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S F Basinger

Publications and source records attributed to S F Basinger.

At least 19 recordsLinked to original sources
PubMed1990

Glycine stimulates calcium-independent release of 3H-GABA from isolated retinas of Xenopus laevis.

A perfusion system was used to monitor the release of [3H]-GABA from isolated retinas of Xenopus laevis. Measurable release was stimulated by glycine at concentrations as low as 200 microM. Glycine-stimulated release was blocked by strychnine, and was not reduced in "calcium-free" Ringer's solution (0 Ca2+/20 mM Mg2+). Glutamate also stimulated calcium-independent release, using concentrations as low as 100 microM. In contrast, release stimulated by 25 mM potassium was reduced by 80% in calcium-free medium. In most experiments, agonists were applied in six consecutive 4-min pulses separated by 10-min washes with Ringer's solution. Under these conditions, the release stimulated by 0.5 mM glutamate or 25 mM potassium decreased by at least 50% from the first to the second pulse, and then gradually decreased with successive applications. In contrast, the response to 0.5 mM glycine at first increased and then only gradually decreased with successive pulses. These patterns of response to different agonists were similar in calcium-free medium. Somatostatin (-14 or -28) also stimulated release, and this effect was inhibited by AOAA, an inhibitor of GABA degradation. In the presence of AOAA, somatostatin had little effect, except at high concentrations of somatostatin (5 microM), which increased both basal and glycine-stimulated release. In contrast to somatostatin, glycine-stimulated release was much larger in the presence of AOAA. Autoradiography was used to investigate which cell types released [3H]-GABA under our conditions. Autoradiograms showed that horizontal cells and a population of apparent "off" bipolar cells were well-labeled by [3H]-GABA high-affinity uptake. In addition, light labeling was seen over numerous amacrine cells. After application of glycine, glutamate, or potassium, there was a decrease in label density over horizontal cells.

Aminooxyacetic Acid↗
PubMed1989

Glycine high-affinity uptake labels a subpopulation of somatostatin-like immunoreactive cells in the Rana pipiens retina.

Somatostatin-like immunoreactivity (Som-LI) and glycine high-affinity uptake have been characterized in the Rana pipiens retina. These labels are found in both the outer and inner plexiform layers (OPL and IPL), suggesting that interplexiform cells (IPCs) contain both Som and glycine in this retina. In double-label experiments these labels colocalize to an abundant population of cells in the mid-inner nuclear layer (INL), in the second or third cell layer distal from the IPL. These cells have medium sized spherical or oval somas, each with a single thin descending dendrite which ramifies in the distal IPL. Processes ascending from cells at this location were not visualized by immunocytochemistry, but could be seen by autoradiography of tissue processed for glycine high-affinity uptake. In autoradiographs apparent IPCs were the most intensely labeled cell type in this retina. Som-LI is also found in two types of probable amacrine cells in the proximal INL adjacent to the IPL, neither of which is labeled by glycine high-affinity uptake. One of these is rare (about 10 cells/mm2), and has a large pyriform soma with a thick dendrite that branches in the proximal IPL. The other type is more common (324 +/- 20 cells/mm2), has medium-sized spherical or horizontally elongated elliptical somas, and has multiple thin dendrites projecting into the distal IPL. In addition to the above cell types, faint Som-LI was seen in cells of the ganglion cell layer, possibly indicating the presence of somatostatinergic ganglion cells or displaced amacrine cells.

Animals↗
PubMed1988

Somatostatin-like immunoreactivity and glycine high-affinity uptake colocalize to an interplexiform cell of the Xenopus laevis retina.

Antibodies directed against somatostatin have been used to label a population of interplexiform cells (IPCs) in the Xenopus laevis retina. These cells have spherical soma which lie in the inner nuclear layer (INL), adjacent to or one cell distal to the inner plexiform layer (IPL). Processes from these cells project throughout the IPL, with a fairly dense accumulation of labeled dendrites in the upper two-fifths of the IPL and a dense, narrow band of labeled dendrites adjacent to the ganglion cell layer. These cells also have finer processes, originating at the cell body, that traverse the INL and ramify in the outer plexiform layer (OPL). Double label experiments show that all of the cells that contain somatostatin-like immunoreactivity (SOM-LI) in the INL are also labeled by high-affinity uptake with 3H-glycine. Immunocytochemistry of retinal whole mounts shows that these cells are evenly distributed across the retina at a density of 542 +/- 65 cells/mm2. On the basis of the colocalization experiments and the morphological homogeneity of these cells, we suggest that they represent a single cell type. Interplexiform cell processes were further characterized by electron microscopy after immunocytochemistry or 3H-glycine autoradiography. In the IPL, IPC processes are seen to be postsynaptic at both ribbon and conventional synapses. This input is found almost entirely in the distal two-fifths of the IPL. Interplexiform cell processes are presynaptic to unlabeled processes in both the distal and proximal IPL. In the OPL, labeled processes are found near or contiguous with photoreceptor bases, and are often presynaptic to small-diameter processes. The postsynaptic processes have been identified as bipolar cell dendrites in six cases. Interplexiform cell processes may also contact horizontal cell processes in the OPL.

Animals↗
PubMed1988

FMRFamide-immunoreactive retinopetal fibers in the frog, Rana pipiens: demonstration by lesion and immunocytochemical techniques.

Retinopetal fibers, immunoreactive to a molluscan cardioexcitatory-like peptide (FMRFamide-ir), were examined in Rana pipiens with the use of immunocytochemical and lesion techniques. In intact frogs, FMRFamide-ir retinopetal fibers were found in the optic nerve, optic nerve head, and nerve fiber, ganglion cell and inner plexiform layers of the retina. Presumptive monostratified amacrine cells were also labeled. As observed in flat-mounted retinas, the retinopetal fibers radiated from the optic disc toward the peripheral retina, branched many times along their course and were more prevalent in the dorsal retina. Crushing the optic nerve eliminated retinopetal fibers from all regions except the cerebral stump of the optic nerve, indicating that this projection was of central origin. Bilateral prechiasmatic lesions completely eliminated retinopetal fibers from both retinas, indicating that the fibers arose from the rostral forebrain. Within the rostral brain, FMRFamide-ir perikarya were found in olfactory bulb, diagonal band, medial septum, anterior commissure area, and two regions of the posterior preoptic area. Olfactory bulbectomy and midforebrain lesions equally reduced the numbers of these fibers in the retina, implicating the nervus terminalis as a possible source for some of the retinopetal projection. These data will serve as a foundation for future studies on the function of retinopetal fibers in the frog retina.

Animals↗
PubMed1987

Monensin stimulates glycerolipid incorporation into rod outer segment membranes.

Monensin is an ionophore which disrupts the structure of the Golgi apparatus and inhibits vesicular transport in eukaryotic cells. In this study, we examined the effects of monensin on the incorporation of newly synthesized glycerolipids into retinal rod outer segment (ROS) membranes. Frog retinas were incubated in the presence or absence of monensin (50 nM) with either [1,2,3-3H]glycerol or [9,10-3H]palmitic acid as radiolabeled substrate. Total lipids were extracted from retinas and ROS membranes and resolved into individual phospholipid classes and neutral lipids by thin-layer chromatography. In the presence of monensin, the specific activity of ROS phospholipids was increased about 2-fold with [3H]glycerol and nearly 3-fold with [3H]palmitate as substrates relative to controls. In contrast, the specific activity of total retinal lipids, the relative incorporation of label into ROS and retinal phospholipids, and the total lipid phosphorous content of ROS membranes and retinas were not significantly different from control values. These data suggest that the enhanced labeling of ROS phospholipids in the presence of monensin was due to altered intracellular routing of lipids rather than increased glycerolipid synthesis. Under the same conditions, total retinal protein synthesis was about 90% of control, but light microscopic autoradiography indicated that newly synthesized proteins were not transported to the ROS for assembly into disc membranes. Thus, newly synthesized glycerolipids can be delivered to the ROS by a mechanism which is independent of protein transport to that cellular compartment.

Animals↗
PubMed1986

Localization of the lipid intermediate pathway of protein glycosylation in oviduct cell types.

Oviduct tissue slices were incubated with [3H]-leucine or [3H]-mannose in the presence and absence of tunicamycin, a specific inhibitor of lipid-mediated protein glycosylation. Conditions were established where tunicamycin had maximal effect on [3H]-mannose incorporation (greater than 90% inhibition) but a minimal effect on [3H]-leucine incorporation (less than 10% inhibition) into total TCA-insoluble products. Analysis of incubated tissues by SDS-polyacrylamide gel electrophoresis revealed that in the absence of tunicamycin, [3H]-mannose was incorporated into only a few proteins, of which ovalbumin represented the major radiolabeled component. Tunicamycin markedly reduced the incorporation of [3H]-mannose into ovalbumin and other oviduct glycoproteins. In contrast, analysis by SDS-polyacrylamide gel electrophoresis showed that [3H]-leucine was incorporated into a variety of proteins in the absence of tunicamycin. The radioactivity profile of some of these proteins was shifted toward lower Mr when oviduct slices were incubated in the presence of tunicamycin, with only a minimal decrease in protein labeling. Light microscopic autoradiograms of tissue incubated with [3H]-leucine in either the presence or absence of tunicamycin exhibited extensive labeling of tubular gland and epithelial cells. In the absence of tunicamycin, these cell types also become markedly labeled with [3H]-mannose; however, incorporation of label in both cell types was substantially reduced in the presence of tunicamycin. Qualitatively, labeling of tubular gland cells appeared greater than that of epithelial cells, largely due to the concentration of silver grains over the dense population of secretory vesicles in the tubular gland cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Tunicamycin blocks the incorporation of opsin into retinal rod outer segment membranes.

Isolated frog retinas were incubated with radiolabeled glycoprotein precursors in the presence or absence of tunicamycin (TM), a selective inhibitor of protein N-glycosylation. In dual-label incubations, TM inhibited the incorporation of [3H]mannose into total retina Cl3CCOOH-precipitable material by 85% relative to controls, whereas incorporation of [14C]leucine was not significantly affected. In a companion single-label incubation, TM blocked the incorporation of [3H]leucine into rod outer segment (ROS) membrane Cl3CCOOH-precipitable material by 95% relative to controls. When retinas were labeled with [35S]methionine, fluorograms of NaDodSO4/polyacrylamide gels from control retinas and ROS membranes exhibited a heavily labeled component (apparent Mr approximately 37,000) which had the electrophoretic and antigenic properties of opsin, the rod visual pigment apoglycoprotein. TM-treated retinas exhibited a substantially reduced labeling of the Mr 37,000 component and incorporation of label into a component (apparent Mr approximately 32,000) not found in control retinas, which exhibited the electrophoretic and antigenic behavior of nonglycosylated opsin. ROS membranes isolated from TM-treated retinas contained neither the Mr 37,000 nor the Mr 32,000 radiolabeled species. Light-microscope autoradiograms of retinas incubated with [3H]leucine in the absence of TM exhibited bands of silver grains at the base of ROS, indicative of new membrane assembly. However, no such bands were observed in autoradiograms of TM-treated retinas. These results suggest that glycosylation of opsin is required for its incorporation into ROS membranes.

Animals↗
PubMed1984

Birefringent periodicities in amphibian rod outer segments.

Birefringence variations, seen as regularly spaced altering light and dark rings (bands), have been observed along the length of unfixed, freshly isolated rod outer segments (ROS) of both Rana pipiens and Xenopus laevis. In our hands, the spatial frequency of the banding pattern is from 1.3-1.6u/band in Rana pipiens and 1.8-2.2u/band in Xenopus laevis ROS, both corresponding closely to determinations we made in the same animals of the quantity of new ROS disks added each day. To further probe this correlation, Xenopus laevis were maintained at 16 degrees C to lower the disk renewal rate. A similar correspondence was found, with the banding pattern and renewal rate both at 0.8-1.Ou/day. Further experiments involving Xenopus laevis placed on altered lighting cycles have suggested the existence of two normally superimposed periodicities. The more intense component is driven by the environmental light cycle, and thus may be regarded as diurnal. The less intense component is seen infrequently, suggesting lability, and apparently follows a 24-hour period in both constant light and darkness.

Animals↗
PubMed1984

The effects of monensin on transport of membrane components in the frog retinal photoreceptor. I. Light microscopic autoradiography and biochemical analysis.

We have explored the use of the Na+-H+ ionophore monensin as a potential tool for the investigation of membrane assembly and transport in retinal photoreceptors. Autoradiographic analysis of frog retinas incubated with [3H]leucine in the presence of monensin revealed a lack of concentrated silver grains ("bands") at the base of the rod outer segments, in contrast to controls. This is indicative of a pronounced monensin-induced decrease in disc membrane assembly. Biochemical analyses of whole retinas and isolated rod outer segment membranes showed that protein synthesis (including opsin synthesis) was not significantly inhibited under these conditions, whereas passage of membrane protein to the rod outer segment was blocked. Glycerolipid synthesis was not significantly affected by monensin. The results suggest that membrane proteins (e.g., opsin) destined for incorporation into the rod outer segment must pass through the Golgi apparatus and demonstrate the potential utility of monensin for inhibiting aspects of marcomolecule transport in photoreceptors.

Animals↗
PubMed1983

Simple sugars inhibit rod outer segment disc shedding by the frog retina.

To investigate the hypothesis that sugar molecules might act as markers for ROS disc phagocytosis, frog eyecups were incubated in a normally permissive medium for ROS disc shedding with and without added simple sugars. L-fucose, alpha-methyl-D-mannopyranoside and D-mannose all significantly reduced the numbers of packets of ROS discs found in the retinal pigment epithelium. D-fucose, L-mannose, D-fructose, D-galactose, D-glucose and sucrose were without significant effect at the same concentration. Ultrastructural examination of the retinas indicates that the sugars were effective on the disc shedding process rather than on phagocytosis of already shed disc packets.

Animals↗
PubMed1983

Frog rod outer segment shedding in vitro: histologic and electrophysiologic observations.

Rod outer segment shedding in the frog, Rana pipiens, has been studied using an in vitro eyecup method. Control experiments have shown that shedding responses in vitro are comparable to those in vivo and, like the situation in vivo, shedding in isolated eyecups requires a dark period followed by light onset. We found an initial, rapid and light-evoked component of the shedding response to be critically dependent upon bicarbonate concentration, supporting the initial discovery of a bicarbonate requirement for Xenopus rod shedding by Besharse et al. In Rana, in vitro shedding occurs in the presence of 20 mM aspartate, suggesting that functional integrity of the inner retina is not a prerequisite for rod shedding. Additionally, shedding was found to be suppressed completely in the presence of the local anesthetic MS-222 and the phosphodiesterase inhibitor IBMX. In the case of IBMX, electrophysiologic recording indicated changes in photoreceptor sensitivity in the presence of the drug. Such changes may play a role in the observed inhibition of shedding.

Animals↗
PubMed1982

The effects of local anaesthetics on retinal function.

Isolated frog eyecups were incubated in Ringer containing local anaesthetics to study the effects of these drugs on dark-adaptation of the ERG. Relative to controls, dark-adaptation in eyecups treated with millimolar concentrations of MS-222, benzocaine, and procaine HCl was significantly inhibited during 10 to 120 min following the cessation of the adapting light. These drugs also prevented the recovery of the c-wave during dark-adaptation, resulting in ERG waveforms resembling those found in light-adapted eyecups. Measurements of rhodopsin in the retina were consistent with previous findings showing that rhodopsin regeneration in situ is inhibited by local anaesthetics. In vitro regeneration experiments in which bleached rod outer segment fragments were added to 11-cis retinal showed that preincubation of retinal with MS-222 in ethanol prevents rhodopsin regeneration. Evidence was obtained spectrophotometrically for the formation of a complex between MS-222 and 11-cis retinal with a gamma max of 512 nm. We propose that the formation of a Schiff's base between these two compounds blocks the recombination of rhodopsin, and in situ, leads to the inhibition of dark-adaptation.

Aminobenzoates↗
PubMed1982

Local stimulation induces shedding throughout the frog retina.

Our previous work has demonstrated that rod shedding in the frog retina can be driven by environmental cues such as light onset. Although shedding normally occurs binocularly, we found that shedding could be initiated independently in either eye of the frog by monocular stimulation. Further, rod shedding occurs in vitro in the isolated eyecup under appropriate incubation conditions when provided with a light stimulus following a dark incubation period. Thus, the control mechanism for light induced rod shedding in the frog seems to be located within the eye, and does not seem to be systemically or centrally located. However, the exact link between light onset and shedding of the distal rod tips remains unknown. To elucidate further the control site for initiation of rod shedding, we used a variety of stimulus conditions, including front and rear screens as well as spots and slits projected directly on the retina, to stimulate a small portion of the frog retina with a range of light intensities and stimulus paradigms. In all cases where shedding occurred, it was uniform throughout the retina. Thus, it appears that the light-cued message received by a small population of photoreceptors is sufficient to initiate shedding throughout the retina. These results differ significantly from those found by Easter and Macy for light-induced photomechanical movements, which were found to be locally controlled.

Animals↗
PubMed1980

Metabolism of phosphatidylcholine in the frog retina.

The biosynthesis and the turnover of phosphatidylcholine were studied in the frog retina following either (a) injection into the animal of 32PO4, 33PO4, [1,3-3H]glycerol, [2-3H]glycerol, or [methyl-3H]choline, or (b) incubation of isolated retinas in solutions containing [methyl-3H]choline. 1. Examination of the pools of lipid precursors in the retina demonstrated that the choline and phosphate pools are long-lived compared to the glycerol pool, which is metabolically very active and turns over rapidly. 2. The peak in specific activity of phosphatidylcholine synthesized from labeled glycerol occurred earlier, and was higher in the microsomal fraction than in the rod outer segments, which is consistent with synthesis of phosphatidylcholine on the microsomes of the inner segment and subsequent incorporation into the rod outer segments. 3. Autoradiography of retinas incubated in vitro with tritiated choline revealed a diffuse labeling pattern in the rod outer segments. Biochemical studies following injection of labeled glycerol showed an exponential decline in specific radioactivity of phosphatidylcholine in the rod outer segments, which is consistent with a diffuse labeling of these membranes. 4. The half-life of phosphatidylcholine in the rod outer segments synthesized from labeled glycerol was found to be 18-19 days. Based on these values, calculations were made which indicated that phosphatidylcholine in the outer segments is turning over faster than integral disc membrane proteins.

Animals↗
PubMed1980

Myeloid body associations in the frog pigment epithelium.

Myeloid bodies are found in the retinal pigment epithelium of certain vertebrate species. They are organized structural forms of the smooth endoplasmic reticulum which are usually seen as stacks of flattened, smooth saccules having a circular or lens-shaped configuration. Our findings in the frog Rana pipiens suggest that changes occur in the structure of the myeloid bodies which are related to the phase of the diurnal lighting cycle. At certain times, the myeloid bodies are found closely associated with other cytoplasmic organelles, notably the nucleus and oil droplet. In addition these associations can be induced by incubation of the isolated eyecup in the presence of guanosine 3',5'-monophosphate.

Animals↗