It is all About the Chase: Neurosteroidogenesis in Male Rats is Driven by Control of Mating Pace

BACKGROUND

Masculine sexual behaviors are dependent on androstane-derived steroids; however, the modulatory effects of mating, and of mating control, on androstane neurosteroidogenesis remain largely unknown.

OBJECTIVE

Herein, we investigated the effects of mating control, prior sexual experience, and age on brain region specific neurosteroidogenic responses in male rats.

METHODS

Effects of acute sexual experience were tested in naïve male rats that either remained sexually- naïve, were exposed to a standard mating chamber, or were either given control of the mating pace in a standard mating chamber (male control) or mated wherein the female stimulus rat controlled the mating pace in a paced-mating chamber (female control). Aged (10-12 months) sexually responsive male rats were similarly euthanized from the homecage or engaged in male controlled or female controlled mating. All rats were euthanized immediately following exposure conditions for radioimmunoassay of steroids in midbrain, hypothalamus, hippocampus and cortex.

RESULTS

Consummatory sexual behavior in male vs. female-controlled mating paradigms was altered by age and prior sexual experience. Male-controlled mating increased androstane neurosteroid metabolism, such that complementary increases in the testosterone (T) metabolite 5α-androstane-3α-17β- diol (3α-diol) in the midbrain and hypothalamus of male rats corresponded to decreases in the prohormone, T. 3α-diol were increased in the hippocampus in response to the context alone, and to a lesser degree in response to mating. Mating diminished neurosteroidogenesis in the cortex. Neurosteroidogenesis was overall reduced in aged male rats compared to naïve controls, however, these effects were more prominent in sexually non-responsive aged male rats.

CONCLUSION

Extending previous findings, these results indicate differential production of androstane neurosteroids in a mating exposure, age and brain region dependent manner.

Pregnant women with more seizures have lower allopregnanolone concentrations

Neuroactive steroids have rapid, nongenomic effects on neuronal excitability. The effects in humans are less clear. We compared seizure control and concentrations of neuroactive steroids, known to influence neuroexcitability in animal studies, in pregnant women. Participants were prospectively followed throughout pregnancy with seizure-medication diaries and blood samples, assayed for steroid concentrations with gas chromatography-mass spectrometry. Baseline seizure frequency was calculated for the preconception year, and it was determined if seizure frequency was increased in each trimester. The Wilcoxon rank-sum test was used to compare neuroactive steroid concentrations in between the group with increased frequency to the group without, as calculated for the respective trimester, with the Holm-Bonferroni method to correct for multiple comparisons. Among eighty-three pregnancies included, twenty-eight had increased seizure frequency during at least one trimester (15, 18 and 10, respectively) compared to preconception seizure frequency. Allopregnanolone concentrations were lower in the 3rd trimester (p < 0.001), with a similar trend in the 1st (p = 0.08), for pregnancies with increased compared to those with stable seizure frequency. Other neuroactive steroid concentrations were similar. Our findings suggest that lower allopregnanolone concentrations are associated with increased seizure frequency during pregnancy. Validation of these finding in a larger cohort has potential important clinical applications.

Progesterone's Effects on Cognitive Performance of Male Mice Are Independent of Progestin Receptors but Relate to Increases in GABAA Activity in the Hippocampus and Cortex

Progestogens' (e.g., progesterone and its neuroactive metabolite, allopregnanolone), cognitive effects and mechanisms among males are not well-understood. We hypothesized if progestogen's effects on cognitive performance are through its metabolite allopregnanolone, and not actions via binding to traditional progestin receptors (PRs), then progesterone administration would enhance performance in tasks mediated by the hippocampus and cortex, coincident with increasing allopregnanolone concentrations, brain derived neurotrophic factor (BDNF) and/or muscimol binding of PR knock out (PRKO) and wild-type PR replete mice. Experiment 1: Progesterone (4 mg/kg, subcutaneously (SC; n = 12/grp), or oil vehicle control, was administered to gonadally-intact adult male mice PRKO mice and their wild-type counterparts and cognitive behaviors in object recognition, T-maze and water maze was examined. Progesterone, compared to vehicle, when administered post-training increased time investigating novel objects by the PRKO and wild-type mice in the object recognition task. In the T-maze task, progesterone administration to wild-type and PRKO mice had significantly greater number of spontaneous alternations compared to their vehicle-administered counterparts. In the water maze task, PRKO mice administered vehicle spent significantly fewer seconds in the quadrant associated with the escape platform on testing compared to all other groups. Experiment 2: Progesterone administered to wild-type and PRKO mice increased plasma progesterone and allopregnanolone levels (n = 5/group). PRKO mice had higher allopregnanolone levels in plasma and hippocampus, but not cortex, when administered progesterone and compared to wild-type mice. Experiment 3: Assessment of PR binding revealed progesterone administered wild-type mice had significantly greater levels of PRs in the hippocampus and cortex, compared to all other groups (n = 5/group). Wild-type mice administered progesterone, but not vehicle, had increased BDNF levels in the hippocampus, but not the cortex, compared to PRKOs. Wild-type as well as PRKO mice administered progesterone experienced significant increases in maximal GABAA agonist, muscimol, binding in hippocampus and cortex, compared to their vehicle-administered counterparts. Thus, adult male mice can be responsive to progesterone for cognitive performance, and such effects may be independent of PRs trophic actions of BDNF levels in the hippocampus and/or increases in GABAA activity in the hippocampus and cortex.

Mating Enhances Expression of Hormonal and Trophic Factors in the Midbrain of Female Rats

Among female rats, mating enhances neurosteroid formation in the midbrain ventral tegmental area (VTA; independent of peripheral steroid-secreting glands, ovaries, and adrenals). The sources/targets for these actions are not well understood. In Experiment 1, proestrous rats engaged in a mating paradigm, or did not, and the midbrains had been assessed via the Affymetrix rat genome microarrays. In Experiment 2, the influence of gonadal and adrenal glands on the expression of these genes was assessed in rats that were proestrous, ovariectomized (OVX), or OVX and adrenalectomized (ADX). The microarrays revealed 53 target genes that were significantly up-regulated (>2.0-fold change) in response to mating. Mating significantly enhanced the midbrain mRNA expression of genes involved in hormonal and trophic actions: Gh1, S100g, and Klk1b3 in proestrous, but not OVX and/or ADX, rats; Fshb in all but OVX/ADX rats; and lutenizing hormone β and thyroid-stimulating hormone (TSH) β in all rats. Thus, mating enhances midbrain gene expression independent and dependent of peripheral glands.

Learning and the Lifespan: What's Sex Got to Do With It?

Engagement in sexual behavior can impact neurosteroidogenesis, in particular production of the prohormone testosterone (T) and likely its subsequent metabolism to 5α-androstane-3α-17β-Diol (3α-Diol) or aromatization to estradiol (E₂). Androgens and their metabolites vary across the lifespan and impact many behaviors, including cognition, anxiety, and sexual behavior. Thus, we hypothesized that mating may alter cognitive performance via androstane neurosteroids in an age- and experience-dependent manner. We first investigated if exposure to mating during memory consolidation could enhance performance in the novel object recognition task (NOR). Male rats were trained in NOR and then immediately exposed to mating-relevant or control stimuli. Following a 4 h inter-trial interval (ITI), male rats were tested for object memory. Male rats that were exposed to a receptive female during the ITI had better performance in NOR. We then investigated if these effects were due to novelty associated with mating. Male rats were exposed to mating-relevant stimuli and identified as sexually responsive (SR) or sexually non-responsive (SNR) based on a median split of engagement in mating with the stimulus female. We found that a brief history (10 min session daily for five consecutive days) of sexual history substantially influenced performance in the NOR task, such that SR males had better performance in the NOR task, but only when presented with the opportunity to mate during the ITI. As T levels substantially decrease with age in male rodents, we investigated whether the effects of long-term sexual experience (10 months) influenced neurosteroids and NOR performance in mid-aged (12 months old) males. Mid-aged SR males maintain neural T; however, they have decreased neural E₂ and decreased cognitive performance at 12 months compared to mid-aged SNR rats. In sexually experienced rats, those with better cognitive performance had greater levels of T metabolites (e.g., 3α-Diol in mated SR males, E₂ in mid-aged SNR rats). While naïve males that were mated during the ITI had better cognitive performance, T metabolites were decreased compared to controls. These findings suggest that T metabolites, but not the prohormone, may influence learning dependent on sexual proclivity, experience, and proximate opportunity to mate.

Prenatal resident-intruder stress decreases levels of allopregnanolone in the cortex, hypothalamus, and midbrain of males, and increases levels in the hippocampus and cerebellum of female, juvenile rat offspring

Prenatal stress (PNS) can influence behaviors associated with cognition, reward and emotional regulation, which are controlled by brain areas such as the cortex, hippocampus, hypothalamus, midbrain and cerebellum. Allopregnanolone in these regions modulates behavioral and parasympathetic effects. The current study tested whether exposing pregnant dams to 5 days of resident-intruder stress on prenatal days 15-20 for 10 min altered the levels of allopregnanolone in cortex, hypothalamus, hippocampus, midbrain, and cerebellum of male and female juvenile offspring. In cortex, hypothalamus, and midbrain of male rats exposed to prenatal stress, levels of allopregnanolone were significantly lower compared to all other groups. In the hippocampus and cerebellum, among females exposed to prenatal stress levels were significantly higher compared to all other groups. These differences in allopregnanolone levels varying by prenatal stress, sex and brain regions provide insight in potential mechanism of stress regulation and etiopathophysiology of stress-related disorders.

Central Actions of 3α,5α-THP Involving NMDA and GABAA Receptors Regulate Affective and Sexual Behavior of Female Rats

The neurosteroid, 5α-pregnan-3α-ol-20-one (known as “allopregnanolone” or 3α,5α-THP), is produced in the midbrain ventral tegmental area (VTA), independent of peripheral sources of progestogens, where it has potential actions at N-methyl-D-aspartate (NMDA) and GABA_A receptors to facilitate rodent sexual behavior. Progestogens can also have anti-anxiety effects, but whether these involve actions of centrally-derived 3α,5α-THP or these receptors to support reproductively-relevant behavior is not well understood. We investigated the extent to which 3α,5α-THP’s actions via NMDA and/or GABA_A receptors in the midbrain VTA influence reproductive behaviors. Estradiol-primed, ovariectomized/adrenalectomized (OVX/ADX) rats received midbrain VTA infusions of vehicle, an NMDA receptor blocker (MK-801; 200 ng), or a GABA_A receptor blocker (bicuculline; 100 ng) followed by a second infusion of vehicle or 3α,5α-THP (100 ng). Reproductively-relevant behaviors were assessed: sexual (paced mating), anxiety-like (elevated plus maze), and social (partner preference, social interaction) behavior. Compared to vehicle, intra-VTA infusions of MK-801 exerted anxiolytic-like effects on elevated plus maze behavior and enhanced lordosis. Unlike prior observations in gonadally-intact rats, intra-VTA bicuculline had no effect on the behavior of OVX/ADX rats (likely due to a floor effect). Subsequent infusions of 3α,5α-THP reversed effects on lordosis and infusions of bicuculline inhibited 3α,5α-THP-facilitated lordosis. Thus, NMDA and GABA_A receptors may act as mediators for reproductive behavioral effects of 3α,5α-THP in the midbrain VTA.

The Steroidogenesis Inhibitor Finasteride Reduces the Response to Both Stressful and Rewarding Stimuli

Finasteride (FIN) is the prototypical inhibitor of steroid 5α-reductase (5αR), the enzyme that catalyzes the rate-limiting step of the conversion of progesterone and testosterone into their main neuroactive metabolites. FIN is clinically approved for the treatment of benign prostatic hyperplasia and male baldness; while often well-tolerated, FIN has also been shown to cause or exacerbate psychological problems in vulnerable subjects. Evidence on the psychological effects of FIN, however, remains controversial, in view of inconsistent clinical reports. Here, we tested the effects of FIN in a battery of tests aimed at capturing complementary aspects of mood regulation and stress reactivity in rats. FIN reduced exploratory, incentive, prosocial, and risk-taking behavior; furthermore, it decreased stress coping, as revealed by increased immobility in the forced-swim test (FST). This last effect was also observed in female and orchiectomized male rats, suggesting that the mechanism of action of FIN does not primarily reflect changes in gonadal steroids. The effects of FIN on FST responses were associated with a dramatic decrease in corticotropin release hormone (CRH) mRNA and adrenocorticotropic hormone (ACTH) levels. These results suggest that FIN impairs stress reactivity and reduces behavioral activation and impulsive behavior by altering the function of the hypothalamus-pituitary-adrenal (HPA) axis.

Effects of non-contingent cocaine on 3alpha-androstanediol. I. Disruption of male sexual behavior

One of the hallmarks of drug abuse is a reduction in the salience of, and motivation for, natural rewards, such as mating. The effects of psychostimulants on male sexual interest and performance are conflicting; use of psychostimulants can produce increases in risky sexual behaviors but have detrimental effects on sexual ability. We hypothesize that these conflicting effects on sexual behavior are due to interactions between cocaine and androgens, such as testosterone and its neuroactive metabolite, 3α-androstanediol (3α-diol). Male rats were administered saline or cocaine (5, 10, or 20mg/kg, i.p.). Motor behavior was observed in the first 30min following drug-administration, and then sexual responding was assessed for 15min. Levels of androgens (testosterone, 3ɑ-diol, and testosterone's aromatized metabolite, estradiol) were measured in circulation and brain regions (frontal cortex, hippocampus, hypothalamus/striatum (hypo/str), and midbrain). Cocaine had no effect on measures of sexual interest (i.e. anogenital investigation). However, cocaine had substantial effects on consummatory sexual behaviors, such as the latency to mount/intromit and the number of sexual contacts. Frontal cortex and hypo/str 3α-diol levels were strongly correlated with consummatory behaviors in saline administered rats; however, this relationship was disrupted by cocaine at all dosages, concomitant with impaired sexual behaviors. Additionally, there was a shift in metabolism at low dosages of cocaine to push testosterone metabolism in the midbrain towards 3α-diol. On the contrary, moderate and high dosages of cocaine shifted testosterone metabolism towards estradiol. These data demonstrate that the association between cortical and hypo/str 3α-diol levels and sexual behavior of male rats is disrupted by non-contingent cocaine and that there may be dose-dependent effects of acute cocaine on androgen metabolism.

Effects of non-contingent cocaine on 3 alpha-androstanediol. II. Disruption of lordosis of proestrous rats

Drug use influences sexual behavior, performance, and can be associated with increased sexual risk-taking. Our prior results using an animal model indicate that progestogens contribute to hormonally-mediated changes in sexual behavior of female rodents during acute cocaine exposure. Androgens, such as testosterone, and its metabolite 3ɑ-androstanediol (3α-diol), and estradiol, are known to influence male sexual behavior, but can also alter the expression of sexual behavior of female rodents. As such, we investigated the influence of endogenous androgen and estradiol fluctuations on cocaine-mediated changes in motor behavior and sexual receptivity of rats during diestrous or proestrous phases of the estrous cycle. Female rats were administered saline or cocaine (5, 10, or 20mg/kg, i.p.). Motor behavior was observed in the first 30min following drug administration, and then sexual responding was assessed for 15min. Cocaine decreased aggressive behavior in response to attempted mounts by a male among non-receptive (diestrous) rats and inhibited sexual behavior among sexually receptive (proestrous) rats. Cocaine dose-dependently altered concentrations of testosterone metabolites (estradiol and 3α-diol), but not testosterone, which correlated to motor and sexual behaviors of diestrous and proestrous rats, respectively. These data suggest that actions of 3α-diol may be involved in female sexual and motor behavior in response to cocaine, in a cycle-dependent manner.

Research Brief: Self-Reports of a Constellation of Persistent Antiandrogenic, Estrogenic, Physical, and Psychological Effects of Finasteride Usage Among Men

Our research objective is to understand more, through subjective, self-reports on discussion boards/forums, persons' experiences associated with the use of drugs that alter androgen metabolism, such as finasteride. Finasteride is an orally active, specific inhibitor of 5α-reductase, which is localized to many androgen-dependent tissues. Finasteride inhibits the conversion of testosterone (T) to dihydrotestosterone (DHT), and is commonly used to treat benign prostatic hypertrophy (BPH) and male pattern baldness (MPB), both disorders associated with elevated DHT levels and 5α-reductase activity in the prostate and hair follicles, respectively. It is now acknowledged that long-term use and discontinuation of finasteride has adverse effects (AEs); however, these claims have not been well documented. In this study, discussion board posts (forums) were analyzed as self-reports of what finasteride users indicate is problematic for them. Reports were categorized by the age of subjects as well as the types of AEs described: antiandrogenic, estrogenic, central, and nonspecific/severe. A total of 244 cases were recorded and analyzed on the discussion forum on propeciahelp.com . Among these, 74 (32%) cases reported antiandrogenic affects, 43 (19%) reported estrogenic effects, 70 (30%) reported central effects, 11 (5%) reported nonspecific/severe AEs, and 31 (14%) reported AEs in all categories. The categorization of AEs may prompt further investigation into the pathophysiology of post-finasteride syndrome (PFS). Also, subjective reports may engender greater understanding of the perceived lasting AEs of finasteride.

Progestogens' effects and mechanisms for object recognition memory across the lifespan

This review explores the effects of female reproductive hormones, estrogens and progestogens, with a focus on progesterone and allopregnanolone, on object memory. Progesterone and its metabolites, in particular allopregnanolone, exert various effects on both cognitive and non-mnemonic functions in females. The well-known object recognition task is a valuable experimental paradigm that can be used to determine the effects and mechanisms of progestogens for mnemonic effects across the lifespan, which will be discussed herein. In this task there is little test-decay when different objects are used as targets and baseline valance for objects is controlled. This allows repeated testing, within-subjects designs, and longitudinal assessments, which aid understanding of changes in hormonal milieu. Objects are not aversive or food-based, which are hormone-sensitive factors. This review focuses on published data from our laboratory, and others, using the object recognition task in rodents to assess the role and mechanisms of progestogens throughout the lifespan. Improvements in object recognition performance of rodents are often associated with higher hormone levels in the hippocampus and prefrontal cortex during natural cycles, with hormone replacement following ovariectomy in young animals, or with aging. The capacity for reversal of age- and reproductive senescence-related decline in cognitive performance, and changes in neural plasticity that may be dissociated from peripheral effects with such decline, are discussed. The focus here will be on the effects of brain-derived factors, such as the neurosteroid, allopregnanolone, and other hormones, for enhancing object recognition across the lifespan.

Urine cortisol concentration as a biomarker of stress is unrelated to IVF outcomes in women and men

PURPOSE

Our primary objective was to assess associations between urine cortisol as a biomarker of psychological stress and in vitro fertilization (IVF) outcomes. A secondary objective was to assess associations between toxic metals and cortisol.

METHODS

Urine and blood specimens were collected from 52 women and 28 male partners completing a first IVF procedure, on the day of oocyte retrieval. Urine cortisol was measured with an enzyme-linked immunosorbent assay. Mercury (Hg), cadmium (Cd), and lead (Pb) were determined in blood and Cd in urine by inductively coupled plasma-mass spectrometry.

RESULTS

No associations were indicated for cortisol with IVF outcomes in multivariable regression models adjusted for covariates. However, we detected positive linear associations for cortisol and urine Cd (β = 9.96, 95%CI 1.52, 21.44) and blood Hg (β = 1.44, 95%CI 0.31, 3.18). An exploratory stratified analysis suggested a potential inverse association between urine cortisol and oocyte fertilization among women with low, but not high blood Hg.

CONCLUSION

While limited, these preliminary data suggest that psychological stress may not play a major role in IVF outcomes, which therefore could be one less concern for couples and their clinicians. Our data also raise the possibility for toxic metals to modify associations between cortisol and IVF outcomes among women. However, these preliminary results require corroboration in an experimental animal model and confirmation in a larger, more definitive observational study.

Endocrine-disrupting chemicals: elucidating our understanding of their role in sex and gender-relevant end points

Endocrine-disrupting chemicals (EDCs) are diverse and pervasive and may have significant consequence for health, including reproductive development and expression of sex-/gender-sensitive parameters. This review chapter discusses what is known about common EDCs and their effects on reproductively relevant end points. It is proposed that one way that EDCs may exert such effects is by altering steroid levels (androgens or 17-estradiol, E₂) and/or intracellular E₂ receptors (ERs) in the hypothalamus and/or hippocampus. Basic research findings that demonstrate developmentally sensitive end points to androgens and E₂ are provided. Furthermore, an approach is suggested to examine differences in EDCs that diverge in their actions at ERs to elucidate their role in sex-/gender-sensitive parameters.

Allopregnanolone levels and seizure frequency in progesterone-treated women with epilepsy

OBJECTIVE

To determine whether allopregnanolone (AP) may mediate seizure reduction in progesterone-treated women with epilepsy.

METHODS

The NIH Progesterone Trial compared the efficacy of adjunctive cyclic natural progesterone therapy vs placebo treatment of intractable seizures in 294 subjects, randomized 2:1 to progesterone or placebo, stratified by catamenial vs noncatamenial designation. Treatments were compared on proportions of 50% responders, and changes in seizure frequency from 3 baseline to 3 treatment cycles. Serum AP levels were measured by radioimmunoassay from 155 women with intractable focal-onset seizures who had baseline and treatment-phase midluteal serum samples drawn each cycle for hormone measurements.

RESULTS

There was no significant correlation between percentage changes in AP levels and seizure frequencies from baseline to treatment for either the catamenial or noncatamenial stratum. There was a significant correlation for the subset of subjects who showed a significantly greater responder rate in the post hoc analysis of the trial, i.e., subjects who had a 3-fold or greater increase in average daily seizure frequency perimenstrually compared with the midfollicular and midluteal phases (C1 ≥ 3: r = -0.442, p = 0.013, and specifically for C1 ≥ 3 progesterone-treated subjects [r = -0.452, p = 0.035], but not other groups [C1 ≥ 3 placebo: r = -0.367; C1 <3 progesterone: r = 0.099; C1 <3 placebo: r = 0.131; p = not significant]).

CONCLUSIONS

The findings support AP as a mediator of seizure reduction in progesterone-treated women who have a substantial level of perimenstrually exacerbated seizures.

The pregnane xenobiotic receptor, a prominent liver factor, has actions in the midbrain for neurosteroid synthesis and behavioral/neural plasticity of female rats

A novel factor of interest for growth/plasticity in the brain is pregnane xenobiotic receptor (PXR). PXR is a liver factor known for its role in xenobiotic clearance and cholesterol metabolism. It is expressed in the brain, suggesting a potential role for plasticity, particularly involving cholesterol-based steroids and neurosteroids. Mating induces synthesis of neurosteroids in the midbrain Ventral Tegmental Area (VTA) of female rodents, as well as other “plastic” regions of the brain, including the hippocampus, that may be involved in the consolidation of the mating experience. Reducing PXR in the VTA attenuates mating-induced biosynthesis of the neurosteroid, 5α-pregnan-3α-ol-20-one (3α,5α-THP). The 18 kDA translocator protein (TSPO) is one rate-limiting factor for 3α,5α-THP neurosteroidogenesis. The hypothesis tested was that PXR is an upstream factor of TSPO for neurosteroidogenesis of 3α,5α-THP in the VTA for lordosis, independent of peripheral glands. First, proestrous rats were administered a TSPO blocker (PK11195) and/or 3α,5α-THP following infusions of PXR antisense oligonucleotides (AS-ODNs) or vehicle to the VTA. Inhibiting TSPO with PK11195 reduced 3α,5α-THP levels in the midbrain and lordosis, an effect that could be reversed with 3α,5α-THP administration, but not AS-ODN+3α,5α-THP. Second, proestrous, ovariectomized (OVX), or ovariectomized/adrenalectomized (OVX/ADX) rats were infused with a TSPO enhancer (FGIN 1-27) subsequent to AS-ODNs or vehicle to the VTA. PXR AS-ODNs blocked actions of FGIN 1–27 for lordosis and 3α,5α-THP levels among proestrous > OVX > OVX/ADX rats. Thus, PXR may be upstream of TSPO, involved in neurosteroidogenesis of 3α,5α-THP in the brain for plasticity. This novel finding of a liver factor involved in behavioral/neural plasticity substantiates future studies investigating factors known for their prominent actions in the peripheral organs, such as the liver, for modulating brain function and its augmentation.

Novel receptor targets for production and action of allopregnanolone in the central nervous system: a focus on pregnane xenobiotic receptor

Neurosteroids are cholesterol-based hormones that can be produced in the brain, independent of secretion from peripheral endocrine glands, such as the gonads and adrenals. A focus in our laboratory for over 25 years has been how production of the pregnane neurosteroid, allopregnanolone, is regulated and the novel (i.e., non steroid receptor) targets for steroid action for behavior. One endpoint of interest has been lordosis, the mating posture of female rodents. Allopregnanolone is necessary and sufficient for lordosis, and the brain circuitry underlying it, such as actions in the midbrain ventral tegmental area (VTA), has been well-characterized. Published and recent findings supporting a dynamic role of allopregnanolone are included in this review. First, contributions of ovarian and adrenal sources of precursors of allopregnanolone, and the requisite enzymatic actions for de novo production in the central nervous system will be discussed. Second, how allopregnanolone produced in the brain has actions on behavioral processes that are independent of binding to steroid receptors, but instead involve rapid modulatory actions via neurotransmitter targets (e.g., γ-amino butyric acid-GABA, N-methyl-D-aspartate- NMDA) will be reviewed. Third, a recent focus on characterizing the role of a promiscuous nuclear receptor, pregnane xenobiotic receptor (PXR), involved in cholesterol metabolism and expressed in the VTA, as a target for allopregnanolone and how this relates to both actions and production of allopregnanolone will be addressed. For example, allopregnanolone can bind PXR and knocking down expression of PXR in the midbrain VTA attenuates actions of allopregnanolone via NMDA and/or GABA_A for lordosis. Our understanding of allopregnanolone’s actions in the VTA for lordosis has been extended to reveal the role of allopregnanolone for broader, clinically-relevant questions, such as neurodevelopmental processes, neuropsychiatric disorders, epilepsy, and aging.

Female mice with deletion of Type One 5α-reductase have reduced reproductive responding during proestrus and after hormone-priming

The capacity to form progesterone (P₄)'s 5α-reduced metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP; a.k.a. allopregnanolone), in the brain may be related to facilitation of lordosis among estrogen-primed (E₂) mice. We investigated this idea further by comparing effects of endogenous and exogenous progestogens in mice that are deficient in the Type One 5α-reductase enzyme (5α-reductase knockout mice; 5α-RKO), and their wildtype counterparts for sexual behavior. Comparisons were made following administration of progestogens that are expected to increase 3α,5α-THP or not. Sexual receptivity of 5α-RKO mice and their wildtype counterparts was examined when mice were naturally-cycling (Experiment 1); ovariectomized (OVX), E₂-primed (10 μg, subcutaneous; SC) and administered P₄ (0, 125, 250, or 500 μg SC; Experiment 2); and OVX, E₂-primed and administered P₄, medroxyprogesterone acetate (MPA, 4 mg/kg, SC, which does not convert to 3α,5α-THP) or 3α,5α-THP (4 mg/kg, SC; Experiment 3). The percentage of mounts that elicited lordosis (lordosis quotient) or aggression/rejection behavior (aggression quotient), as well as the quality of lordosis (lordosis rating), was scored. Wildtype, but not 5α-RKO, mice in behavioral estrus demonstrated significantly greater lordosis quotients and lordosis ratings, but similar aggression quotients, compared to their diestrous counterparts. Among OVX and E₂-primed mice, P₄ facilitated lordosis of wildtype, but not 5α-RKO, mice. MPA neither facilitated lordosis of wildtype, nor 5α-RKO mice. 3α,5α-THP administered to wildtype or 5α-RKO mice increased lordosis quotients and lordosis ratings and decreased aggression quotients. 3α,5α-THP levels in the midbrain, one brain region important for sexual behavior, were increased during behavioral estrus, with P4 administered to WT, but not 5α-RKO mice, and 3α,5α-THP administered to WT and 5α-RKO mice. MPA did not increase 3α,5α-THP. Thus, deletion of Type One 5α-reductase among female mice may attenuate reproductive responding during the estrous cycle and after hormone-priming.

Progesterone-facilitated lordosis of estradiol-primed mice is attenuated by knocking down expression of membrane progestin receptors in the midbrain

Evidence is emerging of the role of membrane progestin receptors (referred to as mPRs herein: members of Progestin and AdipoQ Receptor (Paqr) family) as a novel brain target in mammals, such as rats. In the present study, the role of mPRs in mice was assessed to further elucidate the conservation of this mechanism across species. The brain target investigated was the midbrain ventral tegmental area (VTA) given its described role for rapid actions of progestins for reproduction. Studies tested the hypothesis that if mPRs are required for progestin-facilitated lordosis through actions in the VTA, then knockdown of mPRs in the VTA will attenuate lordosis. Ovariectomized (OVX) mice were subcutaneously injected with estradiol (E2) and progesterone (P4), and infused with antisense oligodeoxynucleotides (AS-ODNs) to mPRα (Paqr7) and/or mPRβ (Paqr8) or vehicle to the lateral ventricle or VTA. Mice were assessed for reproductive behavior (lordosis and aggression/rejection quotients) in a standard mating task. Results supported our hypothesis. E2+P4-facilitated lordosis was significantly reduced, and aggression/rejection increased, with infusions of mPRα, mPRβ, or mPRαβ AS-ODNs to the lateral ventricle, compared to vehicle. E2+P4-facilitated lordosis was significantly decreased, and aggression/rejection increased, with mPRβ or mPRαβ AS-ODNs to the VTA of C57/BL6 mice. Both mPRɑ and mPRβ AS-ODNs reduced lordosis, and increased aggression/rejection, of wildtype (C57/BL6x129) mice, but not nuclear PR knockout mice. Thus, mPRs may be a novel target of progestins for reproductive behavior of mice.

Pregnane xenobiotic receptors and membrane progestin receptors: role in neurosteroid-mediated motivated behaviours

Progestogens have actions in the midbrain ventral tegmental area (VTA) to mediate motivated behaviours, such as those involved in reproductive processes, among female rodents. In the VTA, the formation and actions of one progestogen, 5α-pregnan-3α-ol-20-one (3α,5α-THP), are necessary and sufficient to facilitate sexual responding (measured by lordosis) of female rodents. Although 3α,5α-THP can be produced after metabolism of ovarian progesterone, 3α,5α-THP is also a neurosteroid produced de novo in brain regions, such as the VTA. There can be dynamic changes in 3α,5α-THP production associated with behavioural experience, such as mating. Questions of interest are the sources and targets of 3α,5α-THP. Regarding sources, the pregnane xenobiotic receptor (PXR) may be a novel factor involved in 3α,5α-THP metabolism in the VTA (as well as a direct target of 3α,5α-THP). We have identified PXR in the midbrain of female rats, and manipulating PXR in this region reduces 3α,5α-THP synthesis and alters lordosis, as well as affective and social behaviours. Regarding targets, recent studies have focused on the role of membrane progestin receptors (mPRs). We have analysed the expression of two of the common forms of these receptors (mPRα/paqr7 and mPRβ/paqr8) in female rats. The expression of mPRα was observed in peripheral tissues and brain areas, including the hypothalamus and midbrain. The expression of mPRβ was only observed in brain tissues and was abundant in the midbrain and hypothalamus. To our knowledge, studies of these receptors in mammalian models have been limited to expression and regulation, instead of function. One question that was addressed was the functional effects of progestogens via mPRα and mPRβ in the midbrain of hormone-primed rats for lordosis. Studies to date suggest that mPRβ may be an important target of progestogens in the VTA for lordosis. Taken together, the result of these studies demonstrate that PXR is involved in the production of 3α,5α-THP in the midbrain VTA. Moreover, mPRs may be a target for the actions of progestogens in the VTA for lordosis.

Membrane progestin receptors in the midbrain ventral tegmental area are required for progesterone-facilitated lordosis of rats

Progesterone (P₄) and its metabolites, rapidly facilitate lordosis of rats partly through actions in the ventral tegmental area (VTA). The study of membrane progestin receptors (mPRs), of the Progestin and AdipoQ Receptor (PAQR) superfamily, has been limited to expression and regulation, instead of function. We hypothesized that if mPRs are required for progestin-facilitated lordosis in the VTA, then mPRs will be expressed in this region and knockdown will attenuate lordosis. First, expression of mPR was examined by reverse-transcriptase polymerase chain reaction (RT-PCR) in brain and peripheral tissues of proestrous Long-Evans rats. Expression of mPRα (paqr7) was observed in peripheral tissues and brain areas, including hypothalamus and midbrain. Expression of mPRβ (paqr8) was observed in brain tissues and was abundant in the midbrain and hypothalamus. Second, ovariectomized rats were estrogen (E₂; 0.09 mg/kg, SC), and P₄ (4 mg/kg, SC) or vehicle-primed, and infused with antisense oligodeoxynucleotides (AS-ODNs) targeted against mPRα and/or mPRβ intracerebroventricularly or to the VTA. Rats were assessed for motor (open field), anxiety (elevated plus maze), social (social interaction), and sexual (lordosis) behavior. P₄-facilitated lordosis was significantly reduced with administration of AS-ODNs for mPRα, mPRβ, or co-administration of mPRα and mPRβ to the lateral ventricle, compared to vehicle. P₄-facilitated lordosis was reduced, compared to vehicle, by administration of mPRβ AS-ODNs, or co-administration of mPRα and mPRβ AS-ODNs, but not mPRα AS-ODNs alone, to the VTA. No differences were observed for motor, anxiety, or social behaviors. Thus, mPRs in the VTA are targets of progestin-facilitated lordosis of rats.

Progesterone facilitates exploration, affective and social behaviors among wildtype, but not 5α-reductase Type 1 mutant, mice

Progesterone (P4) facilitates exploration, anxiety and social behaviors in estrogen (E2)-primed mice. Some of these effects may be due to actions of its 5α-reduced metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP). In order to address the role of P4 and its metabolite, 3α,5α-THP, a mouse model was utilized. We hypothesized that if P4's metabolism to 3α,5α-THP is essential to facilitate exploratory, anti-anxiety and social behaviors of mice, then wildtype, but not 5α-reductase knockout (5α-RKO), mice will have greater expression of these behaviors. Experiment 1: Mice were ovariectomized (ovx), E2-primed and administered P4 (0, 125, 250, or 500μg) subcutaneously and then tested 4h later in a battery of tasks: open field, elevated plus maze, and social interaction. Experiment 2: Ovx, E2-primed mice were administered P4 (4mg/kg), 3α,5α-THP (4mg/kg), medroxyprogesterone acetate (MPA, which does not convert to 3α,5α-THP; 4mg/kg), or vehicle subcutaneously and tested 4h later. There was a dose-dependent effect of P4 to wildtype, but not 5α-RKO, mice. Neither wildtype, nor 5α-RKO, mice had increased exploration, anti-anxiety or pro-social behavior with MPA administration. Progesterone only exerted effects on anti-anxiety behavior, and increased 3α,5α-THP in the prefrontal cortex and hippocampus, when administered to wildtype mice. 3α,5α-THP to both WT and 5α-RKO mice increased exploration, anti-anxiety and social interaction and 3α,5α-THP levels in the hippocampus and prefrontal cortex. Thus, metabolism of P4 by the 5α-reductase enzyme may be essential for enhancement of these behaviors.

Progesterone, compared to medroxyprogesterone acetate, to C57BL/6, but not 5α-reductase mutant, mice enhances object recognition and placement memory and is associated with higher BDNF levels in the hippocampus and cortex

Progesterone (P4) may influence cognition in part through actions of its 5α-reduced metabolite, allopregnanolone. Ovariectomized mice that were C57BL/6 wildtype (WT), or deficient in the 5α-reductase Type 1 enzyme (5α-reductase knockout; 5αRKO), were administered vehicle, P4, allopregnanolone, or medroxyprogesterone acetate (MPA) after training in the object recognition or placement tasks. WT mice administered P4 or allopregnanolone performed significantly better in the object recognition and placement tasks than did WT mice administered vehicle or MPA. 5αRKO mice administered allopregnanolone, but not P4, MPA, or vehicle showed enhanced performance in the object recognition and placement tasks. Levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and hippocampus were lowest among mice administered MPA. Thus, some of P4s effects to enhance cognitive performance may be incumbent upon its 5α-reduction.

Gestational or acute restraint in adulthood reduces levels of 5α-reduced testosterone metabolites in the hippocampus and produces behavioral inhibition of adult male rats

Stressors, during early life or adulthood, can alter steroid-sensitive behaviors, such as exploration, anxiety, and/or cognitive processes. We investigated if exposure to acute stressors in adulthood may alter behavioral and neuroendocrine responses of male rats that were exposed to gestational stress or not. We hypothesized that rats exposed to gestational and acute stress may show behavioral inhibition, increased corticosterone, and altered androgen levels in the hippocampus. Subjects were adult, male offspring of rat dams that were restrained daily on gestational days 14–20, or did not experience this manipulation. Immediately before testing, rats were restraint stressed for 20 min or not. During week 1, rats were tested in a battery of tasks, including the open field, elevated plus maze, social interaction, tailflick, pawlick, and defensive burying tasks. During week 2, rats were trained and tested 24 h later in the inhibitory avoidance task. Plasma corticosterone and androgen levels, and hippocampal androgen levels, were measured in all subjects. Gestational and acute restraint stress increased plasma levels of corticosterone, and reduced levels of testosterone's 5α-reduced metabolites, dihydrotestosterone (DHT) and 3α-androstanediol (3α-diol), but not the aromatized metabolite, estradiol (E₂), in plasma or the hippocampus. Gestational and acute restraint stress reduced central entries made in the open field, and latencies to enter the shock-associated side of the inhibitory avoidance chamber during testing. Gestational stress reduced time spent interacting with a conspecific. These data suggest that gestational and acute restraint stress can have actions to produce behavioral inhibition coincident with increased corticosterone and decreased 5α-reduced androgens of adult male rats. Thus, gestational stress altered neural circuits involved in the neuroendocrine response to acute stress in early adulthood.

Dissociating behavioral, autonomic, and neuroendocrine effects of androgen steroids in animal models

Developments in behavioral assessment, autonomic and/or baseline reactivity, psychopharmacology, and genetics, have contributed significantly to the assessment of performance-enhancing drugs in animal models. Particular classes of steroid hormones: androgenic steroids are of interest. Anecdotally, the performance enhancing effects of androgens are attributed to anabolic events. However, there is a discrepancy between anecdotal evidence and investigative data. While some androgen steroids may promote muscle growth (myogenesis), effects of androgens on performance enhancement are not always seen. Indeed, some effects of androgens on performance may be attributable to their psychological and cardiovascular effects. As such, we consider androgen effects in terms of their behavioral, autonomic, and neuroendocrine components. Techniques are discussed in this chapter, some of which are well established, while others have been more recently developed to study androgen action. Androgens may be considered for their positive impact, negative consequence, or psychotropic properties. Thus, this review aims to elucidate some of the effects and/or mechanisms of androgens on behavioral, autonomic, and/or neuroendocrine assessment that may underlie their controversial performance enhancing effects.

Effects and Mechanisms of 3α,5α,-THP on Emotion, Motivation, and Reward Functions Involving Pregnane Xenobiotic Receptor

Progestogens [progesterone (P(4)) and its products] play fundamental roles in the development and/or function of the central nervous system during pregnancy. We, and others, have investigated the role of pregnane neurosteroids for a plethora of functional effects beyond their pro-gestational processes. Emerging findings regarding the effects, mechanisms, and sources of neurosteroids have challenged traditional dogma about steroid action. How the P(4) metabolite and neurosteroid, 3α-hydroxy-5α-pregnan-20-one (3α,5α-THP), influences cellular functions and behavioral processes involved in emotion/affect, motivation, and reward, is the focus of the present review. To further understand these processes, we have utilized an animal model assessing the effects, mechanisms, and sources of 3α,5α-THP. In the ventral tegmental area (VTA), 3α,5α-THP has actions to facilitate affective, and motivated, social behaviors through non-traditional targets, such as GABA, glutamate, and dopamine receptors. 3α,5α-THP levels in the midbrain VTA both facilitate, and/or are enhanced by, affective and social behavior. The pregnane xenobiotic receptor (PXR) mediates the production of, and/or metabolism to, various neurobiological factors. PXR is localized to the midbrain VTA of rats. The role of PXR to influence 3α,5α-THP production from central biosynthesis, and/or metabolism of peripheral P(4), in the VTA, as well as its role to facilitate, or be increased by, affective/social behaviors is under investigation. Investigating novel behavioral functions of 3α,5α-THP extends our knowledge of the neurobiology of progestogens, relevant for affective/social behaviors, and their connections to systems that regulate affect and motivated processes, such as those important for stress regulation and neuropsychiatric disorders (anxiety, depression, schizophrenia, drug dependence). Thus, further understanding of 3α,5α-THP's role and mechanisms to enhance affective and motivated processes is essential.

Endocrine disrupters: a review of some sources, effects, and mechanisms of actions on behaviour and neuroendocrine systems

Some environmental contaminants interact with hormones and may exert adverse consequences as a result of their actions as endocrine disrupting chemicals (EDCs). Exposure in people is typically a result of contamination of the food chain, inhalation of contaminated house dust or occupational exposure. EDCs include pesticides and herbicides (such as dichlorodiphenyl trichloroethane or its metabolites), methoxychlor, biocides, heat stabilisers and chemical catalysts (such as tributyltin), plastic contaminants (e.g. bisphenol A), pharmaceuticals (i.e. diethylstilbestrol; 17α-ethinylestradiol) or dietary components (such as phytoestrogens). The goal of this review is to address the sources, effects and actions of EDCs, with an emphasis on topics discussed at the International Congress on Steroids and the Nervous System. EDCs may alter reproductively-relevant or nonreproductive, sexually-dimorphic behaviours. In addition, EDCs may have significant effects on neurodevelopmental processes, influencing the morphology of sexually-dimorphic cerebral circuits. Exposure to EDCs is more dangerous if it occurs during specific 'critical periods' of life, such as intrauterine, perinatal, juvenile or puberty periods, when organisms are more sensitive to hormonal disruption, compared to other periods. However, exposure to EDCs in adulthood can also alter physiology. Several EDCs are xenoestrogens, which can alter serum lipid concentrations or metabolism enzymes that are necessary for converting cholesterol to steroid hormones. This can ultimately alter the production of oestradiol and/or other steroids. Finally, many EDCs may have actions via (or independent of) classic actions at cognate steroid receptors. EDCs may have effects through numerous other substrates, such as the aryl hydrocarbon receptor, the peroxisome proliferator-activated receptor and the retinoid X receptor, signal transduction pathways, calcium influx and/or neurotransmitter receptors. Thus, EDCs, from varied sources, may have organisational effects during development and/or activational effects in adulthood that influence sexually-dimorphic, reproductively-relevant processes or other functions, by mimicking, antagonising or altering steroidal actions.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.

Inhibition of 5α-reductase activity in late pregnancy decreases gestational length and fecundity and impairs object memory and central progestogen milieu of juvenile rat offspring

Psychological, physical and/or immune stressors during pregnancy are associated with negative birth outcomes, such as preterm birth and developmental abnormalities. In rodents, prenatal stressors can alter the expression of 5α-reductase enzymes in the brain and may influence cognitive function and anxiety-type behaviour in the offspring. Progesterone plays a critical role in maintaining gestation. In the present study, it was hypothesised that 5α-reduced progesterone metabolites influence birth outcomes and/or the cognitive and neuroendocrine function of the offspring. 5α-Reduced steroids were manipulated in pregnant Long-Evans rats via the administration of vehicle, the 5α-reduced, neuroactive metabolite of progesterone, 5α-pregnan-3α-ol-20-one (3α,5α-THP, allopregnanolone; 10 mg/kg/ml, s.c.), or the 5α-reductase inhibitor, finasteride (50 mg/kg/ml, s.c.), daily from gestational days 17-21. Compared to vehicle or 3α,5α-THP treatment, finasteride, significantly reduced the length of gestation and the number of pups per litter found in the dams' nests after parturition. The behaviour of the offspring in hippocampus-dependent tasks (i.e. object recognition, open field) was examined on post-natal days 28-30. Compared to vehicle-exposed controls, prenatal 3α,5α-THP treatment significantly increased motor behaviour in females compared to males, decreased progesterone content in the medial prefrontal cortex (mPFC) and diencephalon, increased 3α,5α-THP and 17β-oestradiol content in the hippocampus, mPFC and diencephalon, and significantly increased serum corticosterone concentrations in males and females. Prenatal finasteride treatment significantly reduced object recognition, decreased hippocampal 3α,5α-THP content, increased progesterone concentration in the mPFC and diencephalon, and increased serum corticosterone concentration in female (but not male) juvenile offspring, compared to vehicle-exposed controls. Thus, inhibiting the formation of 5α-reduced steroids during late gestation in rats reduces gestational length, the number of viable pups per litter, and impairs cognitive and neuroendocrine function in the juvenile offspring.

Immune stress in late pregnant rats decreases length of gestation and fecundity, and alters later cognitive and affective behaviour of surviving pre-adolescent offspring

Immune challenge during pregnancy is associated with preterm birth and poor perinatal development. The mechanisms of these effects are not known. 5α-Pregnan-3α-ol-20-one (3α,5α-THP), the neuroactive metabolite of progesterone, is critical for neurodevelopment and stress responses, and can influence cognition and affective behaviours. To develop an immune challenge model of preterm birth, pregnant Long-Evans rat dams were administered lipopolysaccharide [LPS; 30 μg/kg/ml, intraperitoneal (IP)], interleukin-1β (IL-1β; 1 μg/rat, IP) or vehicle (0.9% saline, IP) daily on gestational days 17-21. Compared to control treatment, prenatal LPS or IL-1β reduced gestational length and the number of viable pups born. At 28-30 days of age, male and female offspring of mothers exposed to prenatal IL-1β had reduced cognitive performance in the object recognition task compared to controls. In females, but not males, prenatal IL-1β reduced anxiety-like behaviour, indicated by entries to the centre of an open field. In the hippocampus, progesterone turnover to its 5α-reduced metabolites was lower in prenatally exposed IL-1β female, but not in male offspring. IL-1β-exposed males and females had reduced oestradiol content in hippocampus, medial prefrontal cortex and diencephalon compared to controls. Thus, immune stress during late pregnancy reduced gestational length and negatively impacted birth outcomes, hippocampal function and central neurosteroid formation in the offspring.

Type 1 5α-reductase may be required for estrous cycle changes in affective behaviors of female mice

There are estrous cycle differences in affective behaviors of rodents that are generally attributed to cyclic variations in estradiol, progesterone (P) and its metabolites. A question is the role of the steroid metabolism enzyme, 5α-reductase, for these estrous cycle differences. To address the requirement of 5α-reductase, estrous cycle variations in the behavior of wildtype mice and their littermates that are deficient in the 5α-reductase type 1 enzyme (5αRKO mice) were examined. The hypothesis was that if some of the estrous cycle differences in exploratory (open field) and anxiety (elevated plus maze) are due to P's 5α-reduction to 5α-pregnan-3α-ol-20-one (3α,5α-THP), then wildtype mice will have estrous cycle differences in the expression of these behaviors, but 5αRKO mice will not. Mice were tested in these tasks and then had plasma and brains collected so that steroid levels (estradiol, P, 3α,5α-THP, corticosterone) could be measured in these tissues. Results supported this hypothesis. There were estrous cycle differences among wildtype, but not 5αRKO, mice. Proestrous wildtype mice made more central entries in the open field and spent more time on the open arms of the plus maze, coincident with higher 3α,5α-THP levels in plasma and brain regions important for these behaviors, such as the hippocampus and cortex, compared to their diestrous counterparts. Variability in the open field and elevated plus maze could be explained by circulating and hippocampus levels of 3α,5α-THP, respectively. Thus, 5α-reductase may be required for the estrous cycle variations in affective behavior and 3α,5α-THP levels of female mice.

Progesterone turnover to its 5α-reduced metabolites in the ventral tegmental area of the midbrain is essential for initiating social and affective behavior and progesterone metabolism in female rats

BACKGROUND

Among women and female rodents, progesterone (P) influences social affiliation and affect. These effects may be partly due to formation of its 5α-reduced, 3α- hydroxylated metabolite, 5α-pregnan-3α-ol-20-one (3α,5α- THP).

AIM

To elucidate whether actions of 3α,5α-THP in the midbrain ventral tegmental area (VTA) are both necessary and sufficient to enhance non-sexual and sexual social behaviors, affect, and central 3α,5α-THP metabolism.

MATERIALS AND METHODS

P and 3α,5α-THP formation were unperturbed or blocked in VTA via infusions of vehicle, PK11195 (400 ng), and/or indomethacin (10 μg). Rats then received subsequent infusions of vehicle or 3α,5α-THP (100 ng) and were assessed in a battery of tasks that included open field (exploration), elevated plus maze (anxiety behavior), social interaction (social affiliation), and paced mating (sexual behavior) or were not tested. Metabolic turnover of P to its 5α-reduced metabolites was assessed in plasma, midbrain, hippocampus, frontal cortex, diencephalon, and remaining subcortical tissues (control interbrain).

RESULTS

Infusions of any combination of inhibitors significantly reduced social and affective behavior in all tasks compared to vehicle, concomitant with reduced turnover of P to its 5α-reduced metabolites, in midbrain only. Subsequent infusions of 3α,5α-THP significantly reinstated/enhanced anti- anxiety behavior, lordosis, and P turnover to its 5α-reduced metabolites in midbrain, as well as hippocampus, cortex, and diencephalon (but not plasma or interbrain).

CONCLUSIONS

These data are the first to provide direct evidence that actions of 3α,5α-THP in the VTA are both necessary and sufficient for social and affective behavior, as well as initiation of central 5α-reduction.

Progesterone attenuates depressive behavior of younger and older adult C57/BL6, wildtype, and progesterone receptor knockout mice

Progesterone may have actions independent of intracellular progestin receptors (PRs) to influence depressive behavior. To investigate this, we examined effects of progesterone (P; 10mg/kg, SC) on the depressive behavior of mice in the forced swim test (FST). In Experiment 1, subjects were 4 to 6 months old, intact or ovariectomized (OVX) female and intact or gonadectomized (GDX) male, C57/BL6 mice. Progesterone reduced depressive behavior of young diestrous and OVX mice but male mice were impervious to effects of P. In Experiment 2, subjects were intact aged (20-28 months old) C57/BL6 female and male mice. Progesterone reduced depressive behavior of aged female and male C57/BL6 mice, albeit effects were greater among males. In Experiment 3, effects of P were examined in 4 to 6 months old, gonadally-intact, female and male mice that were wildtype or PR knockouts (PRKOs). Progesterone decreased depressive behavior of young adult, wildtype and PRKO mice, which showed greater immobility than did their wildtype counterparts. In Experiment 4, subjects were 18-24 months old wildtype or PRKO mice (Exp 4). Progesterone decreased immobility among wildtype and PRKO mice (which were not different in terms of their baseline depressive behavior). Together these data demonstrate that P decreases depressive behavior of young and older adult C57/BL6, wildtype and PRKO mice, which suggest that acute anti-depressant effects of P may occur independent of actions at "classic" PRs.

Progesterone, administered before kainic acid, prevents decrements in cognitive performance in the Morris Water Maze

The nature of progesterone (P₄)'s neuroprotective effects is of interest. We investigated effects of P₄ when administered before, or after, kainic acid, which produces ictal activity and damage to the hippocampus, to mediate effects on spatial performance. The hypothesis was that P₄, compared with vehicle, would reduce decrements in Morris Water Maze performance induced by kainic acid. Experiment 1: We examined the effects of kainic acid on plasma stress hormone, corticosterone, and progestogen (P₄ and its metabolites) levels in plasma and the hippocampus after subcutaneous (s.c.) P₄ administration to ovariectomized rats. Rats administered kainic acid had the highest corticosterone levels immediately following injection. P₄ is 5α-reduced to dihydroprogesterone (DHP) and subsequently metabolized to 5α-pregnan-3α-ol-20-one (3α,5α-THP) by 3α-hydroxysteroid dehydrogenase. The regimen of P₄ used produced circulating and hippocampal levels of P₄, DHP, and 3α,5α-THP within a physiological range, which declined at 14 hours postinjection and were not altered by kainic acid. Experiment 2: The physiological P₄ regimen was administered to rats before, or after, kainic acid-induced seizures, and later effects on water maze performance were compared with that of rats administered vehicle. Rats administered kainic acid had significantly poorer performance in the water maze (i.e., increased latencies and distances to the hidden platform) than did rats administered vehicle. Administration of P₄ before, but not after, kainic acid prevented these performance deficits. Thus, these data suggest that a physiological regimen of P₄ can prevent some of the deficits in water maze performance produced by kainic acid.

Progesterone reduces depressive behavior of young ovariectomized, aged progestin receptor knockout, and aged wild type mice in the tail suspension test

Progestins may have effects to reduce depressive behavior, in part through actions of its metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP) at GABA(A) receptors, rather than through intracellular progestin receptors. In this study, we examined the effects of progesterone (10 mg/kg, subcutaneous injection) versus vehicle control (propylene glycol) on the depressive behavior of young and aged mice in the tail suspension test. In Experiment 1, we first characterized progesterone's anti-depressant effects by utilizing young (4-6-month-old) intact or ovariectomized female, and intact or gonadectomized male, C57BL/6 mice. Young female mice showed more depressive behavior than the young male mice. Compared with vehicle administration, progesterone reduced depressive behavior of ovariectomized female, but not male or intact female mice. In Experiment 2, mice were aged (20-24-month-old) intact wild type or progestin receptor knockout mice. Progestin receptor knockout mice showed less depressive behavior than wild type mice. Administration of progesterone to wild type and progestin receptor knockout mice reduced depressive behavior. Together, these data suggest that progesterone can decrease depressive behavior of young adult ovariectomized female, aged wild type and progestin receptor knockout mice. Thus, progesterone's effect to reduce depressive behavior of aged mice may not require actions at the intracellular progestin receptors.

Prenatal Stress Alters Progestogens to Mediate Susceptibility to Sex-Typical, Stress-Sensitive Disorders, such as Drug Abuse: A Review

Maternal-offspring interactions begin prior to birth. Experiences of the mother during gestation play a powerful role in determining the developmental programming of the central nervous system. In particular, stress during gestation alters developmental programming of the offspring resulting in susceptibility to sex-typical and stress-sensitive neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. However, neither these effects, nor the underlying mechanisms, are well understood. Our hypothesis is that allopregnanolone, during gestation, plays a particularly vital role in mitigating effects of stress on the developing fetus and may mediate, in part, alterations apparent throughout the lifespan. Specifically, altered balance between glucocorticoids and progestogens during critical periods of development (stemming from psychological, immunological, and/or endocrinological stressors during gestation) may permanently influence behavior, brain morphology, and/or neuroendocrine-sensitive processes. 5α-reduced progestogens are integral in the developmental programming of sex-typical, stress-sensitive, and/or disorder-relevant phenotypes. Prenatal stress (PNS) may alter these responses and dysregulate allopregnanolone and its normative effects on stress axis function. As an example of a neurodevelopmental, neuropsychiatric, and/or neurodegenerative process, this review focuses on responsiveness to drugs of abuse, which is sensitive to PNS and progestogen milieu. This review explores the notion that allopregnanolone may effect, or be influenced by, PNS, with consequences for neurodevelopmental-, neuropsychiatric-, and/or neurodegenerative- relevant processes, such as addiction.

Juvenile offspring of rats exposed to restraint stress in late gestation have impaired cognitive performance and dysregulated progestogen formation

Gestational stress may have lasting effects on the physical and neurocognitive development of offspring. The mechanisms that may underlie these effects are of interest. Progesterone and its 5α-reduced metabolites, dihydroprogesterone and 5α-pregnan-3α-ol-20-one (3α,5α-THP), maintain pregnancy, have neurotrophic effects, and can enhance cognitive performance. We hypothesized that some of the deleterious effects of gestational stress on the cognitive performance of offspring may be related to progestogen formation. Pregnant rat dams were exposed to restraint under a bright light (thrice daily for 45 min) on gestational days 17-21 or were minimally handled controls. Dams that were exposed to restraint had lower circulating levels of 3α,5α-THP and significantly greater concentrations of corticosterone at the time of birth than did control dams. Male and female offspring, that were gestationally stressed or not, were cross-fostered to non-manipulated dams. Between postnatal days 28-30, offspring were assessed for object recognition, a prefrontal cortex (PFC)-dependent cognitive task. Restraint-exposed offspring performed more poorly in the object recognition task than did control offspring, irrespective of sex. As well, progesterone turnover to its 5α-reduced metabolites in the medial PFC (but not the diencephalon) was significantly reduced among restraint-exposed, compared to control, offspring. Progesterone turnover, and levels of 3α,5α-THP, positively correlated with performance in the object recognition task. Thus, restraint stress in late pregnancy impaired cognitive development and dysregulated progestogen formation in brain.

Neurosteroids for a successful pregnancy

Steroid hormones play a critical role in the initiation and maintenance of pregnancy. In particular, the important role that the progesterone metabolite, and neurosteroid, allopregnanolone, may play in fetal and adolescent development is becoming increasingly evident. Unlike steroid hormones, neurosteroids act at nontraditional targets in the central and peripheral nervous systems, including GABA(A) receptor complexes. This commentary discusses the three works in this issue that elucidate the important role of allopregnanolone in the mechanisms that regulate stress hypo-sensitivity of rodents in late pregnancy, neuroprotective effects in fetal sheep exposed to a hypoxic insult, and the continuing role that prefrontal cortex formation of allopregnanolone may play on the cognitive development of gestationally stressed rat offspring, grown to adolescence. The narrative that these works comprise was facilitated by the 5(th) International Meeting on Steroids and the Nervous System (Torino, Italy), which is organized to update our knowledge on the relationships between steroid hormones synthesized in different organs and the nervous system. Topics covered in this most recent meeting included sex differences in, and hormonal influences on, cannabinoid-regulated biology; steroids and pain; the importance of co-regulatory factors for steroid receptor action in the brain; mechanism and role of estrogen-induced nonclassical signaling in the brain; vitamin D as the forgotten neurosteroid; neurosteroids and GABA(A) receptors; and pathogenic mechanisms mediated by glucocorticoid receptors in psychiatric disorders. The 6(th) International Meeting on Steroids and the Nervous System will be held in Torino, Italy in February 2011.

Effects of neurosteroid actions at N-methyl-D-aspartate and GABA A receptors in the midbrain ventral tegmental area for anxiety-like and mating behavior of female rats

RATIONALE

In the midbrain ventral tegmental area (VTA), actions of neurosteroids, such as the progesterone metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP), can facilitate mating and influence stress-related processes. Some actions of 3α,5α-THP may occur via positive modulation of GABA(A) receptors (GBRs), or negative modulation of N-methyl-D: -aspartate receptors (NMDARs), to influence anxiety-like behavior; but this is not known.

OBJECTIVES

We aimed to assess the role that neurosteroids and stress factors play on intra-VTA NMDAR- and/or GBR-mediated anxiety-like and mating behavior.

METHODS

Estradiol-primed, ovariectomized rats, which were partially or completely adrenalectomized (ADX), received infusions of vehicle, an NMDAR blocker (MK-801; 200 ng), or a GBR antagonist (bicuculline, 100 ng) to the VTA. Rats then received intra-VTA vehicle or a neurosteroidogenesis enhancer (N,N-Dihexyl-2-(4-fluorophenyl)indole-3-acetamide, FGIN 1-27, 5 μg) and anxiety-like and sexual behavior was assessed.

RESULTS

Complete, compared to partial, ADX significantly reduced open arm exploration on an elevated plus maze, the proportion of females that engaged in mating, lordosis quotients, pacing of sexual contacts, and defensive aggression towards a sexually vigorous male. Intra-VTA MK-801 enhanced open arm investigation and the proportion of females that engaged in mating. Infusions of either, MK-801 or FGIN 1-27, enhanced lordosis and, when co-administered, FGIN 1-27 attenuated MK-801's lordosis-enhancing effects. Intra-VTA infusions of bicuculline, prior to FGIN 1-27, blocked FGIN 1-27's effects to enhance lordosis.

CONCLUSIONS

Together, these data suggest that reduced NMDAR activity in the VTA may influence motivation to explore and engage in sexual behavior. These data suggest that neurosteroid actions at NMDARs and GBRs in the VTA are important for exploration and/or sexual behavior.

Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues

17β-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERβ for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERβ related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

Conjugated equine estrogen, with medroxyprogesterone acetate, enhances formation of 5alpha-reduced progestogens and reduces anxiety-like behavior of middle-aged rats

The mechanisms by which progestogens influence affective behaviors in females are poorly understood despite clear changes in mood/affect that are associated with their decline during menopause. Conjugated equine estrogens (CEE), with or without medroxyprogesterone acetate (MPA), are commonly prescribed hormone-replacement, but there is heterogeneity in responses to these pharmacotherapies. One way in which these compounds differ is in their capacity to potentiate metabolism of progesterone to its 5alpha-reduced products, dihydroprogesterone and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). This study investigated whether responses to CEE and MPA may be related to the capacity to metabolize progesterone. Middle-aged female rats that had maintained reproductive status, or those that had a decline, were administered vehicle, CEE and/or MPA. Effects on anxiety-like (open field, elevated plus maze) and social behaviors (social interaction test), and plasma and hippocampus steroid levels were determined. We hypothesized that CEE, but not MPA, would decrease anxiety-like behavior coincident with increased hippocampal metabolism of progesterone. CEE, or CEE+MPA, increased central entries in the open field and time spent on the open arms of the plus maze, but did not alter social interaction of rats that had maintained reproductive status. CEE and/or CEE+MPA increased E2 and 3alpha,5alpha-THP in plasma and/or hippocampus of rats, but MPA increased levels of dihydroprogesterone in the hippocampus of rats with declining reproductive status. Simple regressions showed that hippocampus 3alpha,5alpha-THP levels accounted for a significant proportion of the variance in anxiety-like behavior. Therefore, effects of CEE to reduce anxiety-like behavior of middle-aged rats may be owing, in part, to its capacity to enhance levels of 3alpha,5alpha-THP in the hippocampus.

II. Cognitive performance of middle-aged female rats is influenced by capacity to metabolize progesterone in the prefrontal cortex and hippocampus

Cognitive decline can occur with aging; however, some individuals experience less cognitive decline than do others. Secretion of ovarian hormones is reduced post-menopause and may contribute to cognitive function. The extent to which hormonal effects may be parsed out from other age-related factors to influence cognition is of interest. Middle-aged (12-month-old) female rats that were retired breeders were categorized as maintaining or declining reproductive function based upon their estrous cyclicity (regular 4-5 day cycles), fertility (> 60 % successful pregnancy), and fecundity (>10 pups/litter). Performance in object recognition, Y-maze, water maze, inhibitory avoidance, and contextual-cued fear conditioning was evaluated. Estradiol, progesterone (P(4)), dihydroprogesterone, and 5α-pregnan-3α-ol-20-one (3α,5α-THP) were assessed in medial prefrontal cortex (mPFC) and hippocampus; corticosterone was assessed in plasma. Rats maintaining reproductive function performed significantly better on the object recognition, Y-maze, water maze, inhibitory avoidance, and cued fear conditioning tasks than did rats with declining reproductive function. Steroid concentrations varied greatly within groups. Higher levels of P(4) in mPFC and hippocampus were associated with better Y-maze performance. In mPFC, higher levels of P(4) were associated with poorer inhibitory avoidance performance; greater levels of 3α,5α-THP were associated with better object memory. Neither estradiol nor corticosterone levels significantly contributed to cognitive performance. Thus, the capacity for cortico-limbic P(4) utilization may influence cognitive performance in aging.

Communication, interventions, and scientific advances in autism: a commentary

Autism spectrum disorders (ASD) affect approximately 1 in 150 children across the U.S., and are characterized by abnormal social actions, language difficulties, repetitive or restrictive behaviors, and special interests. ASD include autism (autistic disorder), Asperger Syndrome, and Pervasive Developmental Disorder not otherwise specified (PDD-NOS or atypical autism). High-functioning individuals may communicate with moderate-to-high language skills, although difficulties in social skills may result in communication deficits. Low-functioning individuals may have severe deficiencies in language, resulting in poor communication between the individual and others. Behavioral intervention programs have been developed for ASD, and are frequently adjusted to accommodate specific individual needs. Many of these programs are school-based and aim to support the child in the development of their skills, for use outside the classroom with family and friends. Strides are being made in understanding the factors contributing to the development of ASD, particularly the genetic contributions that may underlie these disorders. Mutant mouse models provide powerful research tools to investigate the genetic factors associated with ASD and its co-morbid disorders. In support, the BTBR T+tf/J mouse strain incorporates ASD-like social and communication deficits and high levels of repetitive behaviors. This commentary briefly reviews the reciprocal relationship between observations made during evidence-based behavioral interventions of high- versus low-functioning children with ASD and the accumulating body of research in autism, including animal studies and basic research models. This reciprocity is one of the hallmarks of the scientific method, such that research may inform behavioral treatments, and observations made during treatment may inform subsequent research.

Corticosteroid and neurosteroid dysregulation in an animal model of autism, BTBR mice

Autism spectrum disorders (ASD) are a constellation of neurodevelopmental disorders associated with disruptions in social, cognitive, and/or motor behaviors. ASD are more prevalent among males than females and characterized by aberrant social and language development, and a dysregulation in stress-responding. Levels of progesterone (P(4)) and its metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) are higher and more variable in females compared to males. 3alpha,5alpha-THP is also a neurosteroid, which can be rapidly produced de novo in the brain, independent of peripheral gland secretion, and can exert homeostatic effects to modulate stress-responding. An inbred mouse strain that has demonstrated an ASD-like behavioral and neuroendocrine phenotype is BTBR T +tf/J (BTBR). BTBR mice have deficits in cognitive and social behaviors and have high circulating levels of the stress hormone, corticosterone. We hypothesized that central 3alpha,5alpha-THP levels would be different among BTBR mice compared to mice on a similar background C57BL/6J (C57/J) and 129S1/SvlmJ (129S1). Tissues were collected from BTBR, C57/J and 129S1 male mice and levels of corticosterone, P(4), and 3alpha,5alpha-THP in plasma and in the hypothalamus, midbrain, hippocampus, and cerebellum were measured by radioimmunoassay. Circulating levels of corticosterone, P(4), and 3alpha,5alpha-THP were significantly higher among BTBR, than C57/J and 129S1, mice. Levels of P(4) in the cerebellum were significantly higher than other brain regions among all mouse strains. Levels of 3alpha,5alpha-THP in the hypothalamus of BTBR mice were significantly higher compared to C57/J and 129S1 mice. These findings suggest that neuroendocrine dysregulation among BTBR mice extends to 3alpha,5alpha-THP.

Fluoxetine-induced decrements in sexual responses of female rats and hamsters are reversed by 3α,5α-THP

INTRODUCTION

Sexual dysfunction, as a result of selective-serotonin reuptake inhibitor (SSRI) treatment among women, is relatively common and is a factor in medication compliance. The mechanisms that underlie these side-effects of SSRIs are not well-understood. SSRIs can alter activity of catabolic enzymes that are involved in progesterone's conversion to 5 α-pregnan-3 α-ol-20-one (3 α,5 α-THP). 3 α,5 α-THP plays a key role in female reproductive physiology and behavior.

AIMS

This study aimed to determine whether 3 α,5 α-THP, in the midbrain ventral tegmental area (VTA) may be a potential mechanism for fluoxetine's reduction in sexual responding of female rodents. We hypothesized that if fluoxetine induces decrements in sexual responding in part through actions of 3 α,5 α-THP, then fluoxetine will inhibit sexual receptivity concomitant with reducing 3 α,5 α-THP levels, effects which can be reversed by 3 α,5 α-THP administration.

METHODS

  Experiment 1 investigated effects of acute systemic fluoxetine [20 mg/kg intraperitoneal (IP)] and/or 3 α,5 α-THP [500 µg, subcutaneous (SC)] administration on sexual responding of ovariectomized, hormone-primed rats. Experiment 2 examined effects of 3 α,5 α-THP administration to the midbrain VTA (100 ng) on fluoxetine-induced decrements in lordosis of ovariectomized, hormone-primed rats and hamsters.

MAIN OUTCOME MEASURES

Sexual responding was determined in rats and hamsters. For rats, the percentage of times that the lordosis response occurred following mounting by a sexually-vigorous male (lordosis quotients) was utilized. For hamsters, lateral displacement, the pelvic movement that females will make to facilitate intromissions by a male hamster, was utilized.

RESULTS

Fluoxetine significantly reduced lordosis, and this was reversed SC 3 α,5 α-THP. Intra-VTA 3 α,5 α-THP attenuated fluoxetine's detrimental effects on lordosis quotients and lateral displacement of rats and hamsters, respectively.

CONCLUSIONS

Thus, fluoxetine's effects to disrupt female sexual responses may involve its effects on progestogens in the midbrain VTA.

3alpha-androstanediol, but not testosterone, attenuates age-related decrements in cognitive, anxiety, and depressive behavior of male rats

Some hippocampally-influenced affective and/or cognitive processes decline with aging. The role of androgens in this process is of interest. Testosterone (T) is aromatized to estrogen, and reduced to dihydrotestosterone (DHT), which is converted to 5α-androstane, 3α, 17α-diol (3α-diol). To determine the extent to which some age-related decline in hippocampally-influenced behaviors may be due to androgens, we examined the effects of variation in androgen levels due to age, gonadectomy, and androgen replacement on cognitive (inhibitory avoidance, Morris water maze) and affective (defensive freezing, forced swim) behavior among young (4 months), middle-aged (13 months), and aged (24 months) male rats. Plasma and hippocampal levels of androgens were determined. In experiment 1, comparisons were made between 4-, 13-, and 24-month-old rats that were intact or gonadectomized (GDX) and administered a T-filled or empty silastic capsule. There was age-related decline in performance of the inhibitory avoidance, water maze, defensive freezing, and forced swim tasks, and hippocampal 3α-diol levels. Chronic, long-term (1–4 weeks) T-replacement reversed the effects of GDX in 4- and 13-month-old, but not 24-month-old, rats in the inhibitory avoidance task. Experiments 2 and 3 assessed whether acute subcutaneous T or 3α-diol, respectively, could reverse age-associated decline in performance. 3α-diol, but not T, compared to vehicle, improved performance in the inhibitory avoidance, water maze, forced swim, and defensive freezing tasks, irrespective of age. Thus, age is associated with a decrease in 3α-diol production and 3α-diol administration reinstates cognitive and affective performance of aged male rats.