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J Callahan

Publications and source records attributed to J Callahan.

At least 55 records · Page 3Linked to original sources
PubMed1988

Mechanisms of mutagenesis by a bulky DNA lesion at the guanine N7 position.

In order to examine the mechanisms of mutagenesis by a bulky DNA lesion at the guanine N7 position, the replicative form DNA of phage M13AB28 (mp8 without the amber codons in phage genes) was modified in vitro with aflatoxin B1-2,3-dichloride and transfected into appropriate Escherichia coli cells. Forward mutations in the lacZ alpha-complementing gene segment were identified as light blue or colorless plaques on appropriate indicator plates, isolated, and defined by DNA sequencing. Transfection of modified DNA into uvrA-/mucAB+ cells without prior UV (SOS) induction increased mutation frequency eight-fold over untreated DNA, whereas this increase was 12-fold upon SOS induction. Transfection of modified DNA after conversion of the primary guanine-aflatoxin lesions to the stable imidazole ring-opened formamidopyrimidine-aflatoxin suggested that these lesions were nearly equally mutagenic. A majority of point mutations under all conditions affected G:C bp. Base substitutions were in the majority, but significant frameshift mutagenesis was also detected in SOS-induced cells. Both G-to-T transversions and G-to-A transitions were produced at equal efficiency and together accounted for virtually all of the base substitutions induced by the primary lesions. Point mutations occurred predominantly at predicted damage hotspots. The characteristics of base substitution and frameshift mutations, together with available information point to multiple mechanisms of mutagenesis by this class of mutagens. The data indicate that primary lesions have the properties of both a noninstructional and pseudo-instructional lesion. In addition, the sequence context appears to play a role in determining whether a frameshift or a base substitution is induced by this bulky lesion.

Aflatoxin B1↗
PubMed1987

Decreased amniotic fluid magnesium concentration in diabetic pregnancy.

Amniotic fluid samples from 21 diabetic pregnant women were pair-matched for gestational age with 21 samples obtained from nondiabetic women, and analyzed for magnesium concentration. Mean +/- standard deviation amniotic fluid magnesium concentration (mg/dL) was 0.86 +/- 0.21 in the diabetic group and 1.06 +/- 0.22 in the control group (P less than .001). It is concluded that in the diabetic pregnancy, a state of fetal magnesium deficiency exists. This deficient state may contribute to neonatal hypocalcemia in infants of diabetic mothers.

Amniotic Fluid↗
PubMed1983

Studies of cultured human T lymphocytes. II. Initiation of paired T- and B-cell lines from healthy donors.

We report the sustained cultivation of both B- and T-lymphoblastoid cell lines from randomly selected healthy donors, and the results of studies defining the frequency with which these cell lines can be established. B-cell lines were initiated using the Epstein-Barr virus. Of 52 attempts, 40 B-cell lines (77% success) were obtained from 24 different donors. T-cell lines were started and propagated in long-term (greater than 100 days) cultures using the T-cell growth factor interleukin-2 (IL-2). Of 55 attempts, 54 (98%) were successful in initiating IL-2-dependent T-cell lines, and these were derived from 28 healthy adults. Likewise, of 45 attempts, 32 (71%) were successful in producing paired lines in which both the B-cell line and T-cell line were cultivated from a single blood collection (N = 22 donors). Phenotypic profiles of these lines were defined using multiple marker assays, including rosette formation, surface immunoglobulins, cytochemistry, karyotype, as well as xenoantisera and monoclonal antibodies defining different membrane antigens. This work demonstrates the feasibility of propagating paired human B and T lymphoblastoid lines suitable for many comparative immunobiological studies.

Adolescent↗
PubMed1982

Passive anti-D.

Explore the source record for details and available documents.

Adult↗
PubMed1982

A geometric model of anorexia and its treatment.

Anorexia is a severe psychological disorder in which a person's dieting turns into compulsive fasting. Some victims develop, after a time, a bulimic phase; their fasting is interrupted at intervals by bouts of indiscriminate gorging. One successful treatment makes use of a naturally occurring trance state, in which the anorexic's obsession with food recedes temporarily, to offer reassurance and rebuild a personality free of the obsession. The proposed model is catastrophe-theoretic. It assumes (a) that the bifurcation of eating attitudes typical of anorexia can be modeled by a cusp whose controls are hunger and eating regimen; and (b) that the normal cycle of falling asleep and waking up can be modeled by a hysteresis loop controlled by alertness. Catastrophe theory predicts two additional controls, and a larger model organized by the E6 singularity. The new controls are identified with loss of self-control and insecurity, and anorexia is correlated with high insecurity. The model makes the following predictions. First, under moderate levels of self-control and eating regimen, an anorexic has access to balanced, nonobsessive attitudes toward food at a reduced level of wakefulness. This is the trance state. Second, a healthy individual has two distinct sleep modes, dominated by cerebral and somatic elements, respectively. Third, with increasing insecurity the distinct modes fuse together, so that an anorexic's sleep patterns are abnormal. The model is geometric because the connection between behavior and controlling factors is made by graphs of certain standard form.

Adolescent↗
PubMed1981

Niemann-Pick disease type C. Pathological, histochemical, ultrastructural and biochemical studies.

Two sisters with Niemann-Pick Disease Type C suffered from a progressive CNS degenerative disease which ended with death at 8 and 7 years. Light microscopic and histochemical studies revealed storage of lipid (principally sphingomyelin) in the viscera and in the central nervous system (predominantly ganglioside). Complex lipid cytosomes containing stacked membranes, concentric laminated bodies with central dense cores and pleomorphic profiles were seen. Biochemical analysis showed an elevation of sphingomyelin in liver and spleen with normal total sphingomyelinase levels. However, by isoelectric focusing, there was a marked reduction of sphingomyelinase activity in the range of pI 4.6--5.2, whereas normal amounts of more acidic components were found. These data are compatible with autosomal recessive inheritance of a sphingomyelin lipidosis associated with deficiency of isoelectric forms of sphingomyelinase.

Central Nervous System↗
PubMed1979

Nutrient blood flow in delayed axial pattern skin flaps in pigs.

Blood flow was investigated in 112 skin flaps (84 delayed and 28 undelayed) in 28 pigs. The flow was significantly (P less than 0.001) increased over the control flow with increasing delay intervals, reaching the greatest flow at one week after the delay (paralleling the increase in tissue survival). This increased blood flow persisted after definitive flap raising. The circulatory adjustments within the first week of the delay constitute the delay phenomenon, and they determine the ultimate viability of the skin flap in this model.

Animals↗