Modulation of short term and long term memory by steroid sexual hormones

The association of caffeine and nandrolone decanoate modulates aversive memory and nociception in rats

Caffeine and anabolic-androgenic steroids (AAS) are commonly used to improve muscle mass and athletic performance. Nandrolone Decanoate (ND) is one of the most abused AAS worldwide, leading to behavioral changes in both humans and rodents. Caffeine, the most widely consumed psychostimulant globally, is present in various thermogenic and gym supplements. Low and moderate doses of caffeine antagonize adenosine receptors and have been linked to improved memory and pain relief. We have previously demonstrated that consuming caffeine prevents the risk-taking behavior triggered by nandrolone. In this study, we aimed to investigate the long-term effects of ND and caffeine, either alone or in combination, on passive avoidance memory and nociception. We used the step-down and hot-plate tasks in male and female Lister Hooded rats. Our results confirmed the antinociceptive effect of caffeine and indicated that chronic administration of the ND-caffeine association promotes the evocation of aversive memory in female rats.

Chronic high-dose testosterone impairs economic decision making, but has no effect on memory in male rats

The goal is to understand consequences of anabolic-androgenic steroid (AAS) abuse on cognitive function, using rats as a model. Economic decision making was evaluated in an operant test of effort value discounting, where subjects choose between 2 levers that deliver large and small rewards differing in maximum value and reward contrast. The hypothesis is that chronic high-dose testosterone increases preference for large rewards. Male rats were treated chronically with testosterone (7.5 mg/kg) or vehicle. Initially, all rats preferred the large reward lever when large and small rewards remained fixed at 3 and 1 sugar pellets, respectively. When different reward values were introduced, and with increasing response requirements, testosterone-treated rats made fewer responses for the large reward, and increased omissions. They earned fewer rewards overall. To determine if testosterone impairs memory, rats were tested for recognition memory with the novel object recognition and social transmission of food preference tasks, and for spatial memory with the radial arm maze and Morris water maze. There was not effect of chronic high-dose testosterone on any memory task. These results suggest that testosterone shifts economic decision making towards larger rewards even when they are disadvantageous, but does not alter memory in rats.

Effects of early life overnutrition and hyperandrogenism on spatial learning and memory in a rat model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a complex disorder characterized by endocrine and metabolic abnormalities such as obesity and insulin resistance. PCOS is also associated with psychiatric disorders and cognitive impairment. The animal model of PCOS was induced by treating rats with 5α-dihydrotestosterone (5α-DHT) and additionally modified to induce adiposity by litter size reduction (LSR). Spatial learning and memory were assessed using the Barnes Maze test, and striatal markers of synaptic plasticity were analyzed. Striatal insulin signaling was estimated by the levels of insulin receptor substrate 1 (IRS1), its inhibitory phosphorylation at Ser307, and glycogen synthase kinase-3α/β (GSK3α/β) activity. Both LSR and DHT treatment significantly decreased striatal protein levels of IRS1, followed by increased GSK3α/β activity in small litters. Results of the behavioral study showed that LSR had a negative effect on learning rate and memory retention, whereas DHT treatment did not induce impairment in memory formation. While protein levels of synaptophysin, GAP43, and postsynaptic density protein 95 (PSD-95) were not altered by the treatments, DHT treatment induced an increase in phosphorylation of PSD-95 at Ser295 in both normal and small litters. This study revealed that LSR and DHT treatment suppressed insulin signaling by downregulating IRS1 in the striatum. However, DHT treatment did not have an adverse effect on learning and memory, probably due to compensatory elevation in pPSD-95-Ser295, which had a positive effect on synaptic strength. This implies that hyperandrogenemia in this setting does not represent a threat to spatial learning and memory, opposite to the effect of overnutrition-related adiposity.

Exogenous estradiol and oxytocin modulate sex differences in hippocampal reactivity during the encoding of episodic memories

Considerable evidence supports sex differences in episodic memory. The hormones estradiol and oxytocin both affect episodic memory and may contribute to these sex differences, but possible underlying hormonal interactions have not been tested in a sample involving both sexes. To this end, we conducted a randomized, placebo-controlled, parallel-group functional magnetic resonance imaging (fMRI) study including healthy free-cycling women (n = 111) and men (n = 115). The fMRI session was conducted under four experimental conditions: 1. transdermal estradiol (2 mg) and intranasal oxytocin (24 IU), 2. transdermal placebo and intranasal oxytocin, 3. transdermal estradiol and intranasal placebo, 4. transdermal placebo and intranasal placebo. Participants were scanned during the encoding of positive, neutral, and negative scenes. Recognition memory was tested three days following the scanning sessions without additional treatments. Under placebo, women showed a significantly better recognition memory and increased hippocampal responses to subsequently remembered items independent of the emotional valence compared to men. The separate treatments with either hormone significantly diminished this mnemonic sex difference and reversed the hippocampal activation pattern. However, the combined treatments produced no significant effect. Collectively, the results suggest that both hormones play a crucial role in modulating sex differences in episodic memory. Furthermore, possible antagonistic interactions between estradiol and oxytocin could explain previously observed opposing hormonal effects in women and men.

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.

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.

Estradiol and hippocampal memory in female and male rodents

Estrogens influence nearly every aspect of hippocampal function, including memory formation. Although this research has traditionally focused on ovariectomized females, more recent work is providing insights into the ways in which estrogens regulate hippocampal function in both sexes. This review provides an overview of estrogenic regulation of hippocampal function in female and male rodents, with a particular emphasis on memory formation. Where applicable, we discuss the involvement of specific estrogen receptors and molecular mechanisms that mediate these effects. The review concludes by suggesting gaps in the literature that need to be filled to provide greater insights into potential sex differences in the effects of estrogens on hippocampal function.

Quantitative Brain MRI in Congenital Adrenal Hyperplasia: In Vivo Assessment of the Cognitive and Structural Impact of Steroid Hormones

Context

Brain white matter hyperintensities are seen on routine clinical imaging in 46% of adults with congenital adrenal hyperplasia (CAH). The extent and functional relevance of these abnormalities have not been studied with quantitative magnetic resonance imaging (MRI) analysis.

Objective

To examine white matter microstructure, neural volumes, and central nervous system (CNS) metabolites in CAH due to 21-hydroxylase deficiency (21OHD) and to determine whether identified abnormalities are associated with cognition, glucocorticoid, and androgen exposure.

Design, Setting, and Participants

A cross-sectional study at a tertiary hospital including 19 women (18 to 50 years) with 21OHD and 19 age-matched healthy women.

Main Outcome Measure

Recruits underwent cognitive assessment and brain imaging, including diffusion weighted imaging of white matter, T1-weighted volumetry, and magnetic resonance spectroscopy for neural metabolites. We evaluated white matter microstructure by using tract-based spatial statistics. We compared cognitive scores, neural volumes, and metabolites between groups and relationships between glucocorticoid exposure, MRI, and neurologic outcomes.

Results

Patients with 21OHD had widespread reductions in white matter structural integrity, reduced volumes of right hippocampus, bilateral thalami, cerebellum, and brainstem, and reduced mesial temporal lobe total choline content. Working memory, processing speed, and digit span and matrix reasoning scores were reduced in patients with 21OHD, despite similar education and intelligence to controls. Patients with 21OHD exposed to higher glucocorticoid doses had greater abnormalities in white matter microstructure and cognitive performance.

Conclusion

We demonstrate that 21OHD and current glucocorticoid replacement regimens have a profound impact on brain morphology and function. If reversible, these CNS markers are a potential target for treatment.

Steroid Receptor Coactivator-1 Knockdown Decreases Synaptic Plasticity and Impairs Spatial Memory in the Hippocampus of Mice

Steroids have been demonstrated to play profound roles in the regulation of hippocampal function by acting on their receptors, which need coactivators for their transcriptional activities. Previous studies have shown that steroid receptor coactivator-1 (SRC-1) is the predominant coactivator in the hippocampus, but its exact role and the underlying mechanisms remain unclear. In this study, we constructed SRC-1 RNA interference (RNAi) lentiviruses, injected them into the hippocampus of male mice, and then examined the changes in the expression of selected synaptic proteins, CA1 synapse density, postsynaptic density (PSD) thickness, and in vivo long-term potentiation (LTP). Spatial learning and memory behavior changes were investigated using the Morris water maze. We then transfected the lentiviruses into cultured hippocampal cells and examined the changes in synaptic protein and phospho-cyclic AMP response element-binding protein (pCREB) expression. The in vivo results showed that SRC-1 knockdown significantly decreased the expression of synaptic proteins and CA1 synapse density as well as PSD thickness; SRC-1 knockdown also significantly impaired in vivo LTP and disrupted spatial learning and memory. The in vitro results showed that while the expression of synaptic proteins was significantly decreased by SRC-1 knockdown, pCREB expression was also significantly decreased. The above results suggest a pivotal role of SRC-1 in the regulation of hippocampal synaptic plasticity and spatial learning and memory, strongly indicating SRC-1 may serve as a novel therapeutic target for hippocampus-dependent memory disorders.

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.

Estradiol enhances retention but not organization of hippocampus-dependent memory in intact male mice

Because estrogens have mostly been studied in gonadectomized females, effects of chronic exposure to environmental estrogens in the general population are underestimated. Estrogens can enhance hippocampus-dependent memory through the modulation of information storage. However, declarative memory, the hippocampus-dependent memory of facts and events, demands more than abilities to retain information. Specifically, memory of repetitive events of everyday life such as "where I parked" requires abilities to organize/update memories to prevent proactive interference from similar memories of previous "parking events". Whether such organizational processes are estrogen-sensitive is unknown. We here studied, in intact young and aged adult mice, drinking-water (1μM) estradiol effects on both retention and organizational components of hippocampus-dependent memory, using a radial-maze task of everyday-like memory. Demand on retention vs organization was manipulated by varying the time-interval separating repetitions of similar events. Estradiol increased performance in young and aged mice under minimized organizational demand, but failed to improve the age-associated memory impairment and diminished performance in young mice under high organizational demand. In fact, estradiol prolonged mnemonic retention of successive events without improving organization abilities, hence resulted in more proactive interference from irrelevant memories. c-Fos imaging of testing-induced brain activations showed that the deterioration of young memory was associated with dentate gyrus dysconnectivity, reminiscent of that seen in aged mice. Our findings support the view that estradiol is promnesic but also reveal that such property can paradoxically impair memory. These findings have important outcomes regarding health issues relative to the impact of environmental estrogens in the general population.

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.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.

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.

GH improves spatial memory and reverses certain anabolic androgenic steroid-induced effects in intact rats

GH has previously been shown to promote cognitive functions in GH-deficient rodents. In this study we report the effects of GH on learning and memory in intact rats pretreated with the anabolic androgenic steroid nandrolone. Male Wistar rats received nandrolone decanoate (15 mg/kg) or peanut oil every third day for 3 weeks and were subsequently treated with recombinant human GH (1.0 IU/kg) or saline for 10 consecutive days. During the GH/saline treatment spatial learning and memory were tested in the Morris water maze (MWM). Also, plasma levels of IGF1 were assessed and the gene expression of the GH receptors (Ghr), Igf1 and Igf2, in hippocampus and frontal cortex was analyzed. The results demonstrated a significant positive effect of GH on memory functions and increased gene expression of Igf1 in the hippocampus was found in the animals treated with GH. In addition, GH was demonstrated to increase the body weight gain and was able to attenuate the reduced body weight seen in nandrolone-treated animals. In general, the rats treated with nandrolone alone did not exhibit any pronounced alteration in memory compared with controls in the MWM, and in many cases GH did not induce any alteration. Regarding target zone crossings, considered to be associated with spatial memory, the difference between GH- and steroid-treated animals was significant and administration of GH improved this parameter in the latter group. In conclusion, GH improves spatial memory in intact rats and can reverse certain effects induced by anabolic androgenic steroid.

Effect of intrahippocampal ghrelin agonist administration on passive avoidance learning and anxiety in rats

Hippocampus, amygdala and dorsal raphe nucleus are the cerebral main structures involved in learning, memory and anxiety. Ghrelin increases the level of several hormones in these structures and affects learning, memory and anxiety-like behaviors. This study was performed to investigate the effect of ghrelin agonist on passive avoidance learning and anxiety in adult female rats in the presence and absence of ovary hormones. Five groups of rats, including control group with no injections, ovariectomized groups; one group receiving normal saline and other group receiving ghrelin agonist solution, surgery shocked (sham operated) groups; one group receiving saline and other group ghrelin agonist solution, were tested. Inside stereotaxis apparatus, two sided CA1 cannulae were used and 1 microL of saline or ghrelin agonist solution, at 3 nmol microL(-1) concentration, was injected into each cannula. Passive avoidance learning was measured by using shuttle box and anxiety by elevated plus- maze. Ghrelin agonist increased the level of learning in surgery shocked group in comparison with control group. Anxiety-like behavior was seen in both ovariectomized and surgery shocked groups. Ghrelin agonist binds its own receptors in the hippocampus, thereby increases learning capability and induces anxiety-like behaviors. Proper management of these behaviors might be useful in controlling some forms of nervous system diseases in humans.

Testosterone has sublayer-specific effects on dendritic spine maturation mediated by BDNF and PSD-95 in pyramidal neurons in the hippocampus CA1 area

Testosterone has a number of important physiological roles and acts on peripheral target tissues and the central nervous system. Testosterone exerts many of its effects through the androgen receptor (AR). ARs are widely distributed in nervous tissues and particularly strongly expressed in hippocampal CA1 pyramidal neurons, which play critical roles in spatial memory tasks. Dendritic spines are specialized to receive synaptic inputs, and a change in spine morphology is correlated with the strength and maturity of each synapse. In this study, we used thy1-GFP transgenic male adult mice to analyze the morphology of dendritic spines in the hippocampal CA1 area. Gonadectomy (GDX) induced aberrant morphologies with less mushroom-type and more stubby- and thin-type spines in the proximal part of the stratum radiatum after two weeks. These morphological changes were also observed in the distal part of the stratum radiatum, whereas there was no change in the stratum lacunosum-moleculare after GDX. Testosterone replacement in GDX mice recovered the changes in spine types to those found in controls. To determine the mechanism of the testosterone-dependent morphological changes, we examined expression of brain-derived neurotrophic factor (BDNF) and its downstream target post-synaptic density protein 95 (PSD-95). GDX induced a significant decrease in the protein levels of BDNF and PSD-95 in the CA1 area, which were prevented by testosterone replacement. These findings reveal a novel role of testosterone in prevented the differential response properties of spine maturation in sublayers of dendritic spines in the CA1 area via the actions of BDNF and PSD-95.

Effect of 3α-anderostanediol and indomethacin on acquisition, consolidation and retrieval stage of spatial memory in adult male rats

BACKGROUND

Testosterone and its metabolites have important roles in learning and memory. The current study has conducted to assess the effect of pre-training, post-training and pre-probe trial intrahippocampal CA1 administration of 3α-anderostanediol (one of the metabolites of testosterone) and indomethacin (as 3α-hydroxysteroid dehydrogenase enzyme blocker) on acquisition, consolidation and retrieval in Morris water maze (MWM) task.

METHODS

Adult male rats were bilaterally cannulated into CA1 region of hippocampus and then received 3α-diol (0.2, 1, 3 and 6 mug/0.5 mul/side), indomethacin (1.5, 3 and 6 mug/0.5 mul/side), indomethacin (3 mug/0.5 mul/side) + 3α-diol (1 mug/0.5 mul/side), 25-35 min before training, immediately after training and 25-35 min before probe trial in MWM task.

RESULTS

Our results showed that injection of 3α-diol and indomethacin significantly increased the escape latency and traveled distance to find hidden platform in acquisition and consolidation stage, but did not have any effect on retrieval of spatial learning as compared with the control group.

CONCLUSION

It is concluded that intra-CA1 administration of 3α-diol and indomethacin could impair spatial learning and memory in acquisition and consolidation stage. Also, intrahippocampal injection of indomethacin + 3α-diol could not change spatial learning and memory impairment effect of indomethacin or 3α-diol in MWM task.

Males show stronger contextual fear conditioning than females after context pre-exposure

Estradiol affects the structure and function of the hippocampus. We have found that repeated estradiol affects neurogenesis and cell death in the hippocampus of adult female, but not male rats. In the present study we sought to determine whether using the same regimen of estradiol would influence hippocampus-dependent behaviour. Adult male and female rats were given estradiol or sesame oil for 15 days, and then tested using a contextual pre-exposure paradigm in which performance depends on the hippocampus. The time spent freezing displayed by rats was scored on subsequent days in (1) the training context, (2) a novel context in which rats had never been shocked, and (3) the training context a second time. Irrespective of treatment, males showed stronger memory for the context by exhibiting greater freezing in both the training context exposures and the novel context. Previous estradiol treatment, in either sex, did not affect the ability to learn and retain information about the training context. However, female rats treated with estradiol and exposed to a novel context after fear conditioning exhibited less freezing behaviour than controls. Taken together, our results demonstrate that gonadectomized male rats outperform females, regardless of previous treatment with estradiol, on a hippocampus-contextual fear conditioning test, and that previous estradiol treatment has a subtle effect on performance in female but not male rats.

EFFECTS OF TESTOSTERONE AND GROWTH HORMONE ON LONG-TERM RETENTION AND EXTINCTION OF A PASSIVE AVOIDANCE RESPONSE IN YOUNG AND AGED RATS

Wistar rats were divided into two blocks: young and aged. Each block was then randomly divided into the following groups: (1) Control (saline solution), (2) Growth Hormone (GH), (3) Testosterone enanthate, and (4) GH plus testosterone enanthate. Animals were trained on a one-trial passive avoidance conditioning and tested for retention 24 h after training and thereafter twice a week until the extinction response occurred. Results showed that GH, testosterone, and GH plus testosterone improved long-term memory in young rats. Both GH and testosterone delayed the extinction process in young and aged rats. The GH-testosterone interaction delayed the extinction only in young rats.

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.

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.

Gene x environment effects: stress and memory dysfunctions caused by stress and gonadal factor irregularities during puberty in control and TGF-alpha hypomorphic mice

The maturation of many neural functions occurs during puberty. An abnormal development of these processes, in the context of genetic vulnerability, may result in sex- and age-dependent penetrance of neuropsychiatric disorders. Reduced transforming growth factors-alpha (TGF-alpha) expression in Waved-1 (Wa-1) mice impairs the stress response and fear memory in adult males, but are absent or far less prominent in adult females and in pubertal males. Gonadectomy around the onset of puberty, when the mutant anatomical and behavioral phenotypes are undetectable, results in significant gene x environment effects. Adult control males show reduced physiological stress response as a result of gonadectomy, but not adult Wa-1 males. In females, pubertal gonadectomy elevates specific anxiety parameters only in adult control mice. There also are general sex-specific effects of pubertal gonadectomy on adult stress and fear memory. Surgical stress alone also induces sex- and genotype-dependent effects, albeit in different behavioral parameters than those affected by gonadectomy. We conclude that normal development of stress and memory processes is reliant on the levels of stress and gonadal factors during puberty, the effects of which are modulated by genetic factors and sex.

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.

Amygdala function in adolescents with congenital adrenal hyperplasia: a model for the study of early steroid abnormalities

Early disruption of steroids affects the development of mammalian neural circuits underlying affective processes. In humans, patients with classic congenital adrenal hyperplasia (CAH) can serve as a natural model to study early hormonal alterations on functional brain development. CAH is characterized by congenital glucocorticoid insufficiency, leading to altered hypothalamic-pituitary-adrenal (HPA) function, and hyperandrogenism. Using fMRI, we compared fourteen adolescents with CAH to 14 healthy controls on amygdala response to a face viewing task. In response to negative facial emotions, CAH females activated the amygdala significantly more than healthy females, whereas CAH males did not differ from control males. Furthermore, females with CAH showed a similar pattern of amygdala activation to control males, suggesting virilized amygdala function in females with CAH. These findings suggest a prominent effect of early hyperandrogenism on the development and function of the amygdala in females with CAH, whereas no effects were detected in males with CAH. This study provides data that can be further tested in a model of the neurobiological mechanisms underlying early androgen organizational effects on amygdala function.

Testosterone potentiates scopolamine-induced disruptions of nonspatial learning in gonadectomized male rats

Whereas research into the effects of the gonadal hormones on learning and memory has primarily focused on estrogen in females, recent evidence suggests that testosterone can also modulate learning in males through an interaction with the cholinergic system. In the present study, the interactive effects of testosterone and scopolamine (0.1- 0.32 mg/kg), a muscarinic receptor antagonist, on complex behavioral processes were investigated in male rats trained to respond under a multiple schedule of repeated acquisition and performance. In the acquisition component, subjects acquired a different 3-response sequence each session, whereas in the performance component, they responded on the same 3-response sequence each session. Although gonadectomy did not disrupt responding in either component, gonadectomized rats were less sensitive to the disruptive effects of scopolamine on both response rate and accuracy. In contrast, after receiving exogenous testosterone replacement, these gonadectomized males were more sensitive to the behavioral disruptions produced by scopolamine (i.e., the effects of scopolamine were similar to those obtained in gonadally intact males). These results suggest that testosterone replacement can enhance scopolamine-induced behavioral effects in gonadectomized male rats responding under a multiple schedule of repeated acquisition and performance, a finding that is in contrast to those previously found for certain spatial tasks. Furthermore, the present findings suggest that testosterone may decrease the activity of the cholinergic system during nonspatial tasks and thereby work in concert with the antagonism produced by scopolamine.

Anastrozole improved testosterone-induced impairment acquisition of spatial learning and memory in the hippocampal CA1 region in adult male rats

Neurohormones like testosterone and estrogen have an important role in learning and memory. Many biological effects of androgens in the brain require the local conversion of these steroids to an estrogen. The current research has conducted to assess the effect of testosterone, estrogen and aromatase inhibitor (anastrozole) on spatial discrimination of rats, using Morris water maze and also the pathway of the effect of testosterone by using anastrozole. Adult male rats were bilaterally cannulated into CA1 region of hippocampus and divided into 15 groups. Different groups received DMSO 0.5 microl and DMSO 0.5 microl + DMSO 0.5 microl as control groups and different doses of testosterone enanthate (TE) (20, 40 and 80 microg/0.5 microl), estradiol valerat (EV) (1, 2.5, 5, 10, and 15 microg/0.5 microl), anastrozole (An) (0.25, 0.5, 1 microg/0.5 microl), TE 80 microg/0.5 microl + anastrozole 0.5 microg/0.5 microl and EV 15 microg/0.5 microl + anastrozole 0.5 microg/0.5 microl all days before training. TE and EV were injected 30-35 min before training and anastrozole was injected 25-30 min before training. Our results have shown both TE 80 microg/0.5 microl and EV 15 microg/0.5 microl groups increase in escape latency and traveled distance to find invisible platform. Also we have shown that anastrozole dose dependently decreases escape latency and traveled distance. We resulted that both TE and EN impaired acquisition of spatial learning and memory but anastrozole improved it. Anastrozole also could be buffered TE-induced impairment effect but not EV.

The effect of gonadal hormones and gender on anxiety and emotional learning

Disorders of anxiety and fear dysregulation are highly prevalent. These disorders affect women approximately 2 times more than they affect men, occur predominately during a woman's reproductive years, and are especially prevalent at times of hormonal flux. This implies that gender differences and sex steroids play a key role in the regulation of anxiety and fear. However, the underlying mechanism by which these factors regulate emotional states in either sex is still largely unknown. This review discusses animal studies describing sex-differences in and gonadal steroid effects on affect and emotional learning. The effects of gonadal hormones on the modulation of anxiety, with particular emphasis on progesterone's ability to reduce the responsiveness of female rats to corticotropin releasing factor and the sex-specific effect of testosterone in the reduction of anxiety in male rats, is discussed. In addition, gonadal hormone and gender modulation of emotional learning is considered and preliminary data are presented showing that estrogen (E2) disrupts fear learning in female rats, probably through the antagonistic effect of ERalpha and ERbeta activation.

Testosterone and photoperiod interact to affect spatial learning and memory in adult male white-footed mice (Peromyscus leucopus)

Gonadal hormones affect spatial learning and memory in mammals and circulating gonadal hormone concentrations fluctuate by season. Most nontropical rodents are spring/summer breeders and males display higher testosterone concentrations during the breeding season compared with the nonbreeding season (fall/winter). Seasonal patterns of testosterone concentration (as well as many other seasonal modifications of physiology, morphology, and behaviour) are induced by manipulation of photoperiod (day length; i.e. short or long days) in the laboratory. Coincident with reducing testosterone concentration, short days also impair spatial learning and memory performance in male white-footed mice (Peromyscus leucopus) compared with long days. We hypothesized that short-day-induced reduction of testosterone concentrations inhibits spatial learning and memory performance compared with long days. Adult male white-footed mice were maintained in long (16 h light/day) or short (8 h light/day) days for 14 weeks following sham-castration, castration plus saline implant, or castration plus testosterone implant treatment. Spatial learning and memory was assessed using a water maze, and photoperiod-evoked changes in gene expression of sex steroid receptors within the hippocampus were also examined. Castrated, short-day mice with testosterone replacement displayed enhanced water maze performance compared with other short-day mice, but no differences among testosterone treatments were observed in long-day mice. Photoperiod did not affect hippocampal androgen, oestrogen alpha, or oestrogen beta receptor gene expression. These results suggest that photoperiod modulates the effects of testosterone on spatial learning performance by mechanisms indirect of the hippocampus.

Differential effect of testosterone and repetitive induction on cataleptic and dorsal immobility in mice

In nature, many species under conditions of stress (e.g., predator attack, pups carried by the mother, mating) show immobility states called "immobility responses" (IRs), which are characterized by the complete absence of movement and a relative unresponsiveness. These IR states can be induced by several kinds of sensorial stimuli. Many brain neurotransmitters from diverse cerebral areas participate in the expression of IRs. Other factors are also involved in IRs, such as learning and hormones, but at present, there is not enough experimental support about these factors. Our purpose was to investigate whether the IRs are subject to sexual hormone modulation and to examine the possible relation to learning processes. We tested the effects of acute testosterone decanoate (30 mg/kg, s.c.) and repetitive induction of two IRs; cataleptic immobility (CAT) and dorsal immobility (DI). These were tested in mice of both sexes which were either gonadectomized or sham-treated. CAT and DI were measured before and then 1 and 5 h after testosterone injection. The results show a differential effect of the repetitive induction on CAT and DI. CAT was augmented with repetition, and DI was decreased. Sex differences of the effects of the acute testosterone treatment were observed. Sham and castrated male mice showed CAT potentiation; in contrast, DI was reduced albeit only in sham male mice. Sham and ovariectomized female mice were not affected by testosterone. These results support the hypothesis that there are multiple immobility systems that can be differentially modulated by brain regions associated with processes of learning.

Ovarian steroids enhance object recognition in naturally cycling and ovariectomized, hormone-primed rats

Learning and memory processes may be influenced by fluctuations in steroid hormones, such as estrogens and progestins. In this study, we have used an animal model to investigate the effects of endogenous fluctuations in ovarian steroids in intact female rats and effects of administration of ovarian steroids to ovariectomized rats for non-spatial, working memory using the object recognition task. Performance in this task relies on cortical and hippocampal function. As such, serum, cortical, and hippocampal concentrations of estradiol (E2), progesterone (P4), and P4's metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), were measured by radioimmunoassay. Experiment 1: Rats in behavioral estrus, compared to those in diestrus or estrus, spent a greater percentage of time exploring a novel object concomitant with increases in serum E2, P4, and 3alpha,5alpha-THP levels. Regression analyses revealed that there was a significant positive relationship between E2 levels in the hippocampus and 3alpha,5alpha-THP levels in the hippocampus and cortex and performance in this task. Experiment 2: Administration of E2 and/or P4 immediately post-training increased the percentage of time spent exploring the novel object and produced levels of E2, P4, and 3alpha,5alpha-THP akin to that of rats in behavioral estrus. Experiment 3: Post-training administration of selective estrogen receptor modulators, including 17beta-E2, propyl pyrazole triol, and diarylpropionitrile increased the percentage of time spent exploring the novel object compared to vehicle-administration. Experiment 4: Post-training P4 or 3alpha,5alpha-THP administration, compared to vehicle, increased the percentage of time spent exploring the novel object and produced P4 and/or 3alpha,5alpha-THP levels within the physiological range typically observed for rats in behavioral estrus. Experiment 5: If post-training administration of E2 and/or P4 was delayed one hour, no enhancement in object recognition was observed. Together, these results suggest that E2 and progestins can have mnemonic effects through actions in the cortex and/or hippocampus.

Role of circulating androgen levels in effects of apoE4 on cognitive function

Compared with apoE2 and E3, apoE4 increases the risk of cognitive impairments and of developing Alzheimer's disease (AD). ApoE4 interacts with female sex, further increasing AD risk. Previously, we showed that female Apoe-/- mice are more susceptible to apoE4-induced cognitive deficits than male mice. Androgens protect against these deficits and apoE4 male mice are more sensitive to acute blockade of androgen receptors than apoE3 male mice. To determine the chronic effects of reduced circulating androgen levels on susceptibility to the effects of apoE4 on cognitive function in males, we castrated and sham-castrated apoE4, apoE3, and Apoe-/- male mice and behaviorally compared them 3 months later. Castration impaired novel location recognition in apoE4, but not apoE3 or Apoe-/-, mice. In contrast, castration impaired novel object recognition and spatial memory retention in the water maze in Apoe-/-, but not apoE3 or apoE4, mice. On the contrary, castrated, but not sham-castrated, apoE4 mice showed improved acquisition over the first two hidden platform sessions and spatial memory retention in the first probe trial. While apoE3 and Apoe-/- mice increased their exploratory times with the objects in the trial with the novel object, apoE4 mice did not. ApoE4 mice required more trials than apoE3 or Apoe-/- mice to reach criterion during passive avoidance training, but castration did not modulate passive avoidance learning or memory. Thus, androgens have differential roles in object recognition and spatial learning and memory in the water maze, depending on whether or not apoE4 is present.

Behavioral performance of tfm mice supports the beneficial role of androgen receptors in spatial learning and memory

In adulthood, androgens and androgen receptors might contribute to the sexually dimorphic performance in spatial learning and memory, but their roles seem complex. To study the potential role of androgen receptors in spatial learning and memory, we tested adult 6-8-month-old mutant mice with a naturally occurring defect in the androgen receptor gene (testicular feminization mutant or tfm) and C57Bl/6J wild-type mice. Because the trait is X-linked, only tfm males are completely androgen insensitive while female tfm mice are heterozygous, carrying one wild-type and one tfm copy of the androgen receptor. Here we show that female tfm carrier mice outperform tfm male mice in the water maze, while there are no gender differences in water maze performance in wild-type mice. In tfm mice, there were no gender differences in measures of anxiety in the open field or plus maze or sensorimotor function, indicating that potential differences in these measures did not contribute to the differences observed in the water maze. There were no differences in tfm and wild-type female and male mice in emotional learning and memory in the passive avoidance test. These findings support a beneficial role for androgen receptors in spatial learning and memory.

The effect of intrahippocampal injection of testosterone enanthate (an androgen receptor agonist) and anisomycin (protein synthesis inhibitor) on spatial learning and memory in adult, male rats

In most mammals, the hippocampus has a well-documented role in spatial memory acquisition. High concentration of androgen receptors in fundamental centers of learning and memory in brain such as hippocampus shows that there may be some relationships between androgen receptors and cognitive aspects of brain. Previous studies, which have shown sex-dependent differences in hippocampal morphology and physiology, suggest a modulatory role for sex steroids in hippocampal function. Androgens have been shown to modulate some hippocampal-mediated behaviors including learning and memory. To study the mechanism of action of androgens in processes underlying learning and memory, anisomycin, a protein synthesis inhibitor was used to prevent the genomic effects of testosterone. Therefore, the effects of anisomycin and testosterone together were assessed on rat's performance in MWM. Rats received anisomycin (2.5 microg/0.5 microl), testosterone (80 microg/0.5 microl) or both anisomycin (2.5 microg/0.5 microl) and testosterone (80 microg/0.5 microl) through the connulas in the CA1 region. Anisomycin was injected 20 min and testosterone was injected 35 min before training each day. The results showed that anisomycin (2.5 microg/0.5 microl) and testosterone (80 microg/0.5 microl) increased latencies to find the invisible platform. But the group that received testosterone and anisomycin together was decrease in latency and traveled distance to find the invisible platform.

5alpha-reduced androgens may have actions in the hippocampus to enhance cognitive performance of male rats

Androgens may improve cognitive performance; however, these effects and mechanisms of androgens are not well understood. Whether testosterone's (T) effects on cognitive performance are mediated by its 5alpha-reduced, non-aromatizable metabolite dihydrotestosterone (DHT) and/or its 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) reduced metabolite 3alpha-androstanediol (3alpha-diol), was investigated. In Experiment 1, male rats that were gonadally intact, or gonadectomized (GDX) and DHT-replaced with a silastic capsule, had better performance in the inhibitory avoidance task, and higher plasma DHT and 3alpha-diol levels, compared to GDX rats. In Experiments 2-4, intra-hippocampal indomethacin, a 3alpha-HSD inhibitor, to intact or DHT-replaced, but not GDX, rats decreased performance in the inhibitory avoidance task and reduced hippocampal 3alpha-diol levels compared to that observed in rats with control implants. Thus, the 5alpha-reduced androgen DHT has cognitive-enhancing effects, independent of E(2), which are attenuated by a 3alpha-HSD inhibitor, indomethacin. These results suggest that 5alpha-reduced androgens may have actions in the hippocampus to improve cognitive performance.

Genomic and nongenomic effects of intrahippocampal microinjection of testosterone on long-term memory in male adult rats

In addition to their well-known genomic effects via intracellular receptors, androgens rapidly alter neuronal excitability through a nongenomic pathway. The nongenomic effect of testosterone, as the main androgen, apart from its traditional effects, was assessed in one of the fundamental centers of learning and memory, the hippocampus, on long-term memory (LTM) in passive avoidance conditioning. Different doses of testosterone enanthate (T) or testosterone-BSA (T-BSA) bilaterally were injected into the CA1 region of the hippocampus 15 min before shock delivery (1 mA during 5 s) in a two-compartment passive avoidance apparatus. After 24 h, animals were tested for passive avoidance retrieval. Bilateral injection of 20 microg T or 55 microg T-BSA into the CA1 significantly decreases step-through latency. Therefore, it seems that testosterone can impair LTM in passive avoidance conditioning both via intracellular receptors and through nongenomic pathway.

Chronic behavioral testing after focal ischemia in the mouse: functional recovery and the effects of gender

Several useful behavioral tests exist for measuring behavioral recovery after ischemia in higher-order animals and rats. With the increasing use of mice in focal stroke research, simple, reliable, and reproducible behavioral testing has become a priority. As neuroprotective agents are tested, long-term outcome must be assessed, especially in studies focused on neuronal plasticity and regeneration after ischemia. Our laboratory and others have previously shown that estrogen (E2) is neuroprotective in rodent stroke paradigms. We examined a battery of behavioral tests in male and female mice subjected to 90 min of middle cerebral artery occlusion (MCAO) to determine the most sensitive tests for detecting sensorimotor dysfunction after stroke, and to determine the functional significance of E2-mediated neuroprotection. Only two tests, the corner test and the cylinder test, were able to differentiate between groups (sham and stroke) after several days of repeated testing. The cylinder test was sensitive to the neuroprotective/neurorestorative effects of E2, but 2 weeks after stroke, the cylinder test was unable to distinguish between sham and stroke animals treated with E2. In contrast, the corner test was able to differentiate stroke and sham animals even 6 weeks after stroke, but did not distinguish animals treated with E2 vs. vehicle. These tests provide a simple, rapid, reliable assessment of sensorimotor dysfunction in the mouse after focal ischemia. Hormonal status influences speed of recovery on cylinder testing in animals of both genders. This suggests that a short battery of tests including the neurological score, cylinder, and corner test may be adequate to rapidly and repeatedly assess sensorimotor dysfunction in mice of both genders.

Behavioral and physiological responses to anabolic-androgenic steroids

Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone originally designed for therapeutic uses to provide enhanced anabolic potency with negligible androgenic effects. Although AAS continue to be used clinically today, the medical benefits of low therapeutic doses of AAS stand in sharp contrast to the potential health risks associated with the excessive doses self-administered not only by elite athletes and body builders, but by a growing number of recreational users, including adolescent boys and girls. The deleterious effects of AAS on peripheral organs and the incidence of altered behaviors in AAS abusers have been well documented in a number of excellent current reviews for clinical populations. However, a comparable synthesis of nonclinical studies has not been made. Our purpose in this review is to summarize the literature for animal models of the effects of supraphysiological doses of AAS (e.g. those that mimic human abuse regimes) on behaviors and on the neural circuitry for these behaviors. In particular, we have focused on studies in rodents that have examined how AAS alter aggression, sexual behaviors, anxiety, reward, learning, and locomotion and how AAS alter the expression and function of neurotransmitter systems and other signaling molecules that underlie these behaviors.

Testosterone, but not nonaromatizable dihydrotestosterone, improves working memory and alters nerve growth factor levels in aged male rats

Recent studies have suggested that testosterone levels are lower in men with Alzheimer's disease and that testosterone treatment improves cognition in older men. Since testosterone can be aromatized to estrogen, testosterone's effects could be due to conversion into estrogen. We treated aged male rats with either testosterone or dihydrotestosterone (DHT), the latter of which is not aromatized to estrogen, in order to determine whether these treatments improve spatial working and reference memory as assessed in the water radial arm maze. We also tested whether such effects are related to beta-amyloid levels in the hippocampus or neurotrophin levels in the hippocampus, entorhinal cortex, frontal cortex, or striatum. Aged rats made more errors than young rats on all memory measures. Testosterone, but not DHT, improved working memory and decreased hippocampal NGF protein in aged rats, while having no effect on beta-amyloid. However, higher beta-amyloid levels were correlated with poorer working memory performance in young rats. Neurotrophin levels in entorhinal cortex were positively correlated with errors for all memory measures in androgen-treated rats. Similar to findings in human studies, in our study androgen treatment lowered circulating estradiol levels in aged rats, suggesting that androgen treatment exerts feedback to the hypothalamic pituitary axis and that conversion to estrogen may not be the underlying biological mechanism of testosterone's effects on memory and growth factor levels. The ratio of estradiol to testosterone, or the actions of the aromatase enzyme itself, may be responsible for the observed effects. These data support the hypothesis that testosterone therapy in aging men may provide positive effects on cognition and that neural regions that are linked to cognition, such as the hippocampus and/or entorhinal cortex, may be involved in such effects.

The differential effect of haloperidol and repetitive induction on four immobility responses in mouse and guinea pig

The modification by haloperidol and repetitive induction on four immobility responses -- tonic immobility, cataleptic immobility, immobility by clamping the neck and dorsal immobility -- were compared in mice and guinea pigs. Without drug, three out of four responses (cataleptic, neck clamp and dorsal immobility) were induced in mice; guinea pigs displayed all four responses. Haloperidol (5 mg/kg i.p.) potentiated the three responses shown by mice, but did not potentiate the four responses in guinea pigs. In both undrugged and haloperidol-treated mice, only the cataleptic immobility response was potentiated by repetition. In guinea pigs, none of the four immobility responses was affected due to repetition, haloperidol or a combination of both. These data are discussed, considering that, although these immobility responses could be mediated by the same neurotransmitters (e.g. dopamine), they are possibly expressed in a differential manner as a function of the kind of stimulus used to trigger the response, characteristics of the species and, in some immobility responses such as cataleptic immobility, as a function of their interaction with habituation or another learning-like process.

Estrogen's effects on activity, anxiety, and fear in two mouse strains

Estrogen has effects on activity levels and emotional reactivity in both humans and rats. In a recent study conducted in ovariectomized (OVX) C57BL/6 (C57) mice we found that treatment with estradiol benzoate (EB) increased anxiety, fear learning, and running wheel activity relative to vehicle control (Veh). The present study was conducted to examine the stability of these findings across mouse strains (C57 and Swiss-Webster; SW), to get a better sense of the magnitude of the anxiety response by reducing baseline anxiety levels, and to discover if EB affects activity levels in a safe environment other than the home-cage running wheel. Mice of both strains treated with EB (s.c. implant, 25 microg in sesame oil, which enters the body over 5 weeks) were more anxious than Veh animals in the open field, elevated plus, and dark-light transition tests. SW animals were less anxious than C57 in the elevated plus. EB-treated animals of both strains were more active in the running wheel than Veh animals, and more active in the test of spontaneous activity in the home cage. EB-treatment also increased fear learning in a step-down avoidance task. EB appears to have a consistent but moderate effect in elevating anxiety and in increasing fear learning in two strains of mice. It is also involved in increasing activity in two different types of locomotion in the safer home cage. We conclude that these results of increased anxiety/fear and increased activity are suggestive of a general increase in arousal, with both sets of responses increasing the likelihood of reproductive behaviors occurring only when the environment predicts success.

Tamoxifen and toremifene cause impairment of learning and memory function in mice

Tamoxifen (TAM) and toremifene (TOR) are two antiestrogen agents frequently used in the treatment of breast cancer. They are currently being assessed as the prophylactic for patients at high risk of developing tumors. However, the side effects of these drugs on memory function have drawn attention in clinical usage. In the present study, it is demonstrated in mice that TAM and TOR significantly shortened the escaping latency or increased the number of errors, respectively, by using the step-down and step-through passive avoidance tests. By using an appetitively motivated task in T-maze, it is demonstrated that TAM and TOR significantly delayed the latency of finding food in well-trained mice. TAM appeared to impair memory consolidation and retrieval processes, rather than acquisition of memory, whereas TOR appeared to impair acquisition, consolidation, and retrieval processes. These results provide experimental support for the clinical findings that have shown that these drugs impaired memory function in patients routinely taking the drugs and suggest that caution should be taken for using these drugs as the prophylactics for those at risk of developing tumors.

Testosterone increases analgesia, anxiolysis, and cognitive performance of male rats

Preliminary evidence suggests that testosterone (T) may have anxiety-reducing and cognitive-enhancing properties in animals and people. Performance in a number of affective and cognitive behavioral tasks was examined in intact, T-depleted, and T-depleted and T-replaced male rats. Rats that were gonadally intact (n = 33), gonadectomized (GDX; n = 30), or GDX with silastic capsules of T implanted (n = 28) were tested through a battery of affective tasks (horizontal crossing, open field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive burying) and in the inhibitory avoidance task for cognitive performance. An additional 6 rats per group had plasma androgen concentrations measured and were determined to be physiological for intact rats, supraphysiological for T-implanted rats, and near the nadir for GDX rats. Testosterone implants produced analgesia as shown by the increased tailflick latencies of the GDX rats with silastic capsules of T implanted, relative to intact or GDX rats. Testosterone also produced anxiolysis. Intact rats spent more time interacting with a conspecific and less time burying an electrified prod than did the GDX or T-implanted rats. Intact rats or GDX rats with T implants also spent more time on the open arms of the elevated plus-maze than did GDX rats. Testosterone also enhanced cognitive performance in the inhibitory avoidance task. Intact rats had longer crossover latencies in the inhibitory avoidance task relative to GDX rats; GDX rats with T implants had longer crossover latencies relative to GDX or intact rats. Together, these data demonstrate that endogenous T or administration of T produced analgesia and enhanced affect and cognitive performance of adult male rats.

Effects of estrogen on activity and fear-related behaviors in mice

Estrogen has been shown to affect nonreproductive behaviors in humans and rodents, including anxiety, fear, and activity levels. Rat studies have shown increases and decreases in these behaviors. Inconsistencies may be due to differences in testing conditions and the extent to which each test measures anxiety, fear, or activity. Few mouse studies have been performed. The present study was conducted to address these issues by examining the effect of estradiol benzoate (EB) in ovariectomized (OVX), C57BL/6 mice on a range of behavioral paradigms measuring anxiety [open field (OF), dark-light transition (DLT), elevated plus maze (EP)], activity [running wheel (RW)], and conditioned fear learning (FCon). In OF, vehicle (Veh) animals spent more time in the center than EB-treated animals and were more active overall. In DLT, Veh animals were more active than EB-treated animals in both the dark and light compartments and made more transitions between the two. In EP, Veh animals entered a greater number of arms. During FCon, EB animals froze more than Veh to the conditioned stimulus. In contrast, in the home cage RW, EB animals were more active than Veh. Factor analysis was used to characterize intertask correlations of females' behavior and to explore the possibility that estrogen may have an impact on a general arousal factor. In sum, estrogen treatment heightened fear responses in a range of fear and anxiety-provoking situations (OF, DLT, EP, and FCon), while increasing activity in the safer RW. We suggest that EB treatment may result in a generally more aroused animal.