Ensemble machine learning model trained on a new synthesized dataset generalizes well for stress prediction using wearable devices

INTRODUCTION

Advances in wearable sensor technology have enabled the collection of biomarkers that may correlate with levels of elevated stress. While significant research has been done in this domain, specifically in using machine learning to detect elevated levels of stress, the challenge of producing a machine learning model capable of generalizing well for use on new, unseen data remain. Acute stress response has both subjective, psychological and objectively measurable, biological components that can be expressed differently from person to person, further complicating the development of a generic stress measurement model. Another challenge is the lack of large, publicly available datasets labeled for stress response that can be used to develop robust machine learning models. In this paper, we first investigate the generalization ability of models built on datasets containing a small number of subjects, recorded in single study protocols. Next, we propose and evaluate methods combining these datasets into a single, large dataset to study the generalization capability of machine learning models built on larger datasets. Finally, we propose and evaluate the use of ensemble techniques by combining gradient boosting with an artificial neural network to measure predictive power on new, unseen data. In favor of reproducible research and to assist the community advance the field, we make all our experimental data and code publicly available through Github at https://github.com/xalentis/Stress. This paper's in-depth study of machine learning model generalization for stress detection provides an important foundation for the further study of stress response measurement using sensor biomarkers, recorded with wearable technologies.

METHODS

Sensor biomarker data from six public datasets were utilized in this study. Exploratory data analysis was performed to understand the physiological variance between study subjects, and the complexity it introduces in building machine learning models capable of detecting elevated levels of stress on new, unseen data. To test model generalization, we developed a gradient boosting model trained on one dataset (SWELL), and tested its predictive power on two datasets previously used in other studies (WESAD, NEURO). Next, we merged four small datasets, i.e. (SWELL, NEURO, WESAD, UBFC-Phys), to provide a combined total of 99 subjects, and applied feature engineering to generate additional features utilizing statistical summaries, with sliding windows of 25 s. We name this large dataset, StressData. In addition, we utilized random sampling on StressData combined with another dataset (EXAM) to build a larger training dataset consisting of 200 synthesized subjects, which we name SynthesizedStressData. Finally, we developed an ensemble model that combines our gradient boosting model with an artificial neural network, and tested it using Leave-One-Subject-Out (LOSO) validation, and on two additional, unseen publicly available stress biomarker datasets (WESAD and Toadstool).

RESULTS

Our results show that previous models built on datasets containing a small number (<50) of subjects, recorded in single study protocols, cannot generalize well to new, unseen datasets. Our presented methodology for generating a large, synthesized training dataset by utilizing random sampling to construct scenarios closely aligned with experimental conditions demonstrate significant benefits. When combined with feature-engineering and ensemble learning, our method delivers a robust stress measurement system capable of achieving 85% predictive accuracy on new, unseen validation data, achieving a 25% performance improvement over single models trained on small datasets. The resulting model can be used as both a classification or regression predictor for estimating the level of perceived stress, when applied on specific sensor biomarkers recorded using a wearable device, while further allowing researchers to construct large, varied datasets for training machine learning models that closely emulate their exact experimental conditions.

CONCLUSION

Models trained on small, single study protocol datasets do not generalize well for use on new, unseen data and lack statistical power. Machine learning models trained on a dataset containing a larger number of varied study subjects capture physiological variance better, resulting in more robust stress detection. Feature-engineering assists in capturing these physiological variance, and this is further improved by utilizing ensemble techniques by combining the predictive power of different machine learning models, each capable of learning unique signals contained within the data. While there is a general lack of large, labeled public datasets that can be utilized for training machine learning models capable of accurately measuring levels of acute stress, random sampling techniques can successfully be applied to construct larger, varied datasets from these smaller sample datasets, for building robust machine learning models.

Generalizable machine learning for stress monitoring from wearable devices: A systematic literature review

INTRODUCTION

Wearable sensors have shown promise as a non-intrusive method for collecting biomarkers that may correlate with levels of elevated stress. Stressors cause a variety of biological responses, and these physiological reactions can be measured using biomarkers including Heart Rate Variability (HRV), Electrodermal Activity (EDA) and Heart Rate (HR) that represent the stress response from the Hypothalamic-Pituitary-Adrenal (HPA) axis, the Autonomic Nervous System (ANS), and the immune system. While Cortisol response magnitude remains the gold standard indicator for stress assessment [1], recent advances in wearable technologies have resulted in the availability of a number of consumer devices capable of recording HRV, EDA and HR sensor biomarkers, amongst other signals. At the same time, researchers have been applying machine learning techniques to the recorded biomarkers in order to build models that may be able to predict elevated levels of stress.

OBJECTIVE

The aim of this review is to provide an overview of machine learning techniques utilized in prior research with a specific focus on model generalization when using these public datasets as training data. We also shed light on the challenges and opportunities that machine learning-enabled stress monitoring and detection face.

METHODS

This study reviewed published works contributing and/or using public datasets designed for detecting stress and their associated machine learning methods. The electronic databases of Google Scholar, Crossref, DOAJ and PubMed were searched for relevant articles and a total of 33 articles were identified and included in the final analysis. The reviewed works were synthesized into three categories of publicly available stress datasets, machine learning techniques applied using those, and future research directions. For the machine learning studies reviewed, we provide an analysis of their approach to results validation and model generalization. The quality assessment of the included studies was conducted in accordance with the IJMEDI checklist [2].

RESULTS

A number of public datasets were identified that are labeled for stress detection. These datasets were most commonly produced from sensor biomarker data recorded using the Empatica E4 device, a well-studied, medical-grade wrist-worn wearable that provides sensor biomarkers most notable to correlate with elevated levels of stress. Most of the reviewed datasets contain less than twenty-four hours of data, and the varied experimental conditions and labeling methodologies potentially limit their ability to generalize for unseen data. In addition, we discuss that previous works show shortcomings in areas such as their labeling protocols, lack of statistical power, validity of stress biomarkers, and model generalization ability.

CONCLUSION

Health tracking and monitoring using wearable devices is growing in popularity, while the generalization of existing machine learning models still requires further study, and research in this area will continue to provide improvements as newer and more substantial datasets become available.

Schizophrenia: a disorder of broken brain bioenergetics

A substantial and diverse body of literature suggests that the pathophysiology of schizophrenia is related to deficits of bioenergetic function. While antipsychotics are an effective therapy for the management of positive psychotic symptoms, they are not efficacious for the complete schizophrenia symptom profile, such as the negative and cognitive symptoms. In this review, we discuss the relationship between dysfunction of various metabolic pathways across different brain regions in relation to schizophrenia. We contend that several bioenergetic subprocesses are affected across the brain and such deficits are a core feature of the illness. We provide an overview of central perturbations of insulin signaling, glycolysis, pentose-phosphate pathway, tricarboxylic acid cycle, and oxidative phosphorylation in schizophrenia. Importantly, we discuss pharmacologic and nonpharmacologic interventions that target these pathways and how such interventions may be exploited to improve the symptoms of schizophrenia.

Adverse childhood experiences and allostatic load: A systematic review

Adverse Childhood Experiences (ACEs) are stressful and/or traumatic experiences associated with an increased lifetime risk of negative health outcomes. The Allostatic Load (AL) is a measure of multisystem dysregulation, resulted by chronic stress. We systematically reviewed the English language literature on the association between ACEs and AL to identify the clinical risk profile, with the exclusion of reviews and preclinical studies. Searches covered the publication period up to the 1^st of February 2022 and identified 25 studies in which ACEs such as maltreatment, abuse, poverty, psychological abuse, and discrimination were investigated in the context of AL. The selected studies used different sets of AL biomarkers resulting in substantial heterogenicity of calculating the AL index. Overall, we found that ACEs are associated with elevated AL and poorer health outcomes in adulthood. Furthermore, health risk behaviors, social support, and coping resources either moderate or mediate this association. These findings suggest that targeting individuals at risk and starting interventions early might reduce AL and its deleterious health consequences.

A Cross-Sectional Study Investigating Canadian and Australian Adolescents' Perceived Experiences of COVID-19: Gender Differences and Mental Health Implications

The coronavirus (COVID-19) disease pandemic has been associated with adverse psychological outcomes. This cross-cultural study (N = 1326, 71% female) aimed to investigate Canadian and Australian adolescents’ subjective experiences of COVID-19, gender differences, and psychological implications. Mixed-methods analyses were used to examine differences in COVID-19 experiences and mental health outcomes between country and gender in a Canadian (N = 913, 78% female) and an Australian sample (N = 413, 57% female) of adolescents. Canadian adolescents reported increased COVID-19 discussions and more concerns related to their COVID-19 experiences compared to Australian adolescents. Girls consistently reported more concerns related to COVID-19 and poorer psychological outcomes compared to boys. School lockdown for the Canadian sample may have played a role in these country differences. Further, girls might be at significantly more risk for mental health concerns during COVID-19, which should be considered in adolescent mental health initiatives during the pandemic. Although school disruption and separation of peers due to the pandemic likely have a role in adolescent perceived stressors and mental health, the differences between Canadian and Australian adolescents were less clear and future investigations comparing more objective pre-COVID-19 data to current data are needed.

Cannabidiol for at risk for psychosis youth: A randomized controlled trial

BACKGROUND

No biological treatment has been firmly established for the at-risk stage of psychotic disorder. In this study we aim to test if subthreshold psychotic symptoms can be effectively treated with cannabidiol (CBD), a non-psychoactive compound of the plant Cannabis sativa. The question has taken on increased importance in the wake of evidence questioning both the need and efficacy of specific pharmacological interventions in the ultra-high risk (UHR) for psychosis group.

METHODS

Three-arm randomized controlled trial of 405 patients (135 per arm) aged 12-25 years who meet UHR for psychosis criteria. The study includes a 6-week lead-in phase during which 10% of UHR individuals are expected to experience symptom remission. Participants will receive CBD (per oral) at doses 600 or 1000 mg per day (fixed schedule) for 12 weeks. Participants in the third arm of the trial will receive matching placebo capsules. Primary outcome is severity of positive psychotic symptoms as measured by the Comprehensive Assessment of At-Risk Mental States at 12 weeks. We hypothesize that CBD will be significantly more effective than placebo in improving positive psychotic symptoms in UHR patients. All participants will also be followed up 6 months post baseline to evaluate if treatment effects are sustained.

CONCLUSION

This paper reports on the rationale and protocol of the Cannabidiol for At Risk for psychosis Youth (CanARY) study. This study will test CBD for the first time in the UHR phase of psychotic disorder.

Building brain capital

Brains are indispensable drivers of human progress. Why not invest more heavily in them? We seek to place Brain Capital at the center of a new narrative to fuel economic and societal recovery and resilience.

Understanding the pathology of psychiatric disorders in refugees

Displacement of people from their homes, families and countries is a current global crisis, with over 70 million people forcibly on the move. A substantial proportion of these people will end up in regions with a different language and culture, where they are registered as refugees or asylum seekers. Due to the underlying reasons for displacement (including conflicts, persecution or violation of human rights), displaced people are severely stress-exposed, which continues into their post-migration life and increases risk for developing psychiatric disorders such as post-traumatic stress disorder and other anxiety disorders and mood disorders. While landmark studies have illustrated the increased prevalence of psychopathology in asylum seeker and refugee populations following pre-/post-displacement stress, few studies add to our understanding of the basic biological mechanisms underpinning risk to psychiatric disorders in these populations. Additionally, the mechanisms underlying resilience despite significant adversity remain unclear. Understanding the molecular mechanisms underpinning the development of psychiatric disorders in refugees can propel treatments (both drug and non-drug) that are capable of influencing biology at the molecular level, and the design of interventions. In the following review, we summarise the status quo of research investigating the pathophysiology of psychiatric disorders in refugees, and propose new ways to address gaps in knowledge with multidisciplinary research.

Stress, allostatic load and mental health in Indigenous Australians

The aim of this narrative review was to demonstrate how the notion of allostatic load (AL) relates directly to the mental health disparities observed between Indigenous and non-Indigenous Australians. We also endeavored to synthesize the results of the limited number of studies examining stress and AL in Indigenous Australians in order to explore the potential public health benefits of the AL concept. A range of literature examining health inequalities, psychosocial determinants of mental illness and AL was explored to demonstrate the applicability of stress biology to the significant mental health burden faced by Indigenous Australians. Furthermore, all original studies indexed in MEDLINE that provided quantitative data on primary stress biomarkers in Indigenous Australians were selected for review. Evidence of hypothalamic-pituitary-adrenal axis dysregulation and increased AL is apparent even in the handful of studies examining stress biomarkers in Indigenous Australians. Urinary, salivary, hair and fingernail cortisol, hair cortisone, urinary epinephrine, heart rate variability and the cortisol awakening response are all AL parameters which have been shown to be dysregulated in Indigenous Australian cohorts. Furthermore, associations between some of these biomarkers, self-perceived discrimination, exposure to stressful life events and symptoms of psychiatric disorders in Indigenous Australians have also been demonstrated. The continued assessment of AL biomarkers and their relationship with past traumas, lifetime stressors and socio-economic factors amongst Indigenous Australians is important to addressing the mental health this population. Measurement of AL biomarkers in a culturally appropriate manner may lead to more targeted preventative measures, interventions and policies, which mitigate the effects of stress at both the individual and societal level.

Social rank does not affect sperm quality in male African wild dogs (Lycaon pictus)

Sperm banking and AI could benefit endangered African wild dog conservation. However, it is unclear whether their dominance hierarchy causes a decrease in reproductive and sperm quality parameters in subordinate males that typically do not breed. In this study, we investigated the effect of social rank on male reproductive parameters, including faecal androgen and glucocorticoid metabolite concentrations, prostate and testes volume, preputial gland size, semen collection success and sperm quality. Samples were obtained from captive males (prebreeding season: n=12 from four packs; breeding season: n=24 from seven packs) that were classified as alpha (dominant), beta or gamma (subordinates) based on the frequency of dominant versus submissive behaviours. In the prebreeding season, semen was successfully collected from all alpha but only half the subordinate males, with urine contamination (associated with lower rank) significantly reducing total and progressive motility, sperm motility index, normal sperm morphology and acrosome integrity. The breeding season was associated with a significant increase in faecal androgens, prostate and testis volume, as well as progressive motility and the total number of spermatozoa ejaculated. However, with the exception of prostate volume (mean±s.e.m: 12.5±4.5, 7.1±1.0 and 7.3±1.0cm3 in alpha, beta and gamma males respectively; P=0.035), all other reproductive and sperm quality parameters did not differ between males of each social rank. In conclusion, reproductive suppression of subordinate males appears to be behaviourally mediated, because males of all social ranks produce semen of similar quality, making them suitable candidates for sperm banking, particularly during the breeding season when sperm quality improves.

Hair cortisol, allostatic load, and depressive symptoms in Australian Aboriginal and Torres Strait Islander people

Chronic stress and adversity are associated with poor mental health and are thought to contribute to the existing mental health gap between Aboriginal and Torres Strait Islander people and other Australians. Hair cortisol and allostatic load (AL) are indices of sustained stress and may be mediators of the effects of stress on health. The aim of this study was to examine the relationship between hair cortisol, AL, and depressive symptoms. This cross-sectional study comprised 329 Aboriginal and Torres Strait Islander adolescents and adults recruited at two health screening programs operating in three communities in north Queensland. We measured hair cortisol and calculated an AL index from 10 biomarkers. We assessed depressive symptoms with a version of the Patient Health Questionnaire-9 adapted for Aboriginal and Torres Strait Islander people (aPHQ-9). We found differences in cortisol and AL between the screening programs and communities, which were not explained by depressive symptoms. Overall aPHQ-9 scores were unrelated to hair cortisol (p = .25 and p = .94) and AL (p = .30 and p = .88) when age, gender and smoking were taken into account. However, anhedonia (p = .007) and insomnia (p = .006) sub-scores were each significantly associated with AL in one study site. Our present data did not demonstrate overall associations of stress biomarkers and multisystem dysregulation with depressive symptoms, which suggests that the relationship between cumulative stress and depression may be better explained by other factors in this population. The specific association between anhedonia and insomnia with AL indicates that chronic multisystem dysregulation plays a role in these features of depression in this population. Lay summary Our study investigated the relationship between symptoms of depression and two biological pathways thought to mediate depression risk - the stress hormone cortisol and allostatic load (AL) - in an Australian Aboriginal and Torres Strait Islander population. Overall, cortisol and AL were unrelated to depression. However, AL was selectively associated with anhedonia (lack of motivation or drive) and sleep disturbances. These results suggest that metabolic dysregulation measured as AL may be relevant to the depression risk in this population.

Dog appeasing pheromone prevents the androgen surge and may reduce contact dominance and active submission after stressful interventions in African wild dogs (Lycaon pictus)

The endangered African wild dog (AWD; Lycaon pictus) is a highly social canid living in packs with a separate male and female hierarchy. Immobilisation, handling and translocations are acute stressors for AWDs, however such interventions are often needed for species management. In addition, new pack formation or temporary pack separation can lead to an increase in intra-pack aggression. The goal of this double-blinded placebo-controlled study conducted in captive zoo populations was to evaluate whether dog appeasing pheromone (DAP) reduces behavioural stress and faecal glucocorticoid metabolite levels (fGCM) normally associated with pack separation, immobilisation and reintroduction (SIR), and to assess whether this reduces aggressive behaviours and faecal androgen metabolite levels (fAM). Four packs (n = 11 males) were treated with DAP and 4 packs (n = 12 males) were treated with a placebo solution, applied at the end of anaesthesia. Behavioural interactions as well as fGCM and fAM were determined from 3 days before until 4-6 days after SIR. No effect of DAP on fGCM was observed, however, fAM increased after SIR in placebo but not DAP treated animals. Moreover, on the day of reintroduction, DAP treated packs tended to have lower rates of contact-dominance and active-submission behaviour, but higher rates of non-contact dominance behaviour. As these effects could decrease the risk of agonistic interactions, DAP may be a useful tool to help manage new pack formations and temporary pack separation.

The Therapeutic Potential of Ketogenic Diet Throughout Life: Focus on Metabolic, Neurodevelopmental and Neurodegenerative Disorders

This chapter reviews the efficacy of the ketogenic diet in a variety of neurodegenerative, neurodevelopmental and metabolic conditions throughout different stages of life. It describes conditions affecting children, metabolic disorders in adults and disorderrs affecting the elderly. We have focused on application of the ketogenic diet in clinical studies and in preclinical models and discuss the benefits and negative aspects of the diet. Finally, we highlight the need for further research in this area with a view of discovering novel mechanistic targets of the ketogenic diet, as a means of maximising the potential benefits/risks ratio.

Cross-sectional association of seafood consumption, polyunsaturated fatty acids and depressive symptoms in two Torres Strait communities

Background Dietary intake of long-chain omega 3 (n-3) polyunsaturated fatty acids (LCPUFA) represents a putative modifiable risk factor for depression, and a high ratio of omega 6 (n-6) to n-3 LCPUFA is frequently observed in patients with major depressive disorder. Recent reports suggest that the availability of fish and seafood may be associated with lower depression rates. The aim of this study was to investigate associations of fish consumption and LCPUFA levels with depressive symptoms.Methods Participants for this cross-sectional study (n=206) were recruited at a community screening programme in two Torres Strait Islander communities (Mer and Waiben). Depressive symptoms were assessed with the adapted Patient Health Questionnaire-9 (aPHQ-9) and diet with a structured questionnaire. LCPUFA concentrations were measured with a capillary dried blood spot system (PUFAcoat). Logistic and quantile regression modelling was used to test the relationship between seafood consumption, membrane LCPUFAs and depression scores.Results A higher blood n-6/3 LCPUFA ratio was associated with moderate/severe depression scores across both study sites (OR=1.59 (95%CI 1.09-2.34), P = .017). Seafood consumption was higher and the proportion of participants with aPHQ-9 scores above the cut-off for depression was lower on Mer (n = 100) compared with Waiben (n = 106). Higher seafood consumption was associated with lower depression scores on Waiben (B = -0.57 (95%CI -0.98 - -0.16), P = .006) but not on Mer.Conclusions Our findings support an association of n-3 LCPUFA from natural sources with depressive symptoms. The availability of fresh seafood in the local diet may represent a protective factor for depression in this setting.

97 Social Dominance does not Affect Semen Quality in African Wild Dogs (Lycaon pictus)

Sperm banking and AI could benefit conservation of endangered African wild dogs (AWD). However, it is not clear whether their strict dominance hierarchy causes subfertility in subdominant males that typically do not breed. Our study investigated the effect of dominance on male reproductive parameters, including faecal glucocorticoids (fGCM) and androgens (fAM), testis and prostate volume, preputial gland size, semen collection success, and the number, motility, morphology, viability, acrosome integrity (PSA-FITC), and DNA integrity (TUNEL) of spermatozoa collected by electroejaculation. Samples were obtained from n = 12 captive AWD (4 US packs) in the pre-breeding season and n = 28 captive AWD (n = 11 from 4 US packs; n = 17 from 3 Namibian packs) in the breeding season. Male hierarchy was clearly determined by behavioural observations in all but 1 Namibian pack. Data were grouped by dominance status and means were compared by ANOVA or t-test; P ≤ 0.05 was significant. In the pre-breeding season, there was no significant difference in body weight, fGCM, fAM, or prostate and testis volume between dominance groups. Semen was successfully collected from all alphas but only half the subdominants; urine contamination was negatively associated with dominance. Sperm quality was low (17.3 ± 10.2% total motility, 12.8 ± 8.5% progressive motility, 27.4 ± 11.5 × 106 ejaculated spermatozoa, 40.6 ± 9.8% normal morphology, 63.1 ± 5.1% viability, 72.6 ± 5.2% acrosome integrity) with no difference observed in any parameter except progressive motility and normal sperm morphology, which were significantly lower in subdominants (27.7 ± 16.8% v. 0.0 ± 0.0% and 59.8 ± 13.0% v. 21.4 ± 5.7%). From pre-breeding to breeding season, testis and prostate volume increased significantly, particularly in beta and gamma males respectively. Prostate volume was higher in alpha than beta males (16.0 ± 6.4 cm3 v. 5.7 ± 1.4 cm3), but testis volume, body weight, fAM, and fGCM did not differ between dominance groups (12.0 ± 0.9 cm3, 28.5 ± 0.8 kg, 0.51 ± 0.07 µg g−1, and 30.6 ± 2.3 ng/g of dry weight). Semen was successfully collected from 75% of males with reduced urine contamination. Collection success, urine contamination, and preputial gland size were not associated with dominance. Sperm quality improved with significantly greater number, viability, and total motility. However, sperm quality did not differ between dominance groups (47.4 ± 6.7% total motility, 30.5 ± 5.8% progressive motility, 32.3 ± 9.2 × 106 ejaculated spermatozoa, 50.9 ± 5.2% normal morphology, 74.4 ± 4.2% viability, 85.6 ± 3.0% acrosome integrity, and 99.7 ± 0.1% DNA integrity). In conclusion, subdominant males are at higher risk of urine contamination and have lower sperm motility and normal morphology when semen is collected in the pre-breeding season. However, their semen is of similar quality to dominant males in the breeding season, indicating that reproductive suppression of subdominant males is only behavioural. Thus, AWD males of all social ranks in the breeding season are suitable candidates for sperm banking.

Adverse effect of early-life high-fat/high-carbohydrate ("Western") diet on bacterial community in the distal bowel of mice

Obesity and other lifestyle diseases in modern society can be related to historical dietary changes from diets balanced in omega-6 and omega-3 to the unbalanced "Western-type" diet. It is recognized that diet influences the murine and human gut microbiome, and most research indicates that microbial diversity and composition are altered by high-fat diets (HFDs). However, good knowledge about the effects of early exposure to HFD on the maturation and structure of the bacterial community is limited. Using mice as model, we hypothesized that an HFD alters the early dynamic of the gut bacterial community toward an unstable/unhealthy state. By sequencing the V3 and V4 regions of the 16S ribosomal ribonucleic acid gene, we investigated the bacterial community in fecal samples of mice fed a control diet and an HFD at weaning (sampling time 1) and after 8 weeks of dietary intervention (11weeks of age; sampling time 2). Natural temporal microbiome maturation was evidenced by a general increase in microbial diversity and shifts in microbial community between sampling times 1 and 2 toward a mature community. However, the HFD led to significant structural segregation of the microbiome compared with controls; the HFD diet repressed health-enhancing bacteria (eg, Bifidobacterium and Akkermansia) and promoted health-detracting bacteria (ie, those associated with gut disorders, eg, Dorea). We suggest that early-life consumption of HFD negatively impacts the natural gut bacterial community maturation leading toward a potentially persistent unhealthy stage.

Omega-6 to omega-3 polyunsaturated fatty acid ratio and subsequent mood disorders in young people with at-risk mental states: a 7-year longitudinal study

While cross-sectional studies suggest that patients with mood disorders have a higher ratio of omega-6 to omega-3 polyunsaturated fatty acids (PUFAs) and lower levels of omega-3 PUFAs, it is unknown if a high n-6/3 ratio indicates vulnerability for depression. We tested this hypothesis in a 7-year follow-up study of young individuals with an ultra-high risk (UHR) phenotype. We conducted a secondary analysis of the Vienna omega-3 study, a longitudinal study of omega-3 PUFAs in individuals at UHR for psychosis (n=69). Levels of n-6 and n-3 PUFAs were measured in the phosphatidylethanolamine fraction of erythrocyte membranes at intake into the study. Mood disorder diagnosis was ascertained with the Structured Clinical Interview for DSM-IV-TR and confirmed by review of medical records and interviews of caregivers. A higher n-6/3 PUFA ratio at baseline predicted mood disorders in UHR individuals over a 7-year (median) follow-up (odds ratio=1.89, 95% CI=1.075-3.338, P=0.03). This association remained significant after adjustment for age, gender, smoking, severity of depressive symptoms at baseline and n-3 supplementation. Consistent results were obtained for individual PUFAs, including lower levels of eicosapentaenoic acid and docosahexaenoic acid. The predictive capacity of these findings was specific to mood disorders as no associations were found for any other psychiatric disorder. To our knowledge, our data provide the first prospective evidence that the n-6/3 PUFA ratio is associated with an increased risk for mood disorders in young people exhibiting an UHR phenotype. These findings may have important implications for treatment and risk stratification beyond clinical characteristics.

Clozapine promotes glycolysis and myelin lipid synthesis in cultured oligodendrocytes

Clozapine displays stronger systemic metabolic side effects than haloperidol and it has been hypothesized that therapeutic antipsychotic and adverse metabolic effects of these drugs are related. Considering that cerebral disconnectivity through oligodendrocyte dysfunction has been implicated in schizophrenia, it is important to determine the effect of these drugs on oligodendrocyte energy metabolism and myelin lipid production. Effects of clozapine and haloperidol on glucose and myelin lipid metabolism were evaluated and compared in cultured OLN-93 oligodendrocytes. First, glycolytic activity was assessed by measurement of extra- and intracellular glucose and lactate levels. Next, the expression of glucose (GLUT) and monocarboxylate (MCT) transporters was determined after 6 and 24 h. And finally mitochondrial respiration, acetyl-CoA carboxylase, free fatty acids, and expression of the myelin lipid galactocerebroside were analyzed. Both drugs altered oligodendrocyte glucose metabolism, but in opposite directions. Clozapine improved the glucose uptake, production and release of lactate, without altering GLUT and MCT. In contrast, haloperidol led to higher extracellular levels of glucose and lower levels of lactate, suggesting reduced glycolysis. Antipsychotics did not alter significantly the number of functionally intact mitochondria, but clozapine enhanced the efficacy of oxidative phosphorylation and expression of galactocerebroside. Our findings support the superior impact of clozapine on white matter integrity in schizophrenia as previously observed, suggesting that this drug improves the energy supply and myelin lipid synthesis in oligodendrocytes. Characterizing the underlying signal transduction pathways may pave the way for novel oligodendrocyte-directed schizophrenia therapies.

An exploratory study of cannabis withdrawal among Indigenous Australian prison inmates: study protocol

INTRODUCTION

Cannabis use and dependence is a serious health and criminal justice issue among incarcerated populations internationally. Upon abrupt, enforced cessation of cannabis, prisoners may suffer irritability and anger that can lead to threatening behaviour, intimidation, violence, sleep disturbances and self-harm. Cannabis withdrawal syndrome, proposed for inclusion in the Diagnostic and Statistical Manual of Mental Disorders in 2013, has not been examined in Indigenous populations. Owing to the exceptionally high rates of cannabis use in the community, high proportions of Australian Indigenous prisoners may suffer from withdrawal upon entry to custody.

METHODS AND ANALYSIS

60 male and 60 female Indigenous prisoners (18-40 years) at a high risk of cannabis dependence will be recruited upon entry to custody. A pictorial representation of the standard Cannabis Withdrawal Scale will be tested for reliability and validity. Cortisol markers will be measured in saliva, as the indicators of onset and severity of cannabis withdrawal and psychological distress. The characteristics will be described as percentages and mean or median values with 95% CI. Receiver operator curve analysis will determine an ideal cut-off of the Cannabis Withdrawal Scale and generalised estimating equations modelling will test changes over time. The acceptability and efficacy of proposed resources will be assessed qualitatively using thematic analysis.

OUTCOMES

A valid and reliable measure of cannabis withdrawal for use with Indigenous populations, the onset and time course of withdrawal symptoms in this population and the development of culturally acceptable resources and interventions to identify and manage cannabis withdrawal.

ETHICS AND DISSEMINATION

The project has been approved by the James Cook University Human Research Ethics Committee (approval number H4651).The results will be reported via peer reviewed publications, conference, seminar presentations and on-line media for national and international dissemination.

Molecular validation of the acute phencyclidine rat model for schizophrenia: identification of translational changes in energy metabolism and neurotransmission

Administration of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (PCP) to rodents is widely used as preclinical model for schizophrenia. Most studies on this model employ methods investigating behavior and brain abnormalities. However, little is known about the corresponding peripheral effects. In this study, we analyzed changes in brain and serum molecular profiles, together with alterations in behavior after acute PCP treatment of rats. Furthermore, abnormalities in peripheral protein expression of first and recent onset antipsychotic free schizophrenia patients were assessed for comparison with the preclinical model. PCP treatment induced hyperlocomotion and stereotypic behavior, which have been related to positive symptoms of schizophrenia. Multiplex immunoassay profiling of serum revealed molecular abnormalities similar to those seen in first and recent onset, antipsychotic free schizophrenia patients. Also, increased insulin levels were detected after administration of a glucose tolerance test (GTT), consistent with previous studies showing changes in insulin signaling in patients with schizophrenia. Finally, schizophrenia-relevant alterations in brain molecules were found in the hippocampus and to a lesser extent in the frontal cortex using liquid-chromatography mass spectrometry and (1)H nuclear magnetic resonance spectroscopy. In conclusion, this study identified behavioral and molecular alterations in the acute PCP rat model, which are also observed in human schizophrenia. We propose that the corresponding changes in serum in both animals and patients may have utility as surrogate markers in this model to facilitate discovery and development of novel drugs for treatment of certain pathological features of schizophrenia.

Corticotropin-releasing factor (CRF) over-expression down-regulates hippocampal dopamine receptor protein expression and CREB activation in mice

BACKGROUND

Stress results in hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, characterized by increased central CRF activity, elevated circulating glucocorticoid levels, impaired glucocorticoid-mediated negative feedback and abnormal hippocampal functions, possibly contributing to the development of behavioral pathologies, such as depression. The hippocampus is critically involved in the control of the HPA axis as well as in explicit memory, contextual aspects of fear, organization of the behavioral response to environmental novelty and in habituation. We have previously shown that mice that over-express CRF in the brain exhibit impaired novelty detection and altered psychophysiological and behavioral habituation, functions linked to dopamine receptor-dependent hippocampal plasticity.

OBJECTIVE AND METHODS

Therefore, the aim of the present study was to measure D1 and D2 dopamine receptor expression and related signaling, such as CREB and ERK protein levels and phosphorylation, in the hippocampus and other brain regions of mice with post-natal CRF over-expression (CRF-OE mice).

RESULTS

We found a region-specific down-regulation of both D1 and D2 protein expression, without altered CRF receptor protein expression, in the hippocampus in CRF-OE mice. This was accompanied by an impaired phosphorylation of hippocampal CREB, but not ERK1 and ERK2, in the same animals.

CONCLUSIONS

These results suggest that post-natal onset CRF over-expression results in an impairment of dopamine signaling in the hippocampus, which may underlie cognitive and motivational aspects of stress-related, CRF-driven mood disorders.

From molecule to market: steroid hormones and financial risk-taking

Little is known about the role of the endocrine system in financial decision-making. Here, we survey research on steroid hormones and their cognitive effects, and examine potential links to trader performance in the financial markets. Preliminary findings suggest that cortisol codes for risk and testosterone for reward. A key finding of this endocrine research is the different cognitive effects of acute versus chronic exposure to hormones: acutely elevated steroids may optimize performance on a range of tasks; but chronically elevated steroids may promote irrational risk-reward choices. We present a hypothesis suggesting that the irrational exuberance and pessimism observed during market bubbles and crashes may be mediated by steroid hormones. If hormones can exaggerate market moves, then perhaps the age and sex composition among traders and asset managers may affect the level of instability witnessed in the financial markets.

Single valproic acid treatment inhibits glycogen and RNA ribose turnover while disrupting glucose-derived cholesterol synthesis in liver as revealed by the [U-C(6)]-d-glucose tracer in mice

Previous genetic and proteomic studies identified altered activity of various enzymes such as those of fatty acid metabolism and glycogen synthesis after a single toxic dose of valproic acid (VPA) in rats. In this study, we demonstrate the effect of VPA on metabolite synthesis flux rates and the possible use of abnormal (13)C labeled glucose-derived metabolites in plasma or urine as early markers of toxicity. Female CD-1 mice were injected subcutaneously with saline or 600 mg/kg) VPA. Twelve hours later, the mice were injected with an intraperitoneal load of 1 g/kg [U-(13)C]-d-glucose. (13)C isotopomers of glycogen glucose and RNA ribose in liver, kidney and brain tissue, as well as glucose disposal via cholesterol and glucose in the plasma and urine were determined. The levels of all of the positional (13)C isotopomers of glucose were similar in plasma, suggesting that a single VPA dose does not disturb glucose absorption, uptake or hepatic glucose metabolism. Three-hour urine samples showed an increase in the injected tracer indicating a decreased glucose re-absorption via kidney tubules. (13)C labeled glucose deposited as liver glycogen or as ribose of RNA were decreased by VPA treatment; incorporation of (13)C via acetyl-CoA into plasma cholesterol was significantly lower at 60 min. The severe decreases in glucose-derived carbon flux into plasma and kidney-bound cholesterol, liver glycogen and RNA ribose synthesis, as well as decreased glucose re-absorption and an increased disposal via urine all serve as early flux markers of VPA-induced adverse metabolic effects in the host.

Decreased expression of multidrug efflux transporters in the brains of GSK-3beta transgenic mice

Multidrug efflux transporters protect cells in the brain from potentially harmful substances but also from therapeutically useful drugs. Thus any condition that causes changes in their expression is of some importance with regard to drug access. In this study, changes in efflux transporter expression are investigated in mice containing a mutant constitutively active glycogen synthase kinase-3 (GSK-3beta) transgene, driven by the Thy-1 promoter so limiting its localization predominantly to neurons and some glial cells. As expected, decreases in beta-catenin were evident via Western blot analyses of cortical homogenates prepared from brains of these transgenic mice. As assessed by real time qRT-PCR, decreased transcript levels of the mdr1b isoform of P-glycoprotein, Mrp1 and Mrp4, (transporters associated with neurons and/or glial cells) were observed in the cortex but not the subventricular zone or hippocampus of the transgenic compared to wild type mouse brains. By contrast, no such decreases were evident with the mdr1a isoform of P-glycoprotein and Bcrp, transporters predominantly found in brain endothelium. Such transporter expression changes could not be accounted for by alterations in blood vessel density or neuronal to glial cell ratios as analyzed both from immunocytochemical staining and from RT-PCR. These observations support previous in vitro data showing that manipulations to GSK-3beta activity that alter signaling via beta-catenin can influence the expression of efflux transporters. Implications from this are that drug distribution into cells within the brain of these transgenic mice could be enhanced, hence warranting further investigation.

Altered behavioural adaptation in mice with neural corticotrophin-releasing factor overexpression

Overproduction of corticotrophin-releasing factor (CRF), the major mediator of the stress response, has been linked to anxiety, depression and addiction. CRF excess results in increased arousal, anxiety and altered cognition in rodents. The ability to adapt to a potentially threatening stimulus is crucial for survival, and impaired adaptation may underlie stress-related psychiatric disorders. Therefore, we examined the effects of chronic transgenic neural CRF overproduction on behavioural adaptation to repeated exposure to a non-home cage environment. We report that CRF transgenic mice show impaired adaptation in locomotor response to the novel open field. In contrast to wild-type (WT) mice, anxiety-related behaviour of CRF transgenic mice does not change during repeated exposure to the same environment over the period of 7 days or at retest 1 week later. We found that locomotor response to novelty correlates significantly with total locomotor activity and activity in the centre at the last day of testing and at retest in WT but not in CRF transgenic mice. Mice were divided into low responders and high responders on the basis of their initial locomotor response to novelty. We found that differences in habituation and re-exposure response are related to individual differences in locomotor response to novelty. In summary, these results show that CRF transgenic mice are fundamentally different from WT in their ability to adapt to an environmental stressor. This may be related to individual differences in stress reactivity. These findings have implications for our understanding of the role of CRF overproduction in behavioural maladaptation and stress-related psychiatric disorders.

The 5-HT(1A) receptor knockout mouse and anxiety

The 5-HT(1A) receptor has been implicated in the modulation of anxiety processes, mainly via pharmacological experiments. The recent production, in three independent research groups, of 5-HT(1A) receptor knockout (R KO) mice in three different genetic backgrounds (C57BL/6J, 129/Sv, Swiss-Webster) led to the intriguing finding that all mice, independent from the genetic background strain from which the null mutants were made, showed an "anxious" phenotype compared to corresponding wild-type mice. The present paper reviews the behavioral findings in these three KO lines and focuses on new findings in the 129/Sv-KO mice. These mice were more anxious or stress-prone only under specific conditions (high stress) and not as broadly as suggested from the initial studies. The 5-HT(1A) R KO made in the Swiss-Webster background displays disturbances in the GABA(A)-benzodiazepine (BZ) receptor system in the brain, including downregulation of GABA(A) alpha1 and alpha2 subunits in the amygdala. In contrast, the GABA(A)-BZ receptor system seems to function normally in the 5-HT(1A) R KO in the 129/Sv background suggesting that changes in the GABA(A)-BZ receptor system may not be a prerequisite for anxiety but rather could have a modifying effect on this phenotype. It can be concluded that the constitutive absence of the 5-HT(1A) receptor gene and receptor leads to a more "anxious" mouse, dependent on the stress level but independent from the strain. Depending on the genetic background, this null mutation may be associated with changes in GABA(A)-ergic neurotransmission. It is as yet unclear which mechanisms are involved in this intriguing differentiation.

The DBA/2J strain and prepulse inhibition of startle: a model system to test antipsychotics?

RATIONALE

Prepulse inhibition (PPI) of the startle response in mice is increasingly used as a paradigm of sensory gating with potential predictive and construct validity towards schizophrenia.

OBJECTIVES

Establishment of a mouse PPI paradigm in which typical and atypical antipsychotic drugs directly improve a low performance PPI.

METHODS

Three strains of mice--C57Bl/6J, 129S6/SvEvTac and DBA/2J--were tested in a startle paradigm with three prepulse intensities, 2, 4 and 8 dB above background.

RESULTS

Under these conditions, risperidone (0, 0.25, 0.5 and 1 mg/kg i.p.) and clozapine (0, 1, 3 and 9 mg/kg i.p.) improved PPI in all three strains, with order of effect in DBA/2J > 129S6SvEvTac > C57Bl/6J. The DBA/2J strain showed larger PPI-enhancing effects, without disturbing the basal startle response. Two alpha7 nicotinic receptor agonists, GTS-21 (1-10 mg/kg i.p.) and AR-R17779 (1-10 mg/kg i.p.) were inactive in the PPI procedure in DBA/2J mice.

CONCLUSIONS

DBA/2J mice were very sensitive to the antipsychotic-like effects of atypical (clozapine) and typical (risperidone) antipsychotics, and this strain is proposed as a model to directly measure sensory gating properties of drugs. Alpha7 Nicotinergic receptor agonists were ineffective in this PPI paradigm.

The role of corticotropin-releasing factor in drug addiction

The goal of this article is to summarize available data examining the physiological significance of brain corticotropin-releasing factor (CRF) systems in mediating the behavioral and physiological effects of several classes of abused drugs, including opioid and psychostimulant drugs, alcohol and sedative hypnotics, nicotine, and cannabinoids. An initial discussion of CRF neurobiology is followed by consideration of the role of CRF in drug-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, the behavioral effects of drugs (e.g., locomotor activity, anxiogenic-like responses), drug self-administration, drug withdrawal, and relapse to drug-seeking. Subsequently, neurochemical changes in brain CRF in response to acute and chronic drug exposure are examined. A major conclusion derived from the data reviewed is that extrahypothalamic brain CRF systems are critically involved in behavioral and physiological manifestations of drug withdrawal and in relapse to drug-taking behavior induced by environmental stressors. On the other hand, it appears that hypothalamic CRF, via its action on the HPA axis, is involved in the reinforcing effects of cocaine and alcohol, and the locomotor activating effects of psychostimulant drugs. These preclinical data may provide a rationale for the development of CRF-based pharmacotherapies for the treatment of compulsive drug use in humans.

Impaired hippocampal-dependent learning and functional abnormalities in the hippocampus in mice lacking serotonin(1A) receptors

The hippocampus is a major limbic target of the brainstem serotonergic neurons that modulate fear, anxiety, and learning through postsynaptic serotonin(1A) receptors (5-HT(1A) receptors). Because chronic stress selectively down-regulates the 5-HT(1A) receptors in the hippocampus, we hypothesized that mice lacking these receptors may exhibit abnormalities reminiscent of symptoms of stress-related psychiatric disorders. In particular, a hippocampal deficit in the 5-HT(1A) receptor could contribute to the cognitive abnormalities often seen in these disorders. To test whether a deficit in 5-HT(1A) receptors impairs hippocampus-related functions, we studied hippocampal-dependent learning and memory, synaptic plasticity in the hippocampus, and limbic neuronal excitability in 5-HT(1A)-knockout (KO) mice. 5-HT(1A)-KO animals showed a deficit in hippocampal-dependent learning and memory tests, such as the hidden platform (spatial) version of the Morris water maze and the delayed version of the Y maze. The performance of KO mice was not impaired in nonhippocampal memory tasks such as the visible platform (nonspatial) version of the Morris water maze, the immediate version of the Y maze, and the spontaneous-alternation test of working memory. Furthermore, paired-pulse facilitation in the dentate gyrus of the hippocampus was impaired in 5-HT(1A)-KO mice. Finally, 5-HT(1A)-KO mice, as compared with wild-type animals, displayed higher limbic excitability manifested as lower seizure threshold and higher lethality in response to kainic acid administration. These results demonstrate that 5-HT(1A) receptors are required for maintaining normal hippocampal functions and implicate a role for the 5-HT(1A) receptor in hippocampal-related symptoms, such as cognitive disturbances, in stress-related disorders.

Adaptive changes in postsynaptic dopamine receptors despite unaltered dopamine dynamics in mice lacking monoamine oxidase B

Monoamine oxidase (MAO) B is considered a key enzyme in dopamine metabolism. The present studies, conducted in MAO B knockout mice, show that lack of MAO B does not alter extracellular levels of dopamine in striatum. Similarly, the synthesis, storage, uptake, and release of dopamine are also unaltered. However, autoradiography revealed a significant up-regulation of the D2-like dopamine receptors in the striatum of MAO B knockout mice. Mutant mice also exhibit a functional supersensitivity of D1-dopamine receptors in the nucleus accumbens. Thus, the agonist SKF 38,393-induced c-Fos immunoreactivity was significantly increased in knockout mice as compared with wild-type controls. In view of the apparently normal basal dopamine dynamics observed in MAO B knockout mice, we hypothesize that a dopamine-independent mechanism underlies adaptations in dopamine receptor function that occur as a consequence of MAO B depletion. Finally, these findings suggest that chronic administration of MAO inhibitors, as occurs in the treatment of Parkinson's disease and depression, may be associated with an increased responsiveness of CNS neurons to dopamine receptor ligands.

Oxytocin and neuroadaptation to cocaine

Oxytocin (OT) has been implicated in neuroadaptive processes such as learning, memory, and social-affiliative behavior as well as in the regulation of physiological responses leading to adaptation to the changing external and internal environment. Drugs of abuse constitute a major challenge to the homeostasis of the body and behavior. Drug tolerance, dependence and addiction may involve neuroadaptive mechanisms related to learning and memory at cellular and systems levels. Considerable effort has been made toward the understanding the neurobiological mechanisms of addictive behavior. Neuropeptides OT and vasopressin (VP) might be involved in these processes based on their effects on neuroadaptation and on their neuroanatomical localization and pharmacological actions. It has been demonstrated that both OT and VP have modulatory effects on opiate and alcohol tolerance and dependence. This chapter summarize the effects of OT, and in lesser extent VP, on neuroadaptation to cocaine, a psychostimulant drug of abuse. We have shown that OT inhibits acute cocaine-induced locomotor hyperactivity, exploratory activity and stereotyped behavior in rodents. Furthermore, OT facilitated, whereas VP inhibited the development of behavioral sensitization to cocaine. In a different model, OT inhibited the development of tolerance to the stereotyped behavior-inducing effects of cocaine as well as cocaine intravenous self-administration in rats. We demonstrated that OT acts through its specific receptors in the basal forebrain and in the hippocampus. OT and VP contents in the hypothalamus and limbic structures were altered by acute and chronic cocaine administration in a dose-dependent and region-selective manner. The differential plasticity of the brain OT-ergic and VP-ergic neurotransmissions in response to cocaine may underlie the differences in the involvement of these neuropeptides in cocaine addiction. Interaction of OT with dopaminergic neurotransmission in the nucleus accumbens, a key brain structure in drug addiction, as well as OT-ergic regulation of hippocampal processes may be among the mechanisms of action through which OT modulates neuroadaptation to cocaine. A better understanding of the role of OT in neuroadaptation to cocaine may provide an insight into both the mechanisms of neuropeptide actions in the brain as well as into the neurobiology of drug addiction.

Oxytocin and addiction: a review

Neuropeptides affect adaptive central nervous system processes related to opiate ethanol and cocaine addiction. Oxytocin (OXT), a neurohypophyseal neuropeptide synthesized in the brain and released at the posterior pituitary, also is released in the central nervous system (CNS). OXT acts within the CNS and has been shown to inhibit the development of tolerance to morphine, and to attenuate various symptoms of morphine withdrawal in mice. In rats, intravenous self-administration of heroin was potently decreased by OXT treatment. In relation to cocaine abuse, OXT dose-dependently decreased cocaine-induced hyperlocomotion and stereotyped grooming behavior. Following chronic cocaine treatment, the behavioral tolerance to the sniffing-inducing effect of cocaine was markedly inhibited by OXT. Behavioral sensitization to cocaine, on the other hand, was facilitated by OXT. OXT receptors in the CNS--mainly those located in limbic and basal forebrain structures--are responsible for mediating various effects of OXT in the opiate- and cocaine-addicted organism. Dopaminergic neurotransmission--primarily in basal forebrain structures--is another important biochemical mediator of the central nervous system effects of OXT. Tolerance to ethanol (e.g. hypothermia-inducing effect of ethanol) also was inhibited by OXT.

Neuroendocrine-related effects of long-term, 'binge' cocaine administration: diminished individual differences in stress-induced corticosterone response

Acute cocaine administration activates behavioral and neuroendocrine processes associated with the stress response. However, much less is known about the effects of chronic, long-term cocaine administration on neuroendocrine adaptations and individual vulnerability to stress. We hypothesized that chronic 'binge' cocaine administration may serve as a chronic pharmacological stressor leading to a hyperactivity of the stress-responsive hypothalamic-pituitary-adrenal (HPA) axis and alterations in its feedback mechanisms. In order to test this hypothesis, the effects of long-term (3 and 6 weeks) 'binge' pattern cocaine administration (3x15 mg/kg cocaine, i.p., daily, during the early phase of the light cycle) on body weight, adrenal gland weight, basal and stress-induced activity of the corticosterone (CORT) and basal plasma testosterone (T) levels were measured. Both 3 and 6 weeks 'binge' cocaine administration decreased body weight gain, increased the weight of adrenal glands and increased basal CORT levels. Plasma T levels were suppressed by both 3 and 6 weeks of cocaine treatment. No correlation was found between elevated CORT and low T levels at any time point. Neither chronic saline nor cocaine administration altered stress-induced CORT secretion. CORT levels 60 min following the restraint stress (recovery) were significantly lower than pre-stress basal levels after 3 and 6 weeks of cocaine, but not saline, administration. Moreover, initial individual differences in stress-induced CORT response, i.e. low and high responsivity to restraint prior to any saline or cocaine injections, were maintained in control rats but became diminished in cocaine-treated rats. These results indicate that chronic binge cocaine administration leads to sustained activation of the HPA axis and alters processes underlying individual vulnerability to stress.

Neurobiology of stress and cocaine addiction. Studies on corticotropin-releasing factor in rats, monkeys, and humans

Stress may contribute to the increased vulnerability to and the development of cocaine addiction. Corticotropin-releasing factor (CRF) activates the hypothalamic-pituitary-adrenal (HPA) axis as well as behavioral and immune processes in response to different environmental and pharmacologic stressors. We hypothesized that CRF might mediate some of the effects of cocaine and as such it may be a link between stressful events and increased vulnerability to cocaine addiction. We demonstrated that blockade of endogenous CRF by a CRF antiserum or a receptor antagonist prevented the cocaine-induced corticosterone response in rats. In male rhesus monkeys and in humans, cocaine selectively increased the amplitude-related, CRF-dependent, elements of pulsatile ACTH release. Cocaine-induced locomotor hyperactivity was antagonized by intracerebroventricular (i.c.v.) administration of a CRF antiserum and a CRF receptor antagonist in rats. In rhesus monkeys, strong correlations were found between behavioral hyperactivity and CRF-dependent elements of pulsatile activity of the HPA axis. Acute cocaine administration induced dose- and time-dependent alterations in hypothalamic and extrahypothalamic/limbic CRF concentrations in rats. Cocaine withdrawal elicited anxiety-like behavior and alterations of CRF concentration in the hypothalamus, amygdala, and basal forebrain. CRF antiserum (i.c.v.) antagonized anxiety-like behavior related to cocaine withdrawal. These data strongly suggest that the HPA axis, brain CRF in particular, may mediate some of the neuroendocrine and behavioral effects of cocaine. The potential involvement of CRF and HPA axis in cocaine-induced psychopathology is hypothesized.

Antisense inhibition of 5-hydroxytryptamine2a receptor induces an antidepressant-like effect in mice

Treatment with different antidepressants is invariably accompanied by the down-regulation of the 5-hydroxytryptamine2A (5-HT2A) receptor. To determine whether receptor down-regulation is an essential part of antidepressant action, we manipulated levels of the 5-HT2A receptor by using a nonpharmacological approach. Here, we report that down-regulation of the 5-HT2A receptor by intracerebroventricular injection of antisense oligonucleotides resulted in an antidepressant-like effect in mice. Animals with 5-HT2A receptor deficiency showed less immobility in the Porsolt's forced swim test, a well established animal model that is used to identify drugs with an antidepressant effect. The overall locomotor activity of the receptor-deficient animals was not altered, demonstrating the specificity of the behavioral change in the Porsolt's forced swim test. Reduced immobility in this test was accompanied by a greater c-Fos response in piriform cortex. Because 5-HT2A receptors have been localized on gamma-aminobutyric acid interneurons, the inhibitory activity of these neurons may be impaired at low receptor levels, leading to a greater c-Fos response in the piriform cortex and increased mobility in the Porsolt's forced swim test. These experiments demonstrate that down-regulation of the 5-HT2A receptor alone is sufficient to achieve an antidepressant-like effect in mice and suggest that receptor down-regulation may be an essential part of the antidepressant drug action.

Time-dependent alterations in corticotropin-releasing factor-like immunoreactivity in different brain regions after acute cocaine administration to rats

Recent data from various laboratories suggest that the activation of endogenous corticotropin-releasing factor (CRF) may contribute to the behavioral and neuroendocrine effects of cocaine. In the present study, the time-dependent variations in CRF-like immunoreactivity (CRF-LI) in the hypothalamus and several extrahypothalamic brain regions were determined after acute cocaine administration to handled rats. The intraperitoneal injection of 7.5 mg/kg cocaine led to a significantly decreased CRF-LI level in the basal forebrain and to a significantly increased CRF-LI level in the amygdala 60 min after administration, while the CRF-LI content was decreased in the hypothalamus and in the hippocampus 180 min after cocaine treatment. These results suggest that the durations of the effects of cocaine on CRF-LI are in the brain region-specific, which might contribute to the mediation of the diverse behavioral and neuroendocrine effects of cocaine.

Effects of cocaine on pulsatile activity of hypothalamic-pituitary-adrenal axis in male rhesus monkeys: neuroendocrine and behavioral correlates

Cocaine stimulates the hypothalamic-pituitary-adrenal (HPA) axis in rodents and in humans. This study examined the acute effects of cocaine (0.4 and 0.8 mg/kg) and saline placebo on pulsatile adrenocorticotropic hormone (ACTH) and cortisol release in seven male rhesus monkeys. Pulsatile ACTH and cortisol release were evaluated with an intensive (2-min) venous blood sampling procedure and cluster analysis. In addition, the behavioral responses to cocaine were analyzed to assess the relationship between HPA axis activation and behavior. Although analysis of group data revealed significant (P < .05) increases in pulse amplitude and incremental peak height of ACTH and cortisol release after cocaine (0.8 mg/kg) administration, examination of individual data indicated that this effect was not consistent across all monkeys. Cocaine (0.8 mg/kg) increased ACTH plasma levels within 4.7 +/- 1.3 min (P < .05) and amplitude-related characteristics (P < .05) of pulsatile ACTH and cortisol release only in those animals that subsequently showed behavioral stimulation (high responders: n = 3). The frequency of pulsatile ACTH and cortisol remained unchanged by cocaine. Cocaine (0.8 mg/kg) decreased the mean amplitude of ACTH peaks with no changes in pulsatile cortisol release in the four monkeys that showed no behavioral stimulation (low responders). These differences in pulsatile ACTH and cortisol release patterns after cocaine could not explained by different plasma cocaine levels. Peak plasma cocaine levels averaged 63.1 +/- 13.4 and 78.0 +/- 21.4 ng/ml within 2 min after lower dose and 183.3 +/- 52.3 and 204.3 +/- 50.8 ng/ml after higher dose of cocaine in high- and low responder groups, respectively (P > .05; N.S.). Base-line cortisol, but not ACTH, levels were higher (P < .05) in low responders before administration of 0.8 mg/kg of cocaine. Peak and valley characteristics of base-line cortisol release were higher in low responders than in high responders and an inverse relationship was found between basal cortisol levels and postcocaine ACTH release and behavior. In summary, cocaine stimulated the pulsatile ACTH and cortisol release by increasing the amplitude of secretory episodes in behaviorally responsive monkeys.

Oxytocin blocks the development of heroin-fentanyl cross-tolerance in mice

The development of cross-tolerance to an analgesic effect was observed between two mu-receptor agonists, heroin and fentanyl. Repeated treatments with heroin twice a day for 4 days resulted in a decreased nociceptive effect to fentanyl on day 5. The fentanyl dose-response line shifted to the right, and was considered to be a sign of the development of cross-tolerance. Peripheral treatment with oxytocin did not block the development of heroin-fentanyl cross-tolerance. However, intracerebroventricular administration of oxytocin blocked the development of tolerance, causing a leftward shift in the dose-response curve and supporting the assumption that oxytocin blocks the development of heroin-fentanyl cross-tolerance via CNS mechanisms.

Effects of cocaine and corticotropin-releasing factor on pulsatile ACTH and cortisol release in ovariectomized rhesus monkeys

Cocaine stimulates ACTH secretion by a corticotropin-releasing factor (CRF)-dependent mechanism in male rats, rhesus monkeys, and humans. To determine the generality of this effect, we examined the effects of acute cocaine administration on the pulsatile release of ACTH and cortisol in three ovariectomized (OVX) rhesus monkeys and compared its effects to stimulation with CRF. Venous blood samples were collected at 2-min intervals for 60 min before and after iv administration of cocaine (0.4 and 0.8 mg/kg) and CRF (1.0 and 10 micrograms/kg). Cluster analysis procedures were used to evaluate the pulsatile characteristics of ACTH and cortisol release. After placebo administration, an ACTH pulse frequency of 3 peaks/h was detected. After cocaine administration, plasma cocaine levels peaked at 92 +/- 3.0 and 201 +/- 60 ng/mL within 2 min. However, in contrast to normal intact males, cocaine did not stimulate the pulsatile release of ACTH in OVX females. Cocaine (0.4 mg/kg) decreased ACTH incremental peak height and valley levels compared with pre-cocaine values, and a higher dose of cocaine produced no changes in ACTH release. Bolus injection of a low dose of CRF (1.0 micrograms/kg, iv) significantly increased ACTH incremental peak height (P < 0.05), and a higher dose of CRF (10 micrograms/kg) increased ACTH peak amplitude, percentage increase in peak amplitude, area under the peaks, and incremental peak heights as well as ACTH valley level and nadir (10 micrograms/kg, iv) (P < 0.05). ACTH pulse frequency did not change after CRF or cocaine administration. Pulsatile release of cortisol was 2.7 peaks/h under placebo conditions and did not change after cocaine or CRF administration. Cortisol pulse amplitude was increased after low and high doses of CRF. High doses of CRF (10 micrograms/kg) also increased the mean level of cortisol valleys. In summary, we found that CRF but not cocaine stimulated pulsatile ACTH and cortisol release in OVX rhesus monkeys. The profound ACTH response to CRF challenge suggests that the CRF sensitivity and the ACTH release capacity of the anterior pituitary corticotroph cells were intact. The lack of stimulatory effects of cocaine on the hypothalamic-pituitary-adrenal axis in OVX monkeys, in contrast to normal male monkeys, may reflect the absence of gonadal steroids.

Brain corticotropin-releasing factor mediates 'anxiety-like' behavior induced by cocaine withdrawal in rats

Anxiety is a key symptom of the cocaine withdrawal syndrome in human addicts, and it is considered to be one of the major factors in precipitating relapse to chronic cocaine abuse. Corticotropin-releasing factor (CRF) plays an important role in the pathophysiology of anxiety and depression, and it may also be involved in the acute behavioral and neuroendocrine actions of cocaine. The role of endogenous CRF in cocaine withdrawal-induced anxiety was investigated in the present study. Animals were subjected to chronic cocaine (20 mg/kg, intraperitoneally, once a day for 14 days) administration. Rats tested 30 min after the last cocaine injection did not show withdrawal anxiety on the elevated plus maze or any alterations in brain CRF levels. Withdrawal (48 h) from chronic cocaine administration produced an intense anxiety-like behavior characterized by decreased open arm exploration. Immunoreactive CRF (CRF-LI) levels were selectively altered in the hypothalamus, in the amygdala and in the basal forebrain structures at the time of the behavioral anxiety, reflecting an increased activity of brain CRF systems. Daily intracerebroventricular (i.c.v.) pretreatment with an immunoserum raised against CRF completely prevented the development of anxiety induced by cocaine withdrawal. These data suggest that extrahypothalamic-limbic CRF hypersecretion may be involved in the development of anxiety related to cocaine withdrawal and that the CRF system may be a useful target for new pharmacotherapies for cocaine withdrawal and relapse.

The acute effects of cocaine on anterior pituitary hormones in ovariectomized rhesus monkeys

Cocaine stimulates a rapid release of gonadotropins in intact rhesus males and females and human males and enhances synthetic luteinizing hormone-releasing hormone (LHRH), stimulated luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This report describes the effects of acute cocaine administration on basal and synthetic LHRH-stimulated anterior pituitary hormones [LH, FSH and prolactin (PRL)] in five ovariectomized female rhesus monkeys. Integrated blood samples were collected every 10 min for 40 min before i.v. administration of cocaine (0.4 or 0.8 mg/kg) or an equal volume of vehicle control solution and for 110 min after cocaine or placebo administration. Synthetic LHRH (100 micrograms i.v.) was administered 10 min after cocaine or placebo-cocaine injection. In contrast to previous observations in rhesus and human males and in early follicular and midluteal phase rhesus females, cocaine did not change basal levels of gonadotropins or PRL in long-term ovariectomized females. LHRH stimulated a significant and sustained increase in LH (P < .01) within 20 min and FSH (P < .05) within 40 min after placebo-cocaine administration. LHRH also stimulated significant increases in LH and FSH after 0.4 and 0.8 mg/kg cocaine administration. Significant increases in LH (P < .05) and FSH (P < .01) were measured 10 min sooner after 0.8 mg/kg cocaine than after placebo-cocaine, but cocaine did not significantly increase the magnitude or duration of LHRH-stimulated increases in gonadotropins in ovariectomized females as it did in follicular phase females. Basal PRL levels (3.6 +/- 0.2 and 5.5 +/- 0.7 ng/ml) did not change after administration of cocaine alone.(ABSTRACT TRUNCATED AT 250 WORDS)

The concordance of pulsatile ultradian release of adrenocorticotropin and cortisol in male rhesus monkeys

The ultradian release of ACTH and cortisol was investigated in six male rhesus monkeys (Macaca mulatta) with an intensive (2-min) blood-sampling procedure to investigate micropulsatile hormone secretory patterns. A sensitive and specific immunoradiometric assay was used to measure plasma ACTH concentrations. An objective pulse detection algorithm (Cluster) was used to assess the pulsatility of ACTH and cortisol release. The temporally coincident release of ACTH and cortisol was also examined. Venous blood samples were collected (over < 15 s) every 2 min for 120 min beginning at 1300 h. The number of ACTH peaks (3.2 peaks/h), interpulse intervals (19 +/- 2.4 min), and pulse amplitudes (9.7 +/- 1.6 pmol/L) in rhesus monkey were similar to corresponding measures of ACTH release in humans (3.3 peaks/h, 18 +/- 0.8 min, and 4.7 +/- 1.0 pmol/L, respectively). The number of cortisol peaks (2.3 peaks/h), interpulse interval (26 +/- 8.6 min), and other characteristics of pulsatile cortisol release were also determined. There was a 32.4% exact concordance of ACTH with cortisol peaks (11 of 34; P < 0.001). Fifty-six percent of ACTH peaks (19 of 34) were followed by a cortisol peak within 10 min (P < 0.02). There was a significant correlation between the ACTH and coincident cortisol pulse amplitudes (P < 0.0001). The amplitudes of ACTH peaks coincident with cortisol peaks at 0 min time lag were significantly higher than ACTH peaks not temporally coupled with cortisol peaks. Our data indicate that 1) high frequency, low amplitude micropulsatile ACTH secretion in rhesus monkeys is very similar to the high frequency ACTH rhythm in humans; 2) temporally concordant ACTH and cortisol release episodes may be amplitude coupled; and 3) an adequate incremental ACTH pulse amplitude may elicit a concurrent cortisol release episode from the adrenal cortex. These data suggest that the rhesus monkey is a potentially useful model for the study of neuroendocrine control of ACTH release.

Cocaine effects on pulsatile secretion of ACTH in men

The effects of cocaine on pulsatile secretion of adrenocorticotropic hormone (ACTH) in men were studied under controlled clinical research ward conditions. Eight men with a Diagnostic and Statistical Manual of the American Psychiatric Association Version III, revised, diagnosis of concurrent cocaine and opioid dependence provided their informed consent for participation in this study. After an overnight fast, a challenge dose of cocaine (30 mg i.v.) or placebo was administered under single-blind conditions in a randomized order on 2 study days. Blood samples were collected at 2-min intervals for 76 min during base line and for an additional 76 min after i.v. administration of the challenge dose. Peak plasma cocaine levels of 313.8 +/- 46.5 ng/ml were detected within 2 min after cocaine administration. The cluster analysis program originally described by Veldhuis and Johnson (1986) was used to characterize ACTH pulsatile secretion (Iranmanesh et al., 1990). Acute cocaine administration (30 mg i.v.) significantly increased ACTH mean peak amplitude (P < .05), mean percent increase in peak amplitude, (P < .05), mean peak area (P < .04), total peak area (P < .04) and incremental peak height (P < .04). Mean ACTH valley levels (P < .02) and mean valley nadir (P < .02) were also significantly increased after cocaine administration. We postulate that cocaine stimulates the release of corticotropin releasing factor and that the cocaine-induced secretion of corticotropin releasing factor increases the amplitude of ACTH pulses, because ACTH pulse frequency was not altered by cocaine.

The role of central corticoliberin in the ether stress-induced secretion of neurohypophyseal hormones and corticosterone in the rat

As corticotropin-releasing factor (CRF) and oxytocin (OXT) are released in response to various stressors and a role of CRF in stress-induced OXT secretion has been proposed by previous authors, the present experiments were scheduled to investigate the participation of the brain CRF system in the stress-evoked release of OXT, arginine-8-vasopressin (AVP) and corticosterone. CRF-antiserum (AS) was given into the lateral ventricle of the brain of Wistar male rats, and 24 h later, the injection was repeated 30 min prior to ether stress followed by decapitation in 5 min. Plasma OXT and AVP were measured by radioimmunoassay and corticosterone by fluorimetry. Ether stress increased the levels of corticosterone and OXT, but not that of AVP. CRF-AS alone did not change the secretion of these hormones. CRF-AS pretreatment blocked the corticosterone-releasing action of ether stress, whereas it exerted no influence on the stress-induced OXT secretion into the circulation. There was no effect of a combined application of CRF-AS and stress on the plasma AVP level. These results suggest that the central CRF system is involved in the ether stress-elicited corticosterone response, however CRF is unlikely to be connected with the regulation of OXT secretion under these experimental conditions.

Role of oxytocin in the neuroadaptation to drugs of abuse

Oxytocin (OXT), a neurohypophyseal hormone, has a wide range of behavioral effects outside its classic peripheral endocrine functions. OXT involvement in adaptive central nervous system processes has been demonstrated as an inhibitory, amnestic action on learning and memory in different paradigms. Because adaptation and learning are likely to be involved in the neural events leading to drug tolerance and dependence, the question logically arose whether OXT is able to influence the development of tolerance of and dependence on abused drugs. In this review, we summarize our results on the effects of OXT on opiate (including morphine, heroin, and the endogenous opiates beta-endorphin and enkephalin) tolerance and dependence, heroin self-administration, psychostimulant-induced behavioral changes, and behavioral tolerance and sensitization. The sites and mechanisms of action and the possible physiological role of OXT are also discussed. In the first part of this review the effects of exogenously administered OXT on both the acute and chronic behavioral effects of opiates and psychostimulants have been summarized. OXT inhibited the development of tolerance to morphine, heroin, beta-endorphin, and enkephalin, OXT also inhibited the development of cross-tolerance between the predominantly mu-agonist heroin and the predominantly delta-agonist enkephalin in mice. Naloxone-precipitated morphine withdrawal syndrome was also attenuated by OXT. Heroin self-administration was decreased by OXT administration in heroin-tolerant rats. OXT inhibited cocaine-induced exploratory activity, locomotor hyperactivity, and stereotyped behavior in rats and in mice. Behavioral tolerance to cocaine was also attenuated by OXT. On the contrary, OXT stimulated the development of behavioral sensitization to cocaine. OXT did not alter the stereotyped behavior induced by amphetamine. In the second series of experiments, the sites of action of OXT on drug-related behavior were investigated. Intracerebro-ventricular (ICV) and intracerebral (IC) administration of an OXT-receptor antagonist inhibited the effects of peripherally administered OXT on morphine tolerance, heroin self-administration, and cocaine-induced sniffing behavior. This suggests the central, intracerebral location of OXT target sites. Local IC microinjection of OXT in physiological doses into the posterior olfactory nucleus, tuberculum olfactorium, nucleus accumbens, central amygdaloid nucleus, and the hippocampus inhibited the development of tolerance to and dependence on morphine as well as cocaine-induced sniffing behavior and tolerance to cocaine. The physiological role of endogenous OXT in acute morphine tolerance has also been demonstrated, since OXT antiserum (ICV) and OXT-receptor antagonist (injected into the basal forebrain structures) potentiated the development of morphine tolerance. Finally, we investigated the possible mechanisms of action of OXT on drug related behavior. Both morphine tolerance and dependence, and cocaine administration, increased dopamine utilization in the mesencephalon and in the nucleus accumbens, respectively. OXT treatment decreased the alpha-methylparatyrosine-induced dopamine utilization in the mesencephalon and in the nucleus accumbens-septal complex. Chronic OXT treatment decreased the number of apparent binding sites of dopamine in the basal forebrain area. It also inhibited a cocaine-induced increase in dopamine utilization in the nucleus accumbens, but not in the striatum. In light of this information, it appears that OXT inhibits the development of opiate tolerance, dependence, and self-administration as well as the acute behavioral actions of and chronic tolerance to cocaine. This suggests the possible role of this neuropeptide in the regulation of drug abuse. Therefore, OXT may act as a neuromodulator on dopaminergic neurotransmission in limbic-basal forebrain structures to regulate adaptive CNS processes leading to drug addiction.