Rabbit Retina Research Articles

Pathological changes in rabbit retina and its relationship with glutamic acid after injuries from high-speed bullets.

To observe the pathological changes in rabbit retinas and the measure of glutamic acid levels in the vitreous body after suffering from high-speed bullet injuries. Rabbits eyeball contusion models were established with high-speed bullets, i.e., the rabbits eyes were shot with a fixed air rifle at a speed of 90m/s (using plastic bullets, weighing 0.20122g, on average). Retinal tissues treated with HE staining and were prepared for light microscopy examination and glutamate levels were tested at different points in time after the injury. Edema, exudation, hemorrhage, and rupture were evident in rabbit retinas following bullet injuries. Meanwhile, glutamate levels gradually increased as time proceeded. Visual impairment is related with retinal damages after high-speed bullet injuries. Increased glutamate concentration serves as a potential factor for aggravating retinal injuries.

Inhibitory Effect of Intravitreal Injection of Bevacizumab on Nerve Growth Factor

Purpose: To investigate the inhibitory effect of intravitreal injection of bevacizumab on the expression of nerve growth factor (NGF) in rabbit retina.Methods: The right eyes of 40 New Zealand white rabbits were injected with 1.25 mg (0.05 cc) bevacizumab three times monthly; as controls, the left eyes received sham injections. Apoptosis in retinal cells was evaluated by immunohistochemical staining for caspase-3, and by in situ terminal deoxynucleotidyl transferase-mediated biotin-deoxyuridine triphosphate nick-end labeling (TUNEL) of DNA fragments. NGF and vascular endothelial growth factor (VEGF) proteins in rabbit retinas were measured quantitatively (Enzyme linked immunosorbent assay (ELISA)) and qualitatively (immunohistochemical staining) 1 and 4 months after injection. NGF and VEGF messenger RNAs in rabbit retinas were evaluated by real-time polymerase chain reaction (RT-PCR).Results: As shown by the TUNEL assay and caspase-3 immunostaining, the bevacizumab-injected group had significantly more apoptotic activity than did the control group. Levels of retinal NGF and VEGF proteins in the bevacizumab group were lower than those in the control group (p < 0.05). Immunohistochemical staining of NGF and VEGF was weaker in the bevacizumab group than in the control group. NGF and VEGF mRNA levels in the bevacizumab group were lower than those of the control group (p < 0.05).Conclusions: Findings of the present study suggest that apoptosis in retinal cells after intravitreal bevacizumab injection is increased by down-regulated NGF, caused by VEGF inhibition in rabbits.

A continuum model of retinal electrical stimulation**This paper was originally submitted for the special issue containing contributions from the Sixth Biennial Research Congress of The Eye and the Chip.

A continuum mathematical model of retinal electrical stimulation is described. The model is represented by a passive vitreous domain, a thin layer of active retinal ganglion cell (RGC) tissue adjacent to deeper passive neural layers of the retina, the retinal pigmented epithelium (RPE) and choroid thus ending at the sclera. To validate the model, in vitro epiretinal responses to stimuli from 50 µm disk electrodes, arranged in a hexagonal mosaic, were recorded from rabbit retinas. 100 µs/phase anodic-first biphasic current pulses were delivered to the retinal surface in both the mathematical model and experiments. RGC responses were simulated and recorded using extracellular microelectrodes. The model's epiretinal thresholds compared favorably with the in vitro data. In addition, simulations showed that single-return bipolar electrodes recruited a larger area of the retina than twin-return or six-return electrodes arranged in a hexagonal layout in which a central stimulating electrode is surrounded by six, eqi-spaced returns. Simulations were also undertaken to investigate the patterns of RGC activation in an anatomically-accurate model of the retina, as well as RGC activation patterns for subretinal and suprachoroidal bipolar stimulation.

Functional expression of ionotropic glutamate receptors in the rabbit retinal ganglion cells

It has been known that retinal ganglion cells (RGCs) with distinct morphologies have different physiological properties. It was hypothesized that different functions of RGCs may in part result from various expressions of N-methyl- d-aspartate (NMDA), α-amino-3-hydroxyl-5-methyl-isoxazole-4-propinoic acid (AMPA), and kainic acid (KA) receptors on their dendrites. In the present study, we aimed to characterize the functional expression of AMPA and NMDA receptors of morphologically identified RGCs in the wholemount rabbit retina. The agmatine (AGB) activation assay was used to reveal functional expression of ionotropic glutamate receptors after the RGCs were targeted by injecting Neurobiotin. To examine the excitability of these glutamate receptors in an agonist specific manner, the lower concentrations of AMPA (2 μM) and NMDA (100 μM) were chosen to examine G7 (ON–OFF direction selective ganglion cells) and G11 (alpha ganglion cells) types of RGCs. We found that less than 40% of G7 type RGCs had salient AGB activation when incubated with 2 μM AMPA or 100 μM NMDA. The G11 type RGCs also showed similar activation frequencies, except that all of the OFF subtype examined had no AGB permeation under the same AMPA concentration. These results suggest that RGCs with large somata (G7 and G11 types) may express various heterogeneous functional ionotropic glutamate receptors, thus in part rendering their functional diversity.

SAFETY OF INTRAVITREAL BEVACIZUMAB IN THE DEVELOPING RABBIT RETINA

The purpose of this was to study the long-term effects of a single intravitreal dose of bevacizumab injected at different postnatal age on retinal function and development of retinal blood vessels in the adult albino rabbit. Bevacizumab was injected into the right eye of newborn rabbits, aged 11 days to 25 days, whereas the left eye of each rabbit was injected with identical volume of saline and served as control. The electroretinogram was recorded 1 week and 10 weeks after injection. Visual evoked potentials were recorded 10 weeks after injection. At termination of the follow-up period, the rabbits were killed and the retinas were prepared for histopathologic studies at the light microscopic level, for glial fibrillary acidic protein immunoreactivity, and for reduced form of nicotinamide adenine dinucleotide phosphate diaphorase histochemistry to assess the integrity of the retinal vascular system. The electroretinogram responses demonstrated normal retinal function in adult rabbits injected at postnatal age of 11 days to 25 days. Mean Vmax and σ values calculated for each group of rabbits, 10 weeks after bevacizumab injection, indicated similar retinal function of the experimental and control eyes. Visual evoked potentials recorded by stimulating each eye separately were also similar. The histopathologic studies yielded similar results; no structural retinal damage was observed in the experimental eyes compared with the control eyes of rabbits from all age groups, and no increased glial fibrillary acidic protein immunoreactivity in Müller cells was observed in the experimental eyes. Staining of blood vessels with reduced form of nicotinamide adenine dinucleotide phosphate diaphorase revealed decreased branching of the capillary network in the experimental eyes compared with the control eyes in all age groups. The electroretinographic and morphologic data showed no deleterious effects of a single intravitreal dose of bevacizumab, injected during the first 30 days postnatally, on the structural and functional integrity of the sensory retina in the adult rabbit. Even partial blockage of vascular endothelial growth factor with bevacizumab applied during retinal development seems to interfere with the development of the retinal vascular system in the albino rabbit. However, extrapolation from rabbits to humans should be made with caution.

Photodiode Circuits for Retinal Prostheses

Photodiode circuits show promise for the development of high-resolution retinal prostheses. While several of these systems have been constructed and some even implanted in humans, existing descriptions of the complex optoelectronic interaction between light, photodiode, and the electrode/electrolyte load are limited. This study examines this interaction in depth with theoretical calculations and experimental measurements. Actively biased photoconductive and passive photovoltaic circuits are investigated, with the photovoltaic circuits consisting of one or more diodes connected in series, and the photoconductive circuits consisting of a single diode in series with a pulsed bias voltage. Circuit behavior and charge injection levels were markedly different for platinum and sputtered iridium-oxide film (SIROF) electrodes. Photovoltaic circuits were able to deliver 0.038 mC/cm(2) (0.75 nC/phase) per photodiode with 50- μm platinum electrodes, and 0.54-mC/cm(2) (11 nC/phase) per photodiode with 50-μ m SIROF electrodes driven with 0.5-ms pulses of light at 25 Hz. The same pulses applied to photoconductive circuits with the same electrodes were able to deliver charge injections as high as 0.38 and 7.6 mC/cm(2) (7.5 and 150 nC/phase), respectively. We demonstrate photovoltaic stimulation of rabbit retina in-vitro, with 0.5-ms pulses of 905-nm light using peak irradiance of 1 mW/mm(2). Based on the experimental data, we derive electrochemical and optical safety limits for pixel density and charge injection in various circuits. While photoconductive circuits offer smaller pixels, photovoltaic systems do not require an external bias voltage. Both classes of circuits show promise for the development of high-resolution optoelectronic retinal prostheses.

Optical coherence tomography imaging of retinal damage in real time under a stimulus electrode**This paper was originally submitted for the special issue containing contributions from the Sixth Biennial Research Congress of The Eye and the Chip.

We have developed a novel method to study the effects of electrical stimulation of the local retina directly under an epiretinal stimulus electrode in real time. Using optical coherence tomography (OCT) and a superfused retinal eyecup preparation, we obtained high-resolution images of the rabbit retina directly under an optically transparent saline-filled fluoropolymer stimulation tube electrode. During OCT imaging, 50 Hz trains of biphasic current pulses 1 ms/phase (23–749 µC cm−2 ph−1) were applied to the retinal surface for 5 min. After imaging, the stimulated regions were stained with the dye propidium iodide (PI) to reveal cytotoxic damage. Pulse train stimulation at 44–133 µC cm−2 ph−1 had little effect on the retina; however, trains ≥442 µC cm−2 ph−1 caused increases in the reflectance of the inner plexiform layer (IPL) and edema. The damage seen in retinal OCT images matched the pattern observed in histological sections, and in the PI staining. With pulse trains ≥442 µC cm−2 ph−1, rapid increases in the reflectivity of the IPL could be observed under the stimulus electrode. Below the electrode, we observed a ring-like pattern of retinal detachment in the subretinal space. The OCT imaging method may be useful for analyzing overstimulation of neuronal tissue by electrodes in many brain regions.

A novel type of complex ganglion cell in rabbit retina

AbstractThe 15–20 physiological types of retinal ganglion cells (RGCs) can be grouped according to whether they fire to increased illumination in the receptive‐field center (ON cells), decreased illumination (OFF cells), or both (ON‐OFF cells). The diversity of RGCs has been best described in the rabbit retina, which has three types of ON‐OFF RGCs with complex receptive‐field properties: the ON‐OFF direction‐selective ganglion cells (DSGCs), the local edge detectors, and the uniformity detectors. Here we describe a novel type of bistratified ON‐OFF RGC that has not been described in either physiological or morphological studies of rabbit RGCs. These cells stratify in the ON and OFF sublaminae of the inner plexiform layer, branching at about 30% and 60% depth, between the ON and OFF arbors of the bistratified DSGCs. Similar to the ON‐OFF DSGCs, these cells respond with transient firing to both bright and dark spots flashed in the receptive field but, unlike the DSGCs, they show no directional preference for moving stimuli. We have termed these cells “transient ON‐OFF” RGCs. Area‐response measurements show that both the ON and the OFF spike responses have an antagonistic receptive‐field organization, but with different spatial extents. Voltage‐clamp recordings reveal transient excitatory inputs at light ON and light OFF; this excitation is strongly suppressed by surround stimulation, which also elicits direct inhibitory inputs to the cells at light ON and light OFF. Thus the receptive‐field organization is mediated both within the presynaptic circuitry and by direct feed‐forward inhibition. J. Comp. Neurol. 519:3128–3138, 2011. © 2011 Wiley‐Liss, Inc.

A novel type of complex ganglion cell in rabbit retina

The 15-20 physiological types of retinal ganglion cells (RGCs) can be grouped according to whether they fire to increased illumination in the receptive-field center (ON cells), decreased illumination (OFF cells), or both (ON-OFF cells). The diversity of RGCs has been best described in the rabbit retina, which has three types of ON-OFF RGCs with complex receptive-field properties: the ON-OFF direction-selective ganglion cells (DSGCs), the local edge detectors, and the uniformity detectors. Here we describe a novel type of bistratified ON-OFF RGC that has not been described in either physiological or morphological studies of rabbit RGCs. These cells stratify in the ON and OFF sublaminae of the inner plexiform layer, branching at about 30% and 60% depth, between the ON and OFF arbors of the bistratified DSGCs. Similar to the ON-OFF DSGCs, these cells respond with transient firing to both bright and dark spots flashed in the receptive field but, unlike the DSGCs, they show no directional preference for moving stimuli. We have termed these cells "transient ON-OFF" RGCs. Area-response measurements show that both the ON and the OFF spike responses have an antagonistic receptive-field organization, but with different spatial extents. Voltage-clamp recordings reveal transient excitatory inputs at light ON and light OFF; this excitation is strongly suppressed by surround stimulation, which also elicits direct inhibitory inputs to the cells at light ON and light OFF. Thus the receptive-field organization is mediated both within the presynaptic circuitry and by direct feed-forward inhibition.

Hyperspectral Computed Tomographic Imaging Spectroscopy of Vascular Oxygen Gradients in the Rabbit Retina In Vivo

Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10–15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology.

Influence of posterior intrascleral iron foreign body on rabbit retina and opticus

Background Iron-containing foreign body trapped in the eyeball wall without affecting the opticus occurs occasionally in clinic. Operation always is performed in an attempt to avoid the deposition of rust in different tissues of the eye-balls. However,a few animal experimental studies showed that a small foreign body does not affect the retina and opticus in the period of three months. The question of whether surgery needs to be carried out is worth discussion. Objective The aim of this study was to evaluate the influence of posterior intrascleral iron foreign body on the rabbit retina and opticus. Methods Twelve healthy adult Japan flap-eared white rabbits were randomly divided into two groups. Medium carbon iron with rust or without rust( size of 2. 0 mm × 1. 0 mm×0. 2 mm) were implanted into the posterior sclera of the left eye to create the animal model with iron foreign body in the eyeball wall. The cornea, anterior chamber, crystalline lens, vitreous and fundus of the rabbits were observed under a slit lamp microscope 1 week before operation and 1 week, 2 weeks, 1 month and 3 months after operation. Flash electroretinogram(F-ERG) and flash visual evoked potential (F-VEP) were recorded at the time points mentioned above. All the rabbits were sacrificed and the eye balls were extracted at the end of the experiment, and the position of the iron foreign body was determined. The histopathological examinations of the retina and opticus were performed under the light microscope. This experiment complied with the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission. Results There were no statistical differences for the a-wave amplitude of F-ERG among different time points( F =1. 885,P =0. 129 ) and different treatment groups ( F =1. 188, P =0. 340 ), as with the ERG b-wave amplitude ( time: F =2. 73, P =0. 064 ; group : F =1. 114, P =0. 367). The differences in the latencies of F-VEP N1-wave were insignificant among the different time points( F =1. 605, P =0. 263 ) as well as various groups ( F=1. 556, P =0.314 ), and those of F-VEP P1 -wave were not evidently changed ( time: F =2. 329, P =0. 092 ; group : F =2. 186, P =0. 103 ). No correlations were seen between the time factor and grouping factor ( P ＞ 0. 05 ). There was no apparent siderosis bulbi change during the follow-up duration. No morphological abnormality in the retina and optical nerve was found under the light microscope. At the end of the experiment,intrascleral iron foreign body was wrapped by surrounding tissue in a stable condition. Conclusions The small posterior intrascleral iron foreign body, whether it is oxidized or not, does not produce distinctive functional or pathological damage on retina and opticus in the short term. Key words: Eye injury ; Scleral/foreign body; Visual electrophysiology ; Visual function ; Pathology

Masked excitatory crosstalk between the ON and OFF visual pathways in the mammalian retina

A fundamental organizing feature of the visual system is the segregation of ON and OFF responses into parallel streams to signal light increment and decrement. However, we found that blockade of GABAergic inhibition unmasks robust ON responses in OFF α-ganglion cells (α-GCs). These ON responses had the same centre-mediated structure as the classic OFF responses of OFF α-GCs, but were abolished following disruption of the ON pathway with L-AP4. Experiments showed that both GABA(A) and GABA(C) receptors are involved in the masking inhibition of this ON response, located at presynaptic inhibitory synapses on bipolar cell axon terminals and possibly amacrine cell dendrites. Since the dendrites of OFF α-GCs are not positioned to receive excitatory inputs from ON bipolar cell axon terminals in sublamina-b of the inner plexiform layer (IPL), we investigated the possibility that gap junction-mediated electrical synapses made with neighbouring amacrine cells form the avenue for reception of ON signals. We found that the application of gap junction blockers eliminated the unmasked ON responses in OFF α-GCs, while the classic OFF responses remained. Furthermore, we found that amacrine cells coupled to OFF α-GCs display processes in both sublaminae of the IPL, thus forming a plausible substrate for the reception and delivery of ON signals to OFF α-GCs. Finally, using a multielectrode array, we found that masked ON and OFF signals are displayed by over one-third of ganglion cells in the rabbit and mouse retinas, suggesting that masked crossover excitation is a widespread phenomenon in the inner mammalian retina.

Retinal remodeling in the Tg P347L rabbit, a large‐eye model of retinal degeneration

AbstractA oblique section through the bipolar cell layer and partial outer plexiform layer (upper left) of a TgP347L rabbit retina early in the degenerative process visualized with sQE :: rgb mapping. At 12–16 weeks, the TgP347L rabbit retina still has photoreceptors, but Müller cell signatures in yellow/orange can be seen indicating early altered metabolic profiles prior to glial hypertrophy. Bipolar cells are functionally switching their phenotypes at this stage as revealed by glutamate channel expression changes and AGB permeation of activated iGluRs, but appear retain their formal small molecular phenotype at this stage. The Journal of Comparative Neurology, Volume 519, Number 14, pages 2713–2733. J. Comp. Neurol., 2011. © 2011 Wiley‐Liss, Inc.

Two distinct types of ON directionally selective ganglion cells in the rabbit retina.

Mammalian retinas contain about 20 types of ganglion cells that respond to different aspects of the visual scene, including the direction of motion of objects in the visual field. The rabbit retina has long been thought to contain two distinct types of directionally selective (DS) ganglion cell: a bistratified ON-OFF DS ganglion cell that responds to onset and termination of light, and an ON DS ganglion cell, which stratifies only in the ON layer and responds only to light onset. This division is challenged by targeted recordings from rabbit retina, which indicate that ON DS ganglion cells occur in two discriminably different types. One of these is strongly tracer-coupled to amacrine cells; the other is never tracer-coupled. These two types also differ in branching pattern, stratification depth, relative latency, and transience of spiking. The sustained, uncoupled ON DS cell ramifies completely within the lower cholinergic band and responds to nicotine with continuous firing. In contrast, the transient, coupled ON DS ganglion cell stratifies above the cholinergic band and is not positioned to receive major input from cholinergic amacrine cells, consistent with its modest response to the cholinergic agonist nicotine. Much data have accrued that directional responses in the mammalian retina originate via gamma-aminobutyric acid (GABA) release from the dendrites of starburst amacrine cells (Euler et al., 2002). If there is an ON DS ganglion cell that does not stratify in the starburst band, this suggests that its GABA-dependent directional signals may be generated by a mechanism independent of starburst amacrine cells.

Two distinct types of ON directionally selective ganglion cells in the rabbit retina

AbstractFour Neurobiotin‐injected coupled ON DS ganglion cells surrounding an ON‐OFF DS ganglion cell (white) show the relative size of these two cell types. The ganglion cells were colored in Adobe Photoshop for clarity. The Journal of Comparative Neurology, Volume 519, Number 13, pages 2509–2521.

Axonal Transmission in the Retina Introduces a Small Dispersion of Relative Timing in the Ganglion Cell Population Response

BackgroundVisual stimuli elicit action potentials in tens of different retinal ganglion cells. Each ganglion cell type responds with a different latency to a given stimulus, thus transforming the high-dimensional input into a temporal neural code. The timing of the first spikes between different retinal projection neurons cells may further change along axonal transmission. The purpose of this study is to investigate if intraretinal conduction velocity leads to a synchronization or dispersion of the population signal leaving the eye.Methodology/Principal FindingsWe ‘imaged’ the initiation and transmission of light-evoked action potentials along individual axons in the rabbit retina at micron-scale resolution using a high-density multi-transistor array. We measured unimodal conduction velocity distributions (1.3±0.3 m/sec, mean ± SD) for axonal populations at all retinal eccentricities with the exception of the central part that contains myelinated axons. The velocity variance within each piece of retina is caused by ganglion cell types that show narrower and slightly different average velocity tuning. Ganglion cells of the same type respond with similar latency to spatially homogenous stimuli and conduct with similar velocity. For ganglion cells of different type intraretinal conduction velocity and response latency to flashed stimuli are negatively correlated, indicating that differences in first spike timing increase (up to 10 msec). Similarly, the analysis of pair-wise correlated activity in response to white-noise stimuli reveals that conduction velocity and response latency are negatively correlated.Conclusion/SignificanceIntraretinal conduction does not change the relative spike timing between ganglion cells of the same type but increases spike timing differences among ganglion cells of different type. The fastest retinal ganglion cells therefore act as indicators of new stimuli for postsynaptic neurons. The intraretinal dispersion of the population activity will not be compensated by variability in extraretinal conduction times, estimated from data in the literature.

D-Allose as ischemic retina injury inhibitor during rabbit vitrectomy

To investigate the protective effects of D-allose, a rare sugar, on pressure-induced ischemia during vitrectomy in the rabbit eye. The rabbits underwent pars plana vitrectomy, and continuous intraocular irrigation at a perfusion pressure of 140 mmHg was performed for 45 min. Intraocular pressure was regulated by adjusting the height of a bottle of balanced saline solution containing D-allose. Morphometric studies were performed to study the effects of D-allose on the histological changes induced by ischemia in the rabbit retina. Electroretinograms (ERGs) were taken before and 1 and 7 days after vitrectomy. Nitroblue tetrazolium was used as an index of superoxide anion (O(2)(·-)) generation. Data were analyzed by use of the unpaired Student's t test. Seven days after ischemia, significant reductions in both number of ganglion cells and the thickness of the inner plexiform layer were observed. D-Allose significantly inhibited ischemic injury of the inner retina (P < 0.05). On postoperative day 7, amplitudes of ERG b-waves were significantly lower in the control group than in the D-allose group (P < 0.05). D-Allose suppressed the production of O(2)(-). Intraocular irrigation with D-allose during vitrectomy may protect the retina against ischemia-induced damage.

Amacrine-to-amacrine cell inhibition: Spatiotemporal properties of GABA and glycine pathways

We measured the spatial and temporal properties of GABAergic and glycinergic inhibition to amacrine cells in the whole-mount rabbit retina. The amacrine cells were parsed into two morphological classes: narrow-field cells with processes spreading less than 200 μm and wide-field cells with processes extending more than 300 μm. The inhibition was also parsed into two types: sustained glycine and transient GABA. Narrow-field amacrine cells receive 1) very transient GABAergic inhibition with a fast onset latency of 140 ± 16 ms decaying to 30% of the peak level within 208 ± 27 ms elicited broadly over a lateral distance of up to 1500 μm and 2) sustained glycinergic inhibition with a medium onset latency of 286 ± 23 ms that was elicited over a spatial area often broader than the processes of the narrow-field amacrine cells. Wide-field amacrine cells received sustained glycinergic inhibition but no broad transient GABAergic inhibition. Surprisingly, neither of these amacrine cell classes received sustained local GABAergic inhibition, commonly found in an earlier study of ganglion cells.

Myelin oligodendrocyte‐specific protein is expressed in Müller cells of myelinated vertebrate retinas

The retina of nonmammalian vertebrates has a loose myelin that enwraps the large axons of the ganglion cells in all areas, whereas that of mammals lacks myelin, with some exceptions, such as the rabbit retina, which shows compact myelin restricted to the myelinated streak. Electron microscopy studies in chicken retina showed processes of Müller cells (MCs) and oligodendrocytes enwrapping ganglion cell axons. How each of these cells contributes to chicken retina myelination and whether the MC of other myelinated retinas is involved in myelination remain unknown. By immunohistochemistry, with a monoclonal antibody against myelin oligodendrocyte-specific protein (MOSP), we show that MOSP is intensely expressed in the MC and the optic-fiber layer (OFL) in myelinated but not in unmyelinated retinas. By immunocytochemistry with isolated MCs from the chick and rabbit retinas, we show that MOSP is concentrated in the innermost domain of the vitread processes. By immunoblotting, we show that protein extracts from myelinated retinas, but not those from unmyelinated retinas, presented a single band labelled with anti-MOSP of molecular weight similar to that of brain MOSP. In addition, we show that the MC of the embryonic chicken retina starts to express MOSP just before myelination starts. Our results agree with those of electron microscopy studies showing myelin in chick retina formed by MC processes and with those of immunohistochemistry studies in rabbit and human retinas showing expression of other myelin molecules in the MC. Altogether, our results suggest that the MC in myelinated retinas might contribute MOSP to myelin.

Expression of α-gustducin in mammalian retinas

α-Gustducin (Gα-gust) is the α subunit of the heterotrimeric G-protein complex specific for taste receptor cells of the tongue. However, it has been shown to be present in ectopic regions, such as airways and digestive tract. Recently, Gα-gust was found within neurons in various regions of the mouse brain. In this study, we tested whether Gα-gust is expressed in the mammalian retina. Gα-gust was identified in mouse, rat, and rabbit retinas by western blot and immunohistochemistry analyses. Double-labeling experiments in the mouse retina clearly showed that Gα-gust is exclusively expressed in the axon terminals of the rod bipolar cells. The evidence suggests that Gα-gust may selectively participate in signal transduction in the axon terminals of rod bipolar cells in the mammalian retina.