Strategies and methods for research on sex differences in brain and behavior

Sex differences in effort-related decision-making: role of dopamine D2 receptor antagonism

RATIONALE

Depressed individuals demonstrate debilitating symptoms, including depressed mood, anhedonia, and effort-related deficits. Effort-related decision-making can be measured through providing subjects with a choice between high effort/reward and low effort/reward options, which is a dopamine (DA)-dependent behavior. While previous research has shown sex differences in depression rates, this has not been examined within operant-based effort-related decision-making tasks nor has DA been shown to underlie this behavior in female rats.

OBJECTIVES

The current study investigated sex differences in an effort-related decision-making task prior to and following administration of the DA D2 receptor antagonist haloperidol (HAL).

METHODS

Adult rats were food restricted or fed freely and trained in an effort-related progressive ratio choice task. After stable responding, HAL was administered acutely (0.05-0.2 mg/kg) prior to testing.

RESULTS

Results indicate a significant effect of sex on training variables, with males having a greater number of lever presses, higher ratios, and longer active lever times. Pretreatment with HAL significantly reduced the same measures in both sexes for the high-valued reward, while increasing chow consumption in the food restricted males. Food restricted rats showed a greater number of total lever presses and achieved higher ratios; however, the effect in male food restricted rats was greatest.

CONCLUSIONS

These data suggest that, although there are sex differences in training, HAL decreases behavior across sexes, demonstrating that the D2 mechanism is similar in both sexes. These findings provide a better understanding of motivational dysfunction in both sexes and potential treatment targets for depression.

Lower estradiol predicts increased reinstatement of fear in women

Low levels of estradiol in women have been associated with impaired fear extinction recall, with suggestions this may promote the return of fear and heighten the female vulnerability for anxiety disorders. A particularly important measure for the return of fear is reinstatement, but no human studies to date have examined the impact of estradiol on fear reinstatement. Forty-two healthy females completed a differential fear conditioning, extinction and reinstatement task with skin conductance response (SCR) amplitude indexing level of conditioned fear. Saliva samples were taken to measure estradiol and progesterone. To examine fear reinstatement, SCR amplitude was compared between the last trial of the late extinction phase to the first re-extinction trial following the unsignaled presentation of two aversive electric shocks. No significant effects of estradiol were found for acquisition of fear conditioning or fear extinction learning. Lower estradiol predicted a significantly larger generalized SCR amplitude at re-extinction (post-reinstatement) in women. This provides novel evidence suggesting a protective role of estradiol in potentially reducing the relapse of fear following re-exposure to aversive stimuli, although further research is necessary in clinical populations to clarify this effect.

Facial Emotion Recognition and Emotional Memory From the Ovarian-Hormone Perspective: A Systematic Review

Background

We review original papers on ovarian-hormone status in two areas of emotional processing: facial emotion recognition and emotional memory. Ovarian-hormone status is operationalized by the levels of the steroid sex hormones 17β-estradiol (E2) and progesterone (P4), fluctuating over the natural menstrual cycle and suppressed under oral contraceptive (OCs) use. We extend previous reviews addressing single areas of emotional processing. Moreover, we systematically examine the role of stimulus features such as emotion type or stimulus valence and aim at elucidating factors that reconcile the inconsistent results.

Methods

We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and included papers published until September 2020 indexed in PubMed and Web of Science databases. Search terms were MeSH terms (emotional OR emotion) AND (X) AND (estrogen OR progesterone OR menstrual cycle OR oral contraceptives) with (X) representing our separately searched areas, resulting in (processing OR recognition OR empathy), and (memory OR recall). To be included, articles had to (1) be written and published in English, (2) examine healthy, non-pregnant adult women in their reproductive age, and (3) measure or at least estimate levels of E2 and P4. In PubMed, the search was (4) limited to humans and (5) to the search term present in the title or abstract.

Results

Features of the provided stimulus material (emotion type and/or valence) constitute a relevant influence that interacts with E2- and P4-related ovarian-hormone status. For instance, recognition of basic emotions appears to be more related to P4- than E2-levels. Quite consistent, OC intake (vs. natural menstrual cycling) was accompanied by impaired recognition accuracy of basic and also complex emotions, although not in a recent large-sample study assessing complex emotions. Memory recall of negative content was mainly enhanced by P4, especially after having been stressed.

Discussion and Conclusion

We document the methodological diversity in the field, presumably contributing to the heterogeneity of results. More studies explicitly contrasting the early follicular phase, mid-cycle phase, mid-luteal, and OC intake while standardizing tasks are needed. Research would take advantage of using within-subject designs and accounting for the recognition of complex emotions.

Male Carollia perspicillata bats call more than females in a distressful context

Distress calls are a vocalization type widespread across the animal kingdom, emitted when the animals are under duress, e.g. when captured by a predator. Here, we report on an observation we came across serendipitously while recording distress calls from the bat species Carollia perspicillata, i.e. the existence of sex difference in the distress calling behaviour of this species. We show that in C. perspicillata bats, males are more likely to produce distress vocalizations than females when hand-held. Male bats call more, their calls are louder, harsher (faster amplitude modulated) and cover lower carrier frequencies than female vocalizations. We discuss our results within a framework of potential hormonal, neurobiological and behavioural differences that could explain our findings, and open multiple paths to continue the study of sex-related differences in vocal behaviour in bats.

Neuroprotective effect of hesperidin against emamectin benzoate-induced neurobehavioral toxicity in rats

Emamectin Benzoate (EMB) is an avermectin insecticide widely used in agriculture and veterinary medicine. Hesperidin (HSP) is a flavanone glycoside predominantly found in citrus fruits and has various beneficial health effects. The current research was conducted to study the neurobehavioral toxic effects of EMB in rats and also to evaluate the protective effect of HSP against these toxic effects. Sixty Sprague-Dawley rats were randomly divided into 4 equal groups: control group, EMB group, HSP group, and EMB + HSP group. EMB (8.8. mg/kg) and/or HSP (100 mg/kg) were administered daily by gavage for 8 weeks. The behavioral assessment demonstrated the adverse effects of EMB on the behavioral, motor, and cognitive brain functions. Exposure to EMB also decreased the activity of antioxidants (catalase and reduced glutathione) and increased the malondialdehyde level in nervous tissue. Moreover, EMB increased the level of inflammatory cytokines (tumor necrosis factor-α and interleukin-1β) and decreased brain-derived neurotrophic factor (BDNF) levels in rats' brains. On the other hand, concurrent administration of HSP ameliorated the toxic effects of EMB as indicated by improvements in neural functions and reduction of oxidative stress and inflammation. The study concluded that exposure to EMB induces toxic effects in the brain of rats and that HSP has a protective effect against these toxic effects.

Serum metabolic signature of binge-like palatable food consumption in female rats by nuclear magnetic resonance spectroscopy

Maladaptive eating behavior is a growing public health problem and compulsively eating excessive food in a short time, or binge eating, is a key symptom of many eating disorders. In order to investigate the binge-like eating behavior in female rats, induced by intermittent food restrictions/refeeding and frustration stress, we analyzed for the first time the metabolic profile obtained from serum of rats, through nuclear magnetic resonance (NMR) spectroscopy. In this experimental protocol, rats were exposed to chow food restricting/refeeding and frustration stress manipulation. This stress procedure consists of 15 min exposure to the odor and sight of a familiar chocolate paste, without access to it, just before offering the palatable food. In this model, a "binge-eating episode" was considered the significantly higher palatable food consumption within 2 h in restricted and stressed rats (R + S) than in the other three experimental groups: rats with no food restriction and no stress (NR + NS), only stressed rats (NR + S) or only restricted rats (R + NS). Serum samples from these four different rat groups were collected. The statistical analysis of the ¹ H NMR spectral profiles of the four sets of samples pointed to O- and N-acetyl glycoproteins as the main biomarkers for the discrimination of restriction effects. Other metabolites, such as threonine, glycine, glutamine, acetate, pyruvate and lactate, showed trends that may be useful to understand metabolic pathways involved in eating disorders. This study suggested that NMR-based metabolomics is a suitable approach to detect biomarkers related to binge-eating behavior.

Studying Sex Differences in Rodent Models of Addictive Behavior

Animal models of addictive behaviors are useful for uncovering neural mechanisms involved in the development of dependence and for identifying risk factors for drug abuse. One such risk factor is biological sex, which strongly moderates drug self-administration behavior in rodents. Female rodents are more likely to acquire drug self-administration behaviors, consume higher amounts of drug, and reinstate drug-seeking behavior more readily. Despite this female vulnerability, preclinical addiction research has largely been done in male animals. The study of sex differences in rodent models of addictive behavior is increasing, however, as more investigators are choosing to include both male and female animals in experiments. This commentary is meant to serve as an introductory guide for preclinical investigators new to the study of sex differences in addiction. We provide an overview of self-administration models, a broad view of female versus male self-administration behaviors, and suggestions for study design and implementation. Inclusion of female subjects in preclinical addiction research is timely, as problem drug and alcohol use in women is increasing. With proper attention, design, and analysis, the study of sex differences in addiction has the potential to uncover novel neural mechanisms and lead to greater translational success for addiction research. © 2021 Wiley Periodicals LLC.

Irisin treatment lowers levels of phosphorylated tau in the hippocampus of pre-symptomatic female but not male htau mice

AIMS

Irisin is a hormone cleaved from fibronectin type-III domain-containing protein 5 in response to exercise and may be therapeutic in Alzheimer's disease (AD). Irisin is shown to repair damage caused by midlife cardiometabolic risk factors for AD (i.e., diabetes mellitus; hypertension), prevent neural amyloid beta aggregation and reduce neuroinflammation. However, there are no investigations of irisin's effect on AD-associated tauopathy in the brain. This study begins to address this gap in knowledge.

METHODS

Transgenic htau mice that selectively develop age-related tauopathy were treated with recombinant irisin (100 µg/kg weekly i.p.) beginning at a pre-symptomatic age (4 months) to determine if irisin could prevent emergence of early neuropathology. One month later, mice were sacrificed to collect brain tissue and serum. Protein levels of ptau (serine 202), inflammatory cytokine tumour necrosis factor alpha (TNFα) and FNDC5 were quantified using capillary-based western blotting (Wes).

RESULTS

Our data show that irisin treatment significantly reduced ptau and TNFα in the hippocampus and serum of female htau mice compared to vehicle-treated controls. Irisin treatment did not alter ptau levels in male htau hippocampus and appeared to enhance both neural and systemic TNFα levels.

CONCLUSIONS

This study provides the first evidence that enhancing the endogenous hormone irisin may be therapeutic against emerging neuropathology in a tauopathy-selective AD model. This is important because there are currently no disease-modifying therapeutics available for AD, and few agents in development address the multiple disease targets irisin appears to-making irisin an intriguing therapeutic candidate for further investigation.

[How to Study the Sex and Gender Effect in Biomedical Research?]

Men and women are different, but this difference has not been well reflected in clinical trials and preclinical studies of biomedical science. Gender medicine, which systematically analyzes research results according to sex and gender, has been emphasized to overcome this problem. On the other hand, researchers still have difficulty in applying gender medicine to their research. To perform rigorous gender medicine, using correct terms, a thorough literature review during research planning, appropriate statistical analysis and reporting, and cautious interpretation of the results are necessary. Applying gender medicine will increase the reproducibility of studies, promote discoveries, expand the study relevance, and ultimately improve patient care in both men and women. Here, this study reviewed the practical issues on applying gender medicine to both preclinical and clinical studies in the field of biomedical science.

Sex and Menstrual Phase Influences on Sleep and Memory

Purposes of Review

This review highlights the effect of sex differences in sleep mediated memory consolidation and cognitive performance. In addition, the role of menstrual cycle and the fluctuating level of sexual hormones (mainly oestrogen and progesterone) are stressed.

Recent Findings

The literature indicates that sex hormones mediate and orchestrate the differences observed in performance of females in comparison with males in a variety of tasks and can also be related to how sleep benefits cognition. Although the exact mechanism of such influence is not clear, it most likely involves differential activation of brain areas, sensitivity to neuromodulators (mainly oestrogen), circadian regulation of sleep and temperature, as well as modification of strategies to solve tasks across the menstrual cycle.

Summary

With the evidence presented here, we hope to encourage researchers to develop appropriate paradigms to study the complex relationship between menstrual cycle, sleep (its regulation, architecture and electrophysiological hallmarks) and performance in memory and other cognitive tasks.

Sex differences in fat taste responsiveness are modulated by estradiol

Sex as a biological variable has been the focus of increasing interest. Relatively few studies have focused, however, on differences in peripheral taste function between males and females. Nonetheless, there are reports of sex-dependent differences in chemosensitivity in the gustatory system. The involvement of endogenous changes in ovarian hormones has been suggested to account for taste discrepancies. Additionally, whether sex differences exist in taste receptor expression, activation, and subsequent signaling pathways that may contribute to different taste responsiveness is not well understood. In this study, we show the presence of both the nuclear and plasma membrane forms of estrogen receptor (ER) mRNA and protein in mouse taste cells. Furthermore, we provide evidence that estrogen increases taste cell activation during the application of fatty acids, the chemical cue for fat taste, in taste receptor cells. We found that genes important for the transduction pathway of fatty acids vary between males and females and that these differences also exist across the various taste papillae. In vivo support for the effect of estrogens in taste cells was provided by comparing the fatty acid responsiveness in male, intact female, and ovariectomized (OVX) female mice with and without hormone replacement. In general, females detected fatty acids at lower concentrations, and the presence of circulating estrogens increased this apparent fat taste sensitivity. Taken together, these data indicate that increased circulating estrogens in the taste system may play a significant role in physiology and chemosensory cellular activation and, in turn, may alter taste-driven behavior.NEW & NOTEWORTHY Using molecular, cellular, and behavioral analyses, this study shows that sex differences occur in fat taste in a mouse model. Female mice are more responsive to fatty acids, leading to an overall decrease in intake and fatty acid preference. These differences are linked to sex hormones, as estradiol enhances taste cell responsiveness to fatty acids during periods of low circulating estrogen following ovariectomy and in males. Estradiol is ineffective in altering fatty acid signaling during a high-estrogen period and in ovariectomized mice on hormone replacement. Thus, taste receptor cells are a direct target for actions of estrogen, and there are multiple receptors with differing patterns of expression in taste cells.

Influence of the natural hormonal milieu on brain and behavior in women who smoke cigarettes: Rationale and methodology

Women experience more severe health consequences from smoking, have greater difficulty quitting, and respond less favorably to nicotine replacement therapy than men. The influence of fluctuating ovarian hormones, specifically estradiol (E) and progesterone (P), on brain and behavioral responses during exposure to smoking reminders (i.e., cues) may be a contributing factor. Results from our laboratory suggest that women in the late follicular phase of their menstrual cycle (MC) have enhanced smoking cue (SC) vulnerabilities and reduced functional connectivity in neurocircuitry underlying cognitive control, potentially placing them at greater risk for continued smoking and relapse. The primary aim of this study is to examine and link hormonal status with brain and behavioral responses to SCs over the course of three monthly MCs in naturally cycling women who are chronic cigarette smokers. This longitudinal, counterbalanced study collects brain and behavioral responses to SCs at three time points during a woman's MC. Participants complete psychological and physical examinations, biochemical hormonal verification visits, and at least three laboratory/neuroimaging scan visits. The scan visits include a 10-min SC task during blood oxygen level-dependent (BOLD) data acquisition and are timed to occur during the early follicular phase (low E and P), late follicular phase (high E, unopposed by P), and mid-luteal phase (high P, high E). The primary outcomes include brain responses to SCs (compared to non-SCs), subjective craving, E and P hormone levels, and behavioral responses to SCs. This study addresses a critical gap in our knowledge: namely, the impact of the natural hormonal milieu on brain and behavioral responses to SCs, a powerful relapse trigger. Additionally, this study will provide a roadmap for human sex differences researchers who are obliged to consider the often confounding cyclic hormonal fluctuations of women.

Sex differences in vulnerability to addiction

This article reviews evidence for sex differences in vulnerability to addiction with an emphasis on the neural mechanisms underlying these differences. Sex differences in the way that the gonadal hormone, estradiol, interacts with the ascending telencephalic dopamine system results in sex differences in motivated behaviors, including drug-seeking. In rodents, repeated psychostimulant exposure enhances incentive sensitization to a greater extent in females than males. Estradiol increases females' motivation to attain psychostimulants and enhances the value of drug related cues, which ultimately increases their susceptibility towards spontaneous relapse. This, along with females' dampened ability to alter decisions regarding risky behaviors, enhances their vulnerability for escalation of drug use. In males, recent evidence suggests that estradiol may be protective against susceptibility towards drug-preference. Sex differences in the actions of estradiol are reviewed to provide a foundation for understanding how future research might enhance understanding of the mechanisms of sex differences in addiction-related behaviors, which are dependent on estradiol receptor (ER) subtype and the region of the brain they are acting in. A comprehensive review of the distribution of ERα, ERβ, and GPER1 throughout the rodent brain are provided along with a discussion of the possible ways in which these patterns differentially regulate drug-taking between the sexes. The article concludes with a brief discussion of the actions of gonadal hormones on the circuitry of the stress system, including the hypothalamic pituitary adrenal axis and regulation of corticotropin-releasing factor. Sex differences in the stress system can also contribute to females' enhanced vulnerability towards addiction.

Behavioral economics of cocaine self-administration in male and female rats

There are sex differences in the development of cocaine addiction. For example, the time that it takes for women from initial use to addiction is significantly shorter than for men. Thus, understanding why females are more vulnerable to cocaine addiction will provide insights into sex differences in the mechanisms underlying cocaine addiction. This study aimed to determine how cocaine demand intensity and elasticity might differ between sexes. In addition, the impact of estrous cycle and cocaine intake on demand was investigated. Male and female rats were trained to self-administer 0.125 mg of cocaine intravenously under a chained schedule in daily 2-h sessions for 2 weeks, and then, the cocaine demand function was determined with a modified within-session threshold procedure. Following the test, the rats began to self-administer a higher dose of cocaine (0.25 mg) to increase the cocaine intake. The demand function was then similarly determined in the same rats after 2 weeks of cocaine self-administration of the higher dose. No sex differences were found in either demand intensity or elasticity. Neither did the level of cocaine intake have an impact on demand. The demand elasticity, but not intensity, was significantly lower during proestrus/estrus compared with diestrus. These data suggest that the faster transition to cocaine addiction in women cannot be explained by sex differences in the demand for cocaine and such a demand may change during different phases of estrus cycle.

Unexpected Role of Physiological Estrogen in Acute Stress-Induced Memory Deficits

Stress may promote emotional and cognitive disturbances, which differ by sex. Adverse outcomes, including memory disturbances, are typically observed following chronic stress, but are now being recognized also after short events, including mass shootings, assault, or natural disasters, events that consist of concurrent multiple acute stresses (MAS). Prior work has established profound and enduring effects of MAS on memory in males. Here we examined the effects of MAS on female mice and probed the role of hormonal fluctuations during the estrous cycle on MAS-induced memory problems and the underlying brain network and cellular mechanisms. Female mice were impacted by MAS in an estrous cycle-dependent manner: MAS impaired hippocampus-dependent spatial memory in early-proestrous mice, characterized by high levels of estradiol, whereas memory of mice stressed during estrus (low estradiol) was spared. As spatial memory requires an intact dorsal hippocampal CA1, we examined synaptic integrity in mice stressed at different cycle phases and found a congruence of dendritic spine density and spatial memory deficits, with reduced spine density only in mice stressed during high estradiol cycle phases. Assessing MAS-induced activation of brain networks interconnected with hippocampus, we identified differential estrous cycle-dependent activation of memory- and stress-related regions, including the amygdala. Network analyses of the cross-correlation of fos expression among these regions uncovered functional connectivity that differentiated impaired mice from those not impaired by MAS. In conclusion, the estrous cycle modulates the impact of MAS on spatial memory, and fluctuating physiological levels of sex hormones may contribute to this effect.SIGNIFICANCE STATEMENT: Effects of stress on brain functions, including memory, are profound and sex-dependent. Acute stressors occurring simultaneously result in spatial memory impairments in males, but effects on females are unknown. Here we identified estrous cycle-dependent effects of such stresses on memory in females. Surprisingly, females with higher physiological estradiol experienced stress-induced memory impairment and a loss of underlying synapses. Memory- and stress-responsive brain regions interconnected with hippocampus were differentially activated across high and low estradiol mice, and predicted memory impairment. Thus, at functional, network, and cellular levels, physiological estradiol influences the effects of stress on memory in females, providing insight into mechanisms of prominent sex differences in stress-related memory disorders, such as post-traumatic stress disorder.

Various aspects of sex and gender bias in biomedical research

The main role of research in medicine is to provide relevant knowledge which, after successful translation to clinical practice, improves the quality of healthcare. The sex bias which is still present in the majority of research disciplines prefers male subjects despite legislation changes in the US grant agencies and European research programme Horizon 2020. Male subjects (cells, animals) still dominate in preclinical research and it has detrimental consequences for women's health and the quality of science. Opposite bias exists for data obtained mainly in animal models utilizing female subjects (e.g. research in multiple sclerosis, osteoporosis) with skewed outcomes for men affected by these diseases. Either way, scientists are producing results which compromise half of the population. Assumptions that females as cohorts are more variable and another assumption that the oestrous cycle should be tracked in case the females are enrolled in preclinical studies were proven wrong. Variability of male versus female cohorts are comparable and do not only stem from hormonal levels. The widespread prevalence of sex differences in human diseases ultimately requires detailed experiments performed on both sexes, unless the studies are specifically addressing reproduction or sex-related behaviors.

Biological sex, not reproductive cycle, influences peripheral blood immune cell prevalence in mice

KEY POINTS

Traditionally the female sex, compared with the male sex, has been perceived as having greater variability in many physiological traits, including within the immune system. We investigated effects of biological sex and the female reproductive cycle on numbers of circulating leukocytes in C57BL/6J mice. We show that biological sex, but not female reproductive cyclicity, has a significant effect on peripheral blood immune cell prevalence and variability, and that sex differences were not consistent amongst common inbred laboratory mouse strains. We found that male C57BL/6J mice, compared with female mice, have greater variability in peripheral blood immunophenotype, and that this was influenced by body weight. We created summary tables for researchers to facilitate experiment planning and sample size calculations for peripheral immune cells that consider the effects of biological sex.

ABSTRACT

Immunophenotyping (i.e. quantifying the number and types of circulating leukocytes) is used to characterize immune changes during health and disease, and in response to pharmacological and other interventions. Despite the importance of biological sex in immune function, there is considerable uncertainty amongst researchers as to the extent to which biological sex or the female reproductive cycle influence blood immunophenotype. We quantified circulating leukocytes by multicolour flow cytometry in young C57BL/6J mice and assessed the effects of the reproductive cycle, biological sex, and other experimental and biological factors on data variability. We found that there are no significant effects of the female reproductive cycle on the prevalence of peripheral blood B cells, NK cells, CD4⁺ T cells, CD8⁺ T cells, monocytes, or neutrophils. Immunophenotype composition and variability do not significantly change between stages of the female reproductive cycle. There are, however, sex-specific differences in immune cell prevalence, with fewer monocytes, neutrophils, and NK cells in female mice. Surprisingly, immunophenotype is more variable in male mice, and weight is a significant contributing factor. We provide tools for researchers to perform a priori sample size calculations for two-group and factorial analyses. We show that immunophenotype varies between inbred mouse strains, and that using equal sample sizes of male and female mice is not always appropriate for within-sex evaluations of immune cell populations in peripheral blood.

Sex differences in executive control: A systematic review of functional neuroimaging studies

The number of studies investigating sex differences in executive functions, particularly those using human functional neuroimaging techniques, has risen dramatically in the past decade. However, the influences of sex on executive function are still underexplored and poorly characterized. To address this, we conducted a systematic literature review of functional neuroimaging studies investigating sex differences in three prominent executive control domains of cognitive set-shifting, performance monitoring, and response inhibition. PubMed, Web of Science, and Scopus were systematically searched. Following the application of exclusion criteria, 21 studies were included, with a total of 677 females and 686 males. Ten of these studies were fMRI and PET, eight were EEG, and three were NIRS. At present, there is evidence for sex differences in the neural networks underlying all tasks of executive control included in this review suggesting males and females engage different strategies depending on task demands. There was one task exception, the 2-Back task, which showed no sex differences. Due to methodological variability and the involvement of multiple neural networks, a simple overarching statement with regard to gender differences during executive control cannot be provided. As such, we discuss limitations within the current literature and methodological considerations that should be employed in future research. Importantly, sex differences in neural mechanisms are present in the majority of tasks assessed, and thus should not be ignored in future research. PROSPERO registration information: CRD42019124772.

Psychosocial and biological risk factors of anxiety disorders in adolescents: a TRAILS report

Anxiety disorders are a common problem in adolescent mental health. Previous studies have investigated only a limited number of risk factors for the development of anxiety disorders concurrently. By investigating multiple factors simultaneously, a more complete understanding of the etiology of anxiety disorders can be reached. Therefore, we assessed preadolescent socio-demographic, familial, psychosocial, and biological factors and their association with the onset of anxiety disorders in adolescence. This study was conducted among 1584 Dutch participants of the TRacking Adolescents' Individual Lives Survey (TRAILS). Potential risk factors were assessed at baseline (age 10-12), and included socio-demographic (sex, socioeconomic status), familial (parental anxiety and depression), psychosocial (childhood adversity, temperament), and biological (body mass index, heart rate, blood pressure, cortisol) variables. Anxiety disorders were assessed at about age 19 years through the Composite International Diagnostic Interview (CIDI). Univariate and multivariate logistic regression analyses were performed with onset of anxiety disorder as a dependent variable and the above-mentioned putative risk factors as predictors. Of the total sample, 25.7% had a lifetime diagnosis of anxiety disorder at age 19 years. Anxiety disorders were twice as prevalent in girls as in boys. Multivariate logistic regression analysis showed that being female (OR = 2.38, p < .01), parental depression and anxiety (OR = 1.34, p = .04), temperamental frustration (OR = 1.31, p = .02) and low effortful control (OR = 0.76, p = .01) independently predicted anxiety disorders. We found no associations between biological factors and anxiety disorder. After exclusion of adolescents with an onset of anxiety disorder before age 12 years, being female was the only significant predictor of anxiety disorder. Being female was the strongest predictor for the onset of anxiety disorder. Psychological and parental psychopathology factors increased the risk of diagnosis of anxiety, but to a lesser extent. Biological factors (heart rate, blood pressure, cortisol, and BMI), at least as measured in the present study, are unlikely to be useful tools for anxiety prevention and intervention strategies.

Therapeutic implications of hypothalamic-pituitaryadrenal-axis modulation in Alzheimer's disease: A narrative review of pharmacological and lifestyle interventions

With disease-modifying treatments for Alzheimer's disease (AD) still elusive, the search for alternative intervention strategies has intensified. Growing evidence suggests that dysfunction in hypothalamic-pituitaryadrenal-axis (HPAA) activity may contribute to the development of AD pathology. The HPAA, may therefore offer a novel target for therapeutic action. This review summarises and critically evaluates animal and human studies investigating the effects of pharmacological and non-pharmacological intervention on HPAA modulation alongside cognitive performance. The interventions discussed include glucocorticoid receptor antagonists and 11β-hydroxysteroid dehydrogenase inhibitors as well as lifestyle treatments such as physical activity, diet, sleep and contemplative practices. Pharmacological HPAA modulators improve pathology and cognitive deficit in animal AD models, but human pharmacological trials are yet to provide definitive support for such benefits. Lifestyle interventions may offer promising strategies for HPAA modification and cognitive health, but several methodological caveats across these studies were identified. Directions for future research in AD studies are proposed.

Effects of ∆9-THC on memory in ovariectomized and intact female rats

The effects of marijuana's major psychoactive cannabinoid, ∆9-tetrahydrocannibinol (∆9-THC), were examined on memory in female rats by training subjects to respond under a repeated acquisition and delayed-performance procedure. During this task, subjects acquired a different 4-response sequence each session, which was then recalled after a delay. Sequence retention was tested following various delays, and quantified by a percent savings measure. Response rate and percent errors were also recorded. Subsequent to training, subjects underwent an ovariectomy (OVX) or sham surgery (intact). The OVX group then underwent implantation of subcutaneous 17β-estradiol capsules while the intact group received chronic administration of 1 mg/kg of the estrogen receptor modifier, tamoxifen. Increasing delays from 1 min to 24 h produced delay-dependent decreases in percent savings in both OVX and intact rats. Acute administration of ∆9-THC (0.32-3.2 mg/kg) dose-dependently decreased retention, increased percent errors, and decreased response rate in both groups when the delay was 1 h. However, intact rats showed a significantly lower percent savings than OVX rats at the 0.56-mg/kg dose. Delays of 3 h enhanced the disruptive effects of ∆9-THC more in intact than OVX rats; furthermore, implantation of 17β-estradiol attenuated ∆9-THC-induced disruptions in OVX rats and significantly increased estradiol levels and uterine weight as compared to intact rats. Although chronic tamoxifen administration did not alter ∆9-THC's effects on memory in intact rats, it did significantly decrease response rate. These results demonstrate the capacity of chronic 17β-estradiol for attenuating ∆9-THC's acute memory-disrupting effects in OVX female rats.

Aberrant reactive aldehyde detoxification by aldehyde dehydrogenase-2 influences endometriosis development and pain-associated behaviors

Endometriosis affects ∼176 million women worldwide, yet on average, women experience pain ∼10 years from symptom onset before being properly diagnosed. Standard treatments (drugs or surgery) often fail to provide long-term pain relief. Elevated levels of reactive aldehydes such as 4-hydroxynonenal (4-HNE) have been implicated in the peritoneal fluid of women with endometriosis and upon accumulation, reactive aldehydes can form protein-adducts and/or generate pain. A key enzyme in detoxifying reactive aldehydes to less reactive forms is the mitochondrial enzyme aldehyde dehydrogenase-2 (ALDH2). Here, we tested the hypothesis that aberrant reactive aldehyde detoxification by ALDH2 underlies endometriosis and its associated pain. We determined, in the eutopic and ectopic endometrium of women with severe (stage IV) peritoneal endometriosis, that ALDH2 enzyme activity was decreased, which was associated with decreased ALDH2 expression and increased 4-HNE adduct formation compared to the eutopic endometrium of controls in the proliferative phase. Using a rodent model of endometriosis and an ALDH2*2 knock-in mouse with decreased ALDH2 activity, we determined that increasing ALDH2 activity with the enzyme activator Alda-1 could prevent endometriosis lesion development as well as alleviate pain-associated behaviors in proestrus. Overall, our findings suggest that targeting the ALDH2 enzyme in endometriosis may lead to better treatment strategies and in the proliferative phase, that increased 4-HNE adduct formation within the endometrium may serve as a less invasive diagnostic biomarker to reduce years of suffering in women.

Various aspects of sex and gender bias in biomedical research

The main role of research in medicine is to provide relevant knowledge which, after successful translation to clinical practice, improves the quality of healthcare. The sex bias which is still present in the majority of research disciplines prefers male subjects despite legislation changes in the US grant agencies and European research programme Horizon 2020. Male subjects (cells, animals) still dominate in preclinical research and it has detrimental consequences for women's health and the quality of science. Opposite bias exists for data obtained mainly in animal models utilizing female subjects (e.g. research in multiple sclerosis, osteoporosis) with skewed outcomes for men affected by these diseases. Either way, scientists are producing results which compromise half of the population. Assumptions that females as cohorts are more variable and another assumption that the oestrous cycle should be tracked in case the females are enrolled in preclinical studies were proven wrong. Variability of male versus female cohorts are comparable and do not only stem from hormonal levels. The widespread prevalence of sex differences in human diseases ultimately requires detailed experiments performed on both sexes, unless the studies are specifically addressing reproduction or sex-related behaviors.

Why do sexes differ in lifespan extension? Sex-specific pathways of aging and underlying mechanisms for dimorphic responses

Males and females typically have different lifespans and frequently differ in their responses to anti-aging interventions. These sex-specific responses are documented in mice and Drosophila species, in addition to other organisms where interventions have been tested. While the prevalence of sex-specific responses to anti-aging interventions is now recognised, the underlying causes remain poorly understood. This review first summarises the main pathways and interventions that lead to sex-specific lifespan responses, including the growth-hormone/insulin-like growth factor 1 (GH-IGF1) axis, mechanistic target of rapamycin (mTOR) signalling, and nutritional and pharmacological interventions. After summarising current evidence, several different potential causes for sex-specific responses are discussed. These include sex-differences in xenobiotic metabolism, differing disease susceptibility, sex-specific hormone production and chromosomes, and the relative importance of different signalling pathways in the control of male and female life-history. Understanding why sex-differences in lifespan-extension occur should provide a greater understanding of the mechanisms that regulate the aging process in each sex, and will be crucial for understanding the full implications of these treatments if they are translated to humans.

Xanthotoxin affects depression-related behavior and neurotransmitters content in a sex-dependent manner in mice

The present study aimed to evaluate xanthotoxin's influence on male and female Swiss mice's depression-like behaviors and investigate the potential mechanism of this effect. Naturally derived furanocoumarin (the Apiaceae family), xanthotoxin, administered acutely (12.5 mg/kg), diminished the immobility level in the forced swim test only in males. The immobility level was lower in females than males, which may be associated with a higher serotonin level in the female prefrontal cortex. A dose-dependent increase of serotonin and noradrenaline was reported in the reverse-phase ion-pair liquid chromatography in the female prefrontal cortex but not in the hippocampus. We suggest that xanthotoxin may exert antidepressant properties and affect males and females differently. The increasing level of serotonin in the male and female prefrontal cortex may underlie this effect.

Nucleus accumbens melanin-concentrating hormone signaling promotes feeding in a sex-specific manner

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide produced in the lateral hypothalamus and zona incerta that increases food intake. The neuronal pathways and behavioral mechanisms mediating the orexigenic effects of MCH are poorly understood, as is the extent to which MCH-mediated feeding outcomes are sex-dependent. Here we investigate the hypothesis that MCH-producing neurons act in the nucleus accumbens shell (ACBsh) to promote feeding behavior and motivation for palatable food in a sex-dependent manner. We utilized ACBsh MCH receptor (MCH1R)-directed pharmacology as well as a dual virus chemogenetic approach to selectively activate MCH neurons that project to the ACBsh. Results reveal that both ACBsh MCH1R activation and activating ACBsh-projecting MCH neurons increase consumption of standard chow and palatable sucrose in male rats without affecting motivated operant responding for sucrose, general activity levels, or anxiety-like behavior. In contrast, food intake was not affected in female rats by either ACBsh MCH1R activation or ACBsh-projecting MCH neuron activation. To determine a mechanism for this sexual dimorphism, we investigated whether the orexigenic effect of ACBsh MCH1R activation is reduced by endogenous estradiol signaling. In ovariectomized female rats on a cyclic regimen of either estradiol (EB) or oil vehicle, ACBsh MCH1R activation increased feeding only in oil-treated rats, suggesting that EB attenuates the ability of ACBsh MCH signaling to promote food intake. Collective results show that MCH ACBsh signaling promotes feeding in an estrogen- and sex-dependent manner, thus identifying novel neurobiological mechanisms through which MCH and female sex hormones interact to influence food intake.

Sex differences and effects of the estrous stage on hippocampal-prefrontal theta communications

Effective communication between the mammalian hippocampus and neocortex is essential to certain cognitive-behavioral tasks critical to survival in a changing environment. Notably, functional synchrony between local field potentials (LFPs) of the ventral hippocampus (vHPC) and the medial prefrontal cortex (mPFC) within the theta band (4-12 Hz) underlies innate avoidance behavior during approach-avoidance conflict tasks in male rodents. However, the physiology of vHPC-mPFC communications in females remains unestablished. Furthermore, little is known about how mPFC subdivisions functionally interact in the theta band with hippocampal subdivisions in both sexes in the absence of task demand. Given the established roles of biological sex and gonadal hormone status on innate avoidance behaviors and neuronal excitability, here, we characterize the effects of biological sex and female estrous stage on hippocampal-prefrontal (HPC-mPFC) theta signaling in freely moving female and male rats. LFPs from vHPC, dorsal hippocampus (dHPC), mPFC-prelimbic (PrL), and mPFC-infralimbic (IL) were simultaneously recorded during spontaneous exploration of a familiar arena. Data suggest that theta phase and power in vHPC preferentially synchronize with PrL; conversely, dHPC and IL preferentially synchronize. Males displayed greater vHPC-PrL theta synchrony than females, despite similar regional frequency band power and inter-regional coherence. Additionally, several significant estrous-linked changes in HPC-mPFC theta dynamics were observed. These findings support the hypothesis that HPC-mPFC theta signaling is sensitive to both biological sex and female estrous stage. These findings establish novel research avenues concerning sex as a biological variable and effects of gonadal hormone status on HPC-mPFC network activity as it pertains to threat evaluation biomarkers.

First Demonstration of Double Dissociation between COMT-Met158 and COMT-Val158 Cognitive Performance When Stressed and When Calmer

We present here the first evidence of the much-predicted double dissociation between the effect of stress on cognitive skills [executive functions (EFs)] dependent on prefrontal cortex (PFC) by catechol-O-methyltransferase (COMT) genotype. The COMT gene polymorphism with methionine (Met) at codon 158 results in more dopamine (DA) in PFC and generally better EFs, while with valine (Val) at codon 158 the result is less PFC DA and generally poorer EFs. Many have predicted that mild stress, by raising PFC DA levels should aid EFs of COMT-Vals (bringing their PFC DA levels up, closer to optimal) and impair EFs of COMT-Mets (raising their PFC DA levels past optimal). We tested 140 men and women in a within-subject crossover design using extremely mild social evaluative stress. On trials requiring EFs (incongruent trials) of the Flanker/Reverse Flanker task, COMT-Val158 homozygotes performed better when mildly stressed than when calmer, while COMT-Met158 carriers performed worse when mildly stressed. Two other teams previously tried to obtain this, but only found stress impairing EFs of COMT-Mets, not improving EFs of COMT-Vals. Perhaps we found both because we used a much milder stressor. Evidently, the bandwidth for stress having a facilitative effect on EFs is exceedingly narrow.

Interactions of the estrous cycle, novelty, and light on female and male rat open field locomotor and anxiety-related behaviors

Animal behavior can be modulated by multiple interacting factors. In rodents such as rats, these factors include, among others, the female estrous cycle, exposure to a novel environment, and light. Here, we used the open field test to disassociate differences in behavior resulting from each of these factors by testing the hypothesis that locomotor and anxiety-related behaviors differ between estrous cycle phases in female rats and that novelty and light exposure concurrently influence these behaviors in both female and male rats. Adult female rats were tested twice under red or white light in estrus and diestrus estrous cycle phases. Adult male rats were also tested twice under either red or white light. In females, an interaction between novelty and estrous cycle phase influenced locomotor and anxiety-related behaviors. In males, novelty influenced locomotor and anxiety-related behaviors differentially under red and white light. Light exposure increased anxiety-related behaviors in both males and females, but reduced locomotor behavior only in females. These findings reveal the complexities of behavioral testing and highlight the importance of factors such as the estrous cycle, novelty, and light exposure.

Influence of sex, menstrual cycle, and hormonal contraceptives on egocentric navigation with or without landmarks

This study examines the influence of sex, menstrual cycle, hormonal contraceptives (HC) and sex hormone levels in following egocentric navigation instructions with or without landmarks. Estradiol seem to bias the reference frame for navigation during estrous cycle of female rats. However, previous studies in humans found no differences in overall navigation between women in their early follicular and mid-luteal menstrual cycle phases, whose performance was worse than that of men. Our study hypothesis was that the performance of women would be improved during the peri-ovulatory phase and would remain the same during placebo and active phases of HC users. The study included 21 men, 62 women with natural menstrual cycle (21 during early follicular phase, 20 during peri-ovulatory phase, and 21 during mid-luteal phase), and 38 women that were receiving HC (13 during placebo phase and 25 during active phase). The men outperformed the women with a natural menstrual cycle when following egocentric instructions without landmarks. However, the women's performance varied according to the phase of their menstrual cycle, differing from men during early follicular and mid-luteal phases but not during the peri-ovulatory phase. The use of HC also improved the performance of women to the extent that the difference with men disappeared. No differences were observed between HC-placebo and HC-active user groups during egocentric navigation without landmarks and among all groups during egocentric navigation with landmarks. Analysis of salivary hormones showed that testosterone levels were higher in men and that estradiol levels in women were higher during peri-ovulatory and mid-luteal phases and also in HC users. Progesterone levels were higher in women during the mid-luteal phase. These results appear compatible with beneficial effect of testosterone and estradiol on egocentric navigation without landmarks and with a block of this effect produced by progesterone.

Acute d-fenfluramine, but not fluoxetine decreases sweet intake in BALB/c, C57BL/6 and SWR inbred mouse strains

Dopamine, opioid and muscarinic receptor antagonists differentially reduce sucrose and saccharin intakes across inbred mouse strains. Whereas these systems stimulate sweet intake, serotonin signaling inhibits food intake. The present study examined whether fluoxetine (0.1-10 mg/kg) or d-fenfluramine (0.1-6 mg/kg) differentially inhibited sucrose or saccharin intake in BALB/c, C57BL/6 and SWR mice. Fluoxetine marginally altered sucrose intake in all strains. d-fenfluramine significantly, but quite similarly reduced (ID₄₀) sucrose and saccharin intake in BALB/c (5.7 vs. 5.8 mg/kg), C57BL/6 (4.4 vs. 4.3 mg/kg) and SWR (4.6 vs. 5.6 mg/kg) mice, suggesting serotonin-induced inhibition of orosensory mechanisms in all three inbred mouse strains.

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

Immunohistochemical Evidence for Glutamatergic Regulation of Nesfatin-1 Neurons in the Rat Hypothalamus

Nesfatin-1, identified as an anorexigenic peptide, regulates the energy metabolism by suppressing food intake. The majority of nesfatin-1-synthesizing neurons are concentrated in various hypothalamic nuclei, especially in the supraoptic (SON), arcuate (ARC) and paraventricular nuclei (PVN). We tested the hypothesis that the glutamatergic system regulates nesfatin-1 neurons through glutamate receptors. Therefore, the first aim of the proposed studies was to examine effects of different glutamate agonists in the activation of nesfatin-1 neurons using c-Fos double immunohistochemical labeling. Experimental groups were formed containing male and female rats which received intraperitoneal injections of glutamate agonists kainic acid, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) while the control rats received vehicle. The significant increase in the number of c-Fos-expressing nesfatin-1 neurons after agonist injections were observed both in female and male subjects and some of these effects were found to be sexually dimorphic. In addition, treatment with specific glutamate antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or dizocilpine (MK-801) before each of the three agonist injections caused a statistically significant reduction in the number of activated nesfatin-1 neurons in the hypothalamic nuclei including supraoptic, paraventricular and arcuate nuclei. The second aim of the study was to determine the expression of glutamate receptor subunit proteins in the nesfatin-1 neurons by using a double immunofluorescence technique. The results showed that the glutamate receptor subunits, which may form homomeric or heteromeric functional receptor channels, were expressed in the nesfatin-1 neurons. In conclusion, the results of this study suggest that nesfatin-1 neurons respond to glutamatergic signals in the form of neuronal activation and that the glutamate receptors that are synthesized by nesfatin-1 neurons may participate in the glutamatergic regulation of these neurons.

Pre-Gestational intake of Lactobacillus helveticus NS8 has anxiolytic effects in adolescent Sprague Dawley offspring

INTRODUCTION

Adolescence is a period of heightened susceptibility to anxiety disorders. Probiotic supplementation had a positive impact on reducing anxiety. The maternal microbiome plays an important role in child health outcomes and in the establishment of the offspring microbiome. Few studies have investigated the impact of gestational probiotic supplementation on the offspring's anxiety.

METHODS

The present study examined the impact of prenatal Lactobacillus helveticus NS8 supplementation (LAC) on Sprague Dawley rat offspring's anxiety-like behavior. The behaviors tested in the present study include the elevated plus maze (EPM), the open field test (OFT), and prepulse inhibition (PPI). Analyses of variance were utilized.

RESULTS

(a) The performance of LAC adolescent rats in the EPM was similar to that in the OFT, both of which reflect that LAC caused an antianxiety effect in adolescent offspring rats and the antianxiety effect without sex differences; (b) LAC did not change performance in PPI and did not change the sex and age differences in PPI; and c. LAC decreased the body mass of rat offspring.

CONCLUSION

Lactobacillus helveticus NS8 supplementation during gestation might have a moderate antianxiety effect in both males and females (especially adolescents) and be helpful for avoiding excessive body mass.

Estradiol promotes and progesterone reduces anxiety-like behavior produced by nicotine withdrawal in female rats

This study assessed sex differences and the role of ovarian hormones in nicotine withdrawal. Study 1 compared physical signs, anxiety-like behavior, and corticosterone levels in male, intact female, and ovariectomized (OVX) female rats during nicotine withdrawal. Estradiol (E2) and progesterone levels were also assessed in intact females that were tested during different phases of the 4-day estrous cycle. Study 2 assessed the role of ovarian hormones in withdrawal by comparing the same measures in OVX rats that received vehicle, E2, or E2+progesterone prior to testing. Briefly, rats received a sham surgery or an ovariectomy procedure. Fifteen days later, rats were prepared with a pump that delivered nicotine for 14 days. On the test day, rats received saline or the nicotinic receptor antagonist, mecamylamine to precipitate withdrawal. Physical signs and anxiety-like behavior were assessed on the elevated plus maze (EPM) and light-dark transfer (LDT) tests. During withdrawal, intact females displayed greater anxiety-like behavior and increases in corticosterone levels as compared to male and OVX rats. Females tested in the estrus phase (when E2 is relatively low) displayed less anxiety-like behavior and had lower corticosterone levels versus all other phases. Anxiety-like behavior and corticosterone levels were positively correlated with E2 and negatively correlated with progesterone levels. Intact females displaying high E2/low progesterone showed greater anxiety-like behavior and corticosterone levels as compared to females displaying low E2/high progesterone. Lastly, OVX-E2 rats displayed greater anxiety-like behavior than OVX-E2+progesterone rats. These data suggest that E2 promotes and progesterone reduces anxiety-like behavior produced by nicotine withdrawal.

Estrogen-dependent hippocampal wiring as a risk factor for age-related dementia in women

Women are more prone than men to develop age-related dementia, such as Alzheimer's disease (AD). This has been linked to the marked decrease in circulating estrogens during menopause. This review proposes to change this perspective and consider women's vulnerability to developing AD as a consequence of sex differences in the neurobiology of memory, focusing on the hippocampus. The hippocampus of cognitively impaired subjects tends to shrink with age; however, in many cases, this can be prevented by exercise or cognitive training, suggesting that if you do not use the hippocampus you lose it. We will review the developmental trajectory of sex steroids-regulated differences on the hippocampus, proposing that the overall shaping action of sex-steroids results in a lower usage of the hippocampus in females, which in turn makes them more vulnerable to the effects of ageing, the "network fragility hypothesis". To explain why women rely less on hippocampus-dependent strategies, we propose a "computational hypothesis" that is based on experimental evidence suggesting that the direct effects of estrogens on hippocampal synaptic and structural plasticity during the estrous-cycle confers instability to the memory-dependent hippocampal network. Finally, we propose to counteract AD with training and/or treatments, such as orienteering, which specifically favour the use of the hippocampus.

Deep learning-based classification of the mouse estrous cycle stages

There is a rapidly growing demand for female animals in preclinical animal, and thus it is necessary to determine animals' estrous cycle stages from vaginal smear cytology. However, the determination of estrous stages requires extensive training, takes a long time, and is costly; moreover, the results obtained by human examiners may not be consistent. Here, we report a machine learning model trained with 2,096 microscopic images that we named the "Stage Estimator of estrous Cycle of RodEnt using an Image-recognition Technique (SECREIT)." With the test dataset (736 images), SECREIT achieved area under the receiver-operating-characteristic curve of 0.962 or more for each estrous stage. A test using 100 images showed that SECREIT provided correct classification that was similar to that provided by two human examiners (SECREIT: 91%, Human 1: 91%, Human 2: 79%) in 11 s. The SECREIT can be a first step toward accelerating the research using female rodents.

Altered cell surface receptor dynamics and circulatory occurrence of neutrophils in a small animal fracture model

INTRODUCTION

Excessive activation of the immune response after femoral fractures and fracture fixation is potentially associated with the development of systemic and local complications, particularly in multiple trauma patients. A dysregulated function of neutrophils, the most prevailing immune cells in circulation, has been discussed as a central pathophysiological background for these unfavourable post-traumatic courses. Our aim was to investigate alterations in activity and functionality as expressed by the cell surface receptor dynamics of circulatory neutrophils after femoral fracture and intramedullary stabilization.

MATERIAL AND METHODS

After intramedullary stabilization, an isolated femur fracture was induced in 18 Sprague-Dawley rats. Animals were terminated at different time points, i.e. after 3 (n = 5, group 3d), 7 (n = 5, group 7d) and 14 (n = 5, Group 14d) days and grouped accordingly. Additionally, baseline measurements were performed in one control animal per study group (n = 3) after anaesthesia induction and termination, without prior intramedullary nailing and fracture induction. The numbers and cell surface expression of CD11b, CD11a, CD62 L, and CD49d of circulating neutrophils were compared between groups.

RESULTS

Neutrophil numbers were significantly reduced at 3 days compared with baseline measurements (1.2 × 10⁵ vs. 6.3 × 10⁵ cells/mL, p < 0.01). By day 7, neutrophil counts significantly increased back to homeostatic levels (p < 0.05). At day 3, CD11b-expression was significantly reduced, whereas CD11a-expression was increased compared with the baseline measurements (p < 0.05). At day 7, the circulatory neutrophil pool exhibited a unique CD11b^high/CD11a^high-neutrophil subset showing a significantly increased co-expression of CD49d. The expression of CD62 L did not change significantly throughout the experiment compared with baseline measurements.

CONCLUSIONS

This descriptive small animal fracture study is the first to show that an intramedullary stabilized femur fracture is associated with a temporary reduction in circulatory neutrophil count and concurrent changes in circulatory neutrophil function. Moreover, we demonstrated that the restoration to homeostatic neutrophil activation status occurs concomitantly with the appearance of a novel neutrophil subtype (CD11b^high/CD11a^high) in circulation. Our fundamental new findings of the changes in circulatory neutrophil count and functionality after trauma form an excellent basis for future studies to further elucidate the role of neutrophils as activators and regulators of different post-traumatic processes, potentially resulting in local (e.g., fracture healing disturbances) or systemic (e.g., MODS) complications. This might result in the development of specific therapies to reduce adverse outcomes after trauma.

Approaching Sex Differences in Cardiovascular Non-Coding RNA Research

Cardiovascular disease (CVD) is the biggest cause of sickness and mortality worldwide in both males and females. Clinical statistics demonstrate clear sex differences in risk, prevalence, mortality rates, and response to treatment for different entities of CVD. The reason for this remains poorly understood. Non-coding RNAs (ncRNAs) are emerging as key mediators and biomarkers of CVD. Similarly, current knowledge on differential regulation, expression, and pathology-associated function of ncRNAs between sexes is minimal. Here, we provide a state-of-the-art overview of what is known on sex differences in ncRNA research in CVD as well as discussing the contributing biological factors to this sex dimorphism including genetic and epigenetic factors and sex hormone regulation of transcription. We then focus on the experimental models of CVD and their use in translational ncRNA research in the cardiovascular field. In particular, we want to highlight the importance of considering sex of the cellular and pre-clinical models in clinical studies in ncRNA research and to carefully consider the appropriate experimental models most applicable to human patient populations. Moreover, we aim to identify sex-specific targets for treatment and diagnosis for the biggest socioeconomic health problem globally.

Maternal separation affects the electrophysiological properties of Aδ-fibres and nociceptive behaviours in male and female mice

AIM

Early life adverse effects have been associated with an increased risk of suffering pain syndromes in adulthood. Although animal models are of great importance to study modifications of pain sensitivity, up to date the results obtained are contradicting due to the varied methodologies used. Therefore, the aim of the present study was to characterise, as a whole, possible modifications in visceral and somatic nociceptive responses in male and female ICR mice, submitted to two different protocols of maternal separation (MS), and possible modifications in the electrophysiological properties of peripheral nociceptive Aδ-primary afferents.

MAIN METHODS

Male and female mice were submitted to 3 or 4-8 hr of daily MS from postnatal day (PND) 2-17 and early weaned. On PND 67 von Frey, hot plate and writhing tests were performed. Afterwards electrophysiological recordings were carried out, using the in vitro skin-saphenous nerve preparation in males.

KEY FINDINGS

The short separation protocol of MS did not modify nociceptive sensitivity; but when mice were separated from their dams for the long separation, mechanical pain thresholds were modified in male and female mice and visceral nociception was increased in female mice. Electrophysiological recordings showed that cutaneous Aδ-fibres were sensitised and their mechanotransduction properties were altered in both MS protocols.

SIGNIFICANCE

Although MS increases the activity and the mechanosensitivity of cutaneous Aδ-afferent fibres at both short and long periods of separation, only the longer interval of time induces nociceptive sensitivity alterations during adulthood. These results highlight the possible influence of a stress free environment during childhood to reduce nociceptive alterations in adulthood.

Sex Chromosomes Are Severely Disrupted in Gastric Cancer Cell Lines

Sex has not received enough attention as an important biological variable in basic research, even though the sex of cells often affects cell proliferation, differentiation, apoptosis, and response to stimulation. Knowing and considering the sex of cells used in basic research is essential as preclinical and clinical studies are planned based on basic research results. Cell lines derived from tumor have been widely used for proof-of-concept experiments. However, cell lines may have limitations in testing the effect of sex on cell level, as chromosomal abnormality is the single most characteristic feature of tumor. To examine the status of sex chromosomes in a cell line, 12 commercially available gastric carcinoma (GC) cell lines were analyzed using several different methods. Loss of Y chromosome (LOY) accompanied with X chromosome duplication was found in three (SNU-484, KATO III, and MKN-1) out of the six male-derived cell lines, while one cell line (SNU-638) showed at least partial deletion in the Y chromosome. Two (SNU-5 and MKN-28) out of six female-derived cell lines showed a loss of one X chromosome, while SNU-620 gained one extra copy of the X chromosome, resulting in an XXX karyotype. We found that simple polymerase chain reaction (PCR)-based sex determination gives a clue for LOY for male-derived cells, but it does not provide detailed information for the gain or loss of the X chromosome. Our results suggest that carefully examining the sex chromosome status of cell lines is necessary before using them to test the effect of sex on cell level.

Sex-steroid-dependent plasticity of brain-stem autonomic circuits

In the central nervous system (CNS), nuclei of the brain stem play a critical role in the integration of peripheral sensory information and the regulation of autonomic output in mammalian physiology. The nucleus tractus solitarius of the brain stem acts as a relay center that receives peripheral sensory input from vagal afferents of the nodose ganglia, integrates information from within the brain stem and higher central centers, and then transmits autonomic efferent output through downstream premotor nuclei, such as the nucleus ambiguus, the dorsal motor nucleus of the vagus, and the rostral ventral lateral medulla. Although there is mounting evidence that sex and sex hormones modulate autonomic physiology at the level of the CNS, the mechanisms and neurocircuitry involved in producing these functional consequences are poorly understood. Of particular interest in this review is the role of estrogen, progesterone, and 5α-reductase-dependent neurosteroid metabolites of progesterone (e.g., allopregnanolone) in the modulation of neurotransmission within brain-stem autonomic neurocircuits. This review will discuss our understanding of the actions and mechanisms of estrogen, progesterone, and neurosteroids at the cellular level of brain-stem nuclei. Understanding the complex interaction between sex hormones and neural signaling plasticity of the autonomic nervous system is essential to elucidating the role of sex in overall physiology and disease.

Improving translational research in sex-specific effects of comorbidities and risk factors in ischaemic heart disease and cardioprotection: position paper and recommendations of the ESC Working Group on Cellular Biology of the Heart

Ischaemic heart disease (IHD) is a complex disorder and a leading cause of death and morbidity in both men and women. Sex, however, affects several aspects of IHD, including pathophysiology, incidence, clinical presentation, diagnosis as well as treatment and outcome. Several diseases or risk factors frequently associated with IHD can modify cellular signalling cascades, thus affecting ischaemia/reperfusion injury as well as responses to cardioprotective interventions. Importantly, the prevalence and impact of risk factors and several comorbidities differ between males and females, and their effects on IHD development and prognosis might differ according to sex. The cellular and molecular mechanisms underlying these differences are still poorly understood, and their identification might have important translational implications in the prediction or prevention of risk of IHD in men and women. Despite this, most experimental studies on IHD are still undertaken in animal models in the absence of risk factors and comorbidities, and assessment of potential sex-specific differences are largely missing. This ESC WG Position Paper will discuss: (i) the importance of sex as a biological variable in cardiovascular research, (ii) major biological mechanisms underlying sex-related differences relevant to IHD risk factors and comorbidities, (iii) prospects and pitfalls of preclinical models to investigate these associations, and finally (iv) will provide recommendations to guide future research. Although gender differences also affect IHD risk in the clinical setting, they will not be discussed in detail here.

Sex Differences and the Role of Estradiol in Mesolimbic Reward Circuits and Vulnerability to Cocaine and Opiate Addiction

Although both men and women become addicted to drugs of abuse, women transition to addiction faster, experience greater difficulties remaining abstinent, and relapse more often than men. In both humans and rodents, hormonal cycles are associated with females' faster progression to addiction. Higher concentrations and fluctuating levels of ovarian hormones in females modulate the mesolimbic reward system and influence reward-directed behavior. For example, in female rodents, estradiol (E2) influences dopamine activity within the mesolimbic reward system such that drug-directed behaviors that are normally rewarding and reinforcing become enhanced when circulating levels of E2 are high. Therefore, neuroendocrine interactions, in part, explain sex differences in behaviors motivated by drug reward. Here, we review sex differences in the physiology and function of the mesolimbic reward system in order to explore the notion that sex differences in response to drugs of abuse, specifically cocaine and opiates, are the result of molecular neuroadaptations that differentially develop depending upon the hormonal state of the animal. We also reconsider the notion that ovarian hormones, specifically estrogen/estradiol, sensitize target neurons thereby increasing responsivity when under the influence of either cocaine or opiates or in response to exposure to drug-associated cues. These adaptations may ultimately serve to guide the motivational behaviors that underlie the factors that cause women to be more vulnerable to cocaine and opiate addiction than men.

Sex differences in murine myocutaneous flap revascularization

Sex differences in susceptibility to ischemia/reperfusion injury have been documented in humans. Premenopausal women have a lower risk of ischemic heart disease than age-matched men, whereas after menopause, the risk is similar or even higher in women. However, little is known about the effects of sex on myocutaneous ischemia/reperfusion. To explore sex differences in wound revascularization, we utilized a murine myocutaneous flap model of graded ischemia. A cranial-based, peninsular-shaped, myocutaneous flap was surgically created on the dorsum of male and female mice. Physiological, pathological, immunohistochemical, and molecular parameters were analyzed. Flaps created on female mice were re-attached to the recipient site resulting in nearly complete viability at post-operative day 10. In contrast, distal full-thickness myocutaneous necrosis was evident at 10 days post-surgery in male mice. Over the 10 day study interval, laser speckle imaging documented functional revascularization in all flap regions in female mice, but minimal distal flap reperfusion in male mice. Day 10 immunostained histologic sections confirmed significant increases in distal flap vessel count and vascular surface area in female compared to male mice. RT-PCR demonstrated significant differences in growth factor and metabolic gene expression between female and male mice at day 10. In conclusion, in a graded-ischemia wound healing model, flap revascularization was more effective in female mice. The recognition and identification of sex-specific wound healing differences may lead to a better understanding of the underlying mechanisms of myocutaneous revascularization and drive novel discovery to improve soft tissue wound healing following tissue transfer for traumatic injury and cancer resection.

Intermittent High-Fat Diet Intake Reduces Sensitivity to Intragastric Nutrient Infusion and Exogenous Amylin in Female Rats

OBJECTIVE

Intermittent (INT) access to a high-fat diet (HFD) can induce excessive-intake phenotypes in rodents. This study hypothesized that impaired satiation responses contribute to elevated intake in an INT-HFD access model.

METHODS

First, this study characterized the intake and meal patterns of female rats that were subjected to an INT HFD in which a 45% HFD was presented for 20 hours every fourth day. To examine nutrient-induced satiation, rats received intragastric infusions of saline or Ensure Plus prior to darkness-onset food access. A similar design was used to examine sensitivity to the satiating effect of amylin. This study then examined whether an INT HFD influences amylin-induced c-Fos in feeding-relevant brain areas.

RESULTS

Upon INT HFD access, rats consumed meals of larger size. The anorexic response to intragastric Ensure infusion and exogenous amylin treatment was blunted in INT rats on both chow-only and INT-HFD days of the diet regimen, compared with chow-maintained and continuous-HFD rats. An INT HFD did not influence amylin-induced c-Fos in the area postrema, nucleus of the solitary tract, and lateral parabrachial nucleus.

CONCLUSIONS

Impaired satiation responses, mediated in part by reduced sensitivity to amylin, may explain the elevated intake observed upon INT HFD access and may play a role in disorders of INT overconsumption, including binge eating.

Starvation promotes histone lysine butyrylation in the liver of male but not female mice

AIMS

Post-translational modifications (PTMs) of histones are regulated by the availability of their respective acyl-CoAs. Among these histone PTMs, the metabolic origin of histone butyrylation (Kbu) is still poorly understood.

MATERIAL AND METHODS

The impact of starvation on the levels of Kbu was determined by western blotting on histones extracted from the liver of fed and fasted C57BL/6 mice and immunohistochemistry on liver paraffin sections.

KEY FINDINGS

Using animal model we provide evidence that the stimulation of ketogenesis following starvation, in addition to histone beta-hydroxybutyrylation (Kbhb), also leads to an increase in histone butyrylation (Kbu). Using an immunohistochemistry (IHC) approach we report first that hepatocytes contained butyrylated histones with important cell-to-cell heterogeneity. More importantly, our investigations based on western blotting and IHC also proposed that the basal levels of Kbu differ between male and female mice, with female mouse hepatocytes containing higher levels of butyrylated histones. Starvation enhanced solely histone Kbu levels in the liver of males but not females.

SIGNIFICANCE

This is the first demonstration of a sex-dependent large-scale stimulation of histone acylation. Our data also point to different basal metabolic conditions of the male and female liver cells with a sex-dependent impact on the hepatocytes' epigenome.

Sex bias and omission in neuroscience research is influenced by research model and journal, but not reported NIH funding

Neuroscience research has historically demonstrated sex bias that favors male over female research subjects, as well as sex omission, which is the lack of reporting sex. Here we analyzed the status of sex bias and omission in neuroscience research published across six different journals in 2017. Regarding sex omission, 16% of articles did not report sex. Regarding sex bias, 52% of neuroscience articles reported using both males and females, albeit only 15% of articles using both males and females reported assessing sex as an experimental variable. Overrepresentation of the sole use of males compared to females persisted (26% versus 5%, respectively). Sex bias and omission differed across research models, but not by reported NIH funding status. Sex omission differed across journals. These findings represent the latest information regarding the complex status of sex in neuroscience research and illustrate the continued need for thoughtful and informed action to enhance scientific discovery.

Cognition, The Menstrual Cycle, and Premenstrual Disorders: A Review

Sex hormones, such as estrogens, progesterone, and testosterone, have a significant influence on brain, behavior, and cognitive functioning. The menstrual cycle has been a convenient model to examine how subtle fluctuations of these hormones can relate to emotional and cognitive functioning. The aim of the current paper is to provide a narrative review of studies investigating cognitive functioning in association with the menstrual cycle in biological females, with a focus on studies that have investigated cognitive functioning across the menstrual cycle in females with premenstrual mood disorders, such as premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD). In line with previous reviews, the current review concluded that there is a lack of consistent findings regarding cognitive functioning across the menstrual cycle. Most studies focused on changes in levels of blood estrogen, and neglected to explore the role of other hormones, such as progesterone, on cognitive functioning. Cognitive research involving premenstrual disorders is in its infancy, and it remains unclear whether any cognitive disturbances that are identified may be attributed to negative experience of mood and psychological symptoms or be a more direct effect of hormonal dysregulation or sensitivity. Suggestions for future research are provided.