Retinal development and photoreceptor synaptic ultrastructure are altered by abnormal rearing light regimes

The effects of light rearing regimen on distal retinal development and photoreceptor ultrastructure were investigated using light and electron microscopy. Zebrafish larvae were reared in constant light, control/cyclic light (14 hr light/10 hr dark), or constant dark conditions until 4 or 8 days postfertilization (dpf). Gross retinal morphology was not altered by light rearing conditions; however, ultrastructural differences were noted both within and between age groups. Significant differences were seen in photoreceptor outer segments (OS) and synaptic ribbons, the size of cone photoreceptor mitochondria, and postsynaptic horizontal cell spinules. Larvae reared in constant dark displayed reduced pigment dispersion; OS development was delayed and cone mitochondria were smaller at 4dpf, two results that reversed by 8dpf. Photoreceptor terminals of larvae reared in all treatment conditions displayed anchored synaptic ribbons with arciform densities and no significant differences in ribbon number. Ribbons were 30- 40% longer in photoreceptor terminals within the constant light treatment. The number of horizontal cell spinules invaginating into cone terminals varied and the spinule-to-ribbon ratio was higher in control and constant light-reared tissue by more than 2x at 4dpf. By 8dpf, this ratio was significantly highest in retinas reared in control/cyclic light conditions. Taken together, these results show that abnormal light rearing conditions affect synaptic structure in distal retina. These changes suggest a mechanism for the physiological and behavioral deficits reported in zebrafish larvae grown under constant light and/or dark conditions

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The effects of rearing light level and duration differences on the optic nerve, brain, and associated structures in developing zebrafish larvae: a light and transmission electron microscope study.

The ultrastructure of the optic nerve, brain, and some associated structures of larval zebrafish, grown under three different light regimens were studied. Fish grown under cyclic light (control), constant dark (CD), and constant light (CL) were studied for 4 and 8 days postfertilization (dpf). We also studied the control and CD fish at 15 dpf. The brains of the control and CL fish were larger at 4 dpf than at 8 dpf. In all 4 dpf fish, the brain occupied the entire expanse between the two retinas and the optic nerve extended the shortest distance between the retina and the brain. The 15 dpf zebrafish had the smallest brain size. Groups of skeletal muscle cells associated with the optic nerves became visible in all older larvae. In the 15 dpf larvae, bulges and dilations in the optic nerve occurred as it reached the brain and optic chiasms occurred proximal to the brain. Electron microscopy yielded information about myelinated and unmyelinated axons in the optic nerve, the dimensions of neurotubules, neurofilaments, and myofilaments, including a unique variation in actin myofilaments, and a confirmation of reported myosin myofilament changes (but with dimensions). We also describe the ultrastructure of a sheath-like structure that is confluent over the optic nerve and the brain, which has not been described before in zebrafish. Also presented are images of associated fibroblasts, epithelial cells lining the mouth, cartilage plates, blood vessels, nerve bundles, and skeletal muscle cells, most of which have not been previously described in the literature.

An unexpected enhancement in methanol electro-oxidation on an ensemble of Pt(111) nanofacets: a case of nanoscale single crystal ensemble electrocatalysis.

Pt nanoparticles having the same size ( approximately 10 nm) but different shapes (cubic or octahedral/tetrahedral), as determined by transmission electron microscopy, were synthesized via a polyol-based synthetic procedure. Their respective electrocatalytic activities for methanol oxidation were characterized by cyclic voltammetry and chronoamperometry in both sulfuric and perchloric acid electrolytes, which showed clear shape (surface orientation) dependences. Furthermore, the octahedral/tetrahedral Pt nanoparticles displayed an unexpectedly large enhancement in methanol electro-oxidation activity; about 3-fold increase in transient intrinsic activity and 10-fold increase in CO tolerance steady-state activity when compared to commercial Pt black. Gaseous and methanolic CO adsorption on the synthesized nanoparticles were also investigated by surface-enhanced IR absorption spectroscopy in perchloric acid electrolyte, which suggested that the different trends observed might be related to the electronic effects specific to a given ensemble of the nanofacets.

A light- and electron-microscope study of hepatocytes of rats fed different diets.

Ketogenic diets are used in the treatment of epilepsy in children refractory to drug therapy. This study identifies changes in liver morphology in rats fed four different diets: a normal rodent chow diet, a calorie-restricted high-fat (ketogenic) diet and each diet supplemented with clofibric acid. Hepatocytes of rats fed the ketogenic diet show many lipid droplets and these are reduced to control levels when clofibrate is present in the diet. Mitochondria are enlarged in the livers of rats fed the ketogenic diet and further enlarged if clofibrate is present. Alterations in the appearance or numbers of other organelles are also found.

Generation of islet-like hormone-producing cells in vitro from adult human pancreas.

Transplantation of pancreatic islets can provide long-lasting insulin independence for diabetic patients, but the current islet supply is limited. Here we describe a new in vitro system that utilizes adult human pancreatic islet-enriched fractions to generate hormone-producing cells over 3-4 weeks of culture. By labeling proliferating cells with a retrovirus-expressing green fluorescent protein, we show that in this system hormone-producing cells are generated de novo. These hormone-producing cells aggregate to form islet-like cell clusters. The cell clusters, when tested in vitro, release insulin in response to glucose and other secretagogues. After transplantation into immunodeficient, nondiabetic mice, the islet-like cell clusters survive and release human insulin. We propose that this system will be useful as an experimental tool for investigating mechanisms for generating new islet cells from the postnatal pancreas, and for designing strategies to generate physiologically competent pancreatic islet cells ex vivo.

A transmission electron microscope study of "New Dawn" climber rose (Rosa wichuraiana x safrano) exhibiting rose rosette disease.

The arrival of rose rosette disease (RRD) in the Washington D.C. area prompted a transmission electron microscope study of ultrathin sections of leaves from symptomatic Rosa wichuraiana x safrano plants. Virus-like particles (VLPs) or double membrane-bound particles (DMPs) resembling those associated with RRD in other types of roses, and found in several other plant diseases, were seen in the cytoplasm of parenchymal and vascular bundle cells and shown, for the first time, in guard cells and budding into the vacuoles. Contrary to previous reports, starch granules were found in chloroplasts of the infected cells. A presumably unique intramitochondrial crystal was also observed. Variations in vacuolar content were noted.

Ultrastructure of the posterior half of the intestine of the channel catfish, Ictalurus punctatus.

The posterior half of the channel catfish intestine has a similar histological organization to that of other teleost fishes. This region is organized into a muscosa, a submucosa, a double layered muscularis and a serosa. A "stratum compactum" of dense connective tissue was confirmed for the submucosa. In its histology and cytology, the midgut resembles the hindgut, except that in the hindgut the muscularis is thicker, the microvilli are shorter, there are fewer absorptive inclusions in the columnar cells and there are more goblet cells. With the exception of the serosa, the tissue layers of the intestine of the 6 cm juvenile catfish are fully developed. The most notable difference between the intestines of the juvenile and adult catfish occurs in the columnar epithelial cells. The mucosal cells of the juvenile catfish contain an abundance of large clear vacuoles while the mucosal cells of the mature catfish contain smaller dense granules. With few exceptions, the ultrastructural details of the cells in the catfish intestine are identical to those of the same cell types of the mammalian intestine.