Biomedical subjects
Publications and source records attributed to N K Das.
The National Institute on Aging (NIA) has established a Mycoplasma Contamination Testing Service for NIA grantees studying cellular aging on cell-culture systems. The contractor is the Institute for Medical Research, Camden, New Jersey.
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Heifers, unadapted to a concentrate ration, were intraruminally inoculated (1 dose) with cultures of ruminal lactic acid-utilizing bacteria or with ruminal fluid from a steer adapted to a concentrate ration. Inoculation with cultures (1 L) of Selenomonas ruminantium or Megasphaera elsdenii did not produce better average daily weight gains or feed efficiency of heifers fed a high-energy ration for 21 days, if these values were compared with the performance of noninoculated heifers. Average daily weight gain and feed efficiency of heifers inoculated with 1 L of Peptococcus asaccharolyticus culture or with 1 L of adapted ruminal fluid and fed a high-energy ration for 21 days were better if these values were compared with the performance of noninoculated heifers.
Changes in the morphology of the sperm nucleus in the egg cytoplasm are mong the immediate events in nucleocytoplasmic interactions during early embryogenesis. Soon after its entrance into the egg cytoplasm, the sperm nucleus of various organisms increases in size with the transformation of condensed chromatin to a diffuse state, resembling the chromatin of an interphase nucleus (2, 13, 15, 16). This is followed by a close association or fusion of male and female pronuclei (2, 13, 15, 16). Cytoplasmic influences on nuclear morphology have also been demonstrated clearly in nuclear transplantation and cell fusion studies (10, 11). Reactivation of the nucleus, such as the transplanted brain nucleus in Xenopus egg cytoplasm or the hen erythrocyte nucleus in interphase cytoplasm of HeLa cells, is accompanied by nuclear enlargement and chromatin dispersion (10, 11). However, premature mitotic-like chromosome condensation takes place in the nuclei of sperm or interphase cells fused with mitotic cells (9, 12). Thus, chromosome dispersion and condensation seem to depend on the state of the cytoplasm in which the nucleus is present. These observations imply that the initial morphological changes in the sperm nucleus after fertilization may very well be dependent on the state of maturation of eggs at the time of sperm entry. Unfertilized eggs of Urechis caupo, a marine echiuroid worm, are stored at the diakinesis stage. These eggs complete maturation division after insemination and this is followed by fusion of male and female pronuclei (5, 8). Therefore, Urechis caupo is a suitable organism in which to study the response of the sperm nucleus to the changing state of the egg cytoplasm during and after postfertilization maturation division.
A mature, rumen-cannulated steer fed Coastal Bermuda grass hay for 8 weeks was adapted to a high-grain ration by stepwise increases in grain over a period of 4 weeks. The grain rations had concentrate-to-roughage ratios of 40:60, 70:30, and 85:15 and were fed for 10, 7, and 11 days, respectively. Numerical estimates of lactate-utilizing bacteria in ruminal fluid of the steer the last 3 days each ration was fed were made by colony counts. Lactate-utilizing bacteria were identified as Megasphaera elsdenii, Peptococcus asaccharolyticus, and Selenomonas ruminantium. Maximal numbers of lactate-utilizing bacteria were observed in the ruminal fluid of the steer during feeding the concentrate-to-roughage ration of 70:30.
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Nucleoli from unfertilized Urechis eggs, labeled with tritiated RNA precursors, have been isolated for simultaneous autoradiographic localization and biochemical analysis of labeled RNA. The production of the ribosomal RNA precursor (38S) and its first cleavage occur at the fibrillar core region of the nucleolus. The products, predominantly 30S RNA, are then rapidly transported and stored in the granular cortex of the nucleolus. The formation of the nucleolar cortex, therefore, seems to result from an accumulation of partially processed ribosomal RNA with its associated proteins.
A chronic infection with Shigella flexneri 2a has been established in mice for the evaluation of compounds for therapeutic potential. Evidence of infection is indicated by prolonged symptomless excretion in the feces and by positive isolation of organisms from different segments of the intestinal tract and from mesenteric lymph nodes. Serum antibody titer reaches a maximum after 9 days of infection and remains at a low level until 32 days postinfection. In this model, five drugs used in human shigellosis were evaluated for efficacy. Ampicillin was found to be the most active followed by oxytetracycline and kanamycin. Neomycin and colistin were the least active in this system.
Rates of DNA synthesis in root tip cells of diploid and autotetraploid snapdragon (Antirrhinum majus) seedlings and in diploid and tetraploid (mononucleate and bidiploid-nucleate) regenerating mouse-liver cells have been studied. The increase in this rate in the tetraploid cells is closely correlated with the increase in nuclear surface area, but not with the nuclear volume; this suggests a possible control of the rate of DNA synthesis by the nuclear membrane.
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Propagation of homologous bacteriophage in a culture of Staphylococcus aureus (1:1 ratio of phage to bacteria) in Trypticase Soy Broth (TSB) and in skim milk indicated more activity of phage in TSB. Early lysis of bacteria in skim milk followed by a pronounced rise in bacterial population suggested that staphylococcal phages were being inactivated by milk. Titration of phages from skim milk, whey, and TSB indicated about 90% adsorption of phages by acid- and heat-precipitable proteins of skim milk, whereas numbers recovered from whey were quite comparable to those recovered from TSB. Reducing the pH from 6.5 to 4.0 increased the percentage of phages recoverable from skim milk from 10 to 56%. Apparently, the changes in electrical charges on the casein micelles at this low pH were responsible for release of many phages from their complex with casein.
Additions of 0.0005 N calcium borogluconate to Trypticase Soy Broth (TSB) produced an increase in phage titer about 1 million-fold, whereas its addition to skim milk resulted in about a 100-fold decrease in the maximal titer. Supplemental calcium had a stimulatory influence on bacterial growth in TSB but not in skim milk. Studies were made of the effect of binding of calcium of skim milk on the proliferation of staphylococcal bacteriophage. Sequestering the calcium with 2% phosphate mixture inactivated the phages without affecting the bacterial growth. However, chelation of calcium by 0.012% ethylenediaminetetraacetic acid produced an inhibitory effect on both the phages and the bacteria.
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