Mitochondrial Activity, Distribution and Segregation in Bovine Oocytes and in Embryos Produced in Vitro

Contents Bovine oocytes and embryos produced in vitro were studied to determine the mitochondrial pattern of distribution, segregation and activity using DIOC 6 and Jc-1 fluorescence. The highest fluorescence level observed in mature oocytes was taken as 100% activity and six activity levels were estimated as follows: (1) 0%, (2) 1-15%, (3) 16-30%, (4) 31-50%, (5) 51-75% and (6) 76-100%. Three patterns of mitochondrial distribution were found: (1) diffused throughout the cytoplasm in oocytes and embryos, (2) pericytoplasmic in oocytes and embryos, and (3) perinuclear only in embryos. The segregation of mitochondria in blastomeres showed two distinct patterns: (1) symmetrical with an even mitochondrial population, and (2) asymmetrical with different numbers of mitochondria in each blastomere. In immature oocytes, mitochondrial activity was very low and the distribution was diffuse or negligible, while in mature oocytes the activity was high and the distribution was diffuse or pericytoplasmic. Competent embryos up to the 16-cell stage showed intermediate levels of activity (16-50%) but activity decreased thereafter up to the blastocyst stage. Non-competent embryos showed low levels of activity (1-15%) at all stages. These results suggest that mitochondria might play an important role during early development and that a minimum threshold of activity regulates the potential competence for reaching the blastocyst stage.     

Assessment of the potential of dogs and cats as urban reservoirs of Ross River and Barmah Forest viruses

Objective To determine whether dogs and cats are potential reservoirs of Ross River (RR) and Barmah Forest (BF) viruses
Method Young seronegative female dogs and cats were experimentally exposed to the viruses using Ochlerotatus vigilax (Skuse) mosquitoes.
Results Only one of the 10 dogs and one of the 10 cats exposed to RR developed neutralising antibody. None of the animals developed detectable viraemia or clinical signs. One dog and three cats exposed to BF developed neutralising antibody. In addition, a serological survey of sera obtained from domestic dogs and cats residing in the Brisbane region indicated that 23.7% and 1.3% of dogs, and 14% and 2% of cats, had neutralising antibodies to RR and BF respectively.
Conclusions Although dogs and cats are exposed naturally to these viruses, and can become infected, they are unlikely to be important urban reservoirs of either virus.     

Giant Piezoelectric Effect in Strontium Titanate at Cryogenic Temperatures

Piezoelectric materials have many applications at cryogenic temperatures. However, the piezoelectric response below 10 kelvin is diminished, making the use of these materials somewhat marginal. Results are presented on strontium titanate (SrTiO3), which exhibits a rapidly increasing piezoelectric response with decreasing temperature below 50 kelvin; the magnitude of its response around 1 kelvin is comparable to that of the best materials at room temperature. This "giant" piezoelectric response may open the way for a broad class of applications including use in ultralow-temperature scanning microscopies and in a magnetic field-insensitive thermometer. These observations, and the possible divergence of the mechanical response to electric fields at even lower temperatures, may arise from an apparent quantum critical point at absolute zero.     

泸州荔枝果园AM真菌菌根及孢子数量调查与分析

[目的]对泸州荔枝园AM真菌进行调查,确认荔枝菌根类型,了解果园土壤中AM真菌孢子种群数量的大致情况。[方法]利用"湿筛法"和Phllips&Hayman的方法对3个泸州荔枝果园春季的土壤AM真菌进行了调查分析。[结果]荔枝菌根是内生菌根,共生真菌为囊泡——丛枝菌根真菌,即AM真菌。春季的菌根感染率在9%~32%之间,普遍低于25%。VA菌根感染率的平均值在15%~21%之间,低于25%。三个荔枝园每25 g土样中AM真菌孢子数平均值为869±76个。[结论]果园生草或对果园进行有机覆盖,是促进荔枝生长,增加荔枝果实产量,改善荔枝果实品质的一种绿色环保途径。     

Last occurrence and survival during winter of the arbovirus vector Culicoides brevitarsis at the southern limits of its distribution

SUMMARY: Linear regression analysis was used to describe the decline in numbers of Culicoides brevitarsis Kieffer into winter with monthly maximum, average and minimum temperatures at the southern limits to its distribution in New South Wales. From this, low temperature thresholds were derived when C brevitarsis would be absent from the field. The low minimum threshold ± 2 SE (95% Confidence Interval) of 8.1 ± 0.3°C was used with historical temperature data to estimate the last month that the species should occur (March to June) and the mean number of months (2 to 6.5) below the threshold at 17 selected sites. Probability for survival during winter at these sites was estimated from years when the number of consecutive months below the threshold was ≤ 2 months. This varied from zero to 51% depending on the location of the site. Last occurrence was 0.7 months later on average and absolute probabilities for survival ranged from zero to 100% when the temperatures were increased by an arbitrary 2°C.