Brain mechanisms for offense, defense, and submission

Hormone-dependent aggression in male and female rats: experiential, hormonal, and neural foundations

Hormone-dependent aggression in both male and female rats includes the distinctive behavioral characteristics of piloerection and lateral attack. In males the aggression is dependent on testicular testosterone and is commonly known as intermale aggression. In females, the aggression is most commonly observed as maternal aggression and is dependent on hormones whose identity is only beginning to emerge. The present review examines the experiential events which activate hormone-dependent aggression, the relation of the aggression to gonadal hormones, and the neural structures that participate in its modulation. In males and females, the aggression is activated by cohabitation with a conspecific of the opposite sex, by competitive experience, and by repeated exposure to unfamiliar conspecifics. In the female, the presence of pups also activates aggression. In both males and females, hormones are necessary for the full manifestation of the aggression. The essential hormone appears to be testosterone in males and a combination of testosterone and estradiol in females. The information available suggests the neural control systems for hormone-dependent aggression may be similar in males and females. It is argued that hormone-dependent aggression is behaviorally and biologically homologous in male and female rats.

Opposite effects of pentylenetetrazol on self-defensive and submissive postures in the rat

In a previous work, using the resident-intruder situation, we have shown that a benzodiazepine inverse agonist could exert a "fear-promoting" effect, in decreasing self-defensive behaviours while increasing submissive postures. To further test this hypothesis, the effects of pentylenetetrazol on different forms of defensive behaviour were examined in male intruder rats confronted with offensive residents. Administration of pentylenetetrazol (10 and 20 mg/kg, IP) increased submissive postures such as immobility and on-the-back, but reduced self-defensive postures. Other active behaviours were not reduced, thus excluding a non-specific behavioural suppression. These results suggest that self-defensive and submissive behaviours can be dissociated and that anxiogenic compounds are more likely to increase submissive behaviours than self-defensive ones.

Rodent models of aggressive behavior and serotonergic drugs

Various models of rodent agonistic behaviour are described, which differentiate between offensive and defensive/flight models. Particular attention is given to one male and one female paradigm for offensive aggression, viz. resident-intruder or territorial (RI) and maternal aggression (MA). After an overview of the serotonin (5-HT) system in the CNS, a description is given of the ligands available. Subsequently the effects of various drugs affecting serotonergic transmission in the RI- and MA-paradigms are described. The 5-HT1A agonists buspirone, ipsapirone and 8-OH-DPAT decreased aggression in RI and MA, but simultaneously led to a marked decrease in social interest and activity, indicative of a non-specific anti-aggressive profile. Non-selective 5-HT1 agonists, such as RU 24969, eltoprazine (DU 28853), and TFMPP reduced aggression quite specific and did not decrease social interest or exploration, but sometimes even increased these behaviours. In RI and MA the behavioural effects of these drugs were roughly similar. In contrast, MA was more sensitive to the treatment with the 5-HT reuptake blocker fluvoxamine, which blocked RI aggression only non-specifically at the highest dose. DOI, a 5-HT2 and 5-HT1C agonist, decreased aggressive behaviour and increased inactivity, without affecting social interest and exploration in RI as well as MA. This was, however, accompanied by 'wet dog shaking', characteristic of 5-HT2-receptor stimulation. The non-specific 5-HT agonist (and 5-HT3 antagonist) quipazine also induced 'wet dog shaking' at doses which suppressed aggression, social interest and exploration but increased inactive behaviours (sitting and lying). The discussion attempts to delineate a role for 5-HT receptor subtype involvement in the modulation of aggression, with the restrictions we clearly face with regard to the lack of specific serotonergic agonists and antagonists for certain receptor subtypes. By and large, male and female rats react similarly to treatment with serotonergic drugs stressing the consistent role of 5-HT in different forms of aggression.

Blood pressure, heart rate, and regional resistance in behavioral defense

Rats were instrumented with arterial catheters and directional pulsed Doppler flow probes for measurement of arterial blood pressure, heart rate, and blood flow in the renal, mesenteric, and hindquarter vascular beds. When tested as intruders in a resident-intruder aggression test, subjects responded to resident attack with species-characteristic defensive behavior and the "defense reaction" pattern of increased heart rate, renal resistance, and mesenteric resistance, and decreased hindquarter resistance. Blood pressure was variable, but sustained increases in blood pressure were rarely observed. The maintenance of blood pressure during species-specific defensive behavior can be contrasted with the sustained pressor responses observed in the centrally elicited defense reaction. The combination of pulsed Doppler technology and the resident-intruder paradigm appears to be a promising method for investigating the mechanisms of cardiovascular adjustment to behavioral defense.

Ethopharmacology: a historical perspective

Ethopharmacology can be defined as the study of behavioral and other effects of drugs through the use of ethological concepts. The study of drug effects on natural action patterns (motor acts and postures listed in ethograms), with respect to natural settings and to behavior as a whole (all identifiable behaviors occurring during the measurement) represents the basic concepts of ethopharmacology. Although pioneers drew attention to the potential of the ethological approach in pharmacology in the early 1960s, the number of publications utilizing this approach has steadily grown only since the mid-1970s. In the 1980s, modern technology, such as videorecorders, microcomputers and software, has been more widely applied in ethopharmacological experiments, greatly facilitating the observation and quantitative analysis of multiple data. Ethopharmacology is not "another" behavioral pharmacology, but an integral part of it. Rather, it represents one of the tools which can be useful (and sometimes even indispensable) in achieving a better understanding of the behavioral effects of drugs. It is to be hoped that it will be used in concert with other approaches in the future.

Heritable variation for aggression as a reflection of individual coping strategies

Evidence is presented in rodents, that individual differences in aggression reflect heritable, fundamentally different, but equally valuable alternative strategies to cope with environmental demands. Generally, aggressive individuals show an active response to aversive situations. In a social setting, they react with flight or escape when defeated; in non-social situations, they react with active avoidance of controllable shocks and with sustained activity during an uncontrollable task. In contrast, non-aggressive individuals generally adopt a passive strategy. In social and non-social aversive situations, they react with immobility and withdrawal. A main aspect of these two alternative strategies is that individuals with an active strategy easily develop routines (intrinsically determined behaviour), and consequently do not react (properly) to 'minor' changes in their environment, whereas in passively reacting animals it is just the other way around (extrinsically determined behaviour). It has become clear that active and passive behavioural strategies represent two different, but equivalent, coping styles. The coping style of the aggressive males is aimed at the removal of themselves from the source of stress or at removal of the stress source itself (i.e. active manipulation). Non-aggressive individuals seem to aim at the reduction of the emotional impact of the stress (i.e. passive confrontation). The success of both coping styles depends upon the variability or stability of the environment. The fact that aggressive males develop routines may contribute to a fast execution of their anticipatory responses, which is necessary for an effective manipulation of events. However, this is only of advantage in predictable (stable) situations, but is maladaptive (e.g. expressed by the development of stress pathologies) when the animal is confronted with the unexpected (variable situations). The flexible behaviour of non-aggressive individuals, depending strongly upon external stimuli, will be of advantage under changing conditions. Studies on wild house mice living under natural conditions show how active and passive coping functions in nature, and how the two types have been brought about by natural selection.

Effects of septal lesions on fear-potentiated startle, and on the anxiolytic effects of buspirone and diazepam

The present study evaluated the effect of septal lesions on baseline startle amplitude, potentiated startle (a measure of conditioned fear), and the ability of either buspirone or diazepam to block potentiated startle. Baseline responding to an acoustic stimulus was obtained for all rats, followed by potentiated startle training (ten light-shock pairings on each of two days). Rats were then given bilateral electrolytic lesions of the septum or sham surgery. Four and seven days following surgery all rats were tested again for baseline startle amplitude. Ten days postsurgery, rats were injected with either 5.0 mg/kg buspirone or vehicle and tested for potentiated startle (increased acoustic startle in the presence of a light previously paired with shock). Five days later septal-lesioned animals were injected with either 5.0 mg/kg of diazepam or vehicle and again tested for potentiated startle. Septal lesions increased baseline startle amplitude significantly, but did not alter the magnitude of potentiated startle or impair the ability of buspirone or diazepam to block potentiated startle. In Experiment 2 rats were trained using the above procedures, and were subsequently given discrete bilateral lesions of the lateral septum or sham surgery. Lateral septal lesions again had no effect on the magnitude of potentiated startle. These findings do not support an involvement of the septum in the inhibition of fear, or in the mediation of the anxiolytic effects of buspirone or diazepam.

Postsynaptic 5-HT1 receptors and offensive aggression in rats: a combined behavioural and autoradiographic study with eltoprazine

The present study was designed to assess whether the antiaggressive effects of eltoprazine are mediated via presynaptic and/or postsynaptic 5-HT1 receptors. We describe the effects of central 5-HT depletion 1) on the behaviour of resident TMD-S3 rats in a territorial situation, 2) on the efficacy of eltoprazine to inhibit offensive aggression, and 3) on the 5-HT1A, 5-HT1B and 5-HT1C receptor binding in brains of rats previously used in behavioural studies. Male resident rats were given combined 5,7-dihydroxytryptamine (5,7-DHT) injections into the dorsal and median raphe nuclei. Two to four weeks after the lesions, rats were confronted with an intruder Wiser rat in their home cage for a 10-min period. The 5,7-DHT treatment resulted in a modest reduction of offensive behaviour, while having no effects on other social and nonsocial behaviours. Oral administration of eltoprazine (1 mg/kg) specifically reduced offensive aggression in both sham- and 5,7-DHT-lesioned animals, leaving social interest and exploration intact or even increasing it. A low dose (0.3 mg/kg) of eltoprazine did not affect the behavioural repertoire of sham-operated rats, whereas this dose significantly reduced offense behaviours in the 5,7-DHT-lesioned residents. Quantitative autoradiographic studies 5 weeks after 5,7-DHT treatment revealed a significant increase in radioligand binding to 5-HT1A, 5-HT1B and 5-HT1C sites in many brain regions studied, except for the raphe nuclei where [3H]8-OH-DPAT binding to 5-HT1A sites was markedly reduced. The concentrations of 5-HT and 5-HIAA in frontal cortex were reduced to approximately 10% of controls. The results indicate that serotonin has a stimulatory rather than an inhibitory influence on offensive aggressive behaviour. Central 5-HT depletion does not prevent the antiaggressive effects of eltoprazine, indicating a role for postsynaptic 5-HT1 receptors in the modulation of offensive aggression. The 5,7-DHT-induced overall upregulation of 5-HT1A, 5-HT1B and 5-HT1C binding sites suggests that these three receptor subtypes receive a tonic serotonergic influence. It is conceivable that this postsynaptic 5-HT1 receptor supersensitivity is reflected by the increased efficacy of eltoprazine to inhibit offensive aggression.

Opposite effects of agonist and inverse agonist ligands of benzodiazepine receptor on self-defensive and submissive postures in the rat

The effects of benzodiazepine receptor ligands on different types of defensive behaviours were examined in intruder male rats confronted with offensive residents. Chronic administration, via a subcutaneous silastic pellet, of a full agonist (diazepam) for 15 days increased self-defensive postures as well as social and non-social behaviour whereas submissive postures and flight were reduced. Acute administration of a partial agonist (ZK 91296) resulted in a similar increase in self-defensive postures and a decrease of submission and non-social elements. Acute administration of a partial inverse agonist (FG 7142) reduced defensive postures and social behaviour whereas submissive postures were increased. These results show that activation of benzodiazepine receptors by full or partial agonists increased self-defensive responses to attacks by a conspecific, while decreasing submissive postures. On the contrary, "inverse activation" of these receptors by an inverse agonist increased submissive postures while decreasing self-defensive responses. These data suggest that benzodiazepine receptors are involved in the control of the animal's strategy to respond to an attack of another rat.

Conditional hypoalgesia is attenuated by naltrexone applied to the periaqueductal gray

The ventrolateral periaqueductal gray (vPAG) is an important component in a brainstem system involved in the endogenous modulation of nociception and defensive behavior. The present study was conducted to determine if opioid receptors within the vPAG contribute to the hypoalgesia seen in rats during presentation of a Pavlovian CS for footshock. Independent groups of animals received microinjections of either 5.0 micrograms naltrexone HCl or vehicle into the vPAG prior to being placed in an observation chamber in which shock had been delivered 24 h earlier. Nociceptive reactivity was measured with the formalin test. Naltrexone treatment attenuated conditional hypoalgesia but did not affect formalin-induced behavior in non-shocked rats. Naltrexone had no effect on the amount of defensive freezing behavior observed during the test session. These results indicate that conditional hypoalgesia as measured by the formalin test involves the activation of documented brainstem antinociceptive systems.

Effects of morphine and midazolam on reactivity to peripheral noxious and central aversive stimuli

Electrical stimulation of the mesencephalic tectum elicits behavioral and autonomic responses similar to those following peripheral noxious stimulation. Benzodiazepine and opioid compounds attenuate escape behavior induced by electrical stimulation of the dorsal periaqueductal gray (PAG) and deep layers of the superior colliculus (SC). The present study determines if microinjections of midazolam and morphine applied to these PAG-SC sites affect both responsiveness to peripheral noxious stimulation and to aversive PAG-SC stimulation. Both aversive brain stimulation or foot-shocks applied at threshold intensities caused running or jumps concomitant with increases in mean arterial blood pressure (MBP) and heart rate (HR). Microinjection of both drugs attenuated the behavioral reaction and increases in MBP and HR induced by mesencephalic tectum stimulation, while attenuating only the increase in heart rate induced by peripheral painful stimulation. These results suggest that the neural substrates of the behavioral and autonomic effects of stimulating the mesencephalic tectum and peripheral nociceptors are different although they may partially overlap.

An ethological model for the study of activation and interaction of pain, memory and defensive systems in the attacked mouse. Role of endogenous opioids

The present work reviews neurochemical, physiological and behavioral data recorded from the attacked mouse and integrates them into a model of coping mechanisms during social conflict. More specifically, the possible relationships between systems of pain, memory and defense are presented, with special emphasis on the role of endogenous opioid peptides (EOPs). In recipients of attack, decreased beta-endorphin-like immunoreactivity and changes in opiate and benzodiazepine binding characteristics are found in structures of the brain defensive system. EOPs mediate the social conflict-induced increase of dopamine synthesis in the periaqueductal grey and frontal cortex. Social conflict analgesia in attacked mice is under the control of central opioid and nonopioid (e.g., benzodiazepine, glutamate) mechanisms, and is modified by experience (e.g., long-term analgesic reaction; tolerance). EOPs and pain-inhibitory mechanisms participate in the organization of behavioral defense, recuperative behavior and the memory of attack experience. The data are considered in relation to the perceptual-defensive-recuperative model of fear and pain, forwarded by Bolles and Fanselow.

Logistic analysis of the defense reaction induced by electrical stimulation of the rat mesencephalic tectum

Subliminal and threshold functions of behavioral output to electrical stimulation of the rat mesencephalic tectum were fitted using the logistic model. The results suggest the existence of isotopic albeit anisotropic freezing and flight mechanisms in the dorsal periaqueductal gray and deep layers of the superior colliculus. Moreover, the marked parallelism of immobility and running threshold functions indicates the probable coupling of these mechanisms through a kind of negative feedback. Finally, the good fitting to the model suggests that the behavioral output to electrical stimulation of these areas follows a logistic function of the logarithm of the stimulus intensity.

Respiratory-related discharge of periaqueductal gray neurons during sleep-waking states

Extracellular single-unit spontaneous activity was recorded from the periaqueductal gray region (PAG) in undrugged, freely moving cats. Two analyses, cross-correlation histograms and linear regression techniques, were used to examine state relationships of neuronal discharge with respiratory patterning. Of 68 cells recorded, 19 (28%) showed a timing relationship (breath-by-breath dependency), 14 of which were state-dependent. Twenty-three (34%) showed a tonic discharge correlation with the respiratory cycle, and activity of all these cells was state-dependent. These results suggest that a subset of PAG cells may play a role in state-related respiratory patterning.

Search after neurobiological profile of individual-specific features of Wistar rats

The first part of this study demonstrates that the bimodal shape of variation in "fleeing" and "nonfleeing" or "freezing" rats of an outbred strain of Wistar rats forms part of an overall biomodal variation in behavioural responses to injections of agents, which selectively alter, or reflect, the noradrenergic or dopaminergic activity in the ventral striatum, and dopaminergic activity in the dorsal striatum, the GABA-ergic activity in the substantia nigra, pars reticulata, and the GABA-ergic activity in the deeper layers of the superior colliculus. It is concluded that the "fleeing" and "nonfleeing" rats, each of them marked by their own trans-situational consistency in pharmacological and behavioural responses, represent the two fundamentally different types of individuals which normally exist in unselected populations of rodents. The second part of this study demonstrates that the pharmacogenetic selection of apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) rats, i.e., one individual-specific feature of the overall bimodal variation for pharmacological responses in our outbred strain of rats, is a valid tool to disperse the above-mentioned individual-specific features as far as possible. First, these lines allowed us to prove that the overall bimodal shape of variation in pharmacological and behavioral responses of individual outbred rats is in part genetically determined. Second, these lines allowed us to prove that a bimodal variation in neurochemical features of the circuitry, in which the ventral striatum is embedded, underlies the overall bimodal variation in pharmacological and behavioural responses. Third, these lines allowed us to demonstrate that a fundamental difference in organizing behaviour with the help of external and internal information has to be considered as a common factor giving rise to the individual differentiation found in the present study. Given the notion that this individual differentiation appears to be valid across lines, substrains and strains of rats, the present study lays the foundation for understanding at least a part of the physiological basis underlying differences between the two fundamentally different types of individuals existing in normal populations of rodents.

Neurochemical profile of eltoprazine

In this paper we present the neurochemical profile of eltoprazine, a drug that specifically inhibits offensive aggression. Eltoprazine interacts selectively with serotonin (5-HT) receptor subtypes (Ki-values for 5-HT1A, 5-HT1B and 5-HT1C receptors are 40, 52 and 81 nM respectively). Affinity for other neurotransmitter receptors is much lower (Ki-values greater than 400 nM) than for 5-HT1 receptors. The selective interaction with 5-HT1 receptor subtypes is confirmed by in vitro autoradiographic studies using radiolabelled eltoprazine. The overall distribution of [3H]eltoprazine bears a strong resemblance to the localization of 5-HT1 binding sites labelled by [3H]5-HT, although some differences are observed. Eltoprazine (1 microM) inhibits the forskolin stimulated c-AMP production in hippocampus slices of the rat, indicating an agonistic action on the 5-HT1A receptor. The K+ stimulated release of 5-HT from rat cortex slices is inhibited by eltoprazine (pD2 = 7.8). The maximal response, however, was clearly less than that of the full agonist 5-HT, indicating partial agonistic activity on the 5-HT1B receptor (alpha = 0.5). Eltoprazine has a weak antagonistic action (IC50 = 7 microM) on the 5-HT1C receptor as revealed by inhibition of the 5-HT-induced accumulation of inositol phosphates in the choroid plexus of the pig. In vivo, eltoprazine reduces 5-HIAA levels in the striatum, without affecting the 5-HT levels. Eltoprazine also reduces the 5-HT synthesis rate as shown by 5-HTP accumulation after decarboxylase inhibition. These data indicate that eltoprazine acts as a 5-HT agonist in vivo in a dose range that affects aggressive behaviour (0.3-3 mg/kg p.o.). Taken together from a variety of neurochemical studies there is strong evidence both in vitro and in vivo that the pharmacological actions of eltoprazine can be attributed to an interaction with the 5-HT system, most probably via a (partial) agonistic action on 5-HT1A and 5-HT1B receptors.

Ethopharmacology: a creative approach to identification and characterisation of novel psychotropics

The present contribution describes the basic fundamentals of animal models in ethopharmacology. After defining the role of ethopharmacology in the development of animal models of relevant human diseases, this methodology is used to classify different categories of aggression. Furthermore, the behavioural aspects of agonistic (aggressive) modelling are outlined and the various models used to describe offensive and defensive behaviours, and some miscellaneous models are summarized. Finally, some remarks on the new class of psychoactive drugs, serenics, are given.

Effects of the heterosomes and maternal environments on aggressive behavior in Mus musculus

This is a study of the offense type of aggression in males of the DBA/1Bg and C57BL/10Bg inbred strains of mice and their two reciprocal F1 hybrids. It uses three test paradigms for dyadic encounters: the homogeneous set test, an identity panel of testers, and the standard opponent test. There were no reciprocal F1 hybrid differences for any of the 12 behavioral measures of aggression in the homogeneous set test or the standard opponent test. For the panel of testers paradigm, reciprocal F1 hybrid differences occurred when the tester (opponent) was an F1 hybrid male, but not when the tester (opponent) was an RB/1 or C57BL10 male. When B10RB1F1 males were the testers (opponents), B10RB1F1 hybrid males were more aggressive than RB1B10F1 hybrid males across 10 of the 12 behavioral measures. Conversely, when RB1B10F1 males were the testers (opponents), RB1B10F1 males were more aggressive than B10RB1F1 males across 9 of the 12 behavioral measures. These results conform to the following empirical rule: A significant difference between reciprocal F1 hybrids is observed for these behavioral measures when one of the hybrids has both of its heterosomes (X and Y chromosomes) and its maternal environment identical to those of its opponent and the other hybrid has none of these identical to those of its opponent. These results are consistent with a model in which on some genetic backgrounds, but not on others, similarity of the heterosomes and maternal environments can influence the display of or response to social or other stimuli for the offense type of aggression in mice. These stimuli may be individual recognition chemosignals in urine.

Spontaneously hypertensive Wistar-derived male rats are more aggressive than those of their normotensive progenitor strain

We compared a group of spontaneously hypertensive rats (SHRs) to a group of Wistar-Kyoto (WKY) rats on each of the three most commonly studied forms of aggressive behavior in rats: muricide, intraspecific aggression, and shock-induced fighting (SIF). A significantly higher proportion of SHRs were muricidal; they also fought more at the lowest shock level. A trend for a higher incidence of intraspecific offense behaviors by SHRs was not significant. SHR flinch and jump thresholds were lower than the respective WKY thresholds. Although there were no significant correlations between shock thresholds and any aspects of SIF, the possibility that strain differences in shock sensitivity may contribute to differences in SIF cannot be ruled out. Within strains, there were no correlations among the different forms of aggression. Several different inherited characteristics may be associated with the accentuation of different forms of aggression in SHRs.

Aggressive behaviors in adult rats deprived of playfighting experience as juveniles

Matched litter mates were reared in one of three conditions: in pairs or in isolation with or without one hour of daily playfighting experience from 20 to 50 days of age. The rats were then regrouped within condition so that they lived with identically reared cagemates for a month. This regrouping eliminated the transient effects of isolation such as increased fearfulness. When tested as adults, there was no effect of early rearing condition on the probability of intraspecific aggression or muricide, although isolation-reared rats were less likely to retrieve the mice. However, isolation rearing reduced the latency to initiate shock-induced defensive aggression and increased both its frequency and intensity. Isolated animals which had been given daily playfighting during development did not show the effects of early social deprivation. The mechanisms through which playfighting experience shapes later defensive behavior remain to be determined.

Attack and defense in rodents as ethoexperimental models for the study of emotion

1. In wild and laboratory rats, offense and defense constitute nonoverlapping behavior patterns seen in response to resource or dominance challenge, or, to predatory, conspecific or environmental threat, respectively. 2. Defensive behaviors are determined by both the threat stimulus and the situation. Defense patterns to discrete, approaching, predators or conspecifics and to nondiscrete, potential, threat have several behaviors in common. However, the latter also includes an important risk assessment complex not seen to discrete, present, threat. Behaviorally and functionally, risk assessment shows considerable similarity to the apprehensive expectation and vigilance and scanning components of generalized anxiety reactions. 3. There are parallels between lower mammal offense and human angry aggression in terms of eliciting stimuli, and a variety of experiential factors including inhibition by fear/pain, and reinforcement effects. 4. A variety of neuroanatomical or pharmacological manipulations have different, often opposite, effects on offense and defense. Differentiation of the two and attention to the specific behaviors involved provide a more precise basis for the use of these patterns as animal models of emotion states.

The measurement of suicidality, aggressivity and impulsivity

1. From an evolutionary point of view aggressive behavior increases the chances of individual survival as well as inclusive fitness. 2. There are brain structures and biochemical systems that are involved in the regulation of aggressive behavior. 3. Genetic studies have revealed genetic contributions to aggressive as well as impulsive behaviors. 4. Research has demonstrated correlations between measures of suicidality, violence and impulsivity. 5. A two-step model of countervailing forces has been developed that identifies amplifiers and attenuators of the aggressive impulse. This model has enabled us to determine a set of variables that influence suicide but not violence and another set that influences violence but not suicide.

Offense and defense after lateral septal lesions in Columba livia

It is generally agreed that there are several different types of animal aggression that may be distinguished in terms of their neural organization and that discrete lesions, in particular brain areas, may affect one but not other types of aggression. In this study the effects of electrolytic, bilateral lesions in lateral septum on offense and defense were examined in pigeons. Subjects were tested by introducing an adult conspecific stranger into their home cage. A postoperative increase in offensive patterns and a long-lasting drop in defense were observed in the lesioned birds. Its remarkable resemblance to the effects of antianxiety drugs, as well as the difference between the behavioral effects of medial septal damage are also discussed.

Dominance and aggression

Dominance is a complex phenomenon mediated by different mechanisms. Various motivations and their mutual correlations determine the tendency to dominate. A subject that is dominant in every situation (i.e., absolutely dominant) is rather an exceptional case. Dominance may be limited to particular situations and exhibited only with some definite partners. One subject may be dominant over one partner and submissive with another. Aggressive behavior is not indispensable to obtain and keep dominance status. It seems that dominance sustained without aggression is more stable than dominance formed on the basis of aggressive display, since experiments on predatory dominance in pairs and groups of cats support such an assumption. Various brain structures were found which are involved in aggressive behavior, but in respect to dominance our experiments point to the role of the dorsal amygdala in predatory dominance.

Inhibition of affective aggression and dominance in rats after thyrotropin-releasing hormone (TRH) microinjection into the nucleus accumbens

The effect of 10 micrograms TRH injected bilaterally into the nucleus accumbens septi on two models of affective aggression and on dominance in a water-competition task was investigated in pairs of male Wistar rats. TRH significantly suppressed affective shock-induced and apomorphine-induced fighting. It also decreased dominance when administered to dominant rats while no effect was noted upon injection into subordinate animals. The peptide influenced neither water consumption in thirsty rats nor the pain threshold in a hot plate test.

No change in intermale aggression after amygdala lesions which reduce freezing

Long-Evans rats with bilateral lesions in the area of the amygdala, or operated controls, were tested with strange male intruders into the subjects' home cages. Various measures of attack toward the intruder, including piloerection, lateral attack, on-top-of and biting showed no difference between the experimental and control animals. However, subjects with amygdaloid damage showed a substantial and significant reduction in freezing in the presence of a cat. This finding of reduced defensiveness to a predator is consistent with previous findings for amygdala lesions, while the failure to find decrements in conspecific offensive attack agrees with some, but not all, previous work in this area. The finding that a clear decrement in defense occurs in the same amygdala-lesioned subjects showing no suggestion of a reduction in offense adds to a body of data which indicates that offense and defense respond differentially to manipulation of a number of important neural and neurochemical systems.

Effects of lesions of the cerebellar vermis on VMH lesion-induced hyperdefensiveness, spontaneous mouse killing, and freezing in rats

In a series of independent experiments, we showed that lesions of the vermis of the cerebellum in rats blocked the hyperdefensiveness induced by lesions of the ventromedial hypothalamus (VMH), attenuated spontaneous mouse killing, and reduced unconditioned freezing and other signs of fear in the presence of a cat. The vermal lesions did not significantly affect foot-shock conditioned freezing. Control lesions of the cerebellar hemispheres did not affect VMH lesion-induced hyperdefensiveness or freezing in the presence of a cat. The hemispheric lesions did attenuate foot-shock conditioned freezing. The data are discussed in terms of the striking similarities and differences between the behavioral effects of cerebellar vermal lesions and amygdala lesions and the interaction of a number of brain areas in modulating agonistic behaviors. The results leave no doubt that the medial cerebellum is significantly involved in the control of species-specific agonistic behaviors. The specific dimension of agonistic behaviors and the details of the interactions with other brain areas remain a puzzle which we approached here by expanding the behavioral profile of animals with lesions of the cerebellar vermis.

Defense reaction induced by microinjections of bicuculline into the inferior colliculus

Behavioral and autonomic effects of microinjections of bicuculline--a GABA receptor antagonist--into ventral aspects of the inferior colliculus (IC) produced a behavioral activation together with jumps. This activation was similar to escape behavior that has been induced from periventricular structures although it was neither as explosive as that observed from the dorsal periaqueductal gray matter (DPAG) nor as coordinated as that obtained from the medial hypothalamus (MH). In anesthetized rats, microinjection of bicuculline into the IC produced a clear rise in mean arterial blood pressure and in heart rate. These effects reached a maximum after 10 min and subsided within 20 min after injection. GABA receptor blockade in the IC of detelencephalated rats also resulted in escape behavior qualitatively similar to that observed in intact animals. These results suggest that in addition to the central gray and medial hypothalamus, GABA also exerts a tonic inhibitory action on neurons of the IC implicated in the generation or elaboration of aversive responses.

The propensity for schedule-induced polydipsia is related to differences in conditioned avoidance behaviour and in defense reactions in a defeat test

In line with previous research showing that animals predisposed to develop schedule-induced polydipsia when submitted to intermittent distribution of food show differential behavioural and neurochemical characteristics, the present experiments investigated the nature of defense reactions to aversive situations in rats that do or do not develop schedule-induced polydipsia. It was found that rats that engage in excessive drinking during intermittent feeding display more rapid active avoidance learning in a 2-way shuttle-box and show less freezing when confronted with an aggressive resident male in a defeat test than those that do not develop schedule-induced polydipsia. These results are consistent with the hypothesis that individual differences in the propensity to exhibit oral consummatory activities in conditions of mild stress are related to the ability to shift behavioural programmes in response to external stimulation.

Ethanol effects on female aggression vary with opponent size and time within session

Female rats displayed different patterns of attack to large and small male intruders into their home cages, as a function of ethanol dose levels. In confrontations with small male intruders, female attack increased significantly at 0.3 g/kg ethanol, declining to saline levels with higher doses (0.6 and 1.2 g/kg). Attack toward large intruders was (nonsignificantly) higher at 0.3 g/kg ethanol, and declined to significantly lower than saline levels with the higher ethanol doses. The attack increases seen with low ethanol doses came in the initial 5-min block of the 30 min test session, and did not persist. These findings suggest that low ethanol doses may especially increase overt aggression in situations in which the tendency to attack is only moderately inhibited by factors such as opponent size or the potential danger of retaliatory attack.

Aggressive behavior

This article considers the major fighting-related activities of the most common food animals. Instead of being seen as a largely pathologic phenomenon born solely of frustration and pain, aggressive behavior is now regarded as a natural part of an animal's behavioral equipment for survival and reproduction. There is a need, spurred by consideration for both productivity and animal well-being, to understand the fundamentals of the aggressive behavior of domestic species so that one can accommodate for this behavior in systems of livestock management.

Postpartum aggression in rats does not influence threshold currents for EBS-induced aggression

Female Wistar rats were tested for aggressive behaviour induced by electrical brain stimulation (EBS) in the lateral hypothalamus. Threshold currents for the induction of aggression were determined on several days before the females were paired with experienced breeder males. Beginning in the second week of pregnancy threshold current values were measured once or twice weekly. No change in thresholds was observed either during pregnancy, the early postpartum period or after weaning. Lactation was the only period during which the females were spontaneously aggressive towards male intruders in their home cage, but not in the EBS cage. Analysis of bite targets revealed no difference between the bite patterns in the postpartum maternal aggression test and the EBS-induced attacks. The results demonstrate that the change in physiological and hormonal status in pregnant and lactating females has no influence on the propensity to attack during EBS. The similarity in wound patterns does not advocate a major difference in the types of aggression studied. We speculate upon the nature of EBS-induced attacks as the activation of a rigid, final pathway of aggression which is rather insensitive to mild modulations.

Glutamate and picrotoxin injections into the preoptic basal forebrain initiate locomotion in the anesthetized rat

This study determined the locomotor effects of glutamate and picrotoxin injections and electrical stimulation in the preoptic basal forebrain. Male rats, anesthetized with Nembutal, were held in a stereotaxic apparatus such that stepping rotated a wheel. Cathodal stimulation (0.5-ms pulses, 50-Hz frequency, 10-s train, less than 100 microA) was applied through a 30-gauge stainless-steel, insulated cannula to find locomotor sites. Glutamate (20 mM or 2 M) or picrotoxin (100 or 200 ng) were injected in volumes of 0.2 or 0.1 microliter of saline at a rate of 1 microliter/5 min. Electrical stimulation elicited locomotion (principally hindlimbs) in 32 sites which included the lateral and medial preoptic areas and the bed nucleus of the stria terminalis (BST). Stimulation in 23 sites, most in the BST and septal area, failed to produce locomotion. Stepping was elicited by glutamate and electrical stimulation in 15 sites. Glutamate was ineffective at 21 sites, at 6 of these sites electrical stimulation was effective. Longer bouts of locomotion were produced by 20 nM glutamate. Picrotoxin produced more intense and prolonged locomotion than glutamate. It was effective in 15 sites, at 12 of which electrical stimulation was also effective. At some ventral sites, picrotoxin-elicited stepping was continuous, at others it appeared in bursts of 5-20 s duration. At dorsal sites, the locomotor bursts were punctuated by episodes of pelvic flexion. Picrotoxin was ineffective at 12 sites, 7 of which were effective with electrical stimulation. These results indicate that activity of neurons in the preoptic basal forebrain can initiate locomotion.

Evidence of Pavlovian conditioned fear following electrical stimulation of the periaqueductal grey in the rat

Stimulation of the periaqueductal grey (PAG) has been used to support aversive conditioning in a variety of species with several experimental paradigms. However, it has not been clearly demonstrated whether the behavioral changes produced by PAG stimulation in these paradigms are mediated by associative or nonassociative mechanisms. The present studies demonstrate that electrical stimulation of the PAG in the rat may be used to support associative learning in a Pavlovian paradigm. In each experiment, a fully controlled conditional emotional response (CER) procedure was used to examine the unconditional aversive properties of PAG stimulation. In Experiment 1a, weak associative conditioning was observed when a light CS was paired with PAG stimulation over 6 conditioning trials. In Experiment 1b, robust associative conditioning was obtained with a light CS when 18 conditioning trials were used. In Experiment 2, robust associative conditioning was demonstrated with a tone CS when 6 conditioning trials were used. The results parallel those found when other aversive stimuli are used as a UCS (e.g., footshock or intraorbital air puff), and because the present experiments included the proper control procedures the results clearly indicate that the behavioral changes produced by PAG stimulation are mediated by associative Pavlovian learning mechanisms rather than nonassociative mechanisms such as sensitization or pseudoconditioning. The present technique may be useful for assessing the neuroanatomical and neurochemical substrates underlying the aversive effects of brain-stimulation, and for screening the effects of drugs on the conditional and unconditional responses produced by such stimulation.

Experimental manipulations of eating: advances in animal models for studying anorectic agents

The material set out in this text has been designed to show the wide range of procedures which have the capacity to modify eating behavior--to produce hyper- or hypophagia, to alter the profile of eating patterns, or to adjust dietary preferences and selection. Accordingly, in investigating anorectic drugs it seems necessary to observe the effects of drug actions in a variety of experimental models. This strategy will provide a more complete description of the effect of a drug, will throw light on the mechanism of action, and will provide a more realistic base for predicting the effects of drugs in man.

A neuropharmacological study of the periventricular neural substrate involved in flight

This paper reviews results obtained in experiments concerning the neurochemical characteristics of the substrate involved in the control of flight reactions and the induction of aversive effects in the rat. These experiments investigated the behavioural effects produced by microinjecting into the periaqueductal grey matter (PAG) or the medial hypothalamus (MH) compounds known to interfere with the functioning of some neurotransmitter systems known to exist in these structures. The data obtained show that: the activity of the substrate involved in the production of flight reactions is tonically inhibited by the release of GABA (gamma-aminobutyric acid); the behavioural reactions produced by microinjecting GABA antagonists can be clearly distinguished, depending on whether such drugs were injected into the PAG or the MH, despite the fact that jumps were produced from either level; behavioural effects, comparable to some extent to those produced by microinjections of GABA antagonists, can be obtained by injecting drugs which act on non-GABAergic neurochemical substrates, namely opioidergic or cholinergic systems; and behavioural effects, comparable to those produced by injecting GABA antagonists into the PAG, can be obtained by injecting such drugs into various sites located in other parts of the tectum such as the inferior colliculus or adjacent structures.

Biological suicide research: outcome and limitations

Empirical study of suicide began early in this century from the sociological (Durkheim 1951) and psychological (Freud 1956) perspective. A decade ago, a biological dimension was added, focusing on two major issues, i.e., are disturbances in brain functioning instrumental in the occurrence of suicidal behavior and/or do such disturbances increase the likelihood of suicidal behavior in an individual exposed to stressful events? Biological suicide research has developed as an offshoot of biological depression research. This is a logical development, as depression is a major precursor of both attempted (Weissman et al. 1973; van Praag 1982a) and completed (Guze and Robins 1970; Miles 1977) suicide. The major biochemical research targets are similar: monoamines and hormones. This paper will review the main findings in suicidal behavior, discuss the methodological shortcomings of this research, and indicate ways of avoiding them.

Differential origin of brainstem serotoninergic projections to the midbrain periaqueductal gray and superior colliculus of the rat

Previous studies have shown that both the midbrain periaqueductal gray (PAG) and the superior colliculus receive a significant serotoninergic (5-HT) innervation. In the present study the origins of these 5-HT projections to the rodent PAG and superior colliculus were analyzed by using a combined immunohistochemical-retrograde transport technique. Thirteen brainstem regions were found to contain double-labelled 5-HT-like immunoreactive neurons following HRP injections into the PAG while only four brainstem nuclei contained double-labelled neurons following superior collicular injections. After HRP deposits into the ventral PAG, the largest percentage of double-labelled neurons was identified in nucleus raphe magnus, pars alpha of the nucleus gigantocellularis, and the paragigantocellular nucleus. The dorsal PAG, on the other hand, received the largest percentage of its 5-HT projections from nuclei raphe dorsalis, raphe obscurus, raphe pontis, and raphe medianis. The 5-HT input to the superior colliculus was found to arise exclusively from nuclei raphe dorsalis, raphe medianis, and raphe pontis and from the contralateral periaqueductal gray. Raphe nuclei were found to contribute serotoninergic projections to both the PAG and the superior colliculus while reticular nuclei contributed 5-HT projections only to the PAG. Injections of the fluorescent retrograde tracers true blue and nuclear yellow were then made into the PAG and superior colliculus to ascertain if neurons located in raphe nuclei that projected to both structures provided axon collaterals to both areas. Generally, less than 10% of raphe neurons projecting to the superior colliculus were identified as providing axon collaterals to the PAG. The present results demonstrate major quantitative and qualitative differences in the origin of 5-HT projections to the ventral PAG and superior colliculus. The origin of 5-HT input to the dorsal PAG, on the other hand, showed many similarities to the origin of 5-HT innervation of the superior colliculus. These data also indicate that approximately 35% of raphe neurons provide nonserotoninergic projections to the PAG and superior colliculus.

The role of anger in the consciousness development of peace activists: where physiology and history intersect

The focus of this paper concerns the role of anger in the development of consciousness in peace activists. By looking at this from 3 perspectives we can see an intersection of physiology and history. Looked at most closely, anger is a physiological event that recurs in the life of an individual. From a broader perspective, anger plays a critical role and a particular step in the development of consciousness. And from the broadest perspective, we may see how individual peace activists play a role in history by helping to resolve those contradictions (such as the present one between war and peace) by which history jerks its way forward. To put the proposition most carefully, it will be argued that anger is the personal fuel in the social motor that resolves the institutional contradictions that arise in the course of history. The materials on which this paper is based come from two sources. First is the study I have conducted in recent years on the development of consciousness in peace activists. Wishing to contribute my scientific skills to the peace movement, I have analyzed autobiographies of famous peace activists and oral histories of contemporary activists in Connecticut where I live. Since results from both the autobiographies and the oral histories are similar for present purposes, I will not make any distinction between them. The second source of material is the work that I and other researchers have conducted for many years on the brain mechanisms, behavioral complexities and evolutionary trends of aggressive behavior in rats, cats and monkeys. This material has been extensively published and is referred to in the bibliography (Adams, 1979, 1980).