Tympanosclerosis in the rat tympanic membrane: an experimental study.

OBJECTIVES/HYPOTHESIS: Tympanosclerosis is a pathologic condition affecting the middle ear and tympanic membrane. It is a common condition in humans, most notably after grommet insertion. However, the pathogenesis of this disease is unclear. The aim of this study was to investigate the development and progression of tympanosclerosis in the pars tensa of rat tympanic membranes at various time intervals after inducing sterile middle ear effusions. METHODS: Fifty-six male-specific, pathogen-free CD Wistar rats (100-170 g) underwent unilateral eustachian tube obstruction. Contralateral ears served as controls. Only specimens from animals with sterile effusions were included in this study. Light and electron microscopic analysis was performed on the pars tensa of rats with induced effusions ranging from 1 to 12 months. RESULTS: Histologic changes consistent with tympanosclerosis were seen in the majority of animals with effusions from 3 months and greater. The process started in the submucosal connective tissue layer and progressed to involve all connective tissue sublayers. The extent of calcium deposition and fibrosis across the membrane was related to the duration of otitis media with effusion. Atrophy was not found in any specimens. CONCLUSIONS: Tympanosclerosis is a progressive disorder, which appears to be the main response of the rat pars tensa to prolonged sterile otitis media with effusion. The extent of involvement of the different sublayers of the pars tensa was closely related to the duration of otitis media with effusion. We propose that this new rat model for prolonged otitis media with sterile effusion is therefore a suitable animal model for the study of tympanosclerosis in the pars tensa.

Protein synthesis during oxygen conformance and severe hypoxia in the mouse muscle cell line C2C12.

Oxygen conformance can be described as the ability to reduce energy demand, and hence oxygen consumption, in response to a decline in oxygen availability without a decrease in the concentration of ATP. It has been proposed that oxygen conformance may enhance cellular survival at low oxygen concentrations. We demonstrate that non-contracting C2C12 cells, a mouse skeletal muscle cell line, are capable of oxygen conformance. Typically, we found oxygen consumption to decline by 30-40% as the concentration of oxygen was reduced from 100 microM to 10 microM. Unexpectedly, the rate of protein synthesis, a major energy consumer in the cell, did not decrease significantly during oxygen conformance. Unlike oxygen conformance, severe hypoxia (<0.5 microM) caused a 36% decline in the concentration of PCr, and under these conditions of energy stress, the rate of protein synthesis declined by 43%. We conclude that there are two distinct metabolic responses to declines in oxygen concentration in non-contracting C2C12 cells.

The effects of lithium on vascular development in the chick area vasculosa.

The effects of lithium on vascular development were examined using the chick embryo area vasculosa in shell-less culture as an experimental model. Embryos were explanted after 48 h in ovo and LiC1 (50, 100, 150 and 200 microg in 10 microl water) was applied to the centre of the blastodisc. Controls were untreated or given equimolar amounts of NaCl. At 24 h and 48 h after treatment, untreated and NaCl controls were identical, having well developed extraembryonic vessels. At doses of 100 microg and greater, LiCl significantly inhibited normal vascular development and expansion of the area vasculosa in the majority of explants. In many specimens blood islands continued to form but their assembly into primitive vessels was prevented, indicating that lithium affects the mechanism regulating the assembly of vascular endothelium. At the same time the embryos were alive but retarded in development compared with controls. When LiCl (150 microg) was applied to cultures explanted after 72 h in ovo (when the primary vascular network had already formed through vasculogenesis) no adverse effects were seen. This suggests that lithium affects vasculogenesis but not angiogenesis. Treatment with myo-inositol completely reversed the effects of lithium in a time dependent manner indicating that the phosphatidylinositol second messenger cycle may be involved in the cellular events of vasculogenesis. Finally the results of this study show that the yolk sac vasculature is particularly vulnerable to lithium and the consequent effects of this interference on embryonic development are discussed.

The effects of lithium on neurulation stage mouse embryos.

The aim of this study was to evaluate the maternal toxicity and teratogenicity of lithium following intraperitoneal injection (i.p.) with lithium carbonate (Li2CO3) in pregnant CD-1 mice at the developmental stage of neurulation (E8; day of vaginal plug, E0). Light (LM) and electron (TEM) microscopic studies were also done to document the tissue and cellular changes occurring in embryonic tissues during the 48 h following treatment with 300 mg/kg body wt. Li2CO3. Controls were untreated or given equimolar amounts of NaCl or Na2CO3. A pharmacokinetic study showed that lithium was rapidly absorbed from the peritoneal cavity after the above-stated dose, achieved peak serum levels of 9.8 mmol/l within 1 h, had a half-life in the blood of 5 h and was completely cleared by 16 to 24 h after injection. Doses of Li2CO3 > 300 mg/kg body wt. were toxic to adult CD-1 mice. The latter dose had no detectable maternal toxicity but caused a 19% resorption rate and 2% incidence of open cranial neural tube defect in gestations terminated on E18. The malformation and resorption rates in gestations terminated on E11, E12 and E14 were not significantly different from those of E18. A strong litter effect was seen both for the resorption and malformation rates at all stages examined. At 3 h after treatment cell death became evident in the neuroepithelium. Cells continued to die for approximately 17 h and all necrotic debris had been cleared by 48 h. Also at 3 h after treatment small densely stained inclusions began to appear in mesodermal cells. TEM showed these to be non-membrane bound with an irregular shape and variable size; the lack of staining for acid phosphatase indicated a non-lysosomal structure; the ultrastructural features suggested a lipoid basis. At 24 h after treatment vascular ruptures and surface ectodermal ruptures were seen in the cranial mesoderm. These ruptures with extravascated blood were also seen at 48 h after treatment. A litter effect was also noted with respect to the tissue and cellular changes. These experiments suggest that the developing vascular system may be a target for lithium. In addition, the possibility is discussed that lithium induced cell death in the neuroepithelium may lead to neural tube defects.

A non-invasive photographic modification for recording early vascular development in the chick.

The chick embryo shell-less culture technique allows continuous observation and access to the developing vessels of the area vasculosa (AV); hence, its value as an angiogenesis assay system. The main drawback of the method is that adequately contrasted photographs cannot be achieved without injection of a contrast medium which kills the embryo making further observation of the same specimen impossible. Furthermore, injection prior to 72 h incubation has a high failure rate. In an attempt to overcome these problems, we explored the possibility of using a high-contrast photographic process. Embryos were explanted into shell-less culture after 48 h incubation and photographed through a stereo microscope. After trials with different films we found that Kodalith ortho Type 3 (Kodak) and Technical Pan film (Kodak) produced images of the vasculature which were identical in contrast and detail to India-ink-injected specimens photographed with conventional film. In addition, excellent images could be recorded as early as 48 h of incubation.