Thyroid gland responses to intermale aggression in an inherently aggressive wild rat

The aim of the present investigation was to ascertain whether intermale aggression (by fighting) affects thyroid gland activity in wild rat. Following intermale aggression for three hours, thyro-follicular epithelial height was significantly decreased and colloidal content in follicular lumen increased only in the subordinate rats whereas the thyroid gland of the dominant rats was not perceptibly changed. Thus, aggression inhibits thyroid gland activity only in the subordinate rats. It is suggested that this effect may be due to psychosomatic rather than physical stress during aggression.     

Intra- and interspecific social and aggressive behaviour in the Siamese fighting fish, Betta splendens

Siamese fighting fish and paradise fish were operantly conditioned to swim through a cylinder to open a door allowing them to explore visually conspecifics, non-conspecifics, or inanimate objects. All stimuli significantly elevated response levels compared to control conditions, but response rate for conspecifics was not higher than for other stimuli. In experiments 2 and 3, fighting fish threatened and attacked non-conspecifics as well as conspecifics, and using a blind procedure, displays to different fish could not be easily differentiated. A final experiment with models failed to reveal any specific shape critical to the elicitation of the threat display. Discussion considers the possibility that the operant behaviour of the fighting fish may be motivated by visual exploration as well as by aggression, and that in actual fighting the social behaviour of the opponent may be more crucial than any particular visual stimulus.     

Detection of nootropic activity indicated by acute inhibition of orientation reaction

Exploratory locomotor activity was studied in the experiments on adult male mice. It was shown that routine nootropic drugs as well as newly synthesized nootropic compounds were able to facilitate the development of inhibition during one registration session. Inhibition may be used for revealing only selective nootropic drugs devoid of sedative and stimulating effects.     

Brain monoamines during footshock-induced aggression in paired rats

Regional brain monoamine concentrations were investigated following footshock induced fighting behaviour in paired rats, by a spectrophotofluorometric method. The dopamine (DA) levels of the diencephalon-midbrain (DM), and that of the caudate nucleus (CN), were significantly augmented as compared to unshocked but paired rats, the increase being substantially more in DM. Noradrenaline (NA) concentrations of both DM and pons-medulla (PM) increased to almost similar extents, though the data remained statistically insignificant in comparison to controls. The 5-hydroxytryptamine (5HT) of both DM and PM, however, recorded a decrease, which was statistically significant in the latter brain area. The biochemical data are consonant with the reported facilitatory effect of central DA, and the inhibitory role of central 5HT, in experimental aggression. The observed changes in NA levels, for which a role in experimental aggression remains equivocal, may be due to the stress of footshock kept minimal due to the coping factor of fighting in response to the shock.     

Calcium channel antagonists decrease the ethanol withdrawal syndrome

Withdrawal from chronic ethanol intake results in a syndrome of tremor and hyperexcitability, which can progress to seizures and death. Drugs used therapeutically to alleviate the syndrome have sedative actions and dependence liability of their own. The basis of the syndrome is unclear, although ethanol affects many neuronal functions, including membrane calcium conductance. Calcium channel blocking drugs have been used in cardiovascular disorders; they bind to high affinity sites in the brain but have few overt actions on the central nervous system. We have tested the effects of four calcium channel antagonists on the ethanol withdrawal syndrome in rats. Nitrendipine and nimodipine abolished all spontaneous seizures and prevented or reduced seizures following an audiogenic stimulus, and mortality. Verapamil significantly decreased seizure incidence and both it and flunarizine lowered mortality. The dihydropyridines were considerably more effective than diazepam in the withdrawal syndrome but had little effect on pentylenetetrazol seizures, against which diazepam gave good protection. The calcium channel inhibitors showed no sedative activity in normal animals. The results provide evidence that alterations in calcium conductance may be involved in the ethanol withdrawal syndrome and offer possibilities for the development of non-sedative therapeutic treatment of this syndrome.     

A New Approach that Eliminates Handling for Studying Aggression and the "Loser" Effect in Drosophila melanogaster

Aggressive behavior in Drosophila melanogaster is composed of the sequential expression of stereotypical behavioral patterns (for analysis see ¹). This complex behavior is influenced by genetic, hormonal and environmental factors. As in many organisms, previous fighting experience influences the fighting strategy of flies and the outcome of later contests: losing a fight increases the probability of losing later contests, revealing "loser" effects that likely involve learning and memory ^2-4. The learning and memory that accompanies expression of complex social behaviors like aggression, is sensitive to pre-test handling of animals ^5,6. Many experimental procedures are used in different laboratories to study aggression ^7-9, however, no routinely used protocol that excludes handling of flies is currently available. Here, we report a new behavioral apparatus that eliminates handling of flies, using instead their innate negative geotactic responses to move animals into or out of fighting chambers. In this protocol, small circular fight arenas containing a food cup are divided into two equal halves by a removable plastic slider prior to introduction of flies. Flies enter chambers from their home isolation vials via sliding chamber doors and geotaxis. Upon removal of plastic sliders, flies are free to interact. After specified time periods, flies are separated again by sliders for subsequent experimentation. All of this is done easily without handling of individual flies. This apparatus offers a novel approach to study aggression and the associated learning and memory, including the formation of "loser" effects in fly fights. In addition, this new general-purpose behavioral apparatus can be employed to study other social behaviors of flies and should, in general, be of interest for investigating experience-related changes in fundamental behavioral processes.     

Effects of physical and social experiences and octopamine receptor agonist on fighting behavior of male crickets Velarifictorus aspersus (Orthoptera: Gryllidae)

Fighting commonly occurs among animals and is very important for resolving conflicts between conspecific individuals over limited resources. The plasticity of fighting strategies and neurobiological mechanisms underlying fighting behavior of insects are not fully understood. In the present study, we examined whether physical and social experiences affected the aggressiveness of males of the cricket Velarifictorus aspersus Walker, and whether an octopamine (OA) receptor agonist could affected the aggressiveness of males exposed to different experiences. We found that flight and winning a fight significantly enhanced male aggressiveness, while losing a fight significantly suppressed male aggressiveness, consistent with the findings of existing studies on other cricket species. We also found that female presence had a stronger enhancing effect on male aggressiveness than flight or winning a fight. These findings demonstrated that physical and social experiences can affect the fighting behavior of male V. aspersus. Topical application of a 0.15?M solution of an OA receptor agonist (chlordimeform, CDM) significantly increased male aggression level, suggesting that OA may play an important role as a neuromodulator in controlling fighting behavior of males of this species. Despite displaying a significantly higher aggression level (level 5 or 6), CDM-treated losers did not escalate to physical combat, while fights between courting males usually resulted in physical escalation. It is likely that fighting behavior is only partly regulated by OA, and additional regulatory pathways may be involved in achieving physical combat.     

A method for quantifying aggression in male Drosophila melanogaster

Aggressive behavior is a complex social behavior that is difficult to measure. Here, we describe a simple method for the quantitative analysis of aggression in male Drosophila melanogaster. Traditional measurements of aggressive behavior have relied on a territorial context with a food territory and a female as factors that induce or enhance aggression. The protocol described here is devoid of a food territory or a female, making it simpler than most existing methods used to measure aggressive behavior. Multiple pairs of males are tested simultaneously to obtain an average fighting score. Four parameters are used to quantify the behavior: frequency, index, latency and intensity of fighting based on unambiguous offensive fighting behaviors. The assay takes 15 min, during which time a frequency score is obtained for 20-35 pairs simultaneously. More in-depth analysis, including latency, index and intensity, can be performed on the videotaped record of the experiment. The assay is highly reproducible and requires limited resources in a simple setup.     

Apomorphine induced biting and fighting behaviour in reserpinized rats and an approach to the mechanism of action

Various patterns of aggressive behaviour have been induced by drugs. In the present study, the biting and the fighting responses were induced in rats by apomorphine alone, and reserpine plus apomorphine combination respectively, and these could be blocked completely by a dopamine receptor blocking agent. Dopamine, norepinephrine and clonidine given intraperitoneally or intraventricularly failed to induce these responses. Chemical agents known to increase the concentration of dopamine in the brain, induced the biting, but not the fighting response, whereas these behavioural patterns were more intense due to apomorphine in the rats pretreated with reserpine and dopamine or α-methyltyrosine and reserpine combinations. In amphetamine pretreated rats, apomorphine induced intense biting after 10 min and a few bouts of fighting after 30 min. It is suggested that (i) the receptors on which apomorphine acts may be called ‘Apomorphine Receptor’ rather than ‘Dopamine Receptor’, (ii) dopamine incompletely activates these receptors which are sensitised in the absence of catecholamines and induce a higher degree of stereotyped behaviour i.e. fighting, due to apomorphine.     

Agonistic behavior in wild male Magellanic penguins: when and how do they interact?

Game-theory models predict that the frequency and type of agonistic interactions should vary with the value of the resource being contested. We describe bill duels and overt fighting in male Magellanic penguins (Spheniscus magellanicus) at a breeding colony and determine whether these behaviors change with the value of the nests over which they interact. Bill duels represent low levels of aggression while overt fighting high levels of aggression. Consistent with predictions, overt fighting was more common before egg laying when nests have the highest potential value while bill duels were more common at failed nests later in the season when nests are less valuable as they could not be used for reproduction until the next season. Contrary to expectations, overt fights were shorter and resulted in fewer cuts before egg laying than after egg laying. Large size asymmetries between opponents before egg laying may enable losers to quickly assess their opponents and leave before they are hurt. As predicted, the duration and damage occurring during overt fights were positively correlated with nest cover, which is correlated with higher reproductive success. We conclude that male Magellanic penguins have rules of engagement that in the most cases follow game-theory predictions on when and how to interact.     

Intrasexual selection favours an immune‐correlated colour ornament in a dragonfly

Sexual signalling is predicted to shape the evolution of sex‐specific ornamentation, and establishing the costs and benefits of ornamentation and the information that ornamentation provides to receivers is necessary to evaluating this adaptive function. Here, we assessed the adaptive function of a common colour ornament in insects, melanin wing ornamentation, using the dragonfly Pachydiplax longipennis. We hypothesized that greater ornamentation would improve territory‐holding success by decreasing aggression that males receive from territorial rivals, but that more ornamented males may have shorter lifespans. Using mark–recapture field observations, we found that more ornamented males had greater territory‐holding success and that viability selection did not act on wing melanization. We then compared the aggression of territorial rivals to decoy males before and after experimentally augmenting wing melanization, finding that males significantly reduced aggression following the manipulation. We next hypothesized that wing melanization would signal fighting ability to territorial rivals by reflecting condition via investment in the costly melanin synthesis pathway. We observed a positive relationship between ornamentation and the likelihood of winning territorial disputes, suggesting that wing melanization provides information about fighting ability to rivals. We also found a positive relationship between melanin‐based immune defence and ornamentation, supporting a link between the signal and condition. We conclude that wing melanization is a condition‐related signal of fighting ability and suggest that this may be a common mechanism promoting the evolution of melanin ornamentation.     

Neurosteroids, GABAA receptors, and escalated aggressive behavior

Aggressive behavior can serve important adaptive functions in social species. However, if it exceeds the species-typical pattern, it may become maladaptive. Very high or escalated levels of aggressive behavior can be induced in laboratory rodents by pharmacological (alcohol-heightened aggression), environmental (social instigation), or behavioral (frustration-induced aggression) means. These various forms of escalated aggressive behavior may be useful in further elucidating the neurochemical control over aggression and violence. One neurochemical system most consistently linked with escalated aggression is the GABAergic system, in conjunction with other amines and peptides. Although direct stimulation of GABA receptors generally suppresses aggression, a number of studies have found that positive allosteric modulators of GABAA receptors can cause increases in aggressive behavior. For example, alcohol, benzodiazepines, and many neurosteroids are all positive modulators of the GABAA receptor and all can cause increased levels of aggressive behavior. These effects are dose-dependent and higher doses of these compounds generally shift from heightening aggressive behavior to being sedative and anti-aggressive. In addition, these modulators interact with each other and can have additive effects on the GABAA receptor and on behavior, including aggression. The GABAA receptor is a heteropentameric protein that can be constituted from various subunits. It has been shown that subunit composition can affect sensitivity of the receptor to some modulators and that subunit composition differentially affects the sedative vs anxiolytic actions of benzodiazepines. Initial studies targeting alpha subunits of the GABAA receptor point to their significant role in the aggression-heightening effects of alcohol, benzodiazepines, and neurosteroids.     

Failure to find sex differences in testosterone activated aggression in two strains of rats

The effect of testosterone (testosterone propionate: TP) on intraspecific aggression in males and females of two strains of rats—WEzob and S3—was examined. Pairs of these rats, gonadectomized and treated either with oil or with testosterone propionate (TP), were tested in three different combinations: OIL against OIL, OIL against TP, and TP against TP-treated animals. Subsequently the effects of TP treatment of the subject and for the opponents interaction with sex and strain on the occurrence of diverse social + aggression behavioral parameters were determined. The results of the S3 strain indicate that testosterone treatment of either the subject or the opponent stimulates aggression in both males and females. No sex difference could be determined with respect to the incidence of aggression. In the WEzob strain a stimulatory effect of TP was shown in females but not in males. The absence of a clear stimulatory effect of TP in WEzob males in terms of changes in the total time spent on aggression, however, could wrongly suggest that TP does not affect aggression in these animals. The possibility of TP having an effect on these males in terms of increasing the intensity of fighting is discussed.     

Effects of female body size and age and male mating status on male combat in Anastatus disparis (Hymenoptera: Eupelmidae)

1. Aggressive behaviour is widely exhibited by animals to acquire important resources and usually shows a dangerous or nondangerous pattern. Dangerous fighting patterns are usually characterized by fights ending with contestants being severely injured or killed. Resource value is an important nonstrategic factor influencing fighting behaviour. Studies of many species addressing nondangerous fighting behaviour have shown that when resource values change, organisms usually adjust their fighting behaviour accordingly. Only a few species show dangerous fighting patterns. Thus, few relevant studies have addressed how variation in resource value affects aggression with a dangerous fighting pattern. 2. Here, an egg parasitoid wasp, Anastatus disparis, which exhibits a dangerous fighting pattern to acquire mating opportunities, was used as an experimental model to study the adjustment of fighting behaviour resulting from a change in resource value. 3. Our results show that the female properties of body size and age affect their objective resource value and that males increased their fighting intensity for relatively large and young females. However, male mating status in A. disparis may not influence the subjective value of mate resources, and fighting intensity did not significantly differ between mated and virgin males. In addition, the number of times a male had previously mated had no significant effect. These results suggest that mating opportunities are important for both virgin and mated males, resulting in neither of them showing any adjustment in fighting for mating opportunities. 4. Generally, A. disparis males with extreme fighting patterns adjust their fighting behaviour according to the variation in resource value, which avoids the meaningless costs of injury and death.     

The coevolution of juvenile play–fighting and adult competition

Although play–fighting is widespread among juvenile mammals, its adaptive significance remains unclear. It has been proposed that play is beneficial for developing skills to improve success in adult contests (motor‐training hypothesis), but the links between juvenile play–fighting and adult aggression are complex and not well understood. In this theoretical study, we investigate the coevolution between juvenile play–fighting and adult aggression using evolutionary computer simulations. We consider a simple life history with two sequential stages: a juvenile phase in which individuals play–fight with other juveniles to develop their fighting skills; and an adult phase in which individuals engage in potentially aggressive contests over access to resources and ultimately mating opportunities, leading to reproductive success. The simulations track genetic evolution in key traits affecting adult contests, such as the level of aggression, as well as juvenile investment in play–fighting, capturing the coevolutionary feedbacks between juvenile and adult decisions. We find that coevolution leads to one of two outcomes: a high‐play, high‐aggression situation with highly aggressive adult contests preceded by a prolonged period of juvenile play–fighting to improve fighting ability, or a low‐play, low‐aggression situation in which adult contests are resolved without fighting and there is minimal investment in play–fighting before individuals mature. Which of these outcomes is favoured depends on the mortality costs and on the type of societal structure: societies with strong reproductive skew, favouring monopolization of resources, show high levels of adult aggression and high investment in juvenile play–fighting, whereas societies with low reproductive skew have both low adult aggression and low levels of play–fighting. A review of empirical evidence, particularly in the primate genus Macaca, highlights some limitations of our model and suggests that other, complementary functional explanations are needed to account for the full range of competitive and cooperative forms of play–fighting. Our study illustrates the power of evolutionary simulations to shed light on the long‐standing puzzle of animal play.     

Extreme aggression in male squid induced by a β-MSP-like pheromone

Male-male aggression is widespread in the animal kingdom and subserves many functions related to the acquisition or retention of resources such as shelter, food, and mates. These functions have been studied widely in the context of sexual selection, yet the proximate mechanisms that trigger or strengthen aggression are not well known for many taxa. Various external sensory cues (visual, audio, chemical) acting alone or in combination stimulate the complex behavioral interactions of fighting behaviors. Here we report the discovery of a 10 kDa protein, termed Loligo β-microseminoprotein (Loligo β-MSP), that immediately and dramatically changes the behavior of male squid from calm swimming and schooling to extreme fighting, even in the absence of females. Females synthesize Loligo β-MSP in their reproductive exocrine glands and embed the protein in the outer tunic of egg capsules, which are deposited on the open sea floor. Males are attracted to the eggs visually, but upon touching them and contacting Loligo β-MSP, they immediately escalate into intense physical fighting with any nearby males. Loligo β-MSP is a distant member of the chordate β-microseminoprotein family found in mammalian reproductive secretions, suggesting that this gene family may have taxonomically widespread roles in sexual competition.     

The Use and Abuse of Tranquillizing Drugs for Chronic Mental Patients

The purpose of this study was to determine the necessity of administering maintenance doses of tranquillizing drugs to chronic mental patients. The behaviour of 16 female psychotic patients in a mental hospital was measured while they received maintenance doses of chlorpromazine (average dose, 50 mg. q.i.d.) and again while receiving identical doses of a placebo. The double-blind technique was employed. Nurses used a behaviour rating scale to measure noisiness, personal cleanliness, interpersonal relations among patients, occupational activities, hostility, activity, co-operation, dress, eating, and sleeping. Patients'' behaviour over a six-week period of chlorpromazine administration was compared with behaviour over an equal period of placebo administration. There was no evident difference in behaviour in 90% of the cases. Among the others there was a slight trend towards improved behaviour while the patients received placebo. It was concluded that tranquillizing drugs are often used needlessly for chronic mental patients. Implications of the use of tranquillizing drugs with chronic mental patients are discussed.     

Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers

Chimpanzee and hunter-gatherer intergroup aggression differ in important ways, including humans having the ability to form peaceful relationships and alliances among groups. This paper nevertheless evaluates the hypothesis that intergroup aggression evolved according to the same functional principles in the two species—selection favoring a tendency to kill members of neighboring groups when killing could be carried out safely. According to this idea chimpanzees and humans are equally risk-averse when fighting. When self-sacrificial war practices are found in humans, therefore, they result from cultural systems of reward, punishment, and coercion rather than evolved adaptations to greater risk-taking. To test this “chimpanzee model,” we review intergroup fighting in chimpanzees and nomadic hunter-gatherers living with other nomadic hunter-gatherers as neighbors. Whether humans have evolved specific psychological adaptations for war is unknown, but current evidence suggests that the chimpanzee model is an appropriate starting point for analyzing the biological and cultural evolution of warfare.     

Neuromodulator mechanism of the inhibitory effect of deoxycorticosterone on the aggressive-defensive behavior of the rat

DOCA (0.3 mg/kg i.p.) inhibited the shock-induced aggression in male rats. This behavioural reaction was also inhibited by activation of brain beta-adrenergic and nicotinic receptors. The inhibitory hormone effect was potentiated to a considerable extent (p less than 0.05-0.001) by central beta-adrenergic stimulation but was blocked by beta-antagonist administration. However, it was independent of facilitatory and inhibitory actions on the brain nicotinic receptors. It is concluded that the DOCA inhibitory effect on the shock-induced defensive fighting involved the facilitation of the brain beta-adrenergic receptor activation.     

Studying aggression in Drosophila (fruit flies)

Aggression is an innate behavior that evolved in the framework of defending or obtaining resources. This complex social behavior is influenced by genetic, hormonal and environmental factors. In many organisms, aggression is critical to survival but controlling and suppressing aggression in distinct contexts also has become increasingly important. In recent years, invertebrates have become increasingly useful as model systems for investigating the genetic and systems biological basis of complex social behavior. This is in part due to the diverse repertoire of behaviors exhibited by these organisms. In the accompanying video, we outline a method for analyzing aggression in Drosophila whose design encompasses important eco-ethological constraints. Details include steps for: making a fighting chamber; isolating and painting flies; adding flies to the fight chamber; and video taping fights. This approach is currently being used to identify candidate genes important in aggression and in elaborating the neuronal circuitry that underlies the output of aggression and other social behaviors.