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

Neonatal overfeeding promotes anxiety, impairs episodic-like memory, and disrupts transcriptional regulation of hippocampal steroidogenic enzymes

The objective of our study was to investigate the impact of neonatal overfeeding on cognitive functions and neurosteroidogenesis in male rats. Offspring were assigned to either small litters (SL; 4 pups/mother), resulting in increased milk intake and body weight gain, or normal litters (NL; 10 pups/mother). On postnatal day (PND) 21, half of the male rats were euthanized, while the remaining were kept under standard conditions (4 rats/cage) until PND70. At this stage, subjects underwent assessments for locomotor activity, anxiety levels via the elevated plus maze, and episodic-like memory (ELM) tests. By PND90, the rats were euthanized for brain dissection. Utilizing micropunch techniques, dentate gyrus (DG), CA1, and CA3 regions were extracted for analysis of mRNA expression and methylation patterns. At PND21, SL rats exhibited increased body and adipose tissue weights, alongside elevated cholesterol, glucose, and triglyceride levels compared to NL counterparts. By PND90, although metabolic disparities were no longer evident, SL rats demonstrated heightened anxiety-like behavior and diminished performance in ELM tests. Early life changes included a decreased expression of aromatase (P450arom) and 3α-HSD in CA1, with increased levels in CA3 and DG among SL rats. Additionally, PND90 rats from SL exhibited increased P450arom and decreased 5α-reductase 1 (5αR-1) expression in DG. Notably, some of these variations were correlated with changes in methylation patterns of their promoter regions. Our findings reveal that neonatal overfeeding exerts a long-term adverse effect on cognitive abilities and neurosteroidogenic pathways, underscoring the lasting impact of nutritional experiences during critical early postnatal development periods.

Allopregnanolone: Metabolism, Mechanisms of Action, and Its Role in Cancer

Allopregnanolone (3α-THP) has been one of the most studied progesterone metabolites for decades. 3α-THP and its synthetic analogs have been evaluated as therapeutic agents for pathologies such as anxiety and depression. Enzymes involved in the metabolism of 3α-THP are expressed in classical and nonclassical steroidogenic tissues. Additionally, due to its chemical structure, 3α-THP presents high affinity and agonist activity for nuclear and membrane receptors of neuroactive steroids and neurotransmitters, such as the Pregnane X Receptor (PXR), membrane progesterone receptors (mPR) and the ionotropic GABA_A receptor, among others. 3α-THP has immunomodulator and antiapoptotic properties. It also induces cell proliferation and migration, all of which are critical processes involved in cancer progression. Recently the study of 3α-THP has indicated that low physiological concentrations of this metabolite induce the progression of several types of cancer, such as breast, ovarian, and glioblastoma, while high concentrations inhibit it. In this review, we explore current knowledge on the metabolism and mechanisms of action of 3α-THP in normal and tumor cells.

A Nested Case-Control Study of Allopregnanolone and Preterm Birth in the Healthy Start Cohort

Context

Chronic stress is a risk factor for preterm birth; however, objective measures of stress in pregnancy are limited. Maternal stress biomarkers may fill this gap. Steroid hormones and neurosteroids such as allopregnanolone (ALLO) play important roles in stress physiology and pregnancy maintenance and therefore may be promising for preterm birth prediction.

Objective

We evaluated maternal serum ALLO, progesterone, cortisol, cortisone, pregnanolone, and epipregnanolone twice in gestation to evaluate associations with preterm birth.

Methods

We performed a nested case-control study using biobanked fasting serum samples from the Healthy Start prebirth cohort. We included healthy women with a singleton pregnancy and matched preterm cases with term controls (1:1; N = 27 per group). We used a new HPLC-tandem mass spectrometry assay to quantify ALLO and five related steroids. We used ANOVA, Fisher exact, χ², t test, and linear and logistic regression as statistical tests.

Results

Maternal serum ALLO did not associate with preterm birth nor differ between groups. Mean cortisol levels were significantly higher in the preterm group early in pregnancy (13w0d-18w0d; P < 0.05) and higher early pregnancy cortisol associated with increased odds of preterm birth (at 13w0d; odds ratio, 1.007; 95% CI, 1.0002-1.014). Progesterone, cortisone, pregnanolone, and epipregnanolone did not associate with preterm birth.

Conclusion

The findings from our pilot study suggest potential utility of cortisol as a maternal serum biomarker for preterm birth risk assessment in early pregnancy. Further evaluation using larger cohorts and additional gestational timepoints for ALLO and the other analytes may be informative.

Development and validation of an LC-MS/MS assay for the quantification of allopregnanolone and its progesterone-derived isomers, precursors, and cortisol/cortisone in pregnancy

Neuroactive steroids are potent neuromodulators that play a critical role in both maternal and fetal health during pregnancy. These stress-responsive compounds are reportedly low in women with perinatal depression and may be associated with poor pregnancy outcomes in animal models. Chronic stress is a risk factor for adverse birth outcomes. Simultaneous quantification of neuroactive steroids, in combination with stress hormones cortisol/cortisone, provides an opportunity to investigate the synergistic relationship of these analytes within the convenience of one assay. A simple, reliable, and sensitive method for quantifying these endogenous compounds is necessary for further research with the potential to advance clinical diagnostic tools during pregnancy. Analytes were extracted from serum with a simple protein precipitation using methanol and then separated and quantified using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After online extraction, analytes were separated using an Agilent Poroschell 120, 50 × 4.6 mm, 2.7 μm particle size, EC-C18 analytical column. The reliable quantification range was from 0.78 to 1000 ng/mL. QC sample inter- and intraday trueness was between 90 and 110% while inter- and intraday imprecision was less than 10%. Extracted samples were stable up to 7 days at 4 °C and extraction recovery was above 95%. Serum samples from 54 women in pregnancy were analyzed using this method. Here, we provide a validated, fast, and specific assay with sufficient sensitivity that allows for simultaneous quantification of blood serum concentrations of allopregnanolone (3α-hydroxy-5α-pregnan-20-one), pregnanolone (3α-hydroxy-5β-pregnan-20-one), epipregnanolone (3β-hydroxy-5β-pregnan-20-one), pregnenolone, progesterone, cortisol, and cortisone in pregnancy for clinical study samples and clinical diagnostics.

Neurosteroid involvement in threatened preterm labour

Introduction

The neurosteroid allopregnanolone modulates oxytocin expression in the brain, and its effects arise from its action on the GABAA receptor. Whether neurosteroid levels and the function of the GABAA receptor are involved in the risk of preterm labour in pregnant women is unknown.

Methods

Pregnant women with (n = 16) or without (n = 20) threatened preterm labour (TPL) in gestational week 33 + 6 days to 37 + 0 days were studied prospectively with procedures including foetal heart rate monitoring, vaginal examination, ultrasound examination and blood tests to determine allopregnanolone, progesterone and oxytocin levels. The GABAA receptor function in both groups was measured with a saccadic eye velocity test (SEVT).

Results

Plasma oxytocin levels were higher in the TPL group than in the control group (41.5 vs. 37.0 pmol/L, respectively, p = .021). Although the allopregnanolone and progesterone levels in both groups did not differ, there was a negative association between blood oxytocin and allopregnanolone (as predictor) levels in the TPL group (B: -3.2, 95% confidence interval (CI): -5.5 to -0.9, p = .012). As a predictor of TPL, progesterone was associated with cervix maturity (odds ratio: 1.02, 95% CI: 1.00-1.04, p = .038). SEVT showed that the women in both groups had similar GABAA receptor functions. In both groups, body mass index correlated with peak saccadic eye velocity (r = .34, p = .044) and negatively with allopregnanolone (r = -.41, p = .013).

Conclusions

Neurosteroid levels were unchanged in the peripheral blood of women with TPL, despite the increase in available oxytocin. Although the function of the GABAA receptor was unchanged in women with TPL, to ensure reliable results, saccadic eye velocity should be investigated during a challenge test with a GABAA receptor agonist.

Neuroimmunology of the female brain across the lifespan: Plasticity to psychopathology

The female brain is highly dynamic and can fundamentally remodel throughout the normal ovarian cycle as well as in critical life stages including perinatal development, pregnancy and old-age. As such, females are particularly vulnerable to infections, psychological disorders, certain cancers, and cognitive impairments. We will present the latest evidence on the female brain; how it develops through the neonatal period; how it changes through the ovarian cycle in normal individuals; how it adapts to pregnancy and postpartum; how it responds to illness and disease, particularly cancer; and, finally, how it is shaped by old age. Throughout, we will highlight female vulnerability to and resilience against disease and dysfunction in the face of environmental challenges.

Reduced Neurosteroid Exposure Following Preterm Birth and Its' Contribution to Neurological Impairment: A Novel Avenue for Preventative Therapies

Children born preterm are at an increased risk of developing cognitive problems and neuro-behavioral disorders such as attention deficit hyperactivity disorder (ADHD) and anxiety. Whilst neonates born at all gestational ages, even at term, can experience poor cognitive outcomes due to birth-complications such as birth asphyxia, it is becoming widely known that children born preterm in particular are at significant risk for learning difficulties with an increased utilization of special education resources, when compared to their healthy term-born peers. Additionally, those born preterm have evidence of altered cerebral myelination with reductions in white matter volumes of the frontal cortex, hippocampus and cerebellum evident on magnetic resonance imaging (MRI). This disruption to myelination may underlie some of the pathophysiology of preterm-associated brain injury. Compared to a fetus of the same post-conceptional age, the preterm newborn loses access to in utero factors that support and promote healthy brain development. Furthermore, the preterm ex utero environment is hostile to the developing brain with a myriad of environmental, biochemical and excitotoxic stressors. Allopregnanolone is a key neuroprotective fetal neurosteroid which has promyelinating effects in the developing brain. Preterm birth leads to an abrupt loss of the protective effects of allopregnanolone, with a dramatic drop in allopregnanolone concentrations in the preterm neonatal brain compared to the fetal brain. This occurs in conjunction with reduced myelination of the hippocampus, subcortical white matter and cerebellum; thus, damage to neurons, astrocytes and especially oligodendrocytes of the developing nervous system can occur in the vulnerable developmental window prior to term as a consequence reduced allopregnanolone. In an effort to prevent preterm-associated brain injury a number of therapies have been considered, but to date, other than antenatal magnesium sulfate and corticosteroid therapy, none have become part of standard clinical care for vulnerable infants. Therefore, there remains an urgent need for improved therapeutic options to prevent brain injury in preterm neonates. The actions of the placentally derived neurosteroid allopregnanolone on GABAA receptor signaling has a major role in late gestation neurodevelopment. The early loss of this intrauterine neurotrophic support following preterm birth may be pivotal to development of neurodevelopmental morbidity. Thus, restoring the in utero neurosteroid environment for preterm neonates may represent a new and clinically feasible treatment option for promoting better trajectories of myelination and brain development, and therefore reducing neurodevelopmental disorders in children born preterm.

Giving a good start to a new life via maternal brain allostatic adaptations in pregnancy

Successful pregnancy requires adjustments to multiple maternal homeostatic mechanisms, governed by the maternal brain to support and enable survival of the growing fetus and placenta. Such adjustments fit the concept of allostasis (stability through change) and have a cost: allostatic load. Allostasis is driven by ovarian, anterior pituitary, placental and feto-placental hormones acting on the maternal brain to promote adaptations that support the pregnancy and protect the fetus. Many women carry an existing allostatic load into pregnancy, from socio-economic circumstances, poor mental health and in 'developed' countries, also from obesity. These pregnancies have poorer outcomes indicating negative interactions (failing allostasis) between pre-pregnancy and pregnancy allostatic loads. Use of animal models, such as adult prenatally stressed female offspring with abnormal neuroendocrine, metabolic and behavioural phenotypes, to probe gene expression changes, and epigenetic mechanisms in the maternal brain in adverse pregnancies are discussed, with the prospect of ameliorating poor pregnancy outcomes.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABA_A), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.

Maternal hormonal milieu influence on fetal brain development

An adverse maternal hormonal environment during pregnancy can be associated with abnormal brain growth. Subtle changes in fetal brain development have been observed even for maternal hormone levels within the currently accepted physiologic ranges. In this review, we provide an update of the research data on maternal hormonal impact on fetal neurodevelopment, giving particular emphasis to thyroid hormones and glucocorticoids. Thyroid hormones are required for normal brain development. Despite serum TSH appearing to be the most accurate indicator of thyroid function in pregnancy, maternal serum free T4 levels in the first trimester of pregnancy are the major determinant of postnatal psychomotor development. Even a transient period of maternal hypothyroxinemia at the beginning of neurogenesis can confer a higher risk of expressive language and nonverbal cognitive delays in offspring. Nevertheless, most recent clinical guidelines advocate for targeted high-risk case finding during first trimester of pregnancy despite universal thyroid function screening. Corticosteroids are determinant in suppressing cell proliferation and stimulating terminal differentiation, a fundamental switch for the maturation of fetal organs. Not surprisingly, intrauterine exposure to stress or high levels of glucocorticoids, endogenous or synthetic, has a molecular and structural impact on brain development and appears to impair cognition and increase anxiety and reactivity to stress. Limbic regions, such as hippocampus and amygdala, are particularly sensitive. Repeated doses of prenatal corticosteroids seem to have short-term benefits of less respiratory distress and fewer serious health problems in offspring. Nevertheless, neurodevelopmental growth in later childhood and adulthood needs further clarification. Future studies should address the relevance of monitoring the level of thyroid hormones and corticosteroids during pregnancy in the risk stratification for impaired postnatal neurodevelopment.

Allopregnanolone promotes proliferation and differential gene expression in human glioblastoma cells

Allopregnanolone (3α-THP) is one of the main reduced progesterone (P₄) metabolites that is recognized as a neuroprotective and myelinating agent. 3α-THP also induces proliferation of different neural cells. It has been shown that P₄ favors the progression of glioblastomas (GBM), the most common and aggressive primary brain tumors. However, the role of 3α-THP in the growth of GBMs is unknown. Here, we studied the effects of 3α-THP on the number of cells, proliferation and gene expression in U87 cell line derived from a human GBM. 3α-THP (10, 100nM and 1μM) increased the number of U87 cells, and at 10nM exerted a similar increase in both the number of total and proliferative U87 cells as compared with P₄ (10nM). Interestingly, finasteride (F; 100nM), an inhibitor of 5α-reductase (5αR), an enzyme necessary to metabolize P₄ and produce 3α-THP, blocked the increase in the number of U87 cells induced by P₄. By using RT-qPCR, we determined that U87 cells express 5α-R isoenzymes 1 and 2 (5αR1 and 5αR2), being 5αR1 the predominant one in these cells. 3α-THP (10nM) increased the expression of TGFβ1, EGFR, VEGF and cyclin D1 genes. P₄ increased TGFβ1 and EGFR expression, and this effect was blocked by F. These data provide evidence that P₄, through its metabolite 3α-THP, can promote in part cell proliferation of human GBM cells by changing the expression of genes involved in tumor progression.

5α-reduced progestogens ameliorate mood-related behavioral pathology, neurotoxicity, and microgliosis associated with exposure to HIV-1 Tat

Human immunodeficiency virus (HIV) is associated with motor and mood disorders, likely influenced by reactive microgliosis and subsequent neural damage. We have recapitulated aspects of this pathology in mice that conditionally express the neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat). Progestogens may attenuate Tat-related behavioral impairments and reduce neurotoxicity in vitro, perhaps via progesterone's 5α-reductase-dependent metabolism to the neuroprotective steroid, allopregnanolone. To test this, ovariectomized female mice that conditionally expressed (or did not express) central HIV-1 Tat were administered vehicle or progesterone (4mg/kg), with or without pretreatment of a 5α-reductase inhibitor (finasteride, 50mg/kg). Tat induction significantly increased anxiety-like behavior in an open field, elevated plus maze and a marble burying task concomitant with elevated protein oxidation in striatum. Progesterone administration attenuated anxiety-like effects in the open field and elevated plus maze, but not in conjunction with finasteride pretreatment. Progesterone also attenuated Tat-promoted protein oxidation in striatum, independent of finasteride pretreatment. Concurrent experiments in vitro revealed Tat (50nM)-mediated reductions in neuronal cell survival over 60h, as well as increased neuronal and microglial intracellular calcium, as assessed via fura-2 AM fluorescence. Co-treatment with allopregnanolone (100nM) attenuated neuronal death in time-lapse imaging and blocked the Tat-induced exacerbation of intracellular calcium in neurons and microglia. Lastly, neuronal-glial co-cultures were labeled for Iba-1 to reveal that Tat increased microglial numbers in vitro and co-treatment with allopregnanolone attenuated this effect. Together, these data support the notion that 5α-reduced pregnane steroids exert protection over the neurotoxic effects of HIV-1 Tat.

Effects of Subchronic Finasteride Treatment and Withdrawal on Neuroactive Steroid Levels and Their Receptors in the Male Rat Brain

The enzymatic conversion of progesterone and testosterone by the enzyme 5alpha-reductase exerts a crucial role in the control of nervous function. The effects of finasteride in the brain, an inhibitor of this enzyme used for the treatment of human benign prostatic hyperplasia and androgenic alopecia, have been poorly explored. Therefore, the effects of a subchronic treatment with finasteride at low doses (3 mg/kg/day) and the consequences of its withdrawal on neuroactive steroid levels in plasma, cerebrospinal fluid and some brain regions as well as on the expression of classical and non-classical steroid receptors have been evaluated in male rats. After subchronic treatment (i.e., for 20 days) the following effects were detected: (i) depending on the compartment considered, alteration in the levels of neuroactive steroids, not only in 5alpha-reduced metabolites but also in its precursors and in neuroactive steroids from other steroidogenic pathways and (ii) an upregulation of the androgen receptor in the cerebral cortex and beta3 subunit of the GABA-A receptor in the cerebellum. One month after the last treatment (i.e., withdrawal period), some of these effects persisted (i.e., the upregulation of the androgen receptor in the cerebral cortex, an increase of dihydroprogesterone in the cerebellum, a decrease of dihydrotestosterone in plasma). Moreover, other changes in neuroactive steroid levels, steroid receptors (i.e., an upregulation of the estrogen receptor alpha and a downregulation of the estrogen receptor beta in the cerebral cortex) and GABA-A receptor subunits (i.e., a decrease of alpha 4 and beta 3 mRNA levels in the cerebral cortex) were detected. These findings suggest that finasteride treatment may have broad consequences for brain function.

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.

Programming the brain and behaviour by early-life stress: a focus on neuroactive steroids

Animal studies have amply demonstrated that stress exposure during pregnancy or in early postnatal life can adversely influence brain development and have long-term 'programming' effects on future brain function and behaviour. Furthermore, a growing body of evidence from human studies supports the hypothesis that some psychiatric disorders may have developmental origins. Here, the focus is on three adverse consequences of early-life stress: dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, heightened anxiety behaviour and cognitive impairments, with review of what is known about the underlying central mechanisms. Neuroactive steroids modulate neuronal activity and play a key role in neurodevelopment. Moreover they can negatively modulate activity of the HPA axis, exert anxiolytic actions and influence cognitive performance. Thus, neuroactive steroids may provide a link between early-life stress and the resultant adverse effects on the brain and behaviour. Here, a role for neuroactive steroids, in particular the 5α-reduced/3α-hydroxylated metabolites of progesterone, testosterone and deoxycorticosterone, is discussed in the context of early-life stress. Furthermore, the impact of early-life stress on the brain's capacity to generate neurosteroids is considered and the evidence for an ability of neuroactive steroids to over-write the negative effects of early-life stress on the brain and behaviour is examined. An enhanced understanding of the influence of early-life stress on brain neurosteroid systems could aid the identification of new targets for developing treatments for stress-related conditions in humans.

Implications of prenatal steroid perturbations for neurodevelopment, behavior, and autism

The prenatal brain develops under the influence of an ever-changing hormonal milieu that includes endogenous fetal gonadal and adrenal hormones, placental and maternal hormones, and exogenous substances with hormonal activity that can cross the placental barrier. This review discusses the influences of endogenous fetal and maternal hormones on normal brain development and potential consequences of pathophysiological hormonal perturbations to the developing brain, with particular reference to autism. We also consider the effects of hormonal pharmaceuticals used for assisted reproduction, the maintenance of pregnancy, the prevention of congenital adrenal hypertrophy, and hormonal contraceptives continued into an unanticipated pregnancy, among others. These treatments, although in some instances life-saving, may have unintended consequences on the developing fetuses. Additional concern is raised by fetal exposures to endocrine-disrupting chemicals encountered universally by pregnant women from food/water containers, contaminated food, household chemicals, and other sources. What are the potential outcomes of prenatal steroid perturbations on neurodevelopmental and behavioral disorders, including autism-spectrum disorders? Our purposes here are 1) to summarize some consequences of steroid exposures during pregnancy for the development of brain and behavior in the offspring; 2) to summarize what is known about the relationships between exposures and behavior, including autism spectrum disorders; 3) to discuss the molecular underpinnings of such effects, especially molecular epigenetic mechanisms of prenatal steroid manipulations, a field that may explain effects of direct exposures, and even transgenerational effects; and 4) for all of these, to add cautionary notes about their interpretation in the name of scientific rigor.

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.

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.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

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.

Allopregnanolone and induction of endogenous opioid inhibition of oxytocin responses to immune stress in pregnant rats

In virgin rats, systemic administration of interleukin (IL)-1β (i.e. to mimic infection), increases oxytocin secretion and the firing rate of oxytocin neurones in the supraoptic nucleus (SON). However, in late pregnancy, stimulated oxytocin secretion is inhibited by an endogenous opioid mechanism, preserving the expanded neurohypophysial oxytocin stores for parturition and minimising the risk of preterm labour. Central levels of the neuroactive metabolite of progesterone, allopregnanolone, increase during pregnancy and allopregnanolone acting on GABA(A) receptors on oxytocin neurones enhances inhibitory transmission. In the present study, we tested whether allopregnanolone induces opioid inhibition of the oxytocin system in response to IL-1β in late pregnancy. Inhibition of 5α-reductase (an allopregnanolone-synthesising enzyme) with finasteride potentiated IL-1β-evoked oxytocin secretion in late pregnant rats, whereas allopregnanolone reduced the oxytocin response in virgin rats. IL-1β increased the number of magnocellular neurones in the SON and paraventricular nucleus (PVN) expressing Fos (an indicator of neuronal activation) in virgin but not pregnant rats. In immunoreactive oxytocin neurones in the SON and PVN, finasteride increased IL-1β-induced Fos expression in pregnant rats. Conversely, allopregnanolone reduced the number of magnocellular oxytocin neurones activated by IL-1β in virgin rats. Treatment with naloxone (an opioid antagonist) greatly enhanced the oxytocin response to IL-1β in pregnancy, and finasteride did not enhance this effect, indicating that allopregnanolone and the endogenous opioid mechanisms do not act independently. Indeed, allopregnanolone induced opioid inhibition over oxytocin responses to IL-1β in virgin rats. Thus, in late pregnancy, allopregnanolone induces opioid inhibition over magnocellular oxytocin neurones and hence on oxytocin secretion in response to immune challenge. This mechanism will minimise the risk of preterm labour and prevent the depletion of neurohypophysial oxytocin stores, which are required for parturition.

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.

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.