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At least 1,009 records · Page 56Linked to original sources
PubMed1999

Expression of mt1 melatonin receptor in rat retina: evidence for multiple cell targets for melatonin.

Melatonin is synthesized in the retina at night and acts as a local modulator within this tissue by mediating the effects of darkness. We investigated the expression and localization of the mt1 (Mel1a) melatonin receptor in rat retina in order to disclose the cellular and molecular bases of melatonin's action in the mammalian retina. Western blotting of the mt1 receptor in rat retina exhibited a single immunoreactive band of approximately 37,000 mol. wt, which corresponds to the predicted molecular size of the receptor. The mt1 receptor was immunocytochemically localized to both the inner and outer plexiform layers. During postnatal development, retina from two-week-old rats showed the highest mt1 immunoreactivity; the outer plexiform layer and horizontal cell bodies were strongly immunolabeled, with weaker labeling in the inner plexiform layer. Expression of mt1 receptor messenger RNA in the rat retina was demonstrated by reverse transcription-polymerase chain reaction and in situ hybridization. mt1 receptor transcripts were localized to ganglion cells, amacrine cells and horizontal cells. These results suggest that melatonin influences retinal physiology by acting on multiple retinal cell types, including ganglion, amacrine and horizontal cells, via the mt1 receptor expressed in their processes.

Animals↗
PubMed1997

Differential effect of taurine and serotonin on the outgrowth from explants or isolated cells of the retina.

The sulfur amino acid taurine and the indoleamine serotonin increases and decreases, respectively, the outgrowth from goldfish retinal explants. Taurine seems to be acting, at least partially, through an increase in calcium fluxes, and the serotonin-inhibiting effect appears to be mediated by serotonin1A receptors and cAMP. Isolated cells of postcrush goldfish retina and of retina from 5-day-old rats were cultured in the presence of taurine or serotonin. In the goldfish, the classical morphology of postcrush ganglion cells was observed. An antibody against the glycoprotein Thy-1 labelled three types of cells in the cultures of goldfish retina. The number of cells outgrowing and the length of the main neurite was measured at 5 days in culture in both species. The number of cells presenting neurites was increased in the goldfish retina by the addition of taurine, and decreased by serotonin. However, the length of the neurites was unaffected by the addition of the modulators. In the rat, only a slight decrease in the number of cells outgrowing was observed in the presence of serotonin. The incorporation of [3H]thymidine was not modified after 5 days in culture in the presence of taurine or serotonin, either in the goldfish or in the rat retina. The antibody Thy 1.1 can label retinal cells of the goldfish in vitro, one of them being ganglion cells. The trophic effect exerted by taurine in the postcrush goldfish retina needs the integrity of the tissue favoring the interaction of cells and factors, because outgrowth increases in retinal explants, but not in isolated cells.

Animals↗
PubMed2000

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.

Animals↗
PubMed1995

The retinal pigmented epithelium is required for development and maintenance of the mouse neural retina.

BACKGROUND: During development of the vertebrate eye, there is a series of reciprocal cellular interactions that determine the fate of the eye components. Although evidence from organ culture suggests that the retinal pigmented epithelium (RPE) organizes the laminar structure of the differentiated neural retina, no role has been identified for the RPE in early eye development, nor has the later function of RPE been demonstrated in vivo. RESULTS: To investigate the role of RPE cells in eye development, we generated transgenic mice that carry the attenuated diphtheria toxin-A gene; this transgene was driven by the promoter of the gene encoding the tyrosinase-related protein-1, which is specifically expressed in pigment cells. Depending on the expression level of the transgene, the retinal epithelium was ablated before or after its differentiation into a pigmented cell layer. We show that an early ablation (embryonic day E10-11) resulted in disorganization of the retinal layer, immediate arrest of eye growth and subsequent eye resorption. A later ablation (E11.5-12.5) allowed the eye to be maintained during embryogenesis, but the laminar structure of the retina became disrupted by the end of gestation, the vitreous failed to accumulate the adults were anophthalmic or severely microphthalmic. In some microphthalmic eyes, a number of RPE cells escaped ablation and formed patches of pigmented cells; the laminar structure of the retina was maintained immediately adjacent to such pigmented areas but disrupted elsewhere. In both cases--early or late ablation of the RPE--the retina appears to be the primary affected tissue. CONCLUSIONS: We conclude that presence of the RPE is required for the normal development of the eye in vivo. Its presence early in development is necessary for the correct morphogenesis of the neural retina. After the neural retina has started to differentiate, the RPE is still necessary, either directly or indirectly, to maintain the organization of the retinal lamina.

Animals↗
PubMed1997

Isoprenoid metabolism in the vertebrate retina.

Herein, studies concerning the biosynthesis, intracellular transport and utilization of isoprenoid lipids in vertebrate retinas are reviewed, with particular regard to rod photoreceptor cells and the assembly of rod outer segment (ROS) disk membranes. Initial in vitro studies with bovine retinas showed that [3H]mevalonate is metabolized primarily to squalene and 'methylated' sterols, rather than to cholesterol. Subsequently, similar results were obtained with frog retinas using [3H]acetate as a precursor, and the absolute rate of the sterol pathway was determined in vitro with 3H2O. With the aid of vesicular transport inhibitors, energy poisons, and reduced temperature, it was demonstrated that lipid and protein trafficking mechanisms in the rod cell are separate and independent from one another. In vivo, the majority of newly synthesized squalene in the frog retina is not metabolized to sterols; rather, it is transported to the ROS, where it turns over in parallel with the disk membranes. The remaining squalene is converted slowly to cholesterol, much of which becomes incorporated into the ROS. In contrast, the in vivo metabolism of [3H]acetate to cholesterol in the rat retina is relatively efficient and rapid. However, in both frog and rat, retinal cholesterol turnover is slow (> 60 days), suggesting the existence of a retention mechanism that minimizes the need for de novo biosynthesis. The use of pharmacological approaches to assess the biological roles of isoprenoid lipids and protein prenylation in the retina and the mechanism of retinal cholesterol homeostasis are discussed.

Animals↗
PubMed1990

A burst of differentiation in the outer posterior retina of the eleven-week human fetus: an ultrastructural study.

Many studies on human retinal development have cited the third gestational month as a period when the posterior retina undergoes rapid differentiation and maturation, including a lining up of cone precursors. Ultrastructural data on the posterior retina during the third month are very limited, and totally lacking for the cone monolayer. We have examined two human fetal retinas between ten and 11 gestational weeks. Before the appearance of the cone monolayer, the outer neural retina consists of a homogeneous population of undifferentiated neuroblasts. Mitotic figures are still evident, even posteriorally. There is no outer plexiform layer (OPL). The interface of neural retina to retinal pigment epithelium (RPE) is largely featureless. By 11 weeks, the posterior retina has a thin OPL that separates the many rows of cells in the developing inner nuclear layer from the single tier of macular cone precursors. The RPE monolayer consists of cuboidal cells whose apical surface elaborates ridges of cytoplasm and branched processes that project into the subretinal space. The large, cuboidal cones are linked to each other and Müller cells at the outer limiting membrane. They show definitive signs of the structural polarity typical of vertebrate photoreceptors. Their apical cytoplasm contains many organelles common to the inner segment, while the basal cytoplasm has synaptic ribbons and vesicles, and receives invaginating contacts from processes in the OPL neuropil arising from differentiating second-order neurons. Lateral cone surfaces are mutually underlain by large subsurface cisterns.

Cell Differentiation↗
PubMed1990

Somatostatin and prosomatostatin in the retina of the rat: an immunohistochemical, in-situ hybridization, and chromatographic study.

Specific antisera, raised in rabbits, against somatostatin 1-14, somatostatin 1-28, the fragment 1-12 of somatostatin 1-28, and prosomatostatin 20-36 were used for immunohistochemistry and gel filtration of the rat retina. With all antisera, immunoreactive perikarya could be located in the inner nuclear and ganglion cell layers. In the inner nuclear layer, amacrine cells with processes extending predominantly into the first sublayer of the inner plexiform layer were observed. Some processes extended also to the ganglion cell layer. In addition, somatostatin-immunoreactive interplexiform cells were present in the inner nuclear layer. In the ganglion cell layer, perikarya were found located in the midperiphery and in the far periphery of the retina. The neurons located in the midperiphery of the retina possessed a round perikaryon from which processes could be followed going into the inner plexiform layer, where they dichotomized in the third and first sublayers. The perikarya in the far periphery of the retina near the ora serrata exhibited an ovoid-shaped cell body from which processes extended horizontally in a bipolar manner in the layer itself. By use of an [35S]-labeled antisense oligonucleotide probe, in situ hybridization of the rat retina showed the presence of perikarya in the inner nuclear layer and ganglion cell layer containing mRNA encoding for prosomatostatin. Gel filtration of the retinal extracts followed by radioimmunoassay showed the presence of somatostatin 1-14, the fragment 1-12 of somatostatin 1-28, and prosomatostatin 1-64. However, somatostatin 1-28 was not detected. The results obtained in this study verify the presence of somatostatin 1-14 in the rat retina located in perikarya and processes in the inner nuclear and ganglion cell layers. The positive in-situ hybridization signals show that the intraneuronal somatostatin immunoreactivity is due to synthesis of the peptide and not uptake in the neurons. The presence of the somatostatin propeptide and fragments of this propeptide, in both intraretinal perikarya and fibers, indicate a posttranslational modification of this neuropeptide in the perikarya and the processes as well.

Animals↗
PubMedDate not supplied

Na(+)- and Cl(-)-dependent neurotransmitter transporters in bovine retina: identification and localization by in situ hybridization histochemistry.

The physiological actions of biogenic amine and amino-acid neurotransmitters are terminated by their removal from the synaptic cleft by specific high-affinity transport proteins. The members of the Na(+)- and Cl(-)-dependent neurotransmitter transporter family expressed in bovine retina and responsible for the uptake of biogenic amine and amino-acid neurotransmitters were identified using a reverse transcriptase-polymerase chain reaction-based approach. cDNA clones encoding bovine homologues of glycine (GLYT-1), gamma-aminobutyric acid (GAT-1), creatine (CreaT), and orphan (NTT4) transporters were identified using this strategy. The expression pattern of mRNAs encoding these proteins in the retina was determined by in situ hybridization histochemistry. GLYT-1, CreaT, NTT4, and GAT-1 mRNAs were expressed in the retina by cells in the inner nuclear, inner plexiform, and ganglion cell layers. They were not expressed at detectable levels in the photoreceptor cells whose cell bodies are in the outer nuclear layer and are the most abundant cell type in the retina. GLYT-1 mRNA was present exclusively in the proximal inner nuclear layer. GAT-1 mRNA was localized to both the inner nuclear and ganglion cell layers. CreaT mRNA was expressed in all cell types in the retina, except photoreceptors, and NTT4 mRNA was expressed by a subpopulation of cells in the ganglion cell layer. Elucidation of the expression pattern of these neurotransmitter transporter mRNAs in the retina provides a basis for studies of the role of glycine, gamma-aminobutyric acid, and creatine transporters in retinal function.

Animals↗
PubMedDate not supplied

Ontogeny of the opioid growth factor, [Met5]-enkephalin, and its binding activity in the rat retina.

The endogenous opioid peptide [Met5]-enkephalin is a tonically active opioid growth factor (OGF) with an inhibitory action on DNA synthesis in the developing rat retina. In this study, the ontogeny of the spatial and temporal expression of OGF and its binding activity was examined. OGF-like immunoreactivity was detected in the retina at gestation day (E) 20, but not at E18, and was localized to ganglion cell and neuroblast layers; immunochemical reaction was no longer seen in the retina by postnatal day 6. Native OGF was further identified and characterized by high-performance liquid chromatography (HPLC) studies and immunodot assays, which revealed that [Met5]-enkephalin was present in the neonatal, but not adult, rat retina. OGF binding activity was detected as early as E18 using [125I]-[Met5]-enkephalin and in vitro receptor autoradiography. Little OGF binding activity was noted for prenatal retinas, but appreciable activity was observed from birth to postnatal day 4; no OGF binding could be detected after postnatal day 5 or in the adult. These results reveal the transient appearance of the OGF, [Met5]-enkephalin, and its receptor binding activity in the developing mammalian retina, and show that their ontogeny coincides with the timetable of DNA synthesis of retinal neuroblasts.

Animals↗
PubMedDate not supplied

Specialized neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle.

There are many regional differences in cell morphology and neurochemistry in the retina. This study examined a specialized population of neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle. Some of the dendritic processes from these peptidergic amacrine cells formed a dense circumferentially oriented nerve fiber plexus which ran parallel to the ora serrata. Collaterals from this plexus projected into and innervated the nonpigmented ciliary epithelium in the pars plana region of the ciliary body. Electron microscopy revealed that the neuropeptide Y- and glucagon-like immunoreactive processes in the ciliary epithelium contained many labeled, large dense-cored vesicles. Small crystals of lipid-soluble fluorescent dye were implanted in the retina near the ora serrata in fixed retinal tissue to search for other peripheral retinal specializations. Numerous thick and thin cell processes oriented parallel to the ora serrata were labeled in the retina by the dye. In addition, many dye-labeled somata with circumferentially oriented dendritic arborizations were seen in the extreme periphery of the retina. Many of these dye-labeled cells and processes were clearly not associated with the neuropeptide Y- and glucagon-like immunoreactive cells described above. This study has shown that some peptidergic neurons in the peripheral retina have a unique morphology in comparison to more centrally located cells. The function of these specialized peripheral cells is not established, but the innervation of the ciliary epithelium by peptidergic amacrine cells suggests that they may be involved in control of aqueous inflow.

Animals↗
PubMedDate not supplied

Light-induced modulation of coupling between AII amacrine cells in the rabbit retina.

The rod-driven, AII amacrine cells in the mammalian retina maintain homologous gap junctions with one another as well as heterologous gap junctions with on-cone bipolar cells. We used background illumination to study whether changes in the adaptational state of the retina affected the permeabilities of these two sets of gap junctions. To access changes in permeability, we injected single AII amacrine cells with the biotinylated tracer, Neurobiotin, and measured the extent of tracer coupling to neighboring AII cells and neighboring cone bipolar cells. We also measured the center-receptive field size of AII cells to assess concomitant changes in electrical coupling. Our results indicate that in well dark-adapted retinas, AII cells form relatively small networks averaging 20 amacrine cells and covering about 75 microns. The size of these networks matched closely to the size of AII cell on-center receptive fields. However, over most of their operating range, AII cells formed dramatically larger networks, averaging 326 amacrine cells, which corresponded to an increased receptive-field size. As the retina was light adapted beyond the operating range of the AII cells, they uncoupled to form networks comparable in size to those seem in well dark-adapted retinas. Our results, then, indicate that the adaptational state of the retina has a profound effect on the extent of electrical coupling between AII amacrine cells. Although we observed light-induced changes in the number of tracer-coupled cone bipolar cells, these appeared to be an epiphenomenon of changes in homologous coupling between AII amacrine cells. Therefore, in contrast to the robust changes in AII-AII coupling produced by background illumination, our data provided no evidence of a light-induced modulation of coupling between AII cells and on-cone bipolar cells.

Adaptation, Physiological↗
PubMedDate not supplied

The fountain amacrine cells of the rabbit retina.

We have characterized a distinctive type of bistratified amacrine cell in the rabbit retina at both the single cell and population levels. These cells correspond to the "fountain" amacrine cells recently identified by MacNeil and Masland (1998). The fountain cells can be distinguished in superfused retinal wholemounts labeled with nuclear dyes, thus enabling them to be targeted for intracellular injection with Neurobiotin. This revealed that the primary dendrites ascend steeply to sublamina b of the inner plexiform layer, where they form an irregular arbor at the border of strata 4 and 5. These dendrites then give rise to multiple varicose processes that descend obliquely to sublamina a, where they form a more extensive arbor in stratum 1. The fountain amacrine cells show strong homologous tracer coupling when injected with Neurobiotin, and this has enabled us to map their density distribution across the retina and to examine the dendritic relationships between neighboring cells. The fountain amacrine cells range in density from 90 to 360 cells/mm2 and they account for 1.5% of the amacrine cells in the rabbit retina. The thick tapering dendrites in sublamina b form highly territorial arbors that tile the retina with minimal overlap, whereas the thin varicose processes intermingle in sublamina a. The fountain cells are immunopositive for y-aminobutyric acid and immunonegative for glycine. We further propose that these cells are homologous to the substance P-immunoreactive (SP-IR) amacrine cells in the cat retina and that they may account for a subset of the SP-IR amacrine cells in the rabbit retina.

3,3'-Diaminobenzidine↗
PubMedDate not supplied

Functional dopamine deficits in the senile rat retina.

The activity of the endogenous retinal dopamine (DA) pathway has been examined in the pigmented rat using retinas obtained from normal adult (approximately 3 months) and senile adults (approximately 24 months) using an in vitro electrophysiological approach. By comparing the pharmacological sensitivity of the horizontal cells (HCs) to exogenous DA, a D1 receptor antagonist (SCH 23390) and a DA-transport inhibitor (nomifensine), it is suggested that there is a functional deficit in the endogenous DA activity in the senile retina. Cells recorded from retinae obtained from senile animals are more sensitive to exogenous DA, whilst the senile retina is insensitive to SCH 23390. In addition, nomifensine was effective in potentiating subthreshold DA applications, but only in the normal adult retina. The data may suggest that endogenous DA release upon the HCs and selective re-uptake are suppressed in these retinae. These functional deficits also appear to be associated with changes in the receptive fields of the HCs, suggesting there is a corresponding deficit in spatial processing at the outer plexiform layer (OPL) of the senile rat.

Aging↗
PubMedDate not supplied

Cholecystokinin-like immunoreactive amacrine cells in the rat retina.

High levels of endogenous cholecystokinin (CCK) are present in the rat retina (Eskay & Beinfeld, 1982), but the cellular localization and physiological actions of CCK in the rat retina are uncertain. The goals of this study were to characterize the cells containing CCK, identify cell types that interact with CCK cells, and investigate the effects of CCK on rod bipolar cells. Rat retinas were labeled with antibody to gastrin-CCK (gCCK) using standard immunofluorescence techniques. Patch-clamp methods were used to record from dissociated rod bipolar cells from rats and mice. Gastrin-CCK immunoreactive (-IR) axons were evenly distributed throughout the retina in stratum 5 of the inner plexiform layer of the rat retina. However, the gCCK-IR somata were only detected in the ganglion cell layer in the peripheral retina. The gCCK-IR cells contained glutamate decarboxylase, and some of them also contained immunoreactive substance P. Labeled axons contacted PKC-IR rod bipolar cells, and recoverin-IR ON-cone bipolar cells. CCK-octapeptide inhibits GABA(C) but not GABA(A) mediated currents in dissociated rod bipolar cells.

Amacrine Cells↗
PubMedDate not supplied

Immuocytochemical analysis of spatial organization of photoreceptors and amacrine and ganglion cells in the tiger salamander retina.

In the present study, using double- or triple-label immunocytochemistry in conjunction with confocal microscopy, we aimed to examine the population and distribution of photoreceptors, GABAergic and glycinergic amacrine cells, and ganglion cells, which are basic but important parameters for studying the structure-function relationship of the salamander retina. We found that the outer nuclear layer (ONL) contained 82,019 +/- 3203 photoreceptors, of which 52% were rods and 48% were cones. The density of photoreceptors peaked at approximately 8000 cells/mm2 in the ventral and dropped to approximately 4000 cells/mm2 in the dorsal retina. In addition, the rod/cone ratio was less than 1 in the central retina but larger than I in the periphery. Moreover, in the proximal region of the inner nuclear layer (INL3), the total number of cells was 50,576 +/- 8400. GABAergic and glycinergic amacrine cells made up approximately 78% of all cells in this layer, including 43% GABAergic, 32% glycinergic, and 3% GABA/glycine colocalized amacrine cells. The density of these amacrine cells was approximately 6500 cells/mm2 in the ventral and approximately 3200 cells/mm2 in the dorsal area. The ratio of GABAergic to glycinergic amacrine cells was larger than 1. Furthermore, in the ganglion cell layer (GCL), among a total of 36,007 +/- 2010 cells, ganglion cells accounted for 65.7 +/- 1.5% of the total cells, whereas displaced GABAergic and glycinergic amacrine cells comprised about 4% of the cells in this layer. The ganglion cell density was approximately 1800 cells/mm2 in the ventral and approximately 600 cells/mm2 in the dorsal retina. Our data demonstrate that all three major cell types are not uniformly distributed across the salamander retina. Instead, they exhibit a higher density in the ventral than in the dorsal retina and their spatial arrangement is associated with the retinal topography. These findings provide a basic anatomical reference for the electrophysiological study of this species.

Amacrine Cells↗
PubMedDate not supplied

Normal photoresponses and altered b-wave responses to APB in the mdx(Cv3) mouse isolated retina ERG supports role for dystrophin in synaptic transmission.

The mdx(Cv3) mouse is a model for Duchenne muscular dystrophy (DMD). DMD is an X-linked disorder with defective expression of the protein dystrophin, and which is associated with a reduced b-wave and has other electro- retinogram (ERG) abnormalities. To assess potential causes for the abnormalities, we recorded ERGs from pieces of isolated C57BL/6J and mdx(Cv3) mouse retinas, including measurements of transretinal and intraretinal potentials. The ERGs from the isolated mdx(Cv3) retina differ from those of control retinas in that they show reduced b-wave amplitudes and increased b-wave implicit times. Photovoltages obtained by recording across the photoreceptor outer segments of the retinas did not differ from normal, suggesting that the likely causes of the reduced b-wave are localized to the photoreceptor to ON-bipolar synapse. At a concentration of 50 microM, the glutamate analog dl-2-amino-4-phosphonobutyric acid (APB) blocks the b-wave component of the ERG, by binding to sites on the postsynaptic membrane. The On-bipolar cell contribution to the ERG was inferred by extracting the component that was blocked by APB. We found that this component was smaller in amplitude and had longer response latencies in the mdx(Cv3) mice, but was of similar overall time course. To assess the sensitivity of sites on the postsynaptic membrane to glutamate, the concentration of APB in the media was systematically varied, and the magnitude of blockage of the light response was quantified. We found that the mdx(Cv3) retina was 5-fold more sensitive to APB than control retinas. The ability of lower concentrations of APB to block the b-wave in mdx(Cv3) suggests that the ERG abnormalities may reflect alterations in either glutamate release, the glutamate postsynaptic binding sites, or in other proteins that modulate glutamate function in ON-bipolar cells.

Aminobutyrates↗
PubMedDate not supplied

Gamma-atrial natriuretic peptide 1-25 is found in bipolar cells in turtle and rat retinas.

Immunocytochemistry was used to reveal a population of bipolar cells that contain gamma-atrial natriuretic peptide 1-25 (gamma-ANP) in turtle retina. This same antibody was also used in rat retina as a comparative control. The retinas were examined by both conventional light microscopy and confocal microscopy with double-labeling to determine whether protein kinase C-alpha-like immunoreactivity (PKC-alpha-LI) was colocalized with the gamma-ANP-LI. Some thick sections of turtle retina immunostained with only the gamma-ANP antibody were also examined by electron microscopy. In rat, a subpopulation of bipolar cells with axons terminating close to the ganglion cell layer was labeled. Double-labeling experiments indicated that the gamma-ANP-LI and PKC-alpha-LI were colocalized in rat retina, and thus all the bipolar cells with gamma-ANP-LI were rod bipolar cells. In turtle, the gamma-ANP antibody labeled certain bipolar cells that were characterized by bistratified axon terminals arborizing on the borders of strata S2/3 and S3/4 in the inner plexiform layer (IPL). Double labeling with PKC-alpha antibody indicated that bipolar cells with gamma-ANP-LI were not the same bipolar cell types with PKC-alpha-LI. Thus, gamma-ANP-LI appears to be a new marker for a distinct type of bipolar cell in turtle retina. At the ultrastructural level, the gamma-ANP-LI was visible throughout the cytoplasm of the bipolar cells from dendrites to axon terminals. In the outer plexiform layer (OPL), labeled dendrites contacted photoreceptor pedicles almost exclusively at narrow-cleft basal junctions, but infrequently formed the central element at a photoreceptor ribbon synapse. In the IPL, axon terminals with gamma-ANP-LI made ribbon synapses onto a combination of amacrine and ganglion cells. Since narrow-cleft basal junctions and photoreceptor ribbon-related junctions are known to be associated with ON-center bipolar cells in turtle, and since the axon terminals of bipolars with gamma-ANP-LI stratify primarily in the ON-strata of the IPL, we suggest that these cells are likely to be ON-center cells. It is possible that the gamma-ANP may be involved in regulating the activity of Na+/K+ ATPase or in the modulation of cGMP levels.

Animals↗
PubMedDate not supplied

The fountain amacrine cells of the rabbit retina.

We have characterized a distinctive type of bistratified amacrine cell in the rabbit retina at both the single cell and population levels. These cells correspond to the "fountain" amacrine cells recently identified by MacNeil and Masland (1998). The fountain cells can be distinguished in superfused retinal wholemounts labeled with nuclear dyes, thus enabling them to be targeted for intracellular injection with Neurobiotin. This revealed that the primary dendrites ascend steeply to sublamina b of the inner plexiform layer, where they form an irregular arbor at the border of strata 4 and 5. These dendrites then give rise to multiple varicose processes that descend obliquely to sublamina a, where they form a more extensive arbor in stratum 1. The fountain amacrine cells show strong homologous tracer coupling when injected with Neurobiotin, and this has enabled us to map their density distribution across the retina and to examine the dendritic relationships between neighboring cells. The fountain amacrine cells range in density from 90 to 360 cells/mm2 and they account for 1.5% of the amacrine cells in the rabbit retina. The thick tapering dendrites in sublamina b form highly territorial arbors that tile the retina with minimal overlap, whereas the thin varicose processes intermingle in sublamina a. The fountain cells are immunopositive for gamma-aminobutyric acid and immunonegative for glycine. We further propose that these cells are homologous to the substance P-immunoreactive (SP-IR) amacrine cells in the cat retina and that they may account for a subset of the SP-IR amacrine cells in the rabbit retina.

3,3'-Diaminobenzidine↗