Thyroid hormones regulate embryonic and fetal neurodevelopment, with the maternal thyroid gland exclusively producing these hormones for the first half of gestation and then a combination of maternal and fetal production occurring during the second half of gestation. Hypothyroidism during pregnancy is common in humans, particularly due to the additional demand put on the thyroid gland as pregnancy proceeds. Epidemiological studies have linked maternal hypothyroidism to an increased risk of attention-deficit/hyperactivity disorder and autism spectrum disorder diagnosis in these children, as well as cognitive deficits and delays. Rodent models have been extensively used to model developmental hypothyroidism and study the long-term effects on offspring. Increases in activity, reductions in anxiety, cognitive impairments, and social alterations have been observed. In this review, I discuss the current understanding of the organizational impacts of hypothyroidism on activity, affective behaviors, cognition, and social behaviors in humans and animal models, paying special attention to critical periods that may underlie these effects. I also review potential interactions between thyroid hormones and steroid hormones known to be important for organization of the brain and behavior during perinatal and adolescent development. Understanding the effects of developmental hypothyroidism is critical, as early developmental exposure to many endocrine-disrupting chemicals may alter behavior through reducing thyroid hormone signaling, and the final section of the paper reviews these interactions. Understanding the organizational effects of thyroid hormones is important for decisions related to screening and interventions during pregnancy.
Sex differences in circulating androgens are well-known to organize and activate neural and behavioral sex differences of traditional animal models, but much less is known about the consequences of intrasexual differences in androgens. One approach to this question is studying the effects of hyperandrogenism in females. Hyperandrogenism is associated with several endocrine conditions affecting women, with polyendocrine metabolic ovarian syndrome (PMOS) being the most common during reproductive years. PMOS symptoms often emerge around puberty, raising the possibility of organizational effects of hyperandrogenism on neurobehavioral phenotype. Using a mouse model of PMOS, we examined how the timing of symptom induction by 5α-dihydrotestosterone (DHT) treatment affects androgen-linked sociosexual behavioral phenotype. Female mice received DHT or vehicle treatment at peripuberty (PND21) and again in adulthood (PND60), generating four treatment groups with distinct developmental treatment histories. Behavioral testing assessed social preference, stereotyped/repetitive behaviors and partnered social interactions following the first and second androgen treatment. Brain FOS following partnered interaction with an age-matched, unfamiliar female was also measured. Peripubertal DHT treatment accelerated pubertal onset, as indicated by earlier vaginal opening and increased body weight. Androgen treatment had no effect on stereotyped/repetitive behavior or FOS expression but peripubertal androgen treatment altered exploratory activity during adult social preference tests, rather than social preference per se. In partnered interaction tests, both peripubertal and adult androgens increased masculine sexual approach responses, including mounting, with minimal effects on social behavior. These results are consistent with other evidence that peripubertal androgenic mechanisms can organize neurobehavioral phenotypes.
Tuco-tucos (Ctenomys coludo) are Neotropical rodents that inhabit the extreme photic environment of the subterranean, thus being intriguing models for chronobiological studies of circadian and seasonal rhythms. Here we characterized day/night profiles of plasma melatonin and glucocorticoids along with their activity/rest rhythms from freshly caught animals during two seasons. Animals were live-trapped in their native Monte Desert (Argentina) during summer (n = 27) and winter (n = 18), housed under constant dark conditions with wheel-running activity recording prior to sample collection. Sampling occurred at six timepoints across day and night to obtain cross-sectional data. Unlike typical lab-based seasonal studies using artificial photoperiods, our approach captures the complexity of environmental cycles by studying wild animals exposed to the full array of environmental variations across seasons. Melatonin, cortisol and corticosterone were analyzed via ELISA. Melatonin levels showed circadian rhythmicity with higher levels during subjective night. Results revealed higher levels of cortisol secretion during subjective night, consistent with the profile of a nocturnal-active animal. Cortisol levels were 25 to 50 times higher than corticosterone. These findings provide the first circadian melatonin and glucocorticoid baseline for C. coludo in two seasons paving the way for future work on their endocrine rhythms and interplay with activity/rest rhythms and other circadian patterns.
The Challenge Hypothesis suggests that decreases in testosterone represents a shift in energetic resources toward more nurturing paternal behavior, and increased testosterone toward competitive mating behavior. More controversial theories have also suggested that elevated testosterone is related to more stereotypically “masculine” behavior. Parenting dynamics are heavily influenced by gender roles, but little research has examined how the proposed roles of testosterone and masculinity might interact in a parenting context. We measured salivary testosterone across 42 father-child interactions and analyzed how the father's traditional masculinity ideology was related to changes in testosterone across the lab visit, hypothesizing that higher traditional masculinity ideology would predict a smaller decrease in testosterone due to notions of caregiving as a traditionally “feminine” responsibility. Contrary to our hypothesis, testosterone declined more in fathers who reported higher alignment with traditionally masculine beliefs, and among those who did not identify as the child's primary caregiver. These findings contradict notions that greater masculinity is related to increased testosterone and suggest that the physiological responses observed during such interactions may be influenced by perceptual factors such as the novelty of the situation.
The inclusion of both sexes in preclinical research has raised practical questions about variability, statistical power, and required sample size. Much of this uncertainty arises from treating sex as a complication rather than as part of the experimental structure. Here I outline the statistical consequences of incorporating sex into experimental design and analysis. Adding sex converts a two-group comparison into a factorial experiment that simultaneously estimates treatment effects, baseline differences, and sex-dependent responses. This article outlines how experiments including both sexes can be designed, how main effects and interactions should be interpreted, how exploratory and confirmatory aims differ, and how visualization and reporting can prevent common errors. Importantly, powering studies for treatment effects generally requires little increase in animal numbers, whereas detecting interactions represent a distinct and inherently more demanding question.
Emotional experience and the regulation thereof are typically studied using picture inventories or short films to induce and modify affective states. These approaches, however, lack ecological validity due to their passive and receptive nature. Recent innovations in virtual reality and mobile neurophysiological technologies have enabled researchers to study the behavioral and neural correlates of more ecologically valid emotional responses. In this preregistered study, 58 healthy participants were randomly assigned to either use cognitive reappraisal (intervention) or to immerse themselves in their senses and surroundings (control) while walking across a wooden plank suspended 80 stories above the ground in virtual reality. We measured subjective fear ratings, salivary alpha amylase and cortisol levels, as well as frontal brain asymmetries, captured using mobile electroencephalography (EEG). Across both conditions, we found decisive evidence of increased subjective fear and salivary alpha amylase, a marker of sympathetic activation. However, we found no increase in cortisol levels following the task suggesting that subjective fear alone is not sufficient to trigger a cortisol response. In contrast to our hypotheses, the reappraisal group did not show any difference compared to the control group for neither emotional, endocrine nor neural measures. On the one hand, our findings may suggest that reappraisal might not be a suitable strategy to regulate realistic and intensely frightening situations. On the other hand, further analyses also indicated that the control group may have also regulated their emotions due to increased mindfulness of their inner states and their environment. Future studies are needed to confirm these observations and ascertain the efficacy of cognitive reappraisal on fear in realistic settings.
Many animals exhibit seasonal changes in physiology and behavior, including reproductive and non-reproductive social behaviors. Some seasonally-breeding animals display increases in territorial aggression during the short days (i.e., winter), despite gonadal regression and reduced circulating steroid hormones. Previous research suggests that melatonin acts via steroid hormones to regulate seasonal aggression in Siberian hamsters (Phodopus sungorus), a species in which males and females exhibit increased territorial aggression during the non-breeding season. Previously, we identified a role for adrenal dehydroepiandrosterone (DHEA) in regulating territorial aggression. Little is known, however, regarding potential seasonal changes in non-territorial aggression in this or other species. Here, we examined how short days and exogenous melatonin influence non-territorial and territorial aggression and explored the neuroendocrine circuits involved in regulating aggression in female hamsters. Specifically, we housed females in long (LD) or short-days (SD), administered timed melatonin (MEL) or control injections, and assessed territorial (i.e., resident-intruder) and non-territorial (i.e., neutral cage) aggression. Further, we quantified serum DHEA and neural activity in specific brain regions by c-Fos immunolabeling. SD and MEL-treated LD animals exhibited reproductive inhibition and increased territorial, but not non-territorial aggression, suggesting the neuroendocrine regulation of seasonal aggression is context-specific. Further, DHEA was elevated following behavioral challenges; c-Fos expression in specific brain regions was both context- and season-dependent. Collectively, these findings highlight the role of melatonin in coordinating a "seasonal switch" in aggression while suggesting the neuroendocrine mechanisms may differ across types of aggression.
Urbanization drastically alters environments, presenting wildlife with novel challenges to which they must adjust to persist. Often, an animal's first response to environmental change is to shift behavior, which requires processing environmental cues into neural signals that can govern adaptive behavior. However, the neural mechanisms underpinning behavioral responses to urbanization are largely unresolved. During the breeding season, urban songbirds of several species are more aggressive than their rural counterparts. Among the many neural mechanisms that regulate aspects of aggression, arginine vasotocin (AVT) is a neuropeptide highly implicated in the regulation of sociality, including territorial aggression. Prior work has shown that the abundance of AVT peptide is associated with behavioral responses to urbanization. However, social behavior is also influenced by AVT receptor availability, making it important to compare receptor distribution and expression between urban and rural birds. To address this gap in understanding of how AVT receptors could contribute to behavioral responses to urbanization, we used in situ hybridization to describe the distribution of one AVT receptor known to influence behavior, AVT3R, throughout the brain of adult urban and rural male song sparrows (Melospiza melodia). Additionally, we used quantitative PCR (qPCR) to compare the relative expression of mRNA for AVTI1 (AVT), and two of its receptors (AVT3R and AVT4R) in the hypothalamus. We predicted that urban males would have a higher abundance of AVT3R transcripts in the lateral septum, greater mRNA expression of AVT receptors in the hypothalamus, and a positive correlation of AVT gene targets with aggression compared to rural males. We observed high AVT3R mRNA signal in the lateral septum, medial bed nucleus of the stria terminalis, hippocampus, nidopallium, cerebellum and optic tectum, with diffuse signal in the lateral hypothalamus and nucleus rotundus. There were no significant differences in the number of AVT3R transcripts in the lateral septum between urban and rural males. When we quantified relative mRNA expression of AVT and two of its receptors using qPCR, we found that urban males had higher relative mRNA expression of AVT3R in the hypothalamus compared to rural males, and aggression immediately before capture was negatively associated with the expression of AVT, AVT3R, and AVT4R. Thus, expression of AVT and its receptors has the potential to contribute to higher aggression in male song sparrows but may not explain habitat-related variation.
Steroid hormones influence affective behavior and its underlying neural networks. However, distinguishing between organizational and activational hormonal effects, along with effects of socialization, remains challenging, limiting the understanding of the mechanisms underlying affective neurobehavioral differences. Individuals with differences in sex development (DSD), such as congenital adrenal hyperplasia (CAH) and complete androgen insensitivity syndrome (CAIS), offer a unique opportunity to examine how alterations in prenatal steroid hormone exposure have a role in shaping brain development and human behaviors. This review aims to examine how, and to what extent CAH and CAIS, can inform broader neuroendocrine mechanisms of affective behavior. It starts with an overview of experimental psychology and human imaging work on the role of steroid hormones in affective behavior, highlighting the main challenges in the field in human research, and the rationale for including CAH and CAIS. It then summarizes findings from behavioral studies, experimental psychology, and neuroimaging research in CAH and CAIS to discuss how this research contributes to the understanding of the organizational role of steroid hormones on affective outcomes. Although the current evidence is limited and heterogeneous, this review highlights the contribution of prenatal hormonal variability, particularly prenatal androgen exposure, in shaping affective behavior and underlying neural networks. It also highlights how steroid hormones, chromosomal sex, timing of hormonal exposure, developmental stage and psychosocial factors interact in influencing affective outcomes. Advancing this work through neuroimaging and standardized experimental paradigms has the potential to specify the mechanistic pathways through which steroid hormone variability influences behavior. This work can also inform targeted interventions and support emotional well-being and quality of life for individuals with CAH and CAIS.
Poor sleep hygiene is reported to impair subjective sleep and disrupt circadian system, yet the association between sleep hygiene and objective alterations in sleep continuity is scarcely studied. Moreover, the role of gender differences is largely neglected. In this pilot study, sixty-five adults (66% females) completed a psychometric assessment including the Sleep Hygiene Index (SHI) and wore an actigraph for one week for the assessment of sleep. No statistically significant gender differences on sleep hygiene practices were found. Bedtime and waketime were later in males than females. Males showed longer sleep onset latency (SOL), and wake after sleep onset (WASO), and lower sleep efficiency compared to females. General linear analyses showed that poorer sleep hygiene was associated with shorter SOL and longer WASO in males but not in females. Age, habitual insomnia and psychological distress did not influence the results. Current findings suggest a differential impact of sleep hygiene behaviors on objective alternations in males. While future research is needed to investigate the role of specific sleep promoting and sleep inhibiting behaviors on objective sleep, current results highlight the importance of considering gender differences in sleep hygiene research. Gender differences in homeostatic, circadian, and neuroendocrine factors related to sleep hygiene should be further investigated in mechanistic studies also considering non-binary participants.
Levonorgestrel (LNG), a contraceptive hormone, is used by millions of women worldwide. We have found that LNG delays habit expression in gonadally-intact female rats, suggesting it influences cognitive processes. The mechanism driving LNG's effect on habit in female rats remains unclear. One explanation is that LNG's androgenic properties impact habit learning. To investigate this, intact female rats were implanted subcutaneously with either cholesterol- (Experiment 1) or LNG- (Experiment 2) capsules. Animals from each group received subcutaneous injections of flutamide, an androgen receptor antagonist, or vehicle prior to sessions of appetitive operant training. After training, half of the rats in each experimental group received outcome devaluation, which rendered the sucrose reward aversive. Subsequently, all rats underwent a short extinction test to ascertain whether behavior was goal-directed or habitual. In Experiment 1, habit was observed in cholesterol-implanted females, and this was not affected by flutamide, replicating our earlier finding that habit is present after moderate training in intact female rats, and additionally showing that blocking androgen receptor activity during training does not alter habit expression. In Experiment 2, LNG-implanted rats exhibited goal-directed behavior, again replicating our previous findings showing that LNG delays habit in female rats. However, LNG-implanted rats treated with flutamide during training displayed habitual behavior, suggesting that the androgenic effects of LNG are responsible, at least in part, for delaying habit expression in intact female rats. This finding suggests that the androgenic properties of LNG are exerting significant effects on cognitive processes related to behavioral flexibility in the female brain.
The Dual Hormone Hypothesis is a biosocial model that describes the interactive effects of testosterone and cortisol on status-relevant behavior. Under this model, testosterone increases status-seeking behavior when cortisol is low, and status-loss-avoidance when cortisol is high. This manifests as high-testosterone individuals preferentially competing against high-status opponents when cortisol is low, and low-status opponents when cortisol is high. However, opponent status indicates both potential status gain as well as opponent strength. The present study separates opponent status from potential gains and losses to understand how testosterone and cortisol interact with different status cues during competition. Results suggest that testosterone increases sensitivity to opponent status while decreasing sensitivity to gains and losses. Cortisol moderates testosterone's effects on status sensitivity while independently increasing reward sensitivity. Furthermore, the present work leverages machine learning to elucidate how testosterone influences behavior in a nonlinear fashion.
This study examined the effects of resistance training (RT) and supraphysiological nandrolone decanoate (ND) administration on hippocampal neurogenesis, neurotrophic signaling, and behavior. Forty 3-month-old male C57BL/6 J mice were randomized to RT or sedentary (SED) conditions. Each group was further divided into sham (S) or ND (38 mg·kg-1·wk.-1) treatment groups. All interventions lasted 7 wk. Adult hippocampal neurogenesis was quantified in the dentate gyrus using BrdU+/NeuN+ immunolabeling. Hippocampal expression of brain-derived neurotrophic factor (BDNF), androgen receptor (AR), estrogen receptor-β (ER-β), insulin-like growth factor-1 (IGF-1), and irisin was assessed by western blot analyses. No significant exercise × treatment interactions were observed for any of the behavior measures. When collapsed across treatments, RT exhibited a greater number of open-arm entries (p = 0.006) and reduced average latency times (p = 0.002) than SED. ND administration did not alter behavioral outcomes. RT (p = 0.001) and ND (p = 0.032) each independently increased hippocampal BrdU+/NeuN+ cell numbers, with no additive effects. AR expression for SED-S was significantly lower (p's < 0.05) than all other groups and IGF-1 expression for RT-S was significantly greater (p's < 0.05) than all other groups. Main effects revealed that RT and ND resulted in significant elevations in AR, ER-β and BDNF expressions. In conclusion, RT enhanced hippocampal plasticity and behavioral performance, whereas supraphysiological ND administration produced distinct molecular changes without conferring additive behavioral or neuroplastic benefit.
Some theories have proposed that children with autism spectrum disorder (ASD) may be exposed to increased levels of androgens during prenatal development, resulting in greater androgenization of testosterone-dependent traits including both peripheral (bodily) and central (brain-related) traits. Empirical support for this hypothesis is scant and inconsistent. In the present work, we studied an ostensible anatomical marker of testosterone exposure (sexually differentiated finger lengths) which develops during the first trimester or early second trimester of gestation. Participants were 25 boys with classic autism, recruited from the clinical practice of a local physician specializing in childhood autism, who met the standardized DSM (Diagnostic and Statistical Manual) criteria for ASD, and 57 normally-developing age- and sex-matched male and female controls (32 males, 25 females); N = 82; Mage = 7.30 yrs., SD = 4.18. Finger length was measured to the nearest 0.5 mm from digital images of the ventral surface of the hands using a validated measurement protocol. Consistent with past reports from adult samples, several of the finger length ratios were confirmed to display sex differences among control children, but the group of boys with ASD showed a female-like finger growth pattern, not the hypermasculine pattern predicted, and were found to differ statistically from the male controls. Boys with ASD thus showed a demasculinized pattern of finger differentiation. Our data do not support theories which suggest that greater fetal testosterone exposure occurs in boys with autism.
Aggression, a conserved social behavior, is orchestrated by a distributed neural network where sex hormone receptors integrate hormonal and experiential signals. This review synthesizes recent rodent studies, highlighting the central role of estrogen receptor alpha (ERα). We delineate a striking functional dichotomy: ERα promotes aggression in the ventromedial hypothalamus (VMHvl) while suppressing it in the medial preoptic area (MPOA). Furthermore, social experiences (e.g., victory, isolation) remodel circuit connectivity, revealing profound experience-dependent plasticity. By integrating molecular, circuit, and behavioral insights, we establish a cohesive framework that not only explains the neural underpinnings of aggression but also informs novel strategies for managing its pathological manifestations.
Pubertal development is regulated by hypothalamic neuroendocrine signaling and is sensitive to interactions between stress- and reproductive-related pathways. In particular, corticotropin-releasing hormone (CRH) signaling via corticotropin-releasing hormone receptor 1 (CRHR1) represents a key point of crosstalk between stress and pubertal maturation. Early-life adversity, such as the maternal separation (MS) model in rodents, has been shown to increase CRH expression and therefore has the potential to dysregulate CRHR1 signaling. We previously reported that MS-exposed female rats display early pubertal onset, with heightened anxiety-like behavior that was correlated with pubertal timing. The current study examined whether CRHR1 dysregulation mediates the effects of MS on both pubertal timing and anxiety-like behavior, as assessed by the acoustic startle response (ASR), in female rats. CRHR1 signaling was pharmacologically manipulated using the CRHR1 antagonist antalarmin during MS exposure. Pubertal development and ASR were assessed, as well as pre-pubertal hypothalamic CRHR1 expression. Protein quantification of pre-pubertal hypothalamic cell membrane and cytoplasmic fractions revealed that MS increases CRHR1 internalization in the arcuate nucleus and in the anterior hypothalamus following MS. As expected, MS significantly advanced pubertal timing; however, accelerated puberty was normalized by treatment with antalarmin during MS. Treatment with a high dose of antalarmin, however, delayed puberty in both MS and control animals. MS also increased ASR in adolescent females, which was prevented by antalarmin treatment during MS. Additionally, antalarmin decreased cFos activity in the basolateral amygdala (BLA) and bed nucleus of stria terminalis (BNST). Together, these findings support a potential model in which altered CRHR1 signaling during negative early environments disrupts HPA-HPG axis crosstalk, triggering early onset of puberty and increased anxiety-like behavior in female rats. Targeting CRHR1 signaling during sensitive developmental windows may provide a therapeutic avenue for mitigating these long-term impacts of early life stress.
Parental care varies across reproductive stages, between sexes, and even within individuals. This flexibility raises a key question: does caregiving correspond to distinct circulating hormone profiles, or does it occur within a shared hormonal background that supports rapid, context-dependent shifts in behavior? We investigated these alternatives in red-winged blackbirds (Agelaius phoeniceus), a species in which females always feed nestlings while males range from no provisioning to high rates of chick care. Using continuous nest video recordings (24-48 h) and a panel of circulating hormones (prolactin and four steroids), we examined how hormone profiles relate to breeding stage, sex, and paternal effort. First, courtship-stage males and nestling-stage males were clearly separated by their hormone profiles, confirming that breeding stage is a major axis of endocrine variation. Second, during the nestling-stage, provisioning females and males differed in hormone profiles and in how hormones related to parental effort, indicating sex-specific hormonal modulation within a shared parental context. Third, provisioning and non-provisioning males overlapped broadly in hormone profiles, and no single hormone reliably predicted whether a male provisioned. Instead, associations with parental effort emerged primarily through interactions among hormonal axes. Together, these results indicate that breeding stage and sex strongly organize circulating hormone profiles and that facultative male care operates within a broadly shared endocrine background rather than through discrete hormonal divergence between caregiving categories.
Adolescence is a developmental period during which rising gonadal hormones drive the maturation of neural circuits underlying adult behaviour. Testosterone acts directly via androgen receptors (AR) or indirectly through aromatization to estradiol, yet the role of estradiol signalling in refining sexual behaviour during adolescence in male rats remains unclear. We tested whether inhibiting aromatase with fadrozole (FAD) from postnatal day 38 to 48 (around the time of puberty) affects adult sexual behaviour. To determine whether any deficits in sexual behaviour were secondary to anxiety-like behaviour and/or altered stress responding, anxiety-like behaviour and corticosterone release in response to a stressor also were measured. As adults, FAD males did not differ from control (CTL) rats in anxiety-like behaviour, in corticosterone release in response to stress, nor in testosterone concentrations. Aromatase inhibition impaired sexual performance: FAD males mounted, intromitted, and ejaculated less frequently, though sexual motivation and partner preference were preserved. The groups did not differ in AR densities or immunoreactive cell counts in either the medial amygdala or medial preoptic area. Estrogen receptor alpha (ERα) was reduced in the medial amygdala only. These results suggest that aromatization during adolescence refines circuits underlying male sexual behaviour.
