CSF testosterone and 5-HIAA correlate with different types of aggressive behaviors

Cerebrospinal fluid monoamine and metabolite concentrations and aggression in rats

In humans and other primates low cerebrospinal fluid (CSF) levels of the major serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) have been correlated to high aggressiveness. This finding forms the basis of the 5-HT deficiency hypothesis of aggression. Surprisingly, this correlation has not been confirmed in rodents so far, while manipulation studies aimed to investigate the link between 5-HT and aggressive behaviour are mostly carried out in rodents. In this study the relation between aggression and CSF monoamine and metabolite concentrations was investigated in male Wildtype Groningen rats. In sharp contrast to the hypothesis and our expectation, a clear positive correlation was found between the individual level of trait-like aggressiveness and CSF concentrations of 5-HT, 5-HIAA, norepinephrine (NE), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC). Shortly after the acute display of aggressive behaviour (as a state-like phenomenon), decreased 5-HT levels and an increase in 5-HIAA/5-HT ratio and NE concentrations were found. Surprisingly, pharmacological challenges known to influence 5-HT transmission and aggressive behaviour did not affect CSF 5-HT and 5-HIAA concentrations, only the NE level was increased. Lesioning 5-HT terminals by 5,7-dihydroxytryptamine (5,7-DHT) administration caused a decrease in CSF 5-HT and 5-HIAA, but without affecting aggressive behaviour. The observed positive correlation between CSF 5-HIAA and trait aggressiveness makes it questionable whether a direct extrapolation of neurobiological mechanisms of aggression between species is justified. Interpretation of CSF metabolite levels in terms of activity of neural substrates requires a far more detailed knowledge of the dynamics and kinetics of a neurotransmitter after its release.

Differential pharmacological treatment of paraphilias and sex offenders

This article gives an overview of current pharmacological treatment of paraphilias and sex offenders focusing on the situation in Germany. Information about selective serotonin reuptake inhibitors (SSRI) is followed by data about established antihormonal substances (cyproterone acetate/CPA, and medroxyprogesterone acetate/MPA), as well as a more detailed account on luteinizing hormone-releasing hormone agonists (LHRH agonists). The results of open, uncontrolled clinical studies with SSRIs (n = 16) and LHRH agonists (n = 11) in paraphilic outpatients confirm the positive effects of these substances. A survey about the use of CPA and LHRH agonists in forensic hospitals in Germany shows that half of the patients treated with any kind of (anti-) hormonal agents received an LHRH agonist. The authors present a protocol on side effects, contraindications, and monitoring of CPA and LHRH agonists and develop an algorithm for differential pharmacotherapy of paraphilias.

Familial correlates of central serotonin function in children with disruptive behavior disorders

Previous findings suggest a relationship between childhood aggression, parental history of aggression and central serotonin (5-HT) function. The present study extended these findings by examining the impact of childhood aggression and central 5-HT function on the incidence of psychopathology in first- and second-degree relatives of pre-pubertal children with disruptive behavior disorders. Family history of psychopathology was obtained for 58 aggressive and 44 non-aggressive clinically referred children who were further sub-divided based on central 5-HT function. Central 5-HT function was assessed by measuring the prolactin response to a 1 mg/kg oral dose of d,l-fenfluramine. Aggressive children with low-prolactin responses to fenfluramine had a significantly greater incidence of first- and second-degree relatives with aggressive and antisocial characteristics compared to both non-aggressive children and aggressive children with high-prolactin responses. No group differences were found in the frequency of relatives with symptoms of cognitive impairment or inattention and hyperactivity. These data suggest that there are both familial and non-familial forms of aggression in children, and that only the familial type is associated with reduced 5-HT function.

Physiological correlates of aggression and impulsivity in free-ranging female primates

We examined the relations among cerebrospinal fluid (CSF) monoamine metabolite concentrations, plasma hormone concentrations, aggression, and impulsive risk-taking behavior in a free-ranging population of female rhesus macaques. We selected 44 juvenile female rhesus macaques as subjects from a population of approximately 3000 macaques that inhabit a 475-acre Sea Island. We obtained CSF and blood samples, and recorded behavioral observations over a subsequent 18-month period. Our results indicate an inverse correlation between CSF concentrations of the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), and the frequency of low-intensity restrained aggression typically associated with matrilineal defense of social status. In contrast, previous research with males has shown an inverse correlation between CSF 5-HIAA concentrations and levels of violent unstrained aggression typically associated with traumatic injury and death. We also noted a negative correlation between plasma concentrations of the stress hormone cortisol and the frequency of low-intensity aggressive acts, a finding not reported in our previous studies with males. Further examination revealed a negative correlation between CSF 5-HIAA concentrations and the rate of long dangerous leaps through the forest canopy, suggesting that the relation between low serotonergic functioning and impulsivity may generalize to both female and male primates. These results indicate that females with low CSF 5-HIAA concentrations, like their male counterparts, are at increased risk for impulsive temperament, but that unlike males, females may be buffered from this risk through intersexual differences in life history patterns and social affiliation.

Association of anger-related traits with SNPs in the TPH gene

Since both aggression-related traits and serotonergic activity are partially heritable and correlate inversely, variations in genes of the serotonergic system might then, to some extent, account for variations in aggression-related behavior. Tryptophan hydroxylase (TPH) is the rate limiting biosynthetic enzyme in the serotonin pathway and regulates levels of serotonin. Recently, a genetic variation in TPH has been associated with aggression and anger-related traits in volunteers. We investigated a sample of community-based healthy volunteers (n = 154) and suicide attempters (n = 86), a clinical population with a high risk for elevated impulsive aggression and related traits. The subjects were genotyped for a A218C and a A779C single nucleotide polymorphism (SNP) located in the TPH gene. All subjects were administered standard psychiatric interviews as well as self-report questionnaires for aggression, irritability and anger-related traits. For anger-related traits, a multivariate effect of the tryptophan hydroxylase genotype and an interaction effect for genotype and diagnosis was observed in healthy volunteers and suicide attempters after controlling for age and educational level. U-carriers in both groups showed higher scores for State Anger, Trait Anger and Angry Temperament. These findings support the hypothesis that the A218C and the A779C SNP in the TPH gene may be associated with anger-related traits in German samples.

Methylenedioxymethamphetamine (MDMA, Ecstasy) neurotoxicity: cellular and molecular mechanisms

Methylenedioxymethamphetamine (MDMA, Ecstasy) is a very popular drug of abuse. This has led to new intense concerns relevant to its nefarious neuropsychiatric effects. These adverse events might be related to the neurotoxic effects of the drug. Although the mechanisms of MDMA-induced neurotoxicity remain to be fully characterized, exposure to the drug can cause acute and long-term neurotoxic effects in animals and nonhuman primates. Recent studies have also documented possible toxic effects in the developing fetus. Nevertheless, there is still much debate concerning the effects of the drug in humans and how to best extrapolate animal and nonhuman primate data to the human condition. Herein, we review the evidence documenting the adverse effects of the drug in some animal models. We also discuss possible mechanisms for the development of MDMA neurotoxicity. Data supporting deleterious effects of this drug on the developing fetus are also described. Much remains to be done in order to clarify the molecular and biochemical pathways involved in the long-term neuroplastic changes associated with MDMA abuse.

CSF 5-HIAA concentration as an early screening tool for predicting significant life history outcomes in female specific-pathogen-free (SPF) rhesus macaques (Macaca mulatta) maintained in captive breeding groups

We examined relationships among cerebrospinal fluid (CSF) concentrations of the major serotonin metabolite (5-HIAA, 5-hydroxyindoleacetic acid) and significant medical and behavioral outcomes for female rhesus macaques. Based on earlier findings with males we predicted that low CSF 5-HIAA concentrations would be associated with a range of negative life history outcomes in our captive specific-pathogen-free (SPF) breeding colony. We found that the mean CSF 5-HIAA concentration among animals that died over the course of the study period was significantly lower than among animals that survived. Further examination indicated an inverse relationship between CSF 5-HIAA concentration and number of treatments for illness, further suggesting a link between serotonergic functioning and overall animal health. Examination of behavioral data indicated that individuals with low CSF 5-HIAA concentrations were more often the targets of aggressive bouts than were individuals with high CSF 5-HIAA concentrations. Finally, we found a positive relationship between CSF 5-HIAA concentration and infant survivorship. These results suggest negative life history consequences of impaired serotonergic functioning in captive female rhesus macaques, and indicate that CSF 5-HIAA concentration sampled early in life may provide a useful tool in facilitating colony management decisions concerning utilization of scarce and increasingly valuable non-human primate resources.

Effects of acute treatment with 8-OH-DPAT and fluoxetine on aggressive behaviour in male song sparrows (Melospiza melodia morphna)

The role of serotonin in modulating male aggressive behaviour was investigated in male song sparrows, Melospiza melodia morphna, using two different serotonergic drugs, fluoxetine and 8-OH-DPAT. Fluoxetine is a selective serotonin reuptake inhibitor of the neuronal reuptake pump increasing synaptic concentrations of serotonin, and 8-OH-DPAT is a specific serotonin (5-HT1A) receptor agonist. The serotonergic control of aggression in passerines has not been previously investigated. We examined these behaviours within a controlled setting using a laboratory simulated territorial intrusion, with a hierarchical scale to quantify male-male aggressive behaviour. Utilizing this scale, we quantified the extent of male aggressive behaviour in two experiments. In experiment 1, song sparrows were given 100 micro l, s.c. injections of either fluoxetine (10 mg/kg) or 8-OH-DPAT (1 mg/kg). Experiment 2 was a dose-response study using three doses of 8-OH-DPAT (0.1, 1 and 10 mg/kg). In both studies, aggressive behaviour was measured 1 h after injection for 10 min in response to the presence of a novel male decoy combined with playback of conspecific song. Both drugs significantly reduced male aggressive behaviour, and 8-OH-DPAT did so in a dose-dependent manner. The effect of the two drugs upon general activity was also measured using infra-red perch hop detectors. Activity levels were not effected by either fluoxetine or 8-OH-DPAT at all of the respective doses, indicating that the reduction in aggressive behaviour was specific. These results demonstrate that, in a passerine species, the serotonergic system negatively regulates male-male aggressive behaviour. These results further demonstrate that aggression can be effectively studied in a laboratory setting and natural aggressive responses can be elicited using this method.

Comparative urinary androstanes in the great apes

Urinary androstanes from seven species of male great apes (human, bonobo, chimpanzee, lowland gorilla, mountain gorilla, Bornean orangutan, and Sumatran orangutan) were separated by HPLC and detected by RIA using two testosterone antibodies. All animals examined showed the presence of testosterone and six additional immunoreactive peaks. Although testosterone was the dominant peak (85%) in human urine, its proportion in urine was much less in the other apes, ranging from a high of 59% in the bonobo and chimpanzee to a low of 24% in the mountain gorilla. Urinary androstanes were also directly visualized using nano-spray mass spectrometry (nanoESI-MS). Although the RIA can qualitatively produce a strong signal for testosterone in unchromatographed urine, it is quantitatively present only as a trace metabolite, as demonstrated by nanoESI-MS. The combination of the two techniques showed large differences in androstane metabolism between the seven species. A previously undescribed testosterone metabolite (tentatively identified as either delta1- or delta6-testosterone sulfate) was present in significant proportions in all of the non-human apes examined. We conclude that in the great apes, testosterone is only a trace metabolite in urine, and as a consequence, its measurement may not produce results that parallel the levels of serum testosterone. The RIA measurement of urinary testosterone in part records additional androstane metabolites, which vary even between closely related genera, making the results neither equivalent with nor comparable to different species.

Effect of tryptophan depletion on impulsive behavior in men with or without a family history of alcoholism

This study investigated the effects of acute serotonin depletion on two measures of impulsive behavior in healthy men with a family history of alcoholism. Serotonin has been implicated in several forms of impulsive behavior, as well as in the etiology of Type II alcoholism. The present study was designed to determine if an acute disturbance of serotonin function would increase impulsive responding on two behavioral indices of impulsivity, and whether this effect would be greater in individuals with a genetic predisposition to alcoholism. Forty healthy men, half of whom had an alcoholic father, participated in a two-session study. Subjects ingested a tryptophan-depleting diet on one session and a balanced diet on the other session, and completed tasks measuring behavioral inhibition and delay discounting. Tryptophan depletion impaired performance on the behavioral inhibition task in the males with a positive family history, relative to the males without alcoholic relatives, whereas it improved behavioral inhibition in the family history negative group. Tryptophan depletion had negligible effects on mood, and it did not alter performance on the delay discounting task. The results provide partial support for the hypothesis that impulsive behavior is related to low serotonin function, and further suggests that the role of serotonin depends on genetic factors related to alcoholism. The results complement the results of a parallel study investigating the effects of serotonin depletion on a similar behavioral inhibition procedure in rats. Parallel studies in rats and humans are important to validate the large body of neurobiological research with non-human species to humans.

Evolutionary underpinnings of excessive alcohol consumption

Given our close phylogenetic relatedness, non-human primates, in principle, could serve as an ideal model for alcoholism. Indeed, many studies in both humans and rhesus macaques show relationships between excessive alcohol consumption, aggression and serotonergic function, as measured by concentrations of the principal metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF). An important behavioral predictor of excessive alcohol consumption in both humans and rhesus monkeys is the propensity toward impulsivity. Integrating behavioral and neuroendocrine data from captive and semi-free-ranging rhesus macaques, we posit that benefits derived from impulsive and aggressive behaviors in some contexts might contribute indirectly to the maintenance of traits involved in alcoholism and excessive alcohol intake.

The finding of an inverse relationship between social dominance and feeding priority among pairs of unfamiliar adult male vervet monkeys (Cercopithecus aethiops sabaeus)

Dominance is often presumed to confer priority of access to resources. This study evaluated the relationship between two assessments of dominance: (1) social dominance, based on agonistic interactions and (2) feeding priority among pairs of unfamiliar adult vervet monkeys (Cercopithecus aethiops sabaeus) differing in scrotal colour, but matched for height, weight and testicular volume, during paired introduction experiments. Results of this investigation showed that neither size differences nor scrotal colour were predictive of feeding priority, and social dominance was inversely related to feeding priority. This finding demonstrates that different assessments of dominance can yield different outcomes even within the same primate taxon. I propose that male dominance rank may best predict access to resources when there is direct contest competition over a resource, which is not immediately exhaustible, whereas highly impulsive low ranking males may gain a competitive edge in scramble competitions for ephemeral and small resources.

Urinary androgen and corticoid levels in captive, male Western lowland gorillas (Gorilla g. gorilla): age- and social group-related differences

Urinary androgen and corticoid levels were measured for 52 captive male Western lowland gorillas to examine age-related variance and potential differences resulting from various social situations. Significant diurnal variation was present in both hormones. Age-related differences in androgens revealed that males experienced two stages of androgen increase and one stage of decrease: increases occurred from juvenile (less than 10 yr of age) to subadult (between 10-13 yr) and subadult to young adult (14-20 yr), whereas decreases occurred from young adult to adult (> 20 yr). Age-related differences in corticoid levels varied depending on the time of day, but morning corticoids were greatest in juvenile males, followed by young adult males. The type of social grouping was associated with differences in corticoid levels, as animals housed socially (in either a heterosexual or all-male group) had similar corticoid levels, whereas solitary males showed greater corticoid levels than their socially-housed counterparts. The increased levels of corticoids in solitary-housed males suggest this management strategy might not be optimal, although more data are needed. Additionally, the significantly greater levels of androgens and corticoids in young adult male gorillas may present management challenges, and thus zoos may need to consider increasing the flexibility of their current management practices with respect to males.

Plasma testosterone and pathological gambling

The authors studied plasma testosterone levels and psychological characteristics of male pathological gamblers. Twenty-nine male pathological gamblers and a group of healthy volunteers matched for age and gender were compared on levels of plasma testosterone and scores on the Eysenck Personality Questionnaire (EPQ) and the Psychopathic Deviance scale of the Minnesota Multiphasic Personality Inventory (MMPI). Plasma testosterone levels were similar in the pathological gambling and comparison group (476.06 ng/100 ml vs. 560.71 ng/100 ml). Patients had higher scores on the Neuroticism subscales of the EPQ (13.83 vs. 10.83) and the Psychopathic Deviance scale of the MMPI (27.03 vs. 21.03), but not on any of the other subscales of the EPQ. Testosterone levels did not correlate with the psychological ratings. Testosterone levels are probably not related to impulsivity in pathological gambling.

Biological markers for suicidal behavior in alcohol dependence

Alcohol-dependent populations have a high lifetime suicide rate (between 7 and 15%, relative risk = 7), and alcoholism is one of the two psychiatric disorders most frequently found in suicidal cases (between 15 and 25%). Biological factors that would detect patients at risk could thus be of value. Carbohydrate-deficient transferrin, monoamine oxidase B, soluble interleukin-2 receptor and cholesterol have been proposed as markers of suicidal risk in alcohol-dependent patients, although nonspecific and with low predictive value. On the other hand, there is large and convergent data stressing the importance of serotonin dysregulation as increasing the risk for aggressive behaviour toward the self, although it is not clear whether serotonin is involved through the altered behavior inhibition system, enhancement of anxiety and depression, or association with specific subtypes of alcohol-dependence, such as early-onset type II alcoholism. Considering the complex but significant impact of alcohol on serotonin metabolism and turnover, it is likely that serotonin mediates a large part of the proneness of ethanol to commit impulsive-aggressive behavior.

Serotonin, testosterone and alcohol in the etiology of domestic violence

In a previous study we administered the panicogenic agent sodium lactate to a select group of perpetrators of domestic violence and comparison groups. Results of that study showed that perpetrators exhibited exaggerated lactate-induced fear, panic and rage. In this current study, we compared the cerebral spinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA) and testosterone obtained from perpetrators of domestic violence and a group of healthy comparison subjects. All subjects were assessed for DSM-III-R diagnoses. Perpetrators with alcohol dependence (DV-ALC) (n=13), perpetrators without alcohol dependence (DV-NALC) (n=10) and healthy comparison subjects (HCS) (n=20) were clinically assessed using the Spielberger Trait Anxiety, Brown-Goodwin Aggression Scale, Buss Durkee Hostility Inventory and Straus Conflict Tactics. Following an overnight fast and bed rest, subjects received a lumbar puncture to obtain CSF concentrations of 5-HIAA and testosterone. Perpetrators scored significantly higher on measures of aggression than HCS. DV-NALC had significantly lower concentrations of CSF 5-HIAA and higher Straus Conflict Tactics (CT) physical violence scores than DV-ALC and HCS. DV-ALC had significantly higher concentrations of CSF testosterone than DV-NALC. DV-ALC also had significantly higher Straus CT physical violence scores than HCS. DV-NALC and DV-ALC differed on 5-HIAA concentrations, testosterone concentrations, Straus CT physical violence scores and alcohol dependence. These results suggest that DV-NALC and DV-ALC groups could have different biological mechanisms mediating domestic violence.

Stress, peer affiliation, and transforming growth factor-beta1 in differentially reared primates

A bidirectional regulatory interaction between the central nervous system and the immune system is largely provided by cytokines and their specific receptors, which are expressed by cells of both systems. Transforming growth factor-beta1 (TGF-beta1), produced by glial cells and lymphocytes and regulated by steroid hormones, is one such cytokine. In the current study, we examined the relationship between TGF-beta1 and peer affiliation in bonnet macaques (Macaca radiata) either reared normally or exposed as infants to conditions in which their mothers faced fluctuating requirements for food procurement (variable foraging demand [VFD]). Rearing under VFD conditions has been previously shown to produce dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in these animals. Serum levels of TGF-beta1 after exposure to a moderate stressor had no correlation with peer affiliation under baseline conditions (r=.07), but were highly correlated with affiliation after subsequent challenge with a fear stimulus (r=.62). Affiliation after the fear stimulus also was inversely correlated with baseline levels of affiliation (r=-.71). These data suggest that changes in peripheral TGF-beta1 may be reflective of latent behavioral and biochemical propensities possibly related to affect. Further examination of the effects of early adversity will improve our understanding of the relationship between the HPA axis and immune function.

Chronic subordination stress in male tree shrews: replacement of testosterone affects behavior and central alpha(2)-adrenoceptors

Subordination stress induced by social defeat in male animals is known to inhibit gonadal functions and it has been discussed whether the resulting deficit in testosterone might play a role in subordination behavior. One of the major transmitter systems involved in regulation of behavior is the noradrenergic system. To analyze whether a testosterone replacement can alter subordination behavior and whether this might be related to changes in the brain noradrenergic system, we quantified alpha(2)-adrenoceptors (alpha(2)-ARs) in the central nervous system of male tree shrews. Animals were submitted to chronic subordination stress and received testosterone at the same time. Behavior was monitored during all phases of the experiment: the control period of 10 days, the period of social stress lasting 10 days when subordinates were confronted daily with a dominant male, and, subsequently, the stress and treatment period of 18 days when in parallel to the stress, animals received either injections of testosterone or vehicle. Brain alpha(2)-ARs were quantified by in vitro receptor autoradiography using the antagonist ligand (3)H-RX821002. Locomotor activity decreased significantly during the stress period and was not re-normalized by testosterone. In contrast, testosterone re-normalized scent marking behavior and autogrooming, parameters that had both been reduced due to the subordination stress. Vehicle injections improved none of these behaviors. In 8 of 10 brain regions that were analyzed, numbers of alpha(2)-adrenergic binding sites were increased in stressed animals that received vehicle injections, but a difference between testosterone and vehicle injected animals was only observed in five regions. These brain regions are all known to be involved in emotional behavior (anterior hypothalamus, medial nucleus of the amygdala, cingulate cortex) or autonomic regulation, respectively (solitary tract nucleus, dorsal motor nucleus of vagus). Therefore, our data show that testosterone influences behavior of male subordinates and modulates alpha(2)-AR expression in their brains. Androgen-mediated alterations in receptors occur in brain regions that are known to be involved in emotionality, e.g., in the anterior hypothalamus which regulates aggressive behavior. One can therefore conclude that alpha(2)-ARs contribute to neuronal functions that are responsible for subordination of stress behavior, and that testosterone-induced receptor changes are related to the partial restoration of normal behavior.

Absence of 5-HT(1B) receptors is associated with impaired impulse control in male 5-HT(1B) knockout mice

BACKGROUND

Serotonin (5-HT) plays a complex regulatory role in processes like anxiety, depression, aggression, and impulse control. Due to the large amount of serotonergic receptors, knockout mice offer an important opportunity to investigate the role of specific receptors. The 5-HT(1B) receptor is thought to mediate aggression and impulse control. This was studied here in mice lacking 5-HT(1B) receptors (5-HT(1B) KO).

METHODS

Wild type and 5-HT(1B) KO mice were exposed to several types of entrained and nonentrained stimuli. With telemetry, body temperature, heart rate, and locomotor activity were measured continuously during the different experiments.

RESULTS

To nonentrained stimuli like disturbance stress and confrontation with an intruder, 5-HT(1B) KO mice showed exaggerated physiologic and behavioral responses. These mice displayed behavioral disinhibition, measured as increased social interest and aggression to an intruder mouse. However, in response to well-entrained stimuli like daily light transitions, responses were smaller in 5-HT(1B) KO than in wild type mice, suggesting that hyperreactivity is stimulus specific.

CONCLUSIONS

Serotonin 1B receptors are essential in impulse control by inhibiting responses to nonentrained stimuli. Therefore, the 5-HT(1B) KO mouse might be an important additional model for studying aspects of disinhibition in aggression and impulse control.

Individual differences in response to a stranger: social impulsivity as a dimension of temperament in vervet monkeys (Cercopithecus aethiops sabaeus)

Social impulsivity in response to a stranger was assessed in male vervet monkeys (Cercopithecus aethiops sabaeus) using the Intruder Challenge Test. Vervets (N = 128, ages 3-18 years) were presented with an unfamiliar adult male at the periphery of the home enclosure. An index of impulsivity reflecting variation in the tendency to rapidly approach, engage, and challenge the intruder was derived from factor analysis of behavioral responses. Scale reliability (alpha = .84) and test-retest consistency (intraclass correlation = .83) were high, indicating that this index reliably and efficiently measures a stable aspect of temperament from impulsive to inhibited. Impulsivity scores peaked at age 4, when vervet males typically emigrate from the natal group. The highest ranking males in each group were more likely to score in the moderate range, whereas lower ranking males were more likely to score in the highest (impulsive) or lowest (inhibited) quartiles.

Aggressive behavior, increased accumbal dopamine, and decreased cortical serotonin in rats

Dopamine (DA) and serotonin have been implicated in the regulation of aggressive behavior, but it has remained challenging to assess the dynamic changes in these neurotransmitters while aggressive behavior is in progress. The objective of this study was to learn about ongoing monoamine activity in corticolimbic areas during aggressive confrontations in rats. Male Long-Evans rats were implanted with a microdialysis probe aimed at the nucleus accumbens (NAC) or medial prefrontal cortex (PFC); next, 10 min samples were collected before, during, and after a 10 min confrontation. Rats continued to display aggressive behavior while being sampled, and they performed two to six attack bites as well as 140 sec of aggressive acts and postures. Dopamine levels in NAC were significantly increased up to 60 min after the confrontation. Peak levels of 140% were achieved approximately 20-30 min after the confrontation. No concurrent changes in accumbal serotonin levels were seen during or after the confrontation. Dopamine and serotonin levels in PFC changed in the opposite direction, with a sustained decrease in serotonin to 80% of baseline levels during and after the confrontation and an increase in dopamine to 120% after the confrontation. The temporal pattern of monoamine changes, which followed rather than preceded the confrontation, points to a significant role of accumbal and cortical DA and 5-hydroxytryptamine in the consequences as opposed to the triggering of aggressive acts. The increase in accumbal DA in aggressive animals supports the hypothesis that this neural system is linked to the execution of biologically salient and demanding behavior.

Relationship between central serotonergic function and aggression in prepubertal boys: effect of age and attention-deficit/hyperactivity disorder

Data indicate that diminished central serotonergic (5-HT) function is related to aggression in adults, but discrepant findings in children suggest that age or the presence of attention-deficit/hyperactivity disorder (ADHD) may influence this relationship. This study examined whether age or ADHD affects the association between 5-HT and aggression in 7-11-year old clinically-referred boys. Forty-six boys were divided into non-aggressive ADHD, aggressive ADHD, and aggressive non-ADHD groups based on responses to interviews and ratings of behavior. Central 5-HT function was assessed by measuring the prolactin response to a 1-mg/kg oral dose of D,L-fenfluramine. There was no significant difference in the prolactin response across the three groups of boys. Furthermore, when examined dimensionally, prolactin response was largely unrelated to ratings of aggression, even after controlling for ADHD. Finally, age was not associated with prolactin response, and had no effect on the relationship between prolactin response and aggression. This study provides further evidence that there is no clear relationship between central 5-HT function and aggression in disruptive boys. Moreover, these data do not confirm the hypothesis that age or the presence of ADHD influence the relationship between 5-HT and childhood aggression.

Increased adrenal androgen functioning in children with oppositional defiant disorder: a comparison with psychiatric and normal controls

OBJECTIVE

To examine the relationship between adrenal androgens and aggression in children with oppositional and antisocial behavior and to compare their levels with those of psychiatric and normal controls.

METHOD

Dehydroepiandrosterone sulfate (DHEAS) was measured in 24 children with oppositional defiant disorder (ODD), 42 psychiatric controls (including 20 children with attention-deficit/hyperactivity disorder [ADHD]), and 30 normal controls. The children's parents filled out the Child Behavior Checklist (CBCL).

RESULTS

Children with ODD had higher DHEAS levels than either the psychiatric control or normal control groups; DHEAS levels of the latter groups did not differ. Moreover, it was possible to classify children as having either ODD or ADHD on the basis of their DHEAS levels, whereas this was not the case on the basis of the CBCL data.

CONCLUSIONS

The results indicate that adrenal androgen functioning is specifically elevated in children with ODD. It is speculated that the mechanism could be a shift in balance of ACTH-beta-endorphin functioning in the hypothalamic-pituitary-adrenal axis due to early stress or genetic factors.

Anabolic androgenic steroids affects alcohol intake, defensive behaviors and brain opioid peptides in the rat

The present study investigated whether a relationship exists between nandrolone decanoate and voluntary ethanol intake in laboratory rats. Animals were subjected to daily subcutaneous injections with nandrolone decanoate (15 mg/kg) during 2 weeks. One group of animals was tested for voluntary alcohol intake 1 week after the end of the 2-week treatment period and another group received alcohol 3 weeks after the treatment. In addition, assessment of defensive behaviors and immunoreactivity (ir) levels of the brain opioid peptides dynorphin B and Met-enkephalin-Arg-Phe (MEAP) were performed. The nandrolone decanoate-treated animals were significantly more aggressive and showed lower fleeing and freeezing reaction than the oil-treated controls. Treatment with nandrolone decanoate enhanced voluntary alcohol intake, regardless if it was presented 1 or 3 weeks after end of the treatment period. These animals had a decreased activity of dynorphin B-ir in the nucleus accumbens, decreased levels of MEAP-ir in the periaqueductal gray (PAG) and higher levels of MEAP-ir in the hypothalamus compared to controls. In line with previous studies, this suggests that the altered dynorphin B-ir activity may promote the rewarding effects of ethanol and thereby increasing alcohol intake, whereas MEAP-ir may be associated with the ability to control the aggressive reaction. Abuse of nandrolone decanoate may thus constitute a risk factor for increased alcohol consumption and defensive aggression. In human, this constellation of behavioral symptoms is closely related to acts of crimes and violence and is often observed among those abusing anabolic androgenic steroids.

Dysfunction in the neural circuitry of emotion regulation--a possible prelude to violence

Emotion is normally regulated in the human brain by a complex circuit consisting of the orbital frontal cortex, amygdala, anterior cingulate cortex, and several other interconnected regions. There are both genetic and environmental contributions to the structure and function of this circuitry. We posit that impulsive aggression and violence arise as a consequence of faulty emotion regulation. Indeed, the prefrontal cortex receives a major serotonergic projection, which is dysfunctional in individuals who show impulsive violence. Individuals vulnerable to faulty regulation of negative emotion are at risk for violence and aggression. Research on the neural circuitry of emotion regulation suggests new avenues of intervention for such at-risk populations.

Plasma total cholesterol concentrations do not predict cerebrospinal fluid neurotransmitter metabolites: implications for the biophysical role of highly unsaturated fatty acids

Low concentrations of a metabolite of serotonin found in cerebrospinal fluid (CSF), 5-hydroxyindolacetic acid (5-HIAA), are strongly associated with suicidal and violent behaviors. Although lowering of plasma total cholesterol has been suggested to increase mortality from suicide and violence by decreasing concentrations of CSF 5-HIAA via changes in membrane biophysical properties, highly unsaturated fatty acids may play a more important role. Violent and nonviolent comparison groups, early- and late-onset alcoholics, and healthy comparison subjects were studied to control for alcohol use and predisposition to violence. Fasting plasma total cholesterol and CSF were assayed under stringently controlled conditions. When all groups were combined (n = 234), plasma cholesterol concentrations had a weak positive correlation with CSF 5-HIAA (r = 0.18, P < 0.01). However, age correlated with both plasma total cholesterol and CSF 5-HIAA concentrations. When age was included in multiple regression models, the correlation between cholesterol and CSF 5-HIAA concentrations was not significant. Cholesterol correlated weakly with CSF 5-HIAA concentrations only in late-onset alcoholics after age was controlled for, but the relation was not significant after correction for multiple testing. CSF homovanillic acid did not correlate with plasma total cholesterol in any group. Plasma total cholesterol had no apparent relation to CSF neurotransmitter metabolites in any group of subjects. Highly unsaturated essential fatty acids, which are also critical determinants of membrane biophysical properties and may be linked to brain serotonin concentrations, should also be considered in studies examining the effect of lowering fat intake on the incidence of suicide and violence.

Salivary prolactin as a marker for central serotonin turnover

Central nervous system (CNS) serotonin deficits have been linked to many pathological behaviors in both human and nonhuman primates. The plasma prolactin response to fenfluramine has been widely used to assess CNS serotonin functioning in humans. Prolactin is also found as an integrated measure in saliva. We hypothesized that salivary prolactin concentrations would correlate positively with cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) in rhesus monkeys. Twenty-seven adult male and female rhesus macaques (Macaca mulatta) were sampled for concurrent saliva, blood, and CSF. Saliva and blood serum were assayed for prolactin concentrations, and CSF was assayed for 5-HIAA, homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG). Salivary prolactin concentrations were positively correlated with CSF 5-HIAA concentrations. No other relationships between any of the measures, including that between salivary prolactin and serum prolactin, were found to be statistically significant. These findings suggest the possibility of using salivary prolactin concentrations as an index of CNS serotonin turnover in humans.

Serum testosterone levels, mental disorders and criminal behaviour

OBJECTIVE

Although previous studies have revealed an association between androgens and aggression, there is a lack of knowledge of this issue in different mental disorders.

METHOD

The associations between serum testosterone levels and criminal behaviour in different mental disorders were examined using data collected from forensic psychiatric male patients (20 schizophrenics and 42 subjects with personality disorders).

RESULTS

Male criminals with personality disorders had significantly higher serum levels of total and free testosterone than criminal schizophrenics. Among schizophrenics, total (P=0.01) and free testosterone (P=0.01) declined significantly more with age compared to healthy controls and patients with personality disorders, and also correlated with duration of neuroleptic drug use (r=-0.60, P=0.000 for total and r=-0.46, P=0.0001 for free testosterone). The recidivists with personality disorder had higher total (P=0.04) and free testosterone (P=0.05) levels than non-recidivists with personality disorder.

CONCLUSION

Personality disordered criminals with multiple offences had high serum testosterone levels. The low testosterone concentrations among schizophrenics may be due either to long-term use of neuroleptic agents or to the mental illness itself and its possible inhibition of the pituitary-gonadal axis.

Reproductive hormone profiles in captive male orangutans: implications for understanding developmental arrest

For many years researchers have described some male orangutans as "subadult." These males are of adolescent to adult age and are reproductive, but have little to no secondary sexual trait development. Until now the only endocrine study of this arrest of secondary sexual trait development was performed by Kingsley (1982, 1988). She found that "subadult" or arrested males have lower testosterone levels than similar age developing adolescents or adult males. In this study, urine samples were collected over a two-year period from 23 captive male orangutans in order to more fully define male endocrine profiles. Three study males were juveniles, seven were arrested adolescents, six were developing adolescents, and seven were mature adults. Morning samples were analyzed by radioimmunoassay for levels of testicular steroids and gonadotropins and group hormone profiles were compared by analysis of variance. Results illustrate that arrested adolescent orangutans have significantly lower testosterone and dihydrotestosterone (DHT) levels than developing adolescents, but significantly higher levels than juveniles. Luteinizing hormone (LH) levels also differed between arrested and developing adolescents, with arrested males having lower levels. However, follicle stimulating hormone (FSH) levels were similar in both morphs of adolescent male. The overall hormone profiles for arrested and developing adolescent male orangutans suggest that arrested males lack levels of LH, testosterone, and DHT necessary for development of secondary sexual traits. However, they have sufficient testicular steroids, LH, and FSH to fully develop primary sexual function and fertility. These endocrine data help define alternative developmental pathways in male orangutans. The authors discuss the relationship between these developmental pathways and male orangutan reproductive strategies, and hypothesize about their prepubertal socioendocrine determination.

Neurotransmitters, neuroendocrine correlates of sensation-seeking temperament in normal humans

Correlations between sensation-seeking (SS) personality dimension and plasma concentrations of norepinephrine (NE), epinephrine, and NE-dependent testosterone (T), cortisol and prolactin (PRL) were studied in 74 physically and psychologically healthy male volunteers, in order to see whether or not the noradrenergic system is involved in the modulation of this personality trait. Novelty-seeking scores by the Temperament and Character Inventory and SS scores on a Visual Analog Scale were positively correlated with plasma NE, T and PRL levels, suggesting that NE and the downstream cascade of NE-dependent hormones, together with other monoaminergic changes, might be responsible for the development and the degree of this temperamental character.

A replication study of violent and nonviolent subjects: cerebrospinal fluid metabolites of serotonin and dopamine are predicted by plasma essential fatty acids

BACKGROUND

Among an independent group of subjects selected for their history of violent, impulsive behaviors and nonviolent control subjects, we attempted to replicate the finding that plasma docosahexaenoic acid concentrations were negatively correlated with cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA) concentrations.

METHODS

CSF 5-HIAA and homovanillic acid (HVA), fasting total cholesterol, and plasma fatty acid concentrations were examined in violent and nonviolent subjects matched for their severity of alcohol dependence.

RESULTS

Violent subjects had significantly higher lifetime violence and hostility ratings and lower concentrations of CSF 5-HIAA than nonviolent subjects. Plasma docosahexaenoic acid was negatively correlated with CSF 5-HIAA only among violent subjects.

CONCLUSIONS

This observational study suggests that dietary essential fatty acids may change neurotransmitter concentrations. Prospective dietary intervention trials will be required to determine if increasing dietary intake of docosahexaenoic acid will increase or decrease either CSF 5-HIAA concentrations or impulsive and violent behaviors.

Adrenal androgens and aggression in conduct disorder prepubertal boys and normal controls

BACKGROUND

The evidence for a role of androgens in human aggression is less convincing than in animals. We examined the relationship between androgens and aggression in prepubertal boys who were diagnosed as suffering from severe aggression and antisocial behavior.

METHODS

Plasma levels of testosterone (T), androstenedione (A), and dehydroepiandrosterone sulphate (DHEAS) were measured in 15 boys with a conduct disorder (CD) and 25 normal control (NC) boys. Parents and teachers of the children rated the intensity of aggression and delinquency over the last 6 months.

RESULTS

CD boys had significantly higher levels of DHEAS and marginally significantly higher levels of A; there were no differences in T. Moreover, DHEAS levels were significantly positively correlated with the intensity of aggression and delinquency as rated by both parents and teachers.

CONCLUSIONS

The results suggest that adrenal androgen functioning plays an important role in the onset and maintenance, of aggression in young boys.

Low central nervous system serotonergic activity is traitlike and correlates with impulsive behavior. A nonhuman primate model investigating genetic and environmental influences on neurotransmission

We have used nonhuman primates to examine developmental and behavioral correlates of CNS serotonergic activity, as measured by concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF). These studies show that interindividual differences in CNS serotonin turnover rate exhibit traitlike qualities and are stable across time and settings, with interindividual differences in CSF 5-HIAA concentrations showing positive correlations across repeated sampling. Primates with low CNS serotonergic activity exhibit behaviors indicative of impaired impulse control, unrestrained aggression, social isolation, and low social dominance. Maternal and paternal genetic influences play major roles in producing low CNS serotonin functioning, beginning early in life. These genetic influences on serotonin functioning are further influenced by early rearing experiences, particularly parental deprivation.

Serotonin, social status and aggression

Serotonin, social status and aggression appear to be linked in many animal species, including humans. The linkages are complex, and, for the most part, details relating the amine to the behavior remain obscure. During the past year, important advances have been made in a crustacean model system relating serotonin and aggression. The findings include the demonstration that serotonin injections will cause transient reversals in the unwillingness of subordinate animals to engage in agonistic encounters, and that at specific synaptic sites involved in activation of escape behavior, the direction of the modulation by serotonin depends on the social status of the animal.

Rhesus macaques with high CSF 5-HIAA concentrations exhibit early sleep onset

The relationship between central nervous system serotonergic activity, as reflected by cerebrospinal fluid (CSF) concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), and sleep/wakefulness behavior was investigated in socially housed, juvenile rhesus macaques. Two cohorts of rhesus monkeys (Macaca mulatta), numbering 42 subjects (seventeen 39-month-olds and twenty-five 20-month-olds) were observed in their home cages between 21.30 h and 23.30 h for 10 nights using an infrared night scope. Over each 90-min observation period, the following states were recorded every 5 min using a scan sampling procedure: Sleep, Drowsy, Passive-awake and Active. After more than one quarter of the animals in the group had fallen asleep, states were recorded as they occurred. Six weeks prior to the collection of the behavioral data, a sample of cisternal CSF was obtained to assay for 5-HIAA concentrations. With cohort effects statistically controlled, there was a negative correlation between latency to fall asleep and CSF 5-HIAA concentrations (i.e., subjects with high CSF 5-HIAA concentrations were more likely to fall asleep early). Subjects with low CSF 5-HIAA concentrations were also more active during the daytime hours. Subjects who fell asleep first were, on average, also less active during nighttime hours. The positive correlation between CSF 5-HIAA and sleep onset was not a result of social status since there was no correlation between social dominance rank and time of sleep onset. These results support the hypothesis that the serotonergic system may play a role in sleep onset and possibly in the regulation of diurnal activity rhythms in non-human primates.

CSF 5-HIAA, testosterone, and sociosexual behaviors in free-ranging male rhesus macaques in the mating season

This study examines sexual behavior, serotonin turnover in the central nervous system, and testosterone in free-ranging non-human primates. Study subjects were 33 young adult male rhesus macaques (Macaca mulatta) living in naturalistic social groups on a 475-acre South Carolina barrier island. Blood and cerebrospinal fluid (CSF) samples were obtained during random trappings, and the subjects were located for observation by radio telemetry. Quantitative behavioral samples totaling 203 observation hours were taken during two mating seasons (September through January) in 1994 and 1995. Control observations (65 h) on 13 subjects were also taken during the non-mating seasons in 1994 and 1995. The results indicate that CSF 5-hydroxyindoleacetic acid (5-HIAA), CSF testosterone, and plasma testosterone concentrations increase significantly during the mating season. During the mating season, there were significant increases in high intensity aggression, low intensity aggression, grooming behavior, and heterosexual mounting. In the mating season, CSF 5-HIAA was significantly correlated with several sociosexual behaviors: consorts per hour, heterosexual mounts per hour, and inseminations per hour. In contrast to previous findings from the non-mating season, CSF 5-HIAA was not correlated with any measures of aggression or sociality, although during consorting, CSF 5-HIAA was positively correlated with grooming. From these findings, we conclude that the lack of correlation between intense and severe aggression and CSF 5-HIAA in the mating season may reflect the use of high intensity aggression in 'normative' male-male competition over access to reproductively active females. We also conclude that CNS serotonin turnover is positively correlated with sexual competence, i.e. males with low CSF 5-HIAA concentrations are less sexually competent than males with higher concentrations.

Serotonin and gender-specific psychiatric disorders

The serotonergic system has been linked to the etiology of several, albeit disparate, psychiatric disorders. The accumulation of many lines of evidence support the view that there are gender differences in the serotonergic system in humans. It is further proposed that a gender differentiated serotonergic system acts as the nidus for the development of gender-specific psychiatric disorders. Depression, anxiety and eating disorders are largely seen in females, whereas alcoholism, aggressivity and suicide predominate in males. Evidence from both animal and human studies suggesting that the serotonergic system mediates between social-environmental experience and biological states is presented and reviewed. A reconceptualization of the serotonergic system as a gender-specific psychobiological interface is proposed. (Int J Psych Clin Prac 1997; 1: 3-13).