Testosterone modulates performance on a spatial working memory task in male rats

Pubertal development underlies optimization of inhibitory control through specialization of ventrolateral prefrontal cortex

Inhibitory control improves into young adulthood after specialization of relevant brain systems during adolescence. However, the biological mechanisms supporting this unique transition are not well understood. Given that adolescence is defined by puberty, we examined relative contributions of chronological age and pubertal maturation to inhibitory control development. 105 8-19-year-olds completed 1-5 longitudinal visits (227 visits total) in which pubertal development was assessed via self-reported Tanner stage and inhibitory control was assessed with an in-scanner antisaccade task. As expected, percentage and latency of correct antisaccade responses improved with age and pubertal stage. When controlling for pubertal stage, chronological age was distinctly associated with correct response rate. In contrast, pubertal stage was uniquely associated with antisaccade latency even when controlling for age. Chronological age was associated with fMRI task activation in several regions including the right dorsolateral prefrontal cortex, while puberty was associated with right ventrolateral prefrontal cortex (VLPFC) activation. Furthermore, task-related connectivity between VLPFC and cingulate was associated with both pubertal stage and response latency. These results suggest that while age-related developmental processes may support maturation of brain systems underlying the ability to inhibit a response, puberty may play a larger role in the effectiveness of generating cognitive control responses.

Sex differences in cognition following variations in endocrine status

Spatial memory, mediated primarily by the hippocampus, is responsible for orientation in space and retrieval of information regarding location of objects and places in an animal's environment. Since the hippocampus is dense with steroid hormone receptors and is capable of robust neuroplasticity, it is not surprising that changes in spatial memory performance occur following a variety of endocrine alterations. Here, we review cognitive changes in both spatial and nonspatial memory tasks following manipulations of the hypothalamic-pituitary-adrenal and gonadal axes and after exposure to endocrine disruptors in rodents. Chronic stress impairs male performance on numerous behavioral cognitive tasks and enhances or does not impact female cognitive function. Sex-dependent changes in cognition following stress are influenced by both organizational and activational effects of estrogen and vary depending on the developmental age of the stress exposure, but responses to gonadal hormones in adulthood are more similar than different in the sexes. Also discussed are possible underlying neural mechanisms for these steroid hormone-dependent, cognitive effects. Bisphenol A (BPA), an endocrine disruptor, given at low levels during adolescent development, impairs spatial memory in adolescent male and female rats and object recognition memory in adulthood. BPA's negative effects on memory may be mediated through alterations in dendritic spine density in areas that mediate these cognitive tasks. In summary, this review discusses the evidence that endocrine status of an animal (presence or absence of stress hormones, gonadal hormones, or endocrine disruptors) impacts cognitive function and, at times, in a sex-specific manner.

Androgens Enhance Recognition Memory and Dendritic Spine Density in the Hippocampus and Prefrontal Cortex of Ovariectomized Female Rats

Estrogen replacement has been repeatedly shown to enhance memory and increase dendritic spine density in the hippocampus and prefrontal cortex of ovariectomized (OVX) female rats. Given the potential deleterious effects of chronic estrogen administration, the present study assessed cognitive function using recognition memory tasks and measured dendritic spine density in the CA1 region of the hippocampus and medial prefrontal cortex after subchronic androgen replacement to adult OVX female rats. All androgens enhanced recognition memory in OVX rats, but object placement (OP) and object recognition (OR) results differed. Only testosterone enhanced OR. Testosterone had no effect on OP while dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT) and androstenedione (AD) enhanced OP. Dendritic spine density was increased by both TP and DHEA in both brain areas (DHT and AD were not tested). Lastly, we used the aromatase inhibitor, letrozole, to discriminate between potential androgenic and estrogenic effects of androgens on behavior. Letrozole alone did not alter recognition memory in OVX rats and did not block the effects of either TP or DHEA on recognition memory suggesting that effects were mediated via androgenic mechanisms. The present results expand previous information on gonadal hormone actions and show that, in addition to estrogens, androgens also improve memory and increase spine density in brains of OVX female rats. While requiring further investigation, these observations provide a basis for therapeutic interventions in the treatment of menopausal, age or disease related memory loss.

High Fructose and High Fat Diet Impair Different Types of Memory through Oxidative Stress in a Sex- and Hormone-Dependent Manner

Metabolic syndrome (MetS) contributes to the spread of cardiovascular diseases, diabetes mellitus type 2, and neurodegenerative diseases. Evaluation of sex- and hormone-dependent changes in body weight, blood pressure, blood lipids, oxidative stress markers, and alterations in different types of memory in Sprague–Dawley rats fed with a high fat and high fructose (HFHF) diet were evaluated. After 12 weeks of feeding the male and female rats with HFHF, body weight gain, increase in blood pressure, and generation of dyslipidemia compared to the animals fed with chow diet were observed. Regarding memory, it was noted that gonadectomy reverted the effects of HFHF in the 24 h novel object recognition task and in spatial learning/memory analyzed through Morris water maze, males being more affected than females. Nevertheless, gonadectomy did not revert long-term memory impairment in the passive avoidance task induced by HFHF nor in male or female rats. On the other hand, sex-hormone–diet interaction was observed in the plasma concentration of malondialdehyde and nitric oxide. These results suggest that the changes observed in the memory and learning of MetS animals are sex- and hormone-dependent and correlate to an increase in oxidative stress.

Social ascent changes cognition, behaviour and physiology in a highly social cichlid fish

When an individual ascends in dominance status within their social community, they often undergo a suite of behavioural, physiological and neuromolecular changes. While these changes have been extensively characterized across a number of species, we know much less about the degree to which these changes in turn influence cognitive processes like associative learning, memory and spatial navigation. Here, we assessed male Astatotilapia burtoni, an African cichlid fish known for its dynamic social dominance hierarchies, in a set of cognitive tasks both before and after a community perturbation in which some individuals ascended in dominance status. We assayed steroid hormone (cortisol, testosterone) levels before and after the community experienced a social perturbation. We found that ascending males changed their physiology and novel object recognition preference during the perturbation, and they subsequently differed in social competence from non-ascenders. Additionally, using a principal component analysis we were able to identify specific cognitive and physiological attributes that appear to predispose certain individuals to ascend in social status once a perturbation occurs. These previously undiscovered relationships between social ascent and cognition further emphasize the broad influence of social dominance on animal decision-making. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Sociability, but not spatial memory, is correlated with regional brain volume variation in the striped mouse Rhabdomys spp

Local environmental conditions associated with different geographic areas may elicit variations in behavioural responses in animals, leading to concomitant differences in functional brain region volumes. We investigated the behavioural correlates of hippocampus and amygdala volumes in three sister taxa of the murid rodent genus Rhabdomys, occurring in different environments. We used a Barnes maze to test spatial memory, dyadic encounters to test social behaviour, and histological brain sections to calculate hippocampus and amygdala volumes. Arid-occurring R. pumilio made fewer errors and had shorter latencies in locating the escape tunnel compared to moist grassland-occurring R. d. dilectus and R. d. chakae in two probe trials, 48 and 96 h after the last learning trial. R. pumilio was more amicable than the R. dilectus subspecies in intra-specific dyadic encounters. R. pumilio had larger hippocampus and amygdala volumes than the other species. Smaller amygdala volumes were correlated with longer latencies in females for probe trial 1, but males showed similar latencies regardless of taxon. Higher amicability scores were correlated with larger amygdala volumes in all taxa. Higher amicability scores were correlated with larger hippocampus volumes in R. pumilio and R. d. chakae but smaller hippocampus volumes in R. d. dilectus. Correlative relationships between spatial memory and amygdala volume appeared 48 h, but not 96 h, after the last learning trial. Local environmental conditions may influence spatial navigation, but social correlates drive regional brain size within cryptic striped mouse taxa.

Spatial working memory is disparately interrelated with social status through different developmental stages in rats

Social life necessitates cognitive competence to meet the dynamic demands of social development. The formation of dominance hierarchy is a general phenomenon in social groups. As an essential element of executive and cognitive function, working memory could influence and be influenced by social status in a dominance hierarchy. However, the direction and degree of the association between them through different developmental stages remain unclear. To address this issue and clarify the "cause or consequence" problem, we investigated the spatial working memory performance in a Y-maze and Morris water maze in home-caged sibling Wistar rats (N = 26 cages, three rats/cage) through three stages of their life: before (week 7), during (week 10), and after (week 20) assumed timings of the social dominance hierarchy formation (SDHF). We used the social dominance tube test during the assumed time of hierarchy formation (weeks 9-11) to measure the relative dominance status in each cage. Here, we found that higher working memory index before SDHF could be predictive of later acquisition of higher social status. Working memory performance declined for all animals during SDHF, in which agonistic conflicts are increased. However, living within an established hierarchical social network for several weeks deteriorated the working memory performance of dominant and middle-ranked animals, while the performance of subordinates improved and got significantly better than higher-ranked animals. In conclusion, while working memory and social status were correlated positively before dominance hierarchy formation, there was a trade-off between them after the formation of it. In contrast to the common view, these results highlight the adverse effect of higher social status on cognitive behavior.

Associations among gonadal hormone, triglycerides and cognitive decline in female patients with major depressive disorders

BACKGROUND

Cognitive impairment has been identified as a core feature of depression. Serum triglycerides (TG), gonadal hormone and sex difference were shown to influence cognitive performance. The purpose of this study was to investigate the associations among serum TG, gonadal hormone, sex difference and cognitive performance in patients with major depressive disorders (MDD).

METHODS

The enrolled 183 patients (male/female = 80/103) meeting DSM-IV criteria for MDD were divided into high TG group (patients-HTG) and normal TG group (patients-NTG) according to TG level. Serum TG, estradiol (E2) and testosterone (T) levels were measured by the glycerokinase peroxidase-peroxidase and chemiluminescence methods. Cognition was assessed by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The study was conducted between August 2016 and January 2020.

RESULTS

In female, patients-HTG had lower immediate memory, language, attention, delayed memory and RBANS total scores than patients-NTG after adjusting for covariates. There were significant differences in serum E2 and T levels between patients-HTG and patients-NTG in female after controlling for covariates. In female patients-HTG, serum E2 level was positively associated with immediate memory, delayed memory and RBANS total scores, and serum T level was positively related to immediate memory, language and RBANS total scores. These findings were not seen in male patients.

CONCLUSIONS

Our data suggested that patients-HTG exhibited poorer cognitive function compared with patients-NTG in female. Moreover, the decline in serum gonadal hormone level might contribute to the high TG development of female MDD, and was further implicated in their cognitive decline.

Effect of androgen deprivation therapy on cognitive functioning in men with prostate cancer: A systematic review

The objective of this study was to review publications assessing cognitive functioning in patients with prostate cancer treated with androgen deprivation therapy. We conducted a systematic review of the literature published in PubMed, Embase, Web of Science, Cochrane Library, and PsycINFO up to February 2020. A total of 31 studies were included. Half of the studies (n = 16) demonstrated that androgen deprivation therapy in patients with prostate carcinoma did not result in a negative effect on cognitive functioning, however, still a substantial proportion of the studies (n = 11) reported a negative effect on cognitive functioning. In four studies the results were inconclusive. In the three studies using additional functional magnetic resonance imaging, no significant effect on neuropsychological tests was found, but grey matter volume, brain activity, and brain connectivity were affected. Given the substantial number of studies showing a significant negative effect of androgen deprivation therapy on cognitive functioning, clinicians should be aware of this side effect. Furthermore, future research should focus on the further examination of brain characteristics using functional magnetic resonance imaging, since these techniques might be more sensitive in detecting brain abnormalities as a result of androgen deprivation therapy.

Sexual Motivation and Sexual Reward in Male Rats are Attenuated by the Gonadotropin-Releasing Hormone Receptor Antagonist Degarelix

BACKGROUND

Preclinical studies that have examined the effects of androgen deprivation therapies (ADTs) on sexual outcomes have either relied on a surgical castration model of ADTs or have largely focused on consummatory sexual behaviors.

AIM

The aim of this study was to examine the effects of a single administration of the gonadotropin-releasing hormone receptor antagonist, degarelix, on sexual incentive motivation (SIM), sexual reward, consummatory sexual behaviors, anxiety-like behavior, and androgen receptor signaling in male rats, and to determine if sexual stimulation attenuates the effects of degarelix on SIM.

METHODS

Male rats were treated with degarelix, or vehicle, and half of the rats in each condition were briefly exposed to a sexually receptive female immediately before SIM trials (experiment 1). Rats treated with degarelix or vehicle were also given a sex-conditioned place preference test (experiment 2A), weekly mating tests (experiment 2B), and an elevated zero maze test (experiment 3). Androgen-sensitive tissues were excised upon completion of testing.

OUTCOMES

SIM was indicated by the percentage of time spent near a sexually receptive female on the SIM tests. The percentage of time spent in the chamber of a conditioned place preference maze associated with sexual experience was indicative of sexual reward. The percentage of trials in which a mount, intromission, and ejaculation occurred was indicative of copulatory ability. Sexual performance was characterized by the average latencies to first exhibit these behaviors, as well as the average frequency of these behaviors. Anxiety-like behavior was indicated by the percentage of time in the open zones of an elevated zero maze. Relative weights of the seminal vesicles and bulbourethral glands were used to quantify androgen activity.

RESULTS

Rats treated with degarelix exhibited lower levels of SIM. In rats treated with degarelix, contact with a female immediately before SIM testing increased activity, but not SIM. Treatment with degarelix reduced the rewarding aspects of sexual behavior, as well as most aspects of copulatory ability and sexual performance. Degarelix treatment reduced androgen signaling, but did not impact anxiety-like behavior.

CLINICAL IMPLICATIONS

The behavioral side effects associated with the use of degarelix may be restricted to sexual behaviors.

STRENGTHS & LIMITATIONS

Strengths include the objective measurement of sexual behaviors. The study is limited in that only one ADT was examined.

CONCLUSION

These findings serve as an extension of previous preclinical studies as they indicate that gonadotropin-releasing hormone receptor antagonism in male rats also attenuates sexual motivation and sexual reward, in addition to copulatory ability and sexual performance. Hawley WR, Kapp LE, Green PA, et al. Sexual Motivation and Reward in Male Rats are Attenuated by the Gonadotropin-Releasing Hormone Receptor Antagonist Degarelix. J Sex Med 2021;18:240-255.

Advances in Knowledge of Androgens: How Intentional and Accidental Neurosteroid Changes Inform Us of Their Action and Role

Purpose of Review

Here, we summarize current knowledge of androgens’ action gained over the recent years.

Recent Findings

Neurosteroids are produced in the brain and peripheral nerves, independent of endocrine glands have been investigated for how they are regulated, and have actions via non-steroid receptor targets to mediate social, affective, and cognitive behavior and to protect the brain. Androgens’ organizing actions in the peri-natal period have effects throughout the lifetime that may be recapitulated later in life during critical periods and at times of challenge. Developmental changes in androgens occur during mid-childhood, adrenarche, puberty, adolescence, young adulthood, middle age, and andropause. Changes in androgens with a 5α-reductase inhibitor, such as finasteride, result in disruptions in organizational and activational functions of androgens that can be unremitting.

Summary

Normal developmental or perturbation in androgens through other means can cause changes in androgen-sensitive phenotypes throughout the lifespan, in part through actions of neurosteroids.

Biological Sex and Sex Hormone Impacts on Deficits in Episodic-Like Memory in a Rat Model of Early, Pre-motor Stages of Parkinson's Disease

Episodic memory deficits are among the earliest appearing and most commonly occurring examples of cognitive impairment in Parkinson's disease (PD). These enduring features can also predict a clinical course of rapid motor decline, significant cognitive deterioration, and the development of PD-related dementia. The lack of effective means to treat these deficits underscores the need to better understand their neurobiological bases. The prominent sex differences that characterize episodic memory in health, aging and in schizophrenia and Alzheimer's disease suggest that neuroendocrine factors may also influence episodic memory dysfunction in PD. However, while sex differences have been well-documented for many facets of PD, sex differences in, and sex hormone influences on associated episodic memory impairments have been less extensively studied and have never been examined in preclinical PD models. Accordingly, we paired bilateral neostriatal 6-hydroxydopamine (6-OHDA) lesions with behavioral testing using the What-Where-When Episodic-Like Memory (ELM) Task in adult rats to first determine whether episodic-like memory is impaired in this model. We further compared outcomes in gonadally intact female and male subjects, and in male rats that had undergone gonadectomy—with and without hormone replacement, to determine whether biological sex and/or sex hormones influenced the expression of dopamine lesioned-induced memory deficits. These studies showed that 6-OHDA lesions profoundly impaired recall for all memory domains in male and female rats. They also showed that in males, circulating gonadal hormones powerfully modulated the negative impacts of 6-OHDA lesions on What, Where, and When discriminations in domain-specific ways. Specifically, the absence of androgens was shown to fully attenuate 6-OHDA lesion-induced deficits in ELM for “Where” and to partially protect against lesion-induced deficits in ELM for “What.” In sum, these findings show that 6-OHDA lesions in rats recapitulate the vulnerability of episodic memory seen in early PD. Together with similar evidence recently obtained for spatial working memory, the present findings also showed that diminished androgen levels provide powerful, highly selective protections against the harmful effects that 6-OHDA lesions have on memory functions in male rats.

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.

Effects of aging on testosterone and androgen receptors in the mesocorticolimbic system of male rats

As males age, systemic testosterone (T) levels decline. T regulates executive function, a collection of cognitive processes that are mediated by the mesocorticolimbic system. Here, we examined young adult (5 months) and aged (22 months) male Fischer 344 × Brown Norway rats, and measured systemic T levels in serum and local T levels in microdissected nodes of the mesocorticolimbic system (ventral tegmental area (VTA), nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC)). We also measured androgen receptor (AR) immunoreactivity (-ir) in the mesocorticolimbic system. As expected, systemic T levels decreased with age. Local T levels in mesocorticolimbic regions - except the VTA - also decreased with age. Mesocorticolimbic T levels were higher than serum T levels at both ages. AR-ir was present in the VTA, NAc, mPFC, and OFC and decreased with age in the mPFC. Taken together with previous results, the data suggest that changes in androgen signaling may contribute to changes in executive function during aging.

Testosterone replacement causes dose-dependent improvements in spatial memory among aged male rats

Testosterone has been shown to have dose-dependent effects on spatial memory in males, but the effects of aging upon this relationship remain unclear. Additionally, the mechanism by which testosterone regulates memory is unknown, but may involve changes in brain-derived neurotrophic factor (BDNF) within specific brain regions. We tested the effects of age and testosterone on spatial memory among male rats using two spatial memory tasks: an object-location memory task (OLMT) and the radial-arm maze (RAM). Castration had minimal effect on performance on the RAM, but young rats (2 months) performed significantly fewer working memory errors than aged rats (20 months), and aged rats performed significantly fewer reference memory errors. Both age and castration impaired performance on the OLMT, with only the young rats with intact gonads successfully performing the task. Subsequent experiments involved daily injections of either drug vehicle or one of four doses of testosterone propionate (0.125, 0.250, 0.500, and 1.00 mg/rat) given to castrated aged males. On the RAM, a low physiological dose (0.125 mg) and high doses (0.500-1.000 mg) of testosterone improved working memory, while an intermediate dose (0.250 mg) did not. On the OLMT, only the 0.250 mg T group showed a significant increase in exploration ratios from the exposure trials to the testing trials, indicating that this group remembered the position of the objects. Brain tissue (prefrontal cortex, hippocampus, and striatum) was collected from all subjects to assay BDNF. We found no evidence that testosterone influenced BDNF, indicating that it is unlikely that testosterone regulates spatial memory through changes in BDNF levels.

Nandrolone improve synaptic plasticity at the hippocampus CA1 area and spatial localization in the Morris water maze of male adolescent rats

Nandrolone is the most popular compound that are mainly abused. Experimental studies have reported that administration of nandrolone affects cognitive performance. So, the aim of this study is to evaluate the effect of nandrolone on spatial localization and synaptic plasticity of male adolescent rats. Experimantal groups received DMSO and nandrolone (10, 30 and 60 μg, i.c.v.). Another aim is to evaluate the role of castration on spatial learning and memory changes induced by nandrolone. Therefore, the rats of fifth and sixth groups were castrated and received DMSO or nandrolone. Analysis showed that escape latency and traveled distance in the group which received nandrolone (60 μg) were significantly lower than control group. Also, the escape latency and traveled distance in the group of castration which received nandrolone was significantly higher than nandrolone treated group. The results of field potential recording showed that fEPSP-LTP in nandrolone-treated group was higher than DMSO-treated group. The magnitude of fEPSP-LTP in the group of castration which received nandrolone was significantly lower than nandrolone-treated group. The results demonstrated that nandrolone improved spatial learning, but castration could abolished nandrolone-induced spatial learning improvement. These results indicating that at least some effect of nandrolone on learning induced through changes in gonadal function.

Testosterone deprivation intensifies cognitive decline in obese male rats via glial hyperactivity, increased oxidative stress, and apoptosis in both hippocampus and cortex

AIM

The study hypothesized that testosterone deprivation aggravates cognitive decline in obesity through increasing oxidative stress, glial activation, and apoptosis.

METHODS

Male Wistar rats (n = 24) were fed with either normal-diet (ND) or high-fat diet (HFD) for 24 weeks. At week 13, ND-fed rats and HFD-fed rats were randomly assigned to two subgroups to receive either a sham-operation or bilateral-orchiectomy (ORX). Rats were evaluated for metabolic parameters and cognition at 4, 8, and 12 weeks after the operation. At the end of protocol, the reactive oxygen species (ROS), glial morphology, and cell apoptosis were determined in hippocampus and cortex.

RESULTS

Both HFD-fed groups developed obese-insulin resistance, but ND-fed rats did not. HFD-fed rats with sham-operation showed cognitive decline, when compared to ND-fed rats with sham-operation at all time points. At 4- and 8-week after ORX, the cognitive impairment of ND-fed rats and both HFD-fed groups was not different. However, 12-week after ORX, cognitive decline and of glial hyperactivity of HFD-fed rats had the greatest increase among all groups. Hippocampal ROS levels and apoptotic cells in both HFD-fed groups were equally increased, but the cortical ROS levels and apoptotic cells of HFD-fed rats with ORX were the highest ones.

CONCLUSIONS

These findings suggest that testosterone deprivation aggravates cognitive decline in obesity via increasing oxidative stress, glial activity and apoptosis.

Supraphysiologic-dose anabolic-androgenic steroid use: A risk factor for dementia?

Supraphysiologic-dose anabolic-androgenic steroid (AAS) use is associated with physiologic, cognitive, and brain abnormalities similar to those found in people at risk for developing Alzheimer's Disease and its related dementias (AD/ADRD), which are associated with high brain β-amyloid (Aβ) and hyperphosphorylated tau (tau-P) protein levels. Supraphysiologic-dose AAS induces androgen abnormalities and excess oxidative stress, which have been linked to increased and decreased expression or activity of proteins that synthesize and eliminate, respectively, Aβ and tau-P. Aβ and tau-P accumulation may begin soon after initiating supraphysiologic-dose AAS use, which typically occurs in the early 20s, and their accumulation may be accelerated by other psychoactive substance use, which is common among non-medical AAS users. Accordingly, the widespread use of supraphysiologic-dose AAS may increase the numbers of people who develop dementia. Early diagnosis and correction of sex-steroid level abnormalities and excess oxidative stress could attenuate risk for developing AD/ADRD in supraphysiologic-dose AAS users, in people with other substance use disorders, and in people with low sex-steroid levels or excess oxidative stress associated with aging.

Comparative effects of sex hormone deprivation on the brain of insulin-resistant rats

Obese-insulin resistance following chronic high-fat diet consumption led to cognitive decline through several mechanisms. Moreover, sex hormone deprivation, including estrogen and testosterone, could be a causative factor in inducing cognitive decline. However, comparative studies on the effects of hormone-deprivation on the brain are still lacking. Adult Wistar rats from both genders were conducted sham operations or orchiectomies/ovariectomies and given a normal diet or high-fat diet for 4, 8, and 12 weeks. Blood was collected to determine the metabolic parameters. At the end of the experiments, rats were decapitated and their brains were collected to determine brain mitochondrial function, brain oxidative stress, hippocampal plasticity, insulin-induced long-term depression, dendritic spine density, and cognition. We found that male and female rats fed a high-fat diet developed obese-insulin resistance by week 8 and brain defects via elevated brain oxidative stress, brain mitochondrial dysfunction, impaired insulin-induced long-term depression, hippocampal dysplasticity, reduced dendritic spine density, and cognitive decline by week 12. In normal diet-fed rats, estrogen-deprivation, not testosterone-deprivation, induced obese-insulin resistance, oxidative stress, brain mitochondrial dysfunction, impaired insulin-induced long-term depression, hippocampal dysplasticity, and reduced dendritic spine density. In high-fat-diet-fed rats, estrogen deprivation, not testosterone-deprivation, accelerated and aggravated obese-insulin resistance and brain defects at week 8. In conclusion, estrogen deprivation aggravates brain dysfunction more than testosterone deprivation through increased oxidative stress, brain mitochondrial dysfunction, impaired insulin-induced long-term depression, and dendritic spine reduction. These findings may explain clinical reports which show more severe cognitive decline in aging females than males with obese-insulin resistance.

Sex Differences in the Rapid Cell Signaling Mechanisms Underlying the Memory-Enhancing Effects of 17β-Estradiol

Little is known about how 17β-estradiol (E₂) mediates memory formation in males. In ovariectomized (OVX) mice, bilateral dorsal hippocampal (DH) infusion of E₂ enhances memory consolidation in object recognition (OR) and object placement (OP) tasks in a manner dependent on activation of extracellular signal-regulated kinase (ERK) and Akt signaling. Here, bilateral DH E₂ infusion enhanced memory consolidation in both tasks among OVX female, gonadally-intact male, and castrated male mice, suggesting comparable facilitation of memory consolidation in both sexes, independent of testicular hormones in males. Contrary to previous reports in OVX mice, E₂ did not increase DH ERK or Akt phosphorylation in males, nor did the ERK inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis (o-aminophenylmercapto) butadiene] prevent E₂ from enhancing memory consolidation among intact and castrated males. These data suggest that ERK activation is not necessary for E₂ to enhance memory consolidation in males, and compared with previous reports in females, reveal novel sex differences in the cell-signaling pathways through which E₂ facilitates memory consolidation. To explore the mechanisms underlying E₂-induced memory enhancements in males, phosphorylation of the transcription factor cAMP response element binding protein (CREB) in the DH was assessed. E₂ increased phospho-CREB levels in both sexes, yet U0126 did not block these increases in castrated or intact males, indicating that E₂ regulates CREB phosphorylation in males via an ERK-independent mechanism. Collectively, these findings suggest that the beneficial effects of hippocampal E₂ on memory consolidation in males and females are mediated by different molecular mechanisms, which has important implications for the development of treatments to reduce memory dysfunction in men and women.

Cognitive Impacts of Estrogen Treatment in Androgen-Deprived Males: What Needs to be Resolved

Background:

Many prostate cancer (PCa) patients are on androgen deprivation therapy (ADT) as part of their cancer treatments but ADT may lead to cognitive impairments. ADT depletes men of both androgen and estrogen. Whether estradiol supplementation can improve cognitive impairments in patients on ADT is understudied.

Objective:

To summarize data on the effects of estradiol treatment on cognitive function of androgen-deprived genetic male populations (PCa patients and male-to-female transsexuals) and castrated male animals.

Method:

Publications were identified by a literature search on PubMed and Google Scholar.

Results:

While some studies showed that estradiol improves cognitive function (most notably, spatial ability) for castrated rats, what remains uninvestigated are: 1) whether estradiol can improve cognition after long-term androgen deprivation, 2) how estradiol affects memory retention, and 3) how early vs. delayed estradiol treatment after castration influences cognition. For androgen-deprived genetic males, estradiol treatment may improve some cognitive functions (e.g., verbal and visual memory), but the findings are not consistent due to large variability in the study design between studies.

Conclusion:

Future studies are required to determine the best estradiol treatment protocol to maximize cognitive benefits for androgen-deprived genetic males. Tests that assess comparable cognitive domains in human and rodents are needed. What particularly under-investigated is how the effects of estradiol on cognitive ability intersect with other parameters; sleep, depression and physical fatigue. Such studies have clinical implications to improve the quality of life for both PCa patients on ADT as well as for male-to-female transsexuals.

Inosine improves cognitive function and decreases aging-induced oxidative stress and neuroinflammation in aged female rats

In the present study, the effect of inosine was evaluated on learning and memory of 18 months old aged female rats. Inosine (50, 100 and 200 mg/kg; i.p.) was administered to separate groups of rats for 15 successive days. Donepezil (1 mg/kg; i.p.), an acetylcholinesterase inhibitor, was used as a standard drug. Behavioral models such as Morris water maze and elevated plus maze were used to evaluate the effect of drugs on learning and memory of rats. After behavioral studies, animals were killed and their brain was isolated and further processed for estimation of various biochemical parameters such as acetylcholinesterase activity, oxidative stress markers, proinflammatory marker and histological examinations. Inosine (100 and 200 mg/kg) significantly improved learning and memory of aged rats. Further, inosine significantly reduced lipid peroxidation and nitrite, and increased the levels of reduced glutathione and superoxide dismutase. However, no significant difference in AChEs activity was observed in inosine-treated rats as compared to aged control rats. TNF-α level was found to be ameliorated in aged rats by inosine. Histopathological evaluation showed that inosine-treated aged rats have less number of pyknotic neurons in hippocampal CA1 region as compared to aged control rats. In conclusion, inosine significantly improved learning and memory of aged female rats possibly through its antioxidant as well as anti-inflammatory effect and improvement of neuronal survival in the hippocampal CA1 region. However, additional studies are required to further explore the downstream signaling pathways involved in the neuroprotective effect of inosine in aged animals.

Orchiectomy and letrozole differentially regulate synaptic plasticity and spatial memory in a manner that is mediated by SRC-1 in the hippocampus of male mice

Hippocampal synaptic plasticity is the basis of spatial memory and cognition and is strongly regulated by both testicular androgens (testosterone, T) and hippocampal estrogens (17β-estradiol, E2) converted from T by aromatase, which is inhibited by letrozole (LET), but the contribution of each pathway to spatial memory and the associated mechanisms are unclear. In this study, we first used orchiectomy (ORX) and LET injection to investigate the effects of T and hippocampal E2 on spatial memory and hippocampal synaptic plasticity. Next, we examined the changes in steroid receptors and steroid receptor coactivator-1 (SRC-1) under these treatments. Finally, we constructed an SRC-1 RNA interference lentivirus and an AROM overexpression lentivirus to explore the roles of SRC-1 under T replacement and AROM overexpression. The results revealed spatial memory impairment only after LET. LET induced more actin depolymerization and greater losses of spines, synapses, and postsynaptic proteins compared with ORX. Moreover, although ERα and ERβ were affected by LET and ORX at similar levels, AR, GPR30, and SRC-1 were dramatically decreased by LET compared with ORX. Finally, the T and AROM overexpression-induced changes in synaptic proteins and actin polymerization were blocked by SRC-1 inhibition. These results demonstrate that testicular androgens play a limited role, whereas local E2 is more important for cognition, which may explain why castrated men such as eunuchs usually do not have cognitive disorders. These results also suggest a pivotal role of SRC-1 in the action of steroids; thus, SRC-1 may serve as a novel therapeutic target for cognitive disorders.

No effect of testosterone on behavior in aged Wistar rats

In men, aging is accompanied by a gradual decline in androgen secretion. Studies suggest beneficial effects of endogenous and exogenous testosterone on affective behavior and cognitive functions. The aim of this study was to describe behavioral and cognitive sex differences and to analyze the effects of long-term androgen deficiency in aged male rats. Thirty-months old rats divided into three groups (males, females and males gonadectomized as young adults) underwent a battery of behavioral tests assessing locomotor activity, anxiety, memory, anhedonia, sociability and depression-like behavior. No major effect of gonadectomy was found in any of the analyzed behavioral measures in male rats. The only consistent sex difference was confirmed in depression-like behavior with longer immobility time observed in males. In an interventional experiment, a single dose of testosterone had no effect on gonadectomized male and female rats in the forced swim test. In contrast to previous studies this comprehensive behavioral phenotyping of aged rats revealed no major role of endogenous testosterone. Based on our results long-term hypogonadism does not alter the behavior of aged male rats, neither does acute testosterone treatment. Whether these findings have any consequences on androgen replacement therapy in aged men remains to be elucidated.

Spatial memory is impaired by peripubertal GnRH agonist treatment and testosterone replacement in sheep

Chronic gonadotropin-releasing hormone agonist (GnRHa) is used therapeutically to block activity within the reproductive axis through down-regulation of GnRH receptors within the pituitary gland. GnRH receptors are also expressed in non-reproductive tissues, including areas of the brain such as the hippocampus and amygdala. The impact of long-term GnRHa-treatment on hippocampus-dependent cognitive functions, such as spatial orientation, learning and memory, is not well studied, particularly when treatment encompasses a critical window of development such as puberty. The current study used an ovine model to assess spatial maze performance and memory of rams that were untreated (Controls), had both GnRH and testosterone signaling blocked (GnRHa-treated), or specifically had GnRH signaling blocked (GnRHa-treated with testosterone replacement) during the peripubertal period (8, 27 and 41 weeks of age). The results demonstrate that emotional reactivity during spatial tasks was compromised by the blockade of gonadal steroid signaling, as seen by the restorative effects of testosterone replacement, while traverse times remained unchanged during assessment of spatial orientation and learning. The blockade of GnRH signaling alone was associated with impaired retention of long-term spatial memory and this effect was not restored with the replacement of testosterone signaling. These results indicate that GnRH signaling is involved in the retention and recollection of spatial information, potentially via alterations to spatial reference memory, and that therapeutic medical treatments using chronic GnRHa may have effects on this aspect of cognitive function.

Effects of long distance translocation on corticosterone and testosterone levels in male rattlesnakes

Translocation is an increasingly common conservation tool used to augment declining populations or to remove nuisance animals from areas of human conflict. Studies show that venomous snakes translocated long distances may wander and experience increased mortality. However, potential sub-lethal physiological effects on translocated snakes remain unknown. We conducted an experimental study on free-ranging rattlesnakes to test the hypothesis that long distance translocation is stressful. The glucocorticoid response to translocation was variable among snakes. There was some evidence that translocation may be stressful, as baseline corticosterone levels in most snakes rose following translocation, whereas levels remained consistent in control snakes. Interestingly, testosterone levels rose dramatically following translocation, possibly reflecting effects of interaction with new environmental cues and/or resident snakes, or effects of navigation in a new environment. Corticosterone and testosterone were positively correlated. Our study shows that long distance translocation can affect steroid hormone concentrations in rattlesnakes, a result that should be taken into consideration when managing nuisance snakes or repatriating animals to the wild.

Gonadectomy but not biological sex affects burst-firing in dopamine neurons of the ventral tegmental area and in prefrontal cortical neurons projecting to the ventral tegmentum in adult rats

The mesocortical and mesolimbic dopamine systems regulate cognitive and motivational processes and are strongly implicated in neuropsychiatric disorders in which these processes are disturbed. Sex differences and sex hormone modulation are also known for these dopamine-sensitive behaviours in health and disease. One relevant mechanism of hormone impact appears to be regulation of cortical and subcortical dopamine levels. This study asked whether this regulation of dopamine tone is a consequence of sex or sex hormone impact on the firing modes of ventral midbrain dopamine neurons. To address this, single unit extracellular recordings made in the ventral tegmental area and substantia nigra were compared among urethane-anaesthetized adult male, female, gonadectomized male rats. These comparisons showed that gonadectomy had no effect on nigral cells and no effects on pacemaker, bursty, single-spiking or random modes of dopamine activity in the ventral tegmental area. However, it did significantly and selectively increase burst firing in these cells in a testosterone-sensitive, estradiol-insensitive manner. Given the roles of prefrontal cortex (PFC) in modulating midbrain dopamine cell firing, we next asked whether gonadectomy's effects on dopamine cell bursting had correlated effects on the activity of ventral tegmentally projecting prefrontal cortical neurons. We found that gonadectomy indeed significantly and selectively increased burst firing in ventral tegmentally projecting but not neighbouring prefrontal cells. These effects were also androgen-sensitive. Together, these findings suggest a working model wherein androgen influence over the activity of PFC neurons regulates its top-down modulation of mesocortical and mesolimbic dopamine systems and related dopamine-sensitive behaviours.

Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.

Gonadal Hormones Rapidly Enhance Spatial Memory and Increase Hippocampal Spine Density in Male Rats

17β-estradiol (E2) rapidly, within minutes, activates behaviors and cognition by binding to membrane estrogen receptors, activating cell signaling cascades and increasing dendritic spines. In female rodents, E2 enhances spatial memory within 2-4 hours, and spine density is increased in the CA1 area of the hippocampus within 30-60 minutes. Although chronic gonadal hormone treatments in male rats alter cognition and spines/spine synapses and acute hormone effects occur in hippocampal slices, effects of acute, in vivo hormone administration in males are unknown. Therefore, we assessed rapid effects of E2 (20 μg/kg) and testosterone (T) (750 μg/kg) on spatial memory using the object placement task and on hippocampal spine density using Golgi impregnation. Orchidectomized rats received hormones immediately after the training trial and were tested for retention 2 hours later. Vehicle-injected orchidectomized males spent equal time exploring objects in the old and new locations, but E2- or T-treated subjects spent more time exploring objects at the new location, suggesting enhanced memory. Both hormones also increased spine density in CA1, but not the dentate gyrus, by 20%-40% at 30 minutes and 2 hours after injections. This report is the first, to our knowledge, to show E2 and T enhancements of memory and spine density within such a short time frame in male rats.

Ecophysiology of cognition: How do environmentally induced changes in physiology affect cognitive performance?

Cognitive performance is based on brain functions, which have energetic demands and are modulated by physiological parameters such as metabolic hormones. As both environmental demands and environmental energy availability change seasonally, we propose that cognitive performance in free-living animals might also change seasonally due to phenotypic plasticity. This is part of an emerging research field, the 'ecophysiology of cognition': environmentally induced changes in physiological traits, such as blood glucose and hormone levels, are predicted to influence cognitive performance in free-living animals. Energy availability for the brain might change, and as such cognition, with changing energetic demands (e.g. reproduction) and changes of energy availability in the environment (e.g. winter, drought). Individuals spending more energy than they can currently obtain from their environment (allostatic overload type I) are expected to trade off energy investment between cognition and other life-sustaining processes or even reproduction. Environmental changes reducing energy availability might thus impair cognition. However, selection pressures such as predation risk, mate choice or social demands may act on the trade-off between energy saving and cognition. We assume that different environmental conditions can lead to three different trade-off outcomes: cognitive impairment, resilience or enhancement. Currently we cannot understand these trade-offs, because we lack information about changes in cognitive performance due to seasonal changes in energy availability and both the resulting changes in homeostasis (for example, blood glucose levels) and the associated changes in the mechanisms of allostasis (for example, hormone levels). Additionally, so far we know little about the fitness consequences of individual variation in cognitive performance. General cognitive abilities, such as attention and associative learning, might be more important in determining fitness than complex and specialized cognitive abilities, and easier to use for comparative study in a large number of species. We propose to study seasonal changes in cognitive performance depending on energy availability in populations facing different predation risks, and the resulting fitness consequences.

Testosterone deprivation has neither additive nor synergistic effects with obesity on the cognitive impairment in orchiectomized and/or obese male rats

OBJECTIVE

Previous studies demonstrated a correlation between cognitive decline and either testosterone deprivation or obesity. However, the effect of obesity combined with testosterone deprivation on cognitive function has not been investigated. This study investigated the effects of obesity on brain insulin sensitivity, brain mitochondrial function, hippocampal synaptic plasticity and cognitive function in testosterone-deprived male rats.

MATERIALS/METHODS

Male Wistar rats were divided into sham-operated (control) and bilateral orchiectomized (ORX) groups. Rats in each group were further divided into two subgroups to receive either a normal diet (ND) or a high fat diet (HFD) for 4, 8 or 12weeks. Blood samples were collected to determine metabolic parameters. Cognitive function was tested using the Morris Water Maze Test. At the end of the study, brains were removed to investigate brain insulin sensitivity, brain mitochondrial function and hippocampal synaptic plasticity.

RESULTS

Both control-obese and ORX-obese rats developed peripheral insulin resistance at week eight, and brain insulin resistance as well as brain mitochondrial dysfunction at week 12. However, the ORX-obese rats developed cognitive impairment and decreased hippocampal synaptic plasticity beginning at week eight, whereas the control-obese rats developed these impairments later at week 12. Although both peripheral and brain insulin resistance were not observed in both the control-lean and ORX-lean rats, impaired cognition and decreased hippocampal synaptic plasticity were found in the ORX-lean rats beginning at week eight.

CONCLUSION

These findings suggest that testosterone deprivation has neither additive nor synergistic effects over obesity in the development of cognitive dysfunction in orchiectomized-obese male rats.

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

BACKGROUND

In the present study, the role of gonadectomy on memory impairment and the density of androgen receptor-immunoreactive neurons in rats' hippocampus as well as the ability of testosterone to compensate of memory and the density of androgen receptors in the hippocampus was evaluated.

METHODS

Adult male rats (except intact-no testosterone group) were bilaterally castrated, and behavioral tests performed 2 weeks later. Animals bilaterally cannulated into lateral ventricles and then received testosterone (10, 40 and 120 µg/0.5 µl DMSO) or vehicle (DMSO; 0.5 µl) for gonadectomized-vehicle group, 30 min before training in water maze test. The androgen receptor-immunoreactive neurons were detected by immunohistochemical technique in the hippocampal areas.

RESULTS

In the gonadectomized male rats, a memory deficit was found in Morris water maze test on test day (5th day) after DMSO administration. Gonadectomy decreased density of androgen receptor-immunoreactive neurons in the rats' hippocampus. The treatment with testosterone daily for 5 days attenuated memory deficits induced by gonadectomy. Testosterone also significantly increased the density of androgen receptor-immunoreactive neurons in the hippocampal areas. The intermediate dose of this hormone (40 µg) appeared to have a significant effect on spatial memory and the density of androgen receptor-immunoreactive neurons in gonadectomized rats' hippocampus.

CONCLUSIONS

The present study suggests that testosterone can compensate memory failure in gonadectomized rats. Also testosterone replacement can compensate the reduction of androgen receptor-immunoreactive neurons density in the rats' hippocampus after gonadectomy.

Protective effects of testosterone on cognitive dysfunction in Alzheimer's disease model rats induced by oligomeric beta amyloid peptide 1-42

Cognitive dysfunction is known to be influenced by circulating sex steroidal hormones. The aim of this study was to examine the protective effect and possible protective mechanism of testosterone (T) on cognitive performance in male rats induced by intrahippocampal injections of beta amyloid 1-42 oligomers (Aβ1-42). Treatment with T as evidenced by the Morris water maze (MWM) test significantly shortened escape latency and reduced path length to reach the platform compared to the control (C). During probe trials, the T group displayed a significantly greater percent of time in the target quadrant and improved the number of platform crossings compared with C, flutamide (F), an antiandrogen, and a combined F and T group. Flutamide markedly inhibited the influence of T on cognitive performance. Following Nissl staining, the number of intact pyramidal cells was significantly elevated in the T group, and the effect of T was blocked by F. Immunohistochemisty and Western blot analysis showed that the protein expression level of Aβ 1-42 was markedly decreased and expression levels of synaptophysin (SYN) significantly increased with T, while F inhibited all T-mediated effects. Our data suggest that the influence of T on cognitive performance was mediated via androgen receptors (AR) to remove beta amyloid, which leads to enhanced synaptic plasticity.

Effects of Testosterone Treatment on Synaptic Plasticity and Behavior in Senescence Accelerated Mice

Learning and memory are known to be influenced by circulating sex steroidal hormones and these behavioral processes are diminished in aging. Thus, the aim of this study was to examine the mechanism underlying testosterone-induced effects on cognitive performance in the senescence accelerated mouse P8 (SAMP8) model. Treatment with testosterone (T) as evidenced by the Morris water maze test produced a significantly shorter escape latency and reduced path length to reach the platform compared to the control (C). No significant differences were noted in mean swim speed among all groups. During the probe trials, the T group spent a significantly greater percent of time in the target quadrant and improved the number of platform crossings. Flutamide (F), an antiandrogen, significantly inhibited the effects of T on behavioral and memory performances indicators. Following Nissl staining, the number of intact pyramidal cells was markedly elevated in the treated mice, and this effect was blocked by F. Immunohistochemistry and Western blot analysis showed that the expression levels of NMDAR1, SYN, and p-CREC/CREB protein levels were significantly increased in the T group, while F inhibited the T-mediated effects. Western blot analysis showed that there were no significant differences in the expression levels of SYN, p-CREC/CREB, and NMDAR1 between C, F, and F + T groups. Reverse-transcription polymerase chain reaction (RT-PCR) analysis showed that the mRNA expression levels of NMDAR1 and SYN were significantly increased in T-administered mice, while F inhibited the T-mediated effects. Data suggest that the T-mediated increase in SYN expression levels resulted in improvement in behavioral performances and learning, which may involve stimulation of central nervous system androgen receptors (AR).

Testosterone replacement attenuates cognitive decline in testosterone-deprived lean rats, but not in obese rats, by mitigating brain oxidative stress

Testosterone replacement improves metabolic parameters and cognitive function in hypogonadism. However, the effects of testosterone therapy on cognition in obese condition with testosterone deprivation have not been investigated. We hypothesized that testosterone replacement improves cognitive function in testosterone-deprived obese rats by restoring brain insulin sensitivity, brain mitochondrial function, and hippocampal synaptic plasticity. Thirty male Wistar rats had either a bilateral orchiectomy (ORX: O, n = 24) or a sham operation (S, n = 6). ORX rats were further divided into two groups fed with either a normal diet (NDO) or a high-fat diet (HFO) for 12 weeks. Then, ORX rats in each dietary group were divided into two subgroups (n = 6/subgroup) and were given either castor oil or testosterone (2 mg/kg/day, s.c.) for 4 weeks. At the end of this protocol, cognitive function, metabolic parameters, brain insulin sensitivity, hippocampal synaptic plasticity, and brain mitochondrial function were determined. We found that testosterone replacement increased peripheral insulin sensitivity, decreased circulation and brain oxidative stress levels, and attenuated brain mitochondrial ROS production in HFO rats. However, testosterone failed to restore hippocampal synaptic plasticity and cognitive function in HFO rats. In contrast, in NDO rats, testosterone decreased circulation and brain oxidative stress levels, attenuated brain mitochondrial ROS production, and restored hippocampal synaptic plasticity as well as cognitive function. These findings suggest that testosterone replacement improved peripheral insulin sensitivity and decreased oxidative stress levels, but failed to restore hippocampal synaptic plasticity and cognitive function in testosterone-deprived obese rats. However, it provided beneficial effects in reversing cognitive impairment in testosterone-deprived non-obese rats.

Sex steroid hormones matter for learning and memory: estrogenic regulation of hippocampal function in male and female rodents

Ample evidence has demonstrated that sex steroid hormones, such as the potent estrogen 17β-estradiol (E2), affect hippocampal morphology, plasticity, and memory in male and female rodents. Yet relatively few investigators who work with male subjects consider the effects of these hormones on learning and memory. This review describes the effects of E2 on hippocampal spinogenesis, neurogenesis, physiology, and memory, with particular attention paid to the effects of E2 in male rodents. The estrogen receptors, cell-signaling pathways, and epigenetic processes necessary for E2 to enhance memory in female rodents are also discussed in detail. Finally, practical considerations for working with female rodents are described for those investigators thinking of adding females to their experimental designs.

Testosterone deficiency, insulin-resistant obesity and cognitive function

Testosterone is an androgenic steroid hormone, which plays an important role in the regulation of male reproduction and behaviors, as well as in the maintenance of insulin sensitivity. Several studies showed that testosterone exerted beneficial effects in brain function, including preventing neuronal cell death, balancing brain oxidative stress and antioxidant activity, improving synaptic plasticity and involving cognitive formation. Although previous studies showed that testosterone deficiency is positively correlated with cognitive impairment and insulin-resistant obesity, several studies demonstrated contradictory findings. Thus, this review comprehensively summarizes the current evidence from in vitro, in vivo and clinical studies of the relationship between testosterone deficiency and insulin-resistant obesity as well as the correlation between either insulin-resistant obesity or testosterone deficiency and cognitive impairment. Controversial reports and the mechanistic insights regarding the roles of testosterone in insulin-resistant obesity and cognitive function are also presented and discussed.

Dipeptidyl peptidase 4 inhibitor improves brain insulin sensitivity, but fails to prevent cognitive impairment in orchiectomy obese rats

It is unclear whether the dipeptidyl peptidase 4 (DPP4) inhibitor can counteract brain insulin resistance, brain mitochondrial dysfunction, impairment of hippocampal synaptic plasticity and cognitive decline in testosterone-deprived obese rats. We hypothesized that DPP4 inhibitor vildagliptin improves cognitive function in testosterone-deprived obese rats by restoring brain insulin sensitivity, brain mitochondrial function and hippocampal synaptic plasticity. Thirty male Wistar rats received either a sham-operated (S, n=6) or bilateral orchiectomy (ORX, n=24). ORX rats were divided into two groups and fed with either a normal diet (ND (NDO)) or a high-fat diet (HFO) for 12 weeks. Then, ORX rats in each dietary group were divided into two subgroups (n=6/subgroup) to receive either a vehicle or vildagliptin (3 mg/kg per day, p.o.) for 4 weeks. After treatment, cognitive function, metabolic parameters, brain insulin sensitivity, hippocampal synaptic plasticity and brain mitochondrial function were determined in each rat. We found that HFO rats exhibited peripheral and brain insulin resistance, brain mitochondrial dysfunction, impaired hippocampal synaptic plasticity and cognitive decline. NDO rats did not develop peripheral and brain insulin resistance. However, impaired hippocampal synaptic plasticity and cognitive decline occurred. Vildagliptin significantly improved peripheral insulin sensitivity, restored brain insulin sensitivity and decreased brain mitochondrial reactive oxygen species production in HFO rats. However, vildagliptin did not restore hippocampal synaptic plasticity and cognitive function in both NDO and HFO rats. These findings suggest that vildagliptin could not counteract the impairment of hippocampal synaptic plasticity and cognitive decline in testosterone-deprived subjects, despite its effects on improved peripheral and brain insulin sensitivity as well as brain mitochondrial function.

On the effects of testosterone on brain behavioral functions

Testosterone influences the brain via organizational and activational effects. Numerous relevant studies on rodents and a few on humans focusing on specific behavioral and cognitive parameters have been published. The results are, unfortunately, controversial and puzzling. Dosing, timing, even the application route seem to considerably affect the outcomes. In addition, the methods used for the assessment of psychometric parameters are a bit less than ideal regarding their validity and reproducibility. Metabolism of testosterone contributes to the complexity of its actions. Reduction to dihydrotestosterone by 5-alpha reductase increases the androgen activity; conversion to estradiol by aromatase converts the androgen to estrogen activity. Recently, the non-genomic effects of testosterone on behavior bypassing the nuclear receptors have attracted the interest of researchers. This review tries to summarize the current understanding of the complexity of the effects of testosterone on brain with special focus on their role in the known sex differences.

Rodent models of osteoporosis

The aim of this protocol is to provide a detailed description of male and female rodent models of osteoporosis. In addition to indications on the methods of performing the surgical procedures, the choice of reliable and safe anaesthetics is also described. Post-operative care, including analgesia administration for pain management, is also discussed. Ovariectomy in rodents is a procedure where ovaries are surgically excised. Hormonal changes resulting from ovary removal lead to an oestrogen-deprived state, which enhances bone remodelling, causes bone loss and increases bone fracture risk. Therefore, ovariectomy has been considered as the most common preclinical model for understanding the pathophysiology of menopause-associated events and for developing new treatment strategies for tackling post-menopausal osteoporosis. This protocol also provides a detailed description of orchidectomy, a model for androgen-deficient osteoporosis in rodents. Endocrine changes following testes removal lead to hypogonadism, which results in accelerated bone loss, increasing osteoporosis risk. Orchidectomised rodent models have been proposed to mimic male osteoporosis and therefore remain a valuable tool for understanding androgen deficiency in aged men. Although it would have been particularly difficult to assemble an internationally acceptable description of surgical procedures, here we have attempted to provide a comprehensive guide for best practice in performing ovariectomy and orchidectomy in laboratory rodents. Research scientists are reminded that they should follow their own institution's interpretation of such guidelines. Ultimately, however, all animal procedures must be overseen by the local Animal Welfare and Ethical Review Body and conducted under licences approved by a regulatory ethics committee.

Short-term testosterone manipulations do not affect cognition or motor function but differentially modulate emotions in young and older male rhesus monkeys

Human aging is characterized by declines in cognition and fine motor function as well as improved emotional regulation. In men, declining levels of testosterone (T) with age have been implicated in the development of these age-related changes. However, studies examining the effects of T replacement on cognition, emotion and fine motor function in older men have not provided consistent results. Rhesus monkeys (Macaca mulatta) are excellent models for human cognitive aging and may provide novel insights on this issue. We tested 10 aged intact male rhesus monkeys (mean age=19, range 15-25) on a battery of cognitive, motor and emotional tasks at baseline and under low or high T experimental conditions. Their performance was compared to that of 6 young males previously tested in the same paradigm (Lacreuse et al., 2009; Lacreuse et al., 2010). Following a 4-week baseline testing period, monkeys were treated with a gonadotropin releasing hormone agonist (Depot Lupron, 200 μg/kg) to suppress endogenous T and were tested on the task battery under a 4-week high T condition (injection of Lupron+T enanthate, 20 mg/kg, n=8) or 4-week low T condition (injection of Lupron+oil vehicle, n=8) before crossing over to the opposite treatment. The cognitive tasks consisted of the Delayed Non-Matching-to-Sample (DNMS), the Delayed Response (DR), and the Delayed Recognition Span Test (spatial-DRST). The emotional tasks included an object Approach-Avoidance task and a task in which monkeys were played videos of unfamiliar conspecifics in different emotional context (Social Playbacks). The fine motor task was the Lifesaver task that required monkeys to remove a Lifesaver candy from rods of different complexity. T manipulations did not significantly affect visual recognition memory, working memory, reference memory or fine motor function at any age. In the Approach-Avoidance task, older monkeys, but not younger monkeys, spent more time in proximity of novel objects in the high T condition relative to the low T condition. In both age groups, high T increased watching time of threatening social stimuli in the Social Playbacks. These results suggest that T affects some aspects of emotional processing but has no effect on fine motor function or cognition in young or older male macaques. It is possible that the duration of T treatment was not long enough to affect cognition or fine motor function or that T levels were too high to improve these outcomes. An alternative explanation for the discrepancies of our findings with some of the cognitive and emotional effects of T reported in rodents and humans may be the use of a chemical castration, which reduced circulating gonadotropins in addition to T. Further studies will investigate whether the luteinizing hormone LH mediates the effects of T on brain function in male primates.

Assessment of the effects of sex and sex hormones on spatial cognition in adult rats using the Barnes maze

Although sex differences and hormone effects on spatial cognition are observed in humans and animals, consensus has not been reached regarding exact impact on spatial working or reference memory. Recent studies in rats suggest that stress and/or reward, which are often different in tasks used to assess spatial cognition, can contribute to the inconsistencies in the literature. To minimize the impact of these sex- and sex hormone-sensitive factors, we used the Barnes maze to compare spatial working memory, spatial reference memory and spatial learning strategy in adult male, female, gonadectomized (GDX) male, and GDX male rats supplemented with 17β-estradiol (E) or testosterone propionate (TP). Rats received four acquisition trials, four trials 24h later, and a single retention trial one week after. Males and females acquired the task during the first four trials and retained the task thereafter. In contrast, GDX rats took longer to acquire the task and showed retention deficits at 1week. All deficits were attenuated similarly by TP and E. Assessment of search patterns also showed that strategies in the males transitioned from random to spatially focused and eventually direct approaches to the goal. However, this transition was faster in control and GDX-TP than in GDX and GDX-E rats. In contrast, the females almost invariantly followed the maze edge in thigmotactic, serial searches. Thus, while Barnes maze reveals activational, in part estrogenic effects on spatial cognition in males, its amenability to animals' use of multiple strategies may limit its ability to resolve mnemonic differences across sex.

Proposed mechanisms for cancer- and treatment-related cognitive changes

OBJECTIVES

To review the proposed mechanisms of cognitive changes associated with non-central nervous system cancers and cancer treatment.

DATA SOURCES

Review and synthesis of databased publications and review articles.

CONCLUSION

Proposed mechanisms include cytokine upregulation, hormonal changes, neurotransmitter dysregulation, attentional fatigue, genetic predisposition, and comorbid symptoms.

IMPLICATIONS FOR NURSING PRACTICE

Oncology nurses need to understand the multiple mechanisms that may contribute to the development of cancer- and treatment-related cognitive changes so that they can identify patients at high risk and help patients understand why these changes occur.

Impacts of stress and sex hormones on dopamine neurotransmission in the adolescent brain

RATIONALE

Adolescence is a developmental period of complex neurobiological change and heightened vulnerability to psychiatric illness. As a result, understanding factors such as sex and stress hormones which drive brain changes in adolescence, and how these factors may influence key neurotransmitter systems implicated in psychiatric illness, is paramount.

OBJECTIVES

In this review, we outline the impact of sex and stress hormones at adolescence on dopamine neurotransmission, a signaling pathway which is critical to healthy brain function and has been implicated in psychiatric illness. We review normative developmental changes in dopamine, sex hormone, and stress hormone signaling during adolescence and throughout postnatal life, then highlight the interaction of sex and stress hormones and review their impacts on dopamine neurotransmission in the adolescent brain.

RESULTS AND CONCLUSIONS

Adolescence is a time of increased responsiveness to sex and stress hormones, during which the maturing dopaminergic neural circuitry is profoundly influenced by these factors. Testosterone, estrogen, and glucocorticoids interact with each other and have distinct, brain region-specific impacts on dopamine neurotransmission in the adolescent brain, shaping brain maturation and cognitive function in adolescence and adulthood. Some effects of stress/sex hormones on cortical and subcortical dopamine parameters bear similarities with dopaminergic abnormalities seen in schizophrenia, suggesting a possible role for sex/stress hormones at adolescence in influencing risk for psychiatric illness via modulation of dopamine neurotransmission. Stress and sex hormones may prove useful targets in future strategies for modifying risk for psychiatric illness.

Pre-pubertal castration improves spatial learning during mid-adolescence in rats

Hippocampus functions, including spatial cognition and stress responses, mature during adolescence. In addition, hippocampus neuronal structures are modified by circulating sex steroids, which dramatically increase during adolescence. Therefore, the effects of castration and the circulating levels of the main sex steroid testosterone on spatial learning and memory were examined across postnatal ages to test whether pre-pubertal castration affected rats' spatial ability in the Morris Water maze (MWM). Male rats were either castrated or sham-castrated at 22d (days of age), or left gonadally intact. They were then trained and tested in the MWM beginning at 28d, 35d, 45d or 60d. We found that all of the intact rats learned the spatial task; however, the males at 22d and 28d required more trials to acquire the task than the males at older ages. The males castrated at 22d and tested at 35d had significantly lower escape latency and traveled distance during training than the sham-castrated males trained at the same age. No differences were observed in mean values of escape latency and traveled distance at 45d even though they had comparable levels of testosterone. We conclude that adult-typical performance for male spatial memory emerges during mid-adolescence and that pre-pubertal castration appears to improve spatial learning during this time.

Amelioratory effects of testosterone treatment on cognitive performance deficits induced by soluble Aβ1-42 oligomers injected into the hippocampus

This study was undertaken to investigate the protective effects and potential mechanism of testosterone (T) on cognitive performance in adult male rats given bilateral intrahippocampal injections of beta amyloid 1-42 oligomers (Aβ1-42) combined with gonadectomy (Aβ+GDX). A series of experiments were designed to verify the optimal administration time and dose of T and to explore its potential protective mechanisms on spatial ability in Aβ+GDX rats in the Morris water maze test. Aβ1-42 was injected only once two weeks before testing, while T and the androgen receptor (AR) antagonist flutamide (F) were administered daily beginning 2 days before and throughout the 6 days of testing. The Aβ1-42 injection and GDX individually impaired cognitive performance, and the combination of these treatments was additive, leading to even greater impairment. The serum T level peaked at 48 h after administration. T doses ranging from 0.25 to 1.00 mg corresponding to serum T levels of 4.5-21.35 ng/ml improved the spatial ability. Animals administered 0.75 mg of T corresponding to the serum T level of 15.2 ng/ml had the most significantly improved behavioral performances. However, higher T doses of 1.50 and 2.00 mg resulting in serum T levels of 34.8 and 45 ng/ml, respectively, impaired the behavioral performances. F had no effect on the serum T level and spatial ability, but it blocked the activational effect of T. These findings indicate that the effect of T on behavioral performances is partly mediated through ARs.