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Results for “Retinal Horizontal Cells”

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At least 199 records · Page 11Linked to original sources

PubMed2005

Synergistic center-surround receptive field model of monkey H1 horizontal cells.

Horizontal cells typical of the vertebrate retina are strongly coupled by gap junctions. The resulting horizontal cell network has extremely large receptive fields that extend well beyond the boundaries of a single dendritic tree. This network has been modeled as a syncytium of cytoplasm bounded by cell membrane (Lamb 1976; Naka & Rushton, 1967). Horizontal cells in the primate retina are also coupled by gap junctions, but their receptive fields are relatively small and in some cases may approximate the span of the dendritic tree of an individual cell (Packer & Dacey, 2002). The receptive field of the macaque H1 horizontal cell type has been modeled as the sum of two spatial components: a strong but small diameter excitatory center, and a weak but broad excitatory surround. Here we explore the hypothesis that the receptive field center of H1 cells derives from direct cone synaptic input and that the synergistic surround derives from gap-junctional coupling among H1 cell neighbors. We measured the receptive field structure of H1 cells in the presence of carbenoxolone, a gap junction blocker, to determine the effects of uncoupling center and surround components and compared these data to a neural simulation of the H1 network in which gap-junctional conductance could be manipulated. Carbenoxolone reduced the surround component and eliminated irregularities in spatial structure thought to be associated with the surround. The effects of carbenoxolone could be mimicked by manipulating gap-junctional conductance in an H1 cell network simulation. These results provide strong support for the two-component model of H1 receptive field structure. In addition, carbenoxolone eliminated a slow depolarization following light onset thought to be mediated by cone-H1 feedback (Kamermans & Spekreijse, 1999). Low concentrations of cobalt, a calcium channel blocker that spares gap junctions, had an effect similar to that of carbenoxolone but did not affect receptive field structure. These results are consistent with a calcium-mediated mechanism of feedback from H1 cells to cones that is independent of the synergistic two-component model of receptive field organization.

Animals↗

PubMed2006

Electrical coupling, receptive fields, and relative rod/cone inputs of horizontal cells in the tiger salamander retina.

Light responses, dendritic/axonal morphology, receptive field diameters, patterns of dye coupling, and relative rod/cone inputs of various types of horizontal cells (HCs) were studied using intracellular recording and Lucifer yellow/neurobiotin dye injection methods in the flatmount tiger salamander retina. Three physiologically and morphologically distinct types of HC entities were identified. 1) The A-type HCs are somas that do not bear axons, with average (+/-SE) soma diameters of 20.01 +/- 0.59 microm, relatively sparse and thick dendrites, and they resemble the A-type HC in mammals. The average receptive field diameter of these cells is 529.6 +/- 10.87 microm and they receive inputs predominantly from cones. 2) The B-type HCs are broad-field somas that bear thin and long axons, with average soma diameters of 17.67 +/- 0.38 microm, thinner dendrites of higher density, and they resemble the B-type HC in mammals. The average receptive field diameter of these cells is 1,633.55 +/- 37.34 microm and they receive mixed inputs from rods and cones. 3) The B-type HC axon terminals are broad-field, coarse axon terminal processes and they resemble the B-type HC axon terminal in rabbits. The average receptive field diameter of these axon terminals is 1,291.67 +/- 24.02 microm and they receive mixed inputs from rods and cones. All these types of HC are dye-coupled with adjacent HCs of the same type. Additionally, B-type HCs and axon terminals are dye-coupled with subpopulations of bipolar cells whose axon terminals ramify in the proximal half of the inner plexiform layer, raising the possibility that these HCs may send feedforward antagonistic surround responses to depolarizing bipolar cells through electrical synapses.

Ambystoma↗

PubMed1999

Non-visual photoreception by a variety of vertebrate opsins.

Extraretinal photoreceptors in animals are involved in a variety of physiological functions such as photo-entrainment of circadian rhythm, photoperiodicity and body colour change. We have identified pinopsin in the chicken pineal gland as a typical 'non-visual' photoreceptive molecule. Pinopsin with bound 11-cis-retinal shows a blue-light sensitivity (lambda max = 468 nm), and it may play a role in synchronizing the phase of the endogenous circadian oscillator with an environmental dark-light cycle. Pinopsin is not a unique pineal opsin in animals. In the zebrafish, we have detected expression of two rhodopsin genes, the nucleotide sequences of which are very similar but distinct from each other. One is canonical rhodopsin expressed in the retina, and the other is expressed in the pineal gland. The latter gene is widely distributed among teleosts, and we named it 'exo-rhodopsin' after extraocular rhodopsin. On the other hand, our effort to identify the 'deep brain opsin' responsible for the photoperiodic gonadal response resulted in the identification of two kinds of opsins; pinopsin in the toad anterior preoptic nucleus and rhodopsin in the pigeon lateral septum. Both of these opsins are localized in the cerebrospinal fluid-contacting neurons in the brain of the two animals. We also identified VAL opsin in zebrafish retinal horizontal cells, which have not been considered as photoreceptive cells. It has become evident that animals employ a wide variety of photoreceptive molecules for 'non-visual' purposes.

Amino Acid Sequence↗

PubMed1990

An unusually small potassium current that is well-suited to a retinal neuron which is chronically depolarized.

Here we describe a sustained outward potassium current (IK) in retinal horizontal cells (HCs). IK is unusually small over the range of membrane potentials normally experienced by these cells, which are chronically depolarized. We hypothesize that this unique IK will reduce the amount of neurotransmitter required to shift the cell's membrane potential over a wide range, and will minimize the redistribution of potassium ions across the post-synaptic membrane when the cell is depolarized.

Animals↗

PubMed1990

Sequential course of uptake of intravitreal 5,7-dihydroxytryptamine by carp retinal cells.

The sequential course of uptake by retinal cells of intravitreally injected 5,7-dihydroxytryptamine (5,7-DHT) together with dopamine (DA) was investigated in juvenile carp retinas, which were removed at various intervals (1-24 h) after injection. The cells taken up 5,7-DHT were visualized immunohistochemically with anti-serotonin (5-HT) antibody and FITC-conjugated IgG. After a mixture of 5,7-DHT and DA (2.5, 10 or 20 micrograms each) was given, large-sized indoleamine (IA) amacrine cells first (1-4 h), and then small-sized indoleamine-accumulating amacrine amacrine (IAA) cells (4-12 h), bipolar cells (8-12 h) and in some cases photoreceptor cells (12-24 h) were sequentially observed, and finally the immunoreactive structures almost disappeared around 24 h after injection. When the mixture of 5,7-DHT and DA (10 micrograms each) was injected into the eyes of reserpinized fish, the same sequential uptake of 5,7-DHT was seen in a faster time course, but additionally various classes of retinal cells (horizontal, ganglion and Müller cells) became visible as irregular clusters. However, DA cells were never visualized at any stages of all the experiments, indicating that DA cells do not take up 5,7-DHT in the carp retina, which was further confirmed by double labeling of 5-HT- and tyrosine hydroxylase-like immunoreactive cells. Double labeling also revealed that 5,7-DHT-accumulating bipolar cells appear to represent a subclass different from that of protein kinase C-like immunoreactive bipolar cells.

5,7-Dihydroxytryptamine↗

PubMed1992

Suppression of a calcium current by CNQX and kynurenate.

During our investigation of a sustained high voltage-activated (HVA) calcium current in retinal horizontal cells, we found that the glutamate receptor antagonists CNQX and kynurenate but not AP7 reversibly reduced the peak amplitude of the HVA current. Changes in the HVA current kinetics or activation voltage were not apparent; there was only a reduction in the peak current. The novel effects of these antagonists on HVA calcium currents reported here could have an impact on many studies involving glutamatergic synaptic transmission.

2-Amino-5-phosphonovalerate↗

PubMed2004

Expression of Fibroblast growth factor 19 (Fgf19) during chicken embryogenesis and eye development, compared with Fgf15 expression in the mouse.

The normal development of eyes relies on proper signaling through Fibroblast growth factor (FGF) receptors, but the source and identity of cognate ligands have remained largely unknown. We have found that Fgf19 is expressed in the developing chicken retina. In situ hybridization discloses dynamic expression patterns for Fgf19 in the optic vesicle, lens primordia and retinal horizontal cells. Overall expression pattern of Fgf19 during chicken embryogenesis was also examined: Fgf19 is expressed in the regions associated with cranial placodes induction, boundary regions of rhombomeres, somites, specific groups of neural cells in midbrain, hindbrain, and those derived from epibranchial placodes, and the apical ectodermal ridge of limb buds. Expression pattern of the Fgf19-orthologous gene Fgf15 was further examined in the mouse developing eye. Fgf15 is expressed in the optic vesicle, a subset of progenitor cells of neural retina, and emerging ganglion and amacrine cells during retinogenesis.

Animals↗

PubMed2006

Reverse genetic analysis of neurogenesis in the zebrafish retina.

To gain an understanding of molecular events that underlie pattern formation in the retina, we evaluated the expression profiles of over 8000 transcripts randomly selected from an embryonic zebrafish library. Detailed analysis of cDNAs that display restricted expression patterns revealed factors that are specifically expressed in single cell classes and are potential regulators of neurogenesis. These cDNAs belong to numerous molecular categories and include cell surface receptors, cytoplasmic enzymes, and transcription factors. To test whether expression patterns that we have uncovered using this approach are indicative of function in neurogenesis, we used morpholino-mediated knockdown approach. The knockdown of soxp, a transcript expressed in the vicinity of the inner plexiform layer, revealed its role in cell type composition of amacrine and ganglion cell layers. Blocking the function of cxcr4b, a chemokine receptor specifically expressed in ganglion cells, suggests a role in ganglion cell survival. These experiments demonstrate that in situ hybridization-based reverse genetic screens can be applied to isolate genetic regulators of neurogenesis. This approach very well complements forward genetic mutagenesis studies previously used to study retinal neurogenesis in zebrafish.

Animals↗

PubMed1996

Xenopus connexin38 forms hemi-gap-junctional channels in the nonjunctional plasma membrane of Xenopus oocytes.

A nonselective cation current activated by depolarization (Ic) is present in the nonjunctional membrane of Xenopus oocytes. This current shares a number of properties with hemi-gap-junctional currents induced by exogenous gap-junctional proteins in oocytes and with a nonjunctional current seen in teleost retinal horizontal cells including nonselective permeability to small cations, block by external divalent cations, and slow activation kinetics. Here we study the effects of depleting or overexpressing Cx38 on Ic. Antisense depletion of Cx38 caused a marked reduction in Ic and blocked endogenous gap-junctional coupling in oocyte pairs. Conversely, expression of cloned Cx38 in oocytes increased the amplitude of Ic and enhanced gap-junctional coupling. Furthermore, there appeared to be a close correlation between the temperature sensitivity of Ic and the temperature sensitivity of assembly of endogenous gap-junctional channels in oocyte pairs. These results suggest that Xenopus connexin38 is involved in the generation of Ic.

Animals↗

PubMedDate not supplied

Gap junction channel gating at bass retinal electrical synapses.

To further characterize the properties of retinal horizontal cell electrical synapses, we have studied the gating characteristics of gap junctions between cone-driven horizontal cells from the hybrid striped bass retina using double whole-cell voltage-clamp techniques. In a total of 105 cell pairs, the macroscopic conductance ranged from 0.4-100 nS with most cell pairs exhibiting junctional conductances between 10 and 30 nS. The junctional current-voltage relationship showed that peak or instantaneous currents (Iinst) were linear within the Vj range of +/- 100 mV and that steady-state junctional currents (Iss) exhibited rectification with increasing voltage beginning around +/- 30-40 mV Vj. The normalized junctional current-voltage relationship was well fit by a two-state Boltzmann distribution, with an effective gating charge of 1.9 charges/channel, a half-maximal voltage of approximately +/- 55 mV, and a normalized residual conductance of 0.28. The decay of junctional current followed a single exponential time course with the time constant decreasing with increasing Vj. Recovery of junctional current from voltage-dependent inactivation takes about 1 s following a pulse of 80 mV, and is about five times slower than the inactivation time course at the same Vj. Single-channel analysis showed that the unitary conductance of junctional channels is 50-70 pS. The overall open probability decreased in a voltage-dependent manner. Both the mean channel open time and the frequency of channel opening decreased, while the channel closure time increased. The ratio of closed time/total recording time significantly increased as Vj increased. Increased Vj reduced the number of events at all levels and shifted the unitary conductance to a lower level. Kinetic analysis of channel open duration showed that the distribution of channel open times was best fit by two exponentials and increased Vj significantly reduced the slower time constant. These results indicate that bass retina horizontal cells exhibit voltage-dependent inactivation of macroscopic junctional current. The inactivation occurs at the single-channel level mainly by increasing the rate of closure of voltage-sensitive channels.

Animals↗

PubMedDate not supplied

Retinal neuromodulation: the role of dopamine.

Dopamine exerts multiple effects on retinal horizontal cells. Dopamine, via cyclic AMP and protein kinase A, reduces the light responsiveness of horizontal cells and the electrical coupling between the cells. The gating kinetics of both gap-junctional and glutamate channels are altered as a result of phosphorylation by protein kinase A. Dopamine also causes a reversible retraction of neurites of horizontal cells maintained in culture. Diacylglycerol analogues as well as phorbol esters mimic this effect of dopamine, but not cyclic AMP analogues or Forskolin. The results suggest that dopamine causes neurite retraction by the activation of protein kinase C via diacylglycerol.

Animals↗

PubMed1992

Dopamine enhances both electrotonic coupling and chemical excitatory postsynaptic potentials at mixed synapses.

The transmitter dopamine reduces electrotonic coupling between retinal horizontal cells and increases their sensitivity to glutamate. Since in other systems single afferents establish mixed electrotonic and chemical excitatory synapses with their targets, dopamine might be expected there to depress one component of excitation while enhancing the other. This hypothesis was tested by applying dopamine locally in the vicinity of the lateral dendrite of the goldfish Mauthner cell (M cell) and monitoring the composite electrotonic and chemical excitatory postsynaptic potentials and currents evoked by ipsilateral eighth nerve stimulation. Dopamine produces persistent enhancements of both components of the postsynaptic response while it also increases input conductance. All these dopamine actions are prevented by superfusing the brain with saline containing the dopamine D1 receptor antagonist SCH-23390. Postsynaptic injections of the cAMP-dependent protein kinase inhibitor (Walsh inhibitor, or PKI5-24) block the dopamine-induced changes in synaptic transmission, implicating a cAMP-dependent mechanism. Furthermore, there is a dopaminergic innervation of the M cell, as demonstrated immunohistochemically with antibodies against dopamine and the rate-limiting enzyme in its synthetic pathway, tyrosine hydroxylase. Varicose immunoreactive fibers lie in the vicinity of the distal part of the lateral dendrite between the large myelinated club endings that establish the mixed synapses. As determined with electron microscopy, the dopaminergic fibers contain small vesicles, and they do not have synaptic contacts with either the afferents or the M cell, remaining instead in the synaptic bed. Taken together, these results suggest that dopamine released at a distance from these terminals increases the gain of this primary sensory input to the M cell, most likely through a phosphorylation mechanism.

Animals↗

PubMed1996

Nitric oxide and cGMP modulate retinal glutamate receptors.

1. In the retina, as in other regions of the vertebrate central nervous system, glutamate receptors mediate excitatory chemical synaptic transmission and are a critical site for the regulation of cellular communication. In this study, retinal horizontal cells from the hybrid less were dissociated in cell culture, voltage clamped by the whole cell recording technique, and the currents evoked by application of excitatory amino acids recorded. 2. Responses to glutamate and its agonist kainate were reduced by approximately 50% in the presence of the nitric oxide (NO) donors sodium nitroprusside and S-nitroso-N-acetylpenicillamine. The effect of these compounds was blocked by the NO scavenger hemoglobin. 3. This effect of NO donors on kainate currents could be mimicked by the application of a membrane permeable guanosine 3',5'-cyclic monophosphate (cGMP) analogue, 8-Br-cGMP. The NO effect was also blocked by application of the guanylate cyclase inhibitor LY-83583, and by a protein kinase G inhibitor peptide. 4. In H1-type horizontal cells, stimulation of endogenous nitric oxide synthase with L-arginine reduced kainate responses, whereas application of D-arginine had no effect. 5. This receptor modulation mechanism may act in concert with other pre- and postsynaptic mechanisms to modify horizontal cell synaptic function according to the adaptational state of the retina and also may protect horizontal cells from glutamate excitotoxicity.

Animals↗

PubMed2000

The minimal local-asperity hypothesis of early retinal lateral inhibition.

Recently we found that the theories related to information theory existent in the literature cannot explain the behavior of the extent of the lateral inhibition mediated by retinal horizontal cells as a function of background light intensity. These theories can explain the fall of the extent from intermediate to high intensities, but not its rise from dim to intermediate intensities. We propose an alternate hypothesis that accounts for the extent's bell-shape behavior. This hypothesis proposes that the lateral-inhibition adaptation in the early retina is part of a system to extract several image attributes, such as occlusion borders and contrast. To do so, this system would use prior probabilistic knowledge about the biological processing and relevant statistics in natural images. A key novel statistic used here is the probability of the presence of an occlusion border as a function of local contrast. Using this probabilistic knowledge, the retina would optimize the spatial profile of lateral inhibition to minimize attribute-extraction error. The two significant errors that this minimization process must reduce are due to the quantal noise in photoreceptors and the straddling of occlusion borders by lateral inhibition.

Animals↗

PubMed1991

Bi-spectral analysis of bioelectric phenomena: a survey.

This article presents five examples of bi-spectral analysis of bioelectric phenomena which show non-Gaussian statistics. Examples include: analysis of the electroencephalogram (EEG), electrical response of retinal horizontal cells to light stimuli, the evoked potential (EVP), the electromyogram (EMG) and spontaneous synaptic potentials (SSP). Readers may find the higher-order spectral analysis useful in extracting information underlying various kinds of bioelectric phenomena.

Animals↗

PubMed1998

Postsynaptic responses of horizontal cells in the tiger salamander retina are mediated by AMPA-preferring receptors.

The postsynaptic responses of sign-preserving second-order retinal neurons (horizontal cells (HCs) and off-bipolar cells) are mediated by CNQX-sensitive AMPA/KA glutamate receptors. In this study we used receptor-specific allosteric regulators of desensitization and selected antagonists to determine the glutamate receptor subtypes in tiger salamander horizontal cells. Two approaches were employed in this study. The first was to measure postsynaptic currents induced by exogenously applied glutamate under voltage clamp conditions in living retinal slices; and the second was to record voltage responses controlled by endogenous glutamate released from photoreceptors in whole retinas. Application of 100 microM cyclothiazide (a specific AMPA receptor desensitization blocker) enhanced the glutamate-induced current by about 5 fold. In contrast, 300 microgram ml-1 Co nA (a specific kainate receptor desensitization blocker), had no effect. GYKI 52466 (a specific AMPA receptor antagonist) at 30 microM almost completely suppressed the glutamate-induced inward current in HCs. Cyclothiazide at 100 microM depolarized the HC dark membrane potential by about 5 mV and reduced the amplitudes of the voltage responses to dim lights, but enhanced the voltage responses to bright lights. Cyclothiazide had no effect on either the dark potential or the light responses of rods and cones. Con A at 300 microgram ml-1 had no effect on either the dark potential or the light responses of the HC. GYKI 52466 (30 microM) hyperpolarized the HC dark membrane potential by about 55 mV and almost completely suppressed the light responses. We conclude from these results that the postsynaptic glutamate- and light-induced responses in the tiger salamander retinal horizontal cells are mediated by AMPA-preferring, and not kainate-preferring glutamate receptors. The functional roles of AMPA receptors and their desensitization kinetics in visual information processing are discussed.

Ambystoma↗

PubMed2003

Gamma-aminobutyric acid-synthesizing cells in the retina of the chameleon Chamaeleo chameleon.

Antibodies directed against gamma-aminobutyric acid (GABA) and L-glutamic acid decarboxylases 65 and 67 kDa (GAD65 and -67) were used to study the GABAergic cell populations of the chameleon retina. GABA immunoreactivity was found in the two main types of retinal interneurons, amacrine and horizontal cells. Amacrine, displaced amacrine, and intra- and interplexiform cells displayed the strongest GABA immunoreactivity of all the retinal cell types. Horizontal cells formed a continuous GABA-immunoreactive cell layer lying against the outermost portion of the inner nuclear layer. In contrast to previous studies (Quesada et al. [1996] Cell Biol. Int. 20:395-400; [1999] Eur. J. Anat. 3:13-25), the present results demonstrate that the horizontal cells of the chameleon retina are GABA immunoreactive and that a subpopulation of these is immunolabelled by an antibody against GAD65. These results indicate that GABAergic synaptic transmission plays a key role in the outer plexiform layer of the vertebrate retina.

Amacrine Cells↗

PubMed2006

Modeling the pre- and post-synaptic components involved in the synaptic modification between cones and horizontal cells in carp retina.

In retinal synapses between cones and luminosity type horizontal cells (LHC), it was previously found in this laboratory that repetitive red flashes progressively strengthened the LHC's response to red flash, whereas weakened the LHC's response to green flash; repetitive green flash remarkably depressed the LHC's red response, but caused little changes in the cell's green response. However, the detailed mechanisms underlying these phenomena are not entirely clear. In the present study, based on an ion-channel model described mainly in the form of Hodgkin-Huxley equations, possible mechanisms of the short-term synaptic modification are investigated. The simulation results suggest that: (1) the auto-enhancement effect might be induced by the Ca2+-dependent process on the post-synaptic AMPA receptors, which could lead to changes of the ionic channel's properties; (2) the asymmetric response to red- and green-flashes and the mutual-chromatic suppression effects might be attributed to the regulatory effects on the presynaptic glutamate release.

Animals↗