Effect of split doses of N-methyl-N-nitrosourea on DNA repair synthesis in cultured mammalian cells

DNA repair was measured in human fibroblasts, mouse C3H 10 T 1/2 fibroblsts and rat hepatocytes by the non-semi-conservative incorporation of [3H]-TdR during DNA repair synthesis using liquid scintillation techniques. Confluent monolayers of these cells grown on cover slips were exposed to split doses (125 or 250 microgram/ml) of the mutagenic and carcinogenic alkylating agent MNU and DNA repair synthesis compared with that produced by a single dose (500 microgram/ml). No significant difference in DNA repair capacity was detected in the three cell lines treated with a single dose or split doses of MNU.     

Performance monitoring of the EC - 1030 system by a microprocessor - based monitor

This paper presents a M6800 microprocessor based hardware monitor for measuring certain selected parameters of the EC-1030 computer system. The motivation for this work was to get an insight into the operation of the system under the present work load and use these results towards improvement and design studies. The three main classes of quantitative indices of computer system performance/productivity, responsiveness and use have been measured using hardware and software tools. This paper describes the hardware monitor design and discusses the measurements made.     

Effects of phentermine on responding maintained under multiple fixed-ratio schedules of food and cocaine presentation in the rhesus monkey

Drugs that decrease drug-maintained responding at doses that do not decrease other behaviors in animals may be suitable candidates for development as medications to treat drug abuse in humans. The present study examined whether this effect could be obtained with phentermine, a drug that has been reported to decrease cocaine intake in humans. Rhesus monkeys were trained under multiple fixed-ratio 30-response schedules of food and i.v. cocaine delivery. Phentermine was always given as a slow, i.v. infusion. Acute treatment with phentermine (0.3-10 mg/kg) decreased cocaine-maintained responding at doses that did not decrease, or decreased less, food-maintained responding for each of three unit doses of cocaine (10-100 microg/kg/injection). Subacute treatment with phentermine (3 or 5.6 mg/kg, daily) also decreased cocaine-maintained responding more than food-maintained responding. After subacute treatment was terminated, rates of cocaine-maintained responding generally recovered to levels comparable to those seen during untreated control sessions. Phentermine (0.3-3 mg/kg) did not generally increase responding associated with a very low (1 microg/kg/injection) unit dose of cocaine, suggesting that the decrease in cocaine-maintained responding at higher unit doses was not the result of a leftward shift in the cocaine unit dose-effect function. Phentermine (0.1-3 mg/kg) decreased responding maintained by 1-[2-[bis(4-fluorophenyl) methoxy]ethyl]-4-[3-phenylpropyl] piperazine (GBR 12909) (30 microg/kg/injection) at doses similar to those that decreased food-maintained responding. These results show that phentermine is effective in decreasing cocaine self-administration and suggest that it may be an effective medication for cocaine abuse.     

Automatic image acquisition, calibration and montage assembly for biological X-ray microscopy

We describe a system for the automatic acquisition and processing of digital images in a high-resolution X-ray microscope, including the formation of large-field high-resolution image montages. A computer-controlled sample positioning stage provides approximate coordinates for each high-resolution subimage. Individual subimages are corrected to compensate for time-varying, non-uniform illumination and CCD-related artefacts. They are then automatically assembled into a montage. The montage assembly algorithm is designed to use the overlap between each subimage and multiple neighbours to improve the performance of the registration step and the fidelity of the result. This is accomplished by explicit use of recorded stage positions, optimized ordering of subimage insertion, and registration of subimages to the developing montage. Using this procedure registration errors are below the resolution limit of the microscope (43 nm). The image produced is a seamless, large-field montage at full resolution, assembled automatically without human intervention. Beyond this, it is also an accurate X-ray transmission map that allows the quantitative measurement of anatomical and chemical features of the sample. Applying these tools to a biological problem, we have conducted the largest X-ray microscopical study to date.