Allopregnanolone-induced rise in intracellular calcium in embryonic hippocampal neurons parallels their proliferative potential

<p>Abstract</p> <p>Background</p> <p>Factors that regulate intracellular calcium concentration are known to play a critical role in brain function and neural development, including neural plasticity and neurogenesis. We previously demonstrated that the neurosteroid allopregnanolone (APα; 5α-pregnan-3α-ol-20-one) promotes neural progenitor proliferation <it>in vitro </it>in cultures of rodent hippocampal and human cortical neural progenitors, and <it>in vivo </it>in triple transgenic Alzheimer's disease mice dentate gyrus. We also found that APα-induced proliferation of neural progenitors is abolished by a calcium channel blocker, nifedipine, indicating a calcium dependent mechanism for the proliferation.</p> <p>Methods</p> <p>In the present study, we investigated the effect of APα on the regulation of intracellular calcium concentration in E18 rat hippocampal neurons using ratiometric Fura2-AM imaging.</p> <p>Results</p> <p>Results indicate that APα rapidly increased intracellular calcium concentration in a dose-dependent and developmentally regulated manner, with an EC₅₀of 110 ± 15 nM and a maximal response occurring at three days <it>in vitro</it>. The stereoisomers 3β-hydroxy-5α-hydroxy-pregnan-20-one, and 3β-hydroxy-5β-hydroxy-pregnan-20-one, as well as progesterone, were without significant effect. APα-induced intracellular calcium concentration increase was not observed in calcium depleted medium and was blocked in the presence of the broad spectrum calcium channel blocker La³⁺, or the L-type calcium channel blocker nifedipine. Furthermore, the GABA_Areceptor blockers bicuculline and picrotoxin abolished APα-induced intracellular calcium concentration rise.</p> <p>Conclusion</p> <p>Collectively, these data indicate that APα promotes a rapid, dose-dependent, stereo-specific, and developmentally regulated increase of intracellular calcium concentration in rat embryonic hippocampal neurons via a mechanism that requires both the GABA_Areceptor and L-type calcium channel. These data suggest that APα-induced intracellular calcium concentration increase serves as the initiation mechanism whereby APα promotes neurogenesis.</p>