SEARCH · Search PubMed

Results for “Photoreceptor”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed1999

A diffusible factor from normal retinal cells promotes rod photoreceptor survival in an in vitro model of retinitis pigmentosa.

Transgenic mice expressing a dominant mutation in the gene for the phototransduction molecule rhodopsin undergo retinal degeneration similar to that experienced by patients with the retinal degenerative disease, retinitis pigmentosa (RP). Although the mutation is thought to cause photoreceptor degeneration in a cell-autonomous manner, the fact that rod photoreceptor degeneration is slowed in chimeric wild-type/mutant mice suggests that cellular interactions are also important for maintaining photoreceptor survival. To more fully characterize the nature of the cellular interactions important for rod degeneration in the RP mutant mice, we have used an in vitro approach. We found that when the retinas of the transgenic mice were isolated from the pigmented epithelium and cultured as explants, the rod photoreceptors underwent selective degeneration with a similar time course to that observed in vivo. This selective rod degeneration also occurred when the cells were dissociated and cultured as monolayers. These data indicate that the mutant rod photoreceptors degenerate when removed from their normal cellular relationships and without contact with the pigmented epithelium, thus confirming the relative cell autonomy of the mutant phenotype. We next tested whether normal retinal cells could rescue the mutant photoreceptors in a coculture paradigm. Coculture of transgenic mouse with wild-type mouse or rat retinal cells significantly enhanced transgenic rod photoreceptor survival; this survival-promoting activity was diffusible through a filter, was heat labile, and not present in transgenic retinal cells. Several peptide growth factors known to be present in the retina were tested as the potential survival-promoting molecule responsible for the effects of the conditioned medium; however, none of them promoted survival of the photoreceptors expressing the Pro23His mutant rhodopsin. Nevertheless, we were able to demonstrate that the mutant photoreceptors could be rescued by an antagonist to a retinoic acid receptor, suggesting that the endogeneous survival-promoting activity may function through this pathway. These data thus confirm and extend the findings of previous work that local trophic interactions are important in regulating rod photoreceptor degeneration in retinitis pigmentosa. A diffusible factor found in normal but not transgenic retinal cells has a protective effect on the survival of rod photoreceptors from Pro23His mutant rhodopsin mice.

Animals↗

PubMed1996

Overexpression of Bcl-2 or Bcl-XL transgenes and photoreceptor degeneration.

PURPOSE: To test the hypothesis that overexpression of genes coding for the anti-apoptotic proteins Bcl-2 or Bcl-XL in photoreceptor cells may prevent or delay photoreceptor degenerations. METHODS: Transgenic mice were generated in which the bcl-2 or bcl-XL transgenes were expressed in photoreceptor cells under the transcriptional control of a rhodopsin gene promoter. Bcl-2 or bcl-XL transgenic mice were crossed separately to a mouse strain carrying the rd/rd mutation and to another mouse line carrying a dominant rhodopsin gene mutation; both genetic defects result in photoreceptor degeneration. Photoreceptor cell death in mice expressing one of the bcl transgenes and carrying either the rd mutation homozygously or the rhodopsin mutation heterozygously was examined by histologic and electroretinographic measurements. Bcl-2 and bcl-XL transgenic mice also were tested for possible resistance to light-induced photoreceptor damage under two different experimental conditions. RESULTS: Bcl-2 or bcl-XL transgenes were expressed in photoreceptor cells of all lines of transgenic mice. In both the rd and the rhodopsin mutant mice, expression of either bcl-2 or bcl-XL transgenes did not prevent or measurably delay photoreceptor degeneration. Apoptosis-related nuclear DNA fragmentation, as assessed by in situ labeling with terminal deoxynucleotidyl transferase, was present in 13-day-old rd/rd mouse retinas with or without transgene expression. Twelve days after exposure to 2 hours of high-intensity light, bcl-2 transgenic mice retained approximately four rows of photoreceptor cells in the central retina as compared to none in littermate controls, whereas bcl-XL transgenic mice showed no increased resistance to light damage. Expression of the bcl-2 but not the bcl-XL transgene also was associated with a reduction in rhodopsin content. CONCLUSIONS: Overexpression of bcl-2 or bcl-XL transgenes does not rescue photoreceptor cells from apoptosis caused by the two genetic mutations tested. Resistance to light damage seen in the bcl-2 transgenic mice is likely from a reduction in rhodopsin content rather than an anti-cell death activity of Bcl-2. Cell death pathways not regulated by Bcl-2 may be operative in photoreceptor degeneration.

Animals↗

PubMed1997

Tissue oxygen during a critical developmental period controls the death and survival of photoreceptors.

PURPOSE: To study the death of photoreceptors in normally developing and dystrophic retina and to test the role of hypoxia in causing that death. METHODS: Death of photoreceptors was detected in the albino, hooded, and Royal College of Surgeons (RCS) strains of rat, and in the rabbit and cat, using the TUNEL technique. Retinas of selected ages from animals raised normally and those from rat pups raised for periods in hyperoxia (75% oxygen) or hypoxia (10% oxygen) were studied. RESULTS: In all species and strains examined, a naturally occurring wave of photoreceptor death was detected during the last stages of retinal development. In the albino rat, this wave, which began approximately at postnatal day 15 (P15) and peaked at P22, was reduced by hyperoxia and was intensified by hypoxia, producing a "hypoxic dystrophy" of photoreceptors. In the RCS rat, photoreceptor death also commenced at approximately P15 and then proceeded to exhaustion. This degeneration was greatly reduced by hyperoxia. In the RCS rat, hyperoxia was effective in photoreceptor rescue only during a discrete period, from P16 to P22. In the albino rat, the effectiveness of hypoxia in inducing photoreceptor death was much greater between P15 and P21 than at earlier ages, or in the adult. CONCLUSIONS: During a critical period extending approximately from P15 to P22, tissue oxygen levels strongly influence photoreceptor death and survival in dystrophic and normally developing strains of rat. This period is evident in normal development as a period of naturally occurring photoreceptor death and is evident experimentally as a period during which hyperoxia is effective in rescuing dying photoreceptors and during which hypoxia is effective in inducing death of otherwise viable photoreceptors.

Animals↗

PubMed1998

Photoreceptor morphogenesis in the human retina: a scanning electron microscopic study.

There are a number of scanning electron microscopic (SEM) studies on retinal photoreceptors of vertebrates. However, most of these are concerned with the adult retina, and only a very few deal with developing photoreceptors. In man, SEM studies have not been carried out on photoreceptor morphogenesis during fetal or postnatal stages. Hence, the present study was undertaken to examine the sequential morphological changes in developing photoreceptors during different gestational ages in the human retina. Retinas of human fetuses of gestational ages of 10-25 weeks and from autopsy of a 5-month-old infant were processed for SEM. The observations show some new information on the morphogenesis of photoreceptors. At 10-11 weeks, the outer and inner neuroblastic zones are well developed and separated from each other by the layer of Chievitz. By 15-16 weeks, the photoreceptor precursors appear as spherical inner segments on the scleral surface of the outer neuroblastic zone. Cilia develop as small protrusions from the apical ends of the inner segments. Photoreceptor inner segments become arranged in mosaic pattern by 18-19 weeks. In the mosaic, large cone inner segments (putative blue cones) stand out prominently from the remaining small cone inner segments (prospective red/green cones). The rod inner segments are identifiable and show cilia. Between 19-20 and 24-25 weeks, the cone inner segments elongate and change in shape from spherical to oval. At 24-25 weeks, the outer segments develop from the distal ends of rod cilia. At this period, the inner segments of rods and cones are interconnected by protoplasmic projections. Although the precursors of both rods and cones appear to be in a similar state of development at 14-15 weeks gestation, the rods undergo morphological maturation earlier than do the cones. Photoreceptor development in the anterior retina lags behind that of the posterior retina by about 10 weeks. At 5 months after birth, the posterior retina possesses fully developed photoreceptors that are comparable to those of the adult. However, the photoreceptors in the ora serrata resemble those in the posterior retina of 24-25 weeks gestation.

Fetus↗

PubMed2005

IGF-1 produced by cone photoreceptors regulates rod progenitor proliferation in the teleost retina.

Teleost eyes grow throughout life by adding neurons and stretching extant tissue. New retinal neurons of all types are added at the ciliary margin and new rod photoreceptors are inserted throughout retina in the outer nuclear layer (ONL). New rod photoreceptors result from the division of progenitor cells located in the ONL amidst functioning rod photoreceptor cell nuclei, but it is not known how new rod addition is regulated. Previous experiments using an organotypic retinal slice preparation revealed that insulin-like growth factor 1 (IGF-1) up-regulates the division of the rod progenitor cells [Dev. Brain Res. 76 (1993) 183], but the site of IGF-1 action was unknown. Here, we show where in the retina IGF-1 is made, where IGF receptors are located, and we identify the role of IGF-1 in adult retinal rod neurogenesis with both gain-and loss-of-function experiments. We found that IGF-1 is expressed by cone photoreceptor cells and its abundance varies with a daily rhythm, being significantly higher at night. In vivo application of exogenous IGF-1 increases rod progenitor cell division, an effect that is greater at night than during the day. We also show that inhibiting the function of IGF receptors decreases proliferation of rod progenitor cells. Finally, we show that IGF receptors are located on rod progenitor cells as well as on cone and rod photoreceptors. Taken together, these data suggest that the rhythmic production and release of IGF-1 plays a role in regulating the insertion of new rod photoreceptors into the retina. The diurnal change in IGF-1 abundance and effects of exogenous IGF-1 are consistent with the previous demonstration that rod progenitor cell division is threefold greater at night than in the day [Brain Res. 673 (1995) 119; Brain Res. 712 (1996) 40]. We also show that the insertion of new rod photoreceptors at the central edge of the ciliary neurogenic zone very likely also depends on IGF-1 production by cone photoreceptors. We propose that addition of new rod photoreceptors into the functioning retina is regulated through a feedback mechanism mediated at least in part via the IGF-1 produced in the cone photoreceptors.

Animals↗

PubMed2005

Structure of ocellus photoreceptors in the ascidian Ciona intestinalis larva as revealed by an anti-arrestin antibody.

Although there have been several studies on the structure of the ocellus photoreceptors in ascidian tadpole larvae using electron microscopy, the overall structure of these photoreceptor cells, especially the projection sites of the axons, has not been revealed completely. The number of photoreceptor cells is also controversial. Here, the whole structure of the ocellus photoreceptors in the larvae of the ascidian Ciona intestinalis was revealed by using an anti-arrestin (anti-Ci-Arr) antibody. The cell bodies of 30 photoreceptor cells covered the right side of the ocellus pigment cell and their outer segments extended through the pigment cell into the pigment cup. The axons of the photoreceptor cells were bundled together ventro-posteriorly in a single tract extending towards the midline. The nerve terminals diverged antero-posteriorly at the midline of the posterior sensory vesicle (SV). The Ci-arr gene was expressed throughout the SV at the embryonic mid-tailbud stage and it became restricted to the neighborhood of the ocellus pigment when ocellus pigmentation occurred. At the same time, the Ci-Arr protein was first detected, suggesting that the photoreceptor cells began to differentiate. The development of photoreceptor cells after hatching was also investigated using the anti-Ci-Arr antibody. Three hours after hatching, the photoreceptor terminals began to ramify and then expanded. Previous behavioral analysis showed that the larvae did not respond to the step-down of light until 2 h after hatching and then the photoresponse became robust. Accordingly, our results suggest that growth of the photoreceptor terminal is critical for the larvae to become photoresponsive.

Animals↗

PubMed2005

Roles of cell-intrinsic and microenvironmental factors in photoreceptor cell differentiation.

Photoreceptor differentiation requires the coordinated expression of numerous genes. It is unknown whether those genes share common regulatory mechanisms or are independently regulated by distinct mechanisms. To distinguish between these scenarios, we have used in situ hybridization, RT-PCR, and real-time PCR to analyze the expression of visual pigments and other photoreceptor-specific genes during chick embryo retinal development in ovo, as well as in retinal cell cultures treated with molecules that regulate the expression of particular visual pigments. In ovo, onset of gene expression was asynchronous, becoming detectable at the time of photoreceptor generation (ED 5-8) for some photoreceptor genes, but only around the time of outer segment formation (ED 14-16) for others. Treatment of retinal cell cultures with activin, staurosporine, or CNTF selectively induced or down-regulated specific visual pigment genes, but many cognate rod- or cone-specific genes were not affected by the treatments. These results indicate that many photoreceptor genes are independently regulated during development, are consistent with the existence of at least two distinct stages of gene expression during photoreceptor differentiation, suggest that intrinsic, coordinated regulation of a cascade of gene expression triggered by a commitment to the photoreceptor fate is not a general mechanism of photoreceptor differentiation, and imply that using a single photoreceptor-specific "marker" as a proxy to identify photoreceptor cell fate is problematic.

Activins↗

PubMed1992

Retinal pigment epithelial cell transplantation in RCS rats: normal metabolism in rescued photoreceptors.

Photoreceptor cells in Royal College of Surgeons (RCS) rats with inherited retinal dystrophy can be rescued by the transplantation of normal, wild-type retinal pigment epithelial (RPE) cells, if done before photoreceptor cell death. In the present study, we have examined several metabolic features of rescued photoreceptors and transplanted RPE cells at 2.3-3.3 months after transplantation. Rescued photoreceptors with a structurally normal RPE interface showed a rod outer segment renewal rate similar to that of normal control rats of 2.2 microns day-1, as measured in autoradiograms. Rod outer segment disc shedding had values indistinguishable from those in normal controls, as measured by the number of phagosomes in the transplanted RPE cells both during the burst of disc shedding soon after the onset of light in the morning and during the middle of the light cycle when disc shedding is low. The interphotoreceptor matrix, which is synthesized by both photoreceptors and the RPE, was distributed normally in the regions where normal-appearing photoreceptors were present underlying normal, transplanted RPE cells. Thus, the rescued photoreceptors show normal metabolic rates and normal interactions with the RPE in each of the parameters examined. These findings, combined with the previous demonstration of opsin and Na+,K(+)-ATPase expression by the rescued photoreceptors, support our interpretation that the surviving, normal-appearing photoreceptors may function normally. Moreover, transplantation of normal RPE cells reversed pathological changes in the photoreceptors that had already occurred by the time of transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Increased retinal synthesis of heparan sulfate proteoglycan and HNK-1 glycoproteins following photoreceptor degeneration.

In an earlier analysis of the retinal biosynthesis of proteoglycan, we noted that, following photoreceptor degeneration in the rd (retinal degeneration) mouse, the remaining inner retina exhibited a marked elevation in synthesis of heparan sulfate proteoglycan (HSPG), well above the level observed in the normal (nondegenerate) retina, as well as a pronounced increase in sulfation of protein substrates. Biochemical and autoradiographic results of 35S-amino acid utilization reported here confirm that the 35SO4(2-) differences seen previously are accompanied by increased protein synthesis in the rd retina. An intact photoreceptor cell layer is neither a barrier to nor a sink for the amino acid precursor. Further, we have examined sulfate utilization in four other rodent strains with photoreceptor degenerations. In each of the models examined, an increase in retinal synthesis of 35SO4(2-)-labeled HSPG and glycoproteins occurs following photoreceptor degeneration. We have metabolically labeled with Na2(35)SO4 isolated retinal cultures from the following: (a) mice with light-induced photoreceptor degeneration; (b) rd mice; (c) transgenic mice with photoreceptor degeneration; (d) RCS rats; and (e) rats with light-induced photoreceptor degeneration. Comparisons were made with concurrent cultures of control nondegenerate retinal tissues. Protein and proteoglycan-enriched fractions were prepared from the incubation media and guanidine HCl/detergent extracts of the retinas by ion-exchange chromatography. The 35SO4(2-)-proteoglycans were identified by chondroitinase ABC and nitrous acid treatments. Retinas lacking photoreceptors produced at least five times the amount of 35SO4(2-)-HSPG found in control incubations. The RCS and light-damaged rats also showed increased synthesis of 35SO4(2-)-chondroitin sulfate proteoglycan relative to the control, through the increase was of lesser magnitude than the HSPG effect. 35SO4(2-)-protein in degenerate and light-damaged retinas always contained at least twice the radioactivity found in comparable control preparations. The bulk of the increased radiolabeling was found in N-linked oligosaccharides, including several recognized by the HNK-1 antibody. These data suggest that a sustained increase in HSPG and HNK-1 glycoprotein synthesis is a consistent response of inner retinal cells following loss of photoreceptors and is independent of the cause of photoreceptor degeneration.

Animals↗

PubMed2002

The chicken RaxL gene plays a role in the initiation of photoreceptor differentiation.

The paired type homeodomain gene, Rax, was previously identified as a key molecule in early eye formation in mice and humans. We report the expression patterns of two Rax family members from chicken, Rax and RaxL, and on the function of RaxL in photoreceptor development. Both Rax and RaxL are expressed in early retinal progenitor cells, with Rax being expressed at a significantly higher level than RaxL. At the time that photoreceptors begin to form, RaxL appears at a relatively high level in a subset of cells within the zone of proliferating progenitor cells. Subsequently, it is expressed in cells migrating to the photoreceptor layer, where it is highly expressed during the initial, but not late, stages of photoreceptor differentiation. To test the function of RaxL, a putative dominant-negative allele of RaxL comprising a fusion of the engrailed repressor domain and a region of RaxL (EnRaxLDeltaC) was introduced in vivo into the early chick eye using a retroviral vector. EnRaxLDeltaC, but not the dominant negative Rax (EnRaxDeltaC), caused a significant reduction in expression of early markers of photoreceptor cells. Examination of the transactivation activity of RaxL on a reporter construct bearing a canonical photoreceptor-specific enhancer element showed that RaxL exhibited significant activation activity, and that this activity was severely diminished in the presence of EnRaxLDeltaC. The effect on photoreceptor gene expression in vivo was specific in that other cell types were unaffected, as was general proliferation in the retina. The reduction in numbers of cells expressing photoreceptor markers was probably due to decreased survival of developing photoreceptor cells, as there was increased apoptosis among cells of the retina expressing dominant-negative RaxL. We propose that RaxL plays a role in the initiation of differentiation, and also possibly commitment, of photoreceptor cells in the chicken retina.

Amino Acid Sequence↗

PubMed2004

A role of ath5 in inducing neuroD and the photoreceptor pathway.

Photoreceptors in the vertebrate retina are light-sensitive neurons, and their degeneration results in irreversible visual loss. Understanding how photoreceptor fate is determined is a prerequisite for developing photoreceptor replacement therapies. Previous studies identified two basic helix-loop-helix genes, neurogenin2 (ngn2) and neuroD, participating in a genetic pathway leading to photoreceptor genesis. Here we present experimental data suggesting that ath5, which is known for its critical role in retinal ganglion cell development, may also lead to photoreceptor production. In the developing retina, ath5 expression was detected in two zones of cells, and coexpression with neuroD was observed in the zone adjacent to young photoreceptor cells accumulating on the retinal pigment epithelial side. Retroviral-driven misexpression of ath5 in retinal cells increased the population of photoreceptor cells, as well as ganglion cells, in a developmental stage-dependent manner that is consistent with ath5 being involved in the development of multiple types of retinal neurons. Ectopic ath5 expression in cultures of non-neural retinal pigment epithelial cells elicited transdifferentiation into cells that expressed photoreceptor-specific genes and displayed photoreceptor-like morphologies. Gene expression analysis showed that ngn2 did not induce ath5, and ath5 did not induce ngn2, but both induced neuroD and RaxL. These data suggest a pathway of "ath5 --> neuroD --> photoreceptor genes" separate from yet convergent with the ngn2 pathway.

Animals↗

PubMed2006

Large functional variability in cockroach photoreceptors: optimization to low light levels.

The compound eyes of insects contain photoreceptors in small eyelets, ommatidia. The photoreceptors generally vary very little from ommatidium to ommatidium. However, in the large compound eyes of the cockroach (Periplaneta americana), previous studies have shown large differences in the optical structure between the ommatidia. The anatomy suggests pooling of 6-20 photoreceptor signals into one second-order cell in the first synapse. Here, we show and characterize an unexpectedly large and seemingly random functional variability in the cockroach photoreceptors in terms of sensitivity, adaptation speed, angular sensitivity, and signal-to-noise ratio. We also investigate the implications of action potentials, triggered by the light-induced membrane depolarization in the photoreceptor axons. The combination of the functional features reported here is unique among the compound eyes. Recordings from the proximal parts of the thin and long photoreceptor axons or small and distant second-order neurons are not practical with the present methods. To alleviate this lack of data, we used computer simulations mimicking the functional variability, spike coding, and pooling of 12 photoreceptor signals, on the basis of our recordings from the photoreceptor somata and distal axons. The predicted responses of a simulated second-order cell follow surprisingly reliably the simulated light stimuli when compared with a simulation of functionally identical photoreceptors. We hypothesize that cockroach photoreceptors use action potential coding and a kind of population coding scheme for making sense of the inherently unreliable light signals at low luminance and for optimization of vision in its mainly dim living conditions.

Action Potentials↗

PubMed1995

Lactate released by Müller glial cells is metabolized by photoreceptors from mammalian retina.

The nature of fuel molecules trafficking between mammalian glial cells and neurons was explored using acute retinal cell preparations of solitary Müller glial cells, Müller cells still attached to photoreceptors (the "cell complex"), and solitary photoreceptors. 14C-Molecules in the cell complex, Müller cells, and respective baths were quantitated following 30 min incubation in bicarbonate-buffered Ringer's solution carrying 5 mM 14C(U)-glucose, and substrate preference by solitary photoreceptors was assessed by measuring 14CO2 production. Müller cells alone metabolized 14C-glucose predominantly to carbohydrate intermediates, while the presence of photoreceptors raised proportionately the amount of radiolabeling in amino acids. 14C-Lactate was the major carbohydrate found in the bath. However, in the presence of photoreceptors, its amount was 70% less than that for Müller cells alone. This decrease matched the expected production of 14CO2 by photoreceptor oxidative metabolism and was antagonized by the addition of unlabeled lactate. Moreover, while solitary photoreceptors consumed both exogenous 14C-lactate and 14C-glucose, lactate was a better substrate for their oxidative metabolism. In the cell complex, the metabolism of amino acids increased and illumination affected primarily glutamate and glutamine production: the specific activity of glutamate changed in parallel with that of lactate, and that of glutamine increased by eightfold in darkness. These results demonstrate transfer of lactate from Müller cells to photoreceptors and underscore a photoreceptor-dependent modulation of lactate and amino acid metabolism. We propose that net production and release of lactate by Müller cells serves to maintain their glycolysis elevated and to fuel mitochondrial oxidative metabolism and glutamate resynthesis in photoreceptors.

Amino Acids↗

PubMed1998

Photoreceptor dystrophy in the RCS rat: roles of oxygen, debris, and bFGF.

PURPOSE: To examine the roles of oxygen, basic fibroblast growth factor (bFGF), and photoreceptor debris in the photoreceptor dystrophy of the Royal College of Surgeons (RCS) rat. METHODS: Pups were exposed during the critical period of their development (postnatal day [P] 16-24) and for some days thereafter to hypoxia and hyperoxia. The effects of these exposures on photoreceptor death, debris accumulation in the subretinal space, and the expression of bFGF protein and mRNA by surviving cells were studied. RESULTS: During the critical period hyperoxia slowed photoreceptor death in a dose-related fashion and decreased bFGF protein levels, whereas hypoxia accelerated death and increased bFGF levels. At the edges of the retina, where photoreceptors survive longest in normoxia, hypoxia had little effect on either photoreceptor death or bFGF protein levels. Oxygen-induced modulation of rates of death could not be related to the accumulation of debris in the subretinal space. After P27, the relationship between oxygen and photoreceptor death changed markedly, hyperoxia no longer delaying and hypoxia no longer accelerating death. CONCLUSIONS: The death of RCS rat photoreceptors in the period P16 to P27 is precipitated by hypoxia that may result from the accumulation of photoreceptor debris in the subretinal space. This debris, the result of the phagocytotic failure of the retinal pigment epithelium in this strain, lies in the normal pathway of oxygen diffusing to the photoreceptors from the choriocapillaris. During this period the retina responds to hypoxia by increasing expression of a potentially protective protein (bFGF), but hypoxia-induced damage overwhelms any protection provided by this or other mechanisms. Later stages of the dystrophy may not be hypoxia-induced.

Animals↗

PubMed1999

Uptake of precursor and synthesis of transmitter in a histaminergic photoreceptor.

As a first step in understanding how the supply of the neurotransmitter histamine is maintained in a photoreceptor, we followed the uptake and metabolism of the immediate precursor of histamine, histidine. [3H]Histidine taken up into photoreceptors and glia was detected using autoradiography, and synthesis of [3H]histamine from [3H]histidine was assayed with thin-layer chromatography. Photoreceptors from barnacles were pulsed (15 min) with [3H]histidine (0.2-200 microM), then maintained in normal saline for up to 24 hr. Autoradiography showed that photoreceptor somata, axons, and presynaptic arbors were labeled, but only weakly, like (nonhistaminergic) ganglion cells. Label instead was concentrated over surrounding glia. Stimulating preparations with light did not increase photoreceptor labeling. Grain counts from photoreceptor axons showed uptake of [3H]histidine into these neurons by a Na+-dependent mechanism with a Km of approximately 50 microM. Over 24 hr only 1% of the [3H]histidine taken up by preparations was converted to [3H]histamine either in the dark or in the light. Injections of [3H]histidine directly into photoreceptors established that synthesis takes place within the photoreceptors and confirmed that stimulation with light did not measurably affect the rate of conversion of [3H]histidine to [3H]histamine. These results suggest that de novo synthesis of transmitter is unlikely to be as important as its reuptake in maintaining neurotransmitter supply in these photoreceptor terminals. In support of this conclusion, photoreceptors accumulated more label when transmitter release was stimulated with high K+ and histamine uptake was antagonized with chlorpromazine.

Animals↗

PubMed2006

Morphogenesis of the different types of photoreceptors of the chicken (Gallus domesticus) retina and the effect of amblyopia in neonatal chicken.

Despite the great variety in chicken photoreceptors, existing morphogenetic studies only deal with two types: rods and cones. We have therefore examined by scanning electron microscopy the first appearance and maturation of different retinal photoreceptors in 36 chicken embryos (Gallus domesticus), aged 5-19 days prehatching. On day 5 of incubation, chicken retinae were only composed of proliferating ventricular cells devoid of photoreceptors. On day 8, outer mitotic cells were separated from inner differentiating photoreceptors, by the transient layer of Chievitz. Ball-like protrusions appeared at the ventricular surface, representing the first signs of photoreceptor inner segment formation. From day 10 onward, double cones, single cones, and rods could be clearly distinguished, and occasional cilia were detected at their tip. On day 12, inner segments had increased in length and diameter, and frequently carried a cilium representing the beginning of outer segment formation. On day 14, most photoreceptors displayed a distinct outer segment. On day 19, photoreceptors had essentially assumed adult morphology. Based on the shape of their outer segments, two subtypes of cones and three subtypes of double cones could be distinguished. Throughout development, we observed microvilli close to maturing photoreceptors, either originating from their lateral sides, from their tip, or from Müller cells. Microvillus density peaked between day 12 and 14, indicating an important role in photoreceptor morphogenesis. Unilateral occlusion of the eyes of posthatching chicken reduced the proportion of double cones to single cones in the retina, indicating dependence of retinal morphogenesis upon functional activity of visual cells.

Amblyopia↗

PubMedDate not supplied

Morphology and spectral absorption characteristics of retinal photoreceptors in the southern hemisphere lamprey (Geotria australis).

The morphology and spectral absorption characteristics of the retinal photoreceptors in the southern hemisphere lamprey Geotria australis (Agnatha) were studied using light and electron microscopy and microspectrophotometry. The retinae of both downstream and upstream migrants of Geotria contained two types of cone photoreceptor and one type of rod photoreceptor. Visual pigments contained in the outer segments of these three photoreceptor types had absorbance spectra typical of porphyropsins and with wavelengths of maximum absorbance (downstream/upstream) at 610/616 nm (long-wavelength-sensitive cone, LWS), 515/515 nm (medium-wavelength-sensitive cone, MWS), and 506/500 nm (medium-wavelength-sensitive rod). A "yellow" photostable pigment was present in the myoid region of all three types of photoreceptor in the downstream migrant. The same short-wavelength-absorbing pigment, which prevents photostimulation of the beta band of the visual pigment in the outer segment, was present in the rods and LWS cones of the upstream migrant, but was replaced by a large transparent ellipsosome in the MWS cones. Using microspectrophotometric and anatomical data, the quantal spectral sensitivity of each photoreceptor type was calculated. Our results provide the first evidence of a jawless vertebrate, represented today solely by the lampreys and hagfishes, with two morphologically and physiologically distinct types of cone photoreceptors, in addition to a rod-like photoreceptor containing a colored filter (a cone-like characteristic). In contrast, all other lampreys studied thus far have either (1) one type of cone and one type of rod, or (2) a single type of rod-like photoreceptor. The evolution or retention of a second type of cone in adult Geotria is presumably an adaptation to life in the brightly lit surface waters of the Southern Ocean, where this species lives during the marine phase of its life cycle. The functional significance of the unique visual system of Geotria is discussed in relation to its life cycle and the potential for color vision.

Absorption↗

PubMed2005

Sexual dimorphism of short-wavelength photoreceptors in the small white butterfly, Pieris rapae crucivora.

The eyes of the female small white butterfly, Pieris rapae crucivora, are furnished with three classes of short-wavelength photoreceptors, with sensitivity peaks in the ultraviolet (UV) (lambda(max) = 360 nm), violet (V) (lambda(max) = 425 nm), and blue (B) (lambda(max) = 453 nm) wavelength range. Analyzing the spectral origin of the photoreceptors, we isolated three novel mRNAs encoding opsins corresponding to short-wavelength-absorbing visual pigments. We localized the opsin mRNAs in the retinal tissue and found that each of the short-wavelength-sensitive photoreceptor classes exclusively expresses one of the opsin mRNAs. We, accordingly, termed the visual pigments PrUV, PrV, and PrB, respectively. The eyes of the male small white butterfly also use three classes of short-wavelength photoreceptors that equally uniquely express PrUV, PrV, and PrB. However, whereas the spectral sensitivities of the male photoreceptors with PrUV and PrB closely correspond to those of the female, the male photoreceptor expressing PrV has a double-peaked blue (dB) spectral sensitivity, strongly deviating from the spectral sensitivity of the female V photoreceptor. The male eyes contain a pigment that distinctly fluoresces under blue-violet as well as UV excitation light. It coexists with the dB photoreceptors and presumably acts as a spectral filter with an absorbance spectrum peaking at 416 nm. The narrow-band spectral sensitivity of the male dB photoreceptors probably evolved to improve the discrimination of the different wing colors of male and female P. rapae crucivora in the short-wavelength region of the spectrum.

Animals↗