What Pre-clinical Rat Models Can Tell Us About Anxiety Across the Menstrual Cycle in Healthy and Clinically Anxious Humans

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.

The modulatory role of serotonin-1A receptors of the basolateral amygdala and dorsal periaqueductal gray on the impact of hormonal variation on the conditioned fear response

Despite significant advances in the study of fear and fear memory formation, little is known about fear learning and expression in females. This omission has been proven surprising, as normal and pathological behaviors are highly influenced by ovarian hormones, particularly estradiol and progesterone. In the current study, we investigated the joint influence of serotonin (5-HT) neurotransmission and estrous cycle phases (low or high levels of estradiol and progesterone) on the expression of conditioned fear in a group of female rats that were previously divided according to their response to stressful stimuli into low or high anxiety-like subjects. The baseline amplitude of the unconditioned acoustic startle responses was high in high-anxiety female rats, with no effect on the estrous cycle observed. Data collected during the proestrus-estrus phase revealed that low-anxiety rats had startle amplitudes similar to those of high-anxiety rats. It is supposed that high-anxiety female rats benefit from increased estradiol and progesterone levels to achieve comparable potentiated startle amplitudes. In contrast, female rats experienced a significant decrease in hormone levels during the Diestrus phase. This decrease is believed to play a role in preventing them from displaying a heightened startle response when faced with strongly aversive stimuli. Data collected after 5-HT and 8-OH-DPAT were administered into the basolateral nuclei and dorsal periaqueductal gray suggest that 5-HT neurotransmission works with progesterone and estrogen to reduce startle potentiation, most likely by activating the serotonin-1A receptor subtype.

Disruptions in reproductive health, sex hormonal profiles, and hypothalamic hormone receptors content in females of the C58/J mouse model of autism

Autism Spectrum Disorder (ASD) is characterized by differences in social communication and interaction, as well as areas of focused interests and/or repetitive behaviors. Recent studies have highlighted a higher prevalence of endocrine and reproductive disturbances among females on the autism spectrum, hinting at potential disruptions within the hypothalamus-pituitary-ovary (HPO) axis. This research aims to explore the reproductive health disparities in ASD using an animal model of autism, the C58/J inbred mouse strain, with a focus on reproductive performance and hormonal profiles compared to the C57BL/6J control strain. Our findings revealed that the estrous cycle in C58/J females is disrupted, as evidenced by a lower frequency of complete cycles and a lack of cyclical release of estradiol and progesterone compared to control mice. C58/J females also exhibited poor performance in several reproductive parameters, including reproductive lifespan and fertility index. Furthermore, estrogen receptor alpha content showed a marked decrease in the hypothalamus of C58/J mice. These alterations in the estrous cycle, hormonal imbalances, and reduced reproductive function imply dysregulation in the HPO axis. Additionally, our in-silico study identified a group of genes involved in infertility carrying single-nucleotide polymorphisms (SNPs) in the C58/J strain, which also have human orthologs associated with autism. These findings could offer valuable insights into the molecular underpinnings of neuroendocrine axis disruption and reproductive issues observed in ASD.

T cells in obesity-associated inflammation: The devil is in the details

Obesity presents a significant health challenge, affecting 41% of adults and 19.7% of children in the United States. One of the associated health challenges of obesity is chronic low-grade inflammation. In both mice and humans, T cells in circulation and in the adipose tissue play a pivotal role in obesity-associated inflammation. Changes in the numbers and frequency of specific CD4+ Th subsets and their contribution to inflammation through cytokine production indicate declining metabolic health, that is, insulin resistance and T2D. While some Th subset alterations are consistent between mice and humans with obesity, some changes mainly characterize male mice, whereas female mice often resist obesity and inflammation. However, protection from obesity and inflammation is not observed in human females, who can develop obesity-related T-cell inflammation akin to males. The decline in female sex hormones after menopause is also implicated in promoting obesity and inflammation. Age is a second underappreciated factor for defining and regulating obesity-associated inflammation toward translating basic science findings to the clinic. Weight loss in mice and humans, in parallel with these other factors, does not resolve obesity-associated inflammation. Instead, inflammation persists amid modest changes in CD4+ T cell frequencies, highlighting the need for further research into resolving changes in T-cell function after weight loss. How lingering inflammation after weight loss affecting the common struggle to maintain lower weight is unknown. Semaglutide, a newly popular pharmaceutical used for treating T2D and reversing obesity, holds promise for alleviating obesity-associated health complications, yet its impact on T-cell-mediated inflammation remains unexplored. Further work in this area could significantly contribute to the scientific understanding of the impacts of weight loss and sex/hormones in obesity and obesity-associated metabolic decline.

Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress

AIMS

Basolateral amygdala (BLA), as a center for stress responses and emotional regulation, is involved in visceral hypersensitivity of irritable bowel syndrome (IBS) induced by stress. In the present study, we aimed to investigate the role of EphB2 receptor (EphB2) in BLA and explore the underlying mechanisms in this process.

METHODS

Visceral hypersensitivity was induced by water avoidance stress (WAS). Elevated plus maze test, forced swimming test, and sucrose preference test were applied to assess anxiety- and depression-like behaviors. Ibotenic acid or lentivirus was used to inactivate BLA in either the induction or maintenance stage of visceral hypersensitivity. The expression of protein was determined by quantitative PCR, immunofluorescence, and western blot.

RESULTS

EphB2 expression was increased in BLA in WAS rats. Inactivation of BLA or downregulation of EphB2 in BLA failed to induce visceral hypersensitivity as well as anxiety-like behaviors. However, during the maintenance stage of visceral pain, visceral hypersensitivity was only partially relieved but anxiety-like behaviors were abolished by inactivation of BLA or downregulation of EphB2 in BLA. Chronic WAS increased the expression of EphB2, N-methyl-D-aspartate receptors (NMDARs), and postsynaptic density protein (PSD95) in BLA. Downregulation of EphB2 in BLA reduced NMDARs and PSD95 expression in WAS rats. However, activation of NMDARs after the knockdown of EphB2 expression still triggered visceral hypersensitivity and anxiety-like behaviors.

CONCLUSIONS

Taken together, the results suggest that EphB2 in BLA plays an essential role in inducing visceral hypersensitivity. In the maintenance stage, the involvement of EphB2 is crucial but not sufficient. The increase in EphB2 induced by WAS may enhance synaptic plasticity in BLA through upregulating NMDARs, which results in IBS-like symptoms. These findings may give insight into the treatment of IBS and related psychological distress.

The Role of Estrogen Signaling and Exercise in Drug Abuse: A Review

BACKGROUND

Discovering how sex differences impact the efficacy of exercise regimens used for treating drug addiction is becoming increasingly important. Estrogen is a hormone believed to explain a large portion of sex differences observed during drug addiction, and why certain exercise regimens are not equally effective between sexes in treatment. Addiction is currently a global hindrance to millions, many of whom are suffering under the influence of their brain's intrinsic reward system coupled with external environmental factors. Substance abuse disorders in the U.S. alone cost billions of dollars annually.

REVIEW SUMMARY

Studies involving the manipulation of estrogen levels in female rodents, primarily via ovariectomy, highlight its impact regarding drug addiction. More specifically, female rodents with higher estrogen levels during the estrus phase increase cocaine consumption, whereas those in the non-estrus phase (low estrogen levels) decrease cocaine consumption. If estrogen is reintroduced, self-administration increases once again. Exercise has been proven to decrease relapse tendency, but its effect on estrogen levels is not fully understood.

CONCLUSIONS

Such findings and results discussed in this review suggest that estrogen influences the susceptibility of females to relapse. Therefore, to improve drug-abuse-related treatment, exercise regimens for females should be generated based on key sex differences with respect to males.

Reproductive experience alters the effects of diazepam and fluoxetine on anxiety-like behaviour, fear extinction, and corticosterone levels in female rats

OVERVIEW

Reproductive experience (pregnancy and motherhood) leads to long-term changes in the neurobiological and hormonal features of anxiety in rats and humans. The aim of this study was to examine whether reproductive experience alters the effects of two pharmacological treatments for anxiety, a benzodiazepine (diazepam) and a selective serotonin reuptake inhibitor (fluoxetine), on animal models of anxiety.

METHODS

In Experiment 1, virgin (n = 47) and age-matched mother (n = 50) rats at 1-month post-weaning were injected with diazepam (1.3 mg/kg or 1.7 mg/kg, i.p.) or vehicle, in the proestrus (high estradiol/progesterone/allopregnanolone) or metestrus (low estradiol/progesterone/allopregnanolone) phase of the estrous cycle 30 min prior to the elevated plus maze (EPM). In Experiment 2, virgin (n = 25) and mother rats (n = 20) were administered fluoxetine (10 mg/kg) or vehicle for 2 weeks prior to being tested on a Pavlovian fear conditioning and extinction protocol, and the EPM.

RESULTS

Replicating past research, in virgin rats, the low dose of diazepam produced anxiolytic-like effects in proestrus, but only the high dose was anxiolytic-like in metestrus. In contrast, in mother rats, both doses of diazepam were anxiolytic-like irrespective of estrous phase. Fluoxetine produced anxiogenic-like effects in virgin rats during fear extinction and the EPM, but had no behavioural effects in mothers. In contrast, fluoxetine increased plasma corticosterone levels measured 30-min post-EPM in mothers, but not virgin rats.

CONCLUSIONS

Reproductive experience alters the dose responsivity and efficacy of common anti-anxiety medications in female rats. These findings highlight the importance of considering reproductive status in studies on anxiety and its treatment.

Sex and estrous cycle-linked differences in the effect of cannabidiol on panic-like responding in rats and mice

Clinical and preclinical studies point towards anxiolytic actions of cannabidiol (CBD), but its effect in panic disorder has been less explored and few studies consider effects in females. We here compared the effect of CBD on the response of male and female rats and mice to a panicogenic challenge; exposure to low O2 (rats) or high CO2 (mice) paying attention in females to possible effects of estrous cycle phase. Male and female Sprague-Dawley rats and C57BL/6 J mice were exposed to 7% O2 for 5 min (rats) or 20% CO2 (mice) and escape behaviour, which has been associated with panic attacks, was quantified as undirected jumps towards the gas chamber's ceiling. The effect of pretreatment with CBD (1-10 mg kg-1 i.p. in rats or 10-60 mg kg-1 i.p. in mice) was tested. The results showed that low O2 (rats) or high CO2 (mice) evoked escape in both sexes. In female rats the response was estrous cycle-sensitive: females in late diestrus made significantly more jumps than females in proestrus. In female mice escape was not influenced by estrous cycle phase and CBD was panicolytic. In female rats CBD attenuated escape behaviour in late diestrus phase but not in proestrus. In male rats and mice CBD had no effect on escape behaviour. Therefore, CBD is panicolytic in female rats and mice but not in males. In rats the effect is estrous cycle-sensitive: rats were most responsive to CBD in late diestrus. In mice higher doses were required to elicit effects and estrous cycle had no effect.

Molecular mechanisms of hormones implicated in migraine and the translational implication for transgender patients

Migraine is a primary headache disorder recognized by the World Health Organization as one of the most poorly understood and debilitating neurological conditions impacting global disability. Chronic pain disorders are more frequently diagnosed among cisgender women than men, suggesting that female sex hormones could be responsible for mediating chronic pain, including migraine and/or that androgens can be protective. This review discusses the major gonadal hormones, estrogens, progesterone, and testosterone in the context of molecular mechanisms by which they play a role in migraine pathophysiology. In addition, the literature to date describing roles of minor sex hormones including prolactin, luteinizing hormone, follicular stimulating hormone, and gonadotropin releasing hormone in migraine are presented. Because transgender and gender non-conforming (trans*) individuals are an underserved patient population in which gender-affirming sex hormone replacement therapy (HRT) is often medically necessary to align biological sex with gender identity, results from cisgender patient populations are discussed in the context of these major and minor sex hormones on migraine incidence and management in trans* patients.

No detectable changes in anxiety-related and locomotor behaviors in adult ovariectomized female rats exposed to estradiol, the ERβ agonist DPN or the ERα agonist PPT

The sex steroid hormone 17β-estradiol (estradiol) and its Estrogen Receptors (ERs) have been linked to modulation of anxiety-related and locomotor behaviors in female rodents. Research suggests that estradiol mitigates anxiety-related behaviors through activating Estrogen Receptor (ER)β and increases locomotor behaviors through ERα. The influence of ERs on these behaviors cannot always be detected. Here we discuss two experiments in which we tested the hypothesis that anxiety-related behaviors would decrease after ERβ activation and locomotor behaviors would increase after ERα activation, and also assessed the persistence of these behavioral effects by varying the timing of behavioral testing. Two cohorts of adult female ovariectomized rats were exposed to estradiol, the ERβ agonist DPN, the ERα agonist PPT, or oil for four consecutive days. Body mass was assessed throughout as a positive control. In both cohorts, open field behaviors were assessed on the first day of exposure. In one cohort (Experiment 1), open field, light/dark box, and elevated plus maze behaviors were assessed on the final day of injections. In the second cohort (Experiment 2), these behaviors were assessed 24 h after the final exposure. As expected, significant differences in body mass were detected in response to estradiol and PPT exposure, validating the estradiol and ER manipulation. No significant differences were observed in anxiety-related or locomotor behaviors across treatment groups, indicating that the efficacy of these agonists as therapeutic agents may be limited. We review these results in the context of previous literature, emphasizing relevant variables that may obscure ER-related actions on behavior.

The impact of the ovarian cycle on anxiety, allopregnanolone, and corticotropin releasing hormone changes after motherhood in female rats and women

Fluctuations in ovarian steroids across the estrous and menstrual cycle in female rats and women, respectively, are associated with changes in anxiety. Pregnancy causes long-term changes to ovarian hormone release, yet research on estrous- and menstrual-related changes in anxiety has focused on reproductively inexperienced females. Therefore, this study assessed whether the impact of estrous and menstrual cycles on anxiety differs pre- versus post-motherhood in female rats (n = 32) and a community sample of women (n = 63). Estrous cycle phase altered anxiety-like behavior in virgin rats, but had no effect in age-matched mother rats tested 1-month post-weaning. In humans, menstrual cycle phase was associated with ecological momentary assessed anxiety and mood in non-mothers, but not mothers; although, the menstrual cycle × reproductive status interaction for anxiety, but not mood, was rendered non-significant with age and cycle length as covariates. These findings suggest that changes in anxiety coincident with cycling hormones is an evolutionarily conserved feature of the estrous and menstrual cycle in rats and women, which is mitigated following motherhood in both species. We identified several potential mechanisms for the observed dissociation in estrous cycle effects on anxiety. Compared to virgin rats, mother rats had a lower peak and blunted decline in circulating allopregnanolone during proestrus, upregulated GABA_A receptor subunit (α1, α2, α5, α4, ß2) mRNA in the ventral hippocampus, and altered corticotropin-releasing hormone mRNA across the estrous cycle in the basolateral amygdala. Together, these findings suggest that the mechanisms underlying anxiety regulation undergo fundamental transformation following pregnancy in female rats and humans.