Anatomy and Histology of the Eye of the Nutria Myocastor coypus: Evidence of Adaptation to a Semi-aquatic Life.

The nutria is a large, semi-aquatic rodent that, being invasive, is having a growing impact on the ecosystem in western Japan. Knowledge regarding physical adaptations to the nutria's lifestyle and habitual activities would be useful for effectively controlling and preventing their spread. Nutrias spend time on land and in water, feeding on agricultural crops and wild grasses growing near the waterside, as well as aquatic plants and shellfish. In the current study, the nutria's visual organ was analyzed anatomically and histologically, and aquatic and light environmental adaptations were evaluated. The results revealed that the nutria eyeball was almost spherical, and the cornea was rounded. The lens was convex and slightly thicker than previously reported for other rodents. These features were not characteristic of aquatic adaptations observed in the eyes of fish or marine mammals. The ratio of lens diameter to eyeball diameter was 0.6, similar to that of nocturnal species. The pupil was a vertical slit, suggesting an ability to adjust the amount of light entering the eyeball during twilight. Photoreceptors were sparsely distributed across the whole retina, and no fovea was observed. Retinal thickness was 90-100 µm, thinner than that in other rodent species. Visual acuity was 1.44-1.58 cycles/degree, higher than that in other rodents, likely because of the nutria's large eyeball and body. These results suggest that the nutria visual system is adapted to recognize large shadows of distant predators rather than viewing objects in detail.

Microbial community analysis in the gills of abalones suggested possible dominance of epsilonproteobacterium in Haliotis gigantea.

Gills are important organs for aquatic invertebrates because they harbor chemosynthetic bacteria, which fix inorganic carbon and/or nitrogen and provide their hosts with organic compounds. Nevertheless, in contrast to the intensive researches related to the gut microbiota, much is still needed to further understand the microbiota within the gills of invertebrates. Using abalones as a model, we investigated the community structure of microbes associated with the gills of these invertebrates using next-generation sequencing. Molecular identification of representative bacterial sequences was performed using cloning, nested PCR and fluorescence in situ hybridization (FISH) analysis with specific primers or probes. We examined three abalone species, namely Haliotis gigantea, H. discus and H. diversicolor using seawater and stones as controls. Microbiome analysis suggested that the gills of all three abalones had the unclassified Spirochaetaceae (one OTU, 15.7 ± 0.04%) and Mycoplasma sp. (one OTU, 9.1 ± 0.03%) as the core microbes. In most libraries from the gills of H. gigantea, however, a previously unknown epsilonproteobacterium species (one OTU) was considered as the dominant bacterium, which accounted for 62.2% of the relative abundance. The epsilonproteobacterium was only detected in the gills of H. diversicolor at 0.2% and not in H. discus suggesting that it may be unique to H. gigantea. Phylogenetic analysis performed using a near full-length 16S rRNA gene placed the uncultured epsilonproteobacterium species at the root of the family Helicobacteraceae. Interestingly, the uncultured epsilonproteobacterium was commonly detected from gill tissue rather than from the gut and foot tissues using a nested PCR assay with uncultured epsilonproteobacterium-specific primers. FISH analysis with the uncultured epsilonproteobacterium-specific probe revealed that probe-reactive cells in H. gigantea had a coccus-like morphology and formed microcolonies on gill tissue. This is the first report to show that epsilonproteobacterium has the potential to be a dominant species in the gills of the coastal gastropod, H. gigantea.

A lambda-shaped retractor lentis muscle in the yellowfin goby Acanthogobius flavimanus.

We identified a morphologically uncommon piscine retractor lentis muscle in the yellowfin goby Acanthogobius flavimanus. This lentis muscle has a shape similar to the Greek small letter lambda (λ). The two legs of the muscle are attached to the retinal periphery at the ventral eyecup, while the tip is connected to the lens surface by a ligament. Scanning electron microscopy showed that the fibers of the lentis muscle run along the length of both the anterior and posterior legs. Immunolabeling with antiacetylated tubulin antibody and neuronal tracing with DiI of the whole lentis muscle revealed that the anterior leg is innervated by one or more nerves. The topographic distribution of ganglion cells in the retina was investigated to identify the visual axis. Three high cell density areas were observed in the dorso-temporal, ventro-nasals and ventro-temporal retina. These findings suggest that the λ-shaped lentis muscle may enable accommodatory movement of the lens toward the temporal as well as the nasal and/or ventral retina.

Visual pigment genes and absorbance spectra in the Japanese sardine Sardinops melanostictus (Teleostei: Clupeiformes).

The spectral absorbance of photoreceptor visual pigments and the opsin gene class of the visual pigments was investigated in Sardinops melanostictus. Microspectrophotometric (MSP) measurements showed that the rod photoreceptors had peak absorbance spectra (λmax) at 502 nm. The spectral sensitivity of single cones was centered at 393 nm. Double cones had a λmax of 493/522 nm, but a few displayed a red-shifted absorbance of the long-wave member at 542 nm. The mRNAs of six different opsins were isolated from the retina, retrotranscribed, cloned, and sequenced. Three genes encoded opsins in the green-sensitive class (RH2), and three genes encoded opsins in the red-sensitive class (LWS), the ultraviolet (UV)-sensitive (SWS1) class, and the rod class (RH1). A Southern blot analysis showed that the blue-sensitive (SWS2) opsin gene is absent from this species, hence it was concluded that the λmax of 393 nm was generated from the SWS1 opsin. Phylogenetic analyses of S. melanostictus RH1, LWS, and SWS1 sequences placed them with orthologs from other species (e.g., the cyprinids Danio rerio and Carrasius auratus) in Otomorpha. However, unexpectedly, the RH2 sequences were more similar to orthologs in members of the Euteleosteomorpha (e.g., Oryzias latipes and Takifugu rubripes) than to cyprinid RH2 opsins.

Morphological characteristics of eyes and retinas of two sardines (Sardinops melanostictus and Etrumeus sadina, Clupeidae) and an anchovy (Engraulis japonicus, Engraulididae).

The morphology of the eyes and distribution of retinal ganglion cells in two sardine species (Sardinops melanostictus and Etrumeus sadina, Clupeidae) and the Japanese anchovy (Engraulis japonicus, Engraulididae) were investigated anatomically and histologically. The eyes of the sardines faced a slightly dorsolateral direction with the visual field extended obliquely upward. In contrast, the eyes in the anchovy were almost laterally directed. It was hypothesized that the sardines may have an advantage in receiving more downward irradiance compared with the anchovy. The lens muscle was larger in these three species than in many other teleosts, and its surface was entirely melanin-pigmented. Also, the lens muscle directly and tightly adhered to the backside surface of the iris. The relative area of the lens muscle to the area of the lens, a referential value of the relative power of visual accommodation were notably larger in the species studied than in other teleost values that have been previously reported. A higher M/L% value of these clupeid fishes could facilitate fast and wide ranging visual accommodation and was considered to be associated with maintaining and/or re-establishing school formations quickly. Analysis of topographical distributions of cells in the ganglion cell layer showed that cell density was highest in the ventrotemporal quadrant of the retina (temporal of the optic cleft) in all three species. Another potentially important role for the black-pigmented lens muscle may be to block the specialized retinal area from intense sunlight that scatters and irradiates upward or laterally in the surface waters that they inhabit. Thus, the sardine and anchovy may take advantage of efficient detection of visual signals in the frontal-upward direction and further improve visibility of the target in this direction.

Retinal ganglion cell topography in juvenile Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel).

The retinal ganglion cell distribution, which is known to reflect fish feeding behavior, was investigated in juvenile Pacific bluefin tuna Thunnus orientalis. During the course of examination, regularly arrayed cells with a distinctive larger soma, which may be regarded as motion-sensitive cells, were found. The topographical distribution of ordinary-sized ganglion cells, which is usually utilized to estimate fish visual axis and/or visual field characteristics, showed that the highest-density area, termed the area centralis, was localized in the ventral-temporal retina. The retinal topography of ordinary-sized ganglion cells seems to reflect the bluefin tuna's foraging behavior; while cruising, cells in the area centralis may signal potential prey, such as small schooling pelagic fishes or squids, that are present in the upward-forward direction. Judging from morphological characteristics, the large ganglion cells localized in the small temporal retinal area seem to be equivalent to physiologically categorized off-center Y-cells of cat, which are stimulated by a transient dark spot in a bright visual field. It was inferred that presumed large off-center cells in the temporal retina detect movements of agile prey animals escaping from bluefin tuna as a silhouette against environmental light.

Three cone opsin genes determine the properties of the visual spectra in the Japanese anchovy, Engraulis japonicus (Engraulidae, Teleostei).

A complement of cone visual pigments was identified in the Japanese anchovy Engraulis japonicus, one of the engraulid fish species that has a retina specialized for polarization and color vision. The nature of the chromophore bound to opsin proteins was investigated using high performance liquid chromatography. The opsin genes were then cloned and sequenced, and the absorption spectra of different types of cones were obtained by microspectrophotometry. Two green (EJ-RH2-1, EJ-RH2-2) and one red (EJ-LWS) cone opsin genes were identified and are presumably related to the vitamin A1-based visual pigments (i.e. rhodopsins) with λmax values of 492, 474 and 512 nm, respectively. The long and short cones from the ventro-temporal retinal zone consisted of a pure population of RH2 class gene-based pigments (λmax=492 nm). The long and short cones from other retinal areas and the lateral components of the triple cones possessed a mixture of RH2 and LWS class gene-based pigments that exhibited a λmax of ~502 nm. The central component of the triple cones contained only RH2 class gene-based pigments (λmax=474 nm). Thus, E. japonicus possesses a middle-wave range of spectral sensitivity and acquires different color vision systems in distinct visual fields.

Identification of mouse mutant cells exhibiting plastic mutant phenotype II; ionizing radiation-induced mutant phenotype plasticity is not dependent on DNA methylation of the hypoxanthine phosphoribosyl transferase gene in mouse FM3A cells.

As we previously reported, we isolated and examined mouse mutant cells exhibiting phenotypic plasticity. Approximately 10% of 6-thioguanine resistant (6TG(R)) cells derived from the irradiated cell population exhibited phenotypic plasticity and reverted to wild type HAT resistance (HAT(R)). Similar mutant cells were also identified in an un-irradiated wild type cell population, but at a lower frequency. Ionizing irradiation enhanced the frequency of the plastic mutation approximately 24 times in our experiments. Treatment with 5-aza-cytidine did not affect phenotypic plasticity. In this study, we further performed detailed molecular analysis of the promoter region of the hypoxanthine phosphoribosyl transferase (Hprt) gene. The analysis revealed that most cytidine residues were not methylated, even in 6TG(R) mutant cells, in which Hprt activity must be down-regulated. These results suggested that DNA methylation was not involved in mutant phenotype plasticity, a new type of genomic instability induced by ionizing radiation. Plasticity in gene regulation may play an important role in radiation carcinogenesis, which is a multiple-stage process.

Relationship between catheter care and catheter-associated urinary tract infection at Japanese general hospitals: a prospective observational study.

BACKGROUND: The risk factors for catheter-associated urinary tract infections (CAUTIs) that are associated with catheter care have not been examined in detail by prospective studies or randomised clinical trials. OBJECTIVES: To examine the patterns of catheter care and to identify the CAUTI risk factors associated with catheter care. DESIGN: Prospective observational study. METHODS: Between January and December 2004, 555 adult patients who were catheterised for 3 days in five general hospitals in Japan were surveyed. One researcher collected the following data twice a week: catheter insertion method, catheter management, and signs and symptoms of urinary tract infections. The relative risk exceeding 1 by the Poisson regression were selected for Cox proportional hazard analysis in order to calculate adjusted risks. In addition, expected reductions in the incidence of CAUTIs by elimination of the risk factors were estimated using the population attributable risk percent. RESULTS: The mean duration of catheterisation was 25 days. The overall incidence of CAUTIs was 3.9 cases per 1000-device days; the incidence of CAUTIs ranged from 0.6 to 7.2 cases per 1000-device days among the five hospitals. Only fecal incontinent patients were analysed since they accounted for 94% of the CAUTI cases. In the univariate analysis, the silver-alloy catheter, which contains antimicrobial property, emerged as a potential risk. Since silver-alloy catheters were used in only one hospital, silver-alloy catheter care was compared with that of the other types of catheter, and a significantly higher percentage of inappropriate care was observed. In the final Cox model, two variables remained: 'non-pre-connected closed system (standard system)' (RR 2.35, 95%CI 1.20-4.60, p = 0.013) and 'no daily cleansing of the perineal area' (RR 2.49, 95%CI 1.32-4.69, p = 0.005). The population attributable risk percent suggested that the use of a 'pre-connected closed system' and 'daily cleansing of the perineal area' could reduce the incidence of CAUTIs by nearly 50%. CONCLUSIONS: Our investigation identified fecal incontinence as the major risk factor for CAUTIs in the study population. However, attributable risk percent indicates that the implementation of two basic elements of catheter care could reduce CAUTIs by nearly 50%. The hospital using silver-alloy catheters had the highest CAUTI rates, strongly suggesting the hazards of relying on the antimicrobial property of silver and the resultant laxity in care.

Computational determination of refractive index distribution in the crystalline cones of the compound eye of Antarctic krill (Euphausia superba).

In order to understand how a compound eye channels light to the retina and forms an image, one needs to know the refractive index distribution in the crystalline cones. Direct measurements of the refractive indices require sections of fresh, unfixed tissue and the use of an interference microscope, but frequently neither is available. Using the eye of the Antarctic krill Euphausia superba (the main food of baleen whales) we developed a computational method to predict a likely refractive index distribution non-invasively from sections of fixed material without the need of an interference microscope. We used a computer model of the eye and calculated the most realistic spatial distribution of the refractive index gradient in the crystalline cone that would enable the eye to produce a sharp image on the retina. The animals are known to see well and on the basis of our computations we predict that for the eyes of the adult a maximum refractive index of 1.45-1.50 in the centre of the cone yields a better angular sensitivity and light absorption in a target receptor of the retina than if N(max) were 1.55. In juveniles with a narrower spatial separation between dioptric structures and retina, however, an N(max) of 1.50-1.55 gives a superior result. Our method to determine the most likely refractive index distribution in the cone without the need of fresh material and an interference microscope could be useful in the study of other invertebrate eyes that are known to possess good resolving power, but for a variety of reasons are not suitable for or will not permit direct refractive index measurements of their dioptric tissues to be taken.

Retinal topography of ganglion cells and putative UV-sensitive cones in two Antarctic fishes: Pagothenia borchgrevinki and Trematomus bernacchii (Nototheniidae).

Accessory corner cones (ACC) have recently been suggested to be UV-sensitive photoreceptor cells. With a view toward explaining prey detection, we examined the topography of retinal ganglion cells and ACCs in two Antarctic nototheniids occupying different ecological niches: the cryopelagic Pagothenia borchgrevinki and the benthic Trematomus bernacchii. Isodensity maps of retinal ganglion cells showed that the main visual axis, coincident with the feeding vector, was in a forward direction in both species. Visual acuity was determined as 3.64 and 4.77 cycles/degree for the respective species. In P. borchgrevinki the highest density of ACCs was associated with the eye's main visual axis. This suggested that this species uses UV-vision during forward-swims and probably in encounters with prey. On the other hand, T. bernacchii possessed two horizontal band-shaped high-density areas of ACCs, which stretched from temporal to nasal and ventral to peripheral retinal regions. Therefore, this species appears to use UV-vision to watch prey across the entire circumference of the lateral area and in the water column above its head.