Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2008 Mar;57(2):470-80.
doi: 10.1016/j.brainresrev.2007.06.009. Epub 2007 Aug 3.

Neuroprogesterone: key to estrogen positive feedback?

Paul Micevych  1 , Kiran K Soma, Kevin Sinchak
Affiliations
Review

Neuroprogesterone: key to estrogen positive feedback?

Paul Micevych et al. Brain Res Rev. 2008 Mar.

Abstract

In the cycling female rat, estradiol and progesterone induce reproductive behavior and the surge of luteinizing hormone (LH) needed for ovulation. Circulating estradiol of ovarian origin induces progesterone receptors in the preoptic area and hypothalamus. Sequential activation of estrogen receptors (ER) and progesterone receptors coordinates reproductive physiology and behavior. In ovariectomized and adrenalectomized (ovx/adx) rats, administration of estradiol alone is sufficient to initiate an LH surge, and central infusion of aminoglutethimide (AGT), a blocker of the P450 side chain cleavage enzyme, disrupted the estrous cycle of intact rats without affecting peripheral estradiol levels, suggesting that an endogenous source of progesterone remains in these animals. In ovx/adx rats, progesterone levels in the hypothalamus increase prior to the LH surge, and inhibition of progesterone synthesis prevents the LH surge, suggesting that hypothalamic neuroprogesterone is necessary for estrogen positive feedback. In support of the idea that estradiol induces neuroprogesterone, estradiol increased expression of the progesterone-synthesizing enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in the hypothalamus before the LH surge. Further, in vitro experiments demonstrate that estradiol stimulates progesterone synthesis in astrocytes, considered to be the most active steroidogenic cells in the CNS. To stimulate neurosteroidogenesis, estradiol acts through membrane ER and type 1a metabotropic glutamate receptors (mGluR1a) to increase free cytoplasmic calcium ([Ca(2+)](i)) via activation of the PLC-IP(3) pathway. Estradiol-induced progesterone synthesis is mimicked by thapsigargin-induced release of IP(3) receptor-sensitive Ca(2+) stores in astrocyte cultures. Thus, estradiol-induced progesterone synthesis is dependent on membrane ERs that act through mGluR1a to activate the PLC-IP(3) pathway. This neuroprogesterone also facilitated proceptive behavior. Blocking either progesterone synthesis or progesterone receptor in estrogen-primed ovx/adx prevented proceptive but not receptive behaviors.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Effect of trilostane, a 3β-HSD inhibitor, was measured on the estradiol-induced LH surge in two-month-old OVX/ADX female rats. Basal concentrations of plasma LH (ng/ml) were measured in venous blood serum samples prior to treatment. On the second day following treatment with 50 µg 17β-estradiol benzoate (EB), or oil vehicle (VEH), or EB + 16.5 mg trilostane (EB+TRI), serial blood samples (250µl) were collected once every 90 min from 1400 to 2130 hr. Plasma was assayed for LH. Data were expressed in terms of NIDDK Rat LHRP-2. EB-treated females showed a significant increase in plasma LH levels compared with those of VEH control. Pretreatment with trilostane blocked the EB-induced LH surge, and attenuated basal LH release. Data are means ± SEM of at least 7 samples. * p < 0.05 versus EB+TRI-treated females. † p < 0.05 versus VEH-treated females. (From (Micevych et al., 2003).
Figure 2
Figure 2
Progesterone concentrations in the hypothalamus (HYP), cerebellum (CRB), parietal cortex (CTX) were measured in OVX/ADX rats following 50 µg estradiol benzoate (EB) or vehicle (VEH) treatment. Data are means ± SEM of 4–6 samples. * = p < 0.05 significantly greater than VEH group within brain regions SNK. (Modified from (Micevych et al., 2003).
Figure 3
Figure 3
A. Effects of estradiol treatment on mRNA levels of 3β-hydroxysteroid dehydrogenase (3β-HSD) in the hypothalamus of OVX-ADX rats. Subjects were treated with 50 µg 17β-estradiol benzoate (EB) for 0, 12, 24 or 44 hr (n=6, 5, 5, 5). The mRNA levels were measured by quantitative RT-PCR and expressed as a percent of baseline (0 hr group). EB treatment significantly increased 3β-HSD mRNA levels (F = 6.075, p = 0.003). * = significantly greater than 0 and 12 hr groups (p<0.05, Fisher’s PLSD). Figure 3B. Effects of EB treatment on 3β-HSD activity in the hypothalamus and amygdala of OVX-ADX rats. Subjects were treated with EB (n=6) or oil vehicle (n=5) 44 hr before the hypothalami were harvested. 3β-HSD activity was determined by measuring the in vitro conversion of [3H]-pregnenolone to [3H]-PROG. * = significantly greater than oil-treated controls within brain region (t-test, t = 2.349, p = 0.04; from (Soma et al., 2005).
Figure 4
Figure 4
A. Effect of estradiol treatment of neonatal and post-pubertal hypothalamic astrocytes in vitro. The cells were steroid-starved for 24 hours and then incubated for 48 hours with indicated concentrations of 17β-estradiol or steroid-free media (0). Levels of progesterone in the supernatants were measured by radioimmunoassay. The neonatal astrocytes did not increase progesterone levels in the media in response to any estradiol dose tested. Post-pubertal astrocytes increased progesterone levels after treatment with estradiol. This increase was statistically significant at 10−6 M 17β-estradiol. Values are reported as mean ± SEM (n=8). * indicates significantly greater within developmental age group compared with 17β-estradiol free group (0) p < 0.05 (SNK). Figure 4B. Antagonism of 17β-estradiol (E2; 10−6 M) induction of progesterone levels in media from primary post-pubertal hypothalamic astrocyte cultures from female rats by blocking estrogen receptors. Steroid-starved astrocytes were incubated for 48 hours with either E2-free media with DMSO (DMSO), the vehicle used to dissolve the 10−6 M ICI 182,780 (ICI), an estrogen receptor antagonist, E2, ICI, or ICI + E2. Levels of progesterone in the supernatants were measured by radioimmunoassay. Data are means ± SEM (n = 4). * indicates values significantly greater than all other treatment groups (p < 0.05, SNK). Figure 4C. Effect of thapsigargin induced release of internal stores of Ca2+ on progesterone synthesis in astrocyte cultures obtained from post-pubertal female rats. Astrocytes were treated with thapsigargin (Thp) or Thp (10−7 M) supplemented with 10−6 M estradiol (E2/Thp) for one hour. The media was collected and replaced with either estradiol-free DMEM/F12 (DMEM Post Thp) or 10−6 M estradiol (E2 48hrs Post Thp). The progesterone concentration in the medium significantly increased following treatment with either E2 for 48 hr, Thp for one hr or Thp+ E2 for one hr. When the media was replaced with DMEM/F12 (DMEM) following Thp treatment there was no increase of progesterone concentration above baseline. Following one hour Thp treatment, subsequent exposure to E2 for 48 hr did not statistically increase the concentration of progesterone in the supernatant. Data are mean ± SEM (n = 4). * = indicates values significantly greater than control media, DMEM + DMSO (DMSO; p < 0.05 SNK; modified from (Micevych et al., 2007).
Figure 5
Figure 5
A. Pharmacological profile of the effect of estradiol on internal calcium concentration [Ca2+]i in neonatal cortical astrocytes. Stimulation of astrocytes with estradiol (E2, 10−6 M) in the presence or absence of extracellular Ca2+ or with E-6-BSA (estradiol conjugated to bovine serum albumin) produced a similar [Ca2+]i increase. Inhibition of estrogen receptors (ER) with ICI 182,780 (E2 + ICI) blocked E2-induced increases in [Ca2+]i. Removing Ca2+ from the media and replacing with membrane impermeable BAPTA (E2 + BAPTA) did not block the E2 induced [Ca2+]i flux. However, blocking the IP3-regulated smooth endoplasmic reticulum Ca2+ channel with 2-APB (E2 + APB) prevented the E2-induced [Ca2+]i flux. Similarly, blocking phospholipase C (PLC) signaling pathway with U73122 (E2 + U73122) blocked the estradiol induced [Ca2+]i flux. These results indicate that the E2 stimulation of [Ca2+]i is via activation of an ER associated with the plasma membrane that stimulates the PLC-IP3 signaling pathway. The number of experiments is indicated in each bar. * indicates significantly less than E2 treatment group (p < 0.05; modified from (Chaban and Micevych, 2005). Figure 5B. Estradiol induced [Ca2+]i flux in hypothalamic astrocytes is attenuated by mGluR1a antagonism. Estradiol (4 nM) was bath applied to post-pubertal hypothalamic astrocytes to determine that they responded to estradiol stimulation. After a 3 min washout, mGlur1a antagonist, LY367385 (50 nM), was applied for 6 mins and then were treated with estradiol again. The number of experiments is indicated in each bar. * indicates significantly different from E2 stimulation at p>0.05; from (Hariri et al., 2006).
Figure 6
Figure 6
A model of estradiol action on hypothalamic cells involved in the regulation of the LH surge. Circulating estradiol acts on both neurons and astrocytes. The astrocyte has been expanded to illustrate the potential intracellular pathway of estradiol signaling that regulates progesterone (PROG) synthesis. Estradiol acts on membrane estrogen receptors (ER); both ERα and ERβ have been reported in astrocyte membranes (Chaban and Micevych, 2005). Activated ER increase [Ca2+]i by interacting with metabotropic glutamate receptor type 1a (mGluR1a) to initiate the phospholipase C (PLC)/ inositol triphosphate receptor (IP3R) mediated increase in [Ca2+]i. The source of the elevated [Ca2+]i is the smooth endoplasmic reticulum (sER). Estradiol-induced release of Ca2+ was mimicked with thapsigargin. Calcium may activate protein kinase A (PKA) and/or protein kinase C (PKC) phosphorylate StAR. StAR mediated transport of cholesterol (CHOL) through the mitochondrial intermembrane space is the rate limiting step of steroidogenesis. In the inner mitochondrial membrane, cholesterol (CHOL) is converted to pregnenolone (PREG) by cytochrome P450side chain cleavage enzyme (P450scc). PREG is converted to PROG in the sER via the action of 3β-hydroxysteroid dehydrogenase isomerase (3β-HSD) and diffuses out of the astrocyte to encounter estradiol induced PROG receptors (PR) in neurons. PR expressing neurons mediate the environmental and circadian signals to neurons stimulating GnRH. GnRH release in the median eminence in turn initiates the LH surge release from anterior pituitary gonadotrophs (modified from (Micevych et al., 2007).
Figure 7
Figure 7
Facilitation of sexually receptive and proceptive behaviors in ovariectomized rats treated with 17-β estradiol benzoate (10 µg) once every four days followed by free estradiol (50 µg) on injection 4. A near maximal LQ score and a low levels of proceptive behaviors (e.g., ear wiggling, darts, and hops) were seen following the third treatment with EB (injection 3). Animals treated with free estradiol (50 µg) four hours before testing reached maximal receptivity and high proceptive behavior (injection 4). The LQ was significantly higher after injections 3 and 4 compared to injection 2 (repeated measures ANOVA; p < 0.05). Proceptive behavior was significantly higher by the injection 4 compared with tests 2 and 3 (Friedman repeated measures ANOVA on Ranks; p < 0.05). Data are means ± SEM of 12 animals. * p < 0.05 significantly greater than proceptive scale score for injections 2 and 3 (Dunnett’s post hoc). † p < 0.05 versus LQ for injection 2 (Newman-Keuls post hoc).
Figure 8
Figure 8
Progesterone receptor activity and neurosteroid synthesis are needed for proceptive, but not receptive sexual behaviors. In OVX/ADX rats, EB (10 µg) was given every 4 days and animals were tested for receptive and proceptive behaviors at 52–54 hours after treatment. Figure 8A. animals were treated with EB and then with either RU486 (EB + RU486; 5 mg) or EB 1 hour prior to testing. Antagonism of progesterone receptors with RU486 had no effect on LQ compare to the EB + VEH treated animals (Mann-Whitney, p > 0.05). However, proceptivity was significantly decreased in the EB + RU486 treated animals compared with EB animals (Mann-Whitney; p < 0.05). Data are means ± SEM of 12 animals. * indicates significantly less than the EB treated animals, p < 0.05. Figure 8B. Aminoglutethimide (EB + AGT; 10 mg), an inhibitor of P450 side chain cleavage enzyme activity, or EB was administered every 24 hours for 3 days prior to testing in EB (10 µg) treated rats. There was no significant change in LQ score between EB + AGT and EB (Mann-Whitney, p<0.05). In contrast to the receptive behavior, AGT significantly decreased the proceptive scale score when compared with EB (Mann-Whitney, p<0.05). Data are means ± SEM of 12 animals. * p < 0.05 versus EB treated control group. Figure 8C. Trilostane (EB + Trilostane 16.5 mg) or EB was administered every 24 hours for 3 days prior to testing. Similar to AGT, LQ score between EB + trilostane and EB was not affected (p > 0.05), but receptive behavior was significantly decreased in the EB + trilostane treated animals compared with EB treated (Mann-Whitney, p < 0.05). Data are means ± SEM of 12 animals. * = indicates less than EB-only treated control animals p < 0.05.
Figure 9
Figure 9
Progesterone concentrations in the cerebellum (CRB), hypothalamus (HYP), and parietal cortex (CTX) were measured in OVX/ADX, nine months old, acyclic female rats treated with estradiol (50 µg). Approximately 56 hrs later, when young female rats would produce an LH surge and increased neuroprogesterone levels, these persistently estrous rats still had measurable levels of progesterone in all the regions examined. However, estradiol did not increase progesterone levels compared with vehicle (VEH) controls as seen in the young rats (see Figure 2). (p > 0.05; ANOVA; data are means ± SEM of 4–6 samples). These results indicate that in female rats that have lost the estrogen-positive feedback of the LH, do not have an estradiol-induced increase in progesterone levels.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Babcock AM, Block GJ, Micevych PE. Injections of cholecystokinin into the ventromedial hypothalamic nucleus inhibit lordosis behavior in the rat. Physiol. Behav. 1988;43:195–199. - PubMed
    1. Baulieu EE. Neurosteroids: a novel function of the brain. Psychoneuroendocrinol. 1998;23:963–987. - PubMed
    1. Blaustein JD, Finkbohner R, Delville Y. Estrogen-induced and estrogen-facilitated female rat sexual behavior is not mediated by progestin receptors. Neuroendocrinol. 1987;45:152–159. - PubMed
    1. Bloch GJ, Babcock AM, Gorski RA, Micevych PE. Cholecystokinin stimulates and inhibits lordosis behavior in female rats. Physiol. Behav. 1987;39:217–224. - PubMed
    1. Bose H, Lingappa VR, Miller WL. Rapid regulation of steroidogenesis by mitochondrial protein import. Nature. 2002;417:87–91. - PubMed

Publication types