Localization of guanylate cyclase-activating protein 2 in mammalian retinas

Guanylate cyclase-activating proteins (GCAP1 and GCAP2) are thought to mediate the intracellular stimulation of guanylate cyclase (GC) by Ca2+, a key event in recovery of the dark state of rod photoreceptors after exposure to light. GCAP1 has been localized to rod and cone outer segments, the sites of phototransduction, and to photoreceptor synaptic terminals and some cone somata. We used in situ hybridization and immunocytochemistry to localize GCAP2 in human, monkey, and bovine retinas. In human and monkey retinas, the most intense immunolabeling with anti-GCAP2 antibodies was in the cone inner segments, somata, and synaptic terminals and, to a lesser degree, in rod inner segments and inner retinal neurons. In bovine retina, the most intense immunolabeling was in the rod inner segments, with weaker labeling of cone myoids, somata, and synapses. By using a GCAP2-specific antibody in enzymatic assays, we confirmed that GCAP1 but not GCAP2 is the major component that stimulates GC in bovine rod outer segment homogenates. These results suggest that although GCAP1 is involved in the Ca2+-sensitive regulation of GC in rod and cone outer segments, GCAP2 may have non-phototransduction functions in photoreceptors and inner retinal neurons.     

Comparison of immunolocalization patterns for the synaptic vesicle proteins p65 and synapsin I in macaque monkey retina

The distributions of the two synaptic vesicle proteins p65 [Matthew et al. (1981) J. Cell Biol., 91:257-269] and synapsin I [De Camilli et al. (1983) J. Cell Biol., 96:1337-1354] were compared in macaque monkey retina using pre-embedding immunocytochemistry for both light and electron microscopy. The monoclonal antibody AB-48 against p65 labeled ribbon-containing synaptic terminals of cone, rod, and bipolar cells as well as many conventional synapses of amacrine cells. In contrast, a polyclonal antiserum against synapsin I (SYN I) labeled many amacrine conventional synapses but no photoreceptor or bipolar ribbon synaptic terminals. Horizontal cell pre- and post-synaptic profiles in the outer plexiform layer were not labeled by either antibody. At the light microscopic level, the banding patterns in the inner plexiform layer also differed for the two antibodies, with four bands of AB-48 immunoreactivity in sublayers S1, S2, S4, and S5 but only three bands of SYN I immunoreactivity in S1, S3, and S5. SYN I also labeled varicose fibers in both the inner nuclear layer and the outer plexiform layer that are probably processes of dopaminergic and GABAergic interplexiform cells. Varicose fibers in the ganglion cell layer were labeled by both antibodies. These results provide the first electron microscopic immunocytochemical labeling for AB-48 and SYN I in intact retina and confirm that AB-48 labels both ribbon and conventional synaptic terminals, whereas SYN I labels only conventional synapses.     

Pathogenesis of neuroimmunologic diseases. Experimental models

Development of the retina, like that of other tissues, occurs via an orderly sequence of cell division and differentiation, producing the functional retina. In teleost fish, however, cell division and differentiation in the retina continue throughout the life of the animal in two distinct ways. Stem cells in a circumferential germinal zone at the periphery of the retina give rise to all retinal cell types and progenitor cells located throughout the retina in the outer nuclear layer (ONL) produce new rod photoreceptors. These processes in adult retina recapitulate in space the embryonic events responsible for forming the retina. Analysis of these events in an African cichlid fish, Haplochromis burtoni, confirmed that cone photoreceptors differentiate first, followed by rod photoreceptors. Correspondingly, at the margin of the eye, cone photoreceptors differentiate nearer to the margin than do rods. Control of photoreceptor production is not understood. Here we present the time of appearance and distribution pattern of GABA and vimentin which are candidates for the control of retinal cell division and differentiation. Antibody staining reveals that both GABA and vimentin exhibit unique patterns of expression during embryonic retinal development. Vimentin immunoreactivity is evident throughout the retina in a spoke-like pattern between developmental Days 4 and 7, as both cone and rod photoreceptors are being formed. GABA is expressed in horizontal cells between Days 5 and 7, corresponding to the onset of rod differentiation in time and in position within the retina. Moreover, the wave of GABAergic staining in the horizontal cells parallels the wave of rod differentiation across the embryonic retina of H. burtoni. Thus, GABA may play a role in the development of rod photoreceptors.     

Identification and localization of an immunoreactive AMPA-type glutamate receptor subunit (GluR4) with respect to identified photoreceptor synapses in the outer plexiform layer of goldfish retina

L-glutamate, the main excitatory synaptic transmitter in the retina, is released from photoreceptors and evokes responses in second-order retinal neurons (horizontal, bipolar cells) which utilize both ionotropic and metabotropic types of glutamate receptors. In the present study, to elucidate the functional roles of glutamate receptors in synaptic transmission, we have identified a specific ionotropic receptor subunit (GluR4) and determined its localization with respect to photoreceptor cells in the outer plexiform layer of the goldfish retina by light and pre-embedding electron-microscopical immunocytochemistry. We screened antisera to mammalian AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate)-preferring ionotropic glutamate receptors (GluR 1-4) of goldfish retina by light- and electron-microscopical immunocytochemistry. Only immunoreactive (IR) GluR4 was found in discrete clusters in the outer plexiform layer. The cones contacted in this manner were identified as long-wavelength ("red") and intermediate-wavelength ("green") cones, which were strongly immunoreactive to monoclonal antibody FRet 43 and antisera to goldfish red and green-cone opsins; and short-wavelength ("blue") cones, which were weakly immunoreactive to FRet 43 but strongly immunoreactive with antiserum to blue-cone opsin. Immunoblots of goldfish retinal homogenate with anti-GluR4 revealed a single protein at M(r) = 110 kDa. Preadsorption of GluR4 antiserum with either the immunizing rat peptide, or its goldfish homolog, reduced or abolished staining in retinal sections and blots. Therefore, we have detected and localized genuine goldfish GluR4 in the outer plexiform layer of the goldfish retina. We characterized contacts between photoreceptor cells and GluR4-IR second-order neurons in the electron microscope. IR-GluR4 was localized to invaginating central dendrites of triads in ribbon synapses of red cones, semi-invaginating dendrites in other cones and rods, and dendrites making wide-cleft basal junctions in rods and cones; the GluR4-IR structures are best identified as dendrites of OFF-bipolar cells. The results of our studies indicate that in goldfish retina GluR4-expressing neurons are postsynaptic to all types of photoreceptors and that transmission from photoreceptors to OFF-bipolars is mediated at least in part by AMPA-sensitive receptors containing GluR4 subunits.     

Circadian clock functions localized in xenopus retinal photoreceptors

A circadian oscillator that regulates visual function is located somewhere within the vertebrate eye. To determine whether circadian rhythmicity is generated by retinal photoreceptors, we isolated and cultured photoreceptor layers from Xenopus retina. On average, 94% of the viable cells in these preparations were rod or cone photoreceptors. Photoreceptor layers produced melatonin rhythmically, with an average period of 24.3 hr, in constant darkness. The phase of the melatonin rhythm was reset by in vitro exposure of the photoreceptor layers to cycles of either light or quinpirole, a D2 dopamine receptor agonist. These data indicate that other parts of the eye are not necessary for generation or entrainment of retinal circadian melatonin rhythms and suggest that rod and/or cone photoreceptors are circadian clock cells.     

Localization of nitric oxide synthase, NADPH diaphorase and soluble guanylyl cyclase in adult rabbit retina

Nitric oxide (NO) acts as a neuronal messenger which activates soluble guanylyl cyclase (SGC) in neighboring cells and produces a wide range of physiological effects in the central nervous system (CNS). Using immunocytochemical and histochemical stains, we have characterized the NO/SGC system in the rabbit retina and to a lesser extent, in monkey retina. Based on staining patterns observed with an antibody to nitric oxide synthase (NOS) type I and a histochemical marker for NADPH diaphorase, a metabolic intermediate required for NOS activity, three major classes of neurons appear to generate NO in the rabbit retina. These include two subclasses of sparsely distributed wide field amacrine cells, rod and cone photoreceptors, and a subpopulation of ganglion cells. Equivalent cell populations were labeled in monkey retina. An antibody to SGC (tested only in rabbit retina), labeled large arrays of cone photoreceptors in the outer nuclear layer, both amacrine and bipolar cells in the inner nuclear layer (INL), as well as populations of neurons in the ganglion cell layer. These data suggest that the ability to generate NO is restricted to relatively few neurons in the inner retina and to photoreceptor cells in the outer retina; while presumptive target cells, containing pools of SGC, are widespread and form contiguous fields across the inner and outer nuclear layers (ONL) as well as the ganglion cell layer.     

Identification and distribution of photoreceptor subtypes in the neotenic tiger salamander retina

The neotenic tiger salamander retina is a major model system for the study of retinal physiology and circuitry, yet there are unresolved issues regarding the organization of the photoreceptors and the photoreceptor mosaic. The rod and cone subtypes in the salamander retina were identified using a combination of morphological and immunocytochemical markers for specific rod and cone opsin epitopes. Because the visual pigment mechanisms present in the tiger salamander retina are well characterized and the antibodies employed in these studies are specific for particular rod and cone opsin epitopes, we also were able to identify the spectral class of the various rod and cone subtypes. Two classes of rods corresponding to the "red" and "green" rods previously reported in amphibian retinas were identified. In serial semithin section analyses, rods and cones comprised 62.4+/-1.4% and 37.6+/-1.4% of all photoreceptors, respectively. One rod type comprising 98.0+/-0.7% of all rods showed the immunological and morphological characteristics of "red" rods, which are maximally sensitive to middle wavelengths. The second rod subtype comprised 2.0+/-0.7% of all rods and possessed the immunological and morphological characteristics of "green" rods, which are maximally sensitive to short wavelengths. By morphology four cone types were identified, showing three distinct immunological signatures. Most cones (84.8+/-1.5% of all cones), including most large single cones, the accessory and principal members of the double cone, and some small single cones, showed immunolabeling by antisera that recognize long wavelength-sensitive cone opsins. A subpopulation of small single cones (8.4+/-1.7% of all cones) showed immunolabeling for short wavelength-sensitive cone opsin. A separate subpopulation of single cones which included both large and small types (6.8+/-1.4% of all cones) was identified as the UV-Cone population and showed immunolabeling by antibodies that recognize rod opsin epitopes. Analysis of flatmounted retinas yielded similar results. All photoreceptor types appeared to be distributed in all retinal regions. There was no obvious crystalline organization of the various photoreceptor subtypes in the photoreceptor mosaic.     

Disease sequence from mutant rhodopsin allele to rod and cone photoreceptor degeneration in man

Mutations in the gene encoding rhodopsin, the visual pigment in rod photoreceptors, lead to retinal degeneration in species from Drosophila to man. The pathogenic sequence from rod cell-specific mutation to degeneration of rods and cones remains unclear. To understand the disease process in man, we studied heterozygotes with 18 different rhodopsin gene mutations by using noninvasive tests of rod and cone function and retinal histopathology. Two classes of disease expression were found, and there was allele-specificity. Class A mutants lead to severely abnormal rod function across the retina early in life; topography of residual cone function parallels cone cell density. Class B mutants are compatible with normal rods in adult life in some retinal regions or throughout the retina, and there is a slow stereotypical disease sequence. Disease manifests as a loss of rod photoreceptor outer segments, not singly but in microscopic patches that coalesce into larger irregular areas of degeneration. Cone outer segment function remains normal until >75% of rod outer segments are lost. The topography of cone loss coincides with that of rod loss. Most class B mutants show an inferior-nasal to superior-temporal retinal gradient of disease vulnerability associated with visual cycle abnormalities. Class A mutant alleles behave as if cytotoxic; class B mutants can be relatively innocuous and epigenetic factors may play a major role in the retinal degeneration.     

Sequential genesis and determination of cone and rod photoreceptors in Xenopus

In this study, we addressed the temporal sequence of photoreceptor fate determination in Xenopus laevis by examining a number of key events during early cone and rod development. We compared the relative timing and spatial pattern of cone and rod specification using a number of cell type-specific markers, including probes to a long wavelength-sensitive opsin which is expressed by the major cone subtype. Our results show that cones are initially more numerous, and can arise in less mature regions of the retina than rods, although both types of photoreceptors begin to express their respective opsins at about the same time. We applied these markers to an assay of cellular determination to identify the stages of embryonic development at which the earliest photoreceptor fates are induced in vivo. The relative birth order of the major cone and rod subtypes was revealed by simultaneous labeling with markers of cell proliferation and terminal differentiation. Although there is much temporal overlap between the periods of cone and rod genesis and determination in Xenopus, we could discern that the earliest cones are both born and determined before the first rods. Thus, even in the rapidly developing retina of Xenopus, photoreceptors achieve their identities in a sequential fashion, suggesting that the inductive cues which determine specific photoreceptor fates may also arise sequentially during development.     

Evidence from normal and degenerating photoreceptors that two outer segment integral membrane proteins have separate transport pathways

Detachment of the neural retina from the retinal pigment epithelium induces photoreceptor degeneration. We studied the effects of this degeneration on the localization of two photoreceptor outer segment-specific integral membrane proteins, opsin and peripherin/rds, in rod photoreceptors. Results from laser scanning confocal microscopic and electron microscopic immunolocalization demonstrate that these two proteins, normally targeted to the newly-forming discs of the outer segments, accumulate in different sub-cellular compartments during photoreceptor degeneration: opsin immunolabeling increases throughout the photoreceptor cell's plasma membrane, while peripherin/rds immunolabeling occurs within cytoplasmic vesicles. The simplest hypothesis to explain our results is that these proteins are transported in different post-Golgi transport vesicles and separately inserted into the plasma membrane. More complex mechanisms involve having the two co-transported and then opsin finds its way into the plasma membrane but peripherin/rds does not, remaining behind in vesicles. Alternatively, both insert into the plasma membrane but peripherin/rds is recycled into cytoplasmic vesicles. We believe the data most strongly supports the first possibility. Although the transport pathways for these proteins have not been fully characterized, the presence of peripherin/rds-positive vesicles adjacent to the striated rootlet suggests a transport role for this cytoskeletal element. The accumulation of these proteins in photoreceptors with degenerated outer segments may also indicate that their rate of synthesis has exceeded the combined rates of their incorporation into newly forming outer segment disc membranes and their degradation. The accumulation may also provide a mechanism for rapid recovery of the outer segment following retinal reattachment and return of the photoreceptor cell to an environment favorable to outer segment regeneration.     

The localization of guanylyl cyclase-activating proteins in the mammalian retina

PURPOSE: To explore the distribution of guanylyl cylase-activating proteins 1 and 2 (GCAP1 and GCAP2) in the mammalian retina. METHODS: Cryostat and vibratome vertical sections and wholemount retinas from mouse, rat, cat, bovine, monkey, and human eyes were prepared for immunocytochemistry and viewing by light and confocal microscopy. RESULTS: In all mammalian retinas investigated, intense GCAP1 immunoreactivity (GCAP1-IR) was seen in cone photoreceptor inner and outer segments, cell bodies, and synaptic regions. Intensity of the GCAP1-IR was strong in inner segments of rods in all species but weaker in outer segments-particularly so in primates and cats. GCAP2 immunoreactivity (GCAP2-IR) was weak in bovine, mouse, and rat cones but was intense in human and monkey cones. In all species except primates, GCAP2 staining was intense in rod inner and outer segments. In primates GCAP2-IR was intense in the rod inner segment but faint in the rod outer segment. A striking difference from the GCAP1 pattern of immunoreactivity was seen with GCAP2 antibodies as far as the inner retina was concerned. GCAP2-IR was evident in certain populations of bipolar, amacrine, and ganglion cells in all species. CONCLUSIONS: GCAP1 and GCAP2, which are involved in Ca2+-dependent stimulation and inhibition of photoreceptor guanylyl cyclase, can be detected in mammalian photoreceptor inner and outer segments, consistent with their physiological function. The occurrence of both GCAPs in the synaptic region of the photoreceptors indicates participation of these proteins in pathways other than regulation of phototransduction. The occurrence of GCAP2 in inner retinal neurons is indicative of second-messenger chemical transduction, possibly in metabotropic glutamate, gamma-aminobutyric acid (GABA) receptor, and nitric oxide-activated neural circuits.     

The effect of peripherin/rds haploinsufficiency on rod and cone photoreceptors

Haploinsufficiency because of a null mutation in the gene encoding peripherin/rds has been thought to be the primary defect associated with the photoreceptor degeneration seen in the retinal degeneration slow (rds) mouse. We have compared the effects of this haploinsufficiency on rod and cone photoreceptors by measuring the levels of rod- and cone-specific gene expression, by determining the relative rates of rod and cone degeneration, and by electroretinography. These analyses were performed at ages before and after the onset of degeneration of the photoreceptor cells. The data were consistent in demonstrating that measures for cone photoreceptors are relatively spared in comparison to comparable measures for rod photoreceptors. Blue cones were retained in higher number than red/green cones for the first 3 months of the degeneration. Our results indicate that the haploinsufficiency present in rds/+ mice has a greater impact on the rod than on the cone photoreceptor, a finding that likely reflects the tight regulation of peripherin/rds and the need for two functional alleles to assemble the structure of the rod outer segment and/or differences between the ultrastructure of the rod and cone outer segments.     

Nerve repair using freezing and fibrin glue: immediate histologic improvement of axonal coaptation

The chicken retina has several types of cone photoreceptor cells, each of which contains a visual pigment, chicken red (iodopsin), green, blue or violet. Although biochemical and photochemical properties of these cone pigments have been well characterized, no information is available about the chicken photoreceptor G-protein, transducin, which couples with the visual pigment to convert a photon signal into a cellular response. To identify alpha-subunits of chicken rod and cone transducins (Tr alpha and Tc alpha, respectively), we produced two site-directed antibodies which discriminate between bovine Tr alpha and Tc alpha. Immunohistochemical studies on chicken retinas revealed that the antibody against bovine Tr alpha specifically stained the rod outer segments. On the other hand, the antibody against bovine Tc alpha uniformly stained the outer segments of the double cones and all types of single cones, while the single cones were immunohistochemically classified into three types by using a combination of antibodies against bovine rhodopsin and chicken iodopsin. Immuno-blot analyses demonstrated that the antibody against Tc alpha recognized a single band of chicken photoreceptor protein, whose molecular weight (42,000) was in good agreement with that of bovine Tc alpha (41,000). The antibody against Tr alpha recognized a protein having the same molecular weight as that of bovine Tr alpha (39,000). These observations strongly suggested that all types of chicken cone cells have a single common Tc alpha (42 kDa) structurally related to bovine Tc alpha, though each cone cell type has a distinct visual pigment.     

Immunocytochemical localization of the postsynaptic density protein PSD-95 in the mammalian retina

Synapse-associated proteins are the scaffold for the selective aggregation of ion channels at synapses; they provide the link to cytoskeletal elements and possibly are involved with the regulation of synaptic efficacy by electrical activity. The localization of the postsynaptic density protein PSD-95 was studied in different mammalian retinae (rat, monkey, and tree shrew) by using immunocytochemical methods. Immunofluorescence for PSD-95 was most prominent in the outer plexiform layer (OPL). The axon terminals of rods and cones, the rod spherules and cone pedicles, were strongly labeled. Electron microscopy, using preembedding immunocytochemistry, showed PSD-95 localized presynaptically within the photoreceptor terminals. Distinct PSD-95 labeling was also present in the inner plexiform layer (IPL). It had a punctate appearance suggesting the synaptic clustering of PSD-95 in the IPL. Electron microscopy showed that PSD-95 was concentrated in processes that were postsynaptic at bipolar cell ribbon synapses (dyads). As a rule, only one of the two postsynaptic members of the dyad was labeled for PSD-95. Double-labeling experiments were performed for PSD-95 and for SAP 102 or PSD-93, respectively, two other members of the family of synapse-associated proteins. All three were found to be colocalized in the synaptic hot spots in the IPL. In the OPL, however, PSD-95 and PSD-93 were found presynaptically, whereas SAP 102 was located postsynaptically at photoreceptor synapses. Double-labeling experiments also were performed for PSD-95 and for the NR1 subunit of the NMDA receptor. They were found to be colocalized in synaptic hot spots in the IPL.     

Histopathology of the human retina in retinitis pigmentosa

The term, 'retinitis pigmentosa', refers to a heterogeneous group of inherited diseases that cause degeneration of rod and cone photoreceptors in the human retina. Loss of photoreceptor cells is usually followed by alterations in the retinal pigment epithelium and retinal glia. Ultimately, degenerative changes occur in the inner retinal neurons, blood vessels, and optic nerve head. This chapter provides background information on the genetics of retinitis pigmentosa and a summary of the histopathologic alterations in human retinas caused by this disease. Detailed information is provided on the effects of the primary disease process on the rod photoreceptors and changes in the other retinal components, all of which are important considerations for understanding and developing therapies for retinitis pigmentosa.     

Immunocytochemical localization of the NMDA-R2A receptor subunit in the cat retina

Immunocytochemical studies were performed to determine the distribution and cellular localization of the NMDA-R2A receptor subunit (R2A) in the cat retina. R2A-immunoreactivity (R2A-IR) was noted in all layers of the retina, with specific localizations in the outer segments of red/green and blue cone photoreceptors, B-type horizontal cells, several types of amacrine cells, Müller cells and the majority of cells in the ganglion cell layer. In the inner nuclear layer, 48% of all cells residing in the amacrine cell layer were R2A-IR including a cell resembling the GABAergic A17 amacrine cell. Interestingly, the AII rod amacrine cell was devoid of R2A-IR. Although the localization of the R2A subunit was anticipated in ganglion cells, amacrines and Müller cells, the presence of this receptor subunit to the cells in the outer retina was not expected. Here, both the R2A and the R2B subunits were found to be present in the outer segments of cone photoreceptors and to the tips of rod outer segments. Although the function of these receptor subunits in rod and cone photoreceptors remains to be determined, the fact that both R2A and R2B receptor subunits are localized to cone outer segments suggests a possible alternative pathway for calcium entry into a region where this cation plays such a crucial role in the process of phototransduction. To further classify the cells that display NR2A-IR, we performed dual labeling experiments showing the relationship between R2A-labeled cells with GABA. Results showed that all GABAergic-amacrines and displaced amacrines express the R2A-subunit protein. In addition, approximately 11% of the NR2A-labeled amacrines, did not stain for GABA. These findings support pharmacological data showing that NMDA directly facilitates GABA release in retina and retinal cultures [I.L. Ferreira, C.B. Duarte, P.F. Santos, C.M. Carvalho, A.P. Carvalho, Release of [3H]GABA evoked by glutamate receptor agonist in cultured chick retinal cells: effect of Ca2+, Brain Res. 664 (1994) 252-256; G.D. Zeevalk, W.J. Nicklas, Action of the anti-ischemic agent ifenprodil on N-methyl-d-aspartate and kainate-mediated excitotoxicity, Brain Res. 522 (1990) 135-139; R. Huba, H.D. Hofmann, Transmitter-gated currents of GABAergic amacrine-like cells in chick retinal cultures, Vis. Neurosci. 6 (1991) 303-314; M. Yamashita, R. Huba, H.D. Hofmann, Early in vitro development of voltage- and transmitter-gated currents in GABAergic amacrine cells, Dev. Brain Res. 82 (1994) 95-102; R. Ientile, S. Pedale, V. Picciurro, V. Macaione, C. Fabiano, S. Macaione, Nitric oxide mediates NMDA-evoked [3H]GABA release from chick retina cells, FEBS Lett. 417 (1997) 345-348; R.C. Kubrusly, M.C. deMello, F.G. deMello, Aspartate as a selective NMDA agonist in cultured cells from the avian retina, Neurochem. Intl. 32 (1998) 47-52] or reduction of GABA in vivo [N.N. Osborn, A.J. Herrera, The effect of experimental ischaemia and excitatory amino acid agonist on the GABA and serotonin immunoreactivities in the rabbit retina, Neurosci. 59 (1994) 1071-1081]. Since the majority of GABAergic synapses in the inner retina are onto both rod and cone bipolar axon terminals [R.G. Pourcho, M.T. Owzcarzak, Distribution of GABA immunoreactivity in the cat retina: A light and electron-microscopic study, Vis. Neurosci. 2 (1989) 425-435], we hypothesize that the NMDA-receptor plays a crucial role in providing feedback inhibition onto rod and cone bipolar cells.     

The kinesin motor KIF3A is a component of the presynaptic ribbon in vertebrate photoreceptors

Kinesin motors are presumed to transport various membrane compartments within neurons, but their specific in vivo functions, cargoes, and expression patterns in the brain are unclear. We have investigated the distribution of KIF3A, a member of the heteromeric family of kinesins, in the vertebrate retina. We find KIF3A at two distinct sites within photoreceptors: at the basal body of the connecting cilium axoneme and at the synaptic ribbon. Immunoelectron microscopy of the photoreceptor ribbon synapse shows KIF3A to be concentrated both at the ribbon matrix and on vesicles docked at the ribbon, a result that is consistent with the presence of both detergent-extractable and resistant KIF3A fractions at these synapses. KIF3A is also present in the inner plexiform layer, again at presynaptic ribbons. These findings suggest that within a single cell, the photoreceptor, one kinesin polypeptide, KIF3A, can serve two distinct functions, one specific for ribbon synapses.     

Median nerve neuropathy from an old lunate dislocation

We performed a histopathologic and immunohistochemical study of eyes obtained at autopsy of an 84-year-old man from a family with X-linked cone degeneration in which affected members have a 6.5-kilobase deletion in the red cone pigment gene. At his most recent ocular examination, at age 71 years, this patient had had a visual acuity of 20/200 OU, fundus changes suggestive of macular degeneration, borderline-normal full-field rod electroretinograms, and profoundly reduced full-field cone electroretinograms. Histopathologic examination demonstrated marked loss of cone and rod photoreceptors and the retinal pigment epithelium in the central macula. The peripheral cone population was reduced, while the peripheral rod population was relatively preserved. Immunohistochemical examination with an antibody to both red and green cone opsin and an antibody to blue cone opsin disclosed a prominent loss of the red and green cone population and preservation of the blue cone population. These findings show that a defect in the red cone pigment gene can result in extensive degeneration of the red and green cone population across the retina.