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PubMed1989

Optic nerve crush modulates proliferation of rod precursor cells in the goldfish retina.

Tritiated thymidine ([3H]TdR) autoradiography revealed a correlation between the rate of cell proliferation of rod precursor cells in the outer nuclear layer (ONL) of the goldfish retina and the postoperative interval after crush of the optic nerve (ONC). Ten days after unilateral ONC there were more labeled nuclei in the ONL of the nerve-crushed retina than in the intact, contralateral retina of the same fish one day after single bilateral intraocular injections of [3H]TdR. From 15 to 25 days after ONC, however, fewer labeled nuclei were found in the ONL of nerve-crushed retinae than in controls, illustrating a decrease in the number of cells entering the S-phase of the cell cycle; by 35 days the differences had disappeared, demonstrating that cell birth recovered to normal. When examined one month after [3H]TdR injection, fewer labeled cells were present in the nerve-crushed retina at all postoperative intervals. Examination of the numbers of labeled cells at various postoperative periods following bilateral ONC, when one retina was examined one day and the other retina was examined one month after [3H]TdR administration revealed that the ratios of labeled cells between the two retinae varied as a function of time after ONC. Therefore, optic nerve crush appears to enhance the proportion of initially labeled cells in the ONL that are either fated to undergo further cell generation cycles or to die.

Animals↗
PubMed2001

Melatonin receptor RNA is expressed in photoreceptors and displays a diurnal rhythm in Xenopus retina.

Melatonin is an output signal of an endogenous circadian clock of retinal photoreceptors, with highest levels occurring at night. Melatonin synthesized in the retina appears to act as a paracrine signal by binding to specific receptors in the eye. We have previously demonstrated that RNA encoding the Mel(1b) and Mel(1c) melatonin receptor subtypes is expressed in the Xenopus laevis retina. The goal of this study was to determine the distribution of the Mel(1b) and Mel(1c) receptor subtype RNA expression in the retina, and to determine if the level of expression of these receptors exhibits a diurnal rhythm. Sections of frog neural retina were analyzed by in situ hybridization with 35S-labeled Xenopus Mel(1c) and Mel(1b) riboprobes. Hybridization was present in cells of the inner nuclear layer and the ganglion cell layer. Moreover, there was hybridization in the photoreceptors, which has not been previously reported. To test the hypothesis that retinal melatonin receptor mRNA undergoes a diurnal rhythm of expression, total RNA was isolated from frog neural retinas obtained at 3-h intervals during a 24-h period. The total RNA was used in real-time PCR assays to quantify the differences in Mel(1b) and Mel(1c) receptor mRNA expression at various circadian times. Both the Mel(1b) and Mel(1c) receptor RNA demonstrated a diurnal rhythm of expression, with peak levels occurring late in the light period, and lowest levels late in the dark period. These results support the hypothesis that RNA encoding melatonin receptors undergo a diurnal rhythm of expression. To further investigate the possible expression of the Mel(1a) receptor subtype in Xenopus retina, we generated Mel(1a) PCR products in genomic DNA, and in reverse-transcribed neural retina and retinal pigment epithelium (RPE) RNA. The identity of the PCR product was confirmed by sequencing. Therefore, all three known Xenopus melatonin receptor subtypes appear to be expressed in the neural retina and RPE.

Animals↗
PubMed2006

An endothelin type A receptor antagonist reverses upregulated VEGF and ICAM-1 levels in streptozotocin-induced diabetic rat retina.

Diabetic retinopathy, a cause of blindness, is often associated with the upregulation of vascular endothelial growth factor (VEGF) in the retina. Recently, leukocyte adhesion (leukostasis) is claimed for the occlusion of retinal capillary vascularity, which ultimately assists in the progression of diabetic retinopathy. In addition, intercellular adhesion molecule-1 (ICAM-1), a representative factor for leukostasis, is increased in diabetic retina. Endothelin (ET)-1, a potent vasoconstrictor peptide, is closely linked to the pathogenesis of diabetic retinopathy. Different therapeutic interventions concerning VEGF have already been proposed to prevent diabetic retinopathy. However, no study has yet reported concerning the effects of ET-1 receptor antagonist on the upregulated VEGF and ICAM-1 in morphologically intact diabetic retina. The current study investigated the effect of ET(A) receptor antagonist (TA-0201; 1 mg kg(-1) day(-1)) on the expressions of VEGF and ICAM-1 in rat diabetic retina. Diabetes was induced by intraperitoneal injection of streptozotocin (70 mg/kg) in Sprague-Dawley rats, whereas control rats (Cont) received only citrate buffer. After 1 week, the streptozotocin-administered rats were randomly divided into two groups: ET(A) receptor antagonist-treated group (DM+TA-0201) and saline-treated group (DM+vehicle). After the treatment for 4 weeks, the retina was removed from the eyeball. In DM+vehicle group, the VEGF expression of retina was significantly increased (33.5 pg/mg) in comparison with that in the Cont group (25.1 pg/mg), and the upregulation of VEGF was reversed in DM+TA-0201 group (26.9 pg/mg), a phenomenon consistent with the change in VEGF mRNA levels. The expression of retinal ICAM-1 was increased in DM+vehicle group (55.1 pg/mg) compared with Cont group (43.8 pg/mg), and ET antagonism completely blocked this increase (43.8 pg/mg). Moreover, an increased leukostasis by 3.3-fold in DM+vehicle retina was returned to the control level by ET antagonism. In the current study, there was no obvious retinal morphological alteration from both the hematoxylin and eosin staining and the FITC-dextran angiography. Thus, ET(A) receptor antagonist might be useful in preventing the progression of diabetic retinopathy, as evidenced by suppressing the increase in VEGF and ICAM-1 levels as well as leukostasis in morphologically intact diabetic retina.

Animals↗
PubMed2005

Murine cytomegalovirus (MCMV) spreads to and replicates in the retina after endotoxin-induced disruption of the blood-retinal barrier of immunosuppressed BALB/c mice.

The goal of this study was to determine whether disruption of the blood-retinal barrier (BRB) facilitates spread of MCMV to the retina in immunosuppressed (IS) BALB/c mice. IS mice were inoculated intravenously (i.v.) with murine cytomegalovirus (MCMV) or with macrophages infected with MCMV for 4 days in vitro. The BRB was disrupted by injection of sodium iodate (i.v.) or lipopolysaccharide (LPS, i.v. or anterior chamber). Frozen sections of ocular tissue were examined for MCMV antigens. The results showed that MCMV-infected cells were observed only in the choroid and ciliary body in IS mice with an intact BRB. After LPS injection, a few positive cells were observed in the retina of IS mice after i.v. injection of MCMV. In lipopolysaccharide (LPS)-treated IS mice, a few PKH-26-positive macrophages or MCMV-positive cells were observed in the retina at 1 or 2 days after injection of macrophages. No PKH-26-positive cells or virus-infected cells were noted in the retina of phosphate-buffered saline (PBS)-treated mice. Ten days after injection of virus-infected macrophages, MCMV-infected cells were observed in choroid and ciliary body of both LPS- and PBS-treated mice, but they were observed in the retina only in LPS-treated mice. The results support the idea that disruption of the BRB allows MCMV to spread to the retina of IS mice and that monocytes/macrophages disseminate MCMV to the retina in mice with a disrupted BRB. By extrapolation, damage to the BRB in immunosuppressed patients may facilitate spread of CMV-infected monocytes/macrophages to the retina.

Animals↗
PubMed1981

Prognosis of visual acuity after surgery for detached retina, with special reference to the unaffected eye.

In 600 patients with successfully operated unilateral retinal detachment, the visual acuity prognosis of the operated eye was studied in relation to that of the normal eye. Within 2 years after operation, most of these patients were in the following three groups: (1) visual acuity worse than 0.5 in the non-detached retina and worse than 0.1 in the reattached one; (2) visual acuity better than 1.0 in the non-detached retina and worse than 0.3 in the reattached one; and (3) visual acuity better than 1.0 in the non-detached retina and better than 0.8 in the reattached one. Some of the patients in group 2 showed greater improvement of the visual acuity in the reattached retina, which occasionally became superior to that in the non-detached one. In spite of possible improvement until 2 years after operation, the visual acuity in the reattached retina was apt to decrease after more than 5 years following operation. The presence of macular detachment was ill for the recovery of visual acuity. About 30% of the patients with a visual acuity of about 1.0 in the non-detached retina showed no improvement of the visual acuity in the reattached retina. About 50% of the patients with successful surgery for retinal detachment had a difference of more than 0.6 in visual acuity between the non-detached and the detached retinas.

Adult↗
PubMed1999

Dopamine mediates circadian rhythms of rod-cone dominance in the Japanese quail retina.

A circadian clock modulates the functional organization of the Japanese quail retina. Under conditions of constant darkness, rods dominate electroretinogram (ERG) b-wave responses at night, and cones dominate them during the day, yielding a circadian rhythm in retinal sensitivity and rod-cone dominance. The activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, also exhibits a circadian rhythm in the retina with approximately threefold higher levels during the day than at night. The rhythm of tyrosine hydroxylase activity is opposite in phase to the circadian activity of tryptophan hydroxylase, the first enzyme in the melatonin biosynthetic pathway. We tested whether dopamine may be related to the physiological rhythms of the retina by examining the actions of pharmacological agents that effect dopamine receptors. We found that blocking dopamine D2 receptors in the retina during the day mimics the nighttime state by increasing the amplitude of the b-wave and shifting the retina to rod dominance. Conversely, activating D2 receptors at night mimics the daytime state by decreasing the amplitude of the b-wave and shifting the retina to cone dominance. A selective antagonist for D1 dopamine receptors has no effect on retinal sensitivity or rod-cone dominance. Reducing retinal dopamine partially abolishes rhythms in sensitivity and yields a rod-dominated retina regardless of the time of day. These results suggest that dopamine, under the control of a circadian oscillator, has a key role in modulating sensitivity and rod-cone dominance in the Japanese quail retina.

Adaptation, Ocular↗
PubMed2003

Metabolic effects of hypothermia and its neuroprotective effects on the recovery of metabolic and electrophysiological function in the ischemic retina in vitro.

OBJECTIVE: Reduction in energy usage has been investigated as the mechanism by which hypothermia provides protection during ischemia. We describe experiments using hypothermia in the rabbit retina in vitro that show a correlation between hypothermia-induced reductions in energy usage and neuroprotection. METHODS: We examined energy metabolism and electrophysiological function under control/nonischemic conditions during 1 or 2 hours of "ischemia" (induced by decreasing glucose from 6 to 1 mmol/L and oxygen from 95 to 15%) and during 3 to 4 hours of "return-to-control" conditions. Glucose utilization and lactate production were measured as indices of energy metabolism, and light-evoked compound action potentials were monitored to assess functional recovery. RESULTS: Nonischemic retinas subjected to both mild (33 +/- 0.5 degrees C) and moderate (30 +/- 0.5 degrees C) hypothermia exhibited a decrease of 38% in the rate of glucose utilization and lactate production compared with normothermic retinas (36 +/- 0.5 degrees C) (analysis of variance, P < 0.001). In retinas that were made ischemic, mild or moderate hypothermia further reduced the rates of glucose utilization (18 and 39%, respectively) and lactate production (21 and 28%, respectively) (P < 0.001 for glucose, P < 0.01 for lactate). Retinas that had been mildly or moderately hypothermic during ischemia exhibited improved recovery of glucose utilization (65 and 57%, respectively) and lactate production (72 and 74%, respectively) compared with normothermic retinas (18% for glucose and 54% for lactate; repeated-measures analysis of variance, P < 0.001). Recovery of compound action potentials for retinas kept at 36, 33, and 30 degrees C was 15, 36, and 53%, respectively (repeated-measures analysis of variance, P < 0.001). CONCLUSION: Our studies in an avascular neuronal model of ischemia demonstrate that hypothermia protects against ischemic injury. We interpret the smaller reductions in energy generation and usage caused by ischemia when the retinas were hypothermic as evidence that hypothermia had reduced energy requirements more than energy production, and we propose that this at least in part explains its protection.

Animals↗
PubMed1988

Modulation of cone horizontal cell activity in the teleost fish retina. I. Effects of prolonged darkness and background illumination on light responsiveness.

The effects of prolonged (greater than 2 hr) darkness and background illumination on the light responsiveness of cone horizontal cells were examined in isolated, superfused white perch retinas. In retinas from fish maintained in complete darkness for more than 2 hr, cone horizontal cells had a resting membrane potential of about -18 mV, and they generated only slow, low-amplitude (3-4 mV) responses even when stimulated with bright flashes. Following the presentation of dim background light, the cone horizontal cells slowly hyperpolarized and thereafter remained at a more hyperpolarized level (about -25 mV). Concurrently, their light responses were dramatically enhanced in size, and response amplitudes to bright flashes eventually increased to about 50 mV. This was accompanied by noticeable changes in response waveforms; following light exposure, the responses became faster and showed initial on-transients. The increase in cone horizontal cell responsiveness was graded with intensity of the background light. A similar enhancement in response amplitudes of cone horizontal cells occurred after presenting bright flashes repetitively at intervals of 9 sec. This background sensitization phenomenon was observed in both L- and C-type cone horizontal cells. When light-sensitized isolated retinas were maintained in darkness for long periods (greater than 30 min), the light responsiveness of cone horizontal cells gradually decreased. The changes in membrane potential and response waveform were opposite to those that occurred when prolonged dark-adapted retinas were exposed to background lights; the cells depolarized by 5-7 mV and light-evoked responses became slower. Effects of background illumination on rod-driven horizontal cells were examined as well. Rod horizontal cells were about 2 log units more sensitive to white light than were cone horizontal cells. When recorded in prolonged dark-adapted retinas, rod horizontal cells showed large responses (approximately 50 mV), which could not be further enhanced by background illumination. Cone horizontal cell responsiveness in the carp retina was also depressed by prolonged darkness and increased by illumination in a fashion similar to that observed in the white perch retina. The change in response amplitude was only about 2-fold in carp compared with 5- to 10-fold changes observed in white perch. These results indicate that the light responsiveness of cone horizontal cells in the teleost retina is suppressed in prolonged darkness and that background lights release the cells from suppression.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Systemic hyperoxia decreases vascular endothelial growth factor gene expression in ischemic primate retina.

OBJECTIVES: To determine whether systemic hyperoxia can reverse retinal hypoxia and decrease vascular endothelial growth factor (VEGF) gene expression in ischemic nonhuman primate retina. METHODS: Six eyes of 3 cynomolgus monkeys were studied. Retinal ischemia was induced via laser vein occlusion and confirmed with fluorescein angiography. Animals were randomly assigned to treatment with either 21% or 100% inhaled oxygen. Arterial PO2 was monitored while systemic acid-base status was maintained. An oxygen microelectrode on a micromanipulator was used to measure preretinal oxygen concentrations in ischemic and nonischemic retina in situ. RNA was isolated from fresh whole retinas, and VEGF messenger RNA levels were quantified with Northern blotting. RESULTS: The preretinal PO2 in ischemic retina was less than the PO2 in nonischemic retina in animals breathing 21% oxygen (intervascular zone PO2, 14.3+/-0.53 vs 21.8+/-0.55 mm Hg; P=.002). After 8 hours of systemic hyperoxia (arterial PO2, 512+/-18 mm Hg), the preretinal PO2 in ischemic retina increased to 166.2+/-15.6 mm Hg (21.8% oxygen) and retinal VEGF messenger RNA levels were reduced by an average of 55%. CONCLUSIONS: These data demonstrate that systemic hyperoxia can lower retinal VEGF gene expression and reoxygenate ischemic adult primate retina.

Animals↗
PubMed1996

Comparison of photoreceptor spatial density and ganglion cell morphology in the retina of human, macaque monkey, cat, and the marmoset Callithrix jacchus.

We studied the relationship between the morphology of ganglion cells and the spatial density of photoreceptors in the retina of two Old World primates, human and macaque monkey; the diurnal New World marmoset Callithrix jacchus; and the cat. Ganglion cells in macaque and marmoset were labelled by intracellular injection with Neurobiotin or by DiI diffusion labelling in fixed tissue. Cone photoreceptor densities were measured from the same retinas. Supplemental data for macaque and data for human and cat were taken from published studies. For the primates studied, the central retina is characterised by a constant numerical convergence of cones to ganglion cells. Midget ganglion cells derive their input, via a midget bipolar cell, from a single cone. Parasol cells derive their input from 40-140 cones. Outside the central retina, the convergence increases with eccentricity. The convergence to beta cells in the cat retina is very close to that for parasol cells in primate retina. The convergence of rod photoreceptors to ganglion cells is similar in human, macaque, and marmoset, with parasol cells receiving input from 10-15 times more rods than midget cells. The low convergence of cones to midget cells in human and macaque retinas is associated with distinctive dendritic "clusters" in midget cells' dendritic fields. Convergence in marmoset is higher, and the clusters are absent. We conclude that the complementary changes in photoreceptor density and ganglion cell morphology should be considered when forming linking hypotheses between dendritic field, receptive field, and psychophysical properties of primate vision.

Animals↗
PubMed1996

Interphotoreceptor retinoid-binding protein (IRBP): expression in the adult and developing Xenopus retina.

Apposition of the neural retina and pigment epithelium is critical to photoreceptor development and function. Interphotoreceptor retinoid-binding protein (IRBP) is a major component of the extracellular matrix separating these epithelia in the African clawed frog Xenopus laevis (Gonzalez-Fernandez et al., [1993], J. Cell Sci. 105:7-21). In the adult retina, IRBP appears to mediate the transport of hydrophobic molecules, particularly retinoids and fatty acids, within the hydrophilic extracellular domain. In this paper, we compare the distribution of IRBP and its mRNA in adult and embryonic Xenopus retina. Xenopus IRBP antisense RNA, labeled with tritium or digoxigenin, was used for in situ hybridizaton studies. For immunohistochemistry, we used an antiserum against Xenopus IRBP expressed in Escherichia coli. In the adult, we found that IRBP is synthesized at similar levels by both rods and cones. The protein is restricted to the interphotoreceptor matrix, with lesser amounts in the pigment epithelial cytoplasm. In the embryo, expression of the mRNA for IRBP is restricted to the central retina, where photoreceptor differentiation has taken place. By contrast, the protein is distributed throughout the embryonic subretinal space. Therefore, the presence of IRBP precedes photoreceptor differentiation. In summary, IRBP is synthesized by both rods and cones and may be internalized by the pigment epithelium. In the embryo, IRBP is synthesized by the central retina and diffuses through the matrix, reaching the undifferentiated peripheral retina. In view of its ligand-binding properties, diffusion of IRBP may provide the peripheral neural retina with a vehicle to transport retinoids and docosahexaenoic acid (molecules critical to normal retinal development) from the pigment epithelium.

Animals↗
PubMed1999

Immunochemical localization of calretinin in the retina of the turbot (Psetta maxima) during development.

The expression of the calcium-binding protein calretinin was analysed by immunohistochemistry techniques in the retina of turbot (Psetta maxima) from embryonic to juvenile stages. Calretinin immunoreactivity was first detected in retinae from newly hatched larvae, in which the anlage of the inner plexiform layer and a subset of amacrine and ganglion cells displayed a faint immunolabelling. First appearance of photoreceptors during larval life coincided with an increase in the intensity of the labelling. During subsequent larval development, the expression of calretinin affected distinctive retinal components. The inner plexiform layer, optic fiber layer, and a population of amacrine and ganglion cells were invariably labelled. Occasional bipolar cells were labelled at the end of the larval period. By metamorphosis, calretinin is sequentially expressed in horizontal cells, and bipolar immunoreactive cells become numerous. The pattern of calretinin immunoreactivity of the inner plexiform layer changes from the larval to juvenile period. In all cases, calretinin immunoreactivity exhibited variations between the peripheral retina, which contains the most recently differentiated retinal components, and the remainder of the differentiated retina. Our results suggest that the progressive expression of calretinin in the turbot retina appears associated with some degree of neuronal differentiation. Once the definitive pattern of calretinin immunoreactivity is established in the turbot retina, both similarities and differences with the calretinin location in the retina of other vertebrates can be demonstrated.

Animals↗
PubMed1996

Localization of cytosolic aldehyde dehydrogenase in the developing chick retina: in situ hybridization and immunohistochemical analyses.

Cytosolic aldehyde dehydrogenase (ALDH) mRNA is present at high levels in the undifferentiated chick retina. Tissue maturation is accompanied by a 20-25x decrease in transcript levels. To determine the spatial and temporal distribution pattern of the ALDH transcript and its encoded protein in the developing retina, in situ hybridization and immunohistochemical analyses were carried out using chick embryos at different stages of development. The ALDH transcript and protein were detected at the earliest stage tested, in the inner layer of the optic cup of stage 14 (day 2) embryos. Both the ALDH transcript and protein were found in the dorsal retina of chick embryos from stage 18 (day 3) to day 16 of incubation. Accumulation of the ALDH protein in the neurites of ganglion cells could readily be detected at early developmental stages. Staining of this ganglion fiber layer was strong in the dorsal retina and could be followed up to and into the optic nerve. By day 11, ALDH mRNA was located primarily in the ciliary margin and in the inner nuclear layer of the dorsal retina. In addition to these areas, the ALDH protein was also found in the inner plexiform and optic nerve fiber layers. These results suggest that environmental or transcriptional factors involved in the regulation of the ALDH gene are restricted to the dorsal retina at early developmental stages and that there is a requirement for the compartmentalization of the ALDH transcript/protein in the undifferentiated chick retina.

Aldehyde Dehydrogenase↗
PubMed2001

Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas.

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Animals↗
PubMed2000

Glial cells in the bird retina: immunochemical detection.

The avian retina is remarkably different from its mammalian counterpart in macroglial cell appearance. First, it is completely devoid of astrocytes. Thus, Müller cells constitute the only astrocytic-like cell population in avian retinae, whereas mammalian retinae also contain astrocytes in close association with blood vessels. Second, axons in the optic nerve layer of the retina of birds are myelinated, unlike those found in most mammalian species, with the exception of the rabbit, in which the medullary rays of the retina are myelinated by oligodendrocytes. Recent studies have revealed evidence that bird retinae contain a large number of oligodendrocytes, but which glial cell type myelinates axons intraretinally is still controversial. Apart from macroglial appearance, microglia in the bird retina show a very similar pattern of distribution to that of mammalian counterparts. This article reviews the existing data, including our new observations, and discusses the issues that remain to be resolved.

Animals↗
PubMed2000

Synaptology of the inner plexiform layer in the anuran retina.

The inner plexiform layer of the retina is a synaptic layer mostly devoid of perikarya. It contains the processes of three major neuron types: the bipolar cells, which carry information from the photoreceptors, the ganglion cells, which are the output elements of the retina, and the amacrine cells, which are able to influence the communication between the former two. Since amacrine cells are the most diverse retinal neurons, they are in a position to carve out and delineate the neural circuits of the inner retina. The aim of this review is to offer a summary of findings related to the general synaptology of the inner retina in frogs and also to provide some insight into the synaptic organization of neurochemically identified amacrine cells. The main conclusions of this paper are as follows: (i) Most contacts are formed between amacrine cells. (2) Direct bipolar to ganglion cell synapses exist, but are rare in the anuran retina. (3) All neurochemically identified amacrine cell types receive inputs from bipolar cells, but not all of them form reciprocal contacts with bipolar cell axon terminals. (4) A major inhibitory transmitter, gamma-aminobutyric acid, is involved in more than 50% of the synapses. Since contacts between inhibitory elements were often observed, disinhibitory circuits must also play a role in retinal information processing. (5) Reciprocal relationship between dopaminergic and gamma-aminobutyric acid-containing cells have been confirmed. Similar situation was observed in case of serotoninergic and gamma-aminobutyric acid-positive elements. No contacts were verified between serotoninergic and dopaminergic elements. (6) Both monoamine- and neuropeptide-containing amacrine cells establish direct contacts with ganglion cell dendrites, providing a morphological basis for neuromodulatory influence on the output elements of the retina. Unfortunately, only a handful of studies have been carried out to identify the synaptic connections between neurochemically identified cells in the anuran retina. Double-label studies at the electron microscope level to reveal the synaptic relationship of cell populations containing two different transmitters/modulators are extremely rare. Further insight into retinal synaptic circuitries could be gained with a combination of electrophysiology and morphology at the electron microscopic level. These studies must also involve identification of the transmitter receptors on identified cell types. Only after this step can the function of different synaptic circuitries be better approximated.

Animals↗
PubMed2006

Characterization of glucagon-expressing neurons in the chicken retina.

We recently identified large glucagon-expressing neurons that densely ramify neurites in the peripheral edge of the retina and regulate the proliferation of progenitors in the circumferential marginal zone (CMZ) of the postnatal chicken eye (Fischer et al. [2005] J Neurosci 25:10157-10166). However, nothing is known about the transmitters and proteins that are expressed by the glucagon-expressing neurons in the avian retina. We used antibodies to cell-distinguishing markers to better characterize the different types of glucagon-expressing neurons. We found that the large glucagon-expressing neurons were immunoreactive for substance P, neurofilament, Pax6, AP2alpha, HuD, calretinin, trkB, and trkC. Colocalization of glucagon and substance P in the large glucagon-expressing neurons indicates that these cells are the "bullwhip cells" that have been briefly described by Ehrlich et al. ([1987] J Comp Neurol 266:220-233). Similar to the bullwhip cells, the conventional glucagon-expressing amacrine cells were immunoreactive for calretinin, HuD, Pax6, and AP2alpha. Unlike bullwhip cells, the conventional glucagon-expressing amacrine cells were immunoreactive for GABA. While glucagon-immunoreactive amacrine cells were negative for substance P in central regions of the retina, a subset of this type of amacrine cell was immunoreactive for substance P in far peripheral regions of the retina. An additional type of glucagon/substance P-expressing neuron, resembling the bullwhip cells, was found in far peripheral and dorsal regions of the retina. Based on morphology, distribution within the retina, and histological markers, we conclude that there may be four different types of glucagon-expressing neurons in the avian retina.

Animals↗
PubMed1980

Gradients between nasal and temporal areas of the cat retina in the properties of retinal ganglion cells.

Evidence is presented of gradients between nasal and temporal areas of the cat's retina in the properties of their ganglion cell populations. Mean ganglion cell size is greater in temporal retina than in nasal retina, partly because the alpha- and beta-cells of temporal retina are distinctly bigger than their counterparts in nasal retina, and partly because more medium-sized cells, and fewer small cells, are to be found in temporal retina. This high proportion of medium-sized ganglion cells may reflect a high proportion of beta-cells or of the medium sized gamma-cells described by Stone and Clarke ('80). Several of these differences can be related to prior morphological, electrophysiological, and behavioural observations in the cat, and similar differences have been reported in several other mammalian species. Evidence is presented that, in the cat, at least some of these differences are less marked near the vertical meridian of the retina than more temporally or nasally. The present results may therefore, be evidence of a nasal-temporal gradient in retinal structure and funtion common to many mammals, and distinct from previously recognised gradients in ganglion cell properties related to the area centralis and visual streak specialisations.

Animals↗