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PubMed1985

Glucagon and VIP in the retina.

Immunoreactive glucagon and immunoreactive vasoactive intestinal polypeptide (VIP) have been demonstrated in neuronal elements in the retina of a number of species by immunohistochemistry. In the present study, the concentrations of glucagon-like and VIP-like material in retinae from different species were determined by radioimmunoassay. The retinal concentration of glucagon-like immunoreactivity was 10-35 pg/mg in goldfish, chicken, pigeon, and frog, whereas retinae from cow, pig, rabbit, and rat contained very little. Retinae from the latter four species were on the other hand rich in VIP-like material whereas retinae from cat, guinea pig, and goldfish contained very little. The glucagon-like immunoreactive material in chicken and frog retina was subjected to gel chromatography and high performance liquid chromatography (HPLC). The results indicate that the extracted protein is of similar molecular size as porcine pancreatic glucagon, distinct from porcine glicentin. VIP immunoreactive material extracted from bovine retina was similar in molecular size as authentic porcine VIP by gel chromatography.

Animals↗
PubMed1984

Alpha-2 adrenoceptors modulate [3H]dopamine release from rabbit retina.

In the rabbit retina, preloaded in vitro with [3H]dopamine, calcium-dependent release of radioactivity was elicited by a 1-min period of field stimulation at 3 Hz (20 mA, 2 msec). In the presence of the catecholamine uptake inhibitor nomifensine (30 microM), unlabeled catecholamines (0.01-3 microM), namely, dopamine, norepinephrine and epinephrine, inhibited in a concentration-dependent manner the field stimulation-evoked release of [3H]dopamine from the retina. The concentrations of dopamine, norepinephrine or epinephrine which inhibited by 50% the release of [3H]dopamine (IC50) were 0.30, 0.25 and 0.25 microM, respectively. In the presence of 30 microM nomifensine, S-sulpiride (1 microM) significantly increased the calcium-dependent release of [3H]dopamine, suggesting that this dopamine antagonist blocks a receptor tonically activated by endogenous dopamine in the rabbit retina. In contrast, the alpha receptor antagonist phentolamine (1 microM) alone did not affect the release of [3H]dopamine from the retina. The inhibitory effect of norepinephrine and epinephrine on [3H]dopamine overflow was not modified by S-sulpiride which, on the contrary, selectively antagonized the effect of exogenous dopamine. Phentolamine (1 microM) competitively antagonized the inhibitory effect of norepinephrine and epinephrine on [3H]dopamine release, suggesting that these catecholamines activate alpha adrenoceptors in retina. In the absence of nomifensine, the selective alpha-2 agonist clonidine (IC50 = 0.056 microM) inhibited the stimulation-evoked release of [3H]dopamine from retina, whereas the alpha agonist methoxamine was without effect. The inhibitory effect of clonidine was antagonized by yohimbine (1 microM), but not prazosin, suggesting that the release modulating alpha receptors of the retina are of the alpha-2 subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Cyclic nucleotides of cone-dominant retinas. Reduction of cyclic AMP levels by light and by cone degeneration.

Dark-adapted retinas or whole eyes of 13-line ground squirrels (Citellus tridecemlineatus) and western fence lizards (Sceloporus occidentalis) contain higher levels of cyclic AMP than of cyclic GMP. In these cone-dominant retinas, light reduces cyclic AMP content selectively. Freezing of dark- or light-adapted retinas or eyes also reduces cyclic AMP content, with only minimal changes in cyclic GMP levels. In addition, exposure of frozen retinas of dark-adapted ground squirrel to light results in a significant decrease in cyclic AMP content. The destruction of cone visual cells of ground squirrel retina by iodoacetic acid injection decreases the cyclic nucleotide content of the dark-adapted retina. Considering the relative loss of cyclic nucleotides from cone degeneration, we estimate that the content of cyclic AMP in visual cells of ground squirrel retina is about four times greater than that of cyclic GMP.

Animals↗
PubMed1980

Opiate binding sites in the retina: properties and distribution.

The presence of opiate binding sites in rat retina was confirmed and their properties and distribution were investigated. Etorphine, naloxone and methionine enkephalin exhibit high affinity, saturable binding to retinal membrane preparations. Scatchard analysis of the binding data yielded linear plots for each ligand. The P1 subcellular fraction contains the greatest density of sites per milligram of protein. The response of the binding of all ligands to sodium ions was similar in the retina to that observed in the brain. Competition experiments using naloxone and methionine enkephalin indicated that a homogeneous class of binding sites exists in the rat retina. Opiate binding sites were also demonstrated in the retina of cow, toad and skate. Methionine enkephalin-like immunoreactivity was not clearly detectable in rat retina but was present in toad retina. The physiological role of the opiate binding sites in the retina remains to be elucidated.

Animals↗
PubMed1984

Calmodulin stimulates adenylate cyclase activity and increases dopamine activation in bovine retina.

Adenylate cyclase activity in bovine retina is highly responsive to Ca2+ and the endogenous Ca2+-binding protein, calmodulin (CaM). CaM stimulated adenylate cyclase activity in washed particulate fractions of bovine retina by 6.6-fold in a Ca2+-dependent manner. Activation of adenylate cyclase activity by CaM was maximal at 0.12 microM free Ca2+. The apparent Ka for calmodulin stimulation of adenylate cyclase was 67 nM and the apparent Vmax was 116 pmol/min/mg of protein above basal activity. Adenylate cyclase activity in bovine retina was stimulated approximately 50% by guanosine 5'-triphosphate (GTP), but the nonhydrolyzable GTP analogue, guanosine-5'-(beta, gamma-imido)triphosphate (Gpp(NH)p), was able to activate the enzyme nearly 5-fold. CaM and Gpp(NH)p appeared to be partially competitive activators of adenylate cyclase in the retina particulate fraction. Dopamine stimulated adenylate cyclase activity in the presence of GTP with an apparent Ka of 1.0 microM and an apparent Vmax of 66 pmol/min/mg of protein. Ca2+ and CaM increased the apparent Vmax of the dopamine-stimulated adenylate cyclase activity more than 2-fold to a level of 146 pmol/min/mg of protein but did not alter the apparent Ka. This suggests that CaM is an endogenous modulator of dopamine-stimulated adenylate cyclase activity in the retina. CaM-stimulated adenylate cyclase activity may be a common component to retina since we found this activity in retinas from rabbit, rat, and goldfish as well as cow.

Adenylyl Cyclases↗
PubMed1983

Origin of macrophage in photocoagulated rabbit retina.

To identify the hematogenous origin of macrophages in the photocoagulated retina, a technique of labeling blood monocytes with colloidal carbon prior to the coagulation was used. Colloidal carbon was given intravenously to adult pigmented rabbits twice daily for 5 days, and 3 days after the last injection xenon flash photocoagulation was performed on the retina. The circulating blood cells and the coagulated portions of the retina and choroid were then examined using electron microscopy. At the time of photocoagulation, circulating blood monocytes contained several clusters of carbon granules in the cytoplasm. Two days after coagulation, monocytes with carbon granules were observed to penetrate the Bruch's membrane. In the coagulated retina, macrophages with carbon granules were observed, while retinal pigment epithelial cells contained no carbon granules. Two months after coagulation, macrophages with carbon granules remained in the retina, and a few proliferated pigment epithelial cells contained carbon granules in the cytoplasm. These carbon granules were considered to be derived from degenerated macrophages. These results indicate that hematogenous monocytes invade the retina from the choroid through the Bruch's membrane and are transformed into macrophages, some of which degenerate in the retina and are phagocytized by pigment epithelial cells.

Animals↗
PubMed1983

Retina of river dolphin Lipotes Vexillifer.

The structure of retina of the Lipotes Vexillifer has been studied quantitatively under light microscope. The results obtained are as follows. (i) The thickness of the retina is 268 micrometer. The lamination of retina can be clearly distinguished. It consists of 10 layers. The thicknesses of the layers from pigment epithelium to internal limiting membrane are 12 micrometer, 44 micrometer, 2 micrometer, 48 micrometer, 20 micrometer, 36 micrometer, 68 micrometer, 32 micrometer, 8 micrometer and 2 micrometer respectively. (ii) The number of cells in the outer nuclear layer is larger than that in the inner nuclear layer. Two types of cell can be distinguished in this layer. The number of receptors and ganglion cells is in a ratio of 12 to 1. These results show that the retina type of the Lipotes corresponds to that of nocturnal animals. (iii) The diameters of ganglion cells range 1.5-37 micrometer with two peaks at 6 micrometer and 35 micrometer. This means that the ganglion cells fall into two groups according to size, and this has been proved by the observation on morphology of ganglion cells in the whole-mount preparation and sections of the retina. The percentages of large cells and small cells are 3% and 97% respectively. The proportion of small cells to large cells does not change greatly in different parts of the retina. (iv) No fovea and visual streak have been found in the retina.

Animals↗
PubMed1978

Influence of embryonic stage on the transdifferentiation of chick neural retina cells in culture.

Neural retina cells from chick embryos up to 15 days of incubation can transdifferentiate in culture into both lentoids and pigment cells. Some transdifferentiation into pigment cells but none into lentoids was found in cultures of 17-day embryonic neural retina. No transdifferentiation occurred in cultures of neural retina from embryos immediately before hatching. In general, lentoids and pigment cells develop more rapidly and in greater numbers in cultures of neural retina from the earlier embryonic stages, and lens-specific crystallins also appear earlier and accumulate in greater amounts in these cultures. Delta crystallin accumulation is much greater in transdifferentiating cultures of early embryonic neural retina, wheras alpha and beta crystallins become proportionately more prominent in cultures of late embryonic neural retina. Traces of alpha and beta but not delta crystallin are detectable in 60-day cultures of 17-day embryonic neural retina. Analogies between these results and the ontogeny of crystallin polypeptides in lens cells in vivo are discussed.

Animals↗
PubMed1995

Oxygen consumption in the inner and outer retina of the cat.

PURPOSE: Oxygen consumption rate (QO2) was determined in the outer and inner halves of the cat retina in dark and light adaptation. METHODS: Double-barreled oxygen microelectrodes were used to measure oxygen tension (PO2) across the retina of anesthetized cats while the single retinal artery supplying that area was occluded. During the measurements of these PO2 profiles, the cats were ventilated with 100% O2. Retinal PO2 profiles were fitted to a diffusion model, and inner and outer retinal QO2s were determined from the fitted parameters. RESULTS: A four-layer model, in which two layers consumed oxygen, fitted the data well. One consuming layer corresponded to the photoreceptor inner segments, as in previous studies, and a single region of uniform consumption was used to describe the profile in the inner half of the retina. Under dark-adapted conditions, outer and inner retinal QO2 were 3.9 +/- 2.8 and 3.5 +/- 1.7 ml O2/(100 g.min) (mean +/- SD; 9 cats), respectively. With steady illumination, outer retinal (photoreceptor) QO2 decreased to 1.4 +/- 0.9 ml O2/(100 g.min), but inner retinal QO2 remained unchanged at 3.7 +/- 1.5 ml O2/(100 g.min) (5 cats). CONCLUSIONS: The total QO2 of the inner retina was found to be the same as that of the dark-adapted outer retina. Oxygen use was distributed uniformly throughout the inner retina but was confined to the photoreceptor inner segments, which occupied approximately 20% of the thickness of the outer retina. Steady illumination had no effect on inner retinal QO2.

Animals↗
PubMed1994

Fatty acid-binding protein from embryonic chick retina resembles mammalian heart fatty acid-binding protein.

PURPOSE: Fatty acid-binding proteins (FABP) make up a family of cytosolic proteins of unknown function found in many tissues, including the embryonic chick retina. To further understand its function in the developing retina, the protein from embryonic chicks was purified and characterized. The tissue distribution of this protein in embryonic and hatched chicks was determined using polyclonal antiserum prepared against this FABP. METHODS: FABP was purified by column chromatography and native gel electrophoresis; denaturing gel electrophoresis and isoelectric focusing were used to characterize the protein. Polyclonal antiserum prepared in rabbits demonstrated immunoreactivity with a single protein from retina cytosolic fraction. Tissue distribution of retinal FABP was determined by immunoblotting and localization of FABP in eyes of E15 and adult chickens was studied by immunohistochemistry on paraffin sections. RESULTS: Retinal FABP has a molecular weight of approximately 15,100 and an isoelectric point of 4.4. An immunoreactive protein of the same apparent molecular weight is present in the brain, heart, adipose tissue, and red muscle; a trace of FABP is present in white muscle, lung, and liver. There is no apparent cross-reactivity with a protein in intestine or in retinal pigment epithelium/choroid. Immunostaining of sections of the adult eye at the region of the ora serrata revealed little staining of the retina, but intense staining of the nonpigmented layer of the ciliary epithelium. CONCLUSIONS: Retinal FABP resembles the heart subtype of FABP (H-FABP) with respect to molecular weight, isoelectric point, and tissue distribution. However, as retinas do not use fatty acids for beta-oxidation, a process H-FABP is believed to participate in, there must be some other function for FABP in the chick eye, especially at early stages of development. In the mature retina, this function is apparently not needed, because there is little staining of the retina in adults but obvious immunoreactivity in the ciliary epithelium, implying some other role for FABP in this tissue.

Animals↗
PubMed1995

Somatostatin in the retina.

One single gene codes for the peptide somatostatin in mammals. Among species the propeptide shows a high degree of homology as the porcine and human propeptides are identical and only differs in two positions compared with the rat propeptide. Somatostatin and prosomatostatin are therefore very suitable for a comparative investigation of the posttranslatoric processing. Antibodies directed against four putative parts of the processing products of the prosomatostatin molecule were used in order to investigate the comparative biosynthetic processing of the precursor for the neuropeptide somatostatin, in the retina from frog, rat, gerbil, mink and monkey. The antibodies were employed to quantify, characterize, and localize somatostatin and prosomatostatin by biochemical and histochemical techniques. Further, somatostatin producing cells were demonstrated by in-situ hybridization using an antisense probe for somatostatin. Somatostatin and prosomatostatin were demonstrated in retinal extracts from all five species investigated. Retinal posttranslational processing of the prosomatostatin molecule varies between the species. In rat and monkey only one form of the bioactive somatostatin (SS-14) is present. In frog, gerbil and mink two known bioactive forms of somatostatin (SS-14 and SS-28) were present. In all five species prosomatostatin-64 (proSS-64) was recognized. In addition, the fragment somatostatin 1-28(1-12) was detected in rat and monkey retinae. In the rat somatostatin and prosomatostatin were demonstrated in subpopulations of amacrine cells located in the inner part of the retina. Cell bodies were labelled at the proximal boarder of the inner nuclear layer and in the ganglion cell layer. From these cells processes were limited to the plexiform layers of the retina and were never observed leaving the retina. By in-situ hybridization autoradiographic signals were demonstrated according to the cell bodies represented by immunohistochemistry. No seasonal variation was observed in the processing pattern of the peptide, investigated in the frog retina. However, the concentration measured during wintertime was almost two fold the concentration measured during summertime. In conclusion, the findings indicate that somatostatin and prosomatostatin are well conserved peptides in vertebrate retinae. Species differences in posttranslational processing excist. The physiological implication of this fact needs to be solved.

Amino Acid Sequence↗
PubMed1996

Microglia in human retina: a heterogeneous population with distinct ontogenies.

Microglia of the adult human retina are a heterogeneous population of cells, some having characteristics of dendritic antigen presenting cells (DC) and others resembling macrophages, or MPS cells. Studies of the development of microglial distributions in human retina suggest that cells bearing macrophage markers are ontogenetically distinct from microglia that do not. Quantitative studies indicate that macrophage antigen immunoreactive microglia are a subpopulation CD45- and MHC-immunoreactive microglia. While CD45 and MHC-I and -II immunoreactive microglia are seen in the retina prior to the arrival of the vasculature, significant numbers of macrophage-positive microglia only arrive along with the vascular precursors, at about 14 to 15 weeks of gestation. Microglia appear to enter the retina from the ciliary margin prior to vascularization but from both the optic disc and ciliary margin, postvascularization. Macrophage antigen positive microglia enter the retina mainly via the optic nerve head. It is argued that macrophage-antigen positive microglia become established in the retina as vessel associated (perivascular and paravascular) microglia and that the MHC-positive, but macrophage-antigen negative microglia (representing DC), become established as the parenchymal, ramified microglia of adult retina.

Adult↗
PubMed1996

Transient expression of an atypical D1-like dopamine receptor system during avian retina differentiation.

Intact cultured retina cells from chick embryos at stage E9C5 (cultures initiated with retinae from 9-day old embryos followed by 5 days in culture), preincubated with 2 nM unlabelled SCH 23390 (R(+)-7- chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride) for 20 to 60 min at 37 degrees C and then washed 5 to 25 times (approximately 1.5 min/wash) with 2 ml SCH 23390-free medium, responded to dopamine with cAMP accumulation that corresponded to 30-50% of the dopamine-promoted cAMP accumulation observed in untreated cells or in cells exposed to the inactive isomer of SCH 23390. Therefore, 50 to 70% of the dopamine response of SCH 23390-pretreated cells was inhibited after extensive washings of the cultures. At E9C12 the fraction of the dopamine response that remained inhibited by SCH 23390 after the washings declined to 30% of the control cultures or the cultures exposed to the SCH 23390 enantiomer. Cultures at stage E9C5 treated with SCH 23390 followed by extensive washings as above and then used for measuring the number of [3H]-SCH 23390 specific binding sites revealed that 60% of the sites did not interact with the tritiated compound when compared to untreated cultures or to cultures preincubated with the inactive isomer of SCH 23390. When E9C12 cultures were subjected to the same experimental protocol less than 10% of D1-like sites did not interact with [3H]-SCH 23390 after the cells had been exposed to the unlabelled compound. Dissociated cells prepared from intact retinae obtained from 12-13-day old embryos also displayed a subpopulation of D1-like sites that interacted irreversibly with SCH 23390 in a stereospecific way. These sites corresponded to 25% of the total number of D1-like sites present in the retina at this developmental stage. In retina cells obtained from one-day old posthatched chicks these sites were no longer detected. These data show that cultured retina cells as well as cells obtained from retina developing in ovo display two populations of D1-like receptors. One interacts irreversibly with SCH 23390 and is present only in the undifferentiated tissue or in cells at the early stages of culture and the other has a lower affinity for SCH 23390 with which its interaction follows reversible kinetics. These sites are present throughout the differentiation stages studied.

Animals↗
PubMed1997

Light exposure induces ubiquitin conjugation and degradation activities in the rat retina.

PURPOSE: To evaluate the consequences of light exposure on retinal ubiquitin (Ub) conjugation and degradation. METHODS: Two-month-old Long Evans pigmented rats were exposed to constant light (180 foot-candles) or were left in complete darkness for 18 hours. Rats used for cyclic light and diurnal rhythm experiments were removed from their light cycles at different times (24-hour clock): 0700 (before the light was turned on), 1000 (3 hours into the light cycle), 1000D (continued in the dark cycle), 1900 (before the light was turned off), 2200 (3 hours into the dark cycle), and 2200L (continued in the light cycle). The retinas were examined for Ub conjugation, adenosine triphosphate-Ub-dependent degradation, levels of Ub messenger RNA, and localization of Ub immunocytochemistry. RESULTS: There was a statistically significant increase in Ub conjugation and degradation in retinas isolated from light-exposed animals compared with degradation in retinas of dark-adapted animals. However, no significant differences were observed in the levels of Ub messenger RNA from cyclic light, or light-exposed or dark-adapted retinas, suggesting that light-stress-induced changes do not reflect increased transcriptional activity. The daily variations observed in Ub conjugation and degradation suggest that these processes are probably the result of a circadian rhythm. Results of immunohistochemical studies revealed that Ub and its conjugates were uniformly distributed throughout the retinal cell layers in light- and dark-adapted retinas. However, in light-exposed retinas, a strong positive immunoreactivity was observed in the inner retina, specifically in horizontal and ganglion cells. CONCLUSIONS: These results suggest that light exposure may play a role in inducing Ub-conjugating activity in certain retinal cells. Furthermore, the results support the hypothesis that Ub is a stress protein that plays an important role in protecting cells under stress conditions.

Adenosine Triphosphate↗
PubMedDate not supplied

[Lactate dehydrogenase isoenzymes from teleost fish retina, cardiac and skeletal muscle].

Kinetic analysis, electrophoresis and selective inactivation were used in studies of isozymic composition of LDH in the retina, cardiac and skeletal muscles in 8 species of marine teleost fishes. In the retina, the number of isoenzymes in all the fishes studied varied from 2 to 7, the predominant ones being B4 and E4. The isoenzyme E4 was found only in the retina of Hexagrammus octogrammus, Pleurogrammus monopterygius, Liopsetts pannifasciata, Limanda yokohamae, Eleginus gracilis, Therarga chalcogramma. In two last species, the electric charge of E4, B4 and A4 is opposite to that of the corresponding isoenzyme in terrestrial animals, resulting in opposite migration of these isoenzymes during electrophoresis. In the retina of fishes containing the isoenzyme E4, double heterotetramers B1E3, B2E2, B3E1 were also found. The retina in Leuciscus brandti, Clupea harengus harengus does not contain the isoenzyme E4. Investigation of the distribution pattern of the isoenzymes in cellular fractions of the retina in P. monopterygius revealed that hyaloplasm and nuclei contain A4, B4, B3E1, E2B2, E3B1 and E4, which corresponds to the situation found after the extraction of LDH from the whole retina tissue. In the mitochondria B4 and E4 were found, while in the outer segments--only B4. Skeletal muscles in all the fishes studied differ by the predominance of the isoenzyme A4 which is present as a sole component (P. monopterygius, H. octogrammus, L. pannifasciata, L yokohamae, L. brandti) or together with B4 (T. chalcogramma, C. harengus harengus). In the cardiac muscles of four species of fishes (except L. yokohamae, L. pannifasciata, H. octogrammus, P. monopterygius), the predominant isoenzyme was found to be B4, although the total number and the ratio of the isoenzymes varied: A4, A2B2, B4 (E. gracilis), A4B4 (T. chalcogramma, C. harengus harengus), A4, A3B1, A2B2, A1B3, B4 (L. brandti). The LDH in the heart of L. yokohamae, L. pannifasciata, H. octogrammus, P. monopterygius has only one isoenzyme A4.

Animals↗
PubMed1997

Ageing has a differential effect on nitric oxide synthase-containing and catecholaminergic amacrine cells in the human and rat retina.

In this study, we assessed the effects of normal ageing on the number, distribution, and somal area of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive (NADPHd+) and tyrosine hydroxylase-immunoreactive (TH-IR) amacrine cells in human and rat retina. By using a double-labelling immunohistochemical technique, we have shown that these two enzymes are located in separate amacrine cell populations in the human retina. In normal human retinas from organ donors, we have shown that there was no change in the number, somal area, or retinal distribution of NADPHd+ neurons over an age range of 19-89 years. In contrast, there was a significant decrease (P < 0.05) of 52% in the total number of TH-IR neurons in the group aged 65-89 years compared with the group aged 19-64 years. CA1 and CA2 TH-IR neurons were reduced by 44% and 55%, respectively. In young (3 months) and old (2 years) rats, the number of NADPHd+ neurons did not decrease with ageing, but the number of TH-IR neurons was significantly reduced by 21% (P < 0.05). In a companion study on monkey retina, we have shown that a postmortem delay of 12.5 hours between death and fixation results in a decrease of 33% in the number of both NADPHd+ and TH-IR neurons in the retina compared with the number in retinas fixed immediately after death. The findings of this study on the two subsets of amacrine cells, therefore, are likely to demonstrate the consequences of ageing in the retina and might contribute to visual impairment in the elderly.

Adult↗
PubMed1998

Regeneration of the newt retina: order of appearance of photoreceptors and ganglion cells.

The adult newt regenerates a functional retina following removal or destruction of the original retina. We studied the order of appearance of cell types in the regenerating retina by using immunohistochemical techniques. An antibody that recognizes the alpha subunit (260 kDa) of voltage-dependent Na+ channels was found to label a 255-kDa band in Western blots of crude membrane fractions from the normal retina. Cryosections of normal retina revealed intense Na+ channel immunoreactivity in somata and axons of ganglion cells, weaker immunoreactivity in somata of amacrine cells, and no immunoreactivity in the inner plexiform layer. In the same sections, immunoreactivity to a monoclonal antibody (RB-1) specific to newt cones was intense in the photoreceptor layer. In regenerating retinas, double staining with the Na+ channel antibody as a possible marker of ganglion cells and RB-1 antibody first revealed immunoreactive cells at the intermediate stage (three to five cells thick), which does not exhibit segregated synaptic layers. Na+ channel-immunoreactive ganglion cells appeared before the RB-1-immunoreactive photoreceptors. Because ganglion cells also appear before photoreceptor cells in normal development, common mechanisms may control both the generation and the regeneration of the newt retina.

Animals↗
PubMed1998

Distribution of gap junctions in the chicken retina.

Coupling between cells of neuronal tissue can be due to electrical or chemical synapses. The molecular basis of an electrical synapse is the gap junction channel. Gap junctions have been found between neurones and glial cells, however, in some tissue their presence in the membranes of different cell types is still under discussion. In the retina of vertebrates, which is a true part of the CNS, the presence of gap junctions in the specialised glial cells of the retina, the Müller cells is not clear for chicken. Since these cells span the whole retina vertically, for some tasks, like spatial buffering of potassium, such gap junctions would not be required, in contrast to other parts of the CNS. The spatial buffering of potassium among others plays an important role in the propagation of excitation-depression waves in neuronal tissue, especially in the chicken retina. However, gap junctions could be involved in creating an electrical syncitium of glial cells, which might also contribute to excitation-depression wave propagation. In this paper we present an about complete screening of the presence of gap junctions in the chicken retina, including the proof that the Müller cells of this retina do not have gap junctions. This finding is discussed considering the highly specialised morphological structure of the Müller cells of the chicken retina, which have an extremely extended endfeet tree.

Animals↗