Synaptic plasticity in the rod terminals after partial photoreceptor cell loss in the heterozygous rds mutant mouse

In the retina of mice heterozygous for the retinal degeneration slow gene (rds/+) the photoreceptor cells, both rods and cones, develop abnormal outer segments but establish normal synaptic contacts. The other retinal layers also show normal structural organization. Starting from the age of 2 months, a very slow loss of photoreceptor cells progresses throughout life. As a result, the photoreceptor cell population in the retina of the affected mice is reduced to less than half at the age of 9-18 months. In some of the surviving rod terminals during this period, an increase in the number of synaptic ribbons is recorded. At the same time, the profiles of processes originating from the second order neurons and participating in these synapses are also increased in number so that the multiple ribbons appear as centres of multiple synaptic sites. Morphometric measurements of the perimeter of the synaptic profiles in rod terminals show a significant increase in the rds/+ retina over that of the control retina. Observations based on serial electron microscopy indicate that multiple synaptic sites are developed while the number of the second order neuronal processes, entering the terminals, remains unchanged. The frequency of terminals with multiple synapses in the rds/+ retina increases with progressive photoreceptor cell loss. Similar changes do not occur in the terminals of the cones. It is postulated that loss of some rod photoreceptor cells within a group that is presynaptic to common bipolars or horizontal cells results in partial deafferentation which in turn stimulates the growth of the remaining synaptic elements. The possible compensatory effect and functional significance of such synaptic growth are discussed.

Chloramphenicol resistant Salmonella typhi: the cause of recent out-break of enteric fever in Calcutta

Fifty one strains of Salmonella typhi were isolated during the recent outbreak of enteric fever in and around Calcutta. Forty strains were multidrug resistant including Chloramphenicol. Minimum inhibitory concentrations (MIC) of Chloramphenicol was between 200 mcg per ml and 500 mcg per ml. All these strains were sensitive to Cephalexine, Gentamicin, Furazolidine and Ciproflexacin. Widal test was done in all the cases but the result was inconclusive.

Autonomic function tests and clinical significance of dysautonomia in chronic liver disease

Autonomic function in 20 patients with chronic liver diseases was assessed clinically and by various tests like Valsalva ratio, expiratory-inspiratory ratio, postural tachycardia index, atropine ratio, blood pressure response to assumption of erect posture, hand immersion in cold water, and finger wrinkling response to hand immersion in warm water. Eighty per cent of the patients showed some clinical evidence of dysautonomia. While a good correlation between various clinical complaints of dysautonomia and the extent of parasympathetic dysfunction was observed in the individual patient, a significantly greater impairment of sympathetic function tests was observed in oliguric cirrhotics as compared to their non-oliguric counterparts.

Gossypol-induced inhibition of glucose uptake in human ejaculated spermatozoa may be mediated by lipid peroxidation

Gossypol, a plant-derived polyphenolic compound known to exert contraceptive actions in men, inhibits 14C-glucose uptake in vitro in human ejaculated spermatozoa. Spermatozoal glucose uptake was found to increase monotonically up to 40 min, and then decreased by 60 min, possibly because of the saturation of the transport loci in the membrane. Gossypol at the concentrations of 5 and 10 microns caused a reduction of both the linear portion of the uptake and the fall afterwards. Gossypol similarly affects both the Na-dependent and -independent glucose uptake. The kinetic parameters of glucose uptake indicate that gossypol might be interfering with the transport/carrier protein as reduction in maximum uptake velocity (Vmax) was observed without any change in the affinity constant (Km). Similarly, gossypol also produced an increase in spermatozoal lipid peroxidation as evidenced by a steep rise in thiobarbituric acid reaction products in the human sperm cells. A significant decrease in total phospholipid level and the individual classes was noted after gossypol addition. Gossypol-induced inhibition of glucose uptake may be related to the generation of lipid peroxides and consequent membrane damage.

Development and degeneration of retina in rds mutant mice: ultraimmunohistochemical localization of S-antigen

In the developing photoreceptor cells of the homozygous rds mutant mice S-antigen is localized over the ciliary protrusion as in the control mice, and to a lesser extent over the inner segments, perikaryal cytoplasma and the cell terminals. As the outer segments develop in the normal retina, the discs become increasingly immunoreactive. In the rds/rds retina the outer segments fail to develop but small membrane bound vesicles, immunoreactive for S-antigen are extruded and phagocytized by the retinal pigment epithelium. In the retina of older mutant mice, as the photoreceptor cells degenerate slowly, the surviving cells continue to show persistent immunoreactivity for S-antigen in the different regions of the photoreceptor cells. In the heterozygotes the outer segments are reduced and appear abnormal, but the localization of S-antigen is similar to normal. In the receptor region of the normal retina and in the deviant membranous structures in the mutant retina the localization of S-antigen is similar to that of opsin. However, some differences in the subcellular localization of these two photoreceptor specific proteins have been observed. It is concluded that the rds gene acts subsequent to the synthesis of these proteins and possibly at the site of disc assembly.

The eye of the blind mole rat, Spalax ehrenbergi. Rudiment with hidden function?

The rudimentary eyes of the mole rat (Spalax ehrenbergi) are located under the skin and do not respond to light stimuli. However, removal of the eyes disturbs photoperiod perception in these animals. To help clarify the possibly remaining function of the eyes in this species, the authors studied their development and ultrastructure. In the early embryos the presumptive eye regions--the epithelium, lens vesicle, and optic cup--appear initially normal. As development progresses, the iris-ciliary body complex originates prematurely from the margin of the optic cup and shows a very rapid and massive growth. This pigment-laden tissue mass remains attached to the corneal stroma, obliterates the anterior chamber, and prevents the formation of the corneal endothelium and Descemet's membrane. In the developing lens the elongation of the lens fibers leads to the formation of a rudimentary lens nucleus that becomes disorganized and vacuolated and eventually also becomes vascularized. The optic fissure fails to close, the eyes remain colobomatous, and the optic disc appears atrophic. In contrast, retinal histogenesis progresses relatively normally, resulting in structurally reduced but well-differentiated photoreceptor, neuronal, and ganglion cell layers in the adult eye. Immunohistochemically, the presence of opsin could be demonstrated in the photoreceptor cells. The latter features may indicate that these rudimentary eyes are still functioning in the complex neuroendocrine pathways mediating photoperiodicity.

Technetium-99m amino acid chelates: correlation of their physico-chemical and physiological parameters. Part I

Ten alpha-aminocarboxylic acids were chelated with 99mTc and purified by sephadex gel chromatography. Their hepatobiliary and renal excretion patterns were determined in rats. It was observed that lipophilicity of these chelates is the only determinant in governing their hepatobiliary excretion, whereas their renal excretion is dependent on some other factors in addition to lipophilicity. Depression of renal excretion in presence of probenecid indicated an interaction of renal tubular transport enzymes with these chelates, which was explained from their hexacoordinated dioxotechnetium (V) chelate structure (II).

Effect of cimetidine on intestinal absorption & digestive functions in mice

Oral administration of cimetidine, an antiulcerogenic drug, at a dose of 100 mg per kg body weight in mice, caused significant inhibition of glucose and amino acid uptake in small intestinal segments either after 2 and 24 h (single treatment) or 15 days (daily). Cimetidine also caused a significant decrease in intestinal brush border membrane associated enzymes, sucrase, lactase, maltase and alkaline phosphatase, but increases the activity of leucine aminopeptidase. Kinetic analysis indicated that cimetidine decreased the maximum of apparent initial enzyme velocity (Vmax) of disaccharidases, while substrate affinity constant (Km) was not altered, indicating the noncompetitive nature of inhibition. However, the inhibition of alkaline phosphatase was found to be of mixed type as both Km and Vmax were altered. In vitro addition of cimetidine also produced significant inhibition of enzymes, the inhibition constant (Ki) for sucrase, lactase, maltase and alkaline phosphatase being 22.8, 4.5, 11.5 and 4.8 mM, respectively. It was further observed that in vitro addition of cimetidine also decreased Vmax in case of maltase, sucrase and lactase, Km was unchanged, whereas in case of alkaline phosphatase there was a decrease in Vmax and increase in Km, as compared to the controls.

Development and degeneration of retina in rds mutant mice: immunoassay of the rod visual pigment rhodopsin

Development and loss of photoreceptor cells in mice, afflicted by the rds (retinal degeneration slow) gene, was analyzed by measuring the ocular visual pigment content as rhodopsin (spectroscopy) and opsin (immunoassay). With regard to the postnatal age, where opsin was just detectable, and to the initial rate of opsin synthesis, the mutants did not strongly deviate from the normal animals. The final maximal visual pigment level was, however, about half of normal for the heterozygous mutants and about 3% of normal for the homozygous mutants, both in the pigmented and in the albino strain. In the pigmented normal or heterozygous mutant the (rhod)opsin levels remain stable up to at least 1 year of age. For the corresponding albino animals this was only observed up to 9 months of age. Thereafter the level declines. In the homozygous mutants, maximal opsin levels were observed at about 3 weeks postnatal. Subsequently, this level gradually declined to about 40% in the pigmented and about 15% in the albino mutant. The results indicate that the rds gene does not directly affect the biosynthetic pathways of opsin. The physiological effect of the rds gene is aggravated by photodamage for which the albino animal is particularly susceptible.

Cysteine, a chelating moiety for synthesis of technetium-99m radiopharmaceuticals: II. Attempt to synthesize renal tubular radiopharmaceuticals

N-acyl glycine residue is known to interact with renal tubular transport enzymes and thereby promotes renal tubular secretion. Recently, a similar renal property was also observed with dioxotechnetium aminocarboxy chelates. Therefore, a radiopharmaceutical was designed containing both the above groups with the expectation that an efficient 99mTc labelled renal tubular agent could be developed by this process with which evaluation of various renal parameters will be possible. The synthesized compound, though secreted through the renal tubular pathway, did not show the expected efficiency. It was indicated that the renal property of the molecule was entirely due to chelated dioxotechnetium moiety and the expected effect of the acyl glycine residue was not observed in the molecule.

Development and degeneration of retina in rds mutant mice: altered disc shedding pattern in the heterozygotes and its relation to ocular pigmentation

In the heterozygous mutant (rds/+) mice, receptor outer segments (ROS) are irregular in form and are shed as abnormally large phagosomes. In the albino rds/+ mice, peak frequency of pigment epithelial (RPE) phagosomes is higher than normal and is recorded near the end of the light period, instead of at the time of light onset as in the normal (+/+) albino mice. In pigmented mice of both genotypes, the maximum numbers of phagosomes in the RPE remain lower than in the albinos. In pigmented +/+ mice the number of phagosomes is already high at the time of light onset. The number rises to peak after one hour and then declines slowly. The lowest frequency is reached after the end of the light period. In pigmented rds/+ mice, the number of phagosomes in the RPE is lowest at the time of light onset. The number rises rapidly to peak level within two hours, then declines and remains low until light onset. If the dark period is prolonged, phagosome frequency in the rds/+ RPE remains lower than in +/+ RPE. If the light period is prolonged, phagosome frequency in the rds/+ RPE remains at a higher level than in the +/+ RPE. This differential response to altered light regimen in the rds/+ and +/+ mice is less pronounced in the pigmented than in the albino individuals. The phagosomes in the rds/+ RPE are larger than in the +/+ RPE in all light regimens. These results show that ocular pigmentation may modify the circadian pattern of ROS disc shedding in the rds/+ retina.

Histotypic differentiation of neonatal mouse retina in organ culture

Retinae from neonatal mice were explanted in toto, with or without the retinal pigment epithelium (RPE) and adjoining mesenchymal cells, and maintained in organ culture for up to 3 weeks. The explants remained flat, rosette formation was minimal and histogenetic changes followed in the normal sequence. After 11, 14 and 21 days in vitro the three cellular layers--the outer nuclear layer including well differentiated rod and cone perikarya, the inner nuclear layer and the ganglion cell layer--with the intervening plexiform layers were comparable to those of the in vivo eyes. Electron microscopic analysis revealed that in the explants without RPE the nuclear layers developed as in vivo, but receptor outer segments (ROS) were not formed. When the RPE was present, receptor inner segments appeared normal and ROS including profuse disc structures were developed. Presence of synaptic elements was also recognized. Mesenchymal cells, when present differentiated into choroidal and scleral tissues and appeared to play a supportive role for the RPE cells. The system is described in detail and its suitability for the analysis of various cellular and metabolic factors in the development of the retina is discussed.

Effect of antiulcerogenic drug, ranitidine, on intestinal absorption and digestive functions in mice

Oral administration of antiulcerogenic drug ranitidine significantly inhibits glucose and amino acid uptake in small intestinal segments. It also inhibits activities of brush border membrane disaccharidases and alkaline phosphatase but increases the activity of leucine aminopeptidase. Kinetic analysis reveals noncompetitive and mixed type of inhibition for disaccharidases and alkaline phosphatase, respectively. In vitro addition of the drug to membrane preparation shows similar type of results as seen in vivo with the inhibition constant (ki) for sucrase, lactase, maltase and alkaline phosphatase as 12.5, 5, 11.5 and 19.5 mM, respectively.

A Field Experiment of Improved Steamdrive With In-Situ Foaming

Summary

This paper reports on the design and execution of a field experiment on recovery of heavy oils by steamdrive enhanced by additives. The goal of this project was to study the effect of injection of a commercial surfactant (Suntech IV) and N2 on the behavior of a conventional steamdrive. Because the laboratory studies leading to the design and implementation of this field experiment have been referenced many times, we emphasize here the field data obtained in reservoir definition, monitoring of the experiment's progress, and production evaluation in a heavy-oil reservoir. Several standard and production evaluation in a heavy-oil reservoir. Several standard and experimental analytical methods were applied, and their validity in the Kern River field test is discussed. Three slugs of surfactant and N2 were injected at different rates. Analysis of the results shows a considerable improvement in oil recovery by steamdrive caused by the addition of surfactant and N2 to the steam. The changes in production behavior of the reservoir caused by the additives are analyzed and discussed. Although the economics of this project is difficult to determine at this point, it looks promising.

Introduction

Stream injection is the most commonly used EOR process for heavy-oil recovery. In the U.S., steamdrive is well established in California, where reservoir conditions of high oil viscosity, low pressure, shallow depth, and high oil saturations are favorable to pressure, shallow depth, and high oil saturations are favorable to thermal recovery techniques. The purpose of injecting steam into a reservoir is to reduce oil viscosity by increasing its temperature, thus improving its mobility and easing the flow toward the producing wells. Because steam is lighter than oil, it has a tendency to flow by gravity segregation through the structurally highest parts of the reservoir. Also, because the mobility of steam is much higher than that of oil the steam tends to channel through the high-permeability zones. Gravity segregation and channeling cause early steam break-through to the producing wells and lower the sweep efficiency; consequently, the actual oil recovery by steamdrive is considerably less than the amount potentially recoverable by this process. The efficiency of steamdrive operations can be improved through the use of additives, which decrease the mobility of steam through the zones of the reservoir that have already been depleted of oil and divert the steam to unswept areas. Surface-active materials can also improve the recovery by reducing the residual oil saturation through lowering of the inter-facial tension between oil and hot water produced by steam condensation and/or modification of the reservoir produced by steam condensation and/or modification of the reservoir wettability. Both mechanisms can be present in a steam-with- additives project. One of our research projects is aimed at improving the efficiency of steam-injection operations by the use of additives to reduce gravity override and channeling. The project began in 1976; in 1977, Marsden et al. reviewed the literature on mobility-control agents and concluded that foam was best suited for this purpose. Foam is a gas/liquid emulsion. To create and propagate a stable foam, a surface-active material (surfactant) must be added to the liquid phase, generally water. In addition, to be effective in the mobility control of a steamdrive, a foam has to meet the following requirements:it must be stable at relatively high temperatures;it must preferentially penetrate the stream-swept zones and reduce their permeability; andthe "blocking" action should persist for an extended period of time under reservoir conditions.

A laboratory study was initiated to evaluate the temperature stability of foaming agents (surfactants) and to characterize their flow properties in porous media. One of the goals of that study was to properties in porous media. One of the goals of that study was to select from the numerous commercial surfactants those that are potentially applicable in steamdrive with foam. potentially applicable in steamdrive with foam. Experimentation showed thatgravity override of injected gases in gasdrive processes could be sharply reduced, so recovery was increased by in-situ generation of foam, andSuntech IV, a surfactant developed under U.S.

DOE funding, was a suitable foamer for steamdrive enhancement. Several other foaming agents have since been shown to have good thermal stability and mobility-reduction characteristics.

Because there are many differences between an idealized laboratory model and an actual reservoir, a controlled, thoroughly monitored field experiment was planned to test the efficiency of Suntech IV improving steamdrive recovery. The field experiment was to be supported by adequate laboratory research and reservoir engineering. Through 1980, field experiments with in-situ foaming in a steam-drive process in the Kern River area had been attempted with some success. Getty Oil tested COR-180-, a steam-diverter foam, on nine injectors to determine its effect on steamflood oil recovery. Radioactive tracer surveys showed that in most of the injection wells, the steam-injection profile was improved. Average daily oil production of the test patterns also increased significantly during the production of the test patterns also increased significantly during the foam-test period. Eson and Fitch also tested COR-180 and COR-GEL in four steam-injection nine-spot patterns in the North Kern Front field. Field investigation showed that these steam-diverter foams altered the steam-injection profiles by preventing excessive steam channeling. Early production data indicated a substantial quantity of incremental oil being produced by the four chemically treated patterns. The CLD groups tested the surfactant Thermophoam TM on the Midway-Sunset field. Here too the test seemed to be at least a technical success. These field experiments tested the foaming and plugging ability of the surfactant without fully monitored tests or thorough laboratory research and reservoir studies. In addition, none of the field experiments used Suntech IV, which we had demonstrated to be a suitable foamer for steamdrive. Doscher and Hammershaimb tested a Suntech product (Sample Code VII-) in the laboratory to establish whether the foaming agent was capable of sustaining a foam at reservoir steam temperatures, Before completion of testing, however, the Suntech surfactant was dropped from further consideration because it was not commercially available. Dilgren et al. reported that Shell Oil Co. conducted a field test of steamdrive with in-situ foaming. They told of a substantial increase in production caused by continuous injection of surfactant and N2. The success of the laboratory studies led to the submission of a proposal to the DOE for a field experiment to test the effectiveness of in-situ foaming as a means of improving heavy-oil recovery by steamdrive and to obtain field-scale data unobtainable in laboratory study. A contract was initiated on Sept. 30, 1980, but because of delays in subcontract negotiations, work on the project did not begin until April 1981. The project was completed at the end of Dec. 1984.

General Site Description

The McManus lease, operated by the Petro-Lewis Corp. was chosen for the site. The lease is located in the Kern River field, near Oildale, CA, about 2 miles 13.2 km) north of Bakersfield in the San Joaquin Valley. The oil is heavy (12 deg. API [0.99 g/cm3] gravity) and the water is slightly brackish (see Table 1).

SPEPE

P. 239

Gossypol inhibition of Ca++ uptake and Ca++-ATPase in human ejaculated spermatozoal plasma membrane vesicles

Gossypol, a plant-derived polyphenolic compound known to exert contraceptive actions in men, inhibits Ca++-transport and Ca++-activated ATPase in isolated plasma membranes of ejaculated human sperm cells. It also inhibits the membrane bound Mg++- and Na+ + K+-dependent ATPases, 5'-nucleotidase and alkaline phosphatase systems. Ca++-ATPase inhibition by gossypol is non-competitive. It abolishes the discontinuity in Arrhenius expression of temperature dependence of Ca++-ATPase and increases the energy of activation. Phosphatidyl choline and Na+-deoxycholate inhibit Ca++-transport activity in the membrane vesicles. The apparent similarity of Ca++-transport inhibition by gossypol and phosphatidyl choline may indicate the possible capability of this compound to induce changes in the lipid microenvironment of the membranes, wherein the integral proteins operate. Inhibitory effect of gossypol on the plasma membrane Ca++-pump suggests that gossypol may affect sperm motility by a mechanism which is related to the structure and functions of the plasma membrane.

Development and degeneration of retina in rds mutant mice: analysis of interphotoreceptor matrix staining in chimaeric retina

Chimaeric mice were produced by aggregating two morulae--one of homozygous rds mutant and another from a strain of mice with normal retina, which also differed in colour genes. The interphotoreceptor matrix in the retinal sections of these chimaeras was studied histochemically. In sections, stained with colloidal iron, regions with rds/rds photoreceptor layer, characteristically lacking the outer segments, showed more intense staining of the interphotoreceptor matrix, while regions with normal receptor outer segments showed less intense staining of the matrix. In sections, stained with toluidine blue, rds/rds regions showed more intense reaction along the pigment epithelial--photoreceptor interface and less intense reaction over the inner segments in comparison to the regions with normal photoreceptors. These differential staining reactions were independent of the overlying retinal pigment epithelial cell genotype and resembled the reaction patterns in the retina of pure strain controls of the same age. Small patches, showing rds/rds type staining were also observed within areas which appeared normal. We suggest that the altered properties of the interphotoreceptor matrix in the rds retina result from gene expression within the photoreceptor cells.

Accumulation of glial fibrillary acidic protein in Müller radial glia during retinal degeneration

Müller radial glia accumulate glial fibrillary acid protein (GFAP) in response to retinal injuries. We have studied the changes in cellular localization of GFAP in genetically caused retinal dystrophy in strains of cat and mouse: Abyssinian cats with progressive retinal dystrophy, and mice homo- and heterozygous for the retinal degeneration (rd) and retinal degeneration slow (rds) genes. The following observations were made: (1) Glial fibrillary acid protein-immunoreactive (GFAP-IR) radial Müller glia are present in normal cat and mouse retinae. (2) There is a general increase with age in numbers of GFAP-IR radial Müller glia, and other GFAP-IR elements in the retina of cat and mice with hereditary retinal dystrophy. (3) The increase in GFAP-accumulating Müller cells seems to proceed from peripheral to central retina in both cats and mice. This might reflect the direction of photoreceptor degeneration, which proceeds in the same direction in the retinal dystrophic cat and in mice bearing the rds gene. However, in the rd mouse photoreceptor degeneration proceeds from central to peripheral retina, indicating that GFAP accumulation is not a local direct effect of photoreceptor damage. (4) Comparing the different mutant mouse strains, there seem to be qualitative differences in the distribution of GFAP-IR elements. The numbers of tangential elements and fibrillary tangles in the inner plexiform and nuclear layers are highest in the +/+ rds/rds retina, followed by the +/+ rds/+, whereas such elements appear to be more scarce in rd/rd rds/rds, followed by the rd/rd +/+ and +/+ +/+ retinae.(ABSTRACT TRUNCATED AT 250 WORDS)

A developmental study of interphotoreceptor retinoid-binding protein (IRBP) in single and double homozygous rd and rds mutant mouse retinae

Interphotoreceptor retinoid-binding protein (IRBP) was studied using immunochemical and immunocytochemical techniques in retinae of mice with allelic combinations at the rd and rds loci at different stages of development and degeneration. Until postnatal day 7 (P7), IRBP is located intracellularly in developing retinae of the different genotypes. Thereafter, IRBP is present mainly in the interphotoreceptor matrix. As previously noted, cell death is slowest in the heterozygous +/+,rds/+ mutant with loss increasing in order in +/+,rds/rds, rd/rd, rds/rds and rd/rd,+/+ animals. The IRBP content of the total retina also approximates this pattern, with lowest amounts by far in rd/rd, rds/rds and rd/rd,+/+ mutants (after P14). Interestingly though, IRBP loss significantly precedes visual cell loss in the rd/rd,rds/rds retina. In all the mutants, the remaining rod cells in the outer nuclear layer exhibit synthesis of intracellularly located IRBP at late stages of degeneration. In the single homozygous rd/rd,+/+ and the double homozygous rd/rd,rds/rds mutants, IRBP is present intracellularly during the entire degenerative process with somewhat less intracellular IRBP in the rd/rd,rds/rds mutant. Retinae of homozygous +/+,rds/rds and heterozygous +/+,rds/+ animals exhibit a normal distribution pattern of IRBP immunoreactivity until loss of photoreceptor cells becomes pronounced at later stages of the disease. Many of the remaining cells at this time are probably cone elements although they are structurally changed. Double labeling with IRBP and S-antigen demonstrates, in many but not all, the presence of both proteins in the same cell body. Immunocytochemistry clearly demonstrated the presence of IRBP in remaining photoreceptor cells at late stages of the disease. Thus, the biochemically measured loss of IRBP appears to be a complex process neither directly dependent on the loss of photoreceptor outer segments and reduced interphotoreceptor matrix space (e.g. there is a sustained IRBP level in rodless rds mutants) nor simply due to cell death (e.g. in the rd/rd,rds/rds mutant, IRBP loss significantly precedes cell loss). That this IRBP is mainly intracellular, however, may indicate an abnormality in secretion which, combined with other factors, induces a degenerated and less differentiated phenotype.

Retinal damage by constant light in chimaeric mice: implications for the protective role of melanin

Adult chimaeric mice, containing varying proportions of albino and pigmented cells in their ocular tissues, were exposed to constant light for 5 weeks and the distribution of the surviving rod perikarya in the retina and of the pigmented cells in various eye tissues were compared. In chimaeras which were mostly albino, the retinal lesion was similar to that in pure strain albino mice; in chimaeras with relatively more pigmented cells in their ocular tissues, the retina was unaffected as in fully pigmented mice. In chimaeras with amounts of pigmented cells in their ocular tissues varying between these two ends, lesions of intermediate degrees could be observed. Surviving rod cells in such chimaeric retinas were always found in regions adjoining the periphery. The location of the rod perikarya in such regions did not show an exact correlation with that of the overlying pigmented cells but regions of the outer nuclear layer with surviving rod perikarya were generally located in the half or quarter of the retina in which the overlying pigment epithelium also contained more pigmented cells than in the other regions. The proportions of the surviving photoreceptor cells varied between such chimaeras. The lesion appeared to be less extensive in individuals with more pigmented cells in the epithelium but no exact correlation was recorded. The findings suggest that while pigmentation in the iris reduces the amount of light reaching the retina, melanin in the pigment epithelium, in addition to preventing light reflection, may also play an antitoxic role, possibly as an antioxidative agent.

Development and degeneration of retina in rds mutant mice: altered disc shedding pattern in the albino heterozygotes and its relation to light exposure

The number of phagosomes in the retinal pigment epithelium (RPE) of normal albino mice, maintained in cyclic light, is highest at the time of onset of light. The number declines to the lowest level around the start of the dark period. If the dark period is prolonged, the pattern of shedding remains cyclic but the phagosome count is higher than normal. If the light period is prolonged the phagosome count remains low and the rise to the peak is delayed. The number of phagosomes in the RPE of albino rds/+ mice, maintained in cyclic light, peaks to higher than normal level and the peak is recorded near the end of the light period. If the dark period is prolonged the phagosome count in the RPE of rds/+ mice remains lower than in the similarly treated normal mice. The phagosome count in the RPE of rds/+ mice, exposed to a prolonged light period, remains higher than in the similarly treated normal mice. In both normal and rds/+ mice, born and reared in total darkness, the pattern of disc shedding is very different but the rds/+ mice show a relatively higher frequency of phagosomes in the RPE than the normal mice. The phagosomes in the rds/+ RPE are larger than normal. An increase in size appears to correspond with increased rate of shedding in the rds/+ mice and to a lesser extent also in normal mice. Thus, the pattern of disc shedding in the albino rds/+ mice, which is different from the normal albino mice, also shows a different reaction to changes in the environmental light.

Ontogeny of alpha-crystallin polypeptides during the lens development of a mutant mouse

The ontogeny of alpha A, alpha B and alpha Ains polypeptides of the alpha-crystallin was investigated by the indirect immunofluorescence staining method with antibodies directed against these three polypeptides in a mutant mouse strain called dyl (27). In this strain cataractogenesis starts around day 16 of lens development but the early development of the lens and the ontogeny of lens crystallins do not differ from the normal genotype (29). The polypeptides were fractionated from normal adult Swiss albino mice total native alpha-crystallin by SDS gel electrophoresis, extracted, lyophilized and injected into young rabbits for production of the antibody. The isolated polypeptides were controlled by SDS gel re-electrophoresis and the antibodies were tested against rat lens native alpha-crystallin by immunoblotting. alpha A and alpha Ains antibodies cross reacted, while alpha B did not show any cross reaction. Results presented here show that alpha A and alpha B appear simultaneously while alpha Ains was detectable at a later stage of lens development. These results are discussed.