Effect And Mechanism Of Dehydroepiandrosterone Sulfate On The Release Of Presynaptic Glutamate In Rat Prelimbic Cortical Neurons

Dehydroepiandrosterone sulfate (DHEAS) is the most abundant neurosteroid in adult plasma. It also has a high concentration in the brain and exert multiple and special effects in the central nervous system (CNS). A number of animal studies indicate that it has significant effect on cognition and memory, but up to now the mechanism is not clear. Prelimbic cortex is the main brain region for cognition and the excitatory synaptic transmission in the pyramidal cells of this region is crucial for its physiological function. So dehydroepiandrosterone sulfate might have effect on this excitatory synaptic transmission, but this hypothesis need to be determined by experiments.In the present study we investigated the effect and its mechanism of dehydroepiandrosterone sulfate on the miniature spontaneous excitatory postsynaptic currents (mEPSCs) and the spontaneous excitatory postsynaptic currents (sEPSCs) in different brain regions using whole-cell patch-clamped recording technique combined with pharmacological approach in rat slices. We also investigated the effect of DHEAS on the activity of protein kinase A in synaptosomes with biochemistry methods. The results showed that DHEAS (20μM) prominently increased the frequency of mEPSCs in the pyramidal cells of the prelimbic cortex and the hippocampus but had no effect in the striatum. And this effect in the prelimbic cortex is concentration dependent. Moreover we used different drugs to study the mechanism of the increasing effect of DHEAS on the frequency of mEPSCs. We found that in the prelimbic cortex NMDA receptor antagonist had no influence on the effect of DHEAS;σ1 receptor antagonist partially blocked the effect of DHEAS; D1 receptor antagonist, protein kinase C inhibitor, adenyl cyclase inhibitor, protein kinase A inhibitor completely blocked the effect of DHEAS. Using biochemistry methods we found that DHEAS markedly increased the activity of protein kinase A in the synaptosomes of the prelimbic cortex and this effect was also completely blocked by D1 receptor antagonist, protein kinase C inhibitor, adenyl cyclase inhibitor and partially blocked byσ1 receptor antagonist. Althoughσ1 receptor agonist had no effect on the activity of protein kinase A, it could enhance the effect of D1 receptor agonist on the activity of protein kinase A. These data suggest that the increasing effect of DHEAS on presynaptic glutamate release is via the activation of bothσ1 receptors and D1 receptors and the pathway of transduction of intracellular signals is through PKC, AC and PKA. While comparing with another neurosteroid pregnenolone sulfate (PREGS), which is in similar structure with DHEAS, we found that PREGS (20μM) could also increase the frequency of mEPSCs in the prelimbic cortex but this effect was not blocked by D1 receptor antagonist suggesting that there were some differences in the mechanism between these two neurosteroids although they are very similar in structure and effect and the differences might be caused by their different branches in molecular structure. In addition, we explored thatσ1 receptor antagonist completely blocked the increasing effect of DHEAS in the hippocampus indicating different mechanisms in this region.In the second part we studied the effect of DHEAS on the evoked excitatory presynaptic glutamate release in rat prelimbic cortex. The results showed that DHEAS (1μM) in low concentration had no effect on high K⁺ or Dopamine-evoked increase in the frequency of sEPSCs and PPF but partially inhibited 5-HT-evoked increase in the frequency of sEPSCs. Interestingly DHEAS (20μM) in high concentration had no influence on the effect of 5-HT. While studying the mechanism of the inhibitory effect of DHEAS on the effect of 5-HT, we found that D1 receptor antagonist did not block the inhibitory effect of DHEAS butσ1 receptor completely blocked it. DHEAS had no effect on the 5-HT_2A/2C receptor agonist evoked increase in the frequency of sEPSCs. The 5-HT₃ receptor antagonist could partially inhibit 5-HT-evoked increase in the frequency of sEPSCs and in the presence of 5-HT₃ receptor antagonist DHEAS could not inhibit the effect of 5-HT any further indicating the involvement of the pathway of 5-HT₃ receptors in the mechanism of DHEAS. These results suggest that DHEAS in low concentration has a selective modulation effect on evoked presynaptic glutamate release. It partially inhibits 5-HT-evoked increase in presynaptic glutamate release and this effect is viaσ1 receptors and involves the pathway of 5-HT₃ receptors.