Biomedical subjects

Masaomi Kitayama

Publications and source records attributed to Masaomi Kitayama.

6 recordsLinked to original sources

PubMed2003

Wavelet analysis for neonatal electroencephalographic seizures.

Electroencepholographs (EEGs) of neonatal seizures differ from those of children and adults. This study evaluated whether wavelet transform analysis, a nonstationary frequency analysis of EEG, can recognize and characterize neonatal seizures. Twenty-second segments were analyzed from 69 EEG seizures in 15 neonatal patients whose seizures lasted 10 seconds or longer. The wavelet transform results were examined, as were EEG seizure durations and dominant frequencies. The wavelet transform results were correlated with the occurrence, after an 18-month follow-up, of postneonatal seizures. Wavelet transform analysis identified 40 seizures (58%) with a "sustained dominant frequency component" that lasted 10 seconds or longer and 29 seizures without a sustained dominant frequency component. The mean seizure duration of the 40 seizures with sustained dominant frequency components was 63.3 seconds, longer than the mean duration (33.6 seconds) of the seizures without sustained dominant frequency components, P < 0.01. Eleven patients manifested postneonatal epileptic seizures. Fifty-two EEG seizures in these 11 patients revealed more sustained dominant frequency components (74%) than 17 seizures in the 4 patients without postneonatal seizures (only 12%), P < 0.05. Wavelet transform analysis can identify neonatal EEG seizures and characterize their epileptic components. The presence of sustained dominant frequency components may predict postneonatal epileptic seizures.

Asphyxia Neonatorum↗

PubMed2003

Ih blockers have a potential of antiepileptic effects.

PURPOSE: The h current (Ih) is an inwardly mixed cationic conductance activated by membrane hyperpolarization and distributed predominantly in the apical dendrites of hippocampal pyramidal neurons. To verify a hypothesis that an anomalous hyperpolarization generates an abnormal excitation by way of Ih channels, we examined the effects of Ih blockers (CsCl and ZD7288) on electrically induced paroxysmal discharges (PADs). METHODS: Fifty-three adult male rabbits were used. We measured the PAD threshold elicited by stimulation to the apical dendritic layer of the hippocampal CA1 region before and after injecting 50 microl of each Ih blocker or saline extracellularly into the same region. RESULTS: In Ih blocker injection groups (n = 26), we obtained a significant increase in PAD threshold (1 mM CsCl: 163%, p < 0.01; 10 mM CsCl: 265%, p < 0.01; 100 mM CsCl: 199%, p < 0.01; 100 microM ZD7288: 192%, p < 0.05; 1 mM ZD7288: 246%, p < 0.05). Conversely, we did not obtain the increase in PAD threshold in a saline injection group (n = 10, 107%). The magnitude as well as duration of the effect had a tendency to depend on concentration of Ih blockers, although a saturated or declining tendency was observed with the 100 mM CsCl injection. CONCLUSIONS: We concluded that Ih channels might contribute to hippocampal epileptiform discharges in vivo. Our hypothesis for epileptogenesis demonstrated in the present experiment offers an idea to develop a new type of antiepileptic drug based on Ih blockers for the treatment of epileptic disorders refractory to current medications.

Animals↗

PubMed2003

Epileptogenesis induced by alternate-site kindling in bilateral hippocampi.

PURPOSE: Alternate-site kindling (AK), which has been known to induce so-called kindling antagonism, was performed in the bilateral hippocampi to reveal neural mechanisms underlying hippocampal kindling. METHODS: Ten adult rabbits were used. Daily kindling stimulation consisted of a 1- s train of 50 pulses (pulse duration, 1 ms) of 80 to 200 microA (base-to-peak), which was higher than the afterdischarge (AD) threshold. The concurrent alternating stimulations were delivered to the right and left hippocampus once every 24 h. RESULTS: All animals developed a stage 5 convulsion with a mean of 28.1 +/- 3.3 (mean +/- SEM) stimulations. The right and left hippocampus received 14.8 +/- 1.7 and 14.6 +/- 1.6 stimulations, respectively. Behavioral stages induced by stimulation of the right or left hippocampus evolved to generalized seizures along a similar course. Kindling antagonism was not observed. The two sides showed similar increases in AD duration, and similar chronologic changes in interictal discharge (IID) frequency. Simple A-type IID and complex types of IID appeared at higher rates, whereas simple B-type IID remained at a relatively low level. CONCLUSIONS: The present AK procedure did not induce kindling antagonism, but it induced progression of kindling manifestations. The origin of simple B-type IID is known to be in the contralateral side, and its intracellular counterpart corresponds to a sequence of small depolarization followed by large hyperpolarization, suggesting that plastic changes in the feed-forward inhibitory system play an important role in hippocampal kindling.

Animals↗

PubMed2003

Characteristics of prolonged afterdischarges in children with malformations of cortical development.

We investigated aberrant cortical excitability in malformations of cortical development From subdural electrodes, we recorded afterdischarges lasting > or = 6 seconds in 12 of 13 patients with malformations of cortical development and 6 of 10 pediatric patients with nonmalformations of cortical development and reviewed amperage thresholds, distribution of afterdischarges, and motor responses. In patients with malformation of cortical development, motor response thresholds were high; afterdischarge and motor response thresholds, which essentially overlapped, inversely correlated with age (P < .01); afterdischarge thresholds declined with age; and 8 patients showed afterdischarges in remote sites. In nonmalformation of cortical development, afterdischarge thresholds did not significantly correlate with age; motor response thresholds tended to decline with age; and 2 patients had remote afterdischarges. Adolescent patients with malformations of cortical development had lower afterdischarge thresholds than adolescents with nonmalformation of cortical development (P < .05). From their high afterdischarge (and motor response) thresholds, we concluded that preadolescent patients with malformation of cortical development have less excitable, immature cortices, whereas adolescent patients with malformation of cortical development with low afterdischarge thresholds have hyperexcitable cortices. Remote afterdischarges over focal dysplastic cortex suggest aberrant cortical excitability and neural circuits.

Adolescent↗

PubMed2002

The extracellular current blocking effect of cesium chloride on the theta wave in the rabbit hippocampal CA1 region.

We studied the extracellular effects of cesium chloride (CsCl), a blocker of the hyperpolarization-activated cationic current (I(h)), on the hippocampal theta wave in pentobarbital-anesthetized rabbits. We recorded spontaneous field potentials at the hippocampal CA1 region before and at three time periods after CsCl or saline injections. We found that CsCl injected into the apical dendritic layer attenuated the theta wave amplitude. CsCl affected neither the frequency nor the phase reversal of the theta wave between the apical and basal dendritic layers. Our findings indicate that I(h) in pyramidal neurons contributes to current generation of the limbic theta wave in vivo.

Animals↗

PubMed2002

Epileptic spikes: magnetoencephalography versus simultaneous electrocorticography.

PURPOSE: To test the sensitivity of extracranial magnetoencephalography (MEG) for epileptic spikes in different cerebral sites. METHODS: We simultaneously recorded MEG and electrocorticography (ECoG) by using subdural electrodes with 1-cm interelectrode distances for one patient with lateral frontal epilepsy and one patient with basal temporal epilepsy. We analyzed MEG spikes associated with ECoG spikes and compared the maximal amplitude and number of electrodes involved. We estimated and evaluated the locations and moments of the equivalent current dipoles (ECDs) of MEG spikes. RESULTS: In patient 1, MEG detected 100 (53%) of 188 ECoG lateral frontal spikes, including 31 (46%) of 67 spikes that activated three subdural electrodes. MEG spike amplitudes correlated with ECoG spike amplitudes and the number of electrodes activated (p < 0.01). ECDs were perpendicular to the superior frontal sulcus. In patient 2, MEG detected 31 (26%) of 121 ECoG basal temporal spikes, but none that activated only three subdural electrodes. ECDs were localized in the entorhinal and parahippocampal gyri, oriented perpendicular to those basal temporal cortical surfaces. The ECD strength was 136.6 +/- 71.5 nAm in the frontal region, but 274.5 +/- 150.6 nAm in the temporal region (p < 0.01). CONCLUSIONS: When lateral frontal ECoG spikes extend >3 cm2 across the fissure, MEG can detect >50%, correlating with spatial activation and voltage. In the basal temporal region, MEG requires higher-amplitude discharges over a more extensive area. MEG shows a significantly higher sensitivity to lateral convexity epileptic discharges than to discharges in isolated deep basal temporal regions.

Adult↗