These results suggest that continuous treatment with E2 at physiological levels prevents cerebral vasospasm following SAH. The beneficial effect of E2 may be in part related to the prevention of augmentation of iNOS expression and the preservation of normal eNOS expression after SAH. Treatment with E2 holds therapeutic promise in the treatment of cerebral vasospasm following SAH and merits further investigation.

The role of N-methyl-D-aspartate (NMDA) receptor in mediating the effect of testosterone exposure prenatally on neuronal apoptosis in the sexual dimorphic nucleus of the preoptic area (SDN-POA) of rats was studied. The endogenous testosterone was diminished by prenatal stress (PNS) or simulated by testosterone exposure (TE) to understand the effect of testosterone on NR(1) (a functional subunit protein of NMDA receptor) expression and neuronal apoptosis. To further study whether the testosterone, after being converted into estradiol, modulates NR(1) expression, 4-androstein-4-ol-3,17-dione (ATD; an aromatase inhibitor) was used to block the conversion of estradiol from testosterone. The expressions of the NR(1) mRNA and NR(1) subunit protein were quantified by RT-PCR and western blotting analysis, respectively. In addition, a noncompetitive antagonist of NMDA receptor, MK-801, was used to find out whether blockage of NMDA receptor affects the naturally occurring apoptosis in SDN-POA. The results showed the following. 1) Expression of perinatal NR(1) subunit protein in the central part of the medial preoptic area of male rats was significantly higher than that of females, especially on postnatal days 1 and 3. 2) The testosterone level of male fetuses on embryonic day 18 was significantly higher than that of females, while the testosterone level of TE females or PNS males was similar to that of intact males or intact females, respectively. 3) The apoptotic incidence of intact male rats was significantly less than that of females, and the apoptosis was stimulated by PNS in male or inhibited by TE in female. 4) The expression of NR(1) subunit protein could be inhibited by PNS or ATD-treatment in male, while stimulated by TE in female. 5) NR(1) mRNA showed no significant difference among intact male, PNS male, ATD-treated male, TE female and intact female rats. 6) The low apoptotic incidence of male rats was significantly increased when NMDA receptor was blocked by MK-801. These results suggest that testosterone, after being converted to estradiol, may prevent the SDN-POA neurons of male rats from apoptosis through enhancing the expression of NR(1) at the posttranscriptional level.

The present study was designed to identify possible signaling pathways, which may play a role in prevention of neuronal apoptosis in the sexually dimorphic nucleus of the preoptic area (SDN-POA) after physiological activation of the N-methyl-D-aspartate (NMDA) receptor. Gene response to the blockage of the NMDA receptor by an antagonist (dizocilpine hydrogen maleate; MK-801) was screened after suppression subtractive hybridization (SSH). The results showed that dfferential screening after SSH detected the presence of some neurotrophic genes (RNA binding motif protein 3 (RBM3), -tubulin) as well as apoptosis-related genes (Bcl-2, cytochrome oxidase subunit II, cytochrome oxidase subunit III) in the SDN-POA of male rats, which were down-regulated by blocking the NMDA receptor. The RT-PCR products of the aforementioned genes in MK-801-treated males were significantly less than that in untreated males. In particular, the expression of Bcl-2 mRNA, including Bcl-2 protein, in male rats were significantly suppressed by MK-801 treatment. Moreover, the binding activity of nuclear factor B (NF B) was significantly higher in male rats than in females, but significantly diminished by blocking the NMDA receptor with MK-801 in male rats. No significant difference in cAMP response element-binding protein (CREB) binding activity was observed among untreated male, MK-801-treated male, untreated female and MK-801-treated female groups. These results suggest that genes regulated by NMDA receptor activation might participate in neuronal growth and/or anti-apoptosis, and support an important signaling pathway of NF B activation and its target gene, Bcl-2, in preventing neuronal apoptosis in the SDN-POA of male rats during sexual development.

This is the first evidence that adenosine A2A receptor agonism is effective in preventing SAH-induced vasospasm without significant complications. The beneficial effect of adenosine A2A receptor agonists may be, at least in part, related to the prevention of augmented expression of iNOS and the preservation of normal eNOS expression following SAH. Adenosine A2A receptor agonism holds promise in the treatment of cerebral vasospasm following SAH and merits further investigation.