Norihiro Katayama

A Novel Extraction Method of Fetal Electrocardiogram From the Composite Abdominal Signal

In contrast to the ultrasonic measurement of fetal heart motion, the fetal electrocardiogram (ECG) provides clinically significant information concerning the electrophysiological state of a fetus. In this paper, a novel method for extracting the fetal ECG from abdominal composite signals is proposed. This method consists of the cancellation of the mothers ECG and blind source separation with the reference signal (BSSR). The cancellation of the mothers ECG component was performed by subtracting the linear combination of mutually orthogonal projections of the heart vector. The BSSR is a fixed-point algorithm, the Lagrange function of which includes the higher order cross-correlation between the extracted signal and the reference signal as the cost term rather than a constraint. This realizes the convexity of the Lagrange function in a simple form, which guarantees the convergence of the algorithm. By practical application, the proposed method has been shown to be able to extract the P and T waves in addition to the R wave. The reliability and accuracy of the proposed method was confirmed by comparing the extracted signals with the directly recorded ECG at the second stage of labor. The gestational age-dependency of the physiological parameters of the extracted fetal ECG also coincided well with that of the magnetocardiogram, which proves the clinical applicability of the proposed method

Theta wave amplitude and frequency are differentially correlated with pontine waves and rapid eye movements during REM sleep in rats.

The present study examined the correlations between the dynamics of hippocampal theta waves and pontine waves (P waves) and rapid eye movements (REMs) densities during REM sleep. Theta wave peak frequency and theta amplitude were estimated as the parameters of theta wave dynamics in each 3s segment. The peak frequency and theta amplitude were positively correlated with P wave and REMs densities, however their detailed correlation properties were distinct from each other. Dependency of peak frequency on P wave/REMs density did not change significantly from that on REMs/P wave density. On the other hand, dependency of the theta amplitude on P wave/REMs density significantly increased with an increased REMs/P wave density. Because hippocampal theta waves and P waves are involved in learning and memory functions during REM sleep, the correlation between theta parameters and P wave density might help to clarify these functions.

Instantaneous acceleration and amplification of hippocampal theta wave coincident with phasic pontine activities during REM sleep

Rapid eye movement (REM) sleep is characterized by hippocampal theta waves and phasic spike-like waves originating from the pons, termed ponto-geniculo-occipital (PGO) waves in cats and pontine (P) waves in rats. While the theta wave and PGO/P wave have been suggested to participate in higher-order brain functions, their generation mechanisms and roles in brain functions have been studied independently. Therefore, the present study investigated instantaneous aspects of the relationship between theta waves and PGO/P waves in both cats and rats. Theta wave was instantaneously accelerated several hundred milliseconds before the negative peak of the PGO/P wave in both animals, and was also amplified just before PGO/P wave occurrence. Considering the integrated knowledge provided by studies of both animals, these results suggest that PGO/P wave-related activities in the pons are delivered to the theta wave generator. The activations of the theta wave coincident with PGO/P wave might facilitate cooperative contribution to higher-order brain functions in REM sleep.

Phase-locking of spontaneous and elicited ponto-geniculo-occipital waves is associated with acceleration of hippocampal theta waves during rapid eye movement sleep in cats.

We investigated the temporal relationship between hippocampal theta waves and ponto-geniculo-occipital waves (PGO) during rapid eye movement sleep (REM sleep) in cats. In addition, we analyzed the relationship between hippocampal theta waves and PGO as elicited by tone stimulus (PGO(E)) in order to quantitively characterize the PGO wave generator mechanism. The results showed that a spontaneous PGO tended to be phase-locked to the theta wave, which was more clearly observed in the single PGO than in the cluster. However, cluster PGO(E) tended to be phase-locked as well as single PGO(E). It was therefore suggested that the generator of PGO is activated in relation to the hippocampal theta wave. An acceleration of the theta wave associated with PGO occurrence was found, and was more markedly observed than with the cluster PGO. Although the magnitude of it was less than in the spontaneous case, an acceleration around the PGO(E) was also observed. These results suggest that the generators of theta and PGO receive some common activations, especially when a cluster PGO is generated. The interaction between PGO and hippocampal theta waves is expected to be involved in the possible functions of REM sleep.

Effects of lindane (γ-BHC) and related convulsants on GABAA receptor-operated chloride channels in frog dorsal root ganglion neurons

Abstract Effects of lindane (γ-benzenehexachloride; γ-BHC) on GABA-evoked Cl − current ( I GABA ) in freshly dissociated frog sensory (dorsal root ganglion) neurons were studied and compared with those of tert -butylbicycloortho benzoate (TBOB) and picrotoxin by the use of the suction-pipette method [13]. Drugs were applied with a rapid drug-application method, “Concentration-clamp” technique. At concentration of GABA of > 3 × 10 −6 M, at least two components of the I GABA were recognized distinct degree of desensitization. Those were defined as the peak and plateau components in the text. At low concentration (> 3 × 10 −7 M of γ-BHC, only the plateau component of I GABA at 10 −5 M were depressed without changing the peak amplitude. While γ-BHC at high concentration (> 3 × 10 −5 M) depressed both the peak and plateau current components. The γ-BHC-induced depression of I GABA seemed to be I GABA -component-dependent. A detailed analysis of the γ-BHC action in the concentration-response relationship for GABA revealed that the I GABA with strong desensitization was preferentially blocked by γ-BHC (> 3 × 10 −5 M). The rate of recovery of the I GABA from γ-BHC-induced block depended on the concentration of GABA. The lower the concentration of GABA, the slower the recovery. The GABA A receptor Cl − channels were proposed to be classified into two types of the γ-BHC-sensitive and -resistant ones. The interposed application of GABA + γ-BHC during generation of I GABA has shown that γ-BHC as well as TBOB or picrotoxin exerted depression of the I GABA under this condition, suggesting that both compounds can act on the GABA A receptor in the activated state. γ-BHC and TBOB were found to compete with picrotoxin in depression of the I GABA . Presence of a specific site within the GABA A receptor-Cl − channel for binding of γ-BHC, TBOB and picrotoxinin, where the convulsants presumably inhibit the Cl − -binding.

A Phase Dynamics Model of Human Circadian Rhythms

Nonphotic entrainment of an overt sleep-wake rhythm and a circadian pacemaker–driving temperature/melatonin rhythm suggests existence of feedback mechanisms in the human circadian system. In this study, the authors constructed a phase dynamics model that consisted of two oscillators driving temperature/melatonin and sleep-wake rhythms, and an additional oscillator generating an overt sleep-wake rhythm. The feedback mechanism was implemented by modifying couplings between the constituent oscillators according to the history of correlations between them. The model successfully simulated the behavior of human circadian rhythms in response to forced rest-activity schedules under free-run situations: the sleep-wake rhythm is reentrained with the circadian pacemaker after release from the schedule, there is a critical period for the schedule to fully entrain the sleep-wake rhythm, and the forced rest-activity schedule can entrain the circadian pacemaker with the aid of exercise. The behavior of human circadian rhythms was reproduced with variations in only a few model parameters. Because conventional models are unable to reproduce the experimental results concerned here, it was suggested that the feedback mechanisms included in this model underlie nonphotic entrainment of human circadian rhythms.

Enhancement of Synchronization Between Hippocampal and Amygdala Theta Waves Associated With Pontine Wave Density

Theta waves in the amygdala are known to be synchronized with theta waves in the hippocampus. Synchronization between amygdala and hippocampal theta waves is considered important for neuronal communication between these regions during the memory-retrieval process. These theta waves are also observed during rapid eye movement (REM) sleep. However, few studies have examined the mechanisms and functions of theta waves during REM sleep. This study examined correlations between the dynamics of hippocampal and amygdala theta waves and pontine (P) waves in the subcoeruleus region, which activates many brain areas including the hippocampus and amygdala, during REM sleep in rats. We confirmed that the frequency of hippocampal theta waves increased in association with P wave density, as shown in our previous study. The frequency of amygdala theta waves also increased with in associated with P wave density. In addition, we confirmed synchronization between hippocampal and amygdala theta waves during REM sleep in terms of the cross-correlation function and found that this synchronization was enhanced in association with increased P wave density. We further studied theta wave synchronization associated with P wave density by lesioning the pontine subcoeruleus region. This lesion not only decreased hippocampal and amygdala theta frequency, but also degraded theta wave synchronization. These results indicate that P waves enhance synchronization between regional theta waves. Because hippocampal and amygdala theta waves and P waves are known to be involved in learning and memory processes, these results may help clarify these functions during REM sleep.

An optimal control model of 1/f fluctuations in heart rate variability

We investigate the generation mechanisms underlying the 1/f fluctuations in HRV in the context of an optimal control of the cardiovascular system. First, the phenomenon is experimentally quantified for human and cat HRV. Second, the relationship between the resulting dynamics of HRV and the regulatory criteria of optimal control is investigated by using a newly proposed cardiovascular system model. Finally, an operational point of the model is hierarchically controlled to simulate changes in physiological states, including the state of consciousness. This hierarchical control mechanism is suggested to be essential for generating the 1/f HRV fluctuations, and their physiological significance is discussed. Through these analyses, a possible control strategy of the cardiovascular system is suggested.

Investigation of the time delay between variations in heart rate and blood pressure

Relationships between fast variations in heart rate and blood pressure are known mainly to reflect parasympathetic activity. To assess parasympathetic function, relationships are investigated using a mutual information analysis, by assuming an information channel between blood pressure (BP) and inter-R-wave interval (RR) derived from the electrocardiogram. The differential sequences of BP and RR are coded into ‘alphabets’ for analysing fast variations. The averaged mutual information (AMI) is obtained as a function of delay d (beats) of the differential sequence of RR with reference to BP. The AMIs for supine and standing positions are compared. For 23 patients with renal failure, the AMI against d shows posture-independent and delayed-transfer characteristics from fast variations in BP to those in RR. The closest relationship is found with a 2-beat delay with an out of phase relationship. The 28 control subjects exhibit the 2-beat delayed transfer characteristics in the standing position, but are almost synchronous in the supine position. The mutual information analysis of the delay between fast variations in BP and PR explicitly shows a deficit in the parasympathetic regulation in the patients with renal failure.

Fluorescent estimation on cytotoxicity of methylmercury in dissociated rat cerebellar neurons: its comparison with ionomycin.

To study the cellular basis of the neurotoxicity of methylmercury, the effects of methylmercury on dissociated rat cerebellar neurons were examined using a flow cytometer, a confocal laser microscope and three fluorescent dyes, fluo-3 for monitoring the changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) and for detecting live neurons, ethidium for assessing the neurons that are dead or have compromised membranes, and 5-chloromethylfluorescein (CMF) for estimating the cellular content of nonprotein thiols. Methylmercury at concentrations of 1 μM or greater increased the [Ca(2+)](i) of almost all neurons. Prolonged exposure to methylmercury (3 and 10 μM) produced a further increase in [Ca(2+)](i), in association with compromising membranes in some neurons. Thereafter, methylmercury induced blebs on membranes of some neurons with increased [Ca(2+)](i). Methylmercury at concentrations of 0.3 μM or greater dose-dependently decreased the cellular content of nonprotein thiols. Results suggest that methylmercury may induce the loss of membrane integrity through destabilized Ca(2+) homeostasis and oxidative stress in mammalian brain neurons.