Pregnenolone sulfate induces G‐protein coupled insertion of NMDA receptors into plasma membrane

The neurosteroid pregnenolone sulfate (PS) rapidly and reversibly modulates ionotropic glutamate and GABA A receptor function on a time scale of seconds, most likely via a direct allosteric interaction. PS has been reported to enhance learning and memory in various in vivo models and to enhance LTP in rat hippocampal slices. We now report a second, delayed (within minutes) phase of NMDAR modulation that requires activation of intracellular signaling mechanisms. Delayed potentiation by PS is observed in chick spinal cord neurons in culture and in Xenopus laevis oocytes expressing NR1/NR2A or NR1/NR2B (but not NR1/NR2C or NR1/NR2D) receptors. Delayed potentiation of NR1/NR2A receptors is evident at PS concentrations as low as 100 nM, below the concentration range that elicits rapid potentiation. Pharmacological studies indicate that delayed potentiation of NMDARs by PS is mediated via a pertussis toxin sensitive G‐protein, leading to activation of phospholipase C and release of Ca 2+ from intracellular inositol‐3‐phosphate sensitive stores, with subsequent activation of PKC. Moreover, an increase in NMDA induced outward current after the release of 9‐aminoacridine reversible blockade indicates that delayed potentiation is associated with an increased number of functional NMDAR channels at the cell surface. Furthermore, our results suggest that insertion of the new NMDARs occurs via SNARE regulated exocytosis, requiring a functional secretory pathway. Findings from the present study suggest a mechanism whereby PS can regulate cell surface expression of the NMDARs at the postsynaptic membrane, therefore modulating neuronal excitability, synaptic strength and plasticity.