Intra hippocampal injection of testosterone impaired acquisition, consolidation and retrieval of inhibitory avoidance learning and memory in adult male rats

Influence of sex hormones on the aggressive behavior during peck order establishment and stabilization in meat and egg type chickens

In the poultry industry, broiler and layer strains are genetically selected for different purposes (e.g., high meat-yield and high egg-production). Genetic selection for productivity can have unintended consequences on the behavioral repertoire of the birds, including aggression. Alongside the increasing societal concern regarding the welfare of animal in agriculture, the number of countries that are advocating the prohibition of using battery cages for laying hens has resulted in the transition and adoption of cage-free or free-range systems. Thus, both broiler and layer chickens are housed in large flocks rather than housed individually in cages. Housing birds in groups increases the opportunity for birds to engage in social behaviors, including aggression, that are used to establish social status. Aggressive interactions are associated with the risk of injury and the potential for a subordinate animal to have unmet needs (e.g., access to feed). The aim of this study was to characterize the relationships among aggressive behavior, neurobiology, and hormones during peck order establishment and social hierarchy stabilization of 2 divergently selected strains (meat- and egg-type chicken). Meat-type strains performed more male on male (P < 0.001), male on female (P < 0.0001), and female on female (P < 0.0001) non-reciprocal aggression behavior (NRA) than egg-type strains. Greater serum testosterone and estradiol concentrations in the weeks after the peck order establishment were observed in meat-type birds compared those in egg-type birds for both males and females (all P < 0.05). Greater (P < 0.05) cellular densities of androgen receptors, but not estrogen receptors, were observed in the hypothalamus of meat-type birds compared to egg-type birds. These findings suggest that greater sex hormone concentrations in the meat-type birds may be a consequence of genetic selection for rapid growth resulting in more sex hormones-induced aggressive behavior.

Sex hormones and cortisol during experimental trauma memory consolidation: Prospective association with intrusive memories

Background Trauma- and stress-related disorders, such as post-traumatic stress disorder (PTSD), are more common in females than in males. Sex hormones affect learning and emotional memory formation and may be associated with the development of PTSD. Most previous studies have indexed these hormones in isolation. Objectives: To investigate associations of sex hormones and cortisol during memory consolidation on the development of intrusive memories. Methods: We employed an experimental trauma film paradigm in 61 healthy women and indexed salivary testosterone, progesterone, estradiol, and cortisol on day one and day two post experimental trauma exposure and their effects on intrusion frequency, distress, and vividness. Intrusive trauma memories were indexed by means of a diary in which participants documented intrusion frequency, distress, and vividness. Results and conclusion: Participants reported an average of 5.3 intrusions over the course of seven days (SD = 4.6, range 0-26). Progesterone, and estradiol indexed on day one predicted intrusion frequency, with higher progesterone and lower estradiol predicting more intrusive memories (p-values AUC progesterone 0.01 and estradiol 0.02). There was no evidence for associations between hormone concentration indices on day two and intrusion outcomes. Further research on the roles of gonadal and adrenal hormones in trauma memory formation is needed to advance our efforts to understand their influence on PTSD development.

Nandrolone administration abolishes hippocampal fEPSP-PS potentiation and passive avoidance learning of adolescent male rats

Despite the chronic effects of nandrolone decanoate (ND), the acute effects of ND on passive avoidance learning (PAL) and memory and its mechanism have not been investigated. This research examines the acute effect of ND on PAL, CA1 synaptic plasticity, testosterone and corticosterone serum levels, and the role of androgenic receptors (ARs). Adolescent male rats were treated with ND, 30 min before training and retention and after training test. AR antagonist was applied 15 min before ND. Hippocampal slices were perfused by ND. ND administration had an inverted U-shape effect on acquisition of PAL and on testosterone and corticosterone serum levels. The consolidation was only affected by high dose of ND. ND significantly decreased the retention of PAL across all doses. The magnitude of field excitatory postsynaptic potential long term potentiation was lower than that of control slices. In addition, an attenuation of field excitatory postsynaptic potential population spike coupling was also observed. Nilutamide could nullify the ND impairment effect. We concluded although a single dose of ND could affect all stages of PAL, its effects were more potent on retrieval, possibly arising from the acute effect of ND on the alterations of CA1 synaptic plasticity. In addition, ND may induce its effects directly through ARs and indirectly through plasma testosterone and corticosterone.

Low-Stress Medication Techniques in Birds and Small Mammals

Low-stress medication principles and techniques are key aspects of optimal health care delivery for birds and small mammals. When paired with the medical details of patient management, by balancing medication techniques, the probability of clinical success on the highest ethical and welfare criteria can be greatly enhanced. This review addresses both the effects and the disadvantages of using forceful, coercive, and fear-evoking methods as well as the benefits, principles, and possible applications of low-stress medication in the veterinary setting.

Expansion of mossy fibers and CA3 apical dendritic length accompanies the fall in dendritic spine density after gonadectomy in male, but not female, rats

Androgen loss is an important clinical concern because of its cognitive and behavioral effects. Changes in androgen levels are also suspected to contribute to neurological disease. However, the available data on the effects of androgen deprivation in areas of the brain that are central to cognition, like the hippocampus, are mixed. In this study, morphological analysis of pyramidal cells was used to investigate if structural changes could potentially contribute to the mixed cognitive effects that have been observed after androgen loss in males. Male Sprague-Dawley rats were orchidectomized or sham-operated. Two months later, their brains were Golgi-impregnated for morphological analysis. Morphological endpoints were studied in areas CA3 and CA1, with comparisons to females either intact or 2 months after ovariectomy. CA3 pyramidal neurons of orchidectomized rats exhibited marked increases in apical dendritic arborization. There were increases in mossy fiber afferent density in area CA3, as well as robust enhancements to dendritic structure in area CA3 of orchidectomized males, but not in CA1. Remarkably, apical dendritic length of CA3 pyramidal cells increased, while spine density declined. By contrast, in females overall dendritic structure was minimally affected by ovariectomy, while dendritic spine density was greatly reduced. Sex differences and subfield-specific effects of gonadal hormone deprivation on the hippocampal circuitry may help explain the different behavioral effects reported in males and females after gonadectomy, or other conditions associated with declining gonadal hormone secretion.

Interactions of nitric oxide with α2 -adrenoceptors within the locus coeruleus underlie the facilitation of inhibitory avoidance memory by agmatine

BACKGROUND AND PURPOSE

Agmatine, a putative neurotransmitter, plays a vital role in learning and memory. Although it is considered an endogenous ligand of imidazoline receptors, agmatine exhibits high affinity for α-adrenoceptors, NOS and NMDA receptors. These substrates within the locus coeruleus (LC) are critically involved in learning and memory processes.

EXPERIMENTAL APPROACH

The hippocampus and LC of male Wistar rat were stereotaxically cannulated for injection. Effects of agmatine, given i.p. or intra-LC, on acquisition, consolidation and retrieval of inhibitory avoidance (IA) memory were measured. The NO donor S-nitrosoglutathione, non-specific (L-NAME) and specific NOS inhibitors (L-NIL, 7-NI, L-NIO), the α2 -adrenoceptor antagonist (yohimbine) or the corresponding agonist (clonidine) were injected intra-LC before agmatine. Intra-hippocampal injections of the NMDA antagonist, MK-801 (dizocilpine), were used to modify the memory enhancing effects of agmatine, SNG and yohimbine. Expression of tyrosine hydroxylase (TH) and eNOS in the LC was assessed immunohistochemically.

KEY RESULTS

Agmatine (intra-LC or i.p.) facilitated memory retrieval in the IA test. S-nitrosoglutathione potentiated, while L-NAME and L-NIO decreased, these effects of agmatine. L-NIL and 7-NI did not alter the effects of agmatine. Yohimbine potentiated, whereas clonidine attenuated, effects of agmatine within the LC. The effects of agmatine, S-nitrosoglutathione and yohimbine were blocked by intra-hippocampal MK-801. Agmatine increased the population of TH- and eNOS-immunoreactive elements in the LC.

CONCLUSIONS AND IMPLICATIONS

The facilitation of memory retrieval in the IA test by agmatine is probably mediated by interactions between eNOS, NO and noradrenergic pathways in the LC.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Testosterone deficiency, insulin-resistant obesity and cognitive function

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

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.

3α-diol administration decreases hippocampal PKA (II) mRNA expression and impairs Morris water maze performance in adult male rats

The effect of testosterone and its metabolites on learning and memory has been the subject of many studies. This study used the Morris water maze task to investigate the effect of intra-hippocampal injection of 3α-diol (one of the metabolites of testosterone) on acquisition stage of spatial memory in adult male rats. During the experiment we observed that 3α-diol, significantly impaired Morris water maze performance in treated rat's compared with controls. Because signaling event mediated by protein kinase A (PKA) especially PKA (II) are critical for many neuronal functions such as learning and memory, the hippocampus was analyzed for mRNA expression of PKA (II) using TaqMan real time RT-PCR. The results indicated that the transcription levels of PKA (II) were significantly decreased in animals treated with 3α-diol compared with controls. Thus, the findings suggest that administration of 3α-diol in hippocampus of adult male rats impairs memory function, possibly via down-regulation of PKA.

Contributions of sex, testosterone, and androgen receptor CAG repeat number to virtual Morris water maze performance

The possibility that androgens contribute to the male advantage typically found on measures of spatial cognition has been investigated using a variety of approaches. To date, evidence to support the notion that androgens affect spatial cognition in healthy young adults is somewhat equivocal. The present study sought to clarify the association between testosterone (T) and spatial performance by extending measurements of androgenicity to include both measures of circulating T as well as an androgen receptor-specific genetic marker. The aims of this study were to assess the contributions of sex, T, and androgen receptor CAG repeat number (CAGr) on virtual Morris water task (vMWT) performance in a group of healthy young men and women. The hypothesis that men would outperform women on vMWT outcomes was supported. Results indicate that CAGr may interact with T to impact navigation performance and suggest that consideration of androgen receptor sensitivity is an important consideration in evaluating hormone-behavior relationships.

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 depletion in adult male rats increases mossy fiber transmission, LTP, and sprouting in area CA3 of hippocampus

Androgens have dramatic effects on neuronal structure and function in hippocampus. However, androgen depletion does not always lead to hippocampal impairment. To address this apparent paradox, we evaluated the hippocampus of adult male rats after gonadectomy (Gdx) or sham surgery. Surprisingly, Gdx rats showed increased synaptic transmission and long-term potentiation of the mossy fiber (MF) pathway. Gdx rats also exhibited increased excitability and MF sprouting. We then addressed the possible underlying mechanisms and found that Gdx induced a long-lasting upregulation of MF BDNF immunoreactivity. Antagonism of Trk receptors, which bind neurotrophins, such as BDNF, reversed the increase in MF transmission, excitability, and long-term potentiation in Gdx rats, but there were no effects of Trk antagonism in sham controls. To determine which androgens were responsible, the effects of testosterone metabolites DHT and 5α-androstane-3α,17β-diol were examined. Exposure of slices to 50 nm DHT decreased the effects of Gdx on MF transmission, but 50 nm 5α-androstane-3α,17β-diol had no effect. Remarkably, there was no effect of DHT in control males. The data suggest that a Trk- and androgen receptor-sensitive form of MF transmission and synaptic plasticity emerges after Gdx. We suggest that androgens may normally be important in area CA3 to prevent hyperexcitability and aberrant axon outgrowth but limit MF synaptic transmission and some forms of plasticity. The results also suggest a potential explanation for the maintenance of hippocampal-dependent cognitive function after androgen depletion: a reduction in androgens may lead to compensatory upregulation of MF transmission and plasticity.

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.

Testosterone levels in healthy men are related to amygdala reactivity and memory performance

Testosterone is a steroid hormone thought to influence both emotional and cognitive functions. It is unknown, however, if testosterone also affects the interaction between these two domains, such as the emotional arousal-induced enhancement of memory. Healthy subjects (N=234) encoded pictures taken from the International Affective Picture System (IAPS) during functional magnetic resonance imaging (fMRI) and underwent a free recall test 10 min after memory encoding. We show that higher endogenous testosterone levels at encoding were associated with higher arousal ratings of neutral pictures in men. fMRI analysis revealed that higher testosterone levels were related to increased brain activation in the amygdala during encoding of neutral pictures. Moreover, endogenous testosterone levels were positively correlated with the number of freely recalled neutral pictures. No such relations were found in women. These findings point to a male-specific role for testosterone in enhancing memory by increasing the biological salience of incoming information.

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.

Gonadectomy differentially regulates steroid receptor coactivator-1 and synaptic proteins in the hippocampus of adult female and male C57BL/6 mice

Hippocampus is one of the most important structures that mediates learning and memory, cognition, and mental behaviors and profoundly regulated by sex hormones in a sex-specific manner, but the mechanism of underlying sex differences regulation is still unclear. We have previously reported that in the male and female mice, steroid receptor coactivator-1 (SRC-1) and some key synaptic proteins share similar developmental profile in the hippocampus, but how circulating sex hormones affect hippocampal SRC-1 as well as these synaptic proteins remain unclear. In this study, we examined how gonad sex hormones regulate hippocampal SRC-1, synaptophysin, PSD-95, and AMPA receptor subtype GluR1 by using immunohistochemistry and Western blot. The results showed that in the female mice, ovariectomy affected hippocampal SRC-1 and GluR1 were only detected at 2 weeks post operation, then it recovered to sham level; synaptophysin was unaffected at any timepoint examined; significant decrease of PSD-95 was only detected at 4 weeks post operation. However, in the male hippocampus, SRC-1 and PSD-95 were decreased from one week and lasted to 4 weeks after orchidectomy, GluR1 decreased from 2 weeks after orchidectomy, but synaptophysin remained unchanged as in the females. Correlation analysis showed the profiles of SRC-1 were positively correlated with GluR1 of the females, PSD-95 and GluR1 of the males, respectively. The above results suggested a distinct regulatory mode between female and male gonad hormones in the regulation of hippocampal SRC-1 and synaptic proteins, which may be one of the mechanisms contributing to the dimorphism of hippocampus during development and ageing.

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.

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.

The androgen receptor gene polyglycine repeat polymorphism is associated with memory performance in healthy Chinese individuals

Cognitive functions such as memory are quantitative traits in human, and have both genetic and environmental influences. Testosterone has been implicated in the modulation of memory function. Therefore, genetic variation which influences testosterone signaling may modulate memory function. The principal receptor for testosterone is the androgen receptor, the gene for which maps to the X chromosome. In the present study, we hypothesized that common variation in two functional polymorphisms in the androgen receptor gene, the polyglutamine (CAG) and/or polyglycine (GGN) repeats, would influence memory function in healthy subjects. Variation in length of either repeat modulates the function of the AR gene, either by changing the amount of protein produced, by altering transactivation of the receptor or by producing toxic polyglycine or polyglutamine fragments. In order to test this hypothesis, we analyzed 449 healthy Chinese individuals. CAG repeats were not associated with memory performance. However we observed a significant association between GGN repeats and Immediate Logical Memory (chi(2)=23.6, d.f.=7, p=0.001) and Delayed Logical Memory (chi(2)=16.3, d.f.=7, p=0.022). The association of GGN repeats with Immediate Logical Memory remained significant after 6000 permutation corrections (p=0.013). There was also a sex difference, as association between GGN repeats and memory was observed only in females (p=0.002 for Immediate and p=0.014 for Delayed Logical Memory), but not in males (p=0.31 and 0.83, respectively). We conclude that functional variation of the androgen receptor gene is able to modulate memory function in women.

Improved effect of Pycnogenol on impaired spatial memory function in partial androgen deficiency rat model

The improved effect of Pycnogenol on impaired spatial memory function was studied in orchidectomized rats. Endogenous testosterone levels were decreased by approximately one-half for 3 months after castration. In the radial arm maze, castration significantly impaired working and reference memory function without lowering motor function. Pycnogenol increased the NGF content in the hippocampus and cortex, and improved the spatial memory impairment. These observations confirmed that diagnostic accuracy can be improved by Pycnogenol in androgen-deficient rats.

Memory impairment induced by an interfering task is reverted by pre-frontal cortex lesions: a possible role for an inhibitory process in memory suppression in mice

Interference theory refers to the idea that forgetting occurs because the recall of certain items interferes with the recall of other items. Recently, it has been proposed that interference is due to an inhibitory control mechanism, triggered by competing memories, that ultimately causes forgetting [Anderson MC (2003) Rethinking interference theory: Executive control and the mechanisms of forgetting. J Mem Lang 49:415-4453]. In the present research we study the interference process by submitting CD1 mice to two different hippocampal-dependent tasks: a place object recognition task (PORT) and a step-through inhibitory avoidance task (IA). Our results show a mutual interference between PORT and IA. To elucidate the possible neural mechanism underlying the interference process, we submit hippocampus- and prefrontal cortex-lesioned mice to PORT immediately before IA training. Results from these experiments show that prefrontal cortex lesions completely revert the impairing effect exerted by PORT administration on IA memory, while hippocampus lesions, that as expected impair memory for both PORT and IA, increase this effect. Altogether our results suggest that interference-induced forgetting is driven by an inhibitory control mechanism through activation of hippocampus-prefrontal cortex circuitry. The hippocampus seems to be crucial for storing information related to both behavioral tasks. Competition between memories triggers the inhibitory control mechanism, by activating prefrontal cortex, and induces memory suppression.