Abstracts

Changes in hippocampal dentate physiology after status epilepticus (SE) may contribute to the development of spontaneous seizures. There is both altered expression of GABA[sub]A[/sub] receptor (GABAR) subunits, and a dramatic increase in the birth of newborn dentate granule neurons (DGNs) after SE. Here we determine whether the newborn, mature or both population of DGNs contribute to the changes in GABA receptor expression after SE during postnatal development.
Post-natal day 20 (P20) rats received either a dose of lithium and saline (control) or lithium-pilocarpine (pilo) to induce SE. They were sacrificed and perfused on P34 and 10 [mu]m frozen sections were stained for PSA-NCAM and NeuN. Immature, PSA-NCAM positive (+) DGN or mature NeuN positive (+) DGN were individually dissected and underwent single cell RNA amplification, the aRNA from each cell was then hybridized against a reverse northern blot for the relative expression of the 16 GABAR subunits.
We find that the mature NeuN+DGN from pilo treated animals have increased relative expression of the GABA [alpha]1,[beta]1,[beta]2,[gamma]2 receptor subunits compared to mature DGN from control animals. The most dramatic increase is a ~5 fold increase in the [alpha]1 subunit. In contrast, immature DGN do not differ in the relative concentrations of these GABAR subunits between control and pilo treated animals.
There are, however differences in GABAR expression between mature and immature DGNS within both the control and pilo treated groups. In control animals, the immature DGN express higher levels of [beta]1, [gamma]2 than mature DGN. However in pilo treated animals, the immature and mature DGN express similar levels of [beta]1, [gamma]2 due to an increased expression of these subunits in mature DGN after SE. The mature DGN from the pilo treated animals now express increased [alpha]1 and [beta]2 compared to the immature DGN due to the increase in [alpha]1 and [beta]2 in the mature DGN after SE.
Immature and mature DGN in both control and pilo treated animals have different patterns of GABAR subunit expression, suggesting that within the dentate as DGN mature, GABAR genes are developmentally regulated. After SE at P20, there is increased expression of [alpha]1, [beta]1, [beta]2, [gamma]2 in mature, but not immature DGN, implying that only DGN present at the time of SE undergo increases in GABAR subunit expression. The pattern of GABAR expression after SE is different depending on the age of the animal at the time of SE, as adult animals after SE have a down regulation of [alpha]1, opposite to our current findings.
[Supported by: NINDS- ABK
Child Neurology Foundation- ABK, BEP]