Hippocampal Kindled Rats Research Articles

Low Frequency Stimulation Reverses the Kindling-Induced Impairment of Learning and Memory in the Rat Passive-avoidance Test.

Introduction:The life quality of patients with epileptic seizures is highly affected by cognitive deficits. Low Frequency Stimulation (LFS) is a novel approach for the treatment of pharmacoresistant epilepsy. The main goal of this research is investigating the possible effect of LFS on seizure-induced cognitive dysfunction.Methods:To this end, the kindled animal were prepared via CA1 electrical stimulation in a semi-rapid way (12 stimulations/day). A group of animals were stimulated with LFS, 4 times at 30 s, 6 h, 24 h, and 30 h after the last kindling stimulation. Applied LFS was administered in 4 packages every 5 minutes. The packages were designed with 200 monophasic 200 monophasic square wave pulses of 0.1 ms duration at 1 Hz. The passive-avoidance test was conducted on all animals in order to measure the learning and memory behavior.Results:Hippocampal kindled rats showed deficits in learning and memory when passive avoidance test was performed. Application of LFS reversed the impairment in learning and memory behavior in kindled rats. At the same time, LFS markedly diminished kindling-induced neuronal loss and atrophy in the hippocampus.Conclusion:LFS may have some protection against seizure-induced cognitive damage in kindled rats.

Lentiviral vector-mediated somatostatin overexpression suppresses seizures induced in hippocampal kindled rats

Objective To explore the effect of lentiviral vector-mediated somatostatin (SST) expression on seizures induced by hippocampal kindling in rats. Methods Adult Sprague-Dawley rats were randomly divided into the sham group (Sham), epilepsy group (EP), Lenti-pSyn-EGFP (LV-EGFP) group and Lenti-pSyn-SST-2A-EGFP (LV-SST) group.The rats in LV-EGFP group were subsequently electrically hippocampal kindled and LV-EGFP (5 μl) was injected into dentate gyrus (DG). The rats in LV-SST group were kindled and LV-SST (5 μl) was injected into the dentate gyrus (DG), medial entorhinal cortex (MEC) or amygdala (Amy). Seizure severity was evaluated and immunohistochemical staining was employed to detect the expression of SST, neuron specific nuclear protein (NeuN) and microtubule associated protein 2 (MAP2). Results The current values to the first stage V seizure of LV-SST (DG) group, LV-SST (MEC) group or LV-SST (Amy) group ((143.8±3.8)μA, (142.5±4.1)μA, (142.5±5.3) μA, respectively) were significantly increased compared with that of epilepsy (EP) group ((136.3±5.3)μA), and V stage current values of LV-SST groups in each stimulation day were higher than that of EP group except the fifth stimulation day (P<0.05). After kindling, SST expression and NeuN-positive neurons of EP group and LV-SST groups were less than that of Sham group in CA1, CA3 and DG. SST and NeuN neurons loss in LV-SST groups were less than that of EP group (P<0.05) and MAP2 immunohistochemistry stainings in LV-SST groups were higher than that in EP group. Conclusion Lentiviral vector-mediated somatostatin expression suppresses seizures and can rescue the neuronal damage of seizure induced by kindling in hippocampus, which may provide a new method of gene therapy for temporal lobe epilepsy. Key words: Epilepsy; Somatostatin; Hippocampus; Lentivirus; Gene therapy

Physicochemical and biological evaluation of a cinnamamide derivative R,S-(2E)-1-(3-hydroxypiperidin-1-yl)-3-phenylprop-2-en-1-one (KM-608) for nervous system disorders.

A cinnamamide scaffold has been successfully incorporated in several compounds possessing desirable pharmacological activities in central and peripheral nervous system such as anticonvulsant, antidepressant, neuroprotective, analgesic, anti-inflammatory, muscle relaxant, and sedative/hypnotic properties. R,S-(2E)-1-(3-hydroxypiperidin-1-yl)-3-phenylprop-2-en-1-one (KM-608), a cinnamamide derivative, was synthesized, its chemical structure was confirmed by means of spectroscopy and crystallography, and additionally, thermal analysis showed that it exists in one crystalline form. The compound was evaluated in vivo in rodents as anticonvulsant, antiepileptogenic, analgesic, and neuroprotective agent. The beneficial properties of the compound were found in animal models of seizures evoked electrically (maximal electroshock test, 6-Hz) and chemically (subcutaneous pentylenetetrazole seizure test) as well as in three animal models of epileptogenesis: corneal-kindled mice, hippocampal-kindled rats, and lamotrigine-resistant amygdala-kindled rats. Quantitative pharmacological parameters calculated for the tested compound were comparable to those of currently used antiepileptic drugs. In vivo pharmacological profile of KM-608 corresponds with the activity of valproic acid.

Selective plasticity of hippocampal GABAergic interneuron populations following kindling of different brain regions.

The vulnerability and plasticity of hippocampal GABAergic interneurons is a topic of broad interest and debate in the field of epilepsy. In this experiment, we used the electrical kindling model of epilepsy to determine whether seizures that originate in different brain regions have differential effects on hippocampal interneuron subpopulations. Long-Evans rats received 99 electrical stimulations of the hippocampus, amygdala, or caudate nucleus, followed by sacrifice and immunohistochemical or western blot analyses. We analyzed markers of dendritic (somatostatin), perisomatic (parvalbumin), and interneuron-selective (calretinin) inhibition, as well as an overall indicator (GAD67) of interneuron distribution across all major hippocampal subfields. Our results indicate that kindling produces selective effects on the number and morphology of different functional classes of GABAergic interneurons. In particular, limbic kindling appears to enhance dendritic inhibition, indicated by a greater number of somatostatin-immunoreactive (-ir) cells in the CA1 pyramidal layer and robust morphological sprouting in the dentate gyrus. We also found a reduction in the number of interneuron-selective calretinin-ir cells in the dentate gyrus of hippocampal-kindled rats, which suggests a possible reduction of synchronized dendritic inhibition. In contrast, perisomatic inhibition indicated by parvalbumin immunoreactivity appears to be largely resilient to the effects of kindling. Finally, we found a significant induction in the number of GAD67-cells in caudate-kindled rats in the dentate gyrus and CA3 hippocampal subfields. Taken together, our results demonstrate that kindling has subfield-selective effects on the different functional classes of hippocampal GABAergic interneurons. J. Comp. Neurol. 525:389-406, 2017. © 2016 Wiley Periodicals, Inc.

FV-137 candidate drug: Novel and selective ion channel modulation for epilepsy and pain

Broad spectrum Anti-Epileptic Drugs (AED) are valued for their potential to treat refractory epilepsy and as general ‘neurostabilizers’ have been employed for a variety of neurological diseases including migrane, biopolar disorder and neuropathic pain. However, the benefits of historical AEDs have been constrained by unintended CNS side effects of these non-selective medicines. Combining proprietary breakthrough chemistry with Fluorinov Pharma and NIH’s in vivo phenotypic screening strategy identified three completely novel candidate drugs, including FV-137 with superior safety and efficacy profiles targeting selective ion channels. FV-137 is a novel, orally administered AED, structurally distinct than any known AED, displaying promising preclinical efficacy and safety. FV-137 emerged from a program whose goal was to identify broad-spectrum anti-epileptic drugs (AED) using gold standard benchmarks such as Depakote ® , Neurontin ® and Keppra ® as primary comparators. FV-137 was extensively screened across all available in vitro and rodent seizure models at ASP, and was found to display an excellent spectrum of anti-seizure activity and safety profiles superior to that produced by Depakote, Neurontin and Keppra. FV-137 has an oral ED50 of 22.7 ± 0.6 and 104.9±4.3 mg/kg in the rat MES (po), mouse PTZ (ip) assays, respectively. FV-137 also produced a dose related protection of a psychomotor seizure syndrome induced by a 6-Hz electrical stimulus with an oral ED50 of 48.5 ± 1mg/kg, and prevented seizures induced by sound in the Audiogenic Seizure (AGS)-susceptible Frings mouse model (i.p) with an ED50 value of 28.9 ± 3.0 mg/kg. In addition, FV-137 displayed significant efficacy in the electrically induced corneally kindled mouse, kindled rat amygdala, kindled rat hippocampal and lamotrigineresistant kindled rat seizures models. Additionally, FV-137 also increased seizure threshold in a dose– dependent manner, therefore, it has the potential to be effective in refractory, or pharmacoresistant, epilepsy. In-vivo pharmacokinetic studies in rat revealed that FV-137 had excellent oral bioavailability (F% = 85%), moderate oral half-life (~3h), and predicted plasma drug levels in the range 5-50μM across multiple models of epilepsy. In addition, drug exposure as measured by Cmax and AUC was shown to be linear with dose. Safety assessment of FV-137 suggests no interaction with the major CYP isoenzymes when tested up to 500 μM, except for 1A2 and 2D6 with IC50 values of 19 uM and 156 uM respectively and no functional hERG activity when tested up to 50 μM. Irwin and acute toxicity studies suggest a maximally tolerated oral dose of greater than 500 mg/kg in the mice and rats. Mechanistically, in whole-cell patch-clamp recordings FV-137 inhibited P/Q-type Ca 2+ Channels, Cav2.1/β4/α2δ1 and Cav2.2/β3/α2δ1, and voltage-gated Na + channels, Nav1.6 and Nav1.7 and no inhibition up to 100 μM in other related ion channels. Importantly, no significant affinities were observed in a CEREP broad profiling screen (10 μM) across 90 known GPCR, ion channel, transporter and enzyme targets. The anticonvulsant profile of FV-137 suggests that it may be useful for treating multiple forms of epilepsy (generalized tonic-clonic, complex partial, absence seizures), including refractory (or pharmacoresistant) epilepsy, at dose levels that confer a good safety margin. Furthermore, in models of neuropathic pain (spinal nerve injury [SNI] and spinal nerve ligation models [SNL]) and formalin inflammatory pain, administration of a single dose showed robust efficacy (SNI: 23 mg/kg ip; SNL: 60mg/kg and formalin: 41 mg/kg ip). On the basis of its pharmacology and superior drug-like properties, FV-137 was identified as a promising AED candidate.

α-Fluoro-2,2,3,3-Tetramethylcyclopropanecarboxamide, a Novel Potent Anticonvulsant Derivative of a Cyclic Analogue of Valproic Acid

2,2,3,3-Tetramethylcyclopropanecarboxylic acid (TMCA, 4) is a cyclic analogue of the antiepileptic drug (AED) valproic acid (VPA) (1). alpha-F, alpha-Cl, alpha-Br, and alpha-methyl derivatives of 4 and their amides were synthesized and tested in rodent models for anticonvulsant potency and AED-induced teratogenicity. In the anticonvulsant rat-maximal electroshock (MES) and subcutaneous metrazol (scMet) tests, alpha-Cl-TMCD (17) had ED(50) values of 97 and 27 mg/kg, respectively. alpha-F-TMCD (11) was 120 times more potent than VPA in the rat-scMet test (ED(50) = 6 mg/kg) and had a protective index (PI = TD(50)/ED(50)) of 20. In the 6 Hz psychomotor mouse model 11 had ED(50) values of 57 mg/kg (32 mA) and 59 mg/kg (44 mA). The ED(50) values of 11 in the hippocampal-kindled rat model and in the pilocarpine-induced-status rat model were 30 and 23 mg/kg, respectively. Unlike 1, 11 was nonteratogenic in mice. This novel compound has the potential to become a candidate for development as a new potent and safe antiepileptic and CNS drug.

Anti‐convulsive and anti‐epileptic properties of brivaracetam (ucb 34714), a high‐affinity ligand for the synaptic vesicle protein, SV2A

Screening of 12,000 compounds for binding affinity to the synaptic vesicle protein 2A (SV2A), identified a high-affinity pyrrolidone derivative, brivaracetam (ucb 34714). This study examined its pharmacological profile in various in vitro and in vivo models of seizures and epilepsy, to evaluate its potential as a new antiepileptic drug. The effects of brivaracetam and levetiracetam on epileptiform activity and seizure expression were examined in rat hippocampal slices, corneally kindled mice, audiogenic seizure-susceptible mice, maximal electroshock and pentylenetetrazol seizures in mice, hippocampal-kindled rats, amygdala-kindled rats and genetic absence epilepsy rats. Brivaracetam and levetiracetam reduced epileptiform responses in rat hippocampal slices, brivaracetam being most potent. Brivaracetam also differed from levetiracetam by its ability to protect against seizures in normal mice induced by a maximal electroshock or maximal dose of pentylenetetrazol. In corneally kindled mice and hippocampal-kindled rats, brivaracetam induced potent protection against secondarily generalized motor seizures and showed anti-kindling properties superior to levetiracetam. In amygdala-kindled rats, brivaracetam induced a significant suppression in motor-seizure severity and, contrary to levetiracetam, reduced the after-discharge at a higher dose. Audiogenic seizure-susceptible mice were protected more potently against the expression of clonic convulsions by brivaracetam than by levetiracetam. Brivaracetam induced a more complete suppression of spontaneous spike-and-wave discharges in genetic absence epilepsy rats than levetiracetam. Brivaracetam has higher potency and efficacy than levetiracetam as an anti-seizure and anti-epileptogenic agent in various experimental models of epilepsy, and a wide therapeutic index.

Hippocampal Kindling Leads to Motor Map Expansion

To determine whether seizure activity, repeatedly elicited in the hippocampus, could alter the functional organization of neocortical movement representations (motor maps) and whether a relation exists between the number of afterdischarges recorded in the sensorimotor neocortex and the size of the motor maps. We electrically kindled the right ventral hippocampus of Long-Evans hooded rats, twice daily, for 40 sessions and recorded the afterdischarges in the stimulated hippocampus and right sensorimotor neocortex. Between 3 and 7 days after the last seizure, we used high-resolution intracortical microstimulation to derive the forelimb-movement representations in the left (un-implanted) sensorimotor neocortex. In the hippocampal kindled rats, we observed a dramatic expansion of the area of neocortex that would elicit forelimb movements compared with sham-kindled controls. The number of afterdischarges recorded in the neocortex was significantly and positively correlated with the size of the motor maps. Seizures propagating from the hippocampus have long-distance effects on the functional organization of motor maps.

Anticonvulsant profile and teratogenicity of N-methyl-tetramethylcyclopropyl carboxamide: a new antiepileptic drug.

The studies presented here represent our efforts to investigate the anticonvulsant activity of N-methyl-tetramethylcyclopropyl carboxamide (M-TMCD) and its metabolite tetramethylcyclopropyl carboxamide (TMCD) in various animal (rodent) models of human epilepsy, and to evaluate their ability to induce neural tube defects (NTDs) and neurotoxicity. The anticonvulsant activity of M-TMCD and TMCD was determined after intraperitoneal (i.p.) administration to CF#1 mice, and either oral or i.p. administration to Sprague-Dawley rats. The ability of M-TMCD and TMCD to block electrical-, chemical-, or sensory-induced seizures was examined in eight animal models of epilepsy. The plasma and brain concentrations of M-TMCD and TMCD were determined in the CF#1 mice after i.p. administration. The induction of NTDs by M-TMCD and TMCD was evaluated after a single i.p. administration at day 8.5 of gestation in a highly inbred mouse strain (SWV) that is susceptible to valproic acid-induced neural tube defects. In mice, M-TMCD afforded protection against maximal electroshock (MES)-induced, pentylenetetrazol (Metrazol)-induced, and bicuculline-induced seizures, as well as against 6-Hz "psychomotor" seizures and sound-induced seizures with ED50 values of 99, 39, 81, 51, and 10 mg/kg, respectively. In rats, M-TMCD effectively prevented MES- and Metrazol-induced seizures and secondarily generalized seizures in hippocampal kindled rats (ED50 values of 82, 45, and 39 mg/kg, respectively). Unlike M-TMCD, TMCD was active only against Metrazol-induced seizures in mice and rats (ED50 values of 57 and 52 mg/kg, respectively). Neither M-TMCD nor TMCD was found to induce NTDs in SWV mice. The results obtained in this study show that M-TMCD is a broad-spectrum anticonvulsant drug that does not induce NTDs and support additional studies to evaluate its full therapeutic potential.

Seizures induce phase shifts of rat circadian rhythms

Rationale: Epileptic seizures may alter neuroendocrinological cycles. Light pulses induce phase shifts in circadian rhythms. Using hippocampal-kindled rats to ensure maximal clinical expression, we determined if seizures likewise induce phase shifts. Methods: We monitored the circadian rhythm of temperature (CRT) with intraperitoneal radiotelemetry in rats ( n=21) isolated from time cues and light for 3-week trials. Seizures were triggered with hippocampal electrical stimulation at different circadian phases. Optimized, least-error phase shifts were calculated from preictal and postictal CRTs. Induced seizures were referenced to CRT ( t max=00:00, 24-h circadian cycle). Results: Phase shifts (individual responses=57) differed across the circadian cycle. Rather than forming a clear phase–response curve, phase shifts were especially variable between 00:00 and 06:00 h. Conclusions: This study demonstrates that electrically-induced seizures induce advances and delays in CRT in a phase-dependent fashion but in a pattern different from typical light-induced phase shifts. Disorders of circadian regulation may contribute to some of the altered endogenous cycles associated with epilepsy.

Septal cholinergic neurons suppress seizure development in hippocampal kindling in rats: comparison with noradrenergic neurons

Widespread lesions of forebrain cholinergic or noradrenergic projections by intraventricular administration of 192 IgG-saporin or 6-hydroxydopamine, respectively, accelerate kindling epileptogenesis. Here we demonstrate both quantitative and qualitative differences between the two lesions in their effects on hippocampal kindling in rats. Epileptogenesis was significantly faster after noradrenergic as compared to cholinergic denervation, and when both lesions were combined, kindling development resembled that in animals with 6-hydroxydopamine lesion alone. Furthermore, whereas the 192 IgG-saporin lesion promoted the development only of the early stages of kindling, administration of 6-hydroxydopamine or both neurotoxins accelerated the late stages also. To investigate the contribution of different subparts of the basal forebrain cholinergic system to its seizure-suppressant action in hippocampal kindling, 192 IgG-saporin was injected into medial septum/vertical limb of the diagonal band of Broca or nucleus basalis magnocellularis, leading to selective hippocampal or cortical cholinergic deafferentation, respectively. The denervation of the hippocampus facilitated kindling similar to the extensive lesion caused by intraventricular 192 IgG-saporin, whereas the cortical lesion had no effect. These results indicate that although both noradrenergic and cholinergic projections to the forebrain exert powerful inhibitory effects on hippocampal kindling epileptogenesis, the action of the cholinergic system is less pronounced and occurs specifically prior to seizure generalization. In contrast, noradrenergic neurons inhibit the development of both focal and generalized seizures. The septo-hippocampal neurons are responsible for the antiepileptogenic effect of the cholinergic system in hippocampal kindling, whereas the cortical projection is not significantly involved. Conversely, we have previously shown [Ferencz I. et al. (2000) Eur. J. Neurosci., 12, 2107–2116] that seizure-suppression in amygdala kindling is exerted through the cortical and not the hippocampal cholinergic projection. This shows that, depending on the location of the primary epileptic focus, i.e. the site of stimulation, basal forebrain cholinergic neurons operate through different subsystems to counteract seizure development in kindling.

A pharmacological profile of clobazam (Mystan), a new antiepileptic drug

Clobazam (CLB) is a new antiepileptic drug that is the first 1,5-benzodiazepine (BZP) having nitrogen atoms in the 1 and 5 positions of the heterocyclic ring, whose chemical structure was designed to give it a different pharmacological profile from that of 1,4-BZPs. Although CLB has a Ki value of 2,130 nM and thus has a lower affinity for the BZP receptor than 1,4-BZPs, it had the selectivity to omega 2 receptor contributing to anticonvulsive actions compared with omega 1 receptor in relation to other CNS activities such as sedation. CLB had a wide spectrum of anticonvulsive actions against seizures in several animal models induced by chemical convulsants and maximal electroshock. CLB reduced both seizure stage and afterdischarge duration in a dose-dependent manner in amygdala or hippocampal kindled rats. Usefulness of an anticonvulsant is generally assessed by quoting the protective index (PI) in the ratio of TD50 to ED50. As the PI for CLB was greater than that for 1,4-BZPs, it suggested that CLB was superior to 1,4-BZPs in tolerability while showing anticonvulsive actions. In clinical studies, CLB was used as an adjunctive treatment in patients with refractory epilepsies. From both experimental and clinical observations, CLB was proven to possess a wide spectrum of activity, high effectiveness and good tolerability in several types of epilepsies.

Intraperitoneal and intraamygdala N(6)-cyclohexyladenosine suppress hippocampal kindled seizures in rats.

Effects of intraperitoneal and intraamygdala N(6)-cyclohexyladenosine (CHA), a selective adenosine A(1) receptor agonist, and 1,3-dimethyl-8-cyclopentylxanthine (CPT), a selective adenosine A(1) receptor antagonist, were examined in fully hippocampal kindled rats. Intraperitoneal administration of CHA (0. 25, 0.5 and 1 mg/kg) decreased hippocampal secondary afterdischarge duration (SAD) and amygdala afterdischarge duration (ADD). Only the 1 mg/kg dose induced a significant increase in latency to stage 4. Intraperitoneal administration of CPT (0.25, 0.5 and 1 mg/kg) induced a significant increase in stage 5 duration, hippocampal SAD and ADD. Pretreatment of animals with CPT (1 mg/kg), antagonized effects of CHA on seizure parameters. Intraamygdala microinfusion (1 microl over 2 min) of CHA (5 nM-1 mM) significantly reduced hippocampal SAD and amygdala ADD. These effects were antagonized by intraamygdala CPT (1 microM). Results obtained suggest that in hippocampal kindled rats, amygdala may be regarded as a relay point for AD propagation specially in recruit activity of the hippocampus.

In vivo hippocampal kindling occludes the development of in vitro kindling-like state in CA1 area of rat hippocampal slices

In our previous work ( Semyanov and Godukhin, 1997), we showed that the repeated short-term extracellular K + (K + 0) increases induced long-lasting reduction of the threshold of evoked epileptiform discharges in CA1 hippocampal slices isolated from normal (nonkindled) rats. This state had some features characteristic of traditional in vivo kindling and was described as in vitro kindling-like state (VKLS). The aim of the present investigations was to determine the features of the VKLS development in CA1 slices isolated from electrical hippocampal kindled (nonepileptic) rats and from genetically-prone to audiogenic seizures audiokindled rats. We found that both forms of in vivo kindling occluded the VKLS development induced by the repeated K + 0 increases in CA1 slices. These data provide more evidence that the in vivo kindling and VKLS developments in CA1 region of hippocampus are based on activation of similar cellular mechanisms. It is suggested that the described model of in vitro kindling can be useful for further studies of the cellular–molecular mechanisms of plastic alterations in neurons associated with the start of kindling induced epileptogenesis.

Suppression of kindling epileptogenesis in rats by intrahippocampal cholinergic grafts.

Selective immunolesioning of the basal forebrain cholinergic system by 192 IgG-saporin, which leads to a dramatic loss of the cholinergic innervation in cortical and hippocampal regions, facilitates the development of hippocampal kindling in rats. The aim of the present study was to explore whether grafted cholinergic neurones are able to reverse the lesion-induced increase of seizure susceptibility. Intraventricular 192 IgG-saporin was administered to rats which 3 weeks later were implanted with rat embryonic, acetylcholine-rich septal-diagonal band tissue ('cholinergic grafts') or cortical tissue/vehicle ('sham grafts') bilaterally into the hippocampal formation. After 3 months, the grafted animals as well as non-lesioned control rats were subjected to daily hippocampal kindling stimulations. In the animals with cholinergic grafts, which had reinnervated the hippocampus and dentate gyrus bilaterally, there was a marked suppression of the development of seizures as compared with the hyperexcitable, sham-grafted rats. This effect was significantly correlated to the density of the graft-derived cholinergic innervation of the host hippocampal formation. The kindling rate in the rats with cholinergic grafts was similar to that in non-lesioned controls. These results provide further evidence that the intrinsic basal forebrain cholinergic system dampens kindling epileptogenesis and demonstrate that this function can be exerted also by grafted cholinergic neurones.

Long-term kindling and interictal emotionality in rats: effect of stimulation site

Long-term amygdala kindling in rats produces increases in emotionality (Kalynchuk et al., Biol. Psychiatry, 41 (1997) 438–451). The present experiment was conducted to investigate whether this hyperemotionality is specific to amygdala kindling or whether it can be produced by kindling other structures. Rats received 99 convulsive or sham stimulations of either the amygdala, the hippocampus, or the caudate nucleus. One day after the stimulation phase, each rat's open-field activity and resistance to capture were assessed; the following day, each rat was tested on an elevated plus maze. The site of stimulation had a significant effect on the results of each of these tests. The amygdala-kindled and hippocampal-kindled rats explored less in the open field, were more resistant to capture from the open field, and engaged in a greater percentage of open-arm activity in the elevated plus maze than did the caudate-kindled rats or the sham-stimulated controls. The caudate-kindled rats were more active in the open field than their sham-stimulated controls, but they did not significantly differ from them in terms of the other measures. These results suggest that kindling-induced emotionality is produced by limbic kindling but not nonlimbic kindling.

Antiepileptic effects of tiagabine, a selective GABA uptake inhibitor, in the rat kindling model of temporal lobe epilepsy.

We determined the antiepileptic profile of tiagabine (TGB), a selective gamma-aminobutyric acid (GABA) uptake inhibitor, in the rat kindling model of temporal lobe epilepsy (TLE). The anticonvulsant and adverse effects of TGB were examined in amygdala- or hippocampal-kindled rats and compared with those of other GABA uptake inhibitors (SKF89976A and NNC-711) and conventional antiepileptic drugs [AEDs: valproate (VPA) and carbamazepine (CBZ)]. In addition, the antiepileptogenic effects of TGB on amygdala kindling development were examined. TGB (2.5-40 mg/kg intraperitoneally, i.p.) had potent and dose-dependent anticonvulsant effects on both amygdala- and hippocampal-kindled seizures. The order of anticonvulsant potency of the three GABA uptake inhibitors tested was: NNC-711 > TGB > SKF-89976A and paralleled the in vitro GABA uptake efficacy. In addition, daily treatment with TGB 10 mg/kg for 10 days significantly retarded kindling development. Although adverse effects of TGB on motor systems were significantly less than those of VPA and CBZ, high toxic doses of TGB often caused EEG paroxysm and myoclonus. Our results indicate the clinical usefulness of TGB for treatment of drug-resistant TLE.

An evaluation of the effect of partial hippocampal kindling on place navigation by rats in the Morris water task

We report the results of two experiments that examine the effects of partial kindling on acquisition and retention of place navigation in the Morris water task. Rats were implanted bilaterally in sub-field CA1 of the hippocampus with electrodes for electrical stimulation and EEG recording. Half of the rats in each experiment received 20 afterdischarges (ADs) on 4 consecutive days; the other half received low-frequency stimulation that did not induce ADs. The rats in the first experiment were trained beginning the day after the last AD to navigate to a platform hidden in a fixed location in the pool. No differences in performance were detected between groups. The rats in the second experiment had received extensive training before ADs with a hidden platform that changed its location within the pool between days. Beginning either 1 day, 1 week, or 1 month after the last AD, these rats were tested in the moving-platform task both in a new room and in the original training room. The rats receiving ADs performed significantly worse in both rooms than did control rats 1 day and 1 week, but not 1 month, after the last AD. These results extend the generality of earlier findings of impaired radial-arm maze performance after partial hippocampal kindling in rats and support the idea that some consequence of hippocampal ADs disrupts normal functioning of these networks in spatial learning.

Anticonvulsant Effects of Magnesium Sulfate in Hippocampal-Kindled Rats.

The objective of the present study was to determine whether magnesium sulfate has anticonvulsant actions in the hippocampal-kindled rat model of epilepsy. Fully kindled rats received acute intraperitoneal injections of magnesium sulfate (270 mg/kg), phenytoin (20 mg/kg) or saline in random order. Electrical seizure duration, behavioral seizure stage and duration of postictal EEG depression were examined 15, 30 and 60 min after injection. In an additional group of rats, kindled seizures were measured before and after chronic (2 h) intraperitoneal injections of magnesium sulfate versus saline. There was a significant decrease in electrical seizure duration (p < 0.01) and behavioral seizure stage (p < 0.01) with acute magnesium sulfate injections compared to saline injections. Phenytoin had no statistically significant effects on hippocampal-kindled seizures. Chronic magnesium sulfate treatment significantly reduced behavioral seizure stage at 2, 24, and 48 h postinjection (p < 0.05), but did not affect seizure duration. There was a significant time by treatment effect for magnesium sulfate on postictal EEG depression (p < 0.01). We conclude that in this model of hippocampal epilepsy-induced (kindled) rats, magnesium sulfate has significant anticonvulsant effects. Copyright 1995 S. Karger AG, Basel

Differential changes in the activities of multiple protein kinase C subspecies in the hippocampal-kindled rat

In previous studies we demonstrated that the membrane-associated protein kinase C (PKC) activities in the right and left hippocampus (HIPP) of rats kindled from the left HIPP increased significantly 4 weeks and 4 months after the last seizure compared with those in matched control rats [6,19]. In this study, we investigated the long-lasting effect of HIPP-kindling on the membrane-associated activities of PKC subspecies in the bilateral HIPP 1 and 4 weeks after the last generalized kindled seizure had occured. The membrane-associated activities of PKC subspecies were found to be subject to differential regulation. The activity of the α-subspecies was unchanged, whereas the respective activities of the β- and γ-subspecies in the kindled group increased significantly, compared with the controls, one (21%, P < 0.0001 for the β-subspecies, and 23%, P < 0.001 for the γ-subspecies) and 4 weeks (19%, P < 0.02 for the β-subspecies, and 19%, P < 0.05 for the γ-subspecies) after the last seizure. There were no significant differences in cytosolic PKC activity between the control and kindled groups for any subspecies examined at either time after the last seizure. These results suggest that activation of the PKC β- and γ-subspecies may play an important role in the enduring seizure susceptibility associated with kindling.