Gonadectomy reduces the density of androgen receptor-immunoreactive neurons in male rat's hippocampus: testosterone replacement compensates it

Beyond Birth Control: The Neuroscience of Hormonal Contraceptives

Hormonal contraceptives (HCs) are one of the most highly prescribed classes of drugs in the world used for both contraceptive and noncontraceptive purposes. Despite their prevalent use, the impact of HCs on the brain remains inadequately explored. This review synthesizes recent findings on the neuroscience of HCs, with a focus on human structural neuroimaging as well as translational, nonhuman animal studies investigating the cellular, molecular, and behavioral effects of HCs. Additionally, we consider data linking HCs to mood disorders and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and stress response as a potential mediator. The review also addresses the unique sensitivity of the adolescent brain to HCs, noting significant changes in brain structure and function when HCs are used during this developmental period. Finally, we discuss potential effects of HCs in combination with smoking-derived nicotine on outcomes of ischemic brain damage. Methodological challenges, such as the variability in HC formulations and user-specific factors, are acknowledged, emphasizing the need for precise and individualized research approaches. Overall, this review underscores the necessity for continued interdisciplinary research to elucidate the neurobiological mechanisms of HCs, aiming to optimize their use and improve women's health.

Effects of estrogen on spatial navigation and memory

RATIONALE

Animal studies suggest that the so-called "female" hormone estrogen enhances spatial navigation and memory. This contradicts the observation that males generally out-perform females in spatial navigation and tasks involving spatial memory. A closer look at the vast number of studies actually reveals that performance differences are not so clear.

OBJECTIVES

To help clarify the unclear performance differences between men and women and the role of estrogen, we attempted to isolate organizational from activational effects of estrogen on spatial navigation and memory.

METHODS

In a double-blind, placebo-controlled study, we tested the effects of orally administered estradiol valerate (E2V) in healthy, young women in their low-hormone menstrual cycle phase, compared to healthy, young men. Participants performed several first-person, environmentally rich, 3-D computer games inspired by spatial navigation and memory paradigms in animal research.

RESULTS

We found navigation behavior suggesting that sex effects dominated any E2 effects with men performing better with allocentric strategies and women with egocentric strategies. Increased E2 levels did not lead to general improvements in spatial ability in either sex but to behavioral changes reflecting navigation flexibility.

CONCLUSION

Estrogen-driven differences in spatial cognition might be better characterized on a spectrum of navigation flexibility rather than by categorical performance measures or skills.

CYP46A1-mediated cholesterol turnover induces sex-specific changes in cognition and counteracts memory loss in ovariectomized mice

The brain-specific enzyme CYP46A1 controls cholesterol turnover by converting cholesterol into 24S-hydroxycholesterol (24OH). Dysregulation of brain cholesterol turnover and reduced CYP46A1 levels are observed in Alzheimer's disease (AD). In this study, we report that CYP46A1 overexpression in aged female mice leads to enhanced estrogen signaling in the hippocampus and improved cognitive functions. In contrast, age-matched CYP46A1 overexpressing males show anxiety-like behavior, worsened memory, and elevated levels of 5α-dihydrotestosterone in the hippocampus. We report that, in neurons, 24OH contributes to these divergent effects by activating sex hormone signaling, including estrogen receptors. CYP46A1 overexpression in female mice protects from memory impairments induced by ovariectomy while having no effects in gonadectomized males. Last, we measured cerebrospinal fluid levels of 24OH in a clinical cohort of patients with AD and found that 24OH negatively correlates with neurodegeneration markers only in women. We suggest that CYP46A1 activation is a valuable pharmacological target for enhancing estrogen signaling in women at risk of developing neurodegenerative diseases.

Central androgen action reverses hypothalamic astrogliosis and atherogenic risk factors induced by orchiectomy and high-fat diet feeding in male mice

Hypogonadism in males confers elevated cardiovascular disease (CVD) risk by unknown mechanisms. Recent radiological evidence suggests that low testosterone (T) is associated with mediobasal hypothalamic (MBH) gliosis, a central nervous system (CNS) cellular response linked to metabolic dysfunction. To address mechanisms linking CNS androgen action to CVD risk, we generated a hypogonadal, hyperlipidemic mouse model with orchiectomy (ORX) combined with hepatic PCSK9 overexpression. After 4 wk of high-fat, high-sucrose diet (HFHS) consumption, despite equal body weights and glucose tolerance, androgen-deficient ORX mice had a more atherogenic lipid profile and increased liver and leukocyte inflammatory signaling compared with sham-operated control mice. Along with these early CVD risk indicators, ORX markedly amplified HFHS-induced astrogliosis in the MBH. Transcriptomic analysis further revealed that ORX and high-fat diet feeding induced upregulation of inflammatory pathways and downregulation of metabolic pathways in hypothalamic astrocytes. To interrogate the role of sex steroid signaling in the CNS in cardiometabolic risk and MBH inflammation, central infusion of T and dihydrotestosterone (DHT) was performed on ORX mice. Central DHT prevented MBH astrogliosis and reduced the liver inflammatory signaling and monocytosis induced by HFHS and ORX; T had a partial protective effect. Finally, a cross-sectional study in 41 adult men demonstrated a positive correlation between radiological evidence of MBH gliosis and plasma lipids. These findings demonstrate that T deficiency in combination with a Western-style diet promotes hypothalamic gliosis concomitant with increased atherogenic risk factors and provide supportive evidence for regulation of lipid metabolism and cardiometabolic risk determinants by the CNS action of sex steroids.NEW & NOTEWORTHY This study provides evidence that hypothalamic gliosis is a key early event through which androgen deficiency in combination with a Western-style diet might lead to cardiometabolic dysregulation in males. Furthermore, this work provides the first evidence in humans of a positive association between hypothalamic gliosis and LDL-cholesterol, advancing our knowledge of CNS influences on CVD risk progression.

Combined effects of the contraceptive hormones, ethinyl estradiol and levonorgestrel, on the use of place and response memory in gonadally-intact female rats

During maze navigation rats can rely on hippocampus-mediated place memory or striatum-mediated response memory. Ovarian hormones bias whether females use place or response memory to reach a reward. Here, we investigated the impact of the contraceptive hormones, ethinyl estradiol (EE) and levonorgestrel (LNG), on memory bias. A total of 63 gonadally-intact female rats were treated with either 10 μg/kg of EE alone, 20 μg/kg of LNG alone, both 10 μg/kg of EE and 20 μg/kg of LNG together, or a sesame oil injection with 5% ethanol as a vehicle control. Rats in the control condition were tested during the diestrus phase of the estrous cycle in order to control for the low circulating levels of gonadotropin and ovarian hormones that occur with oral contraceptive administration. Rats treated with LNG alone had a bias towards the use of place memory compared to diestrus phase control rats. This bias was not observed if LNG was administered in combination with EE. Rats treated with EE or EE+LNG did not have a statistically significant difference in memory bias compared to rats in the control group. These data show that synthetic hormones contained in oral contraceptives administered to females influence which cognitive strategy is predominantly used during navigation.

Aging, testosterone, and neuroplasticity: friend or foe?

Neuroplasticity or neural plasticity implicates the adaptive potential of the brain in response to extrinsic and intrinsic stimuli. The concept has been utilized in different contexts such as injury and neurological disease. Neuroplasticity mechanisms have been classified into neuroregenerative and function-restoring processes. In the context of injury, neuroplasticity has been defined in three post-injury epochs. Testosterone plays a key yet double-edged role in the regulation of several neuroplasticity alterations. Research has shown that testosterone levels are affected by numerous factors such as age, stress, surgical procedures on gonads, and pharmacological treatments. There is an ongoing debate for testosterone replacement therapy (TRT) in aging men; however, TRT is more useful in young individuals with testosterone deficit and more specific subgroups with cognitive dysfunction. Therefore, it is important to pay early attention to testosterone profile and precisely uncover its harms and benefits. In the present review, we discuss the influence of environmental factors, aging, and gender on testosterone-associated alterations in neuroplasticity, as well as the two-sided actions of testosterone in the nervous system. Finally, we provide practical insights for further study of pharmacological treatments for hormonal disorders focusing on restoring neuroplasticity.

Metabolic hormones mediate cognition

Recent biochemical and behavioural evidence indicates that metabolic hormones not only regulate energy intake and nutrient content, but also modulate plasticity and cognition in the central nervous system. Disruptions in metabolic hormone signalling may provide a link between metabolic syndromes like obesity and diabetes, and cognitive impairment. For example, altered metabolic homeostasis in obesity is a strong determinant of the severity of age-related cognitive decline and neurodegenerative disease. Here we review the evidence that eating behaviours and metabolic hormones-particularly ghrelin, leptin, and insulin-are key players in the delicate regulation of neural plasticity and cognition. Caloric restriction and antidiabetic therapies, both of which affect metabolic hormone levels can restore metabolic homeostasis and enhance cognitive function. Thus, metabolic hormone pathways provide a promising target for the treatment of cognitive decline.

Comparison of neuroprotective effects of dihydrotestosterone, 17β-estradiol, and Pueraria mirifica herb extract on cognitive impairment in androgen deficient male rats

This study investigated the neuroprotective effects of dihydrotestosterone (DHT), 17β-estradiol (E₂), and Pueraria mirifica herb extract (PME; an alternative source of natural estrogens) on the (i) learning and memory in androgen-deficient male rats, and on the hippocampus expression levels of (ii) mRNA of genes associated with synaptic transmission and structure, neurofibrillary tangles, and amyloid plaques, and (iii) total and phosphorylated tau proteins. The four-month-old male rats were sham-operated or orchidectomized (ODX). The ODX rats were divided into four groups, and orally treated for 2 months with either 1 mL/d of distilled water or 100 mg/kg/d of PME; or subcutaneously injected with 1 mg/kg/d of DHT or 80 μg/kg/d of E₂. The impairment of spatial learning behavior and memory capacity in the ODX rats was prevented by DHT, E_2, and PME. Recovery of the orchidectomy-induced deterioration of the synaptic plasticity in the hippocampus of rats was ranked as E₂ ≥ PME > DHT. Both DHT and PME mitigated the increased Tau3 and Tau4 mRNA levels, and Tau-5 and P-Tau Ser³⁹⁶ protein levels more than E₂ (DHT ≥ PME > E₂). Only DHT tended to decrease App mRNA expression level. In conclusion, DHT showed a stronger efficacy for mitigation of the impaired spatial learning behavior and memory capacity in androgen-deficient male rats compared to E₂ and PME, and their mechanisms of action are slightly different.

Seasonal variation in gonadal hormones, spatial cognition, and hippocampal attributes: More questions than answers

A large body of research has been dedicated to understanding the factors that modulate spatial cognition and attributes of the hippocampus, a highly plastic brain region that underlies spatial processing abilities. Variation in gonadal hormones impacts spatial memory and hippocampal attributes in vertebrates, although the direction of the effect has not been entirely consistent. To add complexity, individuals in the field must optimize fitness by coordinating activities with the appropriate environmental cues, and many of these behaviors are correlated tightly with seasonal variation in gonadal hormone release. As such, it remains unclear if the relationship among systemic gonadal hormones, spatial cognition, and the hippocampus also exhibits seasonal variation. This review presents an overview of the relationship among gonadal hormones, the hippocampus, and spatial cognition, and how the seasonal release of gonadal hormones correlates with seasonal variation in spatial cognition and hippocampal attributes. Additionally, this review presents other neuroendocrine mechanisms that may be involved in modulating the relationship among seasonality, gonadal hormone release, and the hippocampus and spatial cognition, including seasonal rhythms of steroid hormone binding globulins, neurosteroids, sex steroid hormone receptor expression, and hormone interactions. Here, endocrinology, ecology, and behavioral neuroscience are brought together to present an overview of the research demonstrating the mechanistic effects of systemic gonadal hormones on spatial cognition and the hippocampus, while, at a functional level, superimposing seasonal effects to examine ecologically-relevant circannual changes in gonadal hormones and spatial behaviors.

Astroglial cells as neuroendocrine targets in forebrain development: Implications for sex differences in psychiatric disease

Astroglial cells are the most abundant cell type in the mammalian brain. They are implicated in almost every aspect of brain physiology, including maintaining homeostasis, building and maintaining the blood brain barrier, and the development and maturation of neuronal networks. Critically, astroglia also express receptors for gonadal sex hormones, respond rapidly to gonadal hormones, and are able to synthesize hormones. Thus, they are positioned to guide and mediate sexual differentiation of the brain, particularly neuronal networks in typical and pathological conditions. In this review, we describe astroglial involvement in the organization and development of the brain, and consider known sex differences in astroglial responses to understand how astroglial cell-mediated organization may play a role in forebrain sexual dimorphisms in human populations. Finally, we consider how sexually dimorphic astroglial responses and functions in development may lead to sex differences in vulnerability for neuropsychiatric disorders.

Dose-dependent effects of testosterone on spatial learning strategies and brain-derived neurotrophic factor in male rats

Studies suggest that males outperform females on some spatial tasks. This may be due to the effects of sex steroids on spatial strategy preferences. Past experiments with male rats have demonstrated that low doses of testosterone bias them toward a response strategy, whereas high doses of testosterone bias them toward a place strategy. We investigated the effect of different testosterone doses on the ability of male rats to effectively employ these two spatial learning strategies. Furthermore, we quantified concentrations of brain-derived neurotrophic factor (pro-, mature-, and total BDNF) in the prefrontal cortex, hippocampus, and striatum. All rats were bilaterally castrated and assigned to one of three daily injection doses of testosterone propionate (0.125, 0.250, or 0.500 mg/rat) or a control injection of the drug vehicle. Using a plus-maze protocol, we found that a lower testosterone dose (0.125 mg) significantly improved rats' performance on a response task, whereas a higher testosterone dose (0.500 mg) significantly improved rats' performance on a place task. In addition, we found that a low dose of testosterone (0.125 mg) increased total BDNF in the striatum, while a high dose (0.500 mg) increased total BDNF in the hippocampus. Taken altogether, these results suggest that high and low levels of testosterone enhance performance on place and response spatial tasks, respectively, and this effect is associated with changes in BDNF levels within relevant brain regions.

Age-dependent effects of testosterone on spatial memory in male rats

Decreased spatial memory is common in aging populations and reduces their quality of life. Although its role is still controversial, low testosterone (T) may contribute to impaired cognition in aged men. This study aimed to identify the role of T in age-related deficiencies in spatial memory among male rats. Young adult (3 months old) and aged (21 months old) Wistar rats were assigned to independent groups: intact, orchidectomized, or orchidectomized + subcutaneous pellets of T propionate. The phases of spatial memory acquisition (4 daily trials/4 days) and spatial memory retention (1 trial/day, 3 and 12 days after acquisition) were evaluated using the Barnes maze. Compared with young adults, aged intact rats took longer to find the goal, made more mistakes, and showed only slight improvements in goal sector exploration across the acquisition period. The young orchidectomized rats showed no improvement in performance over the days during the acquisition phase. T treatment in hormonally deprived old rats produced a small improvement in goal sector exploration and number of errors during the acquisition phase. Meanwhile, in young adults, this treatment improved the goal sector searching in the retention phase (12 days after acquisition training). Our results suggested that age-related spatial memory deficits cannot be entirely explained by the decline in T levels; however, this androgen produced subtle and mild beneficial effects on spatial memory in young and old males. Taken together, our findings suggest age differences in the role of T on spatial memory in males.

Androgen Affects the Dynamics of Intrinsic Plasticity of Pyramidal Neurons in the CA1 Hippocampal Subfield in Adolescent Male Rats

Androgen receptor (AR) is abundantly expressed in the preoptico-hypothalamic area, bed nucleus of stria terminalis, and medial amygdala of the brain where androgen plays an important role in regulating male sociosexual, emotional and aggressive behaviors. In addition to these brain regions, AR is also highly expressed in the hippocampus, suggesting that the hippocampus is another major target of androgenic modulation. It is known that androgen can modulate synaptic plasticity in the CA1 hippocampal subfield. However, to date, the effects of androgen on the intrinsic plasticity of hippocampal neurons have not been clearly elucidated. In this study, the effects of androgen on the expression of AR in the hippocampus and on the dynamics of intrinsic plasticity of CA1 pyramidal neurons were examined using immunohistochemistry, Western blotting and whole-cell current-clamp recording in unoperated, sham-operated, orchiectomized (OCX), OCX + testosterone (T) or OCX + dihydrotestosterone (DHT)-primed adolescent male rats. Orchiectomy significantly decreased AR-immunoreactivity, resting membrane potential, action potential numbers, afterhyperpolarization amplitude and membrane resistance, whereas it significantly increased action potential threshold and membrane capacitance. These effects were successfully reversed by treatment with either aromatizable androgen T or non-aromatizable androgen DHT. Furthermore, administration of the AR-antagonist flutamide in intact rats showed similar changes to those in OCX rats, suggesting that androgens affect the excitability of CA1 pyramidal neurons possibly by acting on the AR. Our current study potentially clarifies the role of androgen in enhancing the basal excitability of the CA1 pyramidal neurons, which may influence selective neuronal excitation/activation to modulate certain hippocampal functions.

Testosterone and Adult Neurogenesis

It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear. There is considerable evidence that steroid hormones modulate various stages of adult neurogenesis, and this review provides a focused summary of the effects of testosterone on adult neurogenesis. Initial evidence came from field studies with birds and wild rodent populations. Subsequent experiments with laboratory rodents have tested the effects of testosterone and its steroid metabolites upon adult neurogenesis, as well as the functional consequences of induced changes in neurogenesis. These experiments have provided clear evidence that testosterone increases adult neurogenesis within the dentate gyrus region of the hippocampus through an androgen-dependent pathway. Most evidence indicates that androgens selectively enhance the survival of newly generated neurons, while having little effect on cell proliferation. Whether this is a result of androgens acting directly on receptors of new neurons remains unclear, and indirect routes involving brain-derived neurotrophic factor (BDNF) and glucocorticoids may be involved. In vitro experiments suggest that testosterone has broad-ranging neuroprotective effects, which will be briefly reviewed. A better understanding of the effects of testosterone upon adult neurogenesis could shed light on neurological diseases that show sex differences.

G Protein-Coupled Estrogen Receptor Immunoreactivity Fluctuates During the Estrous Cycle and Show Sex Differences in the Amygdala and Dorsal Hippocampus

G protein-coupled estrogen receptor (GPER) in the amygdala and the dorsal hippocampus mediates actions of estradiol on anxiety, social recognition and spatial memory. In addition, GPER participates in the estrogenic regulation of synaptic function in the amygdala and in the process of adult neurogenesis in the dentate gyrus. While the distribution of the canonical estrogen receptors α and β in the amygdala and dorsal hippocampus are well characterized, little is known about the regional distribution of GPER in these brain regions and whether this distribution is affected by sex or the stages of the estrous cycle. In this study we performed a morphometric analysis of GPER immunoreactivity in the posterodorsal medial, anteroventral medial, basolateral, basomedial and central subdivisions of the amygdala and in all the histological layers of CA1 and the dentate gyrus of the dorsal hippocampal formation. The number of GPER immunoreactive cells was estimated in these different structures. GPER immunoreactivity was detected in all the assessed subdivisions of the amygdaloid nucleus and dorsal hippocampal formation. The number of GPER immunoreactive cells was higher in males than in estrus females in the central (P = 0.001) and the posterodorsal medial amygdala (P < 0.05); higher in males than in diestrus females in the strata orients (P < 0.01) and radiatum-lacunosum-moleculare (P < 0.05) of CA1-CA3 and in the molecular layer of the dentate gyrus (P < 0.01); higher in diestrus females than in males in the basolateral amygdala (P < 0.05); higher in diestrus females than in estrus females in the central (P < 0.01), posterodorsal medial (P < 0.01) and basolateral amygdala (P < 0.01) and higher in estrus females than in diestrus females in the strata oriens (P < 0.05) and radiatum-lacunosum-moleculare (P < 0.05) of CA1-CA3 and in the molecular layer (P < 0.05) and the hilus of the dentate gyrus (P < 0.05). The findings suggest that estrogenic regulation of the amygdala and hippocampus through GPER may be different in males and in females and may fluctuate during the estrous cycle.

Androgens Enhance Adult Hippocampal Neurogenesis in Males but Not Females in an Age-Dependent Manner

Androgens (testosterone and DHT) increase adult hippocampal neurogenesis by increasing survival of new neurons in male rats and mice via an androgen receptor pathway, but it is not known whether androgens regulate neurogenesis in female rats and whether the effect is age-dependent. We investigated the effects of DHT, a potent androgen, on neurogenesis in young adult and middle-aged male and female rats. Rats were gonadectomized and injected with the DNA synthesis marker bromodeoxyuridine (BrdU). The following day, rats began receiving daily injections of oil or DHT for 30 days. We evaluated cell proliferation (Ki67) and survival of new neurons (BrdU and BrdU/NeuN) in the hippocampus of male and female rats by using immunohistochemistry. As expected, DHT increased the number of BrdU+ cells in young males but surprisingly not in middle-aged males or in young and middle-aged females. In middle age, DHT increased the proportion of BrdU/NeuN cells, an effect driven by females. Androgen receptor expression also increased with aging in both female and male rats, which may contribute to a lack of DHT neurogenic effect in middle age. Our results indicate that DHT regulates adult hippocampal neurogenesis in a sex- and age-dependent manner.

Combined dipeptidyl peptidase-4 inhibitor with low-dose testosterone exerts greater efficacy than monotherapy on improving brain function in orchiectomized obese rats

Both obesity and orchiectomy lead to the development of brain pathologies and cognitive decline. Testosterone replacement therapy (2 mg/kg/day TRT) and dipeptidyl peptidase-4 inhibitor (vildagliptin) improved cognition in orchiectomized rats, and obese rats. However, both had no beneficial effects in brain of orchiectomized-obese rats. TRT (>2 mg/kg/day) is possible to attenuate brain defects in those rats, but high dose of TRT causes adverse effects. Then, combined effect of low-dose TRT (1 mg/kg/day) and vildagliptin on brain and cognitive functions in orchiectomized-obese rats should be investigated. Sixty male rats were fed with either a normal diet (ND) or a high-fat diet (HFD) for 28 weeks. At week 13, both ND and HFD-fed rats had either a sham-operation or an orchiectomy. At week 25, orchiectomized rats were treated with either: a vehicle, 2 mg/kg/day TRT, vildagliptin (3 mg/kg/day) or a combined vildagliptin with 1 mg/kg/day TRT for 4 weeks. Then, metabolic parameters, brain and cognitive functions were determined. Hippocampal oxidative stress, apoptosis, dendritic spine loss, microglial hyperactivity, and cognitive decline were found in orchiectomized ND-fed rats and sham-operated HFD-fed rats. Interestingly, orchiectomy aggravated these brain pathologies and cognitive decline in HFD-fed rats. In orchiectomized ND-fed rats, all treatments restored brain and cognitive functions. In orchiectomized HFD-fed rats, monotherapies ameliorated these brain pathologies, while the combined therapies had the greatest beneficial effect on the brains. These findings suggest the combined therapies may be the best therapeutic approach for restoring brain functions in the orchiectomized-obese condition.

Chronic adolescent stress sex-specifically alters the hippocampal transcriptome in adulthood

Chronic adolescent stress alters behavior in a sex-specific manner at the end of adolescence and in adulthood. Although prolonged behavioral repercussions of chronic adolescent stress have been documented, the potential underlying mechanisms are incompletely understood. In this study we demonstrate that a history of chronic adolescent stress modified the adult stress response, as measured by corticosterone concentration, such that a history of chronic adolescent stress resulted in a blunted response to a novel acute stressor. In order to begin to address potential mechanistic underpinnings, we assessed the extent to which chronic adolescent stress impacted global DNA methylation. Reduced global hippocampal methylation was evident in females with a history of chronic adolescent stress; thus, it was possible that chronic adolescent stress altered global transcription in the whole hippocampi of adult male and female rats. In addition, because acute stress can stimulate a genomic response, we assessed the transcriptome following exposure to an acute novel stressor to determine the extent to which a history of chronic adolescent stress modifies the adult transcriptional response to an acute stressor in males and females. In addition to the reduction in global methylation, chronic adolescent stress resulted in distinct patterns of gene expression in the adult hippocampus that differentiated by sex. Furthermore, both sex and a history of chronic adolescent stress influenced the transcriptional response to an acute novel stressor in adulthood, suggesting both latent and functional effects of chronic adolescent stress at the level of gene transcription. Pathway analysis indicated that ESR1 and IFN-α may be particularly influential transcription factors mediating these transcriptional differences and suggest candidate mechanisms for future studies. Collectively, these studies demonstrate sex-specific and enduring effects of adolescent stress exposure that are more pronounced in females than in males.

Beta-blockers and salbutamol limited emotional memory disturbance and damage induced by orchiectomy in the rat hippocampus

AIM

To evaluate the therapeutic potential of ligands of beta-adrenoceptors in cognitive disorders. Testosterone and adrenergic pathways are involved in hippocampal and emotional memory. Moreover, is strongly suggested that androgen diminishing in aging is involved in cognitive deficit, as well as beta-adrenoceptors, particularly beta2-adrenoceptor, participate in the adrenergic modulation of memory. In this regard, some animal models of memory disruption have shown improved performance after beta-drug administration.

MATERIAL AND METHODS

In this work, we evaluated the effects of agonists (isoproterenol and salbutamol) and antagonists (propranolol and carvedilol) on beta-adrenoceptors in orchiectomized rats, as well as their effects in the performance on avoidance task and damage in hippocampal neurons by immunohistochemistry assays.

KEY FINDINGS

Surprisingly, we found that both antagonists and salbutamol (but not isoproterenol) modulate the effects of hormone deprivation, improving memory and decreasing neuronal death and amyloid-beta related changes in some regions (particularly CA1-3 and dentate gyrus) of rat hippocampus.

SIGNIFICANCE

Two β-antagonists and one β2-agonist modulated the effects of hormone deprivation on memory and damage in brain. The mechanisms of signaling of these drugs for beneficial effects remain unclear, even if used β-ARs ligands share a weak activity on β-arrestin/ERK-pathway activation which can be involved in these effects as we proposed in this manuscript. Our observations could be useful for understanding effects suggested of adrenergic drugs to modulate emotional memory. But also, our results could be related to other pathologies involving neuronal death and Aβ accumulation.

Effects of hCG on reduced numbers of hCG receptors in the prefrontal cortex and cerebellum of rat models of Alzheimer's disease

Age-associated changes in the levels of luteinizing hormone and human chorionic gonadotropin (hCG) are potential risk factors for Alzheimer's disease (AD); hCG concentration is related to the incidence of AD. The highest density of hCG receptors is in zones of the brain that are vulnerable to AD and streptozotocin (STZ) can decrease the density of this receptor. We investigated the effects of different doses of hCG on hCG receptor density in the prefrontal cortex and cerebellum in a rat model of STZ-induced AD. AD was induced by intracerebroventricular injection of 3 mg/kg STZ. The resulting AD rats were treated for 3 days with 50, 100 or 200 IU/200 μl hCG, or with saline as a control. Sections of prefrontal cortex and cerebellum were stained immunohistochemically and hCG receptor-immunoreactive (ir) neurons were counted. STZ injected into the lateral ventricles of rat brains reduced the density of hCG receptor-ir neurons in the prefrontal cortex and cerebellum. hCG administration resulted in a significant dose-dependent increase in the number of hCG receptor-ir neurons in the prefrontal cortex and cerebellum. The maximum increase in the number of receptors occurred following the 200 IU dose of hCG. Administration of hCG ameliorated the lowered density of hCG receptor-ir neurons in the cerebellum and prefrontal cortex in STZ-induced AD rats.

The Impact of Hippocampal Sex Hormones Receptors in Modulation of Depressive-Like Behavior Following Chronic Anabolic Androgenic Steroids and Exercise Protocols in Rats

The aim of this study was to evaluate alterations in depressive-like behaviors in rats following chronic administration of a supraphysiological dose of anabolic androgenic steroids (AASs) as well as exposure to a prolonged exercise protocol. The role of hippocampal sex hormones receptors in the modulation of depressive-like behavior was also assessed. A total of 48 male Wistar albino rats were divided into six groups: control, exercise (1 h/day, five consecutive days), nandrolone-decanoate (ND, 20 mg/kg/week, in a single dose), exercise plus ND, testosterone-enanthate (TE, 20 mg/kg/week, in a single dose), and exercise plus TE. After the 6-week protocols were complete, the rats underwent behavioral testing in the tail suspension test (TST). Rats were sacrificed for the collection of blood samples, to determine sex hormones levels, and isolation of the hippocampus, to determine [androgen receptors (AR) and estrogen receptors α (ERα)] expression. ND and TE treatment induced significant depressive-like behavior, opposing the antidepressant effect of exercise. Chronic TE administration elevated testosterone (T) and dihydrotestosterone (DHT) serum levels, and this was augmented by exercise. In contrast, ND and exercise alone did not alter T or DHT levels. There were no changes in serum estradiol levels in any of the groups. Immunohistochemical analysis showed that exercise reduced AR immunoreactivity in all hippocampal regions and increased the ERα expression in the CA1, dentate gyrus (DG), and total hippocampal sections, but not in the CA2/3 region. AASs administration increased AR expression in all hippocampal regions, although not the total hippocampal section in the TE group and did not significantly decrease ERα. The hippocampal AR/ERα expression index was lowered while parvalbumin (PV)-immunoreactivity was enhanced by exercise. AASs administration increased the AR/ERα index and reduced PV-immunoreactivity in the hippocampus. The number of PV-immunoreactive neurons negatively correlated with the antidepressant effects and the AR/ERα ratio. Our results suggest a potential role of the numerical relationship between two sex hormones receptors (stronger correlation than for each individual receptor) in the regulation of depressive-like behavior via the hippocampal GABAergic system in rats, which allow better understanding of the hippocampal sex hormones receptors role in modulation of depressive-like behavior.

Human chorionic gonadotropin attenuates amyloid-β plaques induced by streptozotocin in the rat brain by affecting cytochrome c-ir neuron density

OBJECTIVES

Amyloid β plaques, in Alzheimer's disease, are deposits in different areas of the brain such as prefrontal cortex, molecular layer of the cerebellum, and the hippocampal formation. Amyloid β aggregates lead to the release of cytochrome c and finally neuronal cell death in brain tissue. hCG has critical roles in brain development, neuron differentiation, and function. Therefore, we investigated the effect of hCG on the density of the congophilic Aβ plaque and cytochrome c-ir neurons in the hippocampus, prefrontal cortex, and cerebellum of Streptozotocin (STZ)-treated rats.

MATERIALS AND METHODS

Alzheimer model in rats (except the control group) was induced by streptozotocin (3 mg/kg, Intracerebroventricularly (ICV)). Experimental group rats received streptozotocin and then different doses of hCG (50, 100, and 200 IU, intraperitoneally) for 3 days. 48 hr after last drug injection and after histological processing, the brain sections were stained by congo red for congophilic amyloid β plaques and cytochrome c in the hippocampus, prefrontal cortex, and cerebellum were immunohistochemically stained.

RESULTS

Density of congophilic Aβ plaques and cytochrome c-immunoreactive neurons was significantly higher in ICV STZ treated rats than controls. Treatment with three doses of hCG significantly decreased the density of congophilic Aβ plaques and cytochrome c-immunoreactive neurons in the rat hippocampus, prefrontal cortex, and cerebellum in ICV STZ-treated rats (P<0.05).

CONCLUSION

hCG can be useful in AD patients to prevent the congophilic Aβ plaque formation and decrease cytochrome c-immunoreactive neuron density in the brain.

Metabolic Effects of Testosterone Hormone Therapy in Normal and Orchiectomized Male Rats: From Indirect Calorimetry to Lipolytic Enzymes

BACKGROUND AND AIM

Changes in total energy expenditure (TEE) and substrate metabolism may help explain the metabolic actions of testosterone (T). This study measured respiratory quotient (RQ), TEE, ghrelin, insulin, and key lipolysis enzyme concentrations in relation to body weight (wt) and food intake (FI) in both normal and bilaterally orchiectomized rats with/without T treatment.

METHODS

In total, thirty-two male Wistar rats (300-400 g) were divided into four groups (n = 8/group), including (a) sham-operated and vehicle-injected group (Sham), (b) T-treated sham group (T-Sham) for which sham-operated rats were injected with IM testosterone undecanoate (100 mg/kg, for one week), (c) orchiectomy and vehicle-injected group (Orch), and (d) T-replaced orchiectomy group (T-Orch). After one week, FI and wt were automatically recorded, indirect calorimetry parameters were measured, and blood samples were collected to measure T, ghrelin, insulin, growth hormone (GH), glucose, hormone-sensitive lipase (HSL), adipocyte triglyceride lipase (ATGL), free fatty acids (FFA), and lipid profiles.

RESULTS

Orchiectomy decreased ghrelin, GH, and insulin levels, increased TEE and RQ, and lowered FI and wt. The T-Orch group exhibited increased levels of ghrelin (3-fold), insulin, GH, blood levels of lipolysis products, TEE, and FI in addition to reduced glucose levels (P < 0.05). This group demonstrated no significant changes in wt. In the T-Sham group, T increased ghrelin and insulin levels (P < 0.05) with strong positive correlations (r = 0.663 and 0.644, respectively, P < 0.05), increased ATGL levels, RQ toward carbohydrate utilization ranges, and TEE, and reduced HSL levels (P < 0.05) with insignificant changes in FI or wt.

CONCLUSIONS

T administration in orchiectomized rats significantly increased orexigenic mediators such as ghrelin and insulin without inducing any significant changes in wt. The mechanism for this finding might be the increased TEE and the stimulation of lipolysis through the ATGL enzyme. The associated rise of GH might help in interference with accumulation of lipid in adipose tissue. Apart from the effect on GH, T-Sham showed similar effects of T supplementation.

Alteration of Testosterone Levels Changes Brain Wave Activity Patterns and Induces Aggressive Behavior in Rats

Testosterone is responsible for several changes in the brain, including behavioral and emotional responses, memory, and cognition. Given this, we investigated changes in the brain wave profile caused by supplementation with exogenous testosterone in both castrated and non-castrated rats. We also investigated the serum testosterone levels, renal and hepatic function, and the lipid and behavioral profiles. We found changes in the spectral wave power in both groups (castrated and non-castrated animals) supplemented with exogenous testosterone, consistent with an aggressive/hostile profile. These changes were observed in the electrocorticographic evaluation associated with increased power in low-frequency (delta and theta) and high-frequency (beta and gamma) activity in the supplemented animals. The castrated animals presented a significant decrease of wave power in the alpha frequency. This correlated with a decrease of the performance of the animals in the elevated plus-maze evaluation, given that the alpha wave is linked to the execution and visualization of motor processes. In the behavioral evaluation, the castrated animals presented a reduced permanence time in the elevated-plus maze, although this was prevented by the supplementation of testosterone. Testosterone supplementation induced aggressive behavior in non-castrated animals, but not in castrated ones. Supplemented animals had significantly elevated serum testosterone levels, while their urea levels were significantly lower, but without clinical significance. Our data indicate that testosterone supplementation in non-castrated rats, but not in castrated ones, causes electrocorticographic changes that could be associated with more aggressive and hostile behavior, in addition to indicating a potential for personality disorder. However, further studies are required to elucidate the cellular and molecular changes caused by acute testosterone supplementation.

Effects of vortioxetine and fluoxetine on the level of Brain Derived Neurotrophic Factors (BDNF) in the hippocampus of chronic unpredictable mild stress-induced depressive rats

Vortioxetine is a novel antidepressant capable of improving depressive and cognitive symptoms associated with major depressive disorder (MDD). This study established whether treatment with vortioxetine, fluoxetine or vehicle alters the modulation of brain-derived neurotrophic factor (BDNF) under the 21-day chronic unpredictable mild stress (CUMS) condition in 54 Sprague-Dawley rats. Vortioxetine mitigated the reduction in rearing behavior by CUMS in the OFT on day 7 and 21, as well as sucrose preference on day 21. Histological examination by H&E staining showed that most hippocampal neurons in the CUMS + FLU and CUMS + VOR groups were intact, although some of them demonstrated karyopyknosis. The mean optical density value of hippocampal BDNF was significantly higher in the CUMS + VOR group than the CUMS and CUMS + FLU groups. There was a trend towards a higher number of hippocampal BDNF-positive cells in the CUMS + VOR group, although it did not reach statistical significance. In conclusion, vortioxetine, but not fluoxetine, increased hippocampal BDNF levels in rats subject to CUMS.

Role of the androgen receptor in the central nervous system

The involvement of gonadal androgens in functions of the central nervous system was suggested for the first time about half a century ago. Since then, the number of functions attributed to androgens has steadily increased, ranging from regulation of the hypothalamic-pituitary-gonadal axis and reproductive behaviors to modulation of cognition, anxiety and other non-reproductive functions. This review focuses on the implication of the neural androgen receptor in these androgen-sensitive functions and behaviors.

Neural androgen receptors affect the number of surviving new neurones in the adult dentate gyrus of male mice

Adult hippocampal neurogenesis occurs in many mammalian species. In rats, the survival of new neurones within the hippocampus is modulated by the action of androgen via the androgen receptor (AR); however, it is not known whether this holds true in mice. Furthermore, the evidence is mixed regarding whether androgens act in neural tissue or via peripheral non-neural targets to promote new neurone survival in the hippocampus. We evaluated whether the action of androgen via AR underlies the survival of new neurones in mice, and investigated whether increasing AR selectively in neural tissue would increase new neurone survival in the hippocampus. We used the cre-loxP system to overexpress AR only in neural tissues (Nestin-AR). These males were compared with wild-type males, as well as control males with 1 of the 2 mutations required for overexpression. Mice were gonadectomised and injected with the DNA synthesis marker, bromodeoxyuridine (BrdU) and for 37 days (following BrdU injection), mice were treated with oil or dihydrotestosterone (DHT). Using immunohistochemistry, proliferation (Ki67) and survival (BrdU) of new neurones were both evaluated in the dorsal and ventral dentate gyrus. Dihydrotestosterone treatment increased the survival of new neurones in the entire hippocampus in wild-type mice and control mice that only have 1 of 2 necessary mutations for transgenic expression. However, DHT treatment did not increase the survival of new neurones in mice that overexpressed AR in neural tissue. Cell proliferation (Ki67) and cell death (pyknotic cells) were not affected by DHT treatment in wild-type or transgenic males. These results suggest that androgens act via neural AR to affect hippocampal neurogenesis by promoting cell survival; however, the relationship between androgen dose and new neurone survival is nonlinear.

Gonadal hormones affect alcohol drinking, but not cue+yohimbine-induced alcohol seeking, in male and female rats

Alcohol use disorder (AUD) is a chronic, relapsing disease characterized by maladaptive patterns of alcohol drinking and seeking. Though sex differences exist in the etiology of AUD, much remains to be elucidated concerning the mechanisms underlying sex-related vulnerability to developing excessive alcohol-motivated behavior. While a large body of evidence points to an important role of circulating gonadal hormones in mediating cocaine reinforcement, findings are less consistent with respect to ethanol. Critically, the effects of gonadal hormones on the reinstatement of ethanol seeking, a model of "craving"-like behavior that reveals pronounced sex differences, has not yet been examined. Thus, the goal of the present experiment was to directly compare manipulations of gonadal hormones in male and female rats on ethanol-motivated behavior. Rats received sham or gonadectomy surgery with or without hormone replacement prior to and throughout three weeks of operant ethanol self-administration to determine the effects of chronically high or low gonadal hormone levels on ethanol drinking. Hormone treatment ceased during extinction training, and the effects of an acute injection of either testosterone (in males) or estradiol (in females) on cue+yohimbine-induced reinstatement of ethanol seeking was determined. Separate groups of gonadally-intact female rats went through similar training, but the effects of either the antiestrogen, fulvestrant, the selective estrogen receptor modulator, clomiphene, or the estrogen receptor β antagonist, PHTPP, on the reinstatement of ethanol seeking were determined. Chronic estradiol replacement produced significant increases in ethanol drinking in female rats, while chronic testosterone significantly decreased ethanol drinking in male rats. Gonadectomy alone only produced modest shifts in drinking towards the opposite-sex pattern, and did not eliminate the robust sex differences that persisted regardless of hormone manipulations. Neither prior chronic nor acute hormone manipulations altered cue+yohimbine-induced reinstatement of ethanol seeking, though blockade of estrogen receptors tended to reduce reinstatement in gonadally-intact females. Overall, our findings indicate that gonadal hormones at least partially mediate, but do not totally account for the sex differences evident in ethanol self-administration, and circulating gonadal hormones have little effect on the reinstatement of ethanol seeking. These results provide a foundation for future studies examining the neuronal mechanisms underlying sex differences in ethanol drinking and seeking.

Seasonal changes of androgen receptor, estrogen receptors and aromatase expression in the hippocampus of the wild male ground squirrels (Citellus dauricus Brandt)

The wild ground squirrel is a typical seasonal breeder whose annual life cycle can be roughly divided into the breeding season, the post-breeding season and hibernation. Our previous study has reported the seasonal changes in the expressions of androgen receptor (AR), estrogen receptors α and β (ERα and ERβ), and aromatase cytochrome P450 (P450arom) in the hypothalamus of male wild ground squirrels. To further seek evidence of seasonal expression of steroid hormone receptors and steroid hormone synthases in other brain regions, we investigated the protein and mRNA expressions of AR, ERα, ERβ and P450arom in the hippocampus of the male wild ground squirrels during these different reproductive periods. Histological observation showed that the number of pyramidal cells in Cornu Ammonis 1 (CA1) increased in the breeding season. Both protein and mRNA of AR, ERα, ERβ and P450arom were present in CA1 and CA3 of all seasons. There was significant increment in the immune-signal intensity and mRNA level of AR and ERα during the pre-hibernation, whereas those of ERβ and P450arom were higher during the post-breeding season. In addition, the profile of plasma testosterone concentration showed the nadir in the post-breeding season, a marked elevation in the pre-hibernation, and the summit in the breeding season. These findings suggested that the hippocampus may be a direct target of androgen and estrogen; androgen may play important regulatory roles through its receptor and/or the aromatized estrogen in the hippocampus of the wild male ground squirrels.

5-HT2A Serotonin Receptor Density in Adult Male Rats' Hippocampus after Morphine-based Conditioned Place Preference

INTRODUCTION

A close interaction exists between the brain opioid and serotonin (5-HT) neurotransmitter systems. Brain neurotransmitter 5-HT plays an important role in the regulation of reward-related processing. However, a few studies have investigated the potential role of 5-HT2A receptors in this behavior. Therefore, the aim of the present study was to assess the influence of morphine and Conditioned Place Preference (CPP) on the density of 5-HT2A receptor in neurons of rat hippocampal formation.

METHODS

Morphine (10 mg/kg, IP) was injected in male Wistar rats for 7 consecutive days (intervention group), but control rats received just normal saline (1 mL/kg, IP). We used a hotplate test of analgesia to assess induction of tolerance to analgesic effects of morphine on days 1 and 8 of injections. Later, two groups of rats were sacrificed one day after 7 days of injections, their whole brains removed, and the striatum and PFC immediately dissected. Then, the NR1 gene expression was examined with a semi-quantitative RT-PCR method.

RESULTS

Our data showed that the maximum response was obtained with 2.5 mg/kg of morphine. The density of 5-HT2A receptor in different areas of the hippocampus increased significantly at sham-morphine and CPP groups (P<0.05). On the other hand, the CPP groups had more 5-HT2A receptors than sham-morphine groups and also the sham-morphine groups had more 5-HT2A receptors than the control groups.

CONCLUSION

We concluded that the phenomenon of conditioned place preference induced by morphine can cause a significant increase in the number of serotonin 5-HT2A receptors in neurons of all areas of hippocampus.