Prenatal Exposure of Testosterone Prevents SDN-POA Neurons of Postnatal Male Rats From Apoptosis Through NMDA Receptor

Abstract

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 molecular events occur during MK-801-induced cytochrome oxidase subunit II down-regulation in GT1-7 cells

“…Previously, we have demonstrated that the apoptotic incidence of neurons in SDN-POA of male rats is significantly increased when NMDA receptor is blocked by MK-801 (Hsu et al 2001) and the physiological activation of NMDA receptor may protect against neuronal death by transcriptional increase of some survival-related genes, including COII, in SDN-POA during sexual development (Hsu et al 2005). In this study, we attempted to map the signaling pathway of NMDA receptor-mediated neuronal survival in the GT1-7 cell lines, which were derived from hypothalamic GnRH neurons and expressed NMDA receptor as well as mitochondrial COII genes, by comparing the time course of intracellular events, which have been suggested to be involved in the neuronal apoptosis, induced by blocking the activation of NMDA receptor.…”

“…5 mmol/l spermidine and 1 mmol/l dNTPs at 42 8C for 60 min (Hsu et al 2001). PCR was performed with specific primers for COII, PGC-1, mtTFA, glyceraldehydes-3-phosphate dehydrogenase (GAPDH) and 18S.…”

“…5 h. The cell slides were incubated in a stop/wash buffer for 15 min, stained with 3,3 0 -diaminobenzidine (DAB) solution, and then counterstained with methyl green. The incidence of apoptosis was derived from the quotient of apoptotic nucleus number divided by the sum of total neuron numbers in each slides (Hsu et al 2001). …”

“…Blocking of the NMDA receptor by MK-801 (dizocilpine), a noncompetitive NMDA receptor antagonist, has been shown to promote cell death in the developing brain (Ikonomidou et al 1999), suggesting that physiological activation of the NMDA receptor is an important regulator of neuron survival (Fiske & Brunjes 2001). The apoptotic incidence of neurons in the sexually dimorphic nucleus of the preoptic area (SDN-POA) of male rats is significantly increased when the NMDA receptor is blocked by MK-801 (Hsu et al 2001). Recently, we reported that some neurotropic genes (RNA binding motif protein 3 (RBM3), cytosolic phosphoprotein (P19), cytoskeletal gactin, and a-tubulin) as well as survival-related genes (Bcl-2, cytochrome oxidase subunits II, III (COII), (COIII), and cytochrome b) in SDN-POA of neonatal male rats were significantly down-regulated when the NMDA receptor was blocked (Hsu et al 2005).…”

Gene regulation by NMDA receptor activation in the SDN-POA neurons of male rats during sexual development

“…Therefore, the low apoptotic incidence in the SDN-POA in male rats may contribute to its large volume compared to that in female rats. Our recent report provided evidence that estradiol converted from testosterone might prevent apoptosis in the SDN-POA neurons of male rats by enhancing expression of the N-methyl-D-aspartate (NMDA) receptor (Hsu et al 2001). However, the molecular mechanism by which activation of NMDA receptor mediates the fate of neurons remains unclear.…”