One aspect of the Reactive Scope Model is wear-and-tear, which describes a decrease in an animal’s ability to cope with a stressor, typically because of a period of chronic or repeated stressors. We investigated whether wear-and-tear due to chronic stress would accelerate a transition from phase II to phase III of fasting. We exposed house sparrows (Passer domesticus) to three weeks of daily fasts combined with daily intermittent repeated acute stressors to create chronic stress, followed by two weeks of daily fasts without stressors. We measured circulating glucose, β-hydroxybutyrate (a ketone), and uric acid in both fasted and fed states. We expected birds to be in phase II (high fat breakdown) in a fasted state, but if wear-and-tear accumulated sufficiently, we hypothesized a shift to phase III (high protein breakdown). Throughout the experiment, the birds exhibited elevated β-hydroxybutyrate when fasting but no changes in circulating uric acid, indicating that a transition to phase III did not occur. In both a fasted and fed state, the birds increased glucose mobilization throughout the experiment, suggesting wear-and-tear occurred, but was not sufficient to induce a shift to phase III. Additionally, the birds exhibited a significant decrease in weight, no change in corticosterone, and a transient decrease in neophobia with chronic stress. In conclusion, the birds appear
to have experienced wear-and-tear, but our protocol did not accelerate the transition from phase II to phase III of fasting.
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Varying intensities of chronic stress induce inconsistent responses in weight and plasma metabolites in house sparrows ( Passer domesticus )
One of the biggest unanswered questions in the field of stress physiology is whether variation in chronic stress intensity will produce proportional (a gradient or graded) physiological response. We were specifically interested in the timing of the entrance into homeostatic overload, or the start of chronic stress symptoms. To attempt to fill this knowledge gap we split 40 captive house sparrows (
- Award ID(s):
- 1655269
- NSF-PAR ID:
- 10469511
- Publisher / Repository:
- PeerJ
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 11
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- e15661
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract To further elucidate the role that wear‐and‐tear plays in the transition from acute to chronic stress, we manipulated the intensity and duration of applied chronic stress to determine if behavior would respond proportionately. We brought wild house sparrows into captivity and subjected them to high‐stress, medium‐stress, low‐stress, or captivity‐only. We varied the number of stressors per day and the duration of stress periods to vary wear‐and‐tear, and thus the potential to exhibit chronic stress symptoms. The behaviors we assessed were neophobia (the fear of the new; assessed via food approach latency) and perch hopping (activity). We predicted that our birds would show proportionate decreases in neophobia and activity throughout a long‐term chronic stress paradigm. Our results indicate that neophobia is sensitive to the intensity of chronic stress, however, the birds became more neophobic, which was the opposite of what we expected. Conversely, perch hopping did not differ across treatment groups and is thus not sensitive to the intensity of chronic stress. Together, these data show that different behavioral measurements are impacted differently by chronic stress.
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null (Ed.)Stress is known to affect health throughout life and into future generations, but the underlying molecular mechanisms are unknown. We tested the hypothesis that maternal psychosocial stress influences DNA methylation (DNAm), which in turn impacts newborn health outcomes. Specifically, we analyzed DNAm at individual, regional, and genome-wide levels to test for associations with maternal stress and newborn birth weight. Maternal venous blood and newborn cord blood (n = 24 and 22, respectively) were assayed for methylation at ∼450,000 CpG sites. Methylation was analyzed by examining CpG sites individually in an epigenome-wide association study (EWAS), as regional groups using variably methylated region (VMR) analysis in maternal blood only, and through the epigenome-wide measures using genome-wide mean methylation (GMM), Horvath's epigenetic clock, and mitotic age. These methylation measures were tested for association with three measures of maternal stress (maternal war trauma, chronic stress, and experience of sexual violence) and one health outcome (newborn birth weight). We observed that maternal experiences of war trauma, chronic stress, and sexual assault were each associated with decreased newborn birth weight (p < 1.95 × 10-7 in all cases). Testing individual CpG sites using EWAS, we observed no associations between DNAm and any measure of maternal stress or newborn birth weight in either maternal or cord blood, after Bonferroni multiple testing correction. However, the top-ranked CpG site in maternal blood that associated with maternal chronic stress and sexual violence before multiple testing correction is located near the SPON1 gene. Testing at a regional level, we found increased methylation of a VMR in maternal blood near SPON1 that was associated with chronic stress and sexual violence after Bonferroni multiple testing correction (p = 1.95 × 10-7 and 8.3 × 10-6, respectively). At the epigenomic level, cord blood GMM was associated with significantly higher levels of war trauma (p = 0.025) and was suggestively associated with sexual violence (p = 0.053). The other two epigenome-wide measures were not associated with maternal stress or newborn birth weight in either tissue type. Despite our small sample size, we identified associations even after conservative multiple testing correction. Specifically, we found associations between DNAm and the three measures of maternal stress across both tissues; specifically, a VMR in maternal blood and GMM in cord blood were both associated with different measures of maternal stress. The association of cord blood GMM, but not maternal blood GMM, with maternal stress may suggest different responses to stress in mother and newborn. It is noteworthy that we found associations only when CpG sites were analyzed in aggregate, either as VMRs or as a broad summary measure of GMM.more » « less
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Abstract Chronic stress has been extensively studied in both laboratory and field settings; however, a conclusive and consistent phenotype has not been reached. Several studies have reported attenuation of the hypothalamic–pituitary–adrenal axis during experiments intended to cause chronic stress. We sought to determine whether this attenuation could be indicative of habituation. Importantly, we were not investigating habituation to a specific stimulus—as many stress physiology studies do—but rather we assessed how the underlying physiology and behavior changed in response to repeated stressor presentation. We exposed house sparrows (
Passer domesticus ) to a single stimulus twice per day at random times for 8 consecutive days. We predicted that this period of time would be long enough for the birds to determine that these acute stressors were not, in fact, dangerous and they would, therefore, acclimate. A second control group remained undisturbed for the same period of time. We measured baseline, stress‐induced, negative feedback strength, and maximum production of corticosterone as well as neophobic behavior before, during, and after this 8‐day experiment. When birds experienced a stimulus for 4 days, their negative feedback strength was significantly diminished, but recovered after the second 4 days. Additionally, perch hopping decreased and recovered in this same time frame. These data suggest that distinct physiological and behavioral responses arise when house sparrows are exposed to the same stressor for several consecutive days as opposed to many stressors layered on top of one another. Furthermore, they indicate that habituation—as with chronic stress—can appear differently depending on the metric being examined. -
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Theories such as social baseline theory have argued that social groups serve a regulatory function but have not explored whether this regulatory process carries costs for the group. Allostatic load, the wear and tear on regulatory systems caused by chronic or frequent stress, is marked by diminished stress system flexibility and compromised recovery. We argue that allostatic load may develop within social groups as well and provide a model for how relationship dysfunction operates. Social allostatic load may be characterized by processes such as groups becoming locked into static patterns of interaction and may ultimately lead to up-regulation or down-regulation of a group’s set point, or the optimal range of arousal or affect around which the group tends to converge. Many studies of emotional and physiological linkage within groups have reported that highly correlated states of arousal, which may reflect failure to maintain a group-level regulatory baseline, occur in the context of stress, conflict, and relationship distress. Relationship strain may also place greater demands on neurocognitive regulatory processes. Just as allostatic load may be detrimental to individual health, social allostatic load may corrode relationship quality.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.7717/peerj.15661
