Abstract
Electrocorticograms (ECoGs) and somatosensory evoked potentials (SEPs) were recorded, and convulsion thresholds were determined in rats in which FeCl2 solution was injected into the unilateral sensorimotor cortex. Isolated spikes appeared immediately after the injection of FeCl2 solution in ECoGs of the cortex near the injection site and the contralateral homotopic cortex. The injection of FeCl2 solution produced different electrocorticographic features in which the frequency of isolated spikes was dominant on the side ipsilateral or contralateral to the injection site or nearly equal on the two sides. The spike frequency increased up to 30 to 50 days after the injection, and then was almost constant in most of the rats up to 90 days after the injection. In rats showing nearly equal spike activity on the two sides, there was a tendency for the spike frequency to decrease gradually after 30 to 50 days. Most of the spike and slow wave complexes appeared bilaterally one month or more after the injection in rats in which the isolated spike activity was dominant on the side ipsilateral to the injection site or nearly equal on the two sides. The proportion of rats showing spike and slow wave complexes increased steeply until three months after the injection, and reached 36% of all the FeCl2 solution-injected rats six months after the injection. In ECoGs of these rats, isolated spikes were also detected. In rats showing dominant spike activity on either side of the cortex, most of spikes appeared unilaterally, while in rats showing nearly equal spike activity on the two sides and those showing spike and slow wave complexes, the frequency of almost synchronous spikes on both sides was higher than that of unilateral spikes. In rats showing dominant spike activity on the side contralateral to the injection site, SEPs recorded at the cortex near the injection site were devoid of the initial positive deflection and were monophasic. They were biphasic in other FeCl2 solution-injected rats. In rats showing only isolated spikes, abnormal behavior was seldom observed, and convulsion thresholds were lowered. In most of the rats showing spike and slow wave complexes, head nodding was observed. The induction and development of epileptic focus by FeCl2 solution are discussed.
