The participation of the glutamatergic neurotransmitter system in the pathogenesis of audiogenic seizures (AS) and post-ictal catalepsy (PIC) in Krushinsky–Molodkina (KM) strain rats was analyzed. Effects of D-serine and disocilpine administration were investigated. In intact KM rats, the intensity of AS correlates with the duration of PIC. The administration of D-serine (acute administration, doses of 200, 400 and 600 mg/kg, as well as after chronic administration—5 days of 300 mg/kg, n = 34) had no significant effect on AS and PIC. Disocilpine (MK-801, a non-competitive NMDA antagonist) was administered in an acute experiment at doses of 0.1, 0.2 and 0.4 mg/kg (n = 41). MK-801 dose-dependently reduced the intensity of AS and caused a “two-wave pattern” of seizures in the most of animals, and removed PIC at a lower dose than AS seizures. PIC was completely eliminated already at a dose of 0.2 mg/kg, while the clonic component of AS still persisted. Thus, it was possible to show the “dissociation” between AS and PIC. It is assumed that although dopaminergic control is involved in the mechanisms of PIC development, glutamatergic neurotransmission is also taking part in the PIC manifestation.

Learning difficulties are a fairly common comorbid complication in patients diagnosed with epilepsy. The relationship between the predisposition to epilepsy and the ability to learn is an important problem. The aim of the study was to analyze how the learning capacity differs in rats with different predispositions to reflex audiogenic epilepsy (AE). The success of active avoidance (AAC) conditioning in the shuttle box in rats of 3 strains was evaluated. These were rats predisposed to audiogenic epilepsy—the Krushinsky–Molodkina strain (KM), strain “4” (selected from a population of F2 hybrids of the KM strain and AE non-prone Wistars) and rats of “0” strain, selected for the absence of AE from the same population (i.e. these strains differ radically in AE-proneness, but have a similar genetic background). The training was conducted continuously for 5 days (20 presentations per day). Experiments have shown significantly more successful acquisition of this skill in rats of the “0” strain: in total, 75 of AAC training (70 intermediate—41.7 (8.3 possible to identify more successful learning in rats, selected for the absence of AE seizures (strain “0”) compared to rats of the KM and “4” strains (expressing tonic seizures of maximum intensity in response to sound exposure). The weakest acquisition was revealed in the KM strain, in which the selection process duration for AE proneness was significantly longer than in the rats of the “4” strain.

The results demonstrate and confirm the significant role of monoamine imbalance in the ictogenesis of Krushinsky–Molodkina rats with genetically determined audiogenic epilepsy and in the development of audiogenic kindling (AuK) in them. The experiments were carried out on rats of the Krushinsky–Molodkina (KM) line without sound stimulation (KM-background) and after the development of AuK (KM-AuK). The control group was rats of line “0”, in which convulsions in response to sound were completely absent. AuK was generated using 20-fold sound stimulation (120 dB). Neurochemical analysis was performed by HPLC/ED in the frontal cortex, hippocampus, hypothalamus, nucleus accumbens, and brainstem. It has been established that AuK in KM rats leads to the appearance of myoclonic and attenuation of stem convulsions, which is accompanied by a change in the functional activity of the noradrenergic and serotonergic systems of the brain. KM rats exhibiting tonic convulsions in the “background” have a low content of norepinephrine in the hippocampus and hypothalamus, and when audiogenic myoclonic convulsions develop, norepinephrine deficiency is observed in the frontal cortex. After the formation of AuK, the excessively intense serotonin metabolism revealed in KM slows down in the hippocampus, nucleus accumbens, and, especially, in the brainstem, and the serotonin deficiency in the striatum also disappears. The peculiarities of norepinephrine metabolism in KM rats before and after AuK emphasize the important role of the cortex in the development of myoclonic convulsions, and of the hippocampus and hypothalamus in the implementation of stem convulsions. Excessive functional activity of the serotonergic system, revealed in KM “background” rats, slows down in a number of brain structures during the production of AuK.

Dexamethasone is a synthetic glucocorticosteroid with anti–inflammatoryand immunosuppressive effects. In order to identify new targetsfor pharmacotherapy, as well as to study immune mechanisms in thepathogenesis of epilepsy, the influence of dexamethasone on audiogenicepilepsy and catalepsy in Krushinsky–Molodkina (KM) rats has beenstudied. The chronic (but not acute) infusion of dexamethasone decreasedthe audiogenic seizure fits intensity in male rats of Krushinsky–Molodkina(KM) strain which is highly susceptible to audiogenic epilepsy,but was accompanied by part of animal deaths. In a month after dexamethasoneinjections the audiogenic sensitivity of the rescued animals restoredto the control levels. The “0” strain rats, bred from F2 KM x Wistarhybrids, no dexamethasone induced mortality was found. The acuteand chronic dexamethasone action in rats of “0” strain induced theemergence of catalepsy after the sound exposure, although the audiogenicseizure was found only in one animal. The chronic and acute dexamethasonedecreased the postictal catalepsy in KM rats. Thus, pro-inflammatory mechanismsare involved in the pathogenesis of audiogenic epilepsy. Dexamethasonehad a distinct anticonvulsant effect in the chronic experiment.

Audiogenic epilepsy (AE), inherent to several rodent strains is widely studied as a model of generalized convulsive epilepsy. The molecular mechanisms that determine the manifestation of AE are not well understood. In the present work, we compared transcriptomes from the corpora quadrigemina in the midbrain zone, which are crucial for AE development, to identify genes associated with the AE phenotype. Three rat strains without sound exposure were compared: Krushinsky-Molodkina (KM) strain (100% AE-prone); Wistar outbred rat strain (non-AE prone) and “0” strain (partially AE-prone), selected from F2 KM × Wistar hybrids for their lack of AE. The findings showed that the KM strain gene expression profile exhibited a number of characteristics that differed from those of the Wistar and “0” strain profiles. In particular, the KM rats showed increased expression of a number of genes involved in the positive regulation of the MAPK signaling cascade and genes involved in the positive regulation of apoptotic processes. Another characteristic of the KM strain which differed from that of the Wistar and “0” rats was a multi-fold increase in the expression level of the Ttr gene and a significant decrease in the expression of the Msh3 gene. Decreased expression of a number of oxidative phosphorylation-related genes and a few other genes was also identified in the KM strain. Our data confirm the complex multigenic nature of AE inheritance in rodents. A comparison with data obtained from other independently selected AE-prone rodent strains suggests some common causes for the formation of the audiogenic phenotype.

Behavior in the open field test was compared in rats of two strains differing in terms of the manifestation of convulsions in response to sound (audiogenic epilepsy (AE)). These strains (“4” and “0”) were bred on the basis of a single hybrid population. Testing was performed before a series of exposures to sound (21 days) and after exposure. During sequential presentations of sounds, rats of strain “4” formed myoclonic convulsions, while “0” rats had no AE and, thus, no myoclonic convulsions. In the initial test, the level of locomotion and exploratory activity were greater in “4” rats than in “0” rats. In the second test, “4” rats showed significant changes in many behavioral parameters reflecting general suppression of exploratory activity and locomotion. Rats of strain “0” exposed to sound (but not displaying signs of AE) showed more active behavior in the second test than the first, reflecting acclimation of the animals to the experimental context, though changes in a number of indicators in the second test provided evidence of the complex nature of changes in anxiety levels in these animals (as a result of serial exposure to loud sounds). The similar genetic backgrounds of the two rat strains contrasting in terms of AE leads to the conclusion that changes in the behavior of “4” rats resulted from induction of a series of the epileptiform phenomena of AE. This pair of strains may provide a clear genetic model of convulsive states providing for reliable assessment of the effects of both external actions and pharmacological agents.

We studied the effects of whole body gamma-radiation (4 Gy, dose rate 0.6 Gy/min) and proton-beam head irradiation (with an energy of 150 meV, 4 Gy and a dose rate of 0.8 Gy/min) on the intensity and timing of audiogenic seizures in rats of the Krushinsky–Molodkina selected strain. In experiments using gamma rays the rat behavior was tested in the open field, elevated plus maze, and Morris water maze tests. No changes in audiogenic tonic–clonic seizures (originating in the brain stem) were found during the first exposure to sound after gamma-irradiation. Slower development of seizures and larger latency of the tonic seizure phase were found following serial daily exposure to sound in rats after proton irradiation. It was also noted that audiogenic myoclonic seizures (which developed in the forebrain) in irradiated rats that were exposed daily to sound had shorter durations, while the intensity of these seizures was at a maximum in all groups. The behavioral tests revealed a moderate increase in anxiety after radiation exposure.

The anticonvulsant effect of ethosuximide (T-type calcium channel blocker) was evaluated in Krushinsky–Molodkina rats predisposed to audiogenic epilepsy. Ethosuximide given with drinking water (300 mg/kg/day) over 45 days slightly reduced proneness to audiogenic epilepsy and increased locomotor activity of the animals at the periphery of the open field. Neonatal administration of ethosuximide (3-4 mg per animal, from 2 to 10 days of life) insignificantly modulated the parameters of audiogenic epilepsy in these animals at the age of 1.5 months and reduced manifestation of audiogenic myoclonic convulsion that developed after long daily sound presentation started at the age of 3 months. The findings attested to a weak anticonvulsant effect of ethosuximide on tonic convulsions with its predominant effect on convulsions with forebrain focus location.

Аctuality. The significant proportion of human epilepsy is resistant to anticonvulsant drug therapy, which makes actual the problem of search for new alternative antiepileptic therapies. The goal of this work was the analysis of the effects created by the inhalation of toluene vapor (the strong odorant) on epileptic seizures in rats of Krushinsky-Molodkina strain, which is highly prone to audiogenic epilepsy (AE), the tonic convulsions of the musculature as well as audiogenic myoclonic seizures which develop as the result of serial daily sound exposure. Methods. Rats (n=14) were exposed to 15-s inhalation of toluene vapor with the subsequent (in 20 s) testing of their audiogenic seizure intensity. Results. The toluene action induced a significant reduction in tonic and myoclonic seizure intensity in comparison to the background data of AE sensitivity obtained 1 week prior to the toluene test. In 13 of 14 animals, the seizures ended as the clonic seizures (no tonic seizures developed), while all animals developed tonic seizures in the “background” experiment. All rats developed myoclonic seizures (audiogenic kindling) prior to toluene action while no myoclonic seizures were noted after toluene inhalation in all animals. Conclusion. The results obtained complement the previously published data using WAR strain of rats on the relationship between epilepsy and olfactory system. The anticonvulsive effects of toluene vapor inhalation on the expression of AE signs demonstrate both the importance of genetic models usage in such investigations and the importance of olfactory stimulation as the potential anti-convulsant agent.

Krushinsky-Molodkina rat strain is the widely known genetic model of seizure states. The usage of this strain permits to analyze the epileptogenesis and to evaluate the effectiveness (and universality) of anticonvulsants. The paper contains the short review of the main recent experimental results obtained using these animals. The audiogenis seizures in mice and hamsters are less investigated.

Актуальность. Селектированная на проявление судорог в ответ на сильный звук (аудиогенную эпилепсию, АЭ) линия крыс Крушинского-Молодкиной (КМ) - модель судорожных состояний человека, c быстрым развитием судорожного припадка в ответ на включение звука (100-120 дБ). Однако у крыс с АЭ изменений уровня кортикостерона (КС) в крови в связи с судорогами не определяли, хотя анализ связи АЭ и стресс-реакции - важная практическая задача. Методы. Уровень КС в образцах сыворотки крови определяли с помощью набора у крыс линии КМ, а также у крыс линии «0», селектированных из гибридной популяции КМ х Вистар на отсутствие АЭ, и у крыс популяции Вистар. Результаты. У всех крыс КМ был зарегистрирован аудиогенный припадок, тогда как у крыс линии «0» и Вистар судорог не было. Через 30 мин после действия звука (и судорог) у крыс КМ повышеается уровень КС, тогда как сразу после судорог (через 1-3 мин) данная реакция не обнаруживается. У крыс линии «0» обнаружен достоверно более высокий фоновый уровень КС, по сравнению с КМ и Вистар. Уровень КС у них, как и у крыс Вистар, после действия звука не изменялся. Заключение. Подъем уровня КС в крови после действия звука наблюдали только у крыс КМ через 30 мин после припадка АЭ. Крысы линии «0», у которых нет судорог в ответ на звук, обнаружили более высокий, чем у КМ и Вистар уровень КС в фоне. Aims. The Krushinsky-Molodkina (KM) rat strain, which was selected for a seizure response to a sound (audiogenic epilepsy, AE), is known as a model of human seizure states. Although the association of blood CS with stress reaction is an important practical issue, blood levels of corticosterone (CS) have never been analyzed in rats with AE in relation with seizures. Methods. Serum concentration of CS was measured using IBL International Corticosterone ELISA kits in KM rats, rats of the «0» strain, which was selected (based on F2 KM х Wistar hybrids) for the lack of seizures in response to a sound, and Wistar rats. Results. All KM rats developed AE seizures in response to a sound while no seizures were observed in rats of the «0» strain and Wistar rats. The increase in blood CS was observed only in KM rats at 30 min after AE seizure. At background, the level of CS was significantly higher in rats of the «0» strain, which did not develop seizures in response to a sound, than in KM and Wistar rats. CS levels remained unchanged in both «0» and Wistar rats after the sound exposure. Conclusions. The increase in blood CS occurred in KM rats at 30 min after the seizure episode. At background, the CS level was higher in rats of the «0» strain, which did not respond with seizures to a sound, than in Wistar and KM rats. Therefore, the blood level of CS depends in a complicated way on both AE and the selection history of the «0» rat strain.

The latency of tonic seizure in response to loud sound (in rats of the Krushinsky–Molodkina strain with audiogenic epilepsy) had been slightly (although statistically significantly) longer after chronic uridine injections (100 mg/kg, i.p., three times a day during 9 or 12 days). The recovery time from the tonic seizure was shorter after 12 days of injections in comparison to the 9-day injection period. At the same time, the intensity of tonic seizures provoked by loud sound did not change after chronic uridine injections. The lack of uridine anticonvulsive effect demonstrated in the audiogenic epilepsy model contradicts the anticonvulsant effects of uridine in experiments with other seizure models, in which the epileptic foci were localized in the forebrain structures.