Electrolytic lesions of the bilateral ventrolateral orbital cortex not only directly reduce depression-like behavior but also decreased desperate behavior induced by chronic unpredicted mild stress in rats

Background Previous studies have revealed that ventrolateral orbital cortex (VLO) may play an important role in the regulation of emotional behavior. However, it is not known what effect VLO damage will have on emotion regulation. Results Data showed that damage of VLO increased the anxiety-like behavior in open field test and elevated plus maze, and decreased the depressive behavior in forced swimming test and learned helplessness test. Besides, the impulsive aggressive behaviors were also increased while the attack latency decreased after VLO lesion. What’s more, damage of VLO decreased depressive behaviors induced by chronic unpredicted mild stress in rats. Conclusions These results suggest that the integrity of VLO plays an important role in emotional regulation, and the damage of VLO may inhibit the development of depression-like behavior.

Underwater caustics disrupt prey detection by a reef fish

Natural habitats contain dynamic elements, such as varying local illumination. Can such features mitigate the salience of organism movement? Dynamic illumination is particularly prevalent in coral reefs, where patterns known as ‘water caustics’ play chaotically in the shallows. In behavioural experiments with a wild-caught reef fish, the Picasso triggerfish ( Rhinecanthus aculeatus ), we demonstrate that the presence of dynamic water caustics negatively affects the detection of moving prey items, as measured by attack latency, relative to static water caustic controls. Manipulating two further features of water caustics (sharpness and scale) implies that the masking effect should be most effective in shallow water: scenes with fine scale and sharp water caustics induce the longest attack latencies. Due to the direct impact upon foraging efficiency, we expect the presence of dynamic water caustics to influence decisions about habitat choice and foraging by wild prey and predators.

Diabetic female rats exhibit defensive aggression during mating

Introduction. Few reports have analyzed the putative association between diabetes mellitus type 1 (DM1) and aggressiveness. A previous study using a model of DM1 reported an increase in aggressive behaviors (AB) of females against the male during mating, which was prevented by insulin. However, it was unclear if such aggression was defensive or offensive. Objective. To evaluate the different components of aggressiveness of hyperglycemic female rats in two distinct mating paradigms. Method. DM1 was modeled in OVX Wistar rats by injecting streptozotocin (STZ) diluted in citrate buffer (50 mg/kg, i.p., for 2 consecutive days). Ten days later, female rats were treated with estradiol benzoate (10 microg, -24 hours) and progesterone (3 mg, -4 hours). A group of STZ-treated animals was administered with a long-acting insulin analogue (glargine) every 12 hours for 8 days. Aggression was recorded in non-paced mating (NPM) and paced mating (PM) paradigms. We registered: the first attack latency (FAL), the proportion of females that presented AB and its type (boxing, bites, lateral kicks and twist) and if AB were exhibited defensively or offensively. Results. Hyperglycemic rats showed an increase in lateral kicks in NPM, whereas in PM they exhibited an increase in bites. These behaviors were always defensive and there were no changes in FAL. Insulin reduced AB. Discussion and conclusion. Data indicate that the aggressiveness of hyperglycemic female rats is a form of defense against the proximity of the male and add information about the role of insulin on their modulation.

Eyespots divert attacks by fish

Eyespots (colour patterns consisting of concentric rings) are found in a wide range of animal taxa and are often assumed to have an anti-predator function. Previous experiments have found strong evidence for an intimidating effect of eyespots against passerine birds. Some eyespots have been suggested to increase prey survival by diverting attacks towards less vital body parts or a direction that would facilitate escape. While eyespots in aquatic environments are widespread, their function is extremely understudied. Therefore, we investigated the protective function of eyespots against attacking fish. We used artificial prey and predator-naive three-spined sticklebacks ( Gasterosteus aculeatus ) as predators to test both the diversion (deflection) and the intimidation hypothesis. Interestingly, our results showed that eyespots smaller than the fish’ own eye very effectively draw the attacks of the fish towards them. Furthermore, our experiment also showed that this was not due to the conspicuousness of the eyespot, because attack latency did not differ between prey items with and without eyespots. We found little support for an intimidating effect by larger eyespots. Even though also other markings might misdirect attacks, we can conclude that the misdirecting function may have played an important role in the evolution of eyespots in aquatic environments.

Aggressive and non-aggressive personalities differ in oxidative status in selected lines of mice ( Mus musculus )

Mice selected for aggression and coping (long attack latency (LAL), reactive coping strategy; short attack latency (SAL), pro-active coping strategy) are a useful model for studying the physiological background of animal personalities. These mice also show a differential stress responsiveness, especially in terms of hypothalamic–pituitary–adrenal axis reactivity, to various challenges. Since the stress response can increase the production of reactive oxygen species, we predicted that the basic oxidative status of the lines could differ. We found that LAL showed higher serum antioxidant capacity (OXY) than SAL, while no differences emerged for reactive oxygen metabolites (ROMs) or the balance between ROMs and OXY, reflecting oxidative stress. Moreover, the lines showed inverse relationships between ROMs or OXY and body mass corrected for age. The results indicate that variation in oxidative status is heritable and linked to personality. This suggests that different animal personalities may be accompanied by differences in oxidative status, which may predict differences in longevity.

INDIVIDUAL DIFFERENCES IN BEHAVIOUR: A TEST OF 'COPING STYLE' DOES NOT PREDICT RESIDENT-INTRUDER AGGRESSIVENESS IN PIGS

Temperament traits in animals are those which are stable across time and predictive of behaviour in other situations. Individuals can be identified as showing either active (pro-active) or passive (re-active) responses to a variety of challenges, and these are often referred to as 'coping styles'. Although most studied in rodents, coping styles are found in a variety of vertebrate species. In rodents, the resident-intruder aggressiveness test is a key measure of coping style, whereas in pigs, several recent studies have used a 'backtest' as the key measure of coping: A piglet is held on its back for one minute and the frequency of struggling bouts ('escape attempts') is recorded. In this study, we compared pig behaviour in backtests performed on 3 and 9 days of age, with aggressiveness was measured using 2 resident-intruder tests between 16 and 19 days post-weaning. A smaller unfamiliar intruder was introduced into part of the resident pig's home pen, and resident attack latency was recorded. Struggling bout frequency in the backtests showed a unimodal distribution. Data were analysed both as a continuous distribution and by comparing only the piglets from either extreme of the distribution (for comparison with other studies, top and bottom 25%). There was good repeatability of outcome (struggling frequency) over the two backtests, and over the two resident-intruder tests (attack latency and occurrence of resident attacks). However, no relationship was found between behaviour in the backtests and aggression in the resident-intruder tests, despite exhaustive analysis. Other authors have found that pigs show consistent responses to challenges, suggesting a degree of stable temperament. In line with the present findings though, most found no correlation between social and non-social responses. Other published experiments show that in pigs, the backtest can predict several physiological differences characteristic of coping styles. However, the present study shows that in pigs, aggressiveness and struggling in a backtest are not correlated, suggesting that they do not represent different expressions of the same underlying 'coping' trait.