The effects of intrahippocampal testosterone and flutamide on spatial localization in the Morris water maze

Conditioned preferences: Gated by experience, context, and endocrine systems

Central to the navigation of an ever-changing environment is the ability to form positive associations with places and conspecifics. The functions of location and social conditioned preferences are often studied independently, limiting our understanding of their interplay. Furthermore, a de-emphasis on natural functions of conditioned preferences has led to neurobiological interpretations separated from ecological context. By adopting a naturalistic and ethological perspective, we uncover complexities underlying the expression of conditioned preferences. Development of conditioned preferences is a combination of motivation, reward, associative learning, and context, including for social and spatial environments. Both social- and location-dependent reward-responsive behaviors and their conditioning rely on internal state-gating mechanisms that include neuroendocrine and hormone systems such as opioids, dopamine, testosterone, estradiol, and oxytocin. Such reinforced behavior emerges from mechanisms integrating past experience and current social and environmental conditions. Moreover, social context, environmental stimuli, and internal state gate and modulate motivation and learning via associative reward, shaping the conditioning process. We highlight research incorporating these concepts, focusing on the integration of social neuroendocrine mechanisms and behavioral conditioning. We explore three paradigms: 1) conditioned place preference, 2) conditioned social preference, and 3) social conditioned place preference. We highlight nonclassical species to emphasize the naturalistic applications of these conditioned preferences. To fully appreciate the complex integration of spatial and social information, future research must identify neural networks where endocrine systems exert influence on such behaviors. Such research promises to provide valuable insights into conditioned preferences within a broader naturalistic context.

Testosterone ameliorated the behavioural deficits of gonadectomised rats and counteracted free radicals in a dosage-dependent manner

Testosterone deficiency may induce behavioural changes in individuals. Oxidative stress resulting from a redox imbalance may be implicated in the initiation and progression of neurobehavioural disorders. However, whether exogenous testosterone intervention in male gonadectomised (GDX) rats ameliorates oxidative stress and plays a neuroprotective role remains unknown. Therefore, we examined this hypothesis by performing sham or gonadectomy surgeries on Sprague-Dawley rats with or without supplementation with different doses of testosterone propionate (TP). Open field and Morris water maze tests were performed, the serum and brain testosterone levels, and oxidative stress markers were analysed. GDX and lower TP doses (0.5mg/kg) induced reduced exploratory and motor behaviours, but impaired spatial learning and memory compared to Sham rats. Administration of physiological TP levels (0.75-1.25mg/kg) to the GDX rats restored the behaviour observed in the intact rats. However, higher TP doses (1.5-3.0mg/kg) induced increased exploratory and motor behaviours but impaired spatial learning and memory. These behavioural impairments were accompanied by a marked decrease in levels of antioxidant enzymes (superoxide dismutase and catalase) and an increase in lipid peroxidation levels in the substantia nigra and hippocampus. These findings indicate that TP administration can alter behavioural performance and induce memory and learning impairment, which may result from changes in redox homeostasis in male GDX animals.

Activation of androgen receptors alters hippocampal synaptic plasticity and memory retention through modulation of L-type calcium channels

AIMS

It has been revealed that membrane androgen receptor activation modulates avoidance memory and synaptic plasticity. In a previous study, we showed that Calcineurin, a calcium dependent phosphatase, could be a potential mediator of these AR effects. Also, it is reported that AR activation leads to L-type calcium channel activation. The aim of the current study is to test whether L-type calcium channels are downstream of AR and whether this signal pathway mediates the impairment effect of androgenic steroids on passive avoidance memory and synaptic plasticity.

MATERIALS AND METHODS

We measured the effect of Nandrolone Decanoate (AR agonist), AR antagonist (Nilutamide) plus ND or L-type calcium channel inhibitor (Nifedipine) plus ND on passive avoidance performance of adolescent male rats. For extracellular field potential recordings hippocampal slices were perfused with ND, Nilutamide-ND or Nifedipine-ND.

KEY FINDINGS

Our results clarified that AR activation by ND could impair avoidance behavior as step through latency decreased in ND-treated group while application of both Nilutamide and Nifedipine reestablished normal avoidance behavior. Also, LTP induction in the CA1 area of hippocampus was diminished by ND perfusion and both AR antagonist and L-type calcium channel inhibitor application lead to normal LTP. These findings support our hypothesis that activation of L-type calcium channels are involved in ARs mechanism effects on both avoidance behavior and hippocampal synaptic plasticity.

SIGNIFICANCE

Understanding the biological effects of AR agonists on cognitive processes and its cellular mechanism may be a new/supplementary way to treating fear-related disorders.

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.

Testosterone attenuates sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice

BACKGROUND

Sevoflurane anaesthesia induces phosphorylation of the microtubule-associated protein tau and cognitive impairment in neonatal, but not adult, mice. The underlying mechanisms remain largely to be determined. Sex hormones can be neuroprotective, but little is known about the influence of testosterone on age-dependent anaesthesia effects.

METHODS

Six- and 60-day-old male mice received anaesthesia with sevoflurane 3% for 2 h daily for 3 days. Morris water maze, immunoassay, immunoblotting, co-immunoprecipitation, nanobeam technology, and electrophysiology were used to assess cognition; testosterone concentrations; tau phosphorylation; glycogen synthase kinase-3β (GSK3β) activation; binding or interaction between tau and GSK3β; and neuronal activation in mice, cells, and neurones.

RESULTS

Compared with 60-day-old male mice, 6-day-old male mice had lower testosterone concentrations (3.03 [0.29] vs 0.44 [0.12] ng ml^-1; P<0.01), higher sevoflurane-induced tau phosphorylation in brain (133 [20]% vs 100 [6]% in 6-day-old mice, P<0.01; 103 [8]% vs 100 [13]% in 60-day-old mice, P=0.77), and sevoflurane-induced cognitive impairment. Testosterone treatment increased brain testosterone concentrations (1.76 [0.10] vs 0.39 [0.05] ng ml^-1; P<0.01) and attenuated the sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice. Testosterone inhibited the interaction between tau and GSK3β, and attenuated sevoflurane-induced inhibition of excitatory postsynaptic currents in hippocampal neurones.

CONCLUSIONS

Lower brain testosterone concentrations in neonatal compared with adult male mice contributed to age-dependent tau phosphorylation and cognitive impairment after sevoflurane anaesthesia. Testosterone might attenuate the sevoflurane-induced tau phosphorylation and cognitive impairment by inhibiting the interaction between tau and GSK3β.

Prelimbic of Medial Prefrontal Cortex GABA Modulation through Testosterone on Spatial Learning and Memory

Prefrontal cortex (PFC) is involved in multiple functions including attentional processes, spatial orientation, short-term memory, and long-term memory. Our previous study indicated that microinjection of testosterone in CA1 impaired spatial learning and memory. Some evidence suggests that impairment effect of testosterone is mediated by GABAergic system. In the present study, we investigated the interaction of testosterone (androgenic receptor agonist) and bicuculline (GABA_A receptor antagonist) on spatial learning and memory performance in the prelimbic (PL) of male Wistar rats. Cannulae were bilaterally implanted into the PL region of PFC and drugs were daily microinjected for two minutes in each side. There are 4 experiments. In the first experiment, three sham groups were operated (solvent of testosterone, bicuculline, testosterone plus bicuculline). In the second experiment, different doses of testosterone (40, 80 μg /0.5 μL DMSO/each side) were injected into the PL before each session. In the third experiment, intra PL injections of bicuculline (2, 4 μg/0.5 μL DMSO/each side) were given before every session. In the last experiment, testosterone (80μg/0.5 μL DMSO/each side) along with bicuculline (2 μg/0.5 μL DMSO/each side) was injected into the PL. The results showed there is no difference between control group and sham operated group. Testosterone 80 μg and bicuculline 2 μg, each given separately, and also in combination increased escape latency to find the platform compared to the sham operated and cause to impaired spatial learning and memory. It is shown that intra PL microinjection of bicuculline after testosterone treatment could not rescue the spatial learning and memory impaired induced by testosterone.

Neurobiological mechanisms underlying sex-related differences in stress-related disorders: Effects of neuroactive steroids on the hippocampus

Men and women differ in their vulnerability to a variety of stress-related illnesses, but the underlying neurobiological mechanisms are not well understood. This is likely due to a comparative dearth of neurobiological studies that assess male and female rodents at the same time, while human neuroimaging studies often don't model sex as a variable of interest. These sex differences are often attributed to the actions of sex hormones, i.e. estrogens, progestogens and androgens. In this review, we summarize the results on sex hormone actions in the hippocampus and seek to bridge the gap between animal models and findings in humans. However, while effects of sex hormones on the hippocampus are largely consistent in animals and humans, methodological differences challenge the comparability of animal and human studies on stress effects. We summarise our current understanding of the neurobiological mechanisms that underlie sex-related differences in behavior and discuss implications for stress-related illnesses.

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.

Activation of androgen receptors protects intact male mice from memory impairments caused by aromatase inhibition

Although 17β-estradiol (E₂) is known to regulate hippocampal function, the specific contributions of hippocampally-synthesized E₂ remain unclear. Infusion of the aromatase inhibitor letrozole into the dorsal hippocampus (DH) of ovariectomized mice disrupts object recognition and object placement memory consolidation, suggesting that DH-synthesized E₂ is essential for memory. However, the role of DH-synthesized E₂ in memory among male rodents is unknown. Here, we examined effects of aromatase inhibition on memory consolidation in male mice. Intact and gonadectomized mice were infused with vehicle or letrozole into the DH immediately post-training in object placement and object recognition tasks. Letrozole blocked memory in both tasks among gonadectomized males only, suggesting that circulating androgens, or a rise in hippocampal androgens due to aromatase inhibition, may support memory consolidation in intact males. To test this hypothesis, intact males were infused with the androgen receptor antagonist flutamide into the DH after object training. A dose-dependent impairment was observed in both tasks, indicating that blocking androgen signaling can impair memory consolidation. To test if hippocampal androgen receptor activation protected intact males from the impairing effects of letrozole, a non-impairing dose of flutamide was co-infused with letrozole. Co-administration of both drugs blocked object placement and object recognition memory consolidation, demonstrating that letrozole impairs memory in intact males only if androgen receptors are blocked. Together, these data suggest that DH-synthesized E₂ and androgen receptor activation may work in concert to mediate memory consolidation in intact males, such that androgen receptor activation protects against memory impairments caused by aromatase inhibition.

Androgen treatment effects on hippocampus structure in boys with Klinefelter syndrome

Klinefelter syndrome (KS, 47,XXY) is the most common sex chromosome aneuploidy in males. A variety of complex clinical needs is associated with KS, including physical, cognitive and psychosocial impairments. Standard treatment for KS consists of androgen replacement therapy in adolescence to offset testosterone deficiency. Such treatment has a beneficial effect on the physical and behavioral manifestations of this syndrome. Whether androgen supplementation has a significant influence on the brain, however, is unknown. In the current study, we examined regional gray matter volume in boys with KS to assess whether treatment with oxandrolone, a synthetic hormone analog of testosterone, was associated with structural changes in the brain. Specifically, we focused our investigation on the hippocampus, given (1) its involvement in KS, and (2) the high concentration of androgen receptors found in this region. Structural magnetic resonance imaging data was acquired from a subsample of boys who completed a 2-year double-blind clinical trial in which patients were randomized to treatment with oxandrolone or to placebo, as well as from a sample of typically developing (TD) boys. Group differences in hippocampal volume were examined. A significant main effect of group was observed. Pairwise comparisons indicated smaller hippocampal volume in the placebo group relative to the oxandrolone group, as well as smaller volume in the placebo group relative to the TD control group. No difference in volume was observed between the treatment and TD groups. Moreover, across KS subgroups, a significant positive association was observed between hippocampus volume and performance on a spatial memory task, indicating treatment-based changes in brain structure may underlie cognitive change. These findings confirm prior reports implicating a role of the hippocampus in KS and are important in extending previous research by demonstrating a significant effect of androgens on brain structure.

Androgen receptor is a negative regulator of contextual fear memory in male mice

Although sex-hormones have a well-documented role in memory formation, most literature has focused on estrogens, whereas the role of androgens and their receptor (the androgen receptor; AR) in fear memory is relatively unexplored. To address this gap, we used a transgenic mouse model of AR overexpression (CMV-AR) to determine if AR regulates fear memory, and if this effect can be reversed either by the removal of circulating androgens via gonadectomy, or by antagonising AR activity with flutamide. We found that AR overexpression results in reduced freezing in response to foot shock, and that this difference is reversed with both gonadectomy and flutamide treatment. Differences between genotypes were reinstated by testosterone replacement in gonadectomized mice, suggesting that reduced fear memory in mutants results from AR activation by testosterone and is not secondary to group differences in circulating testosterone. Potential transcriptional mechanisms by which CMV-AR exerts its effects on fear memory were assessed by quantitating the expression of memory-related genes in area CA1 of the hippocampus. Several genes that are altered with AR inhibition and activation, including genes that encode for the histone variant H2A.Z, cholinergic receptors, glutamate receptors, and brain-derived neurotrophic factor. Overall, our findings suggest that AR is a negative regulator of fear memory and identify potential gene targets through which AR may mediate this effect.

Dissociable Effects on Birdsong of Androgen Signaling in Cortex-Like Brain Regions of Canaries

The neural basis of how learned vocalizations change during development and in adulthood represents a major challenge facing cognitive neuroscience. This plasticity in the degree to which learned vocalizations can change in both humans and songbirds is linked to the actions of sex steroid hormones during ontogeny but also in adulthood in the context of seasonal changes in birdsong. We investigated the role of steroid hormone signaling in the brain on distinct features of birdsong using adult male canaries (Serinus canaria), which show extensive seasonal vocal plasticity as adults. Specifically, we bilaterally implanted the potent androgen receptor antagonist flutamide in two key brain regions that control birdsong. We show that androgen signaling in the motor cortical-like brain region, the robust nucleus of the arcopallium (RA), controls syllable and trill bandwidth stereotypy, while not significantly affecting higher order features of song such syllable-type usage (i.e., how many times each syllable type is used) or syllable sequences. In contrast, androgen signaling in the premotor cortical-like brain region, HVC (proper name), controls song variability by increasing the variability of syllable-type usage and syllable sequences, while having no effect on syllable or trill bandwidth stereotypy. Other aspects of song, such as the duration of trills and the number of syllables per song, were also differentially affected by androgen signaling in HVC versus RA. These results implicate androgens in regulating distinct features of complex motor output in a precise and nonredundant manner.SIGNIFICANCE STATEMENT Vocal plasticity is linked to the actions of sex steroid hormones, but the precise mechanisms are unclear. We investigated this question in adult male canaries (Serinus canaria), which show extensive vocal plasticity throughout their life. We show that androgens in two cortex-like vocal control brain regions regulate distinct aspects of vocal plasticity. For example, in HVC (proper name), androgens regulate variability in syntax but not phonology, whereas androgens in the robust nucleus of the arcopallium (RA) regulate variability in phonology but not syntax. Temporal aspects of song were also differentially affected by androgen signaling in HVC versus RA. Thus, androgen signaling may reduce vocal plasticity by acting in a nonredundant and precise manner in the brain.

A comparative study of the effect of the dose and exposure duration of anabolic androgenic steroids on behavior, cholinergic regulation, and oxidative stress in rats

The aim of this study was to assess if the dose and exposure duration of the anabolic androgenic steroids (AAS) boldenone (BOL) and stanazolol (ST) affected memory, anxiety, and social interaction, as well as acetylcholinesterase (AChE) activity and oxidative stress in the cerebral cortex (CC) and hippocampus (HC). Male Wistar rats (90 animals) were randomly assigned to three treatment protocols: (I) 5 mg/kg BOL or ST, once a week for 4 weeks; (II) 2.5 mg/kg BOL or ST, once a week for 8 weeks; and (III) 1.25 mg/kg BOL or ST, once a week for 12 weeks. Each treatment protocol included a control group that received an olive oil injection (vehicle control) and AAS were administered intramuscularly (a total volume of 0.2 ml) once a week in all three treatment protocols. In the BOL and ST groups, a higher anxiety level was observed only for Protocol I. BOL and ST significantly affected social interaction in all protocols. Memory deficits and increased AChE activity in the CC and HC were found in the BOL groups treated according to Protocol III only. In addition, BOL and ST significantly increased oxidative stress in both the CC and HC in the groups treated according to Protocol I and III. In conclusion, our findings show that the impact of BOL and ST on memory, anxiety, and social interaction depends on the dose and exposure duration of these AAS.

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.

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).

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.

Androgen Modulation of Hippocampal Structure and Function

Androgens have profound effects on hippocampal structure and function, including induction of spines and spine synapses on the dendrites of CA1 pyramidal neurons, as well as alterations in long-term synaptic plasticity (LTP) and hippocampally dependent cognitive behaviors. How these effects occur remains largely unknown. Emerging evidence, however, suggests that one of the key elements in the response mechanism may be modulation of brain-derived neurotrophic factor (BDNF) in the mossy fiber (MF) system. In male rats, orchidectomy increases synaptic transmission and excitability in the MF pathway. Testosterone reverses these effects, suggesting that testosterone exerts tonic suppression on MF BDNF levels. These findings suggest that changes in hippocampal function resulting from declining androgen levels may reflect the outcome of responses mediated through normally balanced, but opposing, mechanisms: loss of androgen effects on the hippocampal circuitry may be compensated, at least in part, by an increase in BDNF-dependent MF plasticity.

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.

Sex-specific effect of the anabolic steroid, 17α-methyltestosterone, on inhibitory avoidance learning in periadolescent rats

The illicit use of anabolic androgenic steroids (AAS) has gained popularity among adolescents in the last decade. However, although it is known that exposure to AAS impairs cognition in adult animal models, the cognitive effects during adolescence remain undetermined. An inhibitory avoidance task (IAT) was used to assess the effect of AAS (17α-methyltestosterone; 17α-meT--7.5 mg/kg) in male and female periadolescent rats. A single injection of 17α-meT immediately before the footshock produced significant impairment of inhibitory avoidance learning in males but not females. Generalized anxiety, locomotion, and risk assessment behaviors (RAB) were not affected. Our results show that exposure to a single pharmacological dose of 17α-meT during periadolescence exerts sex-specific cognitive effects without affecting anxiety. Thus, disruption of the hormonal milieu during this early developmental period might have negative impact on learning and memory.

Testosterone influences spatial strategy preferences among adult male rats

Males outperform females on some spatial tasks, and this may be partially due to the effects of sex steroids on spatial strategy preferences. Previous work with rodents indicates that low estradiol levels bias females toward a striatum-dependent response strategy, whereas high estradiol levels bias them toward a hippocampus-dependent place strategy. We tested whether testosterone influenced the strategy preferences in male rats. All subjects were castrated and assigned to one of three daily injection doses of testosterone (0.125, 0.250, or 0.500 mg/rat) or a control group that received daily injections of the drug vehicle. Three different maze protocols were used to determine rats' strategy preferences. A low dose of testosterone (0.125 mg) biased males toward a motor-response strategy on a T-maze task. In a water maze task in which the platform itself could be used intermittently as a visual cue, a low testosterone dose (0.125 mg) caused a significant increase in the use of a cued-response strategy relative to control males. Results from this second experiment also indicated that males receiving a high dose of testosterone (0.500 mg) were biased toward a place strategy. A third experiment indicated that testosterone dose did not have a strong influence on the ability of rats to use a nearby visual cue (floating ball) in the water maze. For this experiment, all groups seemed to use a combination of place and cued-response strategies. Overall, the results indicate that the effects of testosterone on spatial strategy preference are dose dependent and task dependent.

Testosterone modulates spatial recognition memory in male rats

A growing body of research indicates that testosterone influences spatial cognition in male rats; however, the overwhelming majority of studies have been conducted on tasks motivated by either food deprivation or water escape. The hippocampus-dependent version of the Y-maze task, which characterizes spatial recognition memory, capitalizes on the propensity of rats to gravitate toward novel spatial environments and is not contingent upon either appetite or the stress associated with water escape, two factors also affected by testosterone. Accordingly, the aim of the current study was to examine the effects of orchidectomy and subsequent testosterone treatment on spatial recognition memory. Orchidectomy did not impact spatial recognition memory when the delay between the information and retention trials of the Y-maze task was 24h. Alternatively, on the second Y-maze task, which featured a 48-h delay between trials, orchidectomy reduced, and treatments that produced higher levels of testosterone restored, preference for the arm associated with the novel spatial environment. Importantly, there were no differences in activity levels as a function of orchidectomy or testosterone treatment on either of the two tasks. Consistent with previous findings, orchidectomy attenuated, and testosterone treatment restored, both body weight gain and the relative weight of the androgen-sensitive ischiocavernosus muscle, which confirmed the efficacy of orchidectomy and testosterone treatments on physiological outcomes. Therefore, testosterone influenced spatial cognition on a task that minimized the influence of non-mnemonic factors and took advantage of the innate preference of rodents to seek out novel spatial environments.

The effect of testosterone on the formation of brain structures

It has been confirmed in several studies that testosterone can significantly affect brain development. Following metabolism of this hormone by 5α-reductase to dihydrotestosterone, testosterone may act via androgen receptors, or after conversion by aromatase to estradiol, it may act via estrogen receptors. The parts of the brain which are changed under the influence of sex hormones are known as sexually dimorphic nuclei, especially in the preoptic area of the hypothalamus. Nevertheless, evidence suggests that testosterone also influences the structure of the hippocampus, specifically CA1 and CA3 areas of the hippocampus, as well as the amygdala. These brain areas are designed to convert information from short-term into long-term memory. In this review, we summarize the effects of testosterone on the organization of brain structures with respect to spatial cognitive abilities in small rodents.

Behavioral deficits induced by lead exposure are accompanied by serotonergic and cholinergic alterations in the prefrontal cortex

The effects of long-term lead (Pb) exposure producing a blood Pb concentration of lower than 20 μg/dL, i.e. below that associated with overt neurological deficits in occupationally exposed individuals, was studied in adult rats. In order to assess gender differences, we performed parallel behavioral experiments in male and female rats. Exposure to Pb acetate (50 ppm in drinking water) for 6 months induced motor and cognitive alterations, however these effects were gender- and task-dependent. Chronic lead exposure impaired spatial learning assessed in the Morris water maze test (MWM) in both genders, whereas it only induced hyperactivity in the open field and impaired motor coordination in the rotarod test, only in male rats. Hyperactivity in male rats was accompanied by an increase in extracellular level of acetylcholine in the prefrontal cortex. Extracellular dopamine concentration in the prefrontal cortex was unaffected by lead exposure whereas serotonin concentration in the same brain area was significantly decreased in both male and female rats exposed to lead. These results unveil new molecular mechanisms underlying neuropsychiatric alterations induced by chronic lead exposure.

The effect of rapid and depot testosterone and estradiol on spatial performance in water maze

Men and women differ in some cognitive functions including spatial abilities. These differences seem to be affected by sex steroids, but the results are controversial. The aim of this work is to describe the effects of rapid or depot testosterone and estradiol on spatial memory in rats. Thirty-two adult male Wistar rats were divided into 6 groups. Five groups were gonadectomized, and one group was left as control. Castrated groups received sterile oil, testosterone isobutyras, testosterone propionate, estradiol dipropionate or estradiol benzoate. We evaluated spatial performance (escape latency, overall improvement, and time in the quadrant after platform removal) of the rats in a spatial water maze. Animals receiving exogenous sex steroids showed higher plasma concentrations of the particular hormones. Experimental groups improved during the acquisition spatial trials in the water maze. No significant differences between the groups during probe trial were found. In overall improvement, the testosterone depot and estradiol depot groups showed less improvement in comparison to the control groups (P<0.05). No differences in respect to administered hormones were found in corresponding receptor gene expression in hippocampus. In conclusion, exogenous testosterone affects spatial memory of adult castrated males.

The role of testicular hormones and luteinizing hormone in spatial memory in adult male rats

Attempts to determine the influence of testicular hormones on learning and memory in males have yielded contradictory results. The present studies examined whether testicular hormones are important for maximal levels of spatial memory in young adult male rats. To minimize any effect of stress, we used the Object Location Task which is a spatial working memory task that does not involve food or water deprivation or aversive stimuli for motivation. In Experiment 1 sham gonadectomized male rats demonstrated robust spatial memory, but gonadectomized males showed diminished spatial memory. In Experiment 2 subcutaneous testosterone (T) capsules restored spatial memory performance in gonadectomized male rats, while rats with blank capsules demonstrated compromised spatial memory. In Experiment 3, gonadectomized male rats implanted with blank capsules again showed compromised spatial memory, while those with T, dihydrotestosterone (DHT), or estradiol (E) capsules demonstrated robust spatial memory, indicating that T's effects may be mediated by its conversion to E or to DHT. Gonadectomized male rats injected with Antide, a gonadotropin-releasing hormone receptor antagonist which lowers luteinizing hormone levels, also demonstrated spatial memory, comparable to that shown by T-, E-, or DHT-treated males. These data indicate that testicular androgens are important for maximal levels of spatial working memory in male rats, that testosterone may be converted to E and/or DHT to exert its effects, and that some of the effects of these steroid hormones may occur via negative feedback effects on LH.

Testosterone impairs the acquisition of an operant delayed alternation task in male rats

The current study examined the effects of gonadectomy (GDX) and subsequent testosterone treatment of male Long-Evans rats on an operant variable delay spatial alternation task (DSA). Gonadally-intact rats (intact-B), GDX rats receiving implants that delivered a physiological level of testosterone (GDX-T), and GDX rats receiving blank implants (GDX-B) were tested for 25 sessions on a DSA task with variable inter-trial delays ranging from 0 to 18 s. Acquisition of the DSA task was found to be enhanced following GDX in a time and delay dependent manner. Both the GDX-T and the intact-B rats had lower performance accuracies across delays initially, relative to GDX-B rats, and this deficit persisted into subsequent testing sessions at longer delays. The GDX-T and intact-B rats also had a tendency to commit more perseverative errors during the early testing sessions, with both groups persisting in pressing a lever which had not been associated with reinforcement for at least two consecutive trials. However, both the GDX-T and intact-B groups were able to achieve performance accuracy similar to that of the GDX-B rats by the final sessions of testing. Overall, these results suggest that castration of adult male rats enhances their acquisition of an operant DSA task.

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

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

Effects of testosterone on spatial learning and memory in adult male rats

A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how injections of testosterone influenced the spatial working and reference memory of castrated male rats. In the eight-arm radial maze, testosterone injections (0.500 mg/rat) reduced the number of working memory errors during the early blocks of testing but had no effect on the number of reference memory errors relative to the castrated control group. In a reference memory version of the Morris water maze, injections of a wide range of testosterone doses (0.0625-1.000 mg/rat) reduced path lengths to the hidden platform, indicative of improved spatial learning. This improved learning was independent of testosterone dose, with all treatment groups showing better performance than the castrated control males. Furthermore, this effect was only observed when rats were given testosterone injections starting 7 days prior to water maze testing and not when injections were given only on the testing days. We also observed that certain doses of testosterone (0.250 and 1.000 mg/rat) increased perseverative behavior in a reversal-learning task. Finally, testosterone did not have a clear effect on spatial working memory in the Morris water maze, although intermediate doses seemed to optimize performance. Overall, the results indicate that testosterone can have positive activational effects on spatial learning and memory, but the duration of testosterone replacement and the nature of the spatial task modify these effects.

The effects of exogenous testosterone on spatial memory in rats

Testosterone (T) is known to affect spatial abilities in men and women. Studies focusing on this relationship showed that both endogenous variability of T and administration of exogenous T, altered mental rotation and spatial visualization. Organizational and activational effects of T can be separately identified. The aim of our study was to evaluate the activational effects of exogenous T on spatial memory in male and female rats. T was administered 3 times a week over a two week period in either 1 mg/kg for low testosterone group or 10 mg/kg for high testosterone group. The Morris water maze was performed to assess the rat’s working and reference spatial memory. T and estradiol levels were measured in plasma. Increase in plasma T levels was confirmed in the experimental groups in comparison to the control groups (receiving sterile oil, 3 times a week over a two week period). Low dose T impaired working, but improved reference memory in female rats. In male rats the negative effects of T (both doses) on reference memory were shown. This experiment showed that the activational effects of exogenous testosterone on spatial memory of rats were gender and dose-dependent.

Genetic targeting aromatase in male amyloid precursor protein transgenic mice down-regulates beta-secretase (BACE1) and prevents Alzheimer-like pathology and cognitive impairment

As brain testosterone plays both androgenic and estrogenic actions due to its conversion into estrogen via aromatase naturally, it is unclear that the age-related reduction of testosterone increased risk of Alzheimer's disease (AD) in men is mediated through androgen alone or both androgen and estrogen mechanisms. Our previous studies using a gene-based approach in mouse model to block the conversion of testosterone into estrogen (aromatase gene knock-out, ArKO), found a depletion of estrogen and increase in testosterone endogenously in males. Here, we use crossing the ArKO mice with APP23 transgenic mice, a mouse model of AD, to produce APP23/Ar(+/-) mice to study the estrogen-independent effect of testosterone on AD. We found a significant reduction in brain plaque formation, improved cognitive function and increase NEP activity in male APP23/Ar(+/-) mice compared with age-matched male APP23 controls. In addition, we found, for the first time, a reduction of beta-secretase (BACE1) enzyme activity, mRNA level and protein expression in the male APP23/Ar(+/-) mice, suggesting that endogenous testosterone, independent from estrogen, may protect against AD in males via two major mechanisms, downregulation of BACE1 activities at transcriptional level to reduce beta amyloid production and upregulation of NEP activities to enhance bate amyloid degradation.

Effects of neonatal flutamide treatment on hippocampal neurogenesis and synaptogenesis correlate with depression-like behaviors in preadolescent male rats

The prevalence of major depressive disorder (MDD) in adult men is roughly half that of women. Clinical evidence supports a protective effect of androgens against depressive disorders in men. The developing brain is subject to androgen exposure but a potential role for this in depression during adulthood has not been considered. In order to explore this question we treated newborn male rat pups with the androgen receptor antagonist flutamide to block endogenous androgen action and then conducted behavioral tests prior to puberty. Depression-like behaviors were assessed with the Forced Swim Test (FST) and the Sucrose Preference Test (SPT), and anxiety-like behaviors were assessed with the Open Field Test (OFT) and the Novelty-Suppressed Feeding Test (NSFT). Compared to the vehicle-treated controls, neonatal-flutamide treatment caused a significant increase in depression-like behaviors in preadolescent male rats but did not cause any significant difference in anxiety-like behaviors. In separate experiments, male pups with and without flutamide treatment were injected with 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU) from postnatal day (PND) 1 to 4 to label newly produced cells or the hippocampi were Golgi-Cox imbedded and pyramidal neurons visualized. Three lines of evidence indicate neonatal flutamide treatment inhibits hippocampal neurogenesis and neuronal dendritic spine formation in preadolescent male rats. Compared to vehicle controls, flutamide treatment significantly decreased (1) the number of microtubule-associated protein-2+ (MAP-2) neurons in the CA1 region, (2) the number of MAP-2+ neurons in the dentate gyrus (DG) region of the hippocampus, and (3) the density of dendritic spines of pyramidal neurons in the CA1 region. However, there was no effect of flutamide treatment on the number of glial fibrillary acidic protein (GFAP)+ or GFAP+/BrdU+ cells in the hippocampus. This study suggests that the organizational effect of androgen-induced hippocampal neurogenesis is antidepressant.

Transgenic expression of androgen receptors improves spatial memory retention in both sham-irradiated and 137Cs gamma-irradiated female mice

Using a water maze, it has been shown that both wild-type and apoE4-expressing female mice are at greater risk of developing age-related hippocampal-dependent impairments in spatial learning and memory than age-matched male mice of the same genotype. In addition, apoE4-expressing female mice were more sensitive to 137Cs gamma-radiation-induced impairment in spatial learning and memory than age-matched male mice of the same genotype. These findings imply that androgen receptors (ARs) contribute to spatial learning and memory, posing the question as to whether transgenic expression of AR in female mice might modulate hippocampal-dependent learning and memory under baseline conditions and after local brain irradiation. Hippocampal-dependent novel location recognition was comparable in wild-type and AR-Tg female mice. This function was impaired after irradiation in AR-Tg but not wild-type mice. In contrast, sham-irradiated wild-type and AR-Tg female mice showed hippocampal-independent novel location recognition, and this was not affected by radiation. After the second day of hidden platform training, in a water maze probe trial, sham-irradiated and irradiated AR-Tg female mice showed spatial memory retention but irradiated wild-type mice did not. After the third day of hidden platform training, only irradiated wild-type female mice did not show spatial memory retention in the water maze probe trial. Both sham-irradiated and irradiated wild-type and AR-Tg female mice showed passive avoidance learning and memory. These data support an important role for AR in spatial memory retention in water maze probe trials in female mice under baseline conditions and after cranial irradiation.

Nandrolone abuse decreases anxiety and impairs memory in rats via central androgenic receptors

Anabolic androgenic steroids (AASs) affect areas of the central nervous system, which are involved in emotional and cognitive responses such as sexuality, anxiety, and memory. In the present study we imitated the abuse of AASs by administering high doses of the AAS nandrolone decanoate (ND) to rats. Thereafter rats were exposed to an elevated plus-maze and an olfactory social memory test to evaluate their anxiety-like and cognitive behaviour. To reveal whether these emotional and cognitive changes evoked by ND were caused via direct activation of androgenic receptors (ARs) in the brain, the AR antagonist flutamide (FL) was administered intracerebroventricularly (i.c.v.). Male rats were randomly divided in four groups, one group received 15 mg/kg ND subcutaneously, once daily for 6 wk (ND group). In the second group, in addition to ND, a daily dose of 5 microg FL was injected i.c.v. also for 6 wk (ND+FL group). The third group of rats received only FL and in the control group the vehicle was injected. The ND group clearly spent more time investigating the open arms in the maze test and recognizing the juvenile during the olfactory social memory test in comparison to the control group. In the ND+FL group rats showed similar emotional behaviour and cognitive ability to that of the control group. Injection of FL alone did not affect either anxiety or memory. These results indicate that repeated, high-dose administration of ND decreases anxiety and impairs memory in rats via direct activation of central ARs.

Impact of sex and hormones on new cells in the developing rat hippocampus: a novel source of sex dimorphism?

The hippocampus is a key brain region regulating complex cognitive and emotional responses, and is implicated in the etiology of depressive and anxiety disorders, many of which exhibit some degree of sex difference. The male rat hippocampus is consistently reported to be slightly but significantly larger than the female. The majority of studies on the development of volumetric sex differences have focused on the effects of estradiol (E2), with relatively few focusing on androgens. We examined the impact of both E2 and androgens on newly born cells in the developing rat hippocampus, and report that neonatal males have significantly more 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU)+ cells than females. Both testosterone (T) and dihydrotestosterone treatment of females significantly increased the number of BrdU+ cells, an effect blocked by the androgen receptor antagonist, flutamide. However, only T significantly increased the number of neuronal nuclear antigen+ neurons in the female rat hippocampus. Interestingly, E2 treatment also increased BrdU+ cells in females, but had no effect on neuron number. Instead, E2 and T significantly increased the number of newly born glial fibrillary acidic protein or glutamine synthetase+ glial cells in females, indicating that androgens and E2 may act independently to achieve distinct endpoints. Quantification of pyknotic cells at two different developmental time points indicates no sex difference in the number of cells dying, suggesting, but not proving, that gonadal steroids are promoting cell genesis.

AR, apoE, and cognitive function

Reduced androgen levels in aged men and women might be risk factors for age-related cognitive decline and Alzheimer's disease (AD). Ongoing clinical trials are designed to evaluate the potential benefit of estrogen in women and of testosterone in men. In this review, we discuss the potential beneficial effects of androgens and androgen receptors (ARs) in males and females. In addition, we discuss the hypothesis that AR interacts with apolipoprotein (apoE)4, encoded by epsilon4 and a risk factor for age-related cognitive decline and AD, and the potential consequences of this interaction.

Prenatal testosterone improves the spatial learning and memory by protein synthesis in different lobes of the brain in the male and female rat

The high density of the steroid hormone receptors in the structures of temporal lobe involved in learning and memory, such as the hippocampus, perirhinal cortex, entorhinal cortex and amigdaloid complex, shows that there must be a direct relationship between gonadal hormones and organizational effects of steroid hormones in those structures during development of the nervous system. The present study was undertaken in order to investigate the effect of testosterone administration during the third week of gestation on the spatial memory formation of the offspring rats and the level of soluble proteins in the temporal lobe and frontal lobe of brain, as evidence of important organizational effects of androgens during prenatal development in brain sexual dimorphism. Animals have received testosterone undecanoate on days 14, 15, 16 and 19, 20, 21 of gestation. Learning and memory tests were started 100 days after the testosterone treatment. At the end of the experiments, the temporal and frontal lobes of brain were removed for assessing the level of soluble proteins. Testosterone treatment significantly improved spontaneous alternations percentage of male offspring in Y-maze task comparative with female offspring and reference memory in radial 8 arm-maze task (decreasing in number of reference memory errors in both male and female offspring groups), suggesting effects of both short and long-term memory. Also, testosterone significantly increased the brain soluble protein level of treated female rats in 14–16 prenatal days compared with the control group as well as the brain soluble protein level of treated male rats. These results suggest that steroid hormones play an important role in the spatial learning and memory formation by means of protein synthesis in different lobes of the brain.

The role of androgen receptors in the masculinization of brain and behavior: what we've learned from the testicular feminization mutation

Many studies demonstrate that exposure to testicular steroids such as testosterone early in life masculinizes the developing brain, leading to permanent changes in behavior. Traditionally, masculinization of the rodent brain is believed to depend on estrogen receptors (ERs) and not androgen receptors (ARs). According to the aromatization hypothesis, circulating testosterone from the testes is converted locally in the brain by aromatase to estrogens, which then activate ERs to masculinize the brain. However, an emerging body of evidence indicates that the aromatization hypothesis cannot fully account for sex differences in brain morphology and behavior, and that androgens acting on ARs also play a role. The testicular feminization mutation (Tfm) in rodents, which produces a nonfunctional AR protein, provides an excellent model to probe the role of ARs in the development of brain and behavior. Tfm rodent models indicate that ARs are normally involved in the masculinization of many sexually dimorphic brain regions and a variety of behaviors, including sexual behaviors, stress response and cognitive processing. We review the role of ARs in the development of the brain and behavior, with an emphasis on what has been learned from Tfm rodents as well as from related mutations in humans causing complete androgen insensitivity.

Steroid abnormalities and the developing brain: declarative memory for emotionally arousing and neutral material in children with congenital adrenal hyperplasia

Steroid hormones modulate memory in animals and human adults. Little is known on the developmental effects of these hormones on the neural networks underlying memory. Using Congenital adrenal hyperplasia (CAH) as a naturalistic model of early steroid abnormalities, this study examines the consequences of CAH on memory and its neural correlates for emotionally arousing and neutral material in children. Seventeen patients with CAH and 17 age- and sex-matched healthy children (ages 12-14 years) completed the study. Subjects were presented positive, negative and neutral pictures. Memory recall occurred about 30min after viewing the pictures. Children with CAH showed memory deficits for negative pictures compared to healthy children (p<0.01). There were no group differences on memory performance for either positive or neutral pictures (p>0.1). In patients, 24h urinary-free cortisol levels (reflecting glucocorticoid replacement therapy) and testosterone levels were not associated with memory performance. These findings suggest that early steroid imbalances affect memory for negative material in children with CAH. Such memory impairments may result from abnormal brain organization and function following hormonal dysfunction during critical periods of development.

Castration differentially affects spatial working and reference memory in male rats

A male advantage for spatial learning and memory tasks is well documented among humans and rodents. A possible physiological cause for this male advantage is activational effects of androgens among males. The spatial memory of eight castrated and eight sham-castrated adult male rats was compared using a working-reference memory version of the eight-arm radial arm maze followed by a reference memory version of the Morris water maze. After maze testing, blood was collected from each rat, and testosterone levels were determined using radioimmunoassay. In the radial arm maze, castrates committed significantly more working memory errors and significantly fewer reference memory errors than did shams. In the water maze, no statistically significant differences were found for acquisition or retention. There was a trend for shams with higher testosterone levels to have better retention in the water maze, but this seemed to be due to higher levels of perseverance rather than better reference memory. Castration may have affected performance in the radial arm maze and not in the water maze because the radial arm maze was a more difficult task or because the water maze was aversively motivated while the radial arm maze was appetitively motivated. Our results indicate that androgens improve working memory and may impair reference memory, but the effects of androgens on reference memory seem to be task dependent.

Tfm-AR modulates the effects of ApoE4 on cognition

Female mice are more susceptible to apolipoprotein E (apoE4)-induced cognitive deficits than male mice. These deficits can be antagonized by stimulating androgen receptors (ARs). To determine the role of AR in the cognitive effects of apoE4, we backcrossed mutant mice with a naturally occurring defect in the AR [testicular feminization mutant (tfm)] onto the Apoe-/- background to eliminate mouse apoE gene resulting in non-functional AR, and crossed the tfm/Apoe-/- female mice with apoE4 transgenic male mice. We behaviorally compared Apoe-/-, apoE4, tfm, and tfm/apoE4 male mice. Apoe-/-, apoE4, and tfm mice showed hippocampus-dependent novel location recognition but tfm/apoE4 mice did not. In contrast, all groups showed hippocampus-independent novel object recognition. Hippocampus-dependent learning and memory were also assessed in the water maze. In the water maze probe trial following the second day of hidden platform training, Apoe-/- and apoE4 mice showed spatial memory retention, but tfm and tfm/ApoE4 mice did not. In the water maze, probe trial following the third day of hidden platform training, Apoe-/-, apoE4, and tfm/Apoe-/- mice showed spatial memory retention, but tfm mice did not. These data support an important role for AR in protecting against the detrimental effects of apoE4 on hippocampus-dependent learning and memory.

Evidence for the influence of testosterone in the performance of spatial navigation in a virtual water maze in women but not in men

Testosterone (T) may be associated with enhanced spatial navigation in a number of rodent species, although the nature of the relation is equivocal. Similarly, numerous studies in humans generally have found that T is associated with enhanced spatial ability on a variety of paper and pencil tasks that may relate to navigational ability. However, relatively few studies have reported effects of T on navigational ability in humans. We investigated the relationship between endogenous T and performance on a virtual water maze (vWM) and mental rotations test (MROT). ELISA for T was performed on salivary samples that were obtained from participants before and after completion of both spatial tasks. Results indicated that women with low T required more time to locate the hidden platform in the vWM than either group of men or women with high T. Significant negative correlations were found for the entire sample between vWM performance and T, and between vWM latency to escape and MROT. Similar significant correlations were found in women but not men. Thus, our data support the position that T improves performance in the vWM in a linear fashion, most strongly in women. However, further work is needed to confirm this hypothesis in humans.