Shigeya Tanaka

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.

Kainic acid-induced dorsal and ventral hippocampal seizures in rats

Despite reports of differing regional seizure susceptibility in the hippocampus, hippocampal initiation of limbic seizures has not been precisely localized. We compared seizures induced by kainic acid microinjection into the left dorsal and ventral hippocampus of rats. Discharges following ventral injections rapidly propagated to the left amygdala and sensorimotor cortex unlike seizures following dorsal injections. The ventral group showed various ictal behaviors including motor manifestations, while dorsally injected rats showed only immobilization.

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.

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.

Hippocampal transection attenuates kainic acid-induced amygdalar seizures in rats.

Since the dorsal and ventral hippocampus in the rat may act differently from one another in limbic seizures, we studied effects of orthogonal transection between the dorsal and ventral hippocampus upon kainic acid-induced amygdalar seizures. A total of 26 rats were divided into three groups. Ten rats underwent transection using a modified wire knife (transection group); 16 others were untransection group (n=10) and controls (n=6). All the rats then underwent stereotactic implantation of electrodes in the left amygdala (LA), left dorsal hippocampus (LdH), left ventral hippocampus (LvH), and the left sensorimotor cortex (LCx). A stainless steel cannula also was introduced into the LA. Rats except controls later received 1.0 microg of kainic acid (KA) via the cannula. Controls received phosphate buffer solution alone. In the untransection group, multiple spike discharges in the LA immediately propagated concurrently to the LvH and LdH. Propagation involved the LCx to become status epilepticus 1 to 2 h after KA injection. Seizures, characterized by mastication, salivation, facial twitching, forelimb clonus, and sometimes rearing and falling, lasted 1 to 2 days. Microscopic examination revealed severe neuronal cell damage in the LA, LvH, and LdH. In the transection group, multiple spike discharges initiated from the LA and were propagated to LvH, but LdH as well as LCx involvement was slight. Status epilepticus involved only the LA and LvH 1 to 2 h following KA injection. Seizures subsided within 24 h, showing no ictal manifestations except for aggressiveness. Overall, seizures were weak and transient compared with those in controls. Histologically, hippocampal neuronal damage was slight, but damage to amygdalar neurons was similar to that in untransection group. No electroclinical and histological changes were seen in controls. These results indicated that connections between the dorsal and ventral hippocampus are important for full development of KA-induced amygdalar 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.

Kainic acid-induced perirhinal cortical seizures in rats

Seizures induced in rats by kainic acid microinjection into the perirhinal cortex were studied electrophysiologically and behaviorally and compared with known features of seizures following kainic acid injection into the amygdala. Unlike amygdalar seizures, perirhinal cortical seizures did not generalize to become limbic seizures but rather spread to sensorimotor cortex to become manifest as motor seizures. Perirhinal cortical seizures also required larger kainic acid doses for provocation and were briefer.

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.