Pulling apart catalytically active Tn5 synaptic complexes using magnetic tweezers

The Tn5 transposase is an example of a class of proteins that move DNA sequences (transposons) via a process called transposition. DNA transposition is a widespread genetic mobility mechanism that has profoundly affected the genomes of nearly all organisms. We have used single-DNA micromanipulation experiments to study the process by which Tn5 DNA transposons are identified and processed by their transposase protein. We have determined that the energy barrier to disassemble catalytically active synaptic complexes is 16 kcal mol(-1). However, we have found that the looping organization of DNA segments by transposase is less sequence-driven than previously thought. Loops anchored at some non-transposon end sequences display a disassembly energy barrier of 14 kcal mol(-1), nearly as stable as the synapses formed at known transposon end sequences. However, these non-transposon end sequence independent complexes do not mediate DNA cleavage. Therefore, the sequence-sensitivity for DNA binding and looping by Tn5 transposase is significantly less than that required for DNA cleavage. These results have implications for the in vivo down regulation of transposition and the cis-transposition bias of transposase.     

The effects of acute corticosterone administration on anxiety, endogenous corticosterone, and c-Fos expression in the rat brain

The effects of acute pretreatment of rats with corticosterone (5 and 20 mg/kg, s.c.) on emotional behavior, expression of c-Fos protein in brain structures, and serum concentration of corticosterone were studied to model the short-term glucocorticoid-dependent changes in brain functions. Corticosterone was administered 90 min before training of a conditioned fear reaction (a freezing response), and behavioral, hormonal and immunocytochemical effects were examined 1 day later, on the test day. Pretreatment of rats with corticosterone significantly attenuated the freezing reaction in the conditioned fear test. The effect of the corticosterone was accompanied by a selective enhancement of the aversive context-induced c-Fos expression in some brain structures: the parvocellular and magnocellular neurons of the paraventricular hypothalamic nucleus (pPVN and mPVN), the medial amygdala nucleus (MeA), and the cingulate cortex, area 1 (Cg1), as well as an increase in the concentration of aversive context-induced endogenous serum glucocorticoid, 1.5 h and 10 min after the test session, respectively. It is suggested that the behavioral effects of acute pretreatment of rats with corticosterone could be due to changes in the mnemonic processes in the brain, inhibition of brain corticotropin releasing factor (CRF) synthesis, or stimulation of GABA-A receptor modulating neurosteroids synthesis. It is hypothesized that the enhanced activity of Cg1, MeA, pPVN, and mPVN, and the hypothalamic-pituitary-adrenal axis with concomitant increased serum glucocorticoid concentration, might serve to facilitate active coping behavior in a threatening situation.     

Renal clearance of absorbed intact GFP in the frog and rat intestine

Intestine absorption of intact green fluorescent protein (GFP) and its following accumulation in the renal proximal tubule cells after its intragastric administration have been established by confocal microscopy in the rat and frog. Reabsorbed GFP was revealed in the endosomes and lysosomes of the proximal tubule cells by the methods of GFP photooxidation and immunofluorescent microscopy. The GFP intestine absorption rate and GFP accumulation in the kidney were significantly higher in the frog than in the rat. No specific fluorescence was revealed in the liver and colon cells after the GFP intragastric administration. The data obtained indicate the ability of the small intestine in the frog and rat to absorb intact proteins and an important role of the kidney in exogenous protein metabolism.     

Do rats time filled and empty intervals of equal duration differently?

The goal was to determine whether rats time filled and empty intervals of equal duration differently. Each of five rats was trained for 50 sessions on an instrumental appetitive head entry procedure in which food was available (primed) every 120 s. On "empty" cycles, 30s prior to the next food prime, a 0.5-s pulse of white noise was presented. On "filled" cycles, 30s prior to the next food prime, white noise came on and stayed on until food was delivered. The two types of cycles were presented with equal probability. The results showed that the rats timed both the food-to-food interval and the stimulus-to-food interval. A comparison of the response gradients on filled and empty cycles following stimulus presentation showed better temporal discrimination on filled cycles. The results were modeled using a Packet theory of timing, with a linear averaging rule to combine the temporal information provided by the stimulus and food. The model fits to the individual response gradients were evaluated with a Turing test.     

Selenomethionine induces polyamine biosynthesis in regenerating rat liver tissue

Summary. Our study was undertaken to elucidate the effects of selenomethionine (SeMet) on polyamine metabolism in regenerating rat liver tissue, as useful model of rapidly growing normal tissue. We have examined the levels of spermine, spermidine and putrescine in liver tissue. At the same time we have evaluated the activities of polyamine oxidase (PAO) and diamine oxidase (DAO), the catabolic enzymes of polyamine metabolism. The obtained results suggest that polyamine levels in regenerating liver tissue, at 7^th day after two-thirds partial hepatectomy, were higher in comparison with control group. The administration of selenomethionine to hepatectomized animals during seven days, in a single daily dose of 2.5 μg/100 g body weight, increases the amount of spermine and spermidine; the level of putrescine does not change under the influence of SeMet in regenerating rat liver tissue. PAO activity is lower in regenerating hepatic tissue than in control group. Supplementation of hepatectomized animals with SeMet significantly decreases the activity of this enzyme. DAO activity was significantly higher in hepatectomized and in operated animals treated with SeMet compared to the sham-operated and control ones. The differential sensitivity observed in our model of highly proliferating normal tissue to SeMet, compared with the reported anticancer activity of this molecule is discussed.     

Anxiolytic effects of lavender oil inhalation on open-field behaviour in rats

To establish a valid animal model of the effects of olfactory stimuli on anxiety, a series of experiments was conducted using rats in an open-field test. Throughout, effects of lavender oil were compared with the effects of chlordiazepoxide (CDP), as a reference anxiolytic with well-known effects on open-field behaviour. Rats were exposed to lavender oil (0.1-1.0 ml) for 30 min (Experiment 1) or 1h (Experiment 2) prior to open-field test and in the open field or injected with CDP (10 mg/kg i.p.). CDP had predicted effects on behaviour, and the higher doses of lavender oil had some effects on behaviour similar to those of CDP. In Experiment 3, various combinations of pre-exposure times and amounts of lavender oil were used. With sufficient exposure time and quantity of lavender the same effects were obtained as in Experiment 2. Experiment 4 demonstrated that these behavioural effects of lavender could be obtained following pre-exposure, even if no oil was present in the open-field test. In Experiments 2-4, lavender oil increased immobility. Together, these experiments suggest that lavender oil does have anxiolytic effects in the open field, but that a sedative effect can also occur at the highest doses.     

Effect of grapeseed oil on diazinon-induced physiological and histopathological alterations in rats

The pollution of environment by toxic chemicals is a global and chronic problem. Human health risk due to exposure to chemical pollutants is constantly increasing. Pesticides form major toxic chemicals in environment. Scientifically, there is an obviously correlation between the exposure to pesticides and appearance of many diseases. Currently, the significance of natural products for health and medicine has been formidable. The present study investigated the effect of grapeseed oil in male rats exposed to diazinon. The experimental rats were divided into five groups. The rats of the first group were served as control. The experimental animals of the second group were exposed to diazinon (DZN). The animals of the third group were supplemented with grapeseed oil and treated with DZN. The rats of the fourth group were supplemented with grapeseed oil. The experimental rats of the fifth group were supplemented with corn oil. Hematobiochemical and histopathological evaluations were chosen as indicators of DZN toxicity and protective role of grapeseed oil. In rats exposed only to DZN, the levels of serum glucose, triglycerides, cholesterol, low density lipoprotein cholesterol, very low density lipoprotein cholesterol, creatinine, urea nitrogen, uric acid, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, creatine kinase and lactate dehydrogenase were statistically increased, while the level of serum total protein was significantly decreased. Moreover, the histopathological evaluations of the liver, kidney and testis showed that DZN causes several severe alterations. Pretreatment with grapeseed oil exhibited a protective role against DZN toxicity which confirmed by the inhibition of hematobiochemical and histopathological changes due to DZN exposure. Additionally, the present study suggests that the effect of grapeseed oil supplementation against DZN toxicity may be attributed to the antioxidant role of its constituents.     

Influence of olive and rosemary leaves extracts on chemically induced liver cirrhosis in male rats

The current study was undertaken to evaluate the protective activity of olive and rosemary leaves extracts on experimental liver cirrhosis induced by thioacetamide (TAA) in Wistar male rats. Highly significant decline in the values of body weight gain and highly statistically increase of liver/body weight ratio were noted in rats treated with TAA. Furthermore, the levels of serum alanine aminotransferase, aspartate aminotransferase, gamma glutamyl transferase, alkaline phosphatase and total bilirubin were statistically increased. Additionally, light microscopic examination of liver sections from rats treated with TAA showed a marked increase in the extracellular matrix collagen content and bridging fibrosis was prominent. There were bundles of collagen surrounding the lobules that resulted in large fibrous septa and distorted tissue architecture. Interestingly, the findings of this experimental study indicated that the extracts of olive and rosemary leaves and their combination possess hepatoprotective properties against TAA-induced hepatic cirrhosis by inhibiting the physiological and histopathological alterations. Moreover, these results suggest that the hepatoprotective effects of these extracts may be attributed to their antioxidant activities.     

Cyclin D1 regulates p27 stability in B cells

p27^Kip1 is a cyclin-dependent kinase inhibitor that plays a critical role in regulating G₁/S transition, and whose activity is, in part, regulated through interactions with D-type cyclins. We have generated the BD1-9 cell line, a BaF3 pro-B cells derivative in which cyclin D1 can be induced rapidly and reversibly by ponasterone A. The induction of cyclin D1 expression leads to a targeted p27^Kip1 accumulation in both cytoplasmic and nuclear compartments. But, only the p27^Kip1 form phosphorylated on serine 10 (pSer10-p27^Kip1) accumulates in BD1-9 cells. We found that the binding of cyclin D1 and pSer10-p27^Kip1 prevents p27^Kip1 degradation by the cytoplasmic Kip1 ubiquitylation-promoting complex (KPC) proteosomic pathway. Importantly, the nuclear CDK2 activity which is crucial for G₁/S transition is not altered by p27^Kip1 increase. Using siRNA techniques, we revealed that p27^Kip1 inhibition does not affect the distribution of BD1-9 cells in the different phases of the cell cycle. Our study demonstrates that aberrant cyclin D1 expression acts as a p27^Kip1 trap in B lymphocytes but does not induce p27^Kip1 relocation from the nucleus to the cytoplasm and does not modulate the G₁/S transition. Since our cellular model mimics what observed in aggressive lymphomas, our data bring new insights into the understanding of their physiopathology.     

微量失血对左肝外叶切除+ 定容失血性休克大鼠生存率的影响

目的:观察在大鼠左肝外叶切除+定容失血性休克模型制作过程中微量失血对最终大鼠生存率的影响。方法:45只SD大鼠按不同的放血比例分为三组,以Wigger改良法建立左肝外叶切除+定容失血性休克模型,严格标化放血前的各项手术操作和观测指标,比较三组大鼠最终生存率的差异。结果:在分别按2.4ml/100g(A组)、2.5ml/100g(B组)、2.6ml/100g(C组)比例定容失血的大鼠模型中,各组大鼠生存率分别为:A组66.67%,B组42.86%,C组7.69%,A、B两组与C组大鼠的生存率相比较存在明显差异(P<0.05)。结论:即使是0.1ml/100g的微量失血对于该模型大鼠的生存率也是有显著影响的,这一点在大鼠的定容失血性休克模型实验中是不应被忽视的。