Sex diversity in the 21st century: Concepts, frameworks, and approaches for the future of neuroendocrinology

A Review of Sex and Gender Factors in Stimulant Treatment for ADHD: Knowledge Gaps and Future Directions

OBJECTIVE

Stimulant medications are the primary pharmacological intervention for ADHD, yet our understanding of how sex and gender impact stimulant treatment outcomes remains limited. Clinical guidelines do not differ for female and male individuals despite possible sex and gender-related differences in effectiveness, adverse events, and pharmacokinetics. This theoretical framework identifies five key knowledge gaps relating to sex and gender effects in stimulant treatment.

METHOD

We investigate the stimulant treatment trajectories of girls and women with ADHD from diagnosis and prescription to daily use and outcomes. We examine the impact of reproductive life transitions and hormonal fluctuations and their interactions with gender socialization and gendered expectations on treatment effectiveness, stigma, and adherence.

RESULTS

By synthesizing existing literature, proposing testable predictions, and suggesting future research directions, we highlight the urgent need for studies that systematically investigate these factors.

CONCLUSION

Addressing these gaps could significantly improve treatment outcomes for girls and women with ADHD, particularly during biological and gender role transitions.

Ten simple rules for queer data collection and analysis by STEM researchers

Queer people are still underrepresented both as STEM researchers and participants, partially due to a dearth of accurate data on this demographic. The lack of consideration for queer identities in data collection and dissemination causes a vicious cycle of exclusion. To address this invisibility, it is important to collect and report data in an inclusive and accurate manner across all areas of research, including in studies that are not specifically focused on queer populations. However, STEM researchers are often unsure of how to properly collect data in a manner that fairly represents queer people. We have developed a list of Ten Simple rules to aid researchers to perform data collection on queer individuals, focusing on study design and data dissemination. We address several issues in queer data, such as language use, dealing with small populations, and balancing demands. We also discuss how to extend this inclusive practice for studies on animal populations. These rules are aimed at anybody surveying populations which may contain queer individuals, including for example research studies and inclusivity surveys for conferences. By providing practical tips, we hope to alleviate insecurity and confusion around this topic.

Differential Lesion Patterns Associated With Stroke-Induced Apraxia in Women and Men

BACKGROUND

The motor-cognitive syndrome apraxia is a common stroke sequela and severely affects the outcome after stroke by impairing activities of daily living. Notably, like in many health conditions, there is a massive backlog regarding studies on sex differences in patients with apraxia despite common knowledge that sex influences praxis performance in healthy participants. We investigated putative sex differences in apraxic stroke patients at the behavioral and neural levels.

METHODS

We retrospectively analysed the data of a cohort of 102 left-hemisphere stroke patients in the (sub)acute phase who were apraxic according to the Cologne Apraxia Screening (KAS). We conducted voxel-based lesion-symptom mapping (VLSM) to elucidate the lesion patterns. Further, in an age-matched subsample (tolerance of 5 years) with equal numbers of men and women, behavioral comparisons and a VLSM analysis were conducted to explore differential sex-related lesion patterns.

RESULTS

Overall, apraxic deficits were associated with lesions in the parietal, temporal, and frontal regions in the cohort of 102 left-hemisphere stroke patients. The age-matched cohort consisted of 30 women and 30 men and showed no significant differences in demographic and clinical characteristics. There were no performance differences between men and women at the behavioral level regarding praxis functions. In contrast, VLSM revealed differential lesion patterns by sex. Male compared to female apraxic stroke patients significantly more often showed lesions that affected the left inferior frontal gyrus.

CONCLUSION

The data suggest a differential organization of the praxis system in men and women, warranting further exploration.

Depression in adolescence and young adulthood: the difficulty to integrate motivational/emotional systems

Depression is presented as a multi-factorial bio-psycho-social expression that has evolved primarily as an effect of stressors related to the motivational/emotional systems that regulate the BrainMind in our relationship with conspecifics. These stressors may be caused by two sources of threat, firstly, the loss of bonding with the caregiver and later with a partner and/or group which relates to the SEPARATION (PANIC/GRIEF) system, secondly, social defeat as an expression of the social competition and social dominance. The sexual maturity drives the individual to social competition and social dominance, even if the latter often occurs before sexual maturity, e.g., chickens, dogs, non-human primates, and humans. Depression is an evolutionarily conserved mechanism in mammals to terminate both separation anxiety, so as to protect the vulnerable social brain from the consequences of prolonged separation anxiety, and the stress of social competition when social defeat is predictable. Adolescence and Young adulthood are particularly susceptible to these two types of threat because of human developmental characteristics that are summarized by the term neoteny. This refers to the slowing down of growth and development, resulting in both a prolonged period of dependence on a caring/protective adult and the persistence of juvenile characteristics throughout life. Therefore, neoteny makes the transition from childhood to sexual maturity more dramatic, making the integration of the SEPARATION (PANIC/GRIEF) system with the dynamics of social competition and dominance more stressful and a source of depression. Stress is an expression of the HPA-Hypothalamic-Pituitary-Adrenal axis that articulates with other systems, mainly the autonomic nervous system and the immune-inflammatory system. The latter is believed to be one of the most significant components in the dynamics of depressive processes, connected to the prodromes of its activation in childhood, under the pressure of environmental and relational stressors which can lead to learned helplessness. The recurrence of stressors makes it easier for the immune-inflammatory system to be activated in later life, which could make a significant contribution to the establishment of a depressive disease. The possible contribution of children's identification processes with their parents' depressive personalities through observational learning is considered.

Incorporating Sex-Diverse and Gender-Inclusive Perspectives in Higher Education Biology Courses

Inclusive teaching is teaching in a way that reaches all students in the classroom; this is beneficial for everyone, particularly for those with minoritized identities. Instructors play a critical role in scaffolding how students are exposed to and learn science content in the classroom. In this manuscript, we discuss how biology instructors can make their classrooms more inclusive with regard to sex and gender diversity content. Many topics in biology are based on androcentric, heteronormative, and oppressive framing, even though those lenses are more reflective of our own history and culture than they are of the diversity we see in nature. Here, we summarize information presented in the SICB 2024 workshop titled "Incorporating sex diversity and gender inclusivity in biology undergraduate classrooms" and provide instructors with (a) rationale for why inclusive teaching matters, (b) guidance on how to challenge unscientific views and make their curricula more sex diverse and gender inclusive, and (c) practical and easy-to-implement strategies for discussing "contentious" topics in the classroom. Incorporation of this material will be beneficial for students, for science and medicine, and for accurately representing the diversity found across the tree of life.

A Practical Guide to Avoiding Biased Communication in Reproductive Biology

When cultural biases pervade communication, whether visual or text-based, objectivity is impaired. Anthropocentrism (human-centered bias) and androcentrism (male-centered bias) in particular distort perspectives in mammalian reproductive biology. This paper provides a resource for professionals who understand how cultural biases can be reinforced with language, visuals, and conceptual framing. After brief explanations, we present neutral alternatives to biased terminology as well as ways to avoid bias in illustrations. Since this paper is animal-centric, we hope to inspire the creation of similar resources across a more diverse biota and, thus, move towards a more neutral perspective across reproductive biology.

Revisiting the specific and potentially independent role of the gonad in hormone regulation and reproductive behavior

Gonadal sex steroid hormones are well-studied modulators of reproductive physiology and behavior. Recent behavioral endocrinology research has focused on how the brain dynamically responds to - and may even produce - sex steroids, but the gonadal tissues that primarily release these hormones receive much less attention as a potential mediator of behavioral variation. This Commentary revisits mechanisms by which the reproductive hypothalamic-pituitary-gonadal (HPG) axis can be modulated specifically at the gonadal level. These mechanisms include those that may allow the gonad to be regulated independently of the HPG axis, such as receptors for non-HPG hormones, neural inputs and local production of conventional 'neuropeptides'. Here, I highlight studies that examine variation in these gonadal mechanisms in diverse taxa, with an emphasis on recent transcriptomic work. I then outline how future work can establish functional roles of gonadal mechanisms in reproductive behavior and evaluate gonad responsiveness to environmental cues. When integrated with neural mechanisms, further investigation of gonadal hormone regulation can yield new insight into the control and evolution of steroid-mediated traits, including behavior.

Effects of arginine vasopressin on human anxiety and associations with sex, dose, and V1a-receptor genotype

RATIONALE

Arginine vasopressin (AVP) has dose- and sex-specific effects on social behavior, and variation in social responses is related to variation in the V1a receptor gene in animals. Whether such complexity also characterizes AVP effects on anxiety in humans, or whether V1a genotype is related to anxiety and/or AVP's ability to affect it, remains to be determined.

OBJECTIVE

To test if AVP has dose-dependent effects on anxiety in men and/or women and if a particular allele within the RS3 promoter region of the V1a receptor gene is associated with anxiety and/or AVP effects on anxiety.

METHOD

Men and women self-administered 20 IU or 40 IU intranasal arginine vasopressin (AVP) and placebo in a double-blind, within-subjects design, and State (SA) and Trait (TA) anxiety were measured 60 min later. PCR was used to identify allelic variation within the RS3 region of the V1a receptor gene.

RESULTS

AVP decreased SA in men across both doses, whereas only the lower dose had the same effect, across sexes, in individuals who carry at least one copy of a previously identified "risk" allele in the RS3 promoter of the V1a receptor gene. Additionally, after placebo, women who carried a copy of the allele displayed lower TA than women who did not, and AVP acutely increased TA scores in those women.

CONCLUSIONS

Exogenous AVP has modest sex- and dose-dependent effects on anxiety/affect in humans. Further, allelic variation in the V1a promoter appears associated with responsiveness to AVP's effects and, at least in women, to stable levels of anxiety/affect.

Sex differences in the rodent medial prefrontal cortex - What Do and Don't we know?

The prefrontal cortex, particularly its medial subregions (mPFC), mediates critical functions such as executive control, behavioral inhibition, and memory formation, with relevance for everyday functioning and psychopathology. Despite broad characterization of the mPFC in multiple model organisms, the extent to which mPFC structure and function vary according to an individual's sex is unclear - a knowledge gap that can be attributed to a historical bias for male subjects in neuroscience research. Recent efforts to consider sex as a biological variable in basic science highlight the great need to close this gap. Here we review the knowns and unknowns about how rodents categorized as male or female compare in mPFC neuroanatomy, pharmacology, as well as in aversive, appetitive, and goal- or habit-directed behaviors that recruit the mPFC. We propose that long-standing dogmatic concepts of mPFC structure and function may not remain supported when we move beyond male-only studies, and that empirical challenges to these dogmas are warranted. Additionally, we note some common pitfalls in this work. Most preclinical studies operationalize sex as a binary categorization, and while this approach has furthered the inclusion of non-male rodents it is not as such generalizable to what we know of sex as a multidimensional, dynamic variable. Exploration of sex variability may uncover both sex differences and sex similarities, but care must be taken in their interpretation. Including females in preclinical research needs to go beyond the investigation of sex differences, improving our knowledge of how this brain region and its subregions mediate behavior and health. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Estrogenic influences on agonistic behavior in teleost fishes

Teleost fishes show an extraordinary diversity of sexual patterns, social structures, and sociosexual behaviors. Sex steroid hormones are key modulators of social behaviors in teleosts as in other vertebrates and act on sex steroid receptor-containing brain nuclei that form the evolutionarily conserved vertebrate social behavior network (SBN). Fishes also display important differences relative to tetrapod vertebrates that make them particularly well-suited to study the physiological mechanisms modulating social behavior. Specifically, fishes exhibit high levels of brain aromatization and have what has been proposed to be a lifelong, steroid hormone dependent plasticity in the neural substrates mediating sociosexual behavior. In this review, we examine how estrogenic signaling modulates sociosexual behaviors in teleosts with a particular focus on agonistic behavior. Estrogens have been shown to mediate agonistic behaviors in a broad range of fishes, from sexually monomorphic gonochoristic species to highly dimorphic sex changers with alternate reproductive phenotypes. These similarities across such diverse taxa contribute to a growing body of evidence that estrogens play a crucial role in the modulation of aggression in vertebrates. As analytical techniques and genomic tools rapidly advance, methods such as LC-MS/MS, snRNAseq, and CRISPR-based mutagenesis show great promise to further elucidate the mechanistic basis of estrogenic effects on social behavior in the diverse teleost lineage.

Training in the implementation of sex and gender research policies: an evaluation of publicly available online courses

BACKGROUND

Recently implemented research policies requiring the inclusion of females and males have created an urgent need for effective training in how to account for sex, and in some cases gender, in biomedical studies.

METHODS

Here, we evaluated three sets of publicly available online training materials on this topic: (1) Integrating Sex & Gender in Health Research from the Canadian Institutes of Health Research (CIHR); (2) Sex as a Biological Variable: A Primer from the United States National Institutes of Health (NIH); and (3) The Sex and Gender Dimension in Biomedical Research, developed as part of "Leading Innovative measures to reach gender Balance in Research Activities" (LIBRA) from the European Commission. We reviewed each course with respect to their coverage of (1) What is required by the policy; (2) Rationale for the policy; (3) Handling of the concepts "sex" and "gender;" (4) Research design and analysis; and (5) Interpreting and reporting data.

RESULTS

All three courses discussed the importance of including males and females to better generalize results, discover potential sex differences, and tailor treatments to men and women. The entangled nature of sex and gender, operationalization of sex, and potential downsides of focusing on sex more than other sources of variation were minimally discussed. Notably, all three courses explicitly endorsed invalid analytical approaches that produce bias toward false positive discoveries of difference.

CONCLUSIONS

Our analysis suggests a need for revised or new training materials that incorporate four major topics: precise operationalization of sex, potential risks of over-emphasis on sex as a category, recognition of gender and sex as complex and entangled, and rigorous study design and data analysis.

Sex contextualism in laboratory research: Enhancing rigor and precision in the study of sex-related variables

Understanding sex-related variation in health and illness requires rigorous and precise approaches to revealing underlying mechanisms. A first step is to recognize that sex is not in and of itself a causal mechanism; rather, it is a classification system comprising a set of categories, usually assigned according to a range of varying traits. Moving beyond sex as a system of classification to working with concrete and measurable sex-related variables is necessary for precision. Whether and how these sex-related variables matter-and what patterns of difference they contribute to-will vary in context-specific ways. Second, when researchers incorporate these sex-related variables into research designs, rigorous analytical methods are needed to allow strongly supported conclusions. Third, the interpretation and reporting of sex-related variation require care to ensure that basic and preclinical research advance health equity for all.

Rigorous science demands support of transgender scientists

To build a just, equitable, and diverse academy, scientists and institutions must address systemic barriers that sex and gender minorities face. This Commentary summarizes (1) critical context informing the contemporary oppression of transgender people, (2) how this shapes extant research on sex and gender, and (3) actions to build an inclusive and rigorous academy for all.