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At least 451 records · Page 25Linked to original sources
PubMed2001

Mechanisms of spreading depression and hypoxic spreading depression-like depolarization.

Spreading depression (SD) and the related hypoxic SD-like depolarization (HSD) are characterized by rapid and nearly complete depolarization of a sizable population of brain cells with massive redistribution of ions between intracellular and extracellular compartments, that evolves as a regenerative, "all-or-none" type process, and propagates slowly as a wave in brain tissue. This article reviews the characteristics of SD and HSD and the main hypotheses that have been proposed to explain them. Both SD and HSD are composites of concurrent processes. Antagonists of N-methyl-D-aspartate (NMDA) channels or voltage-gated Na(+) or certain types of Ca(2+) channels can postpone or mitigate SD or HSD, but it takes a combination of drugs blocking all known major inward currents to effectively prevent HSD. Recent computer simulation confirmed that SD can be produced by positive feedback achieved by increase of extracellular K(+) concentration that activates persistent inward currents which then activate K(+) channels and release more K(+). Any slowly inactivating voltage and/or K(+)-dependent inward current could generate SD-like depolarization, but ordinarily, it is brought about by the cooperative action of the persistent Na(+) current I(Na,P) plus NMDA receptor-controlled current. SD is ignited when the sum of persistent inward currents exceeds persistent outward currents so that total membrane current turns inward. The degree of depolarization is not determined by the number of channels available, but by the feedback that governs the SD process. Short bouts of SD and HSD are well tolerated, but prolonged depolarization results in lasting loss of neuron function. Irreversible damage can, however, be avoided if Ca(2+) influx into neurons is prevented.

Calcium Channels↗
PubMed1985

[Brain function in patients with plateau waves studied by compressed spectral array in long-term EEG monitoring].

The intracranial pressure, systemic blood pressure and compressed spectral array in EEG monitoring were studied in three patients with typical plateau waves in continuous intracranial pressure recordings. Two patients with brain-tumor and one patient with aqueductal stenosis were included. The intracranial pressure was recorded through an indwelling ventricular catheter attached to a pressure transducer. The systemic blood pressure was recorded through an intraarterial catheter placed in the femoral artery or the dorsalis pedis artery. To obtain continuous and compressed spectral array in the EEG, Berg-Fourier Analyzer by the OET-Biomedica Company of Italy was used. Simultaneous recordings of the intracranial pressure, systemic blood pressure and EEG spectral analysis were made for 180 minutes in each patient. During the plateau waves, the systemic blood pressure did not rise in spite of a marked increase in intracranial pressure, resulting in a marked decrease in the cerebral perfusion pressure. The patients, however, showed no clinical symptoms resulting from ischemia of the brain, such as vasopressor response and impairment of consciousness, but complained only headache. The spectrograms in these patients were characterized by a constant and predominant activity in the alpha or high frequencies. This structural aspect was retained throughout the continuation of plateau waves. The power of low frequencies only appeared transiently. The results suggest that some mechanisms producing and maintaining the fast and/or alpha wave activity may participate in the recurrent appearance of plateau waves.

Adult↗
PubMed1998

Localization analysis of neuronal activities in benign rolandic epilepsy using magnetoencephalography.

Benign epilepsy of childhood with rolandic spikes (BECRS) is an electroclinical syndrome characterized by partial sensorimotor seizures with centrotemporal spikes. We report a detailed localization analysis of spontaneous magnetic brain activities in seven BECRS patients using magnetoencephalography (MEG). All patients had BECRS diagnosis with typical seizures and electroencephalographic findings and five patients had minor psychomotor deficits. MEG was recorded over both parieto-temporal regions using a 2x37-channel biomagnetic system. The collected data were digitally bandpass-filtered (2-6, 14-30, or 1-70 Hz) to analyze slow- and fast-wave magnetic activities and rolandic spikes. Slow-wave activity was increased in four hemispheres of three patients. Increased fast-wave activity was found in all five patients with minor neuropsychological deficits. The presence of increased fast-wave magnetic brain activity appeared to cause functional anomalies in the higher brain function processes. In the spike analysis, the dipoles of rolandic spikes which constantly manifested anterior positivity in direction were concentrated in the superior rolandic region in four cases and the inferior rolandic region in three cases. The localizations of increased slow- and fast-wave activities were identical with those of the spikes. The seizure profiles were frequently characterized by the spike locations. Source localizations of the focal brain activities and rolandic spikes by MEG will contribute to the different diagnosis and pathophysiological elucidation of BECRS.

Adolescent↗
PubMed1996

Slow wave sleep and computed tomographic measures of brain morphology in schizophrenia.

To test the hypothesis that slow wave sleep in schizophrenia is inversely correlated with ventricular system volume, polysomnography and computed tomographic (CT) brain imaging were carried out in 14 psychiatric patients who met Research Diagnostic Criteria for schizophrenia (h = 11) or schizoaffective disorder (n = 3). Three measures of ventricular system volume were analyzed: (1) raw ventricular volume expressed in cm3; (2) ventricle-to-brain ratio; and (3) ventricular volume corrected for normal variation in age and head size expressed as a standardized (z) score. All three quantifications of ventricular volume were significantly and inversely correlated with visually scored measures of stage 3 and stage 4 sleep. This finding suggests that the etiology of slow wave sleep deficits in schizophrenia is related either directly or indirectly to underlying brain dysmorphology.

Adult↗
PubMed1996

Derived-band auditory brain-stem response estimates of traveling wave velocity in humans: II. Subjects with noise-induced hearing loss and Meniére's disease.

Estimates of cochlear traveling wave velocity (TWV) were computed from derived-band auditory brain-stem response (ABR) latencies in subjects with noise-induced hearing loss (NIHL) or Meniére's disease (MD). ABR wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's (1961) place-frequency function for humans. An exponential function of the form I = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the reciprocal of the derivative of the latency function with respect to distance [v = 1/(BCeCd)]. Expected values for subjects' TWV functions were compared to normative data from Donaldson and Ruth (1993) at five cochlear loci. NIHL subjects' TWV estimates fell within normal limits at all cochlear loci, and no relation between severity of high-frequency hearing loss and TWV could be discerned. MD subjects with good low-frequency hearing sensitivity generally yielded normal TWV estimates, whereas MD subjects with low-frequency hearing loss yielded either normal or elevated TWVs. MD subjects' data generally support the hypothesis that endolymphatic hydrops results in increased TWV or, alternatively, a basalward shift in the peak of the traveling wave, in cochleas with presumed normal basilar membrane elasticity.

Adult↗
PubMed1992

Neuronal activity triggers calcium waves in hippocampal astrocyte networks.

The recent discovery that the neurotransmitter glutamate can trigger actively propagating Ca2+ waves in the cytoplasm of cultured astrocytes suggests the possibility that synaptically released glutamate may trigger similar Ca2+ waves in brain astrocytes in situ. To explore this possibility, we used confocal microscopy and the Ca2+ indicator fluo-3 to study organotypically cultured slices of rat hippocampus, where astrocytic and neuronal networks are intermingled in their normal tissue relationships. We find that astrocytic Ca2+ waves are present under these circumstances and that these waves can be triggered by the firing of glutamatergic neuronal afferents with latencies as short as 2 s. The Ca2+ waves closely resemble those previously observed in cultured astrocytes: they propagate both within and between astrocytes at velocities of 7-27 microns/s at 21 degrees C. The ability of tissue astrocyte networks to respond to neuronal network activity suggests that astrocytes may have a much more dynamic and active role in brain function than has been generally recognized.

Animals↗
PubMedDate not supplied

A study of methods used to enhance wave I in the auditory brain stem response.

Auditory brain stem responses (ABR) were recorded in 15 audiometrically and neurologically normal adult subjects. The purpose of the study was to investigate various aspects of stimulus composition (intensity, click rate, and polarity) and response measurement parameters (band-pass filtering and electrode linkage) that might serve to enhance detectability of wave I in the ABR. Amplitude of wave I was significantly enhanced by an increase in intensity, a decrease in click rate, and use of a negative (rarefaction) polarity click. Amplitude of wave I was not significantly influenced by bandwidth of the response filter or by a horizontal (mastoid-to-mastoid) electrode linkage. Use of simultaneous response acquisition from an ipsilateral and contralateral reference electrode array did aid in the detection or visualization of wave I, particularly for lower stimulus intensity levels or faster click rates.

Acoustic Stimulation↗
PubMed1995

The square-wave approach to impedance measurement of brain tissue water dynamics.

Electrical properties of living soft tissue have been used to analyze their structure and function. Presently, the 'admittance locus' method, with the sine-wave signal of changing frequency, is the most informative continuous method for analyzing extra-and intracellular water content in brain tissue. Using the square-wave signal in lieu of the sine-wave signal, we can avoid cumbersome and costly measurements and facilitate real-time data processing. An isolation-calibration device was developed for the present study in order to condition and stabilize electrical current through the brain cortex. This device was also used for impedance calibration before and after the experiments. We propose a simple algorithm for data analysis on the basis of equivalent circuit approach, which allows to develop a computer program for data processing. Preliminary experiments on rat brains were carried out with a 0.2-0.5 mm stainless-steel tetrapolar electrode system. These studies showed good linearity between stimulating currents (I = 5-30 microA) through the external electrodes in the brain cortex and a drop in voltage which was measured by 2 inner electrodes. The results of the device and the program accuracy tests allow us to choose the optimal range for the working current. We can recommend this method for usage in animal experiments.

Algorithms↗
PubMed1995

[Loss of brain stem auditory evoked potential waves I and II during controlled hypotension].

For surgical removal of a malignant choroid melanoma, it is necessary to reduce systolic blood pressure to around 50-60 mmHg in order to prevent choroidal haemorrhages. However, blood pressure reduction is associated with the risk of cerebral ischaemia. We report a patient with a malignant choroid melanoma in whom waves I and II of the brainstem auditory evoked potentials (BAEP) disappeared during surgery under controlled arterial hypotension and hypothermia (31.1 degrees C). The waves could be recorded again immediately after the mean arterial pressure was increased from 48 to 77 mmHg. The oesophageal temperature had dropped by 0.3 degrees C at this time. The 2-channel electroencephalogram (EEG) showed no irregularities during this time period. A bilateral, reversible, apparently blood-pressure-dependent loss of waves I and II during arterial hypotension despite a normal EEG has to our knowledge not been previously described in the literature. The isolated loss of waves I and II with maintenance of waves III, IV, and V is unusual. The literature contains reports of acoustic neurinoma patients in whom only wave V could be recorded. This is regarded as an indication of continued impulse conduction despite the loss of waves I to IV. Others have observed a patient with temporary and reversible loss of BAEP wave I due to vasospasm of the internal auditory artery that apparently occurred during or shortly after manipulation of the internal auditory meatus. Assuming anatomic peculiarities in the blood supply to the generators of the BAEP waves, a stenosis of the basilar artery could be considered as the cause of the bilateral reversible loss of waves I and II. Another potential source could be induced hypothermia, but this does not seem very likely because the patient's temperature was 0.3 degrees C lower at the return of the waves than at their loss.

Choroid Neoplasms↗
PubMedDate not supplied

Late infantile form metachromatic leukodystrophy: report of one case.

Metachromatic leukodystrophy (MLD) is a neurodegenerative disorder with autosomal recessive inheritance, in which cerebroside sulphate (sulphatide) accumulates in the central and peripheral nervous systems due to a deficiency of arylsulphatase A. This article presents a 2-year-old boy who had occasional shortness of breath, horizontal nystagmus and unstable gait for 3 months prior to the entry. He was admitted to our hospital due to shortness of breath, frequent apnea, generalized hypotonia and conscious disturbance. The lumbar puncture, brain CT scan, serum amino acid analysis, urine organic acid assay and nerve conduction velocity of lower extremities all showed negative findings. The electron microscopic finding of muscle elicited lipid deposition. The auditory brainstem response showed bilateral impairment. The routine EEG revealed diffuse slow waves. The brain MRI showed widespread low signals over the white matter of bilateral frontal and parietotemporal areas of the cerebral hemispheres, as well as the white matter of the bilateral cerebellar hemispheres, and the brain stem in the T1-weighted image corresponding the high signals in T2-weighted image. The blood leukocyte lysosomal enzyme activity test revealed arylsulphatase A deficiency. Rapid progressive neurological deterioration was noted since admission. Unfortunately, the patient expired due to respiratory failure in the final.

Bone Marrow Transplantation↗
PubMed1985

[Experimental study of brain lesions after combined coaxial exposure to high-peaked pulse wave form CO2 and Nd: YAG lasers on the brain].

UNLABELLED: The CO2 laser is useful for cutting and vaporization but not for coagulation and hemostasis. On the contrary, YAG laser is effective for coagulation and hemostasis but not for cutting. The purpose of this study is to examine the effect of the exposure of combined, coaxial CO2 and YAG laser on the animal brain to supplement the advantages and draw-backs of each other. To compare these results, each of non-combined pulse wave form CO2 and YAG lasers was employed separately. MATERIALS AND METHODS: The lasers in this study were pulse wave form CO2 and YAG lasers, employed separately or simultaneously using 130 YZ of Nihon Infrared Industries Company. Japanese white rabbits were anesthetized with pentobarbital. Fronto-parietal burr holes were made, the dura was removed and then Evans blue solution was injected intravenously. The lasers were employed to the cerebral cortex without great vessels using a micromanipulator attached to the operative microscope with a distance of 30 cm. The spot size was 700 mu for CO2 laser and 1200 mu for YAG laser. The first experiment was to see the effect of nine combinations of simultaneous coaxial CO2 of 2, 4 and 8 watts and YAG lasers of 10, 20 and 40 watts, 1 sec on the brain. In the second experiment, also combining two lasers, the exposure time of YAG laser was elongated from 1 or 2 seconds into 2 or 4 seconds and the arrangement of powers was the same as that of the first experiment. The lesions were thus made in 18 different conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

A case of high altitude pulmonary edema followed by brain computerized tomography and electroencephalogram.

A case of high altitude pulmonary edema with high altitude cerebral edema was reported. A young Japanese male complained of severe palpitation and shortness of breath on the third day of climbing at 3,000 m above sea level. During the next 2 d at altitude, the following symptoms occurred: cough with foamy sputum, cyanosis, and loss of consciousness. Soon after evacuation, he showed severe hypoxemia and deep coma with decerebrate rigidity; electroencephalogram showed diffuse alpha waves, indicating "alpha wave coma." Brain computerized tomography revealed brain edema, showing small compressed ventricles and diffuse low density of the cerebrum. Pulmonary edema on chest roentgenogram disappeared by the fifth hospital day, and his consciousness recovered gradually during the next 2 weeks after the admission. He was examined serially by electroencephalography and brain computerized tomography. He recovered fully, but there were transient psychological abnormalities soon after discharge and mild brain atrophy was observed by brain computerized tomography 6 years later.

Adult↗
PubMed1994

Interleukin-1 is involved in responses to sleep deprivation in the rabbit.

Interleukin-1 (IL-1) is hypothesized to be involved in sleep regulation. Antibodies directed against interleukin-1 beta (anti-IL-1 beta) were injected intracerebroventricularly (ICV) into normal rabbits to determine the effects of the reduction of endogenous IL-1 beta on spontaneous sleep/wake behavior. A 100 micrograms dose of anti-IL-1 beta reduced non-rapid eye movements sleep (NREMS) by about 20-min during the first 4-h postinjection without affecting REMS, amplitudes of electroencephalographic (EEG) slow waves, or brain temperature. Plasma concentrations of IL-1 beta, as determined by radioimmunoassay, were detectable in 39 of 79 (49%) blood samples taken before and after 4-h total sleep deprivation (SD). Plasma concentrations of IL-1 beta were, on average, significantly elevated following SD. There was a rebound in NREMS duration and of amplitudes of EEG slow waves of about 2-h duration following SD. This rebound in both parameters was exaggerated if rabbits received vehicle or anti-IL-1 beta in conjunction with SD. However, ICV administration of anti-IL-1 beta at the beginning or end of the SD period attenuated, relative to values obtained after administration of vehicle, the NREMS rebound following SD. It is concluded that SD alters the responsiveness of rabbits to experimental manipulation and that responses to SD in the rabbit are mediated, in part, by IL-1.

Animals↗
PubMed1996

Abnormal brain stem auditory evoked potentials in a girl with the central alveolar hypoventilation syndrome.

Brainstem auditory evoked potentials were recorded in a 3-year-old girl with the central alveolar hypoventilation syndrome (Ondine's syndrome). Abnormal findings were seen at the level of the mid to upper brain stem (wave III), which was not reproducibly recordable on the left side. This electrophysiologic abnormality is consistent with a previous finding in a patient with sleep apnea.

Child, Preschool↗
PubMed2004

[Basic mechanism for generation of brain rhythms].

Study of the basic mechanism of brain rhythms adds to our understanding of the underlying processes of neuronal network within the human brain. Electroencephalography (EEG) records summated extracellular field potentials from large pyramidal neurons in the cerebral cortex. The characteristic rhythmic oscillation of brain rhythms are beststudied by sleep spindles, which are generated within the thalamus through a network of thalamic reticular cells, thalamocortical projection cells and cortical pyramidal cells. Fast rhythms including beta and gammaare present during arousal and focused attention. Besides a reflection of activation from the brainstem reticular activating system, fast rhythms also represent an activated state of the underlying neuronal network. Alpha waves are readily recognized brain waves during relaxed wakefulness; however, the origins of alpha rhythm are not well understood. It is presumed that alpha rhythms are generated by contingent pyramidal cell, and by intracortical connections, spread in the cortical layers. Rhythmic alpha spindles probably represent a de-activated state.

Cerebral Cortex↗
PubMed1977

Brain lesions that produce delta waves in the EEG.

Localized delta activity appears in cortex overlying a circumscribed white matter lesion. Less commonly, localized delta activity may result from a localized thalamic lesion. Unilateral diffuse delta activity appears on the side of thalamic or hypothalamic lesions. Bilateral delta activity results from bilateral lesions of the midbrain tegmentum. Localized lesions of the cerebral cortex, unilateral mesencephalic tegmental lesions, and vasogenic edema of the cerebral white matter do not produce delta activity. Marked edema of a cerebral hemisphere when no surgical decompression is provided may produce unilateral delta activity by pressure on or displacement of the brain stem or diencephalon.

Animals↗