Cerebrospinal fluid substance P-like immunoreactivity correlates with aggression in personality disordered subjects

Mapping the neurocircuitry of impulsive aggression through the pharmacologic review of anti-impulsive aggressive agents

Impulsive aggression, in contradistinction to premeditated aggression in humans or predatory aggression in animals, corresponds to defensive aggression in animal models. At the core of the neurocircuitry of impulsive aggression, from murine to feline to human species, it is the medial amygdala-mediobasal hypothalamus-dorsal periaqueductal gray pathway. Here, we update current knowledge on the neurocircuitry of impulsive aggression by placing the neurocircuitry and its neurophysiological substrates into the top-down/bottom-up hypothesis of impulsive aggression. We then reverse the neurotranslational approach, which applies neuroscience to developing therapeutic drugs, and apply current understanding of potential mechanisms of anti-impulsive aggression agents to further clarify, at least heuristically and hypothetically, the dynamic biochemical components of the neurocircuitry of impulsive aggression. To do this, we searched the medical literature for studies attempting to clarify the neurobiological and neurochemical effects of the five most widely studied anti-impulsive aggressive agents, particularly as they pertain to the top-down/bottom-up hypothesis. Multiple different mechanisms are discussed, all of which fitting in the hypothesis by way of either promoting the "top-down" part (i.e., enhancing inhibitory neurotransmitters), or suppressing the "bottom-up" part (i.e., decreasing excitatory neurotransmitters). The hypothesis appears consistent with the current psychopharmacological understanding of these agents, as well as to account for the likely multifactorial etiology of the condition. Limitations of the hypothesis and future directions are finally discussed.

Association between amygdala neurokinin-1 receptor availability and anxiety-related personality traits

Animal studies indicate that substance P (SP) and its preferred neurokinin-1 (NK1) receptor modulate stress and anxiety-related behavior. Alterations in the SP-NK1 system have also been observed in human anxiety disorders, yet little is known about the relation between this system and individual differences in personality traits associated with anxiety propensity and approach-avoidance behavior, including trait anxiety, neuroticism, and extraversion. Exploring this relation could provide important insights into the neurobiological underpinnings of human anxiety and the etiology of anxiety disorders, as anxious traits are associated with increased susceptibility to develop psychopathological conditions. Here we examined the relationship between central NK1 receptor availability and self-rated measures of trait anxiety, neuroticism, and extraversion. The amygdala was chosen as the primary region of interest since this structure has been suggested to mediate the effect of the SP-NK1 system on anxiety. Anxious traits and NK1 receptor availability, determined with positron emission tomography and the radiotracer [¹¹C]GR205171, were measured in 17 healthy individuals. Voxel-wise analyses showed a significant positive correlation between bilateral amygdala NK1 receptor availability and trait anxiety, and a trend in similar direction was observed for neuroticism. Conversely, extraversion was found to be negatively associated with amygdala NK1 receptor availability. Extraversion also correlated negatively with the NK1 measure in the cuneus/precuneus and fusiform gyrus according to exploratory whole-brain analyses. In conclusion, our findings indicate that amygdala NK1 receptor availability is associated with anxiety-related personality traits in healthy subjects, consistent with a modulatory role for the SP-NK1 system in human anxiety.

Social cognition in Intermittent Explosive Disorder and aggression

Social-emotional information processing (SEIP) was assessed in individuals with current DSM-5 Intermittent Explosive Disorder (IED: n = 100) and in healthy (n = 100) and psychiatric (n = 100) controls using a recently developed and validated self-rated questionnaire. SEIP vignettes depicted both direct aggressive and relationally aggressive scenarios of a socially ambiguous nature and were followed by questions assessing subjects' reactions and judgments about the vignettes. IED subjects differed from both healthy and psychiatric controls in all SEIP components. While hostile attribution was highly related to history of aggression, it was also directly correlated with negative emotional response. Further analysis revealed that this component, as well as response valuation and response efficiency, rather than hostile attribution, best explained history of aggressive behavior. A reformulated SEIP model, including self-reported history of childhood trauma, found that negative emotional response and response efficiency were the critical correlates for history of aggressive behavior. Psychosocial interventions of aggressive behavior in IED subjects may do well to include elements that work to reduce the emotional response to social threat and that work to restructure social cognition so that the tendency towards overt, or relationally, aggressive responding is reduced.

Discovery of biochemical biomarkers for aggression: A role for metabolomics in psychiatry

Human aggression encompasses a wide range of behaviors and is related to many psychiatric disorders. We introduce the different classification systems of aggression and related disorders as a basis for discussing biochemical biomarkers and then present an overview of studies in humans (published between 1990 and 2015) that reported statistically significant associations of biochemical biomarkers with aggression, DSM-IV disorders involving aggression, and their subtypes. The markers are of different types, including inflammation markers, neurotransmitters, lipoproteins, and hormones from various classes. Most studies focused on only a limited portfolio of biomarkers, frequently a specific class only. When integrating the data, it is clear that compounds from several biological pathways have been found to be associated with aggressive behavior, indicating complexity and the need for a broad approach. In the second part of the paper, using examples from the aggression literature and psychiatric metabolomics studies, we argue that a better understanding of aggression would benefit from a more holistic approach such as provided by metabolomics. © 2016 Wiley Periodicals, Inc.

Elevated Plasma Oxidative Stress Markers in Individuals With Intermittent Explosive Disorder and Correlation With Aggression in Humans

BACKGROUND

Animal and clinical studies suggest a link between inflammation and oxidative stress. Because oxidative stress is an inherent part of inflammation, and inflammation is associated with behavioral aggression in lower mammals and humans, we hypothesized that markers of oxidative stress would be related to aggression in human subjects. In this case-control study, markers of oxidative stress and aggression were assessed in human subjects with histories of recurrent, problematic, impulsive aggressive behavior and in nonaggressive comparator subjects.

METHODS

Plasma levels of 8-hydroxy-2'-deoxyguanosine and 8-isoprostane were examined in the context of measures of aggression and impulsivity in physically healthy subjects with intermittent explosive disorder (n = 69), nonaggressive subjects with Axis I or II disorders (n = 61), and nonaggressive subjects with no history of Axis I or II disorders (n = 67).

RESULTS

Levels of plasma 8-hydroxy-2'-deoxyguanosine and 8-isoprostane were significantly higher in subjects with intermittent explosive disorder compared with psychiatric or normal control subjects. In addition, both oxidative stress markers correlated with a composite measure of aggression; more specifically, 8-hydroxy-2'-deoxyguanosine correlated with measures reflecting a history of actual aggressive behavior in all subjects.

CONCLUSIONS

These data suggest a positive relationship between plasma markers of oxidative stress and aggression in human subjects. This finding adds to the complex picture of the central neuromodulatory role of aggression in human subjects.

A Systematic Review of Personality Disorders and Health Outcomes

Personality disorders have been associated with a wide swath of adverse health outcomes and correspondingly high costs to healthcare systems. To date, however, there has not been a systematic review of the literature on health conditions among individuals with personality disorders. The primary aim of this article is to review research documenting the associations between personality disorders and health conditions. A systematic review of the literature revealed 78 unique empirical English-language peer-reviewed articles examining the association of personality disorders and health outcomes over the past 15 years. Specifically, we reviewed research examining the association of personality disorders with sleep disturbance, obesity, pain conditions, and other chronic health conditions. In addition, we evaluated research on candidate mechanisms underlying health problems in personality disorders and potential treatments for such disorders. Results underscore numerous deleterious health outcomes associated with PD features and PD diagnoses, and suggest potential biological and behavioural factors that may account for these relations. Guidelines for future research in this area are discussed.

Of Fighting Flies, Mice, and Men: Are Some of the Molecular and Neuronal Mechanisms of Aggression Universal in the Animal Kingdom?

Aggressive behavior is widespread in the animal kingdom, but the degree of molecular conservation between distantly related species is still unclear. Recent reports suggest that at least some of the molecular mechanisms underlying this complex behavior in flies show remarkable similarities with such mechanisms in mice and even humans. Surprisingly, some aspects of neuronal control of aggression also show remarkable similarity between these distantly related species. We will review these recent findings, address the evolutionary implications, and discuss the potential impact for our understanding of human diseases characterized by excessive aggression.

Prolyl endopeptidase and dipeptidyl peptidase IV are associated with externalizing and aggressive behaviors in normal and autistic adolescents

AIMS

Peptides and a dysregulated immune system play a role in the pathophysiology of autism. Dysfunctions in prolyl endopeptidase (PEP) and dipeptidyl peptidase IV (DPP-IV) may underpin both the peptidergic and immune alterations in autism. The aims of this study are to: (i) delineate serum PEP and DPP-IV enzyme activities in autism, and (ii) examine the associations between both peptidases and behavioral characteristics or immune variables.

MAIN METHODS

We included 18 autistic patients and 22 healthy controls and measured the Child Behavior Checklist (CBCL), serum PEP and DPP-IV and immune biomarkers, i.e. the serum protein fractions α1, α2 and γ, and immunoglobulins, i.e. IgG1, IgG2, IgG3 and IgG4. Results were adjusted for possible effects of age and body mass index (BMI).

KEY FINDINGS

There were no significant differences in PEP or DPP-IV between the autistic patients and controls. DPP-IV was significantly and positively associated with the CBCL attention problems, aggressive and externalizing behavior subscales. PEP was significantly and positively associated with the CBCL delinquent, aggressive, externalizing and internalizing behavior subscales. There was a negative correlation between both peptidases and age and Tanner stage. DPP-IV was associated with α2-globulin (positively) and IgG3 (inversely) levels, while PEP activity was correlated with IgG2 levels (inversely). BMI was significantly associated with aggressive and externalizing behaviors.

SIGNIFICANCE

These findings demonstrate an association between peptidases and aggressive and externalizing behaviors, which may be explained by effects of these peptidases cleaving behavioral neuropeptides. Both peptidases are associated with immune biomarkers suggesting multiple bidirectional effects.

Serotonin and impulsive aggression

Aggression is a behavior with evolutionary origins, but is often both destructive and maladaptive in today's society. Research over the past several decades has confirmed the involvement of neurotransmitter function in aggressive behavior. This research has centered around the "serotonin hypothesis." As this literature continues to grow, guided by pre-clinical research and aided by the application of increasingly sophisticated neuroimaging methodology, a more complex picture has emerged. As current pharmacological and therapeutic interventions are effective but imperfect, it is hoped that new insights into the neurobiology of aggression will reveal novel avenues for treatment of this destructive and costly behavior.

Tachykinin-expressing neurons control male-specific aggressive arousal in Drosophila

Males of most species are more aggressive than females, but the neural mechanisms underlying this dimorphism are not clear. Here, we identify a neuron and a gene that control the higher level of aggression characteristic of Drosophila melanogaster males. Males, but not females, contain a small cluster of FruM(+) neurons that express the neuropeptide tachykinin (Tk). Activation and silencing of these neurons increased and decreased, respectively, intermale aggression without affecting male-female courtship behavior. Mutations in both Tk and a candidate receptor, Takr86C, suppressed the effect of neuronal activation, whereas overexpression of Tk potentiated it. Tk neuron activation overcame reduced aggressiveness caused by eliminating a variety of sensory or contextual cues, suggesting that it promotes aggressive arousal or motivation. Tachykinin/Substance P has been implicated in aggression in mammals, including humans. Thus, the higher aggressiveness of Drosophila males reflects the sexually dimorphic expression of a neuropeptide that controls agonistic behaviors across phylogeny.

Cerebrospinal fluid glutamate concentration correlates with impulsive aggression in human subjects

Neurochemical studies have pointed to a modulatory role in human aggression for various central neurotransmitters. Some (e.g., serotonin) appear to play an inhibitory role, while others appear to play a facilitator role. While recent animal studies of glutaminergic activity suggest a facilitator role for central glutamate in the modulation of aggression, no human studies of central glutaminergic indices have yet been reported regarding aggression. Basal lumbar cerebrospinal fluid (CSF) was obtained from 38 physically healthy subjects with DSM-IV Personality Disorder (PD: n = 28) and from Healthy Volunteers (HV: n = 10) and assayed for glutamate, and other neurotransmitters, in CSF and correlated with measures of aggression and impulsivity. CSF Glutamate levels did not differ between the PD and HC subjects but did directly correlate with composite measures of both aggression and impulsivity and a composite measure of impulsive aggression in both groups. These data suggest a positive relationship between CSF Glutamate levels and measures of impulsive aggression in human subjects. Thus, glutamate function may contribute to the complex central neuromodulation of impulsive aggression in human subjects.

Impact and Neuropeptide Substance Pan Inflammatory Compound on Arachidonic Acid Compound Generation

There is much evidence that neuropeptide substance P is involved in neurogenic inflammation and is an important neurotransmitter and neurmodulator compound. In addition, substance P plays an important role in inflammation and immunity. Macrophages can be activated by substance P which provokes the release of inflammatory compounds such as interleukins, chemokines and growth factors. Substance P is involved in the mechanism of pain through the trigeminal nerve which runs through the head, temporal and sinus cavity. Substance P also activates mast cells to release inflammatory mediators such as arachindonic acid compound, cytokines/chemokines and histamine. The release of these chemical mediators is crucial for inflammatory response. Among these mediators there are prostoglandins and leukotrines. Here we review the impact of substance P on inflammatory compounds.