Patterns of brain monoamine activity and aggressive behavior

Selective disruption of the recognition of facial expressions of anger

Appetitive aggression occurs in the context of resource/dominance disputes in a wide variety of species. Hence, the possibility arises that a specific neural system may have evolved to detect and coordinate responses to this specific form of challenge or threat. The dopamine system has been implicated in the processing of signals of aggression in social-agonistic encounters in several species. Here we report that dopaminergic antagonism in healthy male volunteers, following acute administration of the dopamine D2-class receptor antagonist sulpiride, leads to a selective disruption in the recognition of facial expressions of anger (signals of appetitive aggression in humans), but leaves intact recognition of other emotions and the matching of unfamiliar faces.

Effects of 8-OH-DPAT and fluoxetine on activity and attack by female mice towards lactating intruders

1. The impact of the serotoninergic receptor on the attack directed by female mice towards lactating intruders was assessed by studying the effects of 8-OH-DPAT (a serotoninergic agonist) and fluoxetine (an inhibitor of serotonin reuptake) on this paradigm at a range of doses and post-injection durations. 2. The specificity of these drug actions behaviour were examined by studying their effects on wheel running activity and performance in the open field. Non-sedative doses of 200 and 250 micrograms/kg of 8-OH-DPAT reduced attack by resident females on lactating intruders. 3. Higher doses (12-16 mg/kg) of fluoxetine reduced activity measures whereas lower non-sedative doses (up to 8 mg/kg) were without action on this aggression paradigm. 4. Additional studies with specific serotoninergic drugs are needed to clarify the role of this transmitter in attack by female mice on lactating intruders.

Biochemical and pharmacological evidence for central cholinergic regulation of shock-induced aggression in rats

Acetylcholinesterase (AChE) activity was estimated in brain and heart homogenates and plasma of 'aggressive' and 'nonaggressive' rats. Brain homogenates of 'nonaggressive' rats hydrolyzed significantly more substrate when compared to the 'aggressive' rats. Such differences were not seen in the heart homogenates or plasma of these two groups of rats. Acute DFP (0.1, 0.3 and 1.0 mg/kg) attenuated shock-induced aggression (SIA) 2 hr after treatment but facilitated SIA 24 hr and 48 hr after drug administration. Long-term DFP (0.3 mg/kg x 10 days), on the other hand, induced a significant enhancement in the SIA score, whereas atropine (1.0 and 5.0 mg/kg) produced a dose-related attenuation of the same. Pretreatment of rats with atropine (5 mg/kg) antagonized the long-term DFP-induced facilitation of SIA. These results are discussed in the light of an inhibitory central cholinergic mechanism in the regulation of SIA.

Magnesium alters the potency of cocaine and haloperidol on mouse aggression

Magnesium has been shown to have certain behavioral effects similar to the stimulants cocaine and amphetamine, particularly on mouse resident-intruder aggression. Consequently, it was hypothesized that magnesium should interact with the indirect agonist cocaine and the antagonist haloperidol to alter their potency in the mouse resident-intruder model. Acute and chronic drug effects were compared. Results demonstrate an enhancement of cocaine potency by 30 and 125 mg/kg MgCl2 and a lowering of cocaine potency by a 15% required-Mg2+ deficient diet as measured by shifts in the dose response to acutely administered cocaine. Following chronic 0.5 mg/kg cocaine for 15 days, a dose of 125 mg/kg acutely administered MgCl2 prevented the disruptive effects of chronic cocaine on mouse aggression. Acutely administered haloperidol was influenced by Mg2+ treatments in a manner opposite from the effects on cocaine, while the chronic effects of haloperidol were affected in the same manner by Mg2+ treatments as those shown for chronic cocaine. Several mechanisms are suggested to explain these interactions.

Social, motor, and autonomic signs of morphine withdrawal: differential sensitivities to catecholaminergic drugs in mice

Drugs that predominantly influence catecholamines were used in order to simultaneously determine their ability to alter salient signs of social, motor and autonomic activity during morphine withdrawal, and to compare the sensitivity of each of these signs to these drugs. Cocaine, d-amphetamine, apomorphine and L-dopa increased attack and threat, but did not induce defensive behavior in morphine-withdrawn resident mice who were more responsive to the aggression-enhancing effects of these drugs than placebo control mice. Concurrently measured withdrawal jumping was not affected by these drugs, and the sensitivity to the hypothermic effects of these drugs was reduced. In contrast, clonidine decreased attack and threat behaviors, and morphine-withdrawn mice were more sensitive to this inhibitory influence. But like the stimulant drugs, clonidine did not affect withdrawal jumping, and the hypothermic action of clonidine was attenuated in morphine-withdrawn mice. These findings show that in mice, opiate withdrawal leads to altered attack and threat that is further amplified by catecholaminergic drugs. The present pattern of results indicates differential drug effects on social, motor and autonomic functions when the behaviors are measured 48 h following withdrawal.

The effects of phencyclidine on fighting in differentially housed mice

The effects of phencyclidine (PCP) on the fighting of individually housed male mice were examined (1) after different lengths (5-35 days) of individual housing, and (2) in mice of different ages (35, 70 or 170 days old) at the onset of individual housing. Significant increases in the total time spent fighting in a 10-minute aggression test were observed at 19-21 and 32-35 days of individual housing with 1.25 mg/kg PCP and at 10 and 32-35 days with 2.50 mg/kg PCP. Relative to control groups, the percentage of mice fighting after 19-21 and 32-35 days of individual housing was significantly decreased with 2.5 mg/kg. At 1.25 mg/kg, PCP increased total fighting time and decreased the latency to the first fight in mice at 35 or 70, but not 170 days of age at the onset of individual housing. No increases in motor activity in individually housed mice were recorded at these doses. These results suggest that PCP may facilitate fighting in mice when individually housed for a minimum of 10 days.

Involvement of brain transmitters in the modulation of shock-induced aggression in rats by propranolol and related drugs

(+/-)Propranolol (1, 3, 10 and 30 mg/kg) exhibited a differential effect on footshock aggression (FSA) in rats. Lower doses (1 and 3 mg/kg) of the drug facilitated FSA, whereas an inhibitory effect was observed with higher doses (10 and 30 mg/kg) of the same. (+)Propranolol (30 mg/kg) and UM-272 (1 and 10 mg/kg) as well as physostigmine (0.1 and 0.5 mg/kg) all produced inhibition of FSA. Similar FSA inhibitory effects were also observed with salbutamol (1 and 5 mg/kg). Pretreatment with atropine and not methylatropine attenuated the anti-aggressive effect of (+/-)propranolol (10 mg/kg) without appreciably altering the facilitatory effect (1 mg/kg) of the drug on FSA. In addition, at the anti-aggressive doses, (+/-)propranolol (10 mg/kg) and UM-272 (10 mg/kg), significantly inhibited brain cholinesterase enzyme activity when compared to saline controls. (+/-)Propranolol (10 mg/kg) also inhibited significantly the aggression induced by reserpine-apomorphine treatment. It is inferred that a central cholinergic and dopaminergic mechanism is involved in the anti-aggressive effect of (+/-)propranolol, whereas the low dose induced facilitation of affective aggression could be attributed to central beta-adrenoceptor blockade.

Catecholamines and aggression in animals

This paper assesses the evidence for the role of catecholamines in the aggressive behaviour of animals. The effects of manipulating dopamine and noradrenaline function, either alone or in combination, are considered with respect to two categories of aggression, predatory and affective. Affective aggression is further subdivided into shock-induced defensive fighting, isolation-induced aggression and irritable aggression. The results indicate that catecholamines may not have a specific role in aggressive behaviour. Rather, they may act more to excite or inhibit general behavioural systems, although certain treatments do have a specific influence on aggressive behaviour. The review also highlights certain problems concerning the psychopharmacology of aggression; different species may make varying responses to the same treatment, whilst treatments exerting a similar pharmacological action may result in diverse behavioural effects.

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.

Benzodiazepines and their antagonists: a pharmacoethological analysis with particular reference to effects on "aggression"

A review of the literature on chlordiazepoxide indicates that the traditional view of benzodiazepines as antiaggressive drugs represents an inaccurate generalization. In fact, highly variable findings have been reported with the most significant factor in the variability being the type of aggression studied. Furthermore, considerable controversy surrounds the nature of chlordiazepoxide's influence on social conflict in rodents, with opinion divided regarding the selectivity of its inhibitory effect on offensive responding. It is argued that inappropriate behavioural methodology may have substantially contributed to this controversy. A pharmacoethological approach to the analysis of drug effects on social behaviour is described and exemplified by new data on chlordiazepoxide and midazolam. Both agents inhibit offense at doses which do not result in general response inhibition, yet their overall behavioural profiles are somewhat different. Evidence is also presented indicating low dose behavioural activity of the benzodiazepine antagonist Ro15-1788 in two test situations and suggesting possible differences in the effects of Ro15-1788 and CGS8216 on novelty-related responding. Several avenues of research are discussed which may yield insights into the manner whereby benzodiazepines influence social patterns and the significance of benzodiazepine-GABA interactions in such processes.

Behavioral responses to apomorphine and amphetamine in differentially housed mice

The climbing response to apomorphine (AP, 0.075-3.0 mg/kg) and the motor activity response to amphetamine (AMP, 0,3-5.0 mg/kg) were determined in grouped or socially isolated mice. After 4 weeks of differential housing commencing at 5 weeks of age, the individually housed mice showed an increased response only to low doses of these drugs. The responses of the group-housed mice at 5 or 9 weeks of age were identical, ruling out an aging component to the differential responsiveness. Also, the response of separate groups of naive mice to acute treatments of saline, AP (0.15 and 3.0 mg/kg), and AMP (0.3 and 5.0 mg/kg) was examined at 1, 2, 3, and 4 weeks of differential housing. With respect to age-matched group-housed mice, a significantly greater climbing response to AP (0.15 mg/kg) and a significantly greater locomotor activity response to AMP (0.3 mg/kg) were seen after 1 and 3 weeks of individual housing. There were no significant differences in the behavioral responses to the higher doses of AP and AMP.

Molecular mechanisms of neuroendocrine integration in the central nervous system: an approach through the study of the pineal gland and its innervating sympathetic pathway

In the brain specialized cells known as 'neuroendocrine transducers' translate an input of neural activity into a hormonal output, e.g. oxytocin released into the blood stream. Other, more typical neurons make the reverse conversion constituting chemoreceptors which transform the hormonal 'language' into changes in their firing rate ('endocrine-neural' transduction). 'Endocrine-endocrine' transducing events occur at the level of the neurosecretory cells that translate a hormonal signal into another, different, hormone output. This article reviews the molecular aspects of several neuroendocrine integrative processes in the hypothalamus, the pineal gland and the cervical sympathetic pathway. The discussed results indicate that the pineal gland and its innervating sympathetic neurons located in the superior cervical ganglia constitute an easy-to-manipulate model system for the study of basic neuroendocrine mechanisms because: (i) receptors for various hormones exist in the mammalian pineal and sympathetic ganglia; (ii) the pattern of pineal steroid metabolism resembles that of the neuroendocrine hypothalamus; (iii) pineal estrophilic and androphilic receptors as well as the pattern of steroid metabolism are modulated by the sympathetic nerves; (iv) neuronal activity in the cervical sympathetic pathway is modified by hormone treatment at preganglionic, ganglionic and postganglionic sites.

p-Chlorophenylalanine effects on shock-induced attack and pressing responses in rats

The literature concerning the effects of d,1-parachlorophenylalanine (PCPA) upon shock-induced aggression (SIA) was examined and found to be inconsistent. PCPA, a known serotonin depletor, has behavioral effects in a variety of other procedures which collectively suggest that PCPA should produce SIA enhancement. The present study analyzed PCPA (300 mg/kg, IP) effects upon SIA in rats restrained spatially close to an inanimate target and panel operandum. The results showed marked increases in both aggressive biting and panel-pressing for several days following each PCPA treatment, for each subject tested. These data were interpreted to indicate that serotonin depletion by PCPA does indeed enhance SIA but that this effect is not selective for aggression. Potential controlling variables are suggested to account for reports of no effect on SIA after PCPA treatment. It is concluded that procedural variables may be the critical determinants of variation in reported PCPA-aggression effects across studies, rather that hypothesized differences in neurochemical mediators.

Neurotransmitter modulation of steroid action in target cells that mediate reproduction and reproductive behavior

Two major functional interactions between steroid hormones and neurotransmitters are generally recognized. First, steroids affect neurotransmission, and second, through effects on hypothalamic peptides that regulate anterior pituitary function neurotransmitters affect steroid secretion. In recent years, evidence has accumulated which indicates that neurotransmitters can also affect steroid action within postsynaptic steroid target cells. We review evidence for this relationship in pineal, uterus and hypothalamus and propose that the modulation of target cell responsiveness to steroids is an important mechanism by which neurotransmitters affect steroid-dependent processes. The operation of such a mechanism provides a means for environmental, behavioral and emotional events to rapidly and selectively alter steroid effects on behavior and physiology.

Effect of histaminergic drugs on footshock-induced aggressive behaviour in rats

Histamine and 2-pyridylethylamine decreased and 4-methylhistamine increased footshock-induced aggression after their intracerebroventricular administration to rats. Mepyramine and cimetidine had no effect on the fighting response but blocked the effects of the respective agonists. Histamine when given after mepyramine increased and after cimetidine decreased the fighting score, this decrease being more than that with histamine alone. It is inferred that central H1-receptors are inhibitory and H2-receptors facilitatory in footshock aggression and that this is independent of catecholaminergic mechanisms.

Selective inhibition by nicotine of shock-induced fighting in the rat

The frequency of shock-induced fighting, posturing and "no reaction" (running/jumping or freezing), after acute SC injections of 0, 0.1, 0.2 and 0.4 mg/kg nicotine, was measured in 38 pairs of male and 12 pairs of female rats. Sensitivity to footshock was also measured, at the same nicotine doses, in males. Nicotine inhibited shock-induced fighting in 32 pairs of high-frequency fighting males in a dose-dependent fashion, with fighting being gradually replaced by posturing at the 0.1 and 0.2 mg/kg doses. There was a significant increase in the "no reaction" category (especially freezing behavior) only at 0.4 mg/kg, indicating that reduced activity may have been partly responsible for the reduction in fighting seen at that dose. None of the doses had a significant effect on sensitivity to footshock. Nicotine had no effect on shock-induced fighting in the six low-frequency fighting male pairs, and affected the female pairs only at the 0.4 mg/kg level, where fighting was also decreased due to an increase in the "no reaction" category. It could be concluded that small doses of nicotine, under favorable conditions, were capable of inhibiting shock-induced fighting in rats without altering shock sensitivity or depressing activity.

Selective anti-aggressive properties of DU 27725: ethological analyses of intermale and territorial aggression in the male rat

The effects of a new anti-aggressive compound, DU 27725, were evaluated in intermale and territorial aggression. Ethological analysis of intermale aggression showed that DU 27725 (1 to 8 mg/kg IP) strongly decreased aggression, while introductory social behaviour was unaffected or enhanced. The offensive character of aggression disappeared and was replaced by a more defensive pattern. No drastic changes occurred in non-social activities. Sedation, muscle relaxation and motor impairment did not occur at any of the doses tested, suggesting that the anti-aggressive effects were not caused by nonspecific actions of the drug. In territorial aggression, DU 27725 (4 and 8 mg/kg IP) also decreased all aspects of aggression; introductory social behaviour was slightly decreased, and defensive behaviour remained unaffected. At the highest dose (8 mg/kg) sedation was observed. DU 27725 reduced both the number of ultrasonic vocalizations and the number of bites inflicted upon the partners.

Isolation induced aggression and catecholamine variations in discrete brain areas of the mouse

Norepinephrine (NE) and dopamine (DA) levels and turnover were measured in 17 discrete brain regions of Swiss-Webster (NIH) mice made aggressive by prolonged isolation. The NE steady state level was significantly lower in olfactory tubercle and substantia nigra and significantly higher in the septal area of the aggressive mice when compared to the isolated non-fighter controls. NE turnover was only higher in the A-10 region of the aggressors. DA steady state level and turnover was lower in olfactory tubercle and higher in caudate putamen of the aggressors. The significance of these changes in isolation-induced aggression is discussed.