II. Cognitive performance of middle-aged female rats is influenced by capacity to metabolize progesterone in the prefrontal cortex and hippocampus

The effect of late-life environmental enrichment on stress and anxiety: The role of sex and age-related differences in coping with aversive stimuli

Anxiety significantly diminishes the quality of life in older adults, and the drugs used for its treatment often come with risky side effects. Non-pharmacological protocols could be valuable, but more research is needed in this area. Environmental enrichment induces positive effects on anxiety-like behavior in young and adult animals; whether the same happens in aged animals is still elusive. The aged brain undergoes changes that contribute to make it "fragile" and consequently even mild, potentially positive stimuli can trigger dyshomeostasis, worsening rather than ameliorating functioning. Here, by combining behavioral analysis and measurement of serum and brain corticosterone levels, we show that late-life environmental enrichment can induce eustress or distress, depending on sex and hypothalamic-pituitary-adrenal axis function. These findings pave the way for optimizing outcomes and minimizing undesired effects in the clinical setting, underscoring the need to overcome the limits of gender medicine and emphasizing the crucial role of individually tailored therapies.

Evaluations of memory, anxiety, and the growth factor IGF-1R after post-surgical menopause treatment with a highly selective progestin

Progestogens are a key component of menopausal hormone therapies. While some progestogens can be detrimental to cognition, there is preclinical evidence that progestogens with a strong progesterone-receptor affinity benefit some molecular mechanisms believed to underlie cognitive function. Thus, a progestin that maximizes progesterone-receptor affinity and minimizes affinities to other receptors may be cognitively beneficial. We evaluated segesterone-acetate (SGA), a 19-norprogesterone derivative with a strong progesterone-receptor affinity and no androgenic or estrogenic-receptor activity, hypothesizing that it would enhance cognition. Middle-aged rats underwent Sham or Ovariectomy (Ovx) surgery followed by administration of medroxyprogesterone-acetate (MPA; used as a positive control as we have previously shown MPA-induced cognitive deficits), SGA (low or high dose), or vehicle (one Sham and one Ovx group). Spatial working and reference memory, delayed retention, and anxiety-like behavior were assessed, as were memory- and hormone- related protein assays within the frontal cortex, dorsal hippocampus, and entorhinal cortex. Low-dose SGA impaired spatial working memory, while high-dose SGA had a more extensive detrimental impact, negatively affecting spatial reference memory and delayed retention. Replicating previous findings, MPA impaired spatial reference memory and delayed retention. SGA, but not MPA, alleviated Ovx-induced anxiety-like behaviors. On two working memory measures, IGF-1R expression correlated with better working memory only in rats without hormone manipulation; any hormone manipulation or combination of hormone manipulations used herein altered this relationship. These findings suggest that SGA impairs spatial cognition after surgical menopause, and that surgical menopause with or without progestin administration disrupts relationships between a growth factor critical to neuroplasticity.

Differences in learning and memory between middle-aged female and male rats

We observed differences in cognitive functions between middle-aged female and male Wistar rats. Both (like youngsters) discriminated new versus familiar objects, showing similar short- and long-term memory (STM and LTM, respectively). Only females show robust LTM for new location of an object. Both successfully form LTM of inhibitory avoidance, though males appeared to be amnesic for memory persistence. Habituation, locomotion, horizontal exploration, "stereotypies," fear, and anxiety-like behavior were similar for both, while vertical exploration was significantly higher in middle-aged and younger females. Therefore, sex-dependent differences in some cognitive functions and behaviors must be considered when designing and interpreting learning and memory studies.

In vivo proton magnetic resonance spectroscopy detection of metabolite abnormalities in aged Tat-transgenic mouse brain

Most individuals living with HIV in the USA are over 45 years old and are vulnerable to the combined effects of HIV and aging. Antiretroviral therapies reduce HIV morbidity and mortality but do not prevent HIV trans-activator of transcription (Tat) protein expression or development of HIV-associated neurocognitive disorder (HAND), which may be caused by Tat. Tat-transgenic (Tat-tg) mice are used to study Tat's effects, typically after transgene induction with doxycycline. However, uninduced Tat-tg mice experience transgene leak and model aspects of HAND when aged, including neuroinflammation. We used in vivo 9.4-tesla proton magnetic resonance spectroscopy to compare neurochemistry in aged versus young female and male uninduced Tat-tg mice. Aged Tat-tg mice demonstrated measurable tat mRNA brain expression and had lower medial prefrontal cortex (MPFC) GABA, glutamate, and taurine levels and lower striatal GABA and taurine levels. Females had lower MPFC glutathione and taurine and lower striatal taurine levels. Brain testosterone levels were negatively correlated with age in aged males but not females. Aged mice had cortical abnormalities not previously reported in aged wild-type mice including lower MPFC GABA and taurine levels. As glutathione and taurine levels reflect inflammation and oxidative stress, our data suggest that Tat may exacerbate these processes in aged Tat-tg mice. However, additional studies in controls not expressing Tat are needed to confirm this point and to deconvolve individual effects of age and Tat expression. Sex steroid hormone supplements, which counter climacteric effects, increase taurine levels, and reduce inflammation and oxidative stress, could attenuate some of the brain abnormalities we identified in aged Tat-tg mice.

Cognitive Reserve in Model Systems for Mechanistic Discovery: The Importance of Longitudinal Studies

The goal of this review article is to provide a resource for longitudinal studies, using animal models, directed at understanding and modifying the relationship between cognition and brain structure and function throughout life. We propose that forthcoming longitudinal studies will build upon a wealth of knowledge gleaned from prior cross-sectional designs to identify early predictors of variability in cognitive function during aging, and characterize fundamental neurobiological mechanisms that underlie the vulnerability to, and the trajectory of, cognitive decline. Finally, we present examples of biological measures that may differentiate mechanisms of the cognitive reserve at the molecular, cellular, and network level.

Mating Enhances Expression of Hormonal and Trophic Factors in the Midbrain of Female Rats

Among female rats, mating enhances neurosteroid formation in the midbrain ventral tegmental area (VTA; independent of peripheral steroid-secreting glands, ovaries, and adrenals). The sources/targets for these actions are not well understood. In Experiment 1, proestrous rats engaged in a mating paradigm, or did not, and the midbrains had been assessed via the Affymetrix rat genome microarrays. In Experiment 2, the influence of gonadal and adrenal glands on the expression of these genes was assessed in rats that were proestrous, ovariectomized (OVX), or OVX and adrenalectomized (ADX). The microarrays revealed 53 target genes that were significantly up-regulated (>2.0-fold change) in response to mating. Mating significantly enhanced the midbrain mRNA expression of genes involved in hormonal and trophic actions: Gh1, S100g, and Klk1b3 in proestrous, but not OVX and/or ADX, rats; Fshb in all but OVX/ADX rats; and lutenizing hormone β and thyroid-stimulating hormone (TSH) β in all rats. Thus, mating enhances midbrain gene expression independent and dependent of peripheral glands.

Aged rats with different performances at environmental enrichment onset display different modulation of habituation and aversive memory

A wide agreement exists that environmental enrichment (EE) is most beneficial if introduced early in life, but numerous studies reported that also aged animals remain responsive. As age-related memory and cognition impairments are not uniform, an open question is whether EE might exert different effects in animals with different age-related deficits. A 12-week EE protocol was applied to late adult rats pretested for habituation and aversive memory. Animals were classified as low (LP) and high (HP) performers according to percent exploration change in Open Field test (OF) and as impaired (I) and not impaired (NI) according to latency in Step-through Passive Avoidance test (PA). Standard housing (SH) animals pretested by OF and PA, and naïve (non-pretested) EE and SH rats were used as controls. In comparison to pretest, after the housing protocol, EE LP ameliorated while EE HP and both SH HP and LP worsened their habituation pattern. The positive influence of EE on LP was probably due to the more active interaction with and the faster adaptation to surroundings promoted by continuous, multiple stimuli provided during the enriched housing. Regarding HP, EE did not boost the basal behavior, which likely represented the maximum achievable for that age, and the post housing exploration change dropped, as in SH animals, because of the retesting. After EE, a significant percentage of NI animals became I and a significant percentage of I animals became NI. The changes evidenced in the NI group likely depended on EE-related reduction of anxiety and the consequent more efficient coping with fearful situations. This hypothesis was strengthened by the observation that naïve EE animals were almost all I. Pretested EE I rats were not influenced by the rearing condition: their behavior was comparable to SH animals' behavior and determined by retesting. In conclusion, these results demonstrated that, when applied to aging rats, EE produces different effects based on pre-housing cognitive performances. The issue needs further analyses, but the observation that not all animals are able to take advantage of EE to the same extent suggests the opportunity to design individually tailored approaches to optimize their efficacy and minimize possible unwanted consequences.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

Neurosteroidogenesis Today: Novel Targets for Neuroactive Steroid Synthesis and Action and Their Relevance for Translational Research

Neuroactive steroids are endogenous neuromodulators synthesised in the brain that rapidly alter neuronal excitability by binding to membrane receptors, in addition to the regulation of gene expression via intracellular steroid receptors. Neuroactive steroids induce potent anxiolytic, antidepressant, anticonvulsant, sedative, analgesic and amnesic effects, mainly through interaction with the GABAA receptor. They also exert neuroprotective, neurotrophic and antiapoptotic effects in several animal models of neurodegenerative diseases. Neuroactive steroids regulate many physiological functions, such as the stress response, puberty, the ovarian cycle, pregnancy and reward. Their levels are altered in several neuropsychiatric and neurological diseases and both preclinical and clinical studies emphasise a therapeutic potential of neuroactive steroids for these diseases, whereby symptomatology ameliorates upon restoration of neuroactive steroid concentrations. However, direct administration of neuroactive steroids has several challenges, including pharmacokinetics, low bioavailability, addiction potential, safety and tolerability, which limit its therapeutic use. Therefore, modulation of neurosteroidogenesis to restore the altered endogenous neuroactive steroid tone may represent a better therapeutic approach. This review summarises recent approaches that target the neuroactive steroid biosynthetic pathway at different levels aiming to promote neurosteroidogenesis. These include modulation of neurosteroidogenesis through ligands of the translocator protein 18 kDa and the pregnane xenobiotic receptor, as well as targeting of specific neurosteroidogenic enzymes such as 17β-hydroxysteroid dehydrogenase type 10 or P450 side chain cleavage. Enhanced neurosteroidogenesis through these targets may be beneficial not only for neurodegenerative diseases, such as Alzheimer's disease and age-related dementia, but also for neuropsychiatric diseases, including alcohol use disorders.

Bisphenol A, bisphenol F and bisphenol S affect differently 5α-reductase expression and dopamine-serotonin systems in the prefrontal cortex of juvenile female rats

BACKGROUND

Early-life exposure to the endocrine disruptor bisphenol A (BPA) affects brain function and behavior, which might be attributed to its interference with hormonal steroid signaling and/or neurotransmitter systems. Alternatively, the use of structural analogs of BPA, mainly bisphenol F (BPF) and bisphenol S (BPS), has increased recently. However, limited in vivo toxicity data exist.

OBJECTIVES

We investigated the effects of BPA, BPF and BPS on 5α-reductase (5α-R), a key enzyme involved in neurosteroidogenesis, as well as on dopamine (DA)- and serotonin (5-HT)-related genes, in the prefrontal cortex (PFC) of juvenile female rats.

METHODS

Gestating Wistar rats were treated with either vehicle or 10 μg/kg/day of BPA, BPF or BPS from gestational day 12 to parturition. Then, female pups were exposed from postnatal day 1 through day 21 (PND21), when they were euthanized and RT-PCR, western blot and quantitative PCR-array experiments were performed.

RESULTS

BPA decreased 5α-R2 and 5α-R3 mRNA and protein levels, while both BPF and BPS decreased 5α-R3 mRNA levels in PFC at PND21. Further, BPA, BPF and BPS significantly altered, respectively, the transcription of 25, 56 and 24 genes out of the 84 DA and 5-HT-related genes assayed. Of particular interest was the strong induction by all these bisphenols of Cyp2d4, implicated in corticosteroids synthesis.

CONCLUSIONS

Our results demonstrate for the first time that BPA, BPF and BPS differentially affect 5α-R and genes related to DA/5-HT systems in the female PFC. In vivo evidence of the potential adverse effects of BPF and BPS in the brain of mammals is provided in this work, raising questions about the safety of these chemicals as substitutes for BPA.

Astrocytic estrogen receptors and impaired neurotrophic responses in a rat model of perimenopause

In a perimenopausal model of middle-aged rats, the astrocyte estrogen receptor-alpha (ERa): ER-beta (ERb) ratio increased with the onset of acyclicity (constant estrus, CE) in association with impaired neurotrophic responses to estradiol (E2). We report additional data on irregular cycling (IR) from this study of 9 month old perimenopausal subgroups. In particular, irregular cyclers (IR) also show increased ERa:ERb ratio in cerebral cortex astrocytes comparable to acyclic individuals in CE. In mixed glial cultures from these same cycling subgroups, the E2-dependent neurotrophic activity and glial fibrillary acidic protein (GFAP) repression by E2 were impaired in IR to the same degree as in CE-derived glia. The greater importance of cycling status than age during the perimenopause to astrocyte ERs are attributable to individual variations of the residual ovarian follicle pool, which determine the onset of acyclicity. The corresponding loss of E2-dependent GFAP repression and E2-dependent neurotrophic activity add further to the inverse relationship of GFAP expression and astrocyte neurotrophic activity across aging in both sexes. These findings are relevant to impairments of spatial learning and of hippocampal long-term potentiation during the onset of IR in middle-aged rats, and to perimenopausal factors mediating the higher risk of women for Alzheimer disease.

Distinct cognitive effects of estrogen and progesterone in menopausal women

The effects of postmenopausal hormone treatment on cognitive outcomes are inconsistent in the literature. Emerging evidence suggests that cognitive effects are influenced by specific hormone formulations, and that progesterone is more likely to be associated with positive outcomes than synthetic progestin. There are very few studies of unopposed progesterone in postmenopausal women, and none that use functional neuroimaging, a sensitive measure of neurobiological function. In this study of 29 recently postmenopausal women, we used functional MRI and neuropsychological measures to separately assess the effects of estrogen or progesterone treatment on visual and verbal cognitive function. Women were randomized to receive 90 days of either estradiol or progesterone counterbalanced with placebo. After each treatment arm, women were given a battery of verbal and visual cognitive function and working memory tests, and underwent functional MRI including verbal processing and visual working memory tasks. We found that both estradiol and progesterone were associated with changes in activation patterns during verbal processing. Compared to placebo, women receiving estradiol treatment had greater activation in the left prefrontal cortex, a region associated with verbal processing and encoding. Progesterone was associated with changes in regional brain activation patterns during a visual memory task, with greater activation in the left prefrontal cortex and right hippocampus compared to placebo. Both treatments were associated with a statistically non-significant increase in number of words remembered following the verbal task performed during the fMRI scanning session, while only progesterone was associated with improved neuropsychological measures of verbal working memory compared to placebo. These results point to potential cognitive benefits of both estrogen and progesterone.

Progestogens' effects and mechanisms for object recognition memory across the lifespan

This review explores the effects of female reproductive hormones, estrogens and progestogens, with a focus on progesterone and allopregnanolone, on object memory. Progesterone and its metabolites, in particular allopregnanolone, exert various effects on both cognitive and non-mnemonic functions in females. The well-known object recognition task is a valuable experimental paradigm that can be used to determine the effects and mechanisms of progestogens for mnemonic effects across the lifespan, which will be discussed herein. In this task there is little test-decay when different objects are used as targets and baseline valance for objects is controlled. This allows repeated testing, within-subjects designs, and longitudinal assessments, which aid understanding of changes in hormonal milieu. Objects are not aversive or food-based, which are hormone-sensitive factors. This review focuses on published data from our laboratory, and others, using the object recognition task in rodents to assess the role and mechanisms of progestogens throughout the lifespan. Improvements in object recognition performance of rodents are often associated with higher hormone levels in the hippocampus and prefrontal cortex during natural cycles, with hormone replacement following ovariectomy in young animals, or with aging. The capacity for reversal of age- and reproductive senescence-related decline in cognitive performance, and changes in neural plasticity that may be dissociated from peripheral effects with such decline, are discussed. The focus here will be on the effects of brain-derived factors, such as the neurosteroid, allopregnanolone, and other hormones, for enhancing object recognition across the lifespan.

The perimenopausal aging transition in the female rat brain: decline in bioenergetic systems and synaptic plasticity

The perimenopause is an aging transition unique to the female that leads to reproductive senescence which can be characterized by multiple neurological symptoms. To better understand potential underlying mechanisms of neurological symptoms of perimenopause, the present study determined genomic, biochemical, brain metabolic, and electrophysiological transformations that occur during this transition using a rat model recapitulating fundamental characteristics of the human perimenopause. Gene expression analyses indicated two distinct aging programs: chronological and endocrine. A critical period emerged during the endocrine transition from regular to irregular cycling characterized by decline in bioenergetic gene expression, confirmed by deficits in fluorodeoxyglucose-positron emission tomography (FDG-PET) brain metabolism, mitochondrial function, and long-term potentiation. Bioinformatic analysis predicted insulin/insulin-like growth factor 1 and adenosine monophosphate-activated protein kinase/peroxisome proliferator-activated receptor gamma coactivator 1 alpha (AMPK/PGC1α) signaling pathways as upstream regulators. Onset of acyclicity was accompanied by a rise in genes required for fatty acid metabolism, inflammation, and mitochondrial function. Subsequent chronological aging resulted in decline of genes required for mitochondrial function and β-amyloid degradation. Emergence of glucose hypometabolism and impaired synaptic function in brain provide plausible mechanisms of neurological symptoms of perimenopause and may be predictive of later-life vulnerability to hypometabolic conditions such as Alzheimer's.

Hplc-ESI-MS/MS analysis of the water-soluble extract from Ziziphi spinosae semen and its ameliorating effect of learning and memory performance in mice

Background:

Ziziphi Spinosae Semen (ZSS), the seed of Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow., is a traditional herb for insomnia and anxiety in eastern Asia. However, few researches have been concerned with its effect on ameliorating memory and learning performance.

Objective:

To investigate the constituents of ZSS water soluble extract and its ameliorating learning and memory in mice.

Materials and Methods:

A new high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method was developed and validated to determine the main constituents in the extract. The effect of ZSS water soluble extract on memory and learning performance was investigated in mice by Y-maze and passive avoidance test.

Results:

The extract could significantly decrease the number of errors (NOE), and increase the transfer latency time (TLT) and electrical stimuli time (EST). In addition, spinosin, jujuboside A (JuA) and jujuboside B (JuB) were simultaneously identified and quantified in the extract. Their contents in the extract were as followed: Spinosin (223.51mg/g), JuA (63.76mg/g) and JuB (26.29mg/g).

Conclusion:

The extract played a promising role in ameliorating memory in mice with alcohol induced memory retrieval disorders, and might help to improve learning capacity to some extent. Spinosin, JuA and JuB were the predominant constituents, which might be mainly responsible for the definite activity.

Regulation of object recognition and object placement by ovarian sex steroid hormones

The ovarian hormones 17β-estradiol (E2) and progesterone (P4) are potent modulators of hippocampal memory formation. Both hormones have been demonstrated to enhance hippocampal memory by regulating the cellular and molecular mechanisms thought to underlie memory formation. Behavioral neuroendocrinologists have increasingly used the object recognition and object placement (object location) tasks to investigate the role of E2 and P4 in regulating hippocampal memory formation in rodents. These one-trial learning tasks are ideal for studying acute effects of hormone treatments on different phases of memory because they can be administered during acquisition (pre-training), consolidation (post-training), or retrieval (pre-testing). This review synthesizes the rodent literature testing the effects of E2 and P4 on object recognition (OR) and object placement (OP), and the molecular mechanisms in the hippocampus supporting memory formation in these tasks. Some general trends emerge from the data. Among gonadally intact females, object memory tends to be best when E2 and P4 levels are elevated during the estrous cycle, pregnancy, and in middle age. In ovariectomized females, E2 given before or immediately after testing generally enhances OR and OP in young and middle-aged rats and mice, although effects are mixed in aged rodents. Effects of E2 treatment on OR and OP memory consolidation can be mediated by both classical estrogen receptors (ERα and ERβ), and depend on glutamate receptors (NMDA, mGluR1) and activation of numerous cell signaling cascades (e.g., ERK, PI3K/Akt, mTOR) and epigenetic processes (e.g., histone acetylation, DNA methylation). Acute P4 treatment given immediately after training also enhances OR and OP in young and middle-aged ovariectomized females by activating similar cell signaling pathways as E2 (e.g., ERK, mTOR). The few studies that have administered both hormones in combination suggest that treatment can enhance OR and OP, but that effects are highly dependent on factors such as dose and timing of administration. In addition to providing more detail on these general conclusions, this review will discuss directions for future avenues of research into the hormonal regulation of object memory.

Effects of chronic oestradiol, progesterone and medroxyprogesterone acetate on hippocampal neurogenesis and adrenal mass in adult female rats

Both natural oestrogens and progesterone influence synaptic plasticity and neurogenesis within the female hippocampus. However, less is known of the impact of synthetic hormones on hippocampal structure and function. There is some evidence that the administration of the synthetic progestin, medroxyprogesterone acetate (MPA) is not as beneficial as natural progesterone and can attenuate oestrogen-induced neuroprotection. Although the effects of oestradiol have been well studied, little is known about the effects of natural and synthetic progestins alone and in combination with oestradiol on adult neurogenesis in females. In the present study, we investigated the effects of chronic oestradiol, progesterone, MPA and the co-administration of each progestin with oestradiol on neurogenesis within the dentate gyrus of adult ovariectomised female rats. Twenty-four hours after a bromodeoxyuridine (BrdU; 200 mg/kg) injection, female rats were repeatedly administered either progesterone (1 or 4 mg), MPA (1 or 4 mg), oestradiol benzoate (EB), progesterone or MPA in combination with EB (10 μg), or vehicle for 21 days. Rats were perfused on day 22 and brain tissue was analysed for the number of BrdU-labelled and Ki67 (an endogenous marker of cell proliferation)-expressing cells. EB alone and MPA + EB significantly decreased neurogenesis and the number of surviving BrdU-labelled cells in the dorsal region of the dentate gyrus, independent of any effects on cell proliferation. Furthermore, MPA (1 and 4 mg) and MPA + EB treated animals had significantly lower adrenal/body mass ratios and reduced serum corticosterone (CORT) levels. By contrast, progesterone + EB treated animals had significantly higher adrenal/body mass ratios and 1 mg of progesterone, progesterone + EB, and EB significantly increased CORT levels. The results of the present study demonstrate that different progestins alone and in combination with oestradiol can differentially affect neurogenesis (via cell survival) and regulation of the hypothalamic-pituitary-adrenal axis. These findings have implications for women using hormone replacement therapies with MPA for both neuroprotection and stress-related disorders.

Progesterone protects normative anxiety-like responding among ovariectomized female mice that conditionally express the HIV-1 regulatory protein, Tat, in the CNS

Increased anxiety is co-morbid with human immunodeficiency virus (HIV) infection. Actions of the neurotoxic HIV-1 regulatory protein, Tat, may contribute to affective dysfunction. We hypothesized that Tat expression would increase anxiety-like behavior of female GT-tg bigenic mice that express HIV-1 Tat protein in the brain in a doxycycline-dependent manner. Furthermore, given reports that HIV-induced anxiety may occur at lower rates among women, and that the neurotoxic effects of Tat are ameliorated by sex steroids in vitro, we hypothesized that 17β-estradiol and/or progesterone would ameliorate Tat-induced anxiety-like effects. Among naturally-cycling proestrous and diestrous mice, Tat-induction via 7days of doxycycline treatment significantly increased anxiety-like responding in an open field, elevated plus maze and a marble-burying task, compared to treatment with saline. Proestrous mice demonstrated less anxiety-like behavior than diestrous mice in the open field and elevated plus maze, but these effects did not significantly interact with Tat-induction. Among ovariectomized mice, doxycycline-induced Tat protein significantly increased anxiety-like behavior in an elevated plus maze and a marble burying task compared to saline-treated mice, but not an open field (where anxiety-like responding was already maximal). Co-administration of progesterone (4mg/kg), but not 17β-estradiol (0.09mg/kg), with doxycycline significantly ameliorated anxiety-like responding in the elevated plus maze and marble burying tasks. When administered together, 17β-estradiol partially antagonized the protective effects of progesterone on Tat-induced anxiety-like behavior. These findings support evidence of steroid-protection over HIV-1 proteins, and extend them by demonstrating the protective capacity of progesterone on Tat-induced anxiety-like behavior of ovariectomized female mice.

Progesterone and vitamin D: Improvement after traumatic brain injury in middle-aged rats

Progesterone (PROG) and vitamin D hormone (VDH) have both shown promise in treating traumatic brain injury (TBI). Both modulate apoptosis, inflammation, oxidative stress, and excitotoxicity. We investigated whether 21 days of VDH deficiency would alter cognitive behavior after TBI and whether combined PROG and VDH would improve behavioral and morphological outcomes more than either hormone alone in VDH-deficient middle-aged rats given bilateral contusions of the medial frontal cortex. PROG (16 mg/kg) and VDH (5 μg/kg) were injected intraperitoneally 1 h post-injury. Eight additional doses of PROG were injected subcutaneously over 7 days post-injury. VDH deficiency itself did not significantly reduce baseline behavioral functions or aggravate impaired cognitive outcomes. Combination therapy showed moderate improvement in preserving spatial and reference memory but was not significantly better than PROG monotherapy. However, combination therapy significantly reduced neuronal loss and the proliferation of reactive astrocytes, and showed better efficacy compared to VDH or PROG alone in preventing MAP-2 degradation. VDH+PROG combination therapy may attenuate some of the potential long-term, subtle, pathophysiological consequences of brain injury in older subjects.

Progesterone, compared to medroxyprogesterone acetate, to C57BL/6, but not 5α-reductase mutant, mice enhances object recognition and placement memory and is associated with higher BDNF levels in the hippocampus and cortex

Progesterone (P4) may influence cognition in part through actions of its 5α-reduced metabolite, allopregnanolone. Ovariectomized mice that were C57BL/6 wildtype (WT), or deficient in the 5α-reductase Type 1 enzyme (5α-reductase knockout; 5αRKO), were administered vehicle, P4, allopregnanolone, or medroxyprogesterone acetate (MPA) after training in the object recognition or placement tasks. WT mice administered P4 or allopregnanolone performed significantly better in the object recognition and placement tasks than did WT mice administered vehicle or MPA. 5αRKO mice administered allopregnanolone, but not P4, MPA, or vehicle showed enhanced performance in the object recognition and placement tasks. Levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and hippocampus were lowest among mice administered MPA. Thus, some of P4s effects to enhance cognitive performance may be incumbent upon its 5α-reduction.

Age increase of estrogen receptor-α (ERα) in cortical astrocytes impairs neurotrophic support in male and female rats

Rodent models show decreased neuronal responses to estradiol (E2) during aging (E2-desensitization) in association with reduced neuronal estrogen receptor (ER)-α, but little is known about age changes of E2-dependent astrocytic neurotrophic support. Because elevated expression of astrocyte glial fibrillary acidic protein (GFAP) is associated with impaired neurotrophic activity and because the GFAP promoter responds to ERα, we investigated the role of astrocytic ERα and ERβ in impaired astrocyte neurotrophic activity during aging. In vivo and in vitro, ERα was increased greater than 50% with age in astrocytes from the cerebral cortex of male rats (24 vs 3 months), whereas ERβ did not change. In astrocytes from 3-month-old males, experimentally increasing the ERα to ERβ ratio induced the aging phenotype of elevated GFAP and impaired E2-dependent neurite outgrowth. In 24-month-old male astrocytes, lowering ERα reversed the age elevation of GFAP and partially restored E2-dependent neurite outgrowth. Mixed glia (astrocytes to microglia, 3:1) of both sexes also showed these age changes. In a model of perimenopause, mixed glia from 9- to 15-month rats showed E2 desensitization: 9-month regular cyclers retained young-like ERα to ERβ ratios and neurotrophic activity, whereas 9-month noncyclers had elevated ERα and GFAP but low E2-dependent neurotrophic activity. In vivo, ERα levels in cortical astrocytes were also elevated. The persisting effects of ovarian acyclicity in vitro are hypothesized to arise from steroidal perturbations during ovarian senescence. These findings suggest that increased astrocyte ERα expression during aging contributes to the E2 desensitization of the neuronal responses in both sexes.

Loss of CB1 receptors leads to differential age-related changes in reward-driven learning and memory

Previous studies have shown that cannabinoid 1 (CB1) receptor signaling dissociates between reward-associated and aversive memories. The influence of CB1 receptors on the aversion-driven spatial learning in the Morris water maze test is strongly age-dependent: mice with genetic deletion of CB1 receptors (Cnr1^−/−) show superior learning when young but inferior learning when old compared to age-matched wild-type mice. Whether the reward-driven spatial learning is influenced in the same way by CB1 receptor signaling as the aversion-driven learning remains unclear. Thus, we examined the performance of Cn1^−/− and their wild-type littermates at ages of 2-, 5-, and 12-months-old in the eight-arm radial maze test—a reward-motivated model of spatial learning. Interestingly, 2-months-old Cnr1^−/− mice had a superior learning ability to wild-type mice. At the age of 5-months, Cnr1^−/− mice showed the same performance as the wild-type littermates. However, 12-months-old Cnr1^−/− mice showed significantly impaired performances in each parameter of the test. Accordingly, this study provides compelling support for our previous result that genetic deletion of CB1 receptor leads to early onset of age-related memory decline, similarly affecting both reward and aversion-driven learning.

Dissecting the age-related decline on spatial learning and memory tasks in rodent models: N-methyl-D-aspartate receptors and voltage-dependent Ca2+ channels in senescent synaptic plasticity

In humans, heterogeneity in the decline of hippocampal-dependent episodic memory is observed during aging. Rodents have been employed as models of age-related cognitive decline and the spatial water maze has been used to show variability in the emergence and extent of impaired hippocampal-dependent memory. Impairment in the consolidation of intermediate-term memory for rapidly acquired and flexible spatial information emerges early, in middle-age. As aging proceeds, deficits may broaden to include impaired incremental learning of a spatial reference memory. The extent and time course of impairment has been be linked to senescence of calcium (Ca²⁺) regulation and Ca²⁺-dependent synaptic plasticity mechanisms in region CA1. Specifically, aging is associated with altered function of N-methyl-D-aspartate receptors (NMDARs), voltage-dependent Ca²⁺ channels (VDCCs), and ryanodine receptors (RyRs) linked to intracellular Ca²⁺ stores (ICS). In young animals, NMDAR activation induces long-term potentiation of synaptic transmission (NMDAR-LTP), which is thought to mediate the rapid consolidation of intermediate-term memory. Oxidative stress, starting in middle-age, reduces NMDAR function. In addition, VDCCs and ICS can actively inhibit NMDAR-dependent LTP and oxidative stress enhances the role of VDCC and RyR-ICS in regulating synaptic plasticity. Blockade of L-type VDCCs promotes NMDAR-LTP and memory in older animals. Interestingly, pharmacological or genetic manipulations to reduce hippocampal NMDAR function readily impair memory consolidation or rapid learning, generally leaving incremental learning intact. Finally, evidence is mounting to indicate a role for VDCC-dependent synaptic plasticity in associative learning and the consolidation of remote memories. Thus, VDCC-dependent synaptic plasticity and extrahippocampal systems may contribute to incremental learning deficits observed with advanced aging.

Cognitive-impairing effects of medroxyprogesterone acetate in the rat: independent and interactive effects across time

RATIONALE

The synthetic progestin medroxyprogesterone acetate (MPA), widely used in hormone therapy (HT) and as the contraceptive Depo Provera, is implicated in detrimental cognitive effects in women. Recent evidence in aged ovariectomized (Ovx) rodents shows that short-term MPA treatment impairs cognition and alters the GABAergic system.

OBJECTIVES

Using rats, we evaluated the long-lasting cognitive and GABAergic effects of MPA administered in young adulthood (Early-MPA), modeling contraception, and how this early exposure interacts with later MPA treatment (Late-MPA), modeling HT.

METHODS

Early-MPA treatment involved weekly anti-ovulatory MPA injections (3.5 mg) from 4 to 8 months of age in ovary-intact rats. At 10 months old, rats were Ovx and weekly MPA injections were re-initiated and continued throughout testing for Late-MPA treatment.

RESULTS

On the water radial-arm maze, all MPA-treated groups showed working memory impairment compared to Controls (p < 0.05); Early + Late-MPA rats were impaired on multiple dimensions of working memory (p < 0.05). On the Morris maze, Late-MPA rats showed greater overnight forgetting compared to Controls (p < 0.05). At study conclusion, MPA was detected in serum in all MPA-treated groups except Early-MPA, confirming treatment and clearance from serum in Early-MPA rats. In animals with detectable serum MPA, higher MPA levels were associated with less dorsal-hippocampal glutamic acid decarboxylase, the synthesizing enzyme for GABA (p = 0.0059).

CONCLUSIONS

Findings suggest that MPA treatment leads to long-lasting cognitive impairments in the rodent, even in the absence of circulating MPA in animals given prior MPA treatment, which may relate to the GABAergic system. Further research defining the parameters of the negative impact of this widely used progestin on brain and cognition is warranted.

Sex differences in the burying behavior test in middle-aged rats: effects of diazepam

The full behavioral profile displayed during the burying behavior test was studied in middle aged (11-14 months) males, females with irregular estrous cycles, and females in persistent diestrus, with and without diazepam (0.5-2.0mg/kg). Ambulation and motor coordination were also tested to discern behavioral changes from general motor alterations. Without diazepam treatment, middle-aged males showed longer burying behavior latencies, more prod explorations and less freezing than both groups of females. Untreated middle aged males also showed less cumulative burying and more immobility compared to females with irregular cycles. None of the parameters showed any difference between the female groups. Diazepam (0.5 and 1.0mg/kg) increased burying behavior latency in females, but had no effect on any parameter in middle aged males. However, a higher dose (2.0mg/kg) of diazepam increased immobility, freezing and the number of prod shocks and decreased prod explorations and groomings, but impaired motor coordination in males. In contrast with young males and females, diazepam at any dose reduced cumulative burying. Data are discussed on the bases of (1) sex and age differences in burying behavior and on (2) the anxiolytic-like action of diazepam and its side effects.

Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues

17β-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERβ for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERβ related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

Conjugated equine estrogen, with medroxyprogesterone acetate, enhances formation of 5alpha-reduced progestogens and reduces anxiety-like behavior of middle-aged rats

The mechanisms by which progestogens influence affective behaviors in females are poorly understood despite clear changes in mood/affect that are associated with their decline during menopause. Conjugated equine estrogens (CEE), with or without medroxyprogesterone acetate (MPA), are commonly prescribed hormone-replacement, but there is heterogeneity in responses to these pharmacotherapies. One way in which these compounds differ is in their capacity to potentiate metabolism of progesterone to its 5alpha-reduced products, dihydroprogesterone and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). This study investigated whether responses to CEE and MPA may be related to the capacity to metabolize progesterone. Middle-aged female rats that had maintained reproductive status, or those that had a decline, were administered vehicle, CEE and/or MPA. Effects on anxiety-like (open field, elevated plus maze) and social behaviors (social interaction test), and plasma and hippocampus steroid levels were determined. We hypothesized that CEE, but not MPA, would decrease anxiety-like behavior coincident with increased hippocampal metabolism of progesterone. CEE, or CEE+MPA, increased central entries in the open field and time spent on the open arms of the plus maze, but did not alter social interaction of rats that had maintained reproductive status. CEE and/or CEE+MPA increased E2 and 3alpha,5alpha-THP in plasma and/or hippocampus of rats, but MPA increased levels of dihydroprogesterone in the hippocampus of rats with declining reproductive status. Simple regressions showed that hippocampus 3alpha,5alpha-THP levels accounted for a significant proportion of the variance in anxiety-like behavior. Therefore, effects of CEE to reduce anxiety-like behavior of middle-aged rats may be owing, in part, to its capacity to enhance levels of 3alpha,5alpha-THP in the hippocampus.

I. Levels of 5α-reduced progesterone metabolite in the midbrain account for variability in reproductive behavior of middle-aged female rats

At middle-age, the reproductive capacity of female rats begins to decline. Whether there are consequences for social and reproductive behaviors related to changes in estradiol (E(2)), progesterone (P(4)) and its 5α-reduced metabolites, dihydroprogesterone (DHP) and 5α-pregnan-3α-ol-20-one (3α,5α-THP), is of interest. In Experiment 1, 1-year-old female breeder rats that had "maintained their reproductive status" (having 4-5 days estrous cycles, > 60% successful pregnancies after mating, > 10 pups/litter) or their age-matched counterparts with "declining reproductive status" were assessed in social interaction, standard mating, and paced mating when in proestrus. Rats that maintained reproductive status tended to have higher levels of proceptivity, and significantly reduced aggression, towards males, compared to rats with declining reproductive status. Basal midbrain E(2) and DHP levels accounted for a significant proportion of variance in lordosis. In Experiment 2, 1-year-old, age-matched, female breeders that had maintained reproductive status or were in reproductive decline were compared to three-month old, nulliparous females that had regular (4-5 days) or irregular estrous cycles. Age did not influence paced mating but younger rats had greater diencephalon E(2) than did middle-aged rats. After mating, rats with declining/irregular reproductive status had higher P(4) and DHP levels in midbrain than did rats with maintaining/regular reproductive status, albeit differences in midbrain 3α,5α-THP were not seen. Middle-aged rats that maintained reproductive function had greater 3α,5α-THP formation in diencephalon compared to other groups. Thus, age-related changes in central progestogen formation in midbrain or diencephalon may contribute to some variability in expression of reproductive behaviors.