Antiepileptic effects of cerebellar nucleus dentatus electrical stimulation under different conditions of brain epileptisation

It was shown in acute experiments on cats that high frequency (100-300 Hz) electrical stimulation of dentate nucleus led to the solitary epileptic foci of relatively weak intensity suppression and at the same time caused the activation of stronger focal epileptic activity. Electrical stimulation of nucleus dentatus suppressed the epileptic activity of grand mal type and increased seizures in rats with petit mal form of epileptogenesis which was formed in rats during pentylenetatiozol kindling. It was concluded that there is a relation between the antiepileptic effects of nucleus dentatus irritation and intensity as well as the form of epileptic activity induced experimentally.     

A GABA-EEG test of the blood-brain barrier near epileptic foci

The permeability of the blood-brain barrier (BBB) to gamma-aminobutyric acid (GABA) in the region of an epileptic focus may be assessed by infusing GABA and measuring a change in epileptic spike activity on the EEG. GABA does not cross the normal BBB but will suppress epileptic spike activity when it does cross where the BBB is damaged. 9 alumina-cobalt experimental epileptic foci were all initially suppressible, but 7 then became unsuppressible . When the foci were irradiated to lower the BBB, all 7 became temporarily suppressible. The experiments demonstrate that (1) epileptic foci can be equally active both with the BBB 'open' and 'closed'; (2) the intravenous GABA-EEG test can detect whether the BBB near the epileptic focus is open to GABA, and (3) anatomic tests of BBB integrity (in these experiments intravenous trypan blue) cannot determine if whether BBB near the focus is 'open' to GABA. Since the intravenous GABA-EEG test reveals the permeability of the BBB in the immediate environment of the epileptic focus, it may be very useful in the selection of a susceptible therapeutic group for inhibitory amino acid therapy.     

Effect of diazepam on the Na, K-ATPase state in a penicillin--induced hyperactivity focus in the cerebral cortex]

Intramuscular injection of diazepam to rats at doses of 0.01 and 2 mg/kg 25-30 min after penicillin application to the rat brain cortex leads to alteration of periodic appearance of epileptic seizures (ES), to changes in the seizure pattern, and to emergence of periodic acceleration of epileptiform discharges (ED). Injection of diazepam at a dose of 2 mg/kg 20 min before penicillin application results in the reduction of ED latency in the epileptogenic focus and in a decrease in their frequency before seizures as compared to the control animals without diazepam injection. ES appear irregularly, their quantity is markedly reduced while duration is increased. Diazepam injection leads to disappearance of the rat moving reaction during ER and ES. In vivo experiments diazepam (2 mg/kg) does not influence brain cortex Na, K-ATPase of crude synaptosomes. However, diazepam leads to an increase in Na, K-ATPase activity both in the primary and dependent secondary epileptogenic foci. It is suggested that the anticonvulsant action of diazepam may be underlain by its activating effect on Na, K-ATPase of neuronal membranes in the epileptogenic focus.     

Defects in the medial entorhinal cortex and dentate gyrus in the mouse model of Sanfilippo syndrome type B

Sanfilippo syndrome type B (MPS IIIB) is characterized by profound mental retardation in childhood, dementia and death in late adolescence; it is caused by deficiency of α-N-acetylglucosaminidase and resulting lysosomal storage of heparan sulfate. A mouse model, generated by homologous recombination of the Naglu gene, was used to study pathological changes in the brain. We found earlier that neurons in the medial entorhinal cortex (MEC) and the dentate gyrus showed a number of secondary defects, including the presence of hyperphosphorylated tau (Ptau) detected with antibodies raised against Ptau in Alzheimer disease brain. By further use of immunohistochemistry, we now show staining in neurons of the same area for beta amyloid, extending the resemblance to Alzheimer disease. Ptau inclusions in the dentate gyrus of MPS IIIB mice were reduced in number when the mice were administered LiCl, a specific inhibitor of Gsk3β. Additional proteins found elevated in MEC include proteins involved in autophagy and the heparan sulfate proteoglycans, glypicans 1 and 5, the latter closely related to the primary defect. The level of secondary accumulations was associated with elevation of glypican, as seen by comparing brains of mice at different ages or with different mucopolysaccharide storage diseases. The MEC of an MPS IIIA mouse had the same intense immunostaining for glypican 1 and other markers as MPS IIIB, while MEC of MPS I and MPS II mice had weak staining, and MEC of an MPS VI mouse had no staining at all for the same proteins. A considerable amount of glypican was found in MEC of MPS IIIB mice outside of lysosomes. We propose that it is the extralysosomal glypican that would be harmful to neurons, because its heparan sulfate branches could potentiate the formation of Ptau and beta amyloid aggregates, which would be toxic as well as difficult to degrade.     

Effect of nicotinamide on epileptic activity in the cerebral cortex

The experiments on cats showed that intravenous administration of nicotinamide suppresses the epileptic activity in a solitary epileptic focus as well as in the complex of epileptic foci produced by strychnine application to various cortical zones under the influence of the most powerful focus that plays the role of a determinant. After the intravenous injection of nicotinamide (50-70 mg/kg) the complex was destabilized and broken down. The epileptic activity in the dependent foci of the complex disappeared first in the more remote from the determinant focus and then in the nearer one. The determinant focus was the last to disappear. The inhibitory effect of nicotinamide is associated with antiepileptic activity. Nicotinamide is suggested to be one of the endogenous drugs which may suppress brain hyperactivity and activate the antiepileptogenic system.     

Effect of the delta sleep peptide on epileptic activity in the cerebral cortex of rats and cats

In free behaviour experiments on rats it has been shown that the intraperitoneal injection of delta sleep-inducing peptide (DSIP) (100 micrograms/kg) suppressed penicillin-induced relatively moderate epileptic foci which generated spike potentials as well as severe foci with ictal epileptic discharges. In the experiments on cats it was shown that intravenous DSIP injection (100 micrograms/kg) suppressed strychnine-induced epileptic focus and complexes of epileptic foci.     

Levels of Catechols in Epileptogenic and Nonepileptogenic Regions of the Human Brain

Recent reports about tyrosine hydroxylase and alpha 1-adrenoceptors in epileptic foci have suggested increased regional catecholaminergic activity, which may serve a compensatory, inhibitory role. We measured levels of catechols, including the precursor 3,4-dihydroxyphenylalanine (DOPA) and the catecholamines dopamine (DA) and norepinephrine (NE), in surgically removed foci identified by electrocorticography and in nonepileptogenic sites from 23 patients with intractable temporal lobe epilepsy. The following values (mean +/- 1 SD) were obtained: DOPA = 142 +/- 60 ng/g of protein in the focus vs. 115 +/- 39 ng/g in the nonfocus (p less than 0.01); DA = 168 +/- 85 vs. 106 +/- 54 ng/g (p less than 0.001); and NE = 267 +/- 117 vs. 181 +/- 80 ng/g (p less than 0.001). The results are consistent with increased catecholaminergic activity in epileptic foci.     

Enhancement of the antiepileptic efficacy of diazepam at electrical stimulation of the cerebellar cortex

The action of diazepam (0.5 and 1.5 mg/kg, i.v.) on epileptic foci induced by benzylpenicillin (10,000 IU/ml) applications onto thesulc. sygmoid post. was studied in acute experiments on cats. It is demonstrated that under conditions of preceding electrical stimulation of the cerebellar vermis, diazepam more significantly suppresses the epileptic activity than when it is administered to intact animals.     

Anticonvulsant properties of the cerebrospinal fluid during activation of the antiepileptic system of the brain

Cerebrospinal fluid (CSF) was obtained after 30-40 sessions of daily electrical stimulation of the cat cerebellum vermis. The intraventricular injection of CSF (10 microliters) to Wistar rats increased the latent period of initial seizure manifestations, significantly reduced the number of animals with seizures and reduced the severity of seizures induced by korazol injection (40 mg/kg). Analogous seizure changes were observed in rats after intraventricular injection of CSF (10 microliters) from cats subject to 3-10 electroshock seizure fits. Intraventricular injection of CSF (250 microliters) obtained from cats after electroshock to cats with strychnine-induced epileptic foci in the brain cortex led to the suppression of the epileptic activity. The conclusion was made that different ways of antiepileptic system activation cause the accumulation of endogenous antiepileptic substances in CSF.     

Formation of epileptic activity complexes in the cerebral cortex as a result of a determinant focus induced by acetylcholine]

Foci of increased excitability were created by means of weak strychnine and penicillin dilutions in experiments on cats. These foci worked at individual regimens. Creation with acetylcholine and proserine of a hyperactive focus led to increase of the amplitude and frequency of convulsive discharges at first in the nearest activity foci, and then in the ones remote from the hyperactive focus. The next stage was attended by qualitative changes in the activity pattern of strychnine and penicillin foci (the appearance of acetylcholine activity in them) and by the formation of a single functional focal complex working in the regimen of acetylcholine focus. Thus, the latter played the role of a determinant structure. Suppression of the determinant focus activity led to disappearance of the acetylcholine activity in all the other foci, restoration of the initial (penicillin and strychnine) activity, and to the epileptic complex decay.     

Effect of verapamil on focal epileptic activity in the rat cerebral cortex

Experiments were carried out on 64 nonanesthetized male Wistar rats (200-220 g). Epileptic foci were induced by the application of a filter paper saturated with a solution of benzylpenicillin sodium salt (12,000 and 20,000 U/ml) to the sensorimotor cortex. It was shown that subsequent intraperitoneal administration of verapamil (5 mg/kg and 10 mg/kg) during steady focal epileptic activity (EpA) resulted in the suppression of EpA in most animals. The antiepileptic effect of verapamil was manifested in a reduced frequency and amplitude of spike discharges, decreased power of epileptic foci and less frequent appearance of seizure (ictal) discharges. The role of Ca canals of neuronal membranes in the pathogenesis of epilepsy is discussed.     

Changes in the activity of gamma-amino butyric acid transaminase and succinic semialdehyde dehydrogenase in the cobalt and iron experimental epileptogenic foci in the rat brain

GABA-transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSA-DH) activities were measured in the mitochondrial fractions from the cobalt- and FeCl3-induced chronic epileptogenic foci in the rat brain. Electroencephalographically, the FeCl3 epileptogenic focus remained active for a duration longer than that of the cobalt focus. In both the foci SSA-DH activity showed significant increases which were concomitant with the EEG epileptiform activity. In cobalt focus, the GABA-T activity fell whereas, in the FeCl3 focus it was unchanged. In cobalt focus fall in GABA-T activity seemed to be concomitant with EEG epileptiform discharge. The measurements of the enzyme activities in the mirror (secondary) foci showed that, except for a brief stimulation of SSA-DH activity in the mirror focus in FeCl3 epileptic animals, the enzyme activities remained unchanged. Possible significance of the observed enzymatic changes in the physiology of epileptogenic focus is discussed.     

Changes in the Na, K-ATPase of neuronal membranes in penicillin-induced epileptic foci in the cerebral cortex of the rat]

The relationship between electrophysiological changes and Na, K-ATPase activity of neuronal membranes in sodium penicillin-induced epileptic foci was studied. Na,K-ATPase activity is inhibited both in the primary focus and in homotopic contralateral area during latent period and in the stage of forming epileptic activity. In the stage of marked convulsive activity Na, K-ATPase is inhibited only in the primary focus. It is shown that penicillin at a concentration range of 2 x 10(-6)--2 x 10(-3) M does not influence Na,K-ATPase activity of crude synaptosomes of the rat brain cortex. It is suggested that Na,K-ATPase inactivation may serve as a pathogenetic factor in the development of convulsive process.     

Effect of paleocerebellar cortex electrical stimulation on generalized penicillin-induced seizure activity in rats

It was shown that low-frequency electrical stimulation (ES) (10-12 Hz, 0.5 ms) of paleocerebellar cortex (nodulus, uvula) is followed by activation of spike discharges which were induced via i.p. administration of sodium benzilpenicillin salt to alert Wistar rats (300,000 IU/kg). The facilitation of ictal discharges generation was also seen in the course of such an ES. High-frequency (100-300 Hz, 0.25 ms) ES of the same structure was followed by suppression of spike discharges and prevented the ictal discharges precipitation. Antiseizure action was obvious under condition of relatively low level of epileptic activity generation. In the course of such ES the decreasing frequency and amplitude of spike discharges were noted during interstimuli periods. Besides, the life-span of seizure activity was shortened as well. The repeated paleocerebellar ES made after electrocoagulation of irritated tissue did not cause modulations of seizure activity.     

Influence of clonazepam on cortical epileptogenic foci in the rat

The antiepileptic action of clonazepam was studied on epileptogenic foci induced by penicillin in sensorimotor cortex in acute experiments in rats. Clonazepam (1 mg/kg intraperitoneally) only moderately decreased the frequency of interictal discharges of single cortical focus and delayed the propagation of discharges into the ipsilateral occipital region. On the contrary, clonazepam failed to influence the callosal projection of interictal discharges in single unilateral as well as in two symmetrical foci. Spontaneous transition of interictal discharges into ictal phases regularly seen when two symmetrical foci were formed was only delayed but not blocked by clonazepam. It may be concluded that clonazepam exhibits only a weak anticonvulsant action against cortical foci and against secondary generalization of epileptic activity.     

Contrasting effects of stimulation of the caudate nucleus and globus pallidus on paroxysmal hippocampal activity in the cat

The different actions exerted by pallidum and caudate nucleus on electrically induced epileptic activity of hippocampus were analyzed. Caudate appeared to inhibit hippocampal after discharges duration (HAD) while the globus pallidus exerted a facilitatory effect on HAD duration. Both effects were maximal when conditioning stimulation immediately preceded hippocampal test stimulation. The results are discussed considering reciprocal functional connections of the two striatal structures.     

Comparative characteristics of spatial hearing of patients with different forms of cortical epilepsy

Perception of signals modeling directed movement of a sound source by three groups of patients with (1) temporal epilepsy, (2) epileptic foci in the frontal region, and (3) the epileptic syndrome due to local organic lesions in the temporal or frontal lobes was studied. It was established that the features and degree of spatial (binaural) hearing disorders in temporal epilepsy were determined not only by the localization and the extent of a lesion in the temporal lobe, but also by the areas beyond it that were involved in the epileptic process. Patients with organic lesions (tumors, cysts) involving the temporal lobe cortex may reveal more severe spatial hearing disorders than temporal epilepsy patients with the same localization of the foci of convulsive activity. A relatively isolated lesion of the frontal region cortex does not influence the assessment of the parameters of moving sound signals used. Possible neurophysiological mechanisms underlying the found spatial hearing disorders as well as the possibility of using the results obtained to solve the problems of differential diagnosis are considered.     

Structural Remodeling of the Neuronal Network in the Dentate Gyrus of the Epileptically Transformed Murine Hippocampus

Immunohistochemical analysis of the hippocampus of a transgene mutant line of the mice (genetic model of temporal epilepsy) demonstrated a progressive increase in the level of brain-derived neurotrophic factor (BDNF) in granular cells of the dentate gyrus and their axons; this increase correlated with an enhancement of the level of epileptic activity. Epileptogenic reprojection of mossy fibers toward an internal zone of the molecular layer of the hippocampus was also observed. In addition, we observed excessive spreading of the zone of axon branching of GABA-ergic basket cells, as compared with the norm; their maximum collateralization was found within an internal zone of the molecular layer of the dentate gyrus. This allows us to hypothesize that the processes of sprouting of the mossy fibers and recovery of recurrent inhibition of the granular cells are interrelated.     

Role of the pulvinar-lateralis posterior nucleus complex (P-LP) in the experimental epilepsy of the cat

The ability of the pulvinar-lateralis posterior nucleus complex (P-LP) to evoke epileptic activity when stimulated, was studied in 20 adult cats. Twelve animals were analyzed after they recovered from the surgical procedure (chronic model). In seven of them a cannula with electrodes was implanted in the P-LP and one twisted bipolar electrode was placed ipsilaterally in the following structures: hippocampus, superior colliculus, caudate nucleus and cerebral cortex. Through the cannula Na penicillin was injected. The electrodes allowed both to stimulate and to record the electrical activity. In the remaining five cats, the cannula was implanted in hippocampus in order to compare its sensitivity to generate epileptic activity to that of P-LP. Another group of eight cats were surgically implanted and studied in the same day (acute model). In four of them the cannula was placed in the P-LP through the temporal pathway, to avoid crossing the hippocampus and the ventricle. In another four, penicillin was injected in the P-LP after suctioning the cerebral cortex and the hippocampus overlying the former structure. Epileptic activity could be induced in P-LP and it spread rapidly to hippocampus and after a while to the other implanted structures. This was observed both with penicillin and electrical stimulation. The sensitivity of P-LP to generate epileptic activity was lower than that of the hippocampus. In particular, it was necessary to use two to ten times more penicillin and three times the electrical current intensity in the P-LP as compared to the values needed in the hippocampus. These results are discussed in view of the controversial problem about the ability of the thalamus to generate and spread epileptic activity.     

An antagonist of GABA-B receptors potentiates activity of cortical epileptic foci

Cortical epileptic foci elicited by local application of bicuculline methiodide represent a model of interictal epileptic activity with a transition into ictal phases. We studied a role of GABA-B receptors in this model using GABA-B receptor antagonist CGP35348 in adult rats with implanted cortical electrodes and cannula. CGP35348 (100 or 200 mg/kg i.p.) did not affect interictal discharges but it augmented ictal activity. Latency to the first ictal episode was decreased by the lower dose of CGP35348, duration of episodes was increased by the higher dose. GABA-B receptor antagonist did not influence purely cortical epileptic phenomenon but it is proconvulsant in ictal activity generated with participation of subcortical structures.