electrical feedback is most effective in the dark and weaker during light adaptation, which contradicts the experimental data, and 3) electrical negative feedback is associated with much stronger electrical positive feedback from horizontal cells to cones, a phenomenon that has never been reported. Therefore it is likely that negative feedback from horizontal cells to cones is chemical in nature.

Electrical feedback in the cone pedicle: a computational analysis.

Die Grundprinzipien der Neurowissenschaft geh&ouml;rt, dass direkte elektrische Interaktionen zwischen Neuronen nicht ohne spezielle elektrische Kontakte, Gap Junctions, m&ouml;glich sind, weil der transmembrane Widerstand der Neuronen in der Regel viel h&ouml;her als der Widerstand des angrenzenden extrazellul&auml;ren Raumes ist. Jedoch wurde es vorgeschlagen, dass in der Netzhaut direkte elektrische Wechselwirkungen zwischen Zapfen und zweiter Ordnung Neuronen durch bestimmte Morphologie der Kegel synaptische Terminal auftreten. Dieser elektrischen Mechanismus k&ouml;nnte potenziell erkl&auml;ren das Ph&auml;nomen der &quot;Negative R&uuml;ckkopplung&quot; aus horizontalen Zellen Zapfen und die j&uuml;ngste Feststellung, dass die Spitzen der horizontalen Zelle Dendriten Hemichannels enthalten hat Interesse an der Idee neu entfacht. In quantitativer wir die M&ouml;glichkeit, dass Hemichannels und/oder Glutamat Kan&auml;le elektrischen R&uuml;ckf&uuml;hrung aus horizontalen Zellen zu Zapfen vermitteln. Die Berechnungen zeigen, dass es unwahrscheinlich ist, dass ein elektrischer Mechanismus eine wichtige funktionelle Rolle spielt, da 1) die Notwendigkeit der Erhaltung ausreichend Kegel-zu-Horizontal-Zelle synaptischen &Uuml;bertragung beschr&auml;nkt den extrazellul&auml;ren Raum-Widerstand und die Horizontal-Zelle dendritische Transmembran-Widerst&auml;nde auf Werte, bei dem die Wirksamkeit elektrischer R&uuml;ckf&uuml;hrung ist sehr gering und seine elektrische Wirkung auf die Kegel pr&auml;synaptischen Membran ist vernachl&auml;ssigbar, 2) elektrischer R&uuml;ckf&uuml;hrung ist effektivste im Dunkeln und schw&auml;cheren w&auml;hrend Licht Anpassungdem widerspricht die Versuchsdaten und 3) Elektrische negatives Feedback ist verbunden mit viel st&auml;rkere elektrische positives Feedback aus horizontalen Zellen zu Zapfen, ein Ph&auml;nomen, das noch nie vermeldet wurde. Daher ist es wahrscheinlich, dass negative Feedback von horizontalen Zellen zu Zapfen chemische Natur ist.

Elektrischer R&uuml;ckf&uuml;hrung in die Kegel-Pedikelschrauben: a computational Analysis.

The mechanisms in the retina that generate light responses selective for the direction of image motion remain unresolved. Recent evidence indicates that directionally selective light responses occur first in the retina in the dendrites of an interneuron, i.e., the starburst amacrine cell, and that these responses are highly sensitive to the activity of Na-K-2Cl (NKCC) and K-Cl (KCC), two types of chloride cotransporter that determine whether the neurotransmitter GABA depolarizes or hyperpolarizes neurons, respectively. We show here that selective blockade of the NKCC2 and KCC2 cotransporters located on starburst dendrites consistently hyperpolarized and depolarized the starburst cells, respectively, and greatly reduced or eliminated their directionally selective light responses. By mapping NKCC2 and KCC2 antibody staining on these dendrites, we further show that NKCC2 and KCC2 are preferentially located in the proximal and distal dendritic compartments, respectively. Finally, measurements of the GABA reversal potential in different starburst dendritic compartments indicate that the GABA reversal potential at the distal dendrite is more hyperpolarized than at the proximal dendrite due to KCC2 activity. These results thus demonstrate that the differential distribution of NKCC2 on the proximal dendrites and KCC2 on the distal dendrites of starburst cells results in a GABA-evoked depolarization and hyperpolarization at the NKCC2 and KCC2 compartments, respectively, and underlies the directionally selective light responses of the dendrites. The functional compartmentalization of interneuron dendrites may be an important means by which the nervous system encodes complex information at the subcellular level.

Dendritic compartmentalization of chloride cotransporters underlies directional responses of starburst amacrine cells in retina.

Die Mechanismen in der Netzhaut, die selektiv f&uuml;r die Bewegungsrichtung Bild leichte Antworten generieren bleiben ungel&ouml;st. Neuere Beweise gibt, dass Richtungen selektive leichte Reaktionen auftreten, zun&auml;chst in der Netzhaut in die Dendriten der ein Interneuron, d. h. die Sternenexplosion Amacrine Zelle, und diese Antworten sind sehr empfindlich auf die Aktivit&auml;t der Na-K - 2 Cl (NKCC) und K-Cl (KCC), zwei Arten von Chlorid-Kotransporter, die bestimmen, ob der Neurotransmitter GABA depolarizes oder Neuronen, bzw. hyperpolarizes. Hier zeigen wir, dass selektive Blockade der NKCC2 und KCC2 Cotransporters am Sternenexplosion Dendriten konsequent hyperpolarized und ersch&uuml;tterten die Sternenexplosion Zellen, beziehungsweise, und stark reduziert oder ihre Richtungen selektiven leichten Reaktionen eliminiert. Durch die Zuordnung NKCC2 und KCC2 Antik&ouml;rper F&auml;rbung auf diese Dendriten zeigen wir weiter, dass NKCC2 und KCC2 bevorzugt in den proximalen und distalen dendritische F&auml;cher, bzw. befinden. Messungen der GABA Umkehrung Potenzial in verschiedenen Sternenexplosion dendritische F&auml;cher zufolge schlie&szlig;lich die GABA-Umlenkung potential an der distalen Dendrit mehr hyperpolarized als an der proximalen Dendrit durch KCC2-Aktivit&auml;t ist. Diese Ergebnisse zeigen damit, dass die unterschiedlichen Verteilung der NKCC2 auf dem proximalen Dendriten und KCC2 auf die distalen Dendriten der Sternenexplosion GABA hervorgerufen Depolarisation und Hyperpolarisation an die NKCC2 und KCC2-F&auml;cher bzw. Zellen und zugrunde die Richtungen selektiven leichten Reaktionen &uuml;ber die Dendriten liegt. Die funktionale Aufteilung der Interneuron Dendriten m&ouml;glicherweise ein wichtiges Mittel, mit denen das Nervensystem komplexen Informationen auf der subzellul&auml;ren Ebene codiert.

Dendritische Untergliederung der Chlorid-Cotransporters zugrunde gerichtete Reaktionen der Sternenexplosion Amacrine Zellen in der Netzhaut.

Horizontal cells are second order neurons that receive direct synaptic input from photoreceptors. In teleosts horizontal cells can be divided into two categories, cone-connected and rod-connected. Although the anatomy and physiology of fish cone horizontal cells have been extensively investigated, less is known about rod horizontal cells. This study was undertaken to determine whether light and/or the circadian clock regulate gap junctional coupling between goldfish rod horizontal cells. We used fine-tipped, microelectrode intracellular recording to monitor rod horizontal cells under various visual stimulation conditions, and tracer (biocytin) iontophoresis to visualize their morphology and evaluate the extent of coupling. Under dark-adapted conditions, rod horizontal cells were extensively coupled to cells of like-type (homologous coupling) with an average of approximately 120 cells coupled. Under these conditions, no differences were observed between day, night, the subjective day, and subjective night. In addition, under dark-adapted conditions, application of the dopamine D2-like agonist quinpirole (1 microM), the D2-like antagonist spiperone (10 microM), or the D1-like antagonist SCH23390 (10 microM) had no effect on rod horizontal cell tracer coupling. In contrast, the extent of tracer coupling was reduced by approximately 90% following repetitive light (photopic range) stimulation of the retina or application of the D1-agonist SKF38393 (10 microM) during the subjective day and night. We conclude that similarly to cone horizontal cells, rod horizontal cells are extensively coupled to one another in darkness and that the extent of coupling is dramatically reduced by bright light stimulation or dopamine D1-receptor activation. However, in contrast to cone horizontal cells whose light responses are under the control of the retinal clock, the light responses of rod horizontal cells under dark-adapted conditions were similar during the day, night, subjective day, and subjective night thus demonstrating that they are not under the influence of the circadian clock.

Tracer coupling between fish rod horizontal cells: modulation by light and dopamine but not the retinal circadian clock.

Horizontale Zellen sind zweite Bestellung-Neuronen, die synaptische Direkteingabe von Photorezeptoren erhalten. In Teleosts k&ouml;nnen horizontale Zellen in zwei Kategorien unterteilt, Kegel-angeschlossen und Stab-angeschlossen werden. Obwohl die Anatomie und Physiologie der Fische horizontale Kone Zellen wurde ausgiebig untersucht, weniger &uuml;ber Stab horizontale Zellen bekannt ist. Diese Studie wurde durchgef&uuml;hrt, um festzustellen, ob Licht- und/oder die circadian Clock L&uuml;cke junktionale Kupplung zwischen Goldfisch Stab horizontale Zellen regulieren. Wir verwendeten fein-Kreiss&auml;gebl&auml;tter, Mikroelektroden intrazellul&auml;re Aufnahme horizontaler Stab zu &uuml;berwachen Zellen unter verschiedenen Bedingungen visuelle Stimulation und Tracer (Biocytin) Iontophorese zum Visualisieren ihre Morphologie und bewerten das Ausma&szlig; der Kupplung. Unter dark-adapted Bedingungen waren Stab horizontale Zellen ausgiebig mit einem Durchschnitt von ca. 120 Zellen gekoppelt mit Zellen wie Typ (homologe Kopplung) gekuppelt. Unter diesen Bedingungen wurden keine Unterschiede zwischen Tag, Nacht, die subjektive Tag und subjektiven Nacht beobachtet. Dar&uuml;ber hinaus unter dark-adapted Bedingungen, Anwendung von Dopamin-D2-artigen Agonist-Quinpirol (1 MicroM), der D2-artigen Antagonist Spiperone (10 MicroM) oder den D1-artige Antagonisten SCH23390 (10 MicroM) hatte keine Auswirkung auf die Stange horizontale Zelle Tracer Kupplung. Im Gegensatz dazu wurde das Ausma&szlig; des Tracers Kupplung um ca. 90 % nach wiederkehrenden Licht (Photopische Bereich) Stimulation der Netzhaut oder Anwendung der D1-Agonist-SKF38393 reduziert (10 MicroM) w&auml;hrend der subjektiven Tag und Nacht. Wir schlie&szlig;en, dass ebenso um horizontale Zellen Kone, Rute horizontale Zellen ausgiebig miteinander in Dunkelheit gekoppelt sind und das Ausma&szlig; der Kupplung durch helles Licht stimulieren oder Dopamin D1-Rezeptor-Aktivierung drastisch verringert wird. Allerdings waren im Gegensatz zu Kegel horizontale Zellen, deren Licht Antworten unter der Kontrolle der Netzhaut Uhr sind, die leichten Antworten der horizontalen Stange Zellen unter dark-adapted Bedingungen &auml;hnliche w&auml;hrend der Tag, Nacht, subjektive Tag und subjektiven Nacht damit demonstrieren, dass sie nicht unter dem Einfluss der circadianen Uhr.

Tracer Kupplung zwischen Fisch Stab horizontale Zellen: Modulation von Licht und Dopamin aber nicht die Netzhaut circadian Clock.

A GABA- or glycine-induced increase in Cl(-) permeability can produce either a depolarization or hyperpolarization, depending on the Cl(-) equilibrium potential. It has been shown that retinal neurons express the chloride cotransporters, Na-K-2Cl (NKCC) and K-Cl (KCC), the primary molecular mechanisms that control the intracellular Cl(-) concentration. We thus studied (1) the localization of these cotransporters in the fish retina, and (2) how suppression of cotransporter activity in the fish retina affects function. Specific antibodies against NKCC and KCC2 revealed that both cotransporters were expressed in the outer and inner plexiform layers, and colocalized in many putative amacrine cells and in cells of the ganglion cell layer. However, the somata of putative horizontal cells displayed only NKCC immunoreactivity and many bipolar cells were only immunopositive for KCC2. In the outer retina, application of bumetanide, a specific inhibitor of NKCC activity, (1) increased the steady-state extracellular concentration of K+ ([K+](o)) and enhanced the light-induced decrease in the [K+](o), (2) increased the sPIII photoreceptor-dependent component of the ERG, and (3) reduced the extracellular space volume. In contrast, in the outer retina, application of furosemide, a specific inhibitor of KCC activity, decreased sPIII and the light-induced reduction in [K+](o), but had little effect on steady-state [K+](o). In the inner retina, bumetanide increased the sustained component of the light-induced increase in [K+](o). These findings thus indicate that NKCC and KCC2 control the [K+](o) and extracellular space volume in the retina in addition to regulating GABA- and glycine-mediated synaptic transmission. In addition, the anatomical and electrophysiological results together suggest that all of the major neuronal types in the fish retina are influenced by chloride cotransporter activity.

Multiple functions of cation-chloride cotransporters in the fish retina.

Eine GABA oder Glycin-induzierte Erh&ouml;hung Cl(-) Permeabilit&auml;t kann eine Depolarisation oder Hyperpolarisation, abh&auml;ngig von der potentiellen Cl(-) Gleichgewicht f&uuml;hren. Es hat sich gezeigt, dass Netzhaut Neuronen Ausdr&uuml;cken die Chlorid-Cotransporters, Na-K - 2 Cl (NKCC) und K-Cl (KCC), die prim&auml;ren molekularen Mechanismen, die die intrazellul&auml;re Cl(-) Konzentration zu steuern. Wir studierten so (1) die Sprachunterst&uuml;tzung f&uuml;r diese Cotransporters in der Fisch-Netzhaut und (2) wie die Unterdr&uuml;ckung der Cotransporter Aktivit&auml;t in der Fisch-Netzhaut Funktion auswirkt. Spezifische Antik&ouml;rper gegen NKCC und KCC2 ergab, dass beide Cotransporters wurden in die &auml;u&szlig;eren und inneren plexiforme Schichten ausgedr&uuml;ckt und colocalized in viele vermeintliche Amacrine Zellen und Zellen in den Ganglion-Zellschicht. Aber die Somata der vermeintlichen horizontale Zellen angezeigt nur NKCC Immunoreactivity und viele Bipolare Zellen waren nur Immunopositive f&uuml;r KCC2. In der &auml;u&szlig;eren Netzhaut, Anwendung von Bumetanid, einen spezifischen Hemmer NKCC Aktivit&auml;t, (1) erh&ouml;ht die station&auml;ren extrazellul&auml;re Konzentration an K + ([K+](o)) und verbessert den Licht-induzierten R&uuml;ckgang der [K+](o), (2) erh&ouml;ht die sPIII Photorezeptor-abh&auml;ngige Komponente der ERG, und (3) das extrazellul&auml;ren Raum-Volumen reduziert. Im Gegensatz dazu in der &auml;u&szlig;eren Netzhaut, Anwendung von Furosemid, ein bestimmtes Inhibitor der KCC-Aktivit&auml;t, verminderte sPIII und dem Licht-induzierten R&uuml;ckgang [K+](o), hatte aber wenig Auswirkung auf station&auml;ren [K+](o). In der inneren Retina erh&ouml;ht Bumetanid die anhaltende Komponente der Licht-induzierten Zunahme der [K+](o). Diese Befunde zeigen damit, dass NKCC und KCC2 kontrollieren, die [K+](o) und extrazellul&auml;ren Raum Volumen in der Netzhaut zus&auml;tzlich zur Regulierung der synaptischen &Uuml;bertragung GABA und Glycin-vermittelte. Dar&uuml;ber hinaus empfehlen die anatomischen und elektrophysiologische Ergebnisse gemeinsam alle wichtigen neuronalen Typen in der Fisch-Retina von Chlorid-Kotransporter Aktivit&auml;t beeinflusst werden.

Mehrere Funktionen des kations-Chlorid-Cotransporters in der Fisch-Netzhaut.

Although rod and cone photoreceptor cells in the vertebrate retina are anatomically connected or coupled by gap junctions, a type of electrical synapse, rod-cone electrical coupling is thought to be weak. Using tracer labeling and electrical recording in the goldfish retina and tracer labeling in the mouse retina, we show that the retinal circadian clock, and not the retinal response to the visual environment, controls the extent and strength of rod-cone coupling by activating dopamine D(2)-like receptors in the day, so that rod-cone coupling is weak during the day but remarkably robust at night. The results demonstrate that circadian control of rod-cone electrical coupling serves as a synaptic switch that allows cones to receive very dim light signals from rods at night, but not in the day. The increase in the strength and extent of rod-cone coupling at night may facilitate the detection of large dim objects.

The circadian clock in the retina controls rod-cone coupling.

Obwohl Rod und Kegel Sehzellen in der vertebrate Retina anatomisch oder verbunden sind durch Gap Junctions, eine Art elektrische Synapse verbunden ist Stab-Kegel elektrische Kopplung betrachtet, zu schwach. Tracer beschriften und elektrische Aufnahme in die Goldfische Netzhaut und Tracer, die Kennzeichnung in der Netzhaut Maus verwenden wir zeigen, dass die Netzhaut circadian Clock, und nicht die Netzhaut Reaktion auf der visual-Umgebung, steuert das Ausma&szlig; und die St&auml;rke der Rute-Konus-Kupplung durch Aktivierung von Dopamin D (2)-mag Rezeptoren in den Tag, so dass Stab-Konus-Kupplung schwach tags&uuml;ber aber bemerkenswert robust in der Nacht. Die Ergebnisse zeigen, dass circadian Kontrolle der Stab-Kegel elektrische Kopplung als synaptische Switch dient, die Zapfen sehr dim Lichtsignale von Stangen in der Nacht, aber nicht an den Tag zu erhalten zu k&ouml;nnen. Die Zunahme der St&auml;rke und Ausma&szlig; der Stab-Konus-Kupplung in der Nacht kann die Erfassung gro&szlig;er dim Objekte erleichtern.

Die circadian Clock in die Netzhaut Steuerelemente Stab-Konus-Kupplung.

Displaced starburst amacrine cells (SACs) are retinal interneurons that exhibit GABA( A ) receptor-mediated and Cl (-) cotransporter-mediated, directionally selective (DS) light responses in the rabbit retina. They depolarize to stimuli that move centrifugally through the receptive field surround and hyperpolarize to stimuli that move centripetally through the surround (Gavrikov et al, PNAS 100(26):16047-16052, 2003, PNAS 103(49):18793-18798, 2006). They also play a key role in the activity of DS ganglion cells (DS GC; Amthor et al, Vis Neurosci 19:495-509 2002; Euler et al, Nature 418:845-852, 2002; Fried et al, Nature 420:411- 414, 2002; Gavrikov et al, PNAS 100(26):16047-16052, 2003, PNAS 103(49):18793-18798, 2006; Lee and Zhou, Neuron 51:787-799 2006; Yoshida et al, Neuron 30:771-780, 2001). In this paper we present a model of strong DS behavior of SACs which relies on the GABA-mediated communication within a tightly interconnected network of these cells and on the glutamate signal that the SACs receive from bipolar cells (a presynaptic cell that receives input from cones). We describe how a moving light stimulus can produce a large, sustained depolarization of the SAC dendritic tips that point in the direction that the stimulus moves (i.e., centrifugal motion), but produce a minimal depolarization of the dendritic tips that point in the opposite direction (i.e., centripetal motion). This DS behavior, which is quantified based on the relative size and duration of the depolarizations evoked by stimulus motion at dendritic tips pointing in opposite directions, is robust to changes of many different parameter values and consistent with experimental data. In addition, the DS behavior is strengthened under the assumptions that the Cl(-) cotransporters Na( + )-K( + )-Cl( -) and K( + )-Cl( -) are located in different regions of the SAC dendritic tree (Gavrikov et al, PNAS 103(49):18793-18798, 2006) and that GABA evokes a long-lasting response (Gavrikov et al, PNAS 100(26):16047-16052, 2003, PNAS 103(49):18793-18798, 2006; Lee and Zhou, Neuron 51:787-799, 2006). A possible mechanism is discussed based on the generation of waves of local glutamate and GABA secretion, and their postsynaptic interplay as the waves travel between cell compartments.

A model of direction selectivity in the starburst amacrine cell network.

Vertriebenen Sternenexplosion Amacrine Zellen (SACs) sind Netzhaut Interneuronen, die GABA (A) Rezeptor-vermittelte aufweisen und Cl (-)-Kotransporter-vermittelte, Richtungen selektive (DS) leichte Antworten in der Kaninchen-Netzhaut. Sie depolarize auf Reize diese Bewegung GESCHLEUDERTER durch das rezeptive Feld umgeben und hyperpolarize auf Reize, die centripetally durch die Surround zu bewegen (Gavrikov Et al., PNAS 100 (26): 16047-16052, 2003, PNAS 103 (49): 18793-18798, 2006). Sie spielen auch eine Schl&uuml;sselrolle in der T&auml;tigkeit des DS-Ganglienzellen (DS GC; Amthor Et al., Vis Neurosci 19:495-509 2002; Euler Et al., Natur-418:845-852, 2002; Fried Et al., Nature 420:411-414, 2002; Gavrikov Et al., PNAS 100 (26): 16047-16052, 2003, PNAS 103 (49): 18793-18798, 2006; Lee und Zhou, Neuron 51:787-799 2006; Yoshida Et al., Neuron 30:771-780, 2001). In diesem Papier stellen wir ein Modell des starken DS-Verhalten des SACs, die sich st&uuml;tzt auf die GABA-vermittelte Kommunikation innerhalb eines eng miteinander verbundenen Netzwerks dieser Zellen und das Glutamat-Signal, das die T&uuml;ten von bipolaren Zellen (eine pr&auml;synaptische Zelle, die Eingabe von Zapfen empf&auml;ngt) erhalten. Wir beschreiben, wie bewegte Licht Impuls eine gro&szlig;e, anhaltende Depolarisation der SAC dendritische Tipps produzieren kann, die in die Richtung zu weisen, dass der Reiz bewegt (d. h. zentrifugale Bewegung), sondern produzieren einen minimalen Depolarisierung der dendritischen Tipps, die in die entgegengesetzte Richtung (d. h. zentripetalen Bewegung) zeigen. Dieses Verhalten von DS, was basierend auf der relativen Gr&ouml;&szlig;e und Dauer der Depolarizations beziffert wird, hervorgerufen durch Anregung Bewegung an dendritischen Spitzen, die in entgegengesetzte Richtungen zeigt, ist auf &Auml;nderungen von vielen verschiedenen Parameterwerten robust und mit experimentellen Daten konsistent. Dar&uuml;ber hinaus wird das DS-Verhalten verst&auml;rkt, unter den Annahmen, die die Cl(-) Cotransporters Na (+)-K (+)-Cl (-) und K (+)-Cl (-) befinden sich in verschiedenen Regionen der SAC dendritische Struktur (Gavrikov Et al., PNAS 103 (49): 18793-18798, 2006) und dass GABA eine lang anhaltende Reaktion hervorruft (Gavrikov Et al., PNAS 100 (26): 16047-16052, 2003, PNAS 103 (49): 18793-18798, 2006; Lee und Zhou, Neuron 51:787-799, 2006). Ein m&ouml;glichen Mechanismus wird diskutiert, basierend auf der Generation der Wellen der lokalen Glutamat und GABA-Sekretion und ihrer postsynaptisches Wechselwirkungen wie die Wellen zwischen Zelle F&auml;cher Reisen.

Ein Modell der Richtung Selektivit&auml;t im Sternenexplosion Amacrine Zellen Netzwerk.

Although the circadian clock in the mammalian retina regulates many physiological processes in the retina, it is not known whether and how the clock controls the neuronal pathways involved in visual processing.

Identification of a circadian clock-controlled neural pathway in the rabbit retina.

Obwohl die circadiane Clock in der S&auml;ugetier-Netzhaut viele physiologische Prozesse in der Netzhaut reguliert, ist es nicht bekannt, ob und wie die Uhr die neuronalen Bahnen, die visuelle Verarbeitung beteiligt steuert.

Kennung der circadianen Uhr kontrollierten neuronale Weg in der Kaninchen-Netzhaut.

Starburst amacrine cells (SACs) are an essential component of the mechanism that generates direction selectivity in the retina. SACs exhibit opposite polarity, directionally selective (DS) light responses, depolarizing to stimuli that move centrifugally away from the cell through the receptive field surround, but hyperpolarizing to stimuli that move centripetally towards the cell through the surround. Recent findings suggest that 1) the intracellular chloride concentration ([Cl-]i) is high in SAC proximal, but low in SAC distal dendritic compartments, so that GABA depolarizes and hyperpolarizes the proximal and distal compartments, respectively, and 2) this [Cl-]i gradient plays an essential role in generating SAC DS light responses. Employing a biophysically realistic, computational model of SACs, which incorporated experimental measurements of SAC electrical properties and GABA and glutamate responses, we further investigated whether and how an [Cl-]i gradient along SAC dendrites produces their DS responses. Our computational analysis suggests that robust DS light responses would be generated in both the SAC soma and distal dendrites if 1) the Cl- equilibrium potential is more positive in the proximal dendrite and more negative in the distal dendrite than the resting membrane potential, so that GABA depolarizes and hyperpolarizes the proximal and distal compartments, respectively, and 2) the GABA-evoked increase in the Cl- conductance lasts longer than the glutamate-evoked increase in cation conductance. The combination of these two specific GABA-associated spatial and temporal asymmetries, in conjunction with symmetric glutamate excitation, may underlie the opposite polarity, DS light responses of SACs.

GABA-mediated Spatial and Temporal Asymmetries That Contribute to the Directionally Selective Light Responses of Starburst Amacrine Cells in Retina.

Sternenexplosion Amacrine Zellen (SACs) sind ein wesentlicher Bestandteil des Mechanismus, der Richtung Selektivit&auml;t in der Netzhaut erzeugt. T&uuml;ten weisen gegen&uuml;ber Polarit&auml;t, Richtungen selektive (DS) leichte Antworten, depolarisierende Reize, die von der Zelle durch die rezeptive Feld Surround GESCHLEUDERTER bewegen, aber hyperpolarizing auf Reize, die centripetally in Richtung der Zelle durch die Surround zu bewegen. J&uuml;ngste Forschungsergebnisse legen nahe, dass 1) die intrazellul&auml;re Chlorid-Konzentration ([CL-] ich) ist in SAC proximale, aber wenig SAC distale dendritische Abteilen, so dass GABA depolarizes und der proximalen und distalen F&auml;cher, bzw. hyperpolarizes und 2 hoch) diese [CL-] ich Farbverlauf spielt eine wesentliche Rolle bei der Schaffung von SAC DS leichte Antworten. Besch&auml;ftigt ein biophysikalisch realistisch, computational Modell des SACs, die experimentelle Messungen des SAC elektrische Eigenschaften und GABA und Glutamat Reaktionen aufgenommen, untersucht wir weiter ob und wie ein [CL-] ich gradient entlang SAC Dendriten produziert ihre DS-Antworten. Unsere computational Analyse zufolge robuste DS leichte Antworten w&uuml;rde sowohl der distalen Dendriten im SAC Soma generiert werden, wenn 1) das Cl-Gleichgewichts-Potential ist im proximalen Dendrit positiv und negativer in der distalen Dendrit als die ruhelosigkeit Membrane Potential, so dass GABA depolarizes und der proximalen und distalen F&auml;cher, bzw. hyperpolarizes, und 2) der GABA hervorgerufen Anstieg in den Cl-Leitwert l&auml;nger als der Glutamat-hervorgerufen Anstieg kation Leitwert dauert. Die Kombination von diesen zwei spezifischen GABA-assoziierte r&auml;umlichen und zeitlichen Asymmetrien in Verbindung mit symmetrischen Glutamat Erregung, kann zugrunde liegen, die entgegengesetzte Polarit&auml;t, DS leichte Reaktionen von SACs.

GABA-vermittelte r&auml;umliche und zeitliche Asymmetrien, die zu den Richtungen selektiven leichten Reaktionen Starburst Amacrine Zellen in Retina beitragen.

Article	Year
Suppression by zinc of AMPA receptor-mediated synaptic transmission in the retina. Journal of neurophysiology\| PubMed ID: 12205145	2002
Dopamine mediates circadian clock regulation of rod and cone input to fish retinal horizontal cells. The Journal of physiology\| PubMed ID: 12411525	2002
A circadian clock in the fish retina regulates dopamine release via activation of melatonin receptors. The Journal of physiology\| PubMed ID: 14565990	2004
The Journal of comparative neurology\| PubMed ID: 14595771	2003
Cation--chloride cotransporters mediate neural computation in the retina. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 14665697	2003
Retinal pH reflects retinal energy metabolism in the day and night. Journal of neurophysiology\| PubMed ID: 14960560	2004
A circadian clock and light/dark adaptation differentially regulate adenosine in the mammalian retina. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 15634784	2005
Electrical feedback in the cone pedicle: a computational analysis. Journal of neurophysiology\| PubMed ID: 16319220	2006
Dendritic compartmentalization of chloride cotransporters underlies directional responses of starburst amacrine cells in retina. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 17124178	2006
Tracer coupling between fish rod horizontal cells: modulation by light and dopamine but not the retinal circadian clock. Visual neuroscience\| PubMed ID: 17640444	2007
Multiple functions of cation-chloride cotransporters in the fish retina. Visual neuroscience\| PubMed ID: 17900379	2007
The circadian clock in the retina controls rod-cone coupling. Neuron\| PubMed ID: 18786362	2008
A model of direction selectivity in the starburst amacrine cell network. Journal of computational neuroscience\| PubMed ID: 20524107	2010
Identification of a circadian clock-controlled neural pathway in the rabbit retina. PloS one\| PubMed ID: 20548772	2010
GABA-mediated Spatial and Temporal Asymmetries That Contribute to the Directionally Selective Light Responses of Starburst Amacrine Cells in Retina. The Journal of physiology\| PubMed ID: 22289910	2012

Stuart C. Mangel

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