Tatjana Loncar-Turukalo

Temporal analysis of the spontaneous baroreceptor reflex during mild emotional stress in the rat

The effect of emotional stress on the spontaneous baroreceptor reflex (sBRR) in freely moving rats was investigated. Six male Wistar rats equipped with an intra-arterial polyethylene catheter were exposed to a 2-min air-jet stress. For time course analysis of the sBRR response to stress, the records of systolic blood pressure (SBP) and pulse interval (PI) were divided into five regions: baseline (BASELINE), acute exposure to air-jet stress (STRESS), immediate recovery (IMMED. RECOVERY), remaining recovery (RECOVERY), and delayed response (DELAYED RESPONSE). In addition to sBRR sensitivity and effectiveness, we introduce the sequence coverage area and its median for evaluation of the sBRR operating range and set point. During exposure to STRESS and IMMED. RECOVERY, sBRR sensitivity was preserved, its effectiveness was decreased, its operating range was enlarged, and the set point was shifted towards higher SBP and lower PI values. According to the joint symbolic dynamics analysis, the SBP and PI relationship became less predictable hence more prone to respond to stress. In RECOVERY the parameters regained baseline values and DELAYED RESPONSE occurred during which re-setting of sBRR was noted. It follows that emotional stress modulates sBRR differentially during the time course of stress and recovery, affecting both linearity and unpredictability of the BP and PI relationship.

A simple suboptimal construction of cross-bifix-free codes

Cross-bifix-free sets are sets of bifix-free sequences with the property that no prefix of any sequence is a suffix of any other sequence. This paper presents a general construction method for cross-bifix-free sequences based on kernels. The cardinality of cross-bifix-free sets follows the Fibonacci progression. A simplified method, applicable to a limited number of so-called “regular kernel sets”, is proposed as well. Properties of such sequences with an outline for further research are discussed.

Heart rate dynamics in doxorubicin-induced cardiomyopathy

The clinical use of doxorubicin, an effective chemotherapeutic is hampered by the development of irreversible cardiotoxicity. Here we test time-frequency analysis of heart rate (HR) variability (HRV) for early detection of doxorubicin-induced cardiotoxicity. Experiments were conducted in adult male Wistar rats treated for 15 days with doxorubicin (DOXO, total dose 15 mg kg(-1), i.p.) or saline (CONT). DOXO rats exhibited cardiotoxicity confirmed by histological examination without developing heart failure as estimated by echocardiography. However, HR variability increase reflected subtle microscopic changes of cardiac toxicity in DOXO rats. The results recommend time-frequency analysis of HRV for early detection of doxorubicin-induced cardiomyopathy.

Environmental stress: Approximate entropy approach revisited

Radiotelemetred male Wistar outbrad rats and Borderline Hypertensive rats (BHR) were exposed to acute and chronic environmental stress. Approximate entropy (ApEn) approach is applied in order to investigate the pulse interval (PI) response to two different types of environmental stress: shaker and restrain stress. The performance of ApEn method was evaluated from the parameter selection point of view. The purpose of the study is to quantify the complexity of response to stress and period of recovery after the stress in order to gain an insight in consequences of chronic stress exposure.

Joint Symbolic Dynamic of Cardiovascular Time Series of Rats

Insight in complex heart rate and blood pressure interactions reveals the most important aspects of autonomic control. Our main interest was in baroreceptor reflex (BRR), the most important autonomic cardiovascular reflex. We evaluated the joint symbolic dynamics of heart rate and blood pressure variations in assessing the BRR by opening the BRR loop at different levels using pharmacological blockade of β- adrenergic, α-adrenergic and M-cholinergic receptors. Experiments were done in conscious telemetred Wistar out bred male rats. The observed changes between experimental groups are promising for use of symbolic dynamic method in assessment of impaired autonomic control of the cardiovascular system.

Blood pressure and pulse interval coupling: A copula approach

In this paper a copula approach is applied as a tool for assessing the measure of statistical dependence of parallel cardiovascular time series. Families of Archimedean copulas (Clayton, Frank and Gumbel) are applied to pulse interval, systolic and diastolic blood pressure recorded from male Wistar rats at baseline conditions, and to their isodistributional surrogates with the same marginal, but randomized joint distribution functions. The influence of time offset of the parallel time series is explored. The amount of data required for a stable working point is discussed.

Markov model and entropy of sequences in isodistributional surrogate data

Surrogate data method is commonly required to confirm the non-accidental nature of simultaneous fluctuations of heart rate (HR) and blood pressure (BP) due to the spontaneous baroreceptor reflex (sBRR) mechanism. Previously proposed finite, ergodic Markov model with memory, enables derivation of all BRR temporal parameters for isodistributional (ID) surrogate data in closed form, thus eliminating the need for surrogate generation and analysis. The goodness of fit for surrogate time series of 37 healthy humans is tested. The expected values provided by the model showed excellent accordance with calculated time averages. Besides, the study introduces a new feature of sBRR entropy.

Cardiovascular variability and β-ARs gene expression at two stages of doxorubicin – Induced cardiomyopathy

ABSTRACT Using comprehensive analysis of heart rate (HRV) and blood pressure (BPV) short‐term variability we estimated the time course of changes of autonomic nervous system remodeling in two stages of doxorubicin‐induced cardiomyopathy (DCM). We also investigated the level of gene expression of cardiac &bgr;‐1 (&bgr;‐1AR) and &bgr;‐2 (&bgr;‐2AR) adrenoceptors. Experiments were performed in adult male Wistar rats equipped with indwelling catheters for BP recording and blood withdrawal. A 15 mg/kg total cumulative dose of doxorubicin was injected i.p. to rats to induce DCM or saline for control (n=18). Rats were assessed for general toxicity, cardiovascular hemodynamic and echocardiography before treatment (n=6), 35 days (DOX35; n=6) and 70 days (DOX70; n=6) post‐treatment. HRV was evaluated by spectral analysis, Poincaré plots, sample and approximate entropy. Expression of &bgr;‐1AR and &bgr;‐2AR mRNA was evaluated by RT‐qPCR. Doxorubicin‐treated rats exhibited poor general condition and lower survival than saline‐treated rats. In DOX35 rats, there were no echocardiography signs of decompensation, no increase in serum cardiac troponins, but there was an increase of HRV and decrease of HR complexity. In these rats typical microscopic signs of cardiotoxicity were seen along with over‐expression of &bgr;‐1AR mRNA. 70 days post‐treatment echocardiography revealed signs of decompensation and serum cardiac troponin T was increased. At this stage BPV decreased. In conclusion, HRV increase matches transient over‐expression of cardiac &bgr;‐1AR mRNA in compensate stage of DCM while decompensate stage of DCM is characterized by a decrease of BPV and no changes in &bgr;‐1AR and &bgr;‐2AR gene expression. HIGHLIGHTSHRV, BPV, &bgr;‐1AR and &bgr;‐2AR gene expression at two stages of DCM were investigated.Compensate DCM show HRV increase, loss of HR complexity and &bgr;‐1AR over‐expression.Decompensate DCM exhibit a decrease in BPV and no changes in &bgr;‐AR gene expression.Thus, &bgr;‐1AR receptor blockade should be considered in early DCM.

A novel approach to probabilistic characterisation of neural firing patterns

BACKGROUND The advances in extracellular neural recording techniques result in big data volumes that necessitate fast, reliable, and automatic identification of statistically similar units. This study proposes a single framework yielding a compact set of probabilistic descriptors that characterise the firing patterns of a single unit. NEW METHOD Probabilistic features are estimated from an inter-spike-interval time series, without assumptions about the firing distribution or the stationarity. The first level of proposed firing patterns decomposition divides the inter-spike intervals into bursting, moderate and idle firing modes, yielding a coarse feature set. The second level identifies the successive bursting spikes, or the spiking acceleration/deceleration in the moderate firing mode, yielding a refined feature set. The features are estimated from simulated data and from experimental recordings from the lateral prefrontal cortex in awake, behaving rhesus monkeys. RESULTS An efficient and stable partitioning of neural units is provided by the ensemble evidence accumulation clustering. The possibility of selecting the number of clusters and choosing among coarse and refined feature sets provides an opportunity to explore and compare different data partitions. CONCLUSIONS The estimation of features, if applied to a single unit, can serve as a tool for the firing analysis, observing either overall spiking activity or the periods of interest in trial-to-trial recordings. If applied to massively parallel recordings, it additionally serves as an input to the clustering procedure, with the potential to compare the functional properties of various brain structures and to link the types of neural cells to the particular behavioural states.

fMRI resting state analysis using empirical mode decomposition

The paper studies connectivity pattern between two functionally specialized brain areas: the primary motor area and the occipital (visual) cortex in the resting state fMRI using empirical mode decomposition (EMD). EMD enables identification of low frequency oscillatory modes in the resting state range [0, 01-0, 1 Hz]. Three frequency modes were determined in the resting state band in 13 subjects with the mean frequencies 0,07Hz, 0,034Hz and 0,016Hz. The temporal correlations among the oscillatory modes were strongest within homologous (corresponding) sources in left and right hemisphere, and weakest between the motor-occipital fMRI signal pairs. The functional connectivity - spatial distribution of temporal correlations in the resting state - has been identified and refined by the oscillatory modes. Connectivity graph obtained across all subjects and all IMFs showed high connectivity rate between homologous areas in the left and right hemisphere and among the visual cortex areas. Combining EMD with the Hilbert transformation may provide an additional tool for exploring correlations between frequency and amplitude ridges in task related problems.