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PubMed2004

Gender differences in hemispheric organization during divergent thinking: an EEG investigation in human subjects.

This study examined the gender-related differences in EEG patterns during the experimental condition of divergent thinking. The EEG of 36 males and 27 females was recorded from 16 scalp electrodes in rest and while students were solving a creative problem. The spectral power density along with EEG coherence estimates were analyzed in each of the six frequency bands in the 4-30 Hz range. Gender-related differences in the EEG patterns were found during successful divergent thinking. Creative men were characterized by massive increases of amplitude and interhemispheric coherence in the beta2 whereas creative women showed more local increases of the beta2 power and coherence. On the contrary, the task-induced desynchronization of the alpha1 rhythm in creative women was topographically more expanded as compared with men who demonstrated greater interhemispheric coherence than women did. Our results propose a different hemispheric organization in men and women during creative thinking.

Alpha Rhythm↗
PubMed1999

Influence of age on the parasympatholytic property of tricyclic antidepressants.

Clinical evidence indicates that parasympatholytic effects of tricyclic antidepressants increase with age. The aim of the present study was to determine the possible physiological reason for this phenomenon. Subjects included 23 patients (14 female) with major depression, melancholic type, and 23 age- and sex-matched healthy control subjects. Cardiac vagal tone was measured at rest using both spectral analysis and a time domain beat-to-beat method. Results of the spectral and time domain methods for the estimation of vagal tone used in this study were highly correlated in control subjects as well as in medicated depressed subjects. Both patients and control subjects showed an age-related decline in cardiac vagal tone. Tricyclic antidepressants decreased vagal tone significantly by 25-49% depending on age (20-60 years), although the age difference was not significant. The greater effect of tricyclic antidepressants on parasympathetic activity typically seen in older age groups may reflect the fact that predrug levels of vagal tone are already low in older patients. Measurement of vagal tone prior to drug administration may therefore be of prognostic value for anticholinergic side effects.

Adult↗
PubMedDate not supplied

Spectral and polarization sensitivity of photocurrents of amphibian rods in the visible and ultraviolet.

Photocurrents from isolated rods of adults and sub-adults of three species of amphibians, Rana pipiens, Ambystoma tigrinum, and Xenopus laevis, were measured with suction pipette electrodes. The intensity for a half-maximal response was 0.91+/-0.48 photons microm(-2) flash(-1) (mean +/- S.D., 10-ms flashes) for Rana, 0.92+/-0.44 for Ambystoma, and 6.14+/-1.33 for Xenopus. The mean number of photoisomerizations at half-saturation was 22+/-12 for Rana, 50+/-24 for Ambystoma, and 221+/-48 for Xenopus. The photocurrent per photoisomerization is several times smaller in Xenopus rods than in the other two species. Spectral sensitivity was measured from 277-737 nm with light polarized both parallel and perpendicular to the planes of the membrane disks. Dichroism fell in the near UV and was absent in the region of absorption by tryptophan and tyrosine. Maximum sensitivity of Rana was at 503.9+/-2.6 nm (n = 86), and of Ambystoma, 505.8+/-1.8 nm (n = 24). Animals from these same batches that were sampled by HPLC had no 3-dehydroretinal (retinal2). Xenopus containing about 94% retinal2 and 6% retinal1 had lambda(max) at 519.3+/-2.7 nm (n = 11). Spectral position of the beta-band, estimated by the method of Stavenga et al. (1993), appears to be at longer wavelengths in amphibian photoreceptors than in other vertebrates. Fits of log sensitivity to a normalized-frequency template that tracks the long-wavelength tail of the alpha-band (Lamb, 1995) show that the rod pigments of Rana and Ambystoma are slightly narrower than those found in the photoreceptors of fish and mammals.

Ambystoma↗
PubMed1975

Formaldehyde as a probe of DNA structure. II. Reaction with endocyclic imino groups of DNA bases.

We describe the equilibrium and kinetic aspects of the formaldehyde reaction with the endocyclic imino groups of derivatives of thymine, uracil, and a series of halogenated uracils, as well as poly(uridylic acid) and poly(inosinic acid). The main results are: (i) the equilibrium constants for forming a hydroxymethyl adduct remain quite constant at about 2-2.5 (M-1) for all the compounds studied, independent of their pK; (ii) both forward and reverse rate constants with 5'-TMP are specific base catalyzed in the pH range of about 4-9; (iii) the response of the rate constants to temperature and to several solvent additives are measured; (iv) at neutral pH, for the series of pyrimidine compounds, a linear free energy relation is observed between the logarithm of both the forward and the reverse rate constant and the pK for deprotonation; (v) the unstructured polynucleotides, poly(U) and poly(I) react very similarly to their constituent monomers; (vi) a reaction mechanism is proposed; and (vii) some implications for polynucleotide studies are discussed. In an appendix, a method of spectral analysis is derived to obtain accurate estimates of the quite small equilibrium constants; this should be applicable to all similar two-component systems in which the final product is unobtainable, either by isolation or by saturation. Together with the results of the previous paper on the formaldehyde reaction with exocyclic amino groups (J. D. McGhee and P. H. von Hippel, preceding paper), these results form a reasonably comprehensive account of the basic chemical controls required to use formaldehyde as a quantitative probe of DNA structure.

Chemical Phenomena↗
PubMed2006

Static and dynamic quenching of Ru(II) polypyridyl excited states by iodide.

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF(6))(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59 700 M(-1). Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I(2)(*)(-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF(6))(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH(2)Cl(2), and light excitation gave a higher I(2)(*)(-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.

Journal Article↗
PubMed1979

A re-evaluation of some basic structural and functional properties of Pseudomonas cytochrome oxidase.

Determinations of iron content and dry-weight measurements on samples of Pseudomonas cytochrome oxidase were coupled with sodium dodecyl sulphate/polyacrylamide-gel-electrophoresis studies of both the native protein and covalently cross-linked oligomers in order to estimate the enzyme's molecular weight and spectral absorption coefficients. A value of epsilon(ox.) (410)=282x10(3) litre.mol(-1).cm(-1) was calculated for a dimeric protein molecule having a total molecular weight of 122000 (based on iron analysis). Steady-state kinetic observations of the enzyme-catalysed oxidation of reduced azurin by nitrite indicated a marked increase in enzyme inactivation as the pH was raised from 5.7 to 7.2. Since NO, a product of the nitrite reductase activity of Pseudomonas cytochrome oxidase, is known to bind to the enzyme, a study was undertaken to try to assess the potential of NO as a product inhibitor. Investigations showed that samples of the oxidized protein at pH values 4, 5 and 6 bound NO to both haem c and d(1) components, but oxidized enzyme samples at pH7 and above formed their reduced ligand-bound forms when placed under an atmosphere of the gas. Ascorbate-reduced enzyme samples at pH4, 5, 6 and 7 were also found to bind NO at both haem components, although at pH7 the rate of haem c binding was very slow. At pH8 and 9 only the ferrohaem d(1) bound NO. Titration experiments on the reduced protein over the pH range 5-7, with nitrite as a precursor of NO, showed that the haem d(1) had a much higher affinity than the haem c: experiments at pH5.2 and 5.9 with NO-equilibrated solutions revealed the same pattern of behaviour with the oxidized enzyme.

Chemical Phenomena↗
PubMed2001

[Analysis of 180 patients with sensory defect nystagmus (SDN) and congenital idiopathic nystagmus (CIN)].

AIM: Analysis of the diseases underlying congenital nystagmus in a series of patients registered during 6 years as a prerequisite for adequate counselling of the families. PATIENTS AND METHODS: Retrospective study of all patients that presented between 1992 and 1998 with congenital nystagmus not related to visual deprivation or acquired pathologies of the visual pathways. The patients were examined clinically and in dependence on the findings also by electrophysiological (Ganzfeld ERG and VEP, Albino-flash-VEP), psychophysical (colour vision, dark adaptation, spectral sensitivity), and molecular genetic methods. When estimated necessary, family members affected by history and unaffected family members were also examined. In cases of complex neuroophthalmological diseases a neuropaediatric examination including neuroimaging was initiated. RESULTS: In total, 180 patients could be analysed. A sensory defect nystagmus (SDN) was present in 142 patients (79%). The diagnoses were as follows: albinism (any form) in 56 patients (30%), progressive photoreceptor dystrophy in 20 patients (11%), stationary cone dysfunction in 18 patients (10%), bilateral optic nerve hypoplasia in 15 patients (8%), chorioretinal or optic nerve colobomata in 10 patients (6%), aniridia and its variants in 10 patients (6%), familial isolated nystagmus in 8 patients (5%), and congenital stationary night blindness in 5 patients (3%). 38 patients (21%) could not (yet) be classified. DISCUSSION: The prevalence of SDN as the manifesting symptom of a variety of well defined diseases in the present series of at least 79% is similar to that of 90% reported earlier. The precise diagnosis is a prerequisite for counselling the families as to functional prognosis and recurrence risk. Unnecessary neurological examinations including neuroimaging can be avoided.

Adolescent↗
PubMed1999

Two Different Accretion Classes in Seyfert 1 Galaxies and QSOs.

The mass of the central black holes in Seyfert galaxies and QSOs can be determined from the broad emission lines and the reverberation method. Using the measured black hole mass and the bolometric or ionizing luminosity, the accretion rate can be estimated. Compiling a sample of Seyfert 1 galaxies and QSOs with reliable central masses, estimated ionizing luminosities, and X-ray spectral slopes, we find that the X-ray spectral slope strongly correlates with the accretion rate. The objects in the sample are found to be distributed in two distinct classes in the spectral index versus log&parl0;Lion&solm0;LEdd&parr0;-plane. We argue that these two classes may correspond to advection-dominated accretion flow (ADAF) and thin disk accretion. The observations of a "two-state" Seyfert 1 galaxy, 1H 0419-577, confirm our results. Detailed fitting of the spectra of individual Seyfert 1 galaxies and QSOs using ADAF and/or thin disk models should further clarify the two-class classification.

Journal Article↗
PubMed1986

Aluminum equivalence of materials used in diagnostic radiology and its dependence on beam quality.

A semi-empirical theory has been derived that relates the aluminum equivalence of various materials used in diagnostic radiology to their attenuation coefficients. The dependence of the aluminum hardness (AHE) and attenuation (AAE) equivalent on the beam quality is described in terms of effective energy. This 'aluminum equivalence approach' (ALEAP) gives estimates of the aluminum equivalent, regardless of spectral shape, that are usually within +/- 5% except when absorption edges are involved. A reasonable definition for the AHE of K-edge filters is offered. Suggestions are made for methods of testing for compliance with standards and regulations.

Aluminum↗
PubMed2002

Parsimonious basis selection in exponential spectral analysis.

Sums of decaying real exponentials (SDREs) are frequently used in models of time-varying processes. First-order compartmental models are widely employed to describe mass transit in chemical and biological systems. In these models the evolution of compartment concentration versus time is represented as the convolution of an input function with an SDRE. In exponential spectral analysis (ESA) the nonlinear problem of estimating the SDRE rate constants is replaced by the linear estimation of the coefficients of a preselected set of exponential basis functions (EBFs). This work addresses the problem of selecting the number of EBFs and the rate constant of each basis element. Basis dimension is established via model selection, in which approximation error and parameter redundancy are the criteria. The latter is estimated via simulation of the fitted model over multiple noise realizations. A constrained Cramér-Rao lower bound is derived for ESA parameters. The resulting parsimonious ESA algorithm (PESA) ameliorates the inherent problem of non-uniqueness in ESA parameters. Consequently, sets of time series may be compared in a statistically meaningfully way in terms of physically or physiologically significant parameters. PESA is applied to compare the retention of two radiotracers in the artificially perfused rabbit heart.

Algorithms↗
PubMed1991

The amplitude modulation-following response as an audiometric tool.

The amplitude modulation-following response (AMFR) is an auditory scalp-recorded potential, evoked using continuous, amplitude-modulated tones. The current study was designed to explore the audiometric utility of the AMFR by demonstrating the frequency specificity of the response and assessing the relation between behaviorally measured pure-tone thresholds and AMFR detection thresholds. Subjects in this study were six normal-hearing and four hearing-impaired adults. High-pass masking results in the normal hearing subjects demonstrated that the AMFR is associated with a narrow range of activation along the cochlea around the carrier frequency. Frequency-specific results from the hearing-impaired subjects confirmed this finding. Thresholds for the AMFR, defined in spectral terms, were consistent with the behavioral estimates in both the normal and the hearing-impaired subjects.

Acoustic Stimulation↗
PubMed1982

Covalent addition of H2O, enzyme substrates and activators to pyrrolo-quinoline quinone, the coenzyme of quinoproteins.

The fluorescence excitation and the adsorption spectrum of 2,7,9-tricarboxy-1H-pyrrolo [2,3-f]quinoline-4,5-dione (pyrrolo-quinoline quinone, PQQ), measured in the pH range 7.0-10.0, are quite different. However, when the temperature of the solution is lowered, the shape and maxima of these spectra become more similar. 1H-NMR in 2H2O revealed a temperature-dependent equilibrium between PQQ and a hydrated form. Evidence is presented that low temperature favours the formation of the fluorescing species which is PQQ, hydrated at the C-5 position. Even further hydration is possible since absorption, fluorescence and NMR spectroscopy of PQQ in borate buffer pH 10.0 reveal additional hydration at the C-4 position, pointing to a dihydrate. PQQ also reacts with quinoprotein enzyme substrates and activators. Spectroscopic measurements showed the existence of 5-alkoxy-5-hydroxy-PQQ and 5-amino-5-hydroxy-PQQ in the presence of alcohols and 2 M NH4Cl, pH 9.0, respectively. In the latter case, the existence of 5-imino-PQQ could also be demonstrated. Addition compounds with amines appear to be unstable. The amines become probably oxidized because pyrrolo-quinoline quinol (PQQH2) was found as the reaction product. On the other hand, an addition compound containing an imino bond could be isolated after addition of urea to a PQQ solution. Spectral characteristics of PQQ and its addition compounds are presented since these data are necessary for the spectral analysis of quinoproteins and the quantitative estimation of coenzyme.

Chemical Phenomena↗
PubMed1996

Effect of RNA editing and subunit co-assembly single-channel properties of recombinant kainate receptors.

1. Patch-clamp methods have been used to examine single-channel properties of recombinant GluR5 and GluR6 kainate-preferring glutamate receptors which differ in a single amino acid residue as a result of RNA editing at the Q/R (glutamine/arginine) site. Subunits were expressed alone or in combination with the high-affinity kainate receptor subunit KA - 2 in transfected human embryonic kidney (HEK-293) cells. 2. In outside-out patches, unedited homomeric GluR6(Q) receptors exhibited directly resolved domoate-activated single-channel conductances of 8, 15 and 25 pS. Variance analysis of GluR6(Q) responses gave a mean conductance of 5.4 pS, while the edited isoform GluR6(R) had an unusually low channel conductance (225 fS). 3. Homomeric channels composed of GluR5(Q) subunits exhibited three conductance states of 5, 9 and 14 pS characterized by prolonged burst activations in the presence of domoate. In contrast, the GluR5(R) subunit, which has not previously been reported to form functional homomeric receptors, had an extremely low conductance (< 200 fS). 4. Heteromeric GluR6(Q)/KA-2 kainate receptors gave single-channel events indistinguishible from homomeric GluR6(Q) channels. Conversely, openings produced by GluR5(Q)KA-2 and GluR5(Q) receptors differed from each other in their kinetic properties. The primary effect of co-expression of KA-2 with GluR5(Q) was a dramatic shortening in channel burst length. 5. Spectral and variance analyses were used to estimate mean single-channel conductances of heteromeric edited receptor-channels; channel conductances were 950 fS for GluR5(R)KA-2 receptors and 700 fS for GluR6(R)/KA-2 receptors. Both receptor types had significantly higher conductances than the respective homomeric channels, GluR5(R) and GluR6(R). 6. We conclude that Q/R site editing dramatically reduces single-channel conductance. Furthermore, we find similarity between the kainate receptor-channels described in sensory neurones and the recombinant GluR5(Q) homomeric channel. Characterization of recombinant single-channel properties could therefore aid identification of the native kainate receptors.

Action Potentials↗
PubMed1996

Augmented baroreflex heart rate gain after moderate-intensity, dynamic exercise.

The occurrence of a sustained vasodilation and hypotension after acute, dynamic exercise suggests that exercise may alter arterial baroreflex mechanisms. Therefore, we assessed systemic hemodynamics, baroreflex regulation of heart rate, and cardiac vagal tone after 60 min of cycling at 60% peak oxygen consumption in 12 healthy, untrained men and women (ages 21-28 yr). We derived sigmoidal carotid-cardiac baroreflex relations by measurement of R-R interval changes induced by ramped, stepwise, R-wave-triggered changes in external neck pressure from 40 to -65 mmHg. We estimated tonic cardiac vagal control with power spectral analysis of R-R interval variability in the respiratory frequency band (0.2-0.3 Hz) during frequency- and tidal volume-controlled breathing. Both mean arterial pressure and total peripheral resistance were reduced postexercise [pressure: from 86 +/- 2 (mean +/- SE) to 81 +/- 2 mmHg; resistance: from 23 +/- 2 to 16 +/- 1 units; both P < 0.05]. Cardiac output was increased postexercise (from 3.9 +/- 0.3 to 5.5 +/- 0.5 l/min, P < 0.05). Both slope and range of the carotid-cardiac baroreflex relation were increased postexercise (slope: from 4.7 +/- 0.7 to 6.1 +/- 0.9 ms/mmHg; range: from 186 +/- 23 to 238 +/- 30 ms, P < 0.05). Respiratory R-R interval variability (cardiac vagal tone) was not changed at any time after exercise, whereas heart rate and plasma norepinephrine levels were elevated. Thus moderate-intensity, dynamic exercise increases heart rate and cardiac output, reduces peripheral vascular resistance, and augments baroreflex responsiveness. Our data suggest that augmented baroreflex heart rate gain restrains rather than contributes to postexercise hypotension, which appears to be mediated predominately by vasodilation.

Adult↗
PubMed2001

Inspiratory lung impedance in COPD: effects of PEEP and immediate impact of lung volume reduction surgery.

Frequency-dependent characteristics of lung resistance (RL) and elastance (EL) are sensitive to different patterns of airway obstruction. We used an enhanced ventilator waveform (EVW) to measure inspiratory RL and EL spectra in ventilated patients during thoracic surgery. The EVW delivers an inspiratory flow waveform with enhanced spectral excitation from 0.156 to 8.1 Hz. Estimates of the coefficients in a trigonometric approximation of the EVW flow and transpulmonary pressure inspirations yielded inspiratory RL and EL spectra. We applied the EVW in a group with mild obstruction undergoing various thoracoscopic procedures (n = 6), and another group with severe chronic obstructive pulmonary disease undergoing lung volume reduction surgery (n = 8). Measurements were made at positive end-expiratory pressure (PEEP) of 0, 3, and 6 cmH(2)O. Inspiratory RL was similar in both groups despite marked differences in spirometry. The chronic obstructive pulmonary disease patients demonstrated a pronounced frequency-dependent increase in inspiratory EL consistent with severe heterogeneous peripheral airway obstruction. PEEP appears to have beneficial effects by reducing peripheral airway resistance. Lung volume reduction surgery resulted in increased inspiratory RL and EL at all frequencies and PEEPs, possibly due to loss of diseased lung tissue, pulmonary edema, increased mechanical heterogeneity, and/or an improvement in airway tethering.

Adult↗
PubMed1991

Spatial orientation of the vestibular system: dependence of optokinetic after-nystagmus on gravity.

1. Monkeys received optokinetic stimulation at 60 degrees/s about their yaw (animal vertical) and pitch (animal horizontal) axes, as well as about other head-centered axes in the coronal plane. The animals were upright or tilted in right-side-down positions with regard to gravity. The stimuli induced horizontal, vertical, and oblique optokinetic nystagmus (OKN). OKN was followed by optokinetic after-nystagmus (OKAN), which was recorded in darkness. 2. When monkeys were tilted, stimulation that generated horizontal or yaw axis eye velocity during OKN induced a vertical or pitch component of slow phase velocity during OKAN. This has been designated as "cross-coupling" of OKAN. Eigenvalues and eigenvectors associated with the system generating OKAN were found as a function of tilt. They were determined by use of the Levenberg-Marquardt algorithm to minimize the mean square error between the output of a model of OKAN and the data. 3. The eigenvector associated with yaw OKAN (yaw axis eigenvector) was maintained close to the spatial vertical regardless of the angle of tilt. The eigenvector associated with pitch OKAN (pitch axis eigenvector) was always aligned with the body axis. The data indicate that velocity storage can be modeled by a piecewise linear system, the structure of which is dependent on gravity and the yaw axis eigenvector, which tends to align with gravity. 4. Yaw axis eigenvectors were also determined by giving optokinetic stimulation about head-centered axes in the coronal plane with the animal in various angles of tilt. A technique using a spectral analysis of residuals was developed to estimate whether yaw and pitch OKAN slow phase velocities decayed concurrently at the same relative rate and over the same time course. The eigenvectors determined by this method were in agreement with those obtained by analyzing OKAN elicited by yaw OKN. 5. During yaw OKN with the animal in tilted positions, the mean vector of the ensuing nystagmus was closer to the body axis than to the spatial vertical. This suggests that there is suppression of the cross-coupled pitch component during OKN. The direction of the stimulus may be utilized to suppress components of velocity storage not coincident with the direction of stimulus motion. 6. There were similarities between the monkey eigenvectors and human perception of the spatial vertical, and the mean of eigenvectors for upward and downward eye velocities overlay human 1-g perceptual data.(ABSTRACT TRUNCATED AT 400 WORDS)

Acceleration↗
PubMed1985

Reflection mode diffraction tomography.

A reconstruction algorithm is presented which possesses a simple scanning geometry and promises higher resolution than conventional transmission mode diffraction tomography algorithms. This broad-band reflection mode algorithm inherently lacks a certain amount of low frequency information but an estimate of the information is recovered by spectral extrapolation. The resolution of the algorithm will be shown to be limited by the bandwidth and physical size of the single plane wave transducer, as well as the Born approximation.

Computers↗
PubMed2001

Characterization of polymorphs of a novel quinolinone derivative, TA-270 (4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone).

The polymorphic forms and amorphous form of TA-270 (4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone), a newly developed antiallergenic compound, were characterized by powder X-ray diffractometry, thermal analysis, infrared spectroscopy and solid state 13C-NMR. The intrinsic dissolution rates of polymorphic forms were measured using the rotating disk method at 37 degrees C. The dissolution rates correlated well with the thermodynamic stability of each polymorphic form. These dissolution properties were clearly reflected in the oral bioavailability of TA-270 in rats. The transition behavior for each polymorph and for the amorphous form was studied under the high temperature and humidity conditions. The beta- and delta-forms were transformed into the alpha-form by heating. The amorphous form was also easily crystallized into alpha-form by heating, however it was relatively stable under humidified conditions. The internal molecular packing of each polymorph was estimated from IR and solid state NMR spectral analysis.

Absorption↗