Synaptic organization of the amine-containing interplexiform cells of the goldfish and Cebus monkey retinas.

Fluorescence microscopy has revealed a new type of amine-containing retinal neuron, the interplexiform cell, that extends processes in both plexiform layers. After intravitreal injection of 5,6-dihydroxytryptamine in goldfish and Cebus monkey, the processes of these cells can be identified by electron microscopy. In goldfish, the processes are pre- and postsynaptic to amacrine cells in the inner plexiform layer and presynaptic to bipolar and horizontal cells in the outer plexiform layer. Interplexiform cells thus provide an intraretinal centrifugal pathway from inner to outer plexiform layers.

Gap junction protein connexin43 is heterogeneously expressed among glial cells in the adult rabbit retina.

The immunohistochemical distribution and ultrastructural immunolocalization of connexin43 (Cx43) in the neural retina of the rabbit was investigated. Cx43 immunolabeling appeared in the form of distinct puncta distributed on different kinds of glial cells and exclusively in the myelinated fiber region of the neural retina. Double-label immunohistochemistry showed that the most obvious Cx43 labeling occurred at processes of glial fibrillary acidic protein-positive astrocytes and on vimentin-positive Müller cells. Cx43-immunoreactive puncta were also evident on cell bodies and processes of 2'-3'-cyclic nucleotide phosphodiesterase-labeled oligodendrocytes. As shown by electron microscopy, immunoreactivity to Cx43 was restricted to gap junctions among the macroglial cell population. The homologous interastrocytic and Müller cell-to-Müller cell, as well as the heterologous astrocyte-to-Müller cell and astrocyte/Müller-to-oligodendrocyte gap junctions were symmetrically labeled. Our results indicate a specific expression of Cx43 at gap junctions between macroglial cells located in the myelinated streak. The extensive Cx43 immunolabeling suggests a substantial amount of gap junctional coupling that establishes a macroglial syncytium.

Gamma-aminobutyric acidA receptors on a bistratified amacrine cell type in the rabbit retina.

Gamma-Aminobutyric acid (GABA) is considered to be a major inhibitory neurotransmitter in the inner plexiform layer of the retinas of all vertebrate species. It is contained in and released from nearly 40% of the amacrine cells and is known to play a major role in many aspects of visual processing. By using well-characterized antibodies to several subunits of the GABA(A) receptor, we have analyzed their localization on the cell bodies and dendritic trees of two amacrine cell populations in the rabbit retina, which have been either filled intracellularly with Lucifer yellow or stained immunohistochemically. Both populations are selectively stained by intravitreal injection of the fluorescent nuclear dye 4',6-diaminidin-2-phenylindoldihydrochloride (DAPI). We have found that the most significant concentration of the alpha1 and beta2/3 GABA(A) receptor subunits is localized to the DAPI-3 type amacrine cell. The perikarya of the DAPI-3 cells are found in the proximal inner nuclear layer and send their processes into two sublayers in sublaminae a and b of the inner plexiform layer. These processes abut but do not directly overlap those of the two mirror-symmetric populations of starburst amacrine cells. Because the cell bodies of the DAPI-3 cells are the only ones in the inner nuclear layer that stain strongly for either the alpha1 or beta2/3 subunits, such staining is a diagnostic feature of these cells. Their processes also constitute the most strongly staining ones found within the inner plexiform layer. The dendritic trees of DAPI-3 cells, which range from about 150 microm up to about 300 microm, exhibit recurvate looping processes reminiscent of those described for directionally selective ganglion cells. In contrast to the DAPI-3 cell, we have also shown that the starburst amacrine cells exhibit no immunoreactivity for the alpha1 GABA(A) receptor subunit and very little for the beta2/3 subunit. Thus, we have shown that the DAPI-3 cells contain the highest concentrations of the alpha1 and beta2/3 GABA(A) receptor subunits in the rabbit retina. These cells, which costratify near the processes of both the starburst amacrine cells and the ON-OFF directionally selective ganglion cells, thus, are situated both anatomically and by virtue of their receptor content to potentially interact.

Fluorescence and electron microscopical observations on the amine-accumulating neurons of the cebus monkey retina.

The organization of the Cebus monkey regina was analysed after the intraocular injection of 5,6-dihydroxytryptamine. This amine was taken up not only by the previously known dopaminergic neurons, but also by a set of indoleamine-accumulating neurons, whose processes are confined to the inner plexiform layer. The synaptic contacts of the dopaminergic neurons were analysed in the electron microscope after the processes of the indoleamine-accumulating neurons were destroyed by the intravitreal injection of the neurotoxic indoleamine, 5,7-dihydroxytryptamine. The subsequent injection of 5,6-dihydroxytryptamine induces certain changes in the dopaminergic neurons which accumulate the substance: electron-dense cores appear in the synaptic vesicles, and increased electron-density of mitochodrial and cellular membranes is often observed. The dopaminergic neurons were found to be presynaptic to amacrine cell perikarya and processes in the inner plexiform layer. In the outer plexiform layer they were presynaptic to both bipolar and horizontal cells, but they did not contact photoreceptors. The dopaminergic neurons received synapses only in the inner plexiform layer, from amacrine cell processes. It is inferred that in Cebus most dopaminergic neurons belong to a special class of retinal neuron, the interplexiform cells, which appear to transmit information centrifugally within the retina, from the inner to the outer plexiform layers. There are considerable similarities between the synaptology of the dopaminergic interplexiform neurons in the Cebus monkey and the goldfish retina, and the function of interplexiform neurons may therefore be similar in these two species.

Gamma-aminobutyric acid- and glutamic acid decarboxylase-immunoreactive neurons in the retina of different vertebrates.

The localization of gamma-aminobutyric acid (GABA)- and L-glutamate 1 carboxy-lyase (GAD)-immunoreactive neurons was compared in the skate, frog, pigeon, chicken, rabbit, and man. Horizontal cells show both GABA and GAD immunoreactivity in the skate, frog, and bird. Certain amacrine cells show GABA and GAD immunoreactivity in all species. The distribution of GABA- and GAD-immunoreactive cell bodies and cell processes was very similar, if not identical, in the skate and man. In the other species, cell populations with GAD immunoreactivity also showed GABA immunoreactivity. However, in the bird, frog, and rabbit, the GABA-immunoreactive amacrine cells were at least twice as numerous as the GAD-immunoreactive cells. In birds, the distributions of the GAD and GABA immunoreactivities were different in the sublayers of the inner plexiform layer. The reason for the difference is currently unknown. GABA-immunoreactive bipolar-like cells were seen in the frog.

Calcium-independent release of gamma-aminobutyrate from nerve processes in the developing rabbit retina.

Retinas from 3- and 10-day-old rabbits, and from young (29 days), or adult animals were used to study in parallel the development of synaptic vesicles in amacrine cells and the Ca2+ dependence of the K+-stimulated [3H]gamma-aminobutyrate release from them. Few synaptic vesicles were observed in the amacrine cell processes in retinas from the 3-day-old rabbits. The number of vesicles significantly increased between 3 and 10 days and increased further between day 10 and the adult animal. The Ca2+ dependence of the K+-stimulated release decreased with increasing age. There is thus a poor correlation between the Ca2+ dependent transmitter release and the number of synaptic vesicles in the nerve terminal, favouring the existence of a Ca2+ dependent nonvesicular process for the [3H]gamma-aminobutyrate release in the rabbit retina.

Peptide immunoreactive neurons in the human retina.

The distribution of peptide-immunoreactive neurons in the human retina was investigated. Neurons displaying immunoreactivity towards substance P, vasoactive intestinal polypeptide (VIP), somatostatin, neuropeptide Y (NPY) and peptide histidine-isoleucine (PHI) were found in amacrine cells with cell bodies situated in the innermost part of the inner nuclear layer and nerve fibers ramifying in the inner plexiform layer in a manner differing according to the peptide investigated. Two other cell types were found. In the middle of the inner plexiform layer cell bodies showing immunoreactivity towards substance P, VIP and PHI were found. In the ganglion cell layer there were cell bodies showing immunoreactivity towards substance P, somatostatin, VIP and NPY. Substance P immunoreactive, somatostatin and NPY immunoreactive fibers situated at the border between the inner nuclear and outer plexiform layers and traversing the inner nuclear layer were also found.

Graft-host connections in long-term full-thickness embryonic rabbit retinal transplants.

PURPOSE: To establish neuronal connections in the rod and cone pathway between laminated rabbit retinal transplants and the host retina. METHODS: Fourteen adult rabbits received a complete full-thickness embryonic transplant. After survival times of 3 to 10 months, the retinas were studied under light microscope and with immunohistochemistry. Antibodies against protein kinase C (PKC), parvalbumin, and calbindin were used to label rod bipolar cells, AII amacrine cells, and cone bipolar cells, respectively. The AB5 antibody was used to label ganglion cells. RESULTS: The transplants displayed laminated morphology with layers parallel to the host retinal pigment epithelium. In the oldest specimens (10 months after surgery), laminated layers of graft and host approached each other and almost reconstructed the normal retinal appearance. The ganglion and cone bipolar cells of the host survived well, as was seen with AB5 and calbindin double-labeling. Connections between cone bipolar cells in the graft and ganglion cells in the host were not common. PKC-labeled rod bipolar cells and parvalbumin-labeled AII amacrine cells of host and graft showed sprouting activity directed toward an intermediate plexiform layer located between the graft and host. In specimens double-labeled with PKC and parvalbumin, this intermediate plexiform layer was seen to contain numerous PKC- and parvalbumin-labeled processes. Direct connections between rod bipolar and AII amacrine cells in host and graft were seen in the 10-month specimens. CONCLUSIONS: Full-thickness embryonic transplants survive for at least 10 months, and normal laminated morphology develops. Host and graft fuse and together contribute nerve cell processes to an intermediate plexiform layer. Direct graft-host contacts are also present between neuronal types that in the normal retina participate in the rod pathway.

Long-term full-thickness embryonic rabbit retinal transplants.

PURPOSE: To establish the light and electron microscopic morphology of long-term full-thickness embryonic rabbit retinal transplants, with special attention paid to graft- host integration. METHODS: Eighteen rabbits received a complete embryonic neuroretina 19 days after conception. The transplants were positioned under the host retina, flat against the host retinal pigment epithelium with proper polarity, using a vitrectomy technique. After surviving 3 to 10 months, the transplants were examined by light and electron microscopy. RESULTS: The outer retina of the host had degenerated in all specimens. In 16 of the 18 eyes, well-laminated transplants with correct polarity, measuring up to 3.2 mm in length, were found. The transplants displayed long outer segments facing the host retinal pigment epithelium, and they were laminated to the level of the inner plexiform layer in which fusion with the host was often evident. Fusion was more prominent in the oldest transplants. Electron microscopy revealed bundles of neurites at different levels of maturation in close contact with Müller cell fimbriae at regular intervals along the graft-host border. CONCLUSIONS: Full-thickness embryonic rabbit retinal transplants positioned with correct polarity develop into large laminated retinas and survive without immunosuppression for at least 10 months. Host and graft adapt and almost reconstruct the normal retinal appearance. Ultrastructurally, well-developed photoreceptors and many normal synapse types are seen, and neuron sprouting is evident at the graft-host border.

Immunohistochemical analysis of the developing inner plexiform layer in postnatal rat retina.

PURPOSE: To investigate the development from early postnatal life to adulthood of neural cell processes that establish the circuitry of the inner plexiform layer (IPL). Emphasis was focused on the ontogeny of subsets of cGMP- and protein kinase C (PKC)immunoreactive amacrine and bipolar cells. METHODS: Paraformaldehyde-fixed postnatal and adult retinas were used for light microscopic analysis of immunohistochemical labeling of cryo-sections. Synthesis of cGMP in neural structures was achieved by means of an in vitro stimulation with a well-established nitric oxide donor. RESULTS: In vitro stimulation of postnatal and mature retina with the nitric oxide donor results in NO-activated cGMP synthesis in subsets of bipolar and amacrine cells. NO-activated cGMP immunoreactivity is expressed in specific cell populations during the first postnatal week. Other cell subsets, consisting of amacrine cells and rod bipolar cells, express PKC immunoreactivity during postnatal development. An increasing number of rod bipolar cells start to exhibit cGMP labeling after eye opening, and a colocalization with PKC is established in adult retinas. Processes from these cell populations terminate in several sublaminas in the developing IPL, but cGMP- and PKC-labeled terminals appear to be confined to ON-lamina as the retina matures. CONCLUSIONS: The development of cGMP- and PKC-labeled fibers within the IPL appears to be in concert with events of neural differentiation and synaptogenesis. These results suggest that the nitric oxide/cGMP signaling pathway and PKC may participate in activity-dependent processes during development that establish the mature circuitry of synaptic contacts within the IPL. The presence of cGMP in mature rod bipolar cells suggests a role in the signal transduction of rod bipolar cell-AII amacrine cell pathway.

Neuropeptide Y immunoreactive neurons in the guinea-pig uvea and retina.

Neuropeptide Y (NPY) is a recently discovered, amidated 36 amino acid residue neuropeptide present in many but not all sympathetic noradrenergic neurons. In the guinea-pig eye, NPY immunoreactive fibers were found to have the same distribution as noradrenergic fibers except that there were fewer at the iris dilator, in the cornea, and in the chamber angle. In the anterior uvea, the NPY immunoreactive fibers disappeared after excision of the homolateral superior cervical sympathetic ganglion, whereas in the choroid, many NPY immunoreactive fibers remained, indicating that they originate elsewhere. NPY immunoreactivity thus is not found in all sympathetic adrenergic neurons nor is it found only in such nerve fibers. In the retina, NPY immunoreactive fibers formed a single layer of processes in sublamina 1 of the inner plexiform layer. NPY immunoreactive cell bodies were found in the innermost cell row of the inner nuclear layer. The immunoreactivity was concentrated to the hillock region of these cells.

GABA immunoreactivity in the retina.

Presumed GABA neurons were studied in chick, guinea pig, and rabbit retinae with an immunohistochemical procedure aimed at direct demonstration of the endogenous GABA. In all species, a subset of amacrine cells was immunoreactive, as well as numerous fibers in the inner plexiform layer. In the chick, immunoreactivity was also demonstrated in horizontal cells, and single cell processes could be distinguished in both plexiform layers. The study indicates that the endogenous stores of GABA in GABAergic neurons can be visualized with immunohistochemical techniques. This direct approach thus gives additional information and probably is less subject to nonspecific staining than the demonstration of enzymes linked to GABA synthesis and metabolism. It also gives superior resolution in comparison with the autoradiographic techniques currently used for demonstrating GABA neurons. Invest Ophthalmol Vis Sci 27:674-678, 1986.

Identification and localization of retinal cystatin C.

PURPOSE: Cystatin C is a mammalian cysteine protease inhibitor, synthesized in various amounts by many kinds of cells and appearing in most body fluids. There are reports that it may be synthesized in the mammalian retina and that a cysteine protease inhibitor may influence the degradation of photoreceptor outer segment proteins. In the current study cystatin C was identified, quantitated, and localized in mouse, rat, and human retinas. METHODS: Enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), DNA sequencing, Western blot analysis, and immunohistochemistry have been used on mouse, rat, and human retinas (pigment epithelium included). RESULTS: Cystatin C is present in high concentrations in the normal adult rat retina, as it is throughout its postnatal development. Its concentration increases to a peak at the time when rat pups open their eyes and then remains at a high level. It is mainly localized to the pigment epithelium, but also to some few neurons of varying types in the inner retina. Cystatin C is similarly expressed in normal mouse and human retinas. CONCLUSIONS: Cystatin C was identified and the localization described in the retinas of rat, mouse, and human using several techniques. Cystatin C is known to efficiently inactivate certain cysteine proteases. One of them, cathepsin S, is present in the retinal pigment epithelium and affects the proteolytic processing by cathepsin D of diurnally shed photoreceptor outer segments. Hypothetically, it appears possible that retinal cystatin C, given its localization to the pigment epithelium and its ability to inhibit cathepsin S, could be involved in the regulation of photoreceptor degradation.

Nitric oxide-producing cells project from retinal grafts to the inner plexiform layer of the host retina.

PURPOSE: Amacrine cells expressing nitric oxide synthase (NOS) are seen in normal retinas and retinal grafts to extend long processes, which can be followed for long distances. Taking advantage of the morphologic features of these cells, the present study examined whether graft-host connections involve cells capable of producing nitric oxide, a recognized retinal neuromodulatory compound. METHODS: Embryonic day 15 rabbit retinas were transplanted to the subretinal space of adult rabbits. The localization of the neuronal form of NOS was assessed by immunocytochemistry in grafts that had reached the equivalent ages of postnatal days 5, 12, 20, 45, 90, and 102. RESULTS: NOS-containing cells and processes were seen in all the transplants. Processes were found to project mainly toward areas within the graft. Yet, at all survival times examined, single immunolabeled fibers could be seen to cross the graft- host border. In fortuitous cases, it was possible to establish that the bridging fiber originated in the graft. Further, bridging fibers were seen to reach the NOS-immunolabeled host inner plexiform layer. CONCLUSIONS: Graft NOS-containing cells are not only capable of projecting into the host but also of reaching the appropriate target for NOS-containing fibers within the host retina. This indicates that at least some graft-host connections are established by graft cells that retain their ability to synthesize a modulatory compound and which potentially could contact their partner cells in the host retina.

Complementary cone fields of the rabbit retina.

PURPOSE: Complementary cone fields have been considered a unique feature of the mouse retina. In an attempt to map the arrangement of the color-specific cones in other mammals, the authors investigated the rabbit, a commonly used experimental animal for vision research. METHODS: For the identification of the different cone types immunocytochemistry was used with two monoclonal antibodies, each specific to the middle- to long-wave (red-green) and short-wave (blue) sensitive visual pigments, respectively. RESULTS: The major part of the retinal surface, including the visual streak, exhibited a dominance of M (middle-wave sensitive) cones (6 to 13,000/mm2) versus S (short-wave sensitive) cones (1 to 2,500/mm2). In contrast, the lower 5% to 6% of the total retinal area showed a complete lack of green cones and a high density of blue cones (11,000/mm2). The authors designate this crescent-like area the blue streak of the rabbit retina. CONCLUSION: In addition to the visual streak primarily abundant in green cones, there is a specialized area of the rabbit retina that is densely and exclusively populated with blue cones. Although the relative extension of this peculiar cone field is considerably smaller than the S-field of the mouse retina, its position is similar in that it occupies the lowermost part of the retina. The functional implication of this area is unknown.

Vasoactive intestinal peptide nerves in ocular and orbital structures of the cat.

Vasoactive intestinal polypeptide (VIP), a neuronal peptide of ubiquitous occurrence in the body, is known to have strong vasodilatory effects and to promote secretion from many exocrine glands. Nerves displaying VIP immunoreactivity (VIP nerves) were detected in several orbital structures of the cat. Such nerves were numerous in the lacrimal glands and somewhat less numerous in the Harderian glands and the tarsal glands. The nerves surrounded glandular acini and small blood vessels. Intraocularly, VIP nerves were seen in the ciliary processes, in the posterior third of the ciliary muscle, and around small to medium-sized blood vessels in the posterior uvea. VIP nerve fibers were absent from vessels in the anterior uvea. This distribution may explain why intracranial stimulation in the oculomotor nerve exit region dilates the vessels of the choroid but not those of the iris. A large number of VIP-immunoreactive nerve cell bodies were observed in the pterygopalatine ganglion. Extirpation of this ganglion resulted in the disappearance of VIP nerves from the intraocular structures and from the lacrimal and Harderian glands. Removal of the superior cervical ganglion and the ciliary ganglion did not affect the VIP nerve supply. The results suggest that the VIP nerves originate in the pterygopalatine ganglion.

Phenotype of an X-linked retinitis pigmentosa family with a novel splice defect in the RPGR gene.

PURPOSE: To assess the clinical phenotype in a Swedish family with X-linked retinitis pigmentosa (XLRP) resulting from a novel splice defect in the RPGR gene. METHODS: RPGR mutation analysis was performed in one family with XLRP, and several individuals from the family were examined clinically. RESULTS: The causative mutation in the family was demonstrated to be a single base-pair change at the splice donor site in intron 7 that resulted in skipping of the complete exon 7 in the mature RPGR transcript. The aberrant mRNA is predicted to produce an RPGR protein with an in-frame deletion of 53 amino acids, corresponding to an RCC1-homology repeat. Clinical studies that included ophthalmological examination and full-field electroretinography showed that this splice mutation resulted in a comparatively less severe form of RP. CONCLUSIONS: Correlation of a causative RPGR genotype with clinical findings in hemizygotes and carrier heterozygotes is an important step toward predictive diagnosis and should assist in the development of gene-based therapies in the future.

Heterogeneity of receptor immunoreactivity at synapses of glycine-utilizing neurons.

Neurons often contain, and probably release, more than one neuroactive substance that may have diverse or opposite actions on the postsynaptic cell. It remains unexplained how these neurons utilize their multiple neuroactive substances while maintaining appropriate resolution of neurotransmitter functions. Here, we have examined the ultrastructural localization of glycine receptors by using a monoclonal antibody directed to the intracellular domain of the strychnine-sensitive glycine receptor. We have found that glycine receptors are only localized to 56% of the synapses made by presumed 'glycinergic' (more accurately, glycine-utilizing) amacrine cells in the turtle retina. The remaining synapses made by these same boutons show no evidence of glycine receptors. As there is no evidence to suggest the presence of a second type of glycine receptor, these data indicate that only a portion of the postsynaptic sites contacted by the glycine-utilizing neurons can respond to glycine. They also suggest that a neuron containing multiple neuroactive substances can selectively affect postsynaptic elements by means of heterogeneous receptor localization.

Growth of postnatal rat retina in vitro. Development of neurotransmitter systems.

In this study, we demonstrate that explanted neonatal rat retina can be maintained in culture for periods up to 3 weeks. The cultured retinas displayed a distinct layering that was almost identical to litter-matched retinas of the same age, but the majority of the ganglion cells did not survive and photoreceptor outer segments did not develop properly. Distinct synaptophysin immunoreactivity was expressed in both the inner and outer plexiform layers of cultured retina and the pattern mimicked that one observed in vivo. After 2-3 weeks in vitro, the inner retina expressed immunoreactivities to various components of the cholinergic and nitrergic transmitter systems, including nitric oxide activated cyclic GMP immunoreactivity. The investigated cell populations displayed similar distribution patterns as in situ, but morphological differences appeared in vitro. Such differences were mainly observed as irregularities in the arborization patterns in the inner part of the inner plexiform layer. We suggest that these discrepancies may arise as a result of reduced ganglion cell survival. Our observations demonstrate that some neurotransmitter systems develop in vitro and their neural circuitry appears similar to the in vivo situation. The presence of synapses, receptor proteins and transmitter substances implies that neural communication can occur in cultured retinas.

Dose response and duration of action of dorzolamide, a topical carbonic anhydrase inhibitor.

The multiple-dose, dose-response relationship and duration of action of the novel topical carbonic anhydrase inhibitor dorzolamide (previously known as MK-507) were investigated in a double-masked, randomized, placebo-controlled, parallel study in 73 patients with bilateral primary open angle glaucoma or ocular hypertension. Dorzolamide (0.7%, 1.4%, or 2%) or placebo was administered every 12 hours for 5 days and then every 8 hours for 7 days. Intraocular pressure was investigated with multiple 12-hour diurnal curves. All concentrations of dorzolamide demonstrated substantial lowering of intraocular pressure throughout the day when given twice daily (9% to 21%) or three times daily (14% to 24%). Although a dose-dependent response was observed immediately following the first dose, there were no significant differences between concentrations or dose response at either the twice or three times daily dosing regimen. Three times daily administration of 2% dorzolamide demonstrated a mean percent decrease in intraocular pressure of 18% to 22% throughout the day (mean decrease, 4.5 to 6.1 mm Hg). Dorzolamide appears to have substantial potential in the treatment of glaucoma and ocular hypertension.