Some factors affecting the PTA staining of synaptic junctions

Summary An analysis has been made of the staining properties of phosphotungstic acid (PTA) on non-osmicated, glutaraldehyde fixed brain tissue, with regard to differences arising from the commercial source of the PTA, its water content, methanol as opposed to ethanol dehydration, and perfusion as contrasted with immersion fixation. The quality of the micrographs varied depending on the source of the PTA, the principal component of the synaptic junctions to be affected being the cleft material. Variation in the water content of the PTA solution was also reflected in the appearance of the cleft material, tissues stained with high hydration PTA resulting in cleft material with considerably less electronopacity than the corresponding dense projections and postsynaptic thickening. Low hydration PTA produced the typical picture of cleft densities. Methanol dehydration was unsuccessful in this series of experiments, while immersion and perfusion fixation yielded comparable results.Synaptic junctions from cerebral cortex, cerebellar cortex, thalamus, hippocampus and spinal cord of the rat were examined. In addition to the typical paramembranous densities, subjunctional bodies are present in cerebellar and hippocampal junctions, and subsynaptic profiles in some spinal cord ones. The spinal cord junctions are characterized by a prominent synaptic plate and by a postsynaptic thickening which in places appears to be separated from the underlying postsynaptic membrane.This work was supported in part by a grant from the Australian Research Grants Committee. I would like to thank Mr. R.F. Brearley for his excellent technical assistance, and Mr. D. Stuart and Mrs. Z. Gobby for their help with the photography.     

Some factors affecting the catching power of unbaited fish traps†

Perch Perca fluviatilis L. newly introduced into waters were markedly vulnerable to traps for up to four or five days. Thereafter catches tended to be positively correlated with water temperature up to about 10.5°C and negatively correlated at higher temperatures. The catching power of traps is low; at a density of one per 354 m2 water surface, traps caught from 0.9 to 6.8 % and 0.3 to 1.4% of a perch and roach Rutilus rutilus (L.) population per day. Perch did not become ‘trap-shy’ and fin clipping did not affect their vulnerability. Applications of 0.1 to 0.5 ppm copper sulphate resulted in up to an 11-fold increase in catches.     

Extremely short lifespan in the annual fish Nothobranchius furzeri

Evolutionary theories of senescence postulate that lifespan is determined by the age-dependent decrease in the effects of natural selection. Factors that influence survival and reproduction at early life stages have a larger impact on fitness than factors that influence later life stages. According to these views, selection for rapid sexual maturation and a steep age-dependent decrease in fitness drive the evolution of short lifespans. Here, we report on the survival trajectory of Nothobranchius furzeri (Pisces: Ciprinodontidae): a member of a group of annual species found in temporary bodies of water whose life expectancy in the wild is limited to a few months. We find that maximum survival of N. furzeri in the laboratory is less than 12 weeks. The temporal trajectory of survival shows an age-dependent increase in the mortality rate that is typical of organisms with defined lifespans. The lifespan of N. furzeri is exceptionally short for a vertebrate: owing to its small size and the possibility of propagation in captivity, N. furzeri could be used as a convenient model for ageing research.     

Some factors affecting pulmonary oxygen transport

Equations governing oxygen transport from alveolar gas to red blood cells flowing through pulmonary capillaries are written down. Some analytical predictions are made on factors affecting the rate at which this process takes place. Numerical simulations are carried out to investigate the effect of red blood cell shape, capillary dimensions, haematocrit and choice of oxygen dissociation curve on pulmonary oxygen transport. These factors all have an effect on pulmonary transport, with the effect being much more marked for simulations with low oxygen levels, typical of those seen in some subjects with respiratory disease.     

Systematic analysis of intrinsic factors affecting differential display

Differential display (DD) is a widely used method for identifying differentially expressed genes. To improve further the efficiency and reproducibility of the method, this report systematically examines four critical parameters of standard DD-PCR. Specifically, the study determined the optimal annealing temperature, elongation time, dNTP concentration, and arbitrary primer concentration. By using a thermal cycler that was capable of displaying a temperature gradient across a PCR plate, it was possible to determine (in a single experiment) the effect of different annealing temperatures. The optimal annealing temperaturefor a 13-mer arbitrary primer fell within a broad range of 40 degrees C-50 degrees C. Elongation times over a range of 30-120 s worked best. The optimal concentration for dNTPs was within a very broad range of 2-50 microM, with higher amounts allowing for greater pipetting accuracy. The most favorable concentration for the arbitrary primer was also within a broad range of 0.1-2.0 microM. A primer concentration below this range greatly reduced the efficiency of the amplification process. In conclusion, the experimental findings delineated the best possible DD conditions for a more reliable assessment of differential gene expression.     

Some factors affecting the mineralization of organic sulphur in soils

Summary Factors affecting the release of sulphate from a number of eastern Australian soils were studied.All of the soils released sulphate when dried. The amounts released were influenced by the manner in which the soil was dried. Air-drying in the laboratory at 20°C released least sulphate.Sulphate was mineralized in all soils by incubation at 30°C but the amounts mineralized could not be related to soil type or any single soil property. The ratio of nitrogen mineralized: sulphur mineralized varied widely between soils and was generally appreciably greater than the ratio of total nitrogen: organic sulphur in the soils.A rapid flush of mineralization of both sulphur and nitrogen took place when some of the soils were rewetted and incubated after they had been dried in the laboratory and stored for 4 to 5 months. Following this, the rate of mineralization was similar to that in the original undried soil. During this flush, the enhancement of sulphur mineralization was relatively greater than that of nitrogen so that the ratio of nitrogen mineralized: sulphur mineralized was considerably smaller than that during later phases of the incubation or that of the original moist soil. Soils collected after they had remained dry in the field for a similar period of time did not show this type of mineralization although they had initially done so when collected moist and air-dried in the laboratory.The effects of temperature, soil moisture, toluene and formaldehyde, and the addition of calcium carbonate to soils on the mineralization of sulphur were similar to their effects on the mineralization of nitrogen.     

Some factors affecting the chloroplast replication in the mossPlagiomnium trichomanes

Summary Some factors affecting the chloroplast replication were studied using the leaf cells of the mossPlagiomnium trichomanes. There was a significant positive correlation between chloroplast number per cell and cell volume in leaves of any developmental stage. However, when the detached leaves were cultured on nutrient agar, it was observed that the chloroplast replication occurred without cell enlargement regardless of the developmental stage of leaves. This implies that cell enlargement is not an essential factor for the chloroplast replication, but one of the environmental factors affecting it. Light is essential for the chloroplast replication which response to the light intensity. In the dark, there was little increase in chloroplast number per cell. With a light intensity of 50 lux, the increase rate of chloroplast number per cell was about half of that with 3,000 lux. Day length also affected significantly the chloroplast replication.     

Analysis of regenerating hepatic cell replication in vivo by differential chromatid staining

Abstract. The cell cycle of mouse hepatic cells was examined in vivo following partial hepatectomy, by differential chromatid staining in the presence of non-inhibitory concentrations of bromodeoxyuridine (BrdU). Using this technique, distribution curves were obtained for the appearance of metaphase cells in successive generations, and mean cell cycle time (11 hr) was determined. Cell cycle times derived with this technique are several-fold faster than previous reports of regenerating liver which used radionucleotide labelling.     

Analysis of regenerating hepatic cell replication in vivo by differential chromatid staining

The cell cycle of mouse hepatic cells was examined in vivo following partial hepatectomy, by differential chromatid staining in the presence of non-inhibitory concentrations of bromodeoxyuridine (BrdU). Using this technique, distribution curves were obtained for the appearance of metaphase cells in successive generations, and mean cell cycle time (11 hr) was determined. Cell cycle times derived with this technique are several-fold faster than previous reports of regenerating liver which used radionucleotide labelling.