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.     

Effects of activation and lesions of the superior colliculi of the lamina quadrigemina on epileptic activity in rats]

In acute experiments on rats it was shown that activation of SC by bilateral microinjection of penicillin (5-15 IU) or bicuculline (25-50 ng) resulted in the increased latency and decreased severity of i.p. picrotoxin-induced seizures (2 mg/kg). The suppression of behavioral convulsions and the decreased epileptic activity in the hippocampus and cerebral cortex were followed by occurrence of spike discharges in SC with an amplitude of 200-500 mcV and frequency of 5-12/sec which testifies to the formation of penicillin- or bicuculline-induced generator excitation in SC. The lesions of SC by kainic acid administration resulted in the decreased seizure threshold and, also, facilitated the development of seizure under conditions of picrotoxin kindling. The conclusion is made that SC activation plays an important role in the realization of functional integrative activity of the antiepileptic system.     

The effect of the cerebrospinal fluid from rats subjected to picrotoxin-induced kindling on the motor activity and seizure susceptibility of recipient animals

Experiments on rats have shown that repeated administration of primarily subthreshold dose of picrotoxin leads to the occurrence and progressive enhancement of seizure manifestations. During picrotoxin kindling the decrease of locomotor activity in interictal periods was recorded. Microinjection of cerebrospinal fluid (CSF) of kindled rats into lateral brain ventriculi of recipients resulted in decrease of locomotor activity and acute primarily generalized picrotoxin induced seizures. These effects of CSF were blocked by naloxone administration and were observed only if injecting CSF which was preliminarily treated with protease inhibitors. It is concluded that endogenous opioid substances accumulate in CNS during kindling and evoke a decrease in the locomotor activity. These substances act as anticonvulsant factors which control the development of epileptic activity.     

Effects of destruction and activation of limbic structures on formation of convulsive and emotional disorders during picrotoxin kindling

In the experiments on rats it was shown that the picrotoxin kindling, which consists of the progressive increasing of convulsive reactions during daily systemic administration of picrotoxin in subconvulsive dosages results also in the development of the pathologically enhanced defensive reactions. The destruction of hippocampal structures by kainic acid prevented the seizure syndrome, while their activation due to blood injection in hippocampus promoted its development; under these conditions the kindling of pathologically enhanced defensive reactions was not significantly changed. Bilateral amygdalar destruction significantly attenuated the development of pathologically increased defensive behavior; under these conditions the seizure syndrome was not significantly changed. The data are discussed on the theory of generator, and systemic mechanisms of neuropathologic syndromes and show that picrotoxin kindling results in the formation of two different pathologic systems which cause the development of two mentioned syndromes: seizure syndrome and syndrome of pathologically enhanced defensive behavior.     

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.     

Pentylenetetrazol (PTZ)-kindling development in intact and subcortical structure lesioned rats

Kindling was induced in male wistar rats (280-320 g) by daily ip injections of PTZ in subthreshold doses (30 mg/kg). Repeated administration of PTZ to animals resulted in developing of enhanced seizures and also enhanced seizure susceptibility which could be sustained for a long time (6 months) after last seizure paroxysm. The lesioned hippocampus retarded the manifestation of PTZ kindling, where as lesioned caudate nuclei increased the seizure kindling development. Results also revealed hippocampus as a determinant structure in PTZ kindling formation, which stabilize the epileptic manifestations and make them chronic, at the same time caudate nuclei retarded the epileptic seizures stabilization. This role may be only antiepileptic, and not anti-kindling as is known for caudate nuclei.     

Involvement of nitric oxide in pentylenetetrazole-induced kindling in rats

We investigated the role of nitric oxide (NO) and brain-derived neurotrophic factor (BDNF) in the pentylenetetrazole (PTZ)-induced kindling in rats. Seizures were induced by single administration of PTZ, which was associated with an increase in levels of NO metabolites (NOx) in the hippocampus. Pretreatment with a neuronal NO synthase inhibitor, 7-nitroindazole (7-NI), diminished the PTZ-induced increase in NOx levels without affecting the seizure intensity. Repeated administration of PTZ produced a gradual increase in the seizure intensity, leading to the development of kindling. In the kindled rats, PTZ at a dose of 40 mg/kg increased NOx levels in the hippocampus, whereas it had no effect in control animals. Cotreatment of 7-NI with PTZ blocked the development of kindling and attenuated the PTZ-induced increase in NOx levels. A significant increase in BDNF levels was observed in the hippocampus of the kindled rats, which returned to the control levels following seizures induced by PTZ. 7-NI reduced the hippocampal BDNF levels in control rats and suppressed the increase of BDNF levels in the kindled rats. Our findings suggest that NO plays a role in the development of PTZ-induced kindling and that BDNF may contribute to the NO-dependent plastic changes in neuronal excitability.     

Remote effects of early postnatal pituitary hormone melatonin injection on audiogenic seizures in Krushinsky-Molodkina rats

Rats Krushinsky-Molodkina inbred strain (KM) genetically prone to audiogenic seizures were injected with pineal hormone melatonin (50 mg/kg, s.c.) within the period 7th to the 14th posnatal days (PND). The remote effects of this injection adult KM rats consisted in a decrease in the latency and increase in severity of myoclonic seizures produced by audiogenic kindling (20 sound stimuli, 100 dB and 12-15 kHz). As compared to the control, in the cortex and hippocampus of rats of melatonin group, we also found a significant reduction of both total and functional activity of Ca2+/calmodulin-dependent protein kinase II (CAMK II) after audiogenic kindling. On the contrary, melatonin administration within the 1st to 7th PND and the 14th to the 21st PND resulted in a decrease in seizure activity. In the first case, both the total (cortical) and functional (hippocampal) CAMK II activities in melatonin-injected rats were increased as compared to control, whereas in the second case, only a slight increase in Ca2+-independent CAMK II activity in the hippocampus of melatonin-injected rats was observed. Probably, the melatonin administration in the period of early postnatal development changes the features of expression and/or regulation of CAMK II activity, and this could be one of the mechanisms of audiogenic seizure modulation in KM rats.     

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.     

The anticonvulsive action of the intranigral administration of the delta sleep-inducing peptide]

It is shown that injection of delta sleep-inducing peptide (DSIP) into the substantia nigra reticular part (SNrp) suppresses generalized convulsive activity induced in rats by picrotoxin and corazol injection but exerts no influence on the strichnine-induced seizures. The analogous DSIP injection causes the antiepileptic action in rats kindled through picrotoxin injections. The DSIP intranigral anticonvulsant action is blocked by naloxon and enhanced by haloperidol and yohimbin. It can be concluded that DSIP anticonvulsant action may be realized due to activation of SNrp-dependent opioid mechanisms and suppression of dopaminergic ones.     

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.     

GABA metabolism in the substantia nigra,cortex, and hippocampus during status epilepticus

The metabolism of GABA and other amino acids was studied in the substantia nigra, the hippocampus and the parietal cortex of rats following microinjections of GAMMA-vinyl-GABA during status epilepticus induced by lithium and pilocarpine. GABA metabolism showed striking regional variations. In controls, both GABA concentration and rate of GABA synthesis were highest in the substantia nigra and lowest in cortex, as expected. In substantia nigra, status epilepticus resulted in a 2 1/2 fold decline in the rate of GABA synthesis and in a 307% increase in the turnover time of the GABA pool. In hippocampus, the rate of GABA synthesis was not altered significantly, but the turnover time of the GABA pool was 284% of controls, and the size of that pool increased to 208% of controls. By contrast, in cortex, where seizure activity is limited in this model, the rate of GABA synthesis increased to 230% of controls while pool size and turnover time did not change. Aspartate concentration decreased in all three brain regions. These data suggest that the observed reduction of the rate of GABA synthesis in substantia nigra could play a key role in seizure spread in this model of status epilepticus.Special Issue dedicated to Claude Baxter.     

Alterations in the Content of Amino Acid Neurotransmitters Before the Onset and During the Course of Methoxypyridoxine-Induced Seizures in Individual Rabbit Brain Regions

In rabbits, generalized seizures were induced by methoxypyridoxine, and changes in amino acid concentrations of 15 brain regions were investigated before seizure onset and during the course of sustained epileptiform activity. As previously reported, gamma-aminobutyric acid (GABA) concentration decreased preictally in most regions. At the same time, taurine level was elevated in the hypothalamus, thalamus, hippocampus, caudatum, and frontal cortex. After 90 min of seizures, it was significantly decreased in the hypothalamus, periaqueductal grey, substantia nigra, frontal cortex, and cerebellum. Glycine content was reduced preictally only in the substantia nigra; after seizure onset its concentration rose in all brain areas. Glutamate content in the frontal cortex decreased before seizure onset; after 1.5 h of seizures, its concentration in cerebellum, caudatum, and hippocampus was reduced. Aspartate level was decreased in most areas after sustained seizures; in putamen, however, it was elevated. In contrast, glutamine content increased preictally in the superior colliculus and in all brain areas by approximately 200% after 90 min of seizures. Alanine and valine content also rose markedly in most brain areas after prolonged seizures, and threonine showed the same tendency. The single brain regions were observed to respond to methoxypyridoxine in highly individualistic ways. For example, the glycine content of the substantia nigra, which is believed to utilize this amino acid as a neurotransmitter, decreased preictally. The potential importance of the superior colliculus in seizure induction is considered in view of the early rise in glutamine level. The antagonistic preictal behavior of taurine and GABA is discussed with respect to synthesis, uptake from the blood, and antiepileptic properties.     

Excitability cycles of epileptic after-discharges in rats

An epileptic seizure is regularly followed by a postictal depression and then by a phase of increased excitability. The time course of these two phases was described for two types of epileptic after-discharges induced by stimulation of the hippocampus and/or the thalamus in acute experiments in rats. Using hippocampal stimulation, an interval of 10 min was necessary for induction of the second self-sustained after-discharge (SSAD) of the same duration as the first one. Significant prolongation of the second SSAD appeared with a 30-min interstimulation interval. The spike-and-wave rhythm induced by stimulation of thalamic nuclei exhibited a shorter refractory phase - up to 5 min - and also the facilitation took place sooner: with 15-min intervals a significant increase in duration of SSAD was recovered. The results are discussed in connection with the kindling model of epilepsy.     

Differential Changes in the Content of Amino Acid Neurotransmitters in Discrete Regions of the Rat Brain Prior to the Onset and During the Course of Homocysteine-Induced Seizures

Changes in amino acid concentrations were investigated in selected regions of rat brain prior to the onset and during the course of epileptiform seizures induced by L-homocysteine. The concentration of gamma-aminobutyric acid (GABA) decreased preictally in substantia nigra (-18%), caudate putamen (-26%), and inferior colliculus (-46%). After seizure onset, the GABA content was further reduced in substantia nigra (-31%) and additionally in hippocampus (-18%). Preictal taurine levels were elevated in globus pallidus (+26%) and caudate putamen (+13%) but returned to normal after seizure onset. However, in hippocampus, taurine decreased both preictally (-22%) and after seizure onset (-56%). Glycine was reduced preictally only in globus pallidus (-13%). After seizure onset the direction of its concentration change varied in the brain regions studied. Glutamate levels decreased preictally in hippocampus (-10%) and hypothalamus (-46%) but increased in globus pallidus (+14%). Normal levels were detectable after seizure onset in hypothalamus and globus pallidus but a further reduction in hippocampus (-59%) and significant reductions in substantia nigra (-15%) and caudate putamen (-17%) were detected. Aspartate was elevated in hippocampus, both preictally (+49%) and after seizure onset (+21%) while at the same phases in globus pallidus a consistent reduction (-30%) was observed. The glutamine content increased preictally in globus pallidus (+41%) and hypothalamus (+36%), and in all brain areas during the ictal phase of seizure, the hippocampus exhibiting a dramatic increase (approximately 300%). The contents of serine and alanine were altered in most regions studied only after seizure onset, with the exception of the hippocampus, where a decrease (-41%) of serine was observed preictally.     

Mechanisms of seizure control mediated by gamma-aminobutyric acid: role of the substantia nigra

The substantia nigra has been identified as a critical site at which gamma-aminobutyric acid (GABA) agonist drugs act to reduce susceptibility to a number of types of experimentally induced generalized seizures. Moreover, the ability of systemically administered GABA-elevating agents to protect against maximal electroshock seizures is directly correlated with an increase in GABA specifically in the nerve-terminal compartment of substantia nigra. The significance of these findings is discussed in terms of the role of specific nigral synapses for the control of seizure propagation. Evidence from lesion studies, as well as studies with opiates and substance P analogs, further supports the hypothesis that Inhibition of nigral efferents reduces susceptibility to generalized seizures. Inhibition of nigral outflow causes a decreased sensitivity to chemoconvulsants without precluding the animal's ability to exhibit any or all of the motor components of a seizure. We therefore propose that nigral outputs are capable of facilitating seizure propagation and can function as a gating mechanism for the generalization of convulsive activity.     

Effect of delta sleep-inducing peptide, anticonvulsant preparations and nicotinamide on generalized seizure activity

The influence of delta-sleep inducing peptide (DSIP) upon seizures induced by corazol, bicuculline, picrotoxin, strychnine, thiosemicarbazide were investigated in experiments on F1(CBA X C57 BL/6) mice. It was shown that DSIP increased the latency of first seizure manifestation which were induced by corazol, bicuculline and picrotoxin and also resulted in a suppression of seizure severity of corazol and bicuculline induced seizures. Anticonvulsant action of DSIP was evident under the condition of the mild severity seizures development. The effect of DSIP was mostly pronounced in range of its doses from 10 to 100 mcg/kg. DSIP when combined with phenobarbital, carbamazepine, diphenylhydantoin or nicotinamide enhanced the antiepileptic effects of these anticonvulsant drugs.     

Effects of organic calcium antagonists and magnesium on the development of corazol kindling

In experiments on rats it was shown that i.p. administration of finoptin (verapamil), magnesium sulfate or ryodipine (an 1,4-dihydropyridine) 15 min before each daily injection of pentylenetetrazole (PTZ) in a subconvulsive dose (30 mg/kg i.p.) significantly (for 10-12 days delayed the development of pentylenetetrazole-induced kindling and attenuated kindled seizure reaction as compared with the controls. In animals sensitive to PTZ which were selected on the test of their reaction to previous single PTZ injection in a dose of 40 mg/kg finoptin, magnesium or finoptin + magnesium resulted in suppression of kindling development at late stages (after 2-week administration of drugs together with PTZ). After the withdrawal of the drugs there was a tendency to an increase of seizure reaction to the testing PTZ dose (30 mg/kg). The enhanced seizure susceptibility to test PTZ dose has being persisted during all observation period (8 months). Finoptin administered 15 min prior to PTZ had no effect on the severity of seizure reaction of fully kindled animals which had not received the drugs. The results obtained show that organic Ca-antagonists and magnesium delay the development of kindling induced seizure susceptibility, but cannot completely prevent it. The results also suggest that mechanisms of the chronic epileptogenesis (development of kindling induced seizure susceptibility) and those of the acute convulsive reaction to the epileptogen are not similar.     

Effects of extracts of different parts of the brain of kindled animals on seizure activity of recipient rats

The peptide-containing fraction was emitted from the hippocampal and ventral mesencephalic region tissue of rats kindled with subconvulsant doses of corazol. Extracts were prepared by the help of hot acetic acid on the stage of generalized clonic-tonic seizure development. The intraventricular injection of VMR-extracts in relatively high dose increased seizure reactions which were induced in intact recipient rats by intraperitoneal corazol injection. The intraventricular injection of the extract in relatively low dose (100 times less) suppressed corazol-induced seizures in recipients. Data are discussed from the point of view of pathological epileptic system formation and the role played by peptides in supporting it's activity during pharmacological kindling.     

Medial septal region as a target for modulation of seizure discharges in the hippocampus in a model of acute temporal lobe epilepsy

Investigation of changes in the hippocampal EEG produced by GABAergic and cholinergic substances delivered into the medial septum region was performed in awake rabbits. Changes in the threshold of seizure discharges in the hippocampus evoked by perforant path stimulation (model of acute epilepsy) were also examined. Injections of GABAA receptor antagonist picrotoxin or agonist of cholinergic receptors carbacholine in low doses induced an increase in the power of delta- and theta modulation and appearance of 7-12-Hz oscillations. The threshold of hippocampal seizure afterdischarges decreased. In higher doses, these substances evoked 7-15-Hz oscillations followed by seizures. GABAA receptor agonist muscimol and muscarinic receptor antagonist scopolamine decreased the power of the theta rhythm and increased the seizure threshold. Picrotoxin or carbacholine injected after muscimol or scopolamine, respectively, did not evoke seizures. Thus, we have shown the possibility to control hippocampal activity by local changes in the GABAergic and cholinergic systems of the medial septum region.