Stress Hormone Secretion Research Articles

Melatonin attenuates phenotypic flexibility of energy metabolism in a photoresponsive mammal, the Siberian hamster.

The duration of melatonin (MEL) secretion conveys information about day length and initiates a cascade of seasonal phenotypic adjustments in photoresponsive mammals. With shortening days, animals cease reproduction, minimize energy expenditure, enhance thermoregulatory capacity and adjust functioning of the hypothalamic-pituitary-adrenal (HPA) axis to match the winter increase in energy demands. Within each season, stress plays an important role in the flexible adjustments of a phenotype to environmental perturbations. Recent studies have shown that thermal reaction norms of energy metabolism were narrower in winter-acclimated Siberian hamsters, Phodopus sungorus We tested the hypothesis that physiological changes occurring in response to prolonged MEL signals, including changes in the secretion of stress hormones, are responsible for the seasonal decrease in phenotypic flexibility of energy metabolism in photoresponsive mammals. To quantify reaction norms for basal metabolic rate (BMR) and cortisol (CORT) secretion, male Siberian hamsters maintained at a long (16h:8h light:dark) photoperiod were acclimated repeatedly for 12 days to 10 and 28°C. As predicted, the phenotypic flexibility of BMR decreased when animals were supplemented with MEL. However, at the same time, mean CORT concentration and the reaction norm for its secretion in response to changes in acclimation temperature increased. These results suggest that decreased sensitivity of HPA axis to CORT signal, rather than changes in CORT level itself, is responsible for the decreased phenotypic flexibility in photoresponsive species. Our results suggest that decreased phenotypic flexibility in winter, together with increased stress hormone secretion, make photosensitive species more vulnerable to climate change.

Fish Oil Prevents Lipopolysaccharide-Induced Depressive-Like Behavior by Inhibiting Neuroinflammation.

Depression is associated with somatic immune changes, and neuroinflammation is now recognized as hallmark for depressive disorders. N-3 (or omega-3) polyunsaturated fatty acids (PUFAs) are well known to suppress neuroinflammation, reduce oxidative stress, and protect neuron from injury. We pretreated animals with fish oil and induced acute depression-like behaviors with systemic lipopolysaccharide (LPS) injection. The levels of cytokines and stress hormones were determined from plasma and different brain areas. The results showed that fish oil treatment prevent LPS-induce depressive behavior by suppression of neuroinflammation. LPS induced acute neuroinflammation in different brain regions, which were prevented in fish oil fed mice. However, neither LPS administration nor fish oil treatment has strong effect on stress hormone secretion in the hypothalamus and adrenal. Fish oil might provide a useful therapy against inflammation-associated depression.

Effect of Intraoperative Glucose Infusion on Catabolism of Adipose Tissue and Muscle Protein in Patients Anesthetized With Remifentanil in Combination With Sevoflurane During Major Surgery: A Randomized Controlled Multicenter Trial.

A harmful effect of stress hormone secretion during surgery is lipolysis and proteolysis to maintain normal blood glucose levels. A well-titrated general anesthetic improves blood glucose control by suppressing secretion of these stress hormones. The aim of this study was to explore the effect of intraoperative glucose infusion on lipolysis and proteolysis in patients undergoing a general anesthetic consisting of sevoflurane and remifentanil during long (>6 hours) major surgery. In this prospective, single-blinded, randomized, multicenter trial, 80 patients with an expected duration of anesthesia of >6 hours were allocated to either the glucose group, consisting of 40 patients who were infused with acetated Ringer's solution with glucose (2 mg/kg/min), or the no glucose group, consisting of 40 patients who were infused with the same solution, but without glucose. After oxygenation, general anesthesia was induced with propofol, fentanyl, and rocuronium and was maintained with sevoflurane, oxygen, rocuronium, and remifentanil infusions. The rates of remifentanil infusion were titrated based on systolic arterial blood pressure, maintaining this parameter within 10% of its postanesthesia values. Seventy-four patients completed the study. Urinary 3-methylhistidine/creatinine (3-MH/Cre) ratio, acetoacetic acid, 3-hydroxybutyric acid, blood glucose, insulin, and cortisol were measured 3 times: at anesthesia induction (0 hour) and at 3 and 6 hours after anesthesia induction. Urinary 3-MH/Cre ratio was the primary study outcome. In the no glucose group, the urinary 3-MH/Cre ratio at 6 hours was increased compared with that at 0 hour (213 [range, 42-1903] vs 124 [18-672] nmol/μmol; the difference in medians, 89; the 95% confidence interval [CI] of the difference, 82-252; P = .0002). Acetoacetic acid and 3-hydroxybutyric acid levels in the no glucose group were greater than those in the glucose group at 6 hours (110 [8-1036] vs 11 [2-238] μmol/L; the difference in medians, 99; the 95% CI of the difference, 92-196; P < .0001 and 481 [15-2783] vs 19 [4-555] μmol/L; the difference in medians, 462; the 95% CI of the difference, 367-675; P < 0.0001, respectively). Blood glucose and insulin levels in the glucose group were greater than those in the no glucose group at 3 hours (146 [103-190] vs 93 [72-124] mg/dL; the difference in medians, 53; the 95% CI of the difference, 47-55; P < .0001 and 9.8 [1.2-25.4] vs 3.2 [0.4-15.0] μU/mL; the difference in medians, 6.5; the 95% CI of the difference, 4.8-6.8; P < .0001) and 6 hours (139 [92-189] vs 87 [68-126] mg/dL; the difference in medians, 52; the 95% CI of the difference, 44-58; P < .0001 and 8.1 [1.2-22.3] vs 3.2 [0.4-10.1] μU/mL; the difference in medians, 4.9; the 95% CI of the difference, 4.0-5.9; P < .0001). Cortisol levels in both groups were similarly within normal levels at 0, 3, and 6 hours. The study showed that intraoperative glucose infusion suppressed lipolysis and proteolysis in patients anesthetized with remifentanil in combination with sevoflurane during surgery of >6 hours in length.

Role of buprenorphine in acute postoperative pain

Nowadays acute postoperative pain persists as a high prevalence symptom. The incidence, intensity and duration of postoperative pain vary considerably from one patient to another, from one surgery to another, from one hospital to another, and even from one country to another. It is important to learn about recent developments in central sensitisation, as it plays an important role in postoperative pain. Postoperative pain is mainly nociceptive somatic, in response to surgical damage. The surgical trauma and pain cause an endocrine response that increases the secretion of cortisol, catecholamines, and other stress hormones. Tachycardia, hypertension, decreased regional blood flow, impaired immune response, hyperglycaemia, lipolysis, and negative nitrogen balance also occur. All this plays an important role in morbidity and mortality in the postoperative period. Buprenorphine is a semi-synthetic opioid derived from thebaine. It has a binding affinity for the mu, kappa and delta receptors, and has a slow dissociation from these receptors. Because of its action on the mu and kappa receptors it can be used as an analgesic, as well as for maintenance therapy in patients with a history of drug abuse. This article will describe the characteristics of acute postoperative pain, the pharmacology of buprenorphine, and its interference in the management of postoperative pain.

Stress and Pediatric Obesity: Neurobiology and Behavior

AbstractPediatric and adolescent obesity commonly coexist with stress‐related symptoms and disorders. Stress, the state of threatened homeostasis, is associated with the acute activation of the hypothalamic–pituitary–adrenal axis and the sympathetic nervous system. However, the chronic activation of hypothalamic–pituitary–adrenal and sympathetic nervous system axes during chronic or intense stress can lead to a variety of psychopathological and physical conditions. Behavioral and neurobiological mechanisms link chronic stress with pediatric obesity, in a bidirectional relation. Chronically stressed individuals are characterized by low adherence to a healthy lifestyle and by disturbed eating behaviors, whereas alterations in the secretion of stress hormones might also contribute to obesity and obesity‐related complications. Obesity could lead to increased social distress, low self‐esteem, and anxiety, thereby contributing to a vicious cycle between distress and obesity and increasing further the risk of cardiometabolic morbidity. This review article summarizes recent research findings and discusses mechanisms linking stress with pediatric obesity.

Assessment of Faecal Cortisol Levels in Free-Ranging Nilgiri Tahrs (Nilgiritragus hylocrius) in Correlation with Meteorological Parameters: A Non-Invasive Study

The faecal glucocorticoid metabolites of a free-ranging small Nilgiri tahr population of Western Ghats, Tamil Nadu was studied to investigate contributing confounding influences of season, ambient temperature, rainfall and water level on the annual secretion pattern. The was done for a period of one year Oct 2013-Sep 2014. Individuals may cope with environmental challenges through the secretion of stress hormones (glucocorticoids) which allows the integration of environmental change as essential life events such as predator stress, food and water availability, resting cover, influence of tourists and life history events such as birth, death, maintenance of an essential population size by means of an adaptive feedback mechanism. Adaptation and eventually acclimatization to cyclic day-to-day activities, short-term environmental stressors or long-term ecological pressures have been observed with these animals. However, being a highly limited population the animals maintained an effective population size. A clear cut seasonal pattern of glucocorticoid metabolites excretion was detected, with increasing levels in summer and winter. The confounding factors such temperature, rainfall, relative humidity, solar radiation, soil temperature were recorded throughout the study period and did not have any correlation with the stress the animals exhibited. The observed pattern might be due to lack of feed availability both during summer and winter, a declining nutritional intake and reduction of metabolism during winter, clearly the animals were not in their “Thermo comfort Zone”. However, broad retrospective studies are essential to identify potential contingent environmental stressors. This study reports the baseline cortisol level in Nilgiri Tahrs, with the relevant confounding factors correlating with their annual variation level.

Stress, Thyroid Hormone Secretion and Vestibular Stimulation: A Review of the Links

Stress is part and parcel of our daily life. It is defined as a state of disharmony or threatened homeostasis. Stress can specifically influence several systems. Here we review the interactions of stress and thyroid hormone secretion and vestibular stimulation to suggest necessary translational research in this area. Vestibular stimulation may be used as a supplemental therapy for thyroid disorders. We suggest detailed studies in this area to explore importance of vestibular stimulation in the management of thyroid disorders.

Activity mediates conscientiousness' relationship to diurnal cortisol slope in a national sample.

The present study explored pathways from the personality traits of neuroticism and conscientiousness through health-related behaviors to diurnal patterns of the stress hormone cortisol using data from a large national study. Using prospective data from the Midlife in the United States (MIDUS II) study and the National Study of Daily Experiences (NSDE II, a MIDUS substudy), hierarchical linear modeling (HLM) and Monte Carlo estimation for multilevel model mediation were used to test direct and indirect effects (via general activity level, moderate and vigorous physical activity, lifetime history of regular smoking, and alcohol consumption) of neuroticism and conscientiousness on cortisol at wakeup, diurnal cortisol slope, and cortisol awakening response (N = 960). Initial HLM models showed greater levels of conscientiousness were associated with steeper (i.e., healthier) diurnal cortisol slope. Consistent with a hypothesized indirect biobehavioral pathway, when controlling for demographic factors, cortisol-related medications, daily stressors, and positive affect, HLM models showed the relationship between conscientiousness and diurnal cortisol slope was mediated by general activity levels. Lifetime history of smoking was associated with flatter diurnal cortisol slope, but did not mediate the effect of conscientiousness on diurnal cortisol slope. No effects were found for neuroticism. The results support a psychophysiological model of resilience--one that provides a more complete rendering of the health-protective mechanisms of conscientiousness via hypothalamic-pituitary-adrenal axis functioning. Specifically, the mediated pathway suggests greater engagement in the activities of day-to-day life are an instrumental means by which conscientious individuals experience healthier patterns of stress hormone secretion.

Facebook behaviors associated with diurnal cortisol in adolescents: Is befriending stressful?

Facebook© is changing the way people interact and socialize. Despite great interest in psychology and sociology, little is known about Facebook behaviors in relation to physiological markers of stress. Given that the brain undergoes important development during adolescence and that glucocorticoids—a major class of stress hormones—are known to modulate its development, it is important to study psychosocial factors that may influence secretion of stress hormones during adolescence. The goal of the present study was to explore the associations between Facebook behaviors (use frequency, network size, self-presentation and peer-interaction) and basal levels of cortisol among adolescent boys and girls. Eighty-eight adolescents (41 boys, 47 girls) aged between 12 and 17 (14.5±1.8) were recruited. Participants provided four cortisol samples per day for two non-consecutive weekdays. Facebook behaviors were assessed in accordance with the existing literature. Well-validated measures of perceived stress, perceived social support, self-esteem, and depressive symptoms were also included. A hierarchical regression showed that after controlling for sex, age, time of awakening, perceived stress, and perceived social support, cortisol systemic output (area under the curve with respect to ground) was positively associated with the number of Facebook friends and negatively associated with Facebook peer-interaction. No associations were found among depressive symptoms, self-esteem, and cortisol. These results provide preliminary evidence that Facebook behaviors are associated with diurnal cortisol concentrations in adolescents.

Weathering the storm: parental effort and experimental manipulation of stress hormones predict brood survival.

BackgroundUnpredictable and inclement weather is increasing in strength and frequency, challenging organisms to respond adaptively. One way in which animals respond to environmental challenges is through the secretion of glucocorticoid stress hormones. These hormones mobilize energy stores and suppress non-essential physiological and behavioral processes until the challenge passes. To investigate the effects of glucocorticoids on reproductive decisions, we experimentally increased corticosterone levels (the primary glucocorticoid in birds) in free-living female tree swallows, Tachycineta bicolor, during the chick-rearing stage. Due to an unprecedented cold and wet breeding season, 90 % of the nests in our study population failed, which created a unique opportunity to test how challenging environmental conditions interact with the physiological mechanisms underlying life-history trade-offs.ResultsWe found that exogenous corticosterone influenced the regulation of parental decisions in a context-dependent manner. Control and corticosterone-treated females had similar brood failure rates under unfavorable conditions (cold and rainy weather), but corticosterone treatment hastened brood mortality under more favorable conditions. Higher female nest provisioning rates prior to implantation were associated with increased probability of brood survival for treatment and control groups. However, higher pre-treatment male provisioning rates were associated with increased survival probability in the control group, but not the corticosterone-treated group.ConclusionsThese findings reveal complex interactions between weather, female physiological state, and partner parental investment. Our results also demonstrate a causal relationship between corticosterone concentrations and individual reproductive behaviors, and point to a mechanism for why naturally disturbed populations, which experience multiple stressors, could be more susceptible and unable to respond adaptively to changing environmental conditions.

Regular Yoga Practice Improves Antioxidant Status, Immune Function, and Stress Hormone Releases in Young Healthy People: A Randomized, Double-Blind, Controlled Pilot Study.

The aim of the present study is to highlight the beneficial effects of yoga practice on bio-parameters, such as oxidative stress, antioxidant components, immune functions, and secretion of stress hormones, in healthy young people. This study was conducted on healthy volunteers recruited from among university students, who were divided into two groups: a control (no yoga intervention, n=13) group and a yoga (n=12) group. Yoga practice was with an instructor for 90 minutes once a week spread over 12 weeks, with recommendations to practice daily at home for 40 minutes with the help of a DVD. The yoga program consisted of yoga body poses (asanas), exercises involving awareness, voluntary regulation of breath (pranayama), and meditational practices. Whole blood samples were collected when the volunteers had fasted for 8 hours at 0 and 12 weeks. The oxidative stress/antioxidant components, immune-related cytokines, and stress hormones were evaluated in serum or plasma. Serum levels of nitric oxide, F2-isoprostane, and lipid peroxide were significantly decreased by yoga practice (p<0.05 or p=0.01), whereas serum total glutathione (GSH) contents, activities of GSH-peroxidase, and GSH-s-transferase were remarkably increased after yoga practice compared with the control group (p<0.05 or p=0.01). Yoga practice also significantly increased immune-related cytokines, such as interleukin-12, and interferon-γ, in serum (p<0.05 or p=0.01). Yoga practice significantly reduced the plasma levels of adrenalin (p<0.05) and increased plasma levels of serotonin compared with the control group (p<0.05). Regular yoga practice remarkably attenuated oxidative stress and improved antioxidant levels of the body. Moreover, yoga beneficially affected stress hormone releases as well as partially improved immune function.

Repeated exposure to stressful conditions can have beneficial effects on survival

Repeated exposure to stressful circumstances is generally thought to be associated with increased pathology and reduced longevity. However, growing lines of evidence suggest that the effects of environmental stressors on survival and longevity depend on a multitude of factors and, under some circumstances, might be positive rather than negative. Here, using the zebra finch (Taeniopygia guttata), we show that repeated exposure to stressful conditions (i.e. unpredictable food availability), which induced no changes in body mass, was associated with a decrease in mortality rate and an increase in the age of death. As expected, the treated birds responded to the unpredictable food supply by increasing baseline glucocorticoid stress hormone secretion and there were no signs of habituation of this hormonal response to the treatment across time. Importantly, and consistent with previous literature, the magnitude of hormone increase induced by the treatment was significant, but relatively mild, since the baseline glucocorticoid concentrations in the treated birds were substantially lower than the peak levels that occur during an acute stress response in this species. Taken together, these data demonstrate that protracted exposure to relatively mild stressful circumstances can have beneficial lifespan effects.

A meta‐analysis of plasma corticosterone and heterophil : lymphocyte ratios – is there conservation of physiological stress responses over time?

Summary There is growing need for reliable biomarkers of the physiological stress response in basic ecological investigations and conservation‐specific applications. One effect of stress hormone secretion is the alteration of circulating leucocytes, specifically an increase in the heterophil : lymphocyte ratio (HLR). There have been numerous studies and reviews of the relationship between the stress response and HLR, yet the data have not been systematically analysed across studies. Here, we performed meta‐analyses of studies in which paired values of plasma corticosterone (CORT) and HLR were available to investigate the relationship between these parameters. Specifically, we analysed CORT and HLR as baseline measures between treatment (or ‘stressed’ populations) and control (or ‘reference’ populations). Additionally, we investigated the relationship within CORT and HLR to identify temporal patterns of the response as a result of the duration of the stressor. Across studies, we identified that CORT and HLR are significantly elevated in populations subjected to environmentally stressful conditions. While not significantly different, CORT tended to be more elevated than HLR in the stressed populations. We found that there is a significant, negative relationship between CORT and the temporal duration of environmental stress. Additionally, we found a significant break point in this response at 85 days of stress duration, above which there is not a clear relationship between CORT and duration. This indicates that the CORT response to environmental stress attenuates. We found a small but positive significant relationship between HLR and temporal duration of environmental stress. This suggests that the elevation of HLR in response to environmental stress does not decrease over time. Our data identified that data gaps of wild populations of species exist and that more studies pairing physiological stress responses will further our understanding of how populations respond to environmental challenges. We found that CORT and HLR responded differently to stress, depending on captivity status, whether the study population was the domestic chicken, and the sex of the study population.

Neuroendocrinological Findings in Patients with Pathological Gambling and Internet Use Disorder

Background Brain-derived neurotrophic factor (BDNF) plays important roles in neurotransmitter release and synaptic plasticity and has been hypothesized to be involved in the development and maintenance of addictive disorders. Also, alterations in secretion of stress hormones within the hypothalamic–pituitary–adrenal (HPA) axis have repeatedly been found in substance-related addictive disorders. It has been suggested that glucocorticoids might modulate behavioural responses to substances of abuse. Therefore, we investigated alterations of BDNF expression and HPA axis activity in non-substance-related addictive disorders, i.e. pathological gambling (PG) and Internet use disorder (IUD). Methods We measured serum BDNF levels, plasma levels of copeptin, a vasopressin (AVP) surrogate marker, adrenocorticotropic hormone (ACTH) and cortisol in male patients with PG (n=14), IUD (n=11) and carefully matched healthy controls for PG (n=13) and IUD (n=10). Results BDNF serum levels were significantly increased in patients with PG in comparison to healthy control subjects (p = 0.016). Furthermore, cortisol plasma levels correlated negatively with the PG-YBOCS total severity score (r 2 = -.626, p = .039) in patients with PG. There was no significant difference in BDNF serum levels of patients with IUD in comparison to control subjects. Plasma levels of copeptin, ACTH and cortisol in patients with PG and IUD did not differ among groups. Conclusions These preliminary results might suggest that the pathophysiology of PG shares some characteristics with substance-related addictive disorders on a neuroendocrinological level, whereas those similarities could not be observed in IUD.

Acute effects of exposure to a traditional rural environment on urban dwellers: a crossover field study in terraced farmland.

Despite an increasing attention and public preference for rural amenities, little evidence is available on the health benefits of a rural environment. In this study, we identified physiological and psychological benefits of exposure to a rural environment using multiparametric methods. Twelve young male adults participated in a 3-day field experiment (mean ± standard deviation age, 22.3 ± 1.3 years). Sleeping environment, diet program, physical activities, and other factors possibly affecting physiological responses were controlled during experiment period. For all participants, salivary cortisol concentration, heart rate variability, and blood pressure were measured at rural and urban field sites. Self-evaluation questionnaires were administered to analyze the psychological states in two different environments. Volatile compounds in the air were also analyzed to investigate air quality. The data were compared between rural and urban environments. The data showed that exposure to a rural environment reduced stress hormone secretion and sympathetic nervous activity and increased parasympathetic nervous activity. Short-term exposure to a rural environment also improved mood states. Our findings indicate that exposure to a rural environment effectively reduced physiological stress and enhanced psychological well-being.

Hypothalamic–pituitary–adrenal axis activity in patients with pathological gambling and internet use disorder

Alterations in secretion of stress hormones within the hypothalamic–pituitary–adrenal (HPA) axis have repeatedly been found in substance-related addictive disorders. It has been suggested that glucocorticoids might contribute to the development and maintenance of substance use disorders by facilitatory effects on behavioral responses to substances of abuse. The objective of this pilot study was to investigate HPA axis activity in patients with non-substance-related addictive disorders, i.e. pathological gambling and internet use disorder. We measured plasma levels of copeptin, a vasopressin surrogate marker, adrenocorticotropic hormone (ACTH) and cortisol in male patients with pathological gambling (n=14), internet use disorder (n=11) and matched healthy controls for pathological gambling (n=13) and internet use disorder (n=10). Plasma levels of copeptin, ACTH and cortisol in patients with pathological gambling or internet use disorder did not differ among groups. However, cortisol plasma levels correlated negatively with the severity of pathological gambling as measured by the PG-YBOCS. Together with our findings of increased serum levels of brain-derived neurotrophic factor (BDNF) in pathological gambling but not internet use disorder, these results suggest that the pathophysiology of pathological gambling shares some characteristics with substance-related addictive disorders on a neuroendocrinological level, whereas those similarities could not be observed in internet use disorder.

Change of lipid metabolism after trauma and analysis of risk factors

Traumatic stressor could lead to a series of neuroendocrine responses, such as increased sympathetic activity and secretion of stress hormones, because of the local-pathological-changed tissues and stress response. These changes will have a huge impact on nutrient metabolism. In this article, we reviewed the researches on the change in lipid metabolism after trauma, associated factors, possible mechanisms and possible interventions.

Quantitative and qualitative evaluation of CART-containing cells in adrenal glands of male rats with hypertension

Adrenal activity is stimulated and secretion of stress hormones is increased during advanced stages of renovascular hypertension. The literature suggests that the neuropeptide, cocaine and amphetamine regulated transcript (CART), might regulate adrenal secretory function and thus could influence its activity. We assessed potential quantitative and qualitative changes in the cells that contained CART in the adrenal glands of rats with renovascular hypertension. The renal arteries of ten rats were subjected to a clipping procedure, i.e., two-kidney one-clip (2K1C) model of arterial hypertension, and after 6 weeks each rat developed stable hypertension. CART was localized using immunohistochemistry. CART was detected in a large population of cells in the medulla, sparse nerve fibers in the cortex and the capsule of the adrenal gland. The population of CART-positive cells in adrenal glands of two kidney-one clip (2K1C) treated rats was greater and their immunoreactivity was increased compared to controls. Similarly, the length, width, area and diameter of CART-immunoreactive cells were significantly greater in the hypertensive rats than in controls. We demonstrated that renovascular hypertension alters the number and immunoreactivity of CART-containing cells in adrenal glands.

Central actions of hydrogen sulfide (703.1)

Hydrogen sulfide (H2S) is a novel gaseous signaling molecule that has been shown to exert multiple beneficial effects in vivo, including anti‐inflammatory actions and protective effects in the gastrointestinal tract. HS converting enzymes are produced in the central nervous system, and thus may exert important actions in brain. We therefore tested the ability of HS to modulate mean arterial pressure, fluid intake, and stress hormone secretion in adult, male rats, via intracerebroventricular (icv) injection H2S donors (sodium hydrosulfide hydrate). Central administration of H2S donors led to rapid, transient, dose‐related increases in mean arterial pressure in conscious, freely moving male rats, but did not alter water or saline intakes. Furthermore, injection of H2S donors led to an increase in plasma corticosterone levels, but not plasma prolactin levels, in non‐stressed animals. From these data, we conclude that H2S may act as an important signaling molecule in brain, although elucidation of the physiological relevance of this gaseous messenger requires further evaluation.

Olfactory systems and neural circuits that modulate predator odor fear

When prey animals detect the odor of a predator a constellation of fear-related autonomic, endocrine, and behavioral responses rapidly occur to facilitate survival. How olfactory sensory systems process predator odor and channel that information to specific brain circuits is a fundamental issue that is not clearly understood. However, research in the last 15 years has begun to identify some of the essential features of the sensory detection systems and brain structures that underlie predator odor fear. For instance, the main (MOS) and accessory olfactory systems (AOS) detect predator odors and different types of predator odors are sensed by specific receptors located in either the MOS or AOS. However, complex predator chemosignals may be processed by both the MOS and AOS, which complicate our understanding of the specific neural circuits connected directly and indirectly from the MOS and AOS to activate the physiological and behavioral components of unconditioned and conditioned fear. Studies indicate that brain structures including the dorsal periaqueductal gray (DPAG), paraventricular nucleus (PVN) of the hypothalamus, and the medial amygdala (MeA) appear to be broadly involved in predator odor induced autonomic activity and hypothalamic-pituitary-adrenal (HPA) stress hormone secretion. The MeA also plays a key role in predator odor unconditioned fear behavior and retrieval of contextual fear memory associated with prior predator odor experiences. Other neural structures including the bed nucleus of the stria terminalis and the ventral hippocampus (VHC) appear prominently involved in predator odor fear behavior. The basolateral amygdala (BLA), medial hypothalamic nuclei, and medial prefrontal cortex (mPFC) are also activated by some but not all predator odors. Future research that characterizes how distinct predator odors are uniquely processed in olfactory systems and neural circuits will provide significant insights into the differences of how diverse predator odors activate fear.