Effects of cortisol on aggression and locomotor activity in rainbow trout

Hormonal Responses to Noncontact Aggression in Convict Cichlid Fish

This study explored whether convict cichlid fish mount a hormonal response to aggressive encounters where dominance status remains unresolved. Hormone samples were collected at two time points before an aggressive interaction to obtain confinement-induced and baseline measures, and at one time point following a contest across a clear partition (experimental) or exposure to an opaque partition with an opponent on the opposite side (control). There was no overall significant effect of treatment (control vs. experimental) on hormone release rates but there were trends for cortisol and testosterone (T). A priori linear contrasts showed that individuals that engaged in aggressive interactions had lower postfight cortisol and T release rates than controls, suggesting that aggression, in this context, might attenuate the synthesis of both hormones. Cortisol decreased significantly between initial confinement and baseline, indicating that individuals habituate to the water-borne hormone collection procedure. Contrary to expectation, individuals with higher baseline T and 11-ketotestosterone (KT) release rates took longer to initiate conflict. None of the other measures of behavior were predicted by baseline hormone release rates, and contest behavior did not predict postfight hormone release rates. There was a significant positive relationship between KT and T at all time points. As with studies that employ mirror image stimulation, we found no hormonal response to unresolved contests despite high levels of aggressive behavior. Our study is unique because we demonstrate that animals engaged in conflict with live opponents also do not mount a significant hormonal response when clear dominance relationships are not established.

The relationship between handling time and cortisol release rates changes as a function of brain parasite densities in California killifish Fundulus parvipinnis

This study validated a technique for non-invasive hormone measurements in California killifish Fundulus parvipinnis, and looked for associations between cortisol (a stress hormone) and 11-ketotestosterone (KT, an androgen) release rates and the density or intensity of the trematode parasites Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB) in wild-caught, naturally infected F. parvipinnis. In experiment 1, F. parvipinnis were exposed to an acute stressor by lowering water levels to dorsal-fin height and repeatedly handling the fish over the course of an hour. Neither parasite was found to influence cortisol release rates in response to this acute stressor. In experiment 2, different F. parvipinnis were exposed on four consecutive days to the procedure for collecting water-borne hormone levels and release rates of 11-KT and cortisol were quantified. This design examined whether F. parvipinnis perceived the water-borne collection procedure to be a stressor, while also exploring how parasites influenced hormone release rates under conditions less stressful than those in experiment 1. No association was found between RENB and hormone release rates, or between EUHA and 11-KT release rates. The interaction between EUHA density and handling time, however, was an important predictor of cortisol release rates. The relationship between handling time and cortisol release rates was negative for F. parvipinnis harbouring low or intermediate density infections, and became positive for fish harbouring high densities of EUHA.

Allelic variation of the COMT gene in a despotic primate society: A haplotype is related to cortisol excretion in Macaca fuscata

Sequence variations in genes of the monoamine neurotransmitter system and their common function in human and non-human primate species are an ongoing issue of investigation. However, the COMT gene, coding for the catechol-O-methyltransferase, has not yet attracted much scientific attention regarding its functional role in non-human primates. Considering that a polymorphism of the human COMT gene affects the enzyme activity and cortisol level in response to a social stressor, this study investigated the impact of COMT on endocrine stress and behavioural parameters in Japanese macaques (Macaca fuscata). The species exemplifies a despotic hierarchy in which males' social rank positions require an adaptation of behaviour strategies. During the mating period steroid secretion and the frequency of aggressive encounters between males increase. We addressed i) whether this species exhibits potential functional COMT variants, ii) whether these variants are associated with faecal cortisol excretion of males, iii) how they are distributed among different social rank positions and iv) whether they are associated with behavioural strategies during times of mate competition. By genotyping 26 males we identified three COMT haplotypes (HT), including a putative splice mutant (HT3). This variant was associated with increased cortisol excretion. Given the observed inverse correlation between cortisol and physical aggression, we assume that different COMT haplotypes may predispose individuals to pursue more or less aggressive strategies. How these gene-stress effects might favour a specific social role is discussed. Our study of non-invasive genotyping in combination with behavioural and endocrine parameters represents an important step towards the understanding of gene-stress effects in a hierarchically organised primate society.

Effects of a pesticide and a parasite on neurological, endocrine, and behavioral responses of an estuarine fish

In coastal waters, pesticides and parasites are widespread stressors that may separately and interactively affect the physiology, behavior, and survival of resident organisms. We investigated the effects of the organophosphate pesticide chlorpyrifos and the trematode parasite Euhaplorchis californiensis on three important traits of California killifish (Fundulus parvipinnis): neurotransmitter activity, release of the stress hormone cortisol, and behavior. Killifish were collected from a population without E. californiensis, and then half of the fish were experimentally infected. Following a 30 day period for parasite maturation, infected and uninfected groups were exposed to four concentrations of chlorpyrifos (solvent control, 1-3ppb) prior to behavior trials to quantify activity, feeding behavior, and anti-predator responses. Water-borne cortisol release rates were measured non-invasively from each fish prior to infection, one-month post-infection, and following pesticide exposure. Killifish exposed to 3ppb chlorpyrifos exhibited a 74.6±6.8% and 60.5±8.3% reduction in brain and muscle acetylcholinesterase (AChE) activity relative to controls. The rate of cortisol release was suppressed by each chlorpyrifos level relative to controls. Killifish exposed to the medium (2ppb) and high (3ppb) pesticide concentrations exhibited reduced activity and a decrease in mean swimming speed following a simulated predator attack. Muscle AChE was positively related to swimming activity while brain AChE was positively related to foraging behavior. ​No effects of the parasite were observed, possibly because of low metacercariae densities achieved through controlled infections. We found that sublethal pesticide exposure has the potential to modify several organismal endpoints with consequences for reduced fitness, including neurological, endocrine, and behavioral responses in an ecologically abundant fish.

Puffed and bothered: Personality, performance, and the effects of stress on checkered pufferfish

Although consistent individual-level differences in behaviour are widespread and potentially important in evolutionary and ecological processes, relatively few studies focus on the physiological mechanisms that might underlie and regulate these individual-level differences in wild populations. We conducted experiments to determine whether checkered pufferfish (Sphoeroides testudineus), which were collected from a dynamic (in terms of depth and water temperature) tidal mangrove creek environment in The Bahamas, have consistent individual-level differences in locomotor activity and the response to a simulated predator threat, as well as swimming performance and puffing in response to stressors. The relationships between personality and performance traits were evaluated to determine whether they represented stress-coping styles or syndromes. Subsequently, a displacement study was conducted to determine how personality and performance in the laboratory compared to movements in the field. In addition, we tested whether a physiological dose of the stress hormone cortisol would alter individual consistency in behavioural and performance traits. We found that pufferfish exhibited consistent individual differences in personality traits over time (e.g., activity and the duration of a response to a threat) and that performance was consistent between the lab and the natural enclosure. Locomotor activity and the duration of startled behaviour were not associated with swimming and puffing performance. Locomotor activity, puffing performance, and swimming performance were not related to whether fish returned to the tidal creek of capture after displacement. Similarly, a cortisol treatment did not modify behaviour or performance in the laboratory. The results reveal that consistent individual-level differences in behaviour and performance were present in a population from a fluctuating and physiologically challenging environment but that such traits are not necessarily correlated. We also determined that certain individual performance traits were repeatable between the lab and a natural enclosure. However, we found no evidence of a relationship between exogenous cortisol levels and behavioural traits or performance in these fish, which suggests that other internal and external mechanisms may underlie the behaviours and performance tested.

Cortisol stimulates arginine vasotocin and isotocin release from the hypothalamo-pituitary complex of round goby (Neogobius melanostomus): Probable mechanisms of action

There were two aims of this in vitro perfusion study. Firstly, to determine which class of receptors, glucocorticoid (GRs) or mineralocorticoid (MRs), are involved in cortisol regulation of arginine vasotocin (AVT) and isotocin (IT) release from the hypothalamo-pituitary (H-P) complex of round goby (Neogobius melanostomus). Secondly, to determine which pathways, genomic or non-genomic, are involved in the aformentioned process.The H-P explants were perfused with cortisol (1.4 × 10(-) (7)  M, 2.8 × 10(-7) M, 0.4 × 10(-6) M); only the highest dose significantly increased a release of both nonapeptides. In the perfusion of H-P explants, we used cortisol (0.4 × 10(-6) M) in combination with GRs antagonist RU486 (0.3 × 10(-6)  M) or MRs antagonist C03DA01 (0.36 × 10(-6)  M) or transcription inhibitor Actinomycin D (1 × 10(-7)  M). All inhibitors were also tested seperately. The contents of AVT and IT in the perfusion media was determined by high-performance liquid chromatography (HPLC) with UV detection. This study suggested that different mechanisms were involved in the regulation of AVT and IT release from H-P complex in round goby. Apparently it was GRs but not MRs that were involved in cortisol regulation of AVT and IT release. In the case of AVT, our data points to both genomic and non-genomic pathways mediating the effect of cortisol; in the case of IT, it is only the non-genomic pathway. This study presents the first feasible mechanisms of cortisol action on AVT and IT release from the H-P complex in round goby.

Novelty of the arena impairs the cortisol-related increase in the aggression of matrinxã (Brycon amazonicus)

The dichotomic effect of a cortisol level rise in vertebrate behavior has been widely observed. Generally, a chronic increase of the hormone level inhibits aggression, while an acute rise increases aggression. However, in this study, we show that this increase in aggression through an acute rise of cortisol also depends on the context in which the agonistic interaction occurs in the tropical fish matrinxã, Brycon amazonicus. We combined two factors: the type of housing (resident or non-resident in the trial arena) and the level of cortisol at the beginning of the fight (normal level - control, or high level - hydrocortisone-treated fish). The cortisol treatment increased the aggressiveness in the resident fish, but this effect was not observed in the non-resident fish, which fought in an unknown arena. The novelty of the arena may have elicited an "alerted state" in the non-resident fish; in this situation the fight was not the priority, and the cortisol effect in aggression could be impaired by a conflict between motivational systems (fear and aggression). In our knowledge, in fish, the increase of aggression promoted by an acute rise in cortisol levels was always tested and observed in a resident context, and the inhibition of cortisol effect in the agonist behavior is demonstrated for the first time. As the cortisol effect in aggression is observed in several taxa, the inhibition of aggressiveness increased by the novelty of the arena should be investigated in other groups to clarify the dynamics of this effect of cortisol in animal behavior.

Behavioral and physiological indicators of stress coping styles in larval zebrafish

Different individuals cope with stressors in different ways. Stress coping styles are defined as a coherent set of individual behavioral and physiological differences in the response to a stressor which remain consistent across time and context. In the present study, we have investigated coping styles in larval zebrafish (Danio rerio) at 8 days post-fertilization. Larvae were separated into two groups, according to the emergence sequence from a darkened into a novel well-lit environment, early (EE) and late (LE) emergers. We used brief periods of netting as a stressor. Swimming behavior and kinematics before and after netting stress were analyzed, as were whole-body cortisol levels before and at 10, 30 and 60 min after the stress event. The results show that general swimming activity was different between EE and LE larvae, with lower baseline cumulative distance and more erratic swimming movements in EE than in LE larvae. EE larvae showed a faster recovery to baseline levels after stress than LE larvae. Cortisol baseline levels were not different between EE and LE larvae, but peak levels after stress were higher and the recovery towards basal levels was faster in EE than in LE larvae. This study shows that coping styles are manifest in zebrafish larvae, and that behavior and swimming kinematics are associated with different cortisol responses to stress. A better understanding of the expression of coping styles may be of great value for medical applications, animal welfare issues and conservation.

Occurrence, removal, and fate of progestogens, androgens, estrogens, and phenols in six sewage treatment plants around Dianchi Lake in China

The occurrence and behavior of endocrine disrupting chemicals (EDCs) in sewage treatment plants (STPs), especially estrogens and phenols, have been closely concerned in previous studies. However, the systematical researches about progestogens and androgens were scarce in STPs adopting different treatment technologies. This work investigated the occurrence, removal, and fate of one progestogen, three androgens, four estrogens, and six phenols in six STPs around Dianchi Lake in China, where the influents, effluents of primary treatment, secondary treatment, and advanced treatment, as well as excess sludge samples, were analyzed. All of the above EDCs were detected out in influents of the six STPs. Bisphenol A, nonylphenol-mono-ethoxylate, and nonylphenol-diethoxylate were the dominant EDCs detected in those influent samples with the concentrations that varied from 637.6 to 1,684.0 ng/L, 633.8 to 1,540.0 ng/L, and 648.7 to 2,246.0 ng/L, respectively; E1 and dihydrotestosterone were the major steroids with the mean concentration of 126.8 and 277.4 ng/L. For effluents and sludges, phenols showed higher concentration (366.8-1,233.0 ng/L and 1,478.1-6,948.9 ng/g dry weight (dw)) and detection rate (100 %). The total removal rates were more than 80 % for most compounds in wastewater treatment processes, and high removal efficiency (86-100 %) was found for androgens and progestogens compared with estrogens (75-92 %) and phenols (62-85 %). The secondary treatment processes play significant roles on degrading EDCs, whereas the primary sedimentation has little effects. The treatment capacity of anoxic-anaerobic-anoxic membrane bioreactor and anaerobic/anoxic/oxic technologies was superior to the conventional oxidation ditch in the degradation of EDCs. The advanced treatment process, two units of filter (D-type or V-type), and ultraviolet disinfection were adopted and presented effective to remove these compounds. According to fate analysis, it was obvious that biological degradation was the main pathway on the removal of EDCs in STPs compared with adsorption. Risk quotients were calculated to assess ecological risks of those EDCs. Risk quotients of 54 and 61 % were more than 1 in effluents and sludges, respectively, showing potential hazard of effluents and sludges to the environment.

Comparison of triple quadrupole mass spectrometry and Orbitrap high-resolution mass spectrometry in ultrahigh performance liquid chromatography for the determination of veterinary drugs in sewage: benefits and drawbacks

This paper presents a comparison of triple quadrupole tandem mass spectrometry (MS/MS) and Orbitrap high-resolution mass spectrometry (HRMS) combined to ultrahigh performance liquid chromatography for the determination of glucocorticoids and polyether ionophores in sewage, in order to show the major benefits and drawbacks for each mass spectrometry analyser. Overall, HRMS measurements have enhanced performance in terms of confirmatory capabilities than MS/MS measurements. Moreover, similar limits of quantification, limits of detection, linear range and repeatability for glucocorticoids with both the MS/MS and HRMS methods were compared, but in the case of polyether ionophores, slightly better limits of detection and limits of quantification were obtained with the HRMS method because of the high sensitivity obtained when diagnostic ions are used for quantification instead of selected reaction monitoring transitions for these compounds. The two methods have been applied to the analysis of several influent and effluent sewage samples from sewage treatment plants located in the Tarragona region (Catalonia, Spain), showing an excellent correlation between the two methods.

The stress response predicts migration failure but not migration rate in a semelparous fish

Recent findings from iteroparous species suggest that glucocorticoid secretion following acute stress can mediate behavior and survival strategies, ultimately influencing fitness. However, these correlates of the stress response may not exist in semelparous animals given the inability to maximize fitness by delaying reproduction. We measured baseline and stress-induced cortisol concentrations in semelparous sockeye salmon (Oncorhynchus nerka) following exposure to an acute stressor at the mouth of the Fraser River in British Columbia. The homing fish were then radio-tagged and tracked throughout their in-river migration. Findings reveal that the stress response (i.e. change from baseline to stress-induced cortisol) was predictive of mortality; fish failing to leave the release site had a significantly greater stress response (mean±SE=1004.0±75.3ng/mL) compared to fish capable of successfully migrating beyond one of the most difficult areas of passage over 100 river kilometers upstream (mean±SE=780.7±66.7ng/mL). However, there were no associations between swimming behaviors, both immediately following release and to last point of detection, and the stress response. This study also introduced an unique method of tagging migrating salmon that allows for rapid capture and sampling and thus provides the first assessment of true baseline cortisol concentrations at river-entry for migrating Pacific salmon in the wild. Results show the stress response to be linked to survival in a semelparous species and therefore set the stage for further exploration into how the evolutionary theories underlying relationships between stress responsiveness and fitness may differ between semelparous and iteroparous species.

Cortisol influences the antipredator behavior induced by chemical alarm cues in the Frillfin goby

We evaluated the effect of increased plasma cortisol levels on fish antipredator behavior induced by conspecific chemical alarm cues. The experimental model for the study was the Frillfin goby Bathygobius soporator. We first confirmed that the alarm substance induces typical defensive antipredator responses in Frillfin gobies and described their alarm substance cells (epidermal 'club' cells). Second, we confirmed that intraperitoneal cortisol implants increase plasma cortisol levels in this species. We then demonstrated that exogenous cortisol administration and subsequent exposure to an alarm substance decreased swimming activity to a greater extent than the activity prompted by either stimulus alone. In addition, cortisol did not abolish the sheltering response to the alarm chemical cue even though it decreased activity. As predators use prey movements to guide their first contact with the prey, a factor that decreases swimming activity clearly increases the probability of survival. Consequently, this observation indicates that cortisol helps improve the antipredator response in fish.

Effects of acute corticosterone treatment on partner preferences in male and female zebra finches (Taeniopygia guttata)

Stress alters physiology and behavior across species. Most research on the effects of stress on behavior uses chronic stressors, and most are correlational. The effects of acute stressors on physiology and behavior have been mixed. Here, we use zebra finches, a highly gregarious species that forms long-term pair bonds, to test the effects of an acute corticosterone (CORT) on opposite-sex partner preferences over a same-sex individual or a group (the latter is a highly appealing option). We had two competing hypotheses. First, we predicted that acute CORT would alter preferences for the opposite sex bird in both conditions in both sexes. However, since there is a sex difference in the effects of CORT on partner preferences in voles, these effects may be more pronounced in males than in females. To test our hypotheses, we administered 2 doses of CORT (10μg and 20μg) or vehicle (control) using a repeated measures design. In the male vs. female test, there was a significant Sex by Treatment interaction, such that in males, 10μg CORT increased preferences for a female over the male compared to when these same males were treated with saline at baseline. There were no effects of treatment in females. In the opposite-sex vs. group condition, there was an overall effect of Treatment, such that the 10μg dose increased preference for the opposite-sex individual over both saline treatments, regardless of sex. These findings further our understanding of the effects of an acute stressor on sexual partner preferences.

Stress in African catfish (Clarias gariepinus) following overland transportation

Of the many stressors in aquaculture, transportation of fish has remained poorly studied. The objective of this study was therefore to assess the effects of a (simulated) commercial transportation on stress physiology of market-size African catfish (Clarias gariepinus). Catfish weighing approximately 1.25 kg were returned to the farm after 3 h of truck-transportation, and stress-related parameters were measured for up to 72 h following return. Recovery from transportation was assessed through blood samples measuring plasma cortisol, glucose and non-esterified fatty acids (NEFA) and gill histology. Also, the number of skin lesions was compared before and after transport. Pre-transport handling and sorting elevated plasma cortisol levels compared to unhandled animals (before fasting). Plasma cortisol levels were further increased due to transportation. In control fish, plasma cortisol levels returned to baseline values within 6 h, whereas it took 48 h to reach baseline values in transported catfish. Plasma glucose and NEFA levels remained stable and were similar across all groups. Transported catfish did not, on average, have more skin lesions than the handling group, but the number of skin lesions had increased compared to unhandled animals. The macroscopic condition of the gills was similar in control, transported and unhandled catfish; however, light microscopy and immunohistochemistry revealed atypical morphology and chloride cell migration normally associated with adverse water conditions. From our data, we conclude that transportation may be considered a strong stressor to catfish that may add to other stressors and thus inflict upon the welfare of the fish.

The glucocorticoid/aggression relationship in animals and humans: an analysis sensitive to behavioral characteristics, glucocorticoid secretion patterns, and neural mechanisms

Glucocorticoids control a wide array of biological processes from glucose homeostasis to neuronal function. The mechanisms mediating their effects are similarly varied and include rapid and transient nongenomic effects on calcium trafficking, various neurotransmitter receptors, and other membrane/cytoplasmic proteins, as well as slowly developing but durable genomic effects that are mediated by a large number of glucocorticoid-sensitive genes that are affected after variable lag-times. Given this complexity, we suggest that the aggression/glucocorticoid relationship cannot be reduced to the simple "stimulation/inhibition" question. Here, we review the effects of glucocorticoids on aggression by taking into account the complexities of glucocorticoid actions. Acute and chronic effects were differentiated because these are mediated by different mechanisms. The effects of chronic increases and decreases in glucocorticoid production were discussed separately, because the activation of mechanisms that are not normally activated and the loss of normal functions should not be confounded. Findings in healthy/normal subjects and those obtained in subjects that show abnormal forms of behavior or psychopathologies were also differentiated, because the effects of glucocorticoids are indirect, and largely depend on the properties of neurons they act upon, which are altered in subjects with psychopathologies. In addition, the conditions of glucocorticoid measurements were also thoroughly evaluated. Although the role of glucocorticoids in aggression is perceived as controversial by many investigators, a detailed analysis that is sensitive to glucocorticoid and behavioral measure as well as to the mediating mechanism suggests that this role is rather clear-cut; moreover, there is a marked similarity between animal and human findings.

Social descent with territory loss causes rapid behavioral, endocrine and transcriptional changes in the brain

In social species that form hierarchies where only dominant males reproduce, lower-ranking individuals may challenge higher-ranking ones, often resulting in changes in relative social status. How does a losing animal respond to loss of status? Here, using the African cichlid fish Astatotilapia burtoni, we manipulated the social environment, causing males to descend in rank, and then examined changes in behavior, circulating steroids and immediate early gene (IEG) expression (cfos, egr-1) in micro-dissected brain regions as a proxy for neuronal activation. In particular, we examined changes in the conserved 'social behavior network' (SBN), a collection of brain nuclei known to regulate social behaviors across vertebrates. Astatotilapia burtoni has rapidly reversible dominant-subordinate male phenotypes, so that within minutes, descending males lost their bright body coloration, switched to submissive behaviors and expressed higher plasma cortisol levels compared with non-descending and control males. Descending males had higher IEG expression throughout the SBN, but each brain region showed a distinct IEG-specific response in either cfos or egr-1 levels, but not both. Overall, SBN IEG patterns in descending males were distinctly different from the pattern observed in males ascending (subordinate to dominant) in social status. These results reveal that the SBN rapidly coordinates the perception of social cues about status that are of opposite valence, and translates them into appropriate phenotypic changes. This shows for the first time in a non-mammalian vertebrate that dropping in social rank rapidly activates specific socially relevant brain nuclei in a pattern that differs from when males rise to a higher status position.

Effects of an experimental short-term cortisol challenge on the behaviour of wild creek chub Semotilus atromaculatus in mesocosm and stream environments

The consequences of stress on the behaviour of wild creek chub Semotilus atromaculatus outside the reproductive period were studied using a single intra-coelomic injection of cortisol, suspended in coconut butter, to experimentally raise plasma cortisol levels. Behaviour between cortisol-treated, sham-treated (injected with coconut butter) and control S. atromaculatus was compared in a mesocosm system, using a passive integrated transponder array, and in a natural stream system (excluding shams), using surgically implanted radio transmitters. While laboratory time-course studies revealed that the cortisol injection provided a physiologically relevant challenge, causing prolonged (c. 3 days) elevations of plasma cortisol similar to that achieved with a standardized chasing protocol, no differences in fine-scale movements were observed between cortisol-treated, sham-treated and control S. atromaculatus nor in the large-scale movements of cortisol-treated and control S. atromaculatus. Moreover, no differences were observed in diel activity patterns among treatments. Differential mortality, however, occurred starting 10 days after treatment where cortisol-treated S. atromaculatus exhibited nearly twice as many mortalities as shams and controls. These results suggest that, although the experimental manipulation of cortisol titres was sufficient to cause mortality in some individuals, there were compensatory mechanisms that maintained behaviours (i.e. including activity and movement) prior to death. This study is one of the first to use experimental cortisol implants outside a laboratory environment and during the non-reproductive period and yields insight into how wild animals respond to additional challenges (in this case elevated cortisol) using ecologically meaningful endpoints.

Neural plasticity and stress coping in teleost fishes

Physiological and behavioural responses to environmental change are individually variable traits, which manifest phenotypically and are subject to natural selection as correlated trait-clusters (coping styles, behavioural syndromes, or personality traits). Comparative research has revealed a range of neuroendocrine-behavioural associations which are conserved throughout the vertebrate subphylum. Regulatory mechanisms universally mediate a switch between proactive (e.g. active/aggressive) and reactive (e.g. conservation/withdrawal) behaviour in response to unpredictable and uncontrollable events. Thresholds for switching from active coping to behavioural inhibition are individually variable, and depend on experience and genetic factors. Such factors affect physiological stress responses as well as perception, learning, and memory. Here we review the role of an important contributor to neural processing, the set of biochemical, molecular, and structural processes collectively referred to as neural plasticity. We will concentrate on work in teleost fishes, while also elucidating conserved aspects. In fishes, environmental and physiological control of brain cell proliferation and neurogenesis has received recent attention. This work has revealed that the expression of genes involved in CNS plasticity is affected by heritable variation in stress coping style, and is also differentially affected by short- and long-term stress. Chronic stress experienced by subordinate fish in social hierarchies leads to a marked suppression of brain cell proliferation. Interestingly, typically routine dependent and inflexible behaviour in proactive individuals is also associated with low transcription of neurogenesis related genes. The potential for these findings to illuminate stress-related neurobiological disorders in other vertebrates is also discussed.

Elevated cortisol inhibits adrenocorticotropic hormone- and serotonin-stimulated cortisol secretion from the interrenal cells of the Gulf toadfish (Opsanus beta)

Stimulation of the toadfish 5-HT(1A) receptor by serotonin (5-hydroxytryptamine; 5-HT) or 8-OH-DPAT, a 5-HT(1A) receptor agonist, results in a significant elevation in plasma cortisol. Conversely, chronic elevation of plasma cortisol has been shown to decrease brain 5-HT(1A) receptor mRNA and protein levels via the glucocorticoid receptor (GR); however, there appears to be a disconnect between brain levels of the receptor and cortisol release. We hypothesized that elevated plasma cortisol would inhibit both adrenocorticotropic hormone (ACTH)- and 5-HT-stimulated cortisol release from the interrenal cells of Gulf toadfish, that ACTH sensitivity would not be GR-mediated and 5-HT-stimulated cortisol release would not be via the 5-HT(1A) receptor. To test these hypotheses, interrenal cells from uncrowded, crowded, vehicle-, and cortisol-implanted toadfish were incubated with either ACTH, 5-HT or 5-HT receptor agonists, and cortisol secretion was measured. Incubation with ACTH or 5-HT resulted in a stimulation of cortisol secretion in uncrowded toadfish. Cortisol secretion in response to ACTH was not affected in crowded fish; however, interrenal cells from cortisol-implanted toadfish secreted significantly less cortisol than controls, a response that was not reversed upon treatment with the GR antagonist RU486. 5-HT-stimulated cortisol release was significantly lower from both crowded and cortisol-implanted toadfish interrenal cells compared to controls. Incubation with either a 5-HT(4) or a 5-HT(2) receptor agonist significantly stimulated cortisol secretion; however, incubation with 8-OH-DPAT did not, suggesting that the 5-HT(1A) receptor is not a mediator of cortisol release at the level of the interrenal cells. Combined, these results explain in part the disconnect between brain 5-HT(1A) levels and cortisol secretion.

Glucocorticoids, aerobic physiology, and locomotor behavior in California mice

The glucocorticoid hormones corticosterone (CORT) and cortisol influence numerous physiological, morphological, and behavioral functions. However, few studies have addressed possible relationships between individual differences in glucocorticoid concentrations and whole-animal performance or metabolism. Because CORT is important in glucose regulation and energy metabolism and can influence activity levels, we hypothesized that individual variation in baseline circulating CORT levels would correlate with individual differences in energy expenditure (routine and maximal), aerobic physiology, voluntary exercise on wheels, and organ masses. We tested this hypothesis in the California mouse (Peromyscus californicus). We collected data from 54 adult, colony-bred mice on baseline CORT levels (measured near both the circadian peak and the circadian trough), voluntary wheel running and its energetic costs, maximal oxygen consumption during forced treadmill exercise ([Formula: see text]), basal metabolic rate, and relative organ masses. We found surprisingly few statistically significant relationships among CORT, energy metabolism, behavior, and organ masses, and these relationships appeared to differ between males and females. These findings suggest that individual differences in baseline CORT levels are not an important determinant of voluntary activity levels or aerobic performance in California mice.

Steroids in a typical swine farm and their release into the environment

The occurrence and fate of fourteen androgens, four estrogens, five glucocorticoids and five progestagens were investigated by rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS) in a typical swine farm with lagoon waste disposal systems, in south China. Nineteen, 22 and 8 of 28 steroids were detected at concentrations ranging from 2.2 ± 0.1 ng/g (androsta-1,4-diene-3,17-dione) to 14,400 ± 394 ng/g (progesterone) in the feces samples, from 6.1 ± 2.3 ng/L (17β-boldenone) to 10,800 ± 3190 ng/L (norgestrel) in the flush water samples, and from 5.0 ± 0.2 ng/g (progesterone) to 225 ± 79.4 ng/g (5α-dihydrotestosterone) in the suspended particles, respectively. By comparing the types and concentrations of steroids in different treatment stages of the lagoon systems, it demonstrated that the lagoon systems used in the farm were not effective method to reduce various steroids in wastewater. Among the thirteen synthetic steroids detected in the swine feces and flush water, only seven (methyl testosterone, 17α-trenbolone, 17β-trenbolone, 17α-ethynyl estradiol, dexamethasone, medroxyprogesterone, and norgestrel) were regarded as the parent/metabolite compounds of animal exogenous usage. According to the estimated masses of steroids from feces and flush water, the excretion of steroids for sows were mainly from feces, but for piglets or barrows, most excreted steroids were through flush water rather than feces. The total daily excreted masses of androgens, estrogens, glucocortcoids and progestagens in the sow feces were in the range of 90.7-6310 μg/d, which were up to a thousand fold of those in the feces of other growth stages indicating that the proportion of sow number in the swine farm directly influenced the total excretion mass of steroids. In addition, two natural steroids 4-androstene-3,17-dione and progesterone were worth notice due to their relatively high concentrations per sow excretion, 277 μg/d and 6380 μg/d, respectively, which are approximately equivalent to the daily excretion of 100 persons. Some steroids were also detected in the well water, vegetable field and receiving stream, and may pose potential high risks to some sensitive organisms in the receiving environment.

Aggression and related behavioral traits: the impact of winning and losing and the role of hormones

A suite of correlated behaviors reflecting between-individual consistency in behavior across multiple situations is termed a "behavioral syndrome." Researchers have suggested that a cause for the correlation between different behaviors might lie in the neuroendocrine system. In this study, we examined the relationships between aggressiveness (a fish's readiness to perform gill display to its mirror image) and each of boldness (the readiness to emerge from a shelter), exploratory tendency (the readiness to approach a novel shelter), and learning performance (the probability of entering the correct reservoir in a T-maze test) in a mangrove rivulus, Kryptolebias marmoratus. We explored the possibility that the relationships between them arise because these behaviors are all modulated by cortisol and testosterone. We also tested the stability of the relationships between these behaviors shortly after using a winning or losing experience to alter individuals' aggressiveness. The results were that aggressiveness correlated positively with boldness and the tendency to explore, and that these three behavioral traits were all positively correlated with pre-experience testosterone levels. Aggressiveness and boldness also positively correlated with pre-experience cortisol levels; exploratory tendency did not. The relationship between aggressiveness and boldness appeared to be stronger than that between either of them and exploratory tendency. These results suggest that testosterone and cortisol play important roles in mediating the correlations between these behavioral traits. Learning performance was not significantly correlated with the other behavioral traits or with levels of testosterone or cortisol. Recent experience in contests influenced individuals' aggressiveness, tendency to explore, and learning performance but not their boldness; individuals that received a winning experience were quicker to display to their mirror image and performed better in the learning task but were slower to approach a novel object than were individuals that lost. Contest experience did not, however, significantly influence the relationships between aggressiveness and any of boldness, exploratory tendency, or learning performance. The results show that the individual components of a suite of correlated behaviors can preserve a flexibility to respond differently to environmental stimuli.

Seabream (Sparus aurata) long-term dominant-subordinate interplay affects phagocytosis by peritoneal cavity cells

Fish are sensitive to stressful conditions that affect their innate immune systems and increase their susceptibility to diseases. We examined the social stress of paired gilthead seabream (Sparus aurata). Social hierarchies (dominant/subordinate) were characterised by behavioural changes, such as "aggressiveness" and "feeding order"; hierarchical positions were established within an hour of exposure to social stress and remained unchanged for approximately 1 year. To characterise physiological stress, we measured blood plasma levels of cortisol, glucose, and lactate as well as osmolarity and observed that the levels of these stress markers were higher in subordinate individuals than in dominant ones. The discriminant analysis revealed a separation of the subordinate fish groups, and at 15 days, a significant separation among groups was observed. Moreover, diminished phagocytic and respiratory burst activities revealed that social stress appeared to affect the cellular innate immune response of the subordinate specimens. Finally, to examine the effect of cortisol on phagocytosis, peritoneal cavity cells were treated in vitro, and an inhibitory effect was observed.

Pigments, parasites and personalitiy: towards a unifying role for steroid hormones?

A surging interest in the evolution of consistent trait correlations has inspired research on pigment patterns as a correlate of behavioural syndromes, or “animal personalities”. Associations between pigmentation, physiology and health status are less investigated as potentially conserved trait clusters. In the current study, lice counts performed on farmed Atlantic salmon Salmo salar naturally infected with ectoparasitic sea lice Lepeophtheirus salmonis showed that individual fish with high incidence of black melanin-based skin spots harboured fewer female sea lice carrying egg sacs, compared to less pigmented fish. There was no significant association between pigmentation and lice at other developmental stages, suggesting that host factors associated with melanin-based pigmentation may modify ectoparasite development to a larger degree than settlement. In a subsequent laboratory experiment a strong negative correlation between skin spots and post-stress cortisol levels was revealed, with less pigmented individuals showing a more pronounced cortisol response to acute stress. The observation that lice prevalence was strongly increased on a fraction of sexually mature male salmon which occurred among the farmed fish further supports a role for steroid hormones as mediators of reduced parasite resistance. The data presented here propose steroid hormones as a proximate cause for the association between melanin-based pigmentation and parasites. Possible fundamental and applied implications are discussed.

Cortisol and finfish welfare

Previous reviews of stress, and the stress hormone cortisol, in fish have focussed on physiology, due to interest in impacts on aquaculture production. Here, we discuss cortisol in relation to fish welfare. Cortisol is a readily measured component of the primary (neuroendocrine) stress response and is relevant to fish welfare as it affects physiological and brain functions and modifies behaviour. However, we argue that cortisol has little value if welfare is viewed purely from a functional (or behavioural) perspective-the cortisol response itself is a natural, adaptive response and is not predictive of coping as downstream impacts on function and behaviour are dose-, time- and context-dependent and not predictable. Nevertheless, we argue that welfare should be considered in terms of mental health and feelings, and that stress in relation to welfare should be viewed as psychological, rather than physiological. We contend that cortisol can be used (with caution) as a tractable indicator of how fish perceive (and feel about) their environment, psychological stress and feelings in fish. Cortisol responses are directly triggered by the brain and fish studies do indicate cortisol responses to psychological stressors, i.e., those with no direct physicochemical action. We discuss the practicalities of using cortisol to ask the fish themselves how they feel about husbandry practices and the culture environment. Single time point measurements of cortisol are of little value in assessing the stress level of fish as studies need to account for diurnal and seasonal variations, and environmental and genetic factors. Areas in need of greater clarity for the use of cortisol as an indicator of fish feelings are the separation of (physiological) stress from (psychological) distress, the separation of chronic stress from acclimation, and the interactions between feelings, cortisol, mood and behaviour.

The role of CRH in behavioral responses to acute restraint stress in zebrafish

In teleosts, changes in swimming, exploring, general locomotor activity, and anxious state can be a response to stress mediated by the corticotropin-releasing hormone system activation and its effects on glucocorticoid levels. Zebrafish has been widely used to study neuropharmacology and has become a promising animal model to investigate neurobehavioral mechanisms of stress. In this report the animals were submitted to acute restraint stress for different time lengths (15, 60 and 90 min) for further evaluation of behavioral patterns, whole-body cortisol content, and corticotropin-releasing hormone expression. The results demonstrated an increase in the locomotor activity and an alteration in the swimming pattern during a 5-min trial after the acute restraint stress. Interestingly, all groups of fish tested in the novel tank test exhibited signs of anxiety as evaluated by the time spent in the bottom of the tank. Whole-body cortisol content showed a positive correlation with increased behavioral indices of locomotion in zebrafish whereas molecular analysis of corticotropin-releasing hormone showed a late reduction of mRNA expression (90 min). Altogether, we present a model of acute restraint stress in zebrafish, confirmed by elevated cortisol content, as a valid and reliable model to study the biochemical basis of stress behavior, which seems to be accompanied by a negative feedback of corticotropin-release hormone mRNA expression.

Simulating winning in the wild--the behavioral and hormonal response of black redstarts to single and repeated territorial challenges of high and low intensity

In many vertebrates testosterone increases during aggressive interactions and the surges in this hormone may be responsible for the winner effect. So far studies on this relationship have been done in captivity only, because simulating a winning situation for a territory owner in the field is difficult. However, an increasing number of studies show that territorial aggression is not necessarily accompanied by elevated testosterone after a single simulated territorial intrusion (STI) and therefore it has been proposed that STIs may even create a losing experience. We examined whether free-living male black redstarts (Phoenicurus ochruros) show changes in androgens, corticosterone and behavior following repeated STIs of high or low intensity and in contrast to being challenged only once. Repeated intrusions had no influence on androgen and corticosterone levels regardless of intrusion intensity. In contrast, the behavioral response changed over days depending on the intensity of the intrusion. Only birds challenged with high-level intruders approached the decoy significantly faster during the third intrusion than during the first one, stayed closer to the decoy, and sang more songs than males challenged with low-level intruders. Thus, although black redstarts reacted differently to STIs varying in frequency and intensity, these behavioral differences were not reflected in androgen or corticosterone levels. Our data show that it is unlikely that STIs induce a losing experience. Furthermore, they indicate that a hormonal effect of winning an encounter may not be universal in vertebrates and may depend on the ecological or life-history context.

Acute effects of corticosterone injection on paternal behavior in California mouse (Peromyscus californicus) fathers

Glucocorticoids are thought to mediate the disruption of parental behavior in response to acute and chronic stress. Previous research supports their role in chronic stress; however, no study has experimentally tested the effects of acute glucocorticoid elevation on paternal behavior. We tested the prediction that acute corticosterone (CORT) increases would decrease paternal behavior in California mouse fathers and would lead to longer-term effects on reproductive success, as even short-term increases in CORT have been shown to produce lasting effects on the hypothalamic-pituitary-adrenal axis. First-time fathers were injected with 30 mg/kg CORT, 60 mg/kg CORT or vehicle, or left unmanipulated. Interactions between the male and its pup(s) were recorded 1.5-2h after injection and scored for paternal and non-paternal behavior. Treatment groups were combined into control (unmanipulated + vehicle, n = 15) and CORT (30 mg/kg + 60 mg/kg, n = 16) for analysis based on resulting plasma CORT concentrations. CORT treatment did not alter paternal or non-paternal behaviors or any long-term measures (male body mass or temperature, pup growth rate, pup survival, interbirth interval, number or mass of pups born in the second litter). Fathers showed a significant rise in body mass at day 30 postpartum, followed by a decrease in body mass after the birth of the second litter; however, this pattern did not differ between the CORT and control groups. In summary, acute elevation of plasma CORT did not alter direct paternal behavior, body mass, or reproductive outcomes, suggesting that acute CORT elevation alone does not overtly disrupt paternal care in this biparental mammal.

Stressed mothers - troubled offspring: a study of behavioural maternal effects in farmed Salmo salar

Mature female Atlantic salmon Salmo salar were given intraperitoneal cortisol implants 1 week prior to stripping to examine the influence of simulated maternal stress on offspring boldness and social dominance. Behavioural tests originally designed to investigate stress responsiveness and coping styles in salmonids (i.e. feeding in isolation, dominance tests and acute confinement) were carried out on the offspring 1·5 years after hatching. In the feeding test, there were no differences between the two treatment groups in total feeding score or number of pellets eaten, but offspring from the cortisol-implanted females made more unsuccessful feeding attempts than offspring from control females. In dominance tests, there was no difference between controls and cortisol-treated fish regarding propensity to become socially dominant. A higher proportion of individuals with bite marks, however, was observed in the cortisol group when compared to controls. Cortisol-treated offspring that gained dominant rank in the dominance tests performed more aggressive acts after stable dominance-subordinate relationships were established compared to control winners. During acute confinement stress, offspring from cortisol-implanted females showed a reduction in the proportion of time they were moving compared to the controls. These results indicate that the maternal endocrine state at spawning affects several aspects of progeny behaviour potentially related to subsequent success and survival in farmed S. salar.

Glucocorticoid receptor blockade inhibits brain cell addition and aggressive signaling in electric fish, Apteronotus leptorhynchus

When animals are under stress, glucocorticoids commonly inhibit adult neurogenesis by acting through glucocorticoid receptors (GRs). However, in some cases, conditions that elevate glucocorticoids promote adult neurogenesis, and the role of glucocorticoid receptors in these circumstances is not well understood. We examined the involvement of GRs in social enhancement of brain cell addition and aggressive signaling in electric fish, Apteronotus leptorhynchus. In this species, long-term social interaction simultaneously elevates plasma cortisol, enhances brain cell addition and increases production of aggressive electrocommunication signals ("chirps"). We implanted isolated and paired fish with capsules containing nothing (controls) or the GR antagonist, RU486, recorded chirp production and locomotion for 7d, and measured the density of newborn cells in the periventricular zone. Compared to isolated controls, paired controls showed elevated chirping in two phases: much higher chirp rates in the first 5h and moderately higher nocturnal rates thereafter. Treating paired fish with RU486 reduced chirp rates in both phases to those of isolated fish, demonstrating that GR activation is crucial for socially induced chirping. Neither RU486 nor social interaction affected locomotion. RU486 treatment to paired fish had a partial effect on cell addition: paired RU486 fish had less cell addition than paired control fish but more than isolated fish. This suggests that cortisol activation of GRs contributes to social enhancement of cell addition but works in parallel with another GR-independent mechanism. RU486 also reduced cell addition in isolated fish, indicating that GRs participate in the regulation of cell addition even when cortisol levels are low.

Visual information alone changes behavior and physiology during social interactions in a cichlid fish (Astatotilapia burtoni)

Social behavior can influence physiological systems dramatically yet the sensory cues responsible are not well understood. Behavior of male African cichlid fish, Astatotilapia burtoni, in their natural habitat suggests that visual cues from conspecifics contribute significantly to regulation of social behavior. Using a novel paradigm, we asked whether visual cues alone from a larger conspecific male could influence behavior, reproductive physiology and the physiological stress response of a smaller male. Here we show that just seeing a larger, threatening male through a clear barrier can suppress dominant behavior of a smaller male for up to 7 days. Smaller dominant males being “attacked” visually by larger dominant males through a clear barrier also showed physiological changes for up to 3 days, including up-regulation of reproductive- and stress-related gene expression levels and lowered plasma 11-ketotestesterone concentrations as compared to control animals. The smaller males modified their appearance to match that of non-dominant males when exposed to a larger male but they maintained a physiological phenotype similar to that of a dominant male. After 7 days, reproductive- and stress- related gene expression, circulating hormone levels, and gonad size in the smaller males showed no difference from the control group suggesting that the smaller male habituated to the visual intruder. However, the smaller male continued to display subordinate behaviors and assumed the appearance of a subordinate male for a full week despite his dominant male physiology. These data suggest that seeing a larger male alone can regulate the behavior of a smaller male but that ongoing reproductive inhibition depends on additional sensory cues. Perhaps, while experiencing visual social stressors, the smaller male uses an opportunistic strategy, acting like a subordinate male while maintaining the physiology of a dominant male.

Behaviors of glucocorticoids, androgens and progestogens in a municipal sewage treatment plant: comparison to estrogens

This work investigated the behaviors of seven glucocorticoids, eight androgens, and nine progestogens compared to six estrogens in a municipal sewage treatment plant (STP) in Beijing, China. Among all of the hormones considered, androgens were the dominant steroids detected in all samples (total concentrations up to 10 216±912 ng/L for influents, 171±10 ng/L for effluents, and 647±52 ng/g for dehydrated sludge samples), followed by estrogens (102±8 ng/L, 14±2 ng/L, and 14±1 ng/g), progestogens (57±6 ng/L, 8±2 ng/L, and 13±3 ng/g), and glucocorticoids (42±2 ng/L, 0.7±0.1 ng/L, and 1.2±0.3 ng/g). With the exception of 19-nor-4-androstene-3,17-diol (NAD, 67%), removal rates for androgens were relatively high (98-99%), while those for glucocorticoids, estrogens, and all progestogens except 6α-methylhydroxyprogesterone (MHPT) were 85-99%, 78-99%, and 73-96%, respectively. Glucocorticoids, androgens, and progestogens were mainly removed by degradation as with estrogens, while different behaviors were observed in the aerated grit chamber, anaerobic tank, anoxic tank, and aerobic tank units. Many of the detected glucocorticoids, androgens, and progestogens were eliminated in the anaerobic tank, but estrogens were largely degraded in the aerobic one. Significant increases in the mass of 21α-hydroxyprogesterone (21-HPT) and MHPT in the anaerobic tank and anoxic tank, respectively, were due to deconjugation.

Cortisol receptor expression differs in the brains of rainbow trout selected for divergent cortisol responses

In rainbow trout (Oncorhynchus mykiss), selection for divergent post-stress plasma cortisol levels has yielded low (LR)- and high (HR) responsive lines, differing in behavioural and physiological aspects of stress coping. For instance, LR fish display prolonged retention of a fear response and of previously learnt routines, compared to HR fish. This study aims at investigating putative central nervous system mechanisms controlling behaviour and memory retention. The stress hormone cortisol is known to affect several aspects of cognition, including memory retention. Cortisol acts through glucocorticoid receptors 1 and 2 (GR1 and 2) and a mineralcorticoid receptor (MR), all of which are abundantly expressed in the salmonid brain. We hypothesized that different expressions of MR and GRs in LR and HR trout brains could be involved in the observed differences in cognition. We quantified the mRNA expression of GR1, GR2 and MR in different brain regions of stressed and non-stressed LR and HR trout. The expression of MR was higher in LR than in HR fish in all brain parts investigated. This could be associated with reduced anxiety and enhanced memory retention in LR fish. MR and GR1 expression was also subject to negative regulation by stress in a site-specific manner.

Transdermal delivery of corticosterone in terrestrial amphibians

Stressors elicit allostatic responses that allow animals to cope with changing and challenging environments and also cause release of glucocorticoid hormones (GCs). Compared to other vertebrate classes, relatively little is known about amphibian behavioral and physiological responses to GCs. To understand the effects of elevated plasma GCs in amphibians, exogenous application of GCs is necessary, but traditional methods to elevate GCs require handling and/or anesthesia which themselves are stressors. A less invasive alternative successfully used in birds and reptiles utilizes transdermal delivery by applying GCs via a dermal patch. We asked whether dermal patches containing corticosterone (CORT, the main GC in amphibians) would elevate plasma CORT in terrestrial salamanders and frogs. We explored the use of the dermal patch to deliver CORT in an acute, sustained, and repeated manner. Patches adhered well to the amphibians' moist skin and were easily removed to regulate the time course of CORT delivery. Application of CORT treated patches elevated plasma CORT concentrations compared to vehicle patches in all species. Patches delivered physiological levels of plasma CORT in ecologically relevant time frames. Repeated application and removal of CORT patches were used to simulate exposure to repeated stressors. Application of patches did not represent a stressor because plasma CORT concentrations were similar between animals that received vehicle patches and untreated animals. Thus, transdermal delivery of GCs represents a potentially useful tool to better understand amphibian allostatic responses to stressors, and perhaps amphibian population declines.

Seasonal carryover effects following the administration of cortisol to a wild teleost fish

Stress can have sublethal effects that are manifested either immediately or at spatial or temporal scales that are removed from the stress event (i.e., carryover effects). We tested whether a short-term elevation of plasma cortisol would result in seasonal carryover effects in wild largemouth bass Micropterus salmoides. Using exogenous hormone implants, we raised circulating cortisol concentrations in a group of wild fish for approximately 5 d in October 2007. We then compared activity (velocity, distance traveled) of cortisol-treated animals with that of sham-treated and control animals throughout the winter using an automated acoustic telemetry array. Immediately following treatment, the cortisol-treated fish showed increased activity relative to controls. However, this difference disappeared following the cessation of the elevation of circulating cortisol. During the winter of 2007 to 2008, the lake experienced a nearly complete winterkill event, providing insight into how a transient stress response can influence the response of wild animals to subsequent challenges. Most fish carrying acoustic transmitters succumbed during this winterkill event, but cortisol-treated fish died earlier than fish in other groups and showed a decrease in activity relative to controls and sham-treated fish before mortality. This study provides preliminary evidence of seasonal carryover effects in wild fish and yields insight into the ecological consequences of stress across broad temporal scales.

Subclinical effects of saxitoxin and domoic acid on aggressive behaviour and monoaminergic turnover in rainbow trout (Oncorhynchus mykiss)

The algal produced neurotoxins saxitoxin and domoic acid may have serious effects on marine life and can be responsible for the intoxication of for instance sea mammals, sea birds and fish. Given that farmed fish cannot escape algal blooms, they may be more susceptible to intoxication than wild stocks. In the present study, subclinical effects of saxitoxin and domoic on aggressive behaviour and monoaminergic systems in the brain of the rainbow trout (Oncorhynchus mykiss) were investigated. The resident-intruder test was used to measure aggression where only the resident fish were subjected to the toxins and analysed for monoamines and their metabolites. The resident-intruder test was carried out on two consecutive days. On day one basal aggression was measured in the four groups. On day two three of the groups were injected with subclinical doses of one of the following: saxitoxin (1.752 microg/kg bw), domoic (0.75 mg/kg bw) or 0.9% saline solution. This was performed 30 min prior to the aggression test. Handling stress and injection affected aggressive behaviour, cortisol and the serotonergic system in telencephalic brain regions. Cortisol levels were elevated in all of the injected groups when compared to the control group. An increase in serotonergic turnover was evident when all injected groups were pooled and compared to the control group. All together this suggests that the handling stress in connection with the injection was similar in all of the three injected groups. In contrast to both the undisturbed control group and the toxin-injected groups, the saline-injected group displayed a reduction in aggressive behaviour which was evident in increased attack latency. Furthermore the domoic injected group displayed more aggressive attacks towards their conspecifics than the saline-injected group. Consequently the two toxins appear to mask the stress induced alteration in aggressive behaviour. Monoamine levels and monoaminergic turnover could not be demonstrated to be directly affected by the two toxins at the given doses in the investigated brain regions (dorsal and ventral parts of telencephalon, optic tectum, locus coeruleus, raphe nucleus, molecular and granular layer of cerebellum). This could indicate that the toxins mediate aggressive behaviour either through other systems than the monoaminergic systems, such as neuroactive amino acids, or that the mediation occurs in other brain regions.

An acute stressor alters steroid hormone levels and activity but not sexual behavior in male and female Ocoee salamanders (Desmognathus ocoee)

Stressors that are chronic have clear suppressive effects on reproductive behaviors in both males and females. Stressors that are acute have effects on reproductive behavior that are less clear. We measured the effects of an acute bout of handling in laboratory-housed male and female Ocoee salamanders (Desmognathus ocoee), a species with a prolonged mating season. Handling resulted in decreased locomotory activity and elevated plasma corticosterone, a hallmark of the vertebrate stress response. Handling also decreased plasma testosterone in males and elevated plasma estradiol in females. Despite the handling-induced changes in hormone levels, handling had minimal impact on courtship and mating. Other species in which reproduction is insensitive to acute stressors may live in extreme environments with limited reproductive opportunities, whereas Ocoee salamanders live in a relatively temperate environment with multiple reproductive opportunities. Together, these data indicate that an allostatic response to a stressor can alter locomotory activity and elevate corticosterone without suppressing nonessential behaviors like courtship and mating in a species in which reproductive opportunities can occur over a period of multiple months. The lack of reproductive suppression in Ocoee salamanders might be due to the low energetic cost of courtship and mating in this species combined with potentially elevated energetic stores, highlighting the importance of considering energy budgets when making predictions about behavioral effects of acute stressors.