No abstract

The response of olfactory Schwann cells was assessed at 2, 4, and 7 days following intranasal zinc sulfate irrigation in 1-month-old mice. Ultrastructural and immunohistochemical observations showed dramatic differences between experimental and control mice which had been washed with saline intranasally. Two days after zinc sulfate treatment, many olfactory nerve bundles contained patchy areas of axonal degeneration, while the cell bodies of the olfactory Schwann cells appeared to have increased in electron density and to have shifted peripherally. Some of the cell bodies protruded from the surface of the axon fascicle, suggesting that the olfactory Schwann cells were in the initial process of migrating away. On the fourth day when most of the olfactory axons had degenerated, some olfactory Schwann cells were aligned immediately beneath the basal lamina of the olfactory epithelium. These cells were immunopositive for the S-100 protein and possessed an expanded perinuclear space. Many olfactory Schwann cells were present in the region beneath the cribriform plate, while some appeared to have passed through the gaps between the bony plates to reach the olfactory bulb. Hence, the results showed that many olfactory Schwann cells migrated towards the olfactory bulb following loss of axonal contact. Furthermore, on the seventh day following zinc sulfate treatment, some olfactory Schwann cells in the vicinity of the olfactory bulb appeared phagocytic, as indicated by their extension of processes around fragments of cell debris and the presence of lysosome-like organelles in the perikaryon. The control mice which had been intranasally irrigated with saline did not demonstrate massive olfactory axonal degeneration, and the morphology of the nasal cavity region was similar to that of normal mice.

Cultured juvenile silver perch, Bidyanus bidyanus (Mitchell), were affected by epitheliocystis, with a prevalence of up to 75%. The condition affected 2–96% of gill filaments. Granular basophilic cysts ranged from 10 to 87 μm and had a round‐to‐oval shape. The infected cells were positioned centrally within a lamella, often close to its tip, and their identity was difficult to determine, but the involvement of pillar cells could not be precluded. The size of pathogen was within the range previously reported. The pathogen had two morphological forms, which were positioned differently within the cyst. The form located more in the centre was rod‐shaped with an electron‐dense core and electron‐lucent vesicles on the sides of the core. Its mean length was 498.14 nm (SD = 47.68 nm), and its mean width was 145.14 nm (SD = 9.53 nm). The form present in a more peripheral position had an irregular shape, often did not show the electron‐dense core and did not have the electron‐lucent vesicles. Its mean length was 704 nm (SD = 170.29 nm) and its mean width was 152.4 nm (SD = 16.40 nm). Both forms were enclosed by a double trilaminar membrane. This is the first confirmed report of epitheliocystis in Australian freshwater fish.

No abstract

The correlation between detailed kinetic studies and ultrastructural localisation of particles during carbon clearance in normal animals illustrates that single order kinetics are not always obtained and phagocytosis is not always the major clearing process. During the early stages of clearance adherence of particles to platelets and to macrophage surfaces without immediate phagocytosis, as well as aggregation of particles within the blood are important controlling factors in the usual light absorbance techniques used to measure rates of clearance. The importance of the various processes involved varies depending upon the dose of carbon used and the time for which clearance is followed. The ultrastructural studies suggest an early constant rate of phagocytosis by Kupffer cells despite wide changes in dose of particles. At doses of 1 or 2 mg/100 g body weight of colloidal carbon the ultrastructural evidence shows that phagocytosis is the major early clearing process while at doses of 8 mg/100 g body weight and above the other processes are more important in the early clearance. Most clearance studies in the literature do not provide sufficient information to be certain that phagocytosis is the major process involved and such information can only be provided by detailed kinetic studies correlated with ultrastructural localisation of the particles. Many previous studies have used doses of colloidal carbon which invoke a major degree of the clearance processes other than phagocytosis and such studies are often based on a limited number of samples taken over a period when phagocytosis is not the only rate-controlling factor. Particle clearance studies should at least provide information concerning the possible role of platelets before the rates are considered to be measures of phagocytic function.