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

Corticosterone rapidly modulates dorsomedial hypothalamus serotonin and behavior in an estrogen- and progesterone-dependent manner in adult female rats: potential role of organic cation transporter 3 (OCT3)

Previous studies have shown that corticosterone rapidly alters extracellular serotonin (5-hydroxytryptamine; 5-HT) concentrations in the dorsomedial hypothalamus (DMH) of adult male rats, suggesting a role for corticosterone actions in the DMH in regulation of physiological and behavioral responses. Whether or not corticosterone also rapidly alters extracellular serotonin concentrations in the DMH of female rats, and the dependence of this effect on ovarian hormones, is not known. To determine the effects of 17β-estradiol (E2), progesterone (P), and corticosterone on extracellular concentrations of serotonin in the DMH, corticosterone and/or P were delivered into the DMH of ovariectomized rats via reverse microdialysis in E2-primed rats. Combined, but not separate, delivery of corticosterone and P into the DMH rapidly and transiently increased extracellular 5-HT concentrations, a result that was dependent upon circulating E2. This effect of corticosterone on DMH 5-HT was replicated by local perfusion of the organic cation transporter 3 (OCT3) competitive inhibitor normetanephrine. Intra-DMH infusions of either corticosterone or normetanephrine also reversibly suppressed lordosis responses in E2 + P-primed females. These results suggest that ovarian hormones in combination with corticosterone modulate OCT3-mediated 5-HT clearance in the DMH, potentially representing an adaptive mechanism that allows sexually receptive females to respond rapidly to acute stressors.

Psychedelic-like effects induced by 2,5-dimethoxy-4-iodoamphetamine, lysergic acid diethylamide, and psilocybin in male and female C57BL/6J mice

RATIONALE

The head twitch response (HTR) is a spontaneously occurring behavior in mice that is increased in frequency by serotonergic psychedelics. The mouse HTR is often used as a proxy for psychedelic-like drug effects, but limited information is available about sex differences in HTRs evoked by various classes of psychedelics (i.e., phenethylamines, lysergamides, tryptamines).

OBJECTIVE AND METHODS

To examine potential sex differences in responsiveness to structurally-distinct psychedelics, acute effects of subcutaneous 2,5-dimethoxy-4-iodo-amphetamine (DOI, 0.03-10 mg/kg), lysergic acid diethylamide (LSD, 0.003-1 mg/kg), and 4-phosphoryloxy-N,N-dimethyltryptamine (psilocybin, 0.03-10 mg/kg) on HTRs were compared in male and female C57BL/6J mice. For comparison, effects of the drugs on locomotor activity and body temperature were also determined.

RESULTS

Drug potencies for inducing HTRs were similar in males and females for all drugs, with only LSD exhibiting detectable differences due to increased maximal counts in females. Importantly, the maximum number of HTRs observed for all drugs was higher in females, with significant differences between sexes for DOI and LSD. Dose x sex interactions for the dose-response data were statistically significant for psilocybin and LSD, with females displaying more HTRs after the highest or peak doses of all drugs. The acute effects of drugs on locomotion and temperature varied by drug, but were similar in both sexes.

CONCLUSIONS

The present results overall show no substantial sex differences in the potencies to induce HTRs for DOI, LSD, and psilocybin in C57BL/6J mice. However, females uniformly displayed more HTRs at high doses administered across chemotypes. The results further suggest that commonly used doses of psychedelics induce comparable psychedelic-like effects in male and female C57BL/6J mice, but modest differences may emerge at high doses.

Navigating the paradigm shift of sex inclusive preclinical research and lessons learnt

As progress is made in sex-inclusive preclinical research, the author highlights areas of research practice where significant development has been achieved & where more change is needed towards community accepted standards in equitable research

The Sex Inclusive Research Framework to address sex bias in preclinical research proposals

An interactive Sex Inclusive Research Framework (SIRF) supports the evaluation of in vivo and ex vivo research proposals to address the risk of sex bias in preclinical research. The framework delivers a traffic light classification, indicating whether a proposal is appropriate, risky, or insufficient with regard to sex inclusion. This tool is designed for use by researchers, (animal) ethical review boards, and funders to generate a rigorous and reproducible assessment of sex inclusion at the proposal level, thus helping address and resolve the embedded sex bias in preclinical research.

Ramipril ameliorates endometriosis by inducing oxidative stress-mediated apoptosis in the wistar rat

Endometriosis is illustrated by the presence of ectopic endometrial cells capable of evading apoptosis outside the uterus. Apoptotic and anti-apoptotic factors in the extra uterine microenvironment can be compromised by the impairment in oxidative status. Angiotensin Converting Enzyme (ACE) Inhibitors and Nitric Oxide (NO) modulators play pivotal role in inflammation, angiogenesis, apoptosis and in abrogating oxidative imbalance. Therefore, in the current study we investigate the role of ACE inhibitor and or NO modulators in mitigating the proliferation of ectopic endometrial lesions in rat model. Sixty adult female virgin wistar rats were utilized; out of which fifteen were used as donor rats and rest forty-two were randomly divided into seven groups after surgical implantation of endometrial explants into rats (group II-VII). Histomorphometric assessment of uteri and ectopic lesions was performed by Hematoxylin and eosin (H-E) staining, followed by immunohistochemical study for Proliferating cell nuclear antigen (PCNA), Bax and Bcl-2. Oxidative stress parameters were evaluated by biochemical estimations, succeeded by immunoblotting of Poly [ADP-ribose] polymerase 1 (PARP1). Additionally, immunoblotting of Vascular endothelial growth factor (VEGF), Bax, Bcl-2 and caspase-3 was also performed. Significant decrease in the diameter of lesions with diffused staining at the extracellular spaces of stromal cells for PCNA accompanied by significant decrease in the expression of VEGF (p < 0.00001) was observed in group III. Furthermore, increased expression of Bax:Bcl-2 ratio (p < 0.001) and cleaved caspase-3 (p ≤ 0.0001) in ectopic lesions of group III was also observed. Administration of ramipril alone results in triggering oxidative stress mediated cleavage of PARP1, augmenting apoptosis in the ectopic lesions.

Generalization and extinction of platform-mediated avoidance in male and female rats

Understanding anxiety-related disorders can be advanced by studying the fear learning mechanisms implicated in the transition from adaptive to maladaptive fear. Individuals with anxiety disorders often show impaired fear extinction, pervasive avoidance, and overgeneralization of fear. While these characteristics are usually studied in isolation, their interactions are less understood. We modified the platform-mediated avoidance task to chart avoidance, generalization, and extinction in male and female rats. Male rats acquired avoidance, showed a gradient of generalization, and reduced avoidance and fear under extinction. Female rats also learned avoidance, showed gradual generalization, and extinction of defensive behaviors. Sex differences emerged in extinction learning but were subtler than expected. We present an open-source automated system for processing DeepLabCut and SimBA output to score avoidance and freezing behavior. This task effectively probes avoidance, generalization, and extinction of fear in rats, and our automated scoring approach offers a effective method to quantify defensive behaviors.

Sex differences in diet-mediated salivary protein upregulation

Our lab previously established that repeated exposure to a bitter diet can increase salivary protein (SP) expression, which corresponds to an increase in acceptance of the bitter stimulus. However, this work was exclusively in male rodents, here we examine sex differences. We found that there are no differences in SP expression (experiment 1) or quinine diet acceptance (experiment 2) across stage of estrous cycle. Yet, males and females differ in feeding behaviors, SP expression, and responses to a quinine diet (experiment 3). On a quinine diet, males accepted the diet much faster than females. Males displayed a compensatory increase in meal number as meal size and rate of feeding decreased with initial exposure to a quinine diet, whereas females decreased meal size and rate of feeding with no compensation in meal number. There were sex differences in SP expression at day 14 of quinine exposure but these were gone by day 24. Both sexes increased acceptance of quinine in a brief access taste test after the feeding trial concluded. These data suggest that males and females have different patterns of bitter diet acceptance, but extended exposure to quinine diet still results in altered bitter taste responding and changes in SP profiles in females.

Sex differences in blood pressure responses of Pekin ducks to sound stimuli and conspecific vocalizations

We tested Pekin ducks with playbacks of 5 different vocalizations plus a no noise and white noise stimulus as our controls (N = 15 ducks/sex/treatment). The "AM long" call is a common vocalization made by both sexes. "Honk" is also produced by both sexes and is thought to be an alarm or distress call. "Pips" and "harmonics" are common vocalizations made only by hens. The "egg laying squiggle" is also only made by hens. Trials consisted of an initial recording in a quiet condition with 5 consecutive measurements of heart rate, blood pressure and respiratory rate. A specific vocalization was then played on repeat while 8 more measurements of blood pressure, heart rate and respiratory rate were taken. Finally, 5 measurements of heart rate and blood pressure were taken post playback along with a final recording of respiratory rate. Data from all blood pressure measurements (systolic, diastolic and mean arterial pressure [MAP]), heart rate (HR) and respiratory rate (RR) were subject to a principal component analysis (Proc Princomp in SAS 9.4). The significant principal components (Prin 1 loaded strongly on blood pressure and Prin 2 loaded strongly on HR and RR) were then analyzed by ANOVA with repeated measures (Proc Mixed, SAS 9.4, subject=duck ID). Our results showed there was a significant main effect of playback type on the blood pressure of ducks during the playbacks (P = 0.0276). Ducks experienced an increase in blood pressure when played back the honk vocalization, as well as the white noise control. Additionally, there was a significant interaction between sex and treatment on the after-stimulus blood pressure (P = 0.0008): after the harmonic vocalization was played, the drakes still experienced an increase in blood pressure, but the hens experienced a decrease. The drakes, but not the hens, experienced a decrease in blood pressure after the AM long vocalization was played. Our data show that there are sex differences when it comes to vocalization playbacks in Pekin ducks, but overall, the honk vocalization and white noise control significantly increased ducks' blood pressure. This study represents a critical steppingstone toward understanding how Pekin duck vocalizations affect conspecific physiology.

Transport functions of intestinal lymphatic vessels

Lymphatic vessels are crucial for fluid absorption and the transport of peripheral immune cells to lymph nodes. However, in the small intestine, the lymphatic fluid is rich in diet-derived lipids incorporated into chylomicrons and gut-specific immune cells. Thus, intestinal lymphatic vessels have evolved to handle these unique cargoes and are critical for systemic dietary lipid delivery and metabolism. This Review covers mechanisms of lipid absorption from epithelial cells to the lymphatics as well as unique features of the gut microenvironment that affect these functions. Moreover, we discuss details of the intestinal lymphatics in gut immune cell trafficking and insights into the role of inter-organ communication. Lastly, we highlight the particularities of fat absorption that can be harnessed for efficient lipid-soluble drug distribution for novel therapies, including the ability of chylomicron-associated drugs to bypass first-pass liver metabolism for systemic delivery. In all, this Review will help to promote an understanding of intestinal lymphatic-systemic interactions to guide future research directions.

Ramadan fasting model modulates biomarkers of longevity and metabolism in male obese and non-obese rats

The health advantages of Ramadan fasting, a time-restricted eating from dawn to dusk, have garnered attention. Nevertheless, prior observational studies have found inconsistent findings because of challenges regulating variables such as sleep patterns, dietary habits, and physical activity. This study sought to investigate the impact of the Ramadan fasting model (RFM) on longevity and metabolic biomarkers in obese and non-obese rats. For 12 weeks, 48 male Wistar albino rats were separated into two groups and fed either a standard or a high-fat diet (HFD). During the final four weeks, rats in each group were separated into four subgroups to investigate the effect of RFM with/without training (on Treadmill) or glucose administration on the biomarkers of interest. The HFD groups subjected to RFM had significantly lower Insulin-like growth factor 1 (IGF-1) and mechanistic target of rapamycin (mTOR) serum, whereas AMPK, anti-inflammatory, and antioxidative stress serum levels were significantly higher. All groups reported decreased serum levels of Interleukin-6 (IL-6) and Tumor Necrosis Factor-alpha (TNF-α) compared to the HFD control group. Furthermore, the Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR) results indicated a significant elevation in the TP53 gene expression in groups subjected to RFM. The data indicate that RFM can improve longevity and metabolic biomarkers and reduce pro-inflammation and oxidative stress. Also, RFM improves anti-inflammatory and antioxidant markers in HFD-induced obese rats.

Sex and hormonal effects on drug cue-reactivity and its regulation in human addiction

Objective

To study the sex and hormonal effects on cortico-striatal engagement during drug cue-reactivity and its regulation focusing on drug reappraisal.

Methods

Forty-nine men (age=41.96±9.71) with heroin use disorder (HUD) and 32 age-matched women (age=38.85±9.84) with HUD (n=16) or cocaine use disorder (CUD; n=16) were scanned using functional MRI, with a subgroup of women scanned twice, during the late-follicular and mid-luteal phases, to examine sex and menstrual phase differences in cortico-striatal drug cue-reactivity and its cognitive reappraisal and their correlations with ovarian hormones and drug craving.

Results

Women showed higher medial prefrontal cortex (PFC) drug cue-reactivity while men showed higher frontal eye field (FEF)/dorsolateral PFC (dlPFC) drug reappraisal as associated with lower cue-induced drug craving. In the women, drug cue-reactivity was higher during the follicular phase in the FEF/dlPFC, whereas drug reappraisal was higher during the luteal phase in the anterior PFC/orbitofrontal cortex. The more the estradiol during the follicular vs. luteal phase (Δ), the higher the Δdrug cue-reactivity in the vmPFC, which also correlated with higher Δdrug craving (observed also in the inferior frontal gyrus). The more this Δestradiol, the lower the Δdrug reappraisal in the vmPFC, anterior PFC and striatum. Conversely, Δprogesterone/estradiol ratio was positively associated with Δdrug reappraisal in the dlPFC.

Conclusions

Compared to men, women with addiction show more cortico-striatal reactivity to drug cue exposure and less PFC activity during drug reappraisal, driven by the follicular compared to luteal phase and directly related to craving and fluctuations in estrogen and progesterone with the former constituting a vulnerability and the latter a protective factor. This study provides insights for developing precisely timed and hormonally informed treatments for women with addiction.

Effects of sex and estrous cycle on extended-access oxycodone self-administration and cue-induced drug seeking behavior

Introduction

Increasing evidence indicates that sex is a factor that impacts the abuse liability and relapse vulnerability of prescription opioids like oxycodone. However, while women are more likely than men to be prescribed and to use these drugs, the impact of sex and ovarian hormones on prescription opioid use and relapse vulnerability remains unclear. Accurately assessing these measures is complicated by the fact that chronic opioid exposure can lower ovarian hormone levels and cause cycle irregularities.

Methods

Adult male and female Sprague-Dawley rats self-administered oxycodone (0.1 mg/kg/infusion) under extended-access conditions (6 h/day, 10 days) followed by forced abstinence. Separate groups of animals received cue-induced seeking tests in a drug-free state during early (1-2 days) or later periods of abstinence (43-45 days). To track estrous cycle stage, animals were regularly vaginally swabbed throughout the study.

Results

We observed oxycodone-induced estrous cycle dysregulation in the majority (~60%) of the animals during both self-administration and the first month of abstinence. In animals whose cycles were not dysregulated, we found a reduction in oxycodone intake during estrus compared to all other cycle stages (non-estrus). We also found that males but not females showed a time-dependent intensification or incubation of cue-induced oxycodone craving over the first 6 weeks of abstinence. This sex difference was estrous cycle-dependent, driven by a selective reduction in drug seeking during estrus.

Discussion

These findings highlight the importance of tracking drug-induced estrous cyclicity and identify a clear impact of ovarian hormones on oxycodone taking and seeking behavior.

Lactate administration causes long-term neuroprotective effects following neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) is one of the main causes of mortality and long-term disabilities in newborns, and the only clinical approach to treat this condition is therapeutic hypothermia, which shows some limitations. Thus, putative neuroprotective agents have been tested in animal models of HI. Lactate is a preferential metabolic substrate of the neonatal brain and has already been shown to produce beneficial neuroprotective outcomes in neonatal animals exposed to HI. Here, we administered lactate as a treatment in neonatal rats previously exposed to HI and evaluated the impact of this treatment in adulthood. Seven-day-old (P7) male and female Wistar rats underwent permanent common right carotid occlusion combined with an exposition to a hypoxic atmosphere (8% oxygen) for 60 min. Animals were assigned to one of four experimental groups: HI, HI+LAC, SHAM, SHAM+LAC. Lactate was administered intraperitoneally 30 min and 2 h after hypoxia in HI+LAC and SHAM+LAC groups, whereas HI and SHAM groups received vehicle. Animals were tested in the behavioral tasks of negative geotaxis and righting reflex (P8), cylinder test (P24), and the modified neurological severity score was calculated (P25). Open field (OF), and novel object recognition (NOR) were evaluated in adulthood. Animals were killed at P60, and the brains were harvested and processed to evaluate the volume of brain injury. Our results showed that lactate administration reduced the volume of brain lesion and improved sensorimotor and cognitive behaviors in neonatal, juvenile, and adult life in HI animals from both sexes. Thus, lactate administration might be considered as a potential neuroprotective strategy for the treatment of neonatal HI, which is a prevalent disorder affecting newborns.

Conditioning- and reward-related dendritic and presynaptic plasticity of nucleus accumbens neurons in male and female sign-tracker rats

For a subset of individuals known as sign-trackers, discrete Pavlovian cues associated with rewarding stimuli can acquire incentive properties and exert control over behaviour. Because responsiveness to cues is a feature of various neuropsychiatric conditions, rodent models of sign-tracking may prove useful for exploring the neurobiology of individual variation in psychiatric vulnerabilities. Converging evidence points towards the involvement of dopaminergic neurotransmission in the nucleus accumbens core (NAc) in the development of sign-tracking, yet whether this phenotype is associated with specific accumbal postsynaptic properties is unknown. Here, we examined dendritic spine structural organisation, as well as presynaptic and postsynaptic markers of activity, in the NAc core of male and female rats following a Pavlovian-conditioned approach procedure. In contrast to our prediction that cue re-exposure would increase spine density, experiencing the discrete lever-cue without reward delivery resulted in lower spine density than control rats for which the lever was unpaired with reward during training; this effect was tempered in the most robust sign-trackers. Interestingly, this same behavioural test (lever presentation without reward) resulted in increased levels of a marker of presynaptic activity (synaptophysin), and this effect was greatest in female rats. Whilst some behavioural differences were observed in females during initial Pavlovian training, final conditioning scores did not differ from males and were unaffected by the oestrous cycle. This work provides novel insights into how conditioning impacts the neuronal plasticity of the NAc core, whilst highlighting the importance of studying the behaviour and neurobiology of both male and female rats.

Neonatal dysregulation of 2-arachidonoylglycerol induces impaired brain function in adult mice

The endocannabinoid system (ECS) regulates neurotransmission linked to synaptic plasticity, cognition, and emotion. While it has been demonstrated that dysregulation of the ECS in adulthood is relevant not only to central nervous system (CNS) disorders such as autism spectrum disorder, cognitive dysfunction, and depression but also to brain function, there are few studies on how dysregulation of the ECS in the neonatal period affects the manifestation and pathophysiology of CNS disorders later in life. In this study, DO34, a diacylglycerol lipase alpha (DAGLα) inhibitor affecting endocannabinoid 2-AG production, was injected into C57BL/6N male mice from postnatal day (PND) 7 to PND 10, inducing dysregulation of the ECS in the neonatal period. Subsequently, we examined whether it affects neuronal function in adulthood through electrophysiological and behavioral evaluation. DO34-injected mice showed significantly decreased cognitive functions, attributed to impairment of hippocampal synaptic plasticity. The findings suggest that regulation of ECS activity in the neonatal period may induce enduring effects on adult brain function.

Stimulation of central histaminergic transmission attenuates diazepam-induced motor disturbance on rota-rod and beam walking tests in mice

Diazepam administration has been shown to influence the release of histamine in various brain areas involved in motor behavior. Therefore, the present study explored the plausible regulatory role of the central histaminergic system in diazepam-induced deficits in motor performance in mice using the rota-rod and beam walking tests. In this study, several doses of diazepam (0.5, 1, 2, and 3 mg/kg, i.p.) were assessed in mice for changes in motor performance on the rota-rod and beam walking test. In addition, the brain histamine levels were determined after diazepam administration, and the diazepam-induced motor deficits were assessed in mice, pretreated centrally (intracerebroventricular) with histaminergic agents such as histamine (0.1, 10 µg), histamine precursor (L-histidine: 0.1, 2.5 µg), histamine neuronal releaser/H 3 receptor antagonist (thioperamide: 0.5, 10 µg), H 1 and H 2 receptor agonist [2-(3-trifluoromethylphenyl) histamine (FMPH: 0.1, 6.5 µg; amthamine: 0.1, 5 µg)/antagonist (H 1 : cetirizine 0.1 µg) and (H 2 : ranitidine: 50 µg)]. Results indicate that mice treated with diazepam at doses 1, 2 mg/kg, i.p. significantly increased the brain histamine levels. Moreover, in mice pretreated with histaminergic transmission-enhancing agents, the diazepam (2 mg/kg, i.p.)-induced motor incoordination was significantly reversed. Contrastingly, diazepam (1 mg/kg, i.p.) in its subeffective dose produced significant motor deficits in mice preintracerebroventricular injected with histamine H 1 and H 2 receptor antagonists on both the employed tests. Therefore, it is postulated that endogenous histamine operates via H 1 and H 2 receptor activation to alleviate the motor-impairing effects of diazepam.

The impact of estrous cycle on anxiety-like behaviour during unlearned fear tests in female rats and mice: A systematic review and meta-analysis

Anxiety fluctuates across the human menstrual cycle, with symptoms worsening during phases of declining or low ovarian hormones. Similar findings have been observed across the rodent estrous cycle, however, the magnitude and robustness of these effects have not been meta-analytically quantified. We conducted a systematic review and meta-analysis of estrous cycle effects on anxiety-like behaviour (124 articles; k = 259 effect sizes). In both rats and mice, anxiety-like behaviour was higher during metestrus/diestrus (lower ovarian hormones) than proestrus (higher ovarian hormones) (g = 0.44 in rats, g = 0.43 in mice). There was large heterogeneity in the data, which was partially accounted for by strain, experimental task, and reproductive status. Nonetheless, the effect of estrous cycle on anxiety-like behaviour was highly robust, with the fail-safe N test revealing the effect would remain significant even if 21,388 additional studies yielded null results. These results suggest that estrous cycle should be accounted for in studies of anxiety in females. Doing so will facilitate knowledge about menstrual-cycle regulation of anxiety disorders in humans.

Recommendations for the Application of Sex and Gender Medicine in Preclinical, Epidemiological and Clinical Research

Gender medicine studies how health status and diseases differ between men and women in terms of prevention, therapeutic approach, prognosis, and psychological and social impact. Sex and gender analyses have been demonstrated to improve science, contributing to achieving real appropriateness and equity in the cure for each person. Therefore, it is fundamental to consider, both in preclinical and clinical research, the different clinical and biological features associated with sex and/or gender, where sex differences are mainly influenced by biological determinants and gender ones by socio-cultural and economic matters. This article was developed to provide knowledge and methodological tools for the development of studies/research protocols in which sex and gender should be taken into account.

Differential effects of high-fat diet on endocrine, metabolic and depressive-like behaviors in male and female rats

The complications of obesity extend beyond the periphery to the central nervous system (CNS) and include an increased risk of developing neuropsychiatric co-morbidities like depressive illness. Preclinical studies support this concept, including studies that have examined the effects of a high-fat diet (HFD) on depressive-like behaviors. Although women are approximately two-fold more likely to develop depressive illness compared to men, most preclinical studies have focused on the effects of HFD in male rodents. Accordingly, the goal of this study was to examine depressive-like behaviors in male and female rats provided access to a HFD. In agreement with prior studies, male and female rats provided a HFD segregate into an obesity phenotype (i.e., diet-induced obesity; DIO) or a diet resistant (DR) phenotype. Upon confirmation of the DR and DIO phenotypes, behavioral assays were performed in control chow, DR, and DIO rats. In the sucrose preference test, male DIO rats exhibited significant decreases in sucrose consumption (i.e., anhedonia) compared to male DR and male control rats. In the forced swim test (FST), male DIO rats exhibited increases in immobility and decreases in climbing behaviors in the pre-test sessions. Interestingly, male DR rats exhibited these same changes in both the pre-test and test sessions of the FST, suggesting that consumption of a HFD, even in the absence of the development of an obesity phenotype, has behavioral consequences. Female rats did not exhibit differences in sucrose preference, but female DIO rats exhibited increases in immobility exclusively in the test session of the FST, behavioral changes that were not affected by the stage of the estrous cycle. Collectively, these studies demonstrate that access to a HFD elicits different behavioral outcomes in male and female rats.

The effect of corticosterone on the acquisition of Pavlovian conditioned approach behavior in rats is dependent on sex and vendor

Cues in the environment become predictors of biologically relevant stimuli, such as food, through associative learning. These cues can not only act as predictors but can also be attributed with incentive motivational value and gain control over behavior. When a cue is imbued with incentive salience, it attains the ability to elicit maladaptive behaviors characteristic of psychopathology. We can capture the propensity to attribute incentive salience to a reward cue in rats using a Pavlovian conditioned approach paradigm, in which the presentation of a discrete lever-cue is followed by the delivery of a food reward. Upon learning the cue-reward relationship, some rats, termed sign-trackers, develop a conditioned response directed towards the lever-cue; whereas others, termed goal-trackers, approach the food cup upon lever-cue presentation. Here, we assessed the effects of systemic corticosterone (CORT) on the acquisition and expression of sign- and goal-tracking behaviors in male and female rats, while examining the role of the vendor (Charles River or Taconic) from which the rats originated in these effects. Treatment naïve male and female rats from Charles River had a greater tendency to sign-track than those from Taconic. Administration of CORT enhanced the acquisition of sign-tracking behavior in males from Charles River and females from both vendors. Conversely, administration of CORT had no effect on the expression of the conditioned response. These findings demonstrate a role for CORT in cue-reward learning and suggest that inherent tendencies towards sign- or goal-tracking may interact with this physiological mediator of motivated behavior.

Determination of the rat estrous cycle vased on EfficientNet

In the field of biomedical research, rats are widely used as experimental animals due to their short gestation period and strong reproductive ability. Accurate monitoring of the estrous cycle is crucial for the success of experiments. Traditional methods are time-consuming and rely on the subjective judgment of professionals, which limits the efficiency and accuracy of experiments. This study proposes an EfficientNet model to automate the recognition of the estrous cycle of female rats using deep learning techniques. The model optimizes performance through systematic scaling of the network depth, width, and image resolution. A large dataset of physiological data from female rats was used for training and validation. The improved EfficientNet model effectively recognized different stages of the estrous cycle. The model demonstrated high-precision feature capture and significantly improved recognition accuracy compared to conventional methods. The proposed technique enhances experimental efficiency and reduces human error in recognizing the estrous cycle. This study highlights the potential of deep learning to optimize data processing and achieve high-precision recognition in biomedical research. Future work should focus on further validation with larger datasets and integration into experimental workflows.

In vivo brain estrogen receptor density by neuroendocrine aging and relationships with cognition and symptomatology

17β-estradiol, the most biologically active estrogen, exerts wide-ranging effects in brain through its action on estrogen receptors (ERs), influencing higher-order cognitive function and neurobiological aging. However, our knowledge of ER expression and regulation by neuroendocrine aging in the living human brain is limited. This in vivo brain 18F-fluoroestradiol (18F-FES) Positron Emission Tomography (PET) study of healthy midlife women reveals progressively higher ER density over the menopause transition in estrogen-regulated networks. Effects were independent of age, plasma estradiol and sex hormone binding globulin, and were highly consistent, correctly classifying all women as being postmenopausal or premenopausal. Higher ER density in target regions was associated with poorer memory performance for both postmenopausal and perimenopausal groups, and predicted presence of self-reported mood and cognitive symptoms after menopause. These findings provide novel insights on brain ER density modulation by female neuroendocrine aging, with clinical implications for women's health.

Commentary: importance of considering sex and gender when designing cancer care programs

Due to perceived methodological complications, scientific studies have often excluded females. As a result, male-based findings have been generalized to females, despite physiological and biological differences between sexes. Gender has been even less considered in the literature, with little exploration specifically beyond traditional man/woman representation. This practice is compounded by a lack of what sex and gender encompass, including their erroneous use as synonyms. Sex- and gender-based differences, which are not clearly defined and recognized in scientific literature, are disregarded in health care delivery and, specifically relevant to the focus of this commentary, the development of cancer care programs. Conversely, accounting for sex- and gender in anti-cancer treatments and pathways can help create effective and personalized programming which could lead to an increased likelihood of adoption and adherence to treatment protocols. Although sex- and gender-specific programming may not be necessary in all situations, awareness of the concepts and possible impact on cancer care programs is paramount as more inclusive and personalized methodologies take shape. The goals of this commentary are to (a) clarify the terms sex and gender and (b) raise awareness of their applications and considerations for cancer care program design.

Sex mechanisms as nonbinary influences on cognitive diversity

Essentially all neuropsychiatric diagnoses show some degree of sex and/or gender differences in their etiology, diagnosis, or prognosis. As a result, the roles of sex-related variables in behavior and cognition are of strong interest to many, with several lines of research showing effects on executive functions and value-based decision making in particular. These findings are often framed within a sex binary, with behavior of females described as less optimal than male "defaults"-- a framing that pits males and females against each other and deemphasizes the enormous overlap in fundamental neural mechanisms across sexes. Here, we propose an alternative framework in which sex-related factors encompass just one subset of many sources of valuable diversity in cognition. First, we review literature establishing multidimensional, nonbinary impacts of factors related to sex chromosomes and endocrine mechanisms on cognition, focusing on value- based decision-making tasks. Next, we present two suggestions for nonbinary interpretations and analyses of sex-related data that can be implemented by behavioral neuroscientists without devoting laboratory resources to delving into mechanisms underlying sex differences. We recommend (1) shifting interpretations of behavior away from performance metrics and towards strategy assessments to avoid the fallacy that the performance of one sex is worse than another; and (2) asking how much variance sex explains in measures and whether any differences are mosaic rather than binary, to avoid assuming that sex differences in separate measures are inextricably correlated. Nonbinary frameworks in research on cognition will allow neuroscience to represent the full spectrum of brains and behaviors.

Determination of Flavonoids and Phenolic Acids in the Liver of Wistar Rats after a Dietary Enrichment with Corinthian Currant (Vitis vinifera L., var. Apyrena): A Liquid Chromatography-Tandem Mass Spectrometry Study

Corinthian currants are dried fruits produced from Vitis vinifera L. var. Apyrena grape. This study investigated the distribution of phenolic compounds in male Wistar rat livers following two distinct Corinthian currant long-term dietary intake protocols (3 and 10% w/w). Method optimization, comparing fresh and lyophilized tissues, achieved satisfactory recoveries (>70%) for most analytes. Enzymatic hydrolysis conditions (37 °C, pH 5.0) minimally affected phenolics, but enzyme addition showed diverse effects. Hydrolyzed lyophilized liver tissue from rats consuming Corinthian currants (3 and 10% w/w) exhibited elevated levels of isorhamnetin (20.62 ± 2.27 ng/g tissue and 33.80 ± 1.38 ng/g tissue, respectively), along with similar effects for kaempferol, quercetin, and chrysin after prolonged Corinthian currant intake. This suggests their presence as phase II metabolites in the fasting-state liver. This study is the first to explore phenolic accumulation in rat liver, simulating real conditions of dried fruit consumption, as seen herein with Corinthian currant.

Sex-dependent interactions between prodromal intestinal inflammation and LRRK2 G2019S in mice promote endophenotypes of Parkinson's disease

Gastrointestinal (GI) disruptions and inflammatory bowel disease (IBD) are commonly associated with Parkinson's disease (PD), but how they may impact risk for PD remains poorly understood. Herein, we provide evidence that prodromal intestinal inflammation expedites and exacerbates PD endophenotypes in rodent carriers of the human PD risk allele LRRK2 G2019S in a sex-dependent manner. Chronic intestinal damage in genetically predisposed male mice promotes α-synuclein aggregation in the substantia nigra, loss of dopaminergic neurons and motor impairment. This male bias is preserved in gonadectomized males, and similarly conferred by sex chromosomal complement in gonadal females expressing human LRRK2 G2019S. The early onset and heightened severity of neuropathological and behavioral outcomes in male LRRK2 G2019S mice is preceded by increases in α-synuclein in the colon, α-synuclein-positive macrophages in the colonic lamina propria, and loads of phosphorylated α-synuclein within microglia in the substantia nigra. Taken together, these data reveal that prodromal intestinal inflammation promotes the pathogenesis of PD endophenotypes in male carriers of LRRK2 G2019S, through mechanisms that depend on genotypic sex and involve early accumulation of α-synuclein in myeloid cells within the gut.

Effects of age and sex on photoperiod modulation of nucleus accumbens monoamine content and release in adolescence and adulthood

Day length, or photoperiod, is a reliable environmental cue encoded by the brain's circadian clock that indicates changing seasons and induces seasonal biological processes. In humans, photoperiod, age, and sex have been linked to seasonality in neuropsychiatric disorders, as seen in Seasonal Affective Disorder, Major Depressive Disorder, and Bipolar Disorder. The nucleus accumbens is a key locus for the regulation of motivated behaviors and neuropsychiatric disorders. Using periadolescent and young adult male and female mice, here we assessed photoperiod's effect on serotonin and dopamine tissue content in the nucleus accumbens core, as well as on accumbal synaptic dopamine release and uptake. We found greater serotonin and dopamine tissue content in the nucleus accumbens from young adult mice raised in a Short winter-like photoperiod. In addition, dopamine release and clearance were greater in the nucleus accumbens from young adult mice raised in a Long summer-like photoperiod. Importantly, we found that photoperiod's effects on accumbal dopamine tissue content and release were sex-specific to young adult females. These findings support that in mice there are interactions across age, sex, and photoperiod that impact critical monoamine neuromodulators in the nucleus accumbens which may provide mechanistic insight into the age and sex dependencies in seasonality of neuropsychiatric disorders in humans.

The effect of corticosterone on the acquisition of Pavlovian conditioned approach behavior is dependent on sex and vendor

Cues in the environment become predictors of biologically relevant stimuli, such as food, through associative learning. These cues can not only act as predictors but can also be attributed with incentive motivational value and gain control over behavior. When a cue is imbued with incentive salience, it attains the ability to elicit maladaptive behaviors characteristic of psychopathology. We can capture the propensity to attribute incentive salience to a reward cue in rats using a Pavlovian conditioned approach paradigm, in which the presentation of a discrete lever-cue is followed by the delivery of a food reward. Upon learning the cue-reward relationship, some rats, termed sign-trackers, develop a conditioned response directed towards the lever-cue; whereas others, termed goal-trackers, approach the food cup upon lever-cue presentation. Here, we assessed the effects of systemic corticosterone (CORT) on the acquisition and expression of sign- and goal-tracking behaviors in male and female rats, while examining the role of the vendor (Charles River or Taconic) from which the rats originated in these effects. Male and female rats from Charles River had a greater tendency to sign-track than those from Taconic. Administration of CORT enhanced the acquisition of sign-tracking behavior in males from Charles River and females from both vendors. Conversely, administration of CORT had no effect on the expression of the conditioned response. These findings demonstrate a role for CORT in cue-reward learning and suggest that inherent tendencies towards sign- or goal-tracking may interact with this physiological mediator of motivated behavior.

Highlights

Male and female rats from Charles River exhibit more sign-tracking relative to those from Taconic.Corticosterone increases the acquisition of sign-tracking in male rats from Charles River.Corticosterone increases the acquisition of sign-tracking in female rats, regardless of vendor.There is no effect of corticosterone on the expression of sign-tracking behavior in either male or female rats.

Track-by-Day: A standardized approach to estrous cycle monitoring in biobehavioral research

Despite known sex differences in brain function, female subjects are underrepresented in preclinical neuroscience research. This is driven in part by concerns about variability arising from estrous cycle-related hormone fluctuations, especially in fear- and anxiety-related research where there are conflicting reports as to whether and how the cycle influences behavior. The inconsistency may arise from a lack of common standards for tracking and reporting the cycle as opposed to inherent unpredictability in the cycle itself. The rat estrous cycle is conventionally tracked by assigning vaginal cytology smears to one of four qualitatively-defined stages. Although the cytology stages are of unequal length, the stage names are often, but not always, used to refer to the four cycle days. Subjective staging criteria and inconsistent use of terminology are not necessarily a problem in research on the cycle itself, but can lead to irreproducibility in neuroscience studies that treat the stages as independent grouping factors. We propose the explicit use of cycle days as independent variables, which we term Track-by-Day to differentiate it from traditional stage-based tracking, and that days be indexed to the only cytology feature that is a direct and rapid consequence of a hormonal event: a cornified cell layer formed in response to the pre-ovulatory 17β-estradiol peak. Here we demonstrate that cycle length is robustly regular with this method, and that the method outperforms traditional staging in detecting estrous cycle effects on Pavlovian fear conditioning and on a separate proxy for hormonal changes, uterine histology.

Modulatory effects of estrous cycle on ingestive behaviors and energy balance in young adult C57BL/6J mice maintained on a phytoestrogen-free diet

The estrous cycle is known to modify food, fluid, and electrolyte intake behaviors and energy homeostasis in various species, in part through fluctuations in estrogen levels. Simultaneously, commonly commercially available rodent dietary formulations greatly vary in soy protein content, and thereby the delivery of biologically active phytoestrogens. To explore the interactions among the estrous cycle, sodium, fluid, and caloric seeking behaviors, and energy homeostasis, young adult C57BL/6J female mice were maintained on a soy protein-free 2920x diet and provided water, or a choice between water and 0.15 mol/L NaCl drink solution. Comprehensive metabolic phenotyping was performed using a multiplexed Promethion (Sable Systems International) system, and estrous stages were determined via daily vaginal cytology. When provided food and water, estrous cycling had no major modulatory effects on intake behaviors or energy balance. When provided a saline solution drink choice, significant modulatory effects of the transition from diestrus to proestrus were observed upon fluid intake patterning, locomotion, and total energy expenditure. Access to saline increased total daily sodium consumption and aspects of energy expenditure, but these effects were not modified by the estrous stage. Collectively, these results indicate that when supplied a phytoestrogen-free diet, the estrous cycle has minor modulatory effects on ingestive behaviors and energy balance in C57BL/6J mice that are sensitive to sodium supply.NEW & NOTEWORTHY When provided a phytoestrogen-free diet, the estrous cycle had very little effect on food and water intake, physical activity, or energy expenditure in C57BL/6J mice. In contrast, when provided an NaCl drink in addition to food and water, the estrous cycle was associated with changes in intake behaviors and energy expenditure. These findings highlight the complex interactions among estrous cycling, dietary formulation, and nutrient presentation upon ingestive behaviors and energy homeostasis in mice.

Sex as a biological variable for cardiovascular physiology

There have been ongoing efforts by federal agencies and scientific communities since the early 1990s to incorporate sex and/or gender in all aspects of cardiovascular research. Scientific journals provide a critical function as change agents to influence transformation by encouraging submissions for topic areas, and by setting standards and expectations for articles submitted to the journal. As part of ongoing efforts to advance sex and gender in cardiovascular physiology research, the American Journal of Physiology-Heart and Circulatory Physiology recently launched a call for papers on Considering Sex as a Biological Variable. This call was an overwhelming success, resulting in 78 articles published in this collection. This review summarizes the major themes of the collection, including Sex as a Biological Variable Within: Endothelial Cell and Vascular Physiology, Cardiovascular Immunity and Inflammation, Metabolism and Mitochondrial Energy, Extracellular Matrix Turnover and Fibrosis, Neurohormonal Signaling, and Cardiovascular Clinical and Epidemiology Assessments. Several articles also focused on establishing rigor and reproducibility of key physiological measurements involved in cardiovascular health and disease, as well as recommendations and considerations for study design. Combined, these articles summarize our current understanding of sex and gender influences on cardiovascular physiology and pathophysiology and provide insight into future directions needed to further expand our knowledge.

Early- but not late-adolescent Western diet consumption programs for long-lasting memory impairments in male but not female rats

Early life Western diet (WD) consumption leads to impaired memory function, particularly for processes mediated by the hippocampus. However, the precise critical developmental window(s) during which WD exposure negatively impacts hippocampal function are unknown. Here, we exposed male and female rats to a WD model involving free access to a variety of high-fat and/or high-sugar food and drink items during either the early-adolescent period (postnatal days [PN] 26-41; WD-EA) or late-adolescent period (PN 41-56; WD-LA). Control (CTL) rats were given healthy standard chow throughout both periods. To evaluate long-lasting memory capacity well beyond the early life WD exposure periods, we performed behavioral assessments after both a short (4 weeks for WD-EA, 2 weeks for WD-LA) and long (12 weeks for WD-EA, 10 weeks for WD-LA) period of healthy diet intervention. Results revealed no differences in body weight or body composition between diet groups, regardless of sex. Following the shorter period of healthy diet intervention, both male and female WD-EA and WD-LA rats showed deficits in hippocampal-dependent memory compared to CTL rats. Following the longer healthy diet intervention period, memory impairments persisted in male WD-EA but not WD-LA rats. In contrast, in female rats the longer healthy diet intervention reversed the initial memory impairments in both WD-EA and WD-LA rats. Collectively, these findings reveal that early-adolescence is a critical period of long-lasting hippocampal vulnerability to dietary insults in male but not female rats, thus highlighting developmental- and sex-specific effects mediating the relationship between the early life nutritional environment and long-term cognitive health.

The sexually divergent cFos activation map of fear extinction

Objective

Post-traumatic stress disorder (PTSD) is a neuropsychiatric disorder that can develop after experiencing or witnessing a traumatic event. Exposure therapy is a common treatment for PTSD, but it has varying levels of efficacy depending on sex. In this study, we aimed to compare the sexual dimorphism in brain activation during the extinction of fear conditioning in male and female rats by detecting the c-fos levels in the whole brain.

Methods

Thirty-two rats (Male: n = 16; Female: n = 16) were randomly separated into the extinction group as well as the non-extinction group, and fear conditioning was followed by extinction and non-extinction, respectively. Subsequently, brain sections from the sacrificed animal were performed immunofluorescence and the collected data were analyzed by repeated two-way ANOVAs as well as Pearson Correlation Coefficient.

Results

Our findings showed that most brain areas activated during extinction were similar in both male and female rats, except for the reuniens thalamic nucleus and ventral hippocampi. Furthermore, we found differences in the correlation between c-fos activation levels and freezing behavior during extinction between male and female rats. Specifically, in male rats, c-fos activation in the anterior cingulate cortex was negatively correlated with the freezing level, while c-fos activation in the retrosplenial granular cortex was positively correlated with the freezing level; but in female rats did not exhibit any correlation between c-fos activation and freezing level. Finally, the functional connectivity analysis revealed differences in the neural networks involved in extinction learning between male and female rats. In male rats, the infralimbic cortex and insular cortex, anterior cingulate cortex and retrosplenial granular cortex, and dorsal dentate gyrus and dCA3 were strongly correlated after extinction. In female rats, prelimbic cortex and basolateral amygdala, insular cortex and dCA3, and anterior cingulate cortex and dCA1 were significantly correlated.

Conclusion

These results suggest divergent neural networks involved in extinction learning in male and female rats and provide a clue for improving the clinical treatment of exposure therapy based on the sexual difference.

Epigenetic mechanisms underlying sex differences in the brain and behavior

Sex differences are found across brain regions, behaviors, and brain diseases. Sexual differentiation of the brain is initiated prenatally but it continues throughout life, as a result of the interaction of three major factors: gonadal hormones, sex chromosomes, and the environment. These factors are thought to act, in part, via epigenetic mechanisms which control chromatin and transcriptional states in brain cells. In this review, we discuss evidence that epigenetic mechanisms underlie sex-specific neurobehavioral changes during critical organizational periods, across the estrous cycle, and in response to diverse environments throughout life. We further identify future directions for the field that will provide novel mechanistic insights into brain sex differences, inform brain disease treatments and women's brain health in particular, and apply to people across genders.

Practical solutions for including sex as a biological variable (SABV) in preclinical neuropsychopharmacological research

Recently, many funding agencies have released guidelines on the importance of considering sex as a biological variable (SABV) as an experimental factor, aiming to address sex differences and avoid possible sex biases to enhance the reproducibility and translational relevance of preclinical research. In neuroscience and pharmacology, the female sex is often omitted from experimental designs, with researchers generalizing male-driven outcomes to both sexes, risking a biased or limited understanding of disease mechanisms and thus potentially ineffective therapeutics. Herein, we describe key methodological aspects that should be considered when sex is factored into in vitro and in vivo experiments and provide practical knowledge for researchers to incorporate SABV into preclinical research. Both age and sex significantly influence biological and behavioral processes due to critical changes at different timepoints of development for males and females and due to hormonal fluctuations across the rodent lifespan. We show that including both sexes does not require larger sample sizes, and even if sex is included as an independent variable in the study design, a moderate increase in sample size is sufficient. Moreover, the importance of tracking hormone levels in both sexes and the differentiation between sex differences and sex-related strategy in behaviors are explained. Finally, the lack of robust data on how biological sex influences the pharmacokinetic (PK), pharmacodynamic (PD), or toxicological effects of various preclinically administered drugs to animals due to the exclusion of female animals is discussed, and methodological strategies to enhance the rigor and translational relevance of preclinical research are proposed.

Multiple Sex- and Circuit-Specific Mechanisms Underlie Exercise-Induced Stress Resistance

Prior physical activity reduces the risk of future stress-related mental health disorders including depression, anxiety, and post-traumatic stress disorder. Rodents allowed to engage in voluntary wheel running are similarly protected from behavioral consequences of stress. The present review summarizes current knowledge on mechanisms underlying exercise-induced stress resistance. A conceptual framework involving the development (during exercise) and expression (during stress) of stress resistance from exercise is proposed. During the development of stress resistance, adaptations involving multiple exercise signals and molecular mediators occur within neural circuits orchestrating various components of the stress response, which then respond differently to stress during the expression of stress resistance. Recent data indicate that the development and expression of stress resistance from exercise involve multiple independent mechanisms that depend on sex, stressor severity, and behavioral outcome. Recent insight into the role of the prefrontal cortex in exercise-induced stress resistance illustrates these multiple mechanisms. This knowledge has important implications for the design of future experiments aimed at identifying the mechanisms underlying exercise-induced stress resistance.

Brain age prediction using combined deep convolutional neural network and multi-layer perceptron algorithms

The clinical applications of brain age prediction have expanded, particularly in anticipating the onset and prognosis of various neurodegenerative diseases. In the current study, we proposed a deep learning algorithm that leverages brain structural imaging data and enhances prediction accuracy by integrating biological sex information. Our model for brain age prediction, built on deep neural networks, employed a dataset of 3004 healthy subjects aged 18 and above. The T1-weighted images were minimally preprocessed and analyzed using the convolutional neural network (CNN) algorithm. The categorical sex information was then incorporated using the multi-layer perceptron (MLP) algorithm. We trained and validated both a CNN-only algorithm (utilizing only brain structural imaging data), and a combined CNN-MLP algorithm (using both structural brain imaging data and sex information) for age prediction. By integrating sex information with T1-weighted imaging data, our proposed CNN-MLP algorithm outperformed not only the CNN-only algorithm but also established algorithms, such as brainageR, in prediction accuracy. Notably, this hybrid CNN-MLP algorithm effectively distinguished between mild cognitive impairment and Alzheimer's disease groups by identifying variances in brain age gaps between them, highlighting the algorithm's potential for clinical application. Overall, these results underscore the enhanced precision of the CNN-MLP algorithm in brain age prediction, achieved through the integration of sex information.

Elevated gonadotropin levels are associated with increased biomarker risk of Alzheimer's disease in midlife women

Introduction

In preclinical studies, menopausal elevations in pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), trigger Alzheimer's disease (AD) pathology and synaptic loss in female animals. Herein, we took a translational approach to test whether gonadotropin elevations are linked to AD pathophysiology in women.

Methods

We examined 191 women ages 40-65 years, carrying risk factors for late-onset AD, including 45 premenopausal, 67 perimenopausal, and 79 postmenopausal participants with clinical, laboratory, cognitive exams, and volumetric MRI scans. Half of the cohort completed 11C-Pittsburgh Compound B (PiB) amyloid-β (Aβ) PET scans. Associations between serum FSH, LH and biomarkers were examined using voxel-based analysis, overall and stratified by menopause status. Associations with region-of-interest (ROI) hippocampal volume, plasma estradiol levels, APOE-4 status, and cognition were assessed in sensitivity analyses.

Results

FSH levels were positively associated with Aβ load in frontal cortex (multivariable adjusted P≤0.05, corrected for family wise type error, FWE), an effect that was driven by the postmenopausal group (multivariable adjusted PFWE ≤ 0.044). LH levels were also associated with Aβ load in frontal cortex, which did not survive multivariable adjustment. FSH and LH were negatively associated with gray matter volume (GMV) in frontal cortex, overall and in each menopausal group (multivariable adjusted PFWE ≤ 0.040), and FSH was marginally associated with ROI hippocampal volume (multivariable adjusted P = 0.058). Associations were independent of age, clinical confounders, menopause type, hormone therapy status, history of depression, APOE-4 status, and regional effects of estradiol. There were no significant associations with cognitive scores.

Discussion

Increasing serum gonadotropin levels, especially FSH, are associated with higher Aβ load and lower GMV in some AD-vulnerable regions of midlife women at risk for AD. These findings are consistent with preclinical work and provide exploratory hormonal targets for precision medicine strategies for AD risk reduction.

Rat models of diet-induced obesity and metabolic dysregulation: Current trends, shortcomings and considerations for future research

Rat diet-induced obesity and metabolic dysregulation (DIO/DIMD) is widely used as a pre-clinical model for human obesity and for testing weight-loss interventions. The aim of this review was to utilise a systematic literature survey of rat DIO/DIMD studies as a tool to document trends around study design and metabolic outcomes of these studies, and to consider ways in which the design of these studies may be improved to enhance the relevance thereof for human obesity research. In total, 110 comparisons between control and obesogenic dietary groups were included in the survey. Young male rats were found to be the model of choice, but fewer than 50% of studies provided comprehensive information about diet composition and energy intake. In addition, it was found that the majority of expected DIO/DIMD responses (hyperglycemia, hyperinsulinemia, dyslipidemia, hypoadiponectinemia) occurred at < 80% frequency, drawing into question the concept of a "typical" or "appropriate" response. We discuss the impact of differences in diet composition and energy intake on metabolic outcomes against the context of large heterogeneity of obesogenic diets employed in rat DIO/DIMD studies, and provide recommendations for the improvement of reporting standards around diet composition and dietary intake. In addition, we highlight the lack of data from female and older rats and describe considerations around the inclusion of sex and age as a variable in rat DIO/DIMD studies, aiming towards improving the applicability of these studies as a model of human obesity, which is most prevalent in women and older individuals.

Female rats are more responsive than are males to the protective effects of voluntary physical activity against the behavioral consequences of inescapable stress

Common stress-related mental health disorders affect women more than men. Physical activity can provide protection against the development of future stress-related mental health disorders (i.e. stress resistance) in both sexes, but whether there are sex differences in exercise-induced stress resistance is unknown. We have previously observed that voluntary wheel running (VWR) protects both female and male rats against the anxiety- and exaggerated fear-like behavioral effects of inescapable stress, but the time-course and magnitude of VWR-induced stress resilience has not been compared between sexes. The goal of the current study was to determine whether there are sex differences in the time-course and magnitude of exercise-induced stress resistance. In adult female and male Sprague Dawley rats, 6 weeks of VWR produced robust protection against stress-induced social avoidance and exaggerated fear. The magnitude of stress protection was similar between the sexes and was independent of reactivity to shock, general locomotor activity, and circulating corticosterone. Interestingly, 3 weeks of VWR prevented both stress-induced social avoidance and exaggerated fear in females but only prevented stress-induced social avoidance in males. Ovariectomy altered wheel-running behavior in females such that it resembled that of males, however; 3 weeks of VWR still protected females against behavioral consequences of stress regardless of the absence of ovaries. These data indicate that female Sprague Dawley rats are more responsive to exercise-induced stress resistance than are males.

Feeding neurons integrate metabolic and reproductive states in mice

Balance between metabolic and reproductive processes is important for survival, particularly in mammals that gestate their young. How the nervous system coordinates this balance is an active area of study. Herein, we demonstrate that somatostatin (SST) neurons of the tuberal hypothalamus alter feeding in a manner sensitive to metabolic and reproductive states in mice. Whereas chemogenetic activation of SST neurons increased food intake across sexes, ablation decreased food intake only in female mice during proestrus. This ablation effect was only apparent in animals with low body mass. Fat transplantation and bioinformatics analysis of SST neuronal transcriptomes revealed white adipose as a key modulator of these effects. These studies indicate that SST hypothalamic neurons integrate metabolic and reproductive cues by responding to varying levels of circulating estrogens to modulate feeding differentially based on energy stores. Thus, gonadal steroid modulation of neuronal circuits can be context dependent and gated by metabolic status.

The enteric metabolite, propionic acid, impairs social behavior and increases anxiety in a rodent ASD model: Examining sex differences and the influence of the estrous cycle

Research suggests that certain gut and dietary factors may worsen behavioral features of autism spectrum disorder (ASD). Treatment with propionic acid (PPA) has been found to create both brain and behavioral responses in rats that are characteristic of ASD in humans. A consistent male bias in human ASD prevalence has been observed, and several sex-differential genetic and hormonal factors have been suggested to contribute to this bias. The majority of PPA studies in relation to ASD focus on male subjects; research examining the effects of PPA in females is scarce. The present study includes two experiments. Experiment 1 explored sex differences in the effects of systemic administration of PPA (500 mg/kg, ip) on adult rodent social behavior and anxiety (light-dark test). Experiment 2 investigated differential effects of systemic administration of PPA (500 mg/kg) on social behavior and anxiety in relation to fluctuating estrogen and progesterone levels during the adult rodent estrous cycle. PPA treatment impaired social behavior and increased anxiety in females to the same degree in comparison to PPA-treated males. As well, females treated with PPA in their diestrus phase did not differ significantly in comparison to females administered PPA in their proestrus phase, in terms of reduced social behavior and increased anxiety.

Peripheral mechanisms of peripheral neuropathic pain

Peripheral neuropathic pain (PNP), neuropathic pain that arises from a damage or disease affecting the peripheral nervous system, is associated with an extremely large disease burden, and there is an increasing and urgent need for new therapies for treating this disorder. In this review we have highlighted therapeutic targets that may be translated into disease modifying therapies for PNP associated with peripheral neuropathy. We have also discussed how genetic studies and novel technologies, such as optogenetics, chemogenetics and single-cell RNA-sequencing, have been increasingly successful in revealing novel mechanisms underlying PNP. Additionally, consideration of the role of non-neuronal cells and communication between the skin and sensory afferents is presented to highlight the potential use of drug treatment that could be applied topically, bypassing drug side effects. We conclude by discussing the current difficulties to the development of effective new therapies and, most importantly, how we might improve the translation of targets for peripheral neuropathic pain identified from studies in animal models to the clinic.

The mixed legacy of the rat estrous cycle

BACKGROUND

The rat estrous cycle first characterized by Long and Evans in 1922 profoundly affected the course of endocrine research. Investigators took advantage of sex steroid hormone fluctuations associated with the cycle to assess hormonal influences on anxiety, depression, food intake, stress, brain structure and other traits. Similarities of the rat estrous and human menstrual cycles facilitated understanding of human reproductive physiology. I assessed the impact of awareness of the estrous cycle on the emergence of a sex bias that excluded female rats from biomedical research.

METHODS

Beginning with the 1918 volume of the American Journal of Physiology and ending in 1976 when the journal subdivided into several separate disciplinary journals, all studies conducted on rats were downloaded; the use of females, males, both sexes and sex left unspecified was tabulated for 485 articles. A second analysis tracked the number of rat estrous cycle studies across all disciplines listed in PubMed from 1950 to 2021.

RESULTS

The description and awareness of variability associated with the rat estrous cycle was correlated with a precipitous decline in investigations that incorporated both sexes, a marked increase in male-only studies and a striking sex bias that excluded female rats. The number of rat estrous cycles studies increased markedly from earlier decades to a peak in 2021.

CONCLUSIONS

The initial description the rat estrous cycle was correlated with a substantial decline in investigations that incorporated both sexes; one result was a marked increase in male-only studies and a striking sex bias that excluded female rats from biomedical research. Recognition of the advantages of studies that incorporate the rat estrous cycle has resulted in recent years in an increase of such investigations. Female rats and females of several other species are not more variable than their male counterparts across traits, arguing for female inclusion without requiring cycle monitoring. There, remain, however, many advantages of incorporating the estrous cycle in contemporary research.

Unmasking the Adverse Impacts of Sex Bias on Science and Research Animal Welfare

Sex bias in biomedical and natural science research has been prevalent for decades. In many cases, the female estrous cycle was thought to be too complex an issue to model for, and it was thought to be simpler to only use males in studies. At times, particularly when studying efficacy and safety of new therapeutics, this sex bias has resulted in over- and under-medication with associated deleterious side effects in women. Many sex differences have been recognized that are unrelated to hormonal variation occurring during the estrous cycle. Sex bias also creates animal welfare challenges related to animal over-production and wastage, insufficient consideration of welfare (and scientific) impact related to differential housing of male vs female animals within research facilities, and a lack of understanding regarding differential requirements for pain recognition and alleviation in male versus female animals. Although many funding and government agencies require both sexes to be studied in biomedical research, many disparities remain in practice. This requires further enforcement of expectations by the Institutional Animal Care and Use Committee when reviewing protocols, research groups when writing grants, planning studies, and conducting research, and scientific journals and reviewers to ensure that sex bias policies are enforced.

11-Ethoxyviburtinal improves chronic restraint stress-induced anxiety-like behaviors in gender-specific mice via PI3K/Akt and E2 /ERβ signaling pathways

Anxiety disorder is a chronic and disabling psychiatric disorder that is more prevalent in females than in males. 11-Ethoxyviburtinal is an iridoid extracted from Valeriana jatamansi Jones, which has anxiolytic potential. The aim of the present work was to study the anxiolytic efficacy and mechanism of 11-ethoxyviburtinal in gender-specific mice. We first evaluated the anxiolytic-like efficacy of 11-ethoxyviburtinal in chronic restraint stress (CRS) mice of different sexes through behavioral experiments and biochemical indexes. In addition, network pharmacology and molecular docking were used to predict potential targets and important pathways for the treatment of anxiety disorder with 11-ethoxyviburtinal. Finally, the influence of 11-ethoxyviburtinal on phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, estrogen receptor β (ERβ) expression, and anxiety-like behavior in mice was verified by western blotting, immunohistochemistry staining, antagonist intervention methods, and behavioral experiments. 11-ethoxyviburtinal alleviated the anxiety-like behaviors induced by CRS and inhibited neurotransmitter dysregulation and HPA axis hyperactivity. It inhibited the abnormal activation of the PI3K/Akt signaling pathway, modulated estrogen production, and promoted ERβ expression in mice. In addition, the female mice may be more sensitive to the pharmacological effects of 11-ethoxyviburtinal. 11-ethoxyviburtinal may exert its anxiolytic-like effects through PI3K/Akt and E2/ERβ signaling pathways. Meanwhile, by comparing the male and female mice, gender differences may affect the therapy and development of anxiety disorder.

Circulating ovarian hormones interact with protein interacting with C kinase (PICK1) within the medial prefrontal cortex to influence cocaine seeking in female mice

Protein interacting with C kinase 1 (PICK1) is an AMPA receptor binding protein that works in conjunction with glutamate receptor interacting protein (GRIP) to balance the number of GluA2-containing AMPARs in the synapse. In male mice, disrupting PICK1 in the medial prefrontal cortex (mPFC) leads to a decrease in cue-induced cocaine seeking and disrupting GRIP in the mPFC has the opposing effect, consistent with other evidence that removal of GluA2-containing AMPARs potentiates reinstatement. However, PICK1 does not seem to play the same role in female mice, as knockdown of either PICK1 or GRIP in the mPFC leads to similar increases in cue-induced cocaine seeking. These previous findings indicate that the role of PICK1 in the prefrontal cortex is sex specific. The goal of the current study was to examine whether ovarian hormones contribute to the effect of prefrontal PICK1 knockdown on reinstatement of cocaine seeking. While we replicated the increased cue-induced cocaine seeking in prefrontal PICK1 knockdown sham mice, we did not see any difference between the GFP control mice and PICK1 knockdowns following ovariectomy. However, this effect was driven primarily by an increase in cocaine seeking in ovariectomized GFP control mice while there was no effect ovariectomy in PICK1 knockdown mice. Taken together, these findings suggest that circulating ovarian hormones interact with the effects of PICK1 on cue-induced reinstatement.

Are There Prevalent Sex Differences in Psychostimulant Use Disorder? A Focus on the Potential Therapeutic Efficacy of Atypical Dopamine Uptake Inhibitors

Psychostimulant use disorders (PSUD) affect a growing number of men and women and exert sizable public health and economic burdens on our global society. Notably, there are some sex differences in the onset of dependence, relapse rates, and treatment success with PSUD observed in preclinical and clinical studies. The subtle sex differences observed in the behavioral aspects of PSUD may be associated with differences in the neurochemistry of the dopaminergic system between sexes. Preclinically, psychostimulants have been shown to increase synaptic dopamine (DA) levels and may downregulate the dopamine transporter (DAT). This effect is greatest in females during the high estradiol phase of the estrous cycle. Interestingly, women have been shown to be more likely to begin drug use at younger ages and report higher levels of desire to use cocaine than males. Even though there is currently no FDA-approved medication, modafinil, a DAT inhibitor approved for use in the treatment of narcolepsy and sleep disorders, has shown promise in the treatment of PSUD among specific populations of affected individuals. In this review, we highlight the therapeutic potential of modafinil and other atypical DAT inhibitors focusing on the lack of sex differences in the actions of these agents.

Effects of sex and estrous cycle on intravenous oxycodone self-administration and the reinstatement of oxycodone-seeking behavior in rats

Introduction

The increasing misuse of both prescription and illicit opioids has culminated in a national healthcare crisis in the United States. Oxycodone is among the most widely prescribed and misused opioid pain relievers and has been associated with a high risk for transition to compulsive opioid use. Here, we sought to examine potential sex differences and estrous cycle-dependent effects on the reinforcing efficacy of oxycodone, as well as on stress-induced or cue-induced oxycodone-seeking behavior, using intravenous (IV) oxycodone self-administration and reinstatement procedures.

Methods

In experiment 1, adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone according to a fixed-ratio 1 schedule of reinforcement in daily 2-h sessions, and a dose-response function was subsequently determined (0.003-0.03 mg/kg/inf). In experiment 2, a separate group of adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone for 8 sessions, followed by 0.01 mg/kg/inf oxycodone for 10 sessions. Responding was then extinguished, followed by sequential footshock-induced and cue-induced reinstatement tests.

Results

In the dose-response experiment, oxycodone produced a typical inverted U-shape function with 0.01 mg/kg/inf representing the maximally effective dose in both sexes. No sex differences were detected in the reinforcing efficacy of oxycodone. In the second experiment, the reinforcing effects of 0.01-0.03 mg//kg/inf oxycodone were significantly attenuated in females during proestrus/estrus as compared to metestrus/diestrus phases of the estrous cycle. Neither males nor females displayed significant footshock-induced reinstatement of oxycodone seeking, but both sexes exhibited significant cue-induced reinstatement of oxycodone seeking at magnitudes that did not differ either by sex or by estrous cycle phase.

Discussion

These results confirm and extend previous work suggesting that sex does not robustly influence the primary reinforcing effects of oxycodone nor the reinstatement of oxycodone-seeking behavior. However, our findings reveal for the first time that the reinforcing efficacy of IV oxycodone varies across the estrous cycle in female rats.

Pharmacogenomics: Driving Personalized Medicine

Personalized medicine tailors therapies, disease prevention, and health maintenance to the individual, with pharmacogenomics serving as a key tool to improve outcomes and prevent adverse effects. Advances in genomics have transformed pharmacogenetics, traditionally focused on single gene-drug pairs, into pharmacogenomics, encompassing all "-omics" fields (e.g., proteomics, transcriptomics, metabolomics, and metagenomics). This review summarizes basic genomics principles relevant to translation into therapies, assessing pharmacogenomics' central role in converging diverse elements of personalized medicine. We discuss genetic variations in pharmacogenes (drug-metabolizing enzymes, drug transporters, and receptors), their clinical relevance as biomarkers, and the legacy of decades of research in pharmacogenetics. All types of therapies, including proteins, nucleic acids, viruses, cells, genes, and irradiation, can benefit from genomics, expanding the role of pharmacogenomics across medicine. Food and Drug Administration approvals of personalized therapeutics involving biomarkers increase rapidly, demonstrating the growing impact of pharmacogenomics. A beacon for all therapeutic approaches, molecularly targeted cancer therapies highlight trends in drug discovery and clinical applications. To account for human complexity, multicomponent biomarker panels encompassing genetic, personal, and environmental factors can guide diagnosis and therapies, increasingly involving artificial intelligence to cope with extreme data complexities. However, clinical application encounters substantial hurdles, such as unknown validity across ethnic groups, underlying bias in health care, and real-world validation. This review address the underlying science and technologies germane to pharmacogenomics and personalized medicine, integrated with economic, ethical, and regulatory issues, providing insights into the current status and future direction of health care. SIGNIFICANCE STATEMENT: Personalized medicine aims to optimize health care for the individual patients with use of predictive biomarkers to improve outcomes and prevent adverse effects. Pharmacogenomics drives biomarker discovery and guides the development of targeted therapeutics. This review addresses basic principles and current trends in pharmacogenomics, with large-scale data repositories accelerating medical advances. The impact of pharmacogenomics is discussed, along with hurdles impeding broad clinical implementation, in the context of clinical care, ethics, economics, and regulatory affairs.