Gonadal hormones and sex differences in nonreproductive behaviors in rodents: organizational and activational influences

Methyl donor supplementation alters cognitive performance and motivation in female offspring from high-fat diet-fed dams

During gestation, fetal nutrition is entirely dependent on maternal diet. Maternal consumption of excess fat during pregnancy has been linked to an increased risk of neurologic disorders in offspring, including attention deficit/hyperactivity disorder, autism, and schizophrenia. In a mouse model, high-fat diet (HFD)-fed offspring have cognitive and executive function deficits as well as whole-genome DNA and promoter-specific hypomethylation in multiple brain regions. Dietary methyl donor supplementation during pregnancy or adulthood has been used to alter DNA methylation and behavior. Given that extensive brain development occurs during early postnatal life-particularly within the prefrontal cortex (PFC), a brain region critical for executive function-we examined whether early life methyl donor supplementation (e.g., during adolescence) could ameliorate executive function deficits observed in offspring that were exposed to maternal HFD. By using operant testing, progressive ratio, and the PFC-dependent 5-choice serial reaction timed task (5-CSRTT), we determined that F1 female offspring (B6D2F1/J) from HFD-fed dams have decreased motivation (decreased progressive ratio breakpoint) and require a longer stimulus length to complete the 5-CSRTT task successfully, whereas early life methyl donor supplementation increased motivation and shortened the minimum stimulus length required for a correct response in the 5-CSRTT. Of interest, we found that expression of 2 chemokines, CCL2 and CXCL10, correlated with the median stimulus length in the 5-CSRTT. Furthermore, we found that acute adult supplementation of methyl donors increased motivation in HFD-fed offspring and those who previously received supplementation with methyl donors. These data point to early life as a sensitive time during which dietary methyl donor supplementation can alter PFC-dependent cognitive behaviors.-McKee, S. E., Grissom, N. M., Herdt, C. T., Reyes, T. M. Methyl donor supplementation alters cognitive performance and motivation in female offspring from high-fat diet-fed dams.

Sexually Dimorphic Risk Mitigation Strategies in Rats

The scientific understanding of fear and anxiety-in both normal and pathological forms-is presently limited by a predominance of studies that use male animals and Pavlovian fear conditioning-centered paradigms that restrict and assess specific behaviors (e.g., freezing) over brief sampling periods and overlook the broader contributions of the spatiotemporal context to an animal's behavioral responses to threats. Here, we use a risky "closed economy" system, in which the need to acquire food and water and the need to avoid threats are simultaneously integrated into the lives of rats, to examine sex differences in mitigating threat risk while foraging. Rats lived for an extended period (∼2 months) in enlarged chambers that consisted of a safe, bedded nest and a risky foraging area where footshocks could be delivered unpredictably. We observed that male and female rats used different strategies for responding to the threat of footshock. Whereas male rats increased the size of meals consumed to reduce the overall time spent foraging, female rats sacrificed their metabolic needs in order to avoid shocks. Ovarian hormone fluctuations were shown to exert slight but reliable rhythmic effects on risky decision-making in gonadally intact female rats. However, this did not produce significant differences in approach-avoidance trade-offs between ovariectomized and intact female groups, suggesting that male-female sex differences are not due to the activational effects of gonadal hormones but, rather, are likely to be organized during early development.

Ibudilast attenuates expression of behavioral sensitization to cocaine in male and female rats

There are no FDA-approved pharmacotherapies for cocaine use disorder, indicating a need to identify novel reagents with therapeutic potential. Ibudilast is an anti-inflammatory glial attenuator and non-selective phosphodiesterase inhibitor currently undergoing clinical evaluations for methamphetamine, opiate, and alcohol abuse disorders. We previously showed that twice daily (b.i.d.) ibudilast reduces the development of methamphetamine sensitization in male mice. However, nothing is known about the ability of ibudilast to modulate the expression of sensitization that occurs after drug re-exposure during abstinence, effects on cocaine-mediated behaviors, or potentially sexually dimorphic effects. Male and female rats were administered cocaine for 7 days and expression of sensitization was assessed by cocaine challenge after 21 days abstinence. On test days, 15 mg/kg i. p. cocaine was evaluated, whereas 30 mg/kg was administered on intervening days. Lower test doses avoid competition of non-motor behaviors with locomotion. In all measures where sensitization was expressed, ibudilast (7.5 and 10 mg/kg, i. p., b. i.d. for 3 days and once on test day) reversed this behavior to levels seen after acute exposure, but not below. There were some intriguing sexually dimorphic effects that were not a function of estrous cycle. Specifically, distance travelled in the center of the test arena and rearing only sensitized in male rats, and ibudilast reversed these behaviors to levels seen after acute cocaine exposure. In females, center distance travelled was reduced below acute cocaine levels by 7.5 mg/kg ibudilast. Increased distance travelled in the center versus periphery is thought to model anxiolytic-like behavior due to increased predation risk. Taken together, these data suggest that the clinical evaluation of ibudilast could be extended to cocaine use disorder.

Early developmental bisphenol-A exposure sex-independently impairs spatial memory by remodeling hippocampal dendritic architecture and synaptic transmission in rats

Bisphenol-A (BPA, 4, 4'-isopropylidene-2-diphenol), a synthetic xenoestrogen that widely used in the production of polycarbonate plastics, has been reported to impair hippocampal development and function. Our previous study has shown that BPA exposure impairs Sprague-Dawley (SD) male hippocampal dendritic spine outgrowth. In this study, the sex-effect of chronic BPA exposure on spatial memory in SD male and female rats and the related synaptic mechanism were further investigated. We found that chronic BPA exposure impaired spatial memory in both SD male and female rats, suggesting a dysfunction of hippocampus without gender-specific effect. Further investigation indicated that BPA exposure causes significant impairment of dendrite and spine structure, manifested as decreased dendritic complexity, dendritic spine density and percentage of mushroom shaped spines in hippocampal CA1 and dentate gyrus (DG) neurons. Furthermore, a significant reduction in Arc expression was detected upon BPA exposure. Strikingly, BPA exposure significantly increased the mIPSC amplitude without altering the mEPSC amplitude or frequency, accompanied by increased GABAARβ2/3 on postsynaptic membrane in cultured CA1 neurons. In summary, our study indicated that Arc, together with the increased surface GABAARβ2/3, contributed to BPA induced spatial memory deficits, providing a novel molecular basis for BPA achieved brain impairment.

Chronic cannabinoid exposure produces lasting memory impairment and increased anxiety in adolescent but not adult rats

Although many studies have examined the acute behavioural effects of cannabinoids in rodents, few have examined the lasting effects of cannabinoids at different developmental ages. This study compared lasting effects of cannabinoid exposure occurring in adolescence to that occurring in early adulthood. Forty, 30-day old (adolescent) and 18, 56-day old (adult) female albino Wistar rats were injected with vehicle or incremental doses of the cannabinoid receptor agonist (-)- cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]- trans-4-(3-hydroxypropyl) cyclohexanol (CP 55,940) once per day for 21 consecutive days (150, 200 and 300 μg/kg i.p. for 3, 8 and 10 days, respectively). Following a 21-day drug-free period, working memory was assessed using an object recognition task. Locomotor activity was also measured in the object recognition apparatus via a ceiling-mounted passive infrared sensor. Three days later, anxiety was assessed using a social interaction test. In the object recognition task, significantly poorer working memory was observed in the adolescent but not adult CP 55,940-treated rats. Adolescent, but not adult CP 55,940-treated rats, also exhibited a significant decrease in social interaction with a novel conspecific. These results suggest that chronic exposure to a cannabinoid receptor agonist well after the immediate postnatal period, but before reaching sexual maturity, can lead to increased anxiety and a lasting impairment of working memory.

■ REVIEW : Stress and Sex Effects on Associative Learning: For Better or for Worse

It is clear that male and female animals have distinct cognitive capacities and emotional responses. For instance, exposure to a fearful and stressful event of restraint and intermittent tail-shocks impairs instru mental learning in male rats, but has minimal consequence in female rats. Conversely, exposure to a similar stressor facilitates classical conditioning in male rats and dramatically impairs conditioning in female rats. Many such sex differences in learning and responses to stress are attributable to the effects of sex hormones on brain morphology and physiology. Indeed, the stress-induced facilitation of classical conditioning in male rats is dependent on activation of the NMDA type of glutamate receptor in the amygdala, whereas the impaired conditioning in female rats is dependent on activational influences of the ovarian hormone estrogen. The role of estrogen and progesterone in the diametrically opposed effects of stress on learning are dis cussed, as are neuronal mechanisms that underlie sex differences in memory formation. NEUROSCIENTIST 4:353-364, 1998

Association of novelty-related behaviors and intravenous cocaine self-administration in Diversity Outbred mice

RATIONALE

The preference for and reaction to novelty are strongly associated with addiction to cocaine and other drugs. However, the genetic variants and molecular mechanisms underlying these phenomena remain largely unknown. Although the relationship between novelty- and addiction-related traits has been observed in rats, studies in mice have failed to demonstrate this association. New, genetically diverse, high-precision mouse populations including Diversity Outbred (DO) mice provide an opportunity to assess an expanded range of behavioral variation enabling detection of associations of novelty- and addiction-related traits in mice.

METHODS

To examine the relationship between novelty- and addiction-related traits, male (n = 51) and female (n = 47) DO mice were tested on open field exploration, hole board exploration, and novelty preference followed by intravenous cocaine self-administration (IVSA; ten 2-h sessions of fixed ratio 1 and one 6-h session of progressive ratio).

RESULTS

We observed high variation of cocaine IVSA in DO mice with 43 % reaching and 57 % not reaching conventional acquisition criteria. As a group, mice that did not reach these criteria still demonstrated significant lever discrimination. Mice experiencing catheter occlusion or other technical issues (n = 17) were excluded from the analysis. Novelty-related behaviors were positively associated with cocaine IVSA. Multivariate analysis of associations among novelty- and addiction-related traits revealed a large degree of shared variance (45 %).

CONCLUSIONS

Covariation among cocaine IVSA and novelty-related phenotypes in DO mice indicates that this relationship is amenable to genetic dissection. The high genetic precision and phenotypic diversity in the DO may facilitate discovery of previously undetectable mechanisms underlying predisposition to develop addiction disorders.

Endocrine-disrupting chemicals: elucidating our understanding of their role in sex and gender-relevant end points

Endocrine-disrupting chemicals (EDCs) are diverse and pervasive and may have significant consequence for health, including reproductive development and expression of sex-/gender-sensitive parameters. This review chapter discusses what is known about common EDCs and their effects on reproductively relevant end points. It is proposed that one way that EDCs may exert such effects is by altering steroid levels (androgens or 17-estradiol, E₂) and/or intracellular E₂ receptors (ERs) in the hypothalamus and/or hippocampus. Basic research findings that demonstrate developmentally sensitive end points to androgens and E₂ are provided. Furthermore, an approach is suggested to examine differences in EDCs that diverge in their actions at ERs to elucidate their role in sex-/gender-sensitive parameters.

Interaction between pre-weaning undernutrition and post-weaning environmental enrichment on somatic development and behaviour in male and female rats

Male and female rats were undernourished from birth to 30 days by restricting access to the lactating mother, and then fed ad libitum. At weaning, underfed and normally suckled controls were permanently housed either in pairs in standard cages or in groups of 10 in 1 m(3) cages containing ladders, ropes etc. Severe undernutrition during suckling followed by 4 months of refeeding, produced some changes in sexual behaviour in adult males (increased ejaculation frequency) but had no effect on behaviour in open field, dark preference or passive avoidance. Differential post-weaning environment produced significant differences in behaviour, irrespective of previous feeding conditions. Enriched animals were more active and exploratory. Females differed from males in the same direction as enriched from standard, and were more responsive to social and housing conditions.

Behavioural outcome in children with congenital adrenal hyperplasia: experience of a single centre

The aim of this study was to determine the behavioral outcome in children with CAH and to identify the risk factors that may influence it. Participants (aged 6-18 years) included 29 girls and 20 boys with CAH and unaffected siblings (25 girls and 17 boys). Psychological adjustment was assessed with parent reports on the Child Behavior Checklist (CBCL). Information about disease characteristics was obtained from medical records. Our study reveals that there was higher incidence of parent-reported problem of anxious/depressed and withdrawn/depressed behaviours, somatic complaints, social, thought, and attention problems, and rule-breaking, aggressive, internalizing, and externalizing behaviour among children with CAH compared to controls. The prevalence of internalizing behaviour problems was higher in CAH boys compared with that of controls. Psychosocial adjustment of girls with CAH was found to be similar to unaffected female controls and was within the normal population range. Family income may be associated with behavioral outcome. Glucocorticoid dose may reflect disease severity which may be associated with behavioral outcome. We conclude that internalizing behavioral problem was prevalent among boys with CAH reflecting maladaptive adjustment in coping with chronic illness. This highlighted the importance of psychological and social support for the patients and their families.

Inhibitory avoidance in CD1 mice: sex matters, as does the supplier

The purpose of the present work was to study possible differences in the learning of inhibitory avoidance (also called passive avoidance) in male and female CD1 mice acquired from three different suppliers, for which a one-trial step-through version of the paradigm was employed. Ninety-six mice from Charles River (France), Janvier (France) and Harlan (The Netherlands) laboratories were divided by sex and assigned to group C, J or H, respectively (n=16). The animals were tested in the training phase (foot-shock: 0.3mA, 5s) and again for avoidance (no foot-shock delivered) one week later. Inhibitory avoidance learning (test latencies significantly higher than training latencies) was observed in every one of the six groups of animals. The variable Supplier was statistically significant, showing better to worse avoidance in C, J and H mice (in that order). A post hoc analysis showed differences between groups C and H. Females tended to exhibit avoidance learning to a greater extent than males. Our results suggest that inhibitory avoidance learning in CD1 mice varies depending on the breeding facilities from which they originate, and that females should be included in inhibitory avoidance studies.

Evaluation of sensitivity, motor and pain thresholds across the menstrual cycle through medium-frequency transcutaneous electrical nerve stimulation

OBJECTIVES

The aim of this study was to identify variations in nervous thresholds in different phases of the menstrual cycle in eumenorrheic women and users of oral contraceptives.

METHOD

An observational study was performed including 56 volunteers, consisting of 30 eumenorrheic women who were non-users of oral contraceptives and 26 users of oral contraceptives. An electrical stimulator was employed to assess their nervous thresholds, with pulses applied at a fixed frequency of 2,500 Hz, modulated at 50 Hz, with phase variances of 20 μs, 50 μs and 100 μs. Sensitivity, motor and pain thresholds were evaluated during five menstrual cycle phases: phase 1 - menstrual, phase 2 - follicular, phase 3 - ovulatory, phase 4 - luteal and phase 5 - premenstrual.

RESULTS

The results indicated low sensitivity thresholds of 100 μs for non-users of oral contraceptives and 50 μs for oral contraceptive users in phase 5. Low motor thresholds of 20 μs, 50 μs and 100 μs were observed for non-users of oral contraceptives in phase 5, while that of oral contraceptive users was 100 μs. Finally, a low pain threshold of 100 μs was observed in phase 5, but only in the oral contraceptive group.

CONCLUSION

Nervous thresholds vary systematically across the phases of the menstrual cycle, with or without the use of oral contraceptives. These variations should be taken into account during research performed in women.

An update on the cognitive impact of clinically-used hormone therapies in the female rat: models, mazes, and mechanisms

In women, ovarian hormone loss associated with menopause has been related to cognitive decline. Hormone therapy (HT) may ameliorate some of these changes. Understanding the cognitive impact of female steroids, including estrogens, progestogens, and androgens, is key to discovering treatments that promote brain health in women. The preclinical literature has presented elegant and methodical experiments allowing a better understanding of parameters driving the cognitive consequences of ovarian hormone loss and HT. Animal models have been a valuable tool in this regard, and will be vital to future discoveries. Here, we provide an update on the literature evaluating the impact of female steroid hormones on cognition, and the putative mechanisms mediating these effects. We focus on preclinical work that was done with an eye toward clinical realities. Parameters that govern the cognitive efficacy of HT, from what we know thus far, include but are not limited to: type, dose, duration, and route of HT, age at HT initiation, timing of HT relative to ovarian hormone loss, memory type examined, menopause history, and hormone receptor status. Researchers have identified intricate relationships between some of these factors by studying their individual effects on cognition. As of late, there is increased focus on studying interactions between these variables as well as multiple hormone types when administered concomitantly. This is key to translating preclinical data to the clinic, wherein women typically have concurrent exposure to endogenous ovarian hormones as well as exogenous combination HTs, which include both estrogens and progestins. Gains in understanding the parameters of HT effects on cognition provide exciting novel avenues that can inform clinical treatments, eventually expanding the window of opportunity to optimally enhance cognition and brain health in aging women. This article is part of a Special Issue entitled Hormone Therapy.

Sex differences in novelty- and psychostimulant-induced behaviors of C57BL/6 mice

RATIONALE

Women are more sensitive than men to psychostimulants and progress from initial use to drug addiction more quickly. The mouse has been an under-utilized model to study sex differences in psychostimulant action. Mice could serve as an ideal genetically tractable model for mechanistic studies into sex and hormone effects on psychostimulant behavior.

OBJECTIVES

The objective of this study was to characterize psychostimulant effects in male and female mice with a combination of automated data collection and behavioral observation.

METHODS

Male and female C57BL/6 mice (Charles River) were given a single dose or sequential ascending binge doses of D-amphetamine (AMPH) or cocaine (COC). Behavior was assessed in open field chambers using both automated photobeam interruptions and behavioral observations. Brain psychostimulant concentrations were determined at the time of maximum behavioral stimulation.

RESULTS

Psychostimulants induced behavioral activation in mice including both increased locomotion as detected with an automated system and a sequence of behaviors progressing from stereotyped sniffing at low doses to patterned locomotion and rearing at high doses. Females exhibited more patterned locomotion and a shift towards higher behavior scores after either psychostimulant despite having lower AMPH and equivalent COC brain levels as males.

CONCLUSIONS

Female C57BL/6 mice exhibit enhanced psychostimulant-induced behavior compared to males, similar to reports in rats. The combination of automated behavioral measures and behavioral observation was essential for verifying the existence of these differences. These results indicate the importance of testing both sexes when characterizing genetically manipulated mice to control for potential sex-specific effects.

Apolipoprotein E4 causes age- and sex-dependent impairments of hilar GABAergic interneurons and learning and memory deficits in mice

Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer's disease (AD). ApoE4 has sex-dependent effects, whereby the risk of developing AD is higher in apoE4-expressing females than males. However, the mechanism underlying the sex difference, in relation to apoE4, is unknown. Previous findings indicate that apoE4 causes age-dependent impairments of hilar GABAergic interneurons in female mice, leading to learning and memory deficits. Here, we investigate whether the detrimental effects of apoE4 on hilar GABAergic interneurons are sex-dependent using apoE knock-in (KI) mice across different ages. We found that in female apoE-KI mice, there was an age-dependent depletion of hilar GABAergic interneurons, whereby GAD67- or somatostatin-positive–but not NPY- or parvalbumin-positive–interneuron loss was exacerbated by apoE4. Loss of these neuronal populations was correlated with the severity of spatial learning deficits at 16 months of age in female apoE4-KI mice; however, this effect was not observed in female apoE3-KI mice. In contrast, we found an increase in the numbers of hilar GABAergic interneurons with advancing age in male apoE-KI mice, regardless of apoE genotype. Moreover, male apoE-KI mice showed a consistent ratio of hilar inhibitory GABAergic interneurons to excitatory mossy cells approximating 1.5 that is independent of apoE genotype and age, whereas female apoE-KI mice exhibited an age-dependent decrease in this ratio, which was exacerbated by apoE4. Interestingly, there are no apoE genotype effects on GABAergic interneurons in the CA1 and CA3 subregions of the hippocampus as well as the entorhinal and auditory cortexes. These findings suggest that the sex-dependent effects of apoE4 on developing AD is in part attributable to inherent sex-based differences in the numbers of hilar GABAergic interneurons, which is further modulated by apoE genotype.

Determinant factors of gender identity: a commentary

Paediatric specialists involved in the care of children with disorders of sex development may be expected to provide straightforward answers to questions concerning the "true sex" of a child, reflecting common perceptions of sex/gender as an immutable binary biological reality. This article highlights how much more broad and complex the topic of gender identity and its development is. Many theories have been put forward to advance knowledge of gender identity. Against the breadth and depth of this vast topic, the current overview is inevitably incomplete. It begins by arguing for a more consistent use of 'sex' and 'gender'. It considers in turn three influential theoretical frameworks that lend themselves to empirical research. These are: 1) the role of the brain; 2) the role of socialisation; and 3) multi-dimensional gender development. The article ends by suggesting potentially fruitful questions and areas for future research.

Androgen receptor gene expression in the rat central nervous system: Evidence for two mRNA transcripts

Androgen receptor (AR) gene expression in the central nervous system (CNS) and peripheral tissues of male rats was examined using cDNA probes to measure AR mRNA by RNA (Northern) blot analysis and by in situ hybridization. Using a probe from the 5' untranslated region of the rat cDNA (AR-1), a single mRNA species of approximately 11 kb was seen in Northern blots of poly(A)(+) RNA from reproductive tissues, kidney, liver, and muscle. Using a probe from the 5' end of the coding region (AR-2), in addition to the 11-kb band, a novel transcript was seen in whole brain at about 9.3 kb. In poly(A)(+) RNA from dissected brain regions, the 9.3-kb transcript was predominant in the cortex, cerebellum, and brain stem, while in the hippocampus, both transcripts were expressed to a similar degree. AR mRNA levels increased two- to threefold in the prostate on Days 1 and 3 following castration but no significant change was seen in either CNS transcript in whole brain or cortex. Specific in situ hybridization of an (35)S-labeled AR-2 riboprobe was observed in brain regions known to bind radiolabeled androgens. We conclude that two AR RNA species exist in the adult male rat which differ in their 5' untranslated region and that the relative proportion of the two species varies between brain regions. In contrast to observations in the prostate, AR gene expression in the cerebral cortex is not regulated in the short term by androgen withdrawal.

Delayed myelination in an intrauterine growth retardation model is mediated by oxidative stress upregulating bone morphogenetic protein 4

Intrauterine growth retardation (IUGR) is associated with neurological deficits including cerebral palsy and cognitive and behavioral disabilities. The pathogenesis involves oxidative stress that leads to periventricular white matter injury with a paucity of mature oligodendrocytes and hypomyelination. The molecular mechanisms underlying this damage remain poorly understood. We used a rat model of IUGR created by bilateral ligation of the uterine artery at embryonic Day 19 that results in fetal growth retardation and oxidative stress in the developing brain. The IUGR rat pups showed significant delays in oligodendrocyte differentiation and myelination that resolved by 8 weeks. Bone morphogenetic protein 4 (BMP4), which inhibits oligodendrocyte maturation, was elevated in IUGR brains at postnatal time points and returned to near normal by adulthood. Despite the apparent recovery, behavioral deficiencies were found in 8-week-old female animals, suggesting that the early transient myelination defects have permanent effects. In support of these in vivo data, oligodendrocyte precursor cells cultured from postnatal IUGR rats retained increased BMP4 expression and impaired differentiation that was reversed with the BMP inhibitor noggin. Oxidants in oligodendrocyte cultures increased BMP expression, which decreased differentiation; however, abrogating BMP signaling with noggin in vitro and in BMP-deficient mice prevented these effects. Together, these findings suggest that IUGR results in delayed myelination through the generation of oxidative stress that leads to BMP4 upregulation.

Physical and Cognitive Performance of the Least Shrew (Cryptotis parva) on a Calcium-Restricted Diet

Geological substrates and air pollution affect the availability of calcium to mammals in many habitats, including the Adirondack Mountain Region (Adirondacks) of the United States. Mammalian insectivores, such as shrews, may be particularly restricted in environments with low calcium. We examined the consequences of calcium restriction on the least shrew (Cryptotis parva) in the laboratory. We maintained one group of shrews (5 F, 5 M) on a mealworm diet with a calcium concentration comparable to beetle larvae collected in the Adirondacks (1.1 ± 0.3 mg/g) and another group (5 F, 3 M) on a mealworm diet with a calcium concentration almost 20 times higher (19.5 ± 5.1 mg/g). Animals were given no access to mineral sources of calcium, such as snail shell or bone. We measured running speed and performance in a complex maze over 10 weeks. Shrews on the high-calcium diet made fewer errors in the maze than shrews on the low-calcium diet (F1,14 = 12.8, p < 0.01). Females made fewer errors than males (F1,14 = 10.6, p < 0.01). Running speeds did not markedly vary between diet groups or sexes, though there was a trend toward faster running by shrews on the high calcium diet (p = 0.087). Shrews in calcium-poor habitats with low availability of mineral sources of calcium may have greater difficulty with cognitive tasks such as navigation and recovery of food hoards.

Sex differences in behavioral decision-making and the modulation of shared neural circuits

Animals prioritize behaviors according to their physiological needs and reproductive goals, selecting a single behavioral strategy from a repertoire of possible responses to any given stimulus. Biological sex influences this decision-making process in significant ways, differentiating the responses animals choose when faced with stimuli ranging from food to conspecifics. We review here recent work in invertebrate models, including C. elegans, Drosophila, and a variety of insects, mollusks and crustaceans, that has begun to offer intriguing insights into the neural mechanisms underlying the sexual modulation of behavioral decision-making. These findings show that an animal's sex can modulate neural function in surprisingly diverse ways, much like internal physiological variables such as hunger or thirst. In the context of homeostatic behaviors such as feeding, an animal's sex and nutritional status may converge on a common physiological mechanism, the functional modulation of shared sensory circuitry, to influence decision-making. Similarly, considerable evidence suggests that decisions on whether to mate or fight with conspecifics are also mediated through sex-specific neuromodulatory control of nominally shared neural circuits. This work offers a new perspective on how sex differences in behavior emerge, in which the regulated function of shared neural circuitry plays a crucial role. Emerging evidence from vertebrates indicates that this paradigm is likely to extend to more complex nervous systems as well. As men and women differ in their susceptibility to a variety of neuropsychiatric disorders affecting shared behaviors, these findings may ultimately have important implications for human health.

Evidence for individual differences in regulatory focus in rats, Rattus norvegicus

Regulatory focus (Higgins, 1997) builds on the classic approach-avoidance distinction by identifying two important approach orientations: the promotion focus (approaching gains and attainment) and the prevention focus (approaching nonlosses and safety). Though individual differences in regulatory focus have been widely studied in human psychology, it is unknown if such differences exist in other species. To explore this possibility, we designed a series of tests for laboratory rats, paralleling human regulatory focus research on risk taking. In home-cage tests, rats (N = 23) were given an opportunity to prevent a loss by burying a noxious novel object. In solitary tests in a novel enclosure, the same rats had the opportunity to pursue gains (food rewards) and/or safety (darkness). Rats demonstrated stable individual differences on both tests (p's < .001). Complementing the human research, duration of time spent with the noxious novel object was predicted by an individual's tendency to pursue safety (p < .01) and not by the tendency to pursue gains (p > .8). Some aspects of these results were compatible with alternative approaches, such as the bold-shy axis and "if-then" personality profiles (Mischel & Shoda, 1995). Regulatory focus theory, however, was uniquely able to predict the overall pattern, which may be an indication that it could contribute to future research in animal personality, motivation, and welfare.

Behavioral responses to physical vs. social novelty in male and female laboratory rats

Most behavioral tests used with laboratory rodents involve measuring behavioral responses to physical novelty. However, laboratory rodents are often derived from highly social species for which novel social stimuli may induce different levels of fear or curiosity compared to novel physical objects. We hypothesized that behavioral responses will differ in response to novel physical vs. social cues, and that females may show more exploration of social novelty, based on prior studies indicating that females more actively seek social support during duress compared to males. We compared young (55-day-old) Sprague-Dawley rats' responses to an arena filled with novel objects ("physical") or a novel same-sex caged conspecific ("social"). Rats were more active and spent twice as much time in contact with the novel social stimulus compared to novel physical stimuli. Although females were more active than males, females were not particularly more exploratory in the social arena compared to males. The results indicate that a novel social partner (even a caged one with limited ability to interact) elicits more exploration than novel objects for both male and female rats.

Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior

Both sexual orientation and sex-typical childhood behaviors, such as toy, playmate and activity preferences, show substantial sex differences, as well as substantial variability within each sex. In other species, behaviors that show sex differences are typically influenced by exposure to gonadal steroids, particularly testosterone and its metabolites, during early development (prenatally or neonatally). This article reviews the evidence regarding prenatal influences of gonadal steroids on human sexual orientation, as well as sex-typed childhood behaviors that predict subsequent sexual orientation. The evidence supports a role for prenatal testosterone exposure in the development of sex-typed interests in childhood, as well as in sexual orientation in later life, at least for some individuals. It appears, however, that other factors, in addition to hormones, play an important role in determining sexual orientation. These factors have not been well-characterized, but possibilities include direct genetic effects, and effects of maternal factors during pregnancy. Although a role for hormones during early development has been established, it also appears that there may be multiple pathways to a given sexual orientation outcome and some of these pathways may not involve hormones.

Reproductive and behavioral effects of diisononyl phthalate (DINP) in perinatally exposed rats

Diisononyl phthalate (DINP) is a plasticizer abundantly used in consumer products as a substitute for other plasticizers prohibited in certain products due to reproductive toxicity. As anti-androgenic effects of DINP are suspected, DINP effects on reproduction and sexually dimorphic behavior were studied. Pregnant Wistar rats were gavaged from gestation day 7 to postnatal day (PND) 17 with vehicle, 300, 600, 750 or 900 mg DINP/kg bw/day. In fetal testes histopathological effects typical of phthalates were observed. In male offspring, DINP caused increased nipple retention, reduced anogenital distance, reduced sperm motility and increased sperm count. DINP affected spatial learning as female offspring performed better than controls and similarly to control males in the Morris Water Maze, indicating masculinization of behavior in DINP exposed females. These results show that DINP causes anti-androgenic effects on reproductive development, though less potent than DEHP, DBP and BBP, and further safety evaluation of DINP appears warranted.

Sensitivity to the depressogenic effect of stress and HPA-axis reactivity in adolescence: a review of gender differences

Adolescence is characterized by major biological, psychological, and social challenges, as well as by an increase in depression rates. This review focuses on the association between stressful experiences and depression in adolescence, and the possible role of the hypothalamus-pituitary-adrenal cortex (HPA-)axis in this link. Adolescent girls have a higher probability to develop depressive symptoms than adolescent boys and preadolescents. Increasing evidence indicates that girls' higher risk of depression is partly brought about by an increased sensitivity for stressful life events, particularly interpersonal stressors, which are highly prevalent in adolescent girls. Genetic risk factors for depression, as well as those for stress sensitivity, are often expressed differently in girls and boys. Also environmental adversity tends to affect girls' stress responses more than those of boys. These gender-specific association patterns have been reported for both sensitivity to stressful life events and HPA-axis responses to social stress. Together, the findings suggest that girls are more malleable than boys in response to internal and external influences. This postulated greater malleability may be adaptive in many circumstances, but also brings along risk, such as an increased probability of depression.

Congenital adrenal hyperplasia: classification of studies employing psychological endpoints

Psychological outcomes in persons with congenital adrenal hyperplasia (CAH) have received substantial attention. The objectives of this paper were to (1) catalog psychological endpoints assessed in CAH outcome studies and (2) classify the conceptual/theoretical model shaping the research design and interpretation of CAH-related psychological effects. A total of 98 original research studies, published between 1955 and 2009, were categorized based on psychological endpoints examined as well as the research design and conceptual model guiding analysis and interpretation of data. The majority of studies (68%) investigated endpoints related to psychosexual differentiation. The preponderance of studies (76%) examined a direct relationship (i.e., inferring causality) between prenatal androgen exposure and psychological outcomes. Findings are discussed in relation to the observed imbalance between theoretical interest in the role of prenatal androgens in shaping psychosexual differentiation and a broader conceptual model that examines the role of other potential factors in mediating or moderating the influence of CAH pathophysiology on psychological outcomes in both affected females and males. The latter approach offers to identify factors amenable to clinical intervention that enhance both health and quality of life outcomes in CAH as well as other disorders of sex development.

Self-control in male and female rats

Eight male and 8 female Wistar rats were exposed to a discrete-trial procedure in which they chose between the presentation of a small (one pellet) or a large (three pellets) reinforcer. The delay to the small and large reinforcer was 6.0 s in the first condition of Experiment 1. Subjects consistently chose the large reinforcer. When the delay to the small reinforcer was decreased to 0.1 s in the next experimental condition, all subjects continued to choose the large 6.0-s delayed reinforcer. When the contingencies correlated with the two levers were reversed in the next experimental condition, the majority of subjects (5 males and 6 females) still chose the large delayed reinforcer over the small immediately presented reinforcer. The delay to the small reinforcer was maintained at 6.0 s, but the delay to the large reinforcer was varied among 9.0, 15.0, 24.0, and 36.0 s in Experiment 2, in which 4 males and 4 females participated. Most subjects consistently chose the large increasingly delayed reinforcer, although choice for the small 6.0-s delayed reinforcer developed in some females when the large reinforcer was delayed for 24.0 or 36.0 s. These choice patterns were not predicted from a literal application of a model that says choice should favor the alternative correlated with the higher (amount/delay) ratio.

Mental health problems during puberty: Tanner stage-related differences in specific symptoms. The TRAILS study

The aim of this study was to investigate associations between specific mental health problems and pubertal stage in (pre)adolescents participating in the Dutch prospective cohort study TRAILS (first assessment: N=2230, age 11.09±0.56, 50.8% girls; second assessment: N=2149, age 13.56±0.53, 51.0% girls). Mental health was assessed by the Youth Self-Report, pubertal (Tanner) stage by parent-rated drawings of secondary sex characteristics. Overall, higher Tanner stages were related to more reported tiredness, irritability, rule-breaking behaviors, and substance use; and fewer fears and somatic complaints. Girls showed increases in social uncertainty, depressed mood, and worries; boys a decrease in self-criticism. Increasing problems during puberty were mostly related to the process of physical maturation, whereas decreasing problems were rather related to general age-related developments. Pubertal timing was associated with different symptoms than pubertal status or age. Puberty seems to affect girls more negatively than boys.