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Biomedical subjects

J C Smith

Publications and source records attributed to J C Smith.

At least 181 records · Page 10Linked to original sources
PubMed1997

Functional respiratory rhythm generating networks in neonatal mice lacking NMDAR1 gene.

N-methyl-D-aspartate (NMDA) receptor-mediated synaptic transmission is implicated in activity-dependent developmental reorganization in mammalian brain, including sensory systems and spinal motoneuron circuits. During normal development, synaptic interactions important in activity-dependent modification of neuronal circuits may be driven spontaneously (Shatz 1990b). The respiratory system exhibits substantial spontaneous activity in utero; this activity may be critical in assuring essential and appropriate breathing movements from birth. We tested the hypothesis that NMDA receptors are necessary for prenatal development of central neural circuits underlying respiratory rhythm generation by comparing the responsiveness of control mice and mutant mice lacking the NMDA receptor R1 subunit (NMDAR1) gene to glutamate receptor agonists and antagonists and comparing endogenous respiratory-related oscillations generated in vitro by brain stem-spinal cord and medullary slice preparations from control and mutant mice. In control mice, local application of NMDA and the non-NMDA receptor agonist, (R,S)-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid hydrobromide (AMPA), over the pre-Bötzinger Complex, the C4 cervical motor neuron pool, and the hypoglossal motor nucleus produced profound increases in inspiratory frequency, tonic discharge on C4 ventral nerve roots, and inward currents in inspiratory hypoglossal motoneurons, respectively. Responses of mutant mice to AMPA were similar. However, mutant mice were completely unresponsive to NMDA applications. Preparations from mutant mice generated a respiratory rhythm virtually identical to control. Results demonstrate that NMDA receptors are not essential for respiratory rhythm generation or drive transmission in the neonate. More importantly, they suggest that NMDA receptors are not obligatory for the prenatal development of circuits producing respiratory rhythm.

Animals↗
PubMed1997

Analysis of competence and of Brachyury autoinduction by use of hormone-inducible Xbra.

Analysis of gene function in Xenopus development frequently involves over-expression experiments, in which RNA encoding the protein of interest is microinjected into the early embryo. By taking advantage of the fate map of Xenopus, it is possible to direct expression of the protein to particular regions of the embryo, but it has not been possible to exert control over the timing of expression; the protein is translated immediately after injection. To overcome this problem in our analysis of the role of Brachyury in Xenopus development, we have, like Kolm and Sive (1995; Dev. Biol. 171, 267-272), explored the use of hormone-inducible constructs. Animal pole regions derived from embryos expressing a fusion protein (Xbra-GR) in which the Xbra open reading frame is fused to the ligand-binding domain of the human glucocorticoid receptor develop as atypical epidermis, presumably because Xbra is sequestered by the heat-shock apparatus of the cell. Addition of dexamethasone, which binds to the glucocorticoid receptor and releases Xbra, causes formation of mesoderm. We have used this approach to investigate the competence of animal pole explants to respond to Xbra-GR, and have found that competence persists until late gastrula stages, even though by this time animal caps have lost the ability to respond to mesoderm-inducing factors such as activin and FGF. In a second series of experiments, we demonstrate that Xbra is capable of inducing its own expression, but that this auto-induction requires intercellular signals and FGF signalling. Finally, we suggest that the use of inducible constructs may assist in the search for target genes of Brachyury.

Activins↗
PubMed1997

The ALK-2 and ALK-4 activin receptors transduce distinct mesoderm-inducing signals during early Xenopus development but do not co-operate to establish thresholds.

The TGFbeta family member activin induces different mesodermal cell types in a dose-dependent fashion in the Xenopus animal cap assay. High concentrations of activin induce dorsal and anterior cell types such as notochord and muscle, while low concentrations induce ventral and posterior tissues such as mesenchyme and mesothelium. In this paper we investigate whether this threshold phenomenon involves the differential effects of the two type I activin receptors ALK-2 and ALK-4. Injection of RNA encoding constitutively active forms of the receptors (here designated ALK-2* and ALK-4*) reveals that ALK-4* strongly induces the more posterior mesodermal marker Xbra and the dorsoanterior marker goosecoid in animal cap explants. Maximal levels of Xbra expression are attained using lower concentrations of RNA than are required for the strongest activation of goosecoid, and at the highest doses of ALK-4*, levels of Xbra transcription decrease, as is seen with high concentrations of activin. By contrast, the ALK-2* receptor activates Xbra but fails to induce goosecoid to significant levels. Analysis at later stages reveals that ALK-4* signalling induces the formation of a variety of mesodermal derivatives, including dorsal cell types, in a dose-dependent fashion, and that high levels also induce endoderm. By contrast, the ALK-2* receptor induces only ventral mesodermal markers. Consistent with these observations, ALK-4* is capable of inducing a secondary axis when injected into the ventral side of 32-cell stage embryos whilst ALK-2* cannot. Co-injection of RNAs encoding constitutively active forms of both receptors reveals that ventralising signals from ALK-2* antagonise the dorsal mesoderm-inducing signal derived from ALK-4*, suggesting that the two receptors use distinct and interfering signalling pathways. Together, these results show that although ALK-2* and ALK-4* transduce distinct signals, the threshold responses characteristic of activin cannot be due to interactions between these two pathways; rather, thresholds can be established by ALK-4* alone. Furthermore, the effects of ALK-2* signalling are at odds with it behaving as an activin receptor in the early Xenopus embryo.

Activin Receptors, Type I↗
PubMed1997

Two patients with asymmetric crying facies, normal cardiovascular systems and deletion of chromosome 22q11.

We report two unrelated patients with Asymmetric Crying Facies (ACF) and 22q11 deletion. In the first case ACF was the presenting feature. Fluorescent In Situ Hybridization (FISH) revealed 22q11 deletion and subsequent echocardiography demonstrated a normal cardiovascular system. The second presented with hypoparathyroidism, shown on FISH to be secondary to 22q11 deletion. Echocardiography was normal and ACF was found incidentally. Deletion of 22q11 has been reported with ACF occurring as part of the Cardiofacial syndrome (CFS) [Giannotti A, Mingarelli R, (1994): Am J Med Genet 53: 303-304] but this is the first report of ACF with 22q11 deletion in the absence of cardiac abnormalities. A review of the literature pertaining to ACF is presented.

Cardiovascular System↗
PubMed1997

Rats with area postrema lesions have lengthy eating and drinking bouts when fed ad libitum: implications for feedback inhibition of ingestive behavior.

Ad libitum ingestive behavior of rats with area postrema lesions (APX) was monitored electronically every 6 s for 23 hr. Whereas control rats ate on average 32.2 g of food each day in 16.3 distinct bouts, rats with APX ate comparable amounts of food (28.6 g) in much fewer daily bouts (5.8) that were very large. Controls drank 38.4 ml of water daily in 17.8 bouts, whereas rats with APX consumed more than twice as much water (101.5 ml) in a similar number of bouts (18.5). Controls drank 5.3 ml of 0.5 M NaCl daily in 7.0 bouts, whereas rats with APX consumed 9 times as much saline (45.5 ml) in more bouts (18.2) that were relatively large. These and other results suggest that the area postrema plays an important role in detecting inhibitory signals generated by food or fluid intake and that feeding and drinking bouts may increase in size after APX, because the feedback inhibition provided by those signals is diminished.

Afferent Pathways↗
PubMed1997

L-2-chloropropionic acid inhibits glutamate and aspartate release from rat cerebellar slices but does not activate cerebellar NMDA receptors: implications for L-2-chloropropionic acid-induced neurotoxicity.

L-2-Chloropropionic acid (L-CPA), when orally administered at single high dose to rats produces a selective lesion in the cerebellum involving destruction of a high proportion of granule cells by a mechanism which involves N-methyl-D-aspartate (NMDA) receptors. Receptor binding studies demonstrated that L-CPA a had low affinity at the glutamate and glycine binding sites at NMDA receptors (530-660 microM), respectively, whereas L-CPA did not displace [3H]AMPA, [3H]NBQX or [3H]kainate from AMPA or kainate receptors. Whole cell-patch clamp experiments using cultured granule cells failed to demonstrate changes in membrane potential of cultured granule cells when either L-CPA (0.25 or 1 microM) was added alone to the bathing solution, or in combination with glycine (10 microM). Furthermore L-CPA did not alter the magnitude of the inward current produced by application of NMDA (100 microM)) to cultured granule cells, in the presence of glycine, as measured by patch clamp techniques. Experiments were also performed to discover whether L-CPA may alter the release of the excitatory amino acids from the cerebellum, which may then indirectly alter activity at glutamate receptors, leading to neuronal cell death. L-CPA (2 mM) did not affect either basal or stimulated (electrical or high potassium) endogenous aspartate release from superfused cerebellar slices nor did it alter the basal or stimulated release of [3H]aspartate from preloaded slices when introduced into the superfusion medium over 30 min. However, when cerebellar slices were preincubated with 2 mM L-CPA for 2 h at concentrations that are known to be neurotoxic to the brain in vivo, but not in vitro, the stimulated endogenous glutamate and aspartate net release was significantly attenuated, as compared to controls. Basal release was not significantly affected by the introduction of L-CPA-induced cerebellar neurotoxicity may be related to the inhibition of excitatory amino acid release from the cerebellum. In conclusion, although L-CPA does not appear to directly alter NMDA receptor activity the L-CPA-induced cerebellar neurotoxicity may be related to the inhibition of excitatory amino acid release from the cerebellum.

Animals↗
PubMed1997

Picosecond dynamical changes on denaturation of yeast phosphoglycerate kinase revealed by quasielastic neutron scattering.

Quasielastic neutron scattering experiments performed on yeast phosphoglycerate kinase in the native form and denatured in 1.5 M guanidinium chloride reveal a change in the fast (picosecond time scale) diffusive internal dynamics of the protein. The momentum and energy transfer dependences of the scattering for both states are fitted by an analytical model in which, on the experimentally accessible picosecond time scale and angstrom length scale, the dynamics of a fraction of the nonexchangeable hydrogens in the protein is described as a superposition of vibrations with uniform diffusion in a sphere, the rest of the hydrogens undergoing only vibrational motion. The fraction diffusing changes, from approximately 60% in the native protein to approximately 82% in the denatured protein. The radius of the sphere also changes slightly, from approximately 1.8 A in the native protein to approximately 2.2 A in the denatured protein. Possible implications of these results for the general protein folding problem are discussed.

Guanidine↗
PubMed1997

Adjuvant intrapleural amphotericin B therapy for pulmonary mucormycosis in a cardiac allograft recipient.

Infectious complications after heart transplantation remain a major cause of morbidity and mortality. While many viral, bacterial, and protozoal infections can be successfully treated, fungal infections continue to be challenging. Mucormycosis is a rare infection in heart transplant recipients; however, mortality is exceedingly high. We report a case of cavitary Rhizopus lung infection 2 months after cardiac transplantation. The infection was complicated by inadvertent exposure of the pleural cavity to the fungus during surgical resection. Therapy consisted of standard systemic amphotericin B, surgical excision, and for the first time, the use of adjuvant intrapleural amphotericin B. Cure was achieved with no clinical or radiological evidence of disease at 3 months follow-up. Rhizopus pulmonary infection is a rare complication of cardiac transplantation. Treatment consists of the triad of systemic anti-fungal therapy, surgical resection, and control of any underlying predisposing diseases. Adjuvant intrapleural amphotericin B use could also be considered in patients with fungal pneumonias and evidence of chest wall and/or pleural cavity involvement.

Amphotericin B↗
PubMed1996

Signalling by TGF-beta family members: short-range effects of Xnr-2 and BMP-4 contrast with the long-range effects of activin.

BACKGROUND: One way of establishing a morphogen gradient in a developing embryo involves the localized synthesis of an inducing molecule followed by its diffusion into surrounding tissues. The morphogen-like effects of the mesoderm-inducing factor activin provide support for this idea in amphibian development. The questions remain, however, of how activin exerts its long-range effects, and whether long-range signalling is a property of all transforming growth factor beta (TGF-beta) family members. RESULTS: We compare the signalling ranges of activin and two other TGF-beta family members, Xnr-2 and BMP-4. Unlike activin, Xnr-2 and BMP-4 act over short distances. Furthermore, the effects of constitutively active activin receptors are strictly cell-autonomous. These observations suggest that the long-range effects of activin occur through protein diffusion and that "relay' mechanisms are not initiated by any of these TGF-beta family members. Mechanisms limiting the signalling range of Xnr-2 were addressed by studying Xnr-2 processing and secretion. An activin-Xnr-2 fusion protein signals over many cell diameters, suggesting that regulated processing or secretion is one limiting factor. Disaggregation and reaggregation of Xnr-2-producing tissues also extends the range of Xnr-2, suggesting that components of intact tissue restrict spread of the protein. CONCLUSIONS: The long-range effects of activin are likely to occur through the diffusion of activin protein. The short-range effects of Xnr-2 and BMP-4 emphasize that long-range diffusion is not a general property of TGF-beta-related molecules. Finally, signalling ranges may be regulated by constraints on processing or secretion and by interactions with extracellular components of embryonic tissues.

Activin Receptors, Type I↗
PubMed1996

Regulation of embryonic cell division by a Xenopus gastrula-specific protein kinase.

We describe a novel protein kinase, Pk9.7, and its role in cell division in the Xenopus embryo. Pk9.7 is transcribed only during blastula and gastrula stages. Expression of Pk9.7 in Xenopus oocytes induces meiotic maturation, while overexpression in embryos blocks blastomere cleavage in a MAP kinase-independent fashion. In both Pk9.7-injected oocytes and mitotic cells of cleavage-blocked embryos, chromosomes appear detached from abnormal spindles, and in oocytes additional microtubule structures are formed, suggesting that one function of Pk9.7 is to regulate formation of, and chromosome attachment to, the spindle. Consistent with this, Pk9.7 co-immunoprecipitates tubulin and phosphorylates it in vitro. Pk9.7 expression coincides with the switch from maternal to zygotic control of the cell cycle, and with the switch from microtubule independence to microtubule dependence. Our results suggest that Pk9.7 plays a role in these processes.

Animals↗
PubMed1996

Structure of a specific peptide complex of the carboxy-terminal SH2 domain from the p85 alpha subunit of phosphatidylinositol 3-kinase.

We have determined the solution structure of the C-terminal SH2 domain of the p85 alpha subunit of human phosphatidylinositol (PI) 3-kinase (EC 2.7.1.137) in complex with a phosphorylated tyrosine pentapeptide sequence from the platelet-derived growth factor receptor using heteronuclear nuclear magnetic resonance spectroscopy. Overall, the structure is similar to other SH2 domain complexes, but displays different detail interactions within the phosphotyrosine binding site and in the recognition site for the +3 methionine residue of the peptide, the side chain of which inserts into a particularly deep and narrow pocket which is displaced relative to that of other SH2 domains. The contacts made within this +3 pocket provide the structural basis for the strong selection for methionine at this position which characterizes the SH2 domains of PI3-kinase. Comparison with spectral and structural features of the uncomplexed domain shows that the long BG loop becomes less mobile in the presence of the bound peptide. In contrast, extreme resonance broadening encountered for most residues in the beta D', beta E and beta F strands and associated connecting loops of the domain in the absence of peptide persists in the complex, implying conformational averaging in this part of the molecule on a microsecond-to-millisecond time scale.

Amino Acid Sequence↗
PubMed1996

Abortion surveillance--United States, 1992.

PROBLEM/CONDITION: From 1980 through 1992, the number of legal induced abortions reported to the CDC remained stable, varying each year by < or = 5%. REPORTING PERIOD COVERED: This report summarizes and reviews information reported to CDC regarding legal induced abortions obtained in the United States during 1992. This report also includes recently reported abortion-related deaths for 1988-1991 and an update on abortion-related deaths for 1985-1987. DESCRIPTION OF SYSTEM: For each year since 1969, CDC has compiled abortion data received from 52 reporting areas (i.e., the 50 states, the District of Columbia, and New York City). RESULTS: In 1992, 1,359,145 abortions were reported--a 2.1% decrease from 1991. The abortion ratio was 335 legal induced abortions per 1,000 live births, and the abortion rate was 23 per 1,000 women 15-44 years of age. Women who were undergoing an abortion were more likely to be young, white, and unmarried; most had had no previous live births and were obtaining an abortion for the first time. More than half (51%) of all abortions were performed at or before the 8th week of gestation, and 87% were before the 13th week. Approximately 14% of abortions were performed at < or = 6 weeks of gestation, 15% were performed at 7 weeks of gestation, and 22% at 8 weeks of gestation. Younger women (i.e., women < or = 19 years of age) were more likely to obtain abortions later in pregnancy than were older women. Sixteen deaths in 1988, 12 deaths in 1989, and five deaths in 1990 were associated with legal induced abortion. The case-fatality rates for 1988, 1989, and 1990, respectively, were 1.2, 0.9, and 0.3 abortion-related deaths per 100,000 legal induced abortions. INTERPRETATION: Since 1980, the number and rate of abortions have remained relatively stable, with only small year-to-year fluctuations of < or = 5%. However, since 1987, the abortion-to-live-birth ratio has declined; in 1992, the abortion ratio was the lowest recorded since 1977. More pregnant women have been opting to carry their pregnancies to term rather than choosing to have an abortion. As in previous years, deaths associated with legal induced abortions occurred rarely (i.e., one or fewer deaths per 100,000 legal induced abortions). ACTIONS TAKEN: The number and characteristics of women who obtain abortions in the United States should continue to be monitored so that efforts to prevent unintended pregnancy can be assessed and the preventable causes of morbidity and mortality associated with abortions can be identified and reduced.

Abortion, Legal↗
PubMed1996

Transposon tools for recombinant DNA manipulation: characterization of transcriptional regulators from yeast, Xenopus, and mouse.

Transposon Tn1000 has been adapted to deliver novel DNA sequences for manipulating recombinant DNA. The transposition procedure for these "tagged" Tn1000s is simple and applicable to most plasmids in current use. For yeast molecular biology, tagged Tn1000s introduce a variety of yeast selective markers and replication origins into plasmids and cosmids. In addition, the beta-globin minimal promoter and lacZ gene of Tn(beta)lac serve as a mobile reporter of eukaryotic enhancer activity. In this paper, Tn(beta)lac was used to localize a mouse HoxB-complex enhancer in transgenic mice. Other tagged transposons create Gal4 DNA-binding-domain fusions, in either Escherichia coli or yeast plasmids, for use in one- and two-hybrid tests of transcriptional activation and protein-protein interaction, respectively. With such fusions, the Saccharomyces cerevisiae Swi6 G1/S-phase transcription factor and the Xenopus laevis Pintallavis developmental regulator are shown to activate transcription. Furthermore, the same transposon insertions also facilitated mapping of the Swi6 and Pintallavis domains responsible for transcriptional activation. Thus, as well as introducing novel sequences, tagged transposons share the numerous other applications of transposition such as producing insertional mutations, creating deletion series, or serving as mobile primer sites for DNA sequencing.

Animals↗
PubMed1996

Structural model of the anti-snake-toxin antibody, M alpha 2,3.

We present results of structural modeling of the variable fragment of M alpha 2,3, an antibody capable of neutralizing all short snake toxins. Three different methods were used to model the hypervariable loops: the conformational search algorithm CONGEN (Bruccoleri and Karplus, Biopolymers 26:137-168, 1987), high-temperature molecular dynamics (Bruccoleri and Karplus, Biopolymers 29:1847-1862, 1990), and a combined knowledge-based and energy-based algorithm (Martin et al., Proc. Natl. Acad. Sci. USA 86:9268-9272, 1989). Ninety plausible conformations were generated and were clustered into 13 classes. The clustering results indicate that there was little overlap of the conformational space explored by the different methods. Canonical loop structures were found by all methods for two of the loops, in agreement with previously established empirical modeling criteria. Nine of the 13 classes of structure were rejected on the ground of their lacking common features of antibody combining-site structure. The remaining four models were refined using restrained molecular dynamics. It was found that interconversion between the four resulting structures is possible with no significant energy barriers, suggesting that they are in thermodynamic equilibrium at 300 K. Features of the combining-site structure likely to be particularly important for antigen binding are discussed.

Algorithms↗
PubMed1996

Methyl mercury pharmacokinetics in man: a reevaluation.

Data taken from Aberg et al. ((1969) Arch. Environ. Health 19, 478-484) and Miettinen et al. ((1971) Ann. Clin. Res. 3, 116-122) were analyzed by means of models that describe methyl mercury pharmacokinetics in man in terms of parent compound only (Model I) or in terms of parent compound plus metabolite, inorganic mercury (Model II). Fecal and urinary excretion of mercury are linear for both models. In Model I all excreted mercury arises from a common pool. This model successfully simulates the time profiles for body total mercury and fecal excretion but fails to explain the continuous increase in daily urinary mercury that occurs for several weeks following methyl mercury administration. In Model II fecal mercury arises from the methyl mercury compartment and urinary mercury from the inorganic mercury compartment. Simulations from this model are comparable to those from Model I for body total mercury and fecal excretion but are significantly more precise for urinary excretion. Model II also accounts for the observation (Miettinen et al., 1971) that blood mercury comprises a steadily declining proportion of body mercury burden for at least 91 days after methyl mercury dosing. Data simulated by means of Model II, using parameters estimated from Aberg's and Miettinen's data sets, predict methyl mercury half-lives of 51 and 56 days, respectively. These values are comparable to the methyl mercury half-life of 44 days reported by Smith et al. ((1994) Toxicol. Appl. Pharmacol. 128, 251-256) and are approximately 70% of half-lives reported by Aberg and Miettinen.

Body Burden↗