Enhanced multiresolution wavelet analysis of complex dynamics in nonlinear systems.

Multiresolution wavelet analysis (MWA) is a powerful data processing tool that provides a characterization of complex signals over multiple time scales. Typically, the standard deviations of wavelet coefficients are computed depending on the resolution level and such quantities are used as measures for diagnosing different types of system behavior. To enhance the capabilities of this tool, we propose a combination of MWA with detrended fluctuation analysis (DFA) of detail wavelet coefficients. We find that such an MWA&DFA approach is capable of revealing the correlation features of wavelet coefficients in independent ranges of scales, which provide more information about the complex organization of datasets compared to variances or similar statistical measures of the standard MWA. Using this approach, we consider changes in the dynamics of coupled chaotic systems caused by transitions between different types of complex oscillations. We also demonstrate the potential of the MWA&DFA method for characterizing different physiological conditions by analyzing the electrical brain activity in mice.

Extended detrended fluctuation analysis of electroencephalograms signals during sleep and the opening of the blood-brain barrier.

Detrended fluctuation analysis (DFA) is widely used to characterize long-range power-law correlations in complex signals. However, it has restrictions when nonstationarity is not limited only to slow variations in the mean value. To improve the characterization of inhomogeneous datasets, we have proposed the extended DFA (EDFA), which is a modification of the conventional method that evaluates an additional scaling exponent to take into account the features of time-varying nonstationary behavior. Based on EDFA, here, we analyze rat electroencephalograms to identify specific changes in the slow-wave dynamics of brain electrical activity associated with two different conditions, such as the opening of the blood-brain barrier and sleep, which are both characterized by the activation of the brain drainage function. We show that these conditions cause a similar reduction in the scaling exponents of EDFA. Such a similarity may represent an informative marker of fluid homeostasis of the central nervous system.

Increases in Microvascular Perfusion and Tissue Oxygenation via Vasodilatation After Anodal Transcranial Direct Current Stimulation in the Healthy and Traumatized Mouse Brain.

Traumatic brain injury (TBI), causing neurological deficit in 70% of survivors, still lacks a clinically proven effective therapy. Transcranial direct current stimulation (tDCS) has emerged as a promising electroceutical therapeutic intervention possibly suitable for TBI; however, due to limited animal studies the mechanisms and optimal parameters are unknown. Using a mouse model of TBI we evaluated the acute effects of the anodal tDCS on cerebral blood flow (CBF) and tissue oxygenation, and assessed its efficacy in long-term neurologic recovery. TBI was induced by controlled cortical impact leading to cortical and hippocampal lesions with reduced CBF and developed hypoxia in peri-contusion area. Sham animals were subjected to craniotomy only. Repetitive anodal tDCS (0.1 mA/15 min) or sham stimulation was done over 4 weeks for four consecutive days with 3-day intervals, beginning 1 or 3 weeks after TBI. Laser speckle contrast imaging (LSCI) revealed that anodal tDCS causes an increase in regional cortical CBF in both traumatized and Sham animals. On microvascular level, using in-vivo two-photon microscopy (2PLSM), we have shown that anodal tDCS induces arteriolar dilatation leading to an increase in capillary flow velocity and tissue oxygenation in both traumatized and Sham animals. Repetitive anodal tDCS significantly improved motor and cognitive neurologic outcome. The group with stimulation starting 3 weeks after TBI showed better recovery compared with stimulation starting 1 week after TBI, suggesting that the late post-traumatic period is more optimal for anodal tDCS.

Characterizing scaling properties of complex signals with missed data segments using the multifractal analysis.

The scaling properties of complex processes may be highly influenced by the presence of various artifacts in experimental recordings. Their removal produces changes in the singularity spectra and the Hölder exponents as compared with the original artifacts-free data, and these changes are significantly different for positively correlated and anti-correlated signals. While signals with power-law correlations are nearly insensitive to the loss of significant parts of data, the removal of fragments of anti-correlated signals is more crucial for further data analysis. In this work, we study the ability of characterizing scaling features of chaotic and stochastic processes with distinct correlation properties using a wavelet-based multifractal analysis, and discuss differences between the effect of missed data for synchronous and asynchronous oscillatory regimes. We show that even an extreme data loss allows characterizing physiological processes such as the cerebral blood flow dynamics.

EEG biomarkers of activation of the lymphatic drainage system of the brain during sleep and opening of the blood-brain barrier.

The lymphatic drainage system of the brain (LDSB) is the removal of metabolites and wastes from its tissues. A dysfunction of LDSB is an important sign of aging, brain oncology, the Alzheimer's and Parkinson's diseases. The development of new strategies for diagnosis of LDSB injuries can improve prevention of age-related cerebral amyloid angiopathy, neurodegenerative and cerebrovascular diseases. There are two conditions, such as deep sleep and opening of the blood-brain-barrier (OBBB) associated with the LDSB activation. A promising candidate for measurement of LDSB could be electroencephalography (EEG). In this pilot study on rats, we tested the hypothesis, whether deep sleep and OBBB can be an informative platform for an effective extracting of information about the LDSB functions. Using the nonlinear analysis of EEG dynamics and machine learning technology, we discovered that the LDSB activation during OBBB and sleep is associated with similar changes in the EEG θ-activity. The OBBB causes the higher LDSB activation vs. sleep that is accompanied by specific changes in the low frequency EEG activity extracted by the power spectra analysis of the EEG dynamics combined with the coherence function. Thus, our findings demonstrate a link between neural activity associated with the LDSB activation during sleep and OBBB that is an important informative platform for extraction of the EEG-biomarkers of the LDSB activity. These results open new perspectives for the development of technology for the LDSB diagnostics that would open a novel era in the prognosis of brain diseases caused by the LDSB disorders, including OBBB.

Vascular and cardiac effects of stress in albino rats of different sex and age groups.

Stress exposure induced similar cardiac effects in male and female infantile rats, but vascular reactions to stress in males were more pronounced than in females. In mature male rats (but not in females), both cardiac and vascular responses to stress decreased in comparison with infantile animals. In adult rats, cardiac effects of stress were more pronounced than the vascular response; females demonstrated greater cardiac response and less significant vascular reactions than males. Aging was accompanied by a decrease in the cardiac response and increase in the vascular reaction to stress. These changes were more significant in females than in males. In contrast to infantile and adult animals, old females demonstrated greater vascular response to stress than male rats. The observed sex-dependent changes in the ontogeny of vascular and cardiac response to stress are discussed in light of sex- and age-related peculiarities of hypertension development.

Mechanisms for vascular effects of androgens in normotensive and hypertensive rats.

Castration had no effect on baseline BP and vascular sensitivity to acetylcholine and deficiency of nitric oxide and prostacyclin in normotensive specimens. Castration of hypertensive specimens decreased BP and potentiated the hypotensive effects of acetylcholine, but did not modulate vascular sensitivity to the blockade of nitric oxide and prostacyclin synthesis. The removal of the testicles abolished the pressor influence of glybenclamide in hypertensive and, particularly, in normotensive males. These data indicate that the non-endothelial vascular effects of androgens (i.e., stimulation of K(ATP) channels) predominate under normal conditions. The activating effects of androgens on K(ATP) channels decrease during hypertension, which is accompanied by inhibition of endothelium-dependent vasorelaxation. The production of nitric oxide and prostacyclin remains unchanged under these conditions. Our results suggest that endothelium-derived hyperpolarizing factor is involved in these processes.

Effect of age and sex on blood pressure, development of renal hypertension, and concentration of nitric oxide in the blood of albino rats.

The mean blood pressure did not depend on the sex of animals and was characterized by the same ontogenetic changes in males and females. The mean blood pressure in infantile and, particularly, in old rats was higher than in adult animals. The increase in blood pressure in old rats was accompanied by a decrease in NO production. Infantile rats were least resistant to the development of renal hypertension. The degree of hypertension in infantile and adult females was lower than in males. However, the concentration of NO in these females was higher than in male rats. Aging was accompanied by inversion of sex differences in the resistance to renal hypertension. The severity of hypertension in old females was greater than in males. It was accompanied by a significant age-related decrease in NO concentration in female animals. Our results indicate that NO plays an important role in sex differences in the resistance of infantile, adult, and old rats to hypertension, while the decrease in NO concentration during aging leads to blood pressure elevation in females and males.

Analysis of blood pressure dynamics in male and female rats using the continuous wavelet transform.

We study gender-related particularities in cardiovascular responses to stress and nitric oxide (NO) deficiency in rats using HR, mean arterial pressure (MAP) and a proposed wavelet-based approach. Blood pressure dynamics is analyzed: (1) under control conditions, (2) during immobilization stress and recovery and (3) during nitric oxide blockade by N(G)-nitro-L-arginine-methyl ester (L-NAME). We show that cardiovascular sensitivity to stress and NO deficiency depends upon gender. Actually, in females the chronotropic effect of stress is more pronounced, while the pressor effect is weakened compared with males. We conclude that females demonstrate more favorable patterns of cardiovascular responses to stress and more effective NO control of cardiovascular activity than males.

Multiresolution analysis of pathological changes in cerebral venous dynamics in newborn mice with intracranial hemorrhage: adrenorelated vasorelaxation.

Intracranial hemorrhage (ICH) is the major problem of modern neonatal intensive care. Abnormalities of cerebral venous blood flow (CVBF) can play a crucial role in the development of ICH in infants. The mechanisms underlying these pathological processes remain unclear; however it has been established that the activation of the adrenorelated vasorelaxation can be an important reason. Aiming to reach a better understanding of how the adrenodependent relaxation of cerebral veins contributes to the development of ICH in newborns, we study here the effects of pharmacological stimulation of adrenorelated dilation of the sagittal sinus by isoproterenol on the cerebral venous hemodynamics. Our study is performed in newborn mice at different stages of ICH using the laser speckle contrast imaging and wavelet analysis of the vascular dynamics of CVBF. We show that the dilation of the sagittal sinus with the decreased velocity of blood flow presides to the stress-induced ICH in newborn mice. These morphofunctional vascular changes are accompanied by an increased variance of the wavelet-coefficients in the areas of endothelial and non-endothelial (KATP-channels activity of vascular muscle) sympathetic components of the CVBF variability. Changes in the cerebral venous hemodynamics at the latent stage of ICH are associated with a high responsiveness of the sagittal sinus to isoproterenol quantifying by wavelet-coefficients related to a very slow region of the frequency domain. The obtained results certify that a high activation of the adrenergic-related vasodilatory responses to severe stress in newborn mice can be one of the important mechanisms underlying the development of ICH. Thus, the venous insufficiency with the decreased blood outflow from the brain associated with changes in the endothelial and the sympathetic components of CVBF-variability can be treated as prognostic criteria for the risk of ICH during the first days after birth.

Sex-specific peculiarities of cholinergic regulation of the cardiovascular system in normal and hypertensive rats.

Cardiovascular sensitivity to atropine and acetylcholine is reduced in renal hypertension. Hypertension in females is more benign and the hypotensive effects of acetylcholine in them are less attenuated than in males. Cardiovascular sensitivity to cholinergic effects in females is higher in health and hypertension, which improves their resistance to cardiovascular pathology.