Estrous cycle effects on behavior of C57BL/6J and BALB/cByJ female mice: implications for phenotyping strategies

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.

Sex-dependent astrocyte reactivity: Unveiling chronic stress-induced morphological changes across multiple brain regions

Chronic stress is a major precursor to various neuropsychiatric disorders and is linked with increased inflammation in the brain. However, the bidirectional association between inflammation and chronic stress has yet to be fully understood. Astrocytes are one of the key inflammatory regulators in the brain, and the morphological change in reactive astrocytes serves as an important indicator of inflammation. In this study, we evaluated the sex-specific astrocyte response to chronic stress or systemic inflammation in key brain regions associated with mood disorders. We conducted the unpredictable chronic mild stress (UCMS) paradigm to model chronic stress, or lipopolysaccharide (LPS) injection to model systemic inflammation. To evaluate stress-induced morphological changes in astrocyte complexity, we measured GFAP fluorescent intensity for astrocyte expression, branch bifurcation by quantifying branch points and terminal points, branch arborization by conducting Sholl analysis, and calculated the ramification index. Our analysis indicated that chronic stress-induced morphological changes in astrocytes in all brain regions investigated. The effects of chronic stress were region and sex specific. Notably, females had greater stress or inflammation-induced astrocyte activation in the hypothalamus (HYPO), CA1, CA3, and amygdala (AMY) than males. These findings indicate that chronic stress induces astrocyte activation that may drive sex and region-specific effects in females, potentially contributing to sex-dependent mechanisms of disease.

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.

Cannabidiol is a behavioral modulator in BTBR mouse model of idiopathic autism

Introduction

The prevalence of Autism Spectrum Disorder (ASD) has drastically risen over the last two decades and is currently estimated to affect 1 in 36 children in the U.S., according to the center for disease control (CDC). This heterogenous neurodevelopmental disorder is characterized by impaired social interactions, communication deficits, and repetitive behaviors plus restricted interest. Autistic individuals also commonly present with a myriad of comorbidities, such as attention deficit hyperactivity disorder, anxiety, and seizures. To date, a pharmacological intervention for the treatment of core autistic symptoms has not been identified. Cannabidiol (CBD), the major nonpsychoactive constituent of Cannabis sativa, is suggested to have multiple therapeutic applications, but its effect(s) on idiopathic autism is unknown. We hypothesized that CBD will effectively attenuate the autism-like behaviors and autism-associated comorbid behaviors in BTBR T+Itpr3tf/J (BTBR) mice, an established mouse model of idiopathic ASD.

Methods

Male BTBR mice were injected intraperitoneally with either vehicle, 20 mg/kg CBD or 50 mg/kg CBD daily for two weeks beginning at postnatal day 21 ± 3. On the final treatment day, a battery of behavioral assays were used to evaluate the effects of CBD on the BTBR mice, as compared to age-matched, vehicle-treated C57BL/6 J mice.

Results

High dose (50 mg/kg) CBD treatment attenuated the elevated repetitive self-grooming behavior and hyperlocomotion in BTBR mice. The social deficits exhibited by the control BTBR mice were rescued by the 20 mg/kg CBD treatment.

Discussion

Our data indicate that different doses for CBD are needed for treating specific ASD-like behaviors. Together, our results suggest that CBD may be an effective drug to ameliorate repetitive/restricted behaviors, social deficits, and autism-associated hyperactivity.

Tumor necrosis factor-stimulated gene-6 ameliorates early brain injury after subarachnoid hemorrhage by suppressing NLRC4 inflammasome-mediated astrocyte pyroptosis

Subarachnoid hemorrhage is associated with high morbidity and mortality and lacks effective treatment. Pyroptosis is a crucial mechanism underlying early brain injury after subarachnoid hemorrhage. Previous studies have confirmed that tumor necrosis factor-stimulated gene-6 (TSG-6) can exert a neuroprotective effect by suppressing oxidative stress and apoptosis. However, no study to date has explored whether TSG-6 can alleviate pyroptosis in early brain injury after subarachnoid hemorrhage. In this study, a C57BL/6J mouse model of subarachnoid hemorrhage was established using the endovascular perforation method. Our results indicated that TSG-6 expression was predominantly detected in astrocytes, along with NLRC4 and gasdermin-D (GSDMD). The expression of NLRC4, GSDMD and its N-terminal domain (GSDMD-N), and cleaved caspase-1 was significantly enhanced after subarachnoid hemorrhage and accompanied by brain edema and neurological impairment. To explore how TSG-6 affects pyroptosis during early brain injury after subarachnoid hemorrhage, recombinant human TSG-6 or a siRNA targeting TSG-6 was injected into the cerebral ventricles. Exogenous TSG-6 administration downregulated the expression of NLRC4 and pyroptosis-associated proteins and alleviated brain edema and neurological deficits. Moreover, TSG-6 knockdown further increased the expression of NLRC4, which was accompanied by more severe astrocyte pyroptosis. In summary, our study revealed that TSG-6 provides neuroprotection against early brain injury after subarachnoid hemorrhage by suppressing NLRC4 inflammasome activation-induced astrocyte pyroptosis.

Slitrk4 is required for the development of inhibitory neurons in the fear memory circuit of the lateral amygdala

The Slitrk family consists of six synaptic adhesion molecules, some of which are associated with neuropsychiatric disorders. In this study, we aimed to investigate the physiological role of Slitrk4 by analyzing Slitrk4 knockout (KO) mice. The Slitrk4 protein was widely detected in the brain and was abundant in the olfactory bulb and amygdala. In a systematic behavioral analysis, male Slitrk4 KO mice exhibited an enhanced fear memory acquisition in a cued test for classical fear conditioning, and social behavior deficits in reciprocal social interaction tests. In an electrophysiological analysis using amygdala slices, Slitrk4 KO mice showed enhanced long-term potentiation in the thalamo-amygdala afferents and reduced feedback inhibition. In the molecular marker analysis of Slitrk4 KO brains, the number of calretinin (CR)-positive interneurons was decreased in the anterior part of the lateral amygdala nuclei at the adult stage. In in vitro experiments for neuronal differentiation, Slitrk4-deficient embryonic stem cells were defective in inducing GABAergic interneurons with an altered response to sonic hedgehog signaling activation that was involved in the generation of GABAergic interneuron subsets. These results indicate that Slitrk4 function is related to the development of inhibitory neurons in the fear memory circuit and would contribute to a better understanding of osttraumatic stress disorder, in which an altered expression of Slitrk4 has been reported.

A P2RY12 deficiency results in sex-specific cellular perturbations and sexually dimorphic behavioral anomalies

Microglia are sexually dimorphic, yet, this critical aspect is often overlooked in neuroscientific studies. Decades of research have revealed the dynamic nature of microglial-neuronal interactions, but seldom consider how this dynamism varies with microglial sex differences, leaving a significant gap in our knowledge. This study focuses on P2RY12, a highly expressed microglial signature gene that mediates microglial-neuronal interactions, we show that adult females have a significantly higher expression of the receptor than adult male microglia. We further demonstrate that a genetic deletion of P2RY12 induces sex-specific cellular perturbations with microglia and neurons in females more significantly affected. Correspondingly, female mice lacking P2RY12 exhibit unique behavioral anomalies not observed in male counterparts. These findings underscore the critical, sex-specific roles of P2RY12 in microglial-neuronal interactions, offering new insights into basal interactions and potential implications for CNS disease mechanisms.

The impact of stress on the behavior of C57BL/6 mice with liver injury: a comparative study

Introduction

Depressive-like behavior has been shown to be associated with liver damage. This study aimed to evaluate the impact of three different models of depression on the behavior of mice with liver injury.

Methods

During the 4 weeks of methionine/choline deficiency diet (MCD), adult C57BL/6 mice were randomly divided into four groups: MCD (no stress protocol, n = 6), chronic unpredictable mild stress (CUMS, n = 9), acute and repeated forced swim stress [aFSS (n = 9) and rFSS (n = 9)].

Results

All depression protocols induced increased anhedonia and anxiety-like behavior compared to baseline and had no impact on the severity of liver damage, according to ultrasonography. However, different protocols evoked different overall behavior patterns. After the depressive-like behavior induction protocols, animals subjected to aFSS did not exhibit anxiety-like behavior differences compared to MCD animals, while mice subjected to CUMS showed additional weight loss compared to FSS animals. All tested protocols for inducing depressive-like behavior decreased the short-term memory of mice with liver damage, as assessed by the novel object recognition test (NORT).

Discussion

Our results show that the use of all protocols seems to generate different levels of anxiety-like behavior, but only the depressive-like behavior induction procedures associate additional anhedonia and memory impairment in mice with liver injury.

Human mutations in SLITRK3 implicated in GABAergic synapse development in mice

This study reports on biallelic homozygous and monoallelic de novo variants in SLITRK3 in three unrelated families presenting with epileptic encephalopathy associated with a broad neurological involvement characterized by microcephaly, intellectual disability, seizures, and global developmental delay. SLITRK3 encodes for a transmembrane protein that is involved in controlling neurite outgrowth and inhibitory synapse development and that has an important role in brain function and neurological diseases. Using primary cultures of hippocampal neurons carrying patients' SLITRK3 variants and in combination with electrophysiology, we demonstrate that recessive variants are loss-of-function alleles. Immunostaining experiments in HEK-293 cells showed that human variants C566R and E606X change SLITRK3 protein expression patterns on the cell surface, resulting in highly accumulating defective proteins in the Golgi apparatus. By analyzing the development and phenotype of SLITRK3 KO (SLITRK3-/-) mice, the study shows evidence of enhanced susceptibility to pentylenetetrazole-induced seizure with the appearance of spontaneous epileptiform EEG as well as developmental deficits such as higher motor activities and reduced parvalbumin interneurons. Taken together, the results exhibit impaired development of the peripheral and central nervous system and support a conserved role of this transmembrane protein in neurological function. The study delineates an emerging spectrum of human core synaptopathies caused by variants in genes that encode SLITRK proteins and essential regulatory components of the synaptic machinery. The hallmark of these disorders is impaired postsynaptic neurotransmission at nerve terminals; an impaired neurotransmission resulting in a wide array of (often overlapping) clinical features, including neurodevelopmental impairment, weakness, seizures, and abnormal movements. The genetic synaptopathy caused by SLITRK3 mutations highlights the key roles of this gene in human brain development and function.

Cilia loss on distinct neuron populations differentially alters cocaine-induced locomotion and reward

BACKGROUND

Neuronal primary cilia are being recognized for their role in mediating signaling associated with a variety of neurobehaviors, including responses to drugs of abuse. They function as signaling hubs, enriched with a diverse array of G-protein coupled receptors (GPCRs), including several associated with motivation and drug-related behaviors. However, our understanding of how cilia regulate neuronal function and behavior is still limited.

AIMS

The objective of the current study was to investigate the contributions of primary cilia on specific neuronal populations to behavioral responses to cocaine.

METHODS

To test the consequences of cilia loss on cocaine-induced locomotion and reward-related behavior, we selectively ablated cilia from dopaminergic or GAD2-GABAergic neurons in mice.

RESULTS

Cilia ablation on either population of neurons failed to significantly alter acute locomotor responses to cocaine at a range of doses. With repeated administration, mice lacking cilia on GAD2-GABAergic neurons showed no difference in locomotor sensitization to cocaine compared to wild-type (WT) littermates, whereas mice lacking cilia on dopaminergic neurons exhibited reduced locomotor sensitization to cocaine at 10 and 30 mg/kg. Mice lacking cilia on GAD2-GABAergic neurons showed no difference in cocaine conditioned place preference (CPP), whereas mice lacking cilia on dopaminergic neurons exhibited reduced CPP compared to WT littermates.

CONCLUSIONS

Combined with previous findings using amphetamine, our results show that behavioral effects of cilia ablation are cell- and drug type-specific, and that neuronal cilia contribute to modulation of both the locomotor-inducing and rewarding properties of cocaine.

Postweaning Social Isolation Alters Puberty Onset by Suppressing Electrical Activity of Arcuate Kisspeptin Neurons

INTRODUCTION

Postweaning social isolation (PWSI) in rodents is an advanced psychosocial stress model in early life. Some psychosocial stress, such as restrain and isolation, disrupts reproductive physiology in young and adult periods. Mechanisms of early-life stress effects on central regulation of reproduction need to be elucidated. We have investigated the effects of PWSI on function of arcuate kisspeptin (ARCKISS1) neurons by using electrophysiological techniques combining with monitoring of puberty onset and estrous cycle in male and female Kiss1-Cre mice.

METHODS

Female mice were monitored for puberty onset with vaginal opening examination during social isolation. After isolation, the estrous cycle of female mice was monitored with vaginal cytology. Anxiety-like behavior of mice was determined by an elevated plus maze test. Effects of PWSI on electrophysiology of ARCKISS1 neurons were investigated by the patch clamp method after intracranial injection of AAV-GFP virus into arcuate nucleus of Kiss1-Cre mice after the isolation period.

RESULTS

We found that both male and female isolated mice showed anxiety-like behavior. PWSI caused delay in vaginal opening and extension in estrous cycle length. Spontaneous-firing rates of ARCKISS1 neurons were significantly lower in the isolated male and female mice. The peak amplitude of inhibitory postsynaptic currents to ARCKISS1 neurons was higher in the isolated mice, while frequency of excitatory postsynaptic currents was higher in group-housed mice.

CONCLUSION

These findings demonstrate that PWSI alters pre- and postpubertal reproductive physiology through metabolic and electrophysiological pathways.

Sex differences in a corticosterone-induced depression model in mice: Behavioral, neurochemical, and molecular insights

Depression is characterized by a significant sex disparity, with higher rates observed in women compared to men. This study aimed to investigate the impact of sex on depressive behaviors and explore the underlying mechanisms using a corticosterone (CORT)-induced depression model in mice. Behavioral tests, Nissl staining, UPLC-MS/MS, and Western blot analysis were performed to assess behavioral changes, as well as neuronal alterations, neurotransmitter levels, and protein expressions in the hippocampus. The mice in the model group exhibited sex-specific anxiety- and depression-like behaviors. Nissl staining revealed structural abnormalities in the CA3 region of the hippocampus in females. Neurotransmitter analysis indicated decreased serotonin and norepinephrine levels in both sexes, while glutamate levels were elevated in females. Furthermore, female mice demonstrated elevated serum CORT levels. Western blot analysis revealed sex-specific alterations in specific protein expression. Female mice exhibited downregulated glucocorticoid receptor and brain-derived neurotrophic factor expression, whereas male mice showed minimal changes. Additionally, female mice displayed reduced phosphorylated AKT, phosphorylated PI3K, and phosphorylated mTOR levels. These findings enhance our understanding of sex-specific differences in the CORT-induced depression model and provide insights into the underlying mechanisms of depression. This research emphasizes sex in depression studies and supports tailored interventions.

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.

A systematic review of the development and application of home cage monitoring in laboratory mice and rats

BACKGROUND

Traditionally, in biomedical animal research, laboratory rodents are individually examined in test apparatuses outside of their home cages at selected time points. However, the outcome of such tests can be influenced by various factors and valuable information may be missed when the animals are only monitored for short periods. These issues can be overcome by longitudinally monitoring mice and rats in their home cages. To shed light on the development of home cage monitoring (HCM) and the current state-of-the-art, a systematic review was carried out on 521 publications retrieved through PubMed and Web of Science.

RESULTS

Both the absolute (~ × 26) and relative (~ × 7) number of HCM-related publications increased from 1974 to 2020. There was a clear bias towards males and individually housed animals, but during the past decade (2011-2020), an increasing number of studies used both sexes and group housing. In most studies, animals were kept for short (up to 4 weeks) time periods in the HCM systems; intermediate time periods (4-12 weeks) increased in frequency in the years between 2011 and 2020. Before the 2000s, HCM techniques were predominantly applied for less than 12 h, while 24-h measurements have been more frequent since the 2000s. The systematic review demonstrated that manual monitoring is decreasing in relation to automatic techniques but still relevant. Until (and including) the 1990s, most techniques were applied manually but have been progressively replaced by automation since the 2000s. Independent of the year of publication, the main behavioral parameters measured were locomotor activity, feeding, and social behaviors; the main physiological parameters were heart rate and electrocardiography. External appearance-related parameters were rarely examined in the home cages. Due to technological progress and application of artificial intelligence, more refined and detailed behavioral parameters have been investigated in the home cage more recently.

CONCLUSIONS

Over the period covered in this study, techniques for HCM of mice and rats have improved considerably. This development is ongoing and further progress as well as validation of HCM systems will extend the applications to allow for continuous, longitudinal, non-invasive monitoring of an increasing range of parameters in group-housed small rodents in their home cages.

Sex differences in avoidance behavior and cued threat memory dynamics in mice: Interactions between estrous cycle and genetic background

Anxiety disorders are the most prevalent mental illnesses worldwide, exhibit high heritability, and affect twice as many women as men. To evaluate potential interactions between genetic background and cycling ovarian hormones on sex differences in susceptibility to negative valence behaviors relevant to anxiety disorders, we assayed avoidance behavior and cued threat memory dynamics in gonadally-intact adult male and female mice across four common inbred mouse strains: C57Bl/6J, 129S1/SVlmJ, DBA/2J, and BALB/cJ. Independent of sex, C57Bl/6J mice exhibited low avoidance but high threat memory, 129S1/SvlmJ mice high avoidance and high threat memory, DBA/2J mice low avoidance and low threat memory, and BALB/cJ mice high avoidance but low threat memory. Within-strain comparisons revealed reduced avoidance behavior in the high hormone phase of the estrous cycle (proestrus) compared to all other estrous phases in all strains except DBA/2J, which did not exhibit cycle-dependent behavioral fluctuations. Robust and opposing sex differences in threat conditioning and extinction training were found in the C57Bl/6J and 129S1/SvlmJ lines, whereas no sex differences were observed in the DBA/2J or BALB/cJ lines. C57Bl/6J males exhibited enhanced acute threat memory, whereas 129S1/SvlmJ females exhibited enhanced sustained threat memory, compared to their sex-matched littermates. These effects were not mediated by estrous cycle stage or sex differences in active versus passive defensive behavioral responses. Our data demonstrate that core features of behavioral endophenotypes relevant to anxiety disorders, such as avoidance and threat memory, are genetically driven yet dissociable and can be influenced further by cycling ovarian hormones.

Roles of phosphatidylinositol-3-kinases signaling pathway in inflammation-related cancer: Impact of rs10889677 variant and buparlisib in colitis-associated cancer

BACKGROUND

Phosphatidylinositol-3-kinases (PI3K) is a well-known route in inflammation-related cancer. Recent discovery on PI3K-related genes revealed a potential variant that links ulcerative colitis (UC) and colorectal cancer (CRC) with colitis-associated cancer (CAC). PI3K/AKT pathway has been recommended as a potential additional therapeutic option for CRC due to its substantial role in modifying cellular processes. Buparlisib is a pan-class I PI3K inhibitor previously shown to reduce tumor growth.

AIM

To investigate the regulation of rs10889677 and the role of buparlisib in the PI3K signaling pathway in CAC pathogenesis.

METHODS

Genomic DNA from 32 colonic samples, including CAC (n = 7), UC (n = 10) and CRC (n = 15), was sequenced for the rs10889677 mutation. The mutant and wildtype fragments were amplified and cloned in the pmirGLO vector. The luciferase activity of cloned vectors was assessed after transfection into the HT29 cell line. CAC mice were induced by a mixture of a single azoxymethane injection and three cycles of dextran sulphate sodium, then buparlisib was administered after 14 d. The excised colon was subjected to immunohistochemistry for Ki67 and Cleaved-caspase-3 markers and quantitative real-time polymerase chain reaction analysis for Pdk1 and Sgk2.

RESULTS

Luciferase activity decreased by 2.07-fold in the rs10889677 mutant, confirming the hypothesis that the variant disrupted miRNA binding sites, which led to an increase in IL23R expression and the activation of the PI3K signaling pathway. Furthermore, CAC-induced mice had a significantly higher disease activity index (P < 0.05). Buparlisib treatment significantly decreased mean weight loss in CAC-induced mice (P < 0.05), reduced the percentage of proliferating cells by 5%, and increased the number of apoptotic cells. The treatment also caused a downward trend of Pdk1 expression and significantly decreased Sgk2 expression.

CONCLUSION

Our findings suggested that the rs10889677 variant as a critical initiator of the PI3K signaling pathway, and buparlisib had the ability to prevent PI3K-non-AKT activation in the pathophysiology of CAC.

Agomir-331 Suppresses Reactive Gliosis and Neuroinflammation after Traumatic Brain Injury

Traumatic brain injury usually triggers glial scar formation, neuroinflammation, and neurodegeneration. However, the molecular mechanisms underlying these pathological features are largely unknown. Using a mouse model of hippocampal stab injury (HSI), we observed that miR-331, a brain-enriched microRNA, was significantly downregulated in the early stage (0-7 days) of HSI. Intranasal administration of agomir-331, an upgraded product of miR-331 mimics, suppressed reactive gliosis and neuronal apoptosis and improved cognitive function in HSI mice. Finally, we identified IL-1β as a direct downstream target of miR-331, and agomir-331 treatment significantly reduced IL-1β levels in the hippocampus after acute injury. Our findings highlight, for the first time, agomir-331 as a pivotal neuroprotective agent for early rehabilitation of HSI.

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.

Microglial transglutaminase 2 deficiency causes impaired synaptic remodelling and cognitive deficits in mice

Microglia are the primary source of transglutaminase 2 (TGM2) in the brain; however, the roles of microglial TGM2 in neural development and disease are still not well known. The aim of this study is to elucidate the role and mechanisms of microglial TGM2 in the brain. A mouse line with a specific knockout of Tgm2 in microglia was generated. Immunohistochemistry, Western blot and qRT-PCR assays were performed to evaluate the expression levels of TGM2, PSD-95 and CD68. Confocal imaging, immunofluorescence staining and behavioural analyses were conducted to identify phenotypes of microglial TGM2 deficiency. Finally, RNA sequencing, qRT-PCR and co-culture of neurons and microglia were used to explore the potential mechanisms. Deletion of microglial Tgm2 causes impaired synaptic pruning, reduced anxiety and increased cognitive deficits in mice. At the molecular level, the phagocytic genes, such as Cq1a, C1qb and Tim4, are significantly down-regulated in TGM2-deficient microglia. This study elucidates a novel role of microglial TGM2 in regulating synaptic remodelling and cognitive function, indicating that microglia Tgm2 is essential for proper neural development.

Generation of a whole-brain hemodynamic response function and sex-specific differences in cerebral processing of mechano-sensation in mice detected by BOLD fMRI

BOLD fMRI has become a prevalent method to study cerebral sensory processing in rodent disease models, including pain and mechanical hypersensitivity. fMRI data analysis is frequently combined with a general-linear-model (GLM) -based analysis, which uses the convolution of a hemodynamic response function (HRF) with the stimulus paradigm. However, several studies indicated that the HRF differs across species, sexes, brain structures, and experimental factors, including stimulation modalities or anesthesia, and hence might strongly affect the outcome of BOLD analyzes. While considerable work has been done in humans and rats to understand the HRF, much less is known in mice. As a prerequisite to investigate mechano-sensory processing and BOLD fMRI data in male and female mice, we (1) designed a rotating stimulator that allows application of two different mechanical modalities, including innocuous von Frey and noxious pinprick stimuli and (2) determined and statistically compared HRFs across 30 brain structures and experimental conditions, including sex and, stimulus modalities. We found that mechanical stimulation lead to brain-wide BOLD signal changes thereby allowing extraction of HRFs from multiple brain structures. However, we did not find differences in HRFs across all brain structures and experimental conditions. Hence, we computed a whole-brain mouse HRF, which is based on 88 functional scans from 30 mice. A comparison of this mouse-specific HRF with our previously reported rat-derived HRF showed significantly slower kinetics in mice. Finally, we detected pronounced differences in cerebral BOLD activation between male and female mice with mechanical stimulation, thereby exposing divergent processing of noxious and innocuous stimuli in both sexes.

Effect of apparatus characteristics on anxiety-like behavior in young adult and old mice of both sexes assessed by the elevated plus maze assay

Incidence of anxiety-like disorders in humans has been shown to decrease with aging; however, it is still under debate whether there are similarities in mice, which would support the use of mouse models in understanding the neuronal network changes that regulate anxiety-like behavior in aging. One of the most common tests used to assess anxiety-like behavior in laboratory animals is the elevated plus maze (EPM). Although several variables, such as room brightness and width of the maze arms, have been shown to influence the spontaneous animal behavior during the EPM test, none of these variables have ever been evaluated in aging to understand their possible differential effect on younger and older mice. We therefore decided to investigate the effect of apparatus construction on young adult and old mice of both sexes on EPM test performance. Our results show that distance traveled during the test is the variable that is most affected by apparatus characteristics independent of age and sex. We also found that apparatus construction was key in demonstrating that old mice spent more time and had relatively more entries in the open arms as compared to young mice, suggesting a decrease in anxiety-like behavior with age. Taken together, our data demonstrate that EPM apparatus characteristics dramatically affect test outcome with a wider arm apparatus being more effective in revealing age-dependent changes in anxiety-like behavior, thus, suggesting the use of a wider arm EPM when conducting aging studies in mice.

Deletion of AhR attenuates fear memory leaving other types of memory intact

The aryl hydrocarbon receptor (AhR), a classic "environmental sensor", has been found to play an important role in cognitive and emotional function. Recent studies showed AhR deletion led to an attenuated fear memory, providing a potential target against fear memory, whether it is the consequence of attenuated sense of fear or memory ability deficit or both is unclear. Here this study aims to work this out. The freezing time in contextual fear conditioning (CFC) reduced significantly in AhR knockout mice, indicating an attenuated fear memory. Hot plate test and acoustic startle reflex showed that AhR knockout did not change the pain threshold and hearing, excluded the possibility of sensory impairments. Results from NORT, MWM and SBT showed that deletion of AhR had little effects on other types of memory. But the anxiety-like behaviors reduced both in naïve or suffered (tested after CFC) AhR knockout mice, showing that AhR-deficient mice have a reduced basal and stressful emotional response. The basal low-frequency to high-frequency (LF/HF) ratio of the AhR knockout mice was significantly lower than that of the control group, indicating lower sympathetic excitability in the basal state, suggesting a low level of basal stress in the knockout mice. Before and after CFC, the LF/HF ratio of AhR-KO mice tended to be significantly lower than that of WT mice, and their heart rate was significantly lower; and the AhR-KO mice also has a decreased serum corticosterone level after CFC, suggesting a reduced stress response in AhR knockout mice. Altogether, the basal stress level and stress response were significant reduced in AhR knockout mice, which might contribute to the attenuated fear memory with little impairment on other types of memory, suggesting AhR as a "psychologic sensor" additional to "environmental sensor".

Rho kinase inhibitors ameliorate cognitive impairment in a male mouse model of methamphetamine-induced schizophrenia

Schizophrenia (SCZ) is a severe psychiatric disorder characterized by positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic treatment in SCZ improves positive symptoms but has major side effects and little impact on negative symptoms and cognitive impairment. The pathoetiology of SCZ remains unclear, but is known to involve small GTPase signaling. Rho kinase, an effector of small GTPase Rho, is highly expressed in the brain and plays a major role in neurite elongation and neuronal architecture. This study used a touchscreen-based visual discrimination (VD) task to investigate the effects of Rho kinase inhibitors on cognitive impairment in a methamphetamine (METH)-treated male mouse model of SCZ. Systemic injection of the Rho kinase inhibitor fasudil dose-dependently ameliorated METH-induced VD impairment. Fasudil also significantly suppressed the increase in the number of c-Fos-positive cells in the infralimbic medial prefrontal cortex (infralimbic mPFC) and dorsomedial striatum (DMS) following METH treatment. Bilateral microinjections of Y-27632, another Rho kinase inhibitor, into the infralimbic mPFC or DMS significantly ameliorated METH-induced VD impairment. Two proteins downstream of Rho kinase, myosin phosphatase-targeting subunit 1 (MYPT1; Thr696) and myosin light chain kinase 2 (MLC2; Thr18/Ser19), exhibited increased phosphorylation in the infralimbic mPFC and DMS, respectively, after METH treatment, and fasudil inhibited these increases. Oral administration of haloperidol and fasudil ameliorated METH-induced VD impairment, while clozapine had little effect. Oral administration of haloperidol and clozapine suppressed METH-induced hyperactivity, but fasudil had no effect. These results suggest that METH activates Rho kinase in the infralimbic mPFC and DMS, which leads to cognitive impairment in male mice. Rho kinase inhibitors ameliorate METH-induced cognitive impairment, perhaps via the cortico-striatal circuit.

Minimal influence of estrous cycle on studies of female mouse behaviors

Introduction

Sex bias has been an issue in many biomedical fields, especially in neuroscience. In rodent research, many scientists only focused on male animals due to the belief that female estrous cycle gives rise to unacceptable, high levels of variance in the experiments. However, even though female sexual behaviors are well known to be regulated by estrous cycle, which effects on other non-sexual behaviors were not always consistent in previous reports. Recent reviews analyzing published literature even suggested that there is no evidence for larger variation in female than male in several phenotypes.

Methods

To further investigate the impact of estrous cycle on the variability of female behaviors, we conducted multiple behavioral assays, including the open field test, forced swimming test, and resident-intruder assay to assess anxiety-, depression-like behaviors, as well as social interaction respectively. We compared females in the estrus and diestrus stages across four different mouse strains: C57BL/6, BALB/c, C3H, and DBA/2.

Results

Our results found no significant difference in most behavioral parameters between females in these two stages. On the other hand, the differences in behaviors among certain strains are relatively consistent in both stages, suggesting a very minimal effect of estrous cycle for detecting the behavioral difference. Last, we compared the behavioral variation between male and female and found very similar variations in most behaviors between the two sexes.

Discussion

While our study successfully identified behavioral differences among strains and between the sexes, we did not find solid evidence to support the notion that female behaviors are influenced by the estrous cycle. Additionally, we observed similar levels of behavioral variability between males and females. Female mice, therefore, have no reason to be excluded in future behavioral research.

Mechanical and Heat Hyperalgesia upon Withdrawal From Chronic Intermittent Ethanol Vapor Depends on Sex, Exposure Duration, and Blood Alcohol Concentration in Mice

Approximately half of patients with alcohol use disorder report pain and this can be severe during withdrawal. Many questions remain regarding the importance of biological sex, alcohol exposure paradigm, and stimulus modality to the severity of alcohol withdrawal-induced hyperalgesia. To examine the impact of sex and blood alcohol concentration on the time course of the development of mechanical and heat hyperalgesia, we characterized a mouse model of chronic alcohol withdrawal-induced pain in the presence or absence the alcohol dehydrogenase inhibitor, pyrazole. Male and female C57BL/6J mice underwent chronic intermittent ethanol vapor ± pyrazole exposure for 4 weeks, 4 d/wk to induce ethanol dependence. Hind paw sensitivity to the plantar application of mechanical (von Frey filaments) and radiant heat stimuli were measured during weekly observations at 1, 3, 5, 7, 24, and 48 hours after cessation of ethanol exposure. In the presence of pyrazole, males developed mechanical hyperalgesia after the first week of chronic intermittent ethanol vapor exposure, peaking at 48 hours after cessation of ethanol. By contrast, females did not develop mechanical hyperalgesia until the fourth week; this also required pyrazole and did not peak until 48 hours. Heat hyperalgesia was consistently observed only in females exposed to ethanol and pyrazole; this developed after the first weekly session and peaked at 1 hour. We conclude that Chronic alcohol withdrawal-induced pain develops in a sex-, time-, and blood alcohol concentration-dependent manner in C57BL/6J mice. PERSPECTIVE: Alcohol withdrawal-induced pain is a debilitating condition in individuals with AUD. Our study found mice experience alcohol withdrawal-induced pain in a sex and time course specific manor. These findings will aid in elucidating mechanisms of chronic pain and AUD and will help individuals remain abstinent from alcohol.

Reasons for the Sex Bias in Osteoarthritis Research: A Review of Preclinical Studies

Osteoarthritis (OA) is one of the most common degenerative diseases of articular cartilage. During OA, all the elements that contribute to the joint undergo physiological and structural changes that impair the joint function and cause joint pain and stiffness. OA can arise naturally, with the aging population witnessing an increase in diagnoses of this pathology, but the root causes of OA have yet to be identified, and increasing interest is arising towards investigating biological sex as a risk factor. Clinical studies show increased prevalence and worse clinical outcomes for female patients, yet most clinical and preclinical studies have disproportionately focused on male subjects. This review provides a critical overview of preclinical practices in the context of OA, highlighting the underlying need for taking biological sex as both a risk factor and an important component affecting treatment outcome. A unique insight into the possible reasons for female underrepresentation in preclinical studies is offered, including factors such as lack of specific guidelines requiring the analysis of sex as a biological variable (SABV), research-associated costs and animal handling, and wrongful application of the reduction principle. Additionally, a thorough investigation of sex-related variables is provided, stressing how each of them could add valuable information for the understanding of OA pathophysiology, as well as sex-dependent treatment strategies.

Delay eyeblink conditioning performance and brain-wide c-Fos expression in male and female mice

Delay eyeblink conditioning has been extensively used to study associative learning and the cerebellar circuits underlying this task have been largely identified. However, there is a little knowledge on how factors such as strain, sex and innate behaviour influence performance during this type of learning. In this study, we used male and female mice of C57BL/6J (B6) and B6CBAF1 strains to investigate the effect of sex, strain and locomotion in delay eyeblink conditioning. We performed a short and a long delay eyeblink conditioning paradigm and used a c-Fos immunostaining approach to explore the involvement of different brain areas in this task. We found that both B6 and B6CBAF1 females reach higher learning scores compared to males in the initial stages of learning. This sex-dependent difference was no longer present as the learning progressed. Moreover, we found a strong positive correlation between learning scores and voluntary locomotion irrespective of the training duration. c-Fos immunostainings after the short paradigm showed positive correlations between c-Fos expression and learning scores in the cerebellar cortex and brainstem, as well as previously unreported areas. By contrast, after the long paradigm, c-Fos expression was only significantly elevated in the brainstem. Taken together, we show that differences in voluntary locomotion and activity across brain areas correlate with performance in delay eyeblink conditioning across strains and sexes.

Mouse spontaneous behavior reflects individual variation rather than estrous state

Behavior is shaped by both the internal state of an animal and its individual behavioral biases. Rhythmic variation in gonadal hormones during the estrous cycle is a defining feature of the female internal state, one that regulates many aspects of sociosexual behavior. However, it remains unclear whether estrous state influences spontaneous behavior and, if so, how these effects might relate to individual behavioral variation. Here, we address this question by longitudinally characterizing the open-field behavior of female mice across different phases of the estrous cycle, using unsupervised machine learning to decompose spontaneous behavior into its constituent elements.1,2,3,4 We find that each female mouse exhibits a characteristic pattern of exploration that uniquely identifies it as an individual across many experimental sessions; by contrast, estrous state only negligibly impacts behavior, despite its known effects on neural circuits that regulate action selection and movement. Like female mice, male mice exhibit individual-specific patterns of behavior in the open field; however, the exploratory behavior of males is significantly more variable than that expressed by females both within and across individuals. These findings suggest underlying functional stability to the circuits that support exploration in female mice, reveal a surprising degree of specificity in individual behavior, and provide empirical support for the inclusion of both sexes in experiments querying spontaneous behaviors.

Chronic treatment with the anti-diabetic drug metformin rescues impaired brain mitochondrial activity and selectively ameliorates defective cognitive flexibility in a female mouse model of Rett syndrome

Metformin is the most common anti-diabetic drug and a promising therapy for disorders beyond diabetes, including Rett syndrome (RTT), a rare neurologic disease characterized by severe intellectual disability. A 10-day-long treatment rescued aberrant mitochondrial activity and restrained oxidative stress in a female RTT mouse model. However, this treatment regimen did not improve the phenotype of RTT mice. In the present study, we demonstrate that a 4-month-long treatment with metformin (150 mg/Kg/day, delivered in drinking bottles) provides a selective normalization of cognitive flexibility defects in RTT female mice at an advanced stage of disease, but it does not affect their impaired general health status and abnormal motor skills. The 4-month-long treatment also rescues the reduced activity of mitochondrial respiratory chain complex activities, the defective brain ATP production and levels as well as the increased production of reactive oxidizing species in the whole blood of RTT mice. A significant boost of PGC-1α-dependent pathways related to mitochondrial biogenesis and antioxidant defense occurs in the brain of RTT mice that received the metformin treatment. Further studies will have to verify whether these effects may underlie its long-lasting beneficial effects on brain energy metabolism.

Estrous Cycle Mediates Midbrain Neuron Excitability Altering Social Behavior upon Stress

The estrous cycle is a potent modulator of neuron physiology. In rodents, in vivo ventral tegmental area (VTA) dopamine (DA) activity has been shown to fluctuate across the estrous cycle. Although the behavioral effect of fluctuating sex steroids on the reward circuit is well studied in response to drugs of abuse, few studies have focused on the molecular adaptations in the context of stress and motivated social behaviors. We hypothesized that estradiol fluctuations across the estrous cycle acts on the dopaminergic activity of the VTA to alter excitability and stress response. We used whole-cell slice electrophysiology of VTA DA neurons in naturally cycling, adult female C57BL/6J mice to characterize the effects of the estrous cycle and the role of 17β-estradiol on neuronal activity. We show that the estrous phase alters the effect of 17β-estradiol on excitability in the VTA. Behaviorally, the estrous phase during a series of acute variable social stressors modulates subsequent reward-related behaviors. Pharmacological inhibition of estrogen receptors in the VTA before stress during diestrus mimics the stress susceptibility found during estrus, whereas increased potassium channel activity in the VTA before stress reverses stress susceptibility found during estrus as assessed by social interaction behavior. This study identifies one possible potassium channel mechanism underlying the increased DA activity during estrus and reveals estrogen-dependent changes in neuronal function. Our findings demonstrate that the estrous cycle and estrogen signaling changes the physiology of DA neurons resulting in behavioral differences when the reward circuit is challenged with stress.SIGNIFICANCE STATEMENT The activity of the ventral tegmental area encodes signals of stress and reward. Dopaminergic activity has been found to be regulated by both local synaptic inputs as well as inputs from other brain regions. Here, we provide evidence that cycling sex steroids also play a role in modulating stress sensitivity of dopaminergic reward behavior. Specifically, we reveal a correlation of ionic activity with estrous phase, which influences the behavioral response to stress. These findings shed new light on how estrous cycle may influence dopaminergic activity primarily during times of stress perturbation.

Urocortin-3 neurons in the perifornical area are critical mediators of chronic stress on female infant-directed behavior

Infant avoidance and aggression are promoted by activation of the Urocortin-3 expressing neurons of the perifornical area of hypothalamus (PeFA^Ucn3) in male and female mice. PeFA^Ucn3 neurons have been implicated in stress, and stress is known to reduce maternal behavior. We asked how chronic restraint stress (CRS) affects infant-directed behavior in virgin and lactating females and what role PeFA^Ucn3 neurons play in this process. Here we show that infant-directed behavior increases activity in the PeFA^Ucn3 neurons in virgin and lactating females. Chemogenetic inhibition of PeFA^Ucn3 neurons facilitates pup retrieval in virgin females. CRS reduces pup retrieval in virgin females and increases activity of PeFA^Ucn3 neurons, while CRS does not affect maternal behavior in lactating females. Inhibition of PeFA^Ucn3 neurons blocks stress-induced deficits in pup-directed behavior in virgin females. Together, these data illustrate the critical role for PeFA^Ucn3 neuronal activity in mediating the impact of chronic stress on female infant-directed behavior.

Genetic Mapping of Behavioral Traits Using the Collaborative Cross Resource

The complicated interactions between genetic background, environment and lifestyle factors make it difficult to study the genetic basis of complex phenotypes, such as cognition and anxiety levels, in humans. However, environmental and other factors can be tightly controlled in mouse studies. The Collaborative Cross (CC) is a mouse genetic reference population whose common genetic and phenotypic diversity is on par with that of humans. Therefore, we leveraged the power of the CC to assess 52 behavioral measures associated with locomotor activity, anxiety level, learning and memory. This is the first application of the CC in novel object recognition tests, Morris water maze tasks, and fear conditioning tests. We found substantial continuous behavioral variations across the CC strains tested, and mapped six quantitative trait loci (QTLs) which influenced these traits, defining candidate genetic variants underlying these QTLs. Overall, our findings highlight the potential of the CC population in behavioral genetic research, while the identified genomic loci and genes driving the variation of relevant behavioral traits provide a foundation for further studies.

In vivo arterial stiffness, but not isolated artery endothelial function, varies with the mouse estrous cycle

With the increasing appreciation for sex as a biological variable and the inclusion of female mice in research, it is important to understand the influence of the estrous cycle on physiological function. Sex hormones are known to modulate vascular function, but the effects of the mouse estrous cycle phase on arterial stiffness, endothelial function, and arterial estrogen receptor expression remain unknown. In 23 female C57BL/6 mice (6 mo of age), we determined the estrous cycle stage via vaginal cytology and plasma hormone concentrations. Aortic stiffness, assessed by pulse wave velocity, was lower during the estrus phase compared with diestrus. In ex vivo assessment of isolated pressurized mesenteric and posterior cerebral arteries, the responses to acetylcholine, insulin, and sodium nitroprusside, as well as nitric oxide-mediated dilation, were not different between estrous cycle phases. In the aorta, expression of phosphorylated estrogen receptor-α was higher for mice in estrus compared with mice in proestrus. In the cerebral arteries, gene expression for estrogen receptor-β (Esr2) was lowest for mice in estrus compared with diestrus and proestrus. These results demonstrate that the estrus phase is associated with lower in vivo large artery stiffness in mice. In contrast, ex vivo resistance artery endothelial function is not different between estrous cycle phases. Estrogen receptor expression is modulated by the estrus cycle in an artery-dependent manner. These results suggest that the estrous cycle phase should be considered when measuring in vivo arterial stiffness in young female mice.NEW & NOTEWORTHY To design rigorous vascular research studies using young female rodents, the influence of the estrous cycle on vascular function must be known. We found that in vivo aortic stiffness was lower during estrus compared with the diestrus phase in female mice. In contrast, ex vivo mesenteric and cerebral artery endothelial function did not differ between estrous cycle stages. These results suggest that the estrous cycle stage should be accounted for when measuring in vivo arterial stiffness.

Deficits in Cerebellum-Dependent Learning and Cerebellar Morphology in Male and Female BTBR Autism Model Mice

Recently, there has been increased interest in the role of the cerebellum in autism spectrum disorder (ASD). To better understand the pathophysiological role of the cerebellum in ASD, it is necessary to have a variety of mouse models that have face validity for cerebellar disruption in humans. Here, we add to the literature on the cerebellum in mouse models of autism with the characterization of the cerebellum in the idiopathic BTBR T + Itpr3tf/J (BTBR) inbred mouse strain, which has behavioral phenotypes that are reminiscent of ASD in patients. When we examined both male and female BTBR mice in comparison to C57BL/6J (C57) controls, we noted that both sexes of BTBR mice showed motor coordination deficits characteristic of cerebellar dysfunction, but only the male mice showed differences in delay eyeblink conditioning, a cerebellum-dependent learning task that is known to be disrupted in ASD patients. Both male and female BTBR mice showed considerable expansion of, and abnormal foliation in, the cerebellum vermis—including a significant expansion of specific lobules in the anterior cerebellum. In addition, we found a slight but significant decrease in Purkinje cell density in both male and female BTBR mice, irrespective of the lobule. Finally, there was a marked reduction of Purkinje cell dendritic spine density in both male and female BTBR mice. These findings suggest that, for the most part, the BTBR mouse model phenocopies many of the characteristics of the subpopulation of ASD patients that have a hypertrophic cerebellum. We discuss the significance of strain differences in the cerebellum as well as the importance of this first effort to identify both similarities and differences between male and female BTBR mice with regard to the cerebellum.

A touchscreen-based paradigm to measure visual pattern separation and pattern completion in mice

Memory accuracy involves two major processes: pattern separation and pattern completion. Pattern separation refers to the ability to reduce overlap among similar inputs to avoid interference, and pattern completion refers to the ability to retrieve the whole information from partial or degraded cues. Impairments in pattern separation/pattern completion contribute to cognitive deficits in several diseases of the nervous system. Therefore, it is better to evaluate both pattern separation and pattern completion in one apparatus. However, few tools are available to assess pattern separation and pattern completion within the same apparatus for rodents. In this study, we designed a series of images with varying degrees of similarity to the correct image to evaluate pattern separation and pattern completion. First, mice were trained to discriminate between two totally different images, and once the correct percentage reached above 77% for two consecutive days, the images with different degrees of similarity were used to measure pattern separation and pattern completion. The results showed the mice performed progressively worse from S0 to S4 (increasing similarity) when discriminating similar images in pattern separation, and the mice performed progressively worse from C0 to C4 (decreasing cues information) when recalling the correct image according to partial cues in pattern completion, implying a good image similarity-dependent manner for memory accuracy evaluation. In sum, we designed a convenient, effective paradigm to evaluate pattern separation and pattern completion based on a touchscreen pairwise discrimination task, which may provide a new method for the studies of the effects and mechanisms of memory accuracy enhancing drugs.

Innate immune stimulation prevents chronic stress-induced depressive and anxiogenic-like behaviors in female mice

It has been reported that pre-stimulation of the innate immune system can prevent depressive and anxiogenic-like behaviors in chronically stressed male mice. However, it is unclear whether similar effects can be observed in female animals. In the present study, we investigated this question in female mice. Our results showed that a single injection of lipopolysaccharide (LPS; 100 μg/kg) one day before stress exposure prevented increased immobility time in the tail suspension test and forced swimming test and decreased sucrose intake in the sucrose preference test in chronic unpredictable stress (CUS)-treated female mice. The single LPS pre-injection (100 μg/kg) prevented the CUS-induced decrease in (i) time spent in open arms and number of entries into open arms in the elevated plus maze test, (ii) time spent in lit side in the light-dark test, and (iii) time spent in the central region of the open field in the open field test, along with no changes in locomotor activity. It was also found that the single LPS pre-injection in female mice prevented the CUS-induced increase in the expression levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 mRNA in the hippocampus and medial prefrontal cortex. Inhibition of innate immune system stimulation by minocycline pretreatment abrogated the preventive effect of LPS on CUS-induced depressive and anxiogenic-like behaviors and neuroinflammatory responses in the hippocampus and medial prefrontal cortex in female mice. These results suggest that pre-stimulation of the innate immune system by LPS injection may prevent the development of behavioral abnormalities in female mice.

Treatment with FRAX486 rescues neurobehavioral and metabolic alterations in a female mouse model of CDKL5 deficiency disorder

Introduction

CDKL5 deficiency disorder (CDD) is a rare neurodevelopmental condition, primarily affecting girls for which no cure currently exists. Neuronal morphogenesis and plasticity impairments as well as metabolic dysfunctions occur in CDD patients. The present study explored the potential therapeutic value for CDD of FRAX486, a brain‐penetrant molecule that was reported to selectively inhibit group I p21‐activated kinases (PAKs), serine/threonine kinases critically involved in the regulation of neuronal morphology and glucose homeostasis.

Methods

The effects of treatment with FRAX486 on CDD‐related alterations were assessed in vitro (100 nM for 48 h) on primary hippocampal cultures from Cdkl5‐knockout male mice (Cdkl5‐KO) and in vivo (20 mg/Kg, s.c. for 5 days) on Cdkl5‐KO heterozygous females (Cdkl5‐Het).

Results

The in vitro treatment with FRAX486 completely rescued the abnormal neuronal maturation and the number of PSD95‐positive puncta in Cdkl5‐KO mouse neurons. In vivo, FRAX486 normalized the general health status, the hyperactive profile and the fear learning defects of fully symptomatic Cdkl5‐Het mice. Systemically, FRAX486 treatment normalized the levels of reactive oxidizing species in the whole blood and the fasting‐induced hypoglycemia displayed by Cdkl5‐Het mice. In the hippocampus of Cdkl5‐Het mice, treatment with FRAX486 rescued spine maturation and PSD95 expression and restored the abnormal PAKs phosphorylation at sites which are critical for their activation (P‐PAK‐Ser144/141/139) or for the control cytoskeleton remodeling (P‐PAK1‐Thr212).

Conclusions

Present results provide evidence that PAKs may represent innovative therapeutic targets for CDD.

Assessing the importance of sex in a hippocampus-dependent behavioral test battery in C57BL/6NTac mice

Inclusion of male and female subjects in behavioral neuroscience research requires a concerted effort to characterize sex differences in standardized behavioral assays. Sex differences in hippocampus-dependent assays have been widely reported but are still poorly characterized. In the present study, we conducted a parametric analysis of spontaneous alternation, object recognition, and fear conditioning in a commonly used control strain, C57BL/6NTac. Our findings show largely similar performance between males and females across the majority of behavioral end points. However, we identified an important difference in nonassociative fear sensitization, whereby females showed an enhanced fear response to the 75-dB tone that is used as the conditional stimulus. In addition, we observed an impairment in object location performance in females that was ameliorated by more extensive habituation to handling. Together, these findings argue that sex differences in nonassociative fear responses to both novel auditory cues and novel objects need to be considered when designing and interpreting cognitive assays in C57BL/6 mice. Furthermore, this elevated fear sensitization could serve as a novel approach to model the increased incidence of anxiety disorders in women.

Tendinopathy: sex bias starts from the preclinical development of tendon treatments. A systematic review

Tendinopathies are common overuse disorders that arise both in athletes and the general population. Available tendon treatments are used both for women and men without distinction. However, the existence of a sex-based difference in tendon biology is widely demonstrated. Since basic research represents the foundation for treatment development, an equal female–male representation should be pursued in preclinical studies. This systematic review quantified the current evidence by analyzing 150 studies on 8231 animals. Preclinical studies largely neglected the importance of sex, none analyzed sex-based differences, and only 4% of the studies reported disaggregated data suitable for the analysis of treatment results in males and females. There is an alarming female under-representation, in particular in the field of injective therapies. Despite the growing awareness on the importance of investigating treatments in both males and females, the investigated field proved resistant from properly designing studies including both sexes, and the lack of sex-representation remains critical.

Tendinopathy has sex-specific features, with sex hormones affecting tendon metabolism, structure, biomechanical properties, and injury risk.

The preclinical research on tendinopathy treatments still neglects sex-based differences, leading to translation of male data to females which may affect clinical effectiveness in women.

None of the reviewed studies looked at differences between sexes, and only 4% of the studies reported disaggregated data. Besides, female animals are under-represented.

The lack of sex-representation in tendinopathy research remains critical.

Slitrk2 deficiency causes hyperactivity with altered vestibular function and serotonergic dysregulation

SLITRK2 encodes a transmembrane protein that modulates neurite outgrowth and synaptic activities and is implicated in bipolar disorder. Here, we addressed its physiological roles in mice. In the brain, the Slitrk2 protein was strongly detected in the hippocampus, vestibulocerebellum, and precerebellar nuclei—the vestibular-cerebellar-brainstem neural network including pontine gray and tegmental reticular nucleus. Slitrk2 knockout (KO) mice exhibited increased locomotor activity in novel environments, antidepressant-like behaviors, enhanced vestibular function, and increased plasticity at mossy fiber–CA3 synapses with reduced sensitivity to serotonin. A serotonin metabolite was increased in the hippocampus and amygdala, and serotonergic neurons in the raphe nuclei were decreased in Slitrk2 KO mice. When KO mice were treated with methylphenidate, lithium, or fluoxetine, the mood stabilizer lithium showed a genotype-dependent effect. Taken together, Slitrk2 deficiency causes aberrant neural network activity, synaptic integrity, vestibular function, and serotonergic function, providing molecular-neurophysiological insight into the brain dysregulation in bipolar disorders.

•

Slitrk2 KO mice showed antidepressant-like behaviors and enhanced vestibular function

•

Mossy fiber-CA3 synaptic sensitivity to serotonin was reduced in Slitrk2 KO mice

•

Serotonin metabolite was increased in hippocampus and amygdala of Slitrk2 KO mice

•

Numbers of serotonergic neurons in raphe nuclei were decreased in Slitrk2 KO mice

Basolateral amygdala cannabinoid CB1 receptors mediate the antinociceptive activity of harmaline in adolescent male mice

Evidence suggests a clear role for the amygdala endocannabinoid system in pain processing. Harmaline has been also known as the main nociceptive agent extracted from the Peganum harmala plant. In this study, the role of basolateral amygdala (BLA) cannabinoid CB1 receptors in pain sensitivity of harmaline-treated mice were assessed using tail-flick and hot plate methods in adolescent male NMRI mice. Intraperitoneal administration of two higher doses of harmaline (6 and 8 mg/kg) increased tail-flick latency, suggesting an antinociceptive activity. The same result was observed for the higher dose of harmaline in the hot plate test. Intra-BLA microinjection of CB1 receptor agonist ACPA (1 and 1.5 ng/mouse) or (1.5 ng/mouse) enhanced the ineffective dose-response of harmaline on pain threshold in the tail-flick or hot plate tests, respectively. Microinjection of two higher doses of CB1 receptor antagonist AM251 (0.5 and 1 ng/mouse) attenuated the antinociceptive activity of harmaline (8 ng/mouse) in both tail-flick and hot plate tests. Meanwhile, ACPA and AM251 did not alter latency to withdraw from the noxious stimulus in both tests, by themselves. It should be noted that the analgesic dose of the drugs alone or in combination did not affect locomotor activity. The obtained results highlight that BLA CB1 receptors mediate the antinociceptive activity of harmaline.

Leucine-Rich Repeats and Transmembrane Domain 2 Controls Protein Sorting in the Striatal Projection System and Its Deficiency Causes Disturbances in Motor Responses and Monoamine Dynamics

The striatum is involved in action selection, and its disturbance can cause movement disorders. Here, we show that leucine-rich repeats and transmembrane domain 2 (Lrtm2) controls protein sorting in striatal projection systems, and its deficiency causes disturbances in monoamine dynamics and behavior. The Lrtm2 protein was broadly detected in the brain, but it was enhanced in the olfactory bulb and dorsal striatum. Immunostaining revealed a strong signal in striatal projection output, including GABAergic presynaptic boutons of the SNr. In subcellular fractionation, Lrtm2 was abundantly recovered in the synaptic plasma membrane fraction, synaptic vesicle fraction, and microsome fraction. Lrtm2 KO mice exhibited altered motor responses in both voluntary explorations and forced exercise. Dopamine metabolite content was decreased in the dorsal striatum and hypothalamus, and serotonin turnover increased in the dorsal striatum. The prefrontal cortex showed age-dependent changes in dopamine metabolites. The distribution of glutamate decarboxylase 67 (GAD67) protein and gamma-aminobutyric acid receptor type B receptor 1 (GABA_BR1) protein was altered in the dorsal striatum. In cultured neurons, wild-type Lrtm2 protein enhanced axon trafficking of GAD67-GFP and GABA_BR1-GFP whereas such activity was defective in sorting signal-abolished Lrtm2 mutant proteins. The topical expression of hemagglutinin-epitope-tag (HA)-Lrtm2 and a protein sorting signal abolished HA-Lrtm2 mutant differentially affected GABA_BR1 protein distribution in the dorsal striatum. These results suggest that Lrtm2 is an essential component of striatal projection neurons, contributing to a better understanding of striatal pathophysiology.

GPR171 Agonist Reduces Chronic Neuropathic and Inflammatory Pain in Male, But Not Female Mice

Chronic pain is a growing public health crisis that requires exigent and efficacious therapeutics. GPR171 is a promising therapeutic target that is widely expressed through the brain, including within the descending pain modulatory regions. Here, we explore the therapeutic potential of the GPR171 agonist, MS15203, in its ability to alleviate chronic pain in male and female mice using a once-daily systemic dose (10 mg/kg, i.p.) of MS15203 over the course of 5 days. We found that in our models of Complete Freund's Adjuvant (CFA)-induced inflammatory pain and chemotherapy-induced peripheral neuropathy (CIPN), MS15203 did not alleviate thermal hypersensitivity and allodynia, respectively, in female mice. On the other hand, MS15203 treatment decreased the duration of thermal hypersensitivity in CFA-treated male mice following 3 days of once-daily administration. MS15203 treatment also produced an improvement in allodynia in male mice, but not female mice, in neuropathic pain after 5 days of treatment. Gene expression of GPR171 and that of its endogenous ligand BigLEN, encoded by the gene PCSK1N, were unaltered within the periaqueductal gray (PAG) in both male and female mice following inflammatory and neuropathic pain. However, following neuropathic pain in male mice, the protein levels of GPR171 were decreased in the PAG. Treatment with MS15203 then rescued the protein levels of GPR171 in the PAG of these mice. Taken together, our results identify GPR171 as a GPCR that displays sexual dimorphism in alleviation of chronic pain. Further, our results suggest that GPR171 and MS15203 have demonstrable therapeutic potential in the treatment of chronic pain.

Sex Differences in Depression-Like Behaviors in Adult Mice Depend on Endophenotype and Strain

Depression affects women nearly twice as frequently as men. In contrast, rodent models of depression have shown inconsistent results regarding sex bias, often reporting more depression-like behaviors in males. This sex discrepancy in rodents modeling depression may rely on differences in the baseline activity of males and females in depression-related behavioral tests. We previously showed that the baseline despair and anhedonia behaviors, major endophenotypes of depression, are not sex biased in young adolescent wild-type mice of C57BL/6N, DBA/2, and FVB/N strains. Since the prevalence of depression in women peaks in their reproductive years, we here investigated sex differences of the baseline depression-like behaviors in adult mice using these three strains. Similar to the results in young mice, no difference was found between adult male and female mice in behavioral tests measuring despair in both tail suspension and forced swim tests, and anhedonia in the sucrose preference test. We then extended our study and tested apathy, another endophenotype of depression, using the splash test. Adult male and female mice showed significantly different results in the baseline apathy-like behaviors depending on the investigated strain. This study dissects the complex sex effects of different depression endophenotypes, stresses the importance of considering strain, and puts forward a hypothesis of the inconsistency of results between different laboratories investigating rodent models of depression.

Effect of Dietary Grapes on Female C57BL6/J Mice Consuming a High-Fat Diet: Behavioral and Genetic Changes

(1) Background: Adverse effects of a chronic high-fat diet (HFD) on murine behavior, cognition, and memory are well established. Polyphenols such as resveratrol, anthocyanins, and flavonoids, that are known for antioxidative and anti-inflammatory properties, are present in grapes. The objective of this work was to determine if the dietary intake of grapes has the potential of alleviating HFD-induced deficiencies. (2) Methods: The effect of dietary grape intake was studied using behavioral assays and high throughput genome-wide RNA transcriptome analyses with female C57BL6/J mice. (3) Results: Mice that were fed a HFD from 3-weeks of age showed anxiety-like behaviors compared with the standard diet (STD). This HFD-induced effect was attenuated by supplementing the HFD with 1% grape powder (HF1G) (open field test). Similar results were observed with the novel object recognition test; there was a significant difference in time spent exploring a novel object between the HFD and the HF1G groups. There was no significant difference between the HFD1G and the STD groups. Based on the RNA-Seq analysis, genetic expression in the brain varied as a result of diet, with 210, 360, and 221 uniquely expressed genes in the STD, HFD, and HF1G groups, respectively. Cluster analysis revealed that the HFIG group mapped more closely with the STD group than the HFD group. Focusing on some specific areas, based on genetic expression, Dopamine receptor 2 (Drd2) was increased in the HFD group and normalized in the HF1G group, relative to the STD group. In addition, as judged by cluster hierarchy, the expression of genes that are associated with the dopamine receptor 2 pathway were increased in the HFD group, whereas the pattern that was derived from mouse brain from the HF1G group showed greater similarity to the STD group. KEGG pathway analyses were consistent with these results. For example, neuroactive ligand-receptor interaction (KEGG ID: mmu04080) was altered due to HFD compared with STD, but normalized by grape supplementation or the HFD; there was no significant difference between the STD and HF1G groups. In addition, the expression of genes related to feeding behavior, such as Adora2a, Th, and Trh, were also increased in the HFD group compared with the STD group, and attenuated by grape supplementation. (4) Conclusions: Dietary grape consumption has positive effects on behavior and cognition that are impaired by a HFD. Attenuation of these effects correlates with global transcriptional changes in mouse brain.

The AGTPBP1 gene in neurobiology

The function of the Agtpbp1 gene has mainly been delineated by studying Agtpbp1pcd (pcd) mutant mice, characterized by losses in cerebellar Purkinje and granule cells along with degeneration of retinal photoreceptors, mitral cells of the olfactory bulb, thalamic neurons, and alpha-motoneurons. As a result of cerebellar degeneration, cerebellar GABA and glutamate concentrations in Agtpbp1pcd mutants decreased while monoamine concentrations increased. The salient behavioral phenotypes include cerebellar ataxia, a loss in motor coordination, and cognitive deficits. Similar neuropathogical and behavioral profiles have been described in childhood-onset human subjects with biallelic variants of AGTPBP1, including cerebellar ataxia and hypotonia.

Folic acid supplementation during pregnancy alters behavior in male rat offspring: nitrative stress and neuroinflammatory implications

Pregnancy diet can impact offspring's neurodevelopment, metabolism, redox homeostasis, and inflammatory status. In pregnancy, folate demand is increased due to the requirement for one-carbon transfer reactions. The present study was proposed to investigate the effect of folic acid supplementation throughout pregnancy on a battery of behavior tests (olfactory preference, motor activity, exploratory capacity, habituation, memory, anxiety- and depression-like behavior). Redox homeostasis and neuroinflammatory status in cerebral cortex were also investigated. After pregnancy confirmation, the pregnant rats were randomly divided into two groups, according to the diet: group 1, (control) standard diet (2 mg/kg diet of folic acid) and group 2, supplemented diet with 4 mg/kg diet of folic acid. Throughout the gestational period, the pregnant rats received experimental diets. Results show that the supplemented diet with 4 mg/kg diet of folic acid throughout pregnancy impaired memory and motricity of the offspring when compared with control (standard diet). It was also observed an increase in anxiety- and depression-like behavior in this group. Nitrite levels increased in cerebral cortex of the offspring, when compared to control group. In contrast, iNOS expression and immunocontent were not altered. Moreover, we identify an increase in TNF-α, IL-1β, IL-6, IL-10, and MCP-1 gene expression in the cerebral cortex. In conclusion, our study showed that the supplemented diet with 4 mg/kg diet of folic acid throughout pregnancy may cause behavioral and biochemical changes in the male offspringGraphical abstract After pregnancy confirmation, the pregnant rats were randomly divided into two groups, according to the diet: group 1, (control) standard diet (2 mg/kg diet of folic acid) and group 2, supplemented diet with 4 mg/kg diet of folic acid. Throughout the gestational period, the pregnant rats received experimental diets. Results show that folic acid supplementation did not impair the mother-pup relationship. We showed that supplemented diet with 4 mg/kg diet of folic acid during pregnancy impairs memory and motricity of the offspring when compared with standard diet. It was also observed an increase in anxiety- and depression-like behavior in this group. Nitrative stress and neuroinflammation parameters were increased in the cerebral cortex of the offspring. ROS, reactive oxygen species.