Pubertal hormones organize the adolescent brain and behavior

Sex differences in motor performance and motor learning in children and adolescents: an increasing male advantage in motor learning and consolidation phase gains

We investigated gender differences in motor performance in 9-, 12-, and 17-year-olds. The tasks included simple thumb tapping (sTT), handwriting (HW) and finger-to-thumb opposition sequence (FOS) learning. In sTT there was a significant advantage for the 17-year-old males. In HW, 12-year-old females were faster, initially, than the males, but this gap was closed by a single training session; in the 17-year-olds although no significant difference was found initially, the males became faster than the age-matched females post-training. In the FOS, there were no initial gender differences (speed or accuracy). However, males benefited more from training, with the 17-year-old males attaining a significant post-training speed advantage. Moreover, males, of all three age-groups, evolved significantly larger delayed ("off-line") performance gains in the FOS task compared to females; gains which were retained 6-weeks post-training. There may be a male advantage in motor learning rather than in motor performance per-se; this advantage is enhanced during adolescence.

Environmental-like exposure to low levels of estrogen affects sexual behavior and physiology of female rats

Xenoestrogens are endocrine-disrupting chemicals that mimic the action of endogenous estrogen hormones. Effects of xenoestrogen on aquatic wildlife are well documented, whereas the experimental evidence for impairment of reproductive behavior and physiology in mammals after exposure to xenoestrogens has been debated. The strongest arguments against such studies have been that the route, time course, and intensity of exposure did not simulate environmental exposure and that the chemicals tested have additional nonestrogenic toxic effects, hindering generalization of actual xenoestrogenic effects. Here we show that environmental-like exposure to the pure estrogen 17alpha-ethinylestradiol during development alters reproductive behavior and physiology in adult female Sprague-Dawley rats. We simulated environmental exposure by giving low doses (0.4 and 0.004 microg/kg.d) of 17alpha-ethinylestradiol orally to pregnant females from conception to weaning of the pups, which continued to receive the treatment until puberty. We studied the sexual behavior, estrous cycle, and estradiol plasma levels of intact female rats when they reached 3 months of age. Exposure to the higher dose strongly affected female sexual behavior and physiology, with suppression of lordosis and the estrous cycle and enhanced aggression toward males. The lower dose disrupted appetitive components of sexual behavior that influence the rate of copulation. Estradiol plasma levels were not affected by the treatment. Our study revealed that exposure to low oral doses of a pure estrogen during development alters female sexual behavior and physiology. These results suggest potential risks of reproductive failure from xenoestrogen exposure in realistic ecological conditions.

Neuroimaging studies of normal brain development and their relevance for understanding childhood neuropsychiatric disorders

OBJECTIVE

To review the maturational events that occur during prenatal and postnatal brain development and to present neuroimaging findings from studies of healthy individuals that identify the trajectories of normal brain development.

METHOD

Histological and postmortem findings of early brain development are presented, followed by a discussion of anatomical, diffusion tensor, proton spectroscopy, and functional imaging findings from studies of healthy individuals, with special emphasis on longitudinal data.

RESULTS

Early brain development occurs through a sequence of major events, beginning with the formation of the neural tube and ending with myelination. Brain development at a macroscopic level typically proceeds first in sensorimotor areas, spreading subsequently and progressively into dorsal and parietal, superior temporal, and dorsolateral prefrontal cortices throughout later childhood and adolescence. These patterns of anatomical development parallel increasing activity in frontal cortices that subserves the development of higher-order cognitive functions during late childhood and adolescence. Disturbances in these developmental patterns seem to be involved centrally in the pathogenesis of various childhood psychiatric disorders including childhood-onset schizophrenia, attention-deficit/hyperactivity disorder, developmental dyslexia, Tourette's syndrome, and bipolar disorder.

CONCLUSIONS

Advances in imaging techniques have enhanced our understanding of normal developmental trajectories in the brain, which may improve insight into the abnormal patterns of development in various childhood psychiatric disorders.

Pubertal maturation modifies the regulation of insulin-like growth factor-I receptor signaling by estradiol in the rat prefrontal cortex

The transition from adolescence to adulthood is accompanied by substantial plastic modifications in the cerebral cortex, including changes in the growth and retraction of neuronal processes and in the rate of synaptic formation and neuronal loss. Some of these plastic changes are prevented in female rats by prepubertal ovariectomy. The ovarian hormone estradiol modulates neuronal differentiation and survival and these effects are in part mediated by the interaction with insulin-like growth factor-I (IGF-I). In this study, we have explored whether the activation by estradiol of some components of IGF-I receptor signaling is altered in the prefrontal cortex during puberty. Estradiol administration to rats ovariectomized after puberty resulted, 24 h after the hormonal administration, in a sustained phosphorylation of Akt and glycogen synthase kinase 3 beta in the prefrontal cortex. However, this hormonal effect was not observed in animals ovariectomized before puberty. These findings suggest that during pubertal maturation there is a programming by ovarian hormones of the future regulatory actions of estradiol on IGF-I receptor signaling in the prefrontal cortex. The modification in the regulation of IGF-I receptor signaling by estradiol during pubertal maturation may have implications for the developmental changes occurring in the prefrontal cortex in the transition from adolescence to adulthood.

Reading impairment in a patient with missing arcuate fasciculus

We describe the case of a child ("S") who was treated with radiation therapy at age 5 for a recurrent malignant brain tumor. Radiation successfully abolished the tumor but caused radiation-induced tissue necrosis, primarily affecting cerebral white matter. S was introduced to us at age 15 because of her profound dyslexia. We assessed cognitive abilities and performed diffusion tensor imaging (DTI) to measure cerebral white matter pathways. Diffuse white matter differences were evident in T1-weighted, T2-weighted, diffusion anisotropy, and mean diffusivity measures in S compared to a group of 28 normal female controls. In addition, we found specific white matter pathway deficits by comparing tensor-orientation directions in S's brain with those of the control brains. While her principal diffusion direction maps appeared consistent with those of controls over most of the brain, there were tensor-orientation abnormalities in the fiber tracts that form the superior longitudinal fasciculus (SLF) in both hemispheres. Tractography analysis indicated that the left and right arcuate fasciculus (AF), as well as other tracts within the SLF, were missing in S. Other major white matter tracts, such as the corticospinal and inferior occipitofrontal pathways, were intact. Functional MRI measurements indicated left-hemisphere dominance for language with a normal activation pattern. Despite the left AF abnormality, S had preserved oral language with average sentence repetition skills. In addition to profound dyslexia, S exhibited visuospatial, calculation, and rapid naming deficits and was impaired in both auditory and spatial working memory. We propose that the reading and visuospatial deficits were due to the abnormal left and right SLF pathways, respectively. These results advance our understanding of the functional significance of the SLF and are the first to link radiation necrosis with selective damage to a specific set of fiber tracts.

Sex differences in angiotensin signaling in bulbospinal neurons in the rat rostral ventrolateral medulla

Sex differences may play a significant role in determining the risk of hypertension. Bulbospinal neurons in the rostral ventrolateral medulla (RVLM) are involved in the tonic regulation of arterial pressure and participate in the central mechanisms of hypertension. Angiotensin II (ANG II) acting on angiotensin type 1 (AT(1)) receptors in RVLM neurons is implicated in the development of hypertension by activating NADPH oxidase and producing reactive oxygen species (ROS). Therefore, we analyzed RVLM bulbospinal neurons to determine whether there are sex differences in: 1) immunolabeling for AT(1) receptors and the key NADPH oxidase subunit p47 using dual-label immunoelectron microscopy, and 2) the effects of ANG II on ROS production and Ca(2+) currents using, respectively, hydroethidine fluoromicrography and patch-clamping. In tyrosine hydroxylase-positive RVLM neurons, female rats displayed significantly more AT(1) receptor immunoreactivity and less p47 immunoreactivity than male rats (P < 0.05). Although ANG II (100 nM) induced comparable ROS production in dissociated RVLM bulbospinal neurons of female and male rats (P > 0.05), an effect mediated by AT(1) receptors and NADPH oxidase, it triggered significantly larger dihydropyridine-sensitive long-lasting (L-type) Ca(2+) currents in female RVLM neurons (P < 0.05). These observations suggest that an increase in AT(1) receptors in female RVLM neurons is counterbalanced by a reduction in p47 levels, such that ANG II-induced ROS production does not differ between females and males. Since the Ca(2+) current activator Bay K 8644 induced larger Ca(2+) currents in females than in male RVLM neurons, increased ANG II-induced L-type Ca(2+) currents in females may result from sex differences in calcium channel densities or dynamics.

Sex differences in brain developing in the presence or absence of gonads

Brain sexual differentiation results from the interaction of genetic and hormonal influences. This study used a unique agonadal mouse model to determine relative contributions of genetic and gonadal hormone influences in the differentiation of selected brain regions. SF-1 knockout (SF-1 KO) mice are born without gonads and adrenal glands and are not exposed to endogenous sex steroids during fetal/neonatal development. Consequently, male and female SF-1 KO mice are born with female external genitalia and if left on their own, die shortly after birth due to adrenal insufficiency. In this study, SF-1 KO mice were rescued by neonatal adrenal transplantation to examine their brain morphology in adult life. To determine potential brain loci that might mediate functional sex differences, we examined the area and distribution of immunoreactive calbindin and neuronal nitric oxide synthase in the preoptic area (POA) and ventromedial nucleus of the hypothalamus, two areas previously reported to be sexually dimorphic in the mammalian brain. A sex difference in the positioning of cells containing immunoreactive calbindin in a group within the POA was clearly gonad dependent based on the elimination of the sex difference in SF-1 KO mice. Several other differences in the area of ventromedial hypothalamus and in POA were maintained in male and female SF-1 KO mice, suggesting gonad-independent genetic influences on sexually dimorphic brain development.

Influence of ovarian hormones on development of ingestive responding to alterations in fatty acid oxidation in female rats

Adult male rats have been demonstrated to increase food intake in response to administration of drugs that interfere with oxidation of fatty acids (e.g. methyl palmoxirate and mercaptoacetate [MA]), effects that are larger in animals maintained on a high-fat diet. In contrast, while administration of MA has been reported to stimulate food intake in pre-pubertal female rats, food intake is not stimulated by MA in adult female rats. Instead, administration of MA to adult females results in changes in reproductive behavior and physiology. The present experiments were designed to examine the effects of administration of MA on food intake in adult female rats. The results demonstrated that, as previously reported, food intake was stimulated by MA in adult male rats on low-fat and high-fat diets, but food intake was not stimulated by MA in gonadally-intact adult female rats on either low-fat or high-fat diet. Further, MA did not stimulate food intake in female rats ovariectomized as adults. However, when females were ovariectomized prior to the onset of puberty (postnatal day 25-28), food intake was stimulated by administration of MA in adulthood. Finally, cyclic injections of 17-beta-estradiol benzoate given to females ovariectomized prior to the onset of puberty abolished the stimulatory effects of MA on food intake in adult females. Taken together, the data suggest that exposure to estrogens during the time of puberty in female rats can persistently alter adult ingestive responding to signals related to changes in energy utilization.

Stress and the hypothalamic pituitary adrenal axis in the developmental course of schizophrenia

Diathesis-stress models of schizophrenia and other psychotic disorders have dominated theorizing about etiology for over three decades. More recently, with advances in our understanding of the biological processes mediating the effects of stress, these models have incorporated mechanisms to account for the adverse impact of stress on brain function. This review examines recent scientific findings on the role of the hypothalamic-pituitary-adrenal (HPA) axis, one of the primary neural systems triggered by stress exposure, in the expression of vulnerability for schizophrenia. The results indicate that psychotic disorders are associated with elevated baseline and challenge-induced HPA activity, that antipsychotic medications reduce HPA activation, and that agents that augment stress hormone (cortisol) release exacerbate psychotic symptoms. The cumulative findings are discussed in light of a neural diathesis-stress model that postulates that cortisol has the potential to increase activity of dopamine pathways that have been implicated in schizophrenia and other psychotic disorders.

Sex differences and the impact of steroid hormones on the developing human brain

Little is known about the hormonal effects of puberty on the anatomy of the developing human brain. In a voxel-based morphometry study, sex-related differences in gray matter (GM) volume were examined in 46 subjects aged 8-15 years. Males had larger GM volumes in the left amygdala, whereas females had larger right striatal and bilateral hippocampal GM volumes than males. Sexually dimorphic areas were related to Tanner stages (TS) of pubertal development and to circulating level of steroid hormones in a subsample of 30 subjects. Regardless of sex, amygdala and hippocampal volumes varied as a function of TS and were associated with circulating testosterone (TEST) levels. By contrast, striatal GM volumes were unrelated to pubertal development and circulating steroid hormones. Whole-brain regression analyses revealed positive associations between circulating estrogen levels and parahippocampal GM volumes as well as between TEST levels and diencephalic brain structures. In addition, a negative association was found between circulating TEST and left parietal GM volumes. These data suggest that GM development in certain brain regions is associated with sexual maturation and that pubertal hormones might have organizational effects on the developing human brain.

Juvenile male rats display lower cortical metabolic capacity than females

The juvenile brain undergoes marked maturational changes accompanied by major sex hormone changes. In particular, sex differences in neural substrates could underlie male-specific dysfunction in behavioral responses related to the prefrontal cortex. Sex differences in regional metabolic capacity of the cerebral cortex were investigated in juvenile Sprague-Dawley rats. At 6 weeks of age the brains were processed for quantitative histochemistry of cytochrome oxidase, a rate-limiting enzyme in cellular respiration, which is an index of brain metabolic capacity. Quantitative image analysis revealed a main effect of sex with males displaying lower regional metabolic capacity than females in the dorsolateral and orbital prefrontal cortex and in the posterior parietal cortex. In addition, males separated for 6 h/day from their mothers as pups showed greater ambulatory behavior in the novel open field and higher metabolism in the posterior parietal cortex relative to males separated for 15 min/day. This is the first study to show sex differences in brain metabolic capacity in regions such as the prefrontal cortex that may be hypometabolic in juvenile males relative to females.

Steroid-induced sexual differentiation of the developing brain: multiple pathways, one goal

Hormone exposure, including testosterone and its metabolite estradiol, induces a myriad of effects during a critical period of brain development that are necessary for brain sexual differentiation. Nuclear volume, neuronal morphology, and astrocyte complexity are examples of the wide range of effects by which testosterone and estradiol can induce permanent changes in the function of neurons for the purpose of reproduction in adulthood. This review will examine the multitude of mechanisms by which steroid hormones induce these permanent changes in brain structure and function. Elucidating how steroids alter brain development sheds light on how individual variation in neuronal phenotype is established during a critical period.

Females do not express learned helplessness like males do

Women are more likely than men to suffer from stress-related mental disorders, such as depression. In the present experiments, we identified sex differences in one of the most common animal models of depression, that of learned helplessness. Male and female rats were trained to escape a mild footshock each day for 7 days (controllable stress). Each rat was yoked to another rat that could not escape (uncontrollable stress), but was exposed to the same amount of shock. One day later, all stressed rats and unstressed controls were tested on a more difficult escape task in a different context. Most males exposed to uncontrollable stress did not learn to escape and were therefore helpless. In contrast, most females did learn to escape on the more difficult escape task, irrespective of whether they had been exposed to controllable or uncontrollable stress. The sex differences in helplessness behavior were not dependent on the presence of sex hormones in adulthood, because neither ovariectomy of females nor castration of males abolished them. The absence of helplessness in females was neither dependent on organizational effects of testosterone during the day of birth, because masculinized females did not express helplessness as adults. Thus, sex differences in helplessness behavior are independent of gonadal hormones in adulthood and testosterone exposure during perinatal development. Learned helplessness may not constitute a valid model for depressive behavior in women, at least as reflected by the response of female rats to operant conditioning procedures after stressful experience.

Completed suicide in childhood

Suicide in children and young adolescents up to 14 years of age has increased in many countries, warranting research and clinical awareness. International reported suicide rates per 100,000 in this young population vary between 3.1 and 0 (mean rate worldwide, approximately 0.6/100.000; male-female ratio, 2:1). Suicide occurs only in vulnerable children; this vulnerability begins with parental mood disorder and impulsive aggression, and family history of suicide. Childhood affective and disruptive disorders and abuse are the most often reported psychiatric risk factors. Suicide becomes increasingly common after puberty, most probably because of pubertal onset of depression and substance abuse, which substantially aggravate suicide risk. Biologic findings are scarce; however, serotonergic dysfunction is assumed. The most common precipitants are school and family problems and may include actual/anticipated transitions in these environments. Suicides in children and young adolescents up to 14 years of age often follow a brief period of stress. Cognitive immaturity/misjudgment, age-related impulsivity, and availability of suicide methods play an important role. Psychologic autopsy studies that focus on suicides in this age group are needed.

Environmental enrichment during adolescence regulates gene expression in the striatum of mice

We have previously shown that environmental enrichment decreases the activating and rewarding effects of the psychostimulant cocaine and increases resistance to the neurotoxic effect of the Parkinson-inducing drug MPTP. These effects were accompanied by an increase in the striatal expression of the neurotrophin BDNF, an increase in the striatal levels of delta-Fos B and by a decrease in striatal levels of the dopamine transporter, the main molecular target for cocaine and MPTP. Here, we used cDNA arrays to investigate the effects of rearing mice in enriched environments from weaning to adulthood on the profile of expression of genes in the striatum focusing on genes involved in intracellular signalling and functioning. We found that mice reared in an enriched environment show several alterations in the levels of mRNA coding for proteins involved in cell proliferation, cell differentiation, signal transduction, transcription and translation, cell structure and metabolism. Several of these findings were further confirmed by real-time quantitative PCR and, in the case of protein kinase C lambda, also by western blot. These findings are the first description of alterations in striatal gene expression by an enriched environment. The striatal gene expression regulation by environment that we report here may play a role in the resistance to the effects of drugs of abuse and dopaminergic neurotoxins previously reported.

Adolescents and androgens, receptors and rewards

Adolescence is associated with increases in pleasure-seeking behaviors, which, in turn, are shaped by the pubertal activation of the hypothalamo-pituitary-gonadal axis. In animal models of naturally rewarding behaviors, such as sex, testicular androgens contribute to the development and expression of the behavior in males. To effect behavioral maturation, the brain undergoes significant remodeling during adolescence, and many of the changes are likewise sensitive to androgens, presumably acting through androgen receptors (AR). Given the delicate interaction of gonadal hormones and brain development, it is no surprise that disruption of hormone levels during this sensitive period significantly alters adolescent and adult behaviors. In male hamsters, exposure to testosterone during adolescence is required for normal expression of adult sexual behavior. Males deprived of androgens during puberty display sustained deficits in mating. Conversely, androgens alone are not sufficient to induce mating in prepubertal males, even though brain AR are present before puberty. In this context, wide-spread use of anabolic-androgenic steroids (AAS) during adolescence is a significant concern. AAS abuse has the potential to alter both the timing and the levels of androgens in adolescent males. In hamsters, adolescent AAS exposure increases aggression, and causes lasting changes in neurotransmitter systems. In addition, AAS are themselves reinforcing, as demonstrated by self-administration of testosterone and other AAS. However, recent evidence suggests that the reinforcing effects of androgens may not require classical AR. Therefore, further examination of interactions between androgens and rewarding behaviors in the adolescent brain is required for a better understanding of AAS abuse.

Differences in endocrine parameters and psychopathology in girls with premature adrenarche versus on-time adrenarche

Girls with premature adrenarche (PA) are at risk for multiple problems related to exaggerated androgen synthesis. Whether PA carries a risk of psychopathology remains unknown. This study examined group differences in: (a) anthropometric and endocrine parameters, and (b) mood and behavior problems, in 6-8 year-old girls with PA (n = 40) compared to on-time adrenarche girls (n = 36). PA girls were taller (p < or =0.05) and heavier (p < or =0.01) than the on-time adrenarche girls but body mass index showed no difference. PA girls had significantly (p <0.05) higher adrenal androgen and testosterone concentrations but not cortisol or leptin. PA girls also had significantly more oppositional defiant disorder, and higher symptom counts reflecting anxiety, mood or disruptive behavior disorders. PA girls may be more vulnerable to psychopathology than on-time adrenarche girls. The challenge of future studies is to determine which PA girls are at risk for psychopathology and which are more resilient.

Acquisition and maintenance of cocaine self-administration in adolescent rats: effects of sex and gonadal hormones

RATIONALE

Previous work has shown that adult female rats are more sensitive than adult male rats to the reinforcing effects of cocaine, an effect that appears to be due, at least in part, to ovarian hormones.

OBJECTIVE

In this study, we examine sex differences in cocaine self-administration during adolescence, a period of marked hormonal change.

MATERIALS AND METHODS

Adolescent male and female Sprague-Dawley rats were trained to self-administer cocaine (0.75 mg/kg per infusion) under a fixed ratio 1 schedule (i.e., each response was reinforced by an infusion of cocaine) beginning on postnatal day 30. After acquisition, responding was assessed under a progressive-ratio schedule until postnatal day 50 with blood sampling occurring before the first five sessions to determine the relationship between gonadal hormones (i.e., estradiol, progesterone, and testosterone) and motivation for cocaine. Estrous cycle phase was monitored throughout the study. Separate groups of adolescent male and female rats were compared on the acquisition of and progressive-ratio responding for sucrose reinforcement.

RESULTS

Females acquired cocaine self-administration more readily than did males, and a greater percentage of females acquired self-administration. Under progressive-ratio testing conditions, adolescent females responded at higher levels than adolescent males to obtain cocaine infusions, and in females, responding was positively associated with levels of estradiol and greatest during estrus. No sex differences were observed for sucrose reinforcement.

CONCLUSION

These findings suggest that sex differences are relevant during adolescence with evidence implicating circulating estradiol level as a factor that contributes to the enhanced sensitivity in females to the reinforcing effects of cocaine.

A Social Neuroscience Perspective on Adolescent Risk-Taking

This article proposes a framework for theory and research on risk-taking that is informed by developmental neuroscience. Two fundamental questions motivate this review. First, why does risk-taking increase between childhood and adolescence? Second, why does risk-taking decline between adolescence and adulthood? Risk-taking increases between childhood and adolescence as a result of changes around the time of puberty in the brain's socio-emotional system leading to increased reward-seeking, especially in the presence of peers, fueled mainly by a dramatic remodeling of the brain's dopaminergic system. Risk-taking declines between adolescence and adulthood because of changes in the brain's cognitive control system - changes which improve individuals' capacity for self-regulation. These changes occur across adolescence and young adulthood and are seen in structural and functional changes within the prefrontal cortex and its connections to other brain regions. The differing timetables of these changes make mid-adolescence a time of heightened vulnerability to risky and reckless behavior.

Anabolic androgenic steroids differentially affect social behaviors in adolescent and adult male Syrian hamsters

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone used by over half a million adolescents in the United States for their tissue-building potency and performance-enhancing effects. AAS also affect behavior, including reports of heightened aggression and changes in sexual libido. The expression of sexual and aggressive behaviors is a function of complex interactions among hormones, social context, and the brain, which is extensively remodeled during adolescence. Thus, AAS may have different consequences on behavior during adolescence and adulthood. Using a rodent model, these studies directly compared the effects of AAS on the expression of male sexual and aggressive behaviors in adolescents and adults. Male Syrian hamsters were injected daily for 14 days with either vehicle or an AAS cocktail containing testosterone cypionate (2 mg/kg), nandrolone decanoate (2 mg/kg), and boldenone undecylenate (1 mg/kg), either during adolescence (27-41 days of age) or in adulthood (63-77 days of age). The day after the last injection, males were tested for either sexual behavior with a receptive female or agonistic behavior with a male intruder. Adolescent males treated with AAS showed significant increases in sexual and aggressive behaviors relative to vehicle-treated adolescents. In contrast, AAS-treated adults showed significantly lower levels of sexual behavior compared with vehicle-treated adults and did not show heightened aggression. Thus, adolescents, but not adults, displayed significantly higher behavioral responses to AAS, suggesting that the still-developing adolescent brain is more vulnerable than the adult brain to the adverse consequences of AAS on the nervous system and behavior.

An association of early puberty with disordered eating and anxiety in a population of undergraduate women and men

Eating and anxiety disorders are more prevalent in females, increase during adolescence, and are associated with early pubertal development. This study examined whether timing of puberty onset is associated with disordered eating and anxiety in a large sample of postpubertal male and female undergraduate students. Self-report questionnaires assessed timing of puberty, disordered eating, anxiety, alcohol use, personality, and sensation seeking. Females scored significantly higher on measures of disordered eating (binge eating, dietary restraint, eating concerns, and weight and shape concerns) and anxiety (state and trait anxiety) than did males. In addition, early maturing women and men scored significantly higher on measures of disordered eating and anxiety than on time or late maturing women and men. Measures of alcohol use, sensation seeking, and personality characteristics differed in males and females but did not vary with pubertal timing. Findings suggest that early puberty is associated with disordered eating and anxiety, and this association may be due to an organizational effect of pubertal hormones. Despite important differences in body fat composition, both males and females experiencing early puberty had an increased incidence of disordered eating. The fact that early puberty was associated with increased eating and anxiety symptoms in both sexes suggests that puberty may influence these symptoms through both biological and psychosocial mechanisms.

Sex differences in the effects of two stress paradigms on dopaminergic neurotransmission

Sex differences in behavioral and neurobiological responses to stress are considered to modulate the prevalence of some psychiatric disorders, including major depression. In the present study, we compared dopaminergic neurotransmission and behavior in response to two different stress paradigms, the Forced Swim Test (FST) and the Chronic Mild Stress (CMS). Male and female rats were subjected to one session of swim stress for two consecutive days (FST) or to a variety of mild stressors alternating for six weeks (CMS). Subsequently, the tissue levels of dopamine (DA) and its metabolites (HVA and DOPAC) in the hippocampus, the hypothalamus, the prefrontal cortex and the striatum were measured using high-performance liquid chromatography (HPLC). The ratios HVA/DA and DOPAC/DA were also calculated as indices of the dopaminergic activity. Results from the FST determined that males exhibited lower immobility, higher climbing duration and increased dopaminergic activity in the prefrontal cortex and the hippocampus compared to females. CMS induced alterations in sucrose intake in both sexes, while it only decreased dopaminergic activity in the prefrontal cortex of females. These findings show that FST and CMS have different effects on the dopaminergic activity of discrete brain regions depending on the sex of the animal. These data support the growing evidence that females display a differential response and adaptation to stress than males.

Identifying early behavioral and molecular markers of future stress sensitivity

Puberty is a plastic period of neurological development when critical maturation of stress pathways occurs. Abnormal maturation may be predictive of future stress sensitivity and affective disorder risk. To identify potential early markers of stress-related disease predisposition, we examined physiological and behavioral stress responses in male pubertal mice compared with adults, using a genetic model of elevated stress sensitivity, CRF receptor-2 (CRFR2)-deficient mice. Juvenile mice of both genotypes exhibited greater basal and stress-induced corticosterone levels than adult mice, indicating that overall hypothalamic-pituitary-adrenal axis sensitivity diminishes in adulthood. However, juvenile CRFR2-deficient mice displayed a delayed stress recovery typical of adults of this genotype, suggesting an early marker of stress sensitivity. The adult phenotype of reduced hippocampal glucocorticoid receptor expression in these sensitive mice was also detected during puberty. This reduction may account for an impaired hypothalamic-pituitary-adrenal axis negative feedback and as such be an early indicator of a stress-sensitive phenotype. Examination of behavioral responses to stress revealed that CRFR2-deficient mice show exaggerated postpubertal maturation. Although wild-type mice did not alter their burying response to stress-provoking marbles after puberty, CRFR2-deficient mice showed a dramatic increase in burying behavior. We conclude that identification of abnormal pubertal stress pathway maturation may be predictive of adult heightened stress sensitivity and future susceptibility to stress-related affective disorders.

An androgen-dependent sexual dimorphism visible at puberty in the rat hypothalamus

Morphological studies in rodents have well documented the masculinization of the perinatal brain by estradiol derived from aromatized testosterone, and the resulting irreversible quantitative sex-differences generated in cell numbers or expression of chemical phenotypes. Here, using immunohistochemistry, we explored how this applies to the postnatal development and masculinization of the neurokinin B (NKB)-containing system of the arcuate nucleus/median eminence complex (ARC/ME). In adult rats, NKB-immunoreactive neurons exhibit an unusual, qualitative sexual dimorphism of their ventral axonal projections: to the neuropil in females, to capillary vessels in males. In adults, there was no sex-difference in the numbers of NKB-immunoreactive perikarya or capillary vessels in the ARC/ME, suggesting that this sexual dimorphism cannot be explained by the existence of supernumerary structures. At birth (day 0) the NKB system was immature in both sexes, and while its adult features emerged progressively until puberty in females, they did not develop before puberty (day 40) in males, revealing a sexual dimorphism only late postnatally. When males were orchidectomized at day 30, the masculine distribution of NKB-immunoreactive axons expected at day 40 was not seen, while it was apparent after chronic treatment with testosterone or dihydrotestosterone, suggesting a testicular masculinizing action via androgen receptors at puberty. Moreover in these prepubertal-orchidectomized males, the distribution of NKB-immunoreactive axons was surprisingly feminized by chronic estradiol alone, suggesting that NKB neurons are not irreversibly programmed before puberty. Last, in adult females, the distribution of NKB-immunoreactive axons was feminine 30 days after ovariectomy, and it was masculinized after concurrent chronic dihydrotestosterone, suggesting that NKB neurons remain responsive to androgens late in reproductive life. Thus, the sexual differentiation of the hypothalamus proceeds well beyond the perinatal period and includes the epigenetic action of non-aromatizable androgens upon subsets of neurons that have retained bipotent features.

Impact of neonatal hypothyroidism on reproduction in the male hamster, Mesocricetus auratus

Thyroid hormones play an important role in brain development. In the present study, we examined the influence of transient postnatal hypothyroidism on reproductive neuroendocrine and behavioral outcomes in the male Syrian (golden) hamster. Hamster pups were rendered hypothyroid following exposure to the goitrogen, 6-n-propyl-2-thiouracil (PTU), between postnatal (PN) day 0 (birth) and PN25 (weaning). By 15 days after cessation of PTU, exposure (PN40) serum thyroxine levels had returned to control levels. The testes of treated males were approximately 30% heavier than controls and daily sperm production was increased by 73%. Immunocytochemistry for GnRH revealed that the total number of GnRH neurons did not vary between groups; however, a shift in the distribution of GnRH neurons was observed in treated males such that more GnRH immunoreactive neurons were found in the caudal portion of their normal distribution. The shift in GnRH distribution was associated with a significant reduction (40-50%) in pituitary gonadotropin secretion. Behaviorally, treated males took significantly longer to investigate the anogenital region and then mount a receptive female. A corresponding reduction in the total number of anogenital investigations and mounts was observed. This difference between treated males and controls was reduced, but not eliminated, over successive trials and by the third trial the number of intromission was similar between treated and control males. We conclude that the full complement of adult reproductive functions observed in the male golden hamster requires thyroid hormones during the early postnatal period. The severity of the effects induced by early hypothyroidism in this species varies from transient to permanent, depending on the endpoint.

HPA function in adolescence: Role of sex hormones in its regulation and the enduring consequences of exposure to stressors

The hypothalamic-pituitary-adrenal (HPA) axis is one of the physiological systems involved in coping with stressors. There are functional shifts in the HPA axis and its regulation by sex hormones over the lifespan that allow the animal to meet the challenges of the internal and external environment that are specific to each stage of development. Sex differences in HPA function emerge over adolescence, a phenomenon reflecting the concomitant initiation of regulatory effects of sex hormones. The focus of this review is recent research on differences between adolescents and adults in HPA function and the enduring effects of exposure to stressors in adolescence. During adolescence, HPA function is characterized by a prolonged activation in response to stressors compared to adulthood, which may render ongoing development of the brain vulnerable. Although research has been scarce, there is a growing evidence that exposure to stressors in adolescence may alter behavioural responses to drugs and cognitive performance in adulthood. However, the effects reported appear to be stressor-specific and sex-specific. Such research may contribute toward understanding the increased risk for drug abuse and psychopathology that occurs over adolescence in people.

Partner preference in male hamsters: steroids, sexual experience and chemosensory cues

This study investigated the effects of gonadal steroids on sexual motivation in male Syrian hamsters, using partner preference as a model. Male hamsters were assigned to 5 groups: control (n=4), Intact-->Orchx (n=8), Orchx-->Orchx+T (n=7), olfactory bulbectomy (BulbX, n=5), and vomeronasal organ lesion (VnoX, n=8). Each male was tested for partner preference before and after sexual experience. Unlike rats, sexually-inexperienced gonad-intact male hamsters preferred the receptive female to a stimulus male. However, sexual experience did not enhance preference for the stimulus female. Castration (Orchx) reduced sexual motivation: Orchx males showed no significant preference for the stimulus female. Subsequently, intact males were castrated (Intact-->Orchx) and Orchx males received a testosterone implant (Orchx-->Orchx+T) to determine the time course of gonadal hormones on partner preference and mating behavior. Partner preference changed significantly in both groups within 6 weeks. In Intact-->Orchx males, preference for the stimulus female decreased while Orchx-->Orchx+T males increased their preference for the stimulus female. However, significant changes in mating behavior preceded the alterations in partner preference. Chemosensory cues are also important for partner preference. After BulbX, preference for the stimulus female significantly decreased. However, VnoX failed to block partner preference. These results show that partner preference may be even more dependent on testosterone than is sexual behavior. Furthermore, while chemosensory cues are essential for sexual motivation, the vomeronasal organ is not required for partner preference.

Age-dependent change in exploratory behavior of male rats following exposure to threat stimulus: Effect of juvenile experience

The ontogeny of exploratory behavior depending on the intensity of threat in a modified open-field was investigated in male rats aged 40, 65, and 130 days, by comparing with less threatening condition with no shock and more threatening condition where they were exposed to mild electric shock. The number of crossings in a dim peripheral alley was counted as the level of activity. The total duration of stay in the central area was measured as the level of exploration. The number of entries and stretch-attend postures into a bright center square were measured as active exploratory behavior and the risk assessment behavior, respectively. When exposed to mild shock prior to the test, 40-day-old rats decreased these exploratory behaviors, while 65- and 130-day-old rats increased active exploratory behavior (Experiment 1). A lower level of exploratory behavior following a mild shock was found in 65 and 130-day-old rats isolated during the juvenile stage, but not in rats isolated after puberty (Experiment 2). These findings suggest that the direction of changes in exploratory behavior of male rats following an increase in potential danger showed ontogenetic transition, which is mediated by social experiences as juveniles, but not as adults. This transition may be associated with the emergence of active exploratory behavior during the juvenile stage, which is activated by social interaction.

Estrogenic chemicals at puberty change ERα in the hypothalamus of male and female rats

The effects of two environmental endocrine disruptors, the synthetic pharmaceutical estrogen 17-ethinylestradiol (EE) and bisphenol-A (BPA), were analysed in male and female rats in a very sensitive developmental period, puberty. Immunohistochemistry was used to evaluate changes in the number of cells expressing estrogen receptors (ER-alpha) in the arcuate nucleus (ARC), ventromedial nucleus (VMH) and medial preoptic area (MPA) of the hypothalamus. Animals were treated during early puberty, from PND 23 to PND 30, with EE and BPA given orally every day. They were then sacrificed and perfused on PND 37 or PND 90, and blood and brains were collected for hormonal determination (testosterone and estradiol) and immunohistochemistry (estrogen receptors, ER). At PND 37, ER-labelled neurons were higher in males than in females in the ARC and MPA. EE and BPA increased ER-labelled neurons in the ARC and MPA. At PND 90, females showed higher ER-labelled neurons in the VMH. EE and BPA increased ER-labelled neurons in the MPA in females. EE increased testosterone in males at PND 37 and estradiol in females at PND 90. These results indicate the ability of estrogenic chemicals to change the reproductive neural circuits during puberty in male and female rats.

Puberty, hormones, and sex differences in alcohol abuse and dependence

Sex differences in patterns of drinking and rates of alcohol abuse and dependence begin to emerge during the transition from late puberty to young adulthood. Increases in pubertal hormones, including gonadal and stress hormones, are a prominent developmental feature of adolescence and could contribute to the progression of sex differences in alcohol drinking patterns during puberty. This paper reviews experimental and correlational studies of gonadal and stress-related hormone changes and their effects on alcohol drinking and other associated actions of alcohol. Mechanisms are suggested by which reproductive hormones and stress-related hormones may modulate neural circuits within the brain reward system to produce sex differences in alcohol drinking patterns and vulnerability to alcohol abuse and dependence which become apparent during the late pubertal period.

The alcoholism generator

Alcohol exposure largely affects 3 populations: fetuses, adolescents, and adults. These 3 developmental stages are inextricably intertwined such that elevated alcohol exposure at any time increases the probability of exposure at the others. This circular interdependency is called the alcoholism generator. Furthermore, exposure to large amounts of alcohol at these 3 times can cause cognitive dysfunction, largely through mechanisms of alcohol-induced perturbations in neurogenesis and synaptogenesis. Breaking this cycle is key to reducing problem alcohol drinking and the associated sequelae.

Pubertal exposure to estrogenic chemicals affects behavior in juvenile and adult male rats

In this paper, we tested the hypothesis that exposure to estrogens of different source and estrogenic potency at early puberty could affect the development of socio-sexual behavior in the male rat. Puberty is regarded as a second stage of the ontogenetic period, in the sexual maturation of mammals, particularly sensitive to gonadal hormone milieu. We treated animals orally, from postnatal day 23 to 30, with an environmentally compatible dose of bisphenol A (BPA, 40 microg/kg/day) and with a dosage of ethinylestradiol (EE, 0.4 microg/kg/day) comparable to the human oral contraceptives. Exposure to EE altered the temporal pattern of male sexual activity, reducing performance, in the adult animals; slight modifications, in the same direction, were observed with BPA. Short-term behavioral effects were observed in the treated animals, both with BPA and EE: the exploratory drive, directed to a stimulus object and to the environment, as well as to conspecifics, was reduced in the juveniles. Modifications in the circulating T levels were observed after treatments: T was reduced in the juveniles, both with BPA and EE. The decrement persisted in the adult animals but reached significance only in the BPA group. On the whole, effects of pubertal exposure on behavior are more marked with EE than BPA. This can be due to the much higher estrogenic potency of EE; the direction of the behavioral effects of BPA, compared with EE, is however indicative of an estrogenic mechanism.

Aggression, dominance, and affiliation: Their relationships with androgen levels and intelligence in 5-year-old children

This study explores the potential relationship between social behavior (aggression, dominance, and affiliation) and testosterone, androstenedione, and DHEA measurements in 5-year-old children while also analyzing the moderating effect of IQ on the hormone-behavior relationship. 129 healthy normal Iberian children (60 boys and 69 girls) were videotaped in free play interactions in the school playground. Their behavior was then evaluated with particular emphasis on aggression, government, and affiliation. Testosterone, androstenedione, and DHEA levels were measured using an enzyme immunoassay technique in saliva samples. A test (K-BIT) which provides an IQ measurement for children was also administered to subjects. The correlation analysis revealed a positive relationship between the behavioral factor of Provocation and androstenedione in boys, and a regression analysis indicated that this relationship was moderated in a positive direction by the subject's intelligence. In girls, we observed a positive relationship between testosterone and Affectivity, with this relationship being moderated in a negative direction by intelligence.