Abstracts

Rationale: Status Epilepticus (SE) is a potent inducer of neurogenesis in the dentate gyrus. We have found following postnatal day 20 (P20) Li-Pilocarpine induced SE there is an increase in cell birth in the dentate gyrus starting during the episode of SE and lasting for 40 days. Resulting in an increase in the number of immature dentate granule neurons during the latent period. The increase in cell birth corresponds to a shortening of the cell cycle length in dentate gyrus progenitors. Here we have begun to identify cell cycle regulatory molecules that may be responsible for the increase in cell birth and/or differentiation of newborn dentate granule neurons following SE.Methods: Male CD rats from Charles River underwent lithium chloride on P(19) and pilocarpine nitrate or saline on P(20) treatment as previously described (Porter et al. 2005,2006). This induced an episode of SE lasting approximately 5 hours. Animals were sacrificed at 2 hours, 24 hours, 2 weeks and 40 days following SE to measure dentate gyrus protein levels. Proteins analyzed to date include: the cell cycle inhibitors P27/Kip1, Phospho-P27 Ser 10, Phospho-P27 Thr-187, and P15/INK4b; Cyclin dependant kinase regulatory proteins cyclin D1 and D3, and the cyclin dependant kinase 6; the phosphorylated forms of the retinoblastoma protein (phospho- RB 780,795). Results: See TableConclusions: Multiple cell cycle regulatory proteins are expressed in the dentate gyrus and many are altered following SE. Changes include decreased G1 to S regulatory proteins,P15/INK4b and P27/Kip1, which might contribute to the previously described shortening of the cell cycle length. Interestingly P27 has decreased phosphorylation at both Serine 10 and Threonine 187 following SE. Dephosphorylation at these sites has been associated with increased protein degradation, changes in sub-cellular localization and protein-protein interactions. Cyclin D3 is down regulated throughout the latent period concurrent with the time course of increased neurogenesis. The retinoblastoma protein has an immediate decrease in phosphorylation following SE at 2 sites. Loss of cyclins and decreased retinoblastoma protein phosphorylation are associated with inhibition of cell division in many (but not all) tissues suggesting that changes in cyclin D3 and RB may not contribute to the shortened cell cycle length following SE. Decreased RB phosphorylation, however, has been found necessary for neuronal differentiation during development and therefore the decrease in RB phosphorylation may be involved in promoting the maturation of immature dentate granule neurons following SE. Future studies will be directed at determining the functional significance of the identified changes in protein expression. This work was supported by: NINDS