Nanomolar Concentrations of Pregnenolone Sulfate Enhance Striatal Dopamine Overflow in Vivo

The balance between GABA-mediated inhibitory and glutamate-mediated excitatory synaptic transmission represents a fundamental mechanism for controlling nervous system function, and modulators that can alter this balance may participate in the pathophysiology of neuropsychiatric disorders. Pregnenolone sulfate (PS) is a neuroactive steroid that can modulate the activity of ionotropic glutamate and GABA(A) receptors either positively or negatively, depending upon the particular receptor subtype, and modulates synaptic transmission in a variety of experimental systems. To evaluate the modulatory effect of PS in vivo, we infused PS into rat striatum for 20 min via a microdialysis probe while monitoring local extracellular dopamine (DA) levels. The results demonstrate that PS at low nanomolar concentrations significantly increases extracellular DA levels. The PS-induced increase in extracellular DA is antagonized by the N-methyl-D-aspartate (NMDA) receptor antagonist, D-AP5 [D-(-)-2-amino-5-phosphonopentanoic acid], but not by the sigma receptor antagonist, BD 1063 [1(-)[ 2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine]. The results demonstrate that exogenous PS, at nanomolar concentrations, is able to increase DA overflow in the striatum through an NMDA receptor-mediated pathway.