Serotonin modulates oscillation parameters of the membrane potential in isolated spinal neurons in the lamprey

The 5-HT was shown to depolarize branch cells (supposedly motoneurones and interneurones) by 2-6 mV, inducing, however, no MP oscillations. In case the MP oscillations were present (induced by the NMDA, for instance), the 5-HT altered their parameters: increased the amplitude of all types of oscillations, frequency of irregular oscillations, and duration of the depolarising plateau with the AP discharges. This modulation of the induced oscillations may enhance activity of neuronal locomotor network and thus reinforce muscle contractions and increase the intensity of the animal's movements. Possible mechanisms of the receptor modulation, of the AP enhancement, and of the changes in locomotor rhythm parameters, are discussed.     

Organ vessel functions by pulsatile flow

It was found that changes of resistance, capacity and exchange vessel functions of the skeletal muscle depended on values of amplitude and frequency of perfusion blood flow in acute experiments on cats. Amplitude-frequency characteristics of hemodynamic parameters of these functions were nonlinear. Ranges of amplitude and frequency variation with significant shifts of these parameters were determined. Conditions of perfusion (constant flow or constant pressure) changed volume and direction of haemodynamic parameter shifts under the amplitude-frequency modulation of the pulsatile blood flow. The pulsatile blood flow oscillations exerted maximum influence on hemodynamic parameters of exchange vessel function. The author has proposed the wave regulation conception of organ vessel functions.     

Linear Tuning of Gamma Amplitude and Frequency to Luminance Contrast: Evidence from a Continuous Mapping Paradigm

Individual differences in the visual gamma (30–100Hz) response and their potential as trait markers of underlying physiology (particularly related to GABAergic inhibition) have become a matter of increasing interest in recent years. There is growing evidence, however, that properties of the gamma response (e.g., its amplitude and frequency) are highly stimulus dependent, and that individual differences in the gamma response may reflect individual differences in the stimulus tuning functions of gamma oscillations. Here, we measured the tuning functions of gamma amplitude and frequency to luminance contrast in eighteen participants using MEG. We used a grating stimulus in which stimulus contrast was modulated continuously over time. We found that both gamma amplitude and frequency were linearly modulated by stimulus contrast, but that the gain of this modulation (as reflected in the linear gradient) varied across individuals. We additionally observed a stimulus-induced response in the beta frequency range (10–25Hz), but neither the amplitude nor the frequency of this response was consistently modulated by the stimulus over time. Importantly, we did not find a correlation between the gain of the gamma-band amplitude and frequency tuning functions across individuals, suggesting that these may be independent traits driven by distinct neurophysiological processes.     

Investigation of the modulation between EEG alpha waves and slow/fast delta waves in children in different depths of Desflurane anesthesia

ObjectivesInvestigation of the amplitude modulation of alpha-band EEG oscillations (i.e., grouping of alpha-band activities) by delta-band EEG activities in various depths of anesthesia (DOA).MethodsThis modulation, which is a sort of phase dependent amplitude modulation, is studied in 10 children in various depths of Desflurane anesthesia. Two parameters are defined to quantify the modulation: strength of modulation (SOM) and phase of modulation (POM). SOM indicates to what extent delta and alpha activities are related to each other, and POM is the delta phase in which the alpha amplitude is maximal. These parameters are analyzed in different DOA for various formations of delta sub-bands.ResultsThe ability of POM and SOM were explored to characterize mechanisms contributing to delta activities and their correlation with the level of anesthesia. These parameters are influenced by DOA and frequency intervals of delta sub-bands. SOM takes higher values around certain frequency ranges of delta band. According to this, delta band comprises three main sub-bands in various unconsciousness levels. Although boundaries of these sub-bands change with DOA, they are almost in [0.1–0.5] Hz (very slow delta), [0.7–1.7] Hz (slow delta) and [2–4] Hz (fast delta) intervals. POMs relating to slow and fast delta bands increase with consciousness level. This is an indication that delta waves differently modulate alpha EEG activities (in terms of phase lag) in different DOA. In deep anesthesia, POM relating to fast delta correlates with DOA better than POM relating to slow delta does. In light anesthesia this correlation is inversed. Investigation regarding to different formations of delta sub-bands shows that POM relating to [1.8–4] Hz is a proper choice for distinguishing deep, moderate and light anesthesia.ConclusionSOM allows separating mechanisms underlying delta band activities, and POM can be seen as a complementary neurophysiologic-based parameter for quantifying DOA.     

Amplitude and frequency modulation of metabolic signals in leukocytes: synergistic role of IFN-gamma in IL-6- and IL-2-mediated cell activation.

Many stimuli cause intracellular concentration oscillations of second messengers or metabolites, which, in turn, may encode information in their amplitudes and frequencies. We now test the hypothesis that synergistic cellular responses to dual cytokine exposure correlate with cross-talk between metabolic signaling pathways of leukocytes. Polarized RAW264.7 macrophages and human neutrophils and monocytes exhibited NAD(P)H autofluorescence oscillation periods of congruent with20 s. IFN-gamma tripled the NAD(P)H oscillatory amplitude for these cells. Although IL-6 had no effect, incubation of cells with IFN-gamma and IL-6 increased both oscillatory amplitude and frequency. Parallel changes were noted after treatment with IFN-gamma and IL-2. However, IL-1beta and TNF-alpha did not display frequency doubling with or without IFN-gamma exposure. To determine whether frequency doubling required complete IFN-gamma signaling or simply metabolic amplitude modulation, an electric field was applied to cells at NAD(P)H troughs, which has been shown to enhance NAD(P)H amplitudes. Electric field application led to frequency doubling in the presence of IL-6 or IL-2 alone, suggesting that amplitude modulation is crucial to synergism. Because NADPH participates in electron trafficking to NO, we tested NO production during cytokine exposure. Although IL-6 and IL-2 alone had no effect, IFN-gamma plus IL-6 and IFN-gamma plus IL-2 enhanced NO release in comparison to IFN-gamma treatment alone. When NO production was examined for single cells, it incrementally increased with the same phase and period as NAD(P)H. We suggest that amplitude and frequency modulation of cellular metabolic oscillations contribute to intracellular signaling synergy and entrain NO production.     

High-frequency oscillations in a pulse wave signal and their relation to adaptation responses

High-frequency oscillations in a pulse wave signal in the range of 1-50 Hz and their relation to heart rhythms have been investigated. Informative parameters to estimate the adaptation reactions have been determined using the Kohonen maps, the results of simulating the pulse wave signal (single rheocycles), and the experimental data. The coefficient of harmonic variation was used as an informative parameter. It was shown that the space of signs in the frequency range of 1-12.5 Hz, formed on the basis of the coefficient of harmonic variation, possesses a significant degree of structuring relative to the distribution of data for different types of adaptation reactions.     

On the reactions of the human nervous system to complex-frequency optical stimulation

A computerized system for precise stimulation and analysis of electroencephalographic (EEG) reactions to two simultaneously presented frequencies of sine-wave light (one constant, 13 Hz, and the other varying from 1 to 6 Hz and vice versa) was used to study the mechanisms of human brain reactivity to complex rhythmical stimulation. The frequencies were generated by computer and presented to the subjects by three different ways: as a result of their simple summation (additively), as a product of their multiplication (multiplicatively, amplitude modulation of constant frequency by the varying frequency), or by separate presentation to different eyes. The dynamics of electroencephalograms for different types of stimulation were compared. Under all three experimental conditions, the dynamics of EEG spectra has demonstrated the same general pattern of resonance activation, which was similar to that observed for the presented signals in the case of their amplitude modulation. Significant positive shifts in the functional state of subjects were observed as a result of stimulation. The results obtained show the leading role of the processes of amplitude modulation in the interaction of integrative, adaptive, and trace mechanisms of the brain functioning during human perception of complex rhythmical stimuli.     

Role of membrane potential in vasomotion of isolated pressurized rat arteries

Vasomotion, the phenomenon of vessel diameter oscillation, regulates blood flow and resistance. The main parameters implicated in vasomotion are particularly the membrane potential and the cytosolic free calcium in smooth muscle cells. In this study, these parameters were measured in rat perfused-pressurized mesenteric artery segments. The application of norepinephrine (NE) caused rhythmic diameter contractions and membrane potential oscillations (amplitude; 5.3 +/- 0.3 mV, frequency; 0.09 +/- 0.01 Hz). Verapamil (1 microM) abolished this vasomotion. During vasomotion, 10(-5) M ouabain (Na(+)-K(+) ATPase inhibitor) decreased the amplitude of the electrical oscillations but not their frequency (amplitude; 3.7 +/- 0.3 mV, frequency; 0.08 +/- 0.002 Hz). Although a high concentration of ouabain (10(-3) M) (which exhibits non-specific effects) abolished both electrical membrane potential oscillations and vasomotion, we conclude that the Na+-K+ ATPase could not be implicated in the generation of the membrane potential oscillations. We conclude that in rat perfused-pressurized mesenteric artery, the slow wave membrane type of potential oscillation by rhythmically gating voltage-dependent calcium channels, is responsible for the oscillation of intracellular calcium and thus vasomotion.     

Processing of behaviorally relevant temporal parameters of acoustic stimuli by single neurons in the superior olivary nucleus of the leopard frog

Summary Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.Abbreviations SON superior olivary nucleus - DMN dorsal medullary nucleus - TS torus semicircularis - FTC frequency threshold curve - BF best excitatory frequency - PAM pulsatile amplitude modulation - SAM sinusoidal amplitude modulation - SQAM square-wave amplitude modulation - MTF modulation transfer function - PSTH peri-stimulus time histogram     

General properties of predictive population models in red grouse (Lagopus lagopus scoticus)

Summary The general properties of an empirical predictive model of population fluctuations in red grouse are discussed. The model incorporates two observed time-lagged relationships between (a) chick production and spring numbers two years earlier, and (b) overwinter survival and numbers in spring one year earlier. The model produced oscillations which were slowly damped with a period of nine years. The addition of randomly-imposed poor breeding sustained the amplitude of oscillations but did not affect the period. Incorporating immigration at low densities reduced the amplitude but preserved the period. Cycle length varied with the model parameters but was generally between 8–10 years. A model with reduced lags of one and zero years could produce shorter cycles of 4–6 years.     

Computer simulation of sustained oscillations in peroxidase-oxidase reaction

A system of differential equations of second order exhibiting transitional behaviour and sustained oscillations has been obtained for a complete scheme of the peroxidase-oxidase reaction. The concentrations of hydrogen peroxide and of hydrogen donor radicals are slow variables of the system. The most essential reactions responsible for oscillations have been selected. Analysis of the system in phase plane and in parameter space has been carried out. The dependence of oscillation period and amplitude on the parameter values has been investigated.     

Preservation of oscillations in postocclusive reactive hyperemia

Oscillations in skin blood flow (SkBF) during postocclusive reactive hyperemia are believed to be due to locally mediated events in the microcirculation. We characterized the activity of these oscillations in nine healthy young men who underwent 0, 10, and 40 Torr of lower body negative pressure (LBNP). Postocclusive SkBF was estimated in both forearms simultaneously in a stable thermal environment with laser-Doppler velocimetry. Periodic behavior of SkBF was characterized by frequency-domain power spectral analysis. LBNP at 40 Torr increased heart rate, decreased forearm blood flow, and decreased postocclusive SkBF amplitude but did not change the periodicity of SkBF in the frequency response range that is characteristic of postischemic SkBF oscillations (0.11 +/- 0.04 Hz). We observed that LBNP did not alter the frequency response of the postocclusive SkBF as quantified in the periodogram, even though the amplitude of the SkBF was markedly diminished as a part of the general decrease in arm blood flow. We found inferential evidence for a disseminated common pacemaker mechanism that performs similarly at distant sites. We conclude that the LBNP baroreflex-mediated modulation of SkBF reduces the amplitude but does not change the frequency behavior of postocclusive SkBF. We propose on the basis of our findings that the preservation of vasomotion suggests that this phenomenon is an adaptation to the ischemic changes induced by disruption of blood flow.     

Characteristics of slow oscillations of hemodynamics in men and women

The variability of the following spectral parameters was studied in apparently healthy adult subjects: heart rate, stroke volume, left ventricular ejection fraction, amplitude of aortal pulsing, amplitude of peripheral vessel pulsation in the first toe, and systolic blood pressure. The average values of the parameter of blood circulation per 500 heart beats (M), total power of variation spectrum of blood circulation parameter (TP), and absolute and relative powers of the oscillations of blood circulation parameter were estimated in the following spectral bands: ultralow frequency (ULF, % ULF), very low frequency (VLF, % VLF), low frequency (LF, % LF), and high frequency (HF, % HF). The variability of each blood circulation parameter proved to be characterized by a specific ratio of slow oscillations of different frequencies, which was a result of the specific regulation of this parameter. The parameters of central hymodynamics were relatively similar in oscillation structure. The oscillation spectra of the parameters of central and peripheral hemodynamics differed significantly. In adulthood, sex-related differences were determined in spectral parameters of the heart rate variability (ULF and VLF were higher in women), in the ejection fraction (% ULF was higher in women), in the amplitude of aortal pulsation (TP, ULF, VLF, LF and HF were higher in women), in the amplitude of pulsation of the peripheral vessels in the first toe (TP, ULF, VLF, LF and HF were higher in men), and in the blood pressure (% ULF was higher in women).     

L-type Ca2+ channels and K+ channels specifically modulate the frequency and amplitude of spontaneous Ca2+ oscillations and have distinct roles in prolactin release in GH3 cells

GH3 cells showed spontaneous rhythmic oscillations in intracellular calcium concentration ([Ca2+]i) and spontaneous prolactin release. The L-type Ca2+ channel inhibitor nimodipine reduced the frequency of Ca2+ oscillations at lower concentrations (100nM-1 microM), whereas at higher concentrations (10 microM), it completely abolished them. Ca2+ oscillations persisted following exposure to thapsigargin, indicating that inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ stores were not required for spontaneous activity. The K+ channel inhibitors Ba2+, Cs+, and tetraethylammonium (TEA) had distinct effects on different K+ currents, as well as on Ca2+ oscillations and prolactin release. Cs+ inhibited the inward rectifier K+ current (KIR) and increased the frequency of Ca2+ oscillations. TEA inhibited outward K+ currents activated at voltages above -40 mV (grouped within the category of Ca2+ and voltage-activated currents, KCa,V) and increased the amplitude of Ca2+ oscillations. Ba2+ inhibited both KIR and KCa,V and increased both the amplitude and the frequency of Ca2+ oscillations. Prolactin release was increased by Ba2+ and Cs+ but not by TEA. These results indicate that L-type Ca2+ channels and KIR channels modulate the frequency of Ca2+ oscillations and prolactin release, whereas TEA-sensitive KCa,V channels modulate the amplitude of Ca2+ oscillations without altering prolactin release. Differential regulation of these channels can produce frequency or amplitude modulation of calcium signaling that stimulates specific pituitary cell functions.     

Oscillatory depth as a function of temporal frequency

The percept of oscillatory motion in depth was generated by a luminance modulation of a sinusoidal nature induced within each dot pair of a stationary random assembly of paired dots. The dots were miniature sources of polarized light viewed through a rotating ocular polarizer, which facilitated both the percept of oscillations and the modulation of luminance at any desired frequency. Depth responses were studied as a function of frequency within the 0-2 Hz range. A strong amplitude decrease was noticed at a mean frequency of f(1)=0.81 Hz; oscillations were perceived as 'rectified' for f > f(1) with an additional minimum of crossed-disparity depth at f(2)=1.60 Hz. It is suggested that the intensity modulation of the light beams mapping the stationary stimuli onto the retinae was a likely factor responsible for the observed depth minima and the rectification of faster oscillations. Results are compared to those obtained in a traditional setting, where the percept of oscillations in depth had been generated by disparity variations due to lateral motion of the stimuli.     

Investigation of Turing instability for the Gierer–Meinhardt model

The dependence of the emergence of Turing instability for a distributed system of nonlinear differential equations that describe hydra morphogenesis based on the oscillatory properties of the corresponding trajectories of the system was investigated. The limits in the parameter space that provide diffusive instability were obtained. The frequency and amplitude dependences of the resulting spatial self oscillations on the values of the main parameters were investigated. Comparative analysis of the properties of the distributed system and corresponding trajectories of the system was carried out and the analytical conclusions were confirmed by the solutions of the system that were found using MATLAB.

     

Muscle pump function during locomotion: mechanical coupling of stride frequency and muscle blood flow

We imposed opposing oscillations in treadmill speed and grade on nine rats to test for direct mechanical coupling between stride frequency and hindlimb blood flow. Resting hindlimb blood flow was 15.5 +/- 1.7 ml/min. For 90 s at 7.5 m/min, rats alternated walking at -10 degrees for 10 s and +10 degrees for 10 s. This elicited oscillations in hindlimb blood flow having an amplitude of 4.1 +/- 0.5 ml/min (18% of mean flow) with a delay presumably due to metabolic vasodilation. Similar oscillations in speed (5.5-9.5 m/min) elicited oscillations in hindlimb blood flow (amplitude 3.4 +/- 0.5 ml/min, 15% of mean flow) with less of a delay, possibly due to changes in vasodilation and muscle pump function. We then simultaneously imposed these speed and grade oscillations out of phase (slow uphill, fast downhill). The rationale was that the oscillations in vasodilation evoked by the opposing oscillations in speed and grade would cancel each other, thereby testing the degree to which stride frequency affects hindlimb blood flow directly (i.e., muscle pumping). Opposing oscillations in speed and grade evoked oscillations in hindlimb blood flow having an amplitude of 3.3 +/- 0.6 ml/min (16% of mean flow) with no delay and directly in phase with the changes in speed and stride frequency. The finding that hindlimb blood flow changes directly with speed (when vasodilation caused by changes in speed and grade oppose each other) indicates that there is a direct coupling of stride frequency and hindlimb blood flow (i.e., muscle pumping).     

Non-zero mean alpha oscillations revealed with computational model and empirical data

Ongoing oscillations and evoked responses are two main types of neuronal activity obtained with diverse electrophysiological recordings (EEG/MEG/iEEG/LFP). Although typically studied separately, they might in fact be closely related. One possibility to unite them is to demonstrate that neuronal oscillations have non-zero mean which predicts that stimulus- or task-triggered amplitude modulation of oscillations can contribute to the generation of evoked responses. We validated this mechanism using computational modelling and analysis of a large EEG data set. With a biophysical model, we indeed demonstrated that intracellular currents in the neuron are asymmetric and, consequently, the mean of alpha oscillations is non-zero. To understand the effect that neuronal currents exert on oscillatory mean, we varied several biophysical and morphological properties of neurons in the network, such as voltage-gated channel densities, length of dendrites, and intensity of incoming stimuli. For a very large range of model parameters, we observed evidence for non-zero mean of oscillations. Complimentary, we analysed empirical rest EEG recordings of 90 participants (50 young, 40 elderly) and, with spatio-spectral decomposition, detected at least one spatially-filtred oscillatory component of non-zero mean alpha oscillations in 93% of participants. In order to explain a complex relationship between the dynamics of amplitude-envelope and corresponding baseline shifts, we performed additional simulations with simple oscillators coupled with different time delays. We demonstrated that the extent of spatial synchronisation may obscure macroscopic estimation of alpha rhythm modulation while leaving baseline shifts unchanged. Overall, our results predict that amplitude modulation of neural oscillations should at least partially explain the generation of evoked responses. Therefore, inference about changes in evoked responses with respect to cognitive conditions, age or neuropathologies should be constructed while taking into account oscillatory neuronal dynamics.     

Stimulus Phase Locking of Cortical Oscillation for Auditory Stream Segregation in Rats

The phase of cortical oscillations contains rich information and is valuable for encoding sound stimuli. Here we hypothesized that oscillatory phase modulation, instead of amplitude modulation, is a neural correlate of auditory streaming. Our behavioral evaluation provided compelling evidences for the first time that rats are able to organize auditory stream. Local field potentials (LFPs) were investigated in the cortical layer IV or deeper in the primary auditory cortex of anesthetized rats. In response to ABA- sequences with different inter-tone intervals and frequency differences, neurometric functions were characterized with phase locking as well as the band-specific amplitude evoked by test tones. Our results demonstrated that under large frequency differences and short inter-tone intervals, the neurometric function based on stimulus phase locking in higher frequency bands, particularly the gamma band, could better describe van Noorden’s perceptual boundary than the LFP amplitude. Furthermore, the gamma-band neurometric function showed a build-up-like effect within around 3 seconds from sequence onset. These findings suggest that phase locking and amplitude have different roles in neural computation, and support our hypothesis that temporal modulation of cortical oscillations should be considered to be neurophysiological mechanisms of auditory streaming, in addition to forward suppression, tonotopic separation, and multi-second adaptation.