Propagation of amygdala-kindled seizures to the hippocampus in the rat: Electroencephalographic features and behavioural correlates

Abstract

Background The propagation of amygdala-kindled seizures to the dorsal and ventral hippocampus was examined, in rats. The relation of contralateral seizure propagation to the onset of generalized convulsions was also studied. Methods In all subjects, electrodes were implanted in the amygdala. Two additional electrodes were implanted (bilaterally) in the dorsal ( n = 6) or ventral ( n = 8) hippocampus. Kindling stimulations were delivered twice daily (interval 4 h). Results Initially, triggered after-discharges (ADs) were recorded only in the amygdala. With repeated stimulation, the AD propagated to the hippocampus. Rates of propagation were as follows (mean # of stimulations ± SEM): ipsilateral ventral hippocampus, 4.0 ± 0.9; ipsilateral dorsal hippocampus, 6.2 ± 1.4; contralateral dorsal hippocampus, 7.5 ± 1.4; contralateral ventral hippocampus, 8.5 ± 1.0. AD propagation to contralateral sites was significantly slower than to ipsilateral sites. Ipsilateral hippocampal recruitment occurred between stages 1 and 2 (partial seizures), whereas contralateral hippocampal recruitment occurred between stages 2 and 3 (transition to generalized seizures). Summary These results indicate that during amygdala-kindling, it takes several stimulations before discharge propagates to the hippocampus. The close link between contralateral hippocampus involvement and seizure generalization warrants further study, and may lead to a better understanding of the pathways involved in seizure spread.