Biomedical subjects
Publications and source records attributed to J C Smith.
Data are presented showing that rats can discriminate among sucrose solution concentrations by some cue other than taste, possibly by olfaction. Non-taste factors need to be considered in taste discrimination studies.
To examine the influence of inositol phosphates on the uptake and absorption of Fe and Zn, Caco-2 cells were grown on either plastic (uptake studies) or porous membranes in bicameral chambers (transport/absorption studies). Caco-2, a human colon adenocarcinoma cell line, was selected as the test cell because it spontaneously differentiates into polarized enterocyte-like cells at confluency. Uptake of Fe (added as Fe-nitrilotriacetate complex) from a calcium-free solution by fully differentiated cells was 37 pmol/cm2. Addition of 10-fold molar excess of individual inositol phosphates (IP3, IP4, IP5 or IP6) decreased Fe solubility by 13 to 25% and reduced Fe uptake by 50 to 65%. The rate of transport of Fe from the apical solution into the basolateral chamber [1.4 +/- 0.1 pmol/(h.cm2)] decreased (34-96%) in proportion to the degree of phosphorylation of the inositol derivative in the apical compartment. Uptake and transepithelial transport of Zn were 246 +/- 5 pmol/cm2 and 23 +/- 1 pmol/(h.cm2), respectively. The solubility, uptake and rate of transport of Zn also decreased in proportion to the degree of phosphorylation of inositol. These results demonstrate the inhibitory influence of IP3-IP6 on the uptake and transport of Fe and Zn and support the usefulness of the Caco-2 human cell line as an appropriate model for evaluating the effects of specific dietary factors on trace metal bioavailability.
Structural features associated with the ability of a monoclonal antibody (mAb) to discriminate between protein variants are identified and engineered. The variants are the curaremimetic toxin alpha from Naja nigricollis and erabutoxin a or b from Laticauda semifasciata, which differ from each other by 16 substitutions and one insertion. The neutralizing mAb M alpha 1 recognizes with high affinity a topographical epitope on the surface of toxin alpha, but fails to recognize the erabutoxins although they possess most of the residues forming the presumed epitope. Examinations of the toxin alpha and erabutoxin 3-D structures and molecular dynamics simulations reveal several differences between the variants. In particular, the region involving the beta-turn 17-24 is organized differently. Analysis of the differences found in this region suggest that the insertion (or deletion) at position 18 of the variant amino acid sequences is particularly important in determining the differential cross-reactivity. To test this proposal, residue 18 was deleted in one erabutoxin using site-directed mutagenesis, and the biological properties of the resulting mutant were examined. We found that full antigenicity was restored in the previously unrecognized variant. The implications of this finding are discussed.
We reviewed the clinical courses of children < or = 16 years of age with hereditary hemolytic anemias who were admitted to the University of Mississippi Medical Center for aplastic crisis. Constitutional signs, gastrointestinal complaints, and headache were the most frequent findings. Statistically significant decreases in hemoglobin levels, hematocrit, and reticulocyte counts, but not total white blood cell or platelet counts, were found on admission when compared to other times of determination. For 27 of 49 patients, IgM antibody determinations to human parvovirus (B19) were available, and 15 (56%) had positive values. We conclude that erythroid (but not other) blood cell lines are helpful in establishing a clinical diagnosis, and that both acute and convalescent titers are necessary to assess the immune response to the infection. Physicians should continue to search for agents other than B19 parvovirus in patients in whom B19 antibodies cannot be found.
1. The ontogeny of thyrotropin-releasing hormone (TRH) and norepinephrine (NE) potentiation of inspiratory-related hypoglossal (XII) motor nerve discharge was studied in medullary slices from P0-3, P7, and P11-14 mice that retain functional networks for respiration. 2. TRH, applied locally to the XII motor nucleus, had no effect on XII inspiratory burst amplitude in slices from P0-3 mice. By P7 there was significant potentiation of burst amplitude that increased more than three-fold by P11-14. NE applied to the XII nucleus produced significant potentiation in all age groups. Potentiation increased developmentally with the largest increase occurring between P0-3 and P7. 3. Thus catecholamine and TRH modulation of inspiratory-related XII nerve activity increases during the first two weeks of life; the potentiating effects of NE appear prior to those of TRH. 4. With rhythmically active, transverse medullary slices from mice up to 2 wk of age, it is now possible to study the development of XII motoneuron modulation as it relates to respiratory control of the upper airway.
1. We have hypothesized that pacemaker neurons in the pre-Bötzinger complex (pre-BötC) form the kernel for respiratory rhythm generation. A prediction of this hypothesis is that oscillatory behavior in some respiratory neurons could persist in the absence of synaptic transmission. In this study we used extracellular recording of neuronal activity in slice preparations from neonatal rat medulla that generate respiratory rhythm in vitro to determine 1) whether pacemaker properties are present in pre-BötC and unique to respiratory neurons, 2) whether pacemaker properties are common to all respiratory neurons, and 3) the spatiotemporal patterns of pacemaker neuron activity. 2. Whole cell recordings from respiratory neurons verified that bathing the slices in a low-Ca2+/high-Mg2+ solution (low-Ca2+ solution) eliminated endogenous respiratory synaptic inputs and electrically evoked synaptic inputs. 3. Sixty-three neurons spontaneously generated rhythmic bursts of action potentials in low-Ca2+ solution. After we switched to control solution to reactivate the respiratory network, these neurons were classified on the basis of their spike discharge patterns relative to the respiratory cycle as: 1) inspiratory (I) neurons (n = 41), 2) tonic expiratory (tonic E) neurons (n = 4), and 3) tonic neurons (n = 18). 4. In other experiments we tested I and tonic E neurons identified first in control solution for bursting behavior in low-Ca2+ solution. Several I neurons (n = 5 of 33), but none of the tonic E neurons (n = 0 of 13), continued to burst rhythmically. 5. Bursting and nonbursting respiratory neurons were distributed throughout the ventrolateral reticular formation within the pre-BötC as well as in the ventral respiratory group (VRG) immediately caudal to the pre-BötC. 6. We conclude that subpopulations of VRG neurons in vitro have rhythmic bursting properties when synaptic transmission is abolished. Respiratory neurons, especially I neurons, were the most prevalent class of bursting cells. Only a small percentage of respiratory neurons, however, had pacemaker properties. These findings are consistent with the hypothesis that the respiratory oscillator includes specialized neurons with intrinsic oscillatory properties.
Members of the activin family are believed to act as mesoderm-inducing factors during early amphibian development. Little is known, however, about mesoderm formation in the mammalian embryo, and as one approach to investigating this we have studied activin and follistatin expression during early mouse development. Activins are homo- or heterodimers of the beta A or beta B subunits of inhibin, itself a heterodimer consisting of one of the beta subunits together with an alpha subunit. Follistatin is a single-chain polypeptide which inhibits activin function. Expression of the inhibin alpha chain could not be detected in embryonic or extraembryonic tissues at any of the stages studied (5.5 to 8.5 days) and expression of the beta A and beta B subunits could only be observed in the deciduum in cells surrounding the embryo. Expression of follistatin could also be detected in the deciduum, but in a pattern complementary to that of the beta subunits. Embryonic expression of follistatin first occurred in the primitive streak, and at later stages transcripts were detectable in the somites and in rhombomeres 2, 4 and 6 of the hindbrain. These results are consistent with a role for activin in mesoderm formation in the mouse embryo, and suggest functions for follistatin in addition to its role as an inhibitor of activin.
The growth factor activin elicits mesodermal fates when applied to prospective ectodermal cells of the Xenopus blastula stage embryo. Previous experiments with dissociated cells showed that there are at least five different responses separated by closely spaced, sharp dose thresholds. Here we investigate this multithreshold activin response further using probes for genes expressed at early gastrula stages, namely Xbra, goosecoid, noggin, Xwnt-8 and Mix.1. We show that initial dose-response profiles are broad and smooth in contrast to the later threshold-bound patterns. For Xbra, goosecoid and noggin, the later expression ranges are subsets of earlier ones. Unexpectedly, Xwnt-8 is initially induced at high doses only, but later appears only in cells that have received a low dose of activin. Keeping the cells dissociated after activin treatment, rather than allowing them to reaggregate, prevents sustained expression of Xbra and Xwnt-8 but allows that of goosecoid and noggin. However, cell contact is required for sharpening the dose-response threshold of goosecoid. Finally, we show that a previously reported dorsoventral prepattern in the animal cap is also cell-contact dependent and it is not required for the multi-threshold response to activin.
To increase our understanding of haematopoiesis during early vertebrate development, we have studied the expression pattern of the transcription factor GATA-2 in Xenopus embryos, and asked how this is regulated. We show that the blood island precursors of the ventral mesoderm express GATA-2 RNA at neural tube stages, some 5 hours before globin RNA is detected in their derivatives. Prior to this however, GATA-2 is expressed much more widely within the embryo. Maternal transcripts are uniformly distributed, and zygotic transcription is activated during gastrulation throughout ventral and lateral regions of the embryo, with expression highest in the sensorial ectoderm and only weak in the ventral mesoderm. The domain of GATA-2 expression in neurulae outlines the region of the neural plate and suggests a possible wider role in dorsoventral patterning. To identify the signals involved in regulating this pattern of expression, we performed experiments with embryo explants. GATA-2 is activated autonomously in isolated animal caps and this activation is suppressed by the mesoderm-inducing factor activin, but not by FGF. Thus, the down-regulation of GATA-2 observed in the region of the Spemann organiser may be a response to an activin-like signal emanating from the dorsal-vegetal region or Nieuwkoop centre. GATA-2 activation in animal caps and ventral marginal zones was suppressed by co-culturing with dorsal marginal zones, suggesting that a signal from the Spemann organiser is involved in suppression of GATA-2 in the dorsal region of the embryo. Expression of a candidate for this signal, noggin, had the same effect. Taken together, the observations presented here suggest that GATA-2 activation occurs by default in the absence of signals, that the restriction of its expression within the early embryo is controlled by negative signals emanating from the Nieuwkoop centre and the organiser, and that noggin and activin-like molecules play a role in these signalling pathways.
Explore the source record for details and available documents.
Activins are thought to play a role in mesoderm induction in amphibian development. Studies of the expression patterns of activin during mouse embryogenesis are consistent with the proposal that they are also involved in mesoderm formation in mammals. Activins are expressed both maternally and zygotically at preimplantation stages, and at postimplantation stages transcripts are present at high levels in the deciduum, suggesting that mesoderm is induced by maternally-derived activin. The functions of activin can be modulated by follistatin. At postimplantation stages follistatin is expressed in the deciduum in a pattern reciprocal to that of activin. In the embryo proper, follistatin transcripts are localized to the primitive streak region during gastrulation and later in the somites and in rhombomeres 2, 4 and 6 of the hindbrain. In this paper we show that follistatin, like activin, is expressed throughout pre-implantation mouse development. Transcripts are present at low levels in undifferentiated F9 and ES cells, but they increase greatly on differentiation of both cell types. Expression of activin mRNA is decreased in differentiated F9 and ES cells, and the simultaneous increase in follistatin may create an efficient and rapid means of decreasing levels of functional activin.
Estimates of anaerobic work capacity (AWC) were determined in 26 subjects using the critical power concept. AWC estimates were derived using three mathematically equivalent models: nonlinear power-time, linear power-1/time, and linear work-time. We hypothesized that large variability between estimates generated using the three models might reflect systematic error in the data and that large standard errors of estimate (SEE) might reflect random error. Therefore, subjects were grouped according to the variability in the three AWC estimates and according to the magnitude of the SEE of the parameter estimates. Then AWC estimates were compared to a criterion measure of anaerobic capacity, namely maximal oxygen deficit. When variability in the AWC estimates was low (< 10%), all provided accurate measures of oxygen deficit; also, when SEE were low, estimates were accurate. When variability was high, mean AWC estimates derived using linear models differed from oxygen deficit by over 15%; when SEE were high, mean AWC estimates derived using all models differed from oxygen deficit by over 10%. It is concluded that the accuracy of estimates of anaerobic capacity derived using the critical power concept can best be ensured by accepting values only when all three models provide the same value and/or when the SEE of the AWC estimate is small.
PROBLEM/CONDITION: In the United States in 1990, there were an estimated 1 million pregnancies and 521,826 births among women ages 15-19 years. Rates of teenage pregnancy and birth rates by state in 1990 exceeded those in most developed countries. An estimated 95% of teenage pregnancies are unintended (i.e., they occur sooner than desired or are not wanted at any time). REPORTING PERIOD COVERED: This report summarizes and reviews surveillance data for pregnancies, abortions, and births among women ages 15-19, 15-17, and 18-19 years reported by CDC for 1980 and 1990. DESCRIPTION OF SYSTEM: Data for births and abortions were reported to state health departments and other health agencies and sent to CDC. The data from each state included the total number of births and abortions by age and race/ethnicity. RESULTS: Data in this report indicate that pregnancy rates by state among U.S. teenagers ages 15-19 years have changed little since 1980. Moreover, many states have reported increases in birth rates that are probably related to concurrent decreases in abortion rates. Pregnancy rates range from 25 to 75 per 1,000 for 15- to 17-year-olds and from 92 to 165 per 1,000 for 18- to 19-year-olds. INTERPRETATION: States with low rates of teenage pregnancy or birth may have developed and used prevention strategies directed at the needs of both younger and older teenagers; these programs may serve as models for other states where birth rates have remained high or have increased since 1980. ACTIONS TAKEN: CDC will continue to conduct surveillance of and analyze data for pregnancies, abortions, and births among teenagers to monitor progress toward national goals and to assist in targeting program efforts for reducing teenage pregnancy.
CONDITION: Since 1980, the number of legal induced abortions reported to CDC has remained fairly stable, varying each year by < or = 5%. REPORTING PERIOD COVERED: This report summarizes and reviews data received by CDC for legal induced abortions obtained in 1990. DESCRIPTION OF SYSTEM: For each year, CDC compiles abortion data received from 52 reporting areas: 50 states, New York City, and the District of Columbia. RESULTS: In 1990, 1,429,577 abortions were reported--a 2.4% increase from 1989. The abortion ratio for 1990 was 345 legal induced abortions per 1,000 live births, and the abortion rate was 24 per 1,000 women ages 15-44 years. Most women undergoing abortions were young, white, and unmarried; most had had no previous live births and were having the procedure for the first time. Approximately half of all abortions were performed before the 8th week of gestation, and 87% were before the 13th week of gestation. Younger women were more likely to obtain abortions later in pregnancy than were older women. INTERPRETATION: Since 1980, the national number (and rate) of abortions has remained relatively stable, with only small (< or = 5%) year-to-year fluctuations. However, since 1984, the national abortion ratio has declined; in 1990, the abortion ratio was the lowest recorded since 1977. Increasing rates of childbearing may account for some of this decline. ACTIONS TAKEN: The number and characteristics of women having abortions are needed from all states to furnish an accurate characterization of legal induced abortion in the United States and to assist efforts to identify and reduce preventable causes of morbidity and mortality associated with abortions.
The role of macrophages in the host immune response against cancers remains uncertain. Since nitric oxide synthesis represents a significant macrophage antitumor mechanism in vitro, we evaluated whether NO was synthesized during the immune response to growing murine skin cancers. NO synthesis was readily detectable in enzymatically dissociated tumors (RD-995 and LR-298) and was inhibited by N omega-monomethyl-L-arginine (MLA) and by macrophage depletion. Nitrosylation of iron-sulfur and heme complexes was observed in these tumors using electron paramagnetic resonance spectroscopy. NO production in the presence of increasing concentrations of MLA correlated inversely with tumor cell proliferation in vitro. To elucidate the role of NO during in vivo tumor progression, tumor-bearing mice were treated with continuous infusions of the nitric oxide synthase inhibitor MLA. MLA-treated mice demonstrated increased growth and delayed rejection of the highly antigenic UV radiation-induced regressor tumor LR-298. These experiments demonstrate that macrophage-derived NO synthesis can contribute to the antitumor immune response in vivo.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Global features of the structure and dynamics of bacteriorhodopsin are investigated using molecular modelling, dynamical simulations and neutron scattering experiments. The simulations are performed on a model system consisting of one protein molecule plus intrinsic water molecules. The simulation-derived structure is compared with neutron diffraction data on the location of water and with the available electron microscopy structure of highest resolution. The simulated water geometry is in good accord with the neutron data. The protein structure deviates slightly but significantly from the experiment. The low-frequency vibrational frequency distribution of a low-hydration purple membrane is derived from inelastic neutron scattering data and compared with the corresponding simulation-derived quantity.