Microapplicator and micropipette for inoculation of the embryonated chicken egg.

Aflatoxin G2 was used to test the speed and accuracy of the microapplicator and the micropipette. The 50% lethal dose of both assay systems was approximately the same, and 4.0 mug of G2 had an 85% lethal effect in both systems. The 50% lethal dose of the microapplicator and the micropipette was lower than that of the syringe but, of these, only the micropipette can combine the accuracy of the microapplicator and the speed of the syringe.     

An Apparatus for Measuring Volumes of Small Objects

An apparatus for measuring volumes of small objects such as tissue blocks is described. The apparatus measures volumes by fluid displacement and consists of a micropipette adapted to fit the mouth of an Erleiuneyer flask, a Luer adaptor fused to the side of the flask, and a glass syringe. When assembled with fluid enclosed, the fluid rises to a low level in the micropipette. Withdrawal of fluid into the syringe lowers the fluid level below the mouth of the flask. The micropipette is raised, the object to be measured is placed in the flask, and the micropipette is joined to the flask again. Fluid returned to the flask from the syringe rises to a higher level in the micropipette. The difference between the two fluid levels equals the volume of the object measured.

This apparatus gives reproducible measurements and can be calibrated for absolute volume determination. It is inexpensive to construct and easy to use.     

A Technique for Obtaining Replicas of Small Tubular Systems by Microinjection of Vinyl Acetate

A microtechnique has been devised for replicating tubular systems of small organisms. In this case, the reproductive system of a small marine snail was replicated by inserting a micropipette through the gonopore and filling the genital ducts with vinyl acetate from a flow-controlled syringe. Subsequently the tissue was dissolved and the model was photographed. The technique could be adapted to a variety of different systems, particularly small invertebrates such as insects, annelids and molluscs.     

A technique for obtaining replicas of small tubular systems by microinjection of vinyl acetate

A microtechnique has been devised for replicating tubular systems of small organisms. In this case, the reproductive system of a small marine snail was replicated by inserting a micropipette through the gonopore and filling the genital ducts with vinyl acetate from a flow-controlled syringe. Subsequently the tissue was dissolved and the model was photographed. The technique could be adapted to a variety of different systems, particularly small invertebrates such as insects, annelids and molluscs.     

Toxicity of Bacillus thuringiensis subsp. israelensis to adult Aedes aegypti mosquitoes

Adult female Aedes aegypti mosquitoes were killed by the parasporal crystals of Bacillus thuringiensis subsp. israelensis (ONR-60A) when the crystals were introduced into the insect midgut as an enema. The 50% lethal dose for intact parasporal crystals was 0.21 microgram/mg of mosquito (wet weight), and for solubilized crystals the 50% lethal dose was 0.04 microgram/mg. These values were compared with 50% lethal concentrations in a free-feeding larval mosquito bioassay of 0.018 and 1.28 microgram/ml for intact and solubilized crystals, respectively. Preparations from B. thuringiensis subsp. kurstaki were ineffective against both adult and larval mosquitoes. An adult mosquito bioassay is suggested as a direct means of screening potential mosquito control agents.     

Toxicity of Bacillus thuringiensis subsp. israelensis to adult Aedes aegypti mosquitoes.

Adult female Aedes aegypti mosquitoes were killed by the parasporal crystals of Bacillus thuringiensis subsp. israelensis (ONR-60A) when the crystals were introduced into the insect midgut as an enema. The 50% lethal dose for intact parasporal crystals was 0.21 microgram/mg of mosquito (wet weight), and for solubilized crystals the 50% lethal dose was 0.04 microgram/mg. These values were compared with 50% lethal concentrations in a free-feeding larval mosquito bioassay of 0.018 and 1.28 microgram/ml for intact and solubilized crystals, respectively. Preparations from B. thuringiensis subsp. kurstaki were ineffective against both adult and larval mosquitoes. An adult mosquito bioassay is suggested as a direct means of screening potential mosquito control agents.     

乙醇对中华眼镜蛇毒毒性的影响

目的为了探索乙醇对眼镜蛇毒毒性的影响。方法将眼镜蛇毒不同浓度致死量经不同浓度乙醇体外处理后,分别于小白鼠皮下注射、口服,将致死量蛇毒皮下注射后的小白鼠立即于局部注射乙醇,观察蛇毒毒性情况。结果小白鼠经皮下注射致死量眼镜蛇毒后,在局部注射50％（或异蛇米酒）、75％乙醇0．1～0．2ml有一定的保护作用;口服100倍皮下注射致死量眼镜蛇毒未发现有毒性表现,口服经50％乙醇处理后的眼镜蛇毒（100倍皮下注射致死量）未增加小鼠死亡率。结论眼镜蛇毒体外经过乙醇处理后毒性有所下降。口服少量的眼镜蛇毒是安全的。眼镜蛇毒与乙醇混合后口服未见蛇毒毒性增加。     

Radiation factors and their influence on induction of oxygen resistance

Shortly after gamma irradiation, flour beetles exhibited a decline in resistance to oxygen toxicity. Then, about 2 weeks after irradiation, the 50% lethal dose (LD50) exposure time in pure oxygen was much greater than that of nonirradiated beetles, and this enhanced resistance persisted for about 6 months. The magnitude of the enhancement was a function of dose, decreased with increasing age at irradiation, and was modified by radiation factors. Both dose protraction and dose fractionation reduced the development of oxygen resistance to approximately the same degree that it reduced acute radiation lethality. This suggests that both the initial sensitization and the later enhancement of resistance are correlated with the residual biological damage rather than with the physical dose or initial damage.     

Herpes simplex virus type 2 UL24 gene is a virulence determinant in murine and guinea pig disease models

A herpes simplex virus type 2 (HSV-2) UL24 beta-glucuronidase (UL24-betagluc) insertion mutant was derived from HSV-2 strain 186 via standard marker transfer techniques. Cell monolayers infected with UL24-betagluc yielded cytopathic effect with syncytium formation. UL24-betagluc replicated to wild-type viral titers in three different cell lines. UL24-betagluc was not virulent after intravaginal inoculation of BALB/c mice in that all inoculated animals survived doses up to 400 times the 50% lethal dose (LD50) of the parental virus. Furthermore, few UL24-betagluc-inoculated mice developed any vaginal lesions. Intravaginal inoculation of guinea pigs with UL24-betagluc at a dose equivalent to the LD50 of parental virus (approximately 5 x 10(3) PFU) was not lethal (10/10 animals survived). Although genital lesions developed in some UL24-betagluc-inoculated guinea pigs, both the overall number of lesions and the severity of disease were far less than that observed for animals infected with parental strain 186.     

Virulence of cloned variants of Autographa californica nuclear polyhedrosis virus.

The relative virulence of five different genotypic variants of Autographa californica nuclear polyhedrosis virus was tested by determining the 50% lethal dose of occluded virus for larvae of Trichoplusia ni. The 50% lethal dose values of uncloned virus and the five cloned genotypic variants ranged between 10 and 21 polyhedra per larva, and no statistically significant differences were observed. Cloning has therefore neither enhanced nor decreased the virulence of this potential microbial pesticide.     

Acute toxicity of bisphenol A in rats

Bisphenol A (BPA), an estrogenic compound, is used in manufacturing plastics and is known to produce toxic effects on various systems in man and animals. Since the use of plastics in day-to-day life is increasing, exposure to BPA will also increase. Therefore, this study was undertaken to determine the median lethal dose (LD50) of BPA via intraperitoneal and intravenous route in adult rats (by Dixon's up and down method) and also to know the acute systemic changes (in blood pressure, respiration and ECG) produced by lethal dose of BPA. Adult female albino rats of Charles Foster strain were used in the study. LD50 of BPA was 841 and 35.26 mg/kg body weight for ip and iv route, respectively. Injection of lethal dose of BPA (40 mg/kg body weight) produced acute toxicity manifesting as immediate respiratory arrest and hypotension after the injection of BPA followed by bradycardia. The animals died within 7.3 +/- 0.7 min. Volume of ethanol (vehicle; 0.1 mL) present in the lethal dose of BPA was not lethal and had no effect on respiration, blood pressure and heart rate. The results provide evidence that the acute exposure to BPA produces lethality with a very narrow range of lethal and survival dose for iv route. Further, the lethality appears to be due to respiratory arrest and hypotension.     

Antiidiotype modulation of herpes simplex virus infection leading to increased pathogenicity.

Antiidiotype reagents that recognize idiotypic determinants associated with the combining site of monoclonal antibodies to herpes simplex virus type 2 ( HSV2 ) were used to manipulate the immune response to HSV2 in BALB/c mice. The injection of antiidiotype antibodies into mice before challenge with a 50% lethal dose of HSV2 resulted in a shorter survival time than that of mice receiving either preimmune rabbit immunoglobulin G or antiidiotype reagents against hepatitis B surface antigen before HSV2 challenge. These findings indicate that the immune response to HSV2 in mice can be modulated through idiotype- antiidiotype networks, thereby increasing the pathogenicity of HSV2 infections.     

A sample injection device for flow cytometers

BACKGROUND: The sample injection systems of flow cytometers employ either a pressure differential between the sample vial and the sheath fluid reservoir or volumetric injection of the sample from a syringe. The pressure differential method facilitates rapid and efficient flushing to eliminate carryover between samples, but does not allow accurate determination of the rate of sample flow and cell concentration. Volumetric injection, which comprises a valve for switching the sample flow, facilitates highly accurate measurement of the cell concentration, but requires a less efficient and more time-consuming flushing procedure. METHODS: Applying a removable syringe, which connects to the inlet of the sample tubing via a tight sealing, we eliminate the valve and obtain efficient flushing while maintaining the advantage of volumetric sample injection. RESULTS: This device gives highly constant sample flow rates strictly proportional to syringe velocity over the range 0.2-50 microl/min with a settling time of about 2 sec. CONCLUSION: This device has the same precision as the conventional sample injection system, whereas the speed and efficiency of flushing are improved greatly.     

Studies on a murine model for evaluation of virulence of Streptococcus suis capsular type 2 isolates

Five different parameters, time of incubation of the culture, type of culture medium, inoculum, strain of inbred mice, and age of mice, were tested using the LD50 technique to standardize a murine model for the evaluation of the virulence of Streptococcus suis capsular type 2 isolates. A model using 28 day-old mice belonging to CF1 strain appeared to give the best results. The inoculum size was the parameter most influencing the 50% lethal dose obtained with mice. Inoculation with 1-ml volume of a bacterial suspension instead of 0.1 or 0.5 ml decreased the LD50. The standardized model was used to evaluate the virulence of some isolates of known pathogenicity for pigs. The minimum lethal dose was used in the model and it appeared that the virulence of Streptococcus suis capsular type 2 isolates can be measured from highly virulent to totally avirulent.     

Comparison of Streptococcus zooepidemicus and influenza virus pathogenicity in mice by three pulmonary exposure routes

Pulmonary infections may be induced in experimental animals by using several exposure routes. Inhalation of microbial aerosols is often viewed as the most relevant exposure route, although the comparability of either intranasal (i.n.) or intratracheal (i.t.) inoculation to aerosol inhalation is unclear. In these studies, the infection of mice with either Streptococcus zooepidemicus or influenza virus was compared following i.n., i.t., or aerosol challenge. The 50% lethal dose was determined by each exposure route for both microbes, and the organ clearance of a 50% lethal dose was determined. Mice were as or more sensitive to bacterial or viral infection following i.n. or i.t. instillation as compared with aerosol challenge. Organ clearance patterns of virus or bacteria varied slightly with exposure route.     

Comparison of Streptococcus zooepidemicus and influenza virus pathogenicity in mice by three pulmonary exposure routes.

Pulmonary infections may be induced in experimental animals by using several exposure routes. Inhalation of microbial aerosols is often viewed as the most relevant exposure route, although the comparability of either intranasal (i.n.) or intratracheal (i.t.) inoculation to aerosol inhalation is unclear. In these studies, the infection of mice with either Streptococcus zooepidemicus or influenza virus was compared following i.n., i.t., or aerosol challenge. The 50% lethal dose was determined by each exposure route for both microbes, and the organ clearance of a 50% lethal dose was determined. Mice were as or more sensitive to bacterial or viral infection following i.n. or i.t. instillation as compared with aerosol challenge. Organ clearance patterns of virus or bacteria varied slightly with exposure route.     

Vaccination with Streptococcus suis serotype 2 recombinant 6PGD protein provides protection against S. suis infection in swine

Streptococcus suis serotype 2 ( S. suis 2 or SS2) is the causative agent of several diseases in both pigs and humans. 6-Phosphogluconate dehydrogenase (6PGD) is a cell surface protein in SS2. In this study, the immunogenicity and protective efficacy of recombinant 6PGD (r6PGD) from SS2 was evaluated in piglets. Immunization with an r6PGD-containing adjuvant induced a vigorous immunoglobulin G (IgG) response, with the titer of IgG2 being higher than that of IgG1. Immunization of piglets with r6PGD yielded 50% survival upon an intravenous challenge with a lethal dose of SS2. Piglets immunized with the r6PDG vaccine were better protected than those immunized with the adjuvant control. The clinical signs and histopathological changes in the piglets were recorded. Collectively, these results suggest that r6PGD can confer partial protection against SS2 infection and could be useful for the development of subunit vaccines against SS2.     

Therapeutic effect of anti-macrophage inflammatory protein 2 antibody on influenza virus-induced pneumonia in mice

We investigated the effect of anti-macrophage inflammatory protein 2 immunoglobulin G (aMIP-2 IgG) on the progression of influenza virus-induced pneumonia in mice. When mice were infected with a mouse lung-adapted strain of influenza A/PR/8/34 virus by intranasal inoculation, neutrophil counts in the bronchoalveolar lavage fluid (BALF) increased in parallel with the kinetics of MIP-2 production, which peaked 2 days after infection. After intracutaneous injection of a dose of 10 or 100 microg of aMIP-2 IgG once a day on days 0 and 1, neutrophil counts in BALF on day 2 were reduced to 49 or 37%, respectively, of the value in the control infected mice administered anti-protein A IgG. The antibody administration also improved lung pathology without affecting virus replication. Furthermore, by prolonged administration with a higher or lower dose for up to 5 days, body weight loss became slower and finally 40% of mice in both treatment groups survived potentially lethal pneumonia. These findings suggest that MIP-2-mediated neutrophil infiltration during the early phase of infection might play an important role in lung pathology. Thus, MIP-2 was considered to be a novel target for intervention therapy in potentially lethal influenza virus pneumonia in mice.     

Attenuated, replication-competent herpes simplex virus type 1 mutant G207: safety evaluation in mice

Herpes simplex virus type 1 (HSV-1) mutants that are attenuated for neurovirulence are being used for the treatment of cancer. We have examined the safety of G207, a multimutated replication-competent HSV-1 vector, in mice. BALB/c mice inoculated intracerebrally or intracerebroventricularly with 10(7) PFU of G207 survived for over 20 weeks with no apparent symptoms of disease. In contrast, over 80% of animals inoculated intracerebrally with 1.5 x 10(3) PFU of HSV-1 wild-type strain KOS and 50% of animals inoculated intracerebroventricularly with 10(4) PFU of wild-type strain F died within 10 days. Similarly, after intrahepatic inoculation of G207 (3 x 10(7) PFU) all animals survived for over 10 weeks, whereas no animals survived for even 1 week after inoculation with 10(6) PFU of KOS. After intracerebroventricular inoculation, LacZ expression was initially observed in the cells lining the ventricles and subarachnoid space; expression decreased until almost absent within 5 days postinfection, with no apparent loss of ependymal cells. G207 DNA could be detected by PCR in the brains of mice 8 weeks after intracerebral inoculation; however, no infectious virus could be detected after 2 days. As a model for latent HSV in the brain, we used survivors of an intracerebral inoculation of HSV-1 KOS at the 50% lethal dose. Inoculation of a high dose of G207 at the same stereotactic coordinates did not result in reactivation of detectable infectious virus or symptoms of disease. We conclude that G207 is safe at or above doses that were efficacious in mouse tumor studies.     

半数致死量LD50的百分偏差和渐近方差

毒性试验中的剂量与致死百分率平方根反正弦变换仍呈Ｓ形,且方差趋于同质, 半数致死量ＬＤ_(５０)可表示为 Ｌｏｇｉｓｔｉｃ模型参数的函数·因而,通过参数估计值的偏差和渐 过协方差矩阵,可推导出半数致死量ＬＤ_(５０)的百分偏差,渐近方差和ＬＤ_(５０)的置信区间．通 过 ２７个实例分析后建议,若 ＬＤ_(５０)的百分偏差超过 ５％,则 ＬＤ_(５０)估计值的误差较大