Presynaptic modulation of synaptic transmission by pregnenolone sulfate as studied by optical recordings

Chen, Ling and Masahiro Sokabe. Presynaptic modulation of synaptic transmission by pregnenolone sulfate as studied by optical recordings. J Neurophysiol 94: 4131-4144, 2005. First published June 22, 2005; doi: 10.1152/jn. 00755.2004. The effects of pregnenolone sulfate ( PREGS), a putative neurosteroid, on the transmission of perforant path-granule cell synapses were investigated with an optical recording technique in rat hippocampal slices stained with voltage-sensitive dyes. Application of PREGS to the bath solution resulted in an acute augmentation of EPSP in a dose-dependent manner. The PREGS effect was dependent on the extracellular Ca2+ concentration ([Ca2+](O)), but independent of NMDA receptor activation. PREGS caused a decrease in paired-pulse facilitation, which implies that PREGS positively modulates presynaptic neurotransmitter releases. Firmer support for this mechanism was that PREGS augmented the synaptically induced glial depolarization (SIGD) that reflects the activity of electrogenic glutamate transporters in glial cells during the uptake of released glutamate. The selective alpha 7nAChR antagonist alpha-BGT or MLA prevented the SIGD increase by PREGS. Furthermore DMXB, a selective alpha 7nAChR agonist, mimicked the PREGS effect on SIGD and antagonized the effect of PREGS. The presynaptic effect of PREGS was partially attenuated by the L-type Ca2+ channel (VGCC) blocker nifedipine. Based on these findings, we proposed a novel mechanism underlying the facilitated synaptic transmission by PREGS: this neurosteroid sensitizes presynaptic alpha 7nAChR that is followed by an activation of L-type VGCC to increase the presynaptic glutamate release.