Habituation to repeated stress: get used to it

Role of angiotensin receptors in the medial amygdaloid nucleus in autonomic, baroreflex and cardiovascular changes evoked by chronic stress in rats

This study investigated the role of AT₁ , AT₂ and Mas angiotensinergic receptors within the MeA in autonomic, cardiovascular and baroreflex changes evoked by a 10-day (1  hr daily) repeated restraint stress (RRS) protocol. Analysis of cardiovascular function after the end of the RRS protocol indicated increased values of arterial pressure, without heart rate changes. Arterial pressure increase was not affected by acute MeA treatment after the RRS with either the selective AT₁ receptor antagonist losartan, the selective AT₂ receptor antagonist PD123319 or the selective Mas receptor antagonist A-779. Analysis of heart rate variability indicated that RRS increased the sympathetic tone to the heart, which was inhibited by MeA treatment with either losartan, PD123319 or A-779. Baroreflex function assessed using the pharmacological approach via intravenous infusion of vasoactive agents revealed a facilitation of tachycardia evoked by blood pressure decrease in chronically stressed animals, which was inhibited by MeA treatment with losartan. Conversely, baroreflex responses during spontaneous fluctuations of blood pressure were impaired by RRS, and this effect was not affected by injection of the angiotensinergic receptor antagonists into the MeA. Altogether, the data reported in the present study suggest an involvement of both angiotensinergic receptors present in the MeA in autonomic imbalance evoked by RRS, as well as an involvement of MeA AT₁ receptor in the enhanced baroreflex responses during full range of blood pressure changes. Results also indicate that RRS-evoked increase in arterial pressure and impairment of baroreflex responses during spontaneous variations of arterial pressure are independent of MeA angiotensinergic receptors.

The role of acetylcholine in negative encoding bias: Too much of a good thing?

Optimal acetylcholine (ACh) signaling is important for sustained attention and facilitates learning and memory. At the same time, human and animal studies have demonstrated increased levels of ACh in the brain during depressive episodes and increased symptoms of anxiety, depression, and reactivity to stress when ACh breakdown is impaired. While it is possible that the neuromodulatory roles of ACh in cognitive and affective processes are distinct, one possibility is that homeostatic levels of ACh signaling are necessary for appropriate learning, but overly high levels of cholinergic signaling promote encoding of stressful events, leading to the negative encoding bias that is a core symptom of depression. In this review, we outline this hypothesis and suggest potential neural pathways and underlying mechanisms that may support a role for ACh signaling in negative encoding bias.

Hypothalamic-vagal oxytocinergic neurocircuitry modulates gastric emptying and motility following stress

KEY POINTS

Stress triggers and exacerbates the symptoms of functional gastrointestinal disorders, such as delayed gastric emptying and impaired gastric motility. Understanding the mechanisms by which the neural circuits, impaired by stress, are restored may help to identify potential targets for more effective therapeutic interventions. Oxytocin administration or release ameliorates the stress-induced delayed gastric emptying and motility. However, is it unclear whether the effects are mediated via the hypothalamic-pituitary-adrenocortical axis or the oxytocinergic projections from the paraventricular nucleus of the hypothalamus to brainstem neurones of the dorsal vagal complex. We used Cre-inducible designer receptors exclusively activated by designer drugs to demonstrate the fundamental role of the oxytocinergic hypothalamic-vagal projections in the gastric adaptation to stress.

ABSTRACT

Stress triggers and exacerbates the symptoms of functional gastrointestinal (GI) disorders, such as delayed gastric emptying and impaired gastric motility. The prototypical anti-stress hormone, oxytocin (OXT), plays a major role in the modulation of gastric emptying and motility following stress. It is not clear, however, whether the amelioration of dysregulated GI functions by OXT is mediated via an effect on the hypothalamic-pituitary-adrenocortical axis or the oxytocinergic projections from the paraventricular nucleus of the hypothalamus (PVN) to neurones of the dorsal vagal complex (DVC). In the present study we tested the hypothesis that the activity of hypothalamic-vagal oxytocinergic neurocircuits plays a major role in the gastric adaptation to stress. Cre-inducible designer receptors exclusively activated by designer drugs (DREADDs) were injected into the DVC of rats and retrogradely transported to allow selective expression in OXT neurones in the PVN. Following acute stress and either chronic heterotypic (CHe) or chronic homotypic (CHo) stress, gastric emptying was assessed via the [13 C]-octanoic acid breath test, and gastric tone and motility were assessed via strain gauges sewn on the surface of the stomach. Activation of the hypothalamic-vagal oxytocinergic neurocircuitry, by DREADD agonist clozapine-N-oxide (CNO), prevented the delayed gastric emptying observed following acute or CHe stress, and 4th ventricular administration of CNO increased gastric tone and motility. Conversely, CNO-mediated inhibition of the hypothalamic-vagal oxytocinergic neurocircuitry prevented the CHo-induced adaptation in gastric emptying, and an increase in gastric tone and motility. Taken together, the data support the hypothesis that hypothalamic-vagal oxytocinergic neurocircuits play a major role in the modulation of gastric emptying and motility following stress.

Long-term capture and handling effects on body condition, reproduction and survival in a semi-aquatic mammal

In long-term individual-based field studies, several parameters need to be assessed repeatedly to fully understand the potential fitness effects on individuals. Often studies only evaluate capture stress that appears in the immediate weeks or breeding season and even long-term studies fail to evaluate the long-term effects of their capture procedures. We investigated effects of long-term repeated capture and handling of individuals in a large semi-aquatic rodent using more than 20 years of monitoring data from a beaver population in Norway. To investigate the effects, we corrected for ecological factors and analysed the importance of total capture and handling events, years of monitoring and deployment of telemetry devices on measures related to body condition, reproduction and survival of individual beavers. Body mass of dominant individuals decreased considerably with number of capture events (107 g per capture), but we found no statistically clear short or long-term effects of capture and handling on survival or other body condition indices. Annual litter size decreased with increasing number of captures among older individuals. Number of captures furthermore negatively affected reproduction in the beginning of the monitoring, but the effect decreased over the years, indicating habituation to repeated capture and handling. By assessing potential impacts on several fitness-related parameters at multiple times, we can secure the welfare of wild animal populations when planning and executing future conservation studies as well as ensure ecologically reliable research data.

The impact of emotional health on assisted reproductive technology outcomes: a systematic review and meta-analysis

This systematic review and meta-analysis has addressed ongoing controversy surrounding the association between pre-treatment anxiety, stress and depression and assisted reproductive technology (ART) outcomes. Medline, Embase and PsycINFO were searched up to November 2019. The eligibility criterion was observational studies reporting the association between pre-treatment anxiety, stress or depression and ART outcomes in men, women or couples undergoing ART. The association between pre-treatment anxiety, stress and depression and ART outcomes were extracted, and meta-analyses carried out if ≥3 studies assessed the same outcome over the same number of cycles and reported results homogeneously. The review reports a potential association between decreased sperm motility and increased male state anxiety, but no significant association between women's pre-treatment emotional health and ART outcomes in terms of live birth, clinical pregnancy, chemical pregnancy, oocyte retrieval, embryos transferred or fertilization. Meta-analyses showed no significant standardized mean difference (SMD) for anxiety/stress and clinical or chemical pregnancy, or depression and clinical or chemical pregnancy.

Psychosocial stress reactivity habituates following acute physiological stress

Acute and chronic stress are important factors in the development of mental disorders. Reliable measurement of stress reactivity is therefore pivotal. Critically, experimental induction of stress often involves multiple “hits” and it is an open question whether individual differences in responses to an earlier stressor lead to habituation, sensitization, or simple additive effects on following events. Here, we investigated the effect of the individual cortisol response to intravenous catheter placement (IVP) on subsequent neural, psychological, endocrine, and autonomous stress reactivity. We used an established psychosocial stress paradigm to measure the acute stress response (Stress) and recovery (PostStress) in 65 participants. Higher IVP‐induced cortisol responses were associated with lower pulse rate increases during stress recovery (b = −4.8 bpm, p = .0008) and lower increases in negative affect after the task (b = −4.2, p = .040). While the cortisol response to IVP was not associated with subsequent specific stress‐induced neural activation patterns, the similarity of brain responses Pre‐ and PostStress was higher IVP‐cortisol responders (t[64] = 2.35, p = .022) indicating faster recovery. In conclusion, preparatory stress induced by IVP reduced reactivity in a subsequent stress task by modulating the latency of stress recovery. Thus, an individually stronger preceding release of cortisol may attenuate a second physiological response and perceived stress suggesting that relative changes, not absolute levels are crucial for stress attribution. Our study highlights that considering the entire trajectory of stress induction during an experiment is important to develop reliable individual biomarkers.

Perinatal depression: Heterogeneity of disease and in animal models

Perinatal depression (PND) can have either an antepartum or postpartum onset. Although the greatest risk factor for PND is previous depression history,de novoPND occurs with the majority of cases occurring in the postpartum. Timing of depression can impact etiology, prognosis, and response to treatment. Thus, it is crucial to study the impact of the heterogeneity of PND for better health outcomes. In this review, we outline the differences between antepartum and postpartum depression onset of PND. We discuss maternal physiological changes that differ between pregnancy and postpartum and how these may differentially impact depression susceptibility. We highlight changes in the maternal steroid and peptide hormone levels, immune signalling, serotonergic tone, metabolic factors, brain morphology, and the gut microbiome. Finally, we argue that studying the heterogeneity of PND in clinical and preclinical models can lead to improved knowledge of disease etiopathology and treatment outcomes.

Person-centered profiles of parasympathetic physiology, anxiety symptoms, and depressive symptoms in mothers and fathers of young children

Respiratory sinus arrhythmia (RSA) is a biomarker of mental health, but RSA-symptom relations in parents of young children are understudied. We examined how anxiety symptoms, depressive symptoms, resting RSA, and RSA reactivity during challenging parent-child interactions clustered in a community sample of mothers (N = 126) and fathers (N = 87) of 3-year-olds and whether profiles predicted child emotional and behavioral dysregulation at age 4. Mothers fit four profiles (Typical, Mild Risk, Moderate Risk/Withdrawal, and Moderate Risk/Augmentation), suggesting that RSA reactivity was distinct by predominant symptom type at higher levels of risk: specifically, heightened RSA withdrawal was associated with a higher probability of anxiety symptoms and RSA augmentation was associated with a higher probability of depressive symptoms. Fathers fit three profiles (Typical, Mild Risk, and Moderate Risk) where Moderate Risk was characterized by RSA augmentation and a higher probability of both anxiety and depressive symptoms. Mild risk profiles showed heightened resting RSA for mothers and fathers but no differences in RSA reactivity. Both mild and moderate risk profiles predicted higher child dysregulation 1 year later compared to typical profiles. Findings offer preliminary evidence that parasympathetic physiology covaries with symptoms differently for mothers and fathers and that parental profiles of physiology and symptoms inform children's developmental psychopathology.

Reflections on Bruce S. McEwen's contributions to stress neurobiology and so much more

The authors highlight, from a firsthand perspective, Bruce S. McEwen's seminal influence on the field of stress neurobiology and beyond, and how these investigations have yielded important insights, principles and critical questions that continue to guide stress research today. Featured are discussion of: 1) the important inverted-U relationship between stress/glucocorticoids and optimal physiological function, 2) stress adaptation and the role of adaptive stress responses, 3) mechanisms by which the short-term stress response promotes heightened immune function and immunity, and 4) the far reaching impact of the theoretical framework of allostasis and allostatic load-concepts that have created new bridges between stress physiology, biomedical sciences, health psychology and sociology.

Spontaneous recovery, time course, and circadian influence on habituation of the cardiovascular responses to repeated restraint stress in rats

We investigated the spontaneous recovery, time course, and the influence of the time of day on the habituation of the cardiovascular responses with repeated exposure to restraint stress in male rats. Habituation of the corticosterone response to repeated restraint stress was also evaluated. The circulating corticosterone response decreased during both the stress and recovery periods of the tenth session of restraint. Habituation of the cardiovascular responses was identified as a faster return to baseline values of the heart rate (HR) and blood pressure (BP) during the recovery period of the tenth session of restraint. Habituation of the HR and BP was still observed after 10 days of discontinuation of the repeated exposure to restraint stress. However, spontaneous recovery of habituated responses was observed 20 days after the final restraint stress session. Time course analysis revealed decreased HR response during the recovery period of the third restraint session, without further reduction on the fifth, seventh, and tenth sessions. Decreased BP response was identified on the third and fifth sessions, whereas reduced tail skin temperature response was observed only on the fifth and seventh sessions. Regarding the time of day, habituation of the tachycardiac response was identified at the tenth session when repeated restraint stress was performed in the morning and night periods, but not in the afternoon. These findings provided evidence of spontaneous recovery of the habituation of cardiovascular responses to repeated restraint stress. Moreover, cardiovascular habituation was dependent on the number of trials and time of day.

Repeated Restraint Stress Enhances Hepatic TFR2 Expression and Induces Hepatic Iron Accumulation in Rats

Abnormal hepatic iron metabolism is detrimental to health. The objective of this study was to detect repeated restraint stress on liver iron metabolism in rats. Twenty-four male rats aged 7 weeks were randomly divided into 2 groups: control group (Con) and repeated restraint stress group (RS). Rats were subjected to 6 h of daily restraint stress for 14 consecutive days in the repeated restraint stress group. The results showed that repeated restraint stress exposure decreased growth performance including impaired final weight (P = 0.07), reducing average daily gain (P = 0.01), and average daily feed intake (P = 0.00) during the 14-day experimental period. Repeated restraint stress exposure did not affect hemoglobin content and plasma iron parameters except downregulated unsaturated iron-binding capacity (P = 0.04). Repeated restraint stress exposure inhibited liver development (P = 0.03) and induced liver iron accumulation (P = 0.05). In addition, repeated restraint stress downregulated the expression of transferrin (TF) and transferrin receptor 2 (TFR2) at the mRNA level (P < 0.01), but upregulated at the protein level (P = 0.03 for TF; P = 0.00 for TFR2). These results indicated that repeated restraint stress induces hepatic iron accumulation, which is closely related to higher expression of hepatic TFR2 protein in rats.

Acute Regulation of Habituation Learning via Posttranslational Palmitoylation

Habituation is an adaptive learning process that enables animals to adjust innate behaviors to changes in their environment. Despite its well-documented implications for a wide diversity of behaviors, the molecular and cellular basis of habituation learning is not well understood. Using whole-genome sequencing of zebrafish mutants isolated in an unbiased genetic screen, we identified the palmitoyltransferase Huntingtin interacting protein 14 (Hip14) as a critical regulator of habituation learning. We demonstrate that Hip14 regulates depression of sensory inputs onto an identified hindbrain neuron and provide evidence that Hip14 palmitoylates the Shaker-like K+ voltage-gated channel subunit (Kv1.1), thereby regulating Kv1.1 subcellular localization. Furthermore, we show that, like for Hip14, loss of Kv1.1 leads to habituation deficits and that Hip14 is dispensable in development and instead acts acutely to promote habituation. Combined, these results uncover a previously unappreciated role for acute posttranslational palmitoylation at defined circuit components to regulate learning.

The impact of chronic stress on energy metabolism

The brain is exceptionally demanding in terms of energy metabolism. Approximately 20% of the calories consumed are devoted to our cerebral faculties, with the lion's share provided in the form of glucose. The brain's stringent energy dependency requires a high degree of harmonization between the elements responsible for supplying- and metabolizing energetic substrates. However, chronic stress may jeopardize this homeostatic energy balance by disruption of critical metabolic processes. In agreement, stress-related mental disorders have been linked with perturbations in energy metabolism. Prominent stress-induced metabolic alterations include the actions of hormones, glucose uptake and mitochondrial adjustments. Importantly, fundamental stress-responsive metabolic adjustments in humans and animal models bear a striking resemblance. Here, an overview is provided of key findings, demonstrating the pervasive impact of chronic stress on energy metabolism. Furthermore, I argue that medications, aimed primarily at restoring metabolic homeostasis, may constitute a novel approach to treat mental disorders.

Chronic unpredictable restraint stress increases hippocampal pro-inflammatory cytokines and decreases motivated behavior in rats

Most chronic stress protocols are too laborious or do not abide by the two main characteristics of the stress concept: uncontrollability and unpredictability. The goal of this study was to establish a simple and reliable model of chronic stress, while maintaining the main features of the concept. Animals were exposed to chronic movement restraint with variable duration (2, 4 or 6 h, in an unpredictable schedule) for 3 weeks and assessed in several physiological and behavioral readouts known to reflect chronic stress states. Body weight, levels of plasma corticosterone, hippocampal pro-and anti-inflammatory cytokines, anxiety-like (novelty suppressed feeding and elevated plus maze) and motivated behaviors (sucrose negative contrast test and forced swim test) were evaluated three days after the end of the chronic protocol. Stressed animals had a lower body weight gain, higher levels of cytokines in the hippocampus, reduced suppression of a low concentration sucrose solution and increased immobility in the forced swim test. Based on these data, we suggest that chronic movement restraint with variable duration may be a suitable and simple protocol for the study of changes induced by chronic stress and for the testing of possible treatments relevant to psychiatry.

Repeated Gastric Motility Measurement Affects Gastric Motility and Epigastric Symptom Sensation

Background: Gastric motility is an important determinant of gastric emptying, epigastric symptom generation, and intolerance to food. Motility is classically assessed directly using manometry or an intragastric balloon. These diagnostic methods are perceived as stressful and invasive, which, by itself might influence the readout of these assessments. Our hypothesis was that with repeated exposure to an invasive motility test the outcome would be different.

Methods: Gastric motility was assessed with a custom-made orogastric balloon catheter in 10 healthy subjects naive to intubation. A motility index ranging from 0 (no motility) to 1 (maximum motility) was calculated in the fasted state for 3.5 h. Symptoms were surveyed with visual analog scales of 100 mm. Results are presented as median (interquartile range).

Results: Motility index during visit 1 [0.40 (0.37–0.59)] was lower compared to visit 2 [0.50 (0.45–0.66); not significant] and 3 [0.63 (0.50–0.71); p = 0.016]. Nausea and pain scores were significantly higher during visit 1 (35 (2.8–126) and 103 (88–125) mm, respectively) compared with visit 3 [1 (2.8–26) mm (p = 0.016) and 75 (30–100) mm (p = 0.008), respectively]. No adverse events were observed.

Conclusions: Repeated exposure to an invasive method to assess motility resulted in more vigorous motility and lower symptom scores. Caution is warranted when interpreting functional assessments, as prior exposure to invasive tests might confound the obtained results through habituation.

Neuronal hypertrophy dampens neuronal intrinsic excitability and stress responsiveness during chronic stress

KEY POINTS

The hypothalamic-pituitary-adrenal (HPA) axis habituates to repeated stress exposure. We studied hypothalamic corticotropin-releasing hormone (CRH) neurons that form the apex of the HPA axis in a mouse model of stress habituation using repeated restraint. The intrinsic excitability of CRH neurons decreased after repeated stress in a time course that coincided with the development of HPA axis habituation. This intrinsic excitability plasticity co-developed with an expansion of surface membrane area, which increased a passive electric load and dampened membrane depolarization in response to the influx of positive charge. We report a novel structure-function relationship for intrinsic excitability plasticity as a neural correlate for HPA axis habituation.

ABSTRACT

Encountering a stressor immediately activates the hypothalamic-pituitary-adrenal (HPA) axis, but this stereotypic stress response also undergoes experience-dependent adaptation. Despite the biological and clinical importance, how the brain adjusts stress responsiveness in the long term remains poorly understood. We studied hypothalamic corticotropin-releasing hormone neurons that form the apex of the HPA axis in a mouse model of stress habituation using repeated restraint. Using patch-clamp electrophysiology in acute slices, we found that the intrinsic excitability of these neurons substantially decreased after daily repeated stress in a time course that coincided with their loss of stress responsiveness in vivo. This intrinsic excitability plasticity co-developed with an expansion of surface membrane area, which increased a passive electric load, and dampened membrane depolarization in response to the influx of positive charge. Multiphoton imaging and electron microscopy revealed that repeated stress augmented ruffling of the plasma membrane, suggesting an ultrastructural plasticity that may efficiently accommodate the membrane area expansion. Overall, we report a novel structure-function relationship for intrinsic excitability plasticity as a neural correlate for adaptation of the neuroendocrine stress response.

Habituation of the cardiovascular response to restraint stress is inhibited by exposure to other stressor stimuli and exercise training

This study evaluated the effect of exposure to either a chronic variable stress (CVS) protocol or social isolation, as well as treadmill exercise training, in the habituation of the cardiovascular response upon repeated exposure to restraint stress in rats. The habituation of the corticosterone response to repeated restraint stress was also evaluated. For this, animals were subjected to either acute or 10 daily sessions of 60 min of restraint stress. CVS and social isolation protocols lasted for 10 consecutive days, whereas treadmill training was performed for 1 h per day, 5 days per week for 8 weeks. We observed that the increase in serum corticosterone was reduced during both the stress and the recovery period of the 10th session of restraint. Habituation of the cardiovascular response was identified in terms of a faster return of heart rate to baseline values during the recovery period of the 10th session of restraint. The increase in blood pressure and the decrease in tail skin temperature were similar at the 1st and 10th session of restraint. Exposure to CVS, social isolation or treadmill exercise training inhibited the habituation of the restraint-evoked tachycardia. Additionally, CVS increased the blood pressure response at the 10th session of restraint, whereas social isolation enhanced both the tachycardia during the first session and the drop in skin temperature at the 10th session of restraint. Taken together, these findings provide new evidence that pathologies evoked by stress might be related to impairment in the habituation process to homotypic stressors.

The complex Impact of Five Years of Stress Related to Life-Threatening Events on Pregnancy Outcomes: A Preliminary Retrospective Study

Objective:

To study the impact of chronic, life-threatening stressors in the form of daily missile attacks, for five consecutive years, on pregnancy outcomes.

Method:

Charts of deliveries from two neighboring towns in the south of Israel, covering the years 2000 and 2003–2008, were reviewed retrospectively. One city had been exposed to missile attacks, while the other was not. For each year, 100 charts were chosen at random.

Results:

Significant association was found between exposure to stress and frequency of pregnancy complications (P = 0.047) and premature membrane rupture (P = 0.029). A more detailed analysis, based on dividing the stressful years into three distinct periods: early (2003–2004), intermediate (2005–2006) and late (2007–2008), revealed that preterm deliveries were significantly more frequent (P = 0.044) during the intermediate period, as was premature membrane rupture during the late period (P = 0.014).

Conclusion:

Exposure to chronic life-threatening stress resulted in more pregnancy complications and in particular more premature membrane ruptures. The impact was most significant during the middle period of the 5-year-exposure to the stressor. Hence it seems that factors of duration and habituation may play a role in the impact of chronic, life-threatening stressors on pregnancy.

A randomised controlled study of high intensity exercise as a dishabituating stimulus to improve hypoglycaemia awareness in people with type 1 diabetes: a proof-of-concept study

AIMS/HYPOTHESIS

Approximately 25% of people with type 1 diabetes have suppressed counterregulatory hormonal and symptomatic responses to insulin-induced hypoglycaemia, which renders them at increased risk of severe, disabling hypoglycaemia. This is called impaired awareness of hypoglycaemia (IAH), the cause of which is unknown. We recently proposed that IAH develops through habituation, a form of adaptive memory to preceding hypoglycaemia. Consistent with this hypothesis, we demonstrated restoration of defective counterregulatory hormonal responses to hypoglycaemia (referred to as dishabituation) in a rodent model of IAH following introduction of a novel stress stimulus (high intensity training [HIT]). In this proof-of-concept study we sought to further test this hypothesis by examining whether a single episode of HIT would amplify counterregulatory responses to subsequent hypoglycaemia in people with type 1 diabetes who had IAH (assessed by Gold score ≥4, modified Clarke score ≥4 or Dose Adjustment For Normal Eating (DAFNE) hypoglycaemia awareness rating 2 or 3). The primary outcome was the difference in adrenaline response to hypoglycaemia following both a single episode of HIT and rest.

METHODS

In this randomised, crossover study 12 participants aged between 18 and 55 years with type 1 diabetes for ≥5 years and an HbA_1c <75 mmol/mol (9%) were recruited. Individuals were randomised using computer generated block randomisation to start with one episode of HIT (4 × 30 s cycle sprints [2 min recovery] at 150% of maximum wattage achieved during [Formula: see text] assessment) or rest (control). The following day they underwent a 90 min hyperinsulinaemic-hypoglycaemic clamp study at 2.5 mmol/l with measurement of hormonal counterregulatory response, symptom scores and cognitive testing (four-choice reaction time and digit symbol substitution test). Each intervention and subsequent clamp study was separated by at least 2 weeks. The participants and investigators were not blinded to the intervention or measurements during the study. The investigators were blinded to the primary outcome and blood analysis results.

RESULTS

All participants (six male and six female, age 19-54 years, median [IQR] duration of type 1 diabetes 24.5 [17.3-29.0] years, mean [SEM] HbA_1c 56 [3.67] mmol/mol; 7.3% [0.34%]) completed the study (both interventions and two clamps). In comparison with the rest study, a single episode of HIT led to a 29% increase in the adrenaline (epinephrine) response (mean [SEM]) (2286.5 [343.1] vs 2953.8 [384.9] pmol/l); a significant increase in total symptom scores (Edinburgh Hypoglycaemia Symptom Scale: 24.25 [2.960 vs 27.5 [3.9]; p<0.05), and a significant prolongation of four-choice reaction time (591.8 [22.5] vs 659.9 [39.86] ms; p<0.01] during equivalent hypoglycaemia induced the following day.

CONCLUSIONS/INTERPRETATION

These findings are consistent with the hypothesis that IAH develops in people with type 1 diabetes as a habituated response and that introduction of a novel stressor can restore, at least partially, the adapted counterregulatory hormonal, symptomatic and cognitive responses to hypoglycaemia.

TRIAL REGISTRATION

ISRCTN15236211.

Effects of predation risk on egg steroid profiles across multiple populations of threespine stickleback

Predation often has consistent effects on prey behavior and morphology, but whether the physiological mechanisms underlying these effects show similarly consistent patterns across different populations remains an open question. In vertebrates, predation risk activates the hypothalamic-pituitary-adrenal (HPA) axis, and there is growing evidence that activation of the maternal HPA axis can have intergenerational consequences via, for example, maternally-derived steroids in eggs. Here, we investigated how predation risk affects a suite of maternally-derived steroids in threespine stickleback eggs across nine Alaskan lakes that vary in whether predatory trout are absent, native, or have been stocked within the last 25 years. Using liquid chromatography coupled with mass spectroscopy (LC-MS/MS), we detected 20 steroids within unfertilized eggs. Factor analysis suggests that steroids covary within and across steroid classes (i.e. glucocorticoids, progestogens, sex steroids), emphasizing the modularity and interconnectedness of the endocrine response. Surprisingly, egg steroid profiles were not significantly associated with predator regime, although they were more variable when predators were absent compared to when predators were present, with either native or stocked trout. Despite being the most abundant steroid, cortisol was not consistently associated with predation regime. Thus, while predators can affect steroids in adults, including mothers, the link between maternal stress and embryonic development is more complex than a simple one-to-one relationship between the population-level predation risk experienced by mothers and the steroids mothers transfer to their eggs.

Diurnal variation of salivary cortisol in captive African elephants (Loxodonta africana) under routine management conditions and in relation to a translocation event

The present study assessed the diurnal variation in salivary cortisol in captive African elephants during routine management (baseline) and in relation to a potential stressor (translocation) to evaluate to what extent acute stress may affect diurnal cortisol patterns. Under baseline conditions, we collected morning and afternoon saliva samples of 10 animals (three zoos) on different days in two study periods (n = 3-10 per animal, daytime and period). Under stress conditions, we sampled the transported cow (newcomer) and the two cows of the destination zoo before and after the transport in the morning and afternoon (n = 3-9 per animal, daytime and transport phase), as well as after the first introduction of the newcomer to the bull (n = 1 per animal). Cortisol was measured in unextracted samples by enzyme immunoassay. Under baseline conditions, we observed the expected diurnal variation with higher cortisol levels in the morning than in the afternoon. Under stress conditions, neither a significant difference between pre- and posttransport, nor between morning and afternoon levels was found. The percentage difference between morning and afternoon cortisol after the transport, however, was remarkably lower than before the transport in the newcomer potentially indicating a stress response to familiarization. Saliva samples taken immediately after the introduction of the newcomer to the bull revealed a marked cortisol increase. Our findings indicate that stressors may disturb the diurnal cortisol rhythm. Furthermore, provided that samples can be collected promptly, salivary cortisol is a useful minimally invasive measure of physiological stress in the African elephant.

The therapeutic potential of exercise for neuropsychiatric diseases: A review

Exercise is known to have a myriad of health benefits. There is much to be learned from the effects of exercise and its potential for prevention, attenuation and treatment of multiple neuropsychiatric diseases and behavioral disorders. Furthermore, recent data and research on exercise benefits with respect to major health crises, such as, that of opioid and general substance use disorders, make it very important to better understand and review the mechanisms of exercise and how it could be utilized for effective treatments or adjunct treatments for these diseases. In addition, mechanisms, epigenetics and sex differences are examined and discussed in terms of future research implications.

Immunosuppressive effect and global dysregulation of blood transcriptome in response to psychosocial stress in vervet monkeys (Chlorocebus sabaeus)

Psychosocial stressors - life events that challenge social support and relationships - represent powerful risk factors for human disease; included amongst these events are relocation, isolation and displacement. To evaluate the impact of a controlled psychosocial stressor on physiology and underlying molecular pathways, we longitudinally studied the influence of a 28-day period of quarantine on biomarkers of immune signalling, microbial translocation, glycaemic health and blood transcriptome in the wild-born vervet monkey. This event caused a coordinated, mostly transient, reduction of circulating levels of nine immune signalling molecules. These were paralleled by a massive dysregulation of blood transcriptome, including genes implicated in chronic pathologies and immune functions. Immune and inflammatory functions were enriched among the genes downregulated in response to stress. An upregulation of genes involved in blood coagulation, platelet activation was characteristic of the rapid response to stress induction. Stress also decreased neutrophils and increased CD4 + T cell proportions in blood. This model of psychosocial stress, characterised by an immune dysregulation at the transcriptomic, molecular and cellular levels, creates opportunities to uncover the underlying mechanisms of stress-related diseases with an immune component, including cardiovascular diseases and susceptibility to infections.

Corticotropin releasing factor-overexpressing mouse is a model of chronic stress-induced muscle atrophy

Chronic stress and continually high glucocorticoid levels can induce muscle atrophy. Unfortunately, there is a lack of appropriate animal models for stress-induced muscle atrophy research. Corticotropin releasing factor-overexpressing (CRF-OE) mice are a transgenic model of chronic stress that exhibit increased plasma corticosterone levels and Cushing’s syndrome; however, the skeletal muscle pathology of the CRF-OE mouse has not been well studied. We observed that male, 19-week-old CRF-OE mice had significantly lower skeletal muscle mass, average cross-sectional myofiber area, and total muscle protein content than their wild type (WT) littermates. Muscle function determined by grip strength, wire-hang, and open field tests showed that 19-week-old male CRF-OE mice had impaired physical ability. Additionally, the skeletal muscles of CRF-mice exhibited decreased expression of factors involved in the IGF-1/AKT/mTOR protein synthesis pathway and increased ubiquitin proteasome pathway activity compared to the WT control mice. In conclusion, 19-week-old CRF-OE mice display numerous features of muscle atrophy and thus serve as a model for investigating stress-induced muscle atrophy and interventions to target the deleterious effects of stress on skeletal muscle.

Sex differences: Transcriptional signatures of stress exposure in male and female brains

More than two-thirds of patients suffering from stress-related disorders are women but over two-thirds of suicide completers are men. These are just some examples of the many sex differences in the prevalence and manifestations of stress-related disorders, such as major depressive disorder, post-traumatic stress disorder, and anxiety disorders, which have been extensively documented in clinical research. Nonetheless, the molecular origins of this sex dimorphism are still quite obscure. In response to this lack of knowledge, the NIH recently advocated implementing sex as biological variable in the design of preclinical studies across disciplines. As a result, a newly emerging field within psychiatry is trying to elucidate the molecular causes underlying the clinically described sex dimorphism. Several studies in rodents and humans have already identified many stress-related genes that are regulated by acute and chronic stress in a sex-specific fashion. Furthermore, current transcriptomic studies have shown that pathways and networks in male and female individuals are not equally affected by stress exposure. In this review, we give an overview of transcriptional studies designed to understand how sex influences stress-specific transcriptomic changes in rodent models, as well as human psychiatric patients, highlighting the use of different methodological techniques. Understanding which mechanisms are more affected in males, and which in females, may lead to the identification of sex-specific mechanisms, their selective contribution to stress susceptibility, and their role in the development of stress-related psychiatric disorders.

Mid and hindgut transcriptome profiling analysis of Atlantic salmon (Salmon salar) under unpredictable chronic stress

The intestinal epithelium is a selectively permeable barrier for nutrients, electrolytes and water, while maintaining effective protection against pathogens. Combinations of stressors throughout an animal's life, especially in agriculture and aquaculture settings, may affect the regular operativity of this organ with negative consequences for animal welfare. In the current study, we report the effects of a three-week unpredictable chronic stress (UCS) period on the intestinal morphology and transcriptome response of Atlantic salmon (Salmon salar) parr midgut and hindgut. Midgut and hindgut from both control and UCS fish were collected for histology and RNA-sequencing analysis to identify respective changes in the membrane structures and putative genes and pathways responding to UCS. Histological analysis did not show any significant effect on morphometric parameters. In the midgut, 1030 genes were differentially expressed following UCS, resulting in 279 genes which were involved in 13 metabolic pathways, including tissue repair pathways. In the hindgut, following UCS, 591 differentially expressed genes were detected with 426 downregulated and 165 upregulated. A total of 53 genes were related to three pathways. Downregulated genes include cellular senescence pathways, p53 signalling and cytokine-cytokine receptor pathways. The overall results corroborate that salmon parr were at least partly habituating to the UCS treatment. In midgut, the main upregulation was related to cell growth and repair, while in the hindgut there were indications of the activated apoptotic pathway, reduced cell repair and inhibited immune/anti-inflammatory capacity. This may be the trade-off between habituating to UCS and health resilience. This study suggests possible integrated genetic regulatory mechanisms that are tuned when farmed Atlantic salmon parr attempt to cope with UCS.

Psychosocial work stressors, high family responsibilities, and psychological distress among women: A 5-year prospective study

BACKGROUND

Psychological distress is a strong and independent predictor of major depression. Assuming multiple roles (such as being both a mother and an employee) under stressful conditions may lead to psychological distress. This study evaluated, for the first time, the longitudinal effect of the simultaneous exposure to psychosocial work stressors and high family responsibilities on women's psychological distress.

METHODS

Women were assessed at baseline (N = 1307) and at 3- and 5-year follow-ups. Psychosocial work stressors of the demand-control and effort-reward imbalance models were measured with validated questionnaires. Family responsibilities were also self-reported and referred to the number of children and their age(s) as well as housework and childcare. Psychological distress was measured with the validated Psychiatric Symptoms Index questionnaire. Prevalence ratios (PR) of psychological distress were modeled with log-binomial regressions.

RESULTS

Having high family responsibilities did not increase women's prevalence of psychological distress. However, being exposed to either job strain or effort-reward imbalance led to a higher prevalence of psychological distress at the 3- and 5-year follow-ups (PR of 1.25-1.62). Being simultaneous exposed to these psychosocial work stressors and high family responsibilities also increased the prevalence of psychological distress (PR of 1.44-1.87), but no interactions were observed between stressors and responsibilities.

CONCLUSIONS

In this 5-year prospective study, simultaneous exposure to psychosocial work stressors and high family responsibilities increased the prevalence of psychological distress among women. Work stressors were, however, driving most of the effect, which reinforces their importance as modifiable risk factors of women's mental health problems.

Premature birth stunts early growth and is a possible driver of stress-induced maternal effects in the guppy Poecilia reticulata

We tested the effects of gestational stress, principally in the form of alarm cue extracted from the skin of conspecifics, on reproduction in female guppies (Poecilia reticulata) and the growth and behaviour of their offspring. Offspring from mothers exposed to alarm cue exhibited stunted growth in the first few days post-partum, which appeared to be mediated by shortening of the gestation period, the length of which directly correlated with growth rate within the first 6 days post-partum. Mature offspring did not differ in behaviour or stress responses compared with controls and so the effects of maternal predation stress did not appear to persist into adulthood. A different form of gestational stress, dietary restriction, did not significantly affect offspring growth, though brood size was reduced, suggesting that the effects of predation stress were not mediated by differences in resource demand or consumption.

Chronic unpredictable intermittent restraint stress disrupts spatial memory in male, but not female rats

Chronic stress leads to sex-dependent outcomes on spatial memory by producing deficits in males, but not in females. Recently it was reported that compared to daily restraint, intermittent restraint (IR) produced more robust stress and anxiety responses in male rats. Whether IR would be sufficiently robust to impair hippocampal-dependent spatial memory in both male and female rats was investigated. IR involved mixing restraint with non-restraint days over weeks before assessing spatial memory and anxiety profile on the radial arm water maze, object placement, novel object recognition, Y-maze, open field and novelty suppressed feeding. Experiments 1 and 2 used Sprague-Dawley male rats only and determined that IR for 6 h/d (IR6), but not 2 h/d, impaired spatial memory and that task order was important. In experiment 3, IR6 was extended for 6wks before spatial memory testing commenced using both sexes. Unexpectedly, an extended IR6 paradigm failed to impair spatial memory in either sex, suggesting that by 6wks IR6 may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not in females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not in females. We interpret these findings to show that females are more resilient to chronic stress than are males as it pertains to spatial ability.

Repeated Exposure to Multiple Concurrent Stresses Induce Circuit Specific Loss of Inputs to the Posterior Parietal Cortex

Severe loss of excitatory synapses in key brain regions is thought to be one of the major mechanisms underlying stress-induced cognitive impairment. To date, however, the identity of the affected circuits remains elusive. Here we examined the effect of exposure to repeated multiple concurrent stressors (RMS) on the connectivity of the posterior parietal cortex (PPC) in adolescent male mice. We found that RMS led to layer-specific elimination of excitatory synapses with the most pronounced loss observed in deeper cortical layers. Quantitative analysis of cortical projections to the PPC revealed a significant loss of sensory and retrosplenial inputs to the PPC while contralateral and frontal projections were preserved. These results were confirmed by decreased synaptic strength from sensory, but not from contralateral, projections in stress-exposed animals. Functionally, RMS disrupted visuospatial working memory performance, implicating disrupted higher-order visual processing. These effects were not observed in mice subjected to restraint-only stress for an identical period of time. The PPC is considered to be a cortical hub for multisensory integration, working memory, and perceptual decision-making. Our data suggest that sensory information streams targeting the PPC may be impacted by recurring stress, likely contributing to stress-induced cognitive impairment.SIGNIFICANCE STATEMENT Repeated exposure to stress profoundly impairs cognitive functions like memory, attention, or decision-making. There is emerging evidence that stress not only impacts high-order regions of the brain, but may affect earlier stages of cognitive processing. Our work focuses on the posterior parietal cortex, a brain region supporting short-term memory, multisensory integration, and decision-making. We show evidence that repeated stress specifically damages sensory inputs to this region. This disruption of synaptic connectivity is linked to working memory impairment and is specific to repeated exposure to multiple stressors. Altogether, our data provide a potential alternative explanation to ailments previously attributed to downstream, cognitive brain structures.

Evidence for Similar Prefrontal Structural and Functional Alterations in Male and Female Rats Following Chronic Stress or Glucocorticoid Exposure

Previous work of ours and others has documented regressive changes in neuronal architecture and function in the medial prefrontal cortex (mPFC) of male rats following chronic stress. As recent focus has shifted toward understanding whether chronic stress effects on mPFC are sexually dimorphic, here we undertake a comprehensive analysis to address this issue. First, we show that chronic variable stress (14-day daily exposure to different challenges) resulted in a comparable degree of adrenocortical hyperactivity, working memory impairment, and dendritic spine loss in mPFC pyramidal neurons in both sexes. Next, exposure of female rats to 21-day regimen of corticosterone resulted in a similar pattern of mPFC dendritic spine attrition and increase in spine volume. Finally, we examined the effects of another widely used regimen, chronic restraint stress (CRS, 21-day of daily 6-h restraint), on dendritic spine changes in mPFC in both sexes. CRS resulted in response decrements in adrenocortical output (habituation), and induced a pattern of consistent, but less widespread, dendritic spine loss similar to the foregoing challenges. Our data suggest that chronic stress or glucocorticoid exposure induces a relatively undifferentiated pattern of structural and functional alterations in mPFC in both males and females.

The hypothalamic-pituitary-adrenal axis as a substrate for stress resilience: Interactions with the circadian clock

Stress, primarily processed via the hypothalamic-pituitary-adrenal (HPA) axis, engages biological pathways throughout the brain and body which promote adaptation and survival to changing environmental demands. Adaptation to environmental challenges is compromised when these pathways are no longer functioning optimally. The physiological and behavioral mechanisms through which HPA axis function influences stress adaptation and resilience are not fully elucidated. Our understanding of stress biology and disease must take into account the complex interactions between the endocrine system, neural circuits, and behavioral coping strategies. In addition, further consideration must be taken concerning influences of other aspects of physiology, including the circadian clock which is critical for regulation of daily changes in HPA activity. While adding a layer of complexity, it also offers targets for intervention. Understanding the role of HPA function in mediating these diverse biological responses will lead to important insights about how to bolster successful stress adaptation and promote stress resilience.

Stress experience and hormone feedback tune distinct components of hypothalamic CRH neuron activity

Stress leaves a lasting impression on an organism and reshapes future responses. However, the influence of past experience and stress hormones on the activity of neural stress circuits remains unclear. Hypothalamic corticotropin-releasing hormone (CRH) neurons orchestrate behavioral and endocrine responses to stress and are themselves highly sensitive to corticosteroid (CORT) stress hormones. Here, using in vivo optical recordings, we find that CRH neurons are rapidly activated in response to stress. CRH neuron activity robustly habituates to repeated presentations of the same, but not novel stressors. CORT feedback has little effect on CRH neuron responses to acute stress, or on habituation to repeated stressors. Rather, CORT preferentially inhibits tonic CRH neuron activity in the absence of stress stimuli. These findings reveal how stress experience and stress hormones modulate distinct components of CRH neuronal activity to mediate stress-induced adaptations.

Stress activates corticotropin-releasing hormone (CRH) neurons in the hypothalamus, but how their activity is regulated during and after stress is unclear. Here, the authors show that stress habituation and corticosteroid feedback tune different components of CRH neuron activity.

Reframing the individual stress response: Balancing our knowledge of stress to improve responsivity to stressors

Although responses to stressors have both adverse and positive consequences on health, many believe that stress is entirely negative. Research revealed that negative beliefs about stress can hinder well-being and result in the avoidance of stressors. Stress-optimizing interventions that target various stress appraisal processes may be a useful tool to reframe how individuals understand and respond to stressors. The current study extends previous findings on stress reframing and sought to examine the extent to which the presentation of information about stress outcomes may influence the individual to respond to subsequent stressors. Seventy-seven undergraduate students (96% female) were randomized into one of four reframing conditions (balanced stress outcomes, negative stress outcomes, positive stress outcomes, and control) and underwent a psychosocial stressor. Results highlight similarities between balanced and positive framings of stress across measures of heart rate and blood pressure, whereas subjective ratings of stress and electrodermal activity suggest balanced framing may be efficacious in attenuating stress. Findings are discussed in the context of differing stress-optimizing interventions and consider the complexities of the individual stress response.

Older Adults' Empathy and Daily Support Exchanges

Older adults' empathy may shape the frequency and types of support that they exchange with their social partners as well as the implications of these exchanges. This study drew on the Daily Experiences and Well-being Study, which included adults aged 65 and over and tracked them across 5 to 6 days using mobile phone surveys. Participants (n = 293) rated their empathy and reported their daily support exchanges (e.g., emotional support, instrumental support, advice) as well as mood. Findings showed that more empathic older adults provided each type of support more often. They also received more emotional support than less empathic older adults. Moreover, older adults' empathy moderated the associations between providing support and their daily mood. More empathic older adults maintained their mood regardless of whether they provided support. By contrast, less empathic older adults reported reduced positive mood on days when they provided emotional support and increased positive mood when they provided instrumental support. Greater empathy is associated with more frequent support exchanges; however, more empathic older adults appear immune to such exchanges in terms of their mood. Interestingly, less empathic older adults may find providing emotional support draining but instrumental support rewarding, probably because they are less equipped to cope with others' emotions.

Regulation of NMDA Receptor Plasticity in the BNST Following Adolescent Alcohol Exposure

Persistent alterations in synaptic plasticity and neurotransmission are thought to underlie the heightened risk of adolescent-onset drinkers to develop alcohol use disorders in adulthood. The bed nucleus of the stria terminalis (BNST) is a compelling region to study the consequences of early alcohol, as it is innervated by cortical structures which undergo continued maturation during adolescence and is critically involved in stress and negative affect-associated relapse. In adult mice, chronic ethanol induces long-term changes in GluN2B-containing NMDA receptors (NMDARs) of the BNST. It remains unclear, however, whether the adolescent BNST is susceptible to such persistent alcohol-induced modifications and, if so, whether they are preserved into adulthood. We therefore examined the short- and long-term consequences of adolescent intermittent ethanol exposure (AIE) on NMDAR transmission and plasticity in the BNST of male and female mice. Whole-cell voltage clamp recordings revealed greater glutamatergic tone in the BNST of AIE-treated males and females relative to air-controls. This change, which corresponded to an increase in presynaptic glutamate release, resulted in altered postsynaptic NMDAR metaplasticity and enhanced GluN2B transmission in males but not females. Only AIE-treated males displayed upregulated GluN2B expression (determined by western blot analysis). While these changes did not persist into adulthood under basal conditions, exposing adult males (but not females) to acute restraint stress reinstated AIE-induced alterations in NMDAR metaplasticity and GluN2B function. These data demonstrate that adolescent alcohol exposure specifically modifies NMDARs in the male BNST, that the plastic changes to NMDARs are long-lasting, and that they can be engaged by stress.

Effect of cooled perches on the efficacy of an induced molt in White Leghorn laying hens previously exposed to heat stress

This study examined the effect of water-chilled perches on hen production and physiological responses to induced molt during elevated temperatures. A total of 288White Leghorns at 82 wk of age were housed in 36 cages of 6 banks. Each bank was assigned to 1 of 3 treatments: cooled perches, air perches, and no perches. The hens were subjected to 2 heat episodes during their first laying cycle at week 21 to 35 and week 73 to 80, respectively. The hens were subjected to a 28 D nonfasted molting regimen starting at 85 wk of age. Cyclic heat of 32°C (6:00 am to 6:00 pm) was applied daily during the molting period. After molt, hens were returned to a layer diet and housed under thermoneutral condition. Two birds per cage were monitored for BW change during molt. Egg production was recorded daily. Feed utilization was measured during molt at 86 and 88 wk of age. Egg weight and eggshell traits were examined at 84 wk (pre-molt) and post-molt at 92, 96, and 104 wk of age. Rectal temperature and blood samples were collected from 2 birds per cage at the end of molt. Blood samples were used for determining heterophil/lymphocyte ratio, corticosterone, and thyroid hormones. Plumage condition was examined at 22 wk post-molt. Compared to control and air perch hens, cooled perch hens had higher feed usage and greater BW loss, lower heterophil/lymphocyte ratios (P < 0.05) with no difference in thyroid hormones and corticosterone at the end of molt. Cooled perch hens also had higher egg production beginning at 98 wk of age (Ptreatment*age < 0.0001) than control hens and sometimes the air-perch hens. Cooled perch hens had higher rectal temperature than control but not air perch hens at end of molt. Moreover, cooled perch hens had better breast feather scores than air perch hens but worse vent plumage (P ≤ 0.05) than both control and air perch hens. These results indicate that the provision of cooled perches assists hens with better adaptation to stressors, such as induced molt plus heat exposure, resulting in improved post-molt egg production.

Adaptive and maladaptive emotion processing and regulation, and the case of alexithymia

In this conceptual review, we discuss models of emotion and its regulation and identify a spectrum of processes that characterise adaptive adjustment to the affective environment. We describe a dynamic-phasic model of emotion processing and regulation, focusing on five stages: anticipation, response, recovery, habituation and rest as part of a cascade of responses to emotional challenges, as these become progressively expected, proximal, chronic or repeated. We argue for the need to investigate beyond simple reactivity to emotional stimuli, in order to understand mental and physical health conditions where emotional dysregulation plays a role. We propose that a hallmark of an effective and adaptive emotion regulation system is its flexibility, in the service of life goals and values. Consistent with McEwen's model (1998, Stress, adaptation, and disease: Allostasis and allostatic load. Annals of the New York Academy of Sciences, 840(1), 33-44), inflexible emotion regulation can lead to increased allostatic load, from frequent stress, inadequate reactivity, failed shutdown and habituation, which may result in physical and mental illness. Alexithymia exemplifies inflexible emotion regulation, with dysfunctions potentially across all stages of emotion processing, both psychologically and physiologically. These maladaptive processes and their consequence on allostatic load potentially explain the association between alexithymia and physical and mental illness.

The Impact of Situational Test Anxiety on Retest Effects in Cognitive Ability Testing: A Structural Equation Modeling Approach

When a cognitive ability is assessed repeatedly, test scores and ability estimates are often observed to increase across test sessions. This phenomenon is known as the retest (or practice) effect. One explanation for retest effects is that situational test anxiety interferes with a testee's performance during earlier test sessions, thereby creating systematic measurement bias on the test items (interference hypothesis). Yet, the influence of anxiety diminishes with test repetitions. This explanation is controversial, since the presence of measurement bias during earlier measurement occasions cannot always be confirmed. It is argued that people from the lower end of the ability spectrum become aware of their deficits in test situations and therefore report higher anxiety (deficit hypothesis). In 2014, a structural equation model was proposed that specifically allows the comparison of these two hypotheses with regard to explanatory power for the negative anxiety-ability correlation found in cross-sectional assessments. We extended this model for usage in longitudinal studies to investigate the impact of test anxiety on test performance and on retest effects. A latent neighbor-change growth curve was implemented into the model that enables an estimation of retest effects between all pairs of successive test sessions. Systematic restrictions on model parameters allow testing the hypothetical reduction in anxiety interference over the test sessions, which can be compared to retest effect sizes. In an empirical study with seven measurement occasions, we found that a substantial reduction in interference upon the second test session was associated with the largest retest effect in a figural matrices test, which served as a proxy measure for general intelligence. However, smaller retest effects occurred up to the fourth test administration, whereas evidence for anxiety-induced measurement bias was only produced for the first two test sessions. Anxiety and ability were not negatively correlated at any time when the interference effects were controlled for. Implications, limitations, and suggestions for future research are discussed.

Differential effects of dopamine D1-like and D2-like receptor agonists on water drinking behaviour under thirsty conditions in mice with reduced dopamine secretion

The mesolimbic dopamine system is important for reward-oriented behaviours, such as drinking and eating. However, the precise involvement of dopaminergic neurons and dopamine receptors in water drinking behaviour remains unclear. Here, we generated triple transgenic mice harbouring Slc6a3(DAT)-icre/ERT2, Camk2a-loxP-STOP-loxP-tetracycline transactivator and tetO-tetanus toxin constructs, in which the release of dopamine is blocked by tetanus toxin. These mice, referred to as dopamine secretion interference mice, had reduced dopamine secretion in the striatum (61.4%) and the nucleus accumbens (54.5%). They showed adequate limb strength and food consumption, similarly to control mice, but exhibited motor control impairment in a challenging rotarod test. Dopamine secretion interference mice made fewer licks and had fewer bursts than control mice during a licking test under thirsty conditions. To elucidate the influence of dopamine receptors in the altered drinking behaviour, a dopamine D1 or D2/D3 receptor agonist (A68930 or ropinirole, respectively) was administered prior to the licking microstructure analysis. Treatment with the D1 agonist restored the total number of licks but not the burst number in dopamine secretion interference mice. By contrast, the D2/3 agonist impeded water drinking behaviour in both transgenic and control mice. The present findings indicate that D1 receptor activation partially ameliorates the altered drinking behaviour of the dopamine secretion interference mice and suggest that D1 receptor activity impacts drinking under thirsty conditions.

Active behaviour during early development shapes glucocorticoid reactivity

Glucocorticoids are the final effectors of the stress axis, with numerous targets in the central nervous system and the periphery. They are essential for adaptation, yet currently it is unclear how early life events program the glucocorticoid response to stress. Here we provide evidence that involuntary swimming at early developmental stages can reconfigure the cortisol response to homotypic and heterotypic stress in larval zebrafish (Danio rerio), also reducing startle reactivity and increasing spontaneous activity as well as energy efficiency during active behaviour. Collectively, these data identify a role of the genetically malleable zebrafish for linking early life stress with glucocorticoid function in later life.

Sex- and Stress-Dependent Effects on Dendritic Morphology and Spine Densities in Putative Orexin Neurons

We recently found that non-stressed female rats have higher basal prepro-orexin expression and activation of orexinergic neurons compared to non-stressed males, which lead to impaired habituation to repeated restraint stress at the behavioral, neural, and endocrine level. Here, we extended our study of sex differences in the orexin system by examining spine densities and dendritic morphology in putative orexin neurons in adult male and female rats that were exposed to 5 consecutive days of 30-min restraint. Analysis of spine distribution and density indicated that putative orexinergic neurons in control non-stressed females had significantly more dendritic spines than those in control males, and the majority of these were mushroom spines. This morphological finding may suggest more excitatory input onto orexin neurons in female rats. As orexin neurons are known to promote the hypothalamic-pituitary-adrenal response, this morphological change in orexin neurons could underlie the impaired habituation to repeated stress in female rats. Dendritic complexity did not differ between non-stressed males and females, however repeated restraint stress decreased total dendritic length, nodes, and branching primarily in males. Thus, reduced dendritic complexity of putative orexinergic neurons is observed in males but not in females after 5days of repeated restraint stress. This morphological change might be reflective of decreased orexin system function, which may allow males to habituate more fully to repeated restraint than females. These results extend our understanding of the role of orexin neurons in regulating habituation and demonstrate changes in putative orexin cell morphology and spines that may underlie sex differences in habituation.

Adult-generated neurons born during chronic social stress are uniquely adapted to respond to subsequent chronic social stress

Chronic stress is a recognized risk factor for psychiatric and psychological disorders and a potent modulator of adult neurogenesis. Numerous studies have shown that during stress, neurogenesis decreases; however, during the recovery from the stress, neurogenesis increases. Despite the increased number of neurons born after stress, it is unknown if the function and morphology of those neurons are altered. Here we asked whether neurons in adult mice, born during the final 5 days of chronic social stress and matured during recovery from chronic social stress, are similar to neurons born with no stress conditions from a quantitative, functional and morphological perspective, and whether those neurons are uniquely adapted to respond to a subsequent stressful challenge. We observed an increased number of newborn neurons incorporated in the dentate gyrus of the hippocampus during the 10-week post-stress recovery phase. Interestingly, those new neurons were more responsive to subsequent chronic stress, as they showed more of a stress-induced decrease in spine density and branching nodes than in neurons born during a non-stress period. Our results replicate findings that the neuronal survival and incorporation of neurons in the adult dentate gyrus increases after chronic stress and suggest that such neurons are uniquely adapted in the response to future social stressors. This finding provides a potential mechanism for some of the long-term hippocampal effects of stress.