Acute effect of penicillin G on feline models of focal epilepsy

Penicillin is well known as a potent convulsive agent. A cortical topical, intracerebral or systemic administration of penicillin produces abnormal and paroxysmal activity which may lead to seizure, and has been used in the investigation of the mechanisms of epilepsy. This is a report on the studies of an acute effect of potassium penicillin G on two models of experimental focal epilepsy: a) amygdaloid kindling model, and b) kainic acid-induced limbic seizure model. Twelve adult cats for amygdaloid kindling model (kindling group), six for KA-induced limbic seizure model (KA group) and four for a control group were prepared for this study. In kindling group, after completion of kindling procedure, 40-60 X 10(4) unit/kg of potassium penicillin G (PC), dissolved in sterilized normal saline, was injected intraperitoneally during an interictal period. In KA group, 1 micrograms of KA was injected into the left amygdala. Limbic seizures occurred frequently during the initial 5 hours but subsided completely within 3 days. After a latent period, spontaneous secondarily generalized convulsion occurred from 30 to 60 days after KA injection. The cats were completely normal in their behavior during the interictal period. During the interictal stage after the first generalized convulsion has been observed, 15-20 X 10(4) unit/kg of PC was injected intraperitoneally. In the control group, 40-60 X 10(4) unit/kg was injected intraperitoneally. Electroclinical observations were continued until 5 hours after PC injection in three groups. In the control group, no cats developed generalized convulsion. In the kindling group, 4 of 12 cats developed focal amygdaloid seizures with secondary generalization by nearly the identical doses required in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous secondarily generalized seizures induced by a single microinjection of kainic acid into unilateral amygdala in cats

Electrographic and clinical observations were made for 6 months after the injection of kainic acid (KA) solution (1 microgram in 1 microliter of phosphate buffer solution) through a chronically implanted cannula into a unilateral amygdala of freely moving and non-anesthetized cats. The control group (phosphate buffer group) showed no change during the observation period. After the injection of kainic acid, focal status epilepticus in the limbic system was observed for 3 days. Cats recovered clinically but persistent IIDs were observed at the injected site of the amygdala. These IIDs increased in amplitude and frequency and began to trigger spontaneous amygdaloid seizures. Secondary epileptogenic foci were then established in the contralateral amygdala, and amygdaloid seizures began to occur alternatively on both sides and finally trigger frequent limbic seizures from 20 to 40 days after KA injection. Spontaneous secondarily generalized seizures developed about 30 days after KA injection and occurred once or twice a week thereafter. The animals were completely normal in their behavior during the interictal phase. This is an excellent model of experimental epilepsy for the investigation of the mechanism of limbic seizure development and further study using this model will provide informations useful for the therapy of temporal lobe epilepsy in man.     

Complex partial status epilepticus induced by a microinjection of kainic acid into unilateral amygdala in dogs and its brain damage

OBJECTIVE: In order to investigate kainic acid (KA)-induced amygdaloid seizure and seizure-induced brain damage in dogs, and to compare these findings with that in other species, a KA-induced seizure model in dogs was produced. MATERIAL AND METHODS: Normal beagle dogs were used. A Teflon cannula for KA injection was inserted into the left amygdala, and cortical or depth electrodes were positioned. One week after surgery, 1.5 microg of KA was microinjected into the left amygdala. EEGs and the behavior of the animals were monitored for 2 months after KA injection. In addition, neuron-specific enolase levels in the cerebrospinal fluid (CSF-NSE) were measured intermittently. At 2 months after the injection, histopathological studies were performed. RESULTS: KA-treated dogs showed limbic seizures that started from the left amygdala within 30 min after injection. The seizures developed into complex partial status epilepticus (CPSE), and started independently from the bilateral amygdala during the CPSE. The CPSE lasted for 1-3 days, and the animals showed no spontaneous seizures during the 2-month observation period. A significant increase in CSF-NSE was observed immediately after CPSE. Histopathologically, extensive necrosis, which formed large cavity lesions, was observed around the bilateral amygdala. SUMMARY: A microinjection of KA into unilateral amygdala in dogs induced CPSE. The seizures elicited independently from bilateral amygdala, and bilateral limbic structures suffered extensive injury. In addition, CSF-NSE was demonstrated as a useful marker of acute neuronal damage.     

Zonisamide: Electrophysiological and Metabolic Changes in Kainic Acid-Induced Limbic Seizures in Rats

Summary: We studied the pharmacological mechanism of zonisamide (ZNS) using an electrophysiological and autoradiographical method in a limbic seizure model in rats. Limbic seizure status epilepticus was induced by a unilateral microinjection of kainic acid (KA) into the amygdala. Initially, observed seizures were limited to the side of the injected amygdala and then propagated to bilateral sensorimotor cortex. Eighty minutes after injection, secondarily generalized seizure status epilepticus was induced, with each seizure lasting ∼30 s and recurring every 5 min. ZNS 100 mg/kg was administered intravenously (i.v.) during the generalized seizure. Forty minutes after ZNS administration, epileptic activity was observed only at the KA-injected amygdalar site and spikes were not observed in the bilateral sensorimotor cortex. We studied local cerebral glucose utilization (LCGU) after ZNS or saline administration using an autoradiographical method in the same limbic seizure preparation. In the ZNS group, LCGU decreased in the ipsilateral sensorimotor cortex and hippocampus, whereas in the controls LCGU increased in these structures. On the other hand, ZNS did not suppress the epileptic activity of the primary focus and no decrease in LCGU was observed in the KA-injected amygdala. ZNS inhibited seizure propagation from the epileptogenic focus but did not suppress the epileptic activity of the focus. Our results suggest that ZNS is effective for the treatment of secondarily generalized seizure.     

Long-term observation of rats after unilateral intra-amygdaloid injection of kainic acid

Electroencephalographic and clinical observations of the rats were done for 3 months after microinjection of kainic acid (KA, 0.2–1.2 μg)into the unilateral amygdala. With high doses of KA (0.6–1.2μg) injection, 64% of rats developed spontaneous limbic siezures 14–25 days after KA injection. Among those which developed spontaneous limbic seizures, 33% of rats developed secondarily generalized seizures 26–71 days after KA injection. This is one of the best chronic models of spontaneous complex partial seizure secondarily generalized in rats, which is economical and easy to prepare.     

Ibotenic acid-induced limbic seizures and neuronal degeneration

Electrographic and clinical observations were made as long as 2 months after the injection of ibotenic acid (IBO) solution (50 micrograms in 1 microliter of phosphate buffer solution) through a chronically implanted cannula into unilateral amygdala of freely moving and non-anesthetized cats. The control group (phosphate buffer group) showed no change during the observation period. About 30 to 60 minutes after the injection of IBO, focal amygdaloid seizures occurred and propagated to the adjacent limbic structures. Clinically, attention and ipsilateral mydriasis were observed. The seizures occurred only 2 to 5 times and ceased within 4 hours. Cats became electroclinically normal afterwards. Histopathological examination revealed a small necrosis at the injected site of the amygdala. Remarkable pyknosis and gliosis were noted around the necrosis. Remote lesions such as neuronal cell loss and pyknosis were observed in the ipsilateral pyramidal cell layer of the hippocampus. But these changes were mild and not so severe as compared to our previous report of kainic acid microinjection in cats. Authors emphasized that IBO should be an excellent tool for lesion making and also suggested that an aseptic manipulation was essential in the lesion study in cats.     

Regional cerebral blood flow in limbic seizures induced by microinjection of kainic acid into amygdala in cats

The relationship between neuronal epileptic activity and regional cerebral blood flow was studied by means of hydrogen clearance method (rCBF). Measurements of rCBF in the limbic structure and cerebral cortex were performed during limbic seizures induced by a microinjection of kainic acid to the left amygdala under concurrent monitoring of polygraph. Pentobarbital (35 mg/kg, i.p.) anesthesia was induced and cats were artificially ventilated. Physiological parameters such as blood pressure, body temperature, PaO2, PaCO2 and HCO3 were kept stable. After fixation of the cat's head in a stereotaxic device, stainless screw electrodes were placed over bilateral anterior sigmoid gyrus so as to touch the dura mater for cortical EEG monitoring. Bipolar needle electrodes were stereotaxically placed to both amygdala and the left dorsal hippocampus. Platinum electrodes were stereotaxically placed to the left amygdala, dorsal hippocampus and sensorimotor cortex. After measurements of control rCBF, a microsyringe was stereotaxically inserted into the left amygdala and kainic acid solution (2 micrograms) was injected. Polygraphic monitoring followed. Five to 30 minuted after kainic acid injection, continuous multiple spikes appeared in the left amygdala. Forty to 120 minutes later, continuous multiple spikes transmitted to the left hippocampus. Two to five hours later, limbic seizure occurred. The limbic seizure lasted five to eight hours and interictal discharges appeared. Repeated measurements of rCBF were done. In the left amygdala, rCBF increased about two-fold of the control immediately after development of continuous multiple spikes and remained increased as long as the seizure persisted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Secondary Generalization in Kainic Acid-Induced Focal Seizures in Unanesthetized Cats

Abstract: Seizure propagation was studied with different seizure models induced by a kainic acid (KA) microinjection in nonanesthetized cats. These seizures were characterized with a focal onset of seizures followed by secondarily generalized seizures. The mesencephalic reticular formation (MRF) played an important role when an epileptogenic focus was located in a unilateral amygdala, hippocampus, thalamus or visual cortex. When the focus was located in a unilateral lateral geniculate body, a fast, synchronous and bidirectional propagation was observed in the sensorimotor cortex (SMC) and MRF. Brain stem seizure (generalized tonic seizure) was elicited by the KA injection into MRF. The EEG of generalized seizure was characterized by the propagations of seizure activities of MRF immediately to the bilateral SMC and thalamus. The results suggested that MRF participated actively in the generalization of the KA-induced seizures .     

Kainic Acid–Induced Limbic Seizures in Cats: Some Reflections on Sleep–Epilepsy Interactions

Sleep-epilepsy interactions were investigated in a model of temporal lobe seizures induced in cats by intra-amygdaloid kainic acid (KA) microinjections. We found that limbic status epilepticus disrupted sleep for 2 or 3 days after injection. Sleep, in turn, modulated the frequency of interictal discharges. However, such modulation was variable depending on the time elapsed since KA injection. For this and other reasons (such as the occurrence of subclinical seizures during paradoxical sleep), we postulate a dual effect--facilitatory or inhibitory--of paradoxical sleep on limbic epilepsy. A role in seizure induction for bulbopontine structures is proposed on the basis of seizure precipitation during phasic paradoxical sleep. Propagated limbic seizures and paradoxical sleep without atonia displayed similar behavioral patterns. This fact and the possibility that a seizure may substitute for paradoxical sleep, lead us to think that limbic seizures and paradoxical sleep subserve similar functions. One of them might be the elimination of a potentially neurotoxic endogenous product.     

Experimental limbic seizure status epilepticus and focus resection in cats

Status epilepticus is a neurological emergency and refractory one often resulted in neurological damage or death. Since the basic mechanisms of status epilepticus was not fully understood, a surgical treatment was not attempted until now. In the present study, a surgical resection of the epileptic focus was made in experimentally induced limbic status epilepticus and influences of the surgery upon status epilepticus was discussed. Limbic status epilepticus was induced by means of kainic acid (KA) microinjection into unilateral amygdala in cats and effects of focus resection upon limbic seizure status were studied. Ten adult cats were stereotaxically operated on under pentobarbital anesthesia. Bipolar electrodes were placed in bilateral amygdala and hippocampus. An injection cannula, designed for kainic acid injection, was placed in the left amygdala. The cats were then divided into two groups. Group A (5 cats) received 0.5 microgram of KA injection into the amygdala resulted in mild limbic status. Two of them were controls and 3 of them received amygdalotomy after induction of the limbic seizure status. Group B (5 cats) received 2.0 micrograms KA injection resulted in severe limbic status. Moreover, independent spontaneous seizure activities were observed in the ipsilateral hippocampus. Two of them were controls and 3 of them were operated on. After amygdalotomy, limbic seizure stopped in the operated cats of Group A. In the operated cats of Group B, repeated seizures in the epileptogenic focus (amygdala) was completely suppressed, however, spontaneous seizures of the ipsilateral hippocampus persisted even after the surgery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional cerebral blood flow and kainic acid-induced focal limbic seizures in cats

An experimental limbic seizure was induced in cats by microinjection of kainic acid into the left amygdala. Measurement of regional cerebral blood flow (rCBF) in the limbic structure and cerebral cortex was performed by means of the hydrogen clearance method. Immediately after the development of continuous multiple spikes, rCBF increased about 2-fold in the left amygdala (LA) and remained so during the seizure. When continuous multiple spikes were transmitted to the left hippocampus (LH), rCBF in the LH increased to 140% of the baseline value, but in the right amygdala (RA) and left sensorimotor cortex (LCx) it remained unchanged. During limbic seizure in which spike discharges propagated to the LCx, rCBF in the LA, RA, LCx and LH increased to 220%, 130%, 120% and 190%, respectively. In the interictal stage in which interictal spike discharges intermittently appeared in the LA, rCBF returned to baseline values in the primary and secondary foci. The results show that rCBF increased almost simultaneously with the development of the seizure in the primary focus and the areas where seizure propagation were observed, and returned to baseline value once the seizure had disappeared. During the interictal stage, rCBF in the primary focus was only slightly increased in spite of persistence of interictal spike discharges.     

Regional cerebral blood flow during development of limbic seizures induced by kainic acid (KA) microinjection into unilateral amygdala in chronic cats

Regional cerebral blood flow (rCBF) was studied by means of electrolytic hydrogen clearance method in chronically prepared adult cats during development of limbic seizures induced by KA microinjection into the unilateral amygdala. Stereotaxic operation was carried out on 7 adult cats. Bipolar electrodes were placed in the lateral nuclei of bilateral amygdala (LA: left amygdala, RA: right amygdala), and in the ipsilateral dorsal hippocampus (LH). Teflon needles with inner stainless steel needle guides were placed in LA, RA, LH and left anterior sigmoid gyrus (LCx) so as to introduce platinum electrodes for rCBF measurements. The teflon needle placed in LA was also utilized for KA microinjection (1 microgram). Measurements of rCBF were done before (control) and after KA microinjection. Control rCBF were as follows; LA: 41.6 15.9, RA: 40.7 12.2, LH: 39.1 10.9, LCx: 55.4 20.7 (ml/100 g/min). After KA microinjection, measurements of rCBF were made during limbic seizure stage (LSS) and transfer stage (TS). TS was divided into two stages; early TS and late TS. In LSS, 50 to 92% increase of rCBF were noted as follows; LA: 79.7 23.7, RA: 66.1 18.1, RH: 58.6 17.6, LCx: 91.4 17.8 (ml/100 g/min). In early TS, rCBF in all recorded sites returned to the same level as control rCBF. In late TS, rCBF in LA and LH were slightly lower than the level of control rCBF. Pathological examination of LA and LH in early and late TS showed different features. In late TS, astrocytic proliferation was remarkable while it was mild in early TS.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute Effect of Potassium Penicillin G on Experimental Focal Epilepsy

Intraperitoneal PC injections could produce secondarily generalized seizures in both the experimental models of focal epilepsy: amygdaloid kindling models and KA-in-duced limbic seizure models. In the controls, a large amount of PC induced bilateral cortical epileptiform discharges but not in the limbic structures. The epileptic foci induced by the KA injection are more sensitive to PC than the foci induced by kindling.     

Experimental complex partial seizure and its possible clinical application

Clinical applications of experimental models of complex partial seizure were studied using kainic acid-induced limbic seizures and amygdaloid kindling models. The following experiments were done aiming to study the basic approach for the treatment of the intractable complex partial seizures. 1) Degenerative focal lesions were made in bilateral substantia nigra and substantia innominata by a local microinjection of the ibotenic acid and influences upon limbic seizures were studied. Substantia innominata has a facilitatory effect upon secondary generalization of the limbic seizure while substantia nigra has an inhibitory influence. Degenerative lesions of the bilateral hippocampus inhibited development process as well as establishment of the kindling. 2) Resection of the primary epileptic focus in a limbic seizure status resulted in seizure control in cats with a single focus but not in another with multiple foci. 3) An autoradiography was done during limbic seizure status induced by kainic acid microinjection, and local cerebral glucose utilization (LCGU) and local cerebral blood flow were studied in order to study the relationship between cerebral metabolism and cerebral blood flow during limbic seizures. In the pyramidal cell of the hippocampus, an increased ratio of LCGU (x 4.1) is larger than that of LCBF (x 1.6). This uncoupling may be one reason of the neuronal cell damage during the limbic seizure status. 4) Autoradiography of the calcium suggested that one of the causes of hippocampal degeneration in intractable complex partial seizures should be a consequence of calcium influx into pyramidal cells during repeated limbic seizures.     

Perirhinal cortical lesion suppresses the secondary generalization in kainic acid-induced limbic seizure

To elucidate the role of the perirhinal cortex (PRC) in experimental epilepsy, the effects of the lesion of the PRC on kainic acid (KA)-induced limbic seizure were investigated. The PRC lesion was made by means of ibotenic acid (IBO) microinjection. The electroencephalogram in the PRC-lesioned rats demonstrated suppression of the propagation of epileptic discharges from the limbic structures to the sensorimotor cortex. Behaviorally, motor manifestations such as mastication, facial twitching and forelimb clonus were attenuated. These results indicate that the PRC seems to be a potent relay station of the secondary generalization from the limbic structures to the sensorimotor cortex.     

Epileptogenic properties of quisqualic acid: microinjection into the unilateral amygdala in cats

The present studies demonstrated that the microinjection of quisqualic acid (QA) into unilateral amygdala in chronically implanted cats resulted in various types of limbic seizures in accordance with injected doses. The epileptogenic potency of QA in the induction of epileptic seizures was lower then that of kainic acid (KA), which has also been demonstrated in our previous studies. Electroencephalographic changes and clinical manifestations of QA-induced epilepsy were less prominent as compared with those of KA-induced epilepsy. Five micrograms of QA resulted in pure amygdaloid seizures. The moderate dose administration of QA (15 micrograms) was suitable to observe limbic status. Both doses of QA elicited similar characteristic epileptic patterns on EEG, which was quite distinguishable from those of KA. In pathological study, mild degeneration of hippocampal pyramidal cell layer was observed in the cases injected 15 micrograms of QA. These electro-clinical and pathological features are interesting in similarities to those of human complex partial seizures, mesial temporal sclerosis. In conclusion, the strict dose dependency of QA in the production of limbic seizures is a valid advantage for an experimental model of a complex partial epilepsy in man.     

Kainic acid-induced generalized seizures in cats--microinjection into caudate nucleus]

Electroencephalographic and behavioral changes were observed after 2 micrograms of kainic acid (KA) injection through a chronically implanted cannula into unilateral caudate nucleus (CN) of freely moving and non-anesthetized cats. The control group showed no changes on EEG or behavior during the observation period. In KA group, from 2 to 5 minutes after KA injection, the cats showed contralateral circling. On EEG, focal spikes were elicited at the injected site of the right CN. From 15 to 25 minutes after the injection, secondarily generalized seizures were observed on EEG repeatedly. However, the behavioral change was not remarkable and only the behavioral arrest was observed during the electrographic generalized seizure. From 6 to 8 hours after injection, they showed clonic seizure of the contralateral hindlimb followed by generalized tonic-clonic convulsion. These seizures were frequent during 6 to 16 hours after injection. However, these seizures subsided within 48 hours after the injection and the cats became normal afterward. Histopathological examination revealed focal pyknosis and gliosis only at the injection site of caudate nucleus. The results suggested that an epileptogenic focus of the caudate nucleus demonstrated a rapid evolution from the focal seizure status to the secondarily generalized seizure status. This fact explains that the caudate nucleus may be a possible key structure as a relay nucleus for the secondary generalization of a focal seizure.     

Chronic Semichronic Limbic Epilepsy Produced by Microinjection of Tetanus Toxin in Cat Hippocampus

We describe an animal preparation in which a semichronic or chronic limbic epileptiform syndrome can be produced reliably by unilateral microinjection of tetanus toxin in cat ventral hippocampus. Injections were given at 1-week intervals until abnormal EEG activity was observed. After two to five injections, the animals abruptly began to exhibit intermittent spikes and subclinical discharges that soon gave way to spontaneous and recurrent behavioral seizures which gradually increased in frequency, duration, and severity in the next 12-48 h. Anticonvulsant therapy (phenobarbital, PB) was required within the first 3 days of the syndrome, since life-threatening generalized tonic-clonic seizures (GTCS) and status epilepticus would develop if the animal were left untreated. If severe seizures were prevented by antiepileptic drugs (AEDs) there was complete remission of the syndrome and repeat injection was necessary to reinitiate seizures. Animals that experienced severe seizures or that were reinjected after remission developed a chronic seizure syndrome and could be maintained with AEDs for long times (greater than 1 year) without significant debilitation. Although early spikes and subclinical discharges were typically focal to ipsilateral limbic sites, initial seizures appeared explosively in the form of a high-amplitude, high-frequency discharge, which often had an apparently bilateral limbic onset. On the other hand, chronic seizures had much more gradual onset and spread, often consisting of periodic sharp waves or low-amplitude sinusoidal discharge that was more clearly focal to ipsilateral limbic sites. Throughout the syndrome, ictal behavioral manifestations were highly stereotyped and very comparable to those described by other investigators in studies of clinical and experimental limbic epilepsy. All animals exhibited signs of independent contralateral involvement during the syndrome, ranging from independent contralateral spikes to subclinical discharges with a clear contralateral onset. None of the animals exhibited structural lesions on histologic examination at the level of light microscopy.     

红藻氨酸诱导大鼠癫痫发作的电生理机制研究

目的　探讨红藻氨酸 ( KA)诱导大鼠复杂部分性癫痫发作的 EEG特点以及可能的电生理起搏点位置。方法　在立体定位指引下 ,将 EEG记录电极植入 1 2只大鼠双侧海马、额叶皮质或杏仁核中 ,其中 8只为实验组 ,4只为对照组。手术后 1周在大鼠清醒状态下 ,连续描记 KA或盐水注射后 EEG 1 2 0 min,观察 EEG波形、波幅以及频率的变化特点并记录每次电发作的起搏点位置。结果　 ( 1 ) KA注射后大鼠 EEG表现出多种形式的放电波形 ,典型波形有单棘波、多棘波、多相棘波、正相棘波、棘节律、节律性慢波、棘慢波等。 ( 2 )大鼠在凝视发作以及自动症发作时海马、杏仁核和额叶皮质均有异常放电。 ( 3) KA注射后大鼠电发作起搏点不固定。 ( 4 )各导放电频率多数情况下一致 ,偶有不一致现象。 ( 5 )存在亚临床放电。结论　 ( 1 ) KA注射后大鼠 EEG表现为多种形式的电发作活动 ;( 2 )大鼠在复杂部分性发作过程中不仅有边缘系统参与 ,也有边缘外额叶皮质参与 ;( 3)KA模型中 ,电发作起搏点不固定 ,KA注射后大鼠脑内可能存在一个异常的神经元网络 ,在网络中存在放电不均衡现象。     

Change in cerebral glucose metabolism during limbic seizures elicited from lateral septal nucleus

The roles of the amygdala and hippocampus have been extensively studied in limbic seizures. Although the septal nuclei have a close connection to the hippocampus and affect emotional behavior, the effect on limbic seizures is still unclear. We have reported that characteristic sham-rage seizures were observed in cats, by administering a local injection of kainic acid (KA) into the lateral septal nucleus (LSN). This study investigated the electrophysiological features of KA-induced septal seizures in rats and analyzed the process in relation to the cerebral glucose metabolism using [¹⁴C]deoxyglucose autoradiography. On EEG, epileptic discharge eliciting from the LSN rapidly propagated to the hippocampus and the amygdala. Behavioral change was similar to that in limbic seizures induced by intraamygdaloid KA. Sham-rage seizure was not observed in rats. However, the local cerebral glucose metabolism during the seizures increased not only in the limbic structures including the LSN but also in the hypothalamus and periaqueductal grey matter of the midbrain. The findings were distinctive of septal seizures as compared with amygdaloid seizures. The results suggested that sham-rage seizures in cats might be caused by a secondary epileptogenic excitation in the hypothalamus or periaqueductal grey matter of the midbrain. The septal nuclei may play an important role in emotional behavior associated with limbic seizures even if there is a species difference in its function.