Influence of early postnatal gonadal hormones on anxiety in adult male rats

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERβ), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Contributions of gonadal hormones in the sex-specific organization of context fear learning

It is widely established that gonadal hormones are fundamental to modulating and organizing the sex-specific nature of reproductive behaviors. Recently we proposed that context fear conditioning (CFC) may emerge in a sex-specific manner organized prior to the pubertal surge of gonadal hormones. Here we sought to determine the necessity of male and female gonadal hormones secreted at critical periods of development upon context fear learning. We tested the organizational hypothesis that neonatal and pubertal gonadal hormones play a permanent role in organizing contextual fear learning. We demonstrate that the postnatal absence of gonadal hormones by neonatal orchiectomy (oRX) in males and ovariectomy (oVX) in females resulted in an attenuation of CFC in adult males and an enhancement of CFC in adult females. In females, the gradual introduction of estrogen before conditioning partially rescued this effect. However, the decrease of CFC in adult males was not rescued by introducing testosterone before conditioning. Next, at a further point in development, preventing the pubertal surge of gonadal hormones by prepubertal oRX in males resulted in a reduction in adult CFC. In contrast, in females, prepubertal oVX did not alter adult CFC. However, the adult introduction of estrogen in prepubertal oVX rats reduced adult CFC. Lastly, the adult-specific deletion of gonadal hormones by adult oRX or oVX alone or replacement of testosterone or estrogen did not alter CFC. Consistent with our hypothesis, we provide initial evidence that gonadal hormones at early periods of development exert a vital role in the organization and development of CFC in male and female rats.

Cognitive Performances: The Role of Digit Ratio (D2:D4) With a Protective Factor for Anxiety

This study aimed to identify a possible correlation between the D2:D4 ratio and state and/or trait anxiety in adult healthy subjects and, if so, whether it exists any difference between men and women. In addition, we also wanted to observe whether there is a relationship between participants' age and state and/or trait anxiety. The research involved 125 subjects of both sexes, who were calculated the D2:D4 ratio and were administered the self-assessment questionnaire State-Trait Anxiety Inventory (STAI-Y). Results show that there are positive significant correlations between the D2:D4 ratio and score at state anxiety and trait anxiety, in the total sample. However, if men are examined separately from women, it can be observed that only men have a statistically significant relationship between D2:D4 ratios and state anxiety and trait anxiety. Moreover, about possible relations between the age of participants and state and trait anxiety, a significant negative relationship was observed, without differences between men and women. However, only subjects with a D2:D4 ratio ≥ 1, without differences between men and women, showed a statistically significant negative linear correlation between their age and their state and trait anxiety. The present data allow us to conclude that a low D2:D4 ratio (<1) represents a protective factor against anxiety in both men and women and that this protection seems likely to act throughout life.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

Roles for androgens in mediating the sex differences of neuroendocrine and behavioral stress responses

Estradiol and testosterone are powerful steroid hormones that impact brain function in numerous ways. During development, these hormones can act to program the adult brain in a male or female direction. During adulthood, gonadal steroid hormones can activate or inhibit brain regions to modulate adult functions. Sex differences in behavioral and neuroendocrine (i.e., hypothalamic pituitary adrenal (HPA) axis) responses to stress arise as a result of these organizational and activational actions. The sex differences that are present in the HPA and behavioral responses to stress are particularly important considering their role in maintaining homeostasis. Furthermore, dysregulation of these systems can underlie the sex biases in risk for complex, stress-related diseases that are found in humans. Although many studies have explored the role of estrogen and estrogen receptors in mediating sex differences in stress-related behaviors and HPA function, much less consideration has been given to the role of androgens. While circulating androgens can act by binding and activating androgen receptors, they can also act by metabolism to estrogenic molecules to impact estrogen signaling in the brain and periphery. This review focuses on androgens as an important hormone for modulating the HPA axis and behaviors throughout life and for setting up sex differences in key stress regulatory systems that could impact risk for disease in adulthood. In particular, impacts of androgens on neuropeptide systems known to play key roles in HPA and behavioral responses to stress (corticotropin-releasing factor, vasopressin, and oxytocin) are discussed. A greater knowledge of androgen action in the brain is key to understanding the neurobiology of stress in both sexes.

Sensorimotor developmental factors influencing the performance of laboratory rodents on learning and memory

Behavioral studies in animal models have advanced our knowledge of brain function and the neural mechanisms of human diseases. Commonly used laboratory rodents, such as mice and rats, provide a useful tool for studying the behaviors and mechanisms associated with learning and memory processes which are cooperatively regulated by multiple underlying factors, including sensory and motor performance and emotional/defense innate components. Each of these factors shows unique ontogeny and governs the sustainment of behavioral performance in learning tasks, and thus, understanding the integrative processes of behavioral development are crucial in the accurate interpretation of the functional meaning of learning and memory behaviors expressed in commonly employed behavioral test paradigms. In this review, we will summarize the major findings in the developmental processes of rodent behavior on the basis of the emergence of fundamental components for sustaining learning and memory behaviors. Briefly, most sensory modalities (except for vision) and motor abilities are functional at the juvenile stage, in which several defensive components, including active and passive defensive strategies and risk assessment behavior, emerge. Sex differences are detectable from the juvenile stage through adulthood and are considerable factors that influence behavioral tests. The test paradigms addressed in this review include associative learning (with an emphasis on fear conditioning), spatial learning, and recognition. This basic background information will aid in accurately performing behavioral studies in laboratory rodents and will therefore contribute to reducing inappropriate interpretations of behavioral data and further advance research on learning and memory in rodent models.

Neurotrophic factors in the posterodorsal medial amygdala of male and cycling female rats

The posterodorsal medial amygdala (MePD) has a high concentration of receptors for gonadal hormones, is a sexually dimorphic region and dynamically controls the reproductive behavior of both males and females. Neurotrophic factors can promote dendritic spine remodeling and change synaptic input strength in a region-specific manner. Here, we analyzed the gene and protein expression of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-1), polysialylated neural cell adhesion molecule (PSA-NCAM) and Ephrin-A4 in the MePD of adult males and females in diestrus, proestrus and estrus using real-time qPCR and fluorescent immunohistochemistry. The first approach showed their amplification except for Igf1 and the latter revealed that BDNF, IGF-1, PSA-NCAM and Ephrin-A4 are expressed in the MePD of the adult rats. Protein expression of these neurotrophic factors showed no differences between groups. However, proestrus females displayed a higher number of labelled puncta than males for BDNF expression and diestrus females for IGF-1 expression. In conjunction, results indicate that IGF-1 might be released rather than synthetized in the MePD, and the expression of specific neurotrophic factors varies specifically during proestrus. The dynamic modulation of BDNF and IGF-1 during this cyclic phase is coincident with synaptic changes and spine density remodeling in the MePD, the disinhibition of gonadotrophin secretion for ovulation and the display of sexual behavior.

Age and sex differences in the innate defensive behaviors of C57BL/6 mice exhibited in a fear conditioning paradigm and upon exposure to a predatory odor

Defensive responses of mice include an array of specific behaviors that involve adaptive components based on the assessment of the threat of confrontation. The freezing response is represented by a motionless moment without any specific posture or behavioral sequence, and it is widely used in the fear conditioning paradigms and other relevant defensive situations. However, freezing measurements include fragmental components of several defensive behaviors that are exhibited during the session, such as behavioral inhibition, crouching, and a moment of risk assessment behavior. From an ethological view, behavioral analyses of C57BL/6 mice of both sexes and three different ages (postnatal days (P) 25, 35, and 65) revealed a rich variety of defensive behaviors during a fear conditioning session and in response to predatory odor exposure as a nonconditioned behavior. P-25 and 35 mice exhibited more behavioral inhibition than P-65 adult mice, and P-65 mice exhibited a crouching posture more often than younger mice. This age difference was more pronounced in males. The stretch-attend posture (SAP) increased with age, except in P-25 males, which exhibited robust SAP in response to a conditioned cue; this response indicates that P-25 males are defensive in a situation-nonmatching manner. Situation-dependent defense strategies were revealed in P-35 and 65 mice: Fear conditioning paradigm induced more robust defensive responses than predatory odor exposure, to which mice primarily exhibited SAP. A sex-based difference was revealed in adult mice. Males tended to show more passive defensive responses, such as crouching and withdrawal, and females exhibited more active responses, such as SAP. These age- and sex-based differences may stem from the ethological demands and illustrate adolescent ontogenetic processes of defense behavior.

On the Role of Testosterone in Anxiety-Like Behavior Across Life in Experimental Rodents

Testosterone affects brain functions and might explain some of the observed behavioral sex differences. Animal models may help in elucidating the possible involvement of sex hormones in these sex differences. The effects of testosterone have been intensively investigated, especially in anxiety models. Numerous experiments have brought inconsistent results with either anxiolytic or anxiogenic effects. Besides methodological variations, contradictory findings might be explained by the divergent metabolism of testosterone and its recognition by neurons during prenatal and postnatal development. Gonadectomy and subsequent supplementation have been used to study the role of sex hormones. However, the variable duration of hypogonadism might affect the outcomes and the effect of long-term androgen deficiency is understudied. Testosterone can be metabolized to dihydrotestosterone strengthening the androgen signaling, but also to estradiol converting the androgen to estrogen activity. Moreover, some metabolites of testosterone can modulate γ-aminobutyric acid and serotonergic neurotransmission. Here we review the currently available experimental data in experimental rodents on the effects of testosterone on anxiety during development. Based on the experimental results, females are generally less anxious than males from puberty to middle-age. The anxiety-like behavior of females and males is likely influenced by early organizational effects, but might be modified by activational effects of testosterone and its metabolites. The effects of sex hormones leading to anxiogenesis or anxiolysis depend on factors affecting hormonal status including age. The biological and several technical issues make the study of effects of testosterone on anxiety very complex and should be taken into account when interpreting experimental results.

Peri-pubertal exposure to testicular hormones organizes response to novel environments and social behaviour in adult male rats

Previous research has shown that exposure to testicular hormones during the peri-pubertal period of life has long-term, organizational effects on adult sexual behaviour and underlying neural mechanisms in laboratory rodents. However, the organizational effects of peri-pubertal testicular hormones on other aspects of behaviour and brain function are less well understood. Here, we investigated the effects of manipulating peri-pubertal testicular hormone exposure on later behavioural responses to novel environments and on hormone receptors in various brain regions that are involved in response to novelty. Male rodents generally spend less time in the exposed areas of novel environments than females, and this sex difference emerges during the peri-pubertal period. Male Lister-hooded rats (Rattus norvegicus) were castrated either before puberty or after puberty, then tested in three novel environments (elevated plus-maze, light-dark box, open field) and in an object/social novelty task in adulthood. Androgen receptor (AR), oestrogen receptor (ER1) and corticotropin-releasing factor receptor (CRF-R2) mRNA expression were quantified in the hypothalamus, hippocampus and medial amygdala. The results showed that pre-pubertally castrated males spent more time in the exposed areas of the elevated-plus maze and light-dark box than post-pubertally castrated males, and also confirmed that peri-pubertal hormone exposure influences later response to an opposite-sex conspecific. Hormone receptor gene expression levels did not differ between pre-pubertally and post-pubertally castrated males in any of the brain regions examined. This study therefore demonstrates that testicular hormone exposure during the peri-pubertal period masculinizes later response to novel environments, although the neural mechanisms remain to be fully elucidated.

Prenatal LPS-exposure--a neurodevelopmental rat model of schizophrenia--differentially affects cognitive functions, myelination and parvalbumin expression in male and female offspring

Maternal infection during pregnancy increases the risk for the offspring to develop schizophrenia. Gender differences can be seen in various features of the illness and sex steroid hormones (e.g. estrogen) have strongly been implicated in the disease pathology. In the present study, we evaluated sex differences in the effects of prenatal exposure to a bacterial endotoxin (lipopolysaccharide, LPS) in rats. Pregnant dams received LPS-injections (100 μg/kg) at gestational day 15 and 16. The offspring was then tested for prepulse inhibition (PPI), locomotor activity, anxiety-like behavior and object recognition memory at various developmental time points. At postnatal day (PD) 33 and 60, prenatally LPS-exposed rats showed locomotor hyperactivity which was similar in male and female offspring. Moreover, prenatal LPS-treatment caused PPI deficits in pubertal (PD45) and adult (PD90) males while PPI impairments were found only at PD45 in prenatally LPS-treated females. Following prenatal LPS-administration, recognition memory for objects was impaired in both sexes with males being more severely affected. Additionally, we assessed prenatal infection-induced alterations of parvalbumin (Parv) expression and myelin fiber density. Male offspring born to LPS-challenged mothers showed decreased myelination in cortical and limbic brain regions as well as reduced numbers of Parv-expressing cells in the medial prefrontal cortex (mPFC), hippocampus and entorhinal cortex. In contrast, LPS-exposed female rats showed only a modest decrease in myelination and Parv immunoreactivity. Collectively, our data indicate that some of the prenatal immune activation effects are sex dependent and further strengthen the importance of taking into account gender differences in animal models of schizophrenia.

Reconceptualizing sex, brain and psychopathology: interaction, interaction, interaction

In recent years there has been a growing recognition of the influence of sex on brain structure and function, and in relation, on the susceptibility, prevalence and response to treatment of psychiatric disorders. Most theories and descriptions of the effects of sex on the brain are dominated by an analogy to the current interpretation of the effects of sex on the reproductive system, according to which sex is a divergence system that exerts a unitary, overriding and serial effect on the form of other systems. We shortly summarize different lines of evidence that contradict aspects of this analogy. The new view that emerges from these data is of sex as a complex system whose different components interact with one another and with other systems to affect body and brain. The paradigm shift that this understanding calls for is from thinking of sex in terms of sexual dimorphism and sex differences, to thinking of sex in terms of its interactions with other factors and processes. Our review of data obtained from animal models of psychopathology clearly reveals the need for such a paradigmatic shift, because in the field of animal behaviour whether a sex difference exists and its direction depend on the interaction of many factors including, species, strain, age, specific test employed and a multitude of environmental factors. We conclude by explaining how the new conceptualization can account for sex differences in psychopathology.

Sex differences in anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

Individual differences and the characterization of animal models of psychopathology: a strong challenge and a good opportunity

Despite the development of valuable new techniques (i.e., genetics, neuroimage) for the study of the neurobiological substrate of psychiatric diseases, there are strong limitations in the information that can be gathered from human studies. It is thus critical to develop appropriate animal models of psychiatric diseases to characterize their putative biological bases and the development of new therapeutic strategies. The present review tries to offer a general perspective and several examples of how individual differences in animals can contribute to explain differential susceptibility to develop behavioral alterations, but also emphasizes methodological problems that can lead to inappropriate or over-simplistic interpretations. A critical analysis of the approaches currently used could contribute to obtain more reliable data and allow taking full advantage of new and sophisticated technologies. The discussion is mainly focused on anxiety-like and to a lower extent on depression-like behavior in rodents.

Effects of perinatal daidzein exposure on subsequent behavior and central estrogen receptor α expression in the adult male mouse

Daidzein is one of the most important isoflavones present in soy and it is unique as it can be further metabolized to equol, a compound with greater estrogenic activity than other isoflavones. The potential role of daidzein in the prevention of some chronic diseases has drawn public attention and increased its consumption in human, including in pregnant women and adolescent. It is unclear whether perinatal exposure to daidzein through maternal diets affects subsequent behavior and central estrogen receptor α (ERα) expression in male adults. Following developmental exposure to daidzein through maternal diets during perinatal period, subsequent anxiety-like behavior, social behavior, spatial learning and memory of male mice at adulthood were assessed using a series of tests. The levels of central ER α expression were also examined using immunocytochemistry. Compared with the controls, adult male mice exposed to daidzein during the perinatal period showed significantly less exploration, higher levels of anxiety and aggression. They also displayed more social investigation for females and a tendency to improve spatial learning and memory. The mice with this early daidzein treatment demonstrated significantly higher levels of ERα expression in several brain regions such as the bed nucleus of the stria terminalis, medial preoptic, arcuate hypothalamic nucleus and central amygdaloid mucleus, but decreased it in the lateral septum. Our results indicated that perinatal exposure to daidzein enhanced masculinization on male behaviors which is assocciated with alterations in ERα expression levels led by perinatal daidzein exposure.

Male rats with the testicular feminization mutation of the androgen receptor display elevated anxiety-related behavior and corticosterone response to mild stress

Testosterone influences the hypothalamic-pituitary-adrenal axis, anxiety-related behavior, and sensorimotor gating in rodents, but little is known about the role of the androgen receptor (AR) in mediating these influences. We compared levels of the stress hormone corticosterone at baseline and following exposure to a novel object in an open field in wild type (wt) male and female rats, and male rats with the testicular feminization mutation (Tfm) of the AR, which disables its function. Basal corticosterone was equivalent in all groups, but exposure to a novel object in an open field elicited a greater increase in corticosterone in Tfm males and wt females than in wt males. Tfm males also showed increased behavioral indices of anxiety compared to wt males and females in the test. Analysis of the immediate early gene c-Fos expression after exposure to a novel object revealed greater activation in Tfm males than wt males in some regions (medial preoptic area) and lesser activation in others (dentate gyrus, posterodorsal medial amygdala). No differences were found in a measure of sensorimotor gating (prepulse inhibition of the acoustic startle response), although Tfm males had an increased acoustic startle response compared to wt males and females. These findings demonstrate that ARs play a role in regulating anxiety-related behaviors, as well as corticosterone responses and neural activation following exposure to a mild stressor in rats.

The organizational role of testicular hormones and the androgen receptor in anxiety-related behaviors and sensorimotor gating in rats

Perinatal exposure to testosterone (T), which can act upon both the androgen receptor (AR) and, via aromatization of T into estrogens, upon estrogen receptors, organizes many adult behaviors in rodents. We compared behaviors in wild-type (WT) male rats and AR-deficient rats with the testicular feminization mutation (Tfm), which on the day of birth were either gonadectomized (Neo-Gdx) or sham operated. In adulthood, all rats were either gonadectomized or sham operated and implanted with T capsules to equilibrate circulating androgens. In each of four tests of behavior related to anxiety (open field, novel object exposure, light/dark box, and elevated plus maze), Neo-Gdx rats showed decreased indices of anxiety and increased activity compared with rats sham operated on the day of birth, with no differences between WT or Tfm males within treatment groups. These results indicate that testicular hormones act in development to increase adult indices of anxiety and decrease activity in males and that functional ARs are not required for this effect. Acoustic startle response was also reduced by Neo-Gdx, suggesting that postnatal testicular secretions potentiate this behavior as well. Adult corticosterone levels and sensorimotor gating, as measured by prepulse inhibition of the acoustic startle response, were increased by neonatal castration in both WT and Tfm rats. These findings indicate a role of T before adulthood in the organization of anxiety-related behaviors, activity, the hypothalamic-pituitary-adrenal axis, and sensorimotor gating in rats, all of which appears to be AR independent.

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

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

Effects of genistein in the maternal diet on reproductive development and spatial learning in male rats

Endocrine disruptors, chemicals that disturb the actions of endogenous hormones, have been implicated in birth defects associated with hormone-dependent development. Phytoestrogens are a class of endocrine disruptors found in plants. In the current study we examined the effects of exposure at various perinatal time periods to genistein, a soy phytoestrogen, on reproductive development and learning in male rats. Dams were fed genistein-containing (5 mg/kg feed) food during both gestation and lactation, during gestation only, during lactation only, or during neither period. Measures of reproductive development and body mass were taken in the male offspring during postnatal development, and learning and memory performance was assessed in adulthood. Genistein exposure via the maternal diet decreased body mass in the male offspring of dams fed genistein during both gestation and lactation, during lactation only, but not during gestation only. Genistein decreased anogenital distance when exposure was during both gestation and lactation, but there was no effect when exposure was limited to one of these time periods. Similarly, spatial learning in the Morris water maze was impaired in male rats exposed to genistein during both gestation and lactation, but not in rats exposed during only one of these time periods. There was no effect of genistein on cued or contextual fear conditioning. In summary, the data indicate that exposure to genistein through the maternal diet significantly impacts growth in male offspring if exposure is during lactation. The effects of genistein on reproductive development and spatial learning required exposure throughout the pre- and postnatal periods.

Anxiety, sex-linked behaviors, and digit ratios (2D:4D)

The second to fourth (2D:4D) digit ratio, a sexually dimorphic, phenotypic characteristic putatively associated with perinatal androgen action, has been used to evaluate the hypothesized relation between prenatal hormonal factors and a variety of sexually dimorphic behaviors, including sex-linked psychopathology. Smaller digit ratios, suggestive of stronger perinatal androgen action, have been associated with male-linked disorders (e.g., autism), and larger digit ratios, suggestive of weaker perinatal androgen action, have been associated with female-linked disorders (e.g., depression and eating disorders). To evaluate the possible relation between digit ratio and another traditionally female-linked disorder, anxiety, 2D:4D ratios were measured in a non-clinical sample (58 men, 52 women). Participants also completed a battery of anxiety and gender role measures and performed two spatial/cognitive tasks typically showing a male advantage (mental rotation and targeting) and two tasks typically showing a female advantage (location memory and spatial working memory). Men with a more feminine pattern of sex-linked traits and behaviors (including digit ratios) reported greater anxiety. In contrast, greater anxiety in women was associated with both female-typical and male-typical traits and behaviors, but and no significant association between digit ratio and anxiety was found. This pattern of results suggests that the development of anxiety is multiply determined, with contributing factors varying by sex.

Effects of pretest manipulation on elevated plus-maze behavior in adolescent and adult male and female Sprague-Dawley rats

The elevated plus-maze (EPM) is vulnerable to variations in pretest circumstances when testing adult rodents. Because of an increasing interest in adolescence, the present experiments examined the impact of pretest manipulations on anxiety levels in the EPM among adolescent and adult Sprague-Dawley rats of both sexes. In Exp. 1, animals removed from their home cage and immediately placed on the EPM were compared to rats tested following 30 min of social isolation, or following 30-min exposure to a novel context. These pretest manipulations only modestly decreased anxiety levels at both ages. In Exp. 2, more varied pretest conditions were examined: testing directly from the home cage; testing following 30 min of social isolation in a novel environment; or a large saline injection and rehousing 18 h prior to a 30-min period of social isolation in a novelty situation before testing. In adults, anxiety levels decreased linearly as pretest perturbation increased, whereas adolescents showed comparable levels of anxiety with both the moderate and large perturbations. As a result, observed age differences in anxiety differed as a function of pretest circumstances. Therefore, caution is urged when using the EPM for across-age comparisons of anxiolytic and anxiogenic effects of pharmacological or other manipulations.

Neonatal exposure to endocrine active compounds or an ERbeta agonist increases adult anxiety and aggression in gonadally intact male rats

Endocrine active compounds (EACs) have been shown to influence a number of reproductive endpoints but less is known about how they might affect other hormone dependent behaviors including anxiety and aggression. Recent evidence suggests that these effects may be mediated through the beta form of the estrogen receptor (ERbeta). Using male Long Evans rats, we sought to determine how neonatal exposure to EACs affects anxiety and aggression in adulthood. Anxiety was assessed using the elevated plus maze and aggression was assessed 8 weeks later using the resident intruder test. To gain insight into which ER subtype (ERalpha vs ERbeta) might be mediating these effects we used agonists specific for ERalpha (1,3,5-tris(4-Hydroxyphenyl)-4-propyl-1H-pyrazole (PPT)) or ERbeta (Diarylpropionitrile (DPN)) as additional treatment groups. For these experiments the synthetic EAC bisphenol-A (BPA) and the phytoestrogen metabolite equol (EQ) were used. Male neonates were injected with either 0.05 ml sesame oil (control), 50 microg estradiol benzoate (EB), 1 mg/kg DPN, 1 mg/kg PPT, 50 microg/kg BPA, or 10 mg/kg EQ daily for 4 days beginning on the day of birth (PND 0). Compared to the oil treated controls, significantly fewer open arm entries were made by the males neonatally treated with DPN, EQ, or BPA. The DPN and EQ treated males were also more aggressive compared to the controls. These findings suggest that neonatal exposure to EACs with agonistic activity on ERbeta may influence affective behavior in adulthood, including anxiety and aggression.

Developmental exposure to low-dose estrogenic endocrine disruptors alters sex differences in exploration and emotional responses in mice

Estrogenic endocrine disruptors (EEDs) are naturally occurring or man-made compounds present in the environment that are able to bind to estrogen receptors and interfere with normal cellular development in target organs and tissues. There is mounting evidence that EEDs can interfere with the processes of sexual differentiation of brain and behavior in different animal models. We investigated the effects of maternal exposure to EEDs, at concentrations within the range of human exposure and not patently teratogenic, on behavioral responses of male and female house mice (Mus musculus domesticus) before and after puberty. Pregnant dams were trained to spontaneously drink daily doses of corn oil with or without the estrogenic plastic derivative, bisphenol A (BPA 10 microg/kg), or the estrogenic insecticide methoxychlor (MXC 20 microg/kg) from gestation day 11 to postpartum day 8. Their male and female offspring were examined at different ages to examine several components of explorative and emotional behaviors in 3 experimental paradigms: a novelty test before puberty and, as adults, a free-exploratory open-field test and the elevated plus maze test. The main results are sex differences in control mice on a number of behavioral responses at both ages and in all experimental paradigms, while perinatal exposure to BPA or MXC decreased or eliminated such sex differences. The present findings are evidence of long-term consequences of developmental exposure to BPA and MXC on neurobehavioral development and suggest a differential effect of low-dose exposure to these estrogenic chemicals in males and females.

Evidence of altered brain sexual differentiation in mice exposed perinatally to low, environmentally relevant levels of bisphenol A

Humans are routinely exposed to bisphenol A (BPA), an estrogenic chemical present in food and beverage containers, dental composites, and many products in the home and workplace. BPA binds both classical nuclear estrogen receptors and facilitates membrane-initiated estrogenic effects. Here we explore the ability of environmentally relevant exposure to BPA to affect anatomical and functional measures of brain development and sexual differentiation. Anatomical evidence of alterations in brain sexual differentiation were examined in male and female offspring born to mouse dams exposed to 0, 25, or 250 ng BPA/kg body weight per day from the evening of d 8 of gestation through d 16 of lactation. These studies examined the sexually dimorphic population of tyrosine hydroxylase (TH) neurons in the rostral periventricular preoptic area, an important brain region for estrous cyclicity and estrogen-positive feedback. The significant sex differences in TH neuron number observed in control offspring were diminished or obliterated in offspring exposed to BPA primarily because of a decline in TH neuron number in BPA-exposed females. As a functional endpoint of BPA action on brain sexual differentiation, we examined the effects of perinatal BPA exposure on sexually dimorphic behaviors in the open field. Data from these studies revealed significant sex differences in the vehicle-exposed offspring that were not observed in the BPA-exposed offspring. These data indicate that BPA may be capable of altering important events during critical periods of brain development.

Long-lasting changes in behavioural and neuroendocrine indices in the rat following neonatal maternal separation: Gender-dependent effects

Neonatal maternal separation (MS) has been used to model long-term changes in neurochemistry and behaviour associated with exposure to early-life stress. This study characterises changes in behavioural and neuroendocrine parameters following MS. On postnatal days (PND) 3-15, male and female Long-Evans rats underwent 3 h daily MS. Non-handled (NH) control offspring remained with the dams. Starting at PND 90, behaviour was assessed at weekly intervals in the elevated plus-maze, elevated T-maze, and locomotor activity boxes, and body weight monitored throughout. At the end of the study, adrenals were weighed and blood collected for analysis of plasma corticosterone and adrenocorticotropic hormone (ACTH) under basal conditions and following restraint stress. As adults, MS weighed more than NH animals. Activity on the open arms of the plus-maze was similar between MS and NH animals. In the T-maze, MS males had shorter emergence latencies than their NH counterparts. Spontaneous ambulation in a novel environment was significantly higher in MS than in NH animals, and males exhibited overall lower activity than females. Basal plasma corticosterone was lower in MS than in NH females, but no rearing condition difference was observed following restraint stress. Females had higher corticosterone and ACTH levels than males, whereas adrenal glands of MS animals weighed less than those of NH controls. The MS paradigm caused long-term gender dependent effects on behaviour and HPA axis status. The consistent gender differences confirm and expand existing results showing altered anxiety and stress reactivity in male and female rats.

Administration of 17alpha-ethinylestradiol during pregnancy elicits modifications of maternal behavior and emotional alteration of the offspring in the rat

Intraperitoneal administration of 17alpha-ethinylestradiol (15 microg.kg(-1)) in pregnant rats, every day from day 9 to day 14 of pregnancy, elicited a high percentage of abortions. Quantification of maternal behavior showed that treated dams took better care of their pups than control dams, injected with the vehicle only, did. Postnatal reflexes, which reflect maturational rate, were established more promptly in the offspring of treated dams than in the offspring of control dams. However, when adult, the rats born from treated dams developed anxiety- and depressive-like behaviors. All these results are explained by the effects of the exogenous estrogen on the developing brain of the fetuses.

Sexually dimorphic effects of postnatal allopregnanolone on the development of anxiety behavior after early deprivation

Stress early in life exerts persistent detrimental effects on brain development. In this experiment, a rodent model of child neglect, early deprivation (ED), was used to investigate the role of the neurosteroid allopregnanolone [AlloP; 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP)] in the development of anxiety behavior. Subjects were either undisturbed controls or ED: separated individually for 6 h per day from postnatal day (PN) 2 to 6. Control and ED subjects were also either noninjected, vehicle-injected or injected with 5 mg/kg AlloP prior to the isolation. At PN 7, responses to 2.5 or 5 microg icv injections of AlloP were determined for separation-induced ultrasonic vocalizations (USVs). Tolerance to the USV-reducing effect of daily AlloP was seen in control but not ED pups, and daily AlloP reversed the expected ED suppression of USVs. As adults, controls treated with postnatal AlloP were less anxious than all other groups on the elevated plus maze. ED counteracted this effect. Male controls showed a reversal of the typical sex difference. There were no effects on open-field activity. These results suggest that the neonatal brain is responsive to alterations in AlloP levels, and that neuroactive progesterone metabolites may play a role in mediating the development of stress-related sex differences.

Effects of perinatal exposure to bisphenol A on the behavior of offspring in F344 rats

The objective of this investigation is to evaluate whether perinatal maternal exposure to bisphenol A (BPA) at 4, 40, and 400 mg/kg per day affects the behavior of offspring in F344 rats. Perinatal BPA exposure inhibited the body weight increases of male and female offspring in a dose-dependent manner, which continued after weaning. Spontaneous activity analyses revealed that BPA elongated immobile time during the dark phase in female offspring. At 4 weeks of age, male offspring exposed to BPA at 40 and 400 mg/kg per day performed avoidance responses significantly higher in the shuttlebox avoidance test. At 8 weeks of age, however, male offspring only at 4 mg/kg per day showed significantly lower responses. In the open-field behavior test at 8 weeks of age, male offspring exposed to BPA only at 4 mg/kg per day showed a higher percent of grooming than the control male offspring. In conclusion, perinatal exposure to BPA caused the behavioral alterations in the offspring.

Effect of steroid injection to newborn rats on serotonin activity in frontal cortex and raphe

The effects of injecting testosterone propionate or estradiol benzoate to newborn rats on dopaminergic and serotoninergic activity in the frontal cortex, dorsal and median raphe nucleus were analyzed when animals reached adulthood. High performance liquid chromatography was used to measure tissue levels of dopamine, serotonin and its metabolites. Activity was calculated as the metabolite/neurotransmitter ratio. An increase in androgen or estrogen levels at birth caused a significant decrease in serotoninergic activity in the frontal cortex and in the dorsal raphe nucleus, without causing apparent changes in dopaminergic activity; serotinergic activity in the median raphe nucleus was not affected. The results suggest that the transmission of DA and 5-HT in these structures are differentially influenced by early androgenization or estrogenization.

Glial fibrillary acidic protein immunodetection and immunoreactivity in the anterior and posterior medial amygdala of male and female rats

The medial amygdala (MeA) has receptors for gonadal hormones and modulates reproductive behaviors in rats. Adult male and female rats were used for the immunodetection, a less accurate technique, and the immunohistochemistry for the astrocytic marker glial fibrillary acidic protein (GFAP) in the anterior and posterior MeA. Both procedures were done using polyclonal anti-GFAP and were quantified by densitometry. The first technique provided no evidence for a difference between sexes in the immunocontent of GFAP in any region of the MeA (p > 0.1). Nevertheless, the measure of the intensity of GFAP immunoreactivity (GFAP-IR) showed that females had a higher GFAP-IR in the posterodorsal (p < 0.01) and in the posteroventral subregions of the MeA (p < 0.01) than males. No sex difference was found in its anterodorsal part (p > 0.1). The present results point out the differences between these two above-mentioned techniques but add a new finding to the previously described sexual dimorphism in the MeA, i.e., the GFAP-IR. Data also suggest that probably astrocytes can be affected by sex steroids in this brain area. It is likely that this regionally specific difference in the GFAP-IR may contribute to the distinct functional roles that the MeA subregions have in male and female rats.

Neurobehavioral effects of dietary soy phytoestrogens

Phytoestrogens, plant-derived nonsteroidal estrogens found in high abundance in most soy food products, have been studied for their potential beneficial effects against hormone-dependent cancers and age-related diseases. However, little is known about the influence of phytoestrogens on the brain or behavior. This brief review describes mainly our own studies in rodents that have examined the influence of dietary soy isoflavones on certain aspects of brain structure, learning, memory and anxiety along with the brain androgen-metabolizing enzyme, aromatase. These studies used a commercially available diet rich in phytoestrogens (Phyto-rich) vs. a custom diet relatively free of phytoestrogens (Phyto-free). The phytoestrogen content of each diet was determined by high-performance liquid chromatography analysis, circulating plasma phytoestrogen levels were quantified by gas chromatography mass spectroscopy and concentrations of phytoestrogens in specific brain regions were measured by time-resolved fluoroimmunoassay (TR-FIA). Our studies showed that brain aromatase levels were not significantly altered by phytoestrogen diet treatments in perinatal, maternal or adult rats. However, volumes of the sexually dimorphic nucleus of the preoptic area (SDN-POA) were significantly affected by the Phyto-free diet treatment in male rats during adulthood, where SDN-POA volumes were smaller compared to Phyto-rich male values. Additionally, the Phyto-rich diet fed to adult male and female rats produced anxiolytic effects as assessed in the elevated plus maze vs. Phyto-free fed animals. Finally, when learning and memory parameters were examined in a radial arm maze testing visual-spatial memory (VSM), the diet treatments significantly changed the typical sexually dimorphic pattern of VSM. Specifically, adult Phyto-rich fed females outperformed Phyto-free fed females, while in males on the same diets, the opposite pattern of maze performance was observed. When female vs. male performance was compared, Phyto-rich females executed the VSM task in a manner similar to that of Phyto-free fed males, while Phyto-free fed female's VSM was comparable to Phyto-rich males. These results indicate that consumption of dietary phytoestrogens resulting in very high plasma isoflavone levels (in many cases over a relatively short interval of consumption in adulthood) can significantly alter sexually dimorphic brain regions, anxiety, learning and memory. The findings of these studies identify the biological actions of phytoestrogens, specifically isoflavones and their metabolites, found in animal soy-containing diets on brain and behavior and implicate the importance of phytoestrogens given the recognized significance of estrogens in brain and neural disorders, such as Alzheimer's disease, especially in women.

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.

The influence of gender and the estrous cycle on learned helplessness in the rat

Although the etiology of clinical depression is unknown, women are more likely to suffer from major depressive disorder than men. In addition, in some women, there is a clear association between depression and specific phases of the menstrual cycle. Surprisingly little research has examined gender differences and the influences of the estrous cycle in this and other animal behavioral models of clinical depression. Learned helplessness is a valid animal model of stress-induced behavioral depression in which prior exposure to inescapable stress produces deficits in escape testing. Learned helplessness was studied in rats using an inescapable tail shock stress followed by a shuttle box test to determine escape latencies. Animals with mean escape latencies of >or=20 s after shuttle-box testing are defined as learned helpless. Males and normal cycling female rats in the estrus and diestrus II phases were studied. Female rats in the diestrus II phase had significantly higher escape latencies and exhibited a more helpless behavior than female rats in the estrus phase. Male rat escape latencies were intermediate between the two female phases. These results suggest a role for gonadal hormones in the development of stress-induced behavioral depression or 'learned helplessness.'

Dietary soy phytoestrogens produce anxiolytic effects in the elevated plus-maze

Naturally occurring estrogen-like molecules in plants (phytoestrogens), present via soy, in animal diets, exert many of the biological responses evoked by physiological estrogens. This study characterized the effects of dietary phytoestrogens on the expression of body weight, consummatory behavior, and anxiety (as expressed in the elevated plus-maze). Phytoestrogens produced anxiolytic effects in both male and female Long-Evans rats. Additionally, phytoestrogens decreased body weight but increased consumption of food and/or water.

Prenatal exposure to ethinylestradiol elicits behavioral abnormalities in the rat

Pregnant rats were i.p. injected with a solution of 17alpha-ethinylestradiol (15 microg kg(-1)) every day between day 9 and day 14 of pregnancy and the behavior of the offspring was compared to that of rats born from dams injected with the vehicle only during the same gestational period. The percentage of neonatal death was dramatically high in the prenatally treated group. Growth of the surviving animals was even better than that of controls, but when adult, they exhibited a number of behavioral abnormalities: increased spontaneous motor activity, decreased exploratory behavior, impaired cognitive processing, qualitatively different exploratory drive, and/or persevering behavior, increased anxiety-like behavior and social neophobia. These behavioral alterations, which resemble a number of psychiatric syndromes, suggest that ethinylestradiol altered the ontogenesis of different parts of the central nervous system involved in cognitive and emotional processes. However, it cannot be excluded that the changes in behavior of ethinylestradiol exposed offspring were due to the abnormal maternal behavior of the estradiol treated dams.

Effects of antisense to the (alpha)2A-adrenoceptors administered into the region of the locus ceruleus on behaviors in plus-maze and sexual behavior tests in sham-operated and castrated male rats

Clinical and experimental findings have implicated brain alpha2-adrenoceptors in the regulation of many physiological functions, including sexual activity and stress-related behavior. However, which subtypes of the three alpha2-adrenoceptors that have now been cloned (alpha2A, alpha2B, and alpha2C) are involved in these controls have yet to be established. Here, we investigated the contribution of alpha2A-adrenoceptors of the locus ceruleus, the principal source of brain noradrenaline, to exploratory and sexual behaviors. Using administration of antisense oligodeoxynucleotide to inhibit the receptor expression, we found that reductions in brainstem alpha2A-adrenoceptor mRNA levels and alpha2-adrenoceptor densities induced by antisense treatment were not accompanied by any changes in the major characteristics of male sexual activity, such as mount latencies and numbers of mounts. However, in sexual behavior tests, antisense-treated male rats had decreased numbers of rearings and thus have higher percentages of behaviors positively correlated with sexual activity. Besides, antisense-treated animals had decreased anxiety in plus-maze tests. The data demonstrate that inhibition of alpha2A-adrenoceptor expression in the region of the locus ceruleus has an anxiolytic-like effect and facilitates male's attention to female in sexual behavior test.

Effects of neonatal RU486 on adult sexual, parental, and fearful behaviors in rats

Exposure to gonadal hormones during perinatal life influences later behavior. The finding that sex differences exist in progestin receptor expression in the perinatal rat brain suggests differential sensitivity of male and female brains to progesterone (C. K. Wagner, A. N. Nakayama, & G. J. De Vries, 1998). Because these sex differences are in neural sites that influence sexually differentiated sexual, parental, and fearful behaviors in adults, this study examined the effects of administering the progestin receptor antagonist RU486 for the first 10 days after birth on these behaviors in adulthood. Neonatal RU486 significantly reduced sexual behavior in males but did not impair reproduction in females. Neonatal RU486 did not affect parental responses of virgin rats exposed to pups (sensitization) but reduced fear in the elevated plus-maze in both sexes. Treatment of pups with RU486 affected neither mother-litter interactions nor plasma testosterone levels in males during or after treatment. These results suggest that neonatal exposure to progesterone, in addition to androgens and estrogens, influences behavioral development in rats.

Sex specific behavioural alterations in Mas-deficient mice

Male mice lacking the Mas protooncogene have been shown to exhibit an increased anxiety in the Elevated Plus Maze Task and sustained long-term potentiation in the hippocampus without effect on spatial learning in the Morris Water Maze Task. Here, we report behavioural studies in female mice lacking the Mas protooncogene. As for the males, we analysed the learning and anxiety behaviour using both behavioural tasks. With the exception of a trend to a better performance in the Morris Water Maze no differences were found in both tests between control and Mas-deficient females. This implicates that the lack of Mas protein influences spatial learning and anxiety in a sex-specific manner.

Factor analysis shows that female rat behaviour is characterized primarily by activity, male rats are driven by sex and anxiety

This experiment explored sex differences in behaviour using factor analysis to describe the relationship between different behavioral variables. A principal component solution with an orthogonal rotation of the factor matrix was used, ensuring that the extracted factors are independent of one another, and thus reflect separate processes. In the elevated plus-maze test of anxiety, in male rats factor 1 accounted for 75% of the variance and reflected anxiety, factor 2 represented activity, and accounted for 24% of the variance. This contrasted with the finding in female rats in which factor 1 was activity, accounting for 57% of the variance, with the anxiety factor accounting for only 34% of the variance. When behaviour in both the plus-maze and holeboard were analysed, a similar sex difference was found with anxiety emerging as factor 1 in males and holeboard activity as factor 1 in females. Locomotor activity in the inner portion of the holeboard loaded on the anxiety factor for males, but on activity for females. When behaviours in the plus-maze and sexual orientation tests were analysed, anxiety emerged as factor 1 in males, sexual preferences factor 2, and activity factor 3. In females, activity was factor 1, sexual preference factor 2, anxiety factor 3, and social interest factor 4. These results suggest caution should be exercised in interpreting the results from female rats in tests validated on males because the primary controlling factor may be different.

Periodic maternal deprivation induces gender-dependent alterations in behavioral and neuroendocrine responses to emotional stress in adult rats

There is evidence that stressful events during the neonatal "stress hyporesponsive period" may influence both emotional behavior and the maturation of the hypothalamic-pituitary-adrenal (HPA) axis in rats. We tested whether periodic maternal deprivation (180 min daily on postnatal days 3-10, PMD) caused chronic changes in emotional behavior and HPA axis activity in either male or female adult rats, or both. In addition, HPA secretory responses to human/rat corticotropin-releasing factor (CRH, 50 ng/kg i.v.) were determined in the adult males. In the elevated plus-maze test, adult (4-5 months of age) PMD-treated animals of both sexes displayed increased anxiety-related behavior compared to control rats. This was indicated by a reduction in the number of entries (male: 70% reduction, p < 0.01; female: 31% reduction, p < 0.01) and amount of time spent on the open arms (male: 86% reduction, p < 0.01; female: 40% reduction, NS). Neuroendocrine parameters were also altered in PMD-treated rats in a gender-dependent manner. Whereas basal plasma adrenocorticotropin (ACTH) and corticosterone levels did not differ significantly between PMD and control groups of either sex, the ACTH response to elevated plus-maze exposure, a predominantly emotional stressor, was higher in male (p < 0.01), but not female, PMD animals than in the respective controls. In contrast, PMD had no effect on behavioral (duration of struggling) or HPA axis responses to forced swimming (90 s, 19 degrees C), a complex and predominantly physical stressor, in either male or female rats. In response to CRH stimulation, PMD-treated males did not show differences in the ACTH secretion compared to controls, indicating alterations in HPA axis regulation at a suprapituitary level. Thus, PMD caused long-term changes in the emotional behavior of adult rats of both sexes, although to a differing degree in males and females, whereas it appeared to cause predominantly alterations in the HPA axis response in males, depending on the characteristics of the stressor used.

Effects of gonadal hormones on the morphology of neurons from the medial amygdaloid nucleus of rats

The medial amygdala (MeA) has receptors for gonadal hormones and is a sexually dimorphic area in rats. The aims of the present work were (1) to look at sex differences and the effect of gonadal hormone withdrawal in males castrated as offspring or at adulthood on neuronal soma area in the anterior and posterior MeA and (2) to study the dendritic branching and the density of dendritic spines in neurons from the MeA of intact males and females. Animals were adult rats, for which the single-section Golgi method was used. Stellate and bitufted cells were found in the MeA. Comparing data among groups, no significant difference in cell body area was found. Dendrites divide sparingly and have very different lengths, and a statistical difference (p < 0.001, males higher than females) in the spine density in the anterior MeA, but not in the posterior MeA, was found. These results suggest that castration does not alter the somal area in males submitted to gonadectomy during the early postnatal period or at adulthood. In addition, the already described sex difference in this nucleus may be more related to the neuropil than the neuronal somal area, which may be relevant for the function of the MeA.