Dynamic characteristics of the human resonance EEG responses to rhythmic photostimulation

The development of the resonance EEG responses of the left and right occipital areas was studied in right-handed men during prolonged (12 or 120 s) rhythmic, photostimulation with the intensity of 0.7 J and frequencies of 6, 10, and 16 Hz. Analysis of the EEG fine spectral structure was applied to compare the accumulated baseline EEG spectra and EEG spectra during photostimulation, to observe the dynamics of the short-term spectra and to detect power changes in the EEG narrow spectral band sharply coincident with the stimulation frequency. The more pronounced EEG responses to photostimulation were observed in subjects with the initially low EEG baseline, α-rhythm. Two-minute flash trains produced a substantial increase in the EEG power within the stimulation frequency with superposed oscillatory processes with different periods. These fluctuations are considered a reflection of intricate interaction between the adaptive and resonance EEG responses to the presented intermittent stimulation. Under 12-s stimulation the resonance EEG responses are steadily recorded within the first 3 s of stimulation and immediately after the flash cessation EEG power at the stimulation frequency returns to the initial level. The resonance EEG responses were more pronounced in the right hemisphere than in the left one, especially, at the stimulation frequencies of 6 and 16 Hz. With increasing the stimulation frequency, the maximum of resonance EEG responses was reached earlier. Under the stimulation frequency of 6 Hz, the maximal response was recorded 9–12 s after the beginning of flashes, at the frequencies of 10 and 16 Hz, it was recorded within 3–6 and 3 s, respectively.     

Dynamic characteristics of a metabolic reaction of mice with different responses to irradiation.

The course of the reaction of mice placed in a metabolic chamber and afterwards irradiated with an exposure dose of 610 R was studied by assessing total oxygen consumption and the size of its fluctuation. Fluctuation was greater in non-survivors than in survivors in the initial phase of the metabolic reaction only (P is less than 0.05), while the mean oxygen consumption values for the two groups were the same, In the distribution of the individual values there were more non-survivors in the frequency class with a high fluctuation level and, conversely, more survivors in the low level class (P is less than 0.01). Fluctuation during the studied reaction was more variable in survivors, despite its lower level, than in non-survivors. The reciprocal relationship between the size and fluctuation of oxygen consumption, determined for the whole series of experimental mice at given stages of the metabolic reaction, is linear. Attention is drawn to the association between changes measured in the metabolic rate and motor activity and to the possibility that it is determined by the individual's type of nervous activity.     

Dynamic characteristics of motor responses evoked by stimulation of the motor cortex in unanesthetized cats

Temporal characteristics of motor responses evoked in unanesthetized cats by stimulation of the motor cortex through bipolar needle electrodes were investigated in chronic experiments. Isometric and isotonic contractions of the flexor muscles of the hip and knee joints of the limb contralateral to the point of stimulation were recorded. The latent period of response varied from 100 msec or more in the case of low-frequency (100–150 Hz) and low-threshold (1.1–1.2 thresholds) stimulation of the motor cortex to 30–35 msec in the case of "optimal" parameters of stimulation (300–400 Hz, 1.5–1.6 thresholds). If the intensity of stimulation was high enough the rising time constant of evoked contraction was 50–80 msec; values of the falling time constant of muscular contraction after cessation of stimulation were much greater, namely 150–300 msec. The rising time constant of contraction decreased with an increase in both the frequency and strength of motor cortical stimulation. The results are examined and discussed from the standpoint of methods of automatic control theory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 451–458, September–October, 1980.     

Potentially complex biosphere responses to transient global warming

Feedback interactions between terrestrial vegetation and climate could alter predictions of the responses of both systems to a doubling of atmospheric CO₂. Most previous analyses of biosphere responses to global warming have used output from equilibrium simulations of current and future climate, as compared to more recently available transient GCM simulations. We compared the vegetation responses to these two different classes of GCM simulation (equilibrium and transient) using an equilibrium vegetation distribution model, MAPSS. Average climatologies were extracted from the transient GCM simulations for current and doubled (2×) CO₂ concentrations (taken to be 2070–2099) for use by the equilibrium vegetation model. However, the 2 × CO₂ climates extracted from the transient GCM simulations were not in equilibrium, having attained only about 65% of their eventual 2 × CO₂ equilibrium temperature change. Most of the differences in global vegetation response appeared to be related to a very different simulated change in the pole to tropic temperature gradient. Also, the transient scenarios produced much larger increases of precipitation in temperate latitudes, commensurate with a minimum in the latitudinal temperature change. Thus, the (equilibrium) global vegetation response, under the transient scenarios, tends more to a greening than a decline in vegetation density, as often previously simulated. It may be that much of the world could become greener during the early phases of global warming, only to reverse in later, more equilibrial stages. However, whether or not the world's vegetation experiences large drought-induced declines or perhaps large vegetation expansions in early stages could be determined by the degree to which elevated CO₂ will actually benefit natural vegetation, an issue still under debate. There may occur oscillations, perhaps on long timescales, between greener and drier phases, due to different frequency responses of the coupled ocean–atmosphere–biosphere interactions. Such oscillations would likely, of themselves, impart further reverberations to the coupled Earth System.     

Dynamic responses of electrically coupled systems

An identified pair of electrically coupled neurons in the buccal ganglion of the freshwater snail Helisoma trivolvis is an experimentally accessible model of electrical synaptic transmission. In this investigation, electrical synaptic transmission is characterized using sinusoidal frequency (Bode) responses computed by Laplace transforms and responses to brief stimuli. The frequency response of the injected neuron shows a 20-dB/decade attenuation and a phase shift from 0 degree at low frequencies to -90 degrees at high frequencies. The response of a coupled cell shows a 40-dB/decade attenuation and a phase shift from 0 degrees at low frequencies to -180 degrees at high frequencies. A simple mathematical model of electrical synaptic transmission is described that displays each of these crucial features of the measured frequency responses. Methods are described to estimate the frequency responses of coupled systems based on presynaptic measurements. The responses of the coupled system to brief pulses of current were computed using the principle of superposition. The electrical properties of coupled systems impose a minimum delay in reaching a peak in all postsynaptic responses. The delays in the postsynaptic responses to brief stimuli are related to the electrical and anatomical parameters of coupled networks.     

Dynamic structure of human serum transferrin from transient electric birefringence experiments

In order to investigate the secondary, tertiary, and dynamic structure of the iron-free (apo) and iron-saturated (holo) forms of human serum transferrin and its amino (N)-terminal lobe at the physiologically relevant pHs 7.4 and 5.0, we have combined ultraviolet circular dichroism (CD) spectroscopy with transient-electric birefringence (TEB) measurements. No significant changes are found in the protein's secondary structure under the different conditions studied. The tertiary structure as monitored by near-UV CD is affected by iron binding, but does not change upon decrease in pH. In contrast, TEB results indicate dramatic changes in the dynamic structure of transferrin both upon binding of iron and decrease of pH. In apotransferrin freedom of movement is found for the lobes with respect to each other, and for the domains within the lobes. The interlobal flexibility is considerably enhanced at the lower pH. Holotransferrin is found to behave as a rigid molecule. © 1995 Wiley-Liss, Inc.     

A nonlinear model for transient responses from light-adapted wolf spider eyes

A quantitative model is proposed to test the hypothesis that the dynamics of nonlinearities in retinal action potentials from light-adapted wolf spider eyes may be due to delayed asymmetries in responses of the visual cells. For purposes of calculation, these delayed asymmetries are generated in an analogue by a time-variant resistance. It is first shown that for small incremental stimuli, the linear behavior of such a resistance describes peaking and low frequency phase lead in frequency responses of the eye to sinusoidal modulations of background illumination. It also describes the overshoots in linear step responses. It is next shown that the analogue accounts for nonlinear transient and short term DC responses to large positive and negative step stimuli and for the variations in these responses with changes in degree of light adaptation. Finally, a physiological model is proposed in which the delayed asymmetries in response are attributed to delayed rectification by the visual cell membrane. In this model, cascaded chemical reactions may serve to transduce visual stimuli into membrane resistance changes.     

Ensemble cortical responses to rival visual stimuli: Effect of monocular transient

Binocular rivalry is a fascinating perceptual phenomenon that has been characterized extensively at the psychophysical level. However, the underlying neural mechanism remains poorly understood. In particular, the role of the early visual pathway remains controversial. In this study, we used voltage-sensitive dye imaging to measure the spatiotemporal activity patterns in cat area 18 evoked by dichoptic orthogonal grating stimuli. We found that after several seconds of monocular stimulation with an oriented grating, an orthogonal stimulus to the other eye evoked a reversal of the cortical response pattern, which may contribute to flash suppression in perception. Furthermore, after several seconds of rival binocular stimulation with unequal contrasts, transient increase in the contrast of the weak stimulus evoked a long-lasting cortical response. This transient-triggered response could contribute to the perceptual switch during binocular rivalry. Together, these results point to a significant contribution of early visual cortex to transient-triggered switch in perceptual dominance.     

Comparison of transient otoacoustic emission responses from neonatal and adult ears.

Transient otoacoustic emission (TEOAE) responses from neonatal (age: 48 h) and adult subjects (age: 26.6 +/- 10.0 yr) were analyzed by the combined use of recurrence quantification analysis and singular value decomposition. The data from the two age groups showed significant differences and similarities. The neonatal responses presented less deterministic structures than those of the adults in terms of recurrent dynamic features. In both data sets, the same high level of individual specific dynamic features was observed. The results from the singular value decomposition analysis suggest that a large percentage of variability in all of the analyzed responses can be explained by four to five essential modes. This number is lower than that observed in simulated TEOAE responses generated by a five-component gammatone model. A possible explanation is presented, based on simple instrumental and morphoanatomic considerations.     

Model transformations to evaluate transient thermal responses at a tissue surface

For a spatially distributed model describing the transient temperature response of a thermistor-tissue system, Wei et al. [J. Biomech. Eng., 117:74-85, 1995] obtained an approximate transformation for fast analysis of the temperature response at the tissue surface. This approximate transformation reduces the model to a single ordinary differential equation. Here, we present an exact transformation that yields a single differential-integral equation. Numerical solutions from the approximate and exact transformations were compared to evaluate the differences with several sets of parameter values. The maximum difference between the exact and approximate solutions did not exceed 15 percent and occurred for only a short time interval. The root-mean-square error of the approximate solution was no more than 5 percent and within the level of experimental noise. Under the experimental conditions used by Wei et al., the approximate transformation is justified for estimating model parameters from transient thermal responses.     

Postnatal Neospora caninum transmission and transient serologic responses in two dairies

Cattle on two typically managed drylot dairies were serologically monitored from birth through year 1 to year 4 of life to characterise congenital and postnatal Neospora caninum transmission. Of the 456 calves enrolled, 284 were classified as N. caninum negative and 172 were classified as N. caninum positive. Ninety-six percent of congenitally infected calves were seropositive for all samples tested. Seven (4%) of the 172 congenitally infected animals had a period that persisted for 9 to 18 months when they were seronegative; however, all returned to seropositive status by 25 months of age. In N. caninum-negative calves, colostral antibody decayed by 128 days, with an estimated half-life of 19.6 +/- 5.2 days. Of the 284 calves classified as negative, 18% had sporadic, isolated responses to N. caninum, typically between 29 and 35 months of age, without subsequent seroconversion or infection. During the study, 17 animals seroconverted and remained seropositive throughout the follow-up. Thirteen of the seroconversions occurred in the neonatal period; however, in nine of 10 where dam status was available, the dam was N. caninum positive, suggesting late gestation congenital infection rather than postnatal infection. Seroconversion was detected in an additional four animals, between 13 and 22 months of age. The estimate of postnatal infection rate was less than 1% per year despite a high N. caninum seroprevalence in the herds, and the presence of potential definitive and intermediate hosts on the dairy throughout the study. The extremely low rate of postnatal infection, as well as the lifelong persistence of congenital infection, emphasises the importance of congenital transmission in maintaining N. caninum infection in dairies.     

Dynamic involvement of ATG5 in cellular stress responses

Autophagy maintains cell and tissue homeostasis through catabolic degradation. To better delineate the in vivo function for autophagy in adaptive responses to tissue injury, we examined the impact of compromised autophagy in mouse submandibular glands (SMGs) subjected to main excretory duct ligation. Blocking outflow from exocrine glands causes glandular atrophy by increased ductal pressure. Atg5^f/−;Aqp5-Cre mice with salivary acinar-specific knockout (KO) of autophagy essential gene Atg5 were generated. While duct ligation induced autophagy and the expression of inflammatory mediators, SMGs in Atg5^f/−;Aqp5-Cre mice, before ligation, already expressed higher levels of proinflammatory cytokine and Cdkn1a/p21 messages. Extended ligation period resulted in the caspase-3 activation and acinar cell death, which was delayed by Atg5 knockout. Moreover, expression of a set of senescence-associated secretory phenotype (SASP) factors was elevated in the post-ligated glands. Dysregulation of cell-cycle inhibitor CDKN1A/p21 and activation of senescence-associated β-galactosidase were detected in the stressed SMG duct cells. These senescence markers peaked at day 3 after ligation and partially resolved by day 7 in post-ligated SMGs of wild-type (WT) mice, but not in KO mice. The role of autophagy-related 5 (ATG5)-dependent autophagy in regulating the tempo, duration and magnitude of cellular stress responses in vivo was corroborated by in vitro studies using MEFs lacking ATG5 or autophagy-related 7 (ATG7) and autophagy inhibitors. Collectively, our results highlight the role of ATG5 in the dynamic regulation of ligation-induced cellular senescence and apoptosis, and suggest the involvement of autophagy resolution in salivary repair.Autophagy is a catabolic process that has an essential role in cellular adaptation to multiple types of stress by recycling of superfluous cellular material, safeguarding quality control in organelles, removing protein aggregates, and eliminating intracellular pathogens.¹ Conceptually, autophagy serves a pro-survival mechanism by providing sources of energy and biosynthetic building blocks during starvation, removing dysfunctional organelles and large aggregates toxic to cells to avoid unwarranted cell death. However, upon sustained stress conditions, cell death eventually takes place either by excessive autophagy or by the induction of apoptosis and/or necrosis pathways.² The ATG5, autophagy-related 5, has a pivotal role in autophagosome formation. Mouse neonates systemic deficient for ATG5 die within a day of birth,³ whereas mice depleted of Atg5 in selected tissues have abnormalities ranging from neurodegeneration⁴ and age-related cardiomyopathy⁵ to liver tumors.⁶Autophagy and senescence are two distinct, however functionally intertwined, cellular responses to stress.⁷ Cellular senescence is a state of stable growth arrest that is induced by telomere shortening, DNA-damage, oncogenes or other stresses. In general, senescence is a heterogeneous phenotype, which is characterized by a senescent-associated secretory phenotype (SASP), expression of senescence-associated β-galactosidase (SA-β-gal) and other senescent markers, and increased cell size.⁸ In culture system, inhibiting or enhancing autophagy leads to the opposite effect on premature senescence.^{9, 10, 11, 12} While premature senescence can be induced by a plethora of cell-extrinsic and cell-intrinsic stressors,¹³ little is known about the possible role of autophagy in modulating injury-induced cellular senescence in vivo. Rodent salivary duct ligation has been used as an experimental model system to study salivary gland atrophy, which often occurs in patients with Sjögren''s syndrome or receiving head and neck radiation therapy. Although autophagy induction has been implicated in the repair of rapamycin-treated, post-ligated salivary glands,^14,15 the roles played by autophagy in regulating the injury responses in submandibular glands (SMGs) have not been explored.To explore how autophagy contributes to salivary (patho)physiology, we established a transgenic mouse model deficient for ATG5 in the salivary acinar cells. Previously, we have identified a role for basal autophagy in salivary homeostatic mechanisms that restrict acinar cell size and the number of secretory granules.¹⁶ Here, we report that ligation of the major SMG excretory duct triggers the glandular atrophy and the induction of autophagy. By comparing the acute and subacute stress responses from autophagy-impaired and -competent SMGs with duct obstruction, we established the intrinsic roles of ATG5-dependent autophagy in modulating salivary inflammatory responses, stress-induced senescence and cell death, which all occur sequentially in response to tissue injury. Our results provide in vivo evidence that stress-induced autophagic response is indispensable for resolving premature senescence in duct cells of the ligated glands, whereas ATG5 deficiency leads to delayed acinar cell death.     

Dynamic characteristics of multisensory facilitation and inhibition

Multimodal integration, which mainly refers to multisensory facilitation and multisensory inhibition, is the process of merging multisensory information in the human brain. However, the neural mechanisms underlying the dynamic characteristics of multimodal integration are not fully understood. The objective of this study is to investigate the basic mechanisms of multimodal integration by assessing the intermodal influences of vision, audition, and somatosensory sensations (the influence of multisensory background events to the target event). We used a timed target detection task, and measured both behavioral and electroencephalographic responses to visual target events (green solid circle), auditory target events (2 kHz pure tone) and somatosensory target events (1.5 ± 0.1 mA square wave pulse) from 20 normal participants. There were significant differences in both behavior performance and ERP components when comparing the unimodal target stimuli with multimodal (bimodal and trimodal) target stimuli for all target groups. Significant correlation among reaction time and P3 latency was observed across all target conditions. The perceptual processing of auditory target events (A) was inhibited by the background events, while the perceptual processing of somatosensory target events (S) was facilitated by the background events. In contrast, the perceptual processing of visual target events (V) remained impervious to multisensory background events.     

Electrophysiological responses of the cochlea to transient asphyxia are influenced by arachidonate metabolites

The influence of a transient asphyxia on cochlear potentials, i.e. endolymphatic potential (EP), summating potential (SP) and cochlear microphonics (CM) was investigated in guinea pigs when pretreating the animals with various substances interacting with the arachidonic acid (AA) cascade at the level of thromboxane. The controls showed the well-known decline of the EP, CM and the SP increase. When infusing a thromboxane synthetase inhibitor (dazoxiben) or two different thromboxane receptor blockers (daltroban or sulotraban) before the 3-minutes' period of asphyxia was started, the electrophysiological responses of the inner ear (cochlea) could significantly be influenced. The results indicate that a shift of the thromboxane (TXA₂)/prostacyclin (PGI₂)-balance in favour of the last improve the metabolic conditions for a survival of the cochlea when it is challenged.     

Different cell cycle responses of wound healing protagonists to transient in vitro hypoxia

Polyploidization is a process present in cells of many different human tissues. Since it is also prominent in human wound healing in vivo and in vitro, we focused on the influence of hypoxia on the cells proliferation and polyploidization response. The proliferation response of two major cell types, involved in human wound healing, human dermal microvascular endothelial cells (HDMEC) and normal human dermal fibroblasts (NHDF) was quite similar in the in vitro setup: proliferation significantly decreased under the influence of 18 h of hypoxia and was reinitiated after 72 h of reoxygenation. The cells response concerning their tendency towards the development of polyploidy was different: NHDF did not generate any polyploid cells, which stands in contrast to former in vitro studies with human wound-derived fibroblasts, but HDMEC were characterized by the presence of both mononuclear and binuclear tetraploid cells. The number of tetraploids was downregulated during hypoxia and increased during reoxygenation, accompanied by proliferation onset. The immunomicroscopic survey of HDMEC opened up a cell cycle model, which might be useful in the future to evaluate cell cycle modulations leading to polyploidy without the need to apply any additional cell cycle inhibitors.     

Alternative transient states and slow plant community responses after changed flooding regimes

Climate change will have large consequences for flooding frequencies in freshwater systems. In interaction with anthropogenic activities (flow regulation, channel restoration and catchment land‐use) this will both increase flooding and drought across the world. Like in many other ecosystems facing changed environmental conditions, it remains difficult to predict the rate and trajectory of vegetation responses to changed conditions. Given that critical ecosystem services (e.g. bank stabilization, carbon subsidies to aquatic communities or water purification) depend on riparian vegetation composition, it is important to understand how and how fast riparian vegetation responds to changing flooding regimes. We studied vegetation changes over 19 growing seasons in turfs that were transplanted in a full‐factorial design between three riparian elevations with different flooding frequencies. We found that (a) some transplanted communities may have developed into an alternative stable state and were still different from the target community, and (b) pathways of vegetation change were highly directional but alternative trajectories did occur, (c) changes were rather linear but faster when flooding frequencies increased than when they decreased, and (d) we observed fastest changes in turfs when proxies for mortality and colonization were highest. These results provide rare examples of alternative transient trajectories and stable states under field conditions, which is an important step towards understanding their drivers and their frequency in a changing world.