Reciprocal affiliation among adolescent rats during a mild group stressor predicts mammary tumors and lifespan

Evolutionary foundations of human prosocial sentiments

A growing body of evidence shows that humans are remarkably altruistic primates. Food sharing and division of labor play an important role in all human societies, and cooperation extends beyond the bounds of close kinship and networks of reciprocating partners. In humans, altruism is motivated at least in part by empathy and concern for the welfare of others. Although altruistic behavior is well-documented in other primates, the range of altruistic behaviors in other primate species, including the great apes, is much more limited than it is in humans. Moreover, when altruism does occur among other primates, it is typically limited to familiar group members--close kin, mates, and reciprocating partners. This suggests that there may be fundamental differences in the social preferences that motivate altruism across the primate order, and there is currently considerable interest in how we came to be such unusual apes. A body of experimental studies designed to examine the phylogenetic range of prosocial sentiments and behavior is beginning to shed some light on this issue. In experimental settings, chimpanzees and tamarins do not consistently take advantage of opportunities to deliver food rewards to others, although capuchins and marmosets do deliver food rewards to others in similar kinds of tasks. Although chimpanzees do not satisfy experimental criteria for prosociality in food delivery tasks, they help others complete tasks to obtain a goal. Differences in performance across species and differences in performance across tasks are not yet fully understood and raise new questions for further study.

Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues

17β-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERβ for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERβ related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

Strong and consistent social bonds enhance the longevity of female baboons

Longevity is a major component of variation in fitness in long-lived iteroparous species [1-4]. Among female baboons, variation in breeding lifespan accounts for approximately 50% of the variation in lifetime fitness [5, 6]. However, we know little about the causes of variation in longevity in primates or other long-lived mammals. Savannah baboons form strong, equitable, and enduring relationships with specific female partners, particularly with close relatives and agemates [7-10]. The quality of females' social relationships influences their ability to cope with stressful events [11-13] and is associated with variation in female reproductive success [9, 14]. Here we show that dominance rank and the quality of close social bonds have independent effects on the longevity of female chacma baboons (Papio hamadryas ursinus). High-ranking females live longer than lower-ranking females. In addition, females who form stronger and more stable social bonds with other females live significantly longer than females who form weaker and less stable relationships. These data extend our understanding of the adaptive value of social bonds in baboons and complement a growing body of evidence that indicates that social bonds have adaptive value in a range of taxa, from mice to humans [9, 14-19].

Female chacma baboons form strong, equitable, and enduring social bonds

Analyses of the pattern of associations, social interactions, coalitions, and aggression among chacma baboons (Papio hamadryas ursinus) in the Okavango Delta of Botswana over a 16-year period indicate that adult females form close, equitable, supportive, and enduring social relationships. They show strong and stable preferences for close kin, particularly their own mothers and daughters. Females also form strong attachments to unrelated females who are close to their own age and who are likely to be paternal half-sisters. Although absolute rates of aggression among kin are as high as rates of aggression among nonkin, females are more tolerant of close relatives than they are of others with whom they have comparable amounts of contact. These findings complement previous work which indicates that the strength of social bonds enhances the fitness of females in this population and support findings about the structure and function of social bonds in other primate groups.

A murine model of stress controllability attenuates Th2-dominant airway inflammatory responses

Epidemiological and experimental studies suggest a positive correlation between chronic respiratory inflammatory disease and the ability to cope with adverse stress. Interactions between neuroendocrine and immune systems are believed to provide insight toward the biological mechanisms of action. The utility of an experimental murine model was employed to investigate the immunological consequences of stress-controllability and ovalbumin-induced airway inflammation. Pre-conditioned uncontrollable stress exacerbated OVA-induced lung histopathological changes that were typical of Th2-predominant inflammatory response along respiratory tissues. Importantly, mice given the ability to exert control over aversive stress attenuated inflammatory responses and reduced lung pathology. This model represents a means of investigating the neuro-immune axis in defining mechanisms of stress and respiratory disease.

Macrophage migration inhibitory factor-knockout mice are long lived and respond to caloric restriction

Macrophage migration inhibitory factor (MIF) affects inflammation, glucose homeostasis, and cellular proliferation in mammals. Previously, we found that MIF was significantly elevated in multiple long-lived mouse models, including calorie restriction (CR), which led us to hypothesize that MIF might be important in the control of mammalian life span and be necessary for the life-extending effects of CR. To test this hypothesis, we examined the life span of mice with a targeted deletion of the Mif gene on a segregating B6 x 129/Sv background (MIF-KO) under ad libitum (AL) feeding and CR conditions. Control mice were generated by mating C57BL/6J females with 129/SvJ males to make an F1 hybrid, and crossing F1 males to F1 females to produce segregating F2 mice homozygous for the normal MIF allele. Not only did MIF-KO mice show a life span extension in response to CR, they were, unexpectedly, longer lived than controls under standard AL conditions. MIF-KO mice were significantly protected against lethal hemangiosarcoma, but more likely than controls to die of disseminated amyloid, an age-related inflammatory syndrome. Overall, these data refute the suggestion that MIF is required for the CR effect on life span, but raise the possibility that MIF may limit life span in normal mice.

Social isolation dysregulates endocrine and behavioral stress while increasing malignant burden of spontaneous mammary tumors

In a life span study, we examined how the social environment regulates naturally occurring tumor development and malignancy in genetically prone Sprague-Dawley rats. We randomly assigned this gregarious species to live either alone or in groups of five female rats. Mammary tumor burden among social isolates increased to 84 times that of age-matched controls, as did malignancy, specifically a 3.3 relative risk for ductal carcinoma in situ and invasive ductal carcinoma, the most common early breast cancers in women. Importantly, isolation did not extend ovarian function in late middle age; in fact, isolated animals were exposed to lower levels of estrogen and progesterone in the middle-age period of mammary tumor growth, with unchanged tumor estrogen and progesterone receptor status. Isolates, however, did develop significant dysregulation of corticosterone responses to everyday stressors manifest in young adulthood, months before tumor development, and persisting into old age. Among isolates, corticosterone response to an acute stressor was enhanced and recovery was markedly delayed, each associated with increased mammary tumor progression. In addition to being stressed and tumor prone, an array of behavioral measures demonstrated that socially isolated females possessed an anxious, fearful, and vigilant phenotype. Our model provides a framework for studying the interaction of social neglect with genetic risk to identify mechanisms whereby psychosocial stressors increase growth and malignancy of breast cancer.