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PubMedDate not supplied

Identification of cone classes in Xenopus retina by immunocytochemistry and staining with lectins and vital dyes.

The aim of the present study was to determine the number of cone classes in the Xenopus retina. We examined the dimensions and staining properties of cones, utilizing two monoclonal antibodies, COS-1 and OS-2, developed by Szel and Rohlich (1985). Living cones also were reacted with the plant lectins peanut agglutinin (PNA) and wheat germ agglutinin (WGA) and with a fluorescent stilbene dye, DIDS, which binds selectively to red-sensitive cones (Kleinschmidt, 1991; Kleinschmidt & Harosi, 1992a,b). Three cone populations were distinguished based on differences in size and staining properties. Eighty-eight percent of all cones were stained strongly by COS-1, PNA, and DIDS, but weakly by OS-2. The group of cones stained by COS-1 had the largest mean dimensions of outer segment length, width, and oil droplet diameter. COS-1 negative cones were divisible into two groups: a subclass of miniature cones (approximately 4% total cones) was stained strongly by OS-2, PNA, and DIDS. The balance, constituting approximately 9% total cones, were of intermediate size, were not stained by PNA and reacted weakly to OS-2 and DIDS. WGA stained all cones. Large, COS-1+ cones appear to be red-sensitive and belong to the class of anion-tunable cone pigments. We suggest that the intermediate size, COS-1 negative cones are blue-sensitive based on the finding that blue-sensitive chromatic horizontal cells connect to them preferentially (Witkovsky et al., work in progress).(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMedDate not supplied

Retinal light adaptation--evidence for a feedback mechanism.

Light adaptation is the adjustment of retinal response properties to variations in ambient illumination. It enables the encoding of visual information over a millionfold intensity range, from moonlight to broad daylight, despite the relatively small dynamic range of response of visual neurones. We have studied the effects of light adaptation on the dynamics and sensitivity of visual responses of neurones in the turtle retina, by measuring the responses of horizontal cells in the retina to light which was modulated with a sinusoidal time course around various mean levels. As a quantitative measure of the transduction from light to neural signals, we calculated the gain of response at each frequency. Gain is defined as the amplitude of the modulated response component divided by the amplitude of light modulation. We report here that the gain (mV photon-1) at low temporal frequencies decreased as the mean light level increased. Over a 2 log-unit range of mean light levels, low-frequency gain was inversely proportional to the mean light level, as in Weber's law. However, at high temporal frequencies, the gain was almost independent of mean light level. Our results are reminiscent of Kelly's results on human temporal-frequency sensitivity in various states of light adaptation. We found that a family of horizontal-cell temporal frequency responses, measured at various mean light levels, could be accounted for by a negative feedback model in which the feedback strength is proportional to mean light level.

Adaptation, Physiological↗

PubMed1999

Rods and cones project to the inner plexiform layer during development.

Mature rod and cone photoreceptor cells extend terminals to the outer plexiform layer (OPL), where they form characteristic spherules or pedicles, synapsing with the second-order neurons of the inner nuclear layer (INL). The present study demonstrates that, prior to the formation of this connectivity, immature rods and cones in the ferret extend processes beyond the level of the horizontal cells and future OPL, reaching the inner plexiform layer (IPL). The number of processes extending to the IPL increases steadily as the population of photoreceptor cells expands postnatally, reaching a maximum 2 weeks after birth. These processes are immunopositive for synaptophysin, and they terminate in two strata occupied by the dendrites of amacrine cells and ganglion cells. The frequency of these processes declines rapidly during the third postnatal week, and they are no longer detectable by the fourth postnatal week. Their loss is neither a consequence of photoreceptor cell death nor is it due to selective protein trafficking mechanisms that render them immunonegative. Rather, these processes retract to the level of the OPL during this period, coincident with the maturation of bipolar and horizontal cell processes. These results demonstrate that, despite the clear presence of environmental signals presaging the formation of the OPL, photoreceptor terminals initially ignore them to grow beyond this level of the retina. Rather, they detect and respond to signals within the IPL during this period, terminating in proximity to the processes of other cells in the inner retina, where they may contribute to transient retinal circuitry during early development.

Animals↗

PubMed1982

Cytochemical heterogeneity of the glial plasma membrane: 5'-nucleotidase in retinal Müller cells.

Localization of 5'-nucleotidase in the retina of four rodent species was investigated using histochemical and cytochemical techniques. It was revealed by light microscopy that the enzyme is present in the receptor layer, the external nuclear layer and the external plexiform layer. It was found by electro microscopy that the glial cells of the Müller type have a strong activity on their plasmalemma in the enzyme-positive layers. With the exception of weak and scattered activity on some Müller cell processes forming horizontal fibres and the honeycomb meshwork in the ganglion cell layer, none of the internal layers contain 5'-nucleotidase. The asymmetric distribution of this ectoenzyme on the surface of the glial cells is a novel finding and demonstrates a surprising heterogeneity of glial plasmalemma.

5'-Nucleotidase↗

PubMed2005

Glial remodeling and neural plasticity in human retinal detachment with proliferative vitreoretinopathy.

PURPOSE: To investigate glial remodeling and neuronal plasticity in adult human retinal detachment complicated by proliferative vitreoretinopathy (PVR) and to grade pathologic changes with a severity scoring system. METHODS: Sixteen full-thickness retinectomy specimens obtained at retinal relaxing surgery for PVR were fixed in 4% paraformaldehyde immediately after excision and compared to similarly processed normal donor retinas. Agarose-embedded sections (100-microm-thick) were double labeled for immunohistochemistry by confocal microscopy, with antibodies against rod opsin and GFAP; vimentin and M/L-cone opsin; calbindin D and S-cone opsin; and cytochrome oxidase and synaptophysin. These staining patterns formed the basis of a retinal pathology scoring system, and immunohistochemistry was also used to detect CD68, neurofilaments, protein kinase C, growth-associated protein-43, and a pan-cone-specific enzymatic marker. Morphology was also assessed by light microscopy of resin-embedded semithin sections. RESULTS: Prolonged detachment was characterized by photoreceptor degeneration and intracellular redistribution of opsin proteins to the plasma membrane in the outer nuclear layer (ONL). Remodeling of rod synaptic terminals was characterized by terminal retraction and also by axon extension to the inner retina in most specimens. Rod bipolar cell dendrites extended into the ONL, as did fine, horizontal cell processes. Large ganglion cells showed upregulated neurofilament and GAP-43 expression, with neurites sprouting from somata and axon collaterals. Anti-cytochrome oxidase labeling of surviving inner segments was reduced but detectable in all specimens, as was anti-calbindin D labeling of horizontal and amacrine cells. All specimens demonstrated a marked upregulation of Muller cell and astrocyte expression of GFAP and vimentin. More severe degenerative changes correlated with trauma and prolonged detachment duration when scored according to this system. CONCLUSIONS: The neural and glial components of detached neurosensory retina complicated by PVR exhibit pathology that changes characteristically with increasing detachment severity. Even in advanced degeneration, most of the structural motifs necessary for functional recovery are retained. Evidence of remodeling in the first-, second-, and third-order neurons of detached adult human retina may represent an attempt to re-establish synaptic connectivity.

Adolescent↗

PubMedDate not supplied

Expression of nitric oxide synthase during the development of RCS rat retinas.

Nitric oxide (NO) has been reported to be both neurodestructive and neuroprotective in the central nervous system and could possibly play an important role in neurodegenerative disorders. On the assumption that NO synthesis may influence degenerative processes in the retina, we have examined the development and distribution of nitric-oxide-synthase(NOS)-immunoreactive cells in developing Royal College of Surgeons (RCS) rat retinas, which is an animal model for retinal degeneration. An antibody against constitutive neuronal NOS was used for immunocytochemistry on RCS rat retinas from postnatal (PN) days 3, 7, 10, 14, 35, 70 and 281 and compared with that in the normal rats of PN days 3, 7, 10, 14, 54 and adults. Immunoreactive cells were not seen in PN 3 retinas but were distinctly seen in the PN 7 retina along with a plexus in the inner plexiform layer. In both groups (normal and RCS rats) a distinct sublayering of the plexus in the inner plexiform layer could be seen at PN 10, which became more distinct at PN 14. The immunoreactive cells were detected also in the oldest retina examined, which was PN 281 in the case of RCS rats. In both groups, certain amacrine cells, certain bipolar cells and certain horizontal cells were found to be immunoreactive. In conclusion, the developmental timetable of the NOS immunoreactivity was identical in the normal and the RCS rat retinas. The NOS-immunoreactive cells persisted in the RCS retinas even when the retina had degenerated extensively. Abnormalities with the inducible isoforms of NOS cannot be ruled out from this study. We conclude that the chronological and qualitative development of the constitutive neuronal NOS immunoreactivity is normal in RCS rat retinas.

Animals↗

PubMed2000

Neuronal nitric oxide synthase immunoreactive neurons in the mammalian retina.

The development of immunocytochemistry has led to a better understanding of synaptic transmission carried out by neuroactive substances in the mammalian brain, including the retina. In the mammalian retina, nitric oxide (NO) is widely accepted as a neuromodulator. Histochemistry based on NADPH-d and immunocytochemistry based on nitric oxide synthase (NOS) have been used to identify the presence of nitric oxide in the mammalian retina. Certain types of amacrine cells and a class of displaced amacrine cells have been labeled consistently in all mammalian retinae studied to date. Other cell types showing NADPH-d reactivity or NOS immunoreactivity varied between species. NADPH-d reactive or NOS immunoreactive amacrine cells may serve as a source of NO for amacrine, bipolar, and ganglion cells in the inner retina, whereas interplexiform cells, bipolar cells, and horizontal cells may serve as a source of NO for the outer retina of mammals.

Animals↗

PubMed1981

Retinal projections in the goldfish: a study using cobaltous-lysine.

Cobaltous lysine applied to the distal stump of a severed optic nerve was used to study the retinal projections of normal adult goldfish. Both the termination areas of optic axons and the pathways they traveled were established. Contrary to previous descriptions of the goldfish visual system, the optic nerves do not decussate completely at the optic chiasm. Fascicles that entered the ipsilateral optic tract innervated targets in the ipsilateral thalamus and optic tectum. Other optic fibers crossed the posterior commissure from the contralateral side of the brain and also innervated the ipsilateral tectum and thalamus. In addition, optic fibers bilaterally innervated a hypothalamic target in close proximity to the infundibulum that may correspond to the nucleus tuberis lateralis. The contralateral preoptic region contained two discrete areas of innervation, each served by separate fascicles. The ipsilateral preoptic region was similarly innervated, but more sparsely. Fibers that entered the controlateral ventral thalamus originated from three fascicles and terminated in three distinct targets. In contrast, three targets in the contralateral dorsal thalamus were served by one fascicle, and fibers passed from one nucleus to the other two. Innervation of the ipsilateral thalamus was similar to that seen contralaterally. Each main optic tract divided into three tracts, two of which entered the optic tectum, while the other innervated several pretectal areas. Other fibers innervated an accessory optic nucleus located near nucleus glomerulosus. The contralateral tectum contained numerous radially oriented optic fascicles. These fascicles represented optic fibers that left thalamic and pretectal targets to enter the optic tectum from beneath the stratum periventriculare. Optic fibers were also observed in the transverse commissure, tractus rotundus, horizontal commissure, tectobulbar tract, and fasciculus retroflexus. Therefore, it appears that many of the anomalous projections seen after tectal ablation or after optic nerve crush are not in fact aberrant. Such projections probably reflect the presence of unusually large numbers of optic fibers in tracts that normally contain optic axons, as well as increased innervation of areas that normally receive sparse retinal projections. Filled tectal cells that could represent cells projecting to the retina were not observed in either tectal lobe. The ipsilateral retinal projections could not be attributed to cobaltous-lysine being transneuronally transported in readily detectable amounts.

Animals↗

PubMed1996

Activity-dependent transport of GABA analogues into specific cell types demonstrated at high resolution using a novel immunocytochemical strategy.

We have raised antisera against the GABA analogues gamma-vinyl GABA, diaminobutyric acid and gabaculine. These analogues are thought to be substrates for high-affinity GABA transporters. Retinae were exposed to micromolar concentrations of these analogues in the presence or absence of uptake inhibitors and then fixed and processed for immunocytochemistry at the light and electron microscopic levels. Immunolabelling for gamma-vinyl GABA revealed specific labelling of GABAergic amacrine cells and displaced amacrine cells in retinae of rabbits, cats, chickens, fish and a monkey. GABA-containing horizontal cells of cat and monkey retinae failed to exhibit labelling for gamma-vinyl GABA, suggesting that they lacked an uptake system for this molecule. In light-adapted fish, gamma-vinyl GABA was readily detected in H1 horizontal cells; similar labelling was also observed in light-adapted chicken retinae. The pattern of labelling in the fish and chicken retinae was modified by dark adaptation, when labelling was greatly reduced in the horizontal cells, indicating the activity dependence of GABA (analogue) transport. Intraperitoneal injection of gamma-vinyl GABA into rats resulted in its transport across the blood-brain barrier and subsequent uptake into populations of GABAergic neurons. The other analogues investigated in this study exhibited different patterns of transport; gabaculine was taken up into glial cells, whilst diaminobutyric acid was taken up into neurons, glial cells and retinal pigment epithelia. Thus, these analogues are probably substrates for different GABA transporters. We conclude that immunocytochemical detection of the high-affinity uptake of gamma-vinyl GABA permits the identification of GABAergic neurons which are actively transporting GABA, and suggest that this novel methodology will be a useful tool in rapidly assessing the recent activity of GABAergic neurons at the cellular level.

Adaptation, Ocular↗

PubMed2000

The cone pedicle, a complex synapse in the retina.

Cone pedicles, the synaptic terminals of cone photoreceptors, are connected in the macaque monkey retina to several hundred postsynaptic dendrites. Using light and electron microscopy, we found underneath each cone pedicle a laminated distribution of dendritic processes of bipolar and horizontal cells. Superimposed were three strata of glutamate receptor (GluR) aggregates, including a novel layer of glutamate receptors clustered at desmosome-like junctions. They are, most likely, postsynaptic densities on horizontal cell dendrites. GABA(A) and GABA(C) receptors are aggregated on bipolar cell dendrites in a narrow band underneath the cone pedicle. Glutamate released from cone pedicles and GABA released from horizontal cell dendrites act not only through direct synaptic contacts but also (more so) through diffusion to the appropriate receptors.

Animals↗

PubMedDate not supplied

Simulation of an anatomically defined local circuit: the cone-horizontal cell network in cat retina.

The outer plexiform layer of the retina contains a neural circuit in which cone synaptic terminals are electrically coupled and release glutamate onto wide-field and narrow-field horizontal cells. These are also electrically coupled and feed back through a GABAergic synapse to cones. In cat this circuit's structure is known in some detail, and much of the chemical architecture and neural responses are also known, yet there has been no attempt to synthesize this knowledge. We constructed a large-scale compartmental model (up to 50,000 compartments) to incorporate the known anatomical and biophysical facts. The goal was to discover how the various circuit components interact to form the cone receptive field, and thereby what possible function is implied. The simulation reproduced many features known from intracellular recordings: (1) linear response of cone and horizontal cell to intensity, (2) some aspects of temporal responses of cone and horizontal cell, (3) broad receptive field of the wide-field horizontal cell, and (4) center-surround cone receptive field (derived from a "deconvolution model"). With the network calibrated in this manner, we determined which of its features are necessary to give the cone receptive field a Gaussian center-surround shape. A Gaussian-like center that matches the center derived from the ganglion cell requires both optical blur and cone coupling: blur alone is too narrow, coupling alone gives an exponential shape without a central dome-shaped peak. A Gaussian-like surround requires both types of horizontal cell: the narrow-field type for the deep, proximal region and the wide-field type for the shallow, distal region. These results suggest that the function of the cone-horizontal cell circuit is to reduce the influence of noise by spatio-temporally filtering the cone signal before it passes through the first chemical synapse on the pathway to the brain.

Animals↗

PubMed1991

Depth is encoded in the visual cortex by a specialized receptive field structure.

Binocular neurons in the visual cortex are thought to perform the first stage of processing for the fine stereoscopic depth discrimination exhibited by animals with frontally located eyes. Because lateral separation of the eyes gives a slightly different view to each eye, there are small variations in position (disparities), mainly along the horizontal dimension, between corresponding features in the two retinal images. The visual system uses these disparities to gauge depth. We studied neurons in the cat's visual cortex to determine whether the visual system uses the anisotropy in the range of horizontal and vertical disparities. We report here that there is a corresponding anisotropy in the cortical representation of binocular information: receptive-field profiles for left and right eyes are matched for cells that are tuned to horizontal orientations of image contours. For neurons tuned to vertical orientations, left and right receptive fields are predominantly dissimilar. Therefore, a major modification is required of the conventional notion of disparity processing. The modified scheme allows a unified encoding of monocular form and binocular disparity information.

Action Potentials↗

PubMed2000

A series of biotinylated tracers distinguishes three types of gap junction in retina.

Gap junctions serve many important roles in various tissues, but their abundance and diversity in neurons is only beginning to be understood. The tracer Neurobiotin has revealed many different networks interconnected by gap junctions in retina. We compared the relative permeabilities of five different retinal gap junctions by measuring their permeabilities to a series of structurally related tracers. When large tracers were injected, the staining of coupled cells fell off more rapidly in some networks than others relative to Neurobiotin controls. Three distinctly different permeability profiles were found, suggesting that multiple neuronal connexin types were present. The most permeant to large molecules were gap junctions from A-type horizontal cells. The permeability of gap junctions of two types of amacrine cell were not distinguishable from those from B-type horizontal cells. The lowest permeability was found for gap junctions between cone bipolar cells and the AII amacrine cells to which they are coupled. Because only a single neural connexin type has been identified in retina, our results suggest more types remain to be found. To determine whether the unitary permeability of channels is altered by channel modulators, we reduced permeability with octanol and a cAMP analog. Although net permeability was substantially diminished, the proportion by which it declined was constant across tracer size. This suggests that these agents act only to close channels rather than alter individual channel permeabilities. This tracer series can therefore be used to contrast permeability properties of gap junctions in intact circuits, even at the level of individual channels.

Animals↗

PubMed1993

Dihydropyridine-sensitive calcium current mediates neurotransmitter release from bipolar cells of the goldfish retina.

The release of neurotransmitter is evoked by activation of the Ca current (ICa) at presynaptic terminals. Though multiple types of ICa have been reported in various cells, little is known about the properties of presynaptic ICa in the vertebrate CNS. The aim of this article is to identify the type of ICa involved in the release of neurotransmitter from retinal bipolar cells. Bipolar cells with a large axon terminal were isolated enzymatically from the goldfish retina, and studied by the following techniques: (1) recordings of ICa in the whole-cell recording configuration, (2) visualization of intracellular free Ca2+ concentration ([Ca2+]i) with the Fura-2 imaging system, and (3) real-time electrophysiological bioassay of released excitatory amino acid transmitter by a voltage-clamped horizontal cell isolated from the catfish retina. The only ICa found in bipolar cells was the high-voltage-activated, dihydropyridine-sensitive type. This result supports the recent study by Heidelberger and Matthews (1992). When ICa was activated by a short depolarizing pulse, a rapid increase of [Ca2+]i was restricted to the axon terminal. A much slower and smaller increase of [Ca2+]i was sometimes observed at the cell body, probably due to the diffusion of intracellular free Ca2+ from the axon terminal. The increase of [Ca2+]i was completely suppressed by nicardipine, suggesting that Ca2+ entered through dihydropyridine-sensitive Ca channels located mainly at the axon terminal. Activating ICa of the bipolar cell evoked a transmitter-induced current in the excitatory amino acid probe (i.e., the catfish horizontal cell). Both currents were suppressed concomitantly by nifedipine but not by omega-conotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2003

Investigation of the migration path for new rod photoreceptors in the adult cichlid fish retina.

In the retina of adult teleost, precursor cells divide in the outer nuclear layer and give rise to new rod photoreceptors. These new rods migrate from the outer limiting membrane to the inner edge of the outer nuclear layer (ONL) before differentiating. In order to understand which cues these cells use during migration and insertion at the appropriate location we combined cell-specific stains in the retina of the cichlid fish Haplochromis burtoni, viewed with confocal laserscan microscopy: Dividing cells were labeled with bromodeoxyuridine (BrdU), Müller glial cells, cone photoreceptors, and horizontal cells were detected by specific antibodies. During the migration phase (24 to 48 h after BrdU uptake) up to 46% of BrdU-labeled cells were spindle shaped and radially oriented. Most of them were in direct proximity to Müller cell processes. Four days after BrdU-uptake, most labeled cells (91%) were found in the inner portion of the ONL and displayed a spherical shape. This marks the end of the movement of the new rods. At this stage, the labeled cells showed no preference to lie near glial fibers but were often found close to the pedicles of double cones. The leading edge of migrating cells reached into the outer plexiform layer (OPL) but not further than processes of horizontal cells. This is beyond the location of mature rods. We hypothesize that the cells are repelled in the OPL and insert back in the ONL to differentiate as rods.

Animals↗

PubMedDate not supplied

Long term cultures of neural retina and pigment epithelium from newborn rabbits.

In vitro cultures of neural retina, obtained after dispersion and trypsinization of tissue fragments, were composed of 3 morphologically distinct types of neural cells, as demonstrated by silver impregnation. They resembled ganglion or receptor cells, horizontal or amacrine cells, and bipolar cells of the intact retina. Pigment epithelium was cultured without trypsinization. Both kinds of techniques may prove helpful for long term experiments in neurobiology and neurovirology.

Animals↗

PubMedDate not supplied

Background contrast modulates kinetics and lateral spread of responses to superimposed stimuli in outer retina.

Surround enhancement (sensitization) is a poorly understood form of network adaptation in which the kinetics of the responses of retinal neurons to test stimuli become faster, and absolute sensitivity of the responses increases with increasing level of steady, surrounding light. Surround enhancement has been observed in all classes of retinal neurons in lower vertebrates except cones, in some primate retinal ganglion cells, and in human psychophysical studies. In theory, surround enhancement could be mediated by two broad classes of mechanisms, which are not mutually exclusive: one in which the kinetics of the transduction linking cone voltage to postsynaptic current in second-order neurons is modulated, and another in which the transformation of postsynaptic current to membrane voltage is modulated. We report here that both classes of mechanism play a role in surround enhancement measured in turtle horizontal cells (HCs). We stimulated the retina by modulating sinusoidally the illuminance of a bar placed at various positions in the HC receptive field. The bar was surrounded by either equally luminant or dim, steady light. Interpretation of responses in the context of a model for the cone-HC network led to the conclusion that the speeding up of response kinetics--due to selective increase in response gain at high temporal frequencies--by surround illuminance is almost completely accounted for by the change in the kinetics of the transduction linking cone membrane potential to HC postsynaptic current. However, surround illuminance also had an additional, surprising effect on the transformation between postsynaptic current and voltage: the space constant for signal spread in the HC network for the dim-surround condition was roughly twice as large as that for the bright-surround condition. Thus, increasing surround illuminance had analogous effects in the spatial and temporal domains: it restricted the time course and the spatial spread of signal. Both effects were dependent on the contrast between the mean bar illuminance and that of the surround, rather than on overall light level. When the stimulus with the bright surround was dimmed uniformly by a neutral density filter, the space constant did not increase, and response gain at high temporal frequencies did not decrease. Pharmacological experiments performed with dopamine and various agonists and antagonists indicated that, although exogenous dopamine can influence surround enhancement, endogenous dopamine does not play an important role in surround enhancement. We conclude that contrast in background light modulates the spatiotemporal properties of signal processing in the outer retina, and does so by a non-dopaminergic mechanism.

Adaptation, Physiological↗

PubMed2001

Localization of the AMPA subunit GluR2 in the outer plexiform layer of goldfish retina.

L-glutamate, the photoreceptor neurotransmitter, depolarizes horizontal cells and OFF bipolar cells by ionotropic AMPA-glutamate receptors. The AMPA-receptor subunit (GluR4) is localized to dendrites of OFF bipolar cells in goldfish retina. Here, we used immunohistochemical techniques to identify AMPA-receptor subunits on horizontal cell dendrites. A monoclonal antibody against rat GluR2, with high sequence homology to the recently cloned goldfish GluR2a receptor, was used for light- and electron-microscopical immunocytochemistry. Light- and dark-adapted retinas were analyzed, with no major difference in results. GluR2-immunoreactivity (IR) was restricted to a narrow band in the outer plexiform layer, in which it appeared as bright dome-shaped structures amidst numerous puncta. At the ultrastructural level, GluR2-IR was found in horizontal cell dendrites that invaginated cones and rods. Dendrites of OFF bipolar cells were not labeled. GluR2-IR was present mostly in horizontal cell dendrites that were the lateral elements of the triad, rather than in dendrites that were the central elements. In light-adapted retinas, GluR2-IR was found in many horizontal cell spinules. GluR2-IR was observed, on occasion, in a mixed rod/cone (Mb) ON bipolar cell process that innervated rod spherules. Verification of the Mb ON bipolar cell was made by protein kinase C and metabotropic mGluR1alpha immunolabeling. The presence of GluR2-IR in lateral elements suggests that lateral horizontal cell dendrites are postsynaptic to cones rather than only sites of feedback inhibition. All horizontal cell types express the GluR2 subunit, uniquely differentiating themselves from OFF bipolar cells that express the GluR4 subunit. This differentiation most likely has a major influence on the glutamate pharmacology and response kinetics of these cell types to glutamate.

Animals↗