Fedotova Ib

Increase of brain endogenous monoamine oxidase inhibitory activity (tribulin) in experimental audiogenic seizures in rats: Evidence for a monoamine oxidase A inhibiting component of tribulin

Brain tribulin activity in rats with an inherited predisposition to audiogenic epilepsy was studied after seizures of different intensity were induced by an electric bell. Weak seizures (from 0 to 2 arbitrary units) did not produce any changes in endogenous inhibitory activity towards either monoamine oxidase (MAO) A or B. Moderate seizures were characterized by increases in both MAO A and MAO B inhibitory activity (up to 1.9-fold). Complete tonic epileptiform seizures with total areflexia (4 arbitrary units) induced further augmentation (up to 2.5-fold) of MAO A but not of MAO B inhibitory activity. This dissociation between the two inhibitory activities points to the existence of a separate MAO A-inhibiting component of brain tribulin which is different from isatin.

Efficacy of Pirlindole, a Highly Selective Reversible Inhibitor of Monoamine Oxidase Type A, in the Prevention of Experimentally Induced Epileptic Seizures

SummaryIntraperitoneal administration of pirlindole (pirazidole) or ‘soluble pirlindole’ 50 mg/kg body-weight prolonged the onset of seizures and decreased the intensity of seizures in rats genetically selected for high sensitivity to audiogenic hereditary epilepsy [Krushinsky-Molodkina (KM) rats]. In this experimental model of epilepsy, pirlindole prevented qualitative alteration (transformation) in the catalytic activity of membrane-bound type A monoamine oxidases (MAO-A), pathogenetically important for the development of the audiogenic seizures. Modification of the enzymatic properties of the monoamine oxidases causes an increase in γ-aminobutyric acid (GABA) deamination in the mitochondrial fraction of the brain. The data obtained suggest that selective inhibitors of MAO-A, such as pirlindole, may prevent experimental epileptic seizures.

The role of lipid peroxidation in the possible involvement of membrane-bound monoamine oxidases in gamma-aminobutyric acid and glucosamine deamination in rat brain. Focus on chemical pathogenesis of experimental audiogenic epilepsy.

Incubation of rat brain synaptosomes and mitochondria with LPO inducers (Fe2+ and ascorbate) was accompanied by a decrease of deamination of serotonin (substrate of MAO-A) in mitochondria, but not in synaptosomes, with simultaneous stimulation of GABA and GLCA deamination, apparently owing to modification of catalytic properties of brain membrane-bound MAO. Oxidation of PEA (substrate of MAO-B) was insignificantly altered in both fractions. Reactions of deamination of serotonin, GABA, and GLCA (but not PEA), were highly sensitive to a selective inhibitor of MAO-A pyrazidol (pyrlindole). Isoniazid and hydrazides of quinoline carbonic acids (inhibitors of both modified MAO and copper-containing amine oxidases) strongly inhibited deamination of GABA and GLCA. During epileptiformic seizures in rats, genetically selected for high incidence of audiogenic epilepsia, stimulation in brain synaptosomes and mitochondria of LPO was observed. This was accompanied by a marked decrease in serotonin and PEA deamination, with a simultaneous increase in GABA and GLCA deamination in both fractions. The data obtained suggest that appearance of GABA-deaminating activity owing to modification of catalytic properties of MAO, might be an essential pathogenetic component in the development of epileptic seizures.

The relationship between audiogenic seizure (AGS) susceptibility and forebrain tone-responsiveness in genetically AGS-prone Wistar rats.

The present study characterized the intensity-response functions of extracellular field responsiveness of different cortical/subcortical structures of the forebrain following the free-field presentation of tone stimuli, within a population of genetically audiogenic seizure (AGS)-prone KM-Wistar rats. The neural response properties of each case were compared to its propensity to exhibit AGSs during the continuous tone stimulation (15 kHz, 90 s at max.). The amplitudes or slope components of the evoked responses and their peak latencies showed significant positive (amplitude and slope) and negative (peak latency) Bolzmanns sigmoid relationships with the onset-latency of AGS. These relationships, with areal differences in the slopes of saturation functions, applied for the three different data sets recorded simultaneously from the stratum radiatum dendritic layer of the hippocampal CA1 area, primary auditory cortex layers II-IV, and frontal cortex surface. In addition, the similar type of functions between the evoked response variables and AGS onset latency held when all the areas were considered together. These data suggest that the neural responsiveness to acoustic stimulation of the primary sensory, multimodal and association cortices of the forebrain may altogether contribute to the seizure initiation by that modality in the genetically AGS-prone rats. It has been previously shown that there exist abundant and dispersed auditory projections from these forebrain areas to the brain stem and spinal cord, structures that are generally considered to be the key predisposing factors in the generation of AGS. Hence, the types of correlation found reflect the subject-specific stage of forebrain responsiveness, being either related or unrelated to genetic AGS-specific changes, and possibly its triggering impact upon the lower brain AGS network. Accordingly, the mere comparison of forebrain response measures of these AGS-prone animals with those of the AGS-resistant ones could not reveal the result presented.

[Laboratory rat selection for the trait "the absence of audiogenic seizure proneness"].

The hybrids between Krushinsky-Molodkina (KM) inbred strain, selected for high predisposition to audiogenic epilepsy (AE), and Wistar rats non-prone to audiogenic seizure were the initial population for selection. Rats were selected for the trait “the absence of audiogenic seizure proneness”. The creation of such strain in which the significant proportion of animals develop no AE in response to sound and share partly the genetic background of the KM strain is very important for the correct use of KM strain as the laboratory model of seizure states. As alleles which determine the AE proneness are recessive the selection for the “opposite” trait proceeds necessarily slow.

[Genetic analysis of the predisposition to audiogenic seizure fits in Krushinsky-Molodkina rat strain].

The expression of audiogenic seizure fits has been studied in F1 hybrids between audiogenic seizure-prone Krushinsky-Molodkina rat strain and Wistar rats not prone to audiogenic seizures, as well as in two backcross generations. Only 10% of F1 hybrids exhibit audiogenic seizure fits, whereas the frequency of this character in two generations of their backcrosses with Krushinsky-Molodkina rats is about 50%. A digenic model with incomplete penetrance has been put forward to explain the control of audiogenic seizure fits. This model fits the data obtained: the theoretically expected distributions of the character in offsprings of different crosses do not differ significantly from those observed in experiments. The model explains why the distribution of the character is the same in the first and second backcross offsprings.

Audiogenic Seizures - Biological Phenomenon and Experimental Model of Human Epilepsies

Animal models that recapitulate human epilepsies with more or less details are believed to be of importance for clinics – for studies of anticonvulsants (Reigel et al., 1986, Dailey et al., 1996, Fedotova et al., 1996, Kosacheva et al., 1998, Ross, Coleman, 2000 et al.), for dissection of molecular and biochemical pathogenesis of epilepsy, and for the search of epilepsy susceptibility genes. The use of audiogenic epilepsy in rodents as the model for anticovulsant activity of different drugs is popular, the PubMed search for the key words combination “anticonvulsant and audiogenic and model” resulted in about 100 citations. Thus the detailed investigation of this type of seizures has great value for iur knowledge concerning the genesis of seizure (and epileptogenesis) in general and their genetic basis in particular. Apart of its practical importance, the rodent audiogenic epilepsy is the enigmatic biological and genetic phenomenon. Actually the biological significance of high sound sensitivity for rodent survival was never questioned but at the same time its connection with audiogenic epilepsy (AE) was not analyzed from this point of view either. This chapter aims first to introduce several data items concerning investigations of Russian audiogenic prone rat strain (Krushinsky-Molodkina, KM) as they were not fully represented in English literature and second – to discuss the general biological mechanisms of audiogenic seizure. It is well known that the good theory is the best friend of practice. There is some hope that elucidating the origin of animal audiogenic epilepsies will bring us closer to still unsolved problems of seizure states in general. The methods which were used in studies of audiogenic epilepsies marched along with neurobiology methods starting from the middle of XX century. The same is now – new technologies are going to be applied and will be mobilized in future as these valuable models (seizure states developing in response to loud sound) are of great use for medical practice and clinic in particular.

Anxiety and Predisposition to Audiogenic Epilepsy in Rats of Different Genotypes

We studied plus-maze behavior of inbred Krushinskii−Molodkina, Wistar, and black-hooded rats (originating from the Long-Evans outbred strain) differing by predisposition to audiogenic seizures. The severity of audiogenic seizures partially correlated with anxiety and negatively correlated with the total level of locomotor activity in the elevated plus-maze. The anxiety parameters in Krushinskii−Molodkina rats were evaluated after injection of anticonvulsant levetiracetam and anxiolytic afobazol. Levetiracetam and afobazol somewhat stimulated locomotor activity.

Audiogenic kindling changes the subunit composition of BK-channels in dentate gyrus of Krushinskii-Molodkina rats

Subunit composition of voltage- and Ca2+-sensitive high-conductance K+ channels (BK channels) in dentate gyrus (DG) of Krushinskii-Molodkina (KM) rats, genetically prone to audiogenic seizures, was compared with that of normal Wistar rats, resistant to sound effects. Additionally, long-lasting changes in protein expression of α- and β4-subunits in DG of KM rats after audiogenic kindling (model of temporal lobe epilepsy) was investigated. Western blot analysis revealed no differences between the levels of the pore-forming α-subunit expression in DG of KM and Wistar rats. In contrast, the level of brain-specific auxiliary β4-subunit in DG of KM rats was increased twofold in comparison to that in Wistar rats. It is likely that the observed changes in the BK channel α/β4 subunits ratio can prevent the development of excessive neuronal exitability in DG of KM rats. The results obtained on the model of audiogenic kindling (20 convulsion fits) confirmed this assumption. Thus, α-subunit expression levels in DG of KM rats on day 3 and 14 after the last seizure were increased 2.5 times in comparison with intact KM rats. The expression level of β4 in DG of KM rats 3 days after kindling was reduced to 30% of the control level. On day 14 after finishing audiogenic kindling, a further reduction of β4 protein expression level occurred. We suggest that the changes in the subunit composition of BK channels in DG following chronic seizures can alter functional properties of DG as a physiological filter, which normally prevents the propagation of epileptiform activity in the hippocampus.

Binding of Specific Ligand by D2- and NMDA-Receptors of Striatum Cells in Two Rat Strains Predisposed and Resistant to Audiogenic Seizures

We studied parameters of specific receptor binding of D2-dopamine receptor ligand [3H]-sulpiride and NMDA-receptor ligand [3H]-MK-801 on the membranes of striatum cells in Krushinsky–Molodkina rats (predisposed to audiogenic seizures) and strain “0” selected for the absence of audiogenic seizures. No interstrain differences were observed in affinity (Kd) of both D2- and NMDA-receptors to ligands. At the same time, significant interstrain differences in receptor density (Bmax) were found for both D2-receptors and NMDA-receptors. The reduced number of dopamine and glutamate receptors in the striatum can be associated with neurological peculiarities of Krushinsky–Molodkina rat strain (audiogenic seizures and postictal catalepsy).