Age dependent differences in the regulation of hippocampal steroid hormones and receptor genes: relations to motivation and cognition in male rats

Evaluating the impact of age and inflammatory duration on behavioral assessments of nociception

Pain is a prevalent issue for elderly individuals. Unfortunately, it remains unclear how acute and chronic pain differs as a function of age, and surprisingly, there is even disagreement on how the sensory and affective dimensions of pain change with age. Therefore, the current investigation evaluated such age differences with behavioral methodology using a preclinical model of arthritis. The primary factors of interest were age and chronicity of pain using behavioral assessments designed to measure sensory and affective dimensions of pain processing. Mechanical and thermal paw withdrawal thresholds demonstrated unique outcomes associated with sensory processing across age. The processing of pain affect measured by the Place Escape/Avoidance Paradigm (PEAP testing) also demonstrated age related effects. Overall, younger animals appeared more sensitive to nociceptive stimuli than older animals. However, the results from the current study suggest that chronicity of pain can be impactful for how older animals process pain related affect and avoidance. The finding of unique patterns of pain across age and duration of pain highlights the clinical literature. Future research should aim to elucidate mechanisms for affective processing of chronic pain in older subjects.

Striatal Transcriptome Reveals Differences Between Cognitively Impaired and Unimpaired Aged Male Rats

Cognitive processes require striatal activity. The underlying molecular mechanisms are widely unknown. For this reason the striatal transcriptome of young (YM), aged cognitively impaired (OMB), and unimpaired (OMG) male rats was analyzed. The global comparison of transcripts reveal a higher number of differences between OMG and YM as compared to OMB and YM. Hierarchical clustering detects differences in up- and down-regulated gene clusters in OMG and OMB when compared to YM. In OMG we found more single genes to be specifically regulated in this group than in OMB when compared to young. These genes were considered as cognition specific, whereas genes shared in OMG and OMB were considered as age specific. OMB specific up-regulated genes are related to negative control of cell differentiation and transcription (Hopx), to phagocytosis (Cd202) and cell adhesion (Pcdhb21), whereas down-regulated genes are related to associative learning, behavioral fear response and synaptic transmission (Gabra5). OMG specific up-regulated genes are in the context of maintenance of transcription and estrogen receptor signaling (Padi2, Anxa3), signal transduction [Rassf4, Dock8)], sterol regulation (Srebf1), and complement activity (C4a, C4b). Down-regulated genes are related to lipid oxidation reduction processes (Far2) and positive regulation of axon extension (Islr2). These relations were supported by pathway analysis, which reveals cholesterol metabolism processes in both aged group and cholesterol biosynthesis specifically in OMG; adipogenesis and focal adhesion in OMB. In OMG glucuronidation, estrogen metabolism, inflammatory responses and TGF beta signaling where detected as specific for this group. Signal transduction of the sphingosine-1-phospate-receptor (S1P) receptor was the main pathway difference in the comparison of OMB and OMG with downregulated genes in the first group. This difference could also be observed in the OMB vs. YM comparison but not in the OMG vs. YM analysis. Thus, an up-regulation of cognition related genes could be observed in OMG compared to OMB rats. The S1P pathway discriminated between OMB and OMG as well as between OMB and OMG. Since this pathway has been described as essential for cognitive processes in the striatum of mice, it may, among steroid hormone signaling, significantly contribute to the maintenance of cognitive processes in OMG.

Expression of ESR1 and ESR2 oestrogen receptor encoding gene and personality traits - preliminary study

INTRODUCTION

The main objective of the study is to examine the hypothesis claiming a correlation between personality traits measured with the use of the Minnesota Multiphasic Personality Inventory (MMPI-2) personality questionnaire and the expression of the ERα (ESR1) and ERβ (ESR2) encoding gene in patients suffering from depression.

MATERIAL AND METHODS

The experiment was carried out on a group of 44 individuals with depression. The Polish variant of the MMPI-2 was applied with the aim of assessing personality traits. Furthermore, the authors evaluated the expression of the genes encoding the oestrogen receptors (ERα and ERβ) at the mRNA level and protein level in the studied population.

RESULTS

No significant differences in the expression of ERα and ERβ encoding genes were found and confirmed in the patients with the first episode of depression and those suffering from subsequent episodes of the disease. No differences were found between women and men, either. In women a positive relationship was found between the scale of psychopathy (p = 0.04), paranoia (p = 0.01), and mania (p = 0.03) and expression for the ERα encoding gene at the mRNA level. A negative relationship was found between the mania scale and ERβ encoding gene expression at mRNA (p = 0.03) and protein (p = 0.04) levels. In males a positive relationship between anxiety as a personality trait and expression of the ERβ receptor encoding gene at mRNA level (p = 0.03) and protein level (p = 0.03) was found.

CONCLUSIONS

Personality traits may be linked with the expression of genes encoding oestrogen receptors (ERα and ERβ) among patients with depressive disorders.

Repeated abortion in adulthood induces cognition impairment in aged mice

Age-related cognitive decline is one of the major aspects that impede successful aging in humans. Repeated abortion in adulthood can accelerate or aggravate cognitive deficiency during aging. Here we used repeated abortion in female mice adulthood and investigated the consequences of this treatment on cognitive performance during aging. We observed a substantial impairment of learning memory in 15 months old. This cognitive dysfunction was supported by Aβ elevation in CA region. Repeated abortion mice have uniform estrous cycles and decreased ERα expression in hypothalamus and hippocampus. Furthermore, repeated abortion not only significantly increased the HMGB1 expression in hippocampus but also increased the plasma and hippocampal protein levels of IL-1β, IL-6, and TNF-α. Finally, we identified that MPP-induced cell apoptosis and increased HMGB1 expression as well as IL-1β, IL-6, and TNF-α expression as following Aβ elevation. Taken together, our results identify possible molecular mechanisms underlying cognitive impairment during aging, and demonstrated the repeated abortion in adulthood on cognitive function in aged mice.

Nuclear and membrane estrogen receptor antagonists induce similar mTORC2 activation-reversible changes in synaptic protein expression and actin polymerization in the mouse hippocampus

AIMS

Estrogens play pivotal roles in hippocampal synaptic plasticity through nuclear receptors (nERs; including ERα and ERβ) and the membrane receptor (mER; also called GPR30), but the underlying mechanism and the contributions of nERs and mER remain unclear. Mammalian target of rapamycin complex 2 (mTORC2) is involved in actin cytoskeleton polymerization and long-term memory, but whether mTORC2 is involved in the regulation of hippocampal synaptic plasticity by ERs is unclear.

METHODS

We treated animals with nER antagonists (MPP/PHTPP) or the mER antagonist (G15) alone or in combination with A-443654, an activator of mTORC2. Then, we examined the changes in hippocampal SRC-1 expression, mTORC2 signaling (rictor and phospho-AKTSer473), actin polymerization (phospho-cofilin and profilin-1), synaptic protein expression (GluR1, PSD95, spinophilin, and synaptophysin), CA1 spine density, and synapse density.

RESULTS

All of the examined parameters except synaptophysin expression were significantly decreased by MPP/PHTPP and G15 treatment. MPP/PHTPP and G15 induced a similar decrease in most parameters except p-cofilin, GluR1, and spinophilin expression. The ER antagonist-induced decreases in these parameters were significantly reversed by mTORC2 activation, except for the change in SRC-1, rictor, and synaptophysin expression.

CONCLUSIONS

nERs and mER contribute similarly to the changes in proteins and structures associated with synaptic plasticity, and mTORC2 may be a novel target of hippocampal-dependent dementia such as Alzheimer's disease as proposed by previous studies.

Estrogen receptor alpha and beta regulate actin polymerization and spatial memory through an SRC-1/mTORC2-dependent pathway in the hippocampus of female mice

Aging-related decline of estrogens, especially 17β-estradiol (E2), has been shown to play an important role in the impairment of learning and memory in dementias, such as Alzheimer's disease (AD), but the underlying molecular mechanisms are poorly understood. In this study, we first demonstrated decreases in E2 signaling (aromatase, classic estrogen receptor ERα and ERβ and their coactivator SRC-1), mTORC2 signaling (Rictor and phospho-AKTser473) and actin polymerization (phospho-Cofilin, Profilin-1 and the F-actin/G-actin ratio) in the hippocampus of old female mice compared with those levels detected in the adult hippocampus. We then showed that ERα and ERβ antagonists induced a significant decrease in SRC-1, mTORC2 signaling, actin polymerization, and CA1 spine density, as well as impairments of learning and memory; however, ovariectomy-induced changes of these parameters could be significantly reversed by treatment with ER agonists. We further showed that expression of SRC-1, mTORC2 signaling and actin polymerization could be upregulated by E2 treatment, and the effects of E2 were blocked by the ER antagonists but mimicked by the agonists. We also showed that the lentivirus-mediated SRC-1 knockdown significantly inhibited the agonist-activated mTORC2 signaling and actin polymerization, and the lentivirus-mediated Rictor knockdown also significantly inhibited the agonist-activated actin polymerization. Finally, we demonstrated that the ERα and ERβ antagonists induced a disruption in actin polymerization and an impairment of spatial memory, which were rescued by activation of mTORC2. Taken together, the above results clearly demonstrated an mTORC2-dependent regulation of actin polymerization that contributed to the effects of ERα and ERβ on spatial learning, which may provide a novel target for the prevention and treatment of E2-related dementia in the aged population.

Individual Differences in Male Rats in a Behavioral Test Battery: A Multivariate Statistical Approach

Animal models for anxiety, depressive-like and cognitive diseases or aging often involve testing of subjects in behavioral test batteries. The large number of test variables with different mean variations and within and between test correlations often constitute a significant problem in determining essential variables to assess behavioral patterns and their variation in individual animals as well as appropriate statistical treatment. Therefore, we applied a multivariate approach (principal component analysis) to analyse the behavioral data of 162 male adult Sprague-Dawley rats that underwent a behavioral test battery including commonly used tests for spatial learning and memory (holeboard) and different behavioral patterns (open field, elevated plus maze, forced swim test) as well as for motor abilities (Rota rod). The high dimensional behavioral results were reduced to fewer components associated with spatial cognition, general activity, anxiety-, and depression-like behavior and motor ability. The loading scores of individual rats on these different components allow an assessment and the distribution of individual features in a population of animals. The reduced number of components can be used also for statistical calculations like appropriate sample sizes for valid discriminations between experimental groups, which otherwise have to be done on each variable. Because the animals were intact, untreated and experimentally naïve the results reflect trait patterns of behavior and thus individuality. The distribution of animals with high or low levels of anxiety, depressive-like behavior, general activity and cognitive features in a local population provides information of the probability of their appeareance in experimental samples and thus may help to avoid biases. However, such an analysis initially requires a large cohort of animals in order to gain a valid assessment.

Concerted Gene Expression of Hippocampal Steroid Receptors during Spatial Learning in Male Wistar Rats: A Correlation Analysis

Adrenal and gonadal steroid receptor activities are significantly involved and interact in the regulation of learning, memory and stress. Thus, a coordinated expression of steroid receptor genes during a learning task can be expected. Although coexpression of steroid receptors in response to behavioral tasks has been reported the correlative connection is unclear. According to the inverted U-shape model of the impact of stress upon learning and memory we hypothesized that glucocorticoid (GR) receptor expression should be correlated to corticosterone levels in a linear or higher order manner. Other cognition modulating steroid receptors like estrogen receptors (ER) should be correlated to GR receptors in a quadratic manner, which describes a parabola and thus a U-shaped connection. Therefore, we performed a correlational meta-analyis of data of a previous study (Meyer and Korz, 2013a) of steroid receptor gene expressions during spatial learning, which provides a sufficient data basis in order to perform such correlational connections. In that study male rats of different ages were trained in a spatial holeboard or remained untrained and the hippocampal gene expression of different steroid receptors as well as serum corticosterone levels were measured. Expressions of mineralocorticoid (MR) and GR receptors were positively and linearly correlated with blood serum corticosterone levels in spatially trained but not in untrained animals. Training induced a cubic (best fit) relationship between mRNA levels of estrogen receptor α (ERα) and androgen receptor (AR) with MR mRNA. GR gene expression was linearly correlated with MR expression under both conditions. ERα m RNA levels were negatively and linearily and MR and GR gene expressions were cubicely correlated with reference memory errors (RME). Due to only three age classes correlations with age could not be performed. The findings support the U-shape theory of steroid receptor interaction, however the cubic fit suggest a more complex situation, which mechanisms may be revealed in further studies.

Estrogen Effects on Cognitive and Synaptic Health Over the Lifecourse

Estrogen facilitates higher cognitive functions by exerting effects on brain regions such as the prefrontal cortex and hippocampus. Estrogen induces spinogenesis and synaptogenesis in these two brain regions and also initiates a complex set of signal transduction pathways via estrogen receptors (ERs). Along with the classical genomic effects mediated by activation of ER α and ER β, there are membrane-bound ER α, ER β, and G protein-coupled estrogen receptor 1 (GPER1) that can mediate rapid nongenomic effects. All key ERs present throughout the body are also present in synapses of the hippocampus and prefrontal cortex. This review summarizes estrogen actions in the brain from the standpoint of their effects on synapse structure and function, noting also the synergistic role of progesterone. We first begin with a review of ER subtypes in the brain and how their abundance and distributions are altered with aging and estrogen loss (e.g., ovariectomy or menopause) in the rodent, monkey, and human brain. As there is much evidence that estrogen loss induced by menopause can exacerbate the effects of aging on cognitive functions, we then review the clinical trials of hormone replacement therapies and their effectiveness on cognitive symptoms experienced by women. Finally, we summarize studies carried out in nonhuman primate models of age- and menopause-related cognitive decline that are highly relevant for developing effective interventions for menopausal women. Together, we highlight a new understanding of how estrogen affects higher cognitive functions and synaptic health that go well beyond its effects on reproduction.

Sex differences in the neural substrates of spatial working memory during adolescence are not mediated by endogenous testosterone

Adolescence is a developmental period characterized by notable changes in behavior, physical attributes, and an increase in endogenous sex steroid hormones, which may impact cognitive functioning. Moreover, sex differences in brain structure are present, leading to differences in neural function and cognition. Here, we examine sex differences in performance and blood oxygen level-dependent (BOLD) activation in a sample of adolescents during a spatial working memory (SWM) task. We also examine whether endogenous testosterone levels mediate differential brain activity between the sexes. Adolescents between ages 10 and 16 years completed a SWM functional magnetic resonance imaging (fMRI) task, and serum hormone levels were assessed within seven days of scanning. While there were no sex differences in task performance (accuracy and reaction time), differences in BOLD response between girls and boys emerged, with girls deactivating brain regions in the default mode network and boys showing increased response in SWM-related brain regions of the frontal cortex. These results suggest that adolescent boys and girls adopted distinct neural strategies, while maintaining spatial cognitive strategies that facilitated comparable cognitive performance of a SWM task. A nonparametric bootstrapping procedure revealed that testosterone did not mediate sex-specific brain activity, suggesting that sex differences in BOLD activation during SWM may be better explained by other factors, such as early organizational effects of sex steroids or environmental influences. Elucidating sex differences in neural function and the influence of gonadal hormones can serve as a basis of comparison for understanding sexually dimorphic neurodevelopment and inform sex-specific psychopathology that emerges in adolescence.

17β-trenbolone, an anabolic-androgenic steroid as well as an environmental hormone, contributes to neurodegeneration

Both genetic and environmental factors contribute to neurodegenerative disorders. In a large number of neurodegenerative diseases (for example, Alzheimer's disease (AD)), patients do not carry the mutant genes. Other risk factors, for example the environmental factors, should be evaluated. 17β-trenbolone is a kind of environmental hormone as well as an anabolic-androgenic steroid. 17β-trenbolone is used as a growth promoter for livestock in the USA. Also, a large portion of recreational exercisers inject 17β-trenbolone in large doses and for very long time to increase muscle and strength. 17β-trenbolone is stable in the environment after being excreted. In the present study, 17β-trenbolone was administered to adult and pregnant rats and the primary hippocampal neurons. 17β-trenbolone's distribution and its effects on serum hormone levels and Aβ42 accumulation in vivo and its effects on AD related parameters in vitro were assessed. 17β-trenbolone accumulated in adult rat brain, especially in the hippocampus, and in the fetus brain. It altered Aβ42 accumulation. 17β-trenbolone induced apoptosis of primary hippocampal neurons in vitro and resisted neuroprotective function of testosterone. Presenilin-1 protein expression was down-regulated while β-amyloid peptide 42 (Aβ42) production and caspase-3 activities were increased. Both androgen and estrogen receptors mediated the processes. 17β-trenbolone played critical roles in neurodegeneration. Exercisers who inject large doses of trenbolone and common people who are exposed to 17β-trenbolone by various ways are all influenced chronically and continually. Identification of such environmental risk factors will help us take early prevention measure to slow down the onset of neurodegenerative disorders.

Different expression of membrane-bound and cytosolic hippocampal steroid receptor complexes during spatial training in young male rats

Brain steroid receptors are involved in mediating stress responses and cognitive processes throughfast non-genomic signaling of membrane-bound receptors or through the slower genomic actions of cytosolic receptors. Although the contribution of these different pathways in the formation and maintenance of memories has been widely discussed, little is known about the regulation of membrane versus cytosolic receptors during a learning task. Besides the relatively well studied corticosterone-binding glucocorticoid (GR) and mineralocorticoid (MR) receptors, sex steroid hormone receptors, such as the androgen and estrogen (ERα and ERβ) receptors, have also been shown to be involved in the regulation of stress and cognition. Moreover, the latter receptors are known to be functional in both sexes. Therefore, we studied the expression of hippocampal receptors in both cellular fractions during spatial learning in male rats. Membrane and cytosolic GR were shown to be downregulated after memory acquisition and unaffected after consolidation, whereas membrane MR was upregulated after both learning phases and unaffected in the cytosol. Cytosolic ERα was downregulated after both phases and unaffected in the membrane. The remaining receptors were not regulated. The data suggest a specific role of MR and ERα during training as fast and slow mediators, respectively.

Estrogen receptor α functions in the regulation of motivation and spatial cognition in young male rats

Estrogenic functions in regulating behavioral states such as motivation, mood, anxiety, and cognition are relatively well documented in female humans and animals. In males, however, although the entire enzymatic machinery for producing estradiol and the corresponding receptors are present, estrogenic functions have been largely neglected. Therefore, and as a follow-up study to previous research, we sub-chronically applied a specific estrogen receptor α (ERα) antagonist in young male rats before and during a spatial learning task (holeboard). The male rats showed a dose-dependent increase in motivational, but not cognitive, behavior. The expression of hippocampal steroid receptor genes, such as glucocorticoid (GR), mineralocorticoid (MR), androgen (AR), and the estrogen receptor ERα but not ERβ was dose-dependently reduced. The expression of the aromatase but not the brain-derived neurotrophic factor (BDNF) encoding gene was also suppressed. Reduced gene expression and increased behavioral performance converged at an antagonist concentration of 7.4 µmol. The hippocampal and blood serum hormone levels (corticosterone, testosterone, and 17β-estradiol) did not differ between the experimental groups and controls. We conclude that steroid receptors (and BDNF) act in a concerted, network-like manner to affect behavior and mutual gene expression. Therefore, the isolated view on single receptor types is probably insufficient to explain steroid effects on behavior. The steroid network may keep motivation in homeostasis by supporting and constraining the behavioral expression of motivation.

Rapid effects of oestrogen on synaptic plasticity: interactions with actin and its signalling proteins

Oestrogen rapidly enhances fast excitatory postsynaptic potentials, facilitates long-term potentiation (LTP) and increases spine numbers. Each effect likely contributes to the influence of the steroid on cognition and memory. In the present review, we first describe a model for the substrates of LTP that includes an outline of the synaptic events occurring during induction, expression and consolidation. Briefly, critical signalling pathways involving the small GTPases RhoA and Rac/Cdc42 are activated by theta burst-induced calcium influx and initiate actin filament assembly via phosphorylation (inactivation) of cofilin. Reorganisation of the actin cytoskeleton changes spine and synapse morphology, resulting in increased concentrations of AMPA receptors at stimulated contacts. We then use the synaptic model to develop a specific hypothesis about how oestrogen affects both baseline transmission and plasticity. Brief infusions of 17β-oestradiol (E2 ) reversibly stimulate the RhoA, cofilin phosphorylation and actin polymerisation cascade of the LTP machinery; blocking this eliminates the effects of the steroid on transmission. We accordingly propose that E2 induces a weak form of LTP and thereby increases synaptic responses, a hypothesis that also accounts for how it markedly enhances theta burst induced potentiation. Although the effects of E2 on the cytoskeleton could be a result of the direct activation of small GTPases by oestrogen receptors on the synaptic membrane, the hormone also activates tropomyosin-related kinase B receptors for brain-derived neurotrophic factor, a neurotrophin that engages the RhoA-cofilin sequence and promotes LTP. The latter observations raise the possibility that E2 produces its effects on synaptic physiology via transactivation of neighbouring receptors that have prominent roles in the management of spine actin, synaptic physiology and plasticity.