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PubMed2001

Initiation and frequency of pumping and milk production in mothers of non-nursing preterm infants.

This secondary data analysis examined if time of initiation of milk expression and pumping frequency influenced milk weight weeks 2-5 postpartum. Of the 39 subjects in the convenience sample, 20 were in the early initiating (EI) group, (n = 12 high frequency [HF], n = 8 low frequency [LF]), and 19 were in the late intiating (LI) group, (n = 7 HF, n = 12 LF). The EI group initiated pumping < or = 48 hours after birth; the HF group pumped a minimum of 6.25 times daily. A two-way analysis of variance indicated that milk weight was significantly higher in the HF as compared to the LF group. While there was no significant difference in milk weight between the EI and LI groups, there was a significant interaction between frequency and initiation. Milk weight for the LF/EI group appeared to be positively influenced by the initiation of mechanical expression soon after birth.

Adult↗

PubMed2001

Does the source of support matter for different health outcomes? Findings from the Normative Aging Study.

OBJECTIVES: This study investigated the differential relationships between different types and sources of social support and physical and mental health. METHODS: Using data from the Normative Aging Study, 1,386 older men (median age = 62.7 years) were categorized into four groups separately for frequency of interaction with networks and perceived support. RESULTS: More than half the sample reported high levels of support from both sources. One-way ANOVAs revealed that those with high perceived support from both sources reported better physical health and fewer depressive symptoms than those with low support from both sources or high support from family alone. Similarly, those with high perceived support from both sources had lower levels of depressive symptoms than those with low support from both sources, but frequency of contact was unrelated to physical health. DISCUSSION: In general, those with high support from both family and friends reported the highest level of well-being.

Aged↗

PubMed2002

Hemispheric asymmetry in visual discrimination and memory: ERP evidence for the spatial frequency hypothesis.

Event related potentials (ERPs) were recorded during delayed discrimination of simple spatial frequency gratings in the high and low frequency bands. Analyses of the waveforms N170, P220, N310, P400, and slow wave (SW) indicated significant and regionally specific interaction of spatial frequency and hemisphere for N170 amplitude. This interaction was independent of memory conditions, and appeared to be in the opposite direction of what is predicted by the spatial frequency model of hemispheric asymmetry. Additional interactions between spatial frequency and hemisphere were observed for N310 in the encoding process (reference stimulus) and for SW in the retrieval process (test stimulus). The general hypothesis of an interaction of spatial frequency and hemisphere in visual cognition is supported, but the findings indicate caution in interpreting an increase in physiological measures as an indication of more efficient brain processing. Moreover, several stages of information processing may contribute to the asymmetry observed in behavioral studies, and hemispheric balance may change dynamically during the time course of processing.

Adult↗

PubMed1993

The Staats-Heiby theory of depression: the role of event frequency and affect reevaluated.

This paper reports an attempt to replicate and extend a study by Rose and Staats (Behavior Research and Therapy, 26, 489-494, 1988) and reviews their attempts to find support for two subtypes of depression as predicted by the Staats-Heiby theory of unipolar depression. Due to methodological and analytical problems in the work by Rose and Staats (1988) it was felt that the conclusions they drew were unjustified. In this study 160 university students completed the Mood Related subscales of the Pleasant (PES-MR) and Unpleasant Event Schedules (UES-MR) and the Beck Depression Inventory. Overall, the contention that different subtypes of depression could be differentiated on the basis of the interaction between frequency of events and the affective value of events was not supported. However, there was some support for the role of pleasant event frequency, unpleasant event frequency, and event unpleasantness in depression. The results indicate that the relationship between event frequency and hedonic strength differs between the PES-MR and UES-MR. It is argued that the research methodology and analyses used could not adequately assess the hypotheses generated from the Staats-Heiby model.

Adolescent↗

PubMed1989

Nucleic acid composition, codon usage, and the rate of synonymous substitution in protein-coding genes.

Based on the rates of synonymous substitution in 42 protein-coding gene pairs from rat and human, a correlation is shown to exist between the frequency of the nucleotides in all positions of the codon and the synonymous substitution rate. The correlation coefficients were positive for A and T and negative for C and G. This means that AT-rich genes accumulate more synonymous substitutions than GC-rich genes. Biased patterns of mutation could not account for this phenomenon. Thus, the variation in synonymous substitution rates and the resulting unequal codon usage must be the consequence of selection against A and T in synonymous positions. Most of the variation in rates of synonymous substitution can be explained by the nucleotide composition in synonymous positions. Codon-anticodon interactions, dinucleotide frequencies, and contextual factors influence neither the rates of synonymous substitution nor codon usage. Interestingly, the nucleotide in the second position of codons (always a nonsynonymous position) was found to affect the rate of synonymous substitution. This finding links the rate of nonsynonymous substitution with the synonymous rate. Consequently, highly conservative proteins are expected to be encoded by genes that evolve slowly in terms of synonymous substitutions, and are consequently highly biased in their codon usage.

Animals↗

PubMed2003

A neural complexity measure applied to MEG data in Alzheimer's disease.

OBJECTIVE: A measure of neural complexity (C(N)) (Proc. Natl Acad. Sci. USA 91 (1994) 5033) was applied to magnetoencephalography (MEG) data to test the hypothesis that C(N) decreases when information processing in the brain is impaired, as is the case in patients with Alzheimer's Disease (AD). METHODS: One hundred and fifty-one channel MEGs were recorded in 20 AD patients and 20 healthy age-matched controls in a resting condition with eyes open (EO) and eyes closed (EC). Artifact-free epochs of 117 channels were selected for analysis. C(N) and D(2) were computed in different frequency bands, and correlated with the MMSE. RESULTS: The Group x Frequency band interaction was significant for both C(N) and D(2). C(N) was higher in AD, as compared with controls, in the 2-4 and 4-8Hz bands, and D(2) was higher in AD patients in the 14-20 and 20-30Hz bands. The C(N) was higher in the EC condition compared to the EO condition, whereas the D(2) was higher in the EO condition. CONCLUSIONS: The hypothesis of Tononi et al. (Proc. Natl Acad. Sci. USA 91 (1994) 5033) that the neural complexity decreases in AD patients has to be rejected. However, both neural complexity and the correlation dimension did show differences between controls and AD patients which depended on frequency band.

Aged↗

PubMed2002

Investigation of particle interactions in concentrated colloidal suspensions using frequency domain photon migration: monodisperse systems.

Frequency domain photon migration (FDPM) measurements were conducted to assess particle interactions of concentrated, monodisperse, polystyrene samples obtained directly from industry by using multiple scattering light. The angle-integrated static structure factor, S(q), and static structure factor at small wave vector q, S(0), were obtained from FDPM measurements at high volume fractions ranging from 0.05 to 0.3, and were compared with those obtained from the monodisperse hard sphere Percus-Yevick (HSPY) model. Effects of different colloid sizes on structure factor evaluated at two different wavelengths were also investigated. Results show that the monodisperse HSPY model is suitable for accounting for particle interactions and local microstructures in these colloidal suspensions. Upon using the HSPY model, particle sizes of polystyrene suspensions were recovered from FDPM measurements at high volume fractions (up to 0.3), which agree well with the DLS measurement of diluted sample ( approximately 0.001). The study of polydispersity effect shows that the FDPM method can be successfully used for recovering the mean particle size of polydisperse colloidal suspension with low polydispersity (<16%) under the assumption of monodisperse hard sphere systems.

Journal Article↗

PubMed1993

Pharmacokinetic drug interactions with antimicrobial agents.

As new classes of antimicrobial drugs have become available, and new uses found for older drugs, pharmacokinetic drug interactions with antimicrobials have become more common. Macrolides, fluoroquinolones, rifamycins, azoles and other agents can interact adversely with commonly used drugs, usually by altering their hepatic metabolism. The mechanisms by which antimicrobial agents alter the biotransformation of other drugs is increasingly understood to reflect inhibition or induction of specific cytochrome P450 enzymes. Macrolides inhibit cytochrome P450IIIA4 (CYP3A4), which appears to be the most common metabolic enzyme in the human liver and is involved in the metabolism of many drugs, including cyclosporin, warfarin and terfenadine. Some quinolones preferentially inhibit CYP1A2, which is partially responsible for methylxanthine metabolism. Azoles appear to be broad spectrum inhibitors of cytochromes P450. Within each of these antibiotic classes, there is a rank order of inhibitory potency towards specific cytochrome P450 enzymes. By contrast, rifampicin (rifampin) and rifabutin induce several cytochromes P450, including CYP3A4, and hence can enhance the metabolism of many other drugs. By using in vitro preparations of human enzymes it is increasingly possible to predict those antibiotics that will adversely affect the metabolism of other drugs. In addition, between-patient variability in frequency of interaction may relate to differences in the activities of these enzymes. Although the mechanisms and scope of these interactions are becoming well characterised, the remaining challenge is how to best inform the clinician so that the undesirable consequences of interactions may be prevented.

Anti-Bacterial Agents↗

PubMed2006

Impact of defoliation intensity and frequency on N uptake and mobilization in Lolium perenne.

The aim of the study was to evaluate the impact of defoliation intensity, defoliation frequency, and interactions with N supply on N uptake, N mobilization from and N allocation to roots, adult leaves, and growing leaves. Plants of Lolium perenne were grown under two contrasted N regimes. Defoliation intensity treatments consisted of a range of percentage leaf area removal (0, 25, 50, 75, or 100%). These treatments were applied in parallel to a set of plants previously undefoliated, and to a second set of plants which had been defoliated several times at a constant height. A (15)N tracer technique was used to quantify N uptake, mobilization, and allocation over a 7 d period. A significant reduction in plant N uptake was observed with the removal of more than 75% of lamina area, but only with high N supply. As defoliation intensity increased, the amount of N taken up and subsequently allocated to growing leaves during the labelling period was maintained at the expense of N allocation to roots and adult leaves. Increasing defoliation intensity increased the relative contribution of roots supplying mobilized N to growing leaves and decreased the relative contribution of adult leaves. Defoliation frequency did not substantially alter N uptake, mobilization, and allocation between roots, adult and growing leaves on a plant basis. However, tiller number per plant was largely increased under repeated defoliation, hence indicating that allocation and mobilization of N to growing leaves, on the basis of individual tillers, was decreased by defoliation frequency.

Adaptation, Physiological↗

PubMedDate not supplied

Behavioral and biochemical alterations following in utero exposure to methylmercury.

Behavioral changes induced in utero by methylmercury (MeHg) were studied with a non-invasive measure of patterns of effects in 1 to 35 day old rats. Lipid peroxidation (LP) and acetylcholinesterase (AChe) activity were used to compare effects in four different brain regions. MeHg (0, 2 or 6 mg/kg) was administered (PO) at day 6, 7, 8 and 9 of gestation. Rats were videotaped on day 10, 12, 20 and 34 and sacrificed on day 1, 13, 21 and 35. No changes in body or brain weights or other ancillary measures of growth and development occurred between 1-35 days. Cellular injury in brain regions as measured by LP was not altered by MeHg. AChe activity decreased in the anterior cortex and cerebellum on PN12. Frequency, dispersion and interactions of behavioral elements were determined. Frequency of grooming mode elements was decreased at 10, 12 and 34 days for 6 mg/kg, and at 12 and 34 days for 2 mg/kg pups. The frequency of exploratory mode elements increased at days 10 and 12 for 6 mg/kg, days 12 and 20 for 2 mg/kg pups. MeHg increased activities in the attention mode on PN12 at both doses. Behavior patterns were altered on all days observed, but these were not dose related. PN12 was observed to be the beginning of patterning (56 possible interactions). The 6 mg/kg group demonstrated a delay of pattern development at PN12 with a recovery to an altered array of behaviors at PN20. MeHg generally decreased interaction values (Chi2).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗

PubMed1976

Effects of various drugs supposed to interact with serotonin on PGO frequency changes induced by reserpine and 5-hydroxytryptophan.

Reserpine induced ponto-geniculo-occipital (PGO) spikes in the lateral geniculate nucleus. This was used as a model to evaluate the possible anti-reserpine effects of Org GB 94-1,2,3,4,10,14b-hexahydro-2-methyldibenzo[c,f]pyrazino [1,2-alpha]azepine monohydrochloride-methiothepin, imipramine and atropine. In cats, under local anaesthesia, 3.2 mg/kg of methiothepin (a serotonin antagonist and neuroleptic) increased PGO density while 5-hydroxytryptophan (5-HTP) effects were blocked. A dose of 0.32 mg/kg of imipramine or atropine greatly reduced PGO density while potentiating 5-HTP effects. Org GB 94 had no effect in doses up to 10 mg/kg, where a slight decrease of PGO density was found, while 5-HTP effects were unchanged. At 32 mg/kg, EEG was pronouncedly changed by Org GB 94 but only a short-lasting decrease in PGO density was noted. On the basis of these results it seems improbable that the behavioural effects of Org GB 94 are to be explained by the same mechanism (i.e. serotonin uptake inhibition) as that of imipramine.

5-Hydroxytryptophan↗

PubMedDate not supplied

Acute effects of low-frequency electromagnetic fields on leukocyte-endothelial interactions in vivo.

BACKGROUND: To clarify the effect of extremely low frequency electromagnetic field (ELF-EMF) on the microcirculatory system, acute effects on leukocyte-endothelium interactions resulting from ELF-EMF exposure were examined with conscious BALB/c mice by means of a dorsal skinfold chamber. MATERIALS AND METHODS: The fluorescent dye, rhodamine 6G, was injected into the caudal vein to visualize leukocytes in vivo and to analyze leukocyte-endothelium interactions. Mice were exposed in vivo to 50 Hz linear sinusoidal wave EMF at magnetic flux densities of 3, 10 or 30 mT, for 30 minutes. RESULTS: The mean velocity of free flowing leukocytes in the center stream of venules revealed no distinct changes following exposure. However, at a flux density of 30 mT, the number of adherent leukocytes, defined as the total number of rolling and endothelium-adhering leukocytes, increased significantly following ELF-EMF exposure (p<0.05); no significant differences in adherent cell numbers were found in the 3 mT and 10 mT exposure groups or sham controls comparing pre- and post-exposure periods. CONCLUSION: These results demonstrated that high magnetic flux densities of ELF-EMF had an effect on leukocyte-endothelium interactions and indicated that a threshold level for this phenomenon exists in the range of 10-30 mT under these experimental conditions.

Animals↗

PubMed1989

A dissociative word-frequency X levels-of-processing interaction in episodic recognition and lexical decision tasks.

The effects of levels-of-processing and word frequency were directly compared in three different memory tests. In the episodic recognition test, the subjects decided whether or not a word or a pronounceable nonword had been previously studied. In the two lexical decision tests with either pronounceable or unpronounceable nonwords as distractors, the subjects decided whether a test item was a word or a nonword. There were four main results: (1) in all three tests, reaction times (RTs) in response to studied words were faster if they had received semantic rather than rhyme processing during study; (2) in the episodic recognition test, RTs were faster for low- than for high-frequency words; in both lexical decision tests, RTs were faster for high- than for low-frequency words, though less so when the nonword distractors were unpronounceable; (3) prior study facilitated lexical decisions more in response to low- than to high-frequency words, thereby attenuating the word-frequency effect, but more so when the nonword distractors were pronounceable; (4) in the lexical decision test with pronounceable nonword distractors, relative to prior rhyme processing, prior semantic processing facilitated performance more for high- than for low-frequency words, whereas the opposite was the case in the episodic recognition test. Discussion focused on the relationship of these results to current views of the mechanisms by which (1) word frequency and depth of processing affect performance in implicit and explicit memory tests, and (2) repetition priming attenuates word-frequency effects for lexical decisions.

Adult↗

PubMed1981

Acoustic correlates of tonal tinnitus.

A sensitive microphone has been developed which can pick up tonal signals (spontaneous acoustic emissions) in the sealed ear-canal of certain subjects. Various properties of these frequency components suggest that they arise from an active, frequency-selective self-limiting feedback process within the cochlea and that they rely on internal reflection from the middle ear. An external tone can synchronize, frequency-lock, suppress of frequency-shift the acoustic component. These interactions are frequency-dependent in a way suggestive of cochlear tuning properties. Positive or negative middle-ear pressure can also influence the components by increasing their frequency and in some cases can enhance one component at the expense of a neighbouring one. Some subjects hear these components as tinnitus and can report on the measured changes. Other subjects do not hear the measured signals, which otherwise behave similarly. A third group of subjects have tinnitus but no objective sound can be detected. In this last group there are, nevertheless, sometimes notches or other discontinuities in the audiogram which correspond to their tinnitus pitch-matches. It appears likely that the recordable type of tinnitus is essentially non-pathological and represents hypersensitivity of the system, whereas the non-recordable type might be associated with local pathological changes at the end-organ or more centrally.

Acoustic Stimulation↗

PubMed2005

Cooperativity and proton transfer in hydrogen-bonded triads.

Ab initio MP2/6-311+G(3df,2pd) and MP2/aug-cc-pVTZ calculations have been carried out to investigate the structures and properties of AHXHYH(3) (A=F, Cl; X=F, Cl; Y=N, P) hydrogen-bonded complexes. Significant cooperative effects are observed in the XHYH3 dyads in the triads due to the presence of the polar near-neighbor AH. These effects are greater when the polar partner is HF, which is a better proton donor than HCl. Structural changes, red shifts of proton-donor stretching frequencies, nonadditive interaction energies, and electron density redistributions unambiguously demonstrate that the X--HY hydrogen bond (HB) is stronger in the triads than in the corresponding dyads, while the X--H bond of the proton donor becomes weaker. Even more pronounced cooperative effects are observed in the AHXH dyads due to the presence of the YH3 partner. These effects are weaker in complexes having PH3 rather than NH3 as the proton acceptor, since NH3 is a stronger base. Cooperativity also enhances the proton-donating ability of the YH3 moiety, with the result that all complexes except FHFHPH3 are cyclic. Cooperativity, together with the ease of breaking the Cl--H bond in ClHClHNH3 and FHClHNH3, leads to proton transfer (PT), so that these two complexes are better described as approaching hydrogen-bonded ClHCl- x +HNH3 and FHCl- x +HNH3 ion pairs.

Journal Article↗

PubMed2005

Hydration process as an activation of trans- and cisplatin complexes in anticancer treatment. DFT and ab initio computational study of thermodynamic and kinetic parameters.

The thermodynamic and kinetic aspects of hydration reactions of cis-/transplatin were explored. The polarizable continuum model was used for estimation of solvent effects. Using the B3LYP/6-31+G(d) method, the structures were optimized and vibrational frequencies estimated. Interaction energies and activation barriers were determined at the CCSD(T)/6-31++G(d,p) level within the COSMO approach. An associative mechanism was assumed with a trigonal-bipyramidal structure of the transition state. Within the applied model, all the hydration reactions are slightly endothermic. The Gibbs energies of cisplatin hydration amount to 7.0 and 14.2 kcal/mol for the chloride and ammonium replacement, respectively. Analogous values for the transplatin reactions are 6.8 and 11.9 kcal/mol. The determined rate constants are by several (three to four) orders of magnitude larger for the dechlorination process than for deammination. The cisplatin dechlorination rate constant was established as 1.3 x 10(-4) s(-1) in excellent accord with the experiment.

Antineoplastic Agents↗

PubMed1994

Two configurations of the four-ring birdcage coil for 1H imaging and 1H-decoupled 31P spectroscopy of the human head.

The four-ring birdcage resonator, a new class of dual-tuned birdcage resonators, is described. We report two configurations of the coil: the low-pass, high-pass (LP-HP) and the low-pass, low-pass (LP-LP), both of which can be operated in dual quadrature mode at 1.5 T. As head coils, both configurations exhibit greatly reduced tuning interactions between frequencies, permitting rapid, noniterative tuning. Compared with single-tuned, two-ring birdcage resonators of similar volume, the sensitivity and transmitter efficiencies of the resonators are better than 85% for the proton frequency and the same to within 5% for the phosphorus frequency. Circuit models have been developed to refine coil tuning and aid the calculation of B1 field contour plots. Both configurations have been used for integrated examinations involving acquisition of high-quality 1H images and 1H-decoupled 31P CSI spectra of the human head. A scaled-down version of the LP-LP configuration has been demonstrated for use with the human calf.

Head↗

PubMedDate not supplied

NMR study of phase transitions in new ferroelectric Crystal--(C5H5NH)5Bi2Br11.

A T1 minimum at 216 K for Larmor frequency 90 MHz has been detected and for this minimum no analogous T, minimum according to the known quadratic dependence of the Larmor frequency 25 MHz is found. The analysis leads to the conclusion that this T1 minimum is a result of the relaxation of protons via quadrupole nuclei. The Kimmich theoretical treatment of 1H NMR experiments exhibiting the existence of this phenomenon in the case of relaxation of protons of piridinium cations in (C5H5NH)5Bi2Br11 and the estimated averaged quadrupole frequency of interacting quadrupole nuclei has been estimated to be around 71 MHz. Below the phase transition at 118 K a wide symmetric spin-lattice relaxation minimum at 25 MHz is detected and a model of small angle libration of the pyridinium cation has been applied to explain the observed T1 relaxation time minimum.

Magnetic Resonance Spectroscopy↗