Estrogen-Dependent Functional Spine Dynamics in Neocortical Pyramidal Neurons of the Mouse

Increased gene dosage of RFWD2 causes autistic-like behaviors and aberrant synaptic formation and function in mice

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interactions, communication deficits and repetitive behaviors. A study of autistic human subjects has identified RFWD2 as a susceptibility gene for autism, and autistic patients have 3 copies of the RFWD2 gene. The role of RFWD2 as an E3 ligase in neuronal functions, and its contribution to the pathophysiology of ASD, remain unknown. We generated RFWD2 knockin mice to model the human autistic condition of high gene dosage of RFWD2. We found that heterozygous knockin (Rfwd2+/-) male mice exhibited the core symptoms of autism. Rfwd2+/- male mice showed deficits in social interaction and communication, increased repetitive and anxiety-like behavior, and spatial memory deficits, whereas Rfwd2+/- female mice showed subtle deficits in social communication and spatial memory but were normal in anxiety-like, repetitive, and social behaviors. These autistic-like behaviors in males were accompanied by a reduction in dendritic spine density and abnormal synaptic function on layer II/III pyramidal neurons in the prelimbic area of the medial prefrontal cortex (mPFC), as well as decreased expression of synaptic proteins. Impaired social behaviors in Rfwd2+/- male mice were rescued by the expression of ETV5, one of the major substrates of RFWD2, in the mPFC. These findings indicate an important role of RFWD2 in the pathogenesis of autism.

Kamishoyosan Normalizes Dendritic Spine Morphology in the Medial Prefrontal Cortex by Regulating microRNA-18 and Glucocorticoid Receptor Expressions in Postmenopausal Chronic Stress-Exposed Mice

OBJECTIVE

Kamishoyosan (KSS), a traditional Japanese Kampo medicine, is widely used to treat neuropsychiatric symptoms in perimenopausal and postmenopausal women. We aimed to elucidate the functional mechanisms underlying KSS-mediated reduction of stress response behaviors and neuropsychological symptoms in perimenopausal and postmenopausal women.

METHODS

Female mice were bilaterally ovariectomized (OVX) at the age of 12 weeks and exposed to chronic water immersion and restraint stress for three weeks. Among them, mice in the OVX+stress+KSS group were fed chow containing KSS from one week before exposure to chronic stress until the end of the experiment. Firstly, we performed a marble burying test and measured serum corticosterone levels to assess irritability and stress conditions. Next, we examined whether KSS affects microRNA-18 (miR-18) and glucocorticoid receptor (GR) protein expression, as well as the basal dendritic spine morphology of pyramidal neurons in the medial prefrontal cortex (mPFC) of postmenopausal chronic stress-exposed mice. Analyzed data were expressed as mean ± standard deviation. Tukey's post hoc test, followed by analysis of variance (ANOVA), was used for among-group comparisons.

RESULTS

KSS administration normalized chronic stress-induced unstable emotion-like behavior and upregulated plasma corticosterone levels. Furthermore, KSS ameliorated GR protein expression by downregulating miR-18 expression in the mPFC and recovered the immature morphological changes in spine formation of pyramidal neurons in the mPFC of OVX mice following chronic stress exposure.

CONCLUSIONS

KSS administration in postmenopausal chronic stress-exposed mice exerted anti-stress effects and improved the basal dendritic spine morphology of pyramidal neurons by regulating miR-18 and glucocorticoid receptor expression in the mPFC.

Cardiometabolic health, menopausal estrogen therapy and the brain: How effects of estrogens diverge in healthy and unhealthy preclinical models of aging

Research in preclinical models indicates that estrogens are neuroprotective and positively impact cognitive aging. However, clinical data are equivocal as to the benefits of menopausal estrogen therapy to the brain and cognition. Pre-existing cardiometabolic disease may modulate mechanisms by which estrogens act, potentially reducing or reversing protections they provide against cognitive decline. In the current review we propose mechanisms by which cardiometabolic disease may alter estrogen effects, including both alterations in actions directly on brain memory systems and actions on cardiometabolic systems, which in turn impact brain memory systems. Consideration of mechanisms by which estrogen administration can exert differential effects dependent upon health phenotype is consistent with the move towards precision or personalized medicine, which aims to determine which treatment interventions will work for which individuals. Understanding effects of estrogens in both healthy and unhealthy models of aging is critical to optimizing the translational link between preclinical and clinical research.

Steroid Hormone Interaction with Dendritic Spines: Implications for Neuropsychiatric Disease

Dendritic spines, key sites for neural plasticity, are influenced by gonadal steroids. In this chapter, we review the effects of gonadal steroids on dendritic spine density in areas important to cognitive function, the hippocampus, and prefrontal cortex. Most of these animal model studies investigated the effects of estrogen in females, but we also include more recent data on androgen effects in both males and females. The underlying genomic and non-genomic mechanisms related to gonadal steroid-induced spinogenesis are also reviewed. Subsequently, we discuss possible reasons for the observed sex differences in many neuropsychiatric diseases, which appear to be caused, in part, by aberrant synaptic connections that may involve dendritic spine pathology. Overall, knowledge concerning the regulation of dendritic spines by gonadal hormones has grown since the initial discoveries in the 1990s, and current research points to a potential role for aberrant spine functioning in many neuropsychiatric disorders.

Comprehensive Behavioral Analysis of Opsin 3 (Encephalopsin)-Deficient Mice Identifies Role in Modulation of Acoustic Startle Reflex

Opsin-3 (Opn3, encephalopsin) was the first nonvisual opsin gene discovered in mammals. Since then, several Opn3 functions have been described, and in two cases (adipose tissue, smooth muscle) light sensing activity is implicated. In addition to peripheral tissues, Opn3 is robustly expressed within the central nervous system, for which it derives its name. Despite this expression, no studies have investigated developmental or adult CNS consequences of Opn3 loss-of-function. Here, the behavioral consequences of mice deficient in Opn3 were investigated. Opn3-deficient mice perform comparably to wild-type mice in measures of motor coordination, socialization, anxiety-like behavior, and various aspects of learning and memory. However, Opn3-deficient mice have an attenuated acoustic startle reflex (ASR) relative to littermates. This deficit is not because of changes in hearing sensitivity, although Opn3 was shown to be expressed in auditory and vestibular structures, including cochlear outer hair cells. Interestingly, the ASR was not acutely light-dependent and did not vary between daytime and nighttime trials, despite known functions of Opn3 in photoreception and circadian gene amplitude. Together, these results demonstrate the first role of Opn3 on behavior, although the role of this opsin in the CNS remains largely elusive.

Loss of CaV1.3 RNA editing enhances mouse hippocampal plasticity, learning, and memory

L-type Ca_V1.3 calcium channels are expressed on the dendrites and soma of neurons, and there is a paucity of information about its role in hippocampal plasticity. Here, by genetic targeting to ablate Ca_V1.3 RNA editing, we demonstrate that unedited Ca_V1.3^ΔECS mice exhibited improved learning and enhanced long-term memory, supporting a functional role of RNA editing in behavior. Significantly, the editing paradox that functional recoding of Ca_V1.3 RNA editing sites slows Ca²⁺-dependent inactivation to increase Ca²⁺ influx but reduces channel open probability to decrease Ca²⁺ influx was resolved. Mechanistically, using hippocampal slice recordings, we provide evidence that unedited Ca_V1.3 channels permitted larger Ca²⁺ influx into the hippocampal pyramidal neurons to bolster neuronal excitability, synaptic transmission, late long-term potentiation, and increased dendritic arborization. Of note, RNA editing of the Ca_V1.3 IQ-domain was found to be evolutionarily conserved in mammals, which lends support to the importance of the functional recoding of the Ca_V1.3 channel in brain function.

Estradiol and Estrogen-like Alternative Therapies in Use: The Importance of the Selective and Non-Classical Actions

Estrogen is one of the most important female sex hormones, and is indispensable for reproduction. However, its role is much wider. Among others, due to its neuroprotective effects, estrogen protects the brain against dementia and complications of traumatic injury. Previously, it was used mainly as a therapeutic option for influencing the menstrual cycle and treating menopausal symptoms. Unfortunately, hormone replacement therapy might be associated with detrimental side effects, such as increased risk of stroke and breast cancer, raising concerns about its safety. Thus, tissue-selective and non-classical estrogen analogues have become the focus of interest. Here, we review the current knowledge about estrogen effects in a broader sense, and the possibility of using selective estrogen-receptor modulators (SERMs), selective estrogen-receptor downregulators (SERDs), phytoestrogens, and activators of non-genomic estrogen-like signaling (ANGELS) molecules as treatment.

A neural circuit perspective on brain aromatase

This review explores the role of aromatase in the brain as illuminated by a set of conserved network-level connections identified in several vertebrate taxa. Aromatase-expressing neurons are neurochemically heterogeneous but the brain regions in which they are found are highly-conserved across the vertebrate lineage. During development, aromatase neurons have a prominent role in sexual differentiation of the brain and resultant sex differences in behavior and human brain diseases. Drawing on literature primarily from birds and rodents, we delineate brain regions that express aromatase and that are strongly interconnected, and suggest that, in many species, aromatase expression essentially defines the Social Behavior Network. Moreover, in several cases the inputs to and outputs from this core Social Behavior Network also express aromatase. Recent advances in molecular and genetic tools for neuroscience now enable in-depth and taxonomically diverse studies of the function of aromatase at the neural circuit level.

The influence of estradiol and progesterone on neurocognition during three phases of the menstrual cycle: Modulating factors

Estradiol is an ovarian steroid hormone that peaks shortly before ovulation and significantly affects various brain regions and neurotransmitter systems, with similar and differential effects with progesterone, another ovarian hormone. Studies investigating the neurocognitive processes during the menstrual cycle have focused on the early follicular phase (EFP) characterized by low estradiol and progesterone levels and the mid-luteal phase (MLP) with high estradiol and progesterone levels. However, most studies have failed to include the ovulatory phase, characterized by high estradiol and low progesterone levels. Given the various hormonal changes in the menstrual cycle, we revisited studies suggesting that the menstrual cycle did not affect verbal and spatial abilities and observed that many contain mixed results. Comparing these studies makes it possible to identify relevant modulating factors, such as sample size, participant age, accurate selection of days for testing, asymmetrical practice effects, genetic polymorphisms, and task difficulty. More robust findings are related to improved mental rotation capacity during EFP with challenging tasks and differences in brain activation among menstrual cycle phases during the execution of spatial and verbal tasks. During MLP, less robust findings were observed, possibly modulated by the complex effects of the two hormones on the brain. In conclusion, we propose that it is crucial to include all three menstrual cycle phases and consider these modulating factors to avoid confounding findings.

Lithium therapy subdues neuroinflammation to maintain pyramidal cells arborization and rescues neurobehavioural impairments in ovariectomized rats

Oestrogen deprivation as a consequence of menopause alters the brain neuronal circuit and results in the development of neurobehavioural symptoms later. Hormone replacement therapy to some extent helps to overcome these abnormalities but is associated with various adverse events. Lithium therapy is being used to manage multiple neuropsychiatric disorders and is reported to maintain structural synaptic plasticity, suppress neuroinflammation, and promote adult neurogenesis. The present study examined the effect of lithium treatment on the neurobehavioural impairments in ovariectomized rat model mimicking clinical postmenopausal condition. A protective effect of lithium treatment was observed on the reconsolidation of spatial and recognition memory along with depression-like behaviour in ovariectomized rats. The Golgi-Cox staining revealed increased dendritic length and spine density in the pyramidal neurons of the CA1 region of the hippocampus, layer V of the somatosensory cortex, and layer II/III of the prefrontal cortex in the treated group. A significant reduction in pro-inflammatory markers, Il2, II6, and Il1b, was observed in the hippocampus, somatosensory cortex, and prefrontal cortex following lithium treatment. mRNA expression studies of Gfap and Pparg, along with histopathological analysis, suggested reactive astrogliosis to be a major contributor of neuroinflammation in ovariectomized rats that was normalized following lithium treatment. Further, the treatment inhibited Gsk-3β activity and maintained the normal level of β-catenin, CREB, and BDNF. The results revealed a defensive role of lithium against ovariectomy-induced neurobehavioural impairments, thus suggesting it to be a potential therapeutic agent for managing postmenopausal neurological symptoms.

Tamoxifen offers long-term neuroprotection after hippocampal silent infarct in male rats

Silent infarcts (SI) are a cerebral small vessel disease characterized by small subcortical infarcts. These occur in the absence of typical ischemia symptoms but are linked to cognitive decline and dementia. While there are no approved treatments for SI, recent results from our laboratory suggest that tamoxifen, a selective estrogen receptor modulator, is a viable candidate. In the present study, we induced SI in the dorsal hippocampal CA1 region of rats and assessed the effects of systemic administration of tamoxifen (5 mg/kg, twice) 21 days after injury on cognitive and pathophysiological measures, including cell loss, apoptosis, gliosis and estrogen receptors (ERs). We found that tamoxifen protected against the SI-induced cognitive dysfunction on the hippocampal-dependent, place recognition task, cell and ER loss, and increased apoptosis and gliosis in the CA1. Exploratory data analyses using a scatterplot matrix and principal component analysis indicated that SI-tamoxifen rats were indistinguishable from sham controls while they differed from SI rats, who were characterized by enhanced cell loss, apoptosis and gliosis, lower ERs, and recognition memory deficit. Supervised machine learning using support vector machine (SVM) determined predictors of progression from the early ischemic state to the dementia-like state. It showed that caspase-3 and ERα in the CA1 and exploration proportion were reliable and accurate predictors of this progression. Importantly, tamoxifen ameliorated SI-induced effects on all three of these variables, providing further evidence for its viability as a candidate treatment for SI and prevention of associated dementia.

Neural basis for estrous cycle-dependent control of female behaviors

Females display changes in distinct behaviors along the estrous cycle. Levels of circulating ovarian sex steroid hormones peak around ovulation, which occur around estrus phase of the cycle. This increase of sex hormones is thought to be important for changes in behaviors, however, neural circuit mechanisms of periodic behavioral changes in females are not understood well. Different lines of research indicate sex hormonal effects on several forms of neuronal plasticity. This review provides an overview of behavioral and plastic changes that occur in an estrous cycle-dependent manner and explores the current research linking these changes to understand neural circuit mechanisms that control female behaviors.

Treadmill Exercise Reverses the Change of Dendritic Morphology and Activates BNDF-mTOR Signaling Pathway in the Hippocampus and Cerebral Cortex of Ovariectomized Mice

A decline of estrogen level leads to spatial learning and memory impairments, which mediated by hippocampus and cortex. Accumulating evidences demonstrated that aerobic exercise improved memory of postmenopausal women and ovariectomized (OVX) mice. However, the molecular mechanisms for this protection of exercise are not completely clear. Accordingly, the present study was designed to examine the effect of aerobic exercise on the dendritic morphology in the hippocampus and cerebral cortex, as well as the BNDF-mTOR signaling pathway of OVX mice. Adult female C57BL/6 mice were divided into four groups (n = 10/group): sham-operated (SHAM/CON), sham-operated with 8-week treadmill exercise (SHAM/EX), ovariectomized operated (OVX/CON), and ovariectomized operated with exercise (OVX/EX). Aerobic exercise improved the impairment of dendritic morphology significantly induced by OVX that was tested by Golgi staining, and it also upregulated the synaptic plasticity-related protein expression of PSD95 and GluR1 as well as activated BDNF-mTOR signaling pathway in the hippocampus and cerebral cortex. In conclusion, aerobic exercise reversed the change of dendritic morphology and increased the synaptic plasticity-related protein expression in the hippocampus and cerebral cortex of OVX mice. The positive effects induced by exercise might be mediated through the BDNF-mTOR signaling pathway.

It takes a neural village: Circuit-based approaches for estrogenic regulation of episodic memory

Cognitive behaviors, such as episodic memory formation, are complex processes involving coordinated activity in multiple brain regions. However, much of the research on hormonal regulation of cognition focuses on manipulation of one region at a time or provides a single snapshot of how a systemic treatment affects multiple brain regions without investigating how these regions might interact to mediate hormone effects. Here, we use estrogenic regulation of episodic memory as an example of how circuit-based approaches may be incorporated into future studies of hormones and cognition. We first review basic episodic memory circuitry, rapid mechanisms by which 17β-estradiol can alter circuit activity, and current knowledge about 17β-estradiol's effects on episodic memory. Next, we outline approaches that researchers can employ to consider circuit effects in their estrogen research and provide examples of how these methods have been used to examine hormonal regulation of memory and other behaviors.

Synaptic effects of estrogen

The concept that estradiol may act as a local neuromodulator in the brain, rapidly affecting connectivity and synaptic function, has been firmly established by research over the last 30 years. De novo synthesis of estradiol within the brain as well as signaling mechanisms mediating responses to the hormone have been demonstrated, along with morphological evidence indicating rapid changes in synaptic input following increases in local estradiol levels. These rapid synaptic effects may play important roles in both physiological and pathophysiological responses to changes in circulating hormone levels, as well as in neurodegenerative disease. How local effects of estradiol on synaptic plasticity are integrated into changes in the overall activity of neural networks in the brain, however, remains a subject that is only incompletely understood.

Estrogenic regulation of memory: The first 50 years

This review highlights fifty years of progress in research on estradiol's role in regulating behavior(s). It was initially thought that estradiol was only involved in regulating estrus/menstrual cycles and concomitant sexual behavior, but it is now clear that estradiol also influences the higher order neural function of cognition. We provide a brief overview of estradiol's regulation of memory and some mechanisms which underlie its effects. Given systemically or directly into the hippocampus, to ovariectomized female rodents, estradiol or specific agonists, enhance learning and/or memory in a variety of rodent cognitive tasks. Acute (within minutes) or chronic (days) treatments enhance cognitive functions. Under the same treatment conditions, dendritic spine density on pyramidal neurons in the CA1 area of the hippocampus and medial prefrontal cortex increase which suggests that these changes are an important component of estrogen's ability to impact memory processes. Noradrenergic, dopaminergic and serotoninergic activity are also altered in these areas following estrogen treatments. Memory enhancements and increased spine density by estrogens are not limited to females but are also present in castrate males. In the next fifty years, neuroscientists need to determine how currently described neural changes mediate improved memory, how interactions among areas important for memory promote memory and the potential significance of neurally derived estrogens in normal cognitive processing. Answering these questions may provide significant advances for treatment of dementias as well as age and neuro-degenerative disease related memory loss.