Organization of Sporulated Oocysts of Eimeria funduli in the Gulf Killifish, Fundulus grandis

Oocysts of Eimeria funduli were studied by transmission electron microscopy in naturally-infected livers of the Gulf killifish, Fundulus grandis. Tissues were cryo-processed because membranous structures in the oocyst appear to hinder routine fixation and embedment. The oocyst wall (about 25 nm thick) was adjacent to the host cell and consisted of an outer membrane that limited the host cell cytoplasm and an inner membrane separated from the outer membrane by a narrow space. In some specimens, dense material was applied to the inner face of the inner membrane. Individual sporocysts were surrounded by a membranous "veil" (about 25 nm thick) that consisted of two unit membranes. Sporopodia, projections of the sporocyst wall, supported the veil. The sporocyst wall (130-150 nm thick) consisted of two layers, a thin electron-lucent outer layer (about 10 nm thick) and a thick electron dense inner layer (about 130 nm thick). Depending on the plane of section, the inner layer had transverse striations with periods of 3 to 4 nm or 12 to 15 nm. A narrow fissure, broadest at the anterior pole of the sporocyst, extended about one-third the length of the sporocyst wall. The posterior pole of the sporocyst was characterized by a bulbous swelling. Although this swelling resembled a Stieda body in light microscopic preparations, ultrastructurally, the swelling was a knoblike thickening in the sporocyst wall and did not plug a gap in this wall

Impact of Solvent Quality on the Density Profiles of Looped Triblock Copolymer Brushes by Neutron Reflectivity Measurements

Preferential adsorption of poly(2-vinylpyridine)-deuterated polystyrene-poly(2-vinylpyridine) (PVP-dPS-PVP) triblock copolymers from toluene onto silicon leads to the formation of dPS loops tethered by the PVP end blocks. Using neutron reflectometry, we have determined the segment density profiles of these looped polymer brushes in toluene, a good solvent for the dPS block, and in cyclohexane at 20 °C (poor solvent), 32 °C, (near-Θ solvent), and 50 °C (marginal solvent). While the swelling behavior qualitatively agrees with that observed for singly grafted brushes, there are interesting differences in the local structural details: In a good solvent, the segment density profiles are composed of an inner parabolic region and a long, extended tail. In cyclohexane, the profiles are described by exponential decays. We ascribe these features to a novel polydispersity effect that arises due to tethering the PS loops by both ends. The results also show that the less dense layers undergo more significant changes in swollen height as solvent quality is changed and that the looped brushes of different molecular weight, asymmetry, and tethering density adhere to scaling relationships derived for lightly cross-linked polymer gels.