Audiogenic kindling in WAG/Rij rats: change in behavioral and electrophysiological responses to repetitive short acoustic stimulation

Running and tonic convulsions induced by sound stimulation (audiogenic seizures, AS) are known to be brainstem-dependent, but their repeated induction leads to the recruiting forebrain structures into AS expression manifested by the development of clonic convulsions and cortical epileptic activity (audiogenic kindling). Behavioral and electrophysiological manifestations of audiogenic kindling were studied in AS-prone WAG/Rij rats exhibiting two types of genetically determined generalized seizures: convulsive audiogenic and nonconvulsive absence (spontaneous spike-wave discharges generated by thalamocortical circuits). Twenty three repeated (with 2 days intervals) sound stimulations inducing a short running episode led to a progressive increase in AS duration from 6.2 +/- 0.4 s to 24.7 +/- 2.9 s mainly due to the appearance of additional postrunning facial-forelimb clonic convulsions of increasing duration and severity. Fully kindled (Racine's stage 5) seizures were accompanied by a bilateral slow-potential wave of cortical spreading depression (SD) nonsynaptically propagating to both striata and by a long-term postictal suppression of spontaneous absence seizures. Neither corticostriatal SD, nor the spike-wave discharges suppression were observed after running induced by sound in non-kindled rats or by attenuated (subthreshold for clonus) sound in kindled rats. Subthreshold stimulation of kindled rats provoked postictal high-amplitude spiking in the cortex. It is concluded that the recruitment of the cortex into a kindled AS network triggers a corticostriatal SD which may underlie the postictal inhibition of non-convulsive seizures, which follow the kindled AS.     

Influence of cerebro-spinal fluid of picrotoxin kindled rats on seizure susceptibility and locomotor activity of recipients.

Repeated picrotoxin administration (ip) in subthreshold doses in rats resulted in kindling of generalized seizures. Decrease of locomotor activity in kindled rats occurred in interictal periods. Intra-cerebroventricular microinjection to intact recipients of cerebrospinal fluid (CSF) of kindled but not intact rats or those after acute picrotoxin-induced convulsions, induced a decrease of locomotor activity and severity of acute picrotoxin induced seizures. These effects of CSF were blocked by naloxone pretreatment and were absent after injection of CSF to which protease inhibitors were not added. It is concluded that the release of endogenous opioid peptide substance(s) takes place in CSF of kindled animals which cause the interictal decrease of locomotor activity and may play the role of endogenous anticonvulsive factors controlling epileptic activity induction.     

Amygdala kindled seizure stage is related to altered benzodiazepine binding site density

Benzodiazepine receptor binding was examined in rats at 3 stages of amygdaloid kindling (i.e., initial afterdischarge, Stage 3 and Stage 5) immediately or 24 hr after seizure. 3H-diazepam binding site density (Bmax) was significantly increased 24 hr after Stage 3 and Stage 5 kindled seizures in the hippocampus but not in the amygdala. There were no significant differences in the dissociation constants (KD) between kindled and control rats at any time point examined for either brain region. These results demonstrate that changes in benzodiazepine binding are observed with partial kindled seizures (i.e., Stage 3), indicating that generalized seizures are not prerequisite to increased benzodiazepine receptor site density.     

Generalized convulsive seizures are associated with ketamine anesthesia in a rhesus macaque (Macaca mulatta) undergoing urodynamic studies and transcutaneous spinal cord stimulation

A female rhesus macaque developed two episodes of generalized convulsions during transcutaneous spinal cord stimulation (TSCS) and urodynamic studies under ketamine anesthesia. The seizures took place in the absence of active TSCS and bladder pressure elevation. Ketamine anesthesia remains the primary risk factor for the convulsions during these experimental procedures.     

Na, K-ATP-ase and acetylcholinesterase activity of the membrane structures of the rat brain and spinal cord during the seizure process]

The activity of ATP-ase and acetylcholinesterase (AChE) in crude mitochondrial fraction (CMF) and microsomal fraction of rat brain cortex and the spinal cord was studied in clonic seizures evoked by electroshock and 5 min after them. Inhibition of the Na, K-ATP-ase activity of the CMF of the brain at the clonic phase of convulsions and an increase in the activity of this enzyme in all the fractions of the tissues under study at the postconvulsive period were revealed. The activity of Ca-ATP-ase in the CMF of the brain increased during the convulsions and decreased at the postconfulsive period. The activity of Mg-ATP-ase remained unchanged. The AChE activity, as a rule increased during the convulsions, and grew even more during the postconvulsive period; the spinal cord tissue displayed a reduction of the activation effect. A possibility of structural reconstructions in the excitable neuron membranes during the convulsive activity is discussed.     

Repeated 6-Hz Corneal Stimulation Progressively Increases FosB/ΔFosB Levels in the Lateral Amygdala and Induces Seizure Generalization to the Hippocampus

Exposure to repetitive seizures is known to promote convulsions which depend on specific patterns of network activity. We aimed at evaluating the changes in seizure phenotype and neuronal network activation caused by a modified 6-Hz corneal stimulation model of psychomotor seizures. Mice received up to 4 sessions of 6-Hz corneal stimulation with fixed current amplitude of 32 mA and inter-stimulation interval of 72 h. Video-electroencephalography showed that evoked seizures were characterized by a motor component and a non-motor component. Seizures always appeared in frontal cortex, but only at the fourth stimulation they involved the hippocampus, suggesting the establishment of an epileptogenic process. Duration of seizure non-motor component progressively decreased after the second session, whereas convulsive seizures remained unchanged. In addition, a more severe seizure phenotype, consisting of tonic-clonic generalized convulsions, was predominant after the second session. Immunohistochemistry and double immunofluorescence experiments revealed a significant increase in neuronal activity occurring in the lateral amygdala after the fourth session, most likely due to activity of principal cells. These findings indicate a predominant role of amygdala in promoting progressively more severe convulsions as well as the late recruitment of the hippocampus in the seizure spread. We propose that the repeated 6-Hz corneal stimulation model may be used to investigate some mechanisms of epileptogenesis and to test putative antiepileptogenic drugs.     

The effect of multiple audiogenic seizures upon the sleep organization in rats

The organization of sleep during and after frequentative convulsions, consisting of 2, 3, or 5 comparatively rare seizures (following one another with a 90-minute interval) or of 3, 5 or 9 comparatively frequent seizures (following one another with a 45-minute interval) of generalized tonic-clonic character in Krushinskii-Molodkina strain rats with inherited predisposition to audiogenic convulsions, was studied. In frequentative convulsions with rare seizures, between separate seizures, passive wakefulness (75.2 +/- 4.6% time) prevailed under low (24.8 +/- 4.3%) slow-wave sleep and full absence of fast-wave sleep. In rats under frequentative convulsions with frequent seizures, in interictal period, only passive wakefulness was observed under reduction of slow-wave sleep and fast-wave sleep, i.e. total sleep deprivation. Minimal latensy of first episodes of the slow-wave sleep after frequentative convulsions was 59.9 +/- 10.8, and of fast-wave sleep: 158.2 +/- 13.4 min. First episodes of slow-wave sleep and fast-wave sleep had normal structure, though they were lesser and shorter than in control experiments. In spite of long-lasting (up to 7 hrs) absence of slow-wave sleep during seizure and prolonged (8.5 hrs) reduction of fast-wave sleep with no subsequent compensatory increase, these conditions occurred in the wakefulness-sleep cycle during 12-hour reconstruction after convulsions. The reconstruction period after frequentative convulsions was characterized by increase in general share of wakefulness and reduction of total slow-wave and fast-wave sleep as compared with control data. Paroxysmal status seems to disorganize work of the brain somnogenic structures. The function of systems responsible for slow-wave sleep are affected to a lesser extent, but disorganization of the system responsible for fast-wave sleep is more significant and associated with mechanisms of starting the phase of sleep in the first place.     

Kindling of the limbic structures with a shortened interstimulus interval

We investigated the possibility to produce hippocampal or amygdala kindling syndrome in rabbits which had been electrically stimulated at a fixed interval between stimuli at 5 min. Animals were prepared with chronically implanted electrodes (neocortex, hippocampus, amygdala, nucleus caudatus). The initial stimuli produced only localized effect, but repeated applications of the stimuli progressively increased the seizure activity resulting in generalized kindled convulsions after 2-4 h period. At the first stage generalized seizures were followed by long lasting refractory period, but at the end of the procedure almost all stimuli evoke major motor seizures and recurrent widely spread electrographic epileptic changes. The most noteworthy findings emerging from this study is the inhibition of postictal seizure inhibition period. This effect was independent of whether stimulated the electrode was positioned in the hippocampus or amygdala, but the hippocampal formation occupied the central position for the once and propagation of the seizure activity in all cases. When established this syndrome persisted without any attenuation for some weeks. It was concluded that this model of rapid development of kindling syndrome is useful for investigation of the nature of epilepsy and postictal seizure inhibition.     

Neuropharmacological actions of panchagavya formulation containing Emblica officinalis Gaerth and Glycyrrhiza glabra Linn in mice

A panchagavya Ayurvedic formulation containing E. officinalis, G. glabra, and cow's ghee was evaluated for its effect on pentobarbital-induced sleeping time, pentylenetetrazol-induced seizures, maximal electroshock-induced seizures, spontaneous motor activity, rota-rod performance (motor coordination) and antagonism to amphetamine in mice. The formulation (300, 500 mg/kg, po) produced a significant prolongation of pentobarbital-induced sleeping time and reduced spontaneous locomotor activity. The formulation also significantly antagonised the amphetamine induced hyper-locomotor activity (500, 750 mg/kg, po) and protected mice against tonic convulsions induced by maximal electroshock (500, 750 mg/kg, po). The formulation slightly prolonged the phases of seizure activity but did not protect mice against lethality induced by pentylenetetrazole. The formulation did not show neurotoxicity. The results suggest that the panchagavya formulation is sedative in nature.     

The role of the opiate mechanisms of the hippocampus and substantia nigra in the behavioral and convulsive disorders in picrotoxin-induced kindling]

It was shown in the experiments on rats that the repeated picrotoxin administration resulted in the kindling of generalized seizures. Generalized convulsions were followed by the development of either postictal depression or explosiveness. The injection of mu-opiate agonist met-enkephalin into hippocampus of kindled rats resulted in the increase in the severity of seizure reactions which were induced by picrotoxin and also in the increase in the number of animals with postictal explosiveness. The injection of dynorphin-A-1-13 (kappa-opiate agonist) into substantia nigra reticulata induced the locomotor depression which was like one in postictal period and resulted in the decrease of picrotoxin-induced seizures severity. It was concluded that mu-opiate system of hippocampus took part in the formation of generator of pathologically enhanced excitation in the structure during kindling and the development of seizure syndrome, providing also the postictal explosiveness. Kappa-opiate system of substantia nigra plays an important role in the activation of the antiepileptic system, limitation of seizures and the development of postictal depression.     

Neuroanatomical localization of structures responsible for seizures in the GEPR: lesion studies

Identification of the neural substrates subserving audiogenic convulsions in the GEPR is an important task and while it is not yet complete, many laboratories employing various techniques have contributed importantly to our current understanding. The present review focuses on the use of lesions to identify the neural substrates of audiogenic convulsions. Lesions in brain stem nuclei appear to have a much greater ability to attenuate audiogenic convulsions than do forebrain lesions. In fact, some forebrain lesions (dorsal hippocampus, caudate, intralaminar thalamic nuclei) appear to enhance the severity of audiogenic seizures. On the other hand, bilateral lesions in the inferior colliculus (IC) have been shown to completely abolish audiogenic convulsions, while lesions in the pontine reticular formation (PRF nucleus) abolish all aspects except the running episode suggesting that these two brain stem structures are important neural substrates involved in the expression of audiogenic convulsions. Large bilateral lesions of the substantia nigra also appear to attenuate audiogenic convulsions. The effect of lesions on audiogenic convulsions is basically similar to their effect on other generalized seizure models and the data appear to support the hypothesis that there are two anatomical systems involved in the expression of all generalized convulsions: a forebrain system responsible for the expression of face and forelimb clonus; and a brain stem system responsible in the expression of running-bouncing clonus and tonus.     

An avian model of genetic reflex epilepsy

The Fayoumi strain of chickens (Fepi) carries a recessive autosomal gene mutation in which homozygotes are afflicted with a photogenic and audiogenic reflex epilepsy. Seizures consist of stimulus-locked motor symptoms followed by generalized self sustained convulsions. EEG recordings show spikes and spike and waves patterns at rest which are suppressed during seizures and replaced by a desynchronized pattern of activity. Neurones of the prosencephalon discharge in bursts at rest, while neurones of the mesencephalon are bursting during seizures. Living neural chimeras were obtained by replacing specific embryonic brain vesicles in a normal chicken embryo with equivalent vesicles from a Fepi donor. These chimeras show that the epileptic phenotype can be totally or partially transferred from the Fepi to the normal chickens. Total transfer of photogenic and audiogenic seizures was obtained by substitution of both the prosencephalon and mesencephalon, while substitution of the prosencephalon alone resulted in transfer of interictal paroxysmal activity and substitution of the mesencephalon alone resulted principally in transfer of ictal motor symptoms. Increased expression of the c-fos protooncogene, as revealed by the western blot technique, confirmed the distinct encephalic localizations of the symptoms of the photogenic and audiogenic reflex epilepsy of the Fepi shown with the methods of electrophysiology and brain chimeras. We conclude that the Fepi is a good model of brain stem reflex epilepsy and suggest that the brain stem is a generator of some other animal and human genetic reflex "epileptic syndromes".     

Effects of antiepileptic drugs on brain energy reserves during convulsions

Cerebral cortical ATP, P-creatine, glucose, and lactate were measured 6 sec after 1 sec of 150/sec rectangular pulses, at 0,20 v, 40 v, 60 v, 80 v, or 100 v, applied to the heads of intact mice which had been given either no drug, phenobarbitone (25 mg/kg), trimethadione (600 mg/kg), or diphenylhydantoin (40 mg/kg), intraperitoneally. In general, regardless of stimulus strength or drug used, animals which exhibited maximal (tonic-clonic) convulsions showed similar striking decreases in brain P-creatine, decreases in ATP and glucose, and increases in lactate. On the other hand, in animals which exhibited less than maximal clinical response, there was little or no change in these metabolites. An exception was the case of diphenylhydantoin. Tonic-clonic seizures did not occur after diphenylhydantoin administration, even with 100 v stimuli, but substrate changes at this voltage were, nevertheless, similar to those observed in brains of other mice undergoing maximal convulsions.     

The effect of taurine on kindled seizures in the rat

Recently, it has been reported that taurine, an amino acid with anticonvulsant properties, does not suppress experimental seizures generated by the "kindling" technique. This finding seems somewhat paradoxical since taurine antagonizes other sorts of experimental convulsion and since kindled seizures are easily suppressed by other anticonvulsant drugs. Further tests were therefore conducted during which taurine's anticonvulsant effects were assessed: (1) when kindling stimulation was dropped to near-threshold levels; (2) when cortical as well as limbic kindled foci were stimulated; (3) when developing as well as fully kindled seizures were involved; and (4) when taurine was introduced directly into the ventricles of the brain. Even in these tests which were specifically designed to favour the appearance of anticonvulsant effects, no taurine antagonism of kindled seizures was found.     

Anti-epileptic effect of the new calcium channel blocker IOS-1.1212]

In experiments on freely moving male Wistar rats it was shown that IOS-1.1212 (1,4-dihydropyridine) in a dose 2 and 10 mg/kg (i. p.) suppressed the penicillin-induced focal epileptic activity in cerebral cortex. Similar suppressing effect of IOS-1.1212 was shown on acute generalized tonic-clonic pentylenetetrazol (PTZ) seizures (75 mg/kg i. p.) and on chronic PTZ administration (PTZ-kindling, 30 mg/kg i. p. during 30 days): when injected 30 min before each PTZ administration it delayed the development of kindling-induced seizures susceptibility in randomized animals (series 1) and attenuated the severity of seizures in PTZ-sensitive animals (series 2). However, IOS-1.1212 had no effect on the strychnine-induced focal epileptic activity. In male Icr:Icl mice IOS-1.1212 in a dose 1.5 and 5 mg/kg also influenced the PTZ convulsions (i. v. titration of 1% solution at a rate of 0.01 ml/s) and had no effect on the strychnine convulsions (i. v. titration of 0.01% solution at a rate of 0.01 ml/s) and on maximal electroshock. In addition, IOS-1.1212 significantly increased antiepileptic effect of phenobarbital on maximal electroshock.     

Role of the brain-stem reticular formation in tonic-clonic seizures: lesion and pharmacological studies

Bilateral lesions of the pontine tegmentum involving the superior cerebellar peduncles and the nucleus reticularis pontis oralis have been shown to attenuate the tonic components of maximal seizures induced by electroshock, sound stimulation (audiogenic), or pentylenetetrazol, although having no effect on clonus in three separate seizure models. The pontine tegmental lesion also abolishes the clonus of minimal audiogenic seizures that have a motor pattern different from that of other clonic models, and are believed to originate in the brain stem. The preponderant suppression of tonus by the pontine tegmental lesion as well as the inhibition of clonus in audiogenic seizures is strikingly similar to the effects of phenytoin in these same seizure models. The findings presented are consistent with the hypothesis that the pontine reticular formation (RF) plays a key role in the generation and/or expression of tonic convulsions. Additional findings are presented that suggest that serotonin may attenuate the tonic components of maximal electroshock seizures by an action on the brain stem. Thus, it seems likely that pontine tegmental lesions as well as antiepileptic drugs and neurotransmitters with preferential effects on tonic seizures act on a common neural substrate that appears to include the brain-stem RF.     

The convulsive effects of dopamine sulfate conjugates in rat brain

The administration of 40 μg or more of dopamine sulfate conjugate, the predominant form of dopamine in the peripheral nervous system, into the left lateral ventricle of Sprague Dawley rat led to seizures. The severe and generalized convulsions with clonic extension of forelimbs and hindlimbs occurred within 2–6 minutes of the injection, and lasted for 10–20 minutes. No convulsion was observed when dopamine, norepinephrine, nitrocatechol sulfate or a hydrolyzed solution of dopamine sulfate conjugate were similarly injected. The dopamine sulfate- induced seizures were not blocked by pretreatment of rats with phenoxybenzamine, metoclopramide or haloperidol but were reduced by propranolol and suppressed by diazepam. Dopamine sulfate conjugates which were recently detected in discrete areas of rat brain and in human cerebrospinal fluid may thus have certain function in the brain different from that of free dopamine.     

Effect of brain extracts from rats subjected to korazol kindling on generalized epileptic activity

The pharmacological kindling was induced in rats by corazol repeated injections in subthreshold doses. The peptide-containing fraction was emitted from animal brains by the help of hot acetic acid on the stage of generalized clonic-tonic seizures development. Intraperitoneal injection of brain extracts of kindled rats significantly increased corazol and picrotoxin induced seizure severity in mice. The effect was removed by preliminary injection of naloxone or by preventive incubation of extracts with pronase. Intraventricular injection of extracts to intact rats increased the seizure severity which was provoked by corazol and in high doses induced in rats generalized seizure reactions.     

Angiotensin peptides modulatory system: how is it implicated in the control of seizure susceptibility?

Accumulated studies support the concept that angiotensin peptides, ANG II, ANG III, and ANG IV act as neurotransmitters or neuromodulators in specific neuronal pathways in the brain stem, the hypothalamus, and the forebrain. They have been implicated in the regulation of several physiological processes, particularly in excitable brain structures that express high concentration of their receptors. With the help of pharmacological approaches it was shown that angiotensin peptides appear to be anticonvulsant in a variety of experimental seizure models. Thus, ANG II increases the threshold for pentylenetetrazol (PTZ)-, bicuculline-and picrotoxin-induced seizures in mice. It also attenuates the intensity of clonic seizures evoked by PTZ and 3-mercaptopropionic acid and is effective in the maximal electroshock test. Furthermore, ANG II, ANG III, and ANG IV protect against the clonic convulsions in the PTZ kindling model of epilepsy in mice. From the accumulated results it could be assumed that the angiotensin peptides appear to realize their effects acting directly on their receptors (AT(1), AT(2) and AT(4)) and through close interaction with different neurotransmitter/neuromodulator systems as dopamine (DA)-, gamma-aminobutyric acid (GABA)-and adenosine. This may contribute to a new potential use of angiotensin drugs either alone or in combination with other neuroprotective agents acting through the above mentioned systems, thus providing a more rational strategy for the treatment of neurodegenerative disorders such as epilepsy.