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Biomedical subjects

S M Clark

Publications and source records attributed to S M Clark.

At least 73 records · Page 4Linked to original sources
PubMed1988

Automation of dideoxynucleotide DNA sequencing reactions using a robotic workstation.

We report here a system for automation of the dideoxynucleotide DNA sequencing method. The system consists of a Beckman Biomek 1000 robotic workstation which has been modified by the addition of a thin heater/cooler block directly on the instrument table. The heater/cooler block, which is regulated by a user-specified program integrated into the Biomek software, facilitates the use of both single- and double-stranded DNA sequencing procedures. Using this system, we are able to perform 24 sets of dideoxynucleotide DNA sequencing reactions in approximately 45 min. The reactions are performed in 96-well microtiter plates, using a prepared reagent pack which includes primer, enzyme, nucleotide mixes and radioactive label. Using standard gel electrophoresis technology, we are able to resolve over 500 nucleotides per sequencing reaction in about 5 h. Currently, we are able to perform three runs of 24 samples each, with subsequent gel analysis per 8-h period. Excluding autoradiography, this represents a daily data output of 36,000 base pairs.

DNA↗
PubMed1986

Direct mailing as a means of disseminating NIH consensus statements. A comparison with current techniques.

The Office of Medical Applications of Research of the National Institutes of Health conducted a survey to evaluate the effectiveness of mass mailing of consensus statements as compared with traditional dissemination methods. The consensus statement on osteoporosis, published earlier in JAMA, was selected for study. Physicians (N = 695) within each of five relevant specialties in two comparable metropolitan areas were surveyed. Findings suggest that while a small but significant increase of awareness resulted from direct mailing, this increase should be weighed against costs and effectiveness of other methods.

Information Services↗
PubMed1983

Effects of morphine on body temperature of squirrel monkeys of various ages.

Increased sensitivity to certain drugs is believed to contribute to dysthermia in the elderly. To learn whether the temperature-altering effects of an opiate are increased in aged primates, injections of morphine sulfate (0.5-4 mg/kg) were given SC in randomly assigned order to squirrel monkeys ranging in age from 3.5 to over 17 years. Hyperthermia was the predominant response with no clear relationship to age, although hypothermic and biphasic responses also occurred, most commonly after the highest dose. Lateral cerebral ventricular injections of 0.625 and 1.25 micrograms morphine sulfate evoked hyperthermia in monkeys over 8 years of age but did not affect the temperature of animals less than 5 years old. Doses of 2.5 and 5 micrograms usually elicited hyperthermia regardless of age, but 10 micrograms induced hypothermia in a majority of monkeys. Naloxone was given intraventricularly to several monkeys to limit the degree of hypothermia after high doses of morphine given peripherally or centrally. Thus in these primates, as in other species such as the rat, lower doses of morphine usually evoked hyperthermia, but sufficiently high doses caused body temperature to fall. Unlike the case in the squirrel monkey with diazepam and with endogenous substances such as leukocytic pyrogen and taurine, there was not a strong or consistent relationship between age and morphine-induced temperature changes.

Aging↗
PubMed1982

Inhibition of rotaviruses by selected antiviral substances: mechanisms of viral inhibition and in vivo activity.

Several RNA virus inhibitors were evaluated against simian (SA11) rotavirus infections in vitro and murine rotavirus gastroenteritis in vivo. Test compounds included 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin), 3-deazaguanine (3-DG), 3-deazauridine, and 9-(S)-(2,3-dihydroxypropyl)adenine [(S)-DHPA]. All drugs inhibited total infectious SA11 virus yields in MA-104 cells. Ribavirin, 3-DG, and (S)-DHPA affected [3H]uridine uptake into uninfected MA-104 cells in both the acid-soluble and -insoluble fractions. All drugs reduced the levels of dense (precursor) and light (complete) SA11 particle yields compared with control but did not alter the relative amounts of dense compared with light particles, suggesting that the agents did not interfere with virus assembly. Ribavirin and 3-DG inhibited SA11 polypeptide synthesis, as determined by polyacrylamide gel electrophoresis studies. None of the agents or mono- and triphosphate derivatives of ribavirin inhibited SA11 RNA polymerase activity. In murine rotavirus studies, oral therapy with ribavirin-2',3',5'-triacetate and (S)-DHPA increased mean survival time, but no increase in survivor rate was observed. 3-DG- and (S)-DHPA-treated mice had a more rapid weight gain than controls, suggesting a probable lessening of the severity of the disease.

Adenine↗
PubMed1981

Effects of diazepam on body temperature of the aged squirrel monkey.

Hypothermia was produced by IM administration of diazepam (0.125-0.5 mg/kg) to squirrel monkeys of various ages (2-16 years) in a thermoneutral (23 +/- 0.5 degrees C) environment with animals over eight years of age having slightly greater responses. Hypothermia caused by an intermediate dose (0.25 mg/kg) was augmented in a cold environment (15 degrees C), especially in the older animals. There was no marked alteration in the temperature change/age regression after 0.25 mg/kg diazepam in a hot environment (30 degrees C) compared with the control response. Injections of diazepam (1.25-5.0 microgram) into the lateral cerebral ventricle in a thermoneutral environment produced hyperthermia rather than hypothermia in all animals, and the magnitude of the induced hyperthermia was smaller in older monkeys. The results support previous case reports in man and suggest that this commonly used drug can induce hypothermia, especially in older primates exposed to cold. The drug action responsible for this temperature change appears to take place peripherally rather than within the brain.

Aging↗
PubMed1981

Hypothermia produced in aged squirrel monkeys by central administration of taurine.

Accidental hypothermia and heatstroke are more common in aged populations. While peripheral factors are undoubtedly important to the high incidence of dysthermia in the aged, alterations in central temperature controls associated with aging may be primarily responsible. It has been shown that the sensitivity of the hypothalamus to neurotransmitters is changed in aged animals, and it may be that similar alterations in central temperature controls underlie the increased susceptibility to dysthermia. As a first step in testing this hypothesis the responsiveness of central temperature controls of aged squirrel monkeys to taurine, a putative inhibitory neurotransmitter or neuromodulator, was tested. Intracerebroventricular (i.c.v.) administration of this sulfonated amino acid (0.5-4.0 mg) produced dose-related hypothermia in squirrel monkeys over nine years of age in a thermoneutral environment (23 degrees C). Younger animals had significantly smaller hypothermias. In a hot environment (30 degree C) there were no significant differences between the temperature decreases of the two age groups after any dose. However, in a cold environment (17 degrees C), in which young animals developed slightly larger hypothermias than in the thermoneutral environment, core temperature of the aged squirrel monkeys dropped so rapidly in response to even the lowest dose that they had to be removed and warmed to prevent death by hypothermia. The temperature controls of the aged squirrel monkey appear to be extremely sensitive to taurine. The findings indicate that a rise in central taurine concentration in old primates can, in a cold environment, produce an effect very much like accidental hypothermia in aged man.

Aging↗
PubMed1981

Inhibition of bluetongue and Colorado tick fever orbiviruses by selected antiviral substances.

The effects of four ribonucleic acid virus inhibitors were evaluated in cell cultures and in mice to determine inhibitory effects against bluetongue virus and Colorado tick fever virus (CTFV). Test compounds included 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin), 3-deazaguanine, 3-deazauridine, and 9-(S)-(2,3-dihydroxypropyl)adenine. Ribavirin-2',3',5'-triacetate (ribavirin triacetate) was evaluated in vivo against CTFV. Inhibition of cytopathic effect and plaque reduction were used to evaluate antiviral activity. In cytopathic effect inhibition studies, bluetongue virus was markedly inhibited by 3-deazaguanine and 3-deazauridine in Vero cells with moderate inhibition by the other agents. Ribavirin and 3-deazaguanine markedly inhibited CTFV in MA-104 cells, 3-deazauridine was slightly less active, and 9-(S)-(2,3-dihydroxypropyl)adenine was negative. Ribavirin was less effective in Vero cells against CTFV. When mice were inoculated intracerebrally with CTFV and treated by a single intracerebral injection with drug, ribavirin triacetate increased the number of survivors, 3-deazaguanine increased mean survival time, and ribavirin was negative. Intraperitoneal treatment of infected mice with ribavirin triacetate for 1 week significantly increased the number of survivors and mean survival time, providing strong evidence that the agent is active across the blood-brain barrier.

3-Deazauridine↗
PubMed1981

Trypsin enhancement of rotavirus infectivity: mechanism of enhancement.

The infectivity of most rotaviruses is enhanced by treatment with trypsin. We studied the mechanism of enhancement of examining the effect of trypsin on rotavirus infectivity, aggregation, early interactions with host cells, and structure. The results indicated that trypsin does not increase levels of infectious virus by dispersion of aggregates or affect the efficiency or rate of attachment of virus to cells. A fraction of virus that was not infections without trypsin treatment was found to attach to cells, but did not initiate antigen synthesis. When cells were infected with labeled, purified virus, increased levels of uncoated particles were found in cells infected with trypsin-treated virus. Infection of cells with trypsin-treated virus also led to greater levels of RNA synthesis early in the infection. The results suggest that trypsin converts a noninfectious fraction of virus into infectious virus by allowing this fraction to uncoat in the infected cell. Trypsin was found to cleave an 88,000-dalton structural polypeptide of bovine rotavirus generating 67,000- and 20,000-dalton cleavage products.

Animals↗
PubMed1980

Role of two particle types in bovine rotavirus morphogenesis.

The involvement of light (L) and dense (D) bovine rotavirus particle types during virus replication has been studied. It was found that infectious parental L virions are uncoated in vivo to a particle similar to native D particles. Differences in the rate of synthesis and relative yields of L and D particles in MDBK and MA-104 cells have been detected. Results from pulse-chase labeling experiments indicate that D particles serve as morphogenic precursors to the complete L virion.

Animals↗
PubMed1979

Production of high-titer bovine rotavirus with trypsin.

Titers of bovine rotavirus in excess of 10(9) immunofluorescent infectious units per ml of culture fluids have been produced, using trypsin treatment of the virus. Infectivity of preparations of the virus can be increased with as little as 1 ng of trypsin per ml, with maximum increases of 1 to 2 log10 with 1 microgram of trypsin per ml. The virus grows to titers in excess of 10(5) immunofluorescent units per ml in MDBK, LLC-MK2, MA-104, and HeLa cells. When MDBK cells are infected with a multiplicity of infection of 20, maximum yields of cell-associated, trypsin-enhanceable virus are obtained 4 to 8 h postinfection. Maximum yields of cell-free, trypsin-enhanceable virus are produced 16 to 20 h postinfection. The results presented here indicate that trypsin can be used to produce high-titer stocks of bovine rotavirus.

Animals↗