Abstracts

RATIONALE: Proliferation of neuronal precursors persists in the adult mammalian hippocampal dentate gyrus. Newborn neurons populate the dentate granule cell (DGC) layer, and their birth increases after seizure activity in the adult rat. Newly generated granule neuron-like cells also appear ectopically in the hilus after chemoconvulsant-induced status epilepticus (SE). We sought to determine the origin and phenotype of the hilar ectopic neurons generated in the adult rat pilocarpine model of temporal lobe epilepsy. This activity should enable the participant to discuss basic mechanisms of temporal lobe epilepsy.
METHODS: Adult rats received systemic pilocarpine to induce SE for 2 h. Proliferating cells were labeled with bromodeoxyuridine (BrdU) 7 d after SE, and animals survived an additional 2 h or 2, 7, 14 or 28 d. Immunostaining of coronal brain sections was performed using antibodies to BrdU, the DGC marker Prox-1, calbindin, and the immature neuronal markers doublecortin (DCx), collapsin response mediator protein-4 (CRMP-4) and polysialylated neural cell adhesion molecule (PSA-NCAM). BrdU- and Prox-1-immunoreactive (IR) cells in the dentate hilus were quantified at 14 and 35 d after SE and in saline-treated controls.
RESULTS: The number of BrdU-IR cells in the dentate hilus increased markedly between 7 and 14 d after SE, and were still present after 35 d. Hilar BrdU-IR cell number was significantly greater 14 and 35 d following pilocarpine-induced SE compared to controls (p [lt] 0.01). Few DCx- or Prox-1-IR cells were found in the dentate hilus of controls or at 7 d after SE. By 14 d after SE, many DCx- and Prox-IR cells appeared in the dentate hilus. DCx-IR decreased at 35 d post-pilocarpine treatment, but many Prox-1-IR cells persisted in the hilus. No calbindin-IR hilar granule-like neurons were seen at any timepoint in pilocarpine- or saline-treated rats. CRMP-4, PSA-NCAM, and DCx immunostaining showed chains of cells with migrating neuroblast morphology extending from the inner DGC layer to the hilus.
CONCLUSIONS: These data confirm previous findings of hilar ectopic granule-like neuron generation after SE. Moreover, the hilar ectopic neurons appear to migrate from the DGC layer to the hilus and differentiate into DGCs as evidenced by expression of a DGC-specific marker. Additional study of this process may provide insight into the mechanisms of neuronal precursor migration and differentiation after injury, and their potential role in epileptogenesis.
[Supported by: NINDS NS02006 (JMP) and NS35628, NS39950 (DHL).]