Abstract
We previously reported that transient application of PREGS, one of the most important neurosteroids, to hippocampal slices in rat (4 weeks) evoked a rapid and sustained potentiation of EPSP over 60 min at the dentate gyrus (DG), termed PREGS-inuced long-lasting potentiation (LLPPREGS). LLPPREGS was external Ca2+ dependent and prevented by NMDA receptor antagonist (AP5), GluRε2 subunit inhibitor (Ifenprodil) and open-channel blocker (MK-801), suggesting that a Ca2+ entry through NMDA receptors is involved in the LLPPREGS. The present study aims to directly examine whether PREGS elicits elevation of intracellular Ca2+ in hippocampal granule cells. A Ca2+ indicator, Indo-1 AM (1 mM), was injected into the lateral part of the molecular layer of DG in horizontal slice. Indo-1 AM could be taken into the soma and dendrites of multiple granule cells within 15 min after injection. Changes in intrasomatic Ca2+ concentration ([Ca2+]i) in several stained granule cells were measured using a two-photon laser scanning microscope (wave length 720nm). The result revealed that the pre-treatment of the slice with PREGS (50 μM) caused a potentiation of the rise in [Ca2+]i induced by an application of 5 μM glutamate for 1-2 min. This finding strongly suggests that LLPPREGS induction is due, in part, to an augmentation of the glutamate action to NMDA receptors. [Jpn J Physiol 54 Suppl:S151 (2004)]
