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Biomedical subjects

T P O'Connor

Publications and source records attributed to T P O'Connor.

At least 19 recordsLinked to original sources
PubMed2006

The anti-invasive compound motuporamine C is a robust stimulator of neuronal growth cone collapse.

Neuronal outgrowth is a fundamental process for normal development of the nervous system. Despite recent advances, the molecular mechanisms governing neuronal motility are still poorly understood. To provide insight into the intracellular signaling mechanisms required for neuronal outgrowth, we have characterized the effects of a compound previously identified for its anti-motility effects on transformed cells. We show that this compound, motuporamine C, acts as a robust inhibitor of chick neurite outgrowth in a dose-dependent fashion. Furthermore, in the presence of motuporamine C, growth cone collapse is observed, followed by neurite retraction. After removal, growth cones re-extend lamellipodial and filopodial processes and re-establish motility. Neurons exposed to motuporamine C exhibit a significant upregulation of active Rho-GTP. Additionally, effector-blocking experiments using Rho and Rho-associated kinase inhibitors indicate that the Rho pathway plays a critical role in motuporamine C-mediated growth cone collapse. Thus, we have characterized a novel anti-motility compound that has a robust inhibitory effect on neuronal outgrowth and involves signaling through the Rho-Rho kinase collapse pathway. Due to these robust effects, motuporamine C may serve as a valuable tool in further examining the intracellular mechanisms associated with growth cone motility.

Alkaloids↗
PubMed2005

Fine structure of the 1s3p 3PJ level in atomic 4He: theory and experiment.

The fine structure intervals in helium have been the focus of many theoretical and experimental studies in recent years with most of them concentrating on the 1s2p (3)P(J) levels. Here, we report on a theoretical calculation and an experimental determination of the 1s2p (3)P(J) fine structure intervals. The values from the theoretical calculation are 8113.730(6) and 658.801(6) MHz for the nu(01) and nu(12) intervals, respectively. The laser spectroscopic measurement reported here yields 8113.714(28) and 658.810(18) MHz for these intervals and is in excellent agreement with the theoretical calculation. Both, however, disagree significantly with the previous most precise experimental results.

Journal Article↗
PubMed2004

Laser spectroscopic determination of the 6He nuclear charge radius.

We have performed precision laser spectroscopy on individual 6He (t(1/2)=0.8 s) atoms confined and cooled in a magneto-optical trap, and measured the isotope shift between 6He and 4He to be 43 194.772+/-0.056 MHz for the 2(3)S1-3(3)P2 transition. Based on this measurement and atomic theory, the nuclear charge radius of 6He is determined for the first time in a method independent of nuclear models to be 2.054+/-0.014 fm. The result is compared with the values predicted by a number of nuclear structure calculations and tests their ability to characterize this loosely bound halo nucleus.

Journal Article↗
PubMed2004

Counting individual 41Ca atoms with a magneto-optical trap.

Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of 41Ca present in biomedical samples with isotopic abundance levels between 10(-8) and 10(-10). The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of 2x10(-7). Within 1 h of observation time, its 3-sigma detection limit on the isotopic abundance of 41Ca reaches 4.5x10(-10).

Calcium Radioisotopes↗
PubMed2004

Search for anomalously heavy isotopes of helium in the earth's atmosphere.

Our knowledge of the possible existence in nature of stable exotic particles depends solely upon experimental observation. Using a sensitive laser spectroscopy technique, we searched for a doubly charged particle accompanied by two electrons as an anomalously heavy isotope of helium in the Earth's atmosphere. The concentration of noble-gas-like atoms in the atmosphere and the subsequent very large depletion of the light (3,4)He isotopes allow stringent upper limits to be set on the abundance: 10(-12)-10(-17) per atom in the solar system over the mass range of 20-10 000 amu.

Journal Article↗
PubMed2004

Fatty acid profile, tocopherol, squalene and phytosterol content of walnuts, almonds, peanuts, hazelnuts and the macadamia nut.

Nuts are high in fat but have a fatty acid profile that may be beneficial in relation to risk of coronary heart disease. Nuts also contain other potentially cardioprotective constituents including phytosterols, tocopherols and squalene. In the present study, the total oil content, peroxide value, composition of fatty acids, tocopherols, phytosterols and squalene content were determined in the oil extracted from freshly ground walnuts, almonds, peanuts, hazelnuts and the macadamia nut. The total oil content of the nuts ranged from 37.9 to 59.2%, while the peroxide values ranged from 0.19 to 0.43 meq O2/kg oil. The main monounsaturated fatty acid was oleic acid (C18:1) with substantial levels of palmitoleic acid (C16:1) present in the macadamia nut. The main polyunsaturated fatty acids present were linoleic acid (C18:2) and linolenic acid (C18:3). alpha-Tocopherol was the most prevalent tocopherol except in walnuts. The levels of squalene detected ranged from 9.4 to 186.4 microg/g. beta-Sitosterol was the most abundant sterol, ranging in concentration from 991.2 to 2071.7 microg/g oil. Campesterol and stigmasterol were also present in significant concentrations. Our data indicate that all five nuts are a good source of monounsaturated fatty acid, tocopherols, squalene and phytosterols.

Arachis↗
PubMed2003

Dnase1l3 deficiency in lupus-prone MRL and NZB/W F1 mice.

Loss of deoxyribonuclease I (Dnase1) function is associated with systemic lupus erythematosus (SLE) in humans and mice; however, no coding mutations in Dnase1 are found in polygenic murine models. Instead, both MRL-lpr strains and NZB/W F1 hybrids are homozygous for T89I missense in the macrophage-DNASE, desoxyribonuclease I-like 3 (Dnase1l3). By in vitro expression studies, this substitution decreases this enzyme's nuclease activity against free DNA by only approximately twofold; however, the mutation has a greater effect on the capacity of media conditioned with Dnase1l3 to confer a barrier to liposomal gene transfection to HeLa cells. The 89I substitution decreases the Dnase1l3 barrier function in vitro by eightfold (P < 0.01). In splenocytes and BM-derived macrophages of SLE mice, while cellular Dnase1l3 levels are induced relative to C57BL/6 (control) mice, levels of FD-nuclease activity are similar. Finally, media conditioned by MRL and NZB/W F1 macrophages, relative to control, contains a weak interferon-gamma (IFN-gamma) inducible Dnase1l3-associated barrier to transfection. This barrier function is hypothesized to reflect the inability of SLE mice to degrade membrane-enveloped DNA-associated antigens, such as apoptotic bodies, which are predicted to stimulate the characteristic autoimmunity of SLE. Our results for these two generally independent models strongly suggest that Dnase1l3 deficiency increases the susceptibility of these mice to polygenic SLE.

Animals↗
PubMed2001

The permissive cue laminin is essential for growth cone turning in vivo.

The proper guidance of migrating growth cones relies on the balance of multiple guidance cues in the embryonic environment. In addition to guidance cues, growth cones are in contact with other substrates that may contribute to the pathfinding of neurons. For example, in the developing insect peripheral nervous system, pioneer neurons migrate on and between layers of the basal lamina. Previous studies have demonstrated that one basal lamina molecule, laminin, promotes outgrowth of many classes of neurons in vitro. In this study, the simple grasshopper nervous system was used to investigate the role of laminin in neuronal pathfinding. Laminin expression precedes axonogenesis of the Tibial (Ti1) pioneer neurons in the developing limb bud, and expression continues during outgrowth and guidance of the pioneer neurons. The role of a nidogen-binding motif on laminin was investigated using subunit-specific antibodies and peptides as blocking reagents in vivo. Antibodies and peptides that block the nidogen-binding site on laminin resulted in stalled Ti1 axon migration, predominantly at the precise location where they normally turn ventrally. After prolonged culturing, Ti1 axons remained stalled at the same location. Therefore, although Ti1 axons were capable of outgrowth in the presence of blocking reagents, they were not able to navigate an essential turn. This study indicates that the interaction of the Ti1 growth cone with the nidogen-binding site on laminin is vital for neuronal pathfinding in vivo and suggests that permissive cues may be essential for growth cone steering.

Animals↗
PubMed2001

The reconstruction of Kleiber's law at the organ-tissue level.

The relationship between resting energy expenditure (REE) (kJ/d) and body mass (M) (kg) is a cornerstone in the study of energy physiology. By expressing REE as a function of body mass observed across mammals, Kleiber formulated the now classic equation: REE = 293M(0.75). The biological processes underlying Kleiber's law have been a topic of long-standing interest and speculation. In the present report we develop a new perspective of Kleiber's law by developing an organ-tissue level REE model consisting of five components: liver, brain, kidneys, heart and remaining tissues. The resting thermal output of each component is the product of the component's specific resting metabolic rate (K) and mass (T). With increasing body size, the K values for all five components had negative exponents and were directly proportional to M(-0.08--0.27), and all component T values were directly proportional to M(0.76-1.01). The resulting exponents of the product (K x T) were M(0.60-0.86) for the five components. Although the (K x T) values of individual components do not scale equally, their combined formula (286M(0.76)) is similar to that observed by Kleiber on the whole-body level. Modeling mammalian REE at the organ-tissue level provides new insights and pathways for future mechanistic explorations of REE-body composition relationships.

Animals↗
PubMed2000

Effects of a silicone-coated polyamide net dressing and calcium alginate on the healing of split skin graft donor sites: a prospective randomised trial.

An open randomised prospectively controlled trial was performed to assess the healing efficacy, slippage rate and degree of discomfort on removal of calcium alginate and a silicone-coated polyamide net dressing on split skin graft donor sites. Sixteen patients were randomised to the calcium alginate group and 14 to the silicone-coated group. The donor sites were assessed at days 7, 10, 14 and up to day 21. The mean time to healing in the calcium alginate group was 8.75 +/- 0.78 days (range 7 to 14 days) compared to 12 +/- 0.62 days (range 7 to 16 days) for the silicone-coated group (p < 0.01). Although more silicone-coated dressings slipped (5 versus 1), the difference was not statistically significant. Pain during the first dressing change was assessed using a visual analogue pain scale. Although no significant differences were found between the groups, it was necessary to change the dressing protocol in the silicone-coated arm of the trial after entering the first two patients. Overlaid absorbent gauze adhered to the donor site through the fenestrations in the dressing necessitating the placement of paraffin gauze between the experimental dressing and the overlying cotton gauze. There was one infection in the study, occurring in the alginate group. Based on these results we recommend calcium alginate as the dressing of choice for split skin graft donor sites.

Adult↗
PubMed2000

Mechanisms of growth cone guidance and motility in the developing grasshopper embryo.

During neuronal pathfinding in vivo, growth cones must reorient their direction of migration in response to extracellular guidance cues. The developing grasshopper limb bud has proved to be a model system in which to examine mechanisms of growth cone guidance and motility in vivo. In this review we examine the contributions of adhesion and multiple guidance cues (semaphorins 1 and 2) in directing a growth cone steering event. Recent observations have suggested that the tibial pioneer growth cones are not directed via mechanisms of differential adhesivity. We present a model of growth cone steering that suggests a combination of adhesive and guidance receptors are important for a correct steering event and that guidance molecules may be important regulators of adhesive interactions with the actin cytoskeleton.

Animals↗
PubMed2000

Semaphorin function in the developing invertebrate peripheral nervous system.

Different members of the semaphorin family of secreted and transmembrane guidance molecules play important and diverse roles during neuronal development. Within the developing grasshopper limb bud, two semaphorins are expressed in relatively non-overlapping and distinct expression patterns. The establishment of the tibial sensory projection within the limb bud relies on the combinatorial action of both semaphorins. In this review, we describe the function of the two semaphorins in axonal guidance and propose that a hierarchy of cues guide sensory neurons in the developing peripheral nervous system.

Animals↗
PubMed1999

Filopodial adhesion does not predict growth cone steering events in vivo.

Migration of growth cones is in part mediated by adhesive interactions between filopodia and the extracellular environment, transmitting forces and signals necessary for pathfinding. To elucidate the role of substrate adhesivity in growth cone pathfinding, we developed an in vivo assay for measuring filopodial-substrate adhesivity using the well-characterized Ti pioneer neuron pathway of the embryonic grasshopper limb. Using time-lapse imaging and a combination of rhodamine-phalloidin injections and DiI labeling, we demonstrate that the filopodial retraction rate after treatment with cytochalasin D or elastase reflects the degree of filopodial-substrate adhesivity. Measurements of filopodial retraction rates along regions of known differing substrate adhesivities confirmed the use of this assay to examine filopodial-substrate adhesion during in vivo pathfinding events. We analyzed 359 filopodia from 22 Ti growth cones and found that there is no difference between the retraction rates of filopodia extending toward the correct target (on-axis) and filopodia extending away from the correct target (off-axis). These results indicate on-axis and off-axis filopodia have similar substrate adherence. Interestingly, we observed a 300% increase in the extension rates of on-axis filopodia during Ti growth cone turning events. Therefore, in addition to providing filopodia with important guidance information, regional cues are capable of modulating the filopodial extension rate. The homogeneity in filopodial retraction rates, even among these turning growth cones in which differential adhesivity might be expected to be greatest, strongly establishes that differential adhesion does not govern Ti pioneer neuron migration rate or pathfinding. We propose that the presence of local differences in receptor-mediated second messenger cascades and the resulting assembly of force-generating machinery may underlie the ability of filopodial contacts to regulate growth cone steering in vivo.

Animals↗
PubMed1999

Ectopic semaphorin-1a functions as an attractive guidance cue for developing peripheral neurons.

Transmembrane and secreted glycoproteins of the semaphorin family are typically classified as inhibitory neuronal guidance molecules. However, although chemorepulsive activity has been demonstrated for several semaphorin family members, little is known about the function of the numerous transmembrane semaphorins identified to date. Here we demonstrated that the extracellular semaphorin domain of a transmembrane semaphorin, semaphorin-1a, could actively perturb axon pathfinding in vivo when presented homogenously as a recombinant freely soluble factor. When ectopic overexpression was limited to defined epithelial regions, semaphorin-1a could directly steer axons by acting as an attractive guidance molecule.

Amino Acid Sequence↗
PubMed1999

Ontogeny of intestinal safety factors: lactase capacities and lactose loads.

We measured intestinal safety factors (ratio of a physiological capacity to the load on it) for lactose digestion in developing rat pups. Specifically, we assessed the quantitative relationships between lactose load and the series capacities of lactase and the Na+-glucose cotransporter (SGLT-1). Both capacities increased significantly with age in suckling pups as a result of increasing intestinal mass and maintenance of mass-specific activities. The youngest pups examined (5 days) had surprisingly high safety factors of 8-13 for both lactase and SGLT-1, possibly because milk contains lactase substrates other than lactose; it also, however, suggests that their intestinal capacities were being prepared to meet future demands rather than just current ones. By day 10 (and also at day 15), increased lactose loads resulted in lower safety factors of 4-6, values more typical of adult intestines. The safety factor of SGLT-1 in day 30 (weanling) and day 100 (adult) rats was only approximately 1.0. This was initially unexpected, because most adult intestines maintain a modest reserve capacity beyond nutrient load values, but postweaning rats appear to use hindgut fermentation, assessed by gut morphology and hydrogen production assays, as a built-in reserve capacity. The series capacities of lactase and SGLT-1 varied in concert with each other over ontogeny and as lactose load was manipulated by experimental variation in litter size.

Aging↗
PubMed1999

Magnitude of functional adaptation after intestinal resection.

Intestinal adaptation after resection has been much studied, but rarely examined in an integrative context. Hence we assessed the effects of resection and subsequent adaptation on the quantitative relationship between dietary glucose load and gut capacity to transport glucose. The ratio of capacity to load is termed the "safety factor." Our objectives were to determine 1) the time course of intestinal adaptation after resection, 2) whether adaptation is quantitatively complete, 3) whether survival requires maintaining a safety factor of at least 1.0 for glucose transport, 4) the effect of altered energy demands on adaptation, and 5) the relationship between the amount of tissue removed and the magnitude of functional adaptation. We performed 80% resection of the small intestine on Sprague-Dawley rats and measured small intestinal glucose uptake capacity, dietary glucose load, and gut gross morphology at 1, 5, and 10 wk postsurgery. Nearly all aspects of adaptation were complete by 1 wk postsurgery. After resection, remnant small intestine mass increased by over fivefold within 1 wk, to reach 50-70% of its preresection value. However, mass-specific glucose uptake activity was reduced, so that intestinal regeneration restored uptake capacity to only 33% of control values. Increased energetic demands had only modest effects on intestinal adaptation. Although the safety factor for small intestinal glucose uptake remained <1.0 (i.e., capacity < load) after adaptation to resection, nearly all rats survived. Hindgut fermentation of nonabsorbed nutrients appeared to contribute to that survival, despite inadequate small intestinal capacity. After less massive resection surgeries (25, 50, and 75% resections), the percent increase in glucose uptake capacity increased with the amount of tissue removed.

Adaptation, Physiological↗
PubMed1999

Discrete roles for secreted and transmembrane semaphorins in neuronal growth cone guidance in vivo.

From the initial stages of axon outgrowth to the formation of a functioning synapse, neuronal growth cones continuously integrate and respond to multiple guidance cues. To investigate the role of semaphorins in the establishment of appropriate axon trajectories, we have characterized a novel secreted semaphorin in grasshopper, gSema 2a. Sema 2a is expressed in a gradient in the developing limb bud epithelium during Ti pioneer axon outgrowth. We demonstrate that Sema 2a acts as chemorepulsive guidance molecule critical for axon fasciculation and for determining both the initial direction and subsequent pathfinding events of the Ti axon projection. Interestingly, simultaneous perturbation of both secreted Sema 2a and transmembrane Sema I results in a broader range and increased incidence of abnormal Ti pioneer axon phenotypes, indicating that different semaphorin family members can provide functionally distinct guidance information to the same growth cone in vivo.

Amino Acid Sequence↗