Abstracts

Rationale: Recent evidence has shown that cultured neurospheres contain metabotropic glutamate receptors, and that blocking mGluR1 subunits with the antagonist LY 367385 reduces neurogenesis of the subventricular zone (SVZ) and hippocampus. We hypothesized that early-life seizures stimulate proliferation and aberrant migration of progenitors from the SVZ into distant limbic structures and this excessive proliferation or migration may be prevented with a selective mGluR1 antagonist. Methods: Kainic acid (KA) was administered (i.p.) three times (3×KA), on postnatal (P) days P6, P9, and P13 or P20 followed by a 2 hr post-injection of LY 367385. Proliferation and migration were assessed with two complimentary fluorescent dye tracers carbocyanine dye 1,1’-dioctadecyl-3,3,3’,3’-tetramethylindo-carbocyanine perchlorate (DiI) and 4-chloromethyl benzoyl amino tetramethyl rhodamine (CMTMR). These were stereotaxically injected into the SVZ and animals were sacrificed after 5 days. Results: In controls, diffuse DiI labeling was observed near the infusion site and very few precursor-like cells lined the third ventricle. In contrast, P20 rats with 3×KA had enhanced proliferation in ventral limbic structures detected with Ki67. Reduced proliferation was observed in the SVZ and dentate gyrus in rats post-treated with LY 367385. In P13 rat pups with 3×KA and dye injections, many cells migrated from the injection site and formed a chain notably into ventral cortico-amygdala and ventral thalamic structures. A striking increase of cell proliferation was observed within the ventricles. Pups with dye injections and post-treatment with LY 367385 had less migration and much less proliferation locally in the SVZ and distally in the hippocampus and amygdala. A percentage of migrating precursors were immunopositive for Ki67, however, co-labeling was not observed with either of the dyes used in presence of the antagonist. In contrast, co-localization of the dyes was observed with the mGluR1 antibody. Conclusions: In conclusion, precursors may be stimulated by mGluR I type receptors to facilitate proliferation. However, since the mGluR1a antagonist blocked only the proliferation and not the migration process, activation of the mGluR1 subunit appears to play a role in the abnormal development of proliferating cells but not the abnormal migration following early-life seizures.