5-HT(1B) receptor inhibition of alcohol-heightened aggression in mice: comparison to drinking and running

Responses and functions of dopamine in nucleus accumbens core during social behaviors

Social behaviors are among the most important motivated behaviors. How dopamine (DA), a "reward" signal, releases during social behaviors has been a topic of interest for decades. Here, we use a genetically encoded DA sensor, GRABDA2m, to record DA activity in the nucleus accumbens (NAc) core during various social behaviors in male and female mice. We find that DA releases during approach, investigation and consummation phases of social behaviors signal animals' motivation, familiarity of the social target, and valence of the experience, respectively. Positive and negative social experiences evoke opposite DA patterns. Furthermore, DA releases during mating and fighting are sexually dimorphic with a higher level in males than in females. At the functional level, increasing DA in NAc enhances social interest toward a familiar conspecific and alleviates defeat-induced social avoidance. Altogether, our results reveal complex information encoded by NAc DA activity during social behaviors and their multistage functional roles.

The Implication of 5-HT Receptor Family Members in Aggression, Depression and Suicide: Similarity and Difference

Being different multifactorial forms of psychopathology, aggression, depression and suicidal behavior, which is considered to be violent aggression directed against the self, have principal neurobiological links: preclinical and clinical evidence associates depression, aggression and suicidal behavior with dysregulation in central serotonergic (5-HT) neurotransmission. The implication of different types of 5-HT receptors in the genetic and epigenetic mechanisms of aggression, depression and suicidality has been well recognized. In this review, we consider and compare the orchestra of 5-HT receptors involved in these severe psychopathologies. Specifically, it concentrates on the role of 5-HT_1A, 5-HT_1B, 5-HT_2A, 5-HT_2B, 5-HT_2C, 5-HT₃ and 5-HT₇ receptors in the mechanisms underlying the predisposition to aggression, depression and suicidal behavior. The review provides converging lines of evidence that: (1) depression-related 5-HT receptors include those receptors with pro-depressive properties (5-HT_2A, 5-HT₃ and 5-HT₇) as well as those providing an antidepressant effect (5-HT_1A, 5-HT_1B, 5-HT_2C subtypes). (2) Aggression-related 5-HT receptors are identical to depression-related 5-HT receptors with the exception of 5-HT₇ receptors. Activation of 5-HT_1A, 5-HT_1B, 5-HT_2A, 5-HT_2C receptors attenuate aggressiveness, whereas agonists of 5-HT₃ intensify aggressive behavior.

Evolution of stress responses refine mechanisms of social rank

Social rank functions to facilitate coping responses to socially stressful situations and conditions. The evolution of social status appears to be inseparably connected to the evolution of stress. Stress, aggression, reward, and decision-making neurocircuitries overlap and interact to produce status-linked relationships, which are common among both male and female populations. Behavioral consequences stemming from social status and rank relationships are molded by aggressive interactions, which are inherently stressful. It seems likely that the balance of regulatory elements in pro- and anti-stress neurocircuitries results in rapid but brief stress responses that are advantageous to social dominance. These systems further produce, in coordination with reward and aggression circuitries, rapid adaptive responding during opportunities that arise to acquire food, mates, perch sites, territorial space, shelter and other resources. Rapid acquisition of resources and aggressive postures produces dominant individuals, who temporarily have distinct fitness advantages. For these reasons also, change in social status can occur rapidly. Social subordination results in slower and more chronic neural and endocrine reactions, a suite of unique defensive behaviors, and an increased propensity for anxious and depressive behavior and affect. These two behavioral phenotypes are but distinct ends of a spectrum, however, they may give us insights into the troubling mechanisms underlying the myriad of stress-related disorders to which they appear to be evolutionarily linked.

Fighting Females: Neural and Behavioral Consequences of Social Defeat Stress in Female Mice

BACKGROUND

Despite the twofold higher prevalence of major depressive and posttraumatic stress disorders in women compared with men, most clinical and preclinical studies have focused on male subjects. We used an ethological murine model to study several cardinal symptoms of affective disorders in the female targets of female aggression.

METHODS

Intact Swiss Webster (CFW) female resident mice were housed with castrated male mice and tested for aggression toward female intruders. For 10 days, aggressive CFW female residents defeated C57BL/6J (B6) female intruders during 5-minute encounters. Measures of corticosterone, c-Fos activation in hypothalamic and limbic structures, and species-typical behaviors were collected from defeated and control females. Ketamine (20 mg/kg) was tested for its potential to reverse stress-induced social deficits.

RESULTS

Housed with a castrated male mouse, most intact resident CFW females readily attacked unfamiliar B6 female intruders, inflicting >40 bites in a 5-minute encounter. Compared with controls, defeated B6 females exhibited elevated plasma corticosterone and increased c-Fos activation in the medial amygdala, ventral lateral septum, ventromedial hypothalamus, and hypothalamic paraventricular nucleus. Chronically defeated females also showed vigilance-like behavior and deficits in social interactions, novel object investigation, and nesting. The duration of social interactions increased 24 hours after chronically defeated female mice received a systemic dose of ketamine.

CONCLUSIONS

These findings demonstrate that CFW female mice living with male conspecifics can be used as aggressive residents in an ethological model of female social defeat stress. These novel behavioral methods will encourage further studies of sex-specific neural, physiological, and behavioral adaptations to chronic stress and the biological bases for interfemale aggression.

There is no association between rs6296 and alcoholism: a meta-analysis

Previous studies have reported controversial results about the association between rs6296 and alcoholism. Thus, a meta-analysis was performed to further explore this association. A comprehensive search was conducted to identify relevant case-control or cohort studies (up to December 1, 2017). A fixed- or random-effect model was selected as a pooling method depending on the heterogeneity among studies. The heterogeneity was measured by Q test and I² statistic. The Harbord and Peters test was used to estimate publication bias. Fifteen English articles with 16 outcomes and 5,429 participants were included in this meta-analysis. A fixed-effect model was chosen, and the pooled result showed that rs6296 was not related to alcoholism (z = 1.93, p = .053). The Harbord and Peters test showed that there was no publication bias. This meta-analysis indicated that rs6296 may be not be significantly associated with alcoholism, which needs to be further confirmed by future research.

Animal Models of (or for) Aggression Reward, Addiction, and Relapse: Behavior and Circuits

Inappropriate and pathological aggression plays a leading role in the suffering and death of millions of people, and further places an untenable strain on the caregivers and families of those afflicted. In some cases, such as addictive drugs, aggression can be highly rewarding (appetitive) and continually pursued despite short- and long-term negative consequences. Similarly, recidivism (relapse) rates for repeat violent offenders are as high as relapse rates for drug addicts. Appetitive aggression and relapse to aggression seeking can be modeled in mice studies using conditioned place preference and self-administration procedures followed by a period of abstinence and subsequent tests for relapse to aggression preference and aggression seeking. These procedures allow for the study of the mechanisms that control the appetitive versus the consummatory (attack) phases of aggressive behavior. In this review, we first discuss the behavioral procedures developed to probe appetitive aggression in mouse models, spanning from Pavlovian to operant tasks, and we also describe the recently proposed phenomenon of "aggression addiction." Next, we discuss the pharmacological and circuit mechanisms of aggression conditioned place preference and aggression self-administration, seeking, and relapse, highlighting mechanistic congruence and divergence between appetitive and consummatory phases of aggression. We conclude by discussing clinical implications of the studies reviewed.

The association between HTR1B gene rs13212041 polymorphism and onset of alcohol abuse

BACKGROUND

Alcohol dependence displays a wide variety of clinical phenotypes. Various typology classifications of alcoholism include age of onset of alcohol abuse as one of the major phenotypic features. Serotonergic changes have been associated with alcoholism, while serotonin receptors type 1B (5-HT1B) play an important role in regulating serotonergic neurotransmission. The rs13212041 polymorphism modulates the expression of HTR1B gene coding for 5-HT1B receptor. This study examined the association of platelet serotonin (5-HT) and HTR1B gene with the onset of alcohol abuse in alcohol-dependent subjects.

MATERIALS AND METHODS

Determination of platelet 5-HT concentration and genotyping of rs13212041 HTR1B gene polymorphism were performed in 613 alcohol-dependent patients, subdivided according to early/late onset (before/after 25 years of age) of alcohol abuse.

RESULTS

Alcohol-dependent individuals with CC genotype were more frequent in the group with early onset of alcohol abuse compared to carriers of T allele. Besides HTR1B genotype, age and gender, but not platelet 5-HT, were major variables associated with the onset of alcohol abuse. Platelet 5-HT concentration was not significantly different between patients with early and late onset of alcohol abuse, or patients carrying various HTR1B genotypes. Although we observed no influence of co-variables such as age, gender, or somatic and psychiatric comorbidities, platelet 5-HT concentration was significantly affected by smoking.

CONCLUSION

These findings support potential involvement of 5-HT1B receptors in the onset of alcohol abuse and development of alcohol dependence. Additionally, the results of our study emphasize the importance of controlling for smoking status, as one of the significant confounding factors influencing platelet 5-HT concentration.

The Urge to Fight: Persistent Escalation by Alcohol and Role of NMDA Receptors in Mice

Alcohol drinking, in some individuals, culminates in pathologically aggressive and violent behaviors. Alcohol can escalate the urge to fight, despite causing disruptions in fighting performance. When orally administered under several dosing conditions the current study examined in a mouse model if repeated alcohol escalates the motivation to fight, the execution of fighting performance, or both. Specifically, seven daily administrations of alcohol (0, 1.8, or 2.2 g/kg) determined if changes in the motivation to initiate aggressive acts occur with, or without, shifts in the severity of fighting behavior. Responding under the control of a fixed interval (FI) schedule for aggression reinforcements across the initial daily sessions indicated the development of tolerance to alcohol's sedative effect. By day 7, alcohol augmented FI response rates for aggression rewards. While alcohol escalated the motivation to fight, fighting performance remained suppressed across the entire 7 days. Augmented FI responding for aggression rewards in response to a low dose of alcohol (1.0 g/kg) proved to be persistent, as we observed sensitized rates of responding for more than a month after alcohol pretreatment. In addition, this sensitization of motivated aggression did not occur with a general enhancement of motor activity. Antagonism of NMDA or AMPA receptors with ketamine, dizocilpine, or NBQX during later challenges with alcohol were largely serenic without having any notable impact on the expression of alcohol-escalated rates of FI responding. The current dissociation of appetitive and performance measures indicates that discrete neural mechanisms controlling aggressive arousal can be distinctly sensitized by alcohol.

Oxytocin for the treatment of drug and alcohol use disorders

There is growing interest in the use of oxytocin (OT) as a potential treatment for alcohol and other substance-use disorders. OT is a neuropeptide that modulates adaptive processes associated with addiction including reward, tolerance, associative learning, memory, and stress responses. OT exerts its effects through interactions with the hypothalamic-pituitary-adrenal axis and multiple neurotransmitter systems including the dopamine mesolimbic reward and corticotrophin-releasing factor stress systems. The effects of OT on stress systems are of high interest, given the strong link between stress, drug use and relapse, and known dysregulation of hypothalamic-pituitary-adrenal-axis activity associated with substance-use disorders. At the same time, the OT system is itself altered by acute or chronic drug exposure. This review summarizes the preclinical and clinical literature on the OT system and its relevance to drug and alcohol addiction. In addition, findings from recent clinical trials conducted in participants with cocaine, cannabis, or alcohol use disorder are included and evidence that OT may help to normalize blunted stress responses, and attenuate withdrawal-associated hypercortisolism, negative mood, and withdrawal symptoms is summarized.

Effects of a 5-HT1B Receptor Agonist on Locomotion and Reinstatement of Cocaine-Conditioned Place Preference after Abstinence from Repeated Injections in Mice

5-HT_1B receptors (5-HT_1BRs) modulate behavioral effects of cocaine. Here we examined the effects of the 5-HT_1BR agonist 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-pyrrolo[3,2-b]pyridine (CP94253) on spontaneous and cocaine-induced locomotion and on cocaine-primed reinstatement of conditioned place preference (CPP) in male mice given daily repeated injections of either saline or cocaine (15 mg/kg, IP) for 20 days. In the locomotor activity experiment, testing occurred both 1 and 20 days after the final injection. In the CPP experiment, mice underwent conditioning procedures while receiving the last of their daily injections, which were given either during or ≥2 h after CPP procedures. The CPP procedural timeline consisted of baseline preference testing (days 12–13 of the chronic regimen), conditioning (days 14–19, 2 daily 30-min sessions separated by 5 h), CPP test (day 21), extinction (days 22–34; no injections), CPP extinction test (day 35), and reinstatement test (day 36). Mice that had not extinguished received additional extinction sessions prior to reinstatement testing on day 42. On test days, mice were pretreated with either saline or CP94253 (10 mg/kg, IP). Testing began 30 min later, immediately after mice were primed with either saline or cocaine (5 mg/kg for locomotion; 15 mg/kg for reinstatement). We found that CP94253 increased spontaneous locomotion in mice receiving repeated injections of either saline or cocaine when tested 1 day after the last injection, but had no effect on spontaneous locomotion after 20 days abstinence from repeated injections. Surprisingly, cocaine-induced locomotion was sensitized regardless of whether the mice had received repeated saline or cocaine. CP94253 attenuated expression of the sensitized locomotion after 20 days abstinence. A control experiment in noninjected, drug-naïve mice showed that CP94253 had no effect on spontaneous or cocaine-induced locomotion. Mice reinstated cocaine-CPP when given a cocaine prime, and CP94253 pretreatment attenuated cocaine reinstatement.The findings suggest that stress from repeated saline injections and/or co-housing with cocaine-injected mice may cross-sensitize with cocaine effects on locomotion and that CP94253 attenuates these effects, as well as reinstatement of cocaine-CPP. This study supports the idea that 5-HT_1BR agonists may be useful anti-cocaine medications.

Alcohol and violence: neuropeptidergic modulation of monoamine systems

Neurobiological processes underlying the epidemiologically established link between alcohol and several types of social, aggressive, and violent behavior remain poorly understood. Acute low doses of alcohol, as well as withdrawal from long-term alcohol use, may lead to escalated aggressive behavior in a subset of individuals. An urgent task will be to disentangle the host of interacting genetic and environmental risk factors in individuals who are predisposed to engage in escalated aggressive behavior. The modulation of 5-hydroxytryptamine impulse flow by gamma-aminobutyric acid (GABA) and glutamate, acting via distinct ionotropic and metabotropic receptor subtypes in the dorsal raphe nucleus during alcohol consumption, is of critical significance in the suppression and escalation of aggressive behavior. In anticipation and reaction to aggressive behavior, neuropeptides such as corticotropin-releasing factor, neuropeptide Y, opioid peptides, and vasopressin interact with monoamines, GABA, and glutamate to attenuate and amplify aggressive behavior in alcohol-consuming individuals. These neuromodulators represent novel molecular targets for intervention that await clinical validation. Intermittent episodes of brief social defeat during aggressive confrontations are sufficient to cause long-lasting neuroadaptations that can lead to the escalation of alcohol consumption.

The neurobiology of aggression and violence

Aggression and violence represent a significant public health concern and a clinical challenge for the mental healthcare provider. A great deal has been revealed regarding the neurobiology of violence and aggression, and an integration of this body of knowledge will ultimately serve to advance clinical diagnostics and therapeutic interventions. We will review here the latest findings regarding the neurobiology of aggression and violence. First, we will introduce the construct of aggression, with a focus on issues related to its heterogeneity, as well as the importance of refining the aggression phenotype in order to reduce pathophysiologic variability. Next we will examine the neuroanatomy of aggression and violence, focusing on regional volumes, functional studies, and interregional connectivity. Significant emphasis will be on the amygdala, as well as amygdala-frontal circuitry. Then we will turn our attention to the neurochemistry and molecular genetics of aggression and violence, examining the extensive findings on the serotonergic system, as well as the growing literature on the dopaminergic and vasopressinergic systems. We will also address the contribution of steroid hormones, namely, cortisol and testosterone. Finally, we will summarize these findings with a focus on reconciling inconsistencies and potential clinical implications; and, then we will suggest areas of focus for future directions in the field.

Escalated Aggression in Animal Models: Shedding New Light on Mesocorticolimbic Circuits

Recent developments promise to significantly advance the understudied behavioral and neurobiology of aggression: (1) Animal models that capture essential features of human violence and callousness have been developed. These models range from mice that have been selectively bred for short attack latencies, monogamous prairie voles, and glucocorticoid-compromised rats to rodents and non-human primates that escalate their aggression after consuming or when withdrawing from alcohol. (2) Optogenetic stimulation and viral vector-based approaches have begun to identify overlapping and distinctive neural microcircuits and intracellular molecules for adaptive vs. excessive, maladaptive aggressive behavior in several rodent models. Projections from hypothalamic and mesencephalic neurons to the medial prefrontal cortex contain microcircuits that appear pivotal for the escalation of aggression.

Translational clinical neuroscience perspectives on the cognitive and neurobiological mechanisms underlying alcohol-related aggression

Alcohol-related violence, a longstanding, serious, and pervasive social problem, has provided researchers from diverse disciplines with a model to study individual differences in aggressive and violent behavior. Of course, not all alcohol consumers will become aggressive after drinking and similarly, not all individuals with alcohol use disorders will exhibit such untoward behavior. Rather, the relationship is best conceptualized as complex and indirect and is influenced by a constellation of social, cognitive, and biological factors that differ greatly from one person to the next. Animal experiments and human studies have elucidated how these mechanisms and processes explain (i.e., mediate) the relation between acute and chronic alcohol consumption and aggressive behavior. Further, the rich body of literature on alcohol-related aggression has allowed for identification of several potential high-yield targets for clinical intervention, e.g., cognitive training for executive dysfunction; psychopharmacology targeting affect and threat perception, which may also generalize to other psychiatric conditions characterized by aggressive behavior. Here we aim to integrate pertinent findings, derived from different methodological approaches and theoretical models, which explain heterogeneity in aggressive responses to alcohol. A translational platform is provided, highlighting common factors linking alcohol and aggression that warrant further, interdisciplinary study in order to reduce the devastating social impact of this phenomenon.

Anabolic-androgenic steroids and appetitive sexual behavior in male rats

Anabolic-androgenic steroids (AAS) increase libido and sexual behavior, but the underlying behavioral mechanisms are unclear. One way AAS may enhance expression of sexual behavior is by increasing the willingness to work for sex. In the present study, sexually-experienced male rats received daily injections of testosterone at supraphysiologic doses (7.5 mg/kg in water with 13% cyclodextrin) or vehicle and were tested for appetitive sexual behavior measured by operant responding for access to an estrous female. Initially, rats were trained in their home cage to respond on a nose-poke under a 10-min fixed-interval schedule for food reward. Once rats achieved stable response rates, the food was replaced by a female, followed by mating for 10 min. There was no effect of testosterone on operant responding for food (28.1 ± 4.4 responses/10 min for testosterone, 30.6 ± 4.3 for vehicle) or sex (35.0 ± 4.0 responses/10 min for testosterone, 37.3 ± 5.2 for vehicle). However, rats made significantly more responses for sex than for food (p < 0.05), and responses for food and sex were positively correlated among individuals (R(2) = 0.6). Additional groups of rats were trained to respond on a lever for the female under a 2nd-order schedule of reinforcement, where 5 responses opened a door to show the female for 5s. After 15 door openings, the male gained access to the female. There was no effect of testosterone on time to complete 75 responses: 38.4 ± 7.8 min for vehicle controls vs 43.3 ± 6.6 min for testosterone-treated rats (p > 0.05). These findings suggest that chronic high-dose testosterone does not enhance appetitive drive for sexual behavior.

'Roid rage in rats? Testosterone effects on aggressive motivation, impulsivity and tyrosine hydroxylase

In humans and animals, anabolic-androgenic steroids (AAS) increase aggression, but the underlying behavioral mechanisms are unclear. AAS may increase the motivation to fight. Alternatively, AAS may increase impulsive behavior, consistent with the popular image of 'roid rage. To test this, adolescent male rats were treated chronically with testosterone (7.5mg/kg) or vehicle and tested for aggressive motivation and impulsivity. Rats were trained to respond on a nose-poke on a 10 min fixed-interval schedule for the opportunity to fight in their home cage with an unfamiliar rat. Although testosterone increased aggression (6.3±1.3 fights/5 min vs 2.4±0.8 for controls, p<0.05), there was no difference in operant responding (28.4±1.6 nose-pokes/10 min for testosterone, 32.4±7.0 for vehicle). This suggests that testosterone does not enhance motivation for aggression. To test for impulsivity, rats were trained to respond for food in a delay-discounting procedure. In an operant chamber, one lever delivered one food pellet immediately, the other lever gave 4 pellets after a delay (0, 15, 30 or 45 s). In testosterone- and vehicle-treated rats, body weights and food intake did not differ. However, testosterone-treated rats chose the larger, delayed reward more often (4.5±0.7 times in 10 trials with 45 s delay) than vehicle controls (2.5±0.5 times, p<0.05), consistent with a reduction in impulsive choice. Thus, although chronic high-dose testosterone enhances aggression, this does not include an increase in impulsive behavior or motivation to fight. This is further supported by measurement of tyrosine hydroxylase (TH) by Western immunoblot analysis in brain regions important for motivation (nucleus accumbens, Acb) and executive function (medial prefrontal cortex, PFC). There were no differences in TH between testosterone- and vehicle-treated rats in Acb or PFC. However, testosterone significantly reduced TH (to 76.9±3.1% of controls, p<0.05) in the caudate-putamen, a brain area important for behavioral inhibition, motor control and habit learning.

Infralimbic and dorsal raphé microinjection of the 5-HT(1B) receptor agonist CP-93,129: attenuation of aggressive behavior in CFW male mice

RATIONALE

Aggressive behavior and impaired impulse control have been associated with dysregulations in the serotonergic system and with impaired functioning of the prefrontal cortex. 5-HT(1B) receptors have been shown to specifically modulate several types of offensive aggression.

OBJECTIVE

This study aims to characterize the relative importance of two populations of 5-HT(1B) receptors in the dorsal raphé nucleus (DRN) and infralimbic cortex (ILC) in the modulation of aggressive behavior.

METHODS

Male CFW mice were conditioned on a fixed-ratio 5 schedule of reinforcement to self-administer a 6% (w/v) alcohol solution. Mice repeatedly engaged in 5-min aggressive confrontations until aggressive behavior stabilized. Next, a cannula was implanted into either the DRN or the ILC. After recovery, mice were tested for aggression after self-administration of either 1.0 g/kg alcohol or water prior to a microinjection of the 5-HT(1B) agonist, CP-93,129 (0-1.0 μg/infusion).

RESULTS

In both the DRN and ILC, CP-93,129 reduced aggressive behaviors after both water and alcohol self-administration. Intra-raphé CP-93,129 dose-dependently reduced both aggressive and locomotor behaviors. However, the anti-aggressive effects of intra-cortical CP-93,129 were behaviorally specific.

CONCLUSIONS

These findings highlight the importance of the serotonergic system in the modulation of aggression and suggest that the behaviorally specific effects of 5-HT(1B) receptor agonists are regionally selective. 5-HT(1B) receptors in a medial subregion of the prefrontal cortex, the ILC, appear to be critically involved in the attenuation of species-typical levels of aggression.

Whole-hemisphere autoradiography of 5-HT₁B receptor densities in postmortem alcoholic brains

The 5-HT(1B) receptor has been associated with alcohol dependence, impulsive or alcohol-related aggressive behavior, and anxiety. The aim of this study was to determine whether or not the 5-HT(1B) receptor density differs in brain samples from anxiety-prone Cloninger type 1 alcoholics and socially hostile, predominantly male, type 2 alcoholics, and controls. Whole-hemispheric 5-HT(1B) receptor density was measured in eight regions of postmortem brains from 17 alcoholics and 10 nonalcoholic controls by autoradiography with tritiated GR-125743 and unlabeled ketanserin to prevent 5-HT(1D) binding. The 5-HT(1B) receptor density was not altered significantly in any of the studied regions. However, some correlations were observed in types 1 and 2 alcoholics only. The 5-HT(1B) receptor density decreased with age in type 1 alcoholics only. There was a significant positive correlation between 5-HT(1B) receptor and serotonin transporter densities in the head of caudate of type 1 alcoholics only. There was a significant positive correlation between 5-HT(1B) receptor density and dopaminergic terminal density, as estimated by vesicular monoamine transporter 2 measurement in the nucleus accumbens of type 2 alcoholics only. There were no significant correlations between 5-HT(1B) receptor and dopamine transporter or dopamine D2/D3 receptor densities in any of the subject groups. In conclusion, these results do not indicate primary changes in 5-HT(1B) receptor densities among these alcoholics, although the data must be considered as preliminary.

Cognitive and neurobiological mechanisms of alcohol-related aggression

Alcohol-related violence is a serious and common social problem. Moreover, violent behaviour is much more common in alcohol-dependent individuals. Animal experiments and human studies have provided insights into the acute effect of alcohol on aggressive behaviour and into common factors underlying acute and chronic alcohol intake and aggression. These studies have shown that environmental factors, such as early-life stress, interact with genetic variations in serotonin-related genes that affect serotonergic and GABAergic neurotransmission. This leads to increased amygdala activity and impaired prefrontal function that, together, predispose to both increased alcohol intake and impulsive aggression. In addition, acute and chronic alcohol intake can further impair executive control and thereby facilitate aggressive behaviour.

Association between the 5-HTR1B gene polymorphisms and alcohol dependence in a Han Chinese population

The human serotonin receptor 1B (HRT1B) plays an important role in regulating serotonin release. Previous research has suggested that the genetic variation of the HTR1B gene may confer susceptibility to alcoholism or some subtypes of alcohol dependence, but the evidence has been inconsistent. The aim of the present study is to examine whether polymorphic variants of the HTR1B gene are associated with alcohol dependence subtypes or drinking-related behaviors in Chinese Han population. Alcohol-dependent (AD) male patients (n=135) and controls (n=143) were genotyped for two polymorphisms: A161T in the promoter region and the synonymous variation G861C in the coding region of HTR1B. The results showed that the A161T polymorphism was associated with alcohol dependence (T vs. A allele: p=0.002; OR=2.18, 95% CI: 1.32-3.60). This association was strengthened in those with positive family history (OR=3.12, 95% CI: 1.71-5.70) and/or early onset (OR=4.53, 95% CI: 2.18-9.44) of alcohol dependence. The A161T variant was also significantly associated with age of onset of alcoholism (p=0.001). Furthermore, there was a significant difference of haplotypic frequencies between patients and controls (χ(2)=14.84, df=3, p=0.002), with one common haplotype AG of being significantly underrepresented among the patient group compared to the control group (34% vs. 47.7%, permutation p=0.0034; OR=0.56; 95% CI: 0.39-0.79). These findings confirm HTR1B as a susceptibility gene for alcohol dependence in the sample of Chinese Han population. The HTR1B A-161T polymorphism may be particularly valuable as a functional genetic marker for alcoholism and merits additional study.

Flunitrazepam in combination with alcohol engenders high levels of aggression in mice and rats

RATIONALE

Higher doses of benzodiazepines and alcohol induce sedation and sleep; however, in low to moderate doses these drugs can increase aggressive behavior.

OBJECTIVES

To assess firstly the effects of ethanol, secondly the effects of flunitrazepam, a so-called club drug, and thirdly the effects of flunitrazepam plus alcohol on aggression in mice and rats.

METHODS

Exhaustive behavioral records of confrontations between a male resident and a male intruder were obtained twice a week, using CF-1 mice and Wistar rats. The salient aggressive and non-aggressive elements in the resident's repertoire were analyzed. Initially, the effects of ethanol (1.0g/kg), and secondly flunitrazepam (0; 0.01; 0.1; and 0.3mg/kg) were determined in all mice and rats; subsequently, flunitrazepam or vehicle, given intraperitoneally (0; 0.01; 0.1; and 0.3mg/kg) was administered plus ethanol 1.0g/kg or vehicle via gavage.

RESULTS

The most significant finding is the escalation of aggression after a moderate dose of ethanol, and a low dose of flunitrazepam. The largest increase in aggressive behavior occurred after combined flunitrazepam plus ethanol treatment in mice and rats.

CONCLUSIONS

Ethanol can heighten aggressive behavior and flunitrazepam further increases this effect in male mice and rats.

Social instigation and aggressive behavior in mice: role of 5-HT1A and 5-HT1B receptors in the prefrontal cortex

RATIONALE

Social instigation is used in rodents to induce high levels of aggression, a pattern of behavior with certain parallels to that of violent individuals. This procedure consists of a brief exposure to a provocative stimulus male, before direct confrontation with an intruder. Studies using 5-HT1A and 5-HT1B receptor agonists show an effective reduction in aggressive behavior. An important site of action for these drugs is the ventral orbitofrontal cortex (VO PFC), an area of the brain which is particularly relevant in the inhibitory control of aggressive and impulsive behavior.

OBJECTIVES

The objectives of the study are to assess the anti-aggressive effects of 5-HT1A and 5-HT1B agonist receptors [8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT) and CP-93,129] in the VO PFC of socially provoked male mice. To confirm the specificity of the receptor, 5-HT1A and 5-HT1B antagonist receptors (WAY-100,635 and SB-224,289) were microinjected into the same area, in order to reverse the agonist effects.

RESULTS

8-OH-DPAT (0.56 and 1.0 microg) reduced the frequency of attack bites. The lowest dose of CP-93,129 (0.1 microg) also decreased the number of attack bites and lateral threats. 5-HT1A and 5-HT1B receptor agonists differed in their effects on non-aggressive activities, the former decreasing rearing and grooming, and the latter, increasing these acts. Specific participation of the 1A and 1B receptors was verified by reversal of anti-aggressive effects using selective antagonists WAY-100,635 (10.0 microg) and SB-224,289 (1.0 microg).

CONCLUSIONS

The decrease in aggressiveness observed with microinjections of 5-HT1A and 5-HT1B receptor agonists into the VO PFC of socially provoked mice, supports the hypothesis that activation of these receptors modulates high levels of aggression in a behaviorally specific manner.

Neurobiology of escalated aggression and violence

Psychopathological violence in criminals and intense aggression in fruit flies and rodents are studied with novel behavioral, neurobiological, and genetic approaches that characterize the escalation from adaptive aggression to violence. One goal is to delineate the type of aggressive behavior and its escalation with greater precision; second, the prefrontal cortex (PFC) and brainstem structures emerge as pivotal nodes in the limbic circuitry mediating escalated aggressive behavior. The neurochemical and molecular work focuses on the genes that enable invertebrate aggression in males and females and genes that are expressed or suppressed as a result of aggressive experiences in mammals. The fruitless gene, immediate early genes in discrete serotonin neurons, or sex chromosome genes identify sexually differentiated mechanisms for escalated aggression. Male, but not female, fruit flies establish hierarchical relationships in fights and learn from previous fighting experiences. By manipulating either the fruitless or transformer genes in the brains of male or female flies, patterns of aggression can be switched with males using female patterns and vice versa. Work with Sts or Sry genes suggests so far that other genes on the X chromosomes may have a more critical role in female mouse aggression. New data from feral rats point to the regulatory influences on mesocortical serotonin circuits in highly aggressive animals via feedback to autoreceptors and via GABAergic and glutamatergic inputs. Imaging data lead to the hypothesis that antisocial, violent, and psychopathic behavior may in part be attributable to impairments in some of the brain structures (dorsal and ventral PFC, amygdala, and angular gyrus) subserving moral cognition and emotion.