Pregnenolone sulfate augments NMDA receptor mediated increases in intracellular Ca²⁺ in cultured rat hippocampal neurons

The ability of the neuroactive steroid pregnenolone sulfate to alter N-methyl-d-aspartate (NMDA) receptor-mediated elevations in intracellular Ca²⁺ ([Ca²⁺]_i) was studied in cultured fetal rat hippocampal neurons using microspectrofluorimetry and the Ca²⁺ sensitive indicator fura-2. Pregnenolone sulfate (5-250 μM) caused a concentration-dependent and reversible potentiation of the rise (up to ∼ 800%) in [Ca²⁺]_i induced by NMDA. In contrast, the steroid failed to alter basal (unstimulated) [Ca²⁺]_i or to modify the rise in [Ca²⁺]_i that occurs when hippocampal neurons are depolarized by high K⁺ in the presence of the NMDA receptor antagonist CPP. These data suggest that the previously reported excitatory properties of pregnenolone sulfate may be due, in part, to an augmentation of the action of glutamic acid at the NMDA receptor.