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PubMed1996

Quantitative EEG in frontal lobe dementia.

A study on quantitative EEG in 14 patients with frontal lobe dementia (FLD), 14 patients with Alzheimer's disease (AD), and 14 healthy controls was conducted using a complete set of EEG parameters: band power, coherence and fractal dimension. Contrary to earlier studies, we observed higher theta power and sagittal interactions in higher frequency bands in the FLD than in the control group. Lateral interactions of coherence and two indices of fractal dimension were lower in FLD than in controls. There was greater electrophysiological resemblance between the control group and FLD than between any of these groups and AD. This was documented by the results of a discriminant analysis which led to a correct overall classification of 66% of the subjects with misclassifications occurring primarily between control and FLD group.

Analysis of Variance↗
PubMed1989

Sounds of silence--coping with hearing loss and loneliness.

The vast majority of people will suffer presbycusis during the aging process. This hearing loss has potential social consequences, which place these individuals at risk for loneliness. Nurses need to encourage thorough audiological examination and follow through on recommendations to improve hearing. The use of hearing aids needs to be encouraged. A suggested model of interaction among variables influencing loneliness identifies areas amenable to nursing intervention. Frequency of significant interaction and motivation to engage in interactions represent two important variables that influence loneliness.

Adaptation, Psychological↗
PubMed1987

Movement in decline? Oscillatory movement displacement thresholds increase with ageing.

Displacement thresholds for continuous oscillatory movement were determined for ten subjects in each of three age groups--20-23, 40-55 and 60-80 years. Oscillation frequencies of 1, 2, 3, 5, 8, 13 and 20 Hz were used, all subjects having a corrected visual acuity of 6/5. A randomized block factorial design of analysis of variance revealed significant effects of both temporal frequency of oscillation (F6,189 = 4.10, p less than 0.001) and age (F2,189 = 46.98, p much less than 0.001). The deterioration in movement sensitivity occurs equally at both high and low temporal frequencies--no significant interaction effects being revealed (F12,189 = 0.45, p = not significant). The frequency effects are ascribed to underlying mechanisms mediating movement perception. Reasons for decreased movement sensitivity with increasing age are discussed.

Adult↗
PubMed2000

Wave front reversal of a dipolar spin wave pulse in a nonstationary three-wave parametric interaction

The effects of wave front reversal and inversion of the time profile are observed experimentally for a dipolar spin wave pulse (carrier frequency omega(1)) interacting in a yttrium-iron garnet film with a weakly localized nonstationary parametric pumping (carrier frequency omega(p) congruent with 2omega(1)) in a three-wave process with conservation law omega(p) = omega(1)+omega(2), where omega(2) is the carrier frequency of the reversed pulse. Theoretical analysis based on the solution of the system of equations for envelopes of interacting wave packets by means of a Green's function formalism gives a quantitative description of the observed phenomena.

Journal Article↗
PubMed2004

Ruminal and host adaptations to changes in frequency of protein supplementation.

The effect of altering supplementation frequency on host N balance and key N transactions in the ruminal ecosystem were monitored. Four ruminally fistulated beef steers (BW = 513 kg; SEM = 6.5) were used in a 2 x 2 crossover design with two periods and two supplementation frequency treatments. Supplementation frequencies were 2 and 7 d/wk. Steers were fed tallgrass prairie hay (73.1% NDF, 5.3% CP) ad libitum. Supplement (42% CP; DM basis) was fed at 0.36% BW/d to steers supplemented 7 d/wk. Steers supplemented 2 d/wk received the same amount of supplement per week, but it was equally split among the two supplementation events. Steers supplemented 7 d/wk had higher forage (P < 0.02) and total digestible OM intake (P < 0.06), total N intake, fecal N excretion, and N retention. Although both supplementation frequencies were characterized by positive N balance, the decrease in N retention in the steers supplemented 2 d/wk was due to higher (P < 0.01) urinary N loss. Ruminal fluid was sampled at 0, 2, 4, 6, 12, 24, 48, and 72 h after supplementation beginning on a day when both treatments were supplemented. Frequency x hour interactions (P < 0.02) were observed for ruminal N metabolism criteria. Counts of peptide- and AA-fermenting bacteria peaked at 2 h and returned to nadir by 12 h for steers supplemented 7 d/wk. Steers supplemented 2 d/wk peaked at 6 h with a greater population and returned to nadir at 48 h. Ruminal ammonia concentrations followed a similar trend. Specific activity of ammonia production was lower (P < or = 0.05) immediately after supplementation for steers supplemented 2 d/wk, but by 12 h was the same as for 7 d/wk steers. Ruminal peptides and free AA peaked at 2 h for steers supplemented 2 d/wk and were generally higher (P < or = 0.05) during the first 6 h compared with steers supplemented 7 d/wk. Total VFA concentration was not different (P = 0.35) due to supplementation frequency. Frequency x hour interactions (P < 0.01) were observed for all molar proportions of VFA. The molar proportion of acetate and acetate:propionate ratio were lower (P < 0.01) and the molar proportions of propionate and butyrate were higher for steers supplemented 2 d/wk from 4 h to 24 h. In conclusion, forage use and N balance improved with supplementation 7 d/wk, but supplementation 2 d/wk was associated with some desirable shifts in select ruminal events that may contribute to moderating potential negative impacts of supplementing infrequently.

Adaptation, Physiological↗
PubMed1990

Event-related brain potentials dissociate repetition effects of high- and low-frequency words.

Event-related brain potentials (ERPs) were recorded while subjects detected nonwords interspersed among sequences of words of high or low frequency of occurrence. In Phase 1, a proportion of the words were repeated after six intervening items. In Phase 2, which followed after a break of approximately 15 min, the words were either repeats of items presented in the previous phase or new. Unrepeated low-frequency words evoked larger N400 components than did high-frequency items. In Phase 1, this effect interacted with repetition, such that no frequency effects were observed on N400s evoked by repeated words. In addition, the post-500-msec latency region of the ERPs exhibited a substantial repetition effect for low-frequency words, but did not differentiate unrepeated and repeated high-frequency words. In Phase 2, ERPs evoked by "old" and "new" high-frequency words did not differ in any latency region, while those evoked by old and new low-frequency words differed only after 500 msec. The interactive effects of frequency and repetition suggest that these variables act jointly at multiple loci during the processing of a word. The specificity of the post-500-msec repetition effect for low-frequency words may reflect a process responsive to a discrepancy between words' intra and extraexperimental familiarity.

Adult↗
PubMed1991

Role of excitatory amino acids in the generation and transmission of respiratory drive in neonatal rat.

1. The involvement of excitatory amino acids in the generation and transmission of rhythmic respiratory drive was studied in an in vitro neonatal rat brain stem-spinal cord preparation. The subclasses of excitatory amino acid receptors studied included: (i) N-methyl-D-aspartate (NMDA) receptors, (ii) (R, S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) and kainate (non-NMDA) receptors and (iii) 2-amino-4-phosphonobutyric acid (AP-4)-sensitive receptors. Respiratory motoneurone population discharge was recorded from glossopharyngeal (IX), vagus (X), and hypoglossal (XII) cranial nerves, as well as cervical (C1-C5) and thoracic (T2-T5) spinal ventral roots. This activity is generated in the motoneurone pools that transmit respiratory drive to upper airway, accessory, diaphragm and intercostal muscles. Perturbations of motor nerve discharge were analysed after excitatory amino acid receptor antagonists or agonists were added to bathing solutions surrounding either the spinal cord or brain stem. The excitatory amino acid receptor antagonists included: (i) NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imin-H-maleate (MK-801) and (ii) non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The agonists included: (i) NMDA, (ii) non-NMDA receptor agonists AMPA and kainic acid. The effects of perturbations of AP-4-sensitive receptors with AP-4, and of inhibiting excitatory amino acid uptake with dihydrokainic acid (DHK) were also studied. 2. Block of non-NMDA receptors in the medulla by CNQX resulted in an antagonist concentration-dependent decrease in the respiratory motoneuronal burst frequency. Non-NMDA receptor activation with kainic acid or AMPA caused a concentration-dependent increase in burst frequency, with competitive interactions with CNQX. 3. Inhibition of excitatory amino acid uptake in the medulla with DHK resulted in a reversible, dose-dependent increase in respiratory frequency. A similar increase in respiratory frequency was induced by DHK when medullary NMDA receptors were blocked with MK-801, confirming that endogenously released excitatory amino acids act at non-NMDA receptors to modulate rhythm. 4. Non-NMDA receptor block reduced and ultimately abolished the amplitude of integrated cranial and spinal respiratory motoneuronal discharge when added to the solution bathing the medulla and spinal cord, respectively. 5. NMDA receptor block in the medulla with MK-801 did not perturb the spontaneous respiratory burst frequency, although bath application of NMDA produced a dose-dependent increase in frequency, with non-competitive interactions with MK-801. MK-801 also did not perturb the amplitude of cranial or bulbospinal premotoneurone discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1999

Modeling lexical decision and word naming as a retrieval process.

We argue that rule-like phenomena in naming and lexical decision reflect the collapsing of information that occurs during retrieval from the lexicon, and that complex patterns in performance reflect the pattern of correlation that exists in the reader's lexicon rather than mapping rules wired into, or learned by, the processing apparatus. By using a lexicon built to scale, we show that simple retrieval operations applied to a large corpus of words correctly predict an interaction of word frequency by spelling-to-sound regularity in naming, a frequency main effect in lexical decision, sensitivity to orthographically defined syllable-like structures in lexical decision, and an interaction of number of syllables with word frequency in naming.

Decision Making↗
PubMed1994

Source of catalysis in the lactate dehydrogenase system. Ground-state interactions in the enzyme-substrate complex.

The Raman spectra of both the NAD-pyruvate and the pyridine aldehyde adenine dinucleotide (PAAD)-pyruvate bound to pig heart, pig muscle, and Bacillus stearothermophilus lactate dehydrogenases were measured and are nearly the same, which is consistent with the conserved shell of residues surrounding the active-site cavity in these enzymes. The symmetrical stretching mode of the pyruvate carboxylate group, found at 1398 cm-1, is shifted only slightly when complexed to these enzymes, which shows that the group remains ionized in the ion pair complex with Arg-171 on the enzyme. The vibrational mode for the carbonyl stretch of the bound pyruvate moiety is shifted about 35 cm-1 to a lower frequency than observed for the carbonyl of unliganded pyruvate in the bacterial enzyme because of polarization of the carbonyl bond. Thus, the bacterial enzyme shows the same substrate activation because of the C(+)-O- charge separation that was seen previously with the mammalian enzymes. On the basis of an empirical Badger-Bauer relationship between frequency shift and interaction enthalpy, this shift in frequency is equivalent to an approximately -14 to -17 kcal/mol interaction between the enzyme and the adduct C = O coordinate, a substantial part of which is an electrostatic interaction (hydrogen bond) between the C V O and the protonated His-195. Thus, while the C = O bond is polarized on the enzyme (which requires energy), the overall ground-state enthalpy of the carbonyl imidazolium part of the reaction coordinate is stability substantially relative to its value in solution, and this is the dominant enthalpic effect on the entire reaction coordinate since the other internal coordinates for the hydride transfer are not much affected during formation of the ternary complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Isoflurane, nitrous oxide, and fentanyl pharmacodynamic interactions in surgical patients as measured by effects on median power frequency.

STUDY OBJECTIVE: To identify and quantify the simultaneous interactions of isoflurane, nitrous oxide (N2O), and fentanyl during surgical procedures. The slowing of the EEG to a median power frequency of 2 Hz to 3 Hz was chosen as the measure of pharmacodynamic drug effect. DESIGN: Prospective, randomized, open label. SETTING: Operating room of a university hospital. PATIENTS: 65 ASA physical status I and II patients undergoing gynecological laparatomies. INTERVENTIONS: 25 patients received no fentanyl. 20 patients received a loading dose of 100 micrograms fentanyl and a continuous infusion of 70 micrograms.h-1 fentanyl. Calculated effect compartment concentrations were 0.7 ng.ml-1 between the first and second hours after induction of anesthesia. Another 20 patients received a loading dose of 200 micrograms fentanyl and a continuous infusion of 150 micrograms.h-1 fentanyl; the respective effect compartment concentrations were 1.5 ng.ml-1. N2O was randomly administered in concentrations of 0, 20, 40, and 60 vol%; in the group that did not receive fentanyl, we additionally investigated 75 vol% N2O. Each patient received two different N2O concentrations, with each combination of N2O and fentanyl finally applied to ten patients. Isoflurane vaporizer settings were chosen so that the median power frequency was held between 2 Hz and 3 Hz. The type and degree of interaction among the three anesthetic drugs was analyzed based on a generalized isobole approach. MEASUREMENTS AND MAIN RESULTS: The interaction of isoflurane, N2O, and fentanyl is compatible with additivity. A model with regard to the relative potencies and age dependency is given by: [formula: see text] with C0,iso = 1.30 vol%, C0,N2O = 177 vol%, C0,fen = 10.6 ng.ml-1, and a = -0.0031 yr-1. where conc. = end-tidal or effect compartment concentrations. CONCLUSION: The potency of N2O and fentanyl to substitute isoflurane in maintaining a median power frequency of 2 Hz to 3 Hz during surgery is less than anticipated from minimum alveolar concentration studies.

Adult↗
PubMed2005

Folic acid deficiency increases chromosomal instability, chromosome 21 aneuploidy and sensitivity to radiation-induced micronuclei.

Folic acid deficiency can lead to uracil incorporation into DNA, hypomethylation of DNA, inefficient DNA repair and increase chromosome malsegregation and breakage. Because ionising radiation increases demand for efficient DNA repair and also causes chromosome breaks we hypothesised that folic acid deficiency may increase sensitivity to radiation-induced chromosome breakage. We tested this hypothesis by using the cytokinesis-block micronucleus assay in 10 day WIL2-NS cell cultures at four different folic acid concentrations (0.2, 2, 20, and 200 nM) that span the "normal" physiological range in humans. The study showed a significant dose-dependent increase in frequency of binucleated cells with micronuclei and/or nucleoplasmic bridges with decreasing folic acid concentration (P<0.0001, P=0.028, respectively). These biomarkers of chromosomal instability were also increased in cells irradiated (1.5 Gy gamma-rays) on day 9 relative to un-irradiated controls (P<0.05). Folic acid deficiency and gamma-irradiation were shown to have a significant interactive effect on frequency of cells containing micronuclei (two-way ANOVA, interaction P=0.0039) such that the frequency of radiation-induced micronucleated cells (i.e. after subtracting base-line frequency of un-irradiated controls) increased with decreasing folic acid concentration (P-trend<0.0001). Aneuploidy of chromosome 21, apoptosis and necrosis were increased by folic acid deficiency but not by ionising radiation. The results of this study show that folate status has an important impact on chromosomal stability and is an important modifying factor of cellular sensitivity to radiation-induced genome damage.

Aneuploidy↗
PubMed2006

Application of high-frequency rheology measurements for analyzing protein-protein interactions in high protein concentration solutions using a model monoclonal antibody (IgG2).

The purpose of this work was to explore the utilization of high-frequency rheology analysis for assessing protein-protein interactions in high protein concentration solutions. Rheology analysis of a model monoclonal immunoglobulin G2 solutions was conducted on indigenously developed ultrasonic shear rheometer at frequency of 10 MHz. Solutions at pH 9.0 behaved as most viscous and viscoelastic whereas those at pH 4.0 and 5.4 exhibited lower viscosity and viscoelasticity, respectively. Intrinsic viscosity, hydrophobicity, and conformational analysis could not account for the rheological behavior of IgG2 solutions. Zeta potential and light scattering measurements showed the significance of electroviscous and specific protein-protein interactions in governing rheology of IgG2 solutions. Specific protein-protein interactions resulted in formation of reversible higher order species of monomer. Solution storage modulus (G'), and not loss modulus or complex viscosity, was the more reliable parameter for predicting protein-protein interactions. Predictions about the nature of protein-protein interactions made on the basis of solution G' were found to be consistent with observed effect of pH and ionic strength on zeta potential and scattered intensity of IgG2 solutions. Results demonstrated the potential of high-frequency storage modulus measurements for understanding behavior of proteins in solutions and predicting the nature of protein-protein interactions.

Algorithms↗
PubMed1983

Distance and contacts: interactions of black urban elderly adults with family and friends.

Distance is the major factor determining the frequency of social interaction with family and friends for elderly whites. Age, sex, marital status, length of residence, and income also affect the number of social contacts. These relationships have not been studied for elderly blacks. Utilizing data from a survey of 655 black urban residents 60 years old and older, this study investigated contacts with family and friends. The major finding was that the neighborhood is an important place for socializing with both family and friends for this population as is the case for working-class white elderly adults. A surprising finding is that, whereas social contacts increase with higher income for working-class elderly whites, for these black elderly adults who are of the working class and poor, social contacts decrease with higher income.

Aged↗
PubMed1999

Interaction of static and extremely low frequency electric and magnetic fields with living systems: health effects and research needs.

An international seminar was held June 4-6, 1997, on the biological effects and related health hazards of ambient or environmental static and extremely low frequency (ELF) electric and magnetic fields (0-300 Hz). It was cosponsored by the World Health Organization (WHO), the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the German, Japanese, and Swiss governments. Speakers provided overviews of the scientific literature that were discussed by participants of the meeting. Subsequently, expert working groups formulated this report, which evaluates possible health effects from exposure to static and ELF electric and magnetic fields and identifies gaps in knowledge requiring more research to improve health risk assessments. The working groups concluded that, although health hazards exist from exposure to ELF fields at high field strengths, the literature does not establish that health hazards are associated with exposure to low-level fields, including environmental levels. Similarly, exposure to static electric fields at levels currently found in the living and working environment or acute exposure to static magnetic fields at flux densities below 2 T, were not found to have demonstrated adverse health consequences. However, reports of biological effects from low-level ELF-field exposure and chronic exposure to static magnetic fields were identified that need replication and further study for WHO to assess any possible health consequences. Ambient static electric fields have not been reported to cause any direct adverse health effects, and so no further research in this area was deemed necessary.

Animals↗
PubMed2002

Mechanical properties of the dorsal fin muscle of seahorse (Hippocampus) and pipefish (Syngnathus).

The dorsal and pectoral fins are the primary locomotor organs in seahorses (Hippocampus) and pipefish (Syngnathus). The small dorsal fins beat at high oscillatory frequencies against the viscous medium of water. Both species are able to oscillate their fins at frequencies likely exceeding the point of flicker fusion for their predators, thus enhancing their ability to remain cryptic. High-speed video demonstrated that seahorse dorsal fins beat at 30-42 Hz, while pipefish dorsal fins oscillate at 13-26 Hz. In both species, the movement of the fin is a sinusoidal wave that travels down the fin from anterior to posterior. Mechanical properties of seahorse and pipefish dorsal fin muscles were tested in vitro by the work loop method. Maximum isometric stress was 176.1 kN/m(2) in seahorse and 111.5 kN/m(2) in pipefish. Work and power output were examined at a series of frequencies encompassing the range observed in vivo, and at a number of strains (percent length change during a contractile cycle) within each frequency. At a given strain, work per cycle declined with increasing frequency, while power output rose to a maximum at an intermediate frequency and then declined. Frequency and strain interacted in a complex fashion; optimal strain was inversely related to cycle frequency over most of the frequency range tested. Seahorse dorsal fin muscle was able to generate positive work at higher cycling frequencies than pipefish. Both species produced positive work at higher frequencies than have been reported for axial and fin muscles from other fish.

Animals↗
PubMed1989

Comodulation masking release for three types of modulator as a function of modulation rate.

To investigate the dependence of 'Comodulation Masking Release' (CMR) on the type and frequency of modulator, thresholds were measured for a 4-kHz tone masked by modulated and unmodulated noises. The maskers were a 400-Hz wide band of noise centered on 4 kHz (NOCUE), the same noise with a 2700-Hz lowpass noise added (LPCUE), and a wideband noise with a passband between 3 and 6 kHz (WBCUE). In each condition three types of modulator were used: a square wave, a sinewave, and a lowpass noise. Several frequencies of each type of modulator were used, allowing measurement of the interaction between envelope frequency (fe) and modulator type. Thresholds were lower in the presence than in the absence of modulation for all modulator types, except when fe was high (e.g. 100 Hz). The 'Modulated-Unmodulated Difference' (MUD) decreased monotonically with increasing fe in all conditions. For any given fe, MUDs generally were greater for square-wave and lowpass-noise modulation than for sinusoidal modulation. As significant MUDs were sometimes obtained even in the NOCUE condition, the MUD was not an accurate measure of CMR. Therefore, CMR was defined as the difference between the MUD obtained in the NOCUE condition and that obtained in each cue condition, for each combination of fe and modulator type. Measured this way, the CMR for our 4-kHz signals did not vary systemically with fc over the range studied. When a CMR was obtained it was smaller for sinusoidal modulation than for either square-wave or lowpass-noise modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1998

Effect of charge interactions on the carboxylate vibrational stretching frequency in c-type cytochromes investigated by continuum electrostatic calculations and FTIR spectroscopy.

The FTIR spectra of the asymmetric carboxylate absorption region of three c-type cytochromes--namely horse heart, yeast and bonito cytochromes c--as well as continuum electrostatic calculations performed on their respective protein matrices, show that these combined methods can target specific protein regions and yield pertinent protein charge information that correlates with the observed spectral data. Deconvolution of the IR carboxylate stretch frequency region (1525-1675 cm-1) in the three cytochromes yield different v(oco)a distributions. In the case of the bonito cytochrome c carboxylates, two v(oco)a populations are clearly distinguishable in the deconvoluted spectra--which is not the case for the more complex v(oco)a deconvolutions of the other two cytochromes. The frequency distributions of the calculated potentials are consistent with the experimental observations and we conclude that the IR carboxylate absorption in proteins can be modified by the electrostatic environment.

Animals↗