Corticotropin-releasing factor and interleukin-1 receptors in the brain-endocrine-immune axis. Role in stress response and infection

A possible role of endogenous central corticotrophin releasing factor in lipopolysaccharide induced thymic involution and cell apoptosis: effect of peripheral injection of corticotrophin releasing factor

The aim of the study was to investigate the role of endogenous peripheral and central corticotrophin-releasing factor (CRF) following lipopolysaccharide (LPS) challenge on thymic involution and apoptosis. Administration of LPS (100 μg/mouse, ip) led to thymic involution, to a decrease of CD4+CD8+ thymocyte subset, and to fragmentation of thymic DNA. Pretreatment of LPS challenged mice with intracerebroventricular α-helical CRF (a CRF antagonist) attenuated the effect of LPS however, intraventricular administered α-helical CRF failed to affect LPS response on thymus. Moreover, the effects of LPS on thymus, examined on 1, 7 and 14 days were wholly abrogated by prior administration of intraventricular CRF (10 μg/animal). The plasma corticosterone levels were found to be decreased with single dose of peripheral CRF in LPS challenged mice. These findings indicate that central endogenous CRF involved in LPS induced thymic atrophy. However, peripheral CRF offers protective effect on LPS induced thymic involution and cell apoptosis.

Stress- and aging-associated modulation of macrophage functions

Effects of environmental (cold) stress and aging on cells in monocyte/macrophage lineage were investigated. We demonstrated that immune suppressive states seen in acute cold-stressed mice (8-10 weeks of age) is attributable to FcγRII(bright) suppressor macrophages. Serum corticosterone levels were markedly increased in acute cold-stressed mice. In addition, expression of glucocorticoids (GC) receptor mRNA was observed in FcγRII(bright) cells from these mice. The increase of FcγRII(bright) cells in peritoneal exudate cells caused by acute cold stress was inhibited by adrenalectomy or administration of a saturating amount of the GC antagonist RU 38486 (mifepristone). On the contrary, administration of the GC agonist, dexamethasone, markedly increased the proportion of FcγRII(bright) cells in peritoneal exudate cells of control mice. These results suggest that the generation of FcγRII(bright) suppressor cells of monocyte/macrophage lineage by acute cold stress was mediated by action of GC through the GC receptor. We likewise found that the proportion of FcγRII(bright) suppressor macrophages is increased in aged mice (22-24 months of age). Meanwhile, activated macrophages which function as antigen presenting cells were decreased in aged rats. Both the basal corticosterone concentrations in serum and the expression of mRNA for GC receptor in peritoneal macrophages increased significantly in aged animals, suggesting that these populational and functional changes of macrophages in aged animals were mediated, in part, by the increased basal levels of GC. This is probably being responsible for immunosenescence.

Intrapituitary cytokines in Cushing's disease: do they play a role?

A large body of in vitro evidence shows that cytokines influence the hypothalamic-pituitary-adrenal axis both in physiological conditions and in Cushing's disease (CD). In order to study in vivo the role of intrapituitary cytokines in CD, we assayed two cytokines known for their action on the pituitary, i.e. interleukin-1 beta (IL-1β) and interleukin-6 (IL-6), and also soluble interleukin-6 receptor (sIL-6R), important for the neural activities of IL-6, in a carefully selected sample of subjects affected by CD undergoing bilateral inferior petrosal sinus sampling. Similarly to ACTH, all cytokines basally showed a higher concentration in the ipsilateral sinus compared to the controlateral one and to that of peripheral blood; after CRH infusion, both ipsilaterally and controlaterally, IL-6 and sIL-6R values increased compared to basal ones, while IL-1β increased significantly up to 5 min after CRH and then decreased significantly compared to basal values in subsequent measurements; peripherically no significant variations in the cytokines were observed after CRH. Again similarly to ACTH, the three cytokines presented a higher increase ipsilaterally than controlaterally; moreover all three interleukins in the ipsilateral sinuses showed positive and significant correlations between their basal value and that of basal ACTH. These findings allow us to hypothesize that the central production of IL-1β and IL-6 could be involved in ACTH hypersecretion which occurs in CD: more specifically, we hypothesize that these cytokines are produced directly by the corticotroph adenoma and have the task of enhancing tumoral secretion of ACTH with an autocrine-paracrine mechanism.

Maternal hurricane exposure and fetal distress risk

Logistic regression and spatial analytic techniques are used to model fetal distress risk as a function of maternal exposure to Hurricane Andrew. First, monthly time series compare the proportion of infants born distressed in hurricane affected and unaffected areas. Second, resident births are analyzed in Miami-Dade and Broward counties, before, during, and after Hurricane Andrew. Third, resident births are analyzed in all Florida locales with 100,000 or more persons, comparing exposed and unexposed gravid females. Fourth, resident births are analyzed along Hurricane Andrew's path from southern Florida to northeast Mississippi. Results show that fetal distress risk increases significantly with maternal exposure to Hurricane Andrew in second and third trimesters, adjusting for known risk factors. Distress risk also correlates with the destructive path of Hurricane Andrew, with higher incidences of fetal distress found in areas of highest exposure intensity. Hurricane exposed African-American mothers were more likely to birth distressed infants. The policy implications of in utero costs of natural disaster exposure are discussed.

Stress, bacterial vaginosis, and the role of immune processes

Bacterial vaginosis (BV), the most common lower genital tract infection in women of reproductive age, is associated with adverse gynecologic and reproductive health outcomes. Women at highest risk for BV are young, unmarried, low income, undereducated, and African American. Behaviors such as vaginal douching, numerous sexual partners, frequent sexual intercourse, receptive oral sex, and substance use may contribute to risk, but they account for only a modest proportion of the observed race/ethnicity variance in BV. These subpopulations are also exposed to more social disadvantages or "stressors" such as poverty, poor housing, crime-infested neighborhoods, and discrimination than other groups. Growing physiologic evidence links psychosocial stress to the development of disease. Evidence supports a statistically significant, independent effect of stress on the risk and observed racial/ethnic disparity in the rate of BV. This paper reviews such evidence.

Recurrent hypoglycemia alters hypothalamic expression of the regulatory proteins FosB and synaptophysin

A limiting factor to the clinical management of diabetes is iatrogenic hypoglycemia. With multiple hypoglycemic episodes, the collective neuroendocrine response that restores euglycemia is impaired. In our animal model of recurrent hypoglycemia (RH), neuroendocrine deficits are accompanied by a decrease in medial hypothalamic activation. Here we tested the hypothesis that the medial hypothalamus may exhibit unique changes in the expression of regulatory proteins in response to RH. We report that expression of the immediate early gene FosB is increased in medial hypothalamic nuclei, anterior hypothalamus, and posterior paraventricular nucleus of the thalamus (THPVN) of the thalamus following RH. We identified the hypothalamic PVN, a key autonomic output site, among the regions expressing FosB. To identify the subtype(s) of neuronal populations that express FosB, we screened candidate neuropeptides of the PVN for coexpression using dual fluorescence immunohistochemistry. Among the neuropeptides analyzed [including oxytocin, vasopressin, thyrotropin-releasing hormone, and corticotropin-releasing factor (CRF)], FosB was only identified in CRF-positive neurons. Inhibitory gamma-aminobutyric acid-positive processes appear to impinge on these FosB-expressing neurons. Finally, we observed a significant decrease in the presynaptic marker synaptophysin within the PVN of RH-treated vs. saline-treated rats, suggesting that rapid alterations of synaptic morphology may occur in association with RH. Collectively, these data suggest that RH stress triggers cellular changes that support synaptic plasticity, in specific neuroanatomical sites, which may contribute to the development of hypoglycemia-associated autonomic failure.

Self-reported experiences of racial discrimination and Black-White differences in preterm and low-birthweight deliveries: the CARDIA Study

OBJECTIVES

We examined the effects of self-reported experiences of racial discrimination on Black-White differences in preterm (less than 37 weeks gestation) and low-birthweight (less than 2500 g) deliveries.

METHODS

Using logistic regression models, we analyzed data on 352 births among women enrolled in the Coronary Artery Risk Development in Young Adults Study.

RESULTS

Among Black women, 50% of those with preterm deliveries and 61% of those with low-birthweight infants reported having experienced racial discrimination in at least 3 situations; among White women, the corresponding percentages were 5% and 0%. The unadjusted odds ratio for preterm delivery among Black versus White women was 2.54 (95% confidence interval [CI]=1.33, 4.85), but this value decreased to 1.88 (95% CI=0.85, 4.12) after adjustment for experiences of racial discrimination and to 1.11 (95% CI=0.51, 2.41) after additional adjustment for alcohol and tobacco use, depression, education, and income. The corresponding odds ratios for low birthweight were 4.24 (95% CI=1.31, 13.67), 2.11 (95% CI=0.75, 5.93), and 2.43 (95% CI=0.79, 7.42).

CONCLUSIONS

Self-reported experiences of racial discrimination were associated with preterm and low-birthweight deliveries, and such experiences may contribute to Black-White disparities in perinatal outcomes.

Women's mental health during pregnancy influences fetal and infant developmental and health outcomes

Women's mental health during pregnancy has important implications not only for the well-being of the mother, but also for the development, health, and well-being of her unborn child. A growing body of empirical evidence from population-based studies suggests that two indicators of women's mental health during pregnancy--psychosocial stress and social support--may exert a significant influence on fetal development and infant birth outcomes, such as birth weight and length of gestation, even after controlling for the effects of established sociodemographic, obstetric, and behavioral risk factors. This paper describes the role of three major biological systems involved in the physiology of pregnancy and stress physiology: neuroendocrine, immune/inflammatory, and cardiovascular systems. These systems have been hypothesized to mediate the effects of maternal mental health on fetal developmental and health outcomes, and a central role has been proposed for placental corticotropin-releasing hormone in this process. However, not all women reporting high prenatal stress and/or low social support proceed to develop adverse birth outcomes, raising the question of the determinants of susceptibility/vulnerability in the context of high stress and/or low social support. In this context, the role of race/ethnicity and genetic predisposition are discussed as two promising avenues of further investigation.

Role of psychosocial and nutritional stress on poor pregnancy outcome

Epidemiological evidence suggests that maternal psychosocial stress, strenuous physical activity and fasting are independent risk factors for preterm birth and low birth weight. Data from clinical studies consistently demonstrate that women in preterm labor have significantly elevated levels of corticotropin-releasing hormone compared with age-matched control subjects. Because production of corticotropin-releasing hormone appears to be stress sensitive, this neuropeptide may play a critical role in the physiological mediation among stressful experiences, work stress and fasting and risk of preterm birth. In addition to the direct effect of elevated corticotropin-releasing hormone on the initiation of labor, it may have an immunomodulatory effect such that women with high levels of corticotropin-releasing hormone may be more susceptible to infection or the pathological consequences of infection. We review the epidemiological data linking maternal stress, physical stain and fasting to preterm birth and low birth weight and review the plausible biological pathways through which these exposures may increase risk of preterm birth. The timing of these exposures is considered important. Future research and clinical programs addressing these exposures must consider assessments and interventions before pregnancy.

Exposure to chronic stress and ethnic differences in rates of bacterial vaginosis among pregnant women

OBJECTIVE

The purpose of this study was to assess the contribution of chronic social stressors to race/ethnic differences in the rate of bacterial vaginosis among pregnant women in the inner-city area.

STUDY DESIGN

We conducted a cross-sectional clinical prevalence study in a sample of 2304 women at the first prenatal visit (14.8 +/- 0.2 weeks of gestation). Bacterial vaginosis was diagnosed by Nugent's method. Stress was measured at the individual and community levels with the use of interviews and administrative records. Logistic regression was used to assess the effects of stress on the odds of bacterial vaginosis occurrence, after adjustment for demographic and behavioral risk.

RESULTS

Black women had significantly higher rates of bacterial vaginosis (64%) compared with white women (35%). Exposure to chronic stressors at the individual level differed by race (eg, 32% of the black women reported threats to personal safety compared with 13% of white women). There were significant racial differences in exposure to stress at the community level (eg, 63% of the black women lived in neighborhoods with aggravated assault rates that were above the citywide mean compared with 25% of the white women). After the adjustment for sociodemographic, behavioral risk, and perceived stress, the odds of the occurrence of bacterial vaginosis that was associated with the community level stressor of "homelessness" was significant (odds ratio, 6.7; 95% CI, 1.6-27.8). Inclusion of both individual and community level stressors reduced the black/white bacterial vaginosis odds ratio by 27%.

CONCLUSION

Stressful exposures are associated positively with bacterial vaginosis in pregnancy in a sample of women of low income in the inner city. The measurement of stressors at multiple levels explained a significant proportion of the racial disparity in the rates of occurrence of bacterial vaginosis.

Stress, infection and preterm birth: a biobehavioural perspective

Preterm birth is currently the most important problem in maternal-child health in the United States. Epidemiological studies have suggested that two factors, maternal stress and maternal urogenital tract infection, are significantly and independently associated with an increased risk of spontaneous preterm birth. These factors are also more prevalent in the population of sociodemographically disadvantaged women who are at increased risk for preterm birth. Studies of the physiology of parturition suggest that neuroendocrine and immune processes play important roles in the physiology and pathophysiology of normal and preterm parturition. However, not all women with high levels of stress and/or infection deliver preterm, and little is understood about factors that modulate susceptibility to pathophysiological events of the endocrine and immune systems in pregnancy. We present here a comprehensive, biobehavioural model of maternal stress and spontaneous preterm delivery. According to this model, chronic maternal stress is a significant and independent risk factor for preterm birth. The effects of maternal stress on preterm birth may be mediated through biological and/or behavioural mechanisms. We propose that maternal stress may act via one or both of two physiological pathways: (a) a neuroendocrine pathway, wherein maternal stress may ultimately result in premature and/or greater degree of activation of the maternal-placental-fetal endocrine systems that promote parturition; and (b) an immune/inflammatory pathway, wherein maternal stress may modulate characteristics of systemic and local (placental-decidual) immunity to increase susceptibility to intrauterine and fetal infectious-inflammatory processes and thereby promote parturition through pro-inflammatory mechanisms. We suggest that placental corticotropin-releasing hormone may play a key role in orchestrating the effects of endocrine and inflammatory/immune processes on preterm birth. Moreover, because neuroendocrine and immune processes extensively cross-regulate one another, we further posit that exposure to both high levels of chronic stress and infectious pathogens in pregnancy may produce an interaction and multiplicative effect in terms of their combined risk for preterm birth. Finally, we hypothesise that the effects of maternal stress are modulated by the nature, duration and timing of occurrence of stress during gestation. A discussion of the components of this model, including a theoretical rationale and review of the available empirical evidence, is presented. A major strength of this biobehavioural perspective is the ability to explore new questions and to do so in a manner that is more comprehensive than has been previously attempted. We expect findings from this line of proposed research to improve our present state of knowledge about obstetric risk assessment for preterm birth by determining the characteristics of pregnant women who are especially susceptible to stress and/or infection, and to broaden our understanding of biological (endocrine, immune, and endocrine-immune interactions) mechanisms that may translate social adversity during pregnancy into pathophysiology, thereby suggesting intervention strategies.

Cytokines and chronic fatigue syndrome

Chronic fatigue syndrome (CFS) patients show evidence of immune activation, as demonstrated by increased numbers of activated T lymphocytes, including cytotoxic T cells, as well as elevated levels of circulating cytokines. Nevertheless, immune cell function of CFS patients is poor, with low natural killer cell cytotoxicity (NKCC), poor lymphocyte response to mitogens in culture, and frequent immunoglobulin deficiencies, most often IgG1 and IgG3. Immune dysfunction in CFS, with predominance of so-called T-helper type 2 and proinflammatory cytokines, can be episodic and associated with either cause or effect of the physiological and psychological function derangement and/or activation of latent viruses or other pathogens. The interplay of these factors can account for the perpetuation of disease with remission/exacerbation cycles. A T-helper type 2 predominance has been seen among Gulf War syndrome patients and this feature may also be present in other related disorders, such as multiple chemical sensitivity. Therapeutic intervention aimed at induction of a more favorable cytokine expression pattern and immune status appears promising.

Cytokines in the neuroendocrine system

Cytokines are important partners in the bidirectional network interrelating the immune and the neuroendocrine systems. These substances and their specific receptors, initially thought to be exclusively present in the immune system, have recently been shown to be also expressed in the neuroendocrine system. Cytokines can modulate the responses of all endocrine axes by acting at both the central and the peripheral levels. To explain how systemic cytokines may gain access to the brain, several mechanisms have been proposed, including an active transport through the blood-brain barrier, a passage at the circumventricular organ level, as well as a neuronal pathway through the vagal nerve. The immune-neuroendocrine interactions are involved in numerous physiological and pathophysiological conditions and seem to play an important role to maintain homeostasis.

Maternal corticotropin-releasing hormone levels in the early third trimester predict length of gestation in human pregnancy

OBJECTIVE

Corticotropin releasing hormone, a hypothalamic neuropeptide, plays a major role in regulating pituitary-adrenal function and the physiologic response to stress. During pregnancy corticotropin-releasing hormone is synthesized in large amounts by the placenta and released into the maternal and fetal circulations. Various endocrine, autocrine, and paracrine roles have been suggested for placental corticotropin-releasing hormone. The aim of this study was to prospectively assess the relationship between maternal plasma concentrations of corticotropin-releasing hormone in the early third trimester of pregnancy and the length of gestation in two groups of deliveries, with and without spontaneous labor.

STUDY DESIGN

In a sample of 63 women with singleton intrauterine pregnancies, maternal plasma samples were collected between 28 and 30 weeks' gestation and corticotropin-releasing hormone concentrations were determined by radioimmunoassay. Each pregnancy was dated on the basis of last menstrual period and early ultrasonography. Parity, antepartum risk conditions, presence or absence of spontaneous labor, and birth outcomes were abstracted from the medical record.

RESULTS

Maternal corticotropin-releasing hormone levels between 28 and 30 weeks' gestation significantly and negatively predicted gestational length (P < .01) after adjustment for antepartum risk. Moreover, subjects who were delivered preterm had significantly higher corticotropin-releasing hormone levels in the early third trimester (P < .01) than did those who were delivered at term. In deliveries preceded by spontaneous onset of labor, maternal third-trimester corticotropin-releasing hormone levels significantly and independently predicted earlier onset of labor (P < .01) and preterm labor (P < .05), whereas in deliveries effected by induction of labor or cesarean delivery, maternal corticotropin-releasing hormone levels were a marker of antepartum risk but not a statistically independent predictor of gestational length.

CONCLUSION

These findings support the premise that placental corticotropin-releasing hormone is potentially implicated in the timing of human delivery in at least two ways. First, placental corticotropin-releasing hormone may play a role in the physiology of parturition. Premature or accelerated activation of the placental corticotropin-releasing hormone system, as reflected by precocious elevation of maternal corticotropin-releasing hormone levels, may therefore be associated with earlier onset of spontaneous labor and resultant delivery. Second, placental corticotropin-releasing hormone may be a marker of antepartum risk for preterm delivery and therefore an indirect predictor of earlier delivery. The implications of these findings are discussed in the context of the neuroendocrinology of placental corticotropin-releasing hormone and human parturition. Furthermore, the role of corticotropin-releasing hormone as a possible effector of prenatal stress in producing alterations in the timing of normal delivery is detailed.

Immune-endocrine interactions in the mammalian adrenal gland: facts and hypotheses

Several cytokines, which are the major mediators of the inflammatory responses, are well-known to stimulate the hypothalamopituitary corticotropin-releasing hormone (CRH)/adrenocorticotropic hormone (ACTH) system, thereby evoking secretory responses by the adrenal cortex. Many of these cytokines, including interleukin-1 (IL-1), IL-2, IL-6, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (INF-gamma) are synthesized in the adrenal gland by both parenchymal cells and resident macrophages, and the release of some of them (e.g., IL-6 and TNF-alpha) is regulated by the main agonists of steroid hormone secretion (e.g., ACTH and angiotensin-II) and bacterial endotoxins. Adrenocortical and adrenomedullary cells are provided with specific receptors for IL-1, IL-2, and IL-6. IL-1 and TNF-alpha directly inhibit aldosterone secretion of zona glomerulosa cells, whereas IL-6 enhances it. IL-2, IL-3, IL-6, and INF-alpha are able to directly stimulate glucocorticoid production by zona fasciculata and zona reticularis cells, whereas IL-1 exerts an analogous effect through an indirect mechanism involving the stimulation of catecholamine release by chromaffin cells and/or the activation of the intramedullary CRH/ACTH system; again, TNF-alpha depresses glucocorticoid synthesis. IL-6 raises androgen secretion by inner adrenocortical layers. IL-1 enhances the proliferation of adrenocortical cells, and findings suggest that cytokines may control the apoptotic deletion of senescent zona reticularis cells. The relevance of the intraadrenal cytokine system in the fine-tuning of the secretion and growth of the adrenal cortex under normal conditions remains to be explored. However, indirect proof is available that local immune-endocrine interactions may play an important role in modulating adrenal responses to inflammatory and immune challenges and stresses.

A fetal systemic inflammatory response is followed by the spontaneous onset of preterm parturition

OBJECTIVE

There is no evidence for the participation of the human fetus in the mechanisms responsible for the onset of preterm labor. We propose that preterm labor in the setting of infection results from the actions of proinflammatory cytokines secreted as part of the fetal and/or maternal host response to microbial invasion. The objective of this study was to determine whether a systemic fetal inflammatory response, defined as an elevation of fetal plasma interleukin-6 concentrations, has a temporal relationship with the commencement of labor.

STUDY DESIGN

After informed consent was obtained, amniocentesis and cordocentesis were performed in 41 patients with preterm premature rupture of membranes who were not in labor on admission. Amniotic fluid was cultured for both aerobic and anaerobic bacteria, as well as for mycoplasmas. Fetal plasma interleukin-6 was assayed by a sensitive and specific immunoassay. Statistical analyses included contingency tables and survival analysis with time-dependent Cox regression hazard modeling.

RESULTS

Microbial invasion of the amniotic cavity was present in 58.5% (24/41) of patients. Fetuses with fetal plasma interleukin-6 concentrations > 11 pg/mL had a higher rate of spontaneous preterm delivery within 48 and 72 hours of the procedure than those with fetal plasma interleukin-6 levels < or = 11 pg/mL (88% vs 29% and 88% vs 35%, respectively; P < .05 for all comparisons). Moreover, patients with initiation of labor and delivery within 48 hours of the procedure had a higher proportion of fetuses with plasma interleukin-6 values > 11 pg/mL than patients delivered > 48 hours (58% [7/12] vs 8% [1/13], respectively; P < .05). Survival analysis indicated that fetuses with elevated fetal plasma interleukin-6 levels had a shorter cordocentesis-to-delivery interval than those without elevated fetal plasma interleukin-6 concentrations (median 0.8 days [range 0.1 to 5] vs median 6 days [range 0.2 to 33.6], respectively; P < .05). Time-dependent Cox regression hazard modeling indicated that fetal plasma interleukin-6 level was the only covariate significantly associated with the duration of pregnancy after we adjusted for gestational age, amniotic fluid interleukin-6 level, and the microbiologic state of the amniotic cavity (P < .01).

CONCLUSION

A systemic fetal proinflammatory cytokine response is followed by the onset of spontaneous preterm parturition in patients with preterm premature rupture of membranes.

An increase in basal glucocorticoid concentration with age induces suppressor macrophages with high-density Fc gamma RII/III

Ageing is usually accompanied by a decline in immune and neuroendocrine functions. To elucidate the mechanisms underlying age-related immunosuppression, the functions and surface phenotypes of peritoneal cells in the monocyte/macrophage lineage from old mice were investigated. The role of glucocorticoids (GC) in the immunomodulation was also examined. Proliferative responses of spleen cells from control mice stimulated with concanavalin A (Con A) were significantly suppressed by adding peritoneal exudate cells from old mice. Flow cytometry analysis revealed that the proportion of MAC-1+ cells with a high density of type II or type III receptor for the Fc portion of IgG (Fc gamma RII/IIIbright cells) was increased markedly in the periotoneal exudate cells from old mice. The prominent suppressor activity for Con A responses of control spleen cells was found in the Fc gamma RII/IIIbright cells, whereas MAC-1+ cells with a low density of Fc gamma RII/III (Fc gamma RII/IIIdull cells) did not suppress the Con A responses. On the other hand, both the basal corticosterone concentrations in serum and the mRNA expression for GC receptor in peritoneal exudate cells increased significantly in old mice. Furthermore, the proportion of Fc gamma RII/IIIbright cells in peritoneal exudate cells from old mice was normalized on administration of the GC antagonist RU 38,486 (mifepristone). These results suggest that the increase in basal corticosterone concentrations in old mice induces the generation of Fc gamma RII/IIIbright suppressor cells, possibly leading to the immune-suppressive state.

CRH and the immune system

Inflammatory cytokines released during immune system activation can stimulate the hypothalamic-pituitary-adrenal axis and cause increased secretion of corticotropin-releasing hormone (CRH), adrenocorticotropin and glucocorticoids. Identification of CRH peptide and mRNA, as well as its receptors in immune tissues, suggested a role for this peptide as a mediator of the neuroendocrine-immune interactions. Experimental evidence suggests that CRH may modulate the immune and inflammatory responses via two pathways: an antiinflammatory one operated by centrally released CRH, most likely through stimulation of glucocorticoid and catecholamine release, and one proinflammatory, through direct action of peripherally released CRH. This review highlights these concepts. In addition preliminary data on immune activation and inflammatory response in CRH-deficient mice created in our laboratory are discussed.

Prenatal psychosocial factors and the neuroendocrine axis in human pregnancy

OBJECTIVE

Physiological processes including neuroendocrine function have been proposed as mediators of the relationship between prenatal psychological state and pregnancy outcome; however, there are virtually no human studies that have systematically assessed such mechanisms. Neuroendocrine processes are significantly altered during pregnancy, and are characterized by the evolution of a transient neuroendocrine system, the placenta, and modifications in endocrine control mechanisms. Because these alterations have implications for neuroendocrine responsivity to exogenous conditions, the aim of the present study was to examine the cross-sectional association between prenatal psychosocial factors and stress-related neuroendocrine parameters during human pregnancy.

METHOD

Fifty-four adult women with a singleton, intrauterine pregnancy were recruited before 28 weeks of gestation. Maternal antecubital venous blood samples were withdrawn at 28 weeks of gestation for bioassays of adrenocorticotropin hormone (ACTH), beta-endorphin (beta E), and cortisol. Measures of prenatal stress, social support, and personality were collected using a two-part, self-report questionnaire administered at 28 and 30 weeks of gestation. Biomedical data were obtained from the medical record. Factors known to influence neuropeptide and hormone levels during pregnancy were controlled, including gestational age, circadian variation, and obstetric risk.

RESULTS

In the present sample, prenatal psychosocial stress, social support, and personality variables were associated with neuroendocrine parameters in two primary ways. First, certain psychosocial factors were significantly associated with plasma levels of ACTH, beta E, and cortisol, and second, psychosocial factors were associated with a measure of disregulation of the normal relationship between two pro-opiomelanocortin (POMC) derivatives, ACTH and beta E. Furthermore, a combination of the maternal psychosocial and sociodemographic factors during pregnancy accounted for 36% of the variance in ACTH, 22% of the variance in the ACTH-beta E disregulation index, 13% of the variance in cortisol, and 3% of the variance in beta E.

CONCLUSIONS

The present findings are consistent with the premise that maternal-placental-fetal neuroendocrine parameters are significantly associated, both in magnitude and specificity, with features of maternal psychosocial functioning in pregnancy despite the systemic alterations associated with the endocrinology of pregnancy. These findings provide a basis for further investigations of the role of the neuroendocrine system as a putative mediating pathway between prenatal psychosocial factors and birth outcome, and possibly also as a mechanism linking features of the maternal psychosocial environment to fetal/infant brain development.

The protective role of the hypothalamic-pituitary-adrenal axis against lethality produced by immune, infectious, and inflammatory stress

We have shown that ADX and HYPOX rats exhibit a markedly increased sensitivity to the lethal effects of IL-1-beta and LPS compared to sham controls with an intact HPAA. These results indicated that the reports of lethal effects of cytokines and LPS which generates cytokines in mice with a compromised HPAA were not idiosyncratic or specific to mice but represented a general response that would have been expected in any organism with a compromised HPAA. We further demonstrated that protection against lethal effects due to IL-1-beta or LPS could be produced by treating ADX rats with glucocorticoid in a quantity estimated to be equivalent to corticosterone secretion provoked during stress. In contrast, we found that acutely stalk-sectioned rats with pituitaries disconnected from hypothalamic regulation did not show a markedly increased susceptibility to lethal effects of LPS as did ADX or HYPOX rats. Although a minority of stalk-sectioned rats were killed by LPS, the majority of rats were protected from lethal actions of LPS. This response suggested that an intact pituitary-adrenal axis without the normal hypothalamic control could still provide significant protection presumably due to generation of cytokines which stimulated the pituitary over several hours. The results from our lethality studies clearly underscore the importance of activating the stress axis and increasing glucocorticoid secretion to protect against potentially lethal effects of cytokines that can be induced by immune, infectious, or inflammatory stimuli. Cytokine-stimulated effects can initially result in beneficial actions to the host by promoting immune/inflammatory responses that are protective in nature and help defend against a variety of invading stimuli (infectious, immune, inflammatory, traumatic, neoplastic). Normally the HPAA responds to cytokine stimulation by ultimately increasing glucocorticoid secretion in order to counterregulate cytokine actions, modulate the host response, and protect the host from excessively catabolic effects of unregulated cytokine generation and actions. For many years, clinicians have recognized that patients with deficient glucocorticoid secretion (e.g., Addison's disease or pituitary ACTH deficiency) require increased glucocorticoid replacement during episodes of fever, infection, or inflammatory stress. However, the reasons why stress-equivalent glucocorticoid replacement were required were not entirely clear. Now, we understand that glucocorticoids are critically important for protecting the host against its own defense mechanisms so that the stimulation of cytokines can facilitate a protective response against an invading insult without also killing the host.

Physiological bases for parasite-induced alterations of host behaviour

Parasitism is defined in various ways as an intimate relationship in which one partner, the parasite, lives on or in another, the host, generally at the expense of the latter. Parasitism commonly results in a unique array of host physiological responses and adaptations. Most studies of the physiological effects of parasitism have focused on the pathological consequence of infection and disease. While many physiological changes contribute to pathogenesis, it is now recognized that parasitic infections at sub-clinical levels also produce physiological effects that either ameliorate or may not contribute to the disease process. Moreover, these physiological changes are often manifested by altered host behaviour. Behavioural studies have enabled an ecological- and evolutionary-oriented evaluation of host responses. In this fashion, physiological effects may be assessed as to whether they affect fitness and confer benefit or harm to one or both of the symbionts involved. We briefly examine how these physiological responses, specifically neural, endocrine, neuromodulatory, and immunomodulatory components, may interact to modify host behaviors. We consider the adaptiveness of these responses and how the behavioural patterns elicited may simultaneously appear adaptive for the parasite as well as the host. In addition, we address how parasite-host physiological and behavioural interactions may be altered during the course of parasitism.