Epileptic activity in the cat perirhinal cortex in response to amygdala kindling

Specific amygdaloid nuclei are involved in suppression or propagation of epileptiform activity during transition stage between oral automatisms and generalized clonic seizures

Kindling is a model of the neural plasticity that occurs following stimulation to the brain, which can result in epileptogenesis. The amygdala (Am), one of the most sensitive structures from which to induce electrical kindling, is comprised of distinct nuclei that possess differences in threshold for seizure initiation, unique cellular and molecular morphology, and specific neuroanatomical connections within the amygdala and, to other cortical and subcortical brain structures. The aim of this study was to map the spread of epileptiform activity throughout the ipsilateral and contralateral hemispheres during the transition stage between oral automatisms and generalized clonic seizures, by measuring changes in mRNA expression for c-fos, NGFI-A, and BDNF. The stimulating electrode was implanted in either the basolateral (BL) or the lateral (CeL) or medial (CeM) subdivisions of the central nucleus of the amygdala. The rats were kindled once daily using afterdischarge-threshold electrical stimulation until the first forelimb clonic seizure was induced. They were sacrificed 30 min later, and their brains were prepared for in situ hybridization to measure mRNA expression of c-fos, NGFI-A and BDNF. The results demonstrate that: (1) the threshold to elicit an afterdischarge from the BL was lower than that of either the medial (CeM) or lateral (CeL) subdivisions of the Ce, which did not differ from each other; (2) the patterns of mRNA expression for c-fos, NGFI-A and BDNF were highly similar to each other when the stimulation site was the BL or the CeL, and included mainly limbic cortical and subcortical areas ipsilateral to the electrode; (3) c-fos was the only probe to be expressed in the contralateral hemisphere following the first motor seizure, and the pattern of its expression reflected a subset of structures recruited in the ipsilateral hemisphere including the claustrum, insular and perirhinal cortices; (4) unexpectedly, stimulation of the CeM elicited seizures and afterdischarges of shorter duration than those evoked by stimulation of the BL or CeL, and failed to increase mRNA expression for any of the probes in the hippocampus or in the contralateral hemisphere. A neuroanatomical model of Am-induced seizure propagation is proposed suggesting that the Claust-Ins-PRh play a pivotal role during the transition between oral automatisms and generalized clonic convulsions.

A behavioral and immunohistochemical study on the development of perirhinal cortical kindling: a comparison with other types of limbic kindling

We have previously reported that the perirhinal cortex (PRC) plays an important role in the generalization of kindled seizures. In the present study, we kindled the rat PRC and made a comparison with amygdala (AM) and dorsal hippocampal (dHIPP) kindling. In order to produce a functional map of the seizure generalization pathway from these limbic foci, we also stained for Fos protein in sections of the PRC-, AM- and dHIPP-kindled brains using an immunohistochemistry technique. In the generalized seizures of PRC kindling the duration of afterdischarges (ADs) and the latency to forelimb clonus were significantly shorter than those of AM kindling or dHIPP kindling. Typically, the PRC-kindled rats demonstrated moving arrest or exploratory behavior for about 10 days, and then a characteristic 'rapid backward moving' behavior for 1 day, followed by the sudden appearance of generalized motor seizures. Fos protein induction after a single stimulation of the PRC is more widely observed than after a single stimulation of the AM, in that the PRC stimulation produced Fos protein expression in the temporal and parietal neocortices. Following AM and PRC kindling, the Fos-positive areas were asymmetrically propagated from the ipsilateral to the contralateral hemisphere. The contralateral PRC was primarily activated at the generalization of epileptic activity in the contralateral hemisphere. In contrast, the Fos protein distribution of the dHIPP-kindled rats was restricted to the bilateral hippocampi during the early stages, followed by the symmetrical propagation from the limbic system to the neocortex during the generalized seizures. These results indicate that the PRC plays a characteristic role in the seizure generalization of kindling.

Characterization of epileptiform field potentials recorded in the in vitro perirhinal cortex of amygdala-kindled epileptogenesis

The perirhinal cortex (PRC) has recently been reported that the excitatory role of this area is important for the generation and the propagation of kindled seizures. In the present study, we investigated the extracellular electrophysiological properties of the circuitry which contribute to the propagation of seizures in the PRC, and examined the hypothesis that amygdala-kindling changes the electrophysiological nature of the rat PRC slice in vitro. Field potentials elicited in the PRC had extended duration (> 200 ms, most approximately equal to 1 s) with overlying spike components. The potentials showed strong synchronizing effect governed by an all-or-none rule. Although spontaneous epileptiform discharges that were equivalent in appearance to synaptically-activated field potentials were observed in the PRC of both amygdala-kindled and control rats, the number of slices showing spontaneous activity was significantly larger in the kindled group than in the control group (chi 2-test, P < 0.01). The occurrence of tetanus-induced afterdischarges in kindled rats was significantly higher than in control rats (chi 2-test, P < 0.01). The afterdischarge durations of control slices were generally short and the afterdischarges did not consist of the typical "tonic-clonic' phases. However, the occurrence of the electrographical seizure in the high K+ ACSF were not affected by amygdala-kindling operation. These results indicate that amygdala-kindling lowers the threshold for transsynaptic excitability and enhances the synchronized activity of the PRC induced by episodic proconvulsive manipulations such as tetanus stimulation.