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PubMed1978

Myoclonus developing after vermisectomy in photosensitive Papio papio.

Two vermisectomized photosensitive baboons exhibited two different types of myoclonus, one induced by intermittent light stimulation (ILS) and the other occuring "spontaneously". The characteristics of these two types of myoclonus are described from a clinical and from an ECoG point of view. Myoclonus induced by ILS (ML) started at the eyelids and secondarily invaded the face and body; it was always preceded by frontorolandic spike-waves or polyspike-waves. The "spontaneous" myoclonus which followed vermisectomy (MV) was "massive", but involved firstly the trunk and secondarily the face and limbs; no ECoG paraoxysm accompanied this myoclonus, but we observed a parietal evoked potential of small amplitude, 10--15 msec after its onset. If MLs can be considered as consequences of the fronto-rolandic paroxysmal discharges, MVs seem to originate in the brain stem but appear similar to action myoclonus. This experimental situation showing two types of myoclonus resembles human hereditary degenerative syndromes (dyssynergic cerebellar myoclonus, progressive myoclonic epilepsy), without being exactly comparable. The conditions in which MVs were seen and their modifications during sleep and by different drugs are described. The relationships between MVs and MLs and myoclonic epilepsy are discussed.

Animals↗

PubMed1979

Coupling between neuronal activity and focal blood flow in experimental seizures.

Local blood flow, ECoG and single cortical neurone activity were recorded simultaneously from single microelectrodes in 17 cats. Seizures were induced by repeated intravenous injections of pentylenetetrazol (PTZ, 10-20 mg/kg) or by local application of 1 M Na-penicillin. Seven to 20 sec after appearance of burst activity in cortical neurones and ECoG, focal flow increased up to 300% of control. The extent of this flow increase was significantly correlated with the change in firing rate of the neurones. With cessation of seizure activity the flow returned to or below control values. Forty to 70 mg/kg PTZ caused status epilepticus with high voltage rhythmic discharges lasting 30 min-2 h. In 3 cats with status, the flow decreased below control despite persisting seizures, indicative of uncoupling between activity and flow. The delayed coupling between activity and flow during drug-induced seizures indicates a metabolic mediator. Uncoupling observed in cases with long lasting seizures may be due to brain oedema following increased permeability of the blood-brain barrier.

Animals↗

PubMed1977

Slow wave sleep and a state resembling absence epilepsy induced in the rat by gamma-hydroxybutyrate.

The effect of gamma-hydroxybutyrate (GHB) in relatively low doses (12.5--200 mg/kg) on sleep stages, electrocorticogram (ECoG) patterns and behavior was investigated in the rat. 50-100 mg/kg GHB induced slow wave sleep but, in contrast to the cat, not paradoxical sleep. 200 mg/kg induced a hypersynchronous, bilaterally symmetrical ECoG pattern, which was different in amplitude and frequency distribution from normally occurring high amplitude patterns. When the hypersynchrony occurred in bursts, the rats displayed a sudden arrest of motor behavior. Convulsions were not induced. The results, together with the finding of others that GHB is a natural constituent of mammalian brain and our previous observation that the GHB-induced hypersynchrony can be antagonized by anti-absence (anti-petit mal) drugs are discussed in view of the possibility that GHB might play a role in the etiology of absence epilepsy in man.

Animals↗

PubMed1977

Suppression of an eplieptiform type of electrocortical activity in the rat by stimulation in the vicinity of locus coeruleus.

Stimulation of the locus coeruleus, or in the vicinity of this nucleus or of its ascending tracts, could markedly suppress the appearance of epileptiform-like ECoG bursts. The latter were induced in rats by a subconvulsive dose of pentylenetetrazol. Electrode sites were identified histologically. A unilateral stimulus suppressed bursts bilaterally. An individual burst already in progress could be aborted, stopping within less than 0.5-1 sec after onset of a stimulus train. The antiepileptiform actions occurred with no evidence of any desynchronizing effect of the stimulus on the resting ECoG; they appear to be different in sites of origin and nature from those reported for stimulation of the reticular activating system. It is proposed that stimulation of the ascending noradrenergic system in the brain stem may limit the development and spread of hyperexcitatory, epileptiform states.

Animals↗

PubMed1977

The role of dopaminergic systems in gamma-hydroxybutyrate-induced electrocorticogram hypersynchronization in the rat.

The effects of dopaminergic agonists and antagonists on the duration of hypersynchronization induced in the electrocorticogram (ecog) by gamma-hydroxybutyrate (gamma-HB) were tested in rats. Apomorphine (0-2-8 mg kg-1), piribedil (2-5-10 mg kt-1) and haloperidol (0-5-1 mg kg-1) had no influence on the duration of the hypersynchrony. Amphetamine (1-5-6 mg kg-1) inhibited the hypersynchrony, while (3,4-dihydroxyphenylamino)-2-imidazoline (DPI; 5, but not 1, mg kg-1) prolonged its duration. The lack of effect of the dopamine receptor agonists apomorphine and piribedil, and the dopamine receptor blocker haloperidol, on the gamma-HB-induced hypersynchrony might indicate that the inhibition of the impulse flow in the nigrostriatal dopamine system by gamma-HB is not involved in the generation of the hypersynchrony. DPI is thought to be an agonist at a dopamine receptor not sensitive to apomorphine, and its facilitatory effect on gamam-HB-hypersynchrony can be interpreted in terms of a possible involvement of another dopamine system in the ecog hypersynchrony induced by gamma-HB. The antagonism of gamma-HB by amphetamine is possibly due to an indirect stimulatory effect on noradrenergic receptors.

Amphetamine↗

PubMed1977

Respiratory patterns during progressive asphyxia in newborn rabbits.

During acute progressive asphyxia an abrupt transition occurs from regular respiratory efforts to primary apnea and gasping. To study this transition we measured inspiratory duration (TI), expiratory duration (TE), maximal inspiratory tracheal pressure (Pmax), electromyographic activity (EMG) of different muscle groups, and the electrocorticogram (ECoG) of 3- to 5-day-old rabbits following airway occlusion at functional residual capacity (FRC). The onset of primary apnea was associated with other central nervous system events as indicated by decerebrate posture and maximal EMG activity which were followed by relaxation, loss of EMG activity, and an isoelectric ECoG. Indices of inspiratory drive (Pmax and Pmax/TI) were preserved or accentuated following primary apnea despite a reduction of overall respiratory activity (frequency X Pmax). The onset of primary apnea appears to be due to interruption of the respiratory cycling controls rather than failure of the respiratory center which regulates inspiratory force. Gasping appears to be linked with progressive changes in respiratory patterns which are observed prior to primary apnea. These findings do not support the concept of a "gasping" center.

Airway Obstruction↗

PubMedDate not supplied

Bone-conducted stimulation in electrocochleography.

The mechanical vibration patterns close to the cochlea in intact skulls of human cadavers have been studied by means of a miniature accelerometer. A Radioear B70A vibrator and a Brüel & Kjaer Mini Shaker have been used, fed with filtered clicks and with short tone bursts. The tone bursts were found to be superior to the clicks with regard to the vibration spectrum. At 500 Hz a considerable distortion was observed in the accelerometer signal, also when using tone bursts. This distortion was presumably due to resonant vibrations in the skull itself, and may be a source of error not only when using stimuli of short duration as in bone-conduction ECoG but also in conventional bone-conduction audiometry. When the vibrations were applied to the exposed bone surface of the mastoid, vibration levels increased by 10-25 dB compared with when soft tissues covered the point of application. This could be of advantage in bone-conduction ECoG performed at ear surgery.

Acoustic Impedance Tests↗

PubMedDate not supplied

Electrocochleography used as a clinical hearing test in difficult-to-test children.

Thirty difficult-to-test children have been tested with transtympanic ECoG. When possible, informal hearing tests and/or free-field testing were performed. Children in whom no action potential (AP) could be recorded were submitted to conventional radiography of the inner ear, and vestibular tests. The correlation between free-field test thresholds and AP "thresholds" was good, especially in subjects with relatively good hearing. Response amplitude increased, and latency decreased, with increasing frequency of the stimulus implying that different parts of the basilar membrane are stimulated according to the frequency of the stimulus. Input-output curves of response amplitude and latency were plotted, and three different types were distinguished. ECoG can contribute to the evaluation of peripheral hearing in difficult-to-test children, and vestibular tests should always be performed on a child with suspected deafness or sensorineural hearing loss. Conventional radiography of the inner ear, however, seems to be of little value.

Action Potentials↗

PubMedDate not supplied

[Theory of the EEG potential in models of the leptomeninges of the brain. IV. Radial dipoles and their double layers in the depths and on the surface of the brain].

The estimaiton of ECoG-potentials is fulfilled by means of a simple model of the isolated sphere, which is exact enough, as it was proved earlier [1]. A simple limit formula for the qualitative estimation of ECoG-potentials of a source situated in the cerebral cortex is obtained. The EEG as in [2] is obtained using the transformation of the first 20 spheric harmonics. The experimental facts of registration of the evoked potentials of comparatively little subcortical sources were explained theoretically. Numerical results of the model are used to estimate the intensity of the field induced in the brain by two electrodes placed on the scalp.

Brain↗

PubMed1976

Cortical synchronization induced by thermal stimulation of the preoptic area in immobilized rats.

Cortical synchronization characterized by frontal spindles and occipital slow wave activity was induced by bilateral thermal stimulation of 2--4 degrees C of the preoptic area in unanaesthetized immobilized rats. The synchronization was demonstrated by ECoG and its power density spectra. The ECoG of the synchronization was similar to that of slow wave sleep. Switching off the thermal stimulation the original activity was recovered in most of the cases. Frontal spindle activity and slow wave activity recorded over the posterior cortex seemed to be dissociated to some degree. Low frequency stimulation at the points of thermal stimulation resulted in frequency following synchronization. In some cases electrical and thermal stimulation induced gradually developing seizure activity.

Animals↗

PubMed1976

Spectral density analysis of the effects of barbiturates and benzodiazepines on the electrocorticogram of the squirrel monkey.

The effects of pentobarbital and diazepam were compared in a series of tests in squirrel monkeys; the effects of phenobarbital and flurazepam were compared in a second series. Observations were made of gross behavior and on the ECoG; the latter was analyzed by the spectral density technique. The two barbiturates induced sedation,which was occasionally so deep that the monkeys could not be readily aroused. The benzodiazepines induced sedation in some monkeys, but others showed signs of restlessness. The ECoG showed general slowing with the barbiturates, whereas the benzodiazepines produced mixed fast and slow patterns. Spectral density analysis showed that pentobarbital increased activity at frequencies below 40 Hz, with the largest increases occurring below 8 Hz. Phenobarbital increased activity below 8 Hz, but differed from pentobarbital by decreasing activity above 13 Hz. The benzodiazepines increased activity below 8 Hz, decreased it between 8 and 20 Hz, and increased it between 20 and 50 Hz.

Animals↗

PubMedDate not supplied

[Degree of homogeneity of the forms of statistical relationship between the EEG and spike currents of neurons].

The correlation between the spike activity and the waves of surface ECoG was studied in the visual and motor cortex of alert non-immobilized rabbits. A comparison was made between the forms of the obtained correlation functions for the cells with different horizontal and vertical distances between them. The analysis revealed the similarity of such functions in neurones of V-VI cortical layers, situated vertically under each other along the microelectrode track. Similar in form statistic connections between the ECoG and the background spike activity were also found, beginning with the depth of 1.000 mc, in the neurones situated at the same horizontal cortical level; however, with the increased distance between the cells the degree of similarity of these connections decreases in a non-linear way. On the basis of the obtained data a conclusion is made that the tangential sizes of the background functional ensembles of the cortical neurones are within the range of 140-300 mc.

Animals↗

PubMed1979

Mechanism of the cerebrocortical vasodilatation during anoxia.

The possible role of cerebrocortical ion homeostasis, NAD/NADH redox state and of cortical oxygen tension was investigated in the initiation of hypoxic cortical vasodilatation. In addition, changes in cerebrocortical extracellular concentrations of Na+, K+, and Cl- during anoxia were studied. The results were as follows. a) The cerebrocortical reflectance decrease, e.g. cerebral vasodilatation, lagged behind the cortical pO2 decrease by 1-2 sec, but preceded the decrease of arterial blood pressure and ECoG as well as the extracellular Na+, K+, Cl- increases by 20-30 sec. Since the cortical pO2 decreased first and the ion changes lagged behind the onset of vasodilatation by 20-30 sec, it is suggested that the CBF increase in hypoxia is mediated via the cortical pO2 decrease. b) A significant NAD reduction was already present after 20 sec. of nitrogen breathing. Since the ECoG and MABP decreased, and K+ activity increased much later than this, it is presumed that the NAD reduction during the first 30-40 sec of anoxia indicates an increased rate of glycolysis, but not mitochondrial hypoxia. c) In the predepolarization phase a 17% K+, 4% Na+, 5% Cl- increase is probably the result of a reduction of the extracellular spaces caused by water movement and by the migration of Na+ and Cl- from the extracellular to the intracellular space. The large K+, Na+, Cl- changes during terminal depolarization can be interpreted as a result of the failure of the membrane bound Na+ -K+ pump and of the altered ion permeability of the cell membranes.

Action Potentials↗

PubMed1979

Intracellular oxygen tension and energy metabolism in the cat brain cortex during haemorrhagic shock.

The changes in intracellular oxygen tension and energy metabolism of the cat brain cortex were studied by surface fluororeflectometry during haemorrhagic shock. The results may be summarized as follows. (a) Intracellular oxygen tension, i.e. the maximum cortical NAD reduction obtained during nitrogen gas inhalation decreased gradually during the hypovolaemic phase of shock and finally, the brain cortex became ischaemic. (b) Partial uncoupling of the cerebrocortical mitochondrial respiration and oxidative phosphorylation appeared in the very early period of bleeding, as indicated by the overshot of the cortical NAD/NADH redox state towards oxidation subsequent to the cessation of nitrogen gas inhalation. Partial uncoupling of mitochondrial respiration and oxidative phosphorylation became more pronounced during the later phases of bleeding, finally, the mitochondrial electron transport stopped. In line with these changes the frequency and the amplitude of ECoG decreased gradually and markedly during the hypovolaemic phase of shock. (c) Microcirculation and energy metabolism of the cat brain cortex were severely and irreversibly damaged during the hypovolaemic phase of shock. This was clearly shown by the fact that in the majority of experiments the nitrogen anoxia after reinfusion failed to bring about changes in the cortical NAD/NADH redox state and the ECoG changes occurred during bleeding did not improve after reinfusion. It is concluded that the early disturbances of cerebrocortical energy metabolism play an important role in the development of neural and vascular lesions of the brain that occur during haemorrhagic shock.

Action Potentials↗

PubMedDate not supplied

[Role of the median forebrain bundle in organizing the electrical activity of the neocortex].

Bilateral coagulation of the forebrain medial bundle in the lateral hypothalamus enhances the formation of spontaneous spindles and facilitates the recruiting response in the neocortex. This combines with a defect of desynchronizing influences of the posterior hypothalamus and the concurrent dominance of synchronizing effects of the preoptic area (PA). PA stimulation enhances the slow wave and spindle activity in the ECoG of the intact brain. After disruption of PA connections with the bulbar synchronizing apparatus the stimulation effect is manifested only in enhanced spindle activity. It is assumed that in addition to hypnogenic influences which PA shares with the parasolitary apparatus, it maintains a definite level of cortical reactivity after the onset of sleep. Elimination of the orbito-frontal cortex, as well as PA coagulation, does not prevent the appearance of spindles in the ECoG of the preparation with an intersected medial bundle, only limiting them to some extent.

Animals↗

PubMedDate not supplied

[Theory of EEG potential in a model of the thin membranes of the brain].

The methods of estimating a momentary value of the epidural potential using several values of EEG, sampled at the same instant, are explored theoretically. The weights of the summation of these EEG-potentials for the case of simple disposition of electrodes, are single-valued by means of elementary consideration of the potential theory and symmetry. The space filters of EEG obtained in such a way, were analysed on the basis of the model of thin integuments of the brains. The systems of 4--8 electrodes on the scalp are proposed for the estimation of mono- and bipolar ECoG's, which are less sensitive to ECoG of the remote cortex than ordinary derivations of EEG.

Cerebral Cortex↗

PubMed1979

Impairment of cerebral blood flow autoregulation after hypertonic urea administration.

The effect of unilateral intracarotid administration of 3 M urea on resting cerebral blood flow, arterial blood pressure, perfusion pressure-cerebral blood flow relation, ECoG and Evans blue permeability was tested in dogs. The injection of urea was without effect on ECoG and enhanced the arterial blood pressure temporarily. Cerebral blood flow measured 10 min after the urea injection was not affected. Extravasation of Evans blue was observed in the urea-perfused hemisphere for about 40 min following the urea administration. Cerebral perfusion pressure-blood flow relation for the urea affected hemisphere studied at the time when blood-brain barrier to protein was restored revealed loss of the normal autoregulatory response, despite that it was preserved in the control hemisphere.

Animals↗

PubMed1975

[Influence of the anterior and posterior hypothalamus on the conditioned reflex activity and delayed responses of lower simians].

In 4 adult monkeys, electrical stimulation of the anterior hypothalamus followed by subsidence in the animal and the ECoG synchronization evoked also an impairment of conditioned reflex activity and a decrease in the test performance during delayed responses. Strong stimulation of the posterior hypothalamus followed by emotional arousal and desynchronization in the ECoG, on the contrary, improved the conditioned reflex activity and increased the level of the test performance. The hypothalamus is then supposed to play a certain role in memory as an emotiogenic structure.

Animals↗