The vertebrate retina, like most other brain regions, undergoes relatively slow alterations in ne... more The vertebrate retina, like most other brain regions, undergoes relatively slow alterations in neural signaling in response to gradual changes in physiological conditions (e.g., activity changes to rest), or in response to gradual changes in environmental conditions (e.g., day changes into night). As occurs elsewhere in the brain, the modulatory processes that mediate slow adaptation in the retina are driven by extrinsic signals (e.g., changes in ambient light level) and/or by intrinsic signals such as those of the circadian (24-h) clock in the retina. This review article describes and discusses the extrinsic and intrinsic modulatory processes that enable neural circuits in the retina to optimize their visual performance throughout day and night as the ambient light level changes by ~10 billion-fold. In the first synaptic layer of the retina, cone photoreceptor cells form gap junctions with rods and signal cone-bipolar and horizontal cells (HCs). Distinct extrinsic and intrinsic mod...
Adenosine, a major neuromodulator in the central nervous system (CNS), is involved in a variety o... more Adenosine, a major neuromodulator in the central nervous system (CNS), is involved in a variety of regulatory functions such as the sleep/wake cycle. Because exogenous adenosine displays dark- and night-mimicking effects in the vertebrate retina, we tested the hypothesis that a circadian (24 h) clock in the retina uses adenosine to control neuronal light responses and information processing. Using a variety of techniques in the intact goldfish retina including measurements of adenosine overflow and content, tracer labeling, and electrical recording of the light responses of cone photoreceptor cells and cone horizontal cells (cHCs), which are post-synaptic to cones, we demonstrate that a circadian clock in the retina itself—but not activation of melatonin or dopamine receptors—controls extracellular and intracellular adenosine levels so that they are highest during the subjective night. Moreover, the results show that the clock increases extracellular adenosine at night by enhancing ...
Although it is generally accepted that the acid–base ratio of tissue, as represented by the pH, i... more Although it is generally accepted that the acid–base ratio of tissue, as represented by the pH, is strictly regulated to maintain normal function, recent studies in the mammalian nervous system have shown that neuronal activity can result in significant shifts in pH. In the mammalian retina, many cellular phenomena, including neuronal activity, are regulated by a circadian clock. We thus investigated whether a clock regulates retinal pH, using pH-sensitive microelectrodes to measure the extracellular pH (pHo) of thein vitrorabbit retina in the subjective day and night, that is, under conditions of constant darkness. These measurements demonstrated that a circadian clock regulates the pHoof the rabbit retina so that the pHois lower at night than in the day. This day/night difference in retinal pHowas observed when the rabbits were maintained on a normal light/dark cycle and after they were maintained on a light/dark cycle that was phase-delayed by 9 hr. Continuous recordings of retin...
Zinc is strikingly co-localized with glutamate-containing vesicles in the synaptic terminals of r... more 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 μM zinc reduced the whole cell peak current of response to 200 μM glutamate by 2, 30, and 56%, respectively. Zinc suppression of glutamate response persisted in the presence of 10 μM cyclothiazide (CTZ). Glutamate responses of outside-out patches were completely abolished by 30 μM 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466), and the receptor desensitization was blocked by 30 μM CTZ, indicating that receptor target for the zinc action on horizontal cells is α...
The acidic amino acid receptor antagonists, alpha-methylglutamate and alpha-aminoadipate, were ap... more The acidic amino acid receptor antagonists, alpha-methylglutamate and alpha-aminoadipate, were applied to the carp retina to study their effects upon the spectral properties of horizontal cells and to elucidate the synaptic connections between horizontal cells and cones. Application of these antagonists strongly hyperpolarized the L-type cone horizontal cells and reduced the responses of these horizontal cells to red light more than to blue light. Application of Co2+ ions to the retina, a procedure which decreases transmitter release, also hyperpolarized the L-type cone horizontal cells but reduced the response of these horizontal cells to red and blue lights equally. These results suggest that red- or long wavelength-sensitive cones release a different transmitter onto L-type cone horizontal cells than do short wavelength-sensitive cones. Application of the acidic amino acid antagonists also revealed details of the feedback pathway from L- type cone horizontal cells to cones. Previ...
Wang, Yu, Krisztina Harsanyi, and Stuart C. Mangel. Endogenous activation of dopamine D2 receptor... more Wang, Yu, Krisztina Harsanyi, and Stuart C. Mangel. Endogenous activation of dopamine D2 receptors regulates dopamine release in the fish retina. J. Neurophysiol. 78: 439–449, 1997. In the fish retina, horizontal cell electrical coupling and light responsiveness is regulated by activation of dopamine D1 receptors that are located on the horizontal cells themselves. The effects of dopamine and dopamine D2 receptor agonists and antagonists on cone horizontal cell light responses were studied in in vitro superfused goldfish retinas. Horizontal cell light responses and electrical coupling were assessed by monitoring responses to full-field stimuli and to small, centered (0.4 mm diam) spots of light, respectively. Dopamine (0.2–10 μM) application uncoupled horizontal cells and decreased their responses to full-field stimuli. Application of the D2 antagonist eticlopride (10–50 μM) produced similar effects, whereas quinpirole (0.1–10 μM), a D2 agonist, had the opposite effects. The uncoupl...
Proceedings of the National Academy of Sciences, 1992
In the fish retina, interplexiform cells release dopamine onto cone-driven horizontal cells. Dopa... more In the fish retina, interplexiform cells release dopamine onto cone-driven horizontal cells. Dopamine decreases the electrical coupling between horizontal cells by activating adenylate cyclase through dopamine D1 receptors. Using intracellular recording, we have studied the effect of dopamine D2 receptor activation on horizontal cell electrical coupling in the intact goldfish retina. Superfusion of the D2 agonist LY171555 (quinpirole; 0.2-10 microM) increased horizontal cell coupling, as indicated by a decrease in responses to centered spots or slits of light. The length constant of the horizontal cell network increased an average of 31%. Although dopamine (0.5-20 microM) uncoupled horizontal cells, lower concentrations (e.g., 0.2 microM) initially uncoupled and then subsequently increased coupling beyond initial control levels. The coupling effect of LY171555 (10 microM) was blocked completely by prior application of the D1 agonist SKF 38393 at saturating (20 microM) or nonsaturati...
1. The influence of horizontal cells on ganglion cells, the output neuron of the retina, was exam... more 1. The influence of horizontal cells on ganglion cells, the output neuron of the retina, was examined in an in vitro rabbit eyecup preparation. The extracellular spike activity of ganglion cells was monitored while pulsatile DC or sinusoidally modulated current was injected intracellularly into nearby horizontal cells. Interactions between the effects of light stimulation and horizontal cell current injections on ganglion cell responses were also examined. 2. Horizontal cells were found to contribute to the receptive field surround of ganglion cells. In particular, horizontal cells contributed to surround excitability and to surround antagonism of the centre light response. 3. Brisk, sluggish and direction‐selective ganglion cells were all affected by current injections into horizontal cells. However, brisk ganglion cells responded to lower amplitude currents than did sluggish or direction‐selective cells. 4. Horizontal cells with receptive fields that overlap those of ganglion cell...
In addition to chemical synaptic transmission, neurons that are connected by gap junctions can al... more In addition to chemical synaptic transmission, neurons that are connected by gap junctions can also communicate rapidly via electrical synaptic transmission. Increasing evidence indicates that gap junctions not only permit electrical current flow and synchronous activity between interconnected or coupled cells, but that the strength or effectiveness of electrical communication between coupled cells can be modulated to a great extent(1,2). In addition, the large internal diameter (~1.2 nm) of many gap junction channels permits not only electric current flow, but also the diffusion of intracellular signaling molecules and small metabolites between interconnected cells, so that gap junctions may also mediate metabolic and chemical communication. The strength of gap junctional communication between neurons and its modulation by neurotransmitters and other factors can be studied by simultaneously electrically recording from coupled cells and by determining the extent of diffusion of trac...
Although the circadian clock in the mammalian retina regulates many physiological processes in th... more 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. By recording the light responses of rabbit axonless (A-type) horizontal cells under dark-adapted conditions in both the day and night, we found that rod input to these cells was substantially increased at night under control conditions and following selective blockade of dopamine D(2), but not D(1), receptors during the day, so that the horizontal cells responded to very dim light at night but not in the day. Using neurobiotin tracer labeling, we also found that the extent of tracer coupling between rabbit rods and cones was more extensive during the night, compared to the day, and more extensive in the day following D(2) receptor blockade. Because A-type horizontal cells make synaptic contact exclusively with cones, these observations indicate that the circadian clock in the...
Key points Starburst amacrine cells (SACs), interneurons that are essential to the generation of... more Key points Starburst amacrine cells (SACs), interneurons that are essential to the generation of direction selectivity in the retina, depolarize to light stimuli that move centrifugally away from them, but hyperpolarize to stimuli that move centripetally towards them. These directionally selective light responses are dependent on the differential distribution of the Cl− cotransporters NKCC (which mediates GABA‐evoked depolarizations by increasing intracellular Cl−) and KCC2 (which mediates GABA‐evoked hyperpolarizations by decreasing intracellular Cl−) on SAC proximal and distal dendrites, respectively. We show computationally that directionally selective light responses can be produced in both starburst cell bodies and distal dendrites if (1) there is an intracellular Cl− concentration gradient along SAC dendrites and (2) the response of the dendrites to GABA is relatively long lasting. The location of NKCC and KCC2 in different compartments of individual neuronal processes may be...
Although it is generally accepted that the acid/base ratio of tissue, as represented by the pH, i... more Although it is generally accepted that the acid/base ratio of tissue, as represented by the pH, is strictly regulated to maintain normal function, recent studies in the nervous system have shown that neuronal activity can result in significant shifts in pH. In the vertebrate retina, many cellular phenomena, including neuronal activity, are regulated by a circadian clock. We thus investigated whether a circadian clock regulates the pH of the retina. pH‐sensitive microelectrodes were used to measure the extracellular pH of the in vitro goldfish retina superfused with a bicarbonate‐based Ringer solution in the subjective day and night; that is, under conditions of constant darkness. These measurements demonstrated that a circadian clock regulates the pH of the vertebrate retina so that the pH is lower at night compared to the day. This day‐night difference in retinal pH was observed at two different values of Ringer solution pH, indicating that the circadian phenomenon is independent o...
Although many biochemical, morphological and physiological processes in the vertebrate retina are... more 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 µM) 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 (24‐hour) clock regulates the light responses of fish cone horizontal cells, second o... more 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 D2‐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 D2‐like antagonist, or forskolin, an activator of adenylyl cyclase, during the subjective day reduced cone input and increased rod input. SCH2...
Although the purine adenosine acts as an extracellular neuromodulator in the mammalian CNS in bot... more 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 e...
Proceedings of the National Academy of Sciences, 2003
The ability of directionally selective (DS) retinal ganglion cells to respond selectively to stim... more 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 direc...
The vertebrate retina, like most other brain regions, undergoes relatively slow alterations in ne... more The vertebrate retina, like most other brain regions, undergoes relatively slow alterations in neural signaling in response to gradual changes in physiological conditions (e.g., activity changes to rest), or in response to gradual changes in environmental conditions (e.g., day changes into night). As occurs elsewhere in the brain, the modulatory processes that mediate slow adaptation in the retina are driven by extrinsic signals (e.g., changes in ambient light level) and/or by intrinsic signals such as those of the circadian (24-h) clock in the retina. This review article describes and discusses the extrinsic and intrinsic modulatory processes that enable neural circuits in the retina to optimize their visual performance throughout day and night as the ambient light level changes by ~10 billion-fold. In the first synaptic layer of the retina, cone photoreceptor cells form gap junctions with rods and signal cone-bipolar and horizontal cells (HCs). Distinct extrinsic and intrinsic mod...
Adenosine, a major neuromodulator in the central nervous system (CNS), is involved in a variety o... more Adenosine, a major neuromodulator in the central nervous system (CNS), is involved in a variety of regulatory functions such as the sleep/wake cycle. Because exogenous adenosine displays dark- and night-mimicking effects in the vertebrate retina, we tested the hypothesis that a circadian (24 h) clock in the retina uses adenosine to control neuronal light responses and information processing. Using a variety of techniques in the intact goldfish retina including measurements of adenosine overflow and content, tracer labeling, and electrical recording of the light responses of cone photoreceptor cells and cone horizontal cells (cHCs), which are post-synaptic to cones, we demonstrate that a circadian clock in the retina itself—but not activation of melatonin or dopamine receptors—controls extracellular and intracellular adenosine levels so that they are highest during the subjective night. Moreover, the results show that the clock increases extracellular adenosine at night by enhancing ...
Although it is generally accepted that the acid–base ratio of tissue, as represented by the pH, i... more Although it is generally accepted that the acid–base ratio of tissue, as represented by the pH, is strictly regulated to maintain normal function, recent studies in the mammalian nervous system have shown that neuronal activity can result in significant shifts in pH. In the mammalian retina, many cellular phenomena, including neuronal activity, are regulated by a circadian clock. We thus investigated whether a clock regulates retinal pH, using pH-sensitive microelectrodes to measure the extracellular pH (pHo) of thein vitrorabbit retina in the subjective day and night, that is, under conditions of constant darkness. These measurements demonstrated that a circadian clock regulates the pHoof the rabbit retina so that the pHois lower at night than in the day. This day/night difference in retinal pHowas observed when the rabbits were maintained on a normal light/dark cycle and after they were maintained on a light/dark cycle that was phase-delayed by 9 hr. Continuous recordings of retin...
Zinc is strikingly co-localized with glutamate-containing vesicles in the synaptic terminals of r... more 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 μM zinc reduced the whole cell peak current of response to 200 μM glutamate by 2, 30, and 56%, respectively. Zinc suppression of glutamate response persisted in the presence of 10 μM cyclothiazide (CTZ). Glutamate responses of outside-out patches were completely abolished by 30 μM 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466), and the receptor desensitization was blocked by 30 μM CTZ, indicating that receptor target for the zinc action on horizontal cells is α...
The acidic amino acid receptor antagonists, alpha-methylglutamate and alpha-aminoadipate, were ap... more The acidic amino acid receptor antagonists, alpha-methylglutamate and alpha-aminoadipate, were applied to the carp retina to study their effects upon the spectral properties of horizontal cells and to elucidate the synaptic connections between horizontal cells and cones. Application of these antagonists strongly hyperpolarized the L-type cone horizontal cells and reduced the responses of these horizontal cells to red light more than to blue light. Application of Co2+ ions to the retina, a procedure which decreases transmitter release, also hyperpolarized the L-type cone horizontal cells but reduced the response of these horizontal cells to red and blue lights equally. These results suggest that red- or long wavelength-sensitive cones release a different transmitter onto L-type cone horizontal cells than do short wavelength-sensitive cones. Application of the acidic amino acid antagonists also revealed details of the feedback pathway from L- type cone horizontal cells to cones. Previ...
Wang, Yu, Krisztina Harsanyi, and Stuart C. Mangel. Endogenous activation of dopamine D2 receptor... more Wang, Yu, Krisztina Harsanyi, and Stuart C. Mangel. Endogenous activation of dopamine D2 receptors regulates dopamine release in the fish retina. J. Neurophysiol. 78: 439–449, 1997. In the fish retina, horizontal cell electrical coupling and light responsiveness is regulated by activation of dopamine D1 receptors that are located on the horizontal cells themselves. The effects of dopamine and dopamine D2 receptor agonists and antagonists on cone horizontal cell light responses were studied in in vitro superfused goldfish retinas. Horizontal cell light responses and electrical coupling were assessed by monitoring responses to full-field stimuli and to small, centered (0.4 mm diam) spots of light, respectively. Dopamine (0.2–10 μM) application uncoupled horizontal cells and decreased their responses to full-field stimuli. Application of the D2 antagonist eticlopride (10–50 μM) produced similar effects, whereas quinpirole (0.1–10 μM), a D2 agonist, had the opposite effects. The uncoupl...
Proceedings of the National Academy of Sciences, 1992
In the fish retina, interplexiform cells release dopamine onto cone-driven horizontal cells. Dopa... more In the fish retina, interplexiform cells release dopamine onto cone-driven horizontal cells. Dopamine decreases the electrical coupling between horizontal cells by activating adenylate cyclase through dopamine D1 receptors. Using intracellular recording, we have studied the effect of dopamine D2 receptor activation on horizontal cell electrical coupling in the intact goldfish retina. Superfusion of the D2 agonist LY171555 (quinpirole; 0.2-10 microM) increased horizontal cell coupling, as indicated by a decrease in responses to centered spots or slits of light. The length constant of the horizontal cell network increased an average of 31%. Although dopamine (0.5-20 microM) uncoupled horizontal cells, lower concentrations (e.g., 0.2 microM) initially uncoupled and then subsequently increased coupling beyond initial control levels. The coupling effect of LY171555 (10 microM) was blocked completely by prior application of the D1 agonist SKF 38393 at saturating (20 microM) or nonsaturati...
1. The influence of horizontal cells on ganglion cells, the output neuron of the retina, was exam... more 1. The influence of horizontal cells on ganglion cells, the output neuron of the retina, was examined in an in vitro rabbit eyecup preparation. The extracellular spike activity of ganglion cells was monitored while pulsatile DC or sinusoidally modulated current was injected intracellularly into nearby horizontal cells. Interactions between the effects of light stimulation and horizontal cell current injections on ganglion cell responses were also examined. 2. Horizontal cells were found to contribute to the receptive field surround of ganglion cells. In particular, horizontal cells contributed to surround excitability and to surround antagonism of the centre light response. 3. Brisk, sluggish and direction‐selective ganglion cells were all affected by current injections into horizontal cells. However, brisk ganglion cells responded to lower amplitude currents than did sluggish or direction‐selective cells. 4. Horizontal cells with receptive fields that overlap those of ganglion cell...
In addition to chemical synaptic transmission, neurons that are connected by gap junctions can al... more In addition to chemical synaptic transmission, neurons that are connected by gap junctions can also communicate rapidly via electrical synaptic transmission. Increasing evidence indicates that gap junctions not only permit electrical current flow and synchronous activity between interconnected or coupled cells, but that the strength or effectiveness of electrical communication between coupled cells can be modulated to a great extent(1,2). In addition, the large internal diameter (~1.2 nm) of many gap junction channels permits not only electric current flow, but also the diffusion of intracellular signaling molecules and small metabolites between interconnected cells, so that gap junctions may also mediate metabolic and chemical communication. The strength of gap junctional communication between neurons and its modulation by neurotransmitters and other factors can be studied by simultaneously electrically recording from coupled cells and by determining the extent of diffusion of trac...
Although the circadian clock in the mammalian retina regulates many physiological processes in th... more 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. By recording the light responses of rabbit axonless (A-type) horizontal cells under dark-adapted conditions in both the day and night, we found that rod input to these cells was substantially increased at night under control conditions and following selective blockade of dopamine D(2), but not D(1), receptors during the day, so that the horizontal cells responded to very dim light at night but not in the day. Using neurobiotin tracer labeling, we also found that the extent of tracer coupling between rabbit rods and cones was more extensive during the night, compared to the day, and more extensive in the day following D(2) receptor blockade. Because A-type horizontal cells make synaptic contact exclusively with cones, these observations indicate that the circadian clock in the...
Key points Starburst amacrine cells (SACs), interneurons that are essential to the generation of... more Key points Starburst amacrine cells (SACs), interneurons that are essential to the generation of direction selectivity in the retina, depolarize to light stimuli that move centrifugally away from them, but hyperpolarize to stimuli that move centripetally towards them. These directionally selective light responses are dependent on the differential distribution of the Cl− cotransporters NKCC (which mediates GABA‐evoked depolarizations by increasing intracellular Cl−) and KCC2 (which mediates GABA‐evoked hyperpolarizations by decreasing intracellular Cl−) on SAC proximal and distal dendrites, respectively. We show computationally that directionally selective light responses can be produced in both starburst cell bodies and distal dendrites if (1) there is an intracellular Cl− concentration gradient along SAC dendrites and (2) the response of the dendrites to GABA is relatively long lasting. The location of NKCC and KCC2 in different compartments of individual neuronal processes may be...
Although it is generally accepted that the acid/base ratio of tissue, as represented by the pH, i... more Although it is generally accepted that the acid/base ratio of tissue, as represented by the pH, is strictly regulated to maintain normal function, recent studies in the nervous system have shown that neuronal activity can result in significant shifts in pH. In the vertebrate retina, many cellular phenomena, including neuronal activity, are regulated by a circadian clock. We thus investigated whether a circadian clock regulates the pH of the retina. pH‐sensitive microelectrodes were used to measure the extracellular pH of the in vitro goldfish retina superfused with a bicarbonate‐based Ringer solution in the subjective day and night; that is, under conditions of constant darkness. These measurements demonstrated that a circadian clock regulates the pH of the vertebrate retina so that the pH is lower at night compared to the day. This day‐night difference in retinal pH was observed at two different values of Ringer solution pH, indicating that the circadian phenomenon is independent o...
Although many biochemical, morphological and physiological processes in the vertebrate retina are... more 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 µM) 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 (24‐hour) clock regulates the light responses of fish cone horizontal cells, second o... more 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 D2‐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 D2‐like antagonist, or forskolin, an activator of adenylyl cyclase, during the subjective day reduced cone input and increased rod input. SCH2...
Although the purine adenosine acts as an extracellular neuromodulator in the mammalian CNS in bot... more 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 e...
Proceedings of the National Academy of Sciences, 2003
The ability of directionally selective (DS) retinal ganglion cells to respond selectively to stim... more 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 direc...
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