Freeze fracture analysis of apical membranes in cochlear cultures: differences between basal and apicalcoil outer hair cells and effects of neomycin

Summary Previous studies have shown that exposure of cochlear cultures to the ototoxic aminoglycoside antibiotic neomycin leads to the rapid formation of numerous membrane filled protrusions on the apical surface of the hair cells but not on the surrounding supporting cells, and that hair cells in basal-coil cultures are more sensitive to these effects of neomycin than those in the distal end of apical-coil cultures. Freeze-fracture has been used to examine and compare the apical surfaces of hair cells and supporting cells in basal and apical-coil cultures in order to look for features that may explain the differential sensitivity of the various cell types to neomycin, and to characterize the membrane type that forms in response to neomycin and compare it with the normal apical membrane of the hair cell. The apical surface of the highly responsive basal-coil outer hair cells differs significantly from the apical surfaces of apical-coil outer hair cells and supporting cells in both regions of the cochlea in both surface area and the number and density of endocytotic vesicles associated with this surface. Basal-coil hair cells have an average of 120 ± 39 vesicles per cell surface and a density of 3.5 ± 0.89 vesicles per m², whereas apical-coil hair cells have 14.8 ± 15.8 vesicles/cell surface and density of 0.73 ± 0.72 vesicles per m². There are no significant differences in intramembrane particle (IMP) density on the apical surfaces of all the cell types examined, and qualitative observations of filipin-treated specimens indicate that cholesterol densities are also similar. The membrane that accumulates in response to neomycin treatment at the apical pole of the hair cell is IMP free, does not respond to filipin, and fractures in a manner that is indicative of a high content of unsaturated phospholipid in a fluid phase, and is therefore different in several respects from the normal apical surface of the hair cell. The results of this study suggest that apical surface associated endocytotic vesicle numbers may determine the differential sensitivity of apical and basal-coil hair cells to neomycin, and that neomycin may interfere with some aspect of phospholipid metabolism or membrane turnover in sensory hair cells.     

Preincubation of human granulosa cells with gonadotrophin prevents the cloprostenol-induced inhibition of progesterone production.

Human granulosa cells, from women undergoing ovum collection for in-vitro fertilization (IVF), will luteinize in vitro and provide a model for investigating the antigonadotrophic action of a prostaglandin F2 alpha (PGF2 alpha) analogue, cloprostenol, on granulosa-derived luteal cells. The granulosa cells were cultured in a defined medium and exposed to treatments during a preincubation period of 0 to 3 days and a final incubation with low density lipoprotein (LDL) from days 3 to 4. In the absence of human chorionic gonadotrophin (HCG), progesterone production was low, whereas exposure to HCG in the final incubation resulted in a 10-fold increase in progesterone concentrations. The inclusion of cloprostenol with HCG in the final incubation significantly (P less than 0.05) inhibited HCG-stimulated progesterone production. Exposure to HCG during the preincubation prevented the antigonadotrophic action of cloprostenol in the final incubation. The antigonadotrophic action of cloprostenol was retained when the granulosa cells were exposed to cloprostenol during the preincubation. Omission of LDL from the final incubation lowered the production of progesterone but the pattern of responses to HCG and cloprostenol were similar. Prevention of the antigonadotrophic action of cloprostenol after exposure to HCG may be a mechanism through which chorionic gonadotrophin can prevent regression of the corpus luteum in early pregnancy. Cloprostenol does not appear to inhibit LDL-stimulated steroidogenesis in human granulosa cells.     

An Indonesian experience

Having proven that one person can make a difference, a retired administrator writes about his volunteer efforts to start a medical group practice in Indonesia.     

Digitizing the moving face during dynamic displays of emotion

Humans typically decode facial signals during dynamic interactions in which the face moves. In this study, we digitized real time video signals in order to examine movement asymmetries across the face during emotional and nonemotional expressions. Forty dextral males were tested. For each expression, a 400 ms video segment was analyzed for changes in signal value (pixel intensity) over consecutive frames. The upper and lower face regions were examined separately due to differences in the cortical enervation of facial muscles in the upper (bilateral) vs lower face (contralateral). Results revealed distinctly different movement asymmetries over the lower and upper hemiface. In the upper face, more movement occurred over the right side for most facial expressions, regardless of emotionality. The latter finding questions the assumption that muscles of the upper face are symmetrical and/or bilaterally enervated in a symmetrical manner. In the lower face, negative expressions linked to fight-flight emotions (i.e. fear, anger) were associated with greater left sided movement, whereas happiness tended to be associated with more right sided movement. No consistent pattern of movement asymmetry occurred for nonemotional expressions. Although the valence-related movement asymmetries in the lower face are consistent with neuropsychological models of emotional expressivity, it remains unclear whether they reflect activation or inhibitory hemispheric mechanisms. Taken together, these data suggest that multiple factors may contribute to expressive movement asymmetries of the face.