Regulation of hippocampal synaptic plasticity by estrogen and progesterone

Rapid and local neuroestrogen synthesis supports long-term potentiation of hippocampal Schaffer collaterals-cornu ammonis 1 synapse in ovariectomized mice

In aging women, cognitive decline and increased risk of dementia have been associated with the cessation of ovarian hormones production at menopause. In the brain, presence of the key enzyme aromatase required for the synthesis of 17-β-estradiol (E2) allows for local production of E2 in absence of functional ovaries. Understanding how aromatase activity is regulated could help alleviate the cognitive symptoms. In female rodents, genetic or pharmacological reduction of aromatase activity over extended periods of time impair memory formation, decreases spine density, and hinders long-term potentiation (LTP) in the hippocampus. Conversely, increased excitatory neurotransmission resulting in rapid N-methyl-d-aspartic acid (NMDA) receptor activation rapidly promotes neuroestrogen synthesis. This rapid modulation of aromatase activity led us to address the hypothesis that acute neuroestrogens synthesis is necessary for LTP at the Schaffer collateral-cornu ammonis 1 (CA1) synapse in absence of circulating ovarian estrogens. To test this hypothesis, we did electrophysiological recordings of field excitatory postsynaptic potential (fEPSPs) in hippocampal slices obtained from ovariectomized mice. To assess the impact of neuroestrogens synthesis on LTP, we applied the specific aromatase inhibitor, letrozole, before the induction of LTP with a theta burst stimulation protocol. We found that blocking aromatase activity prevented LTP. Interestingly, exogenous E2 application, while blocking aromatase activity, was not sufficient to recover LTP in our model. Our results indicate the critical importance of rapid, activity-dependent local neuroestrogens synthesis, independent of circulating hormones for hippocampal synaptic plasticity in female rodents.

Roles of AMPA receptors in social behaviors

As a crucial player in excitatory synaptic transmission, AMPA receptors (AMPARs) contribute to the formation, regulation, and expression of social behaviors. AMPAR modifications have been associated with naturalistic social behaviors, such as aggression, sociability, and social memory, but are also noted in brain diseases featuring impaired social behavior. Understanding the role of AMPARs in social behaviors is timely to reveal therapeutic targets for treating social impairment in disorders, such as autism spectrum disorder and schizophrenia. In this review, we will discuss the contribution of the molecular composition, function, and plasticity of AMPARs to social behaviors. The impact of targeting AMPARs in treating brain disorders will also be discussed.

Sex hormone mediated change on flexion reflex

It has been shown that estrogen and progesterone receptors are expressed in the spinal cord; therefore, fluctuation in their concentrations may affect the spinal network and modulate the control of movement. Herein, we assessed the neuro-modulatory effect of sex hormones on the polysynaptic spinal network by using a flexion reflex network as a model system. Twenty-four healthy eumenorrheic women (age 21-37 years) were tested every other day for one menstrual cycle. Serum estradiol and progesterone were acquired at the time of testing. The flexion reflex of the tibialis anterior was elicited by sending an innocuous electrical stimulus directly to the posterior tibial nerve or plantar cutaneous afferent. Analyses were performed for each menstrual cycle phase: the follicular phase and the luteal phase. Increases in estradiol or progesterone concentrations were not associated with reflex duration or root mean squared (RMS) amplitude in either the follicular or luteal phases. In the luteal phase, an increase in the estradiol concentration was associated with a longer latency of the reflex (b = 0.23, p = 0.038). The estradiol × progesterone interaction was found towards significance (b = -0.017, p = 0.081). These results highlight the potential synergistic effect of estradiol and progesterone and may provide indirect confirmatory evidence of the observed modulatory effect.

Antidepressant-like effects of the Punica granatum and citalopram combination are associated with structural changes in dendritic spines of granule cells in the dentate gyrus of rats

Introduction: Natural products such as phytoestrogens-enriched foods or supplements have been considered as an alternative therapy to reduce depressive symptoms associated with menopause. It is known that the aqueous extract of Punica granatum (AE-PG) exerts antidepressant-like effects by activating β-estrogen receptors and facilitates the antidepressant response of the clinical drug citalopram (CIT). However, the effects on neuroplasticity are unknown. Objectvie investigated the antidepressant-like response of combining AE-PG and CIT at sub-optimal doses, analyzing their effects on the formation and maturation of dendrite spines in granule cells as well as on the dendrite complexity. Methods: Ovariectomized Wistar rats (3-month-old) were randomly assigned to one of the following groups: A) control (saline solution as vehicle of CIT and AE-PG, B) AE-PG at a sub-threshold dose (vehicle of CIT plus AE-PG at 0.125 mg/kg), C) CIT at a sub-threshold dose (0.77 mg/kg plus vehicle of AE-PG), and D) a combination of CIT plus AE-PG (0.125 mg/kg and 0.77 mg/kg, respectively). All rats were treated intraperitoneally for 14 days. Antidepressant-like effects were evaluated using the force swimming test test (FST). The complexity of dendrites and the number and morphology of dendrite spines of neurons were assessed in the dentate gyrus after Golgi-Cox impregnation. The expressions of the mature brain-derived neurotrophic factor (mBDNF) in plasma and of mBDNF and synaptophysin in the hippocampus, as markers of synaptogenesis, were also determined. Results: Administration of CIT combined with AE-PG, but not alone, induced a significant antidepressant-like effect in the FST with an increase in the dendritic complexity and the number of dendritic spines in the dentate gyrus (DG) of the hippocampus, revealed by the thin and stubby categories of neurons at the granular cell layer. At the same time, an increase of mBDNF and synaptophysin expression was observed in the hippocampus of rats that received the combination of AE-PG and CIT.

Effects of Stimulus Frequency, Intensity, and Sex on the Autonomic Response to Transcutaneous Vagus Nerve Stimulation

This study aimed to determine how transcutaneous vagus nerve stimulation (tVNS) alters autonomic nervous activity by comparing the effects of different tVNS frequencies and current intensities. We also investigated the sex-dependent autonomic response to tVNS. Thirty-five healthy adult participants were stimulated using a tVNS stimulator at the left cymba conchae while sitting on a reclining chair; tVNS-induced waveform changes were then recorded for different stimulus frequencies (Experiment 1: 3.0 mA at 100 Hz, 25 Hz, 10 Hz, 1 Hz, and 0 Hz (no stimulation)) and current intensities (Experiment 2: 100 Hz at 3.0 mA, 1.0 mA, 0.2 mA (below sensory threshold), and 0 mA (no stimulation)) using an electrocardiogram. Pulse widths were set at 250 µs in both experiment 1 and 2. Changes in heart rate (HR), root-mean-square of the difference between two successive R waves (RMSSD), and the ratio between low-frequency (LF) (0.04–0.15 Hz) and high-frequency (HF) (0.15–0.40 Hz) bands (LF/HF) in spectral analysis, which indicates sympathetic and parasympathetic activity, respectively, in heart rate variability (HRV), were recorded for analysis. Although stimulation at all frequencies significantly reduced HR (p = 0.001), stimulation at 100 Hz had the most pronounced effect (p = 0.001) in Experiment 1 and was revealed to be required to deliver at 3.0 mA in Experiment 2 (p = 0.003). Additionally, participants with higher baseline sympathetic activity experienced higher parasympathetic response during stimulation, and sex differences may exist in the autonomic responses by the application of tVNS. Therefore, our findings suggest that optimal autonomic changes induced by tVNS to the left cymba conchae vary depending on stimulating parameters and sex.

Sex Hormones, Sleep, and Memory: Interrelationships Across the Adult Female Lifespan

As the population of older adults grows, so will the prevalence of aging-related conditions, including memory impairments and sleep disturbances, both of which are more common among women. Compared to older men, older women are up to twice as likely to experience sleep disturbances and are at a higher risk of cognitive decline and Alzheimer's disease and related dementias (ADRD). These sex differences may be attributed in part to fluctuations in levels of female sex hormones (i.e., estrogen and progesterone) that occur across the adult female lifespan. Though women tend to experience the most significant sleep and memory problems during the peri-menopausal period, changes in memory and sleep have also been observed across the menstrual cycle and during pregnancy. Here, we review current knowledge on the interrelationships among female sex hormones, sleep, and memory across the female lifespan, propose possible mediating and moderating mechanisms linking these variables and describe implications for ADRD risk in later life.

Cognitive Impairments of Sleep-Deprived Ovariectomized (OVX) Female Rats by Voluntary Exercise

Introduction:

Previous studies demonstrated that forced and voluntary exercise had ameliorative effects on behavioral tasks followed by Sleep Deprivation (SD) in intact female rats. The main goal of this research was evaluating the impact of voluntary exercise on cognitive functions while SD and ovariectomization is induced in female wistar rats.

Methods:

The rats were anesthesized combining dosage of ketamine and xylazine. Then, both ovaries were eliminated and 3 weeks after surgery the animals entered the study. The exercise protocol took 4 weeks of voluntary exercise in a wheel which was connected to home cage. For inducing a 72 hours deprivation the multiple platforms was applied. The cognitive functions were studied by exploiting the Morris Water Maze (MWM) and Novel object recognition tests. Anxiety was evaluated by open field test and corticostrone measurement was carried out by ELISA method. One-way and two-way ANOVA and repeated measures were utilized for data analysis and P<0.05 was considered statistically significant.

Results:

We observed significant spatial and recognition learning and memory impairments in OVX sleep-deprived rats compared to the control group and voluntary exercise alleviated the SD-induced learning and memory defects.

Conclusion:

We concluded that voluntary exercise can improve cognitive impairments followed by SD in OVX female rats.

Cyclic changes and actions of progesterone and allopregnanolone on cognition and hippocampal basal (stratum oriens) dendritic spines of female rats

Ovarian steroids modulate the neuronal structure and function during the estrous cycle, contrasting peak effects during the proestrus cycle and low effects during the metestrus cycle. An ovariectomy (OVX) decreases gonadal hormones and tests the effects of substitutive therapies. We studied female rats with a normal estrous cycle and we also studied the effects of systemic progesterone (P4, 4.0 mg/kg) or its reduced metabolite allopregnanolone (ALLO, 4.0 mg/kg, both for 10 days) in females who had had an OVX 16.5 weeks prior to the study (long-term OVX) with the novel object recognition test (NORT) for associative memory. The dendritic shape and spine density in Golgi-impregnated basal dendrites (stratum oriens) of hippocampal pyramidal neurons was also studied. Proestrus females had a better performance than metestrus or OVX females in short-term memory (tested 1 h after the acquisition phase). Proestrus and metestrus females showed better results than OVX females for long-term memory (24 h after the initial phase). Both P4 and ALLO recovered the cognitive impairment induced by long-term OVX. Also, proestrus females had a higher density of dendritic spines than metestrus females, OVX reduced the density of spines when compared to intact females, whereas both P4 and ALLO treatments increased the dendritic spine density, number of dendritic branches along the dendritic length, and branching order compared to vehicle. These data add the dendrites of the stratum oriens as an additional site for naturally occurring changes in spine density during the estrous cycle and evidence the actions of progestins in both behavioral recovery and the structural dendritic rearrangement of hippocampal pyramidal neurons in long-term OVX female rats.

Characterizing age-related decline of recognition memory and brain activation profile in mice

Episodic memory decline is one of the earlier deficits occurring during normal aging in humans. The question of spatial versus non-spatial sensitivity to age-related memory decline is of importance for a full understanding of these changes. Here, we characterized the effect of normal aging on both non-spatial (object) and spatial (object location) memory performances as well as on associated neuronal activation in mice. Novel-object (NOR) and object-location (OLR) recognition tests, respectively assessing the identity and spatial features of object memory, were examined at different ages. We show that memory performances in both tests were altered by aging as early as 15 months of age: NOR memory was partially impaired whereas OLR memory was found to be fully disrupted at 15 months of age. Brain activation profiles were assessed for both tests using immunohistochemical detection of c-Fos (neuronal activation marker) in 3and 15 month-old mice. Normal performances in NOR task by 3 month-old mice were associated to an activation of the hippocampus and a trend towards an activation in the perirhinal cortex, in a way that did significantly differ with 15 month-old mice. During OLR task, brain activation took place in the hippocampus in 3 month-old but not significantly in 15 month-old mice, which were fully impaired at this task. These differential alterations of the object- and object-location recognition memory may be linked to differential alteration of the neuronal networks supporting these tasks.

The ERM protein Moesin is essential for neuronal morphogenesis and long-term memory in Drosophila

Moesin is a cytoskeletal adaptor protein that plays an important role in modification of the actin cytoskeleton. Rearrangement of the actin cytoskeleton drives both neuronal morphogenesis and the structural changes in neurons that are required for long-term memory formation. Moesin has been identified as a candidate memory gene in Drosophila, however, whether it is required for memory formation has not been evaluated. Here, we investigate the role of Moesin in neuronal morphogenesis and in short- and long-term memory formation in the courtship suppression assay, a model of associative memory. We found that both knockdown and overexpression of Moesin led to defects in axon growth and guidance as well as dendritic arborization. Moreover, reduction of Moesin expression or expression of a constitutively active phosphomimetic in the adult Drosophila brain had no effect on short term memory, but prevented long-term memory formation, an effect that was independent of its role in development. These results indicate a critical role for Moesin in both neuronal morphogenesis and long-term memory formation.

CCAAT/enhancer binding protein β negatively regulates progesterone receptor expression in human glioblastoma cells

Many progesterone (P4) actions are mediated by its intracellular receptor (PR), which has two isoforms (PR-A and PR-B) differentially transcribed from separate promoters of a single gene. In glioblastomas, the most frequent and aggressive brain tumors, PR-B is the predominant isoform. In an in silico analysis we showed putative CCAAT/Enhancer Binding Protein (C/EBP) binding sites at PR-B promoter. We evaluated the role of C/EBPβ in PR-B expression regulation in glioblastoma cell lines, which expressed different ratios of PR and C/EBPβ isoforms (LAP1, LAP2, and LIP). ChIP assays showed a significant basal binding of C/EBPβ, specific protein 1 (Sp1) and estrogen receptor alpha (ERα) to PR-B promoter. C/EBPβ knockdown increased PR-B expression and treatment with estradiol (E2) reduced C/EBPβ binding to the promoter and up-regulated PR-B expression. P4 induced genes were differently regulated when CEBP/β was silenced. These data show that C/EBPβ negatively regulates PR-B expression in glioblastoma cells.

Neurosteroids Involvement in the Epigenetic Control of Memory Formation and Storage

Memory is our ability to store and remember past experiences; it is the result of changes in neuronal circuits of specific brain areas as the hippocampus. During memory formation, neurons integrate their functions and increase the strength of their connections, so that synaptic plasticity is improved and consolidated. All these processes recruit several proteins at the synapses, whose expression is highly regulated by DNA methylation and histone tails posttranslational modifications. Steroids are known to influence memory process, and, among them, neurosteroids are implicated in neurodegenerative disease related to memory loss and cognitive impairment. The epigenetic control of neurosteroids involvement in memory formation and maintenance could represent the basis for neuroregenerative therapies.

Implication of Genetic Deletion of Wdr13 in Mice: Mild Anxiety, Better Performance in Spatial Memory Task, with Upregulation of Multiple Synaptic Proteins

WDR13 expresses from the X chromosome and has a highly conserved coding sequence. There have been multiple associations of WDR13 with memory. However, its detailed function in context of brain and behavior remains unknown. We characterized the behavioral phenotype of 2 month old male mice lacking the homolog of WDR13 gene (Wdr13^−/0). Taking cue from analysis of its expression in the brain, we chose hippocampus for molecular studies to delineate its function. Wdr13^−/0 mice spent less time in the central area of the open field test (OFT) and with the novel object in novel object recognition test (NOR) as compared to the wild-type. However, these mice didn't show any significant changes in total time spent in arms or in frequency of arm entries in elevated plus maze (EPM). In the absence of Wdr13, there was a significant upregulation of synaptic proteins, viz., SYN1, RAB3A, CAMK2A etc. accompanied with increased spine density of hippocampal CA1 neurons and better spatial memory in mice as measured by increased time spent in the target quadrant of Morris water maze (MWM) during probe test. Parallel study from our lab has established c-JUN, ER α/β, and HDAC 1,3,7 as interacting partners of WDR13. WDR13 represses transcription from AP1 (c-JUN responsive) and Estrogen Receptor Element (ERE) promoters. We hypothesized that absence of Wdr13 would result in de-regulated expression of a number of genes including multiple synaptic genes leading to the observed phenotype. Knocking down Wdr13 in Neuro2a cell lines led to increased transcripts of Camk2a and Nrxn2 consistent with in-vivo results. Summarily, our data provides functional evidence for the role of Wdr13 in brain.

L-Type Calcium Channels Modulation by Estradiol

Voltage-gated calcium channels are key regulators of brain function, and their dysfunction has been associated with multiple conditions and neurodegenerative diseases because they couple membrane depolarization to the influx of calcium-and other processes such as gene expression-in excitable cells. L-type calcium channels, one of the three major classes and probably the best characterized of the voltage-gated calcium channels, act as an essential calcium binding proteins with a significant biological relevance. It is well known that estradiol can activate rapidly brain signaling pathways and modulatory/regulatory proteins through non-genomic (or non-transcriptional) mechanisms, which lead to an increase of intracellular calcium that activate multiple kinases and signaling cascades, in the same way as L-type calcium channels responses. In this context, estrogens-L-type calcium channels signaling raises intracellular calcium levels and activates the same signaling cascades in the brain probably through estrogen receptor-independent modulatory mechanisms. In this review, we discuss the available literature on this area, which seems to suggest that estradiol exerts dual effects/modulation on these channels in a concentration-dependent manner (as a potentiator of these channels in pM concentrations and as an inhibitor in nM concentrations). Indeed, estradiol may orchestrate multiple neurotrophic responses, which open a new avenue for the development of novel estrogen-based therapies to alleviate different neuropathologies. We also highlight that it is essential to determine through computational and/or experimental approaches the interaction between estradiol and L-type calcium channels to assist these developments, which is an interesting area of research that deserves a closer look in future biomedical research.

Hippocampal Wnt Signaling: Memory Regulation and Hormone Interactions

Wnt signaling has emerged in recent years as a major player in both nervous system development and adult synaptic plasticity. Of particular relevance to researchers studying learning and memory, Wnt signaling is critical for normal functioning of the hippocampus, a brain region that is essential for many types of memory formation and whose dysfunction is implicated in numerous neurodegenerative and psychiatric conditions. Impaired hippocampal Wnt signaling is implicated in several of these conditions, however, little is known about how Wnt signaling mediates hippocampal memory formation. This review will provide a general overview of Wnt signaling and discuss evidence demonstrating a key role for Wnt signaling in hippocampal memory formation in both normal and disease states. The regulation of Wnt signaling by ovarian sex steroid hormones will also be highlighted, given that the neuroprotection afforded by Wnt-hormone interactions may have significant implications for cognitive function in aging, neurodegenerative disease, and ischemic injury.

Interictal spike frequency varies with ovarian cycle stage in a rat model of epilepsy

In catamenial epilepsy, seizures exhibit a cyclic pattern that parallels the menstrual cycle. Many studies suggest that catamenial seizures are caused by fluctuations in gonadal hormones during the menstrual cycle, but this has been difficult to study in rodent models of epilepsy because the ovarian cycle in rodents, called the estrous cycle, is disrupted by severe seizures. Thus, when epilepsy is severe, estrous cycles become irregular or stop. Therefore, we modified kainic acid (KA)- and pilocarpine-induced status epilepticus (SE) models of epilepsy so that seizures were rare for the first months after SE, and conducted video-EEG during this time. The results showed that interictal spikes (IIS) occurred intermittently. All rats with regular 4-day estrous cycles had IIS that waxed and waned with the estrous cycle. The association between the estrous cycle and IIS was strong: if the estrous cycles became irregular transiently, IIS frequency also became irregular, and when the estrous cycle resumed its 4-day pattern, IIS frequency did also. Furthermore, when rats were ovariectomized, or males were recorded, IIS frequency did not show a 4-day pattern. Systemic administration of an estrogen receptor antagonist stopped the estrous cycle transiently, accompanied by transient irregularity of the IIS pattern. Eventually all animals developed severe, frequent seizures and at that time both the estrous cycle and the IIS became irregular. We conclude that the estrous cycle entrains IIS in the modified KA and pilocarpine SE models of epilepsy. The data suggest that the ovarian cycle influences more aspects of epilepsy than seizure susceptibility.

Structural Components of Synaptic Plasticity and Memory Consolidation

Consolidation of implicit memory in the invertebrate Aplysia and explicit memory in the mammalian hippocampus are associated with remodeling and growth of preexisting synapses and the formation of new synapses. Here, we compare and contrast structural components of the synaptic plasticity that underlies these two distinct forms of memory. In both cases, the structural changes involve time-dependent processes. Thus, some modifications are transient and may contribute to early formative stages of long-term memory, whereas others are more stable, longer lasting, and likely to confer persistence to memory storage. In addition, we explore the possibility that trans-synaptic signaling mechanisms governing de novo synapse formation during development can be reused in the adult for the purposes of structural synaptic plasticity and memory storage. Finally, we discuss how these mechanisms set in motion structural rearrangements that prepare a synapse to strengthen the same memory and, perhaps, to allow it to take part in other memories as a basis for understanding how their anatomical representation results in the enhanced expression and storage of memories in the brain.

C/EBPβ Isoforms Expression in the Rat Brain during the Estrous Cycle

The CCAAT/enhancer-binding protein beta (C/EBPβ) is a transcription factor expressed in different areas of the brain that regulates the expression of several genes involved in cell differentiation and proliferation. This protein has three isoforms (LAP1, LAP2, and LIP) with different transcription activation potential. The role of female sex hormones in the expression pattern of C/EBPβ isoforms in the rat brain has not yet been described. In this study we demonstrate by western blot that the expression of the three C/EBPβ isoforms changes in different brain areas during the estrous cycle. In the cerebellum, LAP2 content diminished on diestrus and proestrus and LIP content diminished on proestrus and estrus days. In the prefrontal cortex, LIP content was higher on proestrus and estrus days. In the hippocampus, LAP isoforms presented a switch on diestrus day, since LAP1 content was the highest while that of LAP2 was the lowest. The LAP2 isoform was the most abundant one in all the three brain areas. The LAP/LIP ratio changed throughout the cycle and was tissue specific. These results suggest that C/EBPβ isoforms expression changes in a tissue-specific manner in the rat brain due to the changes in sex steroid hormone levels presented during the estrous cycle.

Long-term ovariectomy increases BDNF gene methylation status in mouse hippocampus

Estradiol (E) has been suggested to have a neuroprotective effect in young animals but has neutral or harmful effects when it is administered to aged animals. In the present study, we determined whether the post-ovariectomy (post-OVX) timeframe elapsed before the initiation of chronic E treatment is critical for the estrogenic induction of neurotrophins (brain-derived neurotrophic factor, BDNF, and synaptophysin, SYN) in the rodent hippocampus. Adult mice were OVX and, a short period (short-term E (STE) animals) or a long period (long-term E (LTE) animals) after the OVX, were daily treated with E. Control animals were treated with sesame oil (short-term control (STC) and long-term control (LTC) animals). Protein expression was determined using an immunohistochemical approach. Transcriptional activity in the hippocampus of individual BDNF promoters was assessed by real-time quantitative RT-PCR, and the methylation levels of regulatory regions were analyzed by methylation-specific PCR and combined bisulfite restriction analysis. STE animals showed increased BDNF and SYN protein expression and a higher activity of BDNF II, IV, and V promoters. In contrast, LTE animals did not show E induction of neurotrophins. In these animals, the methylation levels of regulatory sequences of the BDNF were higher than in the STE animals in a CpG island of promoter V and in the CRE regulatory site located in promoter IV. With this experiment, we determined that a prolonged period of hypoestrogenicity disrupts the E-induction of neurotrophins, and we postulated that DNA methylation is one of the epigenetic mechanisms that could explain the E-insensitivity of the BDNF after a long period post-OVX.

Allopregnanolone as a mediator of affective switching in reproductive mood disorders

RATIONALE

Reproductive mood disorders, including premenstrual dysphoria (PMD) and postpartum depression (PPD), are characterized by affective dysregulation that occurs during specific reproductive states. The occurrence of illness onset during changes in reproductive endocrine function has generated interest in the role of gonadal steroids in the pathophysiology of reproductive mood disorders, yet the mechanisms by which the changing hormone milieu triggers depression in susceptible women remain poorly understood.

OBJECTIVES

This review focuses on one of the neurosteroid metabolites of progesterone - allopregnanolone (ALLO) - that acutely regulates neuronal function and may mediate affective dysregulation that occurs concomitant with changes in reproductive endocrine function. We describe the role of the "neuroactive" steroids estradiol and progesterone in reproductive endocrine-related mood disorders to highlight the potential mechanisms by which ALLO might contribute to their pathophysiology. Finally, using existing data, we test the hypothesis that changes in ALLO levels may trigger affective dysregulation in susceptible women.

RESULTS

Although there is no reliable evidence that basal ALLO levels distinguish those with PMD or PPD from those without, existing animal models suggest potential mechanisms by which specific reproductive states may unmask susceptibility to affective dysregulation. Consistent with these models, initially euthymic women with PMD and those with a history of PPD show a negative association between depressive symptoms and circulating ALLO levels following progesterone administration.

CONCLUSIONS

Existing animal models and our own preliminary data suggest that ALLO may play an important role in the pathophysiology of reproductive mood disorders by triggering affective dysregulation in susceptible women.

Danggui-Shaoyao-San Improves Learning and Memory in Female SAMP8 via Modulation of Estradiol

Previous studies showed that Danggui-Shaoyao-San (DSS), a traditional Chinese medicinal prescription, could alleviate cognitive dysfunction of Alzheimer's disease (AD) patients. However, the mechanisms remain unclear; we have now examined the effect of DSS on SAMP8 and elucidated the possible mechanism. Animals were treated with DSS for 2 months, and step-down test and Morris water maze (MWM) test were used to evaluated cognitive abilities. The estradiol (E2), NO, and glycine in blood plasma or in hippocampus were detected to explore the possible mechanisms. The latency of SAMP8 in step-down test was shorter than that of age-matched SAMR1, and DSS increased the latency especially in female animals. In MWM test, we got similar results; SAMP8 spent more time to find the platform, and DSS decreased the time before finding the platform, with little effect on swim velocity, during the training sessions. During test session, DSS increased the time spent in target quadrant especially in female SAMP8. In female SAMP8, plasma E2, NO, and glycine were elevated in plasma or hippocampus tissue. In conclusion, DSS could ameliorate deterioration of cognition in SAMP8, especially in female animals. Increasing E2, NO, and glycine might contribute to the cognitive improvement effect of DSS in female SAMP8.

Cognition, mood, and physiological concentrations of sex hormones in the early and late postmenopause

Variations in the hormonal milieu after menopause may influence neural processes concerned with cognition, cognitive aging, and mood, but findings are inconsistent. In particular, cognitive effects of estradiol may vary with time since menopause, but this prediction has not been assessed directly using serum hormone concentrations. We studied 643 healthy postmenopausal women not using hormone therapy who were recruited into early (<6 y after menopause) and late (10+ y after menopause) groups. Women were administered a comprehensive neuropsychological battery and assessed with the Center for Epidemiologic Studies Depression Scale. They provided serum for free estradiol, estrone, progesterone, free testosterone, and sex hormone binding globulin measurements. Cognitive outcomes were standardized composite measures of verbal episodic memory, executive functions, and global cognition. Covariate-adjusted linear regression analyses were conducted for each hormone separately and after adjustment for other hormone levels. Endogenous sex steroid levels were unassociated with cognitive composites, but sex hormone binding globulin was positively associated with verbal memory. Results for early and late groups did not differ significantly, although progesterone concentrations were significantly positively associated with verbal memory and global cognition in early group women. Hormone concentrations were not significantly related to mood. Results fail to support the hypothesis that temporal proximity to menopause modifies the relation between endogenous serum levels of estradiol and verbal memory, executive functions, or global cognition. Physiological variations in endogenous postmenopausal levels of sex steroid hormones are not substantially related to these aspects of cognition or mood; positive associations for progesterone and sex hormone binding globulin merit additional study.

Estrous cycle plasticity in the hyperpolarization-activated current ih is mediated by circulating 17β-estradiol in preoptic area kisspeptin neurons

Circulating gonadal steroid hormones are thought to modulate a wide range of brain functions. However, the effects of steroid fluctuations through the ovarian cycle on the intrinsic properties of neurons are not well understood. We examined here whether gonadal steroids modulated the excitability of kisspeptin neurons located in the rostral periventricular region of the third ventricle (RP3V) of female mice. These cells are strongly implicated in sensing the high levels of circulating estradiol on proestrus to activate gonadotropin-releasing hormone (GnRH) neurons that, in turn, trigger ovulation. Electrophysiological studies were undertaken in brain slices from ovariectomized (OVX), diestrous, and proestrous kisspeptin-GFP mice. RP3V kisspeptin neurons exhibited marked changes in the hyperpolarization-evoked depolarizing sag and rebound firing across these groups. The hyperpolarization-activated current Ih was identified to be responsible for the depolarizing sag and was increased across OVX → diestrous → proestrous mice. Experiments in OVX mice given estradiol replacement identified an estradiol-dependent increase in Ih within RP3V kisspeptin neurons. Ih in these cells was found to contribute to their subthreshold membrane properties and the dynamics of rebound firing following hyperpolarizing stimuli in an estrous cycle-dependent manner. Only a minor role was found for Ih in modulating the spontaneous burst firing of RP3V kisspeptin neurons. These observations identify Ih as an ionic current that is regulated in a cyclical manner by circulating estradiol within the female brain, and suggest that such plasticity in the intrinsic properties of RP3V kisspeptin neurons may contribute to the generation of the preovulatory GnRH surge.

Effects of progesterone and medroxyprogesterone on actin remodeling and neuronal spine formation

Sex steroids are important regulators of neuronal cell morphology, and this is critical for gender differences in brain function and dysfunction. Neuronal morphology is controlled by multiprotein complexes including moesin (a member of the ezrin/radixin/moesin family), focal adhesion kinase (FAK), or the Wiskott-Aldrich syndrome protein-family verprolin homologous (WAVE1) protein, controlling dynamic remodeling of the cytoskeleton and cell membrane. We investigated the actions of natural progesterone (P) and of the synthetic progestin medroxyprogesterone acetate (MPA) on actin remodeling, focal adhesion complex formation, and actin branching in rat cortical neurons. Treatment with P and, to a lesser extent, MPA, increases the number and density of dendritic spines. P increases the phosphorylation of moesin, FAK, and WAVE1, and their redistribution toward cell membrane sites where spines are formed. Signaling to moesin is achieved by PR via a Gα/Gβ-dependent signaling to the small GTPase Ras homolog gene family, member A and its related kinase, Rho-associated kinase-2. In parallel, WAVE1 recruitment is triggered by a Gαi/Gβ-dependent signaling of PR to c-Src, FAK, and Rac1 GTPase. Rac1 recruits cyclin-dependent kinase-5, which phosphorylates WAVE1. Silencing of moesin, FAK, or WAVE1 abrogates the increase in dendritic spines induced by progesterone. In all applications, MPA is found to act similar to P, albeit with a lower efficacy. In conclusion, our findings indicate that the control of actin polymerization and branching and focal adhesion complex formation via moesin, FAK, and WAVE1 is a key function of progesterone receptor in neurons, which may be relevant for the regulation of dendritic spine turnover and neuronal plasticity.

Gender, sex steroid hormones, and Alzheimer's disease

Age-related loss of sex steroid hormones is a established risk factor for the development of Alzheimer's disease (AD) in women and men. While the relationships between the sex steroid hormones and AD are not fully understood, findings from both human and experimental paradigms indicate that depletion of estrogens in women and androgens in men increases vulnerability of the aging brain to AD pathogenesis. We review evidence of a wide range of beneficial neural actions of sex steroid hormones that may contribute to their hypothesized protective roles against AD. Both estrogens and androgens exert general neuroprotective actions relevant to a several neurodegenerative conditions, some in a sex-specific manner, including protection from neuron death and promotion of select aspects of neural plasticity. In addition, estrogens and androgens regulate key processes implicated in AD pathogenesis, in particular the accumulation of β-amyloid protein. We discuss evidence of hormone-specific mechanisms related to the regulation of the production and clearance of β-amyloid as critical protective pathways. Continued elucidation of these pathways promises to yield effective hormone-based strategies to delay development of AD.

Sex and hormonal influences on seizures and epilepsy

Epilepsy is the third most common chronic neurological disorder. Clinical and experimental evidence supports the role of sex and influence of sex hormones on seizures and epilepsy as well as alterations of the endocrine system and levels of sex hormones by epileptiform activity. Conversely, seizures are sensitive to changes in sex hormone levels, which in turn may affect the seizure-induced neuronal damage. The effects of reproductive hormones on neuronal excitability and seizure-induced damage are complex to contradictory and depend on different mechanisms, which have to be accounted for in data interpretation. Both estradiol and progesterone/allopregnanolone may have beneficial effects for patients with epilepsy. Individualized hormonal therapy should be considered as adjunctive treatment in patients with epilepsy to improve seizure control as well as quality of life.

Post-synaptic density-95 (PSD-95) binding capacity of G-protein-coupled receptor 30 (GPR30), an estrogen receptor that can be identified in hippocampal dendritic spines

The estrogen 17β-estradiol (E2) modulates dendritic spine plasticity in the cornu ammonis 1 (CA1) region of the hippocampus, and GPR30 (G-protein coupled estrogen receptor 1 (GPER1)) is an estrogen-sensitive G-protein-coupled receptor (GPCR) that is expressed in the mammalian brain and in specific subregions that are responsive to E2, including the hippocampus. The subcellular localization of hippocampal GPR30, however, remains unclear. Here, we demonstrate that GPR30 immunoreactivity is detected in dendritic spines of rat CA1 hippocampal neurons in vivo and that GPR30 protein can be found in rat brain synaptosomes. GPR30 immunoreactivity is identified at the post-synaptic density (PSD) and in the adjacent peri-synaptic zone, and GPR30 can associate with the spine scaffolding protein PSD-95 both in vitro and in vivo. This PSD-95 binding capacity of GPR30 is specific and determined by the receptor C-terminal tail that is both necessary and sufficient for PSD-95 interaction. The interaction with PSD-95 functions to increase GPR30 protein levels residing at the plasma membrane surface. GPR30 associates with the N-terminal tandem pair of PDZ domains in PSD-95, suggesting that PSD-95 may be involved in clustering GPR30 with other receptors in the hippocampus. We demonstrate that GPR30 has the potential to associate with additional post-synaptic GPCRs, including the membrane progestin receptor, the corticotropin releasing hormone receptor, and the 5HT1a serotonin receptor. These data demonstrate that GPR30 is well positioned in the dendritic spine compartment to integrate E2 sensitivity directly onto multiple inputs on synaptic activity and might begin to provide a molecular explanation as to how E2 modulates dendritic spine plasticity.

Reversal of prenatal morphine exposure-induced memory deficit in male but not female rats

Impaired memory performance in offspring is one of the long-lasting neurobehavioral consequences of prenatal opiate exposure. Here, we studied the effects of prenatal morphine exposure on inhibitory avoidance memory performance in male and female offspring and also investigated whether these deficits are reversible during the postnatal development. Pregnant Wistar rats received morphine sulfate through drinking water, from the first day of gestation up to the day 13, M₁₋₁₃, or to the time of delivery, M₁₋₂₁. Four- and ten-week-old (adolescent and adult, respectively) male and female offspring were subjected to behavioral assays and then analysis of proteins involved in apoptosis or in synaptic plasticity. Results revealed that adolescent and adult female rats failed in passive avoidance retention task in both M₁₋₁₃ and M₁₋₂₁ groups. Adolescent and adult male offspring were similar to control animals in M₁₋₁₃ group. However M₁₋₂₁ impaired retention task in prepubertal male offspring, and this memory loss was repaired in postpubertal stage. Consistently, Bax/Bcl-2 ratio and cleaved caspase-3 were significantly increased in both M₁₋₁₃ and M₁₋₂₁ adolescent and adult female rats, but only in M₁₋₂₁ adolescent male rats. Furthermore, prenatal morphine exposure reduced the expression of brain-derived neurotrophic factor precursor protein in adolescent and adult female offspring and also decreased p-ca(2+)/calmodulin-dependent kinase II/ca(2+)/calmodulin-dependent kinase II ratio in adolescent male and female rats. Altogether, the results show that prenatal morphine exposure, depending on the time or duration of exposure, has distinct effects on male and female rats, and postnatal development may reverse these deficits more likely in males.

Actin cytoskeleton remodelling by sex steroids in neurones

Cell morphology and its interaction with the extracellular environment are integrated processes involving a number of intracellular controllers orchestrating cytoskeletal proteins and their interaction with the cell membrane and anchorage proteins. Sex steroids are effective regulators of cell morphology and tissue organisation, and recent evidence indicates that this is obtained through the regulation of the actin cytoskeleton. Intriguingly, many of these regulatory actions related to cell morphology are achieved through the rapid, nonclassical signalling of sex steroid receptors to kinase cascades, independently from nuclear alteration of gene expression or protein synthesis. The identification of the mechanistic basis for these rapid actions on cell cytoskeleton has special relevance for the characterisation of the effects of sex steroids under physiological conditions, such as for the development of neurone/neurone interconnections and dendritic spine density. This is considered to be critical for gender-specific differences in brain function and dysfunction. Recent advancements in the characterisation of the molecular basis of the extranuclear signalling of sex steroids help to clarify the role of oestrogen and progesterone in the brain, and may turn out to be of relevance for clinical purposes. This review highlights the regulatory effects of oestrogens and progesterone on actin cytoskeleton and neurone morphology, as well as recent progresses in the characterisation of these mechanisms, providing insights and working hypotheses on possible clinical applications for the modulation of these pathways in the central nervous system.

Enhanced expression of Pctk1, Tcf12 and Ccnd1 in hippocampus of rats: Impact on cognitive function, synaptic plasticity and pathology

We previously identified a set of 50 genes that were differentially transcribed in the hippocampal CA1 region of aged, learning-impaired rats compared to aged, superior learning animals during a Morris water maze paradigm. In the current study, we expressed three of these genes (Pctk1, Tcf12 and Ccnd1), which had shown increased transcription in aged, learning impaired rats, in the hippocampus of young rats using viral gene transfer and tested for learning and memory deficits at age 7-14months. Pctk1 injected animals displayed a modest deficit in acquiring latency in both the Morris water maze and the reverse Morris maze. In the radial arm water maze paradigm, Pctk1, Tcf12 and Ccnd1 expressing animals all showed significant deficits in spatial working memory compared to controls. Rats injected with Ccnd1 and Tcf12, but not Pctk1, also showed a significant deficit in spatial reference memory in the radial arm water maze. Electrophysiological experiments revealed no difference in LTP in Ccnd1 and Pctk1 animals. However, LTD induced by low frequency stimulation was observed in control and Ccnd1 animals, but not in Pctk1 treated animals. In addition, neither Ccnd1 nor Pctk1 expression produced any detectable neuropathology. In contrast Tcf12 expressing animals displayed significant neurodegeneration in both CA1 and dentate gyrus. Several Tcf12 animals also developed tumors that appeared to be glioblastomas, suggesting that aberrant Tcf12 expression in the hippocampus is tumorigenic. Thus, behavioral experiments suggested that overexpression of Pctk1 and Ccnd1 produce a deficit in learning and memory, but electrophysiological experiments do not point to a simple mechanism. In contrast, the learning and memory deficits in Tcf12 animals are likely due to neuropathology associated with Tcf12 gene expression.

Progesterone treatment normalizes the levels of cell proliferation and cell death in the dentate gyrus of the hippocampus after traumatic brain injury

Traumatic brain injury (TBI) increases cell death in the hippocampus and impairs hippocampus-dependent cognition. The hippocampus is also the site of ongoing neurogenesis throughout the lifespan. Progesterone treatment improves behavioral recovery and reduces inflammation, apoptosis, lesion volume, and edema, when given after TBI. The aim of the present study was to determine whether progesterone altered cell proliferation and short-term survival in the dentate gyrus after TBI. Male Sprague-Dawley rats with bilateral contusions of the frontal cortex or sham operations received progesterone or vehicle at 1 and 6 h post-surgery and daily through post-surgery Day 7, and a single injection of bromodeoxyuridine (BrdU) 48 h after injury. Brains were then processed for Ki67 (endogenous marker of cell proliferation), BrdU (short-term cell survival), doublecortin (endogenous marker of immature neurons), and Fluoro-Jade B (marker of degenerating neurons). TBI increased cell proliferation compared to shams and progesterone normalized cell proliferation in injured rats. Progesterone alone increased cell proliferation in intact rats. Interestingly, injury and/or progesterone treatment did not influence short-term cell survival of BrdU-ir cells. All treatments increased the percentage of BrdU-ir cells that were co-labeled with doublecortin (an immature neuronal marker in this case labeling new neurons that survived 5 days), indicating that cell fate is influenced independently by TBI and progesterone treatment. The number of immature neurons that survived 5 days was increased following TBI, but progesterone treatment reduced this effect. Furthermore, TBI increased cell death and progesterone treatment reduced cell death to levels seen in intact rats. Together these findings suggest that progesterone treatment after TBI normalizes the levels of cell proliferation and cell death in the dentate gyrus of the hippocampus.

Regulation of calpain-2 in neurons: implications for synaptic plasticity

The family of calcium-dependent neutral proteases, calpains, was discovered more than 30 years ago, but their functional roles in the nervous system under physiological or pathological conditions still remain unclear. Although calpain was proposed to participate in synaptic plasticity and in learning and memory in the early 1980s, the precise mechanism regarding its activation, its target(s) and the functional consequences of its activation have remained controversial. A major issue has been the identification of roles of the two major calpain isoforms present in the brain, calpain-1 and calpain-2, and the calcium requirement for their activation, which exceeds levels that could be reached intracellularly under conditions leading to changes in synaptic efficacy. In this review, we discussed the features of calpains that make them ideally suited to link certain patterns of presynaptic activity to the structural modifications of dendritic spines that could underlie synaptic plasticity and learning and memory. We then summarize recent findings that provide critical answers to the various questions raised by the initial hypothesis, and that further support the idea that, in brain, calpain-2 plays critical roles in developmental and adult synaptic plasticity.

Aging differentially affects male and female neural stem cell neurogenic properties

Purpose

Neural stem cell transplantation as a brain repair strategy is a very promising technology. However, despite many attempts, the clinical success remains very deceiving. Despite clear evidence that sexual dimorphism rules many aspects of human biology, the occurrence of a sex difference in neural stem cell biology is largely understudied. Herein, we propose to determine whether gender is a dimension that drives the fate of neural stem cells through aging. Should it occur, we believe that neural stem cell sexual dimorphism and its variation during aging should be taken into account to refine clinical approaches of brain repair strategies.

Methods

Neural stem cells were isolated from the subventricular zone of three- and 20-month-old male and female Long-Evans rats. Expression of the estrogen receptors, ERα and ERβ, progesterone receptor, androgen receptor, and glucocorticoid receptor was analyzed and quantified by Western blotting on undifferentiated neural stem cells. A second set of neural stem cells was treated with retinoic acid to trigger differentiation, and the expression of neuronal, astroglial, and oligodendroglial markers was determined using Western blotting.

Conclusion

We provided in vitro evidence that the fate of neural stem cells is affected by sex and aging. Indeed, young male neural stem cells mainly expressed markers of neuronal and oligodendroglial fate, whereas young female neural stem cells underwent differentiation towards an astroglial phenotype. Aging resulted in a lessened capacity to express neuron and astrocyte markers. Undifferentiated neural stem cells displayed sexual dimorphism in the expression of steroid receptors, in particular ERα and ERβ, and the expression level of several steroid receptors increased during aging. Such sexual dimorphism might explain, at least in part, the sex difference in neural fate we observed in young and old neural stem cells. These results suggest that sex and aging are two factors to be taken into consideration for future neural stem cell transplantation protocols in brain repair strategies.

Genetic and epigenetic underpinnings of sex differences in the brain and in neurological and psychiatric disease susceptibility

There are numerous examples of sex differences in brain and behavior and in susceptibility to a broad range of brain diseases. For example, gene expression is sexually dimorphic during brain development, adult life, and aging. These differences are orchestrated by the interplay between genetic, hormonal, and environmental influences. However, the molecular mechanisms that underpin these differences have not been fully elucidated. Because recent studies have highlighted the key roles played by epigenetic processes in regulating gene expression and mediating brain form and function, this chapter reviews emerging evidence that shows how epigenetic mechanisms including DNA methylation, histone modifications, and chromatin remodeling, and non-coding RNAs (ncRNAs) are responsible for promoting sexual dimorphism in the brain. Differential profiles of DNA methylation and histone modifications are found in dimorphic brain regions such as the hypothalamus as a result of sex hormone exposure during developmental critical periods. The elaboration of specific epigenetic marks is also linked with regulating sex hormone signaling pathways later in life. Furthermore, the expression and function of epigenetic factors such as the methyl-CpG-binding protein, MeCP2, and the histone-modifying enzymes, UTX and UTY, are sexually dimorphic in the brain. ncRNAs are also implicated in promoting sex differences. For example, X inactivation-specific transcript (XIST) is a long ncRNA that mediates X chromosome inactivation, a seminal developmental process that is particularly important in brain. These observations imply that understanding epigenetic mechanisms, which regulate dimorphic gene expression and function, is necessary for developing a more comprehensive view of sex differences in brain. These emerging findings also suggest that epigenetic mechanisms are, in part, responsible for the differential susceptibility between males and females that is characteristic of a spectrum of neurological and psychiatric disorders.