Tobias Backström

Divergence in behavioural responses to stress in two strains of rainbow trout (Oncorhynchus mykiss) with contrasting stress responsiveness

The aim of this study was to establish whether two lines of rainbow trout divergent for their plasma cortisol response to a standardized stressor would show consistent differences in their behavioural response to a range of challenging situations. Our results show that the high- and low-responding (HR and LR) lines of rainbow trout did not differ in the aggression shown towards an intruder or in their response to the introduction of a novel object to their home environment. However, there was a difference in behaviour between the two selection lines when they were exposed to two unfamiliar environments. These results suggest that the behaviour of the HR and LR fish differs when they are challenged in unfamiliar environments, while their behaviour does not differ when they are challenged in their home environment. These observations are in agreement with studies on mammals that show that individuals with reactive coping styles perform similarly to proactive animals when they are challenged in a familiar environment, while they show different behaviour when they are challenged in unfamiliar environments. Thus, these results provide further evidence that the HR and LR selection lines of rainbow trout exemplify the two different coping styles described in mammals.

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks.

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks. PHYSIOL BEHAV 00(0) 000-000, 2006. Here, we compare the behavioral, endocrine and neuroendocrine responses of individual sticklebacks exposed to either an unfamiliar conspecific or to a predator. We found that the two stressors elicited a similar hypothalamic-pituitary-interrenal response as assessed by whole-body concentrations of cortisol, but produced quite different patterns of change in brain monoamine and monoamine metabolite content as assessed by concentrations of serotonin (5-HT), dopamine (DA), norepinephrine (NE) and the monoamine metabolites 5-hydroxyindole acetic acid (5-HIAA), homovanillic acid (HVA) and 3-4-dihydroxyphenylacetic acid (DOPAC). For example, relative to baseline levels, NE levels were elevated in individuals exposed to a predator but were lower in individuals confronted by a challenging conspecific. Levels of monoamine neurotransmitters in specific regions of the brain showed extremely close links with behavioral characteristics. Frequency of attacking a conspecific and inspecting a predator were both positively correlated with concentrations of NE. However, whereas serotonin was negatively correlated with frequency of attacking a conspecific, it was positively associated with predator inspection. The data indicate that the qualitative and quantitative nature of the neuroendocrine stress response of sticklebacks varies according to the nature of the stressor, and that interindividual variation in behavioural responses to challenge are reflected by neuroendocrine differences.

Aggression and monoamines: Effects of sex and social rank in zebrafish (Danio rerio)

Social defeat is a common model for studies on depression. However, such models are most often used to study aggression in males and sex differences in depression may therefore be overseen. This study investigated the potential of the zebrafish (Danio rerio) as a model for male and female aggression. In addition, effects on the brain serotonergic and dopaminergic neurotransmitter systems after agonistic interaction are well studied in many species, but not in zebrafish. We wanted to explore whether the zebrafish follows the same patterns as many other species. Therefore, the effects of agonistic interaction on brain monoaminergic activity were studied in adult male and female wild-type zebrafish. The fish interacted in pairs with one of the same sex for five days during which agonistic behaviour was quantified daily. Clear dominant/subordinate relationships developed in all pairs, both in males and females. The frequency of aggressive acts increased over time but did not differ between male and female pairs. Further, we found that dyadic agonistic interaction resulted in elevated brain serotonergic activity in subordinate zebrafish, as indicated by elevated hindbrain 5-hydroxyindoleacetic acid to serotonin ratios (5-hydroxyindolacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratios). We also observed a sex difference in forebrain dopamine levels and forebrain 5-HIAA/5-HT ratios, with females displaying higher concentrations of dopamine but lower 5-HIAA/5-HT ratios than males. These results suggest that zebrafish is a suitable model for studies on female aggression and sex differences in brain monoaminergic neurotransmission.

Arginine–vasotocin influence on aggressive behavior and dominance in rainbow trout

The mammalian neuropeptide arginine-vasopressin (AVP) and its non-mammalian homologue arginine-vasotocin (AVT) are involved in social behavior including aggression in vertebrates. Juvenile rainbow trout (Onchorhynchus mykiss) are highly territorial and we tested the effect of two different doses each of AVT and Manning compound, an AVP V(1A) receptor antagonist, on aggressive behavior and the outcome of staged fights for social dominance in size matched pairs. Each pair consisted of one fish receiving AVT or Manning compound through an intracerebroventricular (icv) injection and one fish receiving a similar icv injection of saline. In addition, plasma cortisol and brain serotonergic activity were monitored. Fish receiving AVT at a dose of 200 ng became subordinate whereas AVT at a dose of 20 ng had no effect on the outcome of fights for social dominance. Further, Manning compound had no effect on the outcome of fights for dominance but at a dose of 200 ng it had an effect on fight duration. Fish receiving 200 ng Manning compound and losing dyadic fights appeared to take longer to become subordinate. Neither AVT nor Manning compound had any effects on plasma cortisol levels or brainstem serotonergic activity. The apparent inhibiting effect of AVT on aggression could be centrally mediated.

Stress effects on AVT and CRF systems in two strains of rainbow trout (Oncorhynchus mykiss) divergent in stress responsiveness

The aim for this study was to examine whether the F4 generation of two strains of rainbow trout divergent in their plasma cortisol response to confinement stress (HR: high responder or LR: low responder) would also differ in stress-induced effects on forebrain concentrations of mRNA for corticotropin-releasing factor (CRF), arginine vasotocin (AVT), CRF receptor type 1 (CRF-R1), CRF receptor type 2 (CRF-R2) and AVT receptor (AVT-R). In addition, plasma cortisol concentrations, brainstem levels of monoamines and monoamine metabolites, and behaviour during confinement were monitored. The results confirm that HR and LR trout differ in their cortisol response to confinement and show that fish of these strains also differ in their behavioural response to confinement. The HR trout displayed significantly higher locomotor activity while in confinement than LR trout. Moreover, following 180 min of confinement HR fish showed significantly higher forebrain concentrations of CRF mRNA than LR fish. Also, when subjected to 30 min of confinement HR fish showed significantly lower CRF-R2 mRNA concentrations than LR fish, whereas there were no differences in CRF-R1, AVT or AVT-R mRNA expression between LR and HR fish either at 30 or 180 min of confinement. Differences in the expression of CRF and CRF-R2 mRNA may be related to the divergence in stress coping displayed by these rainbow trout strains.

Central corticotropin releasing factor and social stress.

Social interactions are a main source of stress in vertebrates. Social stressors, as well as other stressors, activate the hypothalamic–pituitary–adrenal (HPA) axis resulting in glucocorticoid release. One of the main components of the HPA axis is corticotropin releasing factor (CRF). The neuropeptide CRF is part of a peptide family including CRF, urocortin 1–3, urotensin 1–3, and sauvagine. The actions of the CRF family are mediated by at least two different receptors with different anatomical distribution and affinities for the peptides. The CRF peptides affect several behavioral and physiological responses to stress including aggression, feeding, and locomotor activity. This review will summarize recent research in vertebrates concerning how social stress interacts with components of the CRF system. Consideration will be taken to the different models used for social stress ranging from social isolation, dyadic interactions, to group dominance hierarchies. Further, the temporal effect of social stressor from acute, intermittent, to chronic will be considered. Finally, strains selected for specific behavior or physiology linked to social stress will also be discussed.

CRF and urotensin I effects on aggression and anxiety-like behavior in rainbow trout

Corticotropin-releasing factor (CRF) is central in the stress response but also modulates several behaviors including anxiety-related behaviors and aggression. In this study, juvenile rainbow trout (Oncorhynchus mykiss) were tested for competitive ability, determined during dyadic fights for dominance, after intracerebroventricular (i.c.v.) administration of CRF, urotensin I (UI), the non-specific CRF antagonist α-helical RF9-41 (ahCRF) or the CRF receptor subtype 1-specific antagonist antalarmin, when paired with a mass-matched con-specific injected with saline. In addition, isolated fish received the same substances. Plasma cortisol and brain monoamines were monitored in all fish. Most fish receiving CRF showed a conspicuous behavior consisting of flaring the opercula, opening the mouth and violent shaking of the head from side to side. When this occurred, the fish immediately forfeited the fight. Similar behavior was observed in most fish receiving UI but no effect on outcome of dyadic fights was noted. This behavior seems similar to non-ambulatory motor activity seen in rats and could be anxiety related. Furthermore, fish receiving CRF at a dose of 1000 ng became subordinate, whereas all other treatments had no effects on the outcome of dyadic fights. In addition, isolated fish receiving ahCRF had lower brain stem concentrations of 5-hydroxyindoleacetic acid, serotonin, 3,4-dihydroxyphenylacetic acid and dopamine. In conclusion, CRF seems to attenuate competitive ability, and both CRF and UI seem to induce anxiety-like behavior.

Behaviour, physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High-activity individuals had higher plasma cortisol levels following stress compared to low-activity individuals. This indicates that high- and low-activity individuals correspond to reactive and proactive stress-coping styles. Further, a pigmentation analysis showed that high-activity individuals had a higher number of carotenoid spots cm⁻² than low-activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress-coping style in S. alpinus.

Developmental exposure to fluoxetine modulates the serotonin system in hypothalamus.

The selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLU, Prozac®) is commonly prescribed for depression in pregnant women. This results in SSRI exposure of the developing fetus. However, there are knowledge gaps regarding the impact of SSRI exposure during development. Given the role of serotonin in brain development and its cross-talk with sex hormone function, we investigated effects of developmental exposure to pharmacologically relevant concentrations of FLU (3 and 30 nM (measured)) on brain neurotransmitter levels, gonadal differentiation, aromatase activity in brain and gonads, and the thyroid system, using the Xenopus tropicalis model. Tadpoles were chronically exposed (8 weeks) until metamorphosis. At metamorphosis brains were cryosectioned and levels of serotonin, dopamine, norepinephrine, and their metabolites 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were measured in discrete regions (telencephalon, hypothalamus and the reticular formation) of the cryosections using high-performance liquid chromatography. Exposure to 30 nM FLU increased the concentration of 5-hydroxyindoleacetic acid in hypothalamus compared with controls. FLU exposure did not affect survival, time to metamorphosis, thyroid histology, gonadal sex differentiation, or aromatase activity implying that the effect on the serotonergic neurotransmitter system in the hypothalamus region was specific. The FLU concentration that impacted the serotonin system is lower than the concentration measured in umbilical cord serum, suggesting that the serotonin system of the developing brain is highly sensitive to in utero exposure to FLU. To our knowledge this is the first study showing effects of developmental FLU exposure on brain neurochemistry. Given that SSRIs are present in the aquatic environment the current results warrant further investigation into the neurobehavioral effects of SSRIs in aquatic wildlife.

Dominance and stress signalling of carotenoid pigmentation in Arctic charr (Salvelinus alpinus): Lateralization effects?

Social conflicts are usually solved by agonistic interactions where animals use cues to signal dominance or subordinance. Pigmentation change is a common cue used for signalling. In our study, the involvement of carotenoid-based pigmentation in signalling was investigated in juvenile Arctic charr (Salvelinus alpinus). Size-matched pairs were analysed for pigmentation both before and after being tested for competitive ability. We found that dominant individuals had fewer carotenoid-based spots on the right and left sides as well as lower plasma cortisol levels compared to subordinate individuals. Further, the number of spots on both sides was positively associated with plasma cortisol levels. These results indicate that carotenoid-based pigmentation in Arctic charr signals dominance and stress coping style. Further, it also appears as if carotenoid-based pigmentation is lateralized in Arctic charr, and that the right side signals aggression and dominance whereas the left side signals stress responsiveness.