Differences in kindling development in seven outbred and inbred rat strains

The kindling phenomenon, i.e., the progressive development of focal and secondarily generalized seizures upon repeated electrical stimulation of a limbic brain region, occurs in various species, but with marked differences in kindling rate between species and also within the same species. In rats, differences in kindling rates have been reported within the same strain and between different strains, and both genetic and environmental influences are thought to be involved in this variability. In most studies on kindling in rats, outbred strains such as Sprague-Dawley have been used. In the present study, we compared rates of amygdala kindling development in two outbred (Sprague-Dawley, Wistar) and five inbred (Lewis, Fischer 344, ACI, Wistar-Kyoto, Brown Norway) rat strains, including several strains which have not been kindled before. We were particularly interested which parts of the stepwise progression of kindling differ among these strains. Furthermore, the sensitivity of the basolateral amygdala to electrical stimulation was determined before and after kindling. Once daily electrical stimulation of the basolateral amygdala resulted in marked interstrain differences in kindling rates, with Sprague-Dawley and Brown-Norway rats exhibiting the lowest number of stimulations to reach fully kindled (stage 5) seizures, and Lewis rats showing the highest number of the 7 strains. In contrast to the significant differences in number of stimulations to reach the fully kindled state, total (cumulative) afterdischarge duration (ADD) to reach stage 5 did not significantly differ among strains, substantiating that cumulative AD is the principal factor in the acquisition of kindled seizures. Marked differences in ADD of a stage 5 seizure were obtained between strains, with strains kindling rapidly exhibiting longer ADD than strains kindling slowly. Postkindling afterdischarge threshold (ADT) varied significantly among strains, but only 3 of the 7 strains showed a decrease of ADT compared to prekindling values. When the stepwise progression of kindling was evaluated, pronounced interstrain differences were determined in the time spent in the initial phase of kindling, i.e., stage 1 seizures, both in terms of stimulations and cumulative ADD, indicating that variations in kindling rates were predominantly due to the time needed to progress from stage 1 to subsequent stages of the kindling process. The data seem to indicate that inbred rat strains offer an interesting resource for dissecting the underlying genetic basis for phenotypic differences in epileptogenesis as induced by kindling, although the high variability of kindling rates seen within some inbred strains weakens this possibility.     

Anticonvulsant activity of felbamate in amygdala kindling model of temporal lobe epilepsy in rats

PURPOSE: Previous studies have demonstrated that felbamate (FBM, 2-phenyl-1,3-propanediol dicarbamate) at nontoxic doses exerts potent anticonvulsant activity in a variety of animal epilepsy or seizure models. We further characterized the anticonvulsant activity of FBM by using the kindling model of temporal lobe epilepsy (TLE). METHODS: The experiments were performed in fully kindled rats. The anticonvulsant effect of FBM was assessed by determining seizure severity, afterdischarge (AD) duration and seizure duration either at the focal seizure threshold, or after suprathreshold stimulation. In addition, the neurological performance of kindled rats after FBM administration was evaluated in the open field and by the rotorod test. RESULTS: FBM at doses of 12.5-50 mg/kg, given intraperitoneally (i.p.) 60 min before testing, dose-dependently increased the AD threshold (ADT). The maximal effect was achieved after the highest dose tested and reached almost 600% of the control ADT. This dose of FBM significantly diminished other seizure parameters, e.g., seizure severity, seizure duration, and AD duration. When the rats were stimulated with suprathreshold current (500 microA) seizure severity was moderately but significantly reduced. No behavioral abnormalities were noted in kindled rats after administration of either of the doses. CONCLUSIONS: FBM potently increases the threshold for focal seizures and reduces seizure severity, seizure duration, and AD duration at doses that produce no adverse behavioral effects in amygdala-kindled rats. These data are thus compatible with clinical experience with FBM in TLE and substantiate that kindling is a good predictor of anticonvulsant activity against TLE.     

Cloning and expression of the human galanin receptor GalR2

We have previously shown that the novel anticonvulsant levetiracetam exerts potent anticonvulsant activity against both focal and secondarily generalized seizures in fully amygdala-kindled rats, i.e. , a model of temporal lobe epilepsy. We examined whether levetiracetam also exhibits antiepileptogenic activity, i.e., prevents or retards acquisition or development of amygdala-kindling in rats. Before the experiments with chronic administration of levetiracetam at different doses, we determined the pharmacokinetics of the drug after i.p. injection. Levetiracetam had a relatively short half-life (about 2-3 hr) in rats, so that any lasting effects of the drug after chronic administration were certainly not due to drug accumulation. When rats were treated with levetiracetam during kindling acquisition at daily i.p. doses of 13, 27 or 54 mg/kg, the drug dose-dependently suppressed the increase in seizure severity and duration induced by repeated amygdala stimulation. After termination of daily treatment with 54 mg/kg, duration of behavioral seizures and of afterdischarges recorded from the amygdala remained to be significantly shorter compared to vehicle controls, although amygdala stimulations were continued in the absence of drug. These data thus indicate that levetiracetam not simply masked the expression of kindled seizures through an anticonvulsant action, but exerted a true antiepileptogenic effect. Adverse effects were not observed at any dose of levetiracetam tested in kindled rats. The powerful antiepileptogenic activity of levetiracetam in the kindling model indicates that levetiracetam is not only an interesting novel drug for symptomatic treatment of epilepsy but might be suited for pharmacological prevention of this disease in patients with a high prospective risk of the development of epilepsy.     

Epileptogenesis in vivo enhances the sensitivity of inhibitory presynaptic metabotropic glutamate receptors in basolateral amygdala neurons in vitro

Modulation of excitatory synaptic transmission by presynaptic metabotropic glutamate receptors (mGluRs) was examined in brain slices from control rats and rats with amygdala-kindled seizures. Using whole-cell voltage-clamp and current-clamp recordings, this study shows for the first time that in control and kindled basolateral amygdala neurons, two pharmacologically distinct presynaptic mGluRs mediate depression of synaptic transmission. Moreover, in kindled neurons, agonists at either group II- or group III-like mGluRs exhibit a 28- to 30-fold increase in potency and suppress synaptically evoked bursting. The group II mGluR agonist (2S,3S,4S)-2-(carboxycyclopropyl)glycine (L-CCG) dose-dependently depressed monosynaptic EPSCs evoked by stimulation in the lateral amygdala with EC50 values of 36 nM (control) and 1.2 nM (kindled neurons). The group III mGluR agonist L-2-amino-4-phosphonobutyrate (L-AP4) was less potent, with EC50 values of 297 nM (control) and 10.8 nM (kindled neurons). The effects of L-CCG and L-AP4 were fully reversible. Neither L-CCG (0.0001-10 microM) nor L-AP4 (0.001-50 microM) caused membrane currents or changes in the current-voltage relationship. The novel mGluR antagonists (2S,3S,4S)-2-methyl-2-(carboxycyclopropyl)-glycine (MCCG; 100 microM) and (S)-2-methyl-2-amino-4-phosphonobutyrate (MAP4; 100 microM) selectively reversed the inhibition by L-CCG and L-AP4 to 81.3 +/- 12% and 65.3 +/- 6.6% of predrug, respectively. MCCG and MAP4 (100-300 microM) themselves did not significantly affect synaptic transmission. The exquisite sensitivity of agonists in the kindling model of epilepsy and the lack of evidence for endogenous receptor activation suggest that presynaptic group II- and group III-like mGluRs might be useful targets for suppression of excessive synaptic activation in neurological disorders such as epilepsy.     

A role for the bilateral involvement of perirhinal cortex in generalized kindled seizure expression

The perirhinal cortex (PRh) has been suggested as a substrate for the expression of generalized clonic seizures in the late stages of kindling development (stages 4-5). Using the induction of Fos as a marker of neuronal activation, the PRh region was investigated after kindling or nonkindling electrical stimulation. Nonkindling electrical stimulation of the PRh elicited stimulus-locked behaviors, without afterdischarge. These behaviors were characterized by rearing and bilateral forelimb clonus which were terminated upon electrical stimulus offset in half of the rats displaying this behavior (with the other half expressing self-sustained seizures). In these animals, Fos immunoreactivity was found throughout neocortical and subcortical structures in the hemisphere ipsilateral to the stimulating electrode. By contrast, Fos-immunoreactivity in the contralateral hemisphere was localized primarily in the PRh and frontal motor cortex. Likewise, similar patterns of Fos immunoreactivity were observed in both hemispheres of rats following kindling to one generalized clonic seizure from several limbic and paleocortical structures. These results suggest that the bilateral involvement of the PRh is critical in producing the bilateral behaviors associated with generalized clonic seizure expression. In support of this interpretation, infusion of 3 M KCl directly into the contralateral PRh of rats kindled to a single stage 4-5 (generalized clonic) seizure from the ipsilateral amygdala reduced seizure manifestations from a generalized clonic seizure (stage 4-5) to a unilateral clonic seizure (stage 3) without affecting measures of focal excitability. Taken together, these data indicate a role for the bilateral involvement of the PRh in generalized clonic seizure expression whether evoked from the naive or kindled state. These results further indicate that bilateral behaviors require the bilateral involvement of the structures necessary for the expression of these behaviors.     

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.     

Comparison of the short- and long-lasting effects of perforant path kindling on radial maze learning.

Compared the long-lasting with the short-lasting effects of kindling the perforant path input to the hippocampal formation on the acquisition of 2 radial maze tasks. Animals in the long-term group were fully kindled (i.e., Stage 5 motor seizures were evoked) prior to a stimulation-free training period. Animals in the short-term group were kindled 30–45 min prior to each learning trial. A 3rd group of animals served as controls and were never kindled. On both 8-arm and 4/8-arm radial maze tasks, learning impairments were apparent only in the short-term group. Thus, the impaired learning is more likely related to the short-term aftereffects of an afterdischarge than to any long-term alterations in the neuronal status of the brain caused by kindling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selection of phenytoin responders and nonresponders in male and female amygdala-kindled Sprague-Dawley rats

PURPOSE: We recently described that, by repeated testing of the anticonvulsant phenytoin (PHT), it is possible to select responders and nonresponders from large populations of amygdala-kindled Wistar rats. Whereas responders show marked and reproducible increases of focal seizure threshold (afterdischarge threshold: ADT) on repeated testing of PHT, 75 mg/kg i.p., nonresponders do not show any significant ADT increase after this dose, thus allowing use of these subgroups in the search for mechanisms of pharmacoresistance in temporal lobe epilepsy. In this study, we examined whether PHT responders and nonresponders can also be selected from large groups of kindled rats of the Sprague-Dawley strain. METHODS: Male and female Sprague-Dawley rats were amygdala kindled, followed by once weekly i.p. testing of PHT. RESULTS: In contrast to recent experiments in Wistar rats, 75 mg/kg PHT did not induce significant ADT increases in Sprague-Dawley rats, indicating strain differences in response to this drug after kindling. When the dose was lowered to 50 or 25 mg/kg, significant and reproducible ADT increases were obtained in Sprague-Dawley rats of both genders. Therefore these doses were used for selection of responders and nonresponders in a total of 42 rats. Almost 50% of the rats were PHT responders, whereas no rat was a nonresponder when tested in up to six subsequent drug trials. Many rats were variable responders (i.e., showed ADT increases in some but not all trials), which was not due to low or variable drug absorption after i.p. injection. CONCLUSIONS: The data indicate that, in contrast to Wistar rats, Sprague-Dawley rats are not suited for selection of PHT nonresponders, but rather are quite responsive to this drug. A further difference to the Wistar strain is the truncated dose-response with loss of anticonvulsant efficacy at 75 mg/kg in kindled Sprague-Dawley rats, which may, at least in part, explain the inconsistent results reported on the anticonvulsant efficacy of PHT in this strain in the literature. The lack of anticonvulsant activity after administration of 75 mg/kg may be a result of kindling, because administration of this dose before kindling causes a significant ADT increase in this strain. This kindling-induced alteration of the anticonvulsant activity of PHT is a phenomenon that contrasts Sprague-Dawley with Wistar rats and deserves further investigation.     

Conformation induction in melanotropic peptides by trifluoroethanol: fluorescence and circular dichroism study

Studies on the anticonvulsant efficacy of the major antiepileptic drug phenytoin in kindled rats have often reported inconsistent effects. It has been proposed that technical and genetic factors or poor and variable absorption of phenytoin after i.p. or oral administration may be involved in the lack of consistent anticonvulsant activity of phenytoin in this model of temporal lobe epilepsy. We examined if kindling itself changes the anticonvulsant efficacy of phenytoin by testing this drug before and after amygdala kindling in male and female Sprague-Dawley rats. To exclude the possible bias of poor and variable absorption, blood was sampled in all experiments for drug analysis in plasma. The threshold for induction of focal seizures (afterdischarge threshold; ADT) was used for determining phenytoin's anticonvulsant activity. Before kindling, phenytoin, 75 mg/kg i.p., markedly increased ADT in both genders, although the effect was more pronounced in males. Following kindling, the anticonvulsant activity obtained with phenytoin, 75 mg/kg, before kindling was totally lost, and female rats even exhibited a proconvulsant effect upon administration of this dose, indicating that kindling had dramatically altered the anticonvulsant efficacy of phenytoin. Plasma levels of phenytoin were comparable before and after kindling, and were within or near to the 'therapeutic range' known from epileptic patients. When the dose of phenytoin was reduced to 50 or 25 mg/kg i.p., significant anticonvulsant effects on ADT were obtained. When phenytoin, 50 mg/kg, was administered i.p. or i.v. in the same group of fully kindled rats, both anticonvulsant activity and plasma drug levels were comparable with both routes, indicating that the i.p. route is suited for such studies. The data indicate that kindling alters the dose-response of phenytoin in that a high anticonvulsant dose becomes ineffective or proconvulsant after kindling, possibly by an increased sensitivity of the kindled brain to proconvulsant effects of phenytoin which normally only occur at much higher doses. If similar alterations evolve in humans during development of chronic epilepsy, this may be involved in the mechanisms leading to intractability of temporal lobe epilepsy.     

Does prolonged implantation of depth electrodes predispose the brain to kindling?

Chronically implanted depth electrodes are widely used for the study of electrical signals generated in deep cerebral locations and for electrical stimulation of such locations. Although the effects of lesions resulting from electrode implantation are generally considered minimal, some reports have shown lasting neurochemical, histological, and behavioral alterations in response to such implantation. Furthermore, there is some evidence that prolonged electrode implantation may decrease the seizure threshold of the implanted region and increases the rate of kindling from this region. This prompted us to undertake a study on different periods of post-surgical delay to onset of electrical stimulation and subsequent characteristics of kindling development. Rats were implanted with a bipolar electrode in the basolateral amygdala, and the threshold for induction of focal paroxysmal activity (afterdischarge threshold, ADT) was determined after post-surgical recovery periods of either 1, 2, 4, or 8 weeks. The animals were then kindled by daily administration of an electrical stimulus until all rats exhibited fully kindled seizures. In fully kindled rats, the ADT was redetermined. Compared to animals with 1 week of electrode implantation, the pre-kindling ADT was significantly lower in rats with 2 and 4 weeks of electrode implantation, but returned towards the 1 week values at 8 weeks. An enhanced kindling rate was seen when kindling stimulations were started after 4 and 8 weeks of electrode implantation. Despite the marked differences in pre-kindling ADT, the post-kindling ADT was similar in the groups with 1, 2, or 4 weeks but significantly lower in the group with 8 weeks post-surgical delay to onset of testing. The data suggest that prolonged implantation of a bipolar electrode into a sensitive region of the limbic system predisposes the brain to kindling. Based on previous observation of iron deposits induced by electrode implantation and the epileptogenic effect of iron in cortical and limbic regions, we propose that the present observations are due to deposition of iron from hemoglobin destruction in local microhemorrhages caused by the implantation.     

Bidirectional transfer between electrical and flurothyl kindling in mice: evidence for common processes in epileptogenesis

PURPOSE: This study sought to determine whether there was a transfer of seizure susceptibility between two models of epileptogenesis, electrical kindling and a newly described model of flurothyl kindling. In this study, we determined the effects of preexposure to one kindling agent on the seizure responsiveness to the other. METHODS: Mice were divided into three groups: (a) six mice (FLK) were kindled with flurothyl, rechallenged with flurothyl after a 28-day incubation phase, implanted with olfactory bulb (OB) electrodes, and electrically kindled; (b) six mice (ELK) were implanted with OB electrodes, electrically kindled to six stage 5 seizures, and given one flurothyl trial 3 days later and a second flurothyl trial after a 28-day incubation period; and (c) six mice (IMP) were implanted with OB electrodes, tested with flurothyl at the same times as the ELK group, and later electrically kindled. RESULTS: Mice that were previously kindled with flurothyl (FLK) had significantly faster electrical kindling rates to one stage 5 seizure or to six stage 5 seizures compared with animals in the ELK and IMP groups. Mice that were previously exposed to either electrical kindling or flurothyl kindling had significantly diminished latencies to generalized seizure onset (flurothyl-induced seizure thresholds) either before or after a 28-day incubation period compared with the IMP control mice. In addition, both the FLK and ELK groups had significantly increased percentages of mice expressing forebrain-brainstem seizures, compared with the IMP group, following either rechallenge with flurothyl after a 28-day incubation or focal electrical kindling. CONCLUSIONS: These findings indicate a near-complete bidirectional transfer between these electrical and flurothyl kindling models. Mice that were previously exposed to either electrical or flurothyl kindling have increased seizure susceptibilities and altered seizure phenotypes when exposed to the other seizure paradigm. Overall, these studies indicate that previous seizures are the critical determinant of the bidirectional transfer of seizure susceptibility observed, and not the electrical or pharmacologic properties of the original kindling agent. Finally, the observation of near identity in transfer characteristics between electrical and flurothyl kindling models suggests that the proepileptogenic processes initiated by exposure to either model are similar.     

Caloric restriction alters seizure disposition and behavioral profiles in seizure-prone (fast) versus seizure-resistant (slow) rats.

Caloric restriction (CR), primarily known for extending life span, has proven anticonvulsant in several seizure models and antiepileptogenic in a strain of inherently seizure susceptible mice. Our animal model consisted of a seizure-prone (Fast) strain that naturally exhibits attention-deficit/hyperactivity disorder (ADHD)-like behaviors and a comparison seizure-resistant (Slow) strain; we evaluated CR’s effect on the typical seizure sensitivities and behavioral profiles of each strain. Fast and Slow rats were fed ad libitum or were calorically restricted to 80% of free-feeding body weight. Rats were then tested in the open field (hyperactivity), Morris water maze (learning and attention), and restraint (impulsivity) paradigms and finally kindled from the amygdala. Ultimately, CR abolished signs of abnormal hyperactivity in the Fast strain and retarded their kindling rates, making it the first manipulation to demonstrate an antiepileptogenic effect in this animal model. CR also shortened seizure durations in fully kindled Slow rats but had no effect on their kindling rates, implying a differential effect of CR on genotype. These results clearly endorse further investigation into the potential benefits of CR for both epilepsy and ADHD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of phenytoin-resistant kindled rats, a new model of drug-resistant partial epilepsy: comparison of inbred strains

PURPOSE: Previous work from our laboratory showed that amygdala-kindled Wistar outbred rats can be selected according to the increase of afterdischarge threshold (ADT) after phenytoin application. Animals that consistently do not respond to phenytoin (PHT) with an ADT increase (non-responders) are the first animal model of pharmacoresistant complex partial seizures. In this study, we determined the ability to respond to PHT in male kindled rats of different inbred strains. METHODS: The experiments were performed in fully kindled rats of five different inbred strains, Wistar-Kyoto, Lewis, Fischer 344, ACI, and Brown Norway. The response type of each rat was revealed by four consecutive PHT applications (75 mg/kg, i.p.) in fully kindled rats. RESULTS: PHT application resulted in plasma concentrations ranging from some 16 microg/ml in Lewis rats to 35 microg/ml in Fischer 344 rats, and in slight ataxia, most strongly in Fischer 344 rats. The rats of each strain did not show a homogeneous response to PHT. A significant increase of ADT was found after 86-97% of applications in Lewis, Wistar-Kyoto, and Fischer 344 rats. In contrast, Brown Norway rats responded in only 34% of experiments. This led to a considerable number of responders (i.e., consistent ADT increase by >20%) in Fischer 344, Wistar-Kyoto, and Lewis rats. The only strain revealing nonresponders (i.e., consistent lack of ADT increase by >20% with PHT treatment) was Brown Norway. CONCLUSIONS: Inbred strains, although genetically more homogenous than outbred strains, differ in their response to PHT. Brown Norway rats can offer advantages for further detailed investigation of the resistance to PHT in the kindling model of complex partial seizures.     

The alpha 2-adrenoreceptor agonist clonidine suppresses seizures, whereas the alpha 2-adrenoreceptor antagonist idazoxan promotes seizures in amygdala-kindled kittens: a comparison of amygdala and pontine microinfusion effects

PURPOSE: We sought to determine whether local, in vivo microinfusion of an alpha 2-adrenoreceptor agonist and antagonist into either the amygdala or the pons (locus ceruleus, LC) would have contrasting effects on evoked amygdala-kindled seizure susceptibility. METHODS: The study population consisted of 6 amygdala-kindled kittens, each undergoing the same protocol, in which the amygdala microinfusion paradigm preceded the pontine microinfusion series. Microinfusions (1 microliter) of the alpha 2-agonist clonidine (CLON) and the alpha 2-antagonist idazoxan (IDA) were made over 1 min through cannulas adjacent to stimulating electrodes in the kindled amygdala or through cannulas adjacent to recording electrodes in the ipsilateral LC. Order of administered drugs (CLON vs. IDA) and dosages (n = 3 each) was partly counterbalanced. Focal and convulsive seizure thresholds were evaluated 10-12 min postinfusion and compared to thresholds obtained during two interspersed control conditions (vehicle control = 1 microliter microinfusion of sterile saline; sham control = needle insertion only). RESULTS: CLON significantly increased focal and generalized seizure thresholds, whereas IDA significantly reduced seizure thresholds when compared to controls. Magnitude of effects was dose dependent and more potent after pontine than amygdala microinfusion. CONCLUSIONS: Our results confirm and extent findings of previous researchers who used unlocalized in vivo manipulations to show that norepinephrine (NE) is a highly antiepileptic agent in the amygdala kindling preparation. With further investigation, the results may ultimately lead to development of microinfusion techniques as an alternative treatment option for limbic epilepsy.     

Short-term rebound anxiolytic effects and long-term changes in platelet benzodiazepine binding after pentylenetetrazole-kindling in two strains of rat

Although there were no differences in response to an acute injection of pentylenetetrazole (PTZ), there were strain differences in the development of kindled seizures to repeated injections (PTZ; 30 mg/kg 3 times weekly for 13 injections), with Wistar rats reaching stage 4 or 5 of clonic-tonic seizures, but hooded Lister rats reaching only stage 2 or 3 of convulsive waves axially through the body. The strains also reacted differently to a test dose of PTZ (20 mg/kg) one week after the end of kindling, with the Wistar strain showing stage 3 and the Lister strain stage 2 seizures. When the rats were tested 24 h after the end of the kindling injections there was an anxiolytic effect in the social interaction test, in both the low light, familiar and the low light, unfamiliar test conditions that reached significance in the Wistar strain. The Wistar kindled rats showed an anxiolytic effect in the elevated plus-maze test of anxiety when they were tested 24 h after the end of kindling. The anxiolytic effects found 24 h after kindling could not be due to the seizure 24 h earlier, since no changes were found in rats tested 24 h after a single seizure from PTZ (60 mg/kg). When the rats were tested 1 week after the end of kindling there were no changes, compared with vehicle-injected controls, in either test of anxiety. There was no change in benzodiazepine binding in platelets of the kindled Lister rats but there was a significant increase in the kindled Wistar rats 1 week after the end of kindling and also 24 h after a single PTZ seizure. The pattern of increased platelet benzodiazepine binding did not correspond with the time course of rebound anxiolytic effects. However, after kindling it seems that there are long-lasting changes in benzodiazepine binding that are similar to the short-term increases that are found following a single seizure.     

Biodistribution of a radiolabelled monoclonal antibody NY3D11 recognizing the neural cell adhesion molecule in tumour xenografts and patients with small-cell lung cancer

In this study, we examined the acute anticonvulsant spectrum of (1) dizocilpine (0.03-3 mg/kg), CGS 19755 (1-10 mg/kg), and 7-chlorokynurenic acid (1-100 nmol) (NMDA receptor/ionophore complex antagonists); (2) muscimol (0.1-10 nmol; direct GABA(A) agonist); (3) YM90K (3-10 mg/kg; AMPA receptor antagonist); and (4) diazepam (2 and 5 mg/kg) and carbamazepine (5 and 20 mg/kg), two standard anticonvulsants, using the partially-kindled hippocampal model for epileptic seizures in freely moving rats. The anticonvulsant effect of these compounds were assessed by determining (1) the afterdischarge (AD), which is indicative of the severity of the seizure and related to seizure maintenance, and (2) the pulse number threshold (PNT), which is indicative of the seizure threshold or initiation. In addition, ataxia, a measure of CNS dysfunction, was assessed for each compound. Overall, our results indicated that the anticonvulsant compounds examined could be classified into three categories based on effects on the AD and PNT: (1) elevation of PNT (carbamazepine, dizocilpine, CGS 19755 and 7-chlorokynurenic acid); (2) reduction of AD (diazepam and muscimol); and (3) mixed action, i.e., increased PNT and decreased AD (YM90K). Behavioral data indicated that all compounds, except carbamazepine, produced a dose- or concentration-dependent ataxia. Overall, our results suggest that NMDA receptors play a role in seizure initiation, whereas the GABA(A) receptors appear to be involved in seizure maintenance and AMPA receptors may be involved in both phenomena.     

The alpha 2-agonist clonidine suppresses seizures, whereas the alpha 2-antagonist idazoxan promotes seizures--a microinfusion study in amygdala-kindled kittens

This is the first report showing that local, in vivo microinfusion of alpha 2-adrenoreceptor agonists and antagonists have contrasting effects on amygdala-kindled seizure susceptibility. Microinfusions (1 microliter) of the alpha 2-agonist clonidine (CLON) and of the alpha 2-antagonist idazoxan (IDA) were made over 1 min through cannulae adjacent to stimulating electrodes in five amygdala-kindled kittens. Order of administered drugs (CLON vs. IDA) and dosages (n = 3 each) was partly counterbalanced. Focal and convulsive seizure thresholds were evaluated 10-12 min post-infusion and compared to thresholds obtained during two, interspersed control conditions (vehicle control: 1 microliter microinfusion of sterile saline; sham control: needle insertion only). CLON significantly elevated focal and generalized seizure thresholds, whereas IDA significantly reduced seizure thresholds when compared to controls. Magnitude of effects was dose-dependent. Results confirm and extend previous findings which employed unlocalized, in vivo manipulations to show that norepinephrine is a potent antiepileptic agent in the amygdala kindling preparation.     

Reciprocal interactions between intralaminar and lateral thalamic nuclei in rats

The effect of the nootropic drug piracetam (100 mg/kg) on kindled seizures, kindling-induced learning deficits, and histological alterations due to changes in central excitability was investigated in Wistar rats. The animals were kindled by repeated i.p. injections of an initially subconvulsive dose of pentylenetetrazol (PTZ). As a control, piracetam or physiological saline was given 60 minutes before PTZ. Twenty-four hours after completion of kindling the rats were tested in a shuttle-box paradigm. Seven days after the final kindling injection, the animals received a challenge dose of PTZ. Finally, the brains of the rats were processed for histological investigation. Pentylenetetrazol-kindled animals showed increasing seizure scores, and a learning deficit in the shuttle-box. Piracetam had no effect either on kindling development or on the reaction to a challenge dose of PTZ, but it protected the animals against the kindling-induced reduction of learning performance. The substance had no effect on learning performance in control animals. In distinct hippocampal structures, a neuronal cell loss was found in kindled rats. Interestingly, piracetam counteracted this damage efficaciously. The effects of piracetam are discussed in terms of its cytoprotective action. It is suggested that a coadministration of piracetam with clinically used antiepileptic drugs might be useful in antiepileptic therapy.     

Attenuation of cocaine kindling by 7-nitroindazole, an inhibitor of brain nitric oxide synthase

Recent studies suggest the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors and nitric oxide synthase (NOS) in the process of increased sensitivity to the convulsive effect of cocaine ("cocaine kindling"). The present study was undertaken to analyze the various behavioral stages in the development of cocaine kindling and to investigate the effect of 7-nitroindazole (7-NI), a relatively selective inhibitor of the neuronal NOS isoform, on the induction and expression of sensitization to the convulsive effect of cocaine. Also, the effect of 7-NI on responses produced by acute systemic administration of cocaine or N-methyl-D,L-aspartate (NMDLA) was investigated. Cocaine kindling was assessed on a five-stage scale following the administration of a sub-convulsant dose of the drug (35 mg/kg/day; i.p.) to Swiss Webster mice for 10 days. Stage 5 seizures developed following the 9th day of cocaine administration. Pre-treatment with 7-NI (25 mg/kg/day; i.p.) 15 min before cocaine for 10 days completely prevented the appearance of stage 4 and 5 seizures, and it significantly attenuated stage 3 behavior in response to a challenge cocaine dose (35 mg/kg) given either 24 hr or 10 days after 7-NI/cocaine administration was stopped. A single injection of 7-NI (25 mg/kg; i.p.) completely prevented the expression of cocaine kindled seizures. Whereas 7-NI had no effect on the responses elicited by acute cocaine administration (60 mg/kg; i.p.), this agent partially attenuated the effects induced by systemic administration of the NMDA receptor agonist NMDLA (250 mg/kg; i.p.). The present study indicates that 7-NI attenuates both the induction and expression of sensitization to the convulsive effect of cocaine. The findings that 7-NI attenuated cocaine kindling and partially blocked the effects produced by activation of the NMDA receptor, but not the effects induced by acute cocaine administration, support the role of the NMDA receptor and brain NOS in the development of cocaine kindling rather than in the acute effects of the drug.