A ROLE FOR THE BILATERAL INVOLVEMENT OF PERIRHINAL CORTEX IN GENERALIZED KINDLED SEIZURE EXPRESSION

The perirhinal cortex (PRh) has been suggested as a substrate for the expression of generalized clonic seizures in the late stages of kindli ng development (stages 4-5). Using the induction of Fos as a marker of neuronal activation, the PRh region was investigated after kindling o r nonkindling electrical stimulation. Nonkindling electrical stimulati on of the PRh elicited stimulus-locked behaviors, without afterdischar ge. These behaviors were characterized by rearing and bilateral foreli mb clonus which were terminated upon electrical stimulus offset in hal f of the rats displaying this behavior (with the other half expressing self-sustained seizures). In these animals, Fos immunoreactivity was found throughout neocortical and subcortical structures in the hemisph ere ipsilateral to the stimulating electrode. By contrast, Fos-immunor eactivity in the contralateral hemisphere was localized primarily in t he PRh and frontal motor cortex. Likewise, similar patterns of Fos imm unoreactivity were observed in both hemispheres of rats following kind ling to one generalized clonic seizure from several limbic and paleoco rtical structures. These results suggest that the bilateral involvemen t of the PRh is critical in producing the bilateral behaviors associat ed with generalized clonic seizure expression. In support of this inte rpretation, infusion of 3 M KCl directly into the contralateral PRh of rats kindled to a single stage 4-5 (generalized clonic) seizure from the ipsilateral amygdala reduced seizure manifestations from a general ized clonic seizure (stage 4-5) to a unilateral clonic seizure (stage 3) without affecting measures of focal excitability. Taken together, t hese data indicate a role for the bilateral involvement of the PRh in generalized clonic seizure expression whether evoked from the naive or kindled state. These results further indicate that bilateral behavior s require the bilateral involvement of the structures necessary for th e expression of these behaviors. (C) 1998 Academic Press.