Search

Significant reduction in glutamate receptor 1 (GluR1)- and GluR2/3-immunopositive neurons was demonstrated in the hilus of the dentate gyrus in mice killed on days 1, 7 and 60 after pilocarpine-induced status epilepticus (PISE). In addition, GluR1 and GluR2/3 immunostaining in the strata oriens, radiatum and lacunosum moleculare of areas CA1-3 decreased drastically on days 7 and 60 after PISE. Neuronal loss observed in the above regions may account, at least in part, for a decrease in GluR immunoreactivity. By contrast, many GluR1-immunopositive neurons were observed in the gliotic area of CA1. Of these, about 42.8% were immunopositive for markers for hippocampal interneurons, namely calretinin (7.6%), calbindin (12.8%) and parvalbumin (22.4%). GluR1 or GluR2/3 and BrdU double-labelling showed that the GluR1- and GluR2/3-immunopositive neurons at 60 days after PISE were neurons that had survived rather than newly generated neurons. Furthermore, anterograde tracer and double-labelling studies performed on animals at 60 days after PISE indicated a projection from the hilus of the dentate gyrus to gliotic areas in both CA3 and CA1, where the projecting fibres apparently established connections with GluR1-immunopositive neurons. The projection to CA1 was unexpected. These novel findings suggest that the intrinsic hippocampal neuronal network is altered after PISE. We speculate that GluR1-immunopositive neurons in gliotic CA1 act as a bridge between dentate gyrus and subiculum contributing towards epileptogenesis.

By intravenous administration of group I metabotropic glutamate receptor antagonists at 1 or 2 h during pilocarpine induced status epilepticus (PISE), we showed that mGluR1 antagonists AIDA or LY367385 (at dosages ranging from 25 to 200 mg/kg), mGluR5 antagonists SIB1757 (at dosages ranging from 25 to 200 mg/kg), SIB1893 (from 25 to 100 mg/kg), MPEP (from 25 to 100 mg/kg) injected at 1 or 2 h during PISE were ineffective in controlling status epilepticus (SE). However, when administered at 1 h during PISE, MPEP at 200 mg/kg, combination of MPEP (200 mg/kg) with MK801 (0.1 mg/kg) or with MK801 (0.1 mg/kg) and diazepam (0.5 mg/kg), combination of SIB1893 (200 mg/kg) with MK801 (0.1 mg/kg) could effectively control behavioral SE, and were neuroprotective. In particular, the combination of MPEP with MK801 and diazepam could stop both behavioral SE and electrical SE (under EEG monitoring) within a few minutes after the administration. HPLC study showed that a high level of MPEP was maintained in the blood and its metabolism rate was slow in experimental mice with PISE. We therefore concluded that the combination of MPEP (200 mg/kg) with MK801 (0.1 mg/kg) and diazepam (0.5 mg/kg) could effectively stop SE and its subsequent neuronal loss in the hippocampus when administered 1 h during PISE. It may provide a new approach to effectively control intractable SE.