Glutamate-vasopressin interactions and the neurobiology of anabolic steroid-induced offensive aggression

Neurobiology of Aggression-Review of Recent Findings and Relationship with Alcohol and Trauma

Aggression can be conceptualized as any behavior, physical or verbal, that involves attacking another person or animal with the intent of causing harm, pain or injury. Because of its high prevalence worldwide, aggression has remained a central clinical and public safety issue. Aggression can be caused by several risk factors, including biological and psychological, such as genetics and mental health disorders, and socioeconomic such as education, employment, financial status, and neighborhood. Research over the past few decades has also proposed a link between alcohol consumption and aggressive behaviors. Alcohol consumption can escalate aggressive behavior in humans, often leading to domestic violence or serious crimes. Converging lines of evidence have also shown that trauma and posttraumatic stress disorder (PTSD) could have a tremendous impact on behavior associated with both alcohol use problems and violence. However, although the link between trauma, alcohol, and aggression is well documented, the underlying neurobiological mechanisms and their impact on behavior have not been properly discussed. This article provides an overview of recent advances in understanding the translational neurobiological basis of aggression and its intricate links to alcoholism and trauma, focusing on behavior. It does so by shedding light from several perspectives, including in vivo imaging, genes, receptors, and neurotransmitters and their influence on human and animal behavior.

Anger management: Mechanisms of glutamate receptor-mediated synaptic plasticity underlying animal aggression

Excessive and recurring violent aggression is a serious concern for society and a symptom of many psychiatric diseases. Substance abuse, attack experience, and social and traumatic stress increase vulnerability to developing this type of aggression. Glutamate receptors are an intriguing target for long-term treatment. This review will assess the importance of glutamate receptors and glutamatergic pathways in aggression, focusing on the role of glutamate receptor-mediated synaptic plasticity in experience-dependent long-lasting aggression. By synthesizing what is known about glutamatergic systems in aggression, it is hoped more effective treatments can be developed.

Valproate selectively suppresses adolescent anabolic/androgenic steroid-induced aggressive behavior: implications for a role of hypothalamic γ-aminobutyric acid neural signaling

Pubertal male Syrian hamsters (Mesocricetus auratus) treated with anabolic/androgenic steroids (AASs) during adolescence (P27-P56) display a highly intense aggressive phenotype that shares many behavioral similarities with pathological aggression in youth. Anticonvulsant drugs like valproate that enhance the activity of the γ-aminobutyric acid (GABA) neural system in the brain have recently gained acceptance as a primary treatment for pathological aggression. This study examined whether valproate would selectively suppress adolescent AAS-induced aggressive behavior and whether GABA neural signaling through GABAA subtype receptors in the latero-anterior hypothalamus (LAH; an area of convergence for developmental and neuroplastic changes that underlie aggression in hamsters) modulate the aggression-suppressing effect of this anticonvulsant medication. Valproate (1.0-10.0 mg/kg, intraperitoneal) selectively suppressed the aggressive phenotype in a dose-dependent fashion, with the effective anti-aggressive effects beginning at 5 mg/kg, intraperitoneally. Microinfusion of the GABAA receptor antagonist bicuculline (7.0-700 ng) into the LAH reversed valproate's suppression of AAS-induced aggression in a dose-dependent fashion. At the 70 ng dose of bicuculline, animals expressed the highly aggressive baseline phenotype normally observed in AAS-treated animals. These studies provide preclinical evidence that the anticonvulsant valproate selectively suppresses adolescent, AAS-induced aggression and that this suppression is modulated, in part, by GABA neural signaling within the LAH.

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.

The glutamatergic system in the preoptic area is involved in the retention of maternal behavior in maternally experienced female rats

Maternally experienced female rats show high maternal behavior performance for a long time after acquisition of maternal experience, although the mechanisms responsible for the retention of maternal behavior are not well understood. The medial preoptic area (MPOA) plays an important role in the onset and maintenance of maternal behavior in female rats. We aimed to determine whether maternal experience affects the glutamatergic system in the MPOA for the retention of maternal behavior in female rats. First, to determine the effects of maternal experience in the postpartum period on dendritic spines, which are the postsynaptic component of excitatory glutamatergic neurotransmission, we examined the number of dendritic spines on MPOA neurons of primiparous mothers that had experienced mothering until weaning (sufficiently experienced mothers) and of primiparous mothers that were separated from their pups on the day of parturition (insufficiently experienced mothers). The number of mushroom spines, but not other types of spine, was significantly greater in the sufficiently experienced mothers compared with that in the insufficiently experienced mothers. Next, to determine the effects of maternal experience in the postpartum period on the expression of ionotropic glutamate receptors, we measured the mRNA levels of AMPA receptor subunits (GluA1-A4) and NMDA receptor subunits (GluN1, GluN2A-2D) in the MPOA of primiparous female rats that were kept with pups until brain sampling. As a result, we found that the mRNA levels of GluA3 and GluN2B were significantly higher in primiparous females on the day of weaning compared with those in primiparous females on the day of parturition. Additionally, we examined the effects of CNQX, an AMPA receptor antagonist, and MK-801, an NMDA receptor antagonist, injected into the MPOA on maternal behavior in maternally experienced primiparous female rats. Maternal behavioral activity was significantly reduced when CNQX or MK-801 was injected into the MPOA. These findings indicate that long-term maternal experience in the postpartum period up-regulates glutamatergic neurotransmission by increasing the number of mushroom spines and glutamate receptor expression, which may be involved in the retention of maternal behavior in maternally experienced female rats.

Potentiation of Divergent Medial Amygdala Pathways Drives Experience-Dependent Aggression Escalation

Heightened aggression can be serious concerns for the individual and society at large and are symptoms of many psychiatric illnesses, such as post-traumatic stress disorder. The circuit and synaptic mechanisms underlying experience-induced aggression increase, however, are poorly understood. Here we find that prior attack experience leading to an increase in aggressive behavior, known as aggression priming, activates neurons within the posterior ventral segment of the medial amygdala (MeApv). Optogenetic stimulation of MeApv using a synaptic depression protocol suppresses aggression priming, whereas high-frequency stimulation enhances aggression, mimicking attack experience. Interrogation of the underlying neural circuitry revealed that the MeApv mediates aggression priming via synaptic connections with the ventromedial hypothalamus (VmH) and bed nucleus of the stria terminalis (BNST). These pathways undergo NMDAR-dependent synaptic potentiation after attack. Furthermore, we find that the MeApv-VmH synapses selectively control attack duration, whereas the MeApv-BNST synapses modulate attack frequency, both with no effect on social behavior. Synaptic potentiation of the MeApv-VmH and MeApv-BNST pathways contributes to increased aggression induced by traumatic stress, and weakening synaptic transmission at these synapses blocks the effect of traumatic stress on aggression. These results reveal a circuit and synaptic basis for aggression modulation by experience that can be potentially leveraged toward clinical interventions.SIGNIFICANCE STATEMENT Heightened aggression can have devastating social consequences and may be associated with psychiatric disorders, such as post-traumatic stress disorder. The circuit and synaptic mechanisms underlying experience-induced aggression escalation, however, are poorly understood. Here we identify two aggression pathways between the posterior ventral segment of the medial amygdala and its downstream synaptic partners, the ventromedial hypothalamus and bed nucleus of the stria terminalis that undergo synaptic potentiation after attack and traumatic stress to enhance aggression. Notably, weakening synaptic transmission in these circuits blocks aggression priming, naturally occurring aggression, and traumatic stress-induced aggression increase. These results illustrate a circuit and synaptic basis of aggression modulation by experience, which can be potentially targeted for clinical interventions.

Mechanisms Underlying Aggressive Behavior Induced by Antiepileptic Drugs: Focus on Topiramate, Levetiracetam, and Perampanel

Antiepileptic drugs (AEDs) are effective against seizures, but their use is often limited by adverse effects, among them psychiatric and behavioral ones including aggressive behavior (AB). Knowledge of the incidence, risk factors, and the underlying mechanisms of AB induced by AEDs may help to facilitate management and reduce the risk of such side effects. The exact incidence of AB as an adverse effect of AEDs is difficult to estimate, but frequencies up to 16% have been reported. Primarily, levetiracetam (LEV), perampanel (PER), and topiramate (TPM), which have diverse mechanisms of action, have been associated with AB. Currently, there is no evidence for a specific pharmacological mechanism solely explaining the increased incidence of AB with LEV, PER, and TPM. Serotonin (5-HT) and GABA, and particularly glutamate (via the AMPA receptor), seem to play key roles. Other mechanisms involve hormones, epigenetics, and “alternative psychosis” and related phenomena. Increased individual susceptibility due to an underlying neurological and/or a mental health disorder may further explain why people with epilepsy are at an increased risk of AB when using AEDs. Remarkably, AB may occur with a delay of weeks or months after start of treatment. Information to patients, relatives, and caregivers, as well as sufficient clinical follow-up, is crucial, and there is a need for further research to understand the complex relationship between AED mechanisms of action and the induction/worsening of AB.

Vasopressin differentially modulates aggression and anxiety in adolescent hamsters administered anabolic steroids

Adolescent Syrian hamsters (Mesocricetus auratus) treated with anabolic/androgenic steroids display increased offensive aggression and decreased anxiety correlated with an increase in vasopressin afferent development, synthesis, and neural signaling within the anterior hypothalamus. Upon withdrawal from anabolic/androgenic steroids, this neurobehavioral relationship shifts as hamsters display decreased offensive aggression and increased anxiety correlated with a decrease in anterior hypothalamic vasopressin. This study investigated the hypothesis that alterations in anterior hypothalamic vasopressin neural signaling modulate behavioral shifting between adolescent anabolic/androgenic steroid-induced offensive aggression and anxiety. To test this, adolescent male hamsters were administered anabolic/androgenic steroids and tested for offensive aggression or anxiety following direct pharmacological manipulation of vasopressin V1A receptor signaling within the anterior hypothalamus. Blockade of anterior hypothalamic vasopressin V1A receptor signaling suppressed offensive aggression and enhanced general and social anxiety in hamsters administered anabolic/androgenic steroids during adolescence, effectively reversing the pattern of behavioral response pattern normally observed during the adolescent exposure period. Conversely, activation of anterior hypothalamic vasopressin V1A receptor signaling enhanced offensive aggression in hamsters exposed to anabolic/androgenic steroids during adolescence. Together, these findings suggest that the state of vasopressin neural development and signaling in the anterior hypothalamus plays an important role in behavioral shifting between aggression and anxiety following adolescent exposure to anabolic/androgenic steroids.

Metabotropic Glutamate Receptor Subtype 7 in the Bed Nucleus of the Stria Terminalis is Essential for Intermale Aggression

Metabotropic glutamate receptor subtype 7 (mGluR7) is a member of group III mGluRs, which localize to the presynaptic active zones of the mammalian central nervous system. Although histological, genetic, and electrophysiological studies ensure the importance of mGluR7, its roles in behavior and physiology remain largely unknown. Using a resident-intruder paradigm, we found a severe reduction in intermale aggressive behavior in mGluR7 knockout (KO) mice. We also found alterations in other social behaviors in male mGluR7 KO mice, including sexual behavior toward male intruders. Because olfaction is critical for rodent social behavior, including aggression, we performed an olfaction test, finding that mGluR7 KO mice failed to show interest in the smell of male urine. To clarify the olfactory deficit, we then exposed mice to urine and analyzed c-Fos-immunoreactivity, discovering a remarkable reduction in neural activity in the bed nucleus of the stria terminalis (BNST) of mGluR7 KO mice. Finally, intra-BNST administration of the mGluR7-selective antagonist 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo[4,5-c]pyridin-4(5H)-one (MMPIP) also reproduced the phenotype of mGluR7 KO mice, including reduced aggression and altered social interaction. Thus mGluR7 may work as an 'enhancer of neural activity' in the BNST and is important for intermale aggression. Our findings demonstrate that mGluR7 is essential for social behavior and innate behavior. Our study on mGluR7 in the BNST will shed light on future therapies for emotional disorders in humans.

Anabolic steroids alter the physiological activity of aggression circuits in the lateral anterior hypothalamus

Syrian hamsters exposed to anabolic/androgenic steroids (AAS) during adolescence consistently show increased aggressive behavior across studies. Although the behavioral and anatomical profiles of AAS-induced alterations have been well characterized, there is a lack of data describing physiological changes that accompany these alterations. For instance, behavioral pharmacology and neuroanatomical studies show that AAS-induced changes in the vasopressin (AVP) neural system within the latero-anterior hypothalamus (LAH) interact with the serotonin (5HT) and dopamine (DA) systems to modulate aggression. To characterize the electrophysiological profile of the AAS aggression circuit, we recorded LAH neurons in adolescent male hamsters in vivo and microiontophoretically applied agonists and antagonists of aggressive behavior. The interspike interval (ISI) of neurons from AAS-treated animals correlated positively with aggressive behaviors, and adolescent AAS exposure altered parameters of activity in regular firing neurons while also changing the proportion of neuron types (i.e., bursting, regular, irregular). AAS-treated animals had more responsive neurons that were excited by AVP application, while cells from control animals showed the opposite effect and were predominantly inhibited by AVP. Both DA D2 antagonists and 5HT increased the firing frequency of AVP-responsive cells from AAS animals and dual application of AVP and D2 antagonists doubled the excitatory effect of AVP or D2 antagonist administration alone. These data suggest that multiple DA circuits in the LAH modulate AAS-induced aggressive responding. More broadly, these data show that multiple neurochemical interactions at the neurophysiological level are altered by adolescent AAS exposure.

Dopamine D2 receptors act upstream of AVP in the latero-anterior hypothalamus to modulate adolescent anabolic/androgenic steroid-induced aggression in Syrian hamsters

In pubertal male Syrian hamsters, exposure to anabolic/androgenic steroids (AAS) during adolescence facilitates a high level of offensive aggression modulated by the enhanced development and activity of the vasopressin (AVP) and dopamine (DA) neural systems within the latero-anterior hypothalamus (LAH), that is, a brain region implicated in the control of aggression. The present studies provide a detailed report of the pharmacologic interactions between AVP and DA D2 receptor signaling within the LAH in the control of adolescent AAS-induced offensive aggression. Male Syrian hamsters were treated with AAS throughout adolescence and tested for aggression after local infusion of the DA D2 receptor antagonist eticlopride (ETIC) alone, or in combination with AVP in the LAH in an effort to determine the influence of DA D2 receptors relative to AVP-receptor mediated aggression mechanisms. As previously shown, ETIC infusion into the LAH suppressed adolescent AAS-induced aggressive responding; however, the AAS-induced aggressive phenotype was rescued by the coinfusion of AVP into the LAH. These behavioral data indicate that interactions between AVP and DA neural systems within the LAH modulate the control of aggression following adolescent exposure to AAS and that DA D2 receptor signaling functions upstream of AVP in the LAH to control this behavioral response.

γ-Aminobutyric acid neural signaling in the lateroanterior hypothalamus modulates aggressive behavior in adolescent anabolic/androgenic steroid-treated hamsters

Male Syrian hamsters (Mesocricetus auratus) treated with anabolic/androgenic steroids (AAS) during adolescence (P27-P56) display highly escalated and mature forms of offensive aggression correlated with increased γ-aminobutyric acid (GABA) afferent development as well as decreased GABAA receptors in the lateroanterior hypothalamus (LAH) - an area of convergence for developmental and neuroplastic changes that underlie offensive aggressive behaviors in hamsters. This study investigated whether microinfusion of a GABAA receptor agonist (muscimol; 0.01-1.0 pmol/l) or antagonist (bicuculline; 0.04-4.0 pmol/l) directly into the LAH modulate adolescent AAS-induced offensive aggression. Activation of LAH GABAA receptors enhanced adolescent AAS-induced offensive aggression, beginning at the 0.1 pmol/l dose, when compared with AAS-treated animals injected with saline into the LAH. Importantly, GABAA receptor agonism within the LAH significantly increased the frequency of belly/rear attacks, while simultaneously decreasing the frequency of frontal attacks. These data identify a neuroanatomical locus where GABAA receptor activation functions to enhance aggression in adolescent AAS-treated animals, while also promoting the display of mature forms of aggression and suppressing juvenile play behaviors.

The effects of vasopressin deficiency on aggression and impulsiveness in male and female rats

The role of vasopressin in aggression received much attention in recent years. However, vasopressin has complex roles on social behavior, which are affected by social experience, motivation and hormonal background, suggesting that its effects depend on the condition of subjects. This hypothesis was tested here by studying the impact of vasopressin deficiency on aggressiveness in reproductively naive and reproductively experienced males, as well as in lactating females, with special reference to the patterns and contexts of attack behavior. We also studied effects on impulsiveness, a behavioral feature strongly related to aggression. Vasopressin deficiency did not affect aggressiveness in reproductively experienced males, decreased the share of violent attacks in reproductively inexperienced males without affecting total attack counts, and suppressed maternal aggression in both early and late phases of lactation; violent forms of attack were decreased in the latter but not the former phase. Changes in aggression appeared unrelated to general changes in maternal behaviors. Impulsivity in the delay discounting task was markedly decreased by vasopressin deficiency in lactating females but not males. Taken together, our findings confirm that vasopressin has an impact on aggressiveness, but show that this impact depends on the condition of subjects, and suggest that the effects of vasopressin on maternal aggression develop in conjunction with impulsivity. Interestingly, overall effects on aggression and specific effects on violent attacks dissociated in both males and females, which hints to the possibility that vasopressin has distinct roles in the development of escalated forms of aggression.

Medial amygdala lesions modify aggressive behavior and immediate early gene expression in oxytocin and vasopressin neurons during intermale exposure

The medial amygdala and neuropeptides oxytocin (OXT) and vasopressin (VSP) have been associated aggressive behavior regulation. However, the specific mechanism involved in OXT and VSP modulation in distinct brain regions during hostile intermale aggressive behavior is undetermined. A retrograde tracer mouse model was employed using male C57BL/6 mice injected with rhodamine-conjugated latex microsphere suspensions in the right hypothalamic paraventricular nucleus. Adult male C57BL/6 mice (aged 14-16 weeks) were subjected to resident-intruder testing using juvenile intruder mice (aged 3 weeks) or adult intruder mice (aged 8 weeks). Following exposure, Fos protein expression was increased in the medial amygdala neurons of resident mice receiving the retrograde tracer. Thus, medial amygdala neurons projecting to or localized in the vicinity of the hypothalamic paraventricular nucleus showed immediate early gene (IEG) expression following resident-intruder testing that was considered an indirect marker of activation. Additionally, intermale aggression-related behaviors were inhibited or modified by exposure to juvenile or adult intruders, respectively, in mice that underwent medial amygdala lesioning. Furthermore, Fos protein expression in OXT-positive neurons was attenuated. Thus, ablation of medial amygdala neurons prevented immediate early gene expression in OXT- and VSP-positive neurons in the hypothalamus, bed nucleus of stria terminalis, and medial preoptic area during intermale exposure. These findings indicate that the medial amygdala likely modulates hostile aggressive behavior associated with immediate early gene expression in OXT and VSP neurons in specific brain areas, which may actually be instrumental in beneficial social interaction-related aggressive responses associated with mating, territorial defense, and offspring protection.

Illicit use of androgens and other hormones: recent advances

PURPOSE OF REVIEW

To summarize recent advances in studies of illicit use of androgens and other hormones.

RECENT FINDINGS

Androgens and other appearance-enhancing and performance-enhancing substances are widely abused worldwide. Three notable clusters of findings have emerged in this field in recent years. First, studies almost unanimously find that androgen users engage in polypharmacy, often ingesting other hormones (e.g., human growth hormone, thyroid hormones, and insulin), ergo/thermogenic drugs (e.g., caffeine, ephedrine, and clenbuterol), and classical drugs of abuse (e.g., cannabis, opiates, and cocaine). Second, reports of long-term psychiatric and medical adverse effects of androgens continue to accumulate. In cardiovascular research particularly, controlled studies have begun to supersede anecdotal evidence, strengthening the case that androgens (possibly acting synergistically with other abused drugs) may cause significant morbidity and even mortality. Third, it is increasingly recognized that androgen use may lead to a dependence syndrome with both psychological and physiological origins. Androgen dependence likely affects some millions of individuals worldwide, and arguably represents the least studied major class of illicit drug dependence.

SUMMARY

Given mounting evidence of the adverse effects of androgens and associated polypharmacy, this topic will likely represent an expanding area of research and an issue of growing public health concern.

The regulation of social recognition, social communication and aggression: vasopressin in the social behavior neural network

Neuropeptides in the arginine vasotocin/arginine vasopressin (AVT/AVP) family play a major role in the regulation of social behavior by their actions in the brain. In mammals, AVP is found within a circuit of recriprocally connected limbic structures that form the social behavior neural network. This review examines the role played by AVP within this network in controlling social processes that are critical for the formation and maintenance of social relationships: social recognition, social communication and aggression. Studies in a number of mammalian species indicate that AVP and AVP V1a receptors are ideally suited to regulate the expression of social processes because of their plasticity in response to factors that influence social behavior. The pattern of AVP innervation and V1a receptors across the social behavior neural network may determine the potential range and intensity of social responses that individuals display in different social situations. Although fundamental information on how social behavior is wired in the brain is still lacking, it is clear that different social behaviors can be influenced by the actions of AVP in the same region of the network and that AVP can act within multiple regions of this network to regulate the expression of individual social behaviors. The existing data suggest that AVP can influence social behavior by modulating the interpretation of sensory information, by influencing decision making and by triggering complex motor outputs. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

The role of the androgen receptor in anabolic androgenic steroid-induced aggressive behavior in C57BL/6J and Tfm mice

Humans self-administer anabolic androgenic steroids (AAS) at superphysiological doses for the purpose of building muscle mass and enhancing physique whereas considerably lower doses of AAS are prescribed in the clinic to treat a variety of disorders. A number of studies have demonstrated that individual AAS influence aggressive behavior in rats and mice, but few studies have examined the aggression-enhancing effects of combinations of AAS. Using the resident-intruder paradigm, Experiment 1 determined whether a cocktail of commonly abused AAS increased aggressive behavior in gonadally-intact male C57BL/6J mice and examined whether the androgen receptor (AR) was involved. Mice given either AAS cocktail or the cocktail and the AR antagonist, flutamide, for 6 weeks were subject to three weekly tests in which the percentage of mice that fought, the latency to initiate an aggressive event and the number of aggressive events per 5-min-fight session were recorded. In C57BL/6J mice, 6 weeks of AAS administration increased the likelihood of fighting, however, within the subset of mice that engaged in aggression, AAS did not specifically modulate the latency to fight or the number of aggressive events per fight. In addition, co-administration of flutamide only slightly altered the likelihood that mice given AAS will initiate a fight. Experiment 2 examined the aggression-promoting effects of AAS in gonadally-intact adult testicular feminization mutant (Tfm) mice, which are deficient in functional ARs. Overall, fewer Tfm mice compared to C57BL/6J mice fought in both drug conditions (vehicle or AAS). Taken together, these data suggest that given the presence of AR during development, AAS enhance adult male aggression in C57BL/6J mice through AR-independent and AR-dependent pathways. In contrast, in adult Tfm mice, the likelihood of AAS-enhanced aggression in adulthood is significantly reduced.