Ethnic differences in diurnal cortisol profiles in healthy adults: A meta-analysis

PURPOSE

Cortisol is a well-known biomarker of the physiological stress system; atypical cortisol patterns have been linked to many psychological and physiological illnesses. Previous studies have found vast health disparities among ethnic groups; however, studies examining the relationship between cortisol and ethnicity have found mixed results. This meta-analysis investigated whether there are differences in diurnal cortisol outcomes among ethnic groups, while considering the moderating roles of various individual factors and methodological approaches.

METHODS

Search phrases were entered into MEDLINE, PsycINFO, EMBASE, Cochrane Library, CINAHL, Scopus, and Web of Science. Effect sizes were extracted for ten diurnal cortisol outcomes, including waking, 30 min after waking, cortisol awakening response, slope, area under the curve, urinary twenty-four-hour secretion, total cortisol output, and midday, evening, and bedtime concentrations, for eight ethnic group comparisons, including Asians, Blacks, Hispanics, Indigenous people, Whites, Minority and Majority groups, and Multiethnic groups. Moderator analyses, including variables such as gender, age, and number of cortisol collection time points, were conducted.

RESULTS

There were significant ethnic differences in diurnal cortisol profiles, including cortisol awakening responses, with more robust differences in ethnic comparisons that included White participants. Differences in diurnal cortisol profiles were also moderated by gender, mean age, and sample size.

CONCLUSIONS

This meta-analysis supports the notion that ethnic groups exhibit distinct diurnal cortisol profiles, which, according to the biopsychosocial model of health, may be a result of unique sociocultural experiences. The limitations of this meta-analysis and future directions for stress research with various ethnic groups are discussed. Statement of contribution What is already known on this subject? Studies have found vast health disparities among ethnic groups. Psychological and physiological illnesses and atypical diurnal cortisol profiles are strongly correlated. Studies have examined the relationship between diurnal cortisol rhythms and ethnicity, but findings are mixed. What does this study add? This study is a systematic examination of the relationship between diurnal cortisol rhythm and ethnicity. Psychosocial and methodological factors moderate the relationship between diurnal cortisol output and ethnicity. This study provides insight on factors that contribute to health disparities among ethnic groups.

A cross-cultural analysis of salivary cortisol patterns in breast cancer survivors

Aim: In this study, we examined whether Chinese and White women with and without a history of breast cancer exhibit differences in physiological and psychological stress profiles. Methods: Diurnal and reactive salivary cortisol profiles and psychological stress patterns of 41 breast cancer survivors and 58 healthy women were assessed. Results: Breast cancer survivors displayed a blunted acute cortisol response but there was no main effect of ethnocultural membership. Subjective appraisals of stress during the acute stressor revealed a significant interaction between ethnocultural group, health status and time (p = 0.032). Conclusion: Our results support the existing literature though suggest group differences in the appraisal of stress; thus, underscoring the importance of cultural sensitivity and awareness among clinicians and existing programs.

Stress reactivity in healthy child offspring of parents with anxiety disorders

Several studies suggest that anxiety disorders (AD) involve dysregulation of the autonomic nervous system (ANS) and hypothalamic-pituitary (HPA) axis. However, it is unknown if alterations in these biological systems are premorbid markers of AD risk or a state-dependent feature of anxiety. This study examined ANS and HPA-axis response to a laboratory stressor in healthy child offspring of parents with (n = 55) and without (n = 98) a history of AD. High frequency heart rate variability (HF-HRV) was assessed during sitting and standing baseline conditions and during a speech task where participants remained standing. Salivary cortisol was measured at baseline and at 15, 30, 45 and 60 min post-speech. Subjective anxiety was assessed with a visual analogue scale. Children of parents with AD displayed reduced HRV and a blunted cortisol response to the speech task compared to children of non-anxious parents. No risk group effect was found for anxiety ratings. These preliminary data suggest that healthy children of anxious parents exhibit altered stress reactivity to an acute laboratory stressor. Further research is needed to confirm findings and identify mechanisms that may account for altered self-regulation processes to a stressor in children at familial risk for AD.

Aerobic physical activity and salivary cortisol levels among women with a history of breast cancer

BACKGROUND

Physical activity (PA) helps reduce cancer-related symptoms and improves overall functioning for women with and without a history of breast cancer (BC). Few researchers have examined the associations between PA and physiological stress measures. The aim of this study was to determine whether aerobic PA was associated with diurnal and reactive cortisol patterns, and whether these associations differed for women with and without a history of BC.

METHODS

Participants were 25 women with a history of BC and 23 women without a history of BC who self-reported aerobic PA frequency. To assess diurnal cortisol patterns, participants provided five saliva samples collected on two consecutive days at the following times: upon awakening, 30 min after waking, 12 PM, 4 PM, and 9 PM. To measure reactive cortisol patterns, participants provided seven saliva samples collected before, during, and after doing the Trier Social Stress Test.

RESULTS

Cortisol patterns differed statistically based on women's cancer history, whereby women without a history of BC had significantly higher overall cortisol reactivity to an acute stressor, and a marginally significant (p = .05) cancer experience by aerobic PA interaction was observed when analyzing diurnal cortisol data.

CONCLUSIONS

Findings suggest that PA may not have the same effect on women with and without a history of BC.

Cancer-related cognitive impairment in breast cancer survivors: An examination of conceptual and statistical cognitive domains using principal component analysis

There is a great deal of variability in the composition of neuropsychological test batteries used in the assessment of cancerrelated cognitive impairment (CRCI). Not only the development of a gold standard approach for CRCI assessment would allow for easier identification of women suffering from CRCI but it would also promote optimal care for survivors. As a first step towards the development of a valid and reliable unified test battery, the objective of this study was to verify whether the theoretical domains commonly used in CRCI assessment are statistically supported, before and after breast cancer treatment. Principal component analyses (PCA) were performed on the results from 23 neuropsychological tests grouped into eight conceptual domains. For baseline data, the Kaiser-Meyer-Olkin was .82 and Bartlett's X2(253, N=95) = 949.48, P<0.001. A five-component solution explained 60.94% of the common variance. For the post-treatment data, the Kaiser-Meyer-Olkin was .83 and Bartlett's X2(253, N=95) = 1007.21, P<0.001 and a five component solution explained 62.03% of the common variance. Although a visual comparison of the theoretical model with those determined via PCA indicated important overlap between conceptual domains and statistical components, significant dissimilarities were also observed.

Strain Differences and Effects of Environmental Manipulation on Astrocytes (Glial Fibrillary Acidic Protein), Glucocorticoid Receptor, and Microglia (Iba1) Immunoreactivity between Wistar-Kyoto and Wistar Females

BACKGROUND

Depression is often associated with an increase in hypothalamic-pituitary-adrenal (HPA) axis reactivity and immune response. To investigate this relationship, we examined the consequences of environmental manipulation on the neural correlates of the HPA axis and immune response in an animal model of depression, the Wistar-Kyoto (WKY) rat. Additionally, female animals are often overlooked in preclinical research because of the hormone fluctuations inherent in the estrous cycle.

METHODS

Female rats were randomly assigned to 1 of 3 environments for 30 days: (1) environmental enrichment (EE), (2) standard housing (SH), and (3) isolated housing (IH). Immunoreactivity of astrocytes (glial fibrillary acidic protein [GFAP]), glucocorticoid receptors (GRs), and microglia (Iba1) in the hippocampus and amygdala were measured using immunohistochemistry.

RESULTS

WKY animals had significantly more GR staining area and Iba1 staining intensity and area in the CA1 of the hippocampus. In enriched Wistar rats, GFAP staining intensity and area were greater in the CA1. A trend towards a greater percent of area stained with GR was found in WKY animals as compared to that of the Wistar animals. This was due to WKY females in EE having significantly higher GR staining intensity and area in the amygdala as compared to that of animals in SH.

DISCUSSION

These strain differences lend support to the use of WKY animals as an animal model of depression. Furthermore, due to the effects of EE on GFAP and GR staining in WKY females, we suggest that EE can be used as an intervention to potentially alleviate the negative effects of depression.

Motherhood and well-being in young breast cancer survivors

Aim: This exploratory study aimed to examine differences in well-being between young breast cancer survivors (BCS) with and without children. Materials & methods: Participants (n = 816) completed an online survey relating to quality of life, illness intrusiveness, fear of cancer recurrence, stress and social support. Results: Exploratory and confirmatory factor analyses revealed similar models of well-being between both groups, but with a stronger relationship between psychological adjustment and illness intrusiveness for BCS with children (r = -0.779, 95% CI: -0.711, -0.848 vs r = -0.525, 95% CI: -0.423, -0.627). Conclusion: Parenting compromises the overall well-being of young BCS with children and they would therefore benefit from interventions and social and oncological support programs, especially for those caring for minor children.

Salivary Alpha-Amylase Reactivity in Breast Cancer Survivors

The two main components of the stress system are the hypothalamic-pituitary-adrenal (HPA) and sympathetic-adrenal-medullary (SAM) axes. While cortisol has been commonly used as a biomarker of HPA functioning, much less attention has been paid to the role of the SAM in this context. Studies have shown that long-term breast cancer survivors display abnormal reactive cortisol patterns, suggesting a dysregulation of their HPA axis. To fully understand the integrity of the stress response in this population, this paper explored the diurnal and acute alpha-amylase profiles of 22 breast cancer survivors and 26 women with no history of cancer. Results revealed that breast cancer survivors displayed identical but elevated patterns of alpha-amylase concentrations in both diurnal and acute profiles relative to that of healthy women, F (1, 39) = 17.95, p < 0.001 and F (1, 37) = 7.29, p = 0.010, respectively. The average area under the curve for the diurnal and reactive profiles was 631.54 ± 66.94 SEM and 1238.78 ± 111.84 SEM, respectively. This is in sharp contrast to their cortisol results, which showed normal diurnal and blunted acute patterns. The complexity of the stress system necessitates further investigation to understand the synergistic relationship of the HPA and SAM axes.

Analysis of the cortisol diurnal rhythmicity and cortisol reactivity in long-term breast cancer survivors

SUMMARY 

Aims: In this paper, we examine the long-term consequences of a breast cancer diagnosis on hypothalamic–pituitary–adrenal axis functioning. Methods: This study provides a comprehensive analysis of the diurnal and reactive cortisol profiles of breast cancer survivors considered ‘disease-free’ compared with women with no history of breast cancer. Results: The results indicate similar diurnal patterns in both groups; however, significant differences in stress reactivity were noted, with breast cancer survivors displaying a relatively flat profile following the acute stress induction. Subjective levels of psychological stress were similar in both groups, suggesting incongruence between perceived stress and the physiological stress response of breast cancer survivors. Conclusion: The patterns suggest a progression towards more typical cortisol reactivity with longer time since diagnosis and may reflect some recovery of hypothalamic–pituitary–adrenal axis functioning as time passes.

Differences in verbal memory retrieval in breast cancer chemotherapy patients compared to healthy controls: a prospective fMRI study

Cognitive complaints by breast cancer survivors receiving chemotherapy have led to an increasing interest in elucidating the possible causes of such impairment. Although a number of neuroimaging studies have been conducted, only a handful of them have taken into account cognitive status pre-chemotherapy. The current study included pre-chemotherapy and post-chemotherapy assessment. In addition, various factors such as depression, anxiety, fatigue and days since surgery were considered during analyses. Breast cancer patients performed an fMRI verbal recall task before and an average of 1 month after chemotherapy. Well matched controls also performed the task with a similar timeline. Pre-chemotherapy analyses revealed that patients activated the anterior cingulate less than controls during memory retrieval when anxiety and fatigue scores were added as covariates during group comparisons. In addition, there were also changes in brain activation from pre- to post-chemotherapy in patients but not in controls. Post-chemotherapy, patients had less activation in the bilateral insula, the left inferior orbitofrontal cortex and the left middle temporal gyrus. Finally, patients also showed significantly less activation when compared to controls. Brain regions included: the right middle and superior temporal gyrus, the right medial frontal gyrus, the right inferior orbitofrontal cortex, the left insula and left superior temporal pole. Importantly, depression, anxiety, and particularly fatigue accounted for some of brain activation differences. Our results suggest that chemotherapy in part plays a role in brain activation differences and it also highlights the importance of rigorously controlling for confounding variables. Only by controlling such factors can we understand the role that chemotherapy may play on cognition.

Bisphenol-A: epigenetic reprogramming and effects on reproduction and behavior

Bisphenol A (BPA) is a synthetic compound used in the production of many polycarbonate plastics and epoxy resins. It is one of the most widely produced chemicals in the world today and is found in most canned goods, plastics, and even household dust. Exposure to BPA is almost universal: most people have measurable amounts of BPA in both urine and serum. BPA is similar in structure to estradiol and can bind to multiple targets both inside and outside the nucleus, in effect acting as an endocrine disruptor. Research on BPA exposure has accelerated in the past decade with findings suggesting that perinatal exposure to BPA can negatively impact both male and female reproduction, create alterations in behavior, and act as a carcinogen. BPA can have both short term and long term effects with the latter typically occurring through epigenetic mechanisms such as DNA methylation. This review will draw on both human and animal studies in an attempt to synthesize the literature and examine the effects of BPA exposure on reproduction, behavior, and carcinogenesis with a focus on the potential epigenetic mechanisms by which it acts.

The impact of motherhood on perceived stress, illness intrusiveness and fear of cancer recurrence in young breast cancer survivors over time

OBJECTIVE

Parenting while coping with breast cancer can be challenging for many young women, yet little is known about the impact of motherhood on their well-being over time.

DESIGN

The first part of this study examined differences in perceived stress, illness intrusiveness and fear of cancer recurrence between young breast cancer survivors with and without children in two separate time frames (0-5 and 5-15 years since diagnosis). The second part identified determinants for these elements of well-being in young mothers exclusively.

MAIN OUTCOME MEASURES

Seven hundred and forty two young North American women previously diagnosed with breast cancer completed measures of perceived stress, illness intrusiveness, fear of cancer recurrence and parenting stress (mothers only) via a web-based survey.

RESULTS

Compared to young survivors without children, young mothers reported higher levels of fear of cancer recurrence and illness intrusiveness in intimate life domains during both time frames. Part 2 revealed how maternal age, age of children, time since diagnosis and parenting stress impacted on well-being in this group.

CONCLUSIONS

Young mothers with breast cancer need support to manage their fears of having a recurrence and to cope with problems in intimacy well into remission. This study identifies the most vulnerable groups of mothers.

Investigation of a neuropsychological screen for chemo-fog

Research on chemotherapy-induced cognitive impairment (the term ‘‘chemo-fog’’ is used by many investigators) supports the occurrence of subtle declines in function for a subset of recipients. Identification of vulnerable individuals via comprehensive neuropsychological batteries is complicated due to their lack of clinical utility and increased risk of misclassification. The goal of this paper was to evaluate the ability of a reduced battery to detect chemotherapy-related cognitive impairments. Data from our previous study (Ouimet et al. J Clin Exp Neuropsychol 31:73–89, 2009) were used to compare a comprehensive neuropsychological test battery comprising 23 tests with a reduced battery consisting of a subset of nine tests. A standardized regression-based approach revealed that a comparable numbers of participants were identified by both batteries, suggesting that individuals vulnerable to chemotherapy-induced cognitive impairment can be identified by a more selective battery. Further work is needed to clarify the neuropsychological tests most sensitive to detecting impairments associated with chemotherapy so that assessment batteries can be limited to these tests.

Investigation of a neuropsychological screen for chemo-fog

Research on chemotherapy-induced cognitive impairment (the term ‘‘chemo-fog’’ is used by many investigators) supports the occurrence of subtle declines in function for a subset of recipients. Identification of vulnerable individuals via comprehensive neuropsychological batteries is complicated due to their lack of clinical utility and increased risk of misclassification. The goal of this paper was to evaluate the ability of a reduced battery to detect chemotherapy-related cognitive impairments. Data from our previous study (Ouimet et al. J Clin Exp Neuropsychol 31:73–89, 2009) were used to compare a comprehensive neuropsychological test battery comprising 23 tests with a reduced battery consisting of a subset of nine tests. A standardized regression-based approach revealed that a comparable numbers of participants were identified by both batteries, suggesting that individuals vulnerable to chemotherapy-induced cognitive impairment can be identified by a more selective battery. Further work is needed to clarify the neuropsychological tests most sensitive to detecting impairments associated with chemotherapy so that assessment batteries can be limited to these tests.

Pre-chemotherapy differences in visuospatial working memory in breast cancer patients compared to controls: an FMRI study

INTRODUCTION

Cognitive deficits are a side-effect of chemotherapy, however pre-treatment research is limited. This study examines neurofunctional differences during working memory between breast cancer (BC) patients and controls, prior to chemotherapy.

METHODS

Early stage BC females (23), scanned after surgery but before chemotherapy, were individually matched to non-cancer controls. Participants underwent functional magnetic resonance imaging (fMRI) while performing a Visuospatial N-back task and data was analyzed by multiple group comparisons. fMRI task performance, neuropsychological tests, hospital records, and salivary biomarkers were also collected.

RESULTS

There were no significant group differences on neuropsychological tests, estrogen, or cortisol. Patients made significantly fewer commission errors but had less overall correct responses and were slower than controls during the task. Significant group differences were observed for the fMRI data, yet results depended on the type of analysis. BC patients presented with increased activations during working memory compared to controls in areas such as the inferior frontal gyrus, insula, thalamus, and midbrain. Individual group regressions revealed a reverse relationship between brain activity and commission errors.

CONCLUSION

This is the first fMRI investigation to reveal neurophysiological differences during visuospatial working memory between BC patients pre-chemotherapy and controls. These results also increase the knowledge about the effects of BC and related factors on the working memory network.

SIGNIFICANCE

This highlights the need to better understand the pre-chemotherapy BC patient and the effects of associated confounding variables.

Environmental-enrichment-related variations in behavioral, biochemical, and physiologic responses of Sprague-Dawley and Long Evans rats

The behavioral, biochemical, and physiologic consequences of 6 wk of environmental enrichment were evaluated in male Long Evans and Sprague-Dawley rats and compared with those of rats in standard single-housing conditions. Standard housing provided little or no social or physical stimulation whereas environmental enrichment comprised group housing for 8 h daily in a 3-story cage equipped with novel stimuli. Dependent measures included performance in the forced swim test, thresholds for brain-stimulation reward, sucrose intake and preference, determination of corticosterone levels before and after brief restraint stress, and rate of weight gain. In forced swimming tests, active behaviors (diving, swimming with struggling, and climbing) tended to dominate over passive behaviors (sinking, floating) in both groups and outbred rat stocks (especially in enriched groups) on the first day. These behaviors were replaced with maintenance behaviors such as grooming and swimming without struggling on the second exposure, with enriched Long Evans rats showing the largest decline in activity. Baseline plasma corticosterone levels were elevated in both rat stocks after 6 wk of enrichment. After restraint stress, hormone levels in enriched animals tended to peak earlier and approach or exceed baseline values more quickly than was observed in the comparable control groups. Rate of body weight gain was greater in enriched Long Evans rats than Sprague-Dawley or control rats. Our observations indicate that stock- and group-associated differences in several indices occur in association with enrichment. The data support the claim that environmental enrichment may render animals more resilient to challenges.

Modeling dad: animal models of paternal behavior

In humans, paternal behaviors have a strong influence on the emotional and social development of children. Fathers, more frequently than mothers, leave the family nucleus, and/or become abusive, leading to offspring that are more likely to grow under stressful conditions and greater susceptibility to abnormal health and social outcomes. Literature on parental behaviors, human or animal, has primarily focused on the interactions between mothers and offspring, with little research directed at understanding paternal behavior. In animal studies, experimenters correlate paternal behaviors with those seen in rodent or primate mothers, often under situations in which behaviors such as nest protection, huddling, pup grooming, and retrieval are artificially induced. In humans, the majority of the studies have looked at paralleling hormonal changes in fathers with those occurring in mothers, or observed paternal behaviors in populations with specific anthropological backgrounds. These studies reveal commonalities in parental behaviors and their underlying neural circuits. However, this work highlights the possibility that paternal behavior has components that are strictly masculine with unique neurobiological mechanisms. This review summarizes this information and provides a current view of a topic that needs further exploration.

Effects of gestational stress: 1. Evaluation of maternal and juvenile offspring behavior

In both humans and animals, stress experienced during gestation is associated with physiological changes and disruptions in emotional function and cognitive ability in offspring; however, much less is known about the effects of such stress in mothers. In animal models, physical restraint is commonly employed to induce stress during gestation and results in elevated postpartum maternal anxiety and changes in maternal care. The purpose of the current study was to evaluate the consequences of restraint stress applied on gestation days 10 through 19 in mother rats and their juvenile offspring. Progeny were reared by birth mothers. Preterm anxiety was assessed in the elevated plus maze and maternal behavior in the retrieval test. Cognitive (T-maze) and anxiety measures (elevated plus maze and emergence) were applied to a subset of male and female offspring at 30-31 days of age. Weight and litter characteristics were also recorded. Mother rats exposed to stress during gestation had attenuated weight gain, elevated anxiety-like behavior, and reduced maternal care. Stressed mothers also had fewer pups and an elevated offspring mortality rate. The consequences of gestational stress in offspring were subtle and gender-dependent. Only juvenile females displayed marginal effects of gestational stress in the form of elevated anxiety-like behavior and attenuated weight gain. In the current study, although gestational stress had robust effects in the mother rat, these did not translate to similar changes in offspring behavior. The importance of focusing research on maternal responses to gestational stress is highlighted by these findings.

The cognitive effects of adjuvant chemotherapy in early stage breast cancer: a prospective study

PURPOSE

The primary purpose of this study was to evaluate the cognitive effects of adjuvant chemotherapy in post-menopausal breast cancer patients.

PATIENTS AND METHODS

Breast cancer patients scheduled to receive adjuvant chemotherapy (n = 61) completed comprehensive cognitive testing before and after treatment. A control group of women receiving adjuvant hormonal therapy (n = 51) was tested at comparable intervals.

RESULTS

Mean scores for both patient groups were within the normal range relative to published norms on all cognitive tests at both time points, and generally inclined or stayed the same from baseline to retest in both groups. However, in an analysis of individual change scores, the chemotherapy patients were 3.3 times more likely than the hormonal patients to show reliable cognitive decline (31 and 12%, respectively). Chemotherapy subjects showing decline were less educated and had higher baseline depression scores than their counterparts who did not decline. Working memory was the cognitive domain most vulnerable to the effects of chemotherapy.

CONCLUSION

These data support previous findings of a subtle negative influence of chemotherapy on cognitive function in a subgroup of breast cancer patients. The results are discussed in terms of the importance of study design.

Influence of housing on the consequences of chronic mild stress in female rats

The chronic mild stress (CMS) paradigm was developed to model anhedonia in animals. The repeated administration of a series of unpredictable, mild stressors attempts to mimic the daily stress associated with the onset of clinical depression in humans. Male animals are predominantly used in these investigations despite significant, well-documented sex differences in human depression. In this study, the CMS procedure was modified to be more ecologically relevant to female animals. The effects of stress on sucrose preference, social interaction, rate of weight gain, and regularity of the estrous cycle in female Sprague-Dawley (SD) rats were evaluated in both single- and paired-housed rats, during 3 weeks each of baseline, CMS, and post-CMS phases. The results indicate that only single-housed rats exposed to stressors have a reduced rate of weight gain, significantly attenuated sucrose preference levels, and increased social interaction scores during the CMS phase of the study. Housing condition more than exposure to stress appeared to contribute to the disruption of estrous cycling in some animals. These data suggest that housing affords some protection from the negative consequences of CMS, at least in female rats, and that lack of social interaction in the single-housing condition may render females more vulnerable to stress-related illnesses. The development of paradigms that model human depression should emphasize sex-specific differences.

Investigating the hedonic effects of interferon-alpha on female rats using brain-stimulation reward

Interferon-alpha (IFN-alpha) is used as a front-line treatment for cancer and other diseases. Reports of depression as a consequence of IFN-alpha therapy scatter the literature, generating interest in the CNS disruptions elicited by this cytokine. In the present work, we investigated the short- and long-term effects of a single systemic injection of vehicle, 10, or 1000 units of IFN-alpha on temperature, body weight, food intake, sickness behaviours, locomotor activity, and brain stimulation reward (BSR) thresholds elicited from the ventral tegmental area in female Long-Evans rats. Pioneered for studying motivational processes, BSR has been exploited as a tool for tracking hedonic status in animal models of depression. In this study, the main findings were that IFN-alpha did not induce anhedonia as defined by no increase in frequency thresholds. However, the analyses of sickness behaviours unveiled a significant increase in piloerection in all sham control animals that received an IFN-alpha injection while the BSR animal scores remained relatively unchanged between pre- and post-injection days. This pattern was also evident in the overall total sickness behaviour scores. Our data suggest that a single exposure to IFN-alpha treatment in female rats elicits long-term somatic effects, without altering hedonic status.

Behavioral and physiological effects of a single injection of rat interferon-alpha on male Sprague-Dawley rats: a long-term evaluation

Interferon-alpha (IFN-alpha) is a cytokine used as a first line of defense against diseases such as cancer and hepatitis C. However, reports indicate that its effectiveness as a treatment is countered by central nervous system (CNS) disruptions in patients. Our work explored the possibility that it may also cause long-term behavioral disruptions by chronicling the behavioral and physiological disturbances associated with a single injection of vehicle, 10, 100, or 1,000 units of IFN-alpha in male Sprague-Dawley rats (n = 5/dose). Following 1 day of locomotor baseline collection, we monitored sickness behaviors (ptosis, piloerection, lethargy, and sleep), food and water intake, body weight, temperature, and motor activity. Observations were recorded 4 days prior to and 4 days following the IFN-alpha injection. Temperature and sickness behaviors were recorded three times daily at 9:00, 15:00, and 21:00 h, and all other indices, once daily. On the injection day, temperature values were highest in the animals receiving the 10-unit IFN-alpha dose 15 min and 13 h post-injection. In the case of sickness behaviors, a significant increase was observed in piloerection in all IFN-alpha groups at each time point measured, while the scores of the rats in the vehicle condition remained unchanged between pre- and post-injection days. Analyses of overall sickness behaviors during morning and night observation periods indicated increased scores in all IFN-alpha groups following injection. Cumulatively, these data suggest that a single IFN-alpha exposure may elicit long-term behavioral disruptions and that its consequences should be thoroughly investigated for its use in clinical populations.

A meta-analysis of the neuropsychological effects of adjuvant chemotherapy treatment in women treated for breast cancer

Given the improvement in mortality rates associated with breast cancer, the importance of understanding the long-term neuropsychological consequences of chemotherapy is becoming increasingly vital. This study applies meta-analytic techniques to the scant literature on the relationship between contemporary adjuvant chemotherapy treatment for breast cancer and cognitive dysfunction as examined through neuropsychological indices. Seven studies (involving more than 300 participants) were selected from over 200 potential articles, based on three inclusion criteria: presence of breast cancer, administration of chemotherapy treatment, and use of neuropsychological tests. From these, nine treatment-control comparisons were used to generate 129 Hedge's d effect sizes across the cognitive domains of simple attention, working memory short- and long-term memory, speed of processing, language, spatial abilities, and motor function. Small to medium cumulative effect sizes, showing diminished cognitive function for chemotherapy treatment groups compared to control groups, were obtained for each of the eight cognitive domains. Overall, these results suggest that women who undergo adjuvant chemotherapy as treatment for breast cancer may experience subtle yet consequential cognitive decline.

Behavioral and physiological effects of chronic mild stress in female rats

Anhedonia, a core symptom of clinical depression, refers to the loss of interest in normally rewarding stimuli; the chronic mild stress paradigm, an animal model of depression, was designed with this as an underlying feature. The procedure consists of the administration of a variety of ecologically relevant stressors over long durations. Its effects have been thoroughly investigated in male but not female rats. This study examines the appropriateness of stressors designed to evaluate the development and progression of depression in two strains of female rats, the effectiveness of two measures of anhedonia, and the relationship between stress reactivity and the estrous cycle. Changes in hedonic status were indexed for three weeks following a three week baseline period using two standard behavioral measures of anhedonia: sucrose intake and preference and thresholds for brain stimulation reward. Decreases in 24 h sucrose intake were observed in both strains during the first week of stress manipulations, and continued to decline thereafter for the remainder of the stress phase; in contrast, sucrose preference was unaffected by the stressors, indicating an overall reduction in fluid intake. No changes in the thresholds for brain stimulation reward were observed. The cyclical pattern of estrous was altered in both strains with a significant reduction in the number of regular cycles as a consequence of both the stressors and brain stimulation reward. Furthermore, cyclicity was not reinstated in many animals even six weeks after stress manipulations and behavioral tests had ceased. While the physiological measures suggest that the mild stressors are disruptive to female rats, the results of the behavioral tests are not consistent with the notion that the stressors induce an anhedonic state.

Short- and long-term effects of interleukin-2 on weight, food intake, and hedonic mechanisms in the rat

In the present work, we investigated the short- and long-term effects of a single systemic injection of rat recombinant interleukin-2 on weight, food intake, and brain stimulation reward thresholds elicited from the ventral tegmental area. An inverted U-shaped dose-function was obtained with 0.5 microg producing the greatest increases in the threshold for rewarding brain stimulation which were sustained during the month long tests. No differences between groups in terms of maximum response rates, a measure of performance, were observed. Although all injected groups showed a minor decline in the rate of weight gain over time, percent efficiency of food utilization (percent weight gain/food intake) was the same across groups, suggesting that metabolic function was not affected by the cytokine. In animals with bilateral ventral tegmental area implants, there was no consistent correspondence between the threshold change obtained from ipsilateral stimulation and that associated with the contralateral site; side-to-side differences ranged from 0 to 100%, suggesting a specific interaction between cytokine activity and the locus of rewarding brain stimulation. These data suggest that peripheral IL-2 significantly modifies hedonic processes arising from medial forebrain bundle stimulation in a long-term manner. We further suggest that since this modulation appears to be notably site-specific, IL-2 receptors or its metabolites may not be evenly distributed within the medial forebrain bundle.

Interhemispheric involvement of the anterior cortical nuclei of the amygdala in rewarding brain stimulation

The amygdaloid complex is one of the structures thought to modulate brain stimulation reward (BSR) elicited from the median forebrain bundle (MFB). Previous metabolic and behavioral data from our laboratory point to the amygdaloid cortical nuclei as key to this process. In this study, thresholds for rewarding stimulation of the MFB were determined for 42 days, 21 days following an electrolytic lesion to amygdaloid nuclei ipsilateral to the stimulation electrode, and 21 days following one applied to the contralateral amygdala. A subset of animals showed post-lesion changes in MFB frequency thresholds that were maintained if not augmented after the second lesion. These ranged from 26% to 150% compared to baseline values, among the largest ever reported to our knowledge. Interestingly, damage to anterior sites within the cortical nuclei was the most effective in producing modifications to the rewarding value of the stimulation. Equally singular was the finding that contralateral lesions tended to alter thresholds more than ipsilateral ones, confirming our earlier finding of interhemispheric connectivity in amygdaloid modulation of MFB reward signals. This interpretation was substantiated by tracking long-term metabolic activity in the amygdala using cytochrome oxidase histochemistry. The density of reaction product at damaged amygdala sites was negatively correlated (r=-0.90) with the increases in thresholds obtained at contralateral MFB loci. Together with the fact that such large lesion effects are seldom obtained, our metabolic results point to the existence of a relationship between these nuclei and reward signals generated at the MFB. Moreover, our data suggest that this communication takes place interhemispherically.

Tracing the Neuroanatomical Profiles of Reward Pathways with Markers of Neuronal Activation

Functional neuroanatomical tools have played an important role in proposing which structures underlie brain stimulation reward circuitry. This review focuses on studies employing metabolic markers of neuronal and glial activation, including 2-deoxyglucose, cytochrome oxidase, and glycogen phosphorylase, and a marker of cellular activation, the immediate early gene c-fos. The principles underlying each method, their application to the study of brain stimulation reward, and their strengths and limitations are described. The usefulness of this strategy in identifying candidate structures, and the degree of overlap in the patterns of activation arising from different markers is addressed in detail. How these data have contributed to an understanding of the organization of reward circuitry and directed our thinking towards an alternative framework of neuronal arrangement is discussed in the final section.

Mapping the Neural Substrate Underlying Brain Stimulation Reward with the Behavioral Adaptation of Double-Pulse Methods

Behavioral adaptations of double-pulse methods--primarily collision and refractory period tests--have been employed to unveil the electrophysiological and anatomical characteristics of neural networks of known function. These paradigms are based on trade-off functions: a determination of different combinations of stimuli that yield the same behavioral output. A detailed explanation of the logic and methodology underlying these techniques is elaborated in this paper. The implementation of such approaches to the study of brain stimulation reward (BSR) has provided a means of discriminating between the neurons underlying this behavior from other cells activated by the stimulating electrode, endowing them with a particularly powerful scientific scope. An increasingly detailed portrait of the BSR substrate, both within and outside the medial forebrain bundle, has been emerging as a result of these investigations and is reviewed in this paper. Finally, the challenges associated with these paradigms are discussed and potential solutions as well as future experimental ventures proposed. Attention is drawn to the major contribution of these methods to our understanding of the neural pathways and characteristics underlying BSR.

Strain and gender specific effects in the forced swim test: effects of previous stress exposure

The chronic mild stress (CMS) procedure was developed in rodents to target anhedonia, the core symptom of depressive melancholia. Stress exposure has been shown to induce a variety of physiological, biochemical and behavioral alterations associated with depression, although its anhedonic consequences as indexed by either sucrose intake and preference or thresholds for brain stimulation reward are less reliably observed. In the present study, we assessed the effects of six weeks of CMS on the latter measure in two strains of male and female rats subsequently challenged with an acute psychophysical stressor, forced swimming; their behavior in the swimming cylinder was evaluated on two consecutive days. While brain stimulation reward thresholds and response rates were unchanged by CMS exposure, significant differences in forced swim behaviors were observed between male control and CMS groups. In particular, male Long Evans rats with a history of CMS showed the largest decrease in the duration of active behaviors on the second test day, a pattern less evident in the Sprague-Dawley strain of rats, or in any of the female groups. The results suggest that the effects of depressogenic manipulations are strain and gender dependent, with male Long Evans rats most susceptible, as demonstrated by the selective reduction of struggling behaviors. Inclusion of multiple measures, including the forced swim test, would provide a better understanding of the psychopathological profile engendered by chronic exposure to mild stressors and its genetic specificity.

Evaluation of the effects of chronic mild stressors on hedonic and physiological responses: sex and strain compared

The chronic mild stress (CMS) paradigm was developed in order to simulate in animals the symptom of anhedonia, a major feature of depression. Typically, changes in hedonic status are interpreted from a decrease in either intake or preference for a mild sucrose solution. Although the incidence of clinical depression is significantly higher in women than in men, the study of this disorder in most animal models of depression has been based on the responses of male rodents. The purpose of this study was to compare the effects of 6 weeks of CMS administration among male and female rats of two rat strains, Sprague-Dawley (SD) and Long Evans (LE), with respect to physiological (body, adrenal gland, and spleen weight) and biochemical (plasma corticosterone levels) indices of stress as well as evaluations of 1 and 24 h sucrose intake and preference. Estrous cycle was tracked throughout the study. Overall, our results indicate a slower rate of weight gain in animals, greater in males, exposed to the chronic stressor regime. Furthermore, CMS is shown to disrupt estrous cycling, predominantly in the Long Evans strain of rats. The main behavioral finding was a significant reduction in 24 h sucrose intake in female treated groups, which was not accompanied by alterations in preference. Corticosterone levels were elevated in CMS-treated animals relative to the singly housed control groups, but exposure to a subsequent stressor was not influenced by the stress history. Taken together, the effects of chronic stressor exposure are evident, based on physiological and biochemical indices, although none of the measures distinguished any striking gender specific reactions. The usefulness of sucrose intake or preference as behavioral indices of CMS-induced anhedonia in males and females is modest at best.

Effects of naloxone on rewarding and aversive brain sites

The effects of naloxone on the rewarding and aversive properties of brain stimulation derived from the ventral tegmental area and the nucleus reticularis gigantocellularis, respectively, were assessed in rats, based on the following measures-the current threshold for latency to escape aversive nucleus reticularis gigantocellularis stimulation, the frequency threshold for rewarding ventral tegmental area stimulation, and the frequency threshold for self-stimulation obtained from delivery of concurrent ventral tegmental area and nucleus reticularis gigantocellularis stimulation, before and after three systemic doses of naloxone (0, 10, and 20mg/kg); in the latter case, the stimulation trains were interdigitated with an interpulse interval of 2 ms. Initially, thresholds for concurrent stimulation were elevated relative to the values obtained for ventral tegmental area stimulation alone, returning to baseline values only when the nucleus reticularis gigantocellularis stimulation no longer induced escape. After each pairing of the two sites, the current threshold for escape gradually increased until the maximum value administered, 700 microA, at which point aversive responses were no longer observed. This required very few pairings, between one and five trials across animals. Drug tests were then begun and produced a significant dose-response threshold increase across animals, without reinstating the latency to escape nucleus reticularis gigantocellularis stimulation. These findings are discussed in terms of a dissociation between the analgesic and rewarding properties of ventral tegmental area stimulation.

Chronic paroxetine infusion influences macronutrient selection in male Sprague-Dawley rats

Decreased intake and weight loss are among the side effects frequently reported with chronic selective serotonin reuptake inhibitor (SSRI) use in both humans and animals. In an earlier study, we documented that paroxetine administered for several weeks induced a weight loss of greater than 10% in some male Sprague-Dawley rats (Pharmacol. Biochem. Behav. 63 (1999) 435). As a follow-up to that work, we investigated in this study whether such treatment influenced dietary macronutrient selection. Animals were first habituated to foods containing principally either proteins, fats, or carbohydrates in a self-selection paradigm, after which they were implanted intraperitoneally with osmotic minipumps that delivered either paroxetine (7.5 mg/kg/day) or vehicle (50:50 ethanol:water) for 28 days; food intake and weight changes were documented during this period. No acute effects of the drug were apparent. By the fifth day of treatment, significant differences in weight gain between groups were observed and thereafter generally maintained for the remainder of the study, with animals receiving paroxetine showing about an 8% decrease in weight gain overall. Carbohydrate and fat intakes were significantly reduced, whereas preference was unchanged in fats and proteins and initially decreased in carbohydrates; in the latter, this pattern reversed and exceeded vehicle animals for the second half of the study. Several hypotheses are discussed with respect to specific and nonspecific effects of paroxetine on feeding and macronutrient selection.

The effects of chronic mild stress on male Sprague-Dawley and Long Evans rats: I. Biochemical and physiological analyses

The chronic unpredictable mild stress (CMS) is a paradigm developed in animals to model the relatively minor and unanticipated irritants that lead to a state of anhedonia in some individuals. However, the effectiveness of CMS is sometimes difficult to establish, for which unique strain sensitivities has been attributed as one contributing factor. These considerations led us to design the present study, which was an investigation of the corticosterone response to CMS in two outbred rat strains--Sprague-Dawley and Long Evans. Animals were exposed to one of two conditions--control or CMS--for 3 weeks during which body weight and fecal count were regularly monitored. At the end of this period, blood was sampled at a variety of time intervals following induction of a brief restraint stressor. First, a significant effect of CMS on corticosterone levels was evident at time 0 (prior to the application of the acute restraint stressor) in both strains. Second, the typical quadratic pattern of stressor-elicited fluctuations in this measure was similar in both Sprague-Dawley and Long Evans rats, with consistently elevated levels for the first hour following exposure to the acute stressor; near baseline values were observed at 2 h. However, only in the Long Evans strain were CMS related values much less than that observed in the control group after restraint stress. Third, both strains showed a reduced weight gain in the CMS groups relative to control groups. Fourth, spleen and adrenal weights were similar across all groups. Fifth, fecal counts remained stable across weeks of treatment in all groups with the exception of the Long Evans rats exposed to CMS; in this group, average counts were systematically reduced over the treatment period. We conclude that a history of chronic stress significantly blunts corticosterone levels in Long Evans but not Sprague-Dawley rats following exposure to an acute stressor. Physiological indices however are less influenced by this experience, at least when the exposure is limited to 3 weeks.

Electrolytic lesions of the cortical and adjacent nuclei in the amygdala differentially influence thresholds for rewarding medial forebrain bundle stimulation

After electrolytic lesions to the cortical and adjacent amygdaloid subnuclei, thresholds for rewarding medial forebrain bundle (MFB) stimulation were tracked in 19 rats with bilateral implants and 8 with single implants. Results were categorized into 3 groups depending on the magnitude of the lesion effect on ipsilateral frequency thresholds: substantial (> 60%), small (> 26%), or none (< 26%), compared with baseline values. Five rats exhibited threshold increases up to 225%, among the largest reported to the authors' knowledge. Small shifts were observed in another 5 rats, and no change in the remaining 17 rats. Threshold changes in the contralateral electrode mirrored ipsilateral ones. Results suggest that specific amygdaloid subnuclei modulate MFB reward signals through a diffuse collateralized organization of fibers and lend support to the existence of interhemispheric links in MFB reward pathways.

The substrate for brain-stimulation reward in the lateral preoptic area: III. Connections to the lateral hypothalamic area

Double-pulse tests were used to estimate the refractory periods and anatomical linkage of the reward-relevant fibers that course between the lateral preoptic and lateral hypothalamic areas. In the 1st study, pairs of conditioning and test pulses were delivered to each site, and the interval between pulses varied; recovery from refractoriness was similar at both sites, with the curves generally rising from 0.6 to 2.0 ms. In the 2nd study, the pairs of pulses were delivered to both sites. Six of 7 rats showed evidence of axonal collision, with estimates of conduction velocity that ranged from 0.48 to 8.95 m/s across rats. These results suggest that a wide spectrum of fiber types characterizes the reward-relevant axons that course uninterruptedly between these 2 regions.

Measuring threshold shifts for brain stimulation reward using the method of limits

Thresholds determined from the frequency of pulses and the current for rewarding brain stimulation were obtained from rats with lateral hypothalamic electrodes. The threshold, defined as the frequency or current corresponding to one-half the maximum response rate, was interpolated from reward summation functions. Daily trials of both ascending and descending sequences of frequency and current yielded no significant difference between order of presentation. While there was more variability in the maximum response rates across the sessions, neither frequency- nor current-based threshold evaluations yielded significant rate effects. Our findings suggest that the threshold procedure is generally not influenced by the sequence of delivery of stimulus values and, thus, may be regarded as a reliable measure of the reinforcing properties of brain-stimulation reward.

The substrate for brain-stimulation reward in the lateral preoptic area: III. Connections to the lateral hypothalamic area

Double-pulse tests were used to estimate the refractory periods and anatomical linkage of the reward-relevant fibers that course between the lateral preoptic and lateral hypothalamic areas. In the 1st study, pairs of conditioning and test pulses were delivered to each site, and the interval between pulses varied; recovery from refractoriness was similar at both sites, with the curves generally rising from 0.6 to 2.0 ms. In the 2nd study, the pairs of pulses were delivered to both sites. Six of 7 rats showed evidence of axonal collision, with estimates of conduction velocity that ranged from 0.48 to 8.95 m/s across rats. These results suggest that a wide spectrum of fiber types characterizes the reward-relevant axons that course uninterruptedly between these 2 regions.