Sex Neurosteroids: hormones made by the brain for the brain

[madman]

ABSTRACT

In general, hippocampal neurons are capable of synthesizing sex steroids de novo from cholesterol, since the brain is equipped with all the enzymes required for the synthesis of estradiol and testosterone, the end products of sex steroidogenesis. Regarding estradiol, its synthesis in hippocampal neurons is homeostatically controlled by Ca2+ transients and is regulated by GnRH. Locally synthesized estradiol and testosterone maintain synaptic transmission and synaptic connectivity. Remarkably, the neurosteroid estradiol is effective in females, but not in males, and vice versa dihydrotestosterone (DHT) is effective in males, but not in females. Experimentally induced inhibition of estradiol synthesis in females and DHT synthesis in males resp. results in synapse loss, impaired LTP, and downregulation of synaptic proteins. GnRH-induced increase in estradiol synthesis appears to provide a link between the hypothalamus and the hippocampus, which may underlie estrous cyclicity of spine density in the female hippocampus. Hippocampal neurons are sex-dependently differentiated with respect to the responsiveness of hippocampal neurons to sex neurosteroids.




NEUROSTEROIDS

*17β-Estradiol is synthesized de novo by hippocampal neurons

*Homeostasis of estradiol synthesis in hippocampal neurons

*Paracrine action of hippocampus-derived estradiol in female animals

*Hypothalamo-Hypophysial axis

*Sex-dependency in the responsiveness of hippocampal neurons to estradiol





Conclusion

In the female, but not in the male hippocampus, locally synthesized estradiol maintains hippocampal connectivity. Inhibition of estradiol synthesis results in a decrease in spine density, spine synapse density, in the expression of synaptic proteins in mice and in rat hippocampal slice cultures, and impaired long-term potentiation in acute and cultivated hippocampal slices. All effects could be rescued by estradiol. Gonadal estradiol very likely exerts an effect via regulation of GnRH release from the hypothalamus, which in turn regulates hippocampal estradiol synthesis, but estradiol of gonadal origin and present in serum is unlikely to have any direct effect on the hippocampus. Comparing the male and female hippocampus, it becomes evident that female neurons specifically respond to estradiol, while male neurons respond to androgens regarding synaptic plasticity in the hippocampus.

 

[madman]

Fig. 1 Estradiol synthesis after knock-down of StAR and after pharmacological inhibition of aromatase using letrozole. (a) Estradiol synthesis was significantly reduced by 40% at a dose of 100 nM letrozole in dispersion cultures. (b) The release of estradiol into the medium was significantly decreased after StAR knock-down. Unconditioned medium: freshly prepared medium that was not used for culturing; mean ± SEM; n=3 cultures per group;*p<0.05, ***p<0.01

 

[madman]

Fig. 2 Estradiol synthesis in response to Ca2+ transients in neurons. (a) Measurements of estradiol by radioimmunoassay in the supernatant of dispersed cultures after various treatments. Short-term treatment with NMDA and with ryanodine at low concentrations, inducing calcium release from internal stores, and with letrozole, phosphorylating aromatase, decreases the release of estradiol into the medium, while U73122/cADPR and ryanodine at high concentrations increase estradiol release by inhibiting calcium release from internal stores. Similarly, thapsigargin, long-term treatment with NMDA (48 h), depleting calcium stores, also increased estradiol secretion into the culture medium. (b) Rescue experiment. Downregulation of estradiol synthesis in response to short-term treatment with NMDA is rescued in the presence of the Ca2+ channel blockers U73122/cADPR.

 

[madman]

Fig. 3 Estradiol phosphorylates aromatase. (a) Primary embryonic neurons in culture after DIV7 were short-term stimulated with thapsigargin 105 M, letrozole 107 M, or 17b-estradiol 107 M and used for immunoprecipitation. Aromatase was precipitated with a polyclonal antibody to aromatase and subjected to SDS-PAGE. The subsequent Western blot was analyzed with either a monoclonal antibody to aromatase (Acris, SM2222P) or a mixture of a monoclonal antibody to phosphoserine/threonine (PM3801, ECM Biosciences) and a monoclonal antibody to phosphotyrosine (Millipore, 05-321). The level of phosphorylation of immunoprecipitated aromatase after treatment of neurons with thapsigargin is decreased as compared to control levels. In contrast, both letrozole and 17b-estradiol treatment resulted in significantly increased levels of phosphorylation. (Mean% SEM%. p 0.05, n = 3 for thapsigargin, n = 19 for 17b- estradiol, n = 5 for letrozole). (b) Aromatase is phosphorylated in female neurons after 17b-estradiol treatment. Female primary hippocampal neurons in the culture at DIV10 were used for immunoprecipitation and treated either under control conditions or with 17bestradiol (107 M). Aromatase was labeled with 32P-orthophosphate and immunoprecipitated with an antibody directed to aromatase (Acris, SM2222P) and subjected to SDS-PAGE. The autoradiogram of 32P-labeled aromatase is shown above. The band at 54kDa indicates phosphorylated aromatase. Aromatase is more strongly phosphorylated after the application of 17b-estradiol in female neurons. (n=3).

 

[madman]

Fig. 4 Letrozole reduces spine synapse number in hippocampal slice cultures of female animals. Electron micrographs of the stratum radiatum of the CA1 region after treatment with letrozole or estradiol. (a–c) No differences between different treatments were observed in the neuropil. (d–f) Framed areas at higher magnification. In all groups, morphologically intact synapses were found (arrows). (g) Quantitative evaluation of synapses in the stratum radiatum of the CA1 region in slice cultures. No differences in the number of shaft synapses were found between treatments. A significant decrease in spine synapses and in bouton number was seen after treatment of the slices with letrozole, whereas spine synapse and bouton numbers did not increase in response to estradiol (n=5; mean±SD;p<0.05 to control)

 

[madman]

Fig. 5 Letrozole impairs LTP in hippocampal slice cultures of female animals. LTP in hippocampal slice cultures of female animals. Theta-burst stimulation was performed after 20 min of stable baseline recording (10 min are shown) and 60 –70 min after theta-burst stimulation (as indicated by gray bars); changes in mean fEPSP slopes were determined. (a) In untreated slices, the average time course of the fEPSP slopes had significantly increased after 60 min up to 215 ± 34%. (b) Theta-burst stimulation did not induce LTP in slice cultures treated with letrozole for 7 d. (c) LTP is rescued by estradiol slice cultures treated with letrozole. After 60 min, the time course of the fEPSP slope had significantly increased to 239 ± 35% (mean ± SEM; n = 6 slice cultures of 3 animals per group; a time course of LTP; b, superimposed recordings of fEPSPs 10 min before and 60 min after theta-burst stimulation).

 

[madman]

HIGHLIGHTS

- Estradiol and testosterone are synthesized in the hippocampus and act in a paracrine manner

- Neurosteroid synthesis is homeostatically regulated

- Stability and plasticity of hippocampal synapses depend on local neurosteroid synthesis

- Hippocampal neurons are responsive to estradiol in females and to androgens in males regarding synaptic plasticity

 

[nippy]

can that be put in engish lolol .