Mothers do it differently: reproductive experience alters fear extinction in female rats and women

The effects of diazepam on fear extinction in nulliparous and primiparous female rats

Benzodiazepines undermine the success of exposure therapy in humans with anxiety disorders, and impair the long-term memory of fear extinction (the laboratory basis of exposure therapy) in rodents. However, most rodent studies on fear extinction and benzodiazepines have been conducted in male rodents. In female rodents, the estrous cycle influences the consolidation of fear extinction memories and sensitivity to benzodiazepines. In addition, pregnancy leads to long-term changes in the neurobiological, hormonal, and behavioural features of fear extinction, as well as the responsivity to benzodiazepines. Therefore, the present experiments examined the impact of benzodiazepines on fear extinction in female rats with and without reproductive experience. Age-matched nulliparous (no reproductive experience) and primiparous (one prior reproductive experience; tested one-month post-weaning) rats received fear conditioning to a discrete cue. The next day, rats were administered the benzodiazepine diazepam (2 mg/kg, s.c), or vehicle, prior to or immediately after extinction training. Rats were then tested the next day, drug free, for extinction retention. Similar to previous findings in males, diazepam impaired extinction retention in both nulliparous and primiparous rats when administered either pre- or post-extinction training. These findings may have potential clinical implications as they suggest that benzodiazepine use in conjunction with exposure therapy may undermine long-term treatment success in women with and without reproductive experience, although this remains to be tested in human populations. Moreover, these findings are theoretically important when considered in light of previous studies showing dissociable mechanisms of fear extinction in females pre- versus post-pregnancy.

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.

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.

The Impacts of Sex Differences and Sex Hormones on Fear Extinction

Fear extinction memories are strongly modulated by sex and hormonal status, but the exact mechanisms are still being discovered. In humans, there are some basal and task-related features in which male and female individuals differ in fear conditioning paradigms. However, analyses considering the effects of sex hormones demonstrate a role for estradiol in fear extinction memory consolidation. Translational studies are taking advantage of the convergent findings between species to understand the brain structures implicated. Nevertheless, the human brain is complex and the transfer of these findings into the clinics remains a challenge. The promising advances in the field together with the standardization of fear extinction methodologies in humans will benefit the design of new personalized therapies.

How Different Factors in Combination Change Fear Extinction Learning: The Case of Sex and Stress Hormones

Effects of a specific factor on fear extinction or exposure therapy have revealed promising results, for example how sex or stress hormones exert the capability to critically change extinction learning and consolidation processes. However, we must acknowledge that in real life these factors do not operate in isolation, they go hand in hand. In this chapter, the available evidence regarding interactions of sex and stress hormones on extinction processes and exposure therapy will be integrated and discussed. First hints exist that these factors in combination critically target extinction learning and consolidation processes, calling for more detailed research on the exact underlying mechanisms. In addition to experiments with high sample sizes, we must aim for a collaborative effort of laboratories across the whole world to be able to identify critical combinations of factors associated with improved, but also impaired extinction processes and exposure therapy success. We expect that the revelation of further relevant factors will not only be limited to the interplay between sex and stress hormones but will include factors such as sleep and exercise as well. In the long run, uncovering the most important interaction effects will give us critical hints for differential treatment options to be realized in the sense of a personalized medicine approach.

Maternal Experience Does Not Predict Fear Extinction and Anxiety-Like Behaviour in Primiparous Rats Post-weaning

Reproductive experience leads to long-lasting changes in anxiety-like behaviour and fear extinction, the laboratory model of exposure therapy for anxiety disorders. For example, fear extinction is influenced by estrous cycle in nulliparous (no reproductive experience) female rats, but this effect is abolished in primiparous (one reproductive experience) females. It is unclear whether such changes are driven by pregnancy, maternal experience of caring for offspring during the postpartum period, or a combination of both experiences. The present study sought to determine the influence of maternal experience (i.e., exposure to pups and mother-pup interactions) on fear extinction in primiparous rats. In Experiment 1, we tested whether pup exposure is necessary to mitigate estrous effects on fear extinction in primiparous rats. Age-matched nulliparous rats, primiparous rats, and primiparous rats who experienced pregnancy but not pup exposure, underwent fear conditioning on day 1 (2 months post-parturition), extinction training during proestrus (high sex hormones) or metestrus (low sex hormones) on day 2, and extinction recall on day 3. Replicating past research, nulliparous rats showed impaired extinction recall when they were extinguished during metestrus compared to proestrus. In contrast, primiparous rats with and without pup exposure showed comparable extinction recall irrespective of estrous phase. In Experiment 2, we assessed whether naturally-occurring variation in mother-pup interactions predict future fear extinction performance and anxiety-like behaviour. During the first week of lactation, primiparous rats were measured for maternal behaviours toward pups. Primiparous rats were then tested on the light-dark box and elevated plus maze to measure anxiety-like behaviour and underwent a fear extinction protocol 1 month post-weaning. We found no significant correlations between maternal behaviour and fear extinction outcomes or anxiety-like behaviour. Our findings suggest that pregnancy, not maternal experience, mitigates the impact of estrous cycle on fear extinction. In addition, natural variation in maternal experience does not appear to contribute to variability in future fear extinction outcomes or anxiety-like behaviour in primiparous rats.

Using Translational Models of Fear Conditioning to Uncover Sex-Linked Factors Related to PTSD Risk

Post-traumatic stress disorder (PTSD) is a debilitating neuropsychiatric disorder that follows exposure to a traumatic event; however, not every person who experiences trauma will develop PTSD. Women are more likely to be diagnosed with PTSD than men even when controlling for type and amount of trauma exposure. Circulating levels of gonadal hormones such as estradiol, progesterone, and testosterone may contribute to differential risk for developing PTSD. In this review, we briefly consider the influence of gonadal hormones on fear conditioning processes including fear acquisition, fear inhibition, extinction learning, and extinction recall within translational neuroscience models. We discuss findings from human studies incorporating samples from both community and traumatized clinical populations to further understand how these hormones might interact with exposure to trauma. Additionally, we propose that special attention should be paid to the specific measure used to examine fear conditioning processes as there is evidence that common psychophysiological indices such as skin conductance response and fear-potentiated startle can reveal quite different results and thus necessitate nuanced interpretations. Continued research to understand the influence of gonadal hormones in fear learning and extinction processes will provide further insight into the increased risk women have of developing PTSD and provide new targets for the treatment and prevention of this disorder.

Sex-Related Predisposition to Post-Traumatic Stress Disorder Development-The Role of Neuropeptides

Post-traumatic stress disorder (PTSD) is characterized by re-experiencing a traumatic event, avoidance, negative alterations in cognitions and mood, hyperarousal, and severe functional impairment. Women have a two times higher risk of developing PTSD than men. The neurobiological basis for the sex-specific predisposition to PTSD might be related to differences in the functions of stress-responsive systems due to the interaction between gonadal hormones and stress peptides such as corticotropin-releasing factor (CRF), orexin, oxytocin, and neuropeptide Y. Additionally, in phases where estrogens levels are low, the risk of developing or exacerbating PTSD is higher. Most studies have revealed several essential sex differences in CRF function. They include genetic factors, e.g., the CRF promoter contains estrogen response elements. Importantly, sex-related differences are responsible for different predispositions to PTSD and diverse treatment responses. Fear extinction (the process responsible for the effectiveness of behavioral therapy for PTSD) in women during periods of high endogenous estradiol levels (the primary form of estrogens) is reportedly more effective than in periods of low endogenous estradiol. In this review, we present the roles of selected neuropeptides in the sex-related predisposition to PTSD development.

Gonadal steroid hormones and emotional memory consolidation: A systematic review and meta-analysis

Anxiety and stress-related disorders are more prevalent in women and associated with negative emotional memory consolidation as well as impaired fear extinction recall. Recent research has identified a role of gonadal steroid hormones in influencing emotional memories and fear extinction, however most individual studies have small samples and employed various protocols. A systematic review and meta-analysis were conducted on studies that examined sex hormones (estrogen, progesterone, testosterone, allopregnanolone, dehydroepiandrosterone) on four aspects of memory, namely, intentional recall (k = 13), recognition memory (k = 7), intrusive memories (k = 9), and extinction recall (k = 11). The meta-analysis on natural cycling women revealed that progesterone level was positively associated with negative recall and negative intrusive memories, and this effect on intentional recall was enhanced under stress induction. Estradiol level was positively associated with extinction recall. This study reveals an important role of progesterone and estradiol in influencing emotional memory consolidation. It highlights the need to control for these hormonal effects and examine progesterone and estradiol concurrently across all menstrual phases in future emotional memory paradigms.

Hormonal, reproductive, and behavioural predictors of fear extinction recall in female rats

The prevalence, severity and chronicity of anxiety disorders is significantly higher in women compared to men. Exposure therapy, the gold-standard treatment for anxiety disorders, can be modelled in the laboratory through Pavlovian fear extinction. Understanding the factors that influence fear extinction in females may aid in optimising the treatment of anxiety disorders in this population. The aim of the current study was therefore to explore the hormonal, reproductive and behavioural predictors of fear extinction recall in female rats by analysing data from nine published experiments that examined fear extinction in female rats. A hierarchical multiple regression analysis revealed that estrous cycle effects on extinction recall may be modulated by reproductive status. While the estrous phase in which nulliparous (virgin) rats undergo extinction training was predictive of extinction recall, no relationship between estrous phase and extinction recall was found among primiparous (one prior reproductive experience) rats. Moreover, estrous cycle predicted the relationship between early extinction and extinction recall in nulliparous rats, but not primiparous rats. Although reproductive status did not predict extinction recall, primiparous rats exhibited poor extinction recall relative to nulliparous rats extinguished during proestrus, and better extinction recall than nulliparous rats extinguished during metestrus. A faster rate of extinction, and lower fear responses at the end of extinction training were predictive of lower levels of CS-elicited fear during extinction recall in both nulliparous and primiparous female rats, while the length of extinction training was not predictive of extinction recall. The potential theoretical and clinical implications of these findings are discussed.

Estradiol Modulates Neural and Behavioral Arousal in Women With Posttraumatic Stress Disorder During a Fear Learning and Extinction Task

BACKGROUND

Fear responding in posttraumatic stress disorder (PTSD) is sexually heterogeneous and varies with hormonal fluctuations throughout the menstrual cycle. While research suggests that estrogen levels affect PTSD symptoms among women, there is a dearth of research on modulatory effects of estrogen on fear responding among women with PTSD, and neural outcome measures are lacking.

METHODS

A sample of 42 women with PTSD underwent 2 consecutive alternating blocks of fear conditioning and extinction training, during which a CS+ conditioned stimulus, but not a CS-, predicted the occurrence of an electric shock in an acquisition context but not in an extinction context. Assayed saliva determined estradiol levels. Skin conductance response and whole-brain voxelwise activity during functional magnetic resonance imaging were outcome variables in linear mixed-effects models, with estradiol level, PTSD severity, and task contrasts as predictors.

RESULTS

Skin conductance response exhibited a significant estradiol × PTSD severity × habituation interaction (t = 3.180, p = .002), such that PTSD severity was correlated with increased arousal responding between training blocks among women with lower estradiol (t = -3.985, p < .001) but not higher estradiol (t = 0.550, p = .583). Voxelwise activity also demonstrated an identical three-way interaction within dorsomedial prefrontal cortex and anterior insula clusters. The skin conductance response and imaging interactions between PTSD severity and estradiol were not specific to conditioned stimulus type or context.

CONCLUSIONS

Estradiol moderated the relationship between PTSD severity and arousal response habituation between fear conditioning and extinction training sessions, such that high estradiol protected against the negative impact of severe PTSD symptoms on fear habituation. These findings suggest that estrogen enhances habituation among women with severe PTSD, potentially influencing the efficacy of extinction-based therapies.

The Role of Hormonal and Reproductive Status in the Treatment of Anxiety Disorders in Women

Exposure therapy, a key treatment for anxiety disorders, can be modelled in the laboratory using Pavlovian fear extinction. Understanding the hormonal and neurobiological mechanisms underlying fear extinction in females, who are twice more likely than males to present with anxiety disorders, may aid in optimising exposure therapy outcomes in this population. This chapter will begin by discussing the role of the sex hormones, estradiol and progesterone, in fear extinction in females. We will also propose potential mechanisms by which these hormones may modulate fear extinction. The second half of this chapter will discuss the long-term hormonal, neurological and behavioural changes that arise from pregnancy and motherhood and how these changes may alter the features of fear extinction in females. Finally, we will discuss implications of this research for the treatment of anxiety disorders in women with and without prior reproductive experience.

d-Cycloserine and estradiol enhance fear extinction in nulliparous but not primiparous female rats

Female reproductive experience has been shown to alter the hormonal, neurobiological and behavioural features of fear extinction, which is the laboratory basis of exposure therapy. This raises uncertainties as to whether pharmacological agents that enhance fear extinction in reproductively inexperienced females are equally effective in reproductively experienced females. The aim of the current study was therefore to compare the effects of two pharmacological enhancers of fear extinction, d-cycloserine (DCS) and estradiol, between nulliparous (virgin) and primiparous (reproductively experienced) female rats. In Experiment 1, nulliparous and primiparous females received systemic administration of either DCS or saline immediately after extinction training, and were tested for extinction recall the following day. DCS enhanced extinction recall in nulliparous females that showed low levels of freezing at the end of extinction training, but not among those that showed high levels of freezing at the end of extinction training. DCS did not enhance fear extinction in primiparous females, regardless of their level of freezing at the end of extinction training. In Experiment 2, nulliparous and primiparous female rats received systemic administration of either estradiol or vehicle prior to extinction training. Estradiol enhanced extinction recall among nulliparous females, but not primiparous females. Increasing the dose of estradiol administered prior to extinction training did not alter the outcomes in primiparous females (Experiment 3). Together, these findings suggest that reproductive status may be an important individual difference factor associated with the response to pharmacological modulators of extinction in rats. The implications of these findings for the pharmacological augmentation of exposure therapy in clinical populations are discussed.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Fear Extinction Retention: Is It What We Think It Is?

There has been an explosion of research on fear extinction in humans in the past 2 decades. This has not only generated major insights, but also brought a new goal into focus: how to maintain extinction memory over time (i.e., extinction retention). We argue that there are still important conceptual and procedural challenges in human fear extinction research that hamper advancement in the field. We use extinction retention and the extinction retention index to exemplarily illustrate these challenges. Our systematic literature search identified 16 different operationalizations of the extinction retention index. Correlation coefficients among these different operationalizations as well as among measures of fear/anxiety show a wide range of variability in four independent datasets, with similar findings across datasets. Our results suggest that there is an urgent need for standardization in the field. We discuss the conceptual and empirical implications of these results and provide specific recommendations for future work.

Sex differences in fear extinction

Despite the exponential increase in fear research during the last years, few studies have included female subjects in their design. The need to include females arises from the knowledge gap of mechanistic processes underlying the behavioral and neural differences observed in fear extinction. Moreover, the exact contribution of sex and hormones in relation to learning and behavior is still largely unknown. Insights from this field could be beneficial as fear-related disorders are twice as prevalent in women compared to men. Here, we review an up-to-date summary of animal and human studies in adulthood that report sex differences in fear extinction from a structural and functional approach. Furthermore, we describe how these factors could contribute to the observed sex differences in fear extinction during normal and pathological conditions.

Reproductive experience alters the involvement of N-methyl-D-aspartate receptors in fear extinction, but not fear conditioning, in female Sprague Dawley rats

Recently, evidence has emerged showing that the behavioural and hormonal features of fear extinction are altered as a result of reproductive experience in both rats and humans. The current set of experiments sought to determine whether reproductive experience also alters the molecular features of fear extinction. In adult male rats, it has been widely demonstrated that the activation of N-methyl-D-aspartate receptors (NMDAR) is essential for fear extinction. We therefore compared the involvement of NMDAR in fear extinction between nulliparous (virgin) and primiparous (reproductively experienced) female rats. Nulliparous and primiparous females received systemic administrations of either MK-801 (a non-competitive NMDAR antagonist) or saline prior to extinction training. MK-801 was found to impair extinction recall in nulliparous females, but not primiparous females. When the same dose of MK-801 was administered prior to conditioning, both groups of rats showed impaired recall of conditioning the following day. The results of these experiments indicate that the extinction, but not the acquisition of fear, may become NMDAR-independent following reproductive experience.

Low estradiol is linked to increased skin conductance, but not subjective anxiety or affect, in response to an impromptu speech task

Low estradiol is associated with impaired extinction of conditioned physiological fear responses (e.g. skin conductance) in females. As fear extinction is the laboratory basis of exposure therapy for anxiety disorders, it has been speculated that estradiol may be related to the effectiveness of treatment for anxiety. The present study extended past research by examining whether estradiol is related to physiological and subjective fear responses during the impromptu speech task, where participants perform a surprise speech to camera. This task elicits psychosocial fear, and thus has relevance for social anxiety disorder (SAD). We used a quasi-experimental design with two groups of women: 39 naturally cycling women, and 19 women taking hormonal contraceptives. Based on the measured serum levels, naturally cycling women were further divided into women with higher- vs. lower estradiol levels. Compared to those with higher estradiol, women with lower estradiol, and those using hormonal contraceptives (chronically suppressed estradiol) displayed higher speech-elicited skin conductance yet reported no differences in subjective anxiety or affect. Conversely, irrespective of estradiol status, compared to those with low self-reported social anxiety, participants with higher social anxiety exhibited greater subjective anxiety and affect, yet no differences in skin conductance. These results demonstrate that the relationship between estradiol and physiological fear responses extends to psychosocial tasks. However, the dissociations between physiological and subjective measures highlight the need to consider the relevance of different response outputs so that the potential impact of estradiol on the treatment of anxiety disorders can be better understood.

Sex differences in the effects of adult short-term isolation rearing on contextual fear memory and extinction

Fear conditioning and extinction is a useful tool for understanding the pathogenesis of fear-related disorders including post-traumatic stress disorder (PTSD) and for developing treatments for them. To investigate the role of sub-brain regions or molecular mechanisms in fear conditioning and extinction, neuroscientists have been employing an optogenetic or in vivo recording technique, in which placement of an optical fiber or an electrode into the brain region of a free-moving mouse is essential. These methods require isolation rearing (at least one week) from the brain surgery to the behavioral test. Although such short-term adult rearing has been shown not to influence fear memory and extinction in males, the effect in females remains unclear. In the present study, we investigated the effect on fear memory and fear extinction of adult isolation rearing during the one week before contextual fear conditioning in both male and female mice. This short-term adult isolation rearing increased fear responses in the contextual fear memory test in females but not in males. On the other hand, the rearing showed no effect on fear responses during fear extinction or the recall test in either sex. In summary, adult short-term isolation rearing enhanced only fear memory, and only in females.

Postnatal stress is associated with impaired fear conditioning and extinction, and heightened hippocampal fibroblast growth factor 2, in mother rats

Rats exposed to early-life maternal separation (MS) exhibit later alterations in fear conditioning and impairments in fear extinction. As MS creates long-lasting anxiety in the mother, the present study assessed the influence of MS on fear conditioning and extinction in mother rats. It also examined whether estrous cycle effects on extinction, which are robust in nulliparous rats, but abolished in primiparous rats, re-emerge after MS. Following parturition, pups were removed from their mothers for 3 h daily from postpartum day 2-14 (MS), or remained housed with their mothers (standard reared condition, SR). Pups were weaned at postpartum day 24, and three months later, mothers received fear conditioning, extinction training, and test for extinction recall over three days. Extinction training took place during Proestrus (high estradiol and progesterone) or Metestrus (low estradiol and progesterone). Similar to past findings in non-stressed mothers, estrous cycle was not associated with conditioned fear expression (indexed by fear responses at the start of extinction training) or extinction recall in either MS or SR mothers. However, MS mothers exhibited weaker conditioned fear expression and impaired extinction recall, relative to SR mothers. Hippocampal fibroblast growth factor-2, a neurotrophin involved in stress regulation and fear expression, was elevated in MS relative to SR mothers. These results indicate that postnatal stress has long-lasting consequences for neural and behavioral systems involved in fear learning and inhibition without altering the involvement of ovarian hormones in these processes.

Estradiol-induced enhancement of fear extinction in female rats: The role of NMDA receptor activation

Converging cross-species evidence indicates that fear extinction (the laboratory basis of exposure therapy for anxiety disorders) in females is modulated by endogenous and exogenous estradiol. The mechanisms underlying estradiol's influences on fear extinction are largely undefined. However, one likely candidate is the NMDA-receptor (NMDAr), activation of which is necessary for estradiol-mediated enhancements in structural and functional neural plasticity, as well as extinction consolidation in males. Here, we demonstrate that systemic co-administration of the non-competitive NMDAr antagonist, MK801, blocked the enhancement of fear extinction by systemic estradiol in ovariectomized rats. In intact rats, MK801 during diestrus (rising estradiol) prevented the enhancement in extinction recall in rats that received extinction training during proestrus (peak estradiol). Systemic administration of the partial NMDAr agonist D-cycloserine (DCS) prior to extinction training facilitated extinction in ovariectomized rats, mimicking the effects of estradiol. In intact rats, DCS administered on the afternoon of proestrus and the morning of estrus (declining estradiol) facilitated extinction in rats that received extinction training during metestrus (low estradiol). Finally, DCS also facilitated extinction in ovariectomized rats when administered immediately after extinction training. Combined, these findings suggest that endogenous and exogenous estradiol enhance fear extinction via NMDAr-dependent mechanisms. Moreover, these findings raise the possibility that fear extinction deficits during periods of low endogenous estradiol levels can be reversed by increasing NMDAr activation via DCS administration, either well prior to, or immediately after, extinction training.

Estradiol moderates the relationship between state-trait anxiety and attentional bias to threat in women

Anxiety disorders are characterized by impaired fear extinction and heightened attentional allocation to threatening stimuli. The sex hormones estradiol and progesterone modulate fear extinction in female rats and women; whether these hormones are similarly related to attentional biases to threat has not been examined. In the present study 74 women (53 cycling, 21 using hormonal contraception), and a comparison group of 30 men, completed standard assessments of state-trait anxiety, as well symptoms of depression, anxiety and stress, followed by a computerized assessment of attentional bias, the dot-probe task. Women's endogenous estradiol and progesterone levels were ascertained by a blood sample. No differences in attentional bias were found dependent on sex or hormonal contraceptive use. Estradiol was the only variable measured that was independently positively correlated with attentional bias to threat. Regression analyses revealed a bi-directional relationship between state-trait anxiety, symptoms of anxiety and stress, and attentional bias that was moderated by estradiol, such that a positive relationship was observed amongst women with higher estradiol, and a negative relationship was observed amongst women with lower estradiol. Together, these results indicate that under conditions of anxiety and stress, women may attend to threat differently depending on endogenous estradiol levels, being avoidant when estradiol is lower, and vigilant when estradiol is higher. A more nuanced understanding of the role for attention in anxiety disorders amongst women may be developed by taking hormonal status into consideration.

The association between estradiol levels, hormonal contraceptive use, and responsiveness to one-session-treatment for spider phobia in women

Preclinical studies have demonstrated that conditioned fear extinction is impaired in females with low endogenous levels of the sex hormone estradiol, due to menstrual fluctuations or hormonal contraceptive use. As fear extinction is a laboratory model of exposure therapy for anxiety and trauma disorders, here we assessed the hypothesis that treatment outcomes may be diminished when exposure therapy occurs during periods of low estradiol. 90 women with spider phobia (60 cycling and 30 using hormonal contraceptives) underwent a one-session exposure treatment for spider phobia, following which, serum estradiol levels were assessed. A median split in estradiol level was used to divide cycling participants into two groups; lower and higher estradiol. Behavioral avoidance and self-reported fear of spiders were measured pre-treatment, post-treatment, and at a 12 week follow-up assessment. Women using hormonal contraceptives exhibited a significantly slower rate of improvement across treatment, greater behavioral avoidance at post-treatment and follow-up, and fewer self-initiated post-treatment exposure tasks, relative to both groups of cycling women, who did not differ. No group differences in self-reported fear were evident. Correlational analyses revealed that across the whole sample, lower estradiol levels were associated with slower rates of improvement across treatment, and greater self-reported fear and behavioral avoidance at post-treatment, but not follow-up. These results provide the first evidence of an association between endogenous estradiol, hormonal contraceptive use, and exposure therapy outcomes in spider phobic women. Hormonal profile may partly account for variability in responsiveness to psychological treatments for anxiety and trauma disorders in women.

Effects of systemic estradiol on fear extinction in female rats are dependent on interactions between dose, estrous phase, and endogenous estradiol levels

Administering estradiol to females during periods of low endogenous estradiol enhances their ability to extinguish fear, the laboratory basis of exposure therapy for anxiety disorders. It has therefore been proposed that estradiol could be a useful adjunct to enhance exposure therapy outcomes. The present study aimed to clarify the boundary conditions under which estradiol could be used for this purpose, by assessing whether the impact of estradiol, administered systemically prior to extinction training, differs depending on dose and estrous phase in adult female rats. Results demonstrated that in rats extinguished during metestrus (naturally low estradiol), a low dose of estradiol reduced freezing during extinction training and augmented extinction recall the following day, whereas a high dose of estradiol had no effect on either extinction training or recall. In rats extinguished during proestrus (naturally high estradiol), a high dose of estradiol impaired extinction recall, whereas a low dose of estradiol had no effect, or impairing effects, on extinction recall in different experiments. A subsequent analysis revealed that estradiol-treated proestrus rats that exhibited impaired extinction recall had significantly higher pre-treatment serum estradiol levels than those that exhibited good extinction recall. Together, these results indicate that systemically administered estradiol interacts with endogenous estradiol to produce an inverted U shaped dose effect on fear extinction, where low and high estradiol levels lead to poor extinction recall, and moderate estradiol levels lead to good extinction recall. These results highlight potential limitations to the use of estradiol as an adjunct to exposure therapy in clinical settings.