Effects of early life adversity on cortisol/salivary alpha-amylase symmetry in free-ranging juvenile rhesus macaques

Early life adversity (ELA) affects physiological and behavioral development. One key component is the relationship between the developing Hypothalamic-Pituitary-Adrenal (HPA) axis and the Sympathetic Nervous System (SNS). Recent studies suggest a relationship between early life adversity and asymmetry in cortisol (a measure of HPA activation) and salivary alpha-amylase (sAA: a correlate of SNS activation) responses to stress among human children, but to our knowledge there have been no comparable studies in nonhumans. Here, we investigate the responses of these two analytes in “low stress” and “high stress” situations in free-ranging juvenile rhesus macaques (Macaca mulatta) on Cayo Santiago, Puerto Rico. Behavioral data on maternal maltreatment were collected during the first 3 months of life to determine individual rates of ELA, and saliva samples were collected from subjects noninvasively during juvenility. Irrespective of ELA, salivary alpha-amylase levels were lower in low stress situations and higher in high stress situations. For cortisol however, high ELA subjects exhibited higher low stress concentrations and blunted acute responses during high stress situations compared to moderate and low ELA subjects. Cortisol and sAA values were positively correlated among low ELA subjects, suggesting symmetry, but were uncorrelated or negatively correlated among moderate and high ELA subjects, suggesting asymmetry in these individuals. These findings indicate dysregulation of the stress response among juveniles maltreated during infancy: specifically, attenuated cortisol reactivity coupled with typical sAA reactivity characterize the stress response profiles of juveniles exposed to higher rates of ELA during the first 3 months of life.     

Differences in Salivary Alpha-Amylase and Cortisol Responsiveness following Exposure to Electrical Stimulation versus the Trier Social Stress Tests

Background

Cortisol is an essential hormone in the regulation of the stress response along the HPA axis, and salivary cortisol has been used as a measure of free circulating cortisol levels. Recently, salivary alpha-amylase (sAA) has also emerged as a novel biomarker for psychosocial stress responsiveness within the sympathetic adrenomedullary (SAM) system.

Principal Findings

We measured sAA and salivary cortisol in healthy volunteers after exposure to the Trier Social Stress Test (TSST) and electric stimulation stress. One hundred forty-nine healthy volunteers participated in this study. All subjects were exposed to both the TSST and electric stimulation stress on separate days. We measured sAA and salivary cortisol levels three times immediately before, immediately after, and 20 min after the stress challenge. The State (STAI-S) and Trait (STAI-T) versions of the Spielberger Anxiety Inventory test and the Profile of Mood State (POMS) tests were administered to participants before the electrical stimulation and TSST protocols. We also measured HF, LF and LF/HF Heart Rate Variability ratio immediately after electrical stimulation and TSST exposure. Following TSST exposure or electrical stimulation, sAA levels displayed a rapid increase and recovery, returning to baseline levels 20 min after the stress challenge. Salivary cortisol responses showed a delayed increase, which remained significantly elevated from baseline levels 20 min after the stress challenge. Analyses revealed no differences between men and women with regard to their sAA response to the challenges (TSST or electric stimulations), while we found significantly higher salivary cortisol responses to the TSST in females. We also found that younger subjects tended to display higher sAA activity. Salivary cortisol levels were significantly correlated with the strength of the applied electrical stimulation.

Conclusions

These preliminary results suggest that the HPA axis (but not the SAM system) may show differential response patterns to distinct kinds of stressors.     

The Combined Propranolol/TSST Paradigm – A New Method for Psychoneuroendocrinology

Upon perception of a stimulus as stressful, the human brain reacts with the activation of the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS), to mobilize energy resources to better cope with the stressor. Since the perception of the stressor is the initial stimulus, a synchronicity between the subjective perception of stress and the physiological stress reactivity should be expected. However, according to a recent meta-analysis, these associations are weak and inconsistent. The goal of the current study was to investigate the interaction between the SNS, HPA and subjective stress perceptions, by introducing an experimental manipulation of this interaction. For this purpose, we combined the SNS inhibitor propranolol with the Trier Social Stress Test, and measured endocrinological and psychological responses to the stressor. Thirty healthy male participants were recruited and randomly assigned to either a propranolol (PROP; n = 15) or placebo (PLC; n = 15) group. All subjects were administered 80 mg of propranolol 60 minutes prior to exposure to psychosocial stress. Salivary cortisol and alpha amylase (sAA), heart rate, blood pressure and subjective stress responses were assessed throughout the study. We observed significantly reduced sAA levels and heart rate increases in the PROP group in response to stress, with no effects of the drug on systolic or diastolic blood pressure changes. In line with previous studies, a significant increase in cortisol was seen in response to the stress exposure. Importantly, the cortisol increase was significantly higher in the PROP group. A typical increase in subjective stress could be seen in both groups, with no significant group differences emerging. Complementing previous work, this study further demonstrates a significant interaction between the HPA and the SNS during acute stress. The HPA activity was found to be elevated in the presence of a suppressed SNS in reactivity to the TSST.     

Psychosocial Stress Increases Salivary Alpha-Amylase Activity Independently from Plasma Noradrenaline Levels

Salivary alpha-amylase activity (sAA) and plasma noradrenaline (NA) concentrations are often considered to be surrogate markers of sympathetic activation in response to stress. However, despite accumulating evidence for a close association between sAA and noradrenaline and other indicators of sympathetic activity, reliability and generality of this relation remains unclear. We employed the Trier Social Stress Test (TSST) in order to directly compare the responses in sAA and NA to psychological stress in healthy volunteers (n = 23). The TSST significantly increased sAA and NA plasma levels with no significant differences in females and males. However, when subjects were divided according to their NA responses into low versus high responders, both groups did not significantly differ in their sAA before, during or after stress exposure. These data suggest that in response to acute psychological stress both plasma NA levels and sAA reflect sympathetic activity, however seemed to increase independently from each other.     

Variation in the oxytocin receptor gene influences neurocardiac reactivity to social stress and HPA function: a population based study

Oxytocin (OT) is a nonapeptide neurohormone that is involved in a broad array of physiological and behavioral processes related to health including hypothalamic-pituitary-adrenal (HPA) axis functioning, autonomic nervous system (ANS) activity and social behaviors. The present study sought to explore the influence of genetic variation in the oxytocin receptor (SNP; rs53576) on autonomic and neurohormonal functioning across both resting and psychological stress conditions in a population based sample of older adults. Results revealed that A carrier males showed higher levels of resting sympathetic cardiac control as compared to their G/G counter parts. However, G/G participants displayed significantly higher levels of sympathetic reactivity to psychological stress with G/G males showing the highest levels of sympathetic response to stress. Although no significant effects were detected for heart rate or parasympathetic cardiac control across resting and stress conditions, results revealed that G/G participants generally displayed heightened stroke volume and cardiac output reactivity to the psychological stressor. Furthermore, analysis of diurnal fluctuations in salivary cortisol revealed that G/G participants displayed lower awakening cortisol levels and less variation in salivary cortisol across the day as compared to A carrier individuals.     

Patterns of cortisol reactivity to laboratory stress

Cortisol responses to a laboratory stress protocol were investigated in 82 male firefighters. Saliva samples were collected during an adaptation period beginning between 9 and 10 am, and then at the end of each of six 10-min trials (a mental arithmetic task, an inter-task recovery period, a speech task, and three recovery periods). Individual differences in the mean cortisol response to the stress tasks were characterized by variation in the direction of the response, as well as the size of the response. Neither pre-stress cortisol levels nor responses were correlated with cardiovascular and mood responses. Cortisol levels before stress task presentation were negatively correlated with recent stress severity. Larger mean cortisol responses were associated with lower reports of recent stress exposure, lower negative affect scores, and a coping style characterized less experience of anger, more control over anger expression, and a tendency to screen out threatening information in stressful situations. Thus, increased cortisol activity was associated with less recent stress exposure and a more adaptive behavioral style than for those whose cortisol levels fell or were largely unchanged in response to a laboratory stressor.     

The Effect of Music on the Human Stress Response

Background

Music listening has been suggested to beneficially impact health via stress-reducing effects. However, the existing literature presents itself with a limited number of investigations and with discrepancies in reported findings that may result from methodological shortcomings (e.g. small sample size, no valid stressor). It was the aim of the current study to address this gap in knowledge and overcome previous shortcomings by thoroughly examining music effects across endocrine, autonomic, cognitive, and emotional domains of the human stress response.

Methods

Sixty healthy female volunteers (mean age = 25 years) were exposed to a standardized psychosocial stress test after having been randomly assigned to one of three different conditions prior to the stress test: 1) relaxing music (‘Miserere’, Allegri) (RM), 2) sound of rippling water (SW), and 3) rest without acoustic stimulation (R). Salivary cortisol and salivary alpha-amylase (sAA), heart rate (HR), respiratory sinus arrhythmia (RSA), subjective stress perception and anxiety were repeatedly assessed in all subjects. We hypothesized that listening to RM prior to the stress test, compared to SW or R would result in a decreased stress response across all measured parameters.

Results

The three conditions significantly differed regarding cortisol response (p = 0.025) to the stressor, with highest concentrations in the RM and lowest in the SW condition. After the stressor, sAA (p=0.026) baseline values were reached considerably faster in the RM group than in the R group. HR and psychological measures did not significantly differ between groups.

Conclusion

Our findings indicate that music listening impacted the psychobiological stress system. Listening to music prior to a standardized stressor predominantly affected the autonomic nervous system (in terms of a faster recovery), and to a lesser degree the endocrine and psychological stress response. These findings may help better understanding the beneficial effects of music on the human body.     

Measurements of Salivary Alpha Amylase and Salivary Cortisol in Hominoid Primates Reveal Within-Species Consistency and Between-Species Differences

Salivary alpha amylase (sAA) is the most abundant enzyme in saliva. Studies in humans found variation in enzymatic activity of sAA across populations that could be linked to the copy number of loci for salivary amylase (AMY1), which was seen as an adaptive response to the intake of dietary starch. In addition to diet dependent variation, differences in sAA activity have been related to social stress. In a previous study, we found evidence for stress-induced variation in sAA activity in the bonobos, a hominoid primate that is closely related to humans. In this study, we explored patterns of variation in sAA activity in bonobos and three other hominoid primates, chimpanzee, gorilla, and orangutan to (a) examine if within-species differences in sAA activity found in bonobos are characteristic for hominoids and (b) assess the extent of variation in sAA activity between different species. The results revealed species-differences in sAA activity with gorillas and orangutans having higher basal sAA activity when compared to Pan. To assess the impact of stress, sAA values were related to cortisol levels measured in the same saliva samples. Gorillas and orangutans had low salivary cortisol concentrations and the highest cortisol concentration was found in samples from male bonobos, the group that also showed the highest sAA activity. Considering published information, the differences in sAA activity correspond with differences in AMY1 copy numbers and match with general features of natural diet. Studies on sAA activity have the potential to complement molecular studies and may contribute to research on feeding ecology and nutrition.     

Social cognition under stress: Differential effects of stress-induced cortisol elevations in healthy young men and women

Humans as social beings often have to perform complex social cognitive tasks while under stress (e.g., during a social conflict). Previous research has established that the brain regions responsible for social cognitive tasks are target regions for stress hormones. However, little experimental research has been done testing the acute effects of stress on social cognition. Here, we investigated whether stress exposure and the ensuing glucocorticoid (i.e., cortisol) elevations affect social cognition. Thirty-two men and 32 women were exposed to either a psychosocial stress or a non-stressful control test before assessing their social cognition using the Reading the Mind in the Eyes Test (RMET) and the Movie for the Assessment of Social Cognition (MASC). Results showed differential effects of stress-induced cortisol responses among men and women for the MASC, but not the RMET. Among men, high cortisol responders displayed elevated MASC scores compared with low cortisol responders. Moreover, for stressed men a positive association between the magnitude of the cortisol responses to the stressor and MASC scores emerged. Among women, enhanced MASC scores were found for low cortisol responders relative to high cortisol responders and non-stressed controls. A strong negative association between cortisol reactivity and MASC scores was found among women. These results imply sex specific effects of glucocorticoids on social cognition and partially support the idea of sex differences in biobehavioral stress responses, with men engaging in fight-or-flight responses while women may react to stress with tending and befriending behavior.     

The cortisol stress response in male round goby (Neogobius melanostomus): effects of living in polluted environments?

Acute exposure to contaminants frequently induces stress, but prolonged exposures, such as those experienced by individuals in wild populations, can impair the capacity to mount a stress response. Using the round goby (Neogobius melanostomus), a small benthic fish and potential sentinel species for habitat contamination in the Great Lakes, we explored the impacts of living in highly polluted areas. Round goby were collected from highly contaminated and less contaminated areas of Hamilton Harbour (a well-known site of polycyclic aromatic hydrocarbon (PAH) and heavy metal contamination). The cortisol stress responses of fish from sites of high and low contamination were compared using an EIA assay on blood collected (n?=?112) either prior to or 0, 10, 30, 60, 240 min and 24 h following the application of a 4-min confined air exposure stressor. Plasma cortisol levels were elevated at 10 and 30 min post-stressor (100.3 and 87.5 ng/mL), and returned to levels similar to baseline (22.3 ng/mL) 1 h after the stressor. In contrast to predictions, round goby from areas of high and low contamination had similar cortisol levels at all timepoints. We also monitored stress responses immediately after a chasing stressor (n?=?19). During the chasing stressor, contaminated-site round goby exhausted faster than individuals from a less contaminated site, although they had similar levels of plasma cortisol (23.5 versus 20.9 ng/mL) and lactate (2.53 versus 1.98 mmol/L). Our results indicate that not all fishes may demonstrate impaired stress responses, even in highly contaminated habitats; however, such animals may still have increased vulnerability to predation.     

Cohesive social behaviour shortens the stress response: the effects of conspecifics on the stress response in lake sturgeon Acipenser fulvescens

An examination was made of whether social interactions can have a beneficial effect through the attenuation of the stress response in a social species. In the first experiment, one larger (mean ± s . e . 194·0 ± 12·5 g) and seven smaller (32·0 ± 2·6 g) juvenile lake sturgeon Acipenser fulvescens were placed in tanks to determine whether a classic dominance effect would be established based on body size ( n = 6). Large fish did not establish a territory or aggressively interact with smaller fish, as there were no significant differences in nearest-neighbour distances and an absence of aggressive behaviour (biting, chasing and pushing). In the second experiment, it was hypothesized that the presence of conspecifics would have a beneficial effect through an attenuation of the stress response. Fish in groups or isolation were stressed by a brief aerial exposure (30 s), and blood plasma was measured at regular time intervals (0, 20, 40, 60, 120 and 240 min) following the stressor via an implanted cannula ( n = 9–11). The presence of conspecifics did not affect the peak cortisol response, however, the overall cortisol response was shorter in duration compared to fish in isolation. Furthermore, secondary stress variables (plasma ions and glucose) showed differences between fish in groups and isolation. The results of these experiments suggest that social interaction plays an important and beneficial role in regulating the stress response in cohesive social species such as A. fulvescens .     

Time course of osmoregulatory, metabolic, and endocrine stress responses of Pacific halibut following a 30-min air exposure

Endocrine, metabolic and osmoregulatory changes in Pacific halibut upon capture and at intervals following a 30‐min air exposure were measured. Concentrations of cortisol, sodium, and chloride in plasma and serum peaked two hours after the stressor. Thirty minutes after a 30‐min air exposure concentrations of glucose in plasma had increased significantly from levels obtained immediately after the stressor and remained elevated for up to 4 h. Plasma lactate was also elevated 30 min after the stress treatment and lactate concentrations increased significantly at each subsequent sampling interval, 2 and 4 h. There was a significant linear increase in plasma lactate for fish sampled from 1.5 to 6.5 h after capture. Incidence of delayed mortality was low; of 22 experimentally stressed animals only one died over a 10‐day monitoring period. These data illustrate the difficulties in using single time‐point plasma indices of stress to assess condition of animals after capture since the time‐course of physiological changes associated with the stress response vary with parameter measured and may take hours to be fully expressed.     

The combined dexamethasone/TSST paradigm--a new method for psychoneuroendocrinology

The two main physiological systems involved in the regulation of the stress response are the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). However, the interaction of these systems on the stress response remains poorly understood. To better understand the cross-regulatory effects of the different systems involved in stress regulation, we developed a new stress paradigm that keeps the activity of the HPA constant when exposing subjects to psychosocial stress. Thirty healthy male participants were recruited and randomly assigned to either a dexamethasone (DEX; n?=?15) or placebo (PLC; n?=?15) group. All subjects were instructed to take the Dexamethasone (2 mg) or Placebo pill the night before coming to the laboratory to undergo the Trier Social Stress Task (TSST). Salivary cortisol, salivary alpha amylase (sAA), heart rate, blood pressure and subjective stress were assessed throughout the protocol. As expected, the DEX group presented with suppressed cortisol levels. In comparison, their heart rate was elevated by approximately ten base points compared to the PLC group, with increases throughout the protocol and during the TSST. Neither sAA, nor systolic or diastolic blood pressures showed significant group differences. Subjective stress levels significantly increased from baseline, and were found to be higher before and after the TSST after DEX compared to placebo. These results demonstrate a significant interaction between the HPA and the SNS during acute stress. The SNS activity was found to be elevated in the presence of a suppressed HPA axis, with some further effects on subjective levels of stress. The method to suppress the HPA prior to inducing stress was found to completely reliable, without any adverse side effects. Therefore, we propose this paradigm as a new method to investigate the interaction of the two major stress systems in the regulation of the stress response.     

Individual differences in preschoolers' salivary cortisol and alpha-amylase reactivity: Relations to temperament and maladjustment

We examined the relations of 84 preschoolers' (43 boys; mean age = 54 months) situational stress reactivity to their observed emotions and mothers' reports of temperament and adjustment. Salivary cortisol and salivary alpha-amylase (sAA) were collected prior to, and following, a frustrating task. Children's anger, sadness, and positive affect were measured, and mothers reported on preschoolers' dispositional emotionality, regulation, impulsivity, and problem behaviors. Forty-seven percent of children had an increase in sAA and 52% had an increase in cortisol following the challenging task. On average, sAA levels showed the predicted pattern of rise following the frustrating task, followed by return to baseline. For cortisol, there was a mean increase from pre-task to 40 min post-test. sAA reactivity was associated with relatively low levels of dispositional anger and impulsivity and relatively high regulation, particularly for girls. sAA reactivity also was related to low externalizing problems for girls, but not boys. Although cortisol reactivity was unrelated to children's emotions and maladjustment, it was positively related to mothers' reports of regulation. The findings suggest that sAA reactivity in response to a frustrating social task may reflect girls' constrained behavior.     

Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout

Better understanding of the mechanisms underlying interindividual variation in stress responses and their links with production traits is a key issue for sustainable animal breeding. In this study, we searched for quantitative trait loci (QTL) controlling the magnitude of the plasma cortisol stress response and compared them to body size traits in five F2 full‐sib families issued from two rainbow trout lines divergently selected for high or low post‐confinement plasma cortisol level. Approximately 1000 F2 individuals were individually tagged and exposed to two successive acute confinement challenges (1 month interval). Post‐stress plasma cortisol concentrations were determined for each fish. A medium density genome scan was carried out (268 markers, overall marker spacing less than 10 cM). QTL detection was performed using qtlmap software, based on an interval mapping method ( http://www.inra.fr/qtlmap ). Overall, QTL of medium individual effects on cortisol responsiveness (<10% of phenotypic variance) were detected on 18 chromosomes, strongly supporting the hypothesis that control of the trait is polygenic. Although a core array of QTL controlled cortisol concentrations at both challenges, several QTL seemed challenge specific, suggesting that responses to the first and to a subsequent exposure to the confinement stressor are distinct traits sharing only part of their genetic control. Chromosomal location of the steroidogenic acute regulatory protein (STAR) makes it a good potential candidate gene for one of the QTL. Finally, comparison of body size traits QTL (weight, length and body conformation) with cortisol‐associated QTL did not support evidence for negative genetic relationships between the two types of traits.     

Beyond physiological hypoarousal: The role of life stress and callous-unemotional traits in incarcerated adolescent males

The development of antisocial behavior in youth has been examined with neurobiological theories that suggest that adolescents who are less responsive to their environments are less likely to develop empathy in the absence of extant physiological arousal. However, little attention is paid to these individuals' social context. Individuals with adverse early experiences can also exhibit attenuated physiological arousal. The current investigation examines whether psychopathic symptoms or life stress exposure is associated with cortisol and its diurnal rhythm within 50 incarcerated adolescent boys (14–18 years old). Ten saliva cortisol samples were collected 1–2 weeks after admission to a maximum-security juvenile facility. Hierarchical Linear Modeling distinguished waking cortisol levels, the awakening response (CAR) and the diurnal rhythm. Multiple interviews and self-report measures of CU traits and stressor exposure were collected. Boys with higher levels of CU traits or greater life stress exposure had flat diurnal rhythms and a steeper awakening response in analyses with lifetime stress exposure specifically. Nonetheless, boys who were elevated on both CU traits and prior stress exposure had steeper diurnal rhythms. These results extend neurobiological theories of cortisol and illustrate that boys with the combination of severe stress with CU traits have a unique physiological profile.     

Psychopathic personality traits and cortisol response to stress: The role of sex, type of stressor, and menstrual phase

Previous research indicates that psychopathic personality traits are associated with lower cortisol secretion in response to stress in men but not in women. The current study explored whether prior null results for women were related to the latency of the cortisol stress response to two different types of stressors. Additionally, accuracy of self-reported menstrual phase was explored via salivary progesterone levels. A mixed-sex sample of 145 participants characterized by high (36 men, 37 women) and low (34 men, 38 women) scores on a screening measure of psychopathic personality traits were randomly assigned to either a performance-based stressor task or a social rejection stressor task. Salivary hormone samples were taken just prior to task onset (baseline) and at 0, 20, 40, and 60 min post-stressor. Results indicated that both men and women characterized by psychopathic personality traits exhibited lower stress-induced cortisol levels to the performance-based task in comparison with controls at 20 min post-stressor. The social rejection task produced a cortisol response 20 min post-stressor in the male controls only. Removal of women with low progesterone from the analyses strengthened the psychopathy group differences. Results could suggest that deficient cortisol production in response to stress might be another important neurobiological feature associated with psychopathic traits, and that biological verification of menstrual phase is an important aspect to obtaining accurate cortisol results in women.     

The impact of acute psychosocial stress on magnetoencephalographic correlates of emotional attention and exogenous visual attention

Stress-induced acute activation of the cerebral catecholaminergic systems has often been found in rodents. However, little is known regarding the consequences of this activation on higher cognitive functions in humans. Theoretical inferences would suggest increased distractibility in the sense of increased exogenous attention and emotional attention. The present study investigated the influence of acute stress responses on magnetoencephalographic (MEG) correlates of visual attention. Healthy male subjects were presented emotional and neutral pictures in three subsequent MEG recording sessions after being exposed to a TSST-like social stressor, intended to trigger a HPA-response. The subjects anticipation of another follow-up stressor was designed to sustain the short-lived central catecholaminergic stress reactions throughout the ongoing MEG recordings. The heart rate indicates a stable level of anticipatory stress during this time span, subsequent cortisol concentrations and self-report measures of stress were increased. With regard to the MEG correlates of attentional functions, we found that the N1m amplitude remained constantly elevated during stressor anticipation. The magnetic early posterior negativity (EPNm) was present but, surprisingly, was not at all modulated during stressor anticipation. This suggests that a general increase of the influence of exogenous attention but no specific effect regarding emotional attention in this time interval. Regarding the time course of the effects, an influence of the HPA on these MEG correlates of attention seems less likely. An influence of cerebral catecholaminergic systems is plausible, but not definite.     

Flash photography does not induce stress in the Ram cichlid Mikrogeophagus ramirezi (Myers & Harry, 1948) in aquaria

The Ram cichlid Mikrogeophagus ramirezi (Myers & Harry, 1948) was used to examine whether flash photography can be a stressor for fish in aquaria. The point in time of the highest cortisol concentration in whole‐body homogenates was determined by the temporal course of the cortisol response following air exposure as stressor. Thus, the potential stress response to camera flashlight was examined 22 min after exposure to a single flash and after repeated flashes by applying 10 flashes per minute for 8 hr/day over 2 weeks. In both experiments the stress parameters cortisol and glucose were not increased due to exposure to the flash light. In contrast, after a single flash mean cortisol values tended to be lower and mean glucose values were significantly lower than in the control group, and after repeated flashes mean cortisol and glucose values were significantly lower than in the control group. Furthermore, treated fish showed less intraspecific aggressive interactions. These results can be explained by a possible dazzling or irritation of the fish by camera flashes, thus reducing the natural aggressive behaviour and, consequently, the concentration of stress hormones and mobilisation of glucose. In summary, the physiological stress parameters cortisol and glucose do not reveal that flash photography induces stress in M. ramirezi, and, on the contrary, might even reduce stress effects by lowering intraspecific aggressive behaviour of the fish.     

Recovery from acute, chronic and transport stress in the pot-bellied seahorse Hippocampus abdominalis

Recovery from acute and chronic stress in the pot-bellied seahorse Hippocampus abdominalis under aquaculture conditions was investigated in this study to evaluate (a) whether these relatively slow and sedentary fish develop the 'fight or flight' response and (b) the impact of transportation stress on pot-bellied seahorse physiology. Fish were exposed to either a control treatment, an acute stressor (air exposure for 60 s) or a chronic stressor (confinement or transportation). Plasma concentrations of cortisol, glucose and lactate did not increase in response to an acute stressor, suggesting that adrenergic activation was absent. In contrast, chronic stress initiated increases in cortisol (77 ng ml⁻¹) and glucose (7 mM), which both returned to pre-stress concentrations (4 ng ml⁻¹, 4 mM respectively) within the subsequent 6 h. Recovery from chronic stress thus fitted the teleost paradigm, i.e. plasma levels of cortisol and glucose returned to pre-stress values in c . 6 h during recovery from a chronic stressor. The seemingly rapid return to homeostasis suggests that special precautions, over and above normal procedures, may not be required for long-distance transportation of pot-bellied seahorses.