Lactation and stress: protective effects of breast-feeding in humans

Whilst most research on breast-feeding has been designed to assess its importance for infant health or to find a human nutrient replacement for infant formula, the effects of breast-feeding on maternal health have received little scientific attention. In several animal studies lactation has been shown to be associated with a marked blunting of physiological and behavioral responses to physical and psychological stress. However, the literature on the effects of lactation on stress in humans remains limited. This review focuses primarily on recent findings on the effects of breast-feeding on neuroendocrine and behavioral responses to acute stress exposure in lactating women. The available data suggest that breast-feeding suppresses the hypothalamic-pituitary-adrenal (HPA) axis response to physical and psychosocial stress. However, lactation in women, in contrast to lactating rats, does not seem to result in a general restraint of the endocrine stress response during the whole period of lactation. Recent data strongly suggest that the blunted HPA axis response to stress in women seems to be counterbalanced if the acute stressor, at least when of a psychosocial nature, occurs later than 1 h after suckling. Further elucidation of the underlying psychobiological mechanisms involved in suppressed stress responses during lactation will no doubt lead to new insights into improved health sequelae of breast-feeding in women and to a better understanding of the psychobiology of human stress protection in general.     

Feedback effects on sequential ordering in humans

Under various feedback conditions, 38 college undergraduates were asked to rearrange abstract graphic characters on a computer screen, placing them in arbitrarily designated “correct” sequences. Two sets of seven horizontally arrayed stimuli were used. In Experiment 1, subjects in Group 1 learned to arrange the first set under Selection Feedback in which a “+” appeared above each character after it was selected in the correct order and to arrange the second set under Order Feedback in which a correct response produced a copy of the character in its correct ordinal position at the top of the screen. For Group 2 the order of these conditions was reversed. In Experiment 2, for subjects in Group 3, correct responses produced neither of these types of feedback. Subjects in Group 4 received Order Feedback only until the first set was correctly ordered once. Order Feedback was more effective than Selection Feedback during initial acquisition of the first set but not during maintenance; no differences were found for the second set. Only 2 of 9 subjects successfully put the characters in correct sequential order under the No Feedback condition. When, in Experiment 2, Order Feedback was eliminated after the first correctly arranged sequence, the steady-state criteria were met more slowly than in Experiment 1.     

Relationship between dispositional optimism/pessimism and stress coping strategies

Recent studies confirm that dispositional pessimism is related with a worse state of physical health, in comparison with dispositional optimism . The efficacy of stress coping strategies has been considered as a mediating mechanism in this relationship. The aim of the present study is to analyze in a sample of university students (n = 200) the association between dispositional optimism/pessimism and different categories of self-reported somatic symptoms , and evaluate the possible mediation of the stress coping strategies in this relationship. The results indicate that: 1) pessimism is positively related with the report of physical symptoms, whereas optimism is negatively associated to somatic complaints; and 2) this relationship can be mainly explained by the differential utilization of the coping strategy denominated self-criticism (characteristic of pessimism).     

Diagnosis of posttraumatic stress disorder with the MMPI: PK scale scores in somatization disorder

Clinic patients with diagnoses of either major depression or somatization disorder were given the MMPI. Women with somatization disorder had high scores on Keane's MMPI scale (PK) for posttraumatic stress disorder. Following the procedure for the MMPI-2 (46 of the 49 PK items and MMPI-2 norms), 59% of the women with somatization disorder and 21% of the women with major depression would have T scores > or = 65 on the MMPI-2 scale although none of them were known to have developed psychiatric disorder after exposure to a life threatening event. The PK scale has little use in the differential diagnosis of women patients with somatization disorder.     

Relationship between parental discipline and children's ability to cope with stress

A questionnaire was developed to assess the use of disciplinary methods by parents regarding their children's approach to fearful situations. The predictive validity of this tool was evaluated by correlational analyses with the assessment of fear (behavioral, subjective, and physiological) in their children during hospitalizations for surgery. The results confirmed the usefulness of the questionnaire. Parents who reported use of positive reinforcement, modeling, and persuasion as ways of encouraging the child to deal with fearful situations had children who were low in anxiety during the actual stressful life experience. The reported use of punishment, force, or reinforcement of dependency was correlated with higher anxiety. Differences in the use of these methods by mothers and fathers are reported. The reliability of the questionnaire and its relationship to social desirability and the sex of the child are discussed.     

Attachment between humans and dogs

The special relationship that dogs have developed with humans has been studied not only from the social sciences perspective, but also from the perspectives of psychology and human medicine. Recently, in cognitive science, it has been suggested that dogs may have acquired the superior cognitive ability to communicate with humans, particularly using human-like visual cues during evolution, and that emotional bonding has developed between humans and dogs by means of similar social cues. This article discusses the biological aspects of human-dog attachment. Attachment requires the distinction of a specific figure using species-specific social cues and specific responses to the figure, brought about by neuroendocrinological homeostatic functions as well as behavioral aspects. It has been shown that dogs can distinguish a particular human figure (e.g. the owner) and exhibit specific autonomic reactions. Moreover, when dogs gaze at their owners, the latter's urinary oxytocin levels increase after the interaction. This understanding of the biological aspect of interspecies attachment suggests the possible elements that form the basis of cross-species empathy and the development of evolutionary cognitive abilities that may depend on not merely their genetic dendrogram.     

Relationship between perceived job stress and physical and psychological strain among university administrators

The relations between eight job stresses and symptoms of physical and psychological strain were examined among 56 university administrators. Only three of the 16 stressor-strain correlations were significant, suggesting that stress is weakly related to individual strain in this sample.     

Early-extinction effects on a force response of humans

Humans were used to investigate changes in response force occurring soon after reinforcement was eliminated. In Experiment 1, in a 300-s baseline phase, 10 participants received a point for holding down a pressure sensor set to operate at a force equal to 85% of the maximum force the participants exerted during a pretest. Following this, during a 600-s extinction phase, criterion responses had no consequence. In Experiment 2, 6 participants worked on the same task, but (a) points were exchangeable for money and (b) after extinction, the reinforcement baseline phase was reinstated. In Experiment 3, 6 participants completed the same task as in Experiment 2, but the required minimum force was 60% of the maximum force exerted during the pretest. In each experiment, increases in response force relative to the mean and peak force exerted during the last 100 s of baseline were observed in most participants when force responses were aggregated into short sample intervals, but less so with longer ones. The increases, however, were not systematic across or within participants, questioning the generality of and the criteria for demonstrating an extinction burst.     

The effects of stressor predictability on lymphocyte proliferation in humans

Abstract

To demonstrate the effects of predictable and unpredictable stressors on immune function, 36 male subjects were randomly assigned to complete ten trials of either a predictable or unpredictable cold pressor task or a non-stressful warm pressor control task. The predictable and no-stressor groups were given information about the duration of each pressor trial and a countdown of seconds passed from beginning to end of each trial. The unpredictable stressor group received no information. Self-report, cardiovascular, and biochemical measures were taken throughout the tasks in order to ascertain the effectiveness of the predictability and stressor manipulations. Lymphocyte proliferation to concanavalin A (Con A) and pokeweed mitogen (PWM) were measured before, during and after the tasks. Lymphocyte proliferation to Con A (10/μg/ml) was significantly reduced only in response to the unpredictable stressor suggesting that predictability buffered the effect of the stressor on immune function. Proliferation to PWM followed a similar pattern but was not statistically significant. Blood pressure responses were negatively correlated with proliferation values suggesting that stressor predictability may attenuate stress-associated immune decreases by reducing sympathetic arousal.     

Relationship between types of humour and stress response and well‐being among children in Japan

This study examined the relationship between three types of children's humour (aggressive, self‐defeating, and playful) and the children's stress response and well‐being in the Japanese context, where a collectivistic culture is prevalent. To do so, 500 study participants (250 elementary and 250 junior high school students) were recruited. The participants reported the types of humour, stress responses, and level of well‐being that they experienced. After correlation analysis, aggressive humour and playful humour showed a positive correlation with stress responses; in addition, aggressive humour showed a negative correlation with well‐being. Self‐defeating humour showed a negative correlation with stress responses and a positive correlation with well‐being. We also conducted a cluster analysis using the scores for the three types of humour, analysing four groups: “aggressive humourists” (respondents who demonstrated above‐average aggressive humour and scored average for all other humours), “nonhumourists” (below‐average humour in all areas), “self‐deprecating humourists” (above‐average self‐defeating humour, below‐average aggressive humour, and average playful humour), and “multiple humourists” (above‐average humour in all areas). Upon comparing the results of stress responses and well‐being scores among the four groups, we found that self‐deprecating humourists reported the highest level of well‐being. These results show that in collectivistic cultures, self‐defeating humour may be adaptive.     

The social dimension of stress reactivity: acute stress increases prosocial behavior in humans

Psychosocial stress precipitates a wide spectrum of diseases with major public-health significance. The fight-or-flight response is generally regarded as the prototypic human stress response, both physiologically and behaviorally. Given that having positive social interactions before being exposed to acute stress plays a preeminent role in helping individuals control their stress response, engaging in prosocial behavior in response to stress (tend-and-befriend) might also be a protective pattern. Little is known, however, about the immediate social responses following stress in humans. Here we show that participants who experienced acute social stress, induced by a standardized laboratory stressor, engaged in substantially more prosocial behavior (trust, trustworthiness, and sharing) compared with participants in a control condition, who did not experience socioevaluative threat. These effects were highly specific: Stress did not affect the readiness to exhibit antisocial behavior or to bear nonsocial risks. These results show that stress triggers social approach behavior, which operates as a potent stress-buffering strategy in humans, thereby providing evidence for the tend-and-befriend hypothesis.     

The effects of exercise withdrawal on mood and inflammatory cytokine responses in humans

Mechanisms underlying the relationship between exercise and mood are not well understood. This study sought to investigate the role of pro- and anti-inflammatory cytokines and autonomic balance in determining the impact of exercise withdrawal on negative mood. Healthy men and women who regularly exercised (N?=?26, mean age?=?25.5 years, SD?=?4.5 years) were randomised to exercise withdrawal or exercise maintenance for 2 weeks. Protocol adherence was monitored using accelerometers. Inflammatory markers from plasma (interleukin-6, IL-6; tumour necrosis factor-alpha; interleukin-10; and interleukin-1 receptor antagonist), heart-rate variability (HRV) and measures of mood (General Health Questionnaire-28 (GHQ) and the Profile of Mood States (POMS)) were assessed at study entry and at 2-week follow-up. Exercise withdrawal resulted in significant increases in negative mood over time on both the GHQ (p?=?0.028) and the POMS (p?=?0.005). Following the intervention, IL-6 concentration was lower in the exercise withdrawal than exercise maintenance condition (p?=?0.05). No intervention effects were observed for other cytokines or HRV. The mood changes were significantly related to changes in IL-6 concentration (β?=?-?0.50, p?=?0.011), indicating that reduction in IL-6 was related to increased negative mood. Our results are consistent with positive effects of exercise on mental health, but further research on inflammatory pathways is warranted.     

Granulocyte activation in humans is modulated by psychological stress and relaxation

Our aim was to study the possible relationship between psychological stress and granulocyte activation primarily in healthy students during an examination period (n = 11) and also in chronically anxious patients (n = 15). We employed cell surface markers: lactoferrin, L-selectin, alphaMbeta2-integrin and CD15s and flow cytometry to detect changes in the activation state of granulocytes, with the start of the stressed state in students at the beginning of an examination period, which was associated with elevated blood plasma cortisol level, and following relaxation hypnosis in both students, during their examination term, and patients. The ratios of all four types of marker-carrier granulocytes increased at the start of the examination period in students; an especially dramatic (ca. 5-fold) enhancement was observed in the proportion of lactoferrin-bearing cells relatively to the pre-examination term value. After hypnosis, the percentage of lactoferrin-exposing granulocytes decreased considerably both in students and in patients, by about half; a similar decrease was observed in the ratio of CD15s-carrier cells in patients. No significant alteration was observed during the study in state or trait anxiety levels, and in total or differential leukocyte counts. Thus, granulocyte activation could be associated with stress, while relaxation may facilitate reducing activation of these cells. In both groups of subjects, granulocyte surface lactoferrin appeared to be a sensitive "stress indicator". This needs further evaluation.     

Relationship between chronic stress and carotid intima-media thickness (IMT) in elderly Alzheimer's disease caregivers

The stress associated with providing care for a spouse diagnosed with Alzheimer's disease can have adverse effects on cardiovascular health. One potential explanation is that chronic caregiving stress may contribute to the development of atherosclerosis. The purpose of this study was to determine whether the duration that one has provided care is associated with the degree of atherosclerotic burden, as measured by carotid artery intima-media thickness (IMT). One hundred and ten Alzheimer caregivers [mean age 74?±?8 (SD) years, 69% female] underwent in-home assessment of carotid artery IMT via B-mode ultrasonography. Data regarding medical history, blood pressure, and multiple indicators of caregiving stress were also collected. Multiple regression indicated that duration of care was positively associated with IMT measured in the internal/bifurcation segments of the carotid artery (β?=?0.202, p?=?0.044) independent of risk factors such as age, gender, body mass index, smoking history, sleep quality, hypertension status, and caregiving stressors. Duration of care was positively associated with IMT in the common carotid artery, but the relationship was not significant. These findings provide more evidence of the link between chronic caregiving stress and cardiovascular disease and indicate that enduring the experience of caregiving over a period of years might be associated with atherosclerotic burden.     

The relationship between testosterone and route-learning strategies in humans

The relationships between route-learning strategies and circulating testosterone and estradiol levels were investigated in men and women. Testosterone and estradiol concentrations were measured by salivary assays and route-learning strategies were assessed using a direction-giving paradigm based on a novel map. Testosterone was positively correlated with the use of male-biased route-learning strategies in men, but not in women. These findings suggest sex-specific patterns of relationships between circulating testosterone and spatial processing, which apply to everyday spatial behavior.     

Communication between domestic dogs and humans: effects of shelter housing upon the gaze to the human

It is widely known that gaze plays an essential role in communicative interactions. Domestic dogs tend to look at the human face in situations of conflict and uncertainty. This study compares the gaze of shelter and pet dogs during acquisition and extinction phases in a situation involving a reward in sight but out of reach. Even though no significant differences between the groups were recorded during acquisition, gaze duration decreased in both groups during extinction, with shelter dogs showing a significant shorter duration. This could be related to their different living conditions and to the fact that through their ordinary everyday interactions, pet dogs have more opportunities to learn to persist in their communicative responses when they do not get what they want. These results highlight the relevance of learning experiences during ontogeny, which would therefore modulate communicative responses.     

The effects of smoked marijuana on progressive-interval schedule performance in humans.

In three experiments, 8 human subjects participated in a study of the effects of smoked marijuana on progressive-interval schedule performance. A two-component chained progressive-interval fixed-interval schedule of point delivery was used. In the progressive-interval component, the interval length began at 20 s and increased either geometrically or arithmetically (by either 20 s, 40 s, 80 s, 100 s, or 160 s) on each subsequent interval. After this interval elapsed, a single button press produced the fixed-interval component, with a total of five reinforcers of varying magnitude ($0.05, $0.20, or $0.40) available on a fixed-interval 20-s schedule. After the five reinforcer deliveries, the schedule returned to the initial progressive-interval component. Several relationships were found among rates of responding, postreinforcement pauses and drug administration in the progressive-interval component: (a) Postreinforcement pauses increased as the temporal requirements of the progressive-interval schedule increased; (b) rates of responding during successive progressive-interval components rapidly decreased to low rates of responding after the first few progressions; (c) postreinforcement pauses decreased systematically as dose of smoked marijuana increased; and (d) rates of responding increased after smoking active marijuana but not after smoking placebo cigarettes. Results are discussed in the context of behavioral control and relevance to other studies that have investigated the effects of smoked marijuana on schedule performance.