Neonatal estradiol exposure to female rats changes GABAA receptor expression and function, and spatial learning during adulthood

Polymorphism of Estrogen Receptor Genes and Its Interactions With Neurodevelopmental Genes in Attention Deficit Hyperactivity Disorder Among Chinese Han Descent

OBJECTIVE

Attention deficit hyperactivity disorder (ADHD) is a polygenic neurodevelopmental disorder with significant gender differences. The sexual dimorphism of ADHD may be associated with estrogen acting through estrogen receptors (ESR). This study investigates the impact of ESR gene polymorphism and its interactions with neurodevelopmental genes on ADHD susceptibility.

METHODS

The study compared genotyping data of single nucleotide polymorphisms in ESR1 and ESR2 in 1,035 ADHD cases and 962 controls. The gene-gene interactions between ESR genes and three neurodevelopmental genes (brain-derived neurotrophic factor [BDNF], synaptosomal-associated protein of 25 kDa gene [SNAP25], and cadherin-13 [CDH13]) in ADHD were investigated using generalized multifactor dimensionality reduction and verified by logistic regression analysis.

RESULTS

The G allele of rs960070/ESR2 (empirical p=0.0076) and the A allele of rs8017441/ESR2 (empirical p=0.0426) were found significantly higher in ADHD cases than in the controls but not in male or female subgroups. Though no difference was found in all subjects or females, the A allele of rs9340817/ESR1 (empirical p=0.0344) was found significantly higher in ADHD cases than controls in males. We also found genetic interaction models between ESR2 gene, neurodevelopmental genes and ADHD susceptibility in males (ESR2 rs960070/BDNF rs6265/BDNF rs2049046/SNAP25 rs362987/CDH13 rs6565113) and females (ESR2 rs960070/BDNF rs6265/BDNF rs2049046) separately, though it was negative in overall subjects.

CONCLUSION

The ESR gene polymorphism associates with ADHD among Chinese Han children, with interactions between ESR genes and neurodevelopmental genes potentially influencing the susceptibility of ADHD.

Estrogenic Modulation of Ionic Channels, Pumps and Exchangers in Airway Smooth Muscle

To preserve ionic homeostasis (primarily Ca²⁺, K⁺, Na⁺, and Cl^-), in the airway smooth muscle (ASM) numerous transporters (channels, exchangers, and pumps) regulate the influx and efflux of these ions. Many of intracellular processes depend on continuous ionic permeation, including exocytosis, contraction, metabolism, transcription, fecundation, proliferation, and apoptosis. These mechanisms are precisely regulated, for instance, through hormonal activity. The lipophilic nature of steroidal hormones allows their free transit into the cell where, in most cases, they occupy their cognate receptor to generate genomic actions. In the sense, estrogens can stimulate development, proliferation, migration, and survival of target cells, including in lung physiology. Non-genomic actions on the other hand do not imply estrogen's intracellular receptor occupation, nor do they initiate transcription and are mostly immediate to the stimulus. Among estrogen's non genomic responses regulation of calcium homeostasis and contraction and relaxation processes play paramount roles in ASM. On the other hand, disruption of calcium homeostasis has been closely associated with some ASM pathological mechanism. Thus, this paper intends to summarize the effects of estrogen on ionic handling proteins in ASM. The considerable diversity, range and power of estrogens regulates ionic homeostasis through genomic and non-genomic mechanisms.

The Allopregnanolone Response to Acute Stress in Females: Preclinical and Clinical Studies

The neuroactive steroid allopregnanolone ((3α,5α)-3-hydroxypregnan-20-one or 3α,5α-THP) plays a key role in the response to stress, by normalizing hypothalamic-pituitary-adrenal (HPA) axis function to restore homeostasis. Most studies have been conducted on male rats, and little is known about the allopregnanolone response to stress in females, despite that women are more susceptible than men to develop emotional and stress-related disorders. Here, we provide an overview of animal and human studies examining the allopregnanolone responses to acute stress in females in the context of stress-related neuropsychiatric diseases and under the different conditions that characterize the female lifespan associated with the reproductive function. The blunted allopregnanolone response to acute stress, often observed in female rats and women, may represent one of the mechanisms that contribute to the increased vulnerability to stress and affective disorders in women under the different hormonal fluctuations that occur throughout their lifespan. These studies highlight the importance of targeting neuroactive steroids as a therapeutic approach for stress-related disorders in women.

How hormonal contraceptives shape brain and behavior: A review of preclinical studies

Steroid hormones influence different aspects of brain function, including development, neurogenesis, neuronal excitability, and plasticity, thus affecting emotional states, cognition, sociality, and reward. In women, their levels fluctuate across the lifespan and through the reproductive stages but are also altered by exogenous administration of hormonal contraceptives (HC). HC are widely used by women throughout their fertile life both for contraceptive and therapeutic benefits. However, awareness of their effects on brain function and behavior is still poorly appreciated, despite the emerging evidence of their action at the level of the central nervous system. Here, we summarize results obtained in preclinical studies, mostly conducted in intact female rodents, aimed at investigating the neurobiological effects of HC. HC can alter neuroactive hormones, neurotransmitters, neuropeptides, as well as emotional states, cognition, social and sexual behaviors. Animal studies provide insights into the neurobiological effects of HC with the aim to improve women's health and well-being.

A Rationale for Allopregnanolone Treatment of Alcohol Use Disorders: Basic and Clinical Studies

For many years, research from around the world has suggested that the neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (allopregnanolone or 3α,5α-THP) may have therapeutic potential for treatment of various symptoms of alcohol use disorders (AUDs). In this critical review, we systematically address all the evidence that supports such a suggestion, delineate the etiologies of AUDs that are addressed by treatment with allopregnanolone or its precursor pregnenolone, and the rationale for treatment of various components of the disease based on basic science and clinical evidence. This review presents a theoretical framework for understanding how endogenous steroids that regulate the effects of stress, alcohol, and the innate immune system could play a key role in both the prevention and the treatment of AUDs. We further discuss cautions and limitations of allopregnanolone or pregnenolone therapy with suggestions regarding the management of risk and the potential for helping millions who suffer from AUDs.

Early postnatal allopregnanolone levels alteration and adult behavioral disruption in rats: Implication for drug abuse

Several studies have highlighted the role that early postnatal levels of allopregnanolone play in the development of the CNS and adult behavior. Changes in allopregnanolone levels related to stress have been observed during early postnatal periods, and perinatal stress has been linked to neuropsychiatric disorders. The alteration of early postnatal allopregnanolone levels in the first weeks of life has been proven to affect adult behaviors, such as anxiety-related behaviors and the processing of sensory inputs. This review focuses on the first studies about the possible relationship between the early postnatal allopregnanolone levels and the vulnerability to abuse of drugs such as alcohol in adulthood, given that (1) changes in neonatal allopregnanolone levels affect novelty exploration and novelty seeking has been linked to vulnerability to drug abuse; (2) early postnatal administration of progesterone, the main allopregnanolone precursor, affects the maturation of dopaminergic meso-striatal systems, which have been related to novelty seeking and drug abuse; and (3) alcohol consumption increases plasma and brain allopregnanolone levels in animals and humans. Manipulating neonatal allopregnanolone by administering finasteride, an inhibitor of the 5α-reductase enzyme that participates in allopregnanolone synthesis, increases alcohol consumption and decreases the locomotor stimulant effects of low alcohol doses. At a molecular level, finasteride decreases dopamine and serotonin in ventral striatum and dopamine release in nucleus accumbens. Preliminary results suggest that serotonin 5HT3 receptors could also be affected. Although an in-depth study is necessary, evidence suggests that there is a relation between early postnatal allopregnanolone and vulnerability to drug use/abuse.

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Early postnatal AlloP levels alteration affects brain maturation and adult behavior.

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Early stress interacts to AlloP influencing neuropsychiatric disorders vulnerability.

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Fluctuations in neonatal AlloP levels play a role in alcohol abuse vulnerability.

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Neonatal finasteride induces novelty-seeking profile and increases ethanol intake.

The brain as a target of hormonal contraceptives: Evidence from animal studies

Hormonal contraceptives are frequently prescribed drugs among women, mainly for their reversible contraceptive purposes but also for beneficial effects in some gynecological pathologies. Despite extensive studies aimed at elucidating the physical effects of hormonal contraceptives and ameliorating some unwanted outcomes, little is known yet about the effects of these drugs on brain function and related behavior, which are known to be modulated by endogenous steroid hormones. We describe the current literature on preclinical studies in animals undertaken to investigate effects of hormonal contraceptives on brain function and behavior. These studies suggest that hormonal contraceptives influence neurohormones, neurotransmitters, neuropeptides, and emotional, cognitive, social and sexual behaviors. Animals allow examination of the basic biological mechanisms of these drugs, devoid of the psychological aspect often associated to hormonal contraceptives' use in women. Understanding the neurobiological effects of these drugs may improve women's health and may help women making informed choices on hormonal contraception.

Microbiota alter metabolism and mediate neurodevelopmental toxicity of 17β-estradiol

Estrogenic chemicals are widespread environmental contaminants associated with diverse health and ecological effects. During early vertebrate development, estrogen receptor signaling is critical for many different physiologic responses, including nervous system function. Recently, host-associated microbiota have been shown to influence neurodevelopment. Here, we hypothesized that microbiota may biotransform exogenous 17-βestradiol (E2) and modify E2 effects on swimming behavior. Colonized zebrafish were continuously exposed to non-teratogenic E2 concentrations from 1 to 10 days post-fertilization (dpf). Changes in microbial composition and predicted metagenomic function were evaluated. Locomotor activity was assessed in colonized and axenic (microbe-free) zebrafish exposed to E2 using a standard light/dark behavioral assay. Zebrafish tissue was collected for chemistry analyses. While E2 exposure did not alter microbial composition or putative function, colonized E2-exposed larvae showed reduced locomotor activity in the light, in contrast to axenic E2-exposed larvae, which exhibited normal behavior. Measured E2 concentrations were significantly higher in axenic relative to colonized zebrafish. Integrated peak area for putative sulfonated and glucuronidated E2 metabolites showed a similar trend. These data demonstrate that E2 locomotor effects in the light phase are dependent on the presence of microbiota and suggest that microbiota influence chemical E2 toxicokinetics. More broadly, this work supports the concept that microbial colonization status may influence chemical toxicity.

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.

Impairment of learning and memory of mice offspring at puberty, young adulthood, and adulthood by low-dose Cd exposure during pregnancy and lactation via GABAAR α5 and δ subunits

Cadmium (Cd) is a pervasive carcinogen and environmental endocrine disruptor. We studied the changes in learning and memory of offspring mice, whose mothers were exposed to 10 mg Cd/L via the drinking water during pregnancy and lactation period, as well as the changes of testosterone and estrogen levels, serum Cd levels, the histopathological changes and the changes in the mRNA and protein levels of different subunits of γ-aminobutyric acid receptor subtype A subunits (G_ABA_ARs) in the hippocampus at the prepuberty, puberty, young adult, and adult stages. At birth, Cd had no obvious effect on mice offspring as statistically accessed based on their body weight, body length, and tail length (all p > 0.05). After grouped, the serum Cd levels increased in the three exposed groups more than in the normal control group at stages (all p < 0.05). Only serum estradiol of female offspring at age 7 weeks was significantly decreased compared with other groups (all p < 0.05). Histopathological results showed that the arrangement of the cells in hippocampal CA1 area of mice offspring was significantly sparse in the exposed groups compared with the control group. At 5 and 7 weeks, two Cd-exposed groups showed prolonged escape latency and exploring time for the platform compared with the normal group in the Morris water maze (all p < 0.05). Only increased protein expression of GABA_ARα5 was found in the Cd group at these two ages. At age 12 weeks, similar impaired learning and memory of female mice, and decreased protein expression of GABA_ARδ was found in Cd-exposed groups. Collectively, low-dose Cd had no effect on the growth of mice offspring but affected their learning and memory, especially female offspring, at puberty, young adulthood, and adulthood through changed structure in the hippocampal CA1 area and protein expression of GABA_ARα5 and GABA_ARδ.

Bilateral Olfactory Mucosa Damage Induces the Disappearance of Olfactory Glomerulus and Reduces the Expression of Extrasynaptic α5GABAARs in the Hippocampus in Early Postnatal Sprague Dawley Rats

Chloroform-induced olfactory mucosal degeneration has been reported in adult rats following gavage. We used fixed-point chloroform infusions on different postnatal days (PNDs) to investigate the effects of early olfactory bilateral deprivation on the main olfactory bulbs in Sprague Dawley rats. The experimental groups included rats infused with chloroform (5 μl) or saline (sham, 5 μl) on PNDs 3 and 8, and rats not receiving infusions (control) (n = 6 in all groups). Rats receiving chloroform on PND 3 showed significant hypoevolutism when compared to those in other groups (P < 0.05). There was a complete disappearance and a significant reduction in the size of olfactory glomeruli in the PND 3 and 8 groups, respectively, when compared to the respective sham groups. Rats receiving chloroform on PND 3 had significant memory impairment (P < 0.01) and increased levels of learned helplessness (P < 0.05), as measured using the Morris water maze and tail suspension tests, respectively. GABA_A receptor alpha5 subunit (α5GABA_AR) expression in hippocampal neurons was significantly lower in rats receiving chloroform on PND 3 than in rats in other groups (P < 0.01), as measured using immunohistochemistry and polymerase chain reaction. There was thus a critical period for the preservation of regenerative ability in olfactory receptor neurons, during which damage and olfactory deprivation led to altered rhinencephalon structure and disappearance of olfactory glomeruli, which induced hypoevolutism. Olfactory deprivation after the critical period had no significant effect on olfactory receptor neuron regeneration, leading to reduced developmental and behavioral effects in Sprague Dawley rats.

Estradiol increases the sensitivity of ventral tegmental area dopamine neurons to dopamine and ethanol

Gender differences in psychiatric disorders such as addiction may be modulated by the steroid hormone estrogen. For instance, 17β-estradiol (E2), the predominant form of circulating estrogen in pre-menopausal females, increases ethanol consumption, suggesting that E2 may affect the rewarding properties of ethanol and thus the development of alcohol use disorder in females. The ventral tegmental area (VTA) is critically involved in the rewarding and reinforcing effects of ethanol. In order to determine the role of E2 in VTA physiology, gonadally intact female mice were sacrificed during diestrus II (high E2) or estrus (low E2) for electrophysiology recordings. We measured the excitation by ethanol and inhibition by dopamine (DA) of VTA DA neurons and found that both excitation by ethanol and inhibition by dopamine were greater in diestrus II compared with estrus. Treatment of VTA slices from mice in diestrus II with an estrogen receptor antagonist (ICI 182,780) reduced ethanol-stimulated neuronal firing, but had no effect on ethanol-stimulated firing of neurons in slices from mice in estrus. Surprisingly, ICI 182,780 did not affect the inhibition by DA, indicating different mechanisms of action of estrogen receptors in altering ethanol and DA responses. We also examined the responses of VTA DA neurons to ethanol and DA in ovariectomized mice treated with E2 and found that E2 treatment enhanced the responses to ethanol and DA in a manner similar to what we observed in mice in diestrus II. Our data indicate that E2 modulates VTA neuron physiology, which may contribute to both the enhanced reinforcing and rewarding effects of alcohol and the development of other psychiatric disorders in females that involve alterations in DA neurotransmission.

Neurosteroid biosynthesis down-regulation and changes in GABAA receptor subunit composition: a biomarker axis in stress-induced cognitive and emotional impairment

By rapidly modulating neuronal excitability, neurosteroids regulate physiological processes, such as responses to stress and development. Excessive stress affects their biosynthesis and causes an imbalance in cognition and emotions. The progesterone derivative, allopregnanolone (Allo) enhances extrasynaptic and postsynaptic inhibition by directly binding at GABA_A receptors, and thus, positively and allosterically modulates the function of GABA. Allo levels are decreased in stress-induced psychiatric disorders, including depression and post-traumatic stress disorder (PTSD), and elevating Allo levels may be a valid therapeutic approach to counteract behavioural dysfunction. While benzodiazepines are inefficient, selective serotonin reuptake inhibitors (SSRIs) represent the first choice treatment for depression and PTSD. Their mechanisms to improve behaviour in preclinical studies include neurosteroidogenic effects at low non-serotonergic doses. Unfortunately, half of PTSD and depressed patients are resistant to current prescribed 'high' dosage of these drugs that engage serotonergic mechanisms. Unveiling novel biomarkers to develop more efficient treatment strategies is in high demand. Stress-induced down-regulation of neurosteroid biosynthesis and changes in GABA_A receptor subunit expression offer a putative biomarker axis to develop new PTSD treatments. The advantage of stimulating Allo biosynthesis relies on the variety of neurosteroidogenic receptors to be targeted, including TSPO and endocannabinoid receptors. Furthermore, stress favours a GABA_A receptor subunit composition with higher sensitivity for Allo. The use of synthetic analogues of Allo is a valuable alternative. Pregnenolone or drugs that stimulate its levels increase Allo but also sulphated steroids, including pregnanolone sulphate which, by inhibiting NMDA tonic neurotransmission, provides neuroprotection and cognitive benefits. In this review, we describe current knowledge on the effects of stress on neurosteroid biosynthesis and GABA_A receptor neurotransmission and summarize available pharmacological strategies that by enhancing neurosteroidogenesis are relevant for the treatment of SSRI-resistant patients. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Changes in stress-stimulated allopregnanolone levels induced by neonatal estradiol treatment are associated with enhanced dopamine release in adult female rats: reversal by progesterone administration

BACKGROUND

Allopregnanolone plays a role in the stress response and homeostasis. Alterations in the estrogen milieu during the perinatal period influence brain development in a manner that persists into adulthood. Accordingly, we showed that a single administration of estradiol benzoate (EB) on the day of birth decreases brain allopregnanolone concentrations in adult female rats.

OBJECTIVE

We examined whether the persistent decrease in allopregnanolone concentrations, induced by neonatal EB treatment, might affect sensitivity to stress during adulthood.

METHODS

Female rats were treated with 10 μg of EB or vehicle on the day of birth. During adulthood, the response to acute foot shock stress was assessed by measuring changes in brain allopregnanolone and corticosterone levels, as well as extracellular dopamine output in the medial prefrontal cortex (mPFC).

RESULTS

Neonatal EB treatment enhanced stress-stimulated allopregnanolone levels in the hypothalamus, as well as extracellular dopamine output in the mPFC; this latest effect is reverted by subchronic progesterone treatment. By contrast, neonatal EB treatment did not alter stress-induced corticosterone levels, sensitivity to hypothalamic-pituitary-adrenal (HPA) axis negative feedback, or abundance of glucocorticoid and mineralocorticoid receptors.

CONCLUSIONS

The persistent decrease in brain allopregnanolone concentrations, induced by neonatal EB treatment, enhances stress-stimulated allopregnanolone levels and extracellular dopamine output during adulthood. These effects are not associated to an impairment in HPA axis activity. Heightened sensitivity to stress is a risk factor for several neuropsychiatric disorders; these results suggest that exposure to estrogen during development may predispose individuals to such disorders.

Paired-Associative Stimulation-Induced Long-term Potentiation-Like Motor Cortex Plasticity in Healthy Adolescents

OBJECTIVE

The objective of this study was to evaluate the feasibility of using paired-associative stimulation (PAS) to study excitatory and inhibitory plasticity in adolescents while examining variables that may moderate plasticity (such as sex and environment).

METHODS

We recruited 34 healthy adolescents (aged 13-19, 13 males, 21 females). To evaluate excitatory plasticity, we compared mean motor-evoked potentials (MEPs) elicited by single-pulse transcranial magnetic stimulation (TMS) before and after PAS at 0, 15, and 30 min. To evaluate inhibitory plasticity, we evaluated the cortical silent period (CSP) elicited by single-pulse TMS in the contracted hand before and after PAS at 0, 15, and 30 min.

RESULTS

All participants completed PAS procedures. No adverse events occurred. PAS was well tolerated. PAS-induced significant increases in the ratio of post-PAS MEP to pre-PAS MEP amplitudes (p < 0.01) at all post-PAS intervals. Neither socioeconomic status nor sex was associated with post-PAS MEP changes. PAS induced significant CSP lengthening in males but not females.

CONCLUSION

PAS is a feasible, safe, and well-tolerated index of adolescent motor cortical plasticity. Gender may influence PAS-induced changes in cortical inhibition. PAS is safe and well tolerated by healthy adolescents and may be a novel tool with which to study adolescent neuroplasticity.