Conventional anticonvulsant drugs in the guinea-pig kindling model of partial seizures: effects of acute carbamazepine

This study addressed the anticonvulsant effect of carbamazepine (CBZ) in the guinea-pig kindling model to further test this model for the screening of anticonvulsant drugs. We analysed plasma concentrations of CBZ at various time intervals after intraperitoneal injection of either 10, 25 or 40 mg/kg CBZ. Behavioural toxicity was assessed at 0.5 h postinjection using quantitative locomotor tests, as well as scores on a sedation/muscle relaxation rating index. The anticonvulsant efficacy of CBZ was evaluated from measurements of afterdischarge threshold (ADT), afterdischarge duration (ADD), and behavioural seizure severity at three phases of kindling: non-kindled, kindling acquisition (early and late) and kindled (50+ ADs). ADD and seizure severity were also measured in response to both threshold and suprathreshold kindling stimulation. Plasma levels of CBZ were within, or higher, than the human therapeutic range at the time of behavioural testing and kindling. CBZ exerted slight effects in guinea-pigs on the sedation rating index but not the behavioural tests. CBZ increased ADT and reduced ADD and seizure severity throughout all phases of kindling, indicating that the guinea-pig model correctly predicts CBZ's anticonvulsant effect. CBZ in the guinea-pig kindling model produced consistent anticonvulsant activity that did not appear to be dependent on stimulation intensity.     

Conventional anticonvulsant drugs in the guinea-pig kindling model of partial seizures: effects of repeated administration

This study addressed the anticonvulsant effects of repeated administration of phenytoin, carbamazepine, phenobarbital, valproate, and ethosuximide in kindled guinea-pigs in order to further substantiate this novel model of partial seizures for the screening of future anticonvulsant drugs. Behavioral toxic effects were assessed at 30 min following drug administration using scores on a sedation/muscle relaxation rating index. In response to suprathreshold stimulation, the anticonvulsant efficacy of the drugs were evaluated from measurements of afterdischarge duration (ADD) and behavioral seizure severity (SS) during a repeated drug treatment schedule in kindled guinea-pigs. All drugs exerted slight to moderate sedative effects in guinea-pigs on our rating index. We found that phenytoin, carbamazepine, and phenobarbital exhibited effective anticonvulsant properties in kindled guinea-pigs by reducing both ADD and SS. We found that valproate consistently reduced ADD throughout the treatment schedule but failed to significantly reduce SS. Lastly, ethosuximide failed to exhibit effective anticonvulsant properties. Our results indicate that the guinea-pig kindling model correctly predicted the actions of these common anticonvulsant drugs in the treatment of partial seizures. Guinea-pig amygdala kindling appears to serve as a useful and valid model for partial epilepsy.     

Conventional anticonvulsant drugs in the guinea pig kindling model of partial seizures: effects of acute phenobarbital,valproate, and ethosuximide

This study addressed the anticonvulsant effects of phenobarbital, valproate, and ethosuximide in the amygdala of kindled guinea pigs to further validate this model for the screening of anticonvulsant drugs. Behavioral toxic effects were assessed at 30 min following drug administration using quantitative locomotor tests, as well as scores on a sedation and muscle relaxation rating index. The anticonvulsant efficacy of the drugs were evaluated from measurements of afterdischarge threshold (ADT), afterdischarge duration (ADD), and behavioral seizure severity (SS) during early and late phases of kindling acquisition, and in kindled guinea pigs. ADD and SS were also measured in response to both threshold and suprathreshold kindling stimulation. All drugs exerted slight to moderate sedative effects in guinea pigs on both the behavioral tests and rating index. We found that phenobarbital exhibited effective anticonvulsant properties in guinea pigs by consistently reducing ADD and SS in response to both threshold and suprathreshold kindling stimulation. Valproate exhibited effective anticonvulsant properties at threshold stimulation and less effective properties at suprathreshold stimulation. Lastly, we found that ethosuximide lacked effective anticonvulsant action at either threshold or suprathreshold kindling stimulation. Our results indicate that the guinea pig kindling model correctly predicted the actions of phenobarbital, valproate, and ethosuximide in the treatment of partial seizures. Guinea pig amygdala kindling appears to serve as a useful and valid model for partial epilepsy.     

The protective effect of dl-tetrahydropalmatine against the development of amygdala kindling seizures in rats

The influence of dl-tetrahydropalmatine (THP), an active component isolated from a Chinese herbal medicine corydalis, was tested on the development of electrically kindled amygdala. The seizure activity was quantified by a ultrasonic system for vertical motion measurements. Intraperitoneal injection of THP (20 or 30 mg kg⁻¹) 30 min before applying the daily kindling stimulus prevented the development of the kindling process. The behavioral seizure score and the motion responses which normally develop during electrical kindling were reduced below their initial values. The results suggest that THP is a very effective antiepileptogenic and anticonvulsant agent when applied to electrically kindled rats.     

Influence of the MTHFR genotype on the rate of malformations following exposure to antiepileptic drugs in utero

Folate deficiency and the presence of the 677C > T (CT) polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene have been implicated in the causation of malformations in the fetus (particularly cleft lip and palate and neural tube defects). These birth defects are also recognised complications of exposure to antiepileptic drugs (AEDs). In pregnant women with epilepsy, the use of AEDs has an added effect on the physiological reduction in folate levels, which may be enhanced further by the presence of the 677C > T polymorphism in the mother.

We studied the MTHFR genotype and rate of major malformations (MM) in 187 mother-child pairs where the mothers had epilepsy and in 236 matched control pairs. Sodium valproate (VPA) was the most commonly used drug and was associated with the highest rate of malformations (9.6%). 49% of mothers, both in the cases and controls were heterozygotes for the 677C > T polymorphism. The rate of MM was increased in offspring of mothers who were heterozygous or homozygous for 677C > T genotype amongst AED-exposed cases, but more so in those exposed to VPA. The effect of the VPA on the rate of MM was much higher [OR 7.79, 95% CI (1.45–41.9)] than the effect of the maternal 677C > T genotype [OR 2.57, 95% CI (0.28–23.7)]. There was no association between the child's MTHFR genotype and the rate of MM. Conclusion: This study indicates that although the maternal MTHFR genotype may confer susceptibility to the teratogenic effect of AEDs, particularly VPA, it is likely that the main teratogenic effects are mediated through other mechanisms.     

The central piriform cortex: anatomical connections and anticonvulsant effect of GABA elevation in the kindling model

The piriform cortex (PC) is thought to be critically involved in the generation and propagation of forebrain (limbic type) seizures in the rat. The PC extends over a large area at the ventrolateral side of the rat brain with an anterior part highly sensitive for bicuculline-induced and a central part most sensitive for electrically induced seizures. Therefore, distinct parts of the PC might be differentially involved in the generation and spread of seizure activity. Since previous studies indicated that a loss of GABAergic inhibition in the PC is involved in the generation of epileptic activity, we microinjected the GABA-transaminase blocker vigabatrin bilaterally in the anterior, central and posterior PC of previously amygdala-kindled rats and repeatedly tested its effect on kindled seizures. Vigabatrin was anticonvulsant in all groups for up to 13 days with a maximal effect 24 h after injection. However, the anticonvulsant effect on seizure generalization was strongest after microinjection in the central PC suggesting that GABAergic synapses in this part are critically involved in the development of generalized seizures. Since differences in anatomical connections of the PC regions may be responsible for differences in seizure susceptibility, we addressed this question by injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin in different PC subregions. Although there were similarities in the projections from different PC subregions, we also found differences between the PC subregions in their projections to structures known to be important in the limbic seizure network, such as the perirhinal cortex, nucleus accumbens, and striatum. These differences in anatomical connectivity between PC subregions may be involved in the differences in seizure susceptibility observed in the present and previous studies.     

The role of the inferior colliculus in a genetic model of audiogenic seizures

Previous studies have shown the functional importance of the inferior colliculus (IC) for the propagation and initiation of audiogenic seizures in several models of epilepsy in rats. A review of the cell types and cytoarchitecture of the IC, including its three major subdivisions, is presented. Significant increases in GABA levels and the number of GABAergic neurons are found in the central nucleus of the IC (ICCN) of genetically epilepsy-prone rats (GEPR-9s) as compared to Sprague-Dawley rats that do not display audiogenic seizures. Two independent anatomical methods were used to determine the number of GABAergic neurons, immunocytochemistry and in situ hybridization. In both types of preparation, the labeled cells in the ICCN appeared to be of different sizes but the number of small cells with diameters less than 15 m showed the greatest increase. Nisslstained sections showed that the total number of neurons in the ICCN was increased in GEPR-9s and indicated that the increase in GABAergic neurons was not due to a change in the phenotype of collicular neurons from non-GABAergic to GABAergic. The number of small neurons in Nissl-stained sections of the ICCN was shown to correlate with seizure severity in the offspring of crosses made between Sprague-Dawley rats and GEPR-9s. Furthermore, the GEPR-3s that display moderate seizures showed a significant increase in the number of small neurons in the ICCN, and the magnitude of this increase was predicted from this correlation. Finally, the use of knife cuts through the midbrain indicated that the ICCN sends an important projection to the external nucleus and that this projection plays a vital role in the propagation of seizure activity from the site of seizure initiation in the ICCN. It remains to be resolved how the increase in small GABAergic neurons in the ICCN is responsible for the known pharmacological defects observed at GABAergic synapses.     

Diversity of kindling effects: EEG manifestations in cats during kindling in the hippocampal formation

The formation and subsequent development of after-discharges (ADs) and spontaneous interictal spikes was investigated in a group of ten kindled cats. The electrodes used for electrical stimulation and EEG recording were located in various parts of the hippocampal formation: in the hippocampal gyrus, dentate gyrus, subiculum and entorhinal cortex. The animals were stimulated once daily with 1 s trains of 50/s electric pulses. The choice of stimulating electrodes, stimulating currents and, in some cases, monitoring of the stability of stimulating conditions was aided by recording hippocampal field potentials evoked by intrahippocampal electrical stimulation. A subgroup of 5 cats was stimulated at AD threshold or near threshold currents of constant intensity. The following patterns of AD development were observed: (i) a long lasting initial phase of stable, a few second-long ADs with subsequent development, culminating in prolonged ADs and complex partial or secondary generalized tonic clonic seizures, after 80-120 days of kindling; (ii) stable pattern of brief ADs (0.3-1.5 s duration) during 120 days of kindling; (iii) gradual development of initially brief ADs (about 5 s) into longer lasting ADs (about 35 s) associated with complex partial seizures, during 220 days of stimulation. Spontaneous interictal spikes developed in this subgroup after 16-15 days of kindling. The second subgroup of 5 animals was subjected to stimulation with gradually increasing AD subthreshold currents. In two animals of this subgroup spontaneous EEG discharges of isolated spikes and clusters of high frequency spikes appeared in the stimulated hippocampal gyrus after 10 days of kindling. Apart from the diversity of after-discharge development patterns the results indicate relative independence of the processes underlying formation of the spontaneous interictal spikes and after-discharges.     

Experimental manipulations of the subthalamic nucleus fail to suppress tonic seizures in the electroshock model of epilepsy

Recently, it has been shown that the subthalamic nucleus (STN) has anticonvulsant effects on epileptic seizures originating from the forebrain. The aim of the present study was to determine whether the anticonvulsant properties of the STN extend to the suppression of tonic seizures originating from the brainstem elicited by electroshock in rats. Three different procedures were used to manipulate activity in the STN and in each case the duration of tonic hindlimb extension elicited by electroshock was used as a measure of seizure-severity. Under general anesthesia, two groups of rats received chronic implants of either bilateral stainless steel guide cannulae or bilateral bipolar stimulating electrodes stereotaxically implanted and aimed at the STN. After 3 days of recovery, each rat in the first group was tested with electroshock on three consecutive days after having received 220 nl bilateral microinjections into the STN of either 200 or 400 pmol of muscimol (a GABA agonist) dissolved in saline or the same volume of normal saline. In the second group the electroshock test was conducted, again on three consecutive days, immediately following high frequency electrical stimulation (HFS) of the STN at 130 or 260 Hz or a no current control condition. In the third group, rats were tested with electroshock before and after bilateral excitotoxic lesions of the STN with either kainic or ibotenic acids. None of these manipulations produced significant suppression of the tonic hind limb extension elicited by electroshock compared with the relevant control conditions. This suggests that, within the limitations of the current procedures, the anticonvulsant properties of the STN appear to be ineffective against tonic seizures originating in the brainstem.     

Balancing the benefits and costs of antibiotic drugs: the TREAT model

TREAT is a computerized decision support system aimed at improving empirical antibiotic treatment of inpatients with suspected bacterial infections. It contains a model that balances, for each antibiotic choice (including ‘no antibiotics’), expected benefit and expected costs. The main benefit afforded by appropriate, empirical, early antibiotic treatment in moderate to severe infections is a better chance of survival. Each antibiotic drug was consigned three cost components: cost of the drug and administration; cost of side effects; and costs of future resistance. ‘No treatment’ incurs no costs. The model worked well for decision support. Its analysis showed, yet again, that for moderate to severe infections, a model that does not include costs of resistance to future patients will always return maximum antibiotic treatment. Two major moral decisions are hidden in the model: how to take into account the limited life-expectancy and limited quality of life of old or very sick patients; and how to assign a value for a life-year of a future, unnamed patient vs. the present, individual patient.     

mGluR7在氯化锂-匹罗卡品反复致癎大鼠海马的表达及作用

目的:通过氯化锂-匹罗卡品反复致癎大鼠模型,探讨代谢型谷氨酸受体7(mGluR7)在癫癎发作过程中的作用。方法:大鼠分为正常对照组和模型组,用氯化锂-匹罗卡品制作癫癎模型,将模型组中致癎成功鼠分为反复刺激组和静止期组,致癎不成功作为不成功组。制作冰冻切片用免疫组化法检测4组大鼠海马CA1、CA3区及齿状回mGluR7光密度值。结果:与正常对照组相比,静止期组大鼠海马各区表达均减弱,以齿状回差别最明显,反复刺激组各区表达均明显增强,不成功组无明显改变。结论:mGluR7表达上调提示癫癎多次发作可能增强了其对谷氨酸释放的负反馈调节和摄取作用; mGluR7在静止期表达下调提示其可能有助于慢性期癫癎环路的形成。     

Pharmacology of glutamate receptor antagonists in the kindling model of epilepsy

It is widely accepted that excitatory amino acid transmitters such as glutamate are involved in the initiation of seizures and their propagation. Most attention has been directed to synapses using NMDA receptors, but more recent evidence indicates potential roles for ionotropic non-NMDA (AMPA/kainate) and metabotropic glutamate receptors as well.Based on the role of glutamate in the development and expression of seizures, antagonism of glutamate receptors has long been thought to provide a rational strategy in the search for new, effective anticonvulsant drugs. Furthermore, because glutamate receptor antagonists, particularly those acting on NMDA receptors, protect effectively in the induction of kindling, it was suggested that they may have utility in epilepsy prophylaxis, for example, after head trauma.However, first clinical trials with competitive and uncompetitive NMDA receptor antagonists in patients with partial (focal) seizures, showed that these drugs lack convincing anticonvulsant activity but induce severe neurotoxic adverse effects in doses which were well tolerated in healthy volunteers. Interestingly, the only animal model which predicted the unfavorable clinical activity of competitive NMDA antagonists in patients with chronic epilepsy was the kindling model of temporal lobe epilepsy, indicating that this model should be used in the search for more effective and less toxic glutamate receptor antagonists.In this review, results from a large series of experiments on different categories of glutamate receptor antagonists in fully kindled rats are summarized and discussed. NMDA antagonists, irrespective whether they are competitive, high- or low-affinity uncompetitive, glycine site or polyamine site antagonists, do not counteract focal seizure activity and only weakly, if at all, attenuate propagation to secondarily generalized seizures in this model, indicating that once kindling is established, NMDA receptors are not critical for the expression of fully kindled seizures.In contrast, ionotropic non-NMDA receptor antagonists exert potent anticonvulsant effects on both initiation and propagation of kindled seizures. This effect can be markedly potentiated by combination with low doses of NMDA antagonists, suggesting that an optimal treatment of focal and secondarily generalized seizures may require combined use of both non-NMDA and NMDA antagonists. Given the promising results obtained with novel AMPA/kainate antagonists and glycine/NMDA partial agonists in the kindling model, the hope for soon having potentially useful glutamate antagonists for use in epileptic patients is increasing.     

Evidences of cannabinoids-induced modulation of paroxysmal events in an experimental model of partial epilepsy in the rat

The anticonvulsant effect of cannabinoids (CB) has been shown to be mediated by the activation of the CB₁ receptor. This study evaluates the anticonvulsant activity of (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-Yl]-1-naphthalenylmethanone (WIN55,212-2, CB agonist) alone or preceded by the administration of N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251, selective CB₁ antagonist) in an experimental in vivo model of complex partial seizures (maximal dentate gyrus activation – MDA) in the rat. WIN55,212-2 (21 mg kg⁻¹) exerted an anticonvulsant effect, significantly reduced by the pre-treatment with AM251 (1 mg kg⁻¹, 30 min interval). Surprisingly, AM251, administered alone at the same dose, failed to induce any modification in MDA responses. Our data suggest the involvement of the CB system in the inhibitory control of hyperexcitability phenomena in a model of acute partial epilepsy. Although the MDA model per se does not induce a basal activation of CB₁ receptors, as suggested by the lack of efficacy of AM251 when administered alone, the partial suppression of WIN55,212-2-induced effects in rats pre-treated with AM251 allows to hypothesise that the WIN55,212-2-induced antiepileptic effect is strictly linked to an increased CB₁ receptor activation or to the involvement of further receptor subtypes.     

Behavioural and electrophysiological studies on the paradoxical antinociceptive effects of an extremely low dose of naloxone in an animal model of acute and localized inflammation

Summary We have previously described the paradoxical antinociceptive effect of low doses of an opiate antagonist, naloxone, in rats suffering from chronic arthritis induced by Freund's adjuvant. In the present work, the appearance of this naloxone sensitivity was studied, using a model of inflammatory hyperalgesia with a more rapid onset, namely carrageenin-induced rat paw edema. In these animals, an extremely low dose of naloxone (3 g/kg i.v.), induced a clear antinociceptive effect (as gauged by the vocalisation threshold to paw pressure), which was observed for both the edematous and the contralateral hind-paw. Small and transient 1 h after carrageenin injection, this effect increased progressively 4 h and 24 h later, reaching a level comparable to that observed with morphine 1 mg/kg i.v. in normal rats, at 24 h. Electrophysiological studies performed in parallel, confirmed the behavioural data so that 24 h after the injection of carrageenin, naloxone (3 g/kg i.v.) reduced the VB thalamic neuronal responses elicited by stimulation of the inflamed paw by 50%. Hypothesis concerning the mechanisms of the paradoxical action of naloxone in models of inflammatory hyperalgesia are discussed.     

Low-frequency stimulation of the hippocampal CA3 subfield is anti-epileptogenic and anti-ictogenic in rat amygdaloid kindling model of epilepsy

Neuromodulation with low-frequency stimulation (LFS), of brain structures other than epileptic foci, is effective in inhibiting seizures in animals and patients, whereas selection of targets for LFS requires further investigation. The hippocampal CA₃ subfield is a key site in the circuit of seizure generation and propagation. The present study aimed to illustrate the effects of LFS of the CA₃ region on seizure acquisition and generalization in the rat amygdaloid kindling model of epilepsy. We found that LFS (monophasic square-wave pulses, 1 Hz, 100 μA and 0.1 ms per pulse) of the CA₃ region significantly depressed the duration of epileptiform activity and seizure acquisition by retarding progression from focal to generalized seizures (GS). Moreover, GS duration was significantly shortened and its latency was significantly increased in the LFS group demonstrating an inhibition of the severity of GS and the spread of epileptiform activity. Furthermore, LFS prevented the decline of afterdischarge threshold (ADT) and elevated GS threshold indicating an inhibition of susceptibility to GS. These results suggest that LFS of the hippocampal CA₃ subfield is anti-epileptogenic and anti-ictogenic. Neuromodulation of CA₃ activity using LFS may be an alternative potential approach for temporal lobe epilepsy treatment.     

Cyclic GMP and cyclic AMP in the cerebral cortex of mice during seizures induced by 3-mercaptopropionic acid: effects of anticonvulsant agents

The onset of clonic seizures induced by 3-mercaptopropionic acid (MP) was associated with an approximately 200% increase of cAMP and a 70% elevation of cGMP in the mouse cerebral cortex. There was a further rise of both nucleotides during the subsequent tonic phase of convulsions; cAMP levels reached 400% and cGMP levels 300% of control values. The levels of both nucleotides did not differ from the controls 20 min after the termination of tonic seizures. When MP convulsions were prevented by Na-phenobarbital, the levels of both nucleotides were not different from control concentrations. Phenytoin prevented the tonic extension, but did not affect the clonic seizures. The accumulation of cAMP was markedly reduced (a residual + 40%), whereas the increased levels of cGMP remained unaffected.     

Delayed effects of hypotensive drugs on structural characteristics of the renal glomerular system in hypertensive NISAG rats

Comparative morphometrical study of the renal glomerular system was carried out in hypertensive NISAG rats treated with hypotensive drugs during the prepubertal period. Blockade of the renin-angiotensin system with enalapril or losartan during the critical period of ontogeny (the 2nd month of life) produced a long-term hypotensive and renoprotective effect. Treatment with α-adrenoblocker terazosin during this period of ontogeny produced a less pronounced hypotensive effect, though with renoprotection. Corinfar (Ca²⁺ channel blocker) was least effective. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 6, pp. 695–699, June, 2007