Abstracts

Hippocampal mossy fiber sprouting (MFS) has been suggested to be a causal mechanism underlying the development of temporal lobe epilepsy both in humans and animal models, and is regarded as evidence for tissue remodeling after seizure. Recently, it is reported that spontaneous seizures were still developed even after MFS inhibition in some experimental temporal epilepsy models. Matrix metalloproteinases (MMPs) degrade a variety of extracellular matrix molecules and are considered to be involved in tissue remodeling. Expression of MMPs has been reported in several experimental seizure models. We assessed the roles of MMPs in MFS after pilocarpine-induced seizure, using MMP-9 inhibitor. Seizures were induced by intraperitoneal administration of pilocarpine (300mg/kg) in adult male C57BL/6 mice after methylscopolamine injection (1mg/kg). Expression of MMPs after pilocarpine-induced seizure was observed by gelatin zymography and Western blotting. To examine the roles of MMP-9, MMP-9 inhibitor was administered intraventrically 1 day after pilocarpine-induced seizure. Spontaneous recurrent seizures (SRS) were evaluated using video-EEG monitoring system fourteen days after pilocarpine-induced seizure. MFS was assessed by using a modified method for Timm staining. Elevated expression of MMP-9 was observed both in gelatin zymography and Western blotting after pilocarpine-induced seizure. Expression of MMP-9 reached its maximum three days after pilocarpine-induced seizure, and declined thereafter. The level of MMP-9 expression returned to the baseline level fourteen days after pilocarpine-induced seizure. Expression of MMP-2 did not change after pilocarpine-induced seizure. After intaventricular administration of MMP-9 inhibitor (10mg/2ml) one day after pilocarpine-induced seizure, the mean MMP-9 expression level decreased by 26% compared to sham-treated mice, three days after pilocarpine-induced seizure. The level of expression of MMP-2 did not change after MMP-9 inhibitor treatment. Fourteen days after pilocarpine-induced seizure, mossy fiber sprouting was observed in all mice (3/3). Mossy fiber sprouting was not observed in MMP-9 inhibitor-treated mice (0/3). SRS were observed in 75% (3/4) of mice 14 days after pilocarpine-induced seizures. MMP-9 inhibitor treatment did not alter induction rate (4/5) and mean numbers of SRS. Elevated expression of MMP-9 was observed after pilocarpine-induced seizure. Expression of MMP-9 was decreased after MMP-9 inhibitor treatment. MFS was ameliorated by MMP-9 inhibitor treatment, but induction rate and mean numbers of SRS were not changed by MMP-9 inhibitor treatment.