Membrane differentiations at sites specialized for cell fusion

Fusion of plasma membranes between Chlamydomonas reinhardtii gametes has been studied by freeze-fracture electron microscopy of unfixed cells. The putative site of cell fusion developes during gametic differentiation and is recognized in thin sections of unmated gametes as a plaque of dense material subjacent to a sector of the anterior plasma membrane (Goodenough, U.W., and R.L. Weiss. 1975.J. Cell Biol. 67:623-637). The overlying membrane proves to be readily recognized in replicas of unmated gametes as a circular region roughly 500 nm in diameter which is relatively free of "regular" plasma membrane particles on both the P and E fracture faces. The morphology of this region is different for mating-type plus (mt+) and mt- gametes: the few particles present in the center of the mt+ region are distributed asymmetrically and restricted to the P face, while the few particles present in the center of the mt- region are distributed symmetrically in the E face. Each gamete type can be activated for cell fusion by presenting to it isolated flagella of opposite mt. The activated mt+ gamete generates large expanses of particle-cleared membrane as it forms a long fertilization tubule from the mating structure region. In the activated mt- gamete, the E face of the mating structure region is transformed into a central dome of densely clustered particles surrounded by a particle-cleared zone. When mt+ and mt- gametes are mixed together, flagellar agglutination triggeeeds to fuse with an activated mt- region. The fusion lip is seen to develop within the particle-dense central dome. We conclude that these mt- particles play an active role in membrane fusion.     

Cardiac function in total anomalous pulmonary venous return before and after surgery

Cardiac performance was evaluated in 12 infants with isolated total anomalous pulmonary venous return. Four had significant pulmonary venous obstruction and severe pulmonary hypertension (group A). Eight had no obvious venous obstruction, and the pulmonary pressures were lower (group B). In all subjects, right ventricular end-diastolic volume was increased (197% of predicted normal) and its ejection fraction was normal. Left ventricular volume was, generally speaking, still in the normal range (87% of predicted normal); however, its ejection fraction was reduced (0.57 vs normal of 0.73) and left ventricular output was low (3.08 L/min/m2 vs normal of 3.98). Left atrial volume was consistently small (53% of predicted normal) with an appendage of normal size. The infants in group A had smaller chamber volumes/m2 BSA than those in group B. Left atrial function was abnormal, characterized by reduced reservoir function and a greater role as "conduit" from right atrium to left ventricle. Left atrial size was not found to be critical in the surgical repair of TAPVR. Cardiac function is restored to normal following surgery.     

Upper bound risk estimates for mixtures of carcinogens

The excess cancer risk that might result from exposure to a mixture of chemical carcinogens usually is estimated with data from experiments conducted on individual chemicals. An upper bound on the total excess risk is estimated commonly by summing individual upper bound risk estimates. The degree to which this approach might overstate the true risk associated with the mixture has not been evaluated previously. This paper reports the results of a Monte Carlo simulation study on the degree of reduction in conservation that might be achieved using alternative methods for calculating mixture upper bounds. An unexpected finding is that for chemicals that exhibit strongly linear dose-response relationships, the summing of multistage-model-based upper bounds on excess risk can be anti-conservative, that is, it can provide less than the nominal 100(1-alpha)% coverage.     

Determinants of postnatal weight in infant rhesus monkeys: implications for the study of interindividual differences in neonatal growth

This paper provides an analysis of infant body weights obtained from a sample of 38 rhesus monkey infants (Macaca mulatta) aged 29-165 days, i.e., animals still nutritionally dependent on their mothers. We examine the data on neonatal weights in relation to a number of factors, most notably, the sex of the infants, and the age and adiposity of their mothers. The infant body weights represent cross-sectional rather than longitudinal data; because they were mostly free-ranging animals, the infants were weighted just once each. Nevertheless, the results of our analysis strongly suggest that early postnatal growth in free-ranging rhesus is dependent on both maternal fatness and age. They also suggest that, although male infants are generally heavier than like-aged female infants, they do not grow any faster during the early postnatal period. Here, we speculate that the associations between infant size and both maternal age and adiposity are the result of between-mother differences in lactational output.     

Effect of acute ethanol ingestion on prolactin in menopausal women using estradiol replacement

The current study was to answer the question: Is enough mercury absorbed from dental amalgam fillings to produce renal damage? One hundred healthy adults (18-44 years old) filled out health questionnaires and voided urine samples. Urine mercury concentration and N-acetyl-beta-glucosaminidase (NAG) were measured. Subjects were grouped into those having amalgam fillings (N = 66) and those without (N = 34). Median (95% Confidence Interval) urine mercury was 1 (1-2) and 0 (0-0.6) ng/ml (P < 0.01) and median urine NAG was 23 (18-27) and 16 (11-18) units (P < 0.05) in the two groups respectively. People with mercury amalgam fillings excreted slightly more mercury than people without them, and have a very small increase in urinary NAG excretion that is probably of no clinical significance. This dose of mercury absorbed from amalgam appears to be too little to be a public health hazard for renal injury.     

Shielding and radiation safety around a superconducting cyclotron neutron therapy facility

Prior to routine operation of the neutron therapy unit a radiation survey was performed in order to confirm the shielding design and to assure the safety of the personnel involved in the operation of the unit. The shielding requirements were calculated in accordance with NCRP Report No. 51. The contributions of the neutron and gamma dose equivalents have been measured separately outside the treatment room. The exposure outside the shield is negligible. In general, the measured values were lower than those derived from the shielding calculations. The highest total dose equivalents were registered at locations corresponding to the highest calculated values.     

A microcholangiographic study of liver disease models in rats

RATIONALE AND OBJECTIVES: Rats develop hepatobiliary injury due to small bowel bacterial overgrowth (SBBO) that, at specimen, resembles cholangiography sclerosing cholangitis. To better visualize the smaller bile ducts, we used microcholangiography to determine the spectrum of biliary lesions in this and five other models of liver disease. METHODS: The models studied were as follows: (1) Surgically created jejunal, self-filling blind loops induce SBBO. (2) Intraperitoneal injection of a bacterial cell wall polymer, peptidoglycan-polysaccharide (PG-PS), causes granulomatous hepatitis. (3) Intraperitoneal injection of endotoxin (lipopolysaccharide) causes sinusoidal congestion and shock. (4) Bile duct ligation induces bile duct proliferation. (5) Alpha-naphthyl-isothiocyanate (ANIT) induces bile duct proliferation. (6) Carbon tetrachloride (CCl4) causes fibrosis and cirrhosis. Warmed barium sulfate, gelatin, and saline were injected in the extrahepatic bile duct. Liver slices (2 mm) underwent microradiographic techniques, and images were correlated with histology. RESULTS: Rats with SBBO had irregular and dilated extrahepatic bile ducts with thickened walls. Rats treated with endotoxin and CCl4 had normal microcholangiograms. Bile duct proliferation was identified following ANIT and bile duct ligation. Rats given PG-PS demonstrated irregular intrahepatic bile ducts. Microcholangiograms following SBBO and PG-PS showed similarities including focal ductal dilatation, narrowing, proliferation, and destruction. CONCLUSION: Various models of liver injury induce characteristic cholangiographic appearances. Microcholangiography is useful in examining biliary tract lesions and complements histology.