[Neuroprotection in epilepsy].

Brain damage and neuronal loss caused by traumatic brain injury, ischemic stroke, and symptomatic status epilepticus can lead to severe long-term consequences, such as impairment in learning and memory and cognitive functions, and development of chronic epilepsy. This can be the result of morphologic and functional changes underlying temporal lobe epilepsy. Epilepsy patients have increased risk of status epilepticus. It is a life-threatening condition when seizures last for more than 30 min and trigger processes leading to neuronal apoptosis and necrosis in various parts of brain. Administration of neuroprotective drugs preventing these pathologic processes could improve the prognosis for such patients. However despite of active research of neuroprotective drugs, the effective ways to prevent brain damage resulting from prolonged seizures are yet to be found. Studies of neuroprotective properties of classic and novel anticonvulsant drugs showed that most of them do not have the sufficient neuroprotective effect and are not able to prevent epileptogenesis. Thus the studies of other potential neuroprotective drugs seem to be promising.

The role of perioral afferentation in the occurrenceof spike-wave discharges in the WAG/Rij modelof absence epilepsy.

According to the focal cortical theory of absence epilepsy, spike-and-wave discharges (SWDs) have a cortical focal origin in the perioral region of the somatosensory cortex in rats. In the present study the role of peripheral afferents of the perioral (snout) region in the occurrence of spontaneous SWDs was investigated in the WAG/Rij (Wistar Albino Glaxo from Rijswijk) rat model of absence epilepsy in order to examine whether an input from peripheral sources is imperative for the occurrence of SWDs. Twelve male WAG/Rij rats were chronically equipped with cortical EEG electrodes. Peripheral afferents of the perioral region of the snout nervus trigeminus were pharmacologically blocked with a local injection of 2% Novocain, a blockade of nervus facialis and saline injections were used as controls. ECoGs were recorded before and after bilateral injection of the drug. Blockade of the n. trigeminus decreased the incidence and duration of SWD, while similar injections with Novocain near the n. facialis had no effect. Injections with saline were also not effective. Our data demonstrate that intact peripheral afferent input may be primarily involved in the initiation of SWDs. It suggests that the cortico-thalamo-cortical circuits need the peripheral stimulations from the snout and vibrissae for an initiation of the spontaneous SWDs.

[A perspective of present approaches to EEG analyses performed with intention to find seizure predictors].

In the late 90-s of the previous century the American Society of Epileptologists defined a priority for research as "possibilities to predict a seizure, early determinate and reduct". A method, which would allow the prediction of epileptical seizure's onset based on the EEG data registered with the patient with an epilepsy disease, would also allow implementing the new approach to treatment. If it became reliably possible to predict a moment of seizure, based on the EEG dynamics, one could create an automated closed loop system to prevent a seizure. In the article a number of works regarding this subject were reviewed. Also own results were discussed which were derived from analyses of brain electrical activity of rats with absence epilepsy and with the use of own developed software. Moreover specifics of absence initiation and course were discussed, as well as formation mechanism of thalamus-cortical loop, existing abilities of reduction not only absences, but also cognitive and emotional dissociations. Also described results of analyses of the EEG time series, that were derived by computation of correlation dimension with own developed software.

The role of the nucleus basalis of Meynert and reticular thalamic nucleus in pathogenesis of genetically determined absence epilepsy in rats: a lesion study.

The role of cholinergic nucleus basalis (of Meynert) and the reticular thalamic nucleus in mechanisms of the generation spontaneous spike-and-wave discharges (SWDs) was investigated in the WAG/Rij rat model of absence epilepsy. Selective lesions were affected by local unilateral intraparenchymal infusions of immunotoxin 192 IgG-saporin and cholinotoxin AF64A to the nucleus basalis and the rostral pole of reticular thalamic nucleus. Injections of 192 IgG-saporin into the nucleus basalis increased the number of spontaneous SWDs, while injections in the reticular thalamic nucleus were not effective. Thereby, a loss of cholinergic activity in the nucleus basalis stimulates the appearance of SWDs. At the same time, AF64A infused into reticular thalamic nucleus, besides the reduction of choline acetyltransferase immunoreactive neurons within contralateral nucleus basalis, produced some unspecified lesion of adjacent neuronal tissue, resulted in decrease of number and duration of SWDs as well as in spectral changes in EEG. Considering that the nucleus basalis is an important source of cortical and thalamic cholinergic afferentation, we conclude that cholinergic excitatory input from this structure is important in the control of SWDs in the WAG/Rij rat model of absence epilepsy.

[Status epilepticus--the new mechanisms and lines of inhibition (the lithium-pilocarpine model)].

This review focuses on the modeling of status epilepticus in animal brain and modern data on the mechanisms of epileptical seizures initiation using the pilocarpine binding with the muscarinic cholinoreceptors (litium pilocarpine model). The character of epileptics seizures in developing brain and adult brain of rats were investigated. The lines of modulation and inhibition epileptics statues by sacricine and intranasal application of neuropeptide thyroliberin in ultra-low doses are demonstrated. The role of the short-term changes (signal regulated kinase signaling cascade, Kv 4.2 potassium channels, hippocampal and cortical spike-wave discharges) and the long-term changes (loss of selective type of interneurons, excitatory circuits by mossy fiber sprouting) that promotion the epileptic state and recurrent seizures in limbic structure are discussed.

[The cortico-thalamic theory for generalised spike-wave discharges]. / Kortikotalamicheskaia teoriia proiskhozhdeniia generalizovannykh pik-volnovykh razriadov.

The origin of generalized absence epilepsy is still not known. In the last century, four theories have dominated the debate about the origin of the bilateral synchronous generalized spike-wave discharges associated with absence seizures: the "centrencephalic" theory [Penfield and Jasper], the "cortical" [Bancaud, Niedermeyer, Luders], the "cortico-reticular" theory [Gloor, Kostop[oulos, Avoli] and the "thalamic clock" theory [Buzsaki]. There is now some evidence that absence epilepsy, as studied in the WAG/Rij model, is a corticothalamic type of epilepsy. A new hypothesis is proposed which suggests that a cortical focus in the somatosensory cortex is driving the widespread corticothalamic networks during spontaneous absence seizures. This modern theory was given the name "hot spot' theory" [Meeren et al., 2002]. According to the present view three brain structures are critically involved and their integrity seems a minimal and sufficient condition for the occurrence of spike-wave discharges. Firstly, the reticular thalamic nucleus is involved and most likely its rostral pole. Secondly, the thalamocortical relay cells in the ventrobasal complex play a role and, thirdly and most importantly, the cerebral cortex with its epileptic zone. The zone in which the epileptic focus seems to be localised is located on the somato-sensory cortex, and more precisely in the area on which the peri-oral region including the upper lip, projects.

[Neuropeptide thyroliberin in ultra low doses--anticonvulsant defense of the brain]. / Neiropeptid tiroliberin--protivosudorozhnaia zashchita mozga v sverkhmalykh dozakh.

Thyroliberin (TRH) promoting endogeneous antidepressive effect is the most general regulator of the central mechanisms and visceral functions (especially respiration). Our group pioneered in applying the anticonvulsant action of TRH after local intranasal application). This application of TRH in ultra-low doses contrast the method of systemic TRH administration in the large doses). In our experiments intranasal application of 10(-8), 10(-10) and 10(-12) mol/l TRH significantly inhibited the severe epileptic motor fits in rats induced by PTZ. EEG also confirms beneficent effect of TRH (TRH suppressed SWD in cortex, amygdala and hippocamp). In the experiment that follows compared effects of TRH (pyroGlu-His-Pro-NH2) and its metabolite dipeptide His-Pro (10(-10), 10(-8) mol/l). The experiments make more precise that only TRH but not His-Pro posses the anticonvulsant properties. There is a good believe that medical potentialities of TRH have not been exhausted and its new possibilities of its usage will be revealed in epileptology.

[Cholinergic mechanisms in the pathogenesis of genetically-caused absence epilepsy]. / Kholinergicheskie mekhanizmy v patogeneze geneticheski obuslovlennoi absansnoi épilepsii.

Frontoparietal cortex and the thalamocortical circuit comprising reticular thalamic nucleus (RTN) and relay nuclei of the ventrolateral thalamus (VLT) are critical structures in the generation of spike-wave discharges (SWD) during absence seizures. The activity of these nuclei is under the control of the ascending cholinergic projections of nucleus basalis of Meynert. The aim of our study is to make an attempt to change the pattern of SWD in WAG/Rij rats by injecting of cholinotoxine AF64A to the area of RTN. Spontaneous SWD were registered in cortex of WAG/Rij rats with genetically determined absences. The spectral content of SWD was analyzed by means of the Fast Fourier Transformation (FFT) procedure. Unilateral injections of AF64A (1 nmol) to RTN led the decrease in duration and number of SWD comparing to the basal EEG recordings 2 days after the lesion. The FFT analysis showed the disappearance of 17-18 Hz spike on the side of the lesion compared with the intact side. The immunohistochemical study for acetylcholinetransferase (ChaT)-containing neurons showed the loss of ChaT-positive cells in the nucleus basalis area on the side of the lesion. The removal of cholinergic afferentation of RTN and cortex from nucleus basalis inhibits the SWD developing most likely due to the decrease of cortical excitability. Moreover, possibly cholinergic transmission is involved in the transforation of the synchronized phenomena (SWD) to another with close mechanism of generation.

[Hippocampal ripple oscillations (200 Hz) in mechanisms of memory consolidation]. / Gippokampal'nye rippl-ostsilliatsii (200 Gts) v mekhanizmakh konsolidatsii pamiati.

A current status of knowledge about high-frequency (140-200 Hz) ripple oscillations in the CA1 hippocampal subfield is summarized and considered in the context of two-stage model of the hippocampal memory processing. A large body of evidence suggests highly-selective recruitment of pyramidal cells and interneurons in the generation of the oscillatory pattern after co-operative sharp-wave-related discharge of CA3 pyramidal neurons. We also discuss a role of transmission via gap junctions in the mechanisms of ripple oscillations as well as their adaptive aminergic (histaminergic) modulation. Patterns of neuronal firing in the hippocampus observed during ripple oscillations reproduce space-dependant neuronal activity from the previous waking period. Together with a data about efficacy of high-frequency stimulation for induction of synaptic modification it points out a role for ripples in the formation of long-term memory. Focal ultra fast ripples (up to 500 Hz) have been shown to participate in the development of temporal lobe epilepsy.

Peptidergic mechanisms of hyperthermia-evoked convulsions in rats in early postnatal ontogenesis.

This report addresses the verification of the hypothesis that arginine-vasopressin affects the formation of hyperthermia-evoked convulsions in early ontogenesis in rats on days 3, 5, 7, and 9 of postnatal life. The modification of experimental febrile convulsions by PACAP (pituitary adenylate cyclase-activating peptide) was investigated; PACAP is a physiological regulator of the neurosecretion of arginine-vasopressin. Arginine-vasopressin (10 microg/rat) and PACAP (0.01 microg/rat) decreased the latency of generalized tonic-clonic convulsions and the time of truncal generalization of convulsive activity on days 3 and 5 of rat development. Animals given arginine-vasopressin (0.1-10 microg/rat) sowed significant increases in the duration of generalized convulsions to the level of status epilepticus on day 9 of life. Conversely, administration of higher doses of PACAP (0.1 microg/rat) increased the threshold of tonic-clonic convulsions on days 3 and 5 and decreased it on days 7 and 9 of postnatal development. The indirect involvement of PACAP in the mechanisms of experimental febrile convulsions is suggested to act via changes in arginine-vasopressin neurosecretion.

[Pregnancy in WAG/Rij rats--changes in the levels of progesterone, estradiol and generalized absence epilepsy]. / Beremennost' krys linii WAG/Rij--izmeneniia urovnei progesterona i éstradiola i generalizovannoi absansnoi épilepsii.

Progesterone and oestradiol serum level was investigated in WAG/Rij rats with genetically determined absences. Blood samples were drawn before and after the pregnancy following the parturition. The serum concentration of progesterone increased after the 3rd day of pregnancy. There is no increasing of oestradiol during pregnancy as large as this. The progesterone is kept high to the 18th day of pregnancy and drastically decreased before the parturition. Common duration of absences--spontaneous spikewave discharges (SWD), frequency and the duration of every SWD decreased from 3rd to 19th days of pregnancy before the parturition. On the basis of these data and modern investigations, regulation of GABAA receptor expression during pregnancy by progesterone (Brusaartd A. B. et al., 1999) it can be assumed that the changes in the parameters of SWD are possibly correlated with the progesterone changes in serum during pregnancy in WAG/Rij rats.

[Neuropeptide thyroliberin--an endogenous anticonvulsant in the brain]. / Neiropeptid tiroliberin--éndogennaia protivosudorozhnaia zashchita mozga.

Thyroliberin (TRH) promoting endogenous antidepressive effect is the most general regulator of the central mechanisms and visceral functions (especially respiration). Our group pioneered in applying the anticonvulsant action of TRH after local intranasal application. This application TRH in ultra-low doses contrast the method of systemic TRH administration (i.v., i.m. or oral in the large doses--mg). In our experiments intranasal application of 10(-9) M, 10(-10) M and 10(-12) M TRH significantly inhibited the severe epileptic motor fits in rats induced by pentylenetetrazole (PTZ). Beneficent effect of TRH is also confirmed by EEG (TRH suppressed SWD in cortex, amygdala and hippocamp). In the experiment that follows compared effects of TRH (pyroGlu-His-Pro-NH2) and its metabolite dipeptide cHis-Pro-NH2 (10(-10) M, 10(-5) M). The experiments make more precise that only TRH but not His-Pro posses the anticonvulsant properties. There is a good believe that medical potentialities of TRH have not been exhausted and its new possibilities of its usage will be revealed in epileptology.

Role of nitric oxide and lipid peroxidation in mechanisms of febrile convulsions in Wistar rat pups.

Generation of nitric oxide and the content of lipid peroxidation products in the brain are increased in rat pups during febrile convulsions. NO-synthase inhibitor N-nitro-L-arginine in a dose of 250 mg/kg prevented hyperthermia-induced accumulation of nitric oxide, increased the latency febrile convulsions, and had no effect on the content of lipid peroxidation products.

[Peptidergic mechanisms of hypothermia-induced seizures in rats during early ontogenesis]. / Peptidergicheskie mekhanizmy gipertermicheski vyzvannykh sudorog u krys v rannem postnatal'nom ontogeneze.

Arginine-vasopressin reduced the tonic-clonic seizures' latency as well as the duration of the seizures brain-stem generalisation on the 3rd and 5th postpartum days in rats. The reduced latency was also observed after the PACAP38 low doses administration, whereas higher doses diminished and then enhanced the threshold of generalised hyperthermia-induced seizures on the 3rd and 5th days and the 7th and 9th days, resp. The arginine-vasopressin-treated animals had a dramatically enhanced duration of the tonic-clonic seizures up to the epileptic status on the 9th postpartum day. The findings suggest the PACAP involvement in mechanisms of experimental febrile seizures through its effect upon arginine-vasopressin neurosecretion.

PTZ-induced seizures in rats: effects of age and strain.

The susceptibility to pentylenetetrazol (PTZ)-induced seizures during postnatal ontogeny [postnatal day (PN) 10-220] was investigated in two rat strains. The WAG/Rij strain, genetically prone for developing generalized absence epilepsy, and Wistar rats were tested and compared at PN 10, 26, 30, 70, 90, 125, and 220 on the PTZ-convulsive threshold. A subconvulsive dose of 25-mg/kg PTZ was administered every 15 min, and the occurrence of clonic and tonic-clonic seizures was scored. The 10-day-old pups were quite sensitive to PTZ and showed mainly clonic seizures. The highest threshold and latency of PTZ-induced clonic and tonic-clonic convulsions were observed at PN 26 in both strains. From that age onwards, the seizure threshold significantly decreased and reached a minimum at PN 220. Between strain comparisons showed that WAG/Rij rats have a lower tonic-clonic seizure threshold than Wistar rats. The data indicate that changes in susceptibility first quickly decreases until PN 26-30 and then tend to monotonically increase with age, and that genetically prone nonconvulsive WAG/Rij rats are more vulnerable to convulsive seizures induced by PTZ than Wistar rats.

[The piriform cortex and the cortical nucleus of the amygdala in epileptogenesis--the role of the rostrocaudal gradient]. / Piriformnaia kora i kortikal'noe iadro mindaliny v épileptogeneze--rol' rostro-kaudal'nogo gradienta.

The seizure susceptibility of amygdaloid complex in rat was investigated. In piriform cortex and cortical nucleus of amygdaloid complex the structural and electrophysiological rostro-caudal differences were found (using relative spectral densities EEG, seizure thresholds, electrical kindling rate). The fundamental dependence of severity of motor seizures from structural (nuclear or cortical) organization of stimulating area was shown. There were more of limbic stages while stimulating anterior and posterior cortical nuclei, and there were more generalized stages while stimulating piriform and periamygdaloid cortex. Using the model of electrical kindling anticonvulsant effects of Sacricin were demonstrated. Sacricin is one of the compounds of polycarbonic acid. Sacricin has fully coped the process of secondary generalization of epileptic seizures.