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Elevation of brain 5-HT activity, POMC expression, and plasma cortisol in socially subordinate rainbow trout.

Agonistic behavior, brain concentrations of serotonin (5-hydroxytryptamine, 5-HT), and 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite), plasma cortisol levels, and the pituitary expression of pro-opiomelanocortin (POMC) A and B mRNA were determined in socially dominant and subordinate rainbow trout after 1 or 7 days of social interaction. Telencephalic and brain stem 5-HIAA/5-HT ratios, plasma cortisol levels, and pituitary POMC mRNA concentrations were elevated in fish being subordinate for 1 day. Furthermore, neither telencephalic 5-HIAA/5-HT ratios nor pituitary POMC A or POMC B mRNA expression showed any decline after 7 days of social interaction. By contrast, plasma cortisol concentrations of subordinate fish declined after 7 days but were still significantly higher than in dominant fish. Furthermore, in subordinate fish, hypothalamic 5-HIAA/5-HT ratios and plasma cortisol levels were highly correlated, suggesting an important role of hypothalamic 5-HT in the regulation of the teleost hypothalamic-pituitary-interrenal (HPI) axis. The number of aggressive acts received and plasma cortisol levels were highly correlated in 1-day subordinates, a relationship not seen in fish subjected to 1 wk of subordination. Thus the chronic stress experienced by subordinates in established dominance hierarchies appears to be more closely related to the threat imposed by the presence of the dominant fish than to actual aggressive encounters. The sustained elevation of pituitary POMC mRNA expression, an effect mainly related to an increase of melanotropic POMC expression, in subordinates could be a mechanism serving to maintain HPI axis excitability and promote acclimation in these individuals.

Animals↗

Urine marking in male mice: responses to natural and synthetic chemosignals.

The effects of natural chemosignals and their synthetic terpenic analogs on urinary marking in mice were investigated. The number and size of marking spots, and percentage of response and avoidance/counter-marking behavior, were measured for dominant and subordinate males. The males' marking behavior was found to differ significantly based on the type of stimulus sample used. Marking behavior in response to female urine was significantly altered by addition of synthetic analogs (farnesene isomers) to it. Both dominant and subordinate males avoided marking the section of the test area soiled with stimulus samples containing either natural or synthetic farnesenes. Differential responses of the dominant and subordinate male mice were observed.

Animal Communication↗

Effect of nucleus accumbens destruction in rat.

The paper presents the effects of nucleus accumbens destruction in rats. There are certain behavioral correlates (e.g., avoidance learning and dominance) which are influenced by the destruction of the nucleus accumbens, while other specific correlates are not significantly affected (namely, open field movements and competition for food). The results are discussed.

Animals↗

The effects of novelty and behavioral stereotype on the development of amnesia in mice.

The aim of the present study was to analyze the significance of the interaction between the basic behavioral strategy, the extinction of the novelty of information, and the efficacy of amnesia-inducing influences. Using a combination of training to passive avoidance with holding the animal in the unsafe sector of the apparatus, comparative analysis was performed of the reproduction of a memory trace in aggressive and submissive mice of line C57BL/6J with and without six sessions of familiarization with the apparatus. These experiments showed that preliminary habituation prevented the development of amnesia in submissive but not aggressive individuals. The cause of these differences in the effects of preexposure on the development of amnesia involves the selectivity of the process of extinction of information novelty characteristic for the behavioral stereotype.

Aggression↗

Effects of dominance and familiarity on behaviour and plasma stress hormones in growing pigs during social confrontation.

Behavioural patterns and plasma adrenaline, noradrenaline and cortisol responses were studied in domestic pigs with different dominance status during 10-h social confrontation tests with a familiar and an unfamiliar group. Eight trials were carried out, where in each trial two groups of nine growing pigs (12 weeks old) were randomly formed. The pigs with the highest (HR) and lowest (LR) rank from each group were selected as test animals, provided with surgically implanted catheters and kept in single housing for 2 to 3 weeks. After this period, each test animal was introduced once into the familiar and once into the unfamiliar group for 10 h. Introduction of the test animals into the groups caused frequent agonistic interactions during the first 30 min and significantly more agonistic interactions during the confrontation with the unfamiliar group. The agonistic behaviour was accompanied by a rapid increase of plasma catecholamines and cortisol. HR pigs showed significantly higher plasma catecholamine concentrations and more agonistic interactions during the first 30 min compared with the LR pigs. During confrontation with the unfamiliar group, HR pigs experienced more defeats and showed a higher increase of plasma cortisol levels than during the confrontation with the familiar group. No influences of rank or familiarity were found on the other behavioural patterns examined. The results show that agonistic behaviour and activation of the sympatho-adrenomedullary and the hypothalamic-pituitary-adrenal system in pigs during a social confrontation test are determined by the former dominance rank of the animals and the familiarity of the group.

Animals↗

Social influences on the arginine vasotocin system are independent of gonads in a sex-changing fish.

Many neuropeptide systems subserving sex-typical behavior are dependent on sex steroids for both their organization early in life and activation during maturity. The arginine vasopressin/vasotocin (AVP/AVT) system is strongly androgen dependent in many species and critically mediates responses to sociosexual stimuli. The bluehead wrasse is a teleost fish that exhibits a female-to-male sex change in response to social cues, and neither the development nor the maintenance of male-typical behavior depends on the presence of gonads. To examine social and gonadal inputs on the AVP/AVT system in the preoptic area (POA) of the hypothalamus, we conducted three field experiments. In the first experiment, we found that AVT mRNA abundance is higher in sex-changing females that attain social dominance and display dominant male behavior than in subordinate females, regardless of whether the dominant females were intact or ovariectomized. However, AVT-immunoreactive (IR) soma size in the gigantocellular POA (gPOA), but not in the magnocellular or parvocellular POA, increased only when females were displaying both dominant male behavior and had developed testes. In the second experiment, castration of dominant terminal-phase males had no effect on AVT mRNA abundance or any behavior we measured but did increase gPOA AVT-IR soma size compared with sham-operated controls. In the third experiment, 11-ketotestosterone implants in socially subordinate, ovariectomized females had no effect on either AVT mRNA abundance or AVT-IR soma size compared with controls. These results demonstrate that the AVT neural phenotype in the bluehead wrasse can be strongly influenced by social status, and that these social influences can be manifested independent of gonads.

Animals↗

Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action.

Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.

Aggression↗

Tonic pain and social behavior in male rabbits.

The 4 subjects each of 6 all-male colonies of rabbits studied in a seminatural setting rapidly established a dominance hierarchy. A combination of behavioral parameters obtained in two experimental situations was used to assign each individual a quantitative score of dominance. The situations were: 'intermale' activity between the residents and 'intruder test', i.e. the reactivity to the introduction of a male conspecific. Fifteen days later, tonic pain (formalin injection) was inflicted on the dominant, and the short-term effects on the treated animal and the social behavior of the group were studied. Licking of the injected foot was used to measure the intensity of pain; this reached a peak 4-8 h after injection and persisted with decreasing intensity into the second day. The painful condition resulted in a general dramatic decrease in motor and social activity including aggressive elements during the intruder test. A positive correlation was found between reduction in motor activity and pain intensity. However, the treated animals did not develop submissive behavior, while the untreated subordinates persisted in their prevalence of submissive over aggressive elements. This contributed to maintain in most cases the behavioral asymmetry of the agonistic activity of the different ranking animals. The possible mechanisms of the observed behavioral modifications are discussed.

Agonistic Behavior↗

Long-term changes in open field behaviour following a single social defeat in rats can be reversed by sleep deprivation.

The long-term consequences of a single social defeat on open field behaviour in rats were studied, with special emphasis on the time course of stress-induced changes. Animals were subjected to social defeat by placing them into the territory of an aggressive male conspecific for 1 h. After the defeat session experimental animals were returned to their home cage and their own room, receiving no further cues from the resident. Other animals serving as controls were placed in a clean and empty cage for 1 h. Five-minute open field tests were performed on days 1, 2, 7, 14, and 28 after defeat, with independent groups of rats. Locomotion of the animals was recorded and analyzed with an automated video system. Social defeat resulted in a strong subsequent reduction in open field activity, which lasted till at least 7 days after the conflict. Differences in total travelled distance were no longer significant 2 weeks after the conflict. The latency for moving to the outer ring of the open field arena after the start of the test was still significantly longer 4 weeks after defeat. The stress-induced reduction in open field locomotion could be reversed by 12-h sleep deprivation during the resting phase, an intervention known to have antidepressant effects in humans. Possible relevance of the present findings with respect to human affective disorders is discussed.

Affect↗

The rank assessed in a food competition test influences subsequent reactivity to immune and social challenges in mice.

The purpose of this study was to investigate whether, in a stable social environment, social interactions are responsible for individual, endocrine and immune differences among group members. Cage-mates were classified according to their rank in a food competition test. The influence of the rank was evaluated in two different situations activating neuroendocrine and immune systems. A first experiment used a context of repeated social stress. A second experiment investigated the influence of rank on the response to a bacterial infection by BCG. Endocrine and immune functions were assessed by measuring plasma corticosterone levels, splenocyte proliferation and in vitro cytokine production. In control undisturbed groups, plasma levels of corticosterone were lower in low ranking (LR) mice than in intermediate (IR) and high ranking (HR) mice. LPS-induced splenocyte proliferation and in vitro cytokine production were independent of rank. In response to social stress, corticosterone increased similarly in all categories but the increase in splenocyte proliferation was more pronounced in HR animals. During BCG infection, the rank influenced the production of IL-10 and IFN-gamma by tuberculin-stimulated splenocytes during the acute phase of the infection but not after 94 days of infection. Cytokine production in response to LPS and bacterial growth were not affected by the rank. Therefore, social interactions emerging in a stable social group may be involved in the individual differences observed in endocrine activity and in immune system reactivity.

Analysis of Variance↗

Antipredator vigilance in birds: modelling the 'edge' effect.

Many animals spend a large proportion of their time either foraging for food or watching out for predators (antipredator vigilance). There have been many theoretical and empirical studies investigating the trade-off between these two activities, especially in birds. Previous models of antipredator vigilance assume that all birds within the group spend the same amount of time feeding. However, many empirical studies have shown that individuals on the edge of flocks are more vigilant. Here we describe a vigilance model which investigates the effect of position on the birds' strategies by dividing the feeding area into an inner and outer region. The model examines how various parameters such as food availability and predation risk affect the strategies of individual birds according to whether they are in the inner or outer region. Our model predicts that birds in the outer group are always more vigilant than those in the inner region. Birds in the centre receive a higher payoff in each of the wide range of scenarios that we have considered, and so our model also indicates why dominant birds would choose to feed in the centre of the group; a prediction in accord with several empirical studies.

Algorithms↗

Androgen dependency of alcohol effects on aggressive behavior: a seasonal rhythm in high-ranking squirrel monkeys.

The relationship between testosterone and alcohol's effects on social behavior within established groups of squirrel monkeys was studied. Consistent behavioral differences between dominant and subordinate monkeys were quantitatively measured using computer assisted, continuous measurement techniques. Blood samples collected during the mating season revealed plasma testosterone measures of 202.9 +/- 13.4 ng/ml in dominant monkeys and 28 +/- 6.2 ng/ml in subordinate monkeys. Alcohol (0.1-1.0 g/kg, PO) produced a dose-related decrease of testosterone levels in dominant monkeys. Concurrently, alcohol produced biphasic effects on the behavior of dominant but not subordinate monkeys; low doses (0.1, 0.3 g/kg) increased the frequency of threats, grasps, and displacements. Subordinate monkeys were not affected at any dose. During the non-mating season, plasma levels of testosterone fell to 55.2 +/- 23.7 ng/ml in dominant monkeys and 7.3 +/- 1.7 ng/ml in subordinate monkeys. Plasma testosterone and the social behavior of both dominant and subordinate monkeys were unaffected by alcohol. These findings provide further evidence of a specific association between alcohol, testosterone and aggression in the non-human primate. High levels of testosterone that are evident during the mating season of dominant, male squirrel monkeys may activate alcohol sensitive brain substrates of aggressive behavior.

Aggression↗

Premenopausal social status and hormone exposure predict postmenopausal atherosclerosis in female monkeys.

OBJECTIVE: To determine whether premenopausal social subordination in female monkeys predicts postmenopausal atherosclerosis, and whether any such effect is altered by chronic exposure to contraceptive steroids or postmenopausal hormone replacement. METHODS: One hundred seventy-seven (177) premenopausal cynomolgus monkeys (Macaca fascicularis) housed in social groups of five or six were fed an atherogenic diet that, for half of the animals, also contained an oral contraceptive (OC). Individuals were judged socially dominant or subordinate based on behavioral observations. After 26 months animals were oophorectomized, biopsied for iliac atherosclerosis, and for the next 36 months were fed one of three atherogenic diets containing soy protein: 1) phytoestrogen-free; 2) phytoestrogens intact; and 3) phytoestrogen-free plus conjugated equine estrogens. Plasma lipids and menstrual cyclicity were also assessed. Finally, all animals were necropsied and the extent of atherosclerosis measured in the coronary and iliac arteries. RESULTS: The interaction of premenopausal social status and OC exposure predicted postmenopausal coronary artery atherosclerosis (P =.02). Subordinate animals not receiving OCs developed twice the coronary atherosclerosis of similarly untreated dominants (P <.01), an outcome mitigated by premenopausal OC exposure (P <.01). These effects occurred across postmenopausal treatment groups and independent of variation in plasma lipids. The same associations were observed in the iliac arteries, and, to a similar extent, both pre- and post-menopausally. Hormone data suggest that untreated premenopausal subordinates may have been estrogen deficient. CONCLUSION: Premenopausal social subordination exacerbates postmenopausal atherosclerosis, an effect possibly mediated by estrogen deficiency and shown here to be prevented by premenopausal OC exposure. These results occur irrespective of postmenopausal treatment.

Animals↗