Aging and physical mobility in group-housed Old World monkeys

While indices of physical mobility such as gait speed are significant predictors of future morbidity/mortality in the elderly, mechanisms of these relationships are not understood. Relevant animal models of aging and physical mobility are needed to study these relationships. The goal of this study was to develop measures of physical mobility including activity levels and gait speed in Old World monkeys which vary with age in adults. Locomotor behaviors of 21 old ([Formula: see text] = 20 yoa) and 24 young ([Formula: see text] = 9 yoa) socially housed adult females of three species were recorded using focal sample and ad libitum behavior observation methods. Self-motivated walking speed was 17% slower in older than younger adults. Likewise, young adults climbed more frequently than older adults. Leaping and jumping were more common, on average, in young adults, but this difference did not reach significance. Overall activity levels did not vary significantly by age, and there were no significant age by species interactions in any of these behaviors. Of all the behaviors evaluated, walking speed measured in a simple and inexpensive manner appeared most sensitive to age and has the added feature of being least affected by differences in housing characteristics. Thus, walking speed may be a useful indicator of decline in physical mobility in nonhuman primate models of aging.

Heritability and genetic correlation of hair cortisol in vervet monkeys in low and higher stress environments

Chronic activation of the hypothalamic-pituitary adrenal (HPA) system is a risk factor for a variety of physical and mental disorders, and yet the complexity of the system has made it difficult to define the role of genetic and environmental factors in producing long-term individual differences in HPA activity. Cortisol levels in hair have been suggested as a marker of total HPA activation over a period of several months. This study takes advantage of a pedigreed nonhuman primate colony to investigate genetic and environmental influences on hair cortisol levels before and after an environmental change. A sample of 226 adult female vervet monkeys (age 3-18) living in multigenerational, matrilineal social groups at the Vervet Research Colony were sampled in a stable low stress baseline environment and 6 months after the entire colony was moved to a new facility with more frequent handling and group disturbances (higher stress environment). Variance components analysis using the extended colony pedigree was applied to determine heritability of hair cortisol levels in the two environments. Bivariate genetic correlation assessed degree of overlap in genes influencing hair cortisol levels in the low and higher stress environments. The results showed that levels of cortisol in hair of female vervets increased significantly from the baseline to the post-move environment. Hair cortisol levels were heritable in both environments (h(2)=0.31), and there was a high genetic correlation across environments (rhoG=0.79), indicating substantial overlap in the genes affecting HPA activity in low and higher stress environments. This is the first study to demonstrate that the level of cortisol in hair is a heritable trait. It shows the utility of hair cortisol as a marker for HPA activation, and a useful tool for identifying genetic influences on long term individual differences in HPA activity. The results provide support for an additive model of the effects of genes and environment on this measure of long term HPA activity.

A novelty seeking phenotype is related to chronic hypothalamic-pituitary-adrenal activity reflected by hair cortisol

Reduced hypothalamic pituitary adrenal (HPA) activity is associated with greater novelty seeking in humans. Hair cortisol represents an integrated proxy measure of total cortisol production/release over an extended period of time and may be a valuable tool for tracking the HPA system. Sampling approaches (collection of blood, saliva, urine, or feces) for socially housed nonhuman primates present a number of technical challenges for collection particularly when repeated sampling is necessary. Herein we describe a relationship between cortisol levels measured in hair collected from 230 socially housed female vervet (Chlorocebus aethiops sabaeus) monkeys and a free-choice novelty seeking phenotype. A predator-like object was placed at the periphery of the outdoor enclosures for 30 min and speed of approach (latency to approach within 1m) and persistence of interest (number of 1 min intervals within 1m) were scored. A composite Novelty Seeking score, combining these two measures, was calculated. The intra-class correlation coefficient (ICC=.68) for two different objects across years indicated that this score reflects a stable aspect of temperament. Hair samples were collected from each subject approximately 3-6 months following the second assessment; cortisol levels were determined from the hair. A significant inverse relationship of Novelty Seeking score with hair cortisol level (p<.01) was noted. The high hair cortisol groups had significantly lower Novelty Seeking scores than the low cortisol groups both years (p's<.05). These results suggest that low average cortisol levels promote novelty seeking, while high average levels inhibit novelty seeking behavior.

Environmental stress alters genetic regulation of novelty seeking in vervet monkeys

Considerable attention has been paid to identifying genetic influences and gene–environment interactions that increase vulnerability to environmental stressors, with promising but inconsistent results. A nonhuman primate model is presented here that allows assessment of genetic influences in response to a stressful life event for a behavioural trait with relevance for psychopathology. Genetic and environmental influences on free-choice novelty seeking behaviour were assessed in a pedigreed colony of vervet monkeys before and after relocation from a low stress to a higher stress environment. Heritability of novelty seeking scores, and genetic correlations within and between environments were conducted using variance components analysis. The results showed that novelty seeking was markedly inhibited in the higher stress environment, with effects persisting across a 2-year period for adults but not for juveniles. There were significant genetic contributions to novelty seeking scores in each year (h² = 0.35–0.43), with high genetic correlations within each environment (rhoG > 0.80) and a lower genetic correlation (rhoG = 0.35, non-significant) between environments. There were also significant genetic contributions to individual change scores from before to after the move (h² = 0.48). These results indicate that genetic regulation of novelty seeking was modified by the level of environmental stress, and they support a role for gene–environment interactions in a behavioural trait with relevance for mental health.

Maternal salivary cortisol differs by fetal sex during the second half of pregnancy

Maternal salivary cortisol was measured at weekly intervals from 24 to 38 weeks gestation. The total sample consisted of 120 women enrolled in staggered intervals in such a way as to generate weekly measures of salivary cortisol during the latter half of pregnancy. Hierarchical linear modeling revealed the expected increase in unbound maternal cortisol during this period, with a slight deceleration in rate of increase at 33 weeks gestation. Women carrying male fetuses had higher levels of salivary cortisol initially as compared to women carrying female fetuses; at 30 weeks gestation there was cross-over such that higher maternal cortisol was observed in women carrying female fetuses beyond this time and through term. Results highlight the importance of considering fetal sex as a moderator of contemporaneous and predictive associations between maternal cortisol and prenatal or postnatal development.

Hair cortisol levels as a retrospective marker of hypothalamic-pituitary axis activity throughout pregnancy: comparison to salivary cortisol

Maternal stress during pregnancy is associated with negative maternal/child outcomes. One potential biomarker of the maternal stress response is cortisol, a product of activity of the hypothalamic-pituitary-adrenal axis. This study evaluated cortisol levels in hair throughout pregnancy as a marker of total cortisol release. Cortisol levels in hair have been shown to be easily quantifiable and may be representative of total cortisol release more than single saliva or serum measures. Hair cortisol provides a simple way to monitor total cortisol release over an extended period of time. Hair cortisol levels were determined from each trimester (15, 26 and 36 weeks gestation) and 3 months postpartum. Hair cortisol levels were compared to diurnal salivary cortisol collected over 3 days (3 times/day) at 14, 18, 23, 29, and 34 weeks gestational age and 6 weeks postpartum from 21 pregnant women. Both salivary and hair cortisol levels rose during pregnancy as expected. Hair cortisol and diurnal salivary cortisol area under the curve with respect to ground (AUCg) were also correlated throughout pregnancy. Levels of cortisol in hair are a valid and useful tool to measure long-term cortisol activity. Hair cortisol avoids methodological problems associated with collection other cortisol measures such as plasma, urine, or saliva and is a reliable metric of HPA activity throughout pregnancy reflecting total cortisol release over an extended period.

Hematological and serum biochemical indices in healthy bonnet macaques (Macaca radiata)

BACKGROUND

Blood reference values for bonnet macaques (Macaca radiata) are limited. The goal of this study was to determine reference ranges for hematological and serum biochemical indices in healthy, socially housed bonnet macaques for males and females over a range of ages.

METHODS

Blood hematological and serum biochemical values were obtained from 50 healthy bonnet macaques of both sexes and aged 10-234 months.

RESULTS

Age and sex differences were present in a number of measures. Globulins, total protein, and creatinine (CREAT) values were highest among older subjects, while alkaline phophatase, albumin, and phosphorus values were higher in juveniles. Sex differences were present in concentrations of red blood cells and CREAT, with higher values in males.

CONCLUSION

The blood parameter data reported here as age-specific reference values for laboratory-housed, healthy bonnet macaques may be used to inform clinical care and laboratory primate research.

Estimates of milk constituents from lactating bonnet macaque (Macaca radiata) mothers between two and seven months post-partum

BACKGROUND

The literature regarding milk composition in non-human primates collected across offspring development is limited. We assayed milk samples from bonnet macaque (Macaca radiata) mothers as part of studies characterizing development of this species.

METHODS

Milk was obtained when possible longitudinally from seven lactating bonnet macaque mothers. Samples were frozen until analysis. Individual samples were analyzed to determine the concentrations of electrolytes including sodium, potassium, calcium, chloride, and magnesium, as well as urea, protein, lipids, glucose, and lactose.

RESULTS

A trend for increased lipids as well as protein percentage was noted with increasing infant age. Chloride and calcium showed an increase with age, whereas other electrolytes remained relatively stable across development.

CONCLUSIONS

The composition of the milk of this particular macaque species was similar to other Old World primates as well as humans. These data add to the limited information available on milk constituents among mammals.

The α7 nicotinic acetylcholine receptor and the acute stress response: maternal genotype determines offspring phenotype

α7 Nicotinic acetylcholine receptors (α7nAchRs) modulate immune activation by suppressing production of pro-inflammatory cytokines in peripheral immune cells. α7nAchRs also modulate inhibitory output in the hippocampus, which provides input to key circuits of the HPA axis. Therefore, the α7 nicotinic acetylcholine receptor gene (CHRNA7) may be associated with cortisol stress response. Polymorphisms in the CHRNA7 promoter decrease its expression and may dampen the cholinergic response, leading to an increase in inflammation. Increased inflammation may change the intrauterine environment, altering neuroendocrine development in the offspring. Maternal CHRNA7 genotype could affect an offspring's HPA regulation via reprogramming in utero. Patients with allergic disorders have a differential cortisol response to stress. This study utilized samples collected from a cohort of 198 adolescents in a previous study of atopic disorders, who demonstrated a disturbance in HPA response associated with atopy. Salivary cortisol samples collected from the adolescents after a series of laboratory procedures and DNA samples collected from the adolescents and their parents were used for further analysis. DNA samples were genotyped for allelic variation in the CHRNA7 promoter. Genetic association analyses with the cortisol levels were performed in the adolescents. Maternal genotype influences were investigated for the CHRNA7 gene. We also included maternal and child atopy diagnosis as covariates in determining cortisol levels and tested for association of CHRNA7 to atopy. Polymorphisms in the CHRNA7 promoter were associated with lower cortisol levels after a small laboratory stress. Our findings also show that although the child's CHRNA7 genotype affects stress response, the maternal genotype has a stronger influence on cortisol release after stress in male offspring. These effects were independent of atopy status.

Child care setting affects salivary cortisol and antibody secretion in young children

Elevated afternoon levels of cortisol have been found repeatedly in children during child care. However, it is unclear whether these elevations have any consequences. Because physiologic stress systems and the immune system are functionally linked, we examined the relationship between salivary cortisol concentration and antibody secretion across the day at home and in child care, and their relationships with parent-reported illnesses. Salivary antibody provides a critical line of defense against pathogens entering via the mouth, but little is known about its diurnal rhythm in young children or the effect of different environmental contexts. Saliva samples were taken at approximately 10:30 a.m., 3:30 p.m. and 8:00 p.m. on two child care and two home days in a sample of 65 3-5-year-old children attending very high quality, full time child care centers. Results indicated that (1) a rising cortisol profile at child care, driven by higher afternoon levels, predicted lower antibody levels on the subsequent weekend, (2) higher cortisol on weekend days was related to greater parent-reported illness, and (3) a declining daily pattern in sIgA was evident on weekend and child care days for older preschoolers, but only on weekend days for younger preschoolers. The results suggest that elevated cortisol in children during child care may be related to both lowered antibody levels and greater illness frequency.

Challenges to bonnet monkey (Macaca radiata) social groups: Mother-infant dyad and infant social interactions

The mother-infant dyad is crucial to early development in a variety of species. The complexity of social groupings in nonhuman primates makes this relationship resilient as well as susceptible to early challenges associated with environmental chaos. Quantitative behavior observations of bonnet monkey mother-infant interactions were collected from 28 mother-infant dyads between one and twelve months of age. Social groups were subjected to several prenatal and/or postnatal housing relocations within a single year resulting in two study groups. One group experienced relocations (ATYPICAL, n = 14) and the second group (TYPICAL, n = 14) was conceived and reared in the same location. Behaviors in the ethogram included mother-infant interactions and infant social interactions with other members of the group. Observations between ages of two to four months were analyzed by a mixed model analysis of variance including fixed effects of per and postnatal history (TYPICAL, ATYPICAL), age, and history by age interaction and random effects of mother and infant nested within mother. A significant effect of relocation history was noted on a number of infant behaviors. ATYPICAL infants were out of direct contact with their mother at an earlier age but remained in her proximity. Control of proximity shifted to offsrping in the ATYPICAL group compared to the TYPICAL group. Furthermore, greater social interactions between two and four months of age with other members of the social group as well as the ir mother were observed in the ATYPICAL group. It is suggested that continuous challenge associated with relocation may affect the infant at later developmental ages due to these early differences in ways that are yet unclear.

Fetal motor activity and maternal cortisol

The contemporaneous association between maternal salivary cortisol and fetal motor activity was examined at 32 and 36 weeks gestation. Higher maternal cortisol was positively associated with the amplitude of fetal motor activity at 32 weeks, r(48) = .39, p < .01, and 36 weeks, r(77) = .27, p < .05, and the amount of time fetuses spent moving at 32 weeks during the 50 min observation period, r(48) = 33, p < .05. Observation of periods of unusually intense fetal motor activity were more common in fetuses of women with higher cortisol, Mann-Whitney U = 58.5. There were no sex differences in fetal motor activity, but the associations between maternal cortisol and fetal motor amplitude and overall movement were significantly stronger for male than female fetuses.

When is enough measurement, enough? Generalizability of primate immunity over time

A statistical generalizability analysis gauges the degree to which a single assessment of a parameter successfully estimates that measure over repeated assessments for that individual. The generalizability of enumerative and functional immune parameters was estimated for two species of macaque monkeys assessed every 3 months between 18 and 42 months of age. Subjects were cross-balanced by species (bonnet, Macaca radiata, n=22; pigtail, Macaca nemestrina, n=21), sex (male, n=21; female, n=22), and brief early maternal separation with reunion (control, n=21; separated, n=22). Cell subset analysis showed the best generalizability (35-69%). Natural cytotoxicity also performed well (44-70%), but when computed on a lysis per cell basis, removing the effect of cell phenotype, it was less stable (15-48%). For most immune parameters, at least 5 assessments would be necessary to establish conventionally reliable (0.80) characterizations of long-term, stable individual differences in immunity, and three for minimally reliable (0.60) characterizations. More reactive parameters, as well as more behaviorally reactive species, yielded more generalizable results. Cell subsets that are typically most sensitive to acute stress (CD8, CD16) were more stable than other subsets (CD4, CD20). Behaviorally reactive species (pigtail) yielded more stable natural cytotoxicity results than the less reactive species (bonnet). Sex and rearing condition (early, brief maternal separation) did not substantially affect generalizability, although females tended to generate more stable results than did males.

Salivary cortisol among American Indians with and without posttraumatic stress disorder (PTSD): gender and alcohol influences

Disruptions in hypothalamic-pituitary-adrenal regulation and immunity have been associated with posttraumatic stress disorder (PTSD). We examined the association of PTSD with diurnal rhythms in salivary cortisol in a convenience sample from a population-based study of male and female American Indians. Subjects with and without PTSD were identified from American Indians living on/near a Northern Plains reservation as part of a larger study. Over two days diurnal saliva samples were collected by staff at the University of Colorado Denver Clinical Research Center at waking, 30min after waking, before lunch, and before dinner. Generalized estimating equations linear regression models investigated the influence of PTSD on cortisol over time. The association of a lifetime diagnosis of PTSD with salivary cortisol level was assessed in subjects with complete data (PTSD: n=27; no PTSD n=32) for age, gender, and alcohol consumption in the past month. Subject mean age was 44 years, and 71% were women. When stratified by gender, women with a lifetime diagnosis of PTSD had significantly higher mean cortisol levels throughout the day than women without PTSD (p=0.01); but there was no significant association between PTSD and cortisol levels in men (p=0.36). The cortisol awakening response - the difference in cortisol levels from waking to 30min after waking - was not associated with PTSD in men or women. A lifetime diagnosis of PTSD may influence diurnal cortisol among American Indian women. These effects were independent of influences of current alcohol use/abuse. The unexpected elevation in cortisol in American Indian women with a lifetime diagnosis of PTSD may reflect acute anxiety associated with experiencing a number of novel tests in a strange location (e.g., cardiac imaging, medical, dental exams, etc.), or concurrent depression.

Coregulation in Salivary Cortisol During Maternal Holding of Premature Infants

Purpose: The purpose of this study was to examine coregulation between mothers and preterm infants in hypothalamic-pituitary-adrenocortical (HPA) system activity, as indicated by salivary cortisol levels, while mothers held their infants. The research questions were (a) does mother—infant coregulation in HPA activity occur during holding? and (b) if mother— infant coregulation in HPA activity exists during holding, do type of holding, antenatal steroids, sound level, and maternal touch influence this coregulation? Sample: The sample consisted of 20 mother— infant dyads with infants at a mean postconceptional age of 34.7 weeks (+0.7) and average postnatal age of 15 days (+9) at the time of cortisol sampling. Design: The design was exploratory using convenience sampling. Maternal and infant cortisol levels were obtained at Time 1 (baseline) and Time 2 (end of holding); at each time, the absolute differences in levels between mother and infant were determined. Coregulation was operationalized as less difference between maternal-infant cortisol levels immediately after holding (Time 2) as compared to before holding (Time 1). Results: The two variables with the highest correlation with the Time 1/Time 2 difference score included antenatal steroids and ambient sound level, which were entered into a linear regression equation as predictor variables. A coregulatory relationship in cortisol levels existed between mothers and infants during holding, which was moderated by sound levels. Nurses in the neonatal intensive care unit (NICU) can facilitate the mother—infant relationship, as reflected in coregulatory measures, by promoting a quiet environment, particularly around mothers who are holding their infants.

Diurnal rhythm of cortisol during late pregnancy: associations with maternal psychological well-being and fetal growth

Maternal psychological functioning during pregnancy affects both maternal and fetal well-being. The hypothalamic-pituitary-adrenal (HPA) axis provides one mechanism through which maternal psychosocial factors may be transduced to the fetus. However, few studies have examined maternal psychological factors or birth outcomes in relation to the diurnal pattern of cortisol across the day. The current study examined maternal psychological well-being, parity status, and birth weight in relation to the maternal cortisol diurnal rhythm in a group of 98 low-risk pregnant women (51 primiparae). At 36 weeks gestation, participants completed both pregnancy-specific and general self-report measures of psychological functioning and provided saliva samples at 8:00, 12:00, and 16:00 h on 2 consecutive working days for the assay of cortisol. The expected diurnal decline in salivary cortisol was observed. Higher trait anxiety was associated with a flatter afternoon decline for all mothers. For primiparae, steeper morning cortisol declines were associated with lower infant birth weight. The findings suggest that regulation of the HPA axis may differ by parity status with downstream implications for fetal growth and development.

Psychosocial influences on immunity, including effects on immune maturation and senescence

Studies investigating the influence of psychosocial factors on immunity played a critical and formative role in the field of psychoneuroimmunology (PNI), and have been a major component of articles published in Brain, Behavior and Immunity (BBI). An analysis of papers during the first two decades of BBI from 1987-2006 revealed three behavior-related topics were most prominent: (1) stress-induced changes in immune responses, (2) immune correlates of psychopathology and personality, and (3) behavioral conditioning of immunity. Important subthemes included the effect of early rearing conditions on immune maturation in the developing infant and, subsequently, psychosocial influences affecting the decline of immunity in the senescent host. The responsiveness of cell functioning in the young and elderly helped to validate the view that our immune competence is malleable. Many technical advances in immune methods were also evident. Initially, there was a greater reliance on in vitro proliferative and cytolytic assays, while later studies were more likely to use cell subset enumerations, cytokine quantification, and indices of latent virus reactivation. The reach of PNI extended from the traditional clinical entities of infection, autoimmunity, and cancer to attain a broader relevance to inflammatory physiology, and thus to asthma, cardiovascular and gastrointestinal disease. There continue to be many theoretical and applied ramifications of these seminal findings. Fortunately, the initial controversies about whether psychological processes could really impinge upon and modify immune responses have now receded into the pages of history under the weight of the empirical evidence.

Fetal responses to induced maternal relaxation during pregnancy

Fetal responses to induced maternal relaxation during the 32nd week of pregnancy were recorded in 100 maternal-fetal pairs using a digitized data collection system. The 18-min guided imagery relaxation manipulation generated significant changes in maternal heart rate, skin conductance, respiration period, and respiratory sinus arrhythmia. Significant alterations in fetal neurobehavior were observed, including decreased fetal heart rate (FHR), increased FHR variability, suppression of fetal motor activity (FM), and increased FM-FHR coupling. Attribution of the two fetal cardiac responses to the guided imagery procedure itself, as opposed to simple rest or recumbency, is tempered by the observed pattern of response. Evaluation of correspondence between changes within individual maternal-fetal pairs revealed significant associations between maternal autonomic measures and fetal cardiac patterns, lower umbilical and uterine artery resistance and increased FHR variability, and declining salivary cortisol and FM activity. Potential mechanisms that may mediate the observed results are discussed.

Salivary cortisol in preterm infants: Validation of a simple method for collecting saliva for cortisol determination

BACKGROUND AND AIMS

The increased use of salivary cortisol as a biomarker of stress and/or diurnal rhythms has facilitated research of Hypothalamic-pituitary-adrenocortical (HPA)function. Saliva collection remains problematic with preterm infants. The twofold purpose of this study is to 1) establish validity of the filter paper method for saliva collection and 2) apply the filter paper method for saliva collection to preterm infants.

DESIGN AND MEASURES

Whole saliva was collected from six normal adult subjects to create a pool. Validation measures included comparison of levels obtained from whole saliva and filter paper, an evaluation of storage effects, assessing spiking recovery, and measurement of linearity of dilution. In the application study, saliva was collected every three hours, before feedings for three consecutive days from 26 hospitalized preterm infants. Diurnal variation in cortisol was examined using hierarchical linear modeling and individual calculation of diurnal pattern using an accepted technique.

RESULTS

Validation studies revealed acceptable recovery of whole saliva from filters, no effect of room temperature storage of filters for up to six months, and acceptable linearity of dilution up to 4. Saliva from preterm infants was easily collected. Only 2% of the samples were lost due to inadequate wetting of the filters. An inverse association was found between postconceptional age and one-minute APGAR scores and infant cortisol levels. Variable daily cortisol patterns and no discernable rhythm were found for this sample; however, four infants appeared to show atypical diurnal pattern.

CONCLUSIONS

The filter paper method is a valid method of saliva collection that is feasible to use with preterm infants.

Hypercortisolism in Alcohol Dependence and Its Relation to Hippocampal Volume Loss

OBJECTIVE

The effects of hypercortisolism on hippocampal volume have not been studied in heavy drinkers. Prior work suggested increased hypothalamic-pituitary-adrenal activity in relation to lowered total hippocampus volume (THV) in heavy-drinking alcohol-dependent (AD) subjects. The present study hypothesized the following: (1) that chronic heavy-drinking subjects would demonstrate significantly higher salivary cortisol concentrations than light-drinking control subjects and (2) that data from the whole sample group would present an inverse relationship between cortisol concentration and THV.

METHOD

In carefully selected test and control subject groups matched for age, gender, and ethnicity, we measured salivary cortisol samples at waking, waking + 30 minutes, noon, and 4 PM on the day of magnetic resonance imaging of the brain. We next compared mean cortisol concentrations between groups and assessed the statistical association between cortisol concentration and hippocampus volume measures.

RESULTS

Comparison of AD test subjects (n = 8) and non-AD control subjects (n = 8) found significantly higher cortisol concentrations at both morning sampling times (mean [SD] at waking: 0.49 [0.23] vs 0.24 [0.14] microg/dl, p = .012; at waking + 30 minutes: 0.57 [0.37] vs 0.28 [0.11] microg/dl, p = 0.043). Controlling for intracranial volume, there was a significant inverse correlation between waking cortisol concentration and THV (p = .007) in the total sample group (N = 16). However, when analyzed separately, only the control group maintained a strong, inverse association (p = .025). There was no association among the heavy drinking subjects.

CONCLUSIONS

These early data in a small sample support the view that chronic heavy drinking results in high salivary cortisol concentrations. What remains unclear is whether hypercortisolism exerts a selectively injurious effect that results in observed hippocampus volume loss. Further research in larger groups using more frequent, monitored sampling must address the following: (1) whether this finding can be replicated and (2) if replicated, whether the lack of an association between low hippocampal volumes and high cortisol levels may indicate an extent of injury beyond which a normal association of the two may be lost.

Tetanus antibody titers and duration of immunity to clinical tetanus infections in free-ranging rhesus monkeys (Macaca mulatta)

Prior to 1985 tetanus was a major cause of mortality in the free-ranging colony of rhesus monkeys on Cayo Santiago, accounting for almost a quarter of annual deaths. In 1985 and 1986 all animals (except infants) received primary and booster doses, respectively, of tetanus toxoid. In subsequent years primary immunizations were given to all yearlings, and boosters were administered to all 2-year-old animals during the annual capture of the colony. The main objectives of the tetanus immunization program were to reduce the pain and suffering caused by tetanus infections and to decrease mortality in the colony. Other objectives were to evaluate the efficacy of the two-dose tetanus toxoid immunization protocol and to determine whether additional boosters might be required to provide adequate long-term protection against tetanus infections. The immediate effect of the mass immunization program was the elimination of clinical tetanus infections in the population and a 42.2% reduction in the overall mortality rate. Since the immunization program began, no cases of tetanus have been observed in the colony, except in two unimmunized infants, and it has not been necessary to give tertiary injections of tetanus toxoid to maintain protection against infection. A sample collected in 2004 of the original cohort of monkeys immunized in 1985 and 1986 showed that 93.3% (14/15) had protective tetanus antibody titers (>0.01 IU/ml) at the ages of 20-23 years, which is close to the life expectancy of the Cayo Santiago rhesus macaques. Two intramuscular doses of tetanus toxoid provided long-term, if not lifelong, protection against tetanus for rhesus monkeys living in a tropical clime where tetanus is enzootic and the risk of infection is great.

Salivary cortisol determined by enzyme immunoassay is preferable to serum total cortisol for assessment of dynamic hypothalamic--pituitary--adrenal axis activity

OBJECTIVE

The aim of this study was to determine whether salivary cortisol measured by a simple enzyme immunoassay (EIA) could be used as a surrogate for serum total cortisol in response to rapid changes and across a wide range of concentrations.

DESIGN

Comparisons of matched salivary and serum samples in response to dynamic hypothalamic-pituitary-adrenal (HPA) axis testing. Subjects Healthy women (n=10; three taking oral oestrogens) and men (n=2), aged 23--65 years, were recruited from the community. Measurements Paired saliva and serum samples were obtained during three protocols: 10 min of exercise at 90% of maximal heart rate (n=8), intravenous administration of corticotrophin-releasing hormone (CRH; n=4), and dexamethasone suppression (n=7). Cortisol was measured in saliva using a commercial high-sensitivity EIA and total cortisol was measured in serum with a commercial radioimmunoassay (RIA). Results The time course of the salivary cortisol response to both the exercise and CRH tests paralleled that of total serum cortisol. Salivary cortisol demonstrated a significantly greater relative increase in response to the exercise and CRH stimuli (697+/- 826%vs. 209+/- 150%, P=0.04 saliva vs. serum). A disproportionately larger increase in free cortisol, compared with total, would be expected when the binding capacity of cortisol-binding globulin (CBG) is exceeded. In response to dexamethasone suppression, relative decreases in cortisol were not significantly different between the two media (-47+/- 56%vs.-84+/- 8%, P=0.13 saliva vs. serum). Although a significant linear correlation was found for all paired salivary and serum total cortisol samples (n=183 pairs, r=0.60, P<0.001), an exponential model provided a better fit (r=0.81, P<0.001). The linear correlations were strengthened when data from subjects on oral oestrogens (n=52 pairs, r=0.75, P < 0.001) were separated from those not taking oestrogens (n=131 pairs, r=0.67, P<0.001). Conclusions Salivary cortisol measured with a simple EIA can be used in place of serum total cortisol in physiological research protocols. Evidence that salivary measures represent the biologically active, free fraction of cortisol includes: (1) the greater relative increase in salivary cortisol in response to tests that raise the absolute cortisol concentration above the saturation point of CBG; (2) the strong exponential relationship between cortisol assessed in the two media; and (3) the improved linear correlations when subjects known to have increased CBG were analysed separately. Thus, an advantage of measuring salivary cortisol rather than total serum cortisol is that it eliminates the need to account for within-subject changes or between-subject differences in CBG.