Biomedical subjects

M A Riley

Publications and source records attributed to M A Riley.

At least 19 recordsLinked to original sources

PubMed2005

p-sd Shell gap reduction in neutron-rich systems and cross-shell excitations in 20 O.

Excited states in 20O were populated in the reaction 10Be(14C,alpha) at Florida State University (FSU). Charged particles were detected with a particle telescope consisting of 4 annularly segmented Si surface barrier detectors and gamma radiation was detected with the FSU gamma detector array. Five new states were observed below 6 MeV from the alpha-gamma and alpha-gamma-gamma coincidence data. Shell model calculations suggest that most of the newly observed states are core-excited 1p-1h excitations across the N=Z=8 shell gap. Comparisons between experimental data and calculations for the neutron-rich O and F isotopes imply a steady reduction of the p-sd shell gap as neutrons are added.

Journal Article↗

PubMed2005

The use of (symmetry) group theory as a predictive tool for studying bimanual coordination.

Symmetry groups-rules that connect different configurations of a given set of components-represent a compact means of coding for effects, a feature that is desirable in both model- and theory-building. The present study was designed to compare the effects of spatial orientation differences with the various other asymmetries (e.g., timing differences, handedness preferences, the direction of attention) that are accommodated by current models of bimanual coordination. The authors used symmetry groups to predict specific patterns of results. In 2 experiments, participants (N = 13, Experiment 1; N = 9, Experiment 2) coordinated the movements of differently oriented (1 downward and 1 upward) pendulum pairs at a low (0.62 Hz) or high (0.82 Hz) movement frequency to establish an in-phase or antiphase pattern. Consistent with previous results (P. G. Amazeen, E. L. Amazeen, & M. T. Turvey, 1998a), the downward-oriented pendulum tended to lead slightly. In contrast to the effects of other bimanual asymmetries, the downward-oriented pendulum lead was amplified at low frequencies. Although the results contradicted the predictions of existing models of bimanual coordination, they were consistent with predictions from symmetry group theory. In the discussion, the authors focus on the application of symmetry groups to both bimanual coordination and other phenomena with more complex symmetric structures.

Adult↗

PubMed2005

Effects of visual and auditory short-term memory tasks on the spatiotemporal dynamics and variability of postural sway.

The authors measured postural sway while participants (N = 20 in each experiment) stood on a rigid or a compliant surface, with their eyes open or closed, and while they did or did not perform a short-term memory (STM) task. In Experiment 1, the STM stimuli were presented visually; in Experiment 2, the stimuli were presented auditorily. In both experiments, fine-scaled, mediolateral postural-sway variability decreased as the cognitive load imposed by the STM task increased. That effect was independent of support surface and vision manipulations. The spatiotemporal profile of postural sway was affected by both visual and auditory STM tasks, but to a greater degree by the auditory task. The authors discuss implications of the results for theories and models of postural control.

Adolescent↗

PubMed2005

Cross-generational effect of prenatal morphine exposure on neurobehavioral development of rat pups.

Prenatal exposure to opiates can have devastating effects on the development of human fetuses and may induce long-term physical and neurobehavioral changes during postnatal maturation. The present study was aimed at identifying cross-generational effects of prenatal morphine exposure in Sprague-Dawley rats. Pregnant rats were injected subcutaneously with either saline or morphine (10 mg/kg) twice daily during gestational days 11-18. Litter size, percentage of males and females, anogenital distances (AGDs), righting reflex, and body weight were assessed in prenatally morphine-exposed pups (first generation) and their offspring (second generation). Both prenatally morphine-exposed pups and offspring of prenatally morphine-exposed dams exhibited an increased latency to right. Additionally, second generation pups were slower in righting than first generation pups. During the early postnatal period the second generation pups weighed less than the first generation regardless of drug exposure. The AGDs of second generation male pups were decreased relative to the first generation. Our data provide important novel information about the trans-generational effects of maternal opiate abuse that may be useful for understanding/evaluating the teratogenic effects of prenatal opiate exposure.

Analgesics, Opioid↗

PubMed2004

High-spin structure beyond band termination in 157Er.

The angular-momentum induced transition from a deformed state of collective rotation to a noncollective configuration has been studied. In 157Er this transition manifests itself as favored band termination near I=45 Planck's. The feeding of these band terminating states has been investigated for the first time using the Gammasphere spectrometer. Many weakly populated states lying at high excitation energy that decay into these special states have been discovered. Cranked Nilsson-Strutinsky calculations suggest that these states arise from weakly collective "core-breaking" configurations.

Journal Article↗

PubMed2004

Field-specific changes in hippocampal opioid mRNA, peptides, and receptors due to prenatal morphine exposure in adult male rats.

Alterations in the opioid system in the hippocampal formation and some of the possible functional consequences were investigated in adult male rats that were prenatally exposed to either saline or morphine (10 mg/kg twice daily on gestational days 11-18). In situ hybridization and Northern blots were used to measure proenkephalin and prodynorphin mRNA, and radioimmunoassays quantified proenkephalin- and prodynorphin-derived peptide levels in the dentate gyrus, CA3, and CA1 subfields of the hippocampal formation. Prenatal morphine exposure in male rats decreases proenkephalin and increases prodynorphin mRNA selectively in the granule cell layer of the dentate gyrus. Similarly, met-enkephalin peptide levels are decreased and dynorphin B peptide levels are increased in the dentate gyrus but not CA3 or CA1 of prenatally morphine-exposed males. In addition, there are decreases in dynorphin-derived peptides in the CA3 subfield. Receptor autoradiography revealed increases in the density of micro but not delta receptor labeling in discrete strata of specific hippocampal subfields in morphine-exposed males. Because alterations in the hippocampal opioid system suggest possible alterations in the excitability of the hippocampal formation, changes in opioid regulation of seizures were examined. Morphine exposure, however, does not alter the latency to onset or number of episodes of wet dog shakes or clonic seizures induced by infusion of 10 nmol [D-Ala2, MePhe4, Gly-ol5]enkephalin into the ventral hippocampal formation. Interestingly, a naloxone (5 mg/kg) injection 30 min before bicuculline administration reverses the increased latency to onset of clonic and tonic-clonic seizures in morphine-exposed males. Thus, the present study suggests that exposure of rats to morphine during early development alters the hippocampal opioid system, suggesting possible consequences for hippocampal-mediated functions.

Animals↗

PubMed2003

A phylogenetic approach to assessing the targets of microbial warfare.

Bacteriocins are the most abundant and diverse defense systems in bacteria. As a result of the specific mechanisms of bacteriocin recognition and translocation into the target cell it is assumed that these toxins mediate intra-specific or population-level interactions. However, no published studies specifically address this question. We present here a survey of bacteriocin production in a collection of enteric bacteria isolated from wild mammals in Australia. A subset of the bacteriocin-producing strains was assayed for the ability to kill a broad range of enteric bacteria from the same bacterial collection. A novel method of estimating killing breadth was developed and used to compare the surveyed bacteriocins in terms of the phylogenetic range over which they kill. The most striking result is that although bacteriocin-producers kill members of their own species most frequently, some kill phylogenetically distant taxa more frequently than they kill closer relatives. This study calls into question the role these toxins play in natural populations. A significant number of bacteriocins are highly effective in killing inter-specific strains and thus bacteriocins may serve to mediate bacterial community interactions.

Bacteriocins↗

PubMed2003

A molecular phylogeny of enteric bacteria and implications for a bacterial species concept.

A molecular phylogeny for seven taxa of enteric bacteria (Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Hafnia alvei, Klebsiella oxytoca, Klebsiella pneumoniae, and Serratia plymuthica) was made from multiple isolates per taxa taken from a collection of environmental enteric bacteria. Sequences from five housekeeping genes (gapA, groEL, gyrA, ompA, and pgi) and the 16S rRNA gene were used to infer individual gene trees and were concatenated to infer a composite molecular phylogeny for the species. The isolates from each taxa formed tight species clusters in the individual gene trees, suggesting the existence of 'genotypic' clusters that correspond to traditional species designations. These sequence data and the resulting gene trees and consensus tree provide the first data set with which to assess the utility of the recently proposed core genome hypothesis (CGH). The CGH provides a genetically based approach to applying the biological species concept to bacteria.

DNA, Bacterial↗

PubMed2002

Quadrupole moments of highly deformed structures in the A approximately 135 region: probing the single-particle motion in a rotating potential.

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei ( >30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.

Journal Article↗

PubMed2001

Characterization and screening of microsatellite loci in a wild lemur population (Propithecus verreauxi verreauxi).

Sixteen dinucleotide microsatellite loci were isolated from the genome of Propithecus verreauxi verreauxi. All loci were polymorphic when genotyped on a minimum of 16 animals. The number of alleles across these loci ranges from two to 11. Additionally, seven of these loci were genotyped across a minimum of 200 animals in order to estimate heterozygosity and their potential for parentage assignment in this population. Using these seven loci, the mean heterozygosity in this population is 0.705, and the combined probability of these seven loci to exclude a random individual from parentage, when one parent is known, is 0.996. These data suggest that these loci will be useful for estimating a variety of population genetic and genealogical parameters in P. v. verreauxi populations.

Alleles↗

PubMed2001

Molecular characterization of the klebicin B plasmid of Klebsiella pneumoniae.

The nucleotide sequence of a bacteriocin-encoding plasmid isolated from Klebsiella pneumoniae (pKlebB-K17/80) has been determined. The encoded klebicin B protein is similar in sequence to the DNase pyocins and colicins, suggesting that klebicin B functions as a nonspecific endonuclease. The klebicin gene cluster, as well as the plasmid backbone, is a chimera, with regions similar to those of pore-former colicins, nuclease pyocins and colicins as well as noncolicinogenic plasmids. Similarities between pKlebB plasmid maintenance functions and those of the colicin E1 plasmid suggest that pKlebB is a member of the ColE1 plasmid replication family.

Amino Acid Sequence↗

PubMed2001

Nucleotide polymorphism in microcin V plasmids.

DNA sequence polymorphism was determined for the microcin V gene cluster encoded on the microcin V plasmids of 12 natural isolates of Escherichia coli. These microcin V gene clusters are similar in DNA sequence, with only 10 of the 683 bp polymorphic. Further, the levels and patterns of microcin V gene cluster polymorphism differ from those of a chromosomal region, trpORF2, sequenced from each of the host isolates. These contrasting levels and patterns of polymorphism suggest that the microcin V gene cluster has experienced an evolutionary history different from that of the host.

Bacteriocins↗

PubMed2001

Deterministic variability and stability in detuned bimanual rhythmic coordination.

We examined the effects of crossing different degrees of cooperation and competition on inphase and antiphase 1:1 frequency locked coordination of left- and right-hand-oscillated pendulums. Degree of cooperation was manipulated through the joint frequency of oscillation specified by a metronome (the higher the frequency, the weaker the cooperation), and degree of competition by length (and, therefore, preferred frequency) differences between the two pendulums (the greater the difference, the stronger the competition). Increasing competition was accompanied by either decreasing cooperation (for six participants) or increasing cooperation (for six different participants). On each trial, a participant attempted to produce a steady-state phase relation phi for a given combination of competition and cooperation. Numerical simulations of the extended Haken-Kelso-Bunz (HKB) equation were used to predict (a) the patterns of shift in phi from either 0 or pi radians due to the different competition-cooperation relations and (b) the patterns of variability in phi. It was expected that the HKB equation would be successful in respect to (a), which it was, but not in respect to (b). The observed failure to confirm (b) was expected from the variability due to the different nonharmonic dynamics of the component oscillators, a source of variability not included in the HKB equation. The experimental results together with simulations and analyses of the phase-plane trajectories of the component oscillators suggest the operation of deterministic in addition to stochastic variability in the phase relation of contralateral limbs.

Adult↗

PubMed2001

Inertial constraints on limb proprioception are independent of visual calibration.

When the coincidence of a limb's spatial axes and inertial eigenvectors is broken, haptic proprioception of the limb's position conforms to the eigenvectors. Additionally, when prisms break the coincidence between an arm's visual and actual positions, haptic proprioception is shifted toward the visual-spatial direction. In 3 experiments, variation of the arm's mass distribution was combined with prism adaptation to investigate the hypothesis that the proprioceptive effects of inertial and visual manipulations are additive. This hypothesis was supported across manipulations of plane of motion, body posture, proprioceptive target, and proprioceptive experience during prism adaptation. Haptic proprioception seems to depend on local, physical reference frames that are relative to the physical reference frames for the body's environmental position and orientation.

Analysis of Variance↗

PubMed2001

Magnets in prosthetic dentistry.

Magnetic retention is a popular method of attaching removable prostheses to either retained roots or osseointegrated implants. This review chronicles the development of magnets in dentistry and summarizes future research in their use. The literature was researched by using the Science Citation Index and Compendex Web from 1981 to 2000. Articles published before 1981 were hand researched from citations in other publications. Articles that discussed the use of magnets in relation to prosthetic dentistry were selected.

Dental Prosthesis Retention↗

PubMed2001

Attunement, calibration, and exploration in fast haptic perceptual learning.

Often, a relatively small number of trials suffices to enhance one's task-specific perceptual capability. In the present experiment, fast perceptual learning was investigated with respect to the perception of the heights or widths of wielded nonvisible rectangular objects. In that haptic perceptual task, inertial differences (mass and moments of inertia) are the basis for perceived size differences. The authors hypothesized that rapid improvement might occur in attunement (attending to the task-relevant inertial variable), calibration (scaling spatial extent to the task-relevant inertial variable), and exploratory behavior (wielding so as to differentiate the task-relevant inertial variable). Twenty-four students performed 25 trials with a set of practice objects; those trials were followed and preceded by 18 trials with a set of test objects. Practice, with knowledge of results (KR), improved both attunement, as measured by regression of perceived spatial extent on the inertial variables, and calibration, as measured by constant and variable error. Of the preceding measures, only variable error improved with practice in the absence of KR. In both KR conditions, however, exploratory behavior decreased in duration and complexity, as measured by recurrence quantification analysis. The present results suggest that the mechanisms involved in fast perceptual learning are more varied and complex than are those encompassed by current accounts.

Adult↗

PubMed2000

Specificity of postural sway to the demands of a precision task.

We examined a precision aiming task in which a handheld laser pointer was controlled by the postural system. The task was performed in two orientations of the body's coronal plane to the target. In the parallel orientation medio-lateral (ML) sway had to be minimized, in the perpendicular orientation antero-posterior (AP) sway had to be minimized. In the parallel orientation ML sway decreased and AP sway increased with target distance and size. The pattern reversed in the perpendicular orientation. Nonlinear measures found independence of the two directions of sway and differences in their deterministic structure. Apparently a postural organization for upright standing and aiming (as in archery) entails two independent postural subsystems with different but reciprocally related dynamics. Furthermore, it seems as if some amount of postural variability is needed to ensure stability in quiet standing; if postural activity is reduced in one direction it is compensated for in the other direction.

Adult↗

PubMed2000

Advantages of rhythmic movements at resonance: minimal active degrees of freedom, minimal noise, and maximal predictability.

Using time delay embedding, the authors applied phase space reconstruction to the time series of rhythmic movements of a hand-held pendulum. Subjects (N = 6) produced the manual oscillations about the wrist at the pendulum's resonant frequency and at a higher and a lower frequency. The number of active degrees of freedom required to capture the dynamics of the rhythmic behavior was 3 for the resonant frequency and 4 for each of the nonresonant frequencies. The residual high-dimensional noise was similarly lowest for the resonant frequency. Whereas 33% and 20%, respectively, of the vectors in the phase spaces of the dynamics higher and lower than resonance were unpredictable, only 12% were unpredictable at resonance. Finally, the predictability of the evolving dynamics extended farther into the future for oscillations at the resonant frequency. At resonance, the prediction horizon was 5 times farther than the prediction horizon for the higher than resonance behavior and 2.5 times farther than that for the lower than resonance behavior. The results suggest that, in pendular oscillations of a limb or limb segment, attunement of the central nervous system to the resonant frequency minimizes the variables to be controlled and maximizes the predictability of the rhythmic movement's chaotic dynamics.

Forecasting↗