抑菌生亚急性毒性实验研究

本项研究的目的：是在一系列毒性试验的基础上进一步观察大鼠皮下给予由枯草芽孢杆菌ＢＳ２２４菌株制成的抑菌生后,对机体产生毒性反应的情况。结果表明：给药组大鼠饮食、活动正常。各项检测指标及病理组织学检查未发现异常,与对照组比较均无差异（Ｐ＞０．０５）,说明抑菌生无毒性反应。     

DNA damage and repair in somatic and germ cells in vivo

Alkylation-induced germ cell mutagenesis in the mouse versus Drosophila is compared based on data from forward mutation assays (specific-locus tests in the mouse and in Drosophila and multiple-locus assays in the latter species) but not including assays for structural chromosome aberrations. To facilitate comparisons between mouse and Drosophila, forward mutation test results have been grouped into three categories. Representatives of the first category are MMS (methyl methanesulfonate) and EO (ethylene oxide), alkylating agents with a high s value which predominantly react with ring nitrogens in DNA. ENU (N-ethyl-N-nitrosourea), MNU (N-methyl-N-nitrosourea), PRC (procarbazine), DEN (N-nitrosodiethylamine), and DMN (N-nitrosodimethylamine) belong to the second category. These agents have in common a considerable ability for modification at oxygens in DNA. Cross-linking agents (melphalan, chlorambucil, hexamethylphosphoramide) from the third category.The most unexpected, but encouraging outcome of this study is the identification of common features for three vastly different experimental indicators of genotoxicity: hereditary damage in Drosophila males, genetic damage in male mice, and tumors (TD₅₀ estimates) in rodents. Based on the above three category classification scheme the following tentative conclusions are drawn. Monofunctional agents belonging to category 1, typified by MMS and EO, display genotoxic effects in male germ cell stages that have passed meiotic division. This phenomenon seems to be the consequence of a repair deficiency during spermiogenesis for a period of 3–4 days in Drosophila and 14 days in the mouse. We suggest that the reason for the high resistance of premeiotic stages, and the generally high TD₅₀ estimates observed for this class in rodents, is the efficient error-free repair of N-alkylation damage. If we accept this hypothesis, then the increased carcinogenic potential in rodents, seen when comparing category 2 (ENU-type mutagens) to category 1 (MMS-type mutagens), along with the ability of category 2 genotoxins to induce genetic damage in premeiotic stages, must presumably be due to their enhanced ability for alkylations at oxygens in DNA; it is this property that actually distinguishes the two groups from each other. In contrast to category 1, examination of class 2 genotoxins (ENU and DEN) in premeiotic cells of Drosophila gave no indication for a significant role of germinal selection, and also removal by DNA repair was less dramatic compared to MMS. Thus category 2 mutagens are expected to display activity in a wide range of both post- and premeiotic germ cell stages. A number of these agents have been demonstrated to be among the most potent carcinogens in rodents. In terms of both hereditary damage and the initiation of cancers (low TD₅₀), cross-linking agents (category 3) comprise a considerable genotoxic hazard. Doubling doses for the mouse SLT have been determined for four cross-linking agents not requiring metabolic conversion and in all four cases the doubling doses for these agents were lower than those for MMS, DES and EMS. In support of this conclusion, two of 10 genotoxic agents, for which data on chromosomal aberrations were available for both somatic cells and germ cells in mice, were cross-linking agents and again the doubling dose estimates are lower than for monofunctional agents. Four cross-linking agents induced mutations in stem cell spermatogonia indicating that this type of agent can be active in a wide range of germ cell stages.Quite in contrast to what is generally observed in unicellular systems and in mammalian cells in culture, both cross-linking agents and MMS-type mutagens (high s value) predominantly produce deletion mutations in postmeiotic male germ cell stages. This is the uniform picture found for both Drosophila and the mouse. It is concluded that in vitro systems, in contrast to Drosophila germ cells, fail to predict this very intriguing feature of mouse germ line mutagenesis. In addition to their potential for induction of deletions and other rearrangements, cross-linking agents are among the most efficient inducers of mitotic recombination in Drosophila. Thus there are several mechanisms by which cross-linking agents may cause loss of heterozygosity for long stretches of DNA sequences, leading to expression of recessive genes. Since a substantial portion of agents used in the chemotherapy of cancers have cross-linking potential, the potential hazards of hereditary damage and cancers associated with this class of genotoxins should, in our opinion, receive more attention than they have in the past.     

Molecular clocks and the incompleteness of the fossil record

Molecular clocks can be evaluated by comparing absolute rates of evolution and by performing relative-rate tests. Typically, calculations of absolute rates are based on earliest observed occurrences in the fossil record. Relative-rate tests, on the other hand, merely require an unambiguous outgroup. A major disadvantage of relative-rate tests is their insensitivity to concomitant and equal rate changes in all lineages. Apparent differences in absolute rates, in turn, may be artifacts that are attributable to an incomplete fossil record.Recently developed methods in quantitative biostratigraphy recognize the incompleteness of the fossil record and allow us to place confidence intervals on the endpoints of taxon ranges. These methods are applicable to taxa whose fossil records are of markedly different quality. When we extend these methods and integrate molecular and paleontologic data, we can test the null hypothesis that seemingly disparate rates of molecular evolution are in fact equal under the simplifying assumption that fossils are randomly and independently distributed over their temporal ranges and that fossils can be accurately placed in a phylogenetic context. We can also estimate the range of ticking rates, if any, that are compatible with known fossil data. Ultimately, more accurate rate estimates for widely divergent taxa should allow for more meaningful comparisons of evolutionary rates.DNA hybridization data for monotremes and marsupials suggest a 17-fold difference for 14 different rate calculations with a mean value of approximately 1% divergence per million years. Variation among marsupials is sevenfold. However, when we apply appropriate statistical tests and make additional allowances for fossils of uncertain taxonomic assignment, etc., all 14 rates are compatible with a molecular clock ticking at approximately 0.4% divergence per million years. In addition, this analysis brings relative- and absolute-rate tests into accord.     

Swim Stress Increases the Potency of Glycine at the N-Methyl-d-Aspartate Receptor Complex

Abstract: We have previously demonstrated that chronic administration of antidepressants results in a reduction in the potency of glycine to displace 5,7-[³H]dichlorokynurenic acid (5,7-[³H]-DCKA) from the strychnine-insensitive glycine recognition site of the NMDA receptor complex. We now report that exposure of rats to the forced swim test results in a 56% increase in the potency of glycine to displace 5,7-[³H]DCKA from frontal cortical homogenates. These data are consistent with the hypothesis that the forced swim test, a preclinical screen sensitive to acute administration of antidepressant drugs and NMDA receptor antagonists, also results in adaptation of the NMDA receptor complex. Moreover, these data lend further support to the hypothesis that glutamatergic pathways are involved in the neurobiological response to stress and, potentially, in the pathophysiology of depression.     

Testing for heterogeneity among phenotypic correlations: a comparison of methods using Monte Carlo simulations

Heterogeneous phenotypic correlations may be suggestive of underlying changes in genetic covariance among life-history, morphology, and behavioural traits, and their detection is therefore relevant to many biological studies. Two new statistical tests are proposed and their performances compared with existing methods. Of all tests considered, the existing approximate test of homogeneity of product-moment correlations provides the greatest power to detect heterogeneous correlations, when based on Hotelling's z*-transformation. The use of this transformation and test is recommended under conditions of bivariate normality. A new distribution-free randomisation test of homogeneity of Spearman's rank correlations is described and recommended for use when the bivariate samples are taken from populations with non-normal or unknown distributions. An alternative randomisation test of homogeneity of product-moment correlations is shown to be a useful compromise between the approximate tests and the randomisation tests on Spearman's rank correlations: it is not as sensitive to departures from normality as the approximate tests, but has greater power than the rank correlation test. An example is provided that shows how choice of test will have a considerable influence on the conclusions of a particular study. This revised version was published online in July 2006 with corrections to the Cover Date.     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

A specific microassay for evaluating hepatic LDH activity in co-cultures of hepatocytes with other cells

This study describes the development of a simple, rapid and reproducible microassay for determining the intracellular LDH activity of rat hepatocytes present in a co-culture system with other cells. The procedure involves treatment of cellular homogenates with an anti-LDH antiserum that specifically inhibits the LDH activity of rat hepatocytes. The assay is performed in 96-well plates and LDH activity can be measured directly in the same wells using a colorimetric method. The difference in LDH activity values measured before and after antiserum incubation reflects the LDH content of the hepatocytes in the sample. The advantages of this method are the small number of cells required, a reduction in sample handling and the possibility of differentiating LDH activity in hepatic and non-hepatic cells. The possible applications of this technique as a parameter for biochemical data and as a test for cytotoxicity studies in co-cultures are also discussed.     

Shoot regeneration after fire or freezing temperatures and its relation to plant life-form for some heathland species

Shoot regeneration after prescribed burning or following the freezing temperatures of winter was monitored for nineteen heathland species present in an Arctostaphyleto-Callunetum community in northeast Scotland. Species whose renewal buds were near the surface of the ground started to grow earlier in the spring than species with renewal buds above the surface, but grouping species according to the position of their renewal bud (i.e. their life-form) did not account for all of the interspecific variation apparent. In the case of shoot regeneration after fire, species whose renewal buds were destroyed by fire because they were above-ground started to regenerate about the same time as species with belowground buds, protected from fire, but reached their maximum frequency of occurrence later. Grouping species by life-form was of limited value as a means of interpreting this interspecific variation in the timing of shoot regeneration after fire. It would be unwise to use plant life-form as the sole basis for interpreting or predicting a species' response to temperature stress when extreme temperatures occur regularly, as they do in heathland. The possible use of other plant traits to interpret and predict interspecific variation in the regeneration rate of heathland plants is discussed.Nomenclature follows Tutin et al. (1964–1980) for vascular plants. Acknowledgements. The Nature Conservancy Council and Mr J. J. Humphries kindly allowed Dinnet Moor to be used for the work presented here. One of us (RJR) received financial support for field work from the Natural Sciences and Engineering Research Council of Canada.