Changes in 5alpha-pregnane steroids and neurosteroidogenic enzyme expression in fetal sheep with umbilicoplacental embolization

Profiling neuroactive steroids in pregnancy. A non-derivatised liquid chromatography tandem mass spectrometry method for the quantitation of allopregnanolone and four related isomers in maternal serum

Neuroactive steroids are metabolites of progesterone, synthesised during pregnancy by the placenta. Here, we describe development of a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for quantitation of allopregnanolone, pregnanolone, isopregnanolone, epipregnanolone and allopregnan-20α-ol-3-one in maternal serum. Following addition of deuterated internal standards, 200 μL of serum was subjected to solid phase extraction. Chromatography was performed using a pentafluorophenyl column, and LC-MS/MS on a Sciex 6500+. Sample injection volume was 20 μL, and injection-to-injection time 10.0 min. The assay was validated according to published guidelines; assay linearity and lower limit of quantification were suitable for analysis of each steroid in maternal serum, for all analytes mean recoveries were 100 % ± 15 %, intra- and inter-assay imprecision <15 %, and matrix effects negligible, and specificity experiments confirmed nil interference from a wide range of endogenous metabolites of progesterone. The method was applied to human serum samples obtained from a large cohort of third trimester pregnancies which were subsequently characterised by normal fetal and maternal outcomes, and relationships between maternal neuroactive steroid concentrations and fetal gestational age assessed. Positive correlations between maternal serum concentration and fetal gestational age were observed for isopregnanolone, allopregnanolone and allopregnan-20α-ol-3-one. The LC-MS/MS method offers significant advantages over previously published approaches for quantitation of neuroactive steroids in human maternal serum, notably obviating the need for derivatisation, whilst achieving exceptional specificity. Characterisation of normal maternal neuroactive steroid concentrations will aid future research as dysregulated placental progesterone metabolism is observed in pregnancies with poor outcomes.

Protection from oxygen-glucose deprivation by neurosteroid treatment in primary neurons and oligodendrocytes

Preterm birth results in an increased risk of neonatal brain injury and neurobehavioural disorders. Despite the seriousness of these adverse outcomes, there are currently no effective therapies to protect the vulnerable developing brain. We propose that neurosteroid replacement therapy may be a novel approach in reducing detrimental neurological outcomes following preterm birth. The use of guinea pig primary neuronal and oligodendrocyte cultures with relevance to late gestation allows insight into the mechanisms behind the effectiveness of these treatments. Primary neuronal and oligodendrocyte cultures were derived from fetal guinea pig frontal cortex brain tissue at gestational age 62 (GA62). Cell cultures were pre-treated with either etifoxine (5 µM) or zuranolone (1 µm) for 24 h prior to insult. Cells were then exposed to either oxygen-glucose deprivation (OGD; 0% O2 and no glucose DMEM; preterm birth insult) or sham (standard cell culture conditions; 25 mM DMEM) for 2 h. Lactate dehydrogenase assay (LDH) was performed following OGD as a measure of cytotoxicity. Relative mRNA expression of key neuronal and oligodendrocyte markers, as well as neuronal receptors and transporters, were quantified using high throughput (Fluidigm) RT-PCR. OGD significantly increased cellular cytotoxicity in both neurons and oligodendrocytes. Additionally, key neuronal marker mRNA expression was reduced following OGD, and oligodendrocytes displayed arrested mRNA expression of key markers of lineage progression. Treatment with etifoxine restored a number of parameters back to control levels, whereas treatment with zuranolone provided a robust improvement in all parameters examined. This study has demonstrated the neuroprotective potential of neurosteroid replacement therapy in a model of hypoxia related to preterm birth. Neuroprotection appears to be mediated through glutamate reduction and increased brain derived neurotrophic factor (BDNF). Future work is warranted in examining these treatments in vivo, with the overall aim to suppress preterm associated brain damage and reduce long term outcomes for affected offspring.

Prenatal Stress Induces Translational Disruption Associated with Myelination Deficits

Disruptions to neurodevelopment are known to be linked to behavioral disorders in childhood and into adulthood. The fetal brain is extremely vulnerable to stimuli that alter inhibitory GABAergic pathways and critical myelination processes, programing long-term neurobehavioral disruption. The maturation of the GABAergic system into the major inhibitory pathway in the brain and the development of oligodendrocytes into mature cells capable of producing myelin are integral components of optimal neurodevelopment. The current study aimed to elucidate prenatal stress-induced mechanisms that disrupt these processes and to delineate the role of placental pathways in these adverse outcomes. Pregnant guinea pig dams were exposed to prenatal stress with strobe light exposure for 2 h/day on gestational age (GA) 35, 40, 45, 50, 55, 60, and 65, and groups of fetuses and placentae were collected after the stress exposure on GA40, GA50, GA60, and GA69 (term). Fetal plasma, placental, and brain tissue were collected for allopregnanolone and cortisol quantification with ELISA. Relative mRNA expression of genes of specific pathways of interest was examined with real-time PCR in placental and hippocampal tissue, and myelin basic protein (MBP) was quantified immunohistochemically in the hippocampus and surrounding regions for assessment of mature myelin. Prenatal stress in mid-late gestation resulted in disruptions to the translational machinery responsible for the production of myelin and decreased myelin coverage in the hippocampus and surrounding regions. The male placenta showed an initial protective increase in allopregnanolone concentrations in response to maternal psychosocial stress. The male and female placentae had a sex-dependent increase in neurosteroidogenic enzymes at term following prenatal stress. Independent from exposure to prenatal stress, at gestational day 60 - a critical period for myelin development, the placentae of female fetuses had increased capability of preventing cortisol transfer to the fetus through expression of 11-beta-hydroxysteroid dehydrogenase types 1 and 2. The deficits early in the process of maturation of myelination indicate that the reduced myelination observed at childhood equivalence in previous studies begins in fetal life. This negative programing persists into childhood, potentially due to dysregulation of MBP translation processes. Expression patterns of neurosteroidogenic enzymes in the placenta at term following stress may identify at-risk fetuses that have been exposed to a stressful in utero environment.

Lack of placental neurosteroid alters cortical development and female somatosensory function

Placental endocrine function is essential to fetal brain development. Placental hormones include neurosteroids such as allopregnanolone (ALLO), a regulator of neurodevelopmental processes via positive allosteric modulation of the GABAA receptor (GABAA-R). Using a mouse model (plKO) in which the gene encoding the ALLO synthesis enzyme is specifically deleted in trophoblasts, we previously showed that placental ALLO insufficiency alters cerebellar white matter development and leads to male-specific autistic-like behavior. We now demonstrate that the lack of placental ALLO causes female-predominant alterations of cortical development and function. Placental ALLO insufficiency disrupts cell proliferation in the primary somatosensory cortex (S1) in a sex-linked manner. Early changes are seen in plKO embryos of both sexes, but persist primarily in female offspring after birth. Adolescent plKO females show significant reduction in pyramidal neuron density, as well as somatosensory behavioral deficits as compared with plKO males and control littermates. Assessment of layer-specific markers in human postmortem cortices suggests that preterm infants may also have female-biased abnormalities in cortical layer specification as compared with term infants. This study establishes a novel and fundamental link between placental function and sex-linked long-term neurological outcomes, emphasizing the importance of the growing field of neuroplacentology.

The Current Status of Neuroprotection in Congenital Heart Disease

Neurological deficits are a serious and common sequelae of congenital heart disease (CHD). While their underlying mechanisms have not been fully characterized, their manifestations are well-known and understood to persist through adulthood. Development of therapies to address or prevent these deficits are critical to attenuate future morbidity and improve quality of life. In this review, we aim to summarize the current status of neuroprotective therapy in CHD. Through an exploration of present research in the pre-operative, intra-operative, and post-operative phases of patient management, we will describe existing clinical and bench efforts as well as current endeavors underway within this research area.

Maternally derived hormones, neurosteroids and the development of behaviour

In a wide range of taxa, there is evidence that mothers adaptively shape the development of offspring behaviour by exposing them to steroids. These maternal effects have major implications for fitness because, by shaping early development, they can permanently alter how offspring interact with their environment. However, theory on parent-offspring conflict and recent physiological studies showing that embryos rapidly metabolize maternal steroids have placed doubt on the adaptive significance of these hormone-mediated maternal effects. Reconciling these disparate perspectives requires a mechanistic understanding of the pathways by which maternal steroids can influence neural development. Here, we highlight recent advances in developmental neurobiology and psychiatric pharmacology to show that maternal steroid metabolites can have direct neuro-modulatory effects potentially shaping the development of neural circuitry underlying ecologically relevant behavioural traits. The recognition that maternal steroids can act through a neurosteroid pathway has critical implications for our understanding of the ecology and evolution of steroid-based maternal effects. Overall, compared to the classic view, a neurosteroid mechanism may reduce the evolutionary lability of hormone-mediated maternal effects owing to increased pleiotropic constraints and frequently influence long-term behavioural phenotypes in offspring.

Progesterone Actions During Central Nervous System Development

Although progesterone is a steroid hormone mainly associated with female reproductive functions, such as uterine receptivity and maintenance of pregnancy, accumulating data have shown its physiological actions to extend to several non-reproductive functions in the central nervous system (CNS) both in males and females. In fact, progesterone is de novo synthesized in specific brain regions by neurons and glial cells and is involved in the regulation of various molecular and cellular processes underlying myelination, neuroprotection, neuromodulation, learning and memory, and mood. Furthermore, progesterone has been reported to be implicated in critical developmental events, such as cell differentiation and neural circuits formation. This view is supported by the increase in progesterone synthesis observed during pregnancy in both the placenta and the fetal brain. In the present review, we will focus on progesterone actions during CNS development.

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.

Brain intracrinology of allopregnanolone during pregnancy and hormonal contraception

Allopregnanolone (ALLO) has a crucial role in brain development and remodeling. Reproductive transitions associated with endocrine changes affect synthesis and activity of ALLO with behavioral/affective consequences. Pregnancy is characterized by an increased synthesis of progesterone/ALLO by the placenta, maternal and fetal brains. This suggests the critical role of these steroids in maternal brain adaptation during pregnancy and the development of the fetal brain. ALLO is brain protective during complications of pregnancy, such as preterm delivery or intrauterine growth restriction (IUGR), reducing the impact of hypoxia, and excitotoxic brain damage. Negative behavioral consequences of altered progesterone/ALLO maternal brain adaptation have been also hypothesized in the post-partum and targeting ALLO is a promising treatment. Hormonal contraception may alter ALLO action, although the effects are mostly related to a specific class of progestins. Understanding the interactions between ALLO and the endocrine environment is crucial for more effective and tailored hormonal treatments.

Hormonal Changes Associated With Intra-Uterine Growth Restriction: Impact on the Developing Brain and Future Neurodevelopment

The environment in which a fetus develops is not only important for its growth and maturation but also for its long-term postnatal health and neurodevelopment. Several hormones including glucocorticosteroids, estrogens and progesterone, insulin growth factor and thyroid hormones, carefully regulate the growth of the fetus and its metabolism during pregnancy by controlling the supply of nutrients crossing the placenta. In addition to fetal synthesis, hormones regulating fetal growth are also expressed and regulated in the placenta, and they play a key role in the vulnerability of the developing brain and its maturation. This review summarizes the current understanding and evidence regarding the involvement of hormonal dysregulation associated with intra-uterine growth restriction and its consequences on brain development.

Effects of progesterone on the neonatal brain following hypoxia-ischemia

Progesterone displays a strong potential for the treatment of neonatal hypoxic-ischemic encephalopathy since it has been shown to be beneficial in the treatment of the central nervous system injuries in adult animals. Here, we evaluated the effects of the administration of progesterone (10 mg/kg) in seven-days-old male Wistar rats submitted to neonatal hypoxia-ischemia (HI). Progesterone was administered immediately before ischemia and/or 6 and 24 h after the onset of hypoxia. The body weight of the animals, the volume of brain lesion and the expression of p-Akt and procaspase-3 in the hippocampus were evaluated. All animals submitted to HI showed a reduction in the body weight. However, this reduction was more remarkable in those animals which received progesterone before surgery. Administration of progesterone was unable to reduce the volume of brain damage caused by HI. Moreover, no significant differences were observed in the expression of p-Akt and procaspase-3 in animals submitted to HI and treated with either progesterone or vehicle. In summary, progesterone did not show a neuroprotective effect on the volume of brain lesion in neonatal rats submitted to hypoxia-ischemia. Furthermore, progesterone was unable to modulate p-Akt and procaspase-3 signaling pathways, which may explain the absence of neuroprotection. On the other hand, it seems that administration of progesterone before ischemia exerts some systemic effect, leading to a remarkable reduction in the body weight.

Effects of combined IUGR and prenatal stress on the development of the hippocampus in a fetal guinea pig model

Intrauterine growth restriction (IUGR) and maternal stress during pregnancy are two compromises that negatively impact neurodevelopment and increase the risk of developing later life neuropsychiatric disorders such as schizophrenia, depression and behavioural disorders. Neurosteroids, particularly allopregnanolone, are important in protecting the developing brain and promoting many essential neurodevelopmental processes. Individually, IUGR and prenatal stress (PS) reduce myelination and neurogenesis within affected fetal brains, however less information is available on the combined effects of these two disorders on the term fetal brain. This study aimed to investigate how IUGR and PS impairs the neurosteroid pathway when combined using a guinea pig model, and how these then disrupt the neurodevelopment of the fetus. Uterine artery blood flow restriction was performed at GA30-35 to induce growth restriction, whilst PS was induced by exposure of the dam to a strobe light during gestation commencing GA40 and repeated every 5 days. Exposure in this model caused reductions in hippocampal CA1 MBP immunostaining of male fetuses in both IUGR alone and IUGR+PS paradigms but only by IUGR in the subcortical white mater, compared with control males. Plasma allopregnanolone was reduced by both stressors irrespective of sex, whereas GFAP or MAP2 expression were not affected by either stressor. Female neurodevelopment, as assessed by these markers, was unimpeded by these compromises. The addition of prenatal stress did not further compound these deficits.

Blocked, delayed, or obstructed: What causes poor white matter development in intrauterine growth restricted infants?

Poor white matter development in intrauterine growth restricted (IUGR) babies remains a major, untreated problem in neonatology. New therapies, guided by an understanding of the mechanisms that underlie normal and abnormal oligodendrocyte development and myelin formation, are required. Much of our knowledge of the mechanisms that underlie impaired myelination come from studies in adult demyelinating disease, preterm brain injury, or experimental models of hypoxia-ischemia. However, relatively less is known for IUGR which is surprising because IUGR is a leading cause of perinatal mortality and morbidity, second only to premature birth. IUGR is also a significant risk factor for the later development of cerebral palsy, and is a greater risk compared to some of the more traditionally researched antecedents - asphyxia and inflammation. Recent evidence suggests that the white matter injury and reduced myelination in the brains of some preterm babies is due to impaired maturation of oligodendrocytes thereby resulting in the reduced capacity to synthesize myelin. Therefore, it is not surprising that the hypomyelination observable in the central nervous system of IUGR infants has similarly lead to investigations identifying a delay or blockade in the progress of maturation of oligodendrocytes in these infants. This review will discuss current ideas thought to account for the poor myelination often present in the neonate's brain following IUGR, and discuss novel interventions that are promising as treatments that promote oligodendrocyte maturation, and thereby repair the myelination deficits that otherwise persist into infancy and childhood and lead to neurodevelopmental abnormalities.

The fetal brain: role of progesterone and allopregnanolone

Progesterone and allopregnanolone have crucial and different roles in brain development, function and recovery after injury. Pregnancy is characterized by an increased synthesis of progesterone and its neuro-active metabolites by the placenta, maternal and fetal brain. This supports the critical role of these steroids in maternal brain adaptation during pregnancy and development of the fetal brain. Moreover, allopregnanolone may play a brain-protective role during complications of pregnancy, complications of pregnancy, such as preterm delivery or intrauterine growth restriction (IUGR), by reducing the impact of hypoxia and excitotoxic brain damage or impairment myelination. Behavioral consequences of altered progesterone/allopregnanolone fetal brain programming have also been hypothesized, although further evidence is needed. New potential applications of allopregnanolone as a treatment strategy have also been proposed, addressing unmet clinical needs in perinatal care.

Removal of stigmasterol from Kraft mill effluent by aerobic biological treatment with steroidal metabolite detection

Stigmasterol is a phytosterol contained in Kraft mill effluent that is able to increase over 100% after aerobic biological treatment. This compound can act as an endocrine disrupter as its structure is similar to that of cholesterol. The aim of this study was to evaluate the removal of stigmasterol from Kraft mill effluents treated by a moving bed biofilm reactor (MBBR) with steroidal metabolite detection. The MBBR was operated for 145 days, with a hydraulic retention time of 2 days. Stigmasterol and steroidal metabolites were detected by gas chromatography with a flame ionization detector during MBBR operation. The results show that the MBBR removed 87.4% of biological oxygen demand (BOD5), 61.5% of chemical oxygen demand (COD), 24.5% of phenol and 31.5% of lignin, expressed in average values. The MBBR system successfully removed 100% of the stigmasterol contained in the influent (33 µg L(-1)) after 5 weeks of operation. In that case, the organic load rate was 0.343 kg COD m(-3) d(-1). Furthermore, different steroidal compounds (e.g., testosterone propionate, stigmast-4-en-3-one, 5α-pregnan-12-one-20α-hydroxy, 5α-pregnane-3,11,20-trione and 3α-hydroxy-5α-androstane-11,17-dione were detected in the Kraft mill effluent as potential products of phytosterol biotransformation.

Long-term effects of prenatal progesterone exposure: neurophysiological development and hospital admissions in twins up to 8 years of age

OBJECTIVES

To perform a neurophysiological follow-up at 48 or 60 months of age in children exposed prenatally to progesterone compared with a placebo and evaluate their medical histories up to 8 years of age.

METHODS

In this study, Danish participants of the PREDICT study, including 989 surviving children from 498 twin pregnancies, were followed-up. PREDICT was a placebo-controlled randomized clinical trial examining the effect of progesterone for prevention of preterm delivery in unselected twin pregnancies. Medical histories of the children were reviewed and neurophysiological development was evaluated by the parent-completed Ages and Stages Questionnaire (ASQ) at either 48 or 60 months after the estimated date of delivery. We used the method of generalized estimating equation to account for the correlation within twins.

RESULTS

A total of 492 children had been exposed prenatally to progesterone and 497 to placebo. There was no difference in the number of admissions to or length of stay in hospital between the treatment groups, and we found no overall difference in the rates of diagnoses made. However, the odds ratios (ORs) for a diagnosis concerning the heart was 1.66 (95% CI, 0.81-3.37), favoring placebo, among all children, 2.38 (95% CI, 1.07-5.30) in dichorionic twins and 8.19 (95% CI, 1.02-65.6) in all children when excluding diagnoses made at outpatient clinic visits. ASQ scores were available for 437 children (progesterone, n = 225; placebo, n = 212). Mean ASQ score was slightly higher in the progesterone group compared with the placebo group (P = 0.03). In dichorionic twins, the risk of having a low ASQ score (< 10(th) centile) was decreased in the progesterone group (OR, 0.34 (95% CI, 0.14-0.86)).

CONCLUSION

Second- and third-trimester exposure of the fetus to progesterone does not seem to have long-term harmful effects during childhood, but future studies should focus on cardiac disease in the child. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Loss of neurosteroid-mediated protection following stress during fetal life

Elevated levels of neurosteroids during late gestation protect the fetal brain from hypoxia/ischaemia and promote neurodevelopment. Suppression of allopregnanolone production during pregnancy leads to the onset of seizure-like activity and potentiates hypoxia-induced brain injury. Markers of myelination are reduced and astrocyte activation is increased. The placenta has a key role in maintaining allopregnanolone concentrations in the fetal circulation and brain during gestation and levels decline markedly after both normal and preterm birth. This leads to the preterm neonate developing in a neurosteroid deficient environment between delivery and term equivalence. The expression of 5α-reductases is also lower in the fetus prior to term. These deficiencies in neurosteroid exposure may contribute to the increase in incidence of the adverse patterns of behaviour seen in children that are born preterm. Repeated exposure to glucocorticoid stimulation suppresses 5α-reductase expression and allopregnanolone levels in the fetus and results in reduced myelination. Both fetal growth restriction and prenatal maternal stress lead to increased cortisol concentrations in the maternal and fetal circulation. Prenatal stress results in reduced expression of key GABAA receptor subunits that normally heighten neurosteroid sensitivity. These stressors also result in altered placental allopregnanolone metabolism pathways. These findings suggest that reduced neurosteroid production and action in the perinatal period may contribute to some of the adverse neurodevelopmental and behavioural outcomes that result from these pregnancy compromises. Studies examining perinatal steroid supplementation therapy with non-metabolisable neurosteroid analogues to improve these outcomes are warranted.

Comparative aspects of neurosteroidogenesis: From fish to mammals

It is now clearly established that the central and peripheral nervous systems have the ability to synthesize de novo steroids referred to as neurosteroids. The major evidence for biosynthesis of neuroactive steroids by nervous tissues is based on the expression of enzymes implicated in the formation of steroids in neural cells. The aim of the present review is to summarize the current knowledge regarding the presence of steroidogenic enzymes in the brain of vertebrates and to highlight the very considerable contribution of Professor Kazuyoshi Tsutsui in this domain. The data indicate that expression of steroid-producing enzymes in the brain appeared early during vertebrate evolution and has been preserved from fish to mammals.

Injury of the developing cerebellum: a brief review of the effects of endotoxin and asphyxial challenges in the late gestation sheep fetus

The vulnerability of the fetal and newborn brain to events in utero or at birth that cause damage arising from perturbations of cerebral blood flow and metabolism, such as the accumulation of free radicals and excitatory transmitters to neurotoxic levels, has received considerable attention over the last few decades. Attention has usually been on the damage to cerebral structures, particularly, periventricular white matter. The rapid growth of the cerebellum in the latter half of fetal life in species with long gestations, such as the human and sheep, suggests that this may be a particularly important time for the development of cerebellar structure and function. In this short review, we summarize data from recent studies with fetal sheep showing that the developing cerebellum is particularly sensitive to infectious processes, chronic hypoxia and asphyxia. The data demonstrates that the cerebellum should be further studied in insults of this nature as it responds differently to the remainder of the brain. Damage to this region of the brain has implications not only for the development of motor control and posture, but also for higher cognitive processes and the subsequent development of complex behaviours, such as learning, memory and attention.

Preterm birth affects GABAA receptor subunit mRNA levels during the foetal-to-neonatal transition in guinea pigs

Modulation of gamma-aminobutyric acid A (GABAA) receptor signalling by the neurosteroid allopregnanolone has a major role in late gestation neurodevelopment. The objective of this study was to characterize the mRNA levels of GABAA receptor subunits (α4, α5, α6 and δ) that are key to neurosteroid binding in the brain, following preterm birth. Myelination, measured by the myelin basic protein immunostaining, was used to assess maturity of the preterm brains. Foetal guinea pig brains were obtained at 62 days’ gestational age (GA, preterm) or at term (69 days). Neonates were delivered by caesarean section, at 62 days GA and term, and maintained until tissue collection at 24 h of age. Subunit mRNA levels were quantified by RT-PCR in the hippocampus and cerebellum of foetal and neonatal brains. Levels of the α6 and δ subunits were markedly lower in the cerebellum of preterm guinea pigs compared with term animals. Importantly, there was an increase in mRNA levels of these subunits during the foetal-to-neonatal transition at term, which was not seen following preterm birth. Myelination was lower in preterm neonatal brains, consistent with marked immaturity. Salivary cortisol concentrations, measured by EIA, were also higher for the preterm neonates, suggesting greater stress. We conclude that there is an adaptive increase in the levels of mRNA of the key GABAA receptor subunits involved in neurosteroid action after term birth, which may compensate for declining allopregnanolone levels. The lower levels of these subunits in preterm neonates may heighten the adverse effect of the premature decline in neurosteroid exposure.

Increased placental neurosteroidogenic gene expression precedes poor outcome in the preterm guinea pig

Placental 5α-reductase (5αR) is influenced by in utero compromises and has a role in regulating neuroactive steroid concentrations in the fetus. The objective of this study was to determine if changes in placental 5αR were associated with neonatal outcome after birth. Guinea pigs were delivered by cesarean section at term (GA69, n=22) or preterm (GA62, n=36) and the placenta collected. Preterm neonates were maintained for 24 h unless their condition deteriorated before this time. Enzyme mRNA expression of 5αR type-1 and 5αR type-2 were determined using real-time PCR. All preterm neonates had significantly higher 5αR2 expression in their placenta compared with placentae from term neonates (P<0.0001). Expression was also markedly higher in the placentae from neonates that did not survive until 24 h, compared with surviving preterm neonates (P=0.04). These findings suggest differences of in utero neurosteroidogenic capacity between surviving and non-surviving preterm guinea pig neonates. The increased 5αR2 mRNA expression in the placenta of non-survivors suggests an induction of the neurosteroid pathway due to prior exposure to an in utero compromise, with such exposure possibly a predisposing factor that contributed to their poor ex utero outcome.

Neuroactive steroids in pregnancy: key regulatory and protective roles in the foetal brain

Neuroactive steroid concentrations are remarkably high in the foetal brain during late gestation. These concentrations are maintained by placental progesterone synthesis and the interaction of enzymes in the placenta and foetal brain. 5α-Pregnane-3α-ol-20-one (allopregnanolone) is a key neuroactive steroid during foetal life, although other 3α-hydroxy-pregnanes may make an additional contribution to neuroactive steroid action. Allopregnanolone modulates GABAergic inhibition to maintain a suppressive action on the foetal brain during late gestation. This action suppresses foetal behaviour and maintains the appropriate balance of foetal sleep-like behaviours, which in turn are important to normal neurodevelopment. Neuroactive steroid-induced suppression of excitability has a key role in protecting the foetal brain from acute hypoxia/ischaemia insults. Hypoxia-induced brain injury is markedly increased if neuroactive steroid levels are suppressed and there is increased seizure activity. There is also a rapid increase in allopregnanolone synthesis and hence levels in response to acute stress that acts as an endogenous protective mechanism. Allopregnanolone has a trophic role in regulating development, maintaining normal levels of apoptosis and increasing myelination during late gestation in the brain. In contrast, chronic foetal stressors, including intrauterine growth restriction, do not increase neuroactive steroid levels in the brain and exposure to repeated synthetic corticosteroids reduce neuroactive steroid levels. The reduced availability of neuroactive steroids may contribute to the adverse effects of chronic stressors on the foetal and newborn brain. Preterm birth also deprives the foetus of neuroactive steroid mediated protection and may increase vulnerability to brain injury and suboptimal development. These finding suggest replacement therapies should be explored. This article is part of a Special Issue entitled 'Pregnancy and steroids'.

Changes in neuroactive steroid concentrations after preterm delivery in the Guinea pig

BACKGROUND

Preterm birth is a major cause of neurodevelopmental disorders. Allopregnanolone, a key metabolite of progesterone, has neuroprotective and developmental effects in the brain. The objectives of this study were to measure the neuroactive steroid concentrations following preterm delivery in a neonatal guinea pig model and assess the potential for postnatal progesterone replacement therapy to affect neuroactive steroid brain and plasma concentrations in preterm neonates.

METHODS

Preterm (62-63 days) and term (69 days) guinea pig pups were delivered by cesarean section and tissue was collected at 24 hours. Plasma progesterone, cortisol, allopregnanolone, and brain allopregnanolone concentrations were measured by immunoassay. Brain 5α-reductase (5αR) expression was determined by Western blot. Neurodevelopmental maturity of preterm neonates was assessed by immunohistochemistry staining for myelination, glial cells, and neurons.

RESULTS

Brain allopregnanolone concentrations were significantly reduced after birth in both preterm and term neonates. Postnatal progesterone treatment in preterm neonates increased brain and plasma allopregnanolone concentrations. Preterm neonates had reduced myelination, low birth weight, and high mortality compared to term neonates. Brain 5αR expression was also significantly reduced in neonates compared to fetal expression.

CONCLUSIONS

Delivery results in a loss of neuroactive steroid concentrations resulting in a premature reduction in brain allopregnanolone in preterm neonates. Postnatal progesterone therapy reestablished neuroactive steroid levels in preterm brains, a finding that has implications for postnatal growth following preterm birth that occurs at a time of neurodevelopmental immaturity.

Progesterone synthesis in the nervous system: implications for myelination and myelin repair

Progesterone is well known as a female reproductive hormone and in particular for its role in uterine receptivity, implantation, and the maintenance of pregnancy. However, neuroendocrine research over the past decades has established that progesterone has multiple functions beyond reproduction. Within the nervous system, its neuromodulatory and neuroprotective effects are much studied. Although progesterone has been shown to also promote myelin repair, its influence and that of other steroids on myelination and remyelination is relatively neglected. Reasons for this are that hormonal influences are still not considered as a central problem by most myelin biologists, and that neuroendocrinologists are not sufficiently concerned with the importance of myelin in neuron functions and viability. The effects of progesterone in the nervous system involve a variety of signaling mechanisms. The identification of the classical intracellular progesterone receptors as therapeutic targets for myelin repair suggests new health benefits for synthetic progestins, specifically designed for contraceptive use and hormone replacement therapies. There are also major advantages to use natural progesterone in neuroprotective and myelin repair strategies, because progesterone is converted to biologically active metabolites in nervous tissues and interacts with multiple target proteins. The delivery of progesterone however represents a challenge because of its first-pass metabolism in digestive tract and liver. Recently, the intranasal route of progesterone administration has received attention for easy and efficient targeting of the brain. Progesterone in the brain is derived from the steroidogenic endocrine glands or from local synthesis by neural cells. Stimulating the formation of endogenous progesterone is currently explored as an alternative strategy for neuroprotection, axonal regeneration, and myelin repair.

Neurosteroids and GABA(A) Receptor Interactions: A Focus on Stress

Since the pioneering discovery of the rapid CNS depressant actions of steroids by the "father of stress," Hans Seyle 70 years ago, brain-derived "neurosteroids" have emerged as powerful endogenous modulators of neuronal excitability. The majority of the intervening research has focused on a class of naturally occurring steroids that are metabolites of progesterone and deoxycorticosterone, which act in a non-genomic manner to selectively augment signals mediated by the main inhibitory receptor in the CNS, the GABA(A) receptor. Abnormal levels of such neurosteroids associate with a variety of neurological and psychiatric disorders, suggesting that they serve important physiological and pathophysiological roles. A compelling case can be made to implicate neurosteroids in stress-related disturbances. Here we will critically appraise how brain-derived neurosteroids may impact on the stress response to acute and chronic challenges, both pre- and postnatally through to adulthood. The pathological implications of such actions in the development of psychiatric disturbances will be discussed, with an emphasis on the therapeutic potential of neurosteroids for the treatment of stress-associated disorders.

The effect of betamethasone treatment on neuroactive steroid synthesis in a foetal Guinea pig model of growth restriction

There are ongoing concerns that antenatal corticosteroids, which are administered to women at high risk of delivering preterm to reduce the incidence of respiratory distress syndrome, have adverse effects on foetal brain development and subsequent effects on behaviour and learning, when administered as repeated courses. The present study aimed to examine whether repeated betamethasone treatment alters the expression of the key-rate limiting enzyme, 5alpha-reductase, in the synthetic pathway of the potent neuroactive steroid allopregnanolone in the brain and placenta and whether this effect is potentiated in growth restricted foetuses. To investigate this, pregnant guinea pigs carrying either control (sham surgery) or growth-restricted foetuses were treated with vehicle or betamethasone (1 mg/kg/day) for 4 days prior to sacrifice (65d). Placental insufficiency was induced by the ablation of uterine artery branches supplying each placenta at mid gestation, resulting in foetal growth restriction characterised by 'brain sparing'. Real-time reverse transcriptase polymerase chain reaction was used to determine relative 5alpha-reductase type 1 and 2 mRNA expression in the placenta and brain. Immunohistochemistry was used to examine the glial fibrillary acidic protein (GFAP) expression in the subcortical white matter, CA1 and dentate regions of the hippocampus. 5alpha-reductase type 2 mRNA expression in the brain was markedly reduced by betamethasone treatment in male foetuses compared to vehicle-treated controls but not in female foetuses. In addition, 5alpha-reductase type 1 expression in the brain was increased by growth restriction and/or betamethasone treatment in female foetuses but expression in males foetuses did not increase. 5alpha-reductase type 2 expression in the placenta was markedly reduced by betamethasone treatment compared to vehicle-treated control. Intrauterine growth restriction and betamethasone treatment reduced GFAP expression in the CA1 region of the hippocampus in the brains of male but not female foetuses. These data indicate that betamethasone treatment suppresses placental expression and has sexually dimorphic effects on expression of neuroactive steroid synthetic enzymes in the brain. These actions may lead to adverse effects on the developing brain, particularly in male foetuses, such as the observed effects on GFAP expression.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Neurosteroids in the fetus and neonate: Potential protective role in compromised pregnancies

Complications during pregnancy and birth asphyxia lead to brain injury, with devastating consequences for the neonate. In this paper we present evidence that the steroid environment during pregnancy and at birth aids in protecting the fetus and neonate from asphyxia-induced injury. Earlier studies show that the placental progesterone production has a role in the synthesis and release of neuroactive steroids or their precursors into the fetal circulation. Placental precursor support leads to remarkably high concentrations of allopregnanolone in the fetal brain and to a dramatic decline with the loss of the placenta at birth. These elevated concentrations influence the distinct behavioral states displayed by the late gestation fetus and exert a suppressive effect that maintains sleep-like behavioral states that are present for much of fetal life. This suppression reduces CNS excitability and suppresses excitotoxicity. With the availability of adequate precursors, mechanisms within the fetal brain ultimately control neurosteroid levels. These mechanisms respond to episodes of acute hypoxia by increasing expression of 5alpha-reductase and P450scc enzymes and allopregnanolone synthesis in the brain. This allopregnanolone response, and potentially that of other neurosteroids including 5alpha-tetrahydrodeoxycorticosterone (TH-DOC), reduces hippocampal cell death following acute asphyxia and suggests that stimulation of neurosteroid production may protect the fetal brain. Importantly, inhibition of neurosteroid synthesis in the fetal brain increases the basal cell death suggesting a role in controlling developmental processes late in gestation. Synthesis of neurosteroid precursors in the fetal adrenal such as deoxycorticosterone (DOC), and their conversion to active neurosteroids in the fetal brain may also have a role in neuroprotection. This suggests that the adrenal glands provide precursor DOC for neurosteroid synthesis after birth and this may lead to a switch from allopregnanolone alone to neuroprotection mediated by allopregnanolone and TH-DOC.

Inhibition of neurosteroid synthesis increases asphyxia-induced brain injury in the late gestation fetal sheep

Allopregnanolone (AP) is a potent GABAergic agonist that suppresses CNS activity, seizure threshold, and excitotoxicity in the adult brain. AP is present in the fetal sheep brain and increases rapidly after asphyxial insult due to increased 5alpha-reductase type-2 (5alphaR-2) expression. The aim of this study was to use finasteride to suppress fetal neurosteroid synthesis, and then determine the effect on brain injury, particularly in the hippocampus, of asphyxia induced in utero by brief occlusion of the umbilical cord. Catheters and an inflatable umbilical cord cuff were implanted in fetal sheep at approximately 125 days gestation. Five days later the fetuses received either finasteride (20 mg/kg/h) or vehicle (40% hydroxypropyl-beta-cyclodextrin) for 2 h. The umbilical cord was occluded (UCO) for 5 min at 30 min after starting the infusion. The fetal brain was obtained 24 h later for examination of activated caspase-3 expression as an index of apoptosis, and to measure AP content. Finasteride treatment alone significantly reduced AP content and increased the number of caspase-3 positive cells in the hippocampus, cerebellum, and the subcallosal bundle, indicating that AP modulates the normal rate of apoptosis in the developing brain. UCO in vehicle and finasteride-treated fetuses produced a similar, marked decrease in O2 saturation (5.8+/-0.6%), but after finasteride treatment UCO caused a significantly greater increase in the number of caspase-3 positive cells in the hippocampal cornu ammonis 3 (CA3) (57.3+/-1.6%) compared with the vehicle-treated fetuses. Thus, 5alpha-reduced steroids such as AP may be protective in reducing cell death following acute fetal asphyxia. Perturbation of normal fetal neurosteroid levels in late gestation (e.g. due to preterm birth, or maternal synthetic steroid treatment to induce fetal lung maturation) could adversely affect brain development and increase its vulnerability to injury.

Hypoxia Potentiates Endotoxin-Induced Allopregnanolone Concentrations in the Newborn Brain

BACKGROUND

Allopregnanolone is a neurosteroid produced in the brain that can alter the excitability of the CNS. Neurosteroids have neuroprotective properties, and their elevation in response to stress may protect the newborn brain following infection or hypoxia. Infection, particularly of the respiratory tract, may lead to episodes of hypoxia. Infection and hypoxia have been identified as factors contributing to neonatal morbidity and mortality.

OBJECTIVES

To determine the effect of acute episodes of hypoxia alone or in combination with lipopolysaccharide (LPS) exposure on plasma and brain allopregnanolone concentrations in lambs 10-21 days old. Also, to examine plasma levels of cortisol and the cytokines, tumour necrosis factor-alpha and interleutkin-6 after these challenges.

RESULTS

Allopregnanolone concentrations in the brain were markedly increased after hypoxia. Hypoxia following prior LPS treatment resulted in greater increases in brain allopregnanolone concentrations compared to either the LPS or hypoxia treatment alone. Importantly, brain regions unaffected by LPS or hypoxia alone (thalamus/hypothalamus, cerebellum) showed significant increases of allopregnanolone content following the combined LPS and hypoxia treatments. Plasma tumour necrosis factor-alpha and interleukin-6 concentrations were increased after LPS treatment with and without hypoxia, but not by hypoxia alone. In contrast, plasma cortisol concentrations were increased after both stressors.

CONCLUSIONS

These results show that the brain of young lambs readily responds to physiological stress by increased production of allopregnanolone. This response may protect the developing brain from the cytotoxicity following hypoxic and infectious episodes.

Stress in pregnancy activates neurosteroid production in the fetal brain

Neurosteroids such as allopregnanolone are potent agonists at the GABA(A) receptor and suppress the fetal CNS activity. These steroids are synthesized in the fetal brain either from cholesterol or from circulating precursors derived from the placenta. The concentrations of allopregnanolone are remarkably high in the fetal brain and rise further in response to acute hypoxic stress, induced by constriction of the umbilical cord. This response may result from the increased 5alpha-reductase and cytochrome P-450(SCC) expression in the brain. These observations suggest that the rise in neurosteroid concentrations in response to acute hypoxia may represent an endogenous protective mechanism that reduces excitotoxicity following hypoxic stress in the developing brain. In contrast to acute stress, chronic hypoxemia induces neurosteroidogenic enzyme expression without an increase in neurosteroid concentrations and, therefore, may pose a greater risk to the fetus. At birth, the allopregnanolone concentrations in the brain fall markedly, probably due to the loss of placental precursors; however, stressors, including hypoxia and endotoxin-induced inflammation, raise allopregnanolone concentrations in the newborn brain. This may protect the newborn brain from hypoxia-induced damage. However, the rise in allopregnanolone concentrations was also associated with increased sleep. This rise in sedative steroid levels may depress arousal and contribute to the risk of sudden infant death syndrome. Our recent findings indicate that acute hypoxic stress in pregnancy initiates a neurosteroid response that may protect the fetal brain from hypoxia-induced cell death, whereas the decline in allopregnanolone levels after birth may result in greater vulnerability to brain injury in neonates.

Increased allopregnanolone levels in the fetal sheep brain following umbilical cord occlusion

Allopregnanolone (AP) is a potent modulator of the GABAA receptor. Brain AP concentrations increase in response to stress, which is thought to provide neuroprotection by reducing excitation in the adult brain. Umbilical cord occlusion (UCO) causes hypoxia and asphyxia in the fetus, which are major risk factors associated with poor neurological outcome for the neonate, and may lead to adverse sequelae such as cerebral palsy. The aims of this study were as follows: (i) to determine the effect of 10 min UCO on AP concentrations in the extracellular fluid of the fetal brain using microdialysis, and (ii) to compare the content of the steroidogenic enzymes P450scc and 5alpha-reductase type II (5alphaRII) with brain and CSF neurosteroid concentrations. UCO caused fetal asphyxia, hypertension, bradycardia and respiratory acidosis, which returned to normal levels after 1-2 h. AP concentrations in dialysate samples from probes implanted in grey and white matter of the parietal cortex were significantly increased 1 h after UCO from control levels of 10.4 +/- 0.4 and 12.4 +/- 0.3 to 26.0 +/- 5.1 and 27.6 +/- 6.4 nmol l(-1), respectively (P < 0.05), before returning to pre-occlusion levels by 3-4 h after UCO. When fetal brains were collected 1 h after a 10 min UCO, the relative increases of AP and pregnenolone content in the parietal cortex were similar to the increase observed in the extracellular (dialysate) fluid. AP, but not pregnenolone, was increased in CSF at this time. P450scc and 5alphaRII enzyme expression was significantly increased in the cerebral cortex in the UCO fetuses compared to control fetuses. These results suggest that the fetal brain is capable of transiently increasing neurosteroid production in response to asphyxia. The action of the increased neurosteroid content at GABAA receptors may serve to diminish the increased excitation due to excitotoxic amino acid release, and provide short-term protection to brain cells during such stress.