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Results for “Retinal Horizontal Cells”

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PubMed1985

Distribution and soma size of ganglion cells in the retina of the eastern chipmunk (Tamias sibiricus asiaticus).

Topographic distribution and soma size of ganglion cells were studied in Nissl-stained, whole-mounted retinas of the eastern chipmunk. High density areas in the central retina were elongated horizontally, making up the visual streak. The total count of ganglion cells was estimated as 410,000. Throughout the retina soma size of ganglion cells showed a uimodal distribution, although a distinct population of large cells was found in the dorso-temporal periphery.

Animals↗

PubMed1992

The ratio of L cones to M cones in the human parafoveal retina.

We present psychophysically-based estimates of the relative numbers of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in the parafovea of three color-normal trichromats. Using methods previously applied to the fovea centralis, we obtained estimates of the relative numbers of L and M cones at retinal eccentricities of 1.0, 1.5, 2.0, 3.0, and 4.0 deg along the horizontal meridian of the temporal retina. Results for three observers indicate that the L to M cone ratio remains approximately invariant from the fovea to 4.0 deg eccentricity, with a mean ratio near 2:1.

Cell Count↗

PubMed2002

Neurons in parafoveal areas V1 and V2 encode vertical and horizontal disparities.

Stereoscopic vision mainly relies on binocular horizontal disparity (HD), and its cortical encoding is well established in the foveal representation of the visual field. The role of vertical disparity (VD) is more controversial. Thus far, in the monkey, very few studies have investigated the HD sensitivity beyond 5 degrees of retinal eccentricity and no evidence of a real encoding of VD exists in the parafoveal representation of areas V1 and V2. Using dynamic random dot stereograms, we have tested both HD and VD selectivities in the parafoveal representation of V1 (calcarine V1) and V2 (eccentricities > 10 degrees ) in a behaving monkey. HD and VD selectivities have been characterized using fitting with Gabor function. A large proportion of the tested cells were both HD and VD selective (47%) and, to a lesser extent, HD selective only (8%) or VD selective only (23%). We found a real encoding of VD, with the same diversity in the tuning profiles as described for HD, that cannot be assimilated to a simple perturbation of the HD matching process. Moreover, the VD encoding had a finer scale than the HD one, which is coherent with the smaller range of naturally occurring VD. For the HD encoding, both the percentage of selective cells and the tuning parameters were close to those reported in foveal V1. These results show that, at parafoveal eccentricities in V1 and V2, disparity detectors are tuned to both horizontal and vertical dimensions of the positional disparity existing between matched features in both retinas.

Animals↗

PubMed1993

Localization and modulatory actions of zinc in vertebrate retina.

Zinc ions are colocalized with glutamatergic synaptic vesicles in vertebrate photoreceptors and may act as a diffusible molecular switch regulating neurotransmitter signaling at two distinct sites in the outer retina. In the dark, extracellular zinc acts presynaptically at rods and cones to minimize the depletion of tonically released glutamate, and selectively reduces GABA-mediated depolarization in horizontal cells, accelerating the response kinetics of the second-order cells. The discovery of zinc ions in photoreceptors provides a mechanism for gain control, kinetics modulation, and the balance of rod vs cone output at the first synapse in the visual system.

Animals↗

PubMed1997

Receptive field dimensions of lateral geniculate cells in the common marmoset (Callithrix jacchus).

We measured the spatial receptive field dimensions of cells in the lateral geniculate nucleus (LGN) of the common marmoset (Callithrix jacchus) using a bipartite field stimulus in which the two halves of the field were modulated identically but in counterphase. Horizontal and vertical edges between the two fields were positioned at different locations in the receptive field. By assuming that centers and surrounds have gaussian profiles, we were able to obtain a satisfactory mathematical description of the data. Receptive field centers were about a factor 1.6 larger than those of macaque LGN cells, in accordance with the smaller marmoset eye. There was a limited correspondence with dendritic tree dimensions of marmoset retinal ganglion cells. We further found that center and surround gaussians were not always concentric, and that the centers of some cells were elongated. This might allow some direction or orientation biases in LGN cells.

Algorithms↗

PubMed1989

Extracellular pH in the isolated retina of the toad in darkness and during illumination.

1. Extracellular pH (pHo) was measured in the isolated retina preparation of the toad, Bufo marinus, using H(+)-selective microelectrodes. During superfusion with phosphate-buffered solution (pH 7.8), which had a low buffering capacity, pHo in the inner retina was 7.0-7.2 and there was a pHo gradient throughout the distal retina and into the bathing solution. 2. The retinal acidity appears to be due in part to the combined reactions of glycolysis and ATP hydrolysis, since anoxia greatly increased the pHo gradient, while superfusion with either glucose-free pyruvate solution or strophanthidin decreased this gradient. 3. Maintained illumination evoked both an acidification in the proximal retina and an alkalinization in the distal retina. Blocking synaptic transmission to second-order neurones (1.0 mM-aspartate) decreased the acidification but had little effect on the alkalinization, consistent with the notion that the alkalinization is of receptoral origin, while the acidification is of post-receptoral origin. 4. Retinal neurones extrude a significant amount of acid via Na(+)-H+ exchange, since 2.0 mM-amiloride, a blocker of Na(+)-H+ exchange, caused a sustained alkalinization in darkness and decreased the light-evoked changes in pHo, while 1.0 mM-4-acetamido-4'-isothiocyanatostilbene-2.2'-disulphonic acid (SITS), a blocker of Cl(-)-HCO3- exchange, produced a much smaller alkalinization. 5. Switching to a bicarbonate-buffered solution having a 75 times greater buffering capacity than the phosphate-buffered solution caused retinal pHo to become less acidic and significantly decreased the amplitude of the light-evoked pHo changes. 6. Addition of 2.0 mM-acetazolamide, a carbonic anhydrase inhibitor, to the bicarbonate-buffered solution increased both the pHo gradient and the light-evoked changes in pHo. These data are consistent with the idea that carbonic anhydrase, which is concentrated in Müller (glial) cells and to a lesser extent in horizontal cells, increases the effectiveness of the bicarbonate buffer system. 7. Switching from bicarbonate-buffered to phosphate-buffered solutions attenuated the b-wave of the electroretinogram, most likely by acidifying pHo. Overall, our results emphasize the importance of the bicarbonate buffer system in buffering pHo during periods of variable acid extrusion in light and in darkness.

Animals↗

PubMed2005

In vitro activation of retinal cells: estimating location of stimulated cell by using a mathematical model.

Activation of neurons at different depths within the retina and at various eccentricities from the stimulating electrode will presumably influence the visual percepts created by a retinal prosthesis. With an electrical prosthesis, neurons will be activated in relation to the stimulating charge that impacts their cell membranes. The common model used to predict charge density is Coulomb's law, also known as the square law. We propose a modified model that can be used to predict neuronal depth that takes into account: (1) finite dimensions related to the position and size of the stimulating and return electrodes and (2) two-dimensional displacements of neurons with respect to the electrodes, two factors that are not considered in the square law model. We tested our model by using in vitro physiological threshold data that we had obtained previously for eight OFF-center brisk-transient rabbit retinal ganglion cells. For our most spatially dense threshold data (25 microm increments up to 100 microm from the cell body), our model estimated the depth of one RGC to be 76 +/- 76 microm versus 87 +/- 62 microm (median: SD) for the square law model, respectively. This difference was not statistically significant. For the seven other RGCs for which we had obtained threshold data up to 800 microm from the cell body, the estimate of the RGC depth (using data obtained along the X axis) was 96 +/- 74 versus 20 +/- 20 microm for the square law and our modified model, respectively. Although this difference was not statistically significant (Student t-test: p = 0.12), our model provided median values much closer to the estimated depth of these RGCs (>>25 microm). This more realistic estimate of cell depth predicted by our model is not unexpected in this latter data set because of the more spatially distributed threshold data points that were evaluated. Our model has theoretical advantages over the traditional square law model under certain conditions, especially when considering neurons that are horizontally displaced from the stimulating electrode. Our model would have to be tested with a larger threshold data pool to permit more conclusive statements about the relative value of our model versus the traditional square law model under special circumstances.

Action Potentials↗

PubMed2005

The involvement of glutamate-gated channels in negative feedback from horizontal cells to cones.

Photoreceptors are the light sensitive cells in the retina. They project to horizontal cells and bipolar cells via a glutamatergic feed forward pathway. Horizontal cells are strongly electrically coupled and integrate in that way the input from the photoreceptors. Horizontal cells feedback to cones negatively. The combined signal from the photoreceptors and the horizontal cells is sent to the bipolar cells. The feedback pathway from horizontal cells to cones is thought to form the basis for the center/surround organization of bipolar cells. The nature of the feedback pathway is an issue of intense debate. It was thought for a long time that this feedback pathway was GABAergic, because cones have GABA-receptors and horizontal cells release GABA via a GABA-transporter working in the reversed direction. However, recently we showed in goldfish that horizontal cells feed back to cones via an alternative mechanism. In goldfish, negative feedback from horizontal cells to cones shifts the calcium current of the cone to more negative potentials. This feedback pathway is independent of GABA, since feedback cannot be blocked by either saturating concentrations of PTX, the GABA-transporter blocker SKF89976A, or application of GABA. The mechanism of negative feedback from horizontal cells to cones involves hemichannels located at the tips of the invaginating horizontal cells, just opposite to the calcium channels of the cones. Current flowing through these hemichannels changes the extracellular potential deep in the synaptic cleft and in that way modulates the calcium current of the cones. Such a modulation of the extracellular potential is called ephaptic. If negative feedback from horizontal cells to cones is indeed ephaptic, other channels present in the synapse should also be able to act as a current source, i.e., should also be able to change the output of the cone. We showed that glutamate-gated channels present at the tips of the horizontal cell dendrites can also mediate feedback responses. Surprisingly, although the glutamate-gated conductance of the horizontal cells is eight times the hemichannel conductance, glutamate-gated channels are not the major current source in negative feedback from horizontal cells to cones. In this chapter we present evidence that this is due to the more focal localization of the hemichannels, compared to a diffuse and extrasynaptic localization of the glutamate-gated channels.

Animals↗

PubMed1998

UV-sensitive input to horizontal cells in the turtle retina.

Microspectrophotometry, electroretinography and behavioural studies have indicated that ultraviolet (UV) light contributes to functional vision in various vertebrate species. Based on behavioural evidence, this was also suggested for turtle vision. In order to reveal the interactions underlying detection of UV light in the distal retina, we recorded intracellularly the photoresponses of cones and horizontal cells in retinas of Pseudemys scripta elegans and Mauremys caspica and calculated the action spectra of these cells under different conditions of adaptation. In the dark-adapted retina, all three types of horizontal cells; luminosity-type, red/green chromaticity-type and yellow/blue chromaticity-type exhibited increased sensitivity in the UV region of the spectrum. However, chromatic adaptation indicated that only the yellow/blue chromaticity-type horizontal cells received excitatory input from UV-sensitive cones with peak sensitivity approximately 360 nm. The enhanced UV sensitivity of luminosity-type horizontal cells probably reflected the beta-band of the long-wavelength sensitive visual pigment as indicated by the action spectra of dark-adapted L-cones. It is suggested that the enhanced UV sensitivity of red/green chromaticity-type horizontal cells reflects the beta-band of the medium-wavelength sensitive visual pigment. Transmission measurements of the optical media (cornea, lens and vitreous) indicated that UV vision can be functional under normal circumstances.

Adaptation, Physiological↗

PubMed1999

Activation of metabotropic glutamate receptors modulates the voltage-gated sustained calcium current in a teleost horizontal cell.

In the teleost retina, cone horizontal cells contain a voltage-activated sustained calcium current, which has been proposed to be involved in visual processing. Recently, several studies have demonstrated that modulation of voltage-gated channels can occur through activation of metabotropic glutamate receptors (mGluRs). Because glutamate is the excitatory neurotransmitter in the vertebrate retina, we have used whole cell electrophysiological techniques to examine the effect of mGluR activation on the sustained voltage-gated calcium current found in isolated cone horizontal cells in the catfish retina. In pharmacological conditions that blocked voltage-gated sodium and potassium channels, as well as N-methyl-D-aspartate (NMDA) and non-NMDA channels, application of L-glutamate or 1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) to voltage-clamped cone horizontal cells acted to increase the amplitude of the calcium current, expand the activation range of the calcium current by 10 mV into the cell's physiological operating range, and shift the peak calcium current by -5 mV. To identify and characterize the mGluR subtypes found on catfish cone horizontal cells, agonists of group I, group II, or group III mGluRs were applied via perfusion. Group I and group III mGluR agonists mimicked the effect of L-glutamate or 1S,3R-ACPD, whereas group II mGluR agonists had no effect on L-type calcium current activity. Inhibition studies demonstrated that group I mGluR antagonists significantly blocked the modulatory effect of the group I mGluR agonist, (S)-3,5-dihydroxyphenylglycine. Similar results were obtained when the group III mGluR agonist, L-2-amino-4-phosphonobutyric acid, was applied in the presence of a group III mGluR antagonist. These results provide evidence for two groups of mGluR subtypes on catfish cone horizontal cells. Activation of these mGluRs is linked to modulation of the voltage-gated sustained calcium current.

Animals↗

PubMed1997

Regenerating ganglion cell axons in the adult rat establish retinofugal topography and restore visual function.

The mechanisms of neuronal network response to axotomy are poorly understood. In one of the favoured models used to study the fate of injured neurons in the adult rat visual system, appreciable numbers of retinal neurons survive optic nerve injury under conditions of microglia-targeted neuroprotection. Rescued neurons can regenerate their axons and become target-dependently stabilised after reconnection with their natural visual centres by means of a peripheral nerve graft, which, in addition to guidance, actively supports axonal growth. The mechanisms that control regenerative axonal growth and resynaptogenesis include coordinated cell-cell interactions between growing neurites and target cells in order to establish a meaningful reconnectivity. Here the function of the regenerating visual circuitry was first studied by monitoring the ability of animals to discriminate spatial patterns, and second by recording visual evoked cortical potentials (VEPs) in the same animals. These functions were correlated with neuroanatomical studies of the retinotopic organisation of regenerating axons. To achieve these goals, adult rats were behaviourally trained in a Y-maze to discriminate between vertical and horizontal stripes. Both optic nerves were transected, and the regenerating axons of one optic nerve were guided into the area of optic tract with a peripheral nerve graft according to the protocols of neuroprotection and simultaneous grafting, in order to enable large numbers of axons to reinnervate the major visual targets in the midbrain and thalamus. Postoperative testing of the animals showed a marked improvement of visual perception and behaviour. The VEPs of the same animals were measurable indicating a restoration of the visual circuitry including the ascending corticopedal connections. Neuroanatomical assessment of the fibre topography within the graft and the area of termination revealed a rough topographic organisation that may account for restoration of the function. These results suggest that interrupted central pathways can be functionally reconnected by providing a neuroprotective environment in combination with peripheral nerve grafts to bypass lesions.

Animals↗

PubMed1990

Effects of early monocular deprivation on response properties and afferents of nucleus of the optic tract in the ferret.

Effects of early monocular deprivation on visual response properties of neurons in the nucleus of the optic tract (NOT) were studied in six adult ferrets. Retinal input to NOT was investigated by orthodromic electrical stimulation of optic chiasm and optic nerves. Electrical stimulation of the ipsilateral primary visual cortex was applied to reveal the presence of a cortical pathway to NOT. All 75 neurons studied in the NOT displayed the typical strongly direction-specific response to horizontal stimulus motion; they were activated by ipsiversively directed motion (i.e. motion towards the recorded hemisphere) similar to NOT-cells in animals with normal visual experience. When tested binocularly most of the NOT-cells preferred velocities of 10 or 20 deg/s, revealing no significant difference from animals reared with normal binocular experience. The most pronounced effect of monocular deprivation was observed on ocular dominance: In the hemisphere contralateral to the non-deprived eye, NOT-cells were almost exclusively driven through the contralateral eye. In the hemisphere contralateral to the deprived eye, three of the six animals studied showed a marked dominance of the ipsilateral, non-deprived eye. In the other three animals, most neurons were binocularly activated, but over all they were significantly more strongly activated by the ipsilateral eye than found in normal animals. In four animals, dependence of ocular dominance on stimulus velocity was tested in the NOT contralateral to the deprived eye. In one of them, neurons were almost exclusively driven by the ipsilateral, non-deprived eye, irrespective of stimulus velocity. In the other animals, ocular dominance shifted from contralateral to ipsilateral with increasing stimulus velocities. Electrical stimulation of the optic chiasm revealed a mean latency of 5.53 +/- 0.48 ms. In both hemispheres, NOT-units could only be activated by stimulation of the contralateral optic nerve. Thus, no significant difference in the retinofugal conduction velocities from the deprived and the normal nerve could be detected. Of 52 cells studied, 28 (= 54%) could be activated by stimulation of primary visual cortex, mean latency being 3.9 +/- 1.7 ms. No significant difference in the percentage of cortically excitable cells between the two hemispheres as well as compared to normal animals was found (contralateral to the deprived eye: 67%, contralateral to the non-deprived eye: 53%). Therefore, cortical projections to NOT seem not to be affected by monocular deprivation. The effects of monocular deprivation in the ferret NOT, especially on ocular dominance and cortical input, are compared to the results previously described for the cat.

Afferent Pathways↗

PubMed1990

Effects of selective neurotoxins on eye growth in the young chick.

We have determined the extent of retinal cell damage and eye growth after treatment with different neurotoxins. Day-old chicks received an intraocular injection containing 2, 10, 50, 100 or 200 nmol of kainic acid (KA), an excitotoxic analogue of glutamate. After 21 days, with 2 nmol KA damage was confined to a small proportion of bipolar cells, whereas with 10-200 nmol KA there was dose-dependent damage to amacrine cells, ganglion cells and photoreceptors. There was an increase in eye weight and size of the vitreal chamber with 10 nmol KA or more. In a similar protocol using 5, 50 or 200 nmol quisqualic acid (QUIS), there was massive loss of amacrine cells and slight loss of horizontal cells, and a large increase in the anterior chamber depth. A single dose of 200 nmol N-methyl-D-aspartate lesioned amacrine cells, but did not alter eye size. Thus, excitotoxins which have different retinotoxic effects also have different effects on eye size. In another study, we examined the effects of KA and QUIS on occlusion-induced eye enlargement. Treatment with 200 nmol QUIS alone resulted in increased depth of the anterior chamber. QUIS combined with occlusion for 3 weeks did not interfere with occlusion-induced growth of the vitreal chamber. Therefore, the loss of a large proportion of amacrine cells did not interfere with occlusion-induced growth. KA results in eye growth in its own right, but restricts occlusion-induced growth. These effects are associated with damage to photoreceptors, amacrine and bipolar cells and a small proportion of ganglion cells. Finally, we examined the effects of an intraocular injection of tunicamycin, a purported photoreceptor-specific neurotoxin in amphibia. Tunicamycin (0.1 or 1 mumg/eye) resulted in a flattened anterior chamber but did not affect growth of the vitreal chamber. Tunicamycin inhibited occlusion-induced growth, and treated retinae displayed massive disruption and loss of all cell types apart from a single row of pigmented retinal epithelium. We conclude that (a) normal and occlusion-induced eye growth may have separate mechanisms of action, (b) the vitreous and anterior chambers have different growth mechanisms, and (c) photoreceptors may play a critical role in occlusion-induced growth of the eye.

Animals↗

PubMed2004

Differential distribution of fibroblast growth factor receptors (FGFRs) on foveal cones: FGFR-4 is an early marker of cone photoreceptors.

PURPOSE: Relatively little is known of the expression and distribution of FGF receptors (FGFR) in the primate retina. We investigated expression of FGFRs in developing and adult Macaca monkey retina, paying particular attention to the cone rich, macular region. METHODS: One fetal human retina was used for diagnostic PCR using primers designed for FGFR1, FGFR2, FGFR3, FGFR4, and FGFR like-protein 1 (FGFrl1) and for probe design to FGFR3, FGFR4, and FGFrl1. Rat cDNA was used to synthesize probes for FGFR1 and FGFR2 with 90% and 93% homology to human, respectively. Paraffin sections of retina from macaque fetuses sacrificed at fetal days (Fd) 64, 73, 85, 105, 115, 120, and 165, and postnatal ages 2.5 and 11 years were used to detect FGF receptors by immunohistochemistry and in situ hybridization. RESULTS: PCR showed each of the FGF receptors are expressed in fetal human retina. In situ hybridization indicated that mRNA for each receptor is expressed in all retinal cell layers during development, but most intensely in the ganglion cell layer (GCL). FGFR2 mRNA is reduced in the adult inner (INL) and outer (ONL) nuclear layers, while FGFrl1 mRNA is virtually absent from the adult ONL. FGFR4 mRNA is particularly intense in fetal and adult cone photoreceptors. Immunoreactivity to FGFR1-FGFR4 was detected in the interphotoreceptor matrix in what appeared to be RPE microvilli associated with developing photoreceptor outer segments, and generally is high in the GCL and low in the INL. Different patterns of FGFR3 and FGFR4 immunoreactivities in the outer plexiform layer (OPL) suggest localization of FGFR3 to horizontal cell processes, with FGFR4 being expressed by both horizontal and bipolar cell processes. FGFR1, FGFR3, and FGFR4 immunoreactivities are present in the inner segments and somata of adult cones. The pedicles of developing and adult cones are FGFR1 and FGFR3 immunoreactive, and the basal, synaptic region is FGFR4 immunoreactive. FGFR4 labels cones almost in their entirety from early in development and is not detected in rods. The fibers of Henle are intensely FGFR4 immunoreactive in adult cones. CONCLUSIONS: The results show high levels of FGF receptor expression in developing and adult retina. Differential distribution of FGF receptors across developing and adult photoreceptors suggests specific roles for FGF signalling in development and maintenance of photoreceptors, particularly the specialized cones of the fovea.

Animals↗

PubMed1990

The synaptic organization of the dopaminergic amacrine cell in the cat retina.

The dopaminergic amacrine cells of the cat retina have been stained by immunocytochemistry using an antibody to tyrosine hydroxylase (Toh). The complete population of Toh+ cells has been studied by light microscopy of retinal wholemounts to evaluate morphological details of dendritic structure and branching patterns. Selected Toh+ amacrine cells have been studied by serial-section electron microscopy to analyse synaptic input and output relationships. The majority of Toh+ amacrine cells occur in the amacrine cell layer of the retina and have their dendrites ramifying and forming the characteristic rings in stratum 1 of the inner plexiform layer. A minority of Toh+ cells have cell bodies displaced to the ganglion cell layer but their dendrites also stratify in stratum 1. All Toh+ cells have some dendritic branches running in stratum 2 as well as in stratum 1, and frequently they have long 'axon-like' processes (500-1000 microns long) dipping down to run in stratum 5 before passing up to rejoin the major dendritic arbors in stratum 1. In addition Toh+ stained processes follow blood vessels in the inner plexiform layer and in the ganglion cell layer. A population of Toh+ cells found in the inferior retina appears to give rise to stained processes that pass to the outer plexiform layer and therein to run for as far as one millimeter. Electron microscopy reveals that Toh+ amacrine cells are postsynaptic to amacrine cells and a few bipolar cell terminals in stratum 1 of the inner plexiform layer and are primarily presynaptic to AII amacrine cell bodies and lobular appendages, and to another type of amacrine cell body and amacrine dendrites hypothesized to be the A17 amacrine cell. The Toh+ dendrites in stratum 2 are presynaptic to AII lobular appendages primarily. Stained 'axon-like' processes running in stratum 5 prove to be presynaptic to AII amacrine dendrites as they approach the rod bipolar axon terminals and they may also be presynaptic to the rod bipolar terminal itself. The Toh+ stained dendrites that have been followed in the outer plexiform layer run along the top of the B-type horizontal cell somata and may have small synapses upon them. The only clear synapses seen in the outer plexiform layer are from the Toh+ profiles upon vesicle filled amacrine-like profiles that are in turn presynaptic to bipolar cell dendrites in the outer plexiform layer. We presume the cells postsynaptic to the Toh+ dendrites in the outer plexiform layer are interplexiform cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1997

Dopaminergic and GABAergic retinal cell populations in mammals.

A number of modern techniques now allow histologists to characterize subpopulations of retinal neurons by their neurotransmitters. The morphologies and connections of these chemically defined neurons can be analyzed precisely at both light and electron microscope levels and lead to a better understanding of retinal circuitry. The dopaminergic neurons form a loose population of special wide-field amacrine cells bearing intraretinal axons within the inner plexiform layer. One subtype, the interplexiform cell, sends an axon to the outer plexiform and outer nuclear layers. The number of interplexiform cells is variable throughout mammalian species. The GABAergic neurons form a dense and heterogeneous population of amacrine cells branching at all levels of the inner plexiform layer. The presence of GABA in horizontal cells seems to be species-dependent. Close relationships occur between dopaminergic and GABAergic cells. GABA antagonizes a number of dopaminergic actions by inhibiting both the release and synthesis of dopamine. This inhibition can be supported by GABA synapses onto dopaminergic cells, but GABA can also diffuse to its targets. Finally, GABA is also contained and synthesized in dopaminergic cells. This colocalization might be the basis of an intracellular modulation of dopamine by GABA.

Animals↗

PubMed1987

Effect of dopamine and haloperidol on the c-wave and light peak of light-induced retinal responses in chick eye.

The relation between dopaminergic cells (and centrifugal fibers), the electroretinogram (ERG) c-wave, and the light peak were electrophysiologically investigated by observing the effects of a retrobulbar conduction block and intravitreal injection of either dopamine or haloperidol on these retinal responses. The retrobulbar conduction block (1% lidocaine) caused a decrease in the amplitude of the c-wave and the light peak in newly hatched chicks. Injections (2-20 microliters) containing dopamine (0.1-10 mM) or haloperidol (1.3-13 mM) were given intravitreously while the responses were recorded. Although intravitreous injection of saline for control resulted in no observable change in the responses, dopamine selectively augmented the c-wave of ERGs and the light peak, but not the a-, b-, and d-waves. Haloperidol decreased first the light peak and later the c-wave. The augmentation of the retinal responses by dopamine and their reduction by haloperidol was statistically significant. The estimated threshold concentration of dopamine in the vitreous cavity was 1-3.5 microM. Since in many species the interplexiform cells have been found to contain dopamine, we hypothesize that the modulatory effects on the c-wave and the light peak in this preparation may be due to a centrifugal feed-back loop which includes the interplexiform cells to the horizontal and bipolar cells and the horizontal cells to the cones.

Animals↗

PubMed1990

Intermediate filament complement of the normal and gliotic canine retina.

Intermediate filament expression of various cell types in the adult canine normal and gliotic retina was determined by an immunoperoxidase method of using monoclonal antibodies on aldehyde-fixed tissues. In the normal retina, vimentin was present in astrocytes in the nerve fibre layer, horizontal cell processes, and Müller cell fibres from the internal limiting membrane to the outer nuclear layer. Neurofilamentous axons were noted in the nerve fibre, inner plexiform layer, and outer plexiform layer, although the degree of staining intensity varied among the three molecular weight neurofilament antisera used. Glial fibrillary acidic protein (GFAP) staining was confined to the nerve fibre and ganglion cell layer; this was interpreted as representing fibrous astrocytes. Astrocyte density varied according to retinal topography with an increased number around retinal blood vessels and in the peripapillary retina. Quantitative, but not qualitative differences in staining for vimentin and the neurofilaments were noted in degenerative, gliotic retinas. In common with several other mammalian species previously studied, the canine Müller cells accumulate or express GFAP under pathological conditions involving a gliotic response.

Animals↗