Effects of acute alcohol intoxication and paroxetine on aggression in men

Comparing behavioral measures of aggression in the laboratory: Taylor Aggression Paradigm versus Point-Subtraction Aggression Paradigm

Aggression refers to a wide range of behaviors with lasting individual and societal consequences. Recurrent, unplanned aggressive behavior is the core diagnostic criterion for intermittent explosive disorder (IED). In this study, we compared two behavioral measures of aggression in the laboratory: the Taylor Aggression Paradigm (TAP) and the Point-Subtraction Aggression Paradigm (PSAP). This sample (n = 528) included community participants who met DSM-5 criteria for IED (n = 156), met DSM-5 criteria for a nonaggressive psychiatric disorder (n = 205), or did not meet DSM-5 criteria for any psychiatric disorder (n = 167). All participants completed the TAP, a single-session PSAP, and relevant self-report measures. MANOVA analyses demonstrated differences between IED participants and nonaggressive participants; however, these group differences were no longer significant for the PSAP after including demographic variables. Correlation analyses found that the TAP and PSAP were positively related to one another and the composite variables associated with aggressive behavior (i.e., history of aggression, impulsivity, and propensity to experience anger) and; dependent correlations revealed that past aggression and trait anger were more strongly related to the TAP. Differences in TAP and PSAP outcomes may be partially attributed to operationalizations of aggression and methods of aggression and provocation. Further, as aggressive and nonaggressive participants differed on the PSAP somewhat mirroring the TAP, our results add to growing evidence of the validity of a single-session PSAP; further research is needed to fully establish single-session PSAP as a laboratory aggression task compared to the multi-session PSAP.

Sex-Specific Impact of Fkbp5 on Hippocampal Response to Acute Alcohol Injection: Involvement in Alterations of Metabolism-Related Pathways

High levels of alcohol intake alter brain gene expression and can produce long-lasting effects. FK506-binding protein 51 (FKBP51) encoded by Fkbp5 is a physical and cellular stress response gene and has been associated with alcohol consumption and withdrawal severity. Fkbp5 has been previously linked to neurite outgrowth and hippocampal morphology, sex differences in stress response, and epigenetic modification. Presently, primary cultured Fkbp5 KO and WT mouse neurons were examined for neurite outgrowth and mitochondrial signal with and without alcohol. We found neurite specification differences between KO and WT; particularly, mesh-like morphology was observed after alcohol treatment and confirmed higher MitoTracker signal in cultured neurons of Fkbp5 KO compared to WT at both naive and alcohol-treated conditions. Brain regions that express FKBP51 protein were identified, and hippocampus was confirmed to possess a high level of expression. RNA-seq profiling was performed using the hippocampus of naïve or alcohol-injected (2 mg EtOH/Kg) male and female Fkbp5 KO and WT mice. Differentially expressed genes (DEGs) were identified between Fkbp5 KO and WT at baseline and following alcohol treatment, with female comparisons possessing a higher number of DEGs than male comparisons. Pathway analysis suggested that genes affecting calcium signaling, lipid metabolism, and axon guidance were differentially expressed at naïve condition between KO and WT. Alcohol treatment significantly affected pathways and enzymes involved in biosynthesis (Keto, serine, and glycine) and signaling (dopamine and insulin receptor), and neuroprotective role. Functions related to cell morphology, cell-to-cell signaling, lipid metabolism, injury response, and post-translational modification were significantly altered due to alcohol. In summary, Fkbp5 plays a critical role in the response to acute alcohol treatment by altering metabolism and signaling-related genes.

Reactive vs proactive aggression: A differential psychobiological profile? Conclusions derived from a systematic review

INTRODUCTION

Scholars have established subcategories of aggressive behavior in order to better understand this construct. Specifically, a classification based on motivational underpinnings makes it possible to differentiate between reactive and proactive aggression. Whereas reactive aggression is characterized by emotional lability, which means it is prone to impulsive reactions after provocation, proactive aggression is driven by low emotionality and high levels of instrumentality to obtain benefits. Some authors have conceived these two types as having a dichotomous nature, but others argue against this conceptualization, considering a complementary model more suitable. Hence, neuroscientific research might help to clarify discussions about their nature because biological markers do not present the same biases as psychological instruments.

AIM

The main objective of this study was to carry out a systematic review of studies that assess underlying biological markers (e.g., genes, brain, psychophysiological, and hormonal) of reactive and proactive aggression.

METHODS

To carry out this review, we followed PRISMA quality criteria for reviews, using five digital databases complemented by hand-searching.

RESULTS

The reading of 3993 abstracts led to the final inclusion of 157 papers that met all the inclusion criteria. The studies included allow us to conclude that heritability accounted for approximately 45% of the explained variance in both types of aggression, with 60% shared by both, especially, for overt and physical expression forms, and 10% specific to each type. Regarding allelic risk factors, whereas low functioning variants affecting serotonin transport and monoaminoxidase increased the risk of reactive aggression, high functioning variants were associated with proactive aggression. Furthermore, brain analysis revealed an overlap between the two types of aggression and alterations in the volume of the amygdala and temporal cortex. Moreover, high activation of the medial prefrontal cortex (PFC) facilitated proneness to both types of aggression equally. Whereas stimulation of the right ventrolateral (VLPFC) and dorsolateral (DLPFC) reduced proneness to aggression, inhibition of the left DLPFC increased it. Finally, psychophysiological and hormonal correlates in general did not clearly differentiate between the two types because they were equally related to each type (e.g., low basal cortisol and vagal variability in response to acute stress) CONCLUSIONS: This study reinforces the complementary model of both types of aggression instead of a dichotomous model. Additionally, this review also offers background about several treatments (i.e., pharmacological, non-invasive brain techniques…) to reduce aggression proneness.

Acute drug effects on habitual and non-habitual responding in crossed high alcohol preferring mice

RATIONALE

Drug reward plays a central role in acquiring drug-seeking behavior. However, subjects may continue using drugs despite negative consequences because self-administration becomes habitual, and divorced from outcome values. Although a history of drug and alcohol use expedite habit acquisition, and in spite of the fact that self-administration leads to intoxication, the acute effects of drugs on habitual responding are not well understood.

OBJECTIVES

We sought to observe how acute ethanol and amphetamine affect the balance between habitual and goal-directed behavior, as measured by a fluid-reinforced operant conditioning task.

METHODS

Selectively bred crossed high-alcohol-preferring (cHAP) mice were trained on an operant conditioning task reinforced on a variable interval schedule with 1% banana solution, which was subsequently devalued via LiCl pairing in half the animals. Ethanol (1.0 g/kg), amphetamine (2.0 mg/kg), or saline was administered prior to a post-devaluation test.

RESULTS

Overall, mice showed habitual behavior, but when divided into high- or low-responding groups based on training response rates, saline-treated, low-responding animals devalued, while saline-treated high-responding animals did not. Furthermore, amphetamine elicited devaluation even in high-responding animals, while ethanol prevented devaluation even in low-responding animals.

CONCLUSIONS

These data show that ethanol shifts animals toward behaving habitually. This may illuminate why alcohol-intoxicated individuals display impaired judgment about the relative merits of drinking, and potentially serve as a mechanism by which intoxicated subjects resume previously devalued behaviors, such as comorbid drug use. These findings also show that high variable interval response rates facilitate a shift from goal-directed to habitual behavior.

Substance use disorders: Relationship with intermittent explosive disorder and with aggression, anger, and impulsivity

BACKGROUND

A relationship between substance use and aggression has been noted for decades. While substance use appears to be associated with an increased risk of aggressive behavior, no study has yet reported on the pattern of comorbidity and temporal relationship between impulsive aggression (i.e., intermittent explosive disorder) and substance use disorders (SUD), specifically.

METHODS

To specify these relationships, we examined DSM-5 diagnosis data from diagnostic interviews of 1355 adults who met one of five non-overlapping diagnostic subgroups: those with intermittent explosive disorder (IED; n = 339), those with SUD (n = 136), IED+SUD (n = 280), adults with psychiatric disorders but no SUD or IED (n = 320), and healthy

CONTROLS

HC, n = 282).

RESULTS

Occurrence of lifetime SUD was elevated in IED vs. all Non-IED subjects (Odds Ratio: 3.61 [95% CI: 2.82-4.63]) and onset of IED preceded SUD in 80% of comorbid IED+SUD cases. Examination of the severity of impulsive aggression and SUD revealed that IED increased SUD severity but the presence of SUD did not increase severity of IED core features, including aggression, anger, or impulsivity.

CONCLUSIONS

Subjects with IED are at increased risk of developing substance use disorder, compared to those without IED. This suggests that history of recurrent, problematic, impulsive aggression is a risk factor for the later development of SUD rather than the reverse. Thus, effective treatment of impulsive aggression, before the onset of substance misuse, may prevent or delay the development of SUD in young individuals.

Explaining alcohol use and suicide risk: a moderated mediation model involving insomnia symptoms and gender

STUDY OBJECTIVES

The purpose of the study was to examine whether insomnia symptoms and nightmares mediated the relation between alcohol use and suicide risk. Further, we examined whether this mediation was moderated by gender.

DESIGN

The study consisted of questionnaires administered online examining insomnia symptoms, nightmares, alcohol use, and suicide risk.

SETTING

University.

PATIENTS OR PARTICIPANTS

375 undergraduate students at a large, public university in the southeastern United States.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Results indicated that insomnia symptoms significantly mediated the relation between alcohol use and suicide risk; however, this mediation was moderated by gender. For women, there was both a direct effect of alcohol use on suicide risk as well as an indirect effect of alcohol use through insomnia symptoms increasing suicide risk. For men, there was no direct effect of alcohol use on suicide risk, but there was a significant indirect effect of alcohol use increasing suicide risk through insomnia symptoms. Nightmares were not related to alcohol use, and the association between nightmares and suicide risk was found to be independent of alcohol use.

CONCLUSIONS

Insomnia symptoms are an important factor in explaining the mechanism by which alcohol use increases suicide risk.

Effects of acute alcohol consumption and processing of emotion in faces: Implications for understanding alcohol-related aggression

The negative consequences of chronic alcohol abuse are well known, but heavy episodic consumption ("binge drinking") is also associated with significant personal and societal harms. Aggressive tendencies are increased after alcohol but the mechanisms underlying these changes are not fully understood. While effects on behavioural control are likely to be important, other effects may be involved given the widespread action of alcohol. Altered processing of social signals is associated with changes in social behaviours, including aggression, but until recently there has been little research investigating the effects of acute alcohol consumption on these outcomes. Recent work investigating the effects of acute alcohol on emotional face processing has suggested reduced sensitivity to submissive signals (sad faces) and increased perceptual bias towards provocative signals (angry faces) after alcohol consumption, which may play a role in alcohol-related aggression. Here we discuss a putative mechanism that may explain how alcohol consumption influences emotional processing and subsequent aggressive responding, via disruption of orbitofrontal cortex (OFC)-amygdala connectivity. While the importance of emotional processing on social behaviours is well established, research into acute alcohol consumption and emotional processing is still in its infancy. Further research is needed and we outline a research agenda to address gaps in the literature.

Serotonin (5-HT) augmentation reduces provoked aggression associated with primary psychopathy traits

Psychopathy has long been associated with aggressive behavior; however, the neurochemical underpinnings of this relationship are poorly understood. Serotonin (5-HT) neurotransmitter system abnormalities have been associated with provoked aggression in general. In addition, 5-HT dysregulation has been linked to empathy, a trait that is lacking in individuals who score high on primary psychopathy. The purpose of this study was to determine if 5-HT modulates the relationship between psychopathic traits and aggression. Participants (N = 47) completed a self-report measure of psychopathy and were then administered either 40 mg paroxetine (acutely augmenting 5-HT) or placebo. Aggression was assessed during a competitive reaction-time game in which electric shocks were exchanged with an increasingly provocative fictitious opponent. Results indicated that primary psychopathy (but not secondary psychopathy) was related to aggressive responding to provocation. Moreover, 5-HT augmentation attenuated this effect, supporting the notion that aggressive responding associated with primary psychopathic traits may be due in part to 5-HT dysregulation.

Serotonin depletion counteracts sex differences in anxiety-related behaviour in rat

BACKGROUND

Numerous studies suggest (1) that a major physiological role of brain serotonin-containing neurons is to modulate sex steroid-driven behaviour such as sex and aggression, (2) that sex steroids influence brain serotonergic neurotransmission and (3) that brain serotonergic neurotransmission displays sexual dimorphism. Such observations indicate that an important task for brain serotonin is to either enhance or counteract sex differences in behaviour.

METHODS

To test this hypothesis, we explored the effect of short-term serotonin depletion on the behaviour of adult male and female rats in a behavioural paradigm in which males and females have been shown to behave differently, i.e. the elevated plus maze.

RESULTS

Two rounds of testing of untreated Wistar rats confirmed the previous observation that females make more entries into open arms (round 1, p = 0.001; round 2, p = 0.008) and spend more time on these arms (round 1, p ≤ 0.001; round 2, p = 0.006) than males; in addition, males displayed fewer entries into closed arms upon habituation, i.e. at the second round (p ≤ 0.001) than did females. Administration of the tryptophan hydroxylase inhibitor para-chloro-phenylalanine, at a regimen (300 mg/kg/day for 3 days), markedly reducing brain content of serotonin, enhanced entries upon open arms (p = 0.01) and time spent on open arms (p = 0.004) in males but exerted no such effects in females (p = 0.9 and p = 0.9, respectively); moreover, it reduced entries into closed arms in females (p ≤ 0.001) but not in males (p = 0.1).

CONCLUSIONS

Serotonin depletion abolishing the sex differences observed at baseline supports the theory that serotonin aids to uphold certain sex differences in behaviour.

Revisiting the serotonin-aggression relation in humans: a meta-analysis

The inverse relation between serotonin and human aggression is often portrayed as "reliable," "strong," and "well established" despite decades of conflicting reports and widely recognized methodological limitations. In this systematic review and meta-analysis, we evaluate the evidence for and against the serotonin deficiency hypothesis of human aggression across 4 methods of assessing serotonin: (a) cerebrospinal fluid levels of 5-hydroxyindoleacetic acid (CSF 5-HIAA), (b) acute tryptophan depletion, (c) pharmacological challenge, and (d) endocrine challenge. Results across 175 independent samples and over 6,500 total participants were heterogeneous, but, in aggregate, revealed a small, inverse correlation between serotonin functioning and aggression, anger, and hostility (r = -.12). Pharmacological challenge studies had the largest mean weighted effect size (r = -.21), and CSF 5-HIAA studies had the smallest (r = -.06). Potential methodological and demographic moderators largely failed to account for variability in study outcomes. Notable exceptions included year of publication (effect sizes tended to diminish with time) and self- versus other-reported aggression (other-reported aggression was positively correlated to serotonin functioning). We discuss 4 possible explanations for the pattern of findings: unreliable measures, ambient correlational noise, an unidentified higher order interaction, and a selective serotonergic effect. Finally, we provide 4 recommendations for bringing much needed clarity to this important area of research: acknowledge contradictory findings and avoid selective reporting practices; focus on improving the reliability and validity of serotonin and aggression measures; test for interactions involving personality and/or environmental moderators; and revise the serotonin deficiency hypothesis to account for serotonin's functional complexity.

Chronic modulation of serotonergic neurotransmission with sertraline attenuates the loudness dependence of the auditory evoked potential in healthy participants

RATIONALE

The loudness dependence of the auditory evoked potential (LDAEP) has been reported to be an effective non-invasive measure of central serotonergic neurotransmission. However, acute manipulations of the serotonergic system in humans and animals have yielded inconsistent findings.

OBJECTIVES

In this study, we examined the chronic effect of serotonergic manipulation using the selective serotonin reuptake inhibitor, sertraline, on the LDAEP. In addition, we examined the influence of 5-HTTLPR genotype and individual differences in plasma drug concentrations on the LDAEP.

METHODS

The study utilised a double-blind, placebo-controlled, between-group design in which 40 (24 female) healthy adults (M age = 22.0 years, SE = 0.7) were tested following placebo or sertraline for an average of 24 days. The LDAEP was assessed 6 h post-final dose, and changes in the slope of amplitude of the N1/P2 across intensities (60, 70, 80, 90, 100 dB) were examined at Cz.

RESULTS

The sertraline group had a significantly smaller LDAEP than the placebo group [F(1,38) = 5.97, p = 0.02]. Drug plasma levels did not correlate with the LDAEP in the sertraline group, and there was no influence of 5-HTTLPR genotype.

CONCLUSIONS

We show for the first time that chronically modulating serotonin neurotransmission alters the LDAEP in healthy adults, consistent with extant literature indicating a moderating role of serotonin on this neurophysiological biomarker. The findings from this study together with previous studies suggest that the LDAEP may be a more sensitive marker of long-term or chronic rather than acute changes in the serotonin system.

Zolmitriptan and human aggression: interaction with alcohol

RATIONALE

The serotonin 1(B/D) (5-HT1(B/D)) receptor has shown potential as a target for decreasing aggression. The 5-HT1(B/D) agonist zolmitriptan's ability to reduce aggressive behavior in humans and its interaction with the well-known aggression-enhancing drug alcohol were examined.

OBJECTIVES

Our objective was to investigate zolmitriptan's potential to modify human aggression in a laboratory paradigm across a range of alcohol doses. Alcohol has been consistently associated with aggression and violence, thus we hoped to expand current understanding of alcohol's role in aggressive behavior via manipulation of the serotonin (5-HT) system.

METHODS

Eleven social drinkers, seven male, were recruited to participate in a research study lasting 3-4 weeks. Aggression was measured using the point-subtraction aggression paradigm (PSAP), a laboratory model widely used in human aggression studies. Subjects were administered 5-mg zolmitriptan and placebo capsules along with alcohol doses of 0.0, 0.4 and 0.8 g/kg in a within-subject, counterbalanced dosing design. Data were analyzed as the ratio of aggressive/monetary-earning responses, to account for possible changes in overall motor function due to alcohol.

RESULTS

There was a significant alcohol by zolmitriptan interaction on the aggressive/monetary response ratio. Specifically, compared to placebo, zolmitriptan decreased the aggressive/monetary ratio at the 0.4- and 0.8-g/kg alcohol doses.

CONCLUSIONS

A 5-mg dose of zolmitriptan effectively reduced alcohol-related aggression in an acute dosing protocol, demonstrating an interaction of 5-HT and alcohol in human aggressive behavior.