Yukichi Yonemasu

Cerebral blood flow and histopathological changes following permanent bilateral carotid artery ligation in Wistar rats

SummaryCerebral blood flow and histopathological changes after bilateral carotid artery ligation (BCAL) in Wistar rats were studied. Eight of the 38 rats (21%) died within one week. In the 30 survivors, the incidence of histopathological change was 90% in the caudate nucleus, 23% in the cortex, 30% in the hippocampus, and 0% in the other structures. Local cerebral blood flow (LCBF) was measured using the quantitative autoradiographic 14C-iodoantipyrine technique in 24 anatomically discrete regions of the brain. BCAL induced ischemia in the entire forebrain. The percent reduction of LCBF was between 25–94% of the control at 2.5 h after BCAL. LCBF tended to recover 1 week after BCAL except for the regions of neuronal damage. These results suggest that neuronal damage does not correlate with the flow rate. In the present study, selective neuronal damage was also observed in rats with chronic cerebral ischemia.

Local cerebral glucose utilisation following acute and chronic bilateral carotid artery ligation in Wistar rats: relation to changes in local cerebral blood flow.

The effects on local cerebral blood flow (LCBF) and glucose utilisation (LCGU) of permanent, bilateral carotid artery ligation (BCAL) were studied in conscious Wistar rats. LCBF and LCGU were measured using quantitative autoradiographic 14C-iodoantipyrine and the 14C-2-deoxyglucose (14C-DG) techniques in 24 anatomically discrete regions of the brain. LCBF in the cerebral hemispheres 2.5 h (acute) after BCAL significantly decreased to 25–87% of the sham control, with the exception of the mammillary body. After acute BCAL, there was a heterogeneous accumulation of 14C-DG in the caudate nucleus and cerebral cortices. Only in the lateral geniculate body did LCGU significantly decrease after BCAL. One week (chronic) later, LCBF was significantly decreased in 15 (containing the caudate nucleus and all the cerebral cortices) of 24 structures. LCGU in ten (containing the caudate nucleus and all the cerebral cortices) of 24 structures after chronic BCAL significantly decreased to 66–77% of the sham control, except for regions with neuronal damage in which there was a heterogeneous uptake of 14C-DG. The ratio of LCBF/ LCGU in chronic BCAL was unchanged in comparison with values in the corresponding sham-operated group. This model of acute and chronic cerebral ischaemia, with impairment in cerebral circulation and/or glucose metabolism, is expected to become a pertinent tool for the neurophysiologist.

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.

Uncoupling of local blood flow and metabolism in the hippocampal CA3 in kainic acid-induced limbic seizure status

Limbic seizure status was induced by microinjection of kainic acid into a unilateral amygdala in rats. Two hours after kainic acid injection, distant neuronal cell damage was produced, especially in the hippocampal CA3 on the kainic acid-injected side. In order to elucidate the mechanism of this neuronal cell damage, local cerebral glucose utilization and local cerebral blood flow were studied by means of an autoradiographic method using [14C]2-deoxyglucose and [14C]iodoantipyrine during kainic acid-induced limbic seizure status. These studies were performed 2 h after kainic acid microinjection into a unilateral amygdala. Both local cerebral glucose utilization and local cerebral blood flow were remarkably increased in the limbic system, ventrobasal complex of the thalamus, septal nucleus, nucleus accumbens, caudate nucleus, substantia nigra and hypothalamus on the kainic acid-injected side. In the hippocampus, local cerebral glucose utilization increased 2.6 times control in CA1 and 4.1 times in CA3, whereas the rates of increase in local cerebral blood flow were similarly low in CA1 and CA3: 1.2 and 1.4 times control, respectively. The results demonstrated that the degree of uncoupling of local cerebral glucose utilization and local cerebral blood flow were higher in CA3 than in CA1, and also suggested that relative hypoxia occurred in CA3 in this high degree of uncoupling, resulting in pyramidal cell damage in CA3 in kainic acid-induced limbic seizure status.

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 micrograms) into the unilateral amygdala. With high doses of KA (0.6-1.2 micrograms) injection, 64% of rats developed spontaneous limbic seizures 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.

Electroclinical features of kainic acid-induced status epilepticus in freely moving cats. Microinjection into the dorsal hippocampus

Electrographic and clinical observations were made after the injection of kainic acid into the unilateral hippocampus of freely moving cats. Vehicle solution (phosphate buffer solution) for control study and kainic acid(1, 4 and 12 micrograms) were administered via a chronically implanted cannula. The control group showed no modification during the observation period. After the injection of 1 microgram of kainic acid, focal status epilepticus was observed for 2-3 days and then cats became normal afterwards. In the group of 4 micrograms kainic acid infection, cats demonstrated limbic status for 3 days, and persistent inter-ictal discharges continued during the observation period. Independent amygdaloid seizures and secondary generalized convulsions developed in the cats administered 12 micrograms of kainic acid. The cats died in the status epilepticus. The dose-dependent and substantial effect of KA without the influences of anesthesia and surgery was demonstrated. The results were discussed in relation to the human medial temporal sclerosis and the effects on the emotional mechanism of the limbic system. We suggest this model to be useful in the study of various types of temporal lobe epilepsy and the emotional mechanisms of the limbic system.

Regional calcium accumulation and kainic acid (KA)-induced limbic seizure status in rats

The sites of calcium accumulation were studied by 45Ca autoradiography during kainic acid (KA)-induced limbic seizure in rats. Two hours after KA injection into unilateral amygdala, calcium accumulated in CA3 of the hippocampus, lateral septal nucleus and thalamic reticular nucleus on KA-injected side. Those sites coincided with the sites where neuronal cell damage appeared 4 h after KA injection. These results suggested that regional calcium accumulation might be responsible for neuronal cell loss induced by seizures.

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.

Various hippocampal lesions induced by multi-fractional ibotenic acid injections and amygdala kindling in rats

Hippocampal degenerative lesions were made bilaterally by means of multiple ibotenic acid injections and development of amygdala kindling was studied. In groups with lesions in either bilateral dorsal or ventral hippocampus, stimulations required for kindling were almost the same as those of controls. In the group with lesion of the entire hippocampus, kindling development was remarkably slow especially in the early stage of the kindling process. However, kindling effect was finally established in all groups.

Ibotenic acid-induced nigral lesion and limbic seizure in cats

The degenerative lesions of bilateral substantia nigra (SN) were made by means of microinjections of ibotenic acid (IBO) solutions and influences upon kainic acid (KA)-induced seizures were studied. IBO solutions were injected bilaterally into SN and circumscribed degenerative lesions were made within the bilateral SN. In a control group, phosphate buffer solutions were injected in the bilateral SN. More than one week after the procedures, 1 microgram KA was injected into unilateral amygdala via implanted cannula and limbic seizures were induced. The destruction of SN accelerated the secondary generalization of the limbic seizure within 3 days after the KA injection while no secondary generalization was observed within 3 days in the control group. The fact suggests that GABAergic systems of the substantia nigra and/or ascending norepinephrine pathway have a strong inhibitory influence on the secondary generalization of limbic seizures. The hypothesis of nigral mechanisms as a control system for secondary generalization is discussed.