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

Salivary cortisol awakening levels are reduced in human subjects with intermittent explosive disorder compared with controls

BACKGROUND

The role of the hypothalamic-pituitary-adrenal (HPA) axis in human aggressive behavior is poorly characterized, though some studies report that, unlike depression, circulating or salivary levels of cortisol are low compared with controls.

METHODS

In this study, we collected three salivary cortisol levels (two in the morning and one in the evening) on three separate days in 78 adult study participants with (n = 28) and without (n = 52) prominent histories of impulsive aggressive behavior. Plasma C-Reactive Protein (CRP) and Interleukin-6 (IL-6) were also collected in most study participants. Aggressive study participants meet DSM-5 criteria for Intermittent Explosive Disorder (IED) while non-aggressive participants either had a history of a psychiatric disorder or no such history (Controls).

RESULTS

Morning, but not evening, salivary cortisol levels were significantly lower in IED (p < 0.05), compared with control, study participants. In addition, salivary cortisol levels correlated with measures of trait anger (partial r = -0.26, p < 0.05) and aggression (partial r = -0.25, p < 0.05) but not with measures of impulsivity, psychopathy, depression, history of childhood maltreatment, or other tested variables that often differ in individuals with IED. Finally, plasma CRP levels correlated inversely with morning salivary cortisol levels (partial r = -0.28, p < 0.05); plasma IL-6 levels showed a similar, though not statistically significant (rp = -0.20, p = 0.12) relationship with morning salivary cortisol levels.

CONCLUSION

The cortisol awakening response appears to be lower in individuals with IED compared with controls. In all study participants, morning salivary cortisol levels correlated inversely with trait anger, trait aggression, and plasma CRP, a marker of systemic inflammation. This suggests the present of a complex interaction between chronic-low level inflammation, the HPA axis, and IED that warrants further investigation.

Neurorehabilitation of Offenders, Consent and Consequentialist Ethics

The new biotechnology raises expectations for modifying human behaviour through its use. This article focuses on the ethical analysis of the not so remote possibility of rehabilitating criminals by means of neurotechnological techniques. The analysis is carried out from a synthetic position of, on the one hand, the consequentialist conception of what is right and, on the other hand, the emphasis on individual liberties. As a result, firstly, the ethical appropriateness of adopting a general predisposition for allowing the neurorehabilitation of prisoners only if it is safe and if they give their consent will be defended. But, at the same time, reasons will be given for requiring, in certain circumstances, the exceptional use of neurotechnology to rehabilitate severely psychopathic prisoners, even against their will, from the same ethical perspective.

Evolutionary and neuroendocrine foundations of human aggression

Humans present a behavioural paradox: they are peaceful in many circumstances, but they are also violent and kill conspecifics at high rates. We describe a social evolutionary theory to resolve this paradox. The theory interprets human aggression as a combination of low propensities for reactive aggression and coercive behaviour and high propensities for some forms of proactive aggression (especially coalitionary proactive aggression). These tendencies are associated with the evolution of groupishness, self-domestication, and social norms. This human aggression profile is expected to demand substantial plasticity in the evolved biological mechanisms responsible for aggression. We discuss the contributions of various social signalling molecules (testosterone, cortisol, oxytocin, vasopressin, serotonin, and dopamine) as the neuroendocrine foundation conferring such plasticity.

Relación de los niveles de Testosterona con el comportamiento del Toro Bravo durante la Lidia

Diversos estudios relacionan la concentración plasmática de testosterona con un comportamiento agresivo del animal. En ellos se han estudiado diferentes especies animales, pero se desconoce cómo es esta relación en el toro de lidia, perteneciente a una raza bovina singular por su selección etológica hacia la agresividad. En este trabajo se analizó de forma objetiva el comportamiento en el ruedo de 302 machos adultos de la raza bovina de lidia. Se registraron 33 parámetros etológicos, el número y gravedad de las caídas experimentadas por el animal y el tiempo de las cuatro fases del espectáculo, para correlacionar dicha información con la concentración plasmática de testosterona. Los resultados mostraron diferencias en la media de concentración plasmática de testosterona entre ganaderías y entre las líneas genéticas de procedencia estudiadas en la muestra. Igualmente se constata una correlación positiva entre la concentración de testosterona y un grupo de ocho parámetros etológicos, que señalan ejercicio físico del animal; por otro lado se observó una correlación negativa con los parámetros etológicos: “sale suelto”, “querencia” y “tardea”, sinónimos de falta de casta, lo que podría indicar una correlación positiva entre la testosterona y la agresividad, como indica la bibliografía.

The Older the Better: Infanticide Is Age-Related for Both Victims and Perpetrators in Captive Long-Tailed Macaques

In wild primates, infanticide is a risk that is especially prevalent when a new male takes over the alpha position. Insight into risk factors related to infanticide may decrease the incidence of infanticide in captivity during male introductions. We investigated several risk factors of infanticide derived from hypotheses explaining infanticide in the wild and tested this in captive long-tailed macaques (Macaca fascicularis) using demographic data spanning a 25.5-year period. Factors that are related to infanticide in the wild explained a large proportion, but not all incidences, of infanticide in captivity. Consistent with the wild data, infants young enough to decrease the interbirth interval (<215 days) were at risk of being killed. In contrast to studies from the wild, infanticidal males were more than 2.5 years younger than non-infanticidal males. This indicates that captive settings can lead to new risks since relatively young males may gain the alpha position, promoting infanticide. Therefore, we propose the adolescent male risk hypothesis as a captive risk factor in which subadult males pose a risk of infanticide. In conclusion, the ages of both males and infants are related to infanticide in captivity and have to be taken into account during male introductions.

Patterning of Sexual Violence against Women across US Cities and Counties

Sexual violence against women is a global public health concern; yet, determining its patterning is still largely understudied. An excess of males has emerged as a central concern given that men are the primary perpetrators of violent behavior, particularly against women. However, it is increasingly unclear as to whether an excess or, rather, a shortage of men drives purported negative social outcomes. To address these conflicting expectations, we target data from the U.S. Census and the National Incident-Based Reporting System to explore the patterning of sexual violence against women across cities and counties in the United States. Through the use of generalized linear mixed models, we assess the role of adult sex ratio imbalance, along with measures of gender inequality, on sexual violence. Our results indicate mixed support for competing predictions. Violence does not simply increase by way of male surplus or shortage, but instead with increasing skew in the sex ratio. That is, balanced sex ratios exhibit the lowest rates of violence. However, rates of sexual violence against women increase more quickly with increasing male scarcity and are lowest at low levels of male excess (51%). Thus, our findings are particularly challenging to interpret from a ‘more males = more violence’ framework because violence increases more quickly with female excess and is rarest with a slight male bias in the population. We argue that these results highlight a need to target the specific types of violent behaviors expected to be motivated by partner availability, rather than overly simplistic predictions of male surfeit or deficit leading to an excess of violence.

Central nervous system monoamine metabolite response to alcohol exposure is associated with future alcohol intake in a nonhuman primate model (Macaca mulatta)

It is widely held that the central monoamine neurotransmitters modulate alcohol intake. Few studies, however, directly assess the relationship between baseline and alcohol-induced monoamine turnover, as well as the change from baseline, as predictors of alcohol intake. Using a nonhuman primate model, this study investigates baseline, alcohol-induced and alcohol-induced change in monoamine activity and their relationship with alcohol intake. Alcohol-naïve, adolescent rhesus macaques (Macaca mulatta, N = 114) were administered a standardized intravenous bolus of alcohol solution (16.8%, v/v) on two occasions, approximately 1 month apart. One month prior to and 1 h following each alcohol infusion, cisternal cerebrospinal fluid (CSF) was obtained and assayed for monoamine metabolite concentrations. Approximately 6-7 months later, subjects were allowed unfettered access to an aspartame-sweetened alcohol solution (8.4%, v/v) for 1 h/day, 5 days/week, over 5-7 weeks. Results showed strong positive correlations between baseline and post-infusion CSF monoamine metabolite concentrations, indicating a trait-like response. Low baseline and post-infusion serotonin and dopamine metabolite concentrations and a smaller change in serotonin and dopamine metabolites from one infusion to the next were associated with higher alcohol intake. Low baseline and post-infusion norepinephrine metabolite concentrations predicted high alcohol intake, but unlike the other monoamines, a greater change in norepinephrine metabolite concentrations from one infusion to the next was associated with higher alcohol intake. These findings suggest that individual differences in naturally occurring and alcohol-induced monoamine activity, as well as the change between exposures, are important modulators of initial alcohol consumption and may play a role in the risk for excessive alcohol intake.

Validation and Ecological Niche Investigation of a New Fungal Intraspecific Competitor as a Biocontrol Agent for the Sustainable Containment of Aflatoxins on Maize Fields

Crop yield and plant products quality are directly or indirectly affected by climate alterations. Adverse climatic conditions often promote the occurrence of different abiotic stresses, which can reduce or enhance the susceptibility to pests or pathogens. Aflatoxin producing fungi, in particular, whose diffusion and deleterious consequences on cereals commodities have been demonstrated to highly depend on the temperature and humidity conditions that threaten increasingly larger areas. Biological methods using intraspecific competitors to prevent fungal development and/or toxin production at the pre-harvest level are particularly promising, even if their efficacy could be affected by the ecological interaction within the resident microbial population. A previously characterized Aspergillus flavus atoxigenic strain was applied in two maize fields to validate its effectiveness as a biocontrol agent against aflatoxin contamination. At one month post-application, at the harvest stage, its persistence within the A. flavus population colonizing the maize kernels in the treated area was assessed, and its efficacy was compared in vitro with a representation of the isolated atoxigenic population. Results proved that our fungal competitor contained the aflatoxin level on maize grains as successfully as a traditional chemical strategy, even if representing less than 30% of the atoxigenic strains re-isolated, and achieved the best performance (in terms of bio-competitive potential) concerning endogenous atoxigenic isolates.

Mismatches in resident and stranger serotonin transporter genotypes lead to escalated aggression, and the target for aggression is mediated by sex differences in male and female rhesus monkeys (Macaca mulatta)

A variety of studies show that the s-allele of the serotonin transporter genotype (5-HTT) is related to aggression. However, influences of sex and 5-HTT genotype of both subject and opponent have not received as much attention in aggression research. Using a nonhuman primate model, the present study explores differences in rates of aggression exhibited by 201 group-housed male and female rhesus monkeys (Macaca mulatta; 122 females; 79 males) exposed to an unfamiliar age- and sex-matched stranger while in the presence of other same-sex members of their social group. The study also assesses whether the rates of aggression increase when the home-cage resident, the unfamiliar stimulus animal, or both possess the short (s) allele of the 5-HTT. Results showed that, when compared to females, males exhibited higher rates of physical aggression toward the stranger, and when both the male resident and the male stranger possessed the s-allele, rates of physical aggression toward the stranger increased five-fold. Resident females also engaged in higher rates of physical aggression when they possessed the s-allele, although unlike the males, their physical aggression was directed toward familiar same-sex members of their social group. The findings of this study indicate that rates of physical aggression are modulated by 5-HTT resident and stranger suggest a role of sexual competition in the phenotype of the 5-HTT genotype. Importantly, when two males with impulse deficits, as a function of the s-allele, are placed together, rates of violence exhibited by the dyad escalate substantially.

The neurobiology of human aggressive behavior: Neuroimaging, genetic, and neurochemical aspects

In modern societies, there is a strive to improve the quality of life related to risk of crimes which inevitably requires a better understanding of brain determinants and mediators of aggression. Neurobiology provides powerful tools to achieve this end. Pre-clinical and clinical studies show that changes in regional volumes, metabolism-function and connectivity within specific neural networks are related to aggression. Subregions of prefrontal cortex, insula, amygdala, basal ganglia and hippocampus play a major role within these circuits and have been consistently implicated in biology of aggression. Genetic variations in proteins regulating the synthesis, degradation, and transport of serotonin and dopamine as well as their signal transduction have been found to mediate behavioral variability observed in aggression. Gene-gene and gene-environment interactions represent additional important risk factors for aggressiveness. Considering the social burden of pathological forms of aggression, more basic and translational studies should be conducted to accelerate applications to clinical practice, justice courts, and policy making.

Effects of water restriction on social behavior and 5-HT neurons density in the dorsal and median raphe nuclei in mice

We explored here the hypothesis that temporary chronic water restriction in mice affects social behavior, via its action on the density of 5-HT neurons in dorsal and median raphe nuclei (DRN and MRN). For that, we submitted adult C57BL/6 J mice to mild and controlled temporary dehydration, i.e., 6 h of water access every 48 h for 15 days. We investigated their social behavior in a social interaction task known to allow free and reciprocal social contact. Results showed that temporary dehydration increases significantly time spent in social contact and social dominance. It also expands 5-HT neuron density within both DRN and MRN and the behavioral and neuronal plasticity were positively correlated. Our findings suggest that disturbance in 5-HT neurotransmission caused by temporary dehydration stress unbalances choice processes of animals in social context.

The World Federation of Societies of Biological Psychiatry (WFSBP) 2020 guidelines for the pharmacological treatment of paraphilic disorders

Objectives: The primary aim of these guidelines is to evaluate the role of pharmacological agents in the treatment and management of patients with paraphilic disorders, with a focus on the treatment of adult males. Because such treatments are not delivered in isolation, the role of specific psychotherapeutic interventions is also briefly covered. These guidelines are intended for use in clinical practice by clinicians who diagnose and treat patients, including sexual offenders, with paraphilic disorders. The aim of these guidelines is to bring together different views on the appropriate treatment of paraphilic disorders from experts representing different countries in order to aid physicians in clinical decisions and to improve the quality of care.Methods: An extensive literature search was conducted using the English-language-literature indexed on MEDLINE/PubMed (1990-2018 for SSRIs) (1969-2018 for hormonal treatments), supplemented by other sources, including published reviews.Results: Each treatment recommendation was evaluated and discussed with respect to the strength of evidence for its efficacy, safety, tolerability, and feasibility. The type of medication used depends on the severity of the paraphilic disorder and the respective risk of behaviour endangering others. GnRH analogue treatment constitutes the most relevant treatment for patients with severe paraphilic disorders.Conclusions: An algorithm is proposed with different levels of treatment for different categories of paraphilic disorders accompanied by different risk levels.

Single-Dose of Testosterone and the MAOA VNTR Polymorphism Influence Emotional and Behavioral Responses in Men During a Non-social Frustration Task

Previous studies suggest that testosterone and several neurotransmitters might interactively influence human aggression. The current study aimed to test potential interactions of a genetic variation linked to the catabolism of serotonin, dopamine, and norepinephrine and exogenous testosterone on the reaction towards non-social provocation. In total, 146 male participants were genotyped for a prominent polymorphism of the monoamine oxidase A (MAOA) gene resulting in a short and long variant. Participants completed a non-social frustration task after receiving either testosterone or a placebo gel in a double-blind set-up. Participants performed a non-social frustration task, where they had to direct a virtually moving ball into a barrel by pulling a joystick (neutral block). During a frustration block, the joystick repeatedly did not respond to participants' reactions thereby causing failed trials to which participants reacted with increased anger and stronger pulling of the joystick. We analyzed the effect of testosterone administration on emotion and behavior in individuals who either carried a low (L) or high (H) activity MAOA variant. Testosterone administration increased provocation-related self-reported anger and abolished the association between trait aggression and joystick deflection in the frustration block. In MAOA-H carriers endogenous testosterone levels at baseline were associated with increased joystick deflection in both blocks. There was, however, no interaction of testosterone administration and genotype. Although preliminary, the results rather indicate independent influences of exogenous testosterone administration and MAOA, but support an interaction of endogenous testosterone levels and MAOA genetics in a frustration task. The administration of testosterone seems to act on the subjective emotional experience in a provoking situation, while endogenous testosterone levels increased pulling impulses only in carriers of the MAOA-H variant.

Are Owls and Larks Different When it Comes to Aggression? Genetics, Neurobiology, and Behavior

This review focuses on the contribution of circadian rhythms to aggression with a multifaceted approach incorporating genetics, neural networks, and behavior. We explore the hypothesis that chronic circadian misalignment is contributing to increased aggression. Genes involved in both circadian rhythms and aggression are discussed as a possible mechanism for increased aggression that might be elicited by circadian misalignment. We then discuss the neural networks underlying aggression and how dysregulation in the interaction of these networks evoked by circadian rhythm misalignment could contribute to aggression. The last section of this review will present recent human correlational data demonstrating the association between chronotype and/or circadian misalignment with aggression. With circadian rhythms and aggression being a burgeoning area of study, we hope that this review initiates more interest in this promising and topical area.

Gender-Specific Effect of 5-HT and 5-HIAA on Threshold Level of Behavioral Symptoms and Sex-Bias in Prevalence of Autism Spectrum Disorder

Platelet hyperserotonemia in a subset of Autism Spectrum Disorder (ASD) probands, efficacy of selective serotonin reuptake inhibitors (SSRIs) in reducing behavioral deficits and gender-bias in normal serotonin (5-hydroxy tryptamine or 5-HT) synthesis suggest disruption in stringent regulation of serotonin metabolism in ASD. Therefore, we investigated the changes in 5-HT and 5-hydroxy indole acetic acid (5-HIAA) in ASD probands to assess its effect on the behavior of male and female probands. ASD cases (n = 215) were examined using childhood autism rating scale (CARS). Platelet 5-HT (104 cases and 26 controls) and platelet/plasma 5-HIAA (73 cases and 17 controls) were estimated using high performance liquid chromatography coupled with electrochemical detector (HPLC-ECD). In male probands, we observed increase in platelet 5-HT content in association with increase in the score for adaptive responses and increase in platelet 5-HIAA levels with concomitant decline in the score for intellectual response. Age did not influence the neurochemical parameters, but imitation, listening responses and nonverbal communication scores decreased with age. Conversely in female probands, plasma 5-HIAA level significantly attenuated with age, when platelet 5-HT content remained unchanged. Interestingly, platelet/plasma 5-HT and plasma 5-HIAA were higher in female controls. Female probands displayed severe autism-associated behaviors. Overall results indicate gender-bias in 5-HT and 5-HIAA regulation, which probably increases the threshold level of ASD phenotypes in the females, thereby affecting ASD prevalence in a sex-specific manner.

Biological Aspects of Aggression and Violence in Schizophrenia

Although the majority of patients with schizophrenia are not actually violent, an increased tendency toward violent behaviors is known to be associated with schizophrenia. There are several factors to consider when identifying the subgroup of patients with schizophrenia who may commit violent or aggressive acts. Comorbidity with substance abuse is the most important clinical indicator of increased aggressive behaviors and crime rates in patients with schizophrenia. Genetic studies have proposed that polymorphisms in the promoter region of the serotonin transporter gene and in the catechol-O-methyltransferase gene are related to aggression. Neuroimaging studies have suggested that fronto-limbic dysfunction may be related to aggression or violence. By identifying specific risk factors, a more efficient treatment plan to prevent violent behavior in schizophrenia will be possible. Management of comorbid substance use disorder may help prevent violent events and overall aggression. Currently, clozapine may be the only effective antipsychotic medication to repress aggressive behavior. With the current medical field moving toward tailored medicine, it is important to identify vulnerable schizophrenia populations and provide efficient treatment.

Differences in how macaques monitor others: Does serotonin play a central role?

Primates must balance the need to monitor other conspecifics to gain social information while not losing other resource opportunities. We consolidate evidence across the fields of primatology, psychology, and neuroscience to examine individual, population, and species differences in how primates, particularly macaques, monitor conspecifics. We particularly consider the role of serotonin in mediating social competency via social attention, aggression, and dominance behaviors. Finally, we consider how the evolution of variation in social tolerance, aggression, and social monitoring might be explained by differences in serotonergic function in macaques. This article is categorized under: Economics > Interactive Decision-Making Psychology > Comparative Psychology Neuroscience > Behavior Cognitive Biology > Evolutionary Roots of Cognition.

High Endogenous Testosterone Levels Are Associated With Diminished Neural Emotional Control in Aggressive Police Recruits

Although police officers are carefully selected for their high emotion-regulation abilities, excessive aggression in police officers has been reported, particularly in socially challenging situations known to elicit high state testosterone levels. Adequate regulation of emotional actions depends on the prefrontal cortex’s control over the amygdala. We investigated the effects of trait aggression and endogenous testosterone on this emotional-control neurocircuitry in 275 healthy, high-functioning police recruits using a functional MRI social-emotional task eliciting impulsive and controlled approach-and-avoidance actions. Higher levels of aggression were counteracted by increased anterior prefrontal cortex (aPFC) control over the amygdala when control over automatic emotional actions was required. Crucially, testosterone had a detrimental effect on this aggression-dependent aPFC recruitment: Police recruits with relatively high trait aggression and high state testosterone showed reduced aPFC control over the amygdala during emotion regulation. This provides a mechanistic explanation for inadequate behavioral control during socially challenging situations in otherwise well-functioning individuals.

Early-life adversity-induced long-term epigenetic programming associated with early onset of chronic physical aggression: Studies in humans and animals

Objectives: To examine whether chronic physical aggression (CPA) in adulthood can be epigenetically programmed early in life due to exposure to early-life adversity. Methods: Literature search of public databases such as PubMed/MEDLINE and Scopus. Results: Children/adolescents susceptible for CPA and exposed to early-life abuse fail to efficiently cope with stress that in turn results in the development of CPA later in life. This phenomenon was observed in humans and animal models of aggression. The susceptibility to aggression is a complex trait that is regulated by the interaction between environmental and genetic factors. Epigenetic mechanisms mediate this interaction. Subjects exposed to stress early in life exhibited long-term epigenetic programming that can influence their behaviour in adulthood. This programming affects expression of many genes not only in the brain but also in other systems such as neuroendocrine and immune. Conclusions: The propensity to adult CPA behaviour in subjects experienced to early-life adversity is mediated by epigenetic programming that involves long-term systemic epigenetic alterations in a whole genome.

The influence of the serotonin transporter gene 5-HTTLPR polymorphism on suicidal behaviors: a meta-analysis

Suicidal Behavior (SB) is the second leading cause of death among youths worldwide and the tenth among all age groups. Inherited genetic differences have a role in suicidality with heritability ranging from 30 to 55%. The SLC6A4 5-HTTLPR gene variant has been largely investigated for association with SB, with controversial results. In this work, we sought to determine whether the results of previous meta-analyses were confirmed or modified subsequent to the inclusion of more recent literature data. An electronic literature search was performed to identify relevant studies published until July 2018. Data were analysed through RevMan v5.3. Subgroup and sensitivity meta-analyses were performed considering different SB sub-phenotypes, ethnicity, gender and psychiatric diagnostic categories. Our literature search yielded 1186 articles; among these, we identified 45 pertinent case-control studies (15,341 subjects). No association was found between low-expressing alleles or genotypes (S + L_G alleles or S' carrier genotypes) and SB in the primary analyses. However, low-expressing alleles (S + L_G) were associated with an increased risk of Violent Suicide Attempt (OR = 1.44, C.I. 1.17-1.78, p = .0007). An effect of the same alleles on SB was found in a subpopulation of substance abusers, but this result was not confirmed after the exclusion of healthy subjects from the control group. The other sensitivity meta-analyses did not show any significant effect. Our findings contribute to clarify the conflicting previous evidence by suggesting an association between the 5-HTTLPR and Violent SB. Nonetheless, many other modulators, including environmental factors and epigenetic mechanisms may act to further increase the level of complexity.

Sex Differences in Rhesus Monkeys' Digit Ratio (2D:4D Ratio) and Its Association With Maternal Social Dominance Rank

Prenatal androgen exposure (PAE) plays a pivotal role in masculinizing the developing body and brain, and extreme exposure may contribute to autism, anxiety disorder and schizophrenia. One commonly used biomarker for PAE is the pointer-to-ring-finger digit length (2D:4D) ratio. Although this biomarker is widely used in human studies, relatively few studies have investigated 2D:4D ratio in nonhuman primates, particularly rhesus macaques (Macaca mulatta), one of the most commonly used animals in biomedical research. Thus far, data suggest that sexual dimorphism in 2D:4D ratio may be in the opposite direction in some monkey species, when compared to the pattern exhibited by humans and great apes. Using a large sample size, we investigated whether rhesus monkeys' 2D:4D ratio shows the same sex-differentiated pattern present in other Old World monkey species. We also investigated whether individual differences in 2D:4D ratio are associated with the social dominance rank of subjects' mothers during pregnancy, and the social dominance rank the subjects attained as adults. Subjects were 335 rhesus monkeys between 3 years and 24 years of age (M = 6.6). Maternal dominance rank during pregnancy and subjects' adult dominance rank were categorized into tertiles (high, middle and low). Results showed that, across both hands, male rhesus monkeys exhibited higher 2D:4D ratio than females, a pattern consistent with other monkey species and a reversal from the pattern typically observed in humans and apes. This sex difference was modulated by maternal dominance rank, with female offspring of high-ranking and middle-ranking mothers exhibiting masculinized 2D:4D ratio, indicating that maternal dominance rank during pregnancy may influence levels of PAE. There was no association between subjects' 2D:4D ratio and the social dominance rank they attained as adults. These findings show a consistent sex difference in Old World monkeys' 2D:4D ratio that diverges from the pattern observed in apes and humans, and suggest maternal social dominance rank modulates PAE in rhesus monkeys.

Effect of Group Density on the Physiology and Aggressive Behavior of Male Brandt's Voles (Lasiopodomys brandtii)

Xin Dai, Ling-Yu Zhou, Jie-Xia Cao, Yan-Qi Zhang, Feng-Ping Yang, Ai-Qin Wang, Wan-Hong Wei, and Sheng-Mei Yang (2018) Population density is well known to influence animal physiology and behavior. How population density affects the aggressive behavior of the Brandt's vole (Lasiopodomys brandtii) is, however, little known. The aim of this study was to investigate the effect of group density on physiologic responses and aggressive behavior of male Brandt's voles and their potential underlying neuro-mechanism. The results show that increasing group density led to elevated serum corticosterone levels and increased spleen weight; it also induced more male-male aggressive behavior. By contrast, it had a negative effect on body growth and the weight of testis and epididymis. Aging also increased male-male aggressive behavior. Higher density reduced mRNA levels of tryptophan hydroxylase 2 (TPH2), 5-hydroxytryptamine receptor 1A (5HT1A), and 5-hydroxytryptamine receptor 1B (5HT1B) in the amygdala and the dorsal raphe nucleus (DRN). Our results demonstrate that higher population density can intensify stress reactions and male-male aggressive behavior in Brandt's voles at the price of inhibiting body growth and reproduction. Serotonergic systems in the amygdala and the DRN may take part in the control of aggressive behavior among male voles. Our results provide novel insights into the neuro-mechanism underlying the influence of population density on aggressive behavior in Brandt's vole, and imply that aggressive behavior may play an important role in the population fluctuation of the animal.

The effects of 5-hydroxytryptophan on attention and central serotonin neurochemistry in the rhesus macaque

Psychiatric disorders, particularly depression and anxiety, are often associated with impaired serotonergic function. However, serotonergic interventions yield inconsistent effects on behavioral impairments. To better understand serotonin's role in these pathologies, we investigated the role of serotonin in a behavior frequently impaired in depression and anxiety, attention. In this study, we used a quantitative, repeated, within-subject, design to test how L-5-hydroxytryptophan (5-HTP), the immediate serotonin precursor, modulates central serotoninergic function and attention in macaques. We observed that intramuscular 5-HTP administration increased cisternal cerebrospinal fluid (CSF) 5-HTP and serotonin. In addition, individuals' baseline looking duration, during saline sessions, predicted the direction and magnitude in which 5-HTP modulated attention. We found that 5-HTP decreased looking duration in animals with high baseline attention, but increased looking duration in low baseline attention animals. Furthermore, individual differences in 5-HTP's effects were also reflected in how engaged individuals were in the task and how they allocated attention to salient facial features-the eyes and mouth-of stimulus animals. However, 5-HTP constricted pupil size in all animals, suggesting that the bi-directional effects of 5-HTP cannot be explained by serotonin-mediated changes in autonomic arousal. Critically, high and low baseline attention animals exhibited different baseline CSF concentrations of 5-HTP and serotonin, an index of extracellular functionally active serotonin. Thus, our results suggest that baseline central serotonergic functioning may underlie and predict variation in serotonin's effects on cognitive operation. Our findings may help inform serotonin's role in psychopathology and help clinicians predict how serotonergic interventions will influence pathologies.

Low Inherent Sensitivity to the Intoxicating Effects of Ethanol in Rhesus Monkeys with Low CSF Concentrations of the Serotonin Metabolite 5-Hydroxyindoleacetic Acid

BACKGROUND

Type 2 alcoholism is characterized by low serotonin system functioning and has a high degree of heritability, with offspring of alcoholics often showing a reduced response to the intoxicating effects of ethanol (EtOH), which is thought to be marker for future alcohol use disorders (AUDs). As such, an important aim of studies investigating the origins of AUDs is to understand the relationship between serotonin system functioning and level of intoxication. A nonhuman primate model was used to evaluate observational ratings of sensitivity to EtOH and to further investigate the relationship between central serotonin activity and behavioral response to EtOH.

METHODS

Cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA) were obtained from 4 cohorts of alcohol-naïve, adolescent rhesus macaques (N = 82, 45 females, 37 males). One to 3 months after the CSF sample, subjects were administered a standardized intravenous EtOH bolus (males: 2.1 g/kg body weight, females: 2.0 g/kg body weight), placed into an open-top, clear plexiglass chamber suspended from the ceiling, and their latency to escape was recorded as a measure of the degree of intoxication. Thereafter, subjects were rated using a Likert scale for the degree of intoxication during a 30-minute observation period.

RESULTS

Our results indicate that latency to escape from the chamber was associated with intoxication ratings (p = 0.0009) following the standardized intravenous administration of EtOH. Low CSF 5-HIAA concentrations predicted short escape latency (p = 0.007) and were associated with low intoxication ratings (p = 0.02), indicating that low central nervous system (CNS) serotonin functioning is related to relative insensitivity to the intoxicating effects of alcohol.

CONCLUSIONS

Our study shows that, in monkeys exposed to alcohol for the first time, objective measures of intoxication are associated with subjective ratings for intoxication, and both were associated with CSF 5-HIAA concentrations. Our data confirm and extend the finding that low CNS serotonin functioning is predictive of intrinsic low sensitivity to the intoxicating effects of EtOH.

OPRM1 genotype interacts with serotonin system dysfunction to predict alcohol-heightened aggression in primates

Although the notion that alcohol promotes violence is widespread, not all individuals are aggressive while intoxicated. Genetic variation could be a contributing factor to individual differences in alcohol-heightened aggression. The present study examines the effects of OPRM1C77G genotype on responses to threat in rhesus macaques under normal conditions and following alcohol administration. Prior studies have shown that a low CSF level of 5-HIAA is a trait marker for individuals prone to escalated aggression. We wanted to examine whether the predictive value for this marker on aggression was moderated by OPRM1 genotype. Animals were administered alcohol (BAC 100-200 mg%), were provoked by a human intruder, and aggressive responses were recorded. Factor analysis was performed to generate aggressive response factors, which were then used as dependent variables for ANOVA, with OPRM1 genotype and CSF 5-HIAA as independent variables. Factor analysis generated three factors ('Threatening', 'Distance Decreasing' and 'High Intensity'). We found that High Intensity aggression was increased among carriers of the OPRM1 G allele, especially among individuals with low CSF levels of 5-HIAA. Aggression in the non-intoxicated state was predicted by 5-HIAA, but not by genotype. This study demonstrates that OPRM1 genotype predicts alcohol-heightened aggression in rhesus macaques with low CSF levels of 5-HIAA. Because OPRM1 variation predicts similar effects on alcohol response and behavior in humans and macaques, this study could suggest a role for OPRM1 genotype in alcohol-heightened aggression in humans. If so, it may be that compounds that block this receptor could reduce alcohol-associated violence in selected patient populations.

Consequences of early adverse rearing experience(EARE) on development: insights from non-human primate studies

Early rearing experiences are important in one's whole life, whereas early adverse rearing experience(EARE) is usually related to various physical and mental disorders in later life. Although there were many studies on human and animals, regarding the effect of EARE on brain development, neuroendocrine systems, as well as the consequential mental disorders and behavioral abnormalities, the underlying mechanisms remain unclear. Due to the close genetic relationship and similarity in social organizations with humans, non-human primate(NHP) studies were performed for over 60 years. Various EARE models were developed to disrupt the early normal interactions between infants and mothers or peers. Those studies provided important insights of EARE induced effects on the physiological and behavioral systems of NHPs across life span, such as social behaviors(including disturbance behavior, social deficiency, sexual behavior, etc), learning and memory ability, brain structural and functional developments(including influences on neurons and glia cells, neuroendocrine systems, e.g., hypothalamic-pituitary-adrenal(HPA) axis, etc). In this review, the effects of EARE and the underlying epigenetic mechanisms were comprehensively summarized and the possibility of rehabilitation was discussed.

The role of serotonin in personality inference: tryptophan depletion impairs the identification of neuroticism in the face

Serotonergic mechanisms mediate the expression of personality traits (such as impulsivity, aggression and anxiety) that are linked to vulnerability to psychological illnesses, and modulate the identification of emotional expressions in the face as well as learning about broader classes of appetitive and aversive signals. Faces with neutral expressions signal a variety of socially relevant information, such that inferences about the big five personality traits, including Neuroticism, Extraversion and Agreeableness, can be accurately made on the basis of emotionally neutral facial photographs. Given the close link between Neuroticism and psychological distress, we investigated the effects of diminished central serotonin activity (achieved by tryptophan depletion) upon the accuracy of 52 healthy (non-clinical) adults' discriminations of personality from facial characteristics. All participants were able to discriminate reliably four of the big five traits. However, the tryptophan-depleted participants were specifically less accurate in discriminating Neuroticism than the matched non-depleted participants. These data suggest that central serotonin activity modulates the identification of not only negative facial emotional expression but also a broader class of signals about personality characteristics linked to psychological distress.

Anger Emotional Stress Influences VEGF/VEGFR2 and Its Induced PI3K/AKT/mTOR Signaling Pathway

Objective. We discuss the influence of anger emotional stress upon VEGF/VEGFR2 and its induced PI3K/AKT/mTOR signal pathway. Methods. We created a rat model of induced anger (anger-out and anger-in) emotional response using social isolation and resident-intruder paradigms and assessed changes in hippocampus' VEGF content, neuroplasticity, and the PI3K/AKT/mTOR signaling pathway. Results. The resident-intruder method successfully generated anger-out and anger-in models that differed significantly in composite aggression score, aggression incubation, open field behavior, sucrose preference, and weight gain. Anger emotional stress decreased synaptic connections and VEGFR2 expression. Anger emotional stress led to abnormal expression of VEGF/VEGFR2 mRNA and protein and disorderly expression of key factors in the PI3K/AKT/mTOR signal pathway. Fluoxetine administration ameliorated behavioral abnormalities and damage to hippocampal neurons caused by anger emotional stress, as well as abnormal expression of some proteins in VEGF/VEGFR2 and its induced PI3K/AKT/mTOR signal pathway. Conclusion. This research provides a detailed classification of anger emotion and verifies its influence upon VEGF and the VEGF-induced signaling pathway, thus providing circumstantial evidence of mechanisms by which anger emotion damages neurogenesis. As VEGFR2 can promote neurogenesis and vasculogenesis in the hippocampus and frontal lobe, these results suggest that anger emotional stress can result in decreased neurogenesis.

Neuromodulation, Emotional Feelings and Affective Disorders

Affective disorders such as anxiety, phobia and depression are a leading cause of disabilities worldwide. Monoamine neuromodulators are used to treat most of them, with variable degrees of efficacy. Here, we review and interpret experimental findings about the relation of neuromodulation and emotional feelings, in pursuit of two goals: (a) to improve the conceptualisation of affective/emotional states, and (b) to develop a descriptive model of basic emotional feelings related to the actions of neuromodulators. In this model, we hypothesize that specific neuromodulators are effective for basic emotions. The model can be helpful for mental health professionals to better understand the affective dynamics of persons and the actions of neuromodulators - and respective psychoactive drugs - on this dynamics.

The developmental origins of chronic physical aggression: biological pathways triggered by early life adversity

Longitudinal epidemiological studies with birth cohorts have shown that physical aggression in humans does not appear suddenly in adolescence as commonly thought. In fact, physically aggressive behaviour is observed as early as 12 months after birth, its frequency peaks around 2-4 years of age and decreases in frequency until early adulthood. However, a minority of children (3-7%) maintain a high frequency of physical aggression from childhood to adolescence and develop serious social adjustment problems during adulthood. Genetic factors and early social experiences, as well as their interaction, have been shown to play an important role in the development of chronic aggressive behaviour. However, the biological mechanisms underlying these associations are just beginning to be uncovered. Recent evidence suggests that epigenetic mechanisms are responsive to adverse environments and could be involved in the development of chronic aggression. Using both gene candidate and genomic approaches, recent studies have identified epigenetic marks, such as DNA methylation alterations in genes involved in the stress response and the serotonin and immune systems to be partly responsible for the long-lasting effects of early adversity. Further longitudinal studies with biological, environmental and behavioural assessments from birth onwards are needed to elucidate the sequence of events that leads to these long-lasting epigenetic marks associated with early adversity and aggression.

Dissociable Effects of Serotonin and Dopamine on the Valuation of Harm in Moral Decision Making

An aversion to harming others is a core component of human morality and is disturbed in antisocial behavior. Deficient harm aversion may underlie instrumental and reactive aggression, which both feature in psychopathy. Past work has highlighted monoaminergic influences on aggression, but a mechanistic account of how monoamines regulate antisocial motives remains elusive. We previously observed that most people show a greater aversion to inflicting pain on others than themselves. Here, we investigated whether this hyperaltruistic disposition is susceptible to monoaminergic control. We observed dissociable effects of the serotonin reuptake inhibitor citalopram and the dopamine precursor levodopa on decisions to inflict pain on oneself and others for financial gain. Computational models of choice behavior showed that citalopram increased harm aversion for both self and others, while levodopa reduced hyperaltruism. The effects of citalopram were stronger than those of levodopa. Crucially, neither drug influenced the physical perception of pain or other components of choice such as motor impulsivity or loss aversion, suggesting a direct and specific influence of serotonin and dopamine on the valuation of harm. We also found evidence for dose dependency of these effects. Finally, the drugs had dissociable effects on response times, with citalopram enhancing behavioral inhibition and levodopa reducing slowing related to being responsible for another's fate. These distinct roles of serotonin and dopamine in modulating moral behavior have implications for potential treatments of social dysfunction that is a common feature as well as a risk factor for many psychiatric disorders.

Androgen metabolites impact CSF amines and axonal serotonin via MAO-A and -B in male macaques

A number of studies have shown that mutations or deletions of the monoamine oxidase-A (MAO-A) gene cause elevated CNS serotonin and elevated impulsive aggression in humans and animal models. In addition, low cerebrospinal fluid (CSF) 5-hydroxyindole acetic acid (5HIAA) has been documented in a limited number of violent criminal populations and in macaques that exhibit impulsive aggression. To reconcile these different analyses, we hypothesized that CSF 5HIAA reflected degradation of serotonin by the activity of MAO-A; and that low MAO-A activity would result in lower CSF 5HIAA, but overall higher serotonin in the CNS. To test this hypothesis, male Japanese macaques (Macaca fuscata) were castrated, rested for 5-7months, and then treated for 3months with [1] placebo, [2] testosterone (T), [3] dihydrotestosterone (DHT; non-aromatizable androgen) and 1,4,6-androstatriene-3,17-dione (ATD) (steroidal aromatase inhibitor), or [4] flutamide (FLUT; androgen antagonist) and ATD (n=5/group). These treatments enable isolation of androgen and estrogen activities. In the dorsal raphe, MAO-A and MAO-B expressions were determined with in situ hybridization (ISH) and protein expression of aromatase was determined with immunohistochemistry (IHC). CSF concentrations of 5HIAA, 3-methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) were determined with liquid chromatography/mass spectrometry (LC/MS). From the same animals, previously published data on serotonin axon density were used as a proxy for CNS serotonin. Aromatase conversion of T to estrogen (E) suppressed MAO-A (positive pixel area, p=0.0045), but androgens increased MAO-B (positive pixel area, p=0.014). CSF 5HIAA was suppressed by conversion of T to E (Cohen's d=0.6). CSF 5HIAA was positively correlated with MAO-A-positive pixel area (r(2)=0.78). CSF 5HIAA was inversely correlated with serotonin axon-positive pixel area (r(2)=0.69). In summary, CSF 5HIAA reflects MAO-A activity rather than global serotonin. Low CSF 5HIAA may, in this paradigm, reflect higher serotonin activity. Androgens lower MAO-A activity via metabolism to E, thus elevating CNS serotonin and decreasing CSF 5HIAA. Since androgens increase certain types of aggression, these data are consistent with studies demonstrating that lower MAO-A activity is associated with elevated serotonin and increased aggression.

Nonhuman primate models of neuropsychiatric disorders: influences of early rearing, genetics, and epigenetics

This report reviews the scientific literature from the past several decades that focuses on nonhuman primates (NHPs) as models of neuropsychiatric disorders, including anxiety, and alcoholism. In particular, we highlight the approaches, advantages, and disadvantages of the rearing, genetic, and epigenetic methodologies behind these studies as a means of evaluating the application of these methods in assessing disorders in NHPs as models of human disease. Finally, we describe the contributions the NHP studies have made to neuropsychiatric research and areas for future research.

Serotonin depletion-induced maladaptive aggression requires the presence of androgens

The sex hormone testosterone and the neurotransmitter serotonin exert opposite effects on several aspects of behavior including territorial aggression. It is however not settled if testosterone exerts its pro-aggressive effects by reducing serotonin transmission and/or if the anti-aggressive effect of serotonin requires the presence of the androgen. Using the resident intruder test, we now show that administration of the serotonin synthesis inhibitor para-chlorophenylalanine (300 mg/kg x 3 days) increases the total time of attack as well as the percentage amount of social behavior spent on attack but not that spent on threat - i.e. that it induces a pattern of unrestricted, maladaptive aggression - in gonadectomized C57Bl/6 male mice receiving testosterone replacement; in contrast, it failed to reinstate aggression in those not given testosterone. Whereas these results suggest the pro-aggressive effect of testosterone to be independent of serotonin, and not caused by an inhibition of serotonergic activity, the pCPA-induced induction of maladaptive aggression appears to require the presence of the hormone. In line with these findings, pCPA enhanced the total time of attack as well the relative time spent on attacks but not threats also in wild-type gonadally intact male C57Bl/6 mice, but failed to reinstate aggression in mice rendered hypo-aggressive by early knock-out of androgen receptors in the brain (ARNesDel mice). We conclude that androgenic deficiency does not dampen aggression by unleashing an anti-aggressive serotonergic influence; instead serotonin seems to modulate aggressive behavior by exerting a parallel-coupled inhibitory role on androgen-driven aggression, which is irrelevant in the absence of the hormone, and the arresting of which leads to enhanced maladaptive aggression.

Localization and regulation of reproductive steroid receptors in the raphe serotonin system of male macaques

We previously showed that tryptophan hydroxylase 2 (TPH2) and serotonin reuptake transporter (SERT) mRNAs are increased by the androgens, testosterone (T) and dihydrotestosterone (DHT) in serotonin neurons of male macaques. In addition, we observed that serotonin in axons of a terminal region were markedly decreased by aromatase inhibition and lack of estradiol (E) from metabolism of T. These observations implicated androgen receptors (AR) and estrogen receptors (ER) in the transduction of steroid hormone actions in serotonin neurons. Due to the longer treatment period employed, the expression of the cognate nuclear receptors was sought. We used single and double immunohistochemistry to quantitate and phenotypically localize AR, ERα and ERβ in the dorsal raphe of male macaques. Male Japanese macaques (Macaca fuscata) were castrated for 5-7 months and then treated for 3 months with [1] placebo, [2] T, [3] DHT (non-aromatizable androgen) plus ATD (steroidal aromatase inhibitor), or [4] Flutamide (FLUT; androgen antagonist) plus ATD (n = 5/group). After single labeling of each receptor, quantitative image analysis was applied and receptor positive neurons were counted. Double-label of raphe neurons for each receptor plus TPH2 determined whether the receptors were localized in serotonin neurons. There were significantly more AR-positive neurons in T- and DHT+ATD-treated groups (p = 0.0014) compared to placebo or FLUT+ATD-treated groups. There was no difference in the number of positive-neurons stained for ERα or ERβ⋅ Double-immunohistochemistry revealed that serotonin neurons did not contain AR. Rather, AR-positive nuclei were found in neighboring cells that are likely neurons. However, approximately 40% of dorsal raphe serotonin neurons contained ERα or ERβ⋅ In conclusion, the stimulatory effect of androgens on TPH2 and SERT mRNA expression is mediated indirectly by neighboring neurons contain AR. The stimulatory effect of E, derived from T metabolism, on serotonin transport is partially mediated directly via nuclear ERs.

Monoamine-sensitive developmental periods impacting adult emotional and cognitive behaviors

Development passes through sensitive periods, during which plasticity allows for genetic and environmental factors to exert indelible influence on the maturation of the organism. In the context of central nervous system development, such sensitive periods shape the formation of neurocircuits that mediate, regulate, and control behavior. This general mechanism allows for development to be guided by both the genetic blueprint as well as the environmental context. While allowing for adaptation, such sensitive periods are also vulnerability windows during which external and internal factors can confer risk to disorders by derailing otherwise resilient developmental programs. Here we review developmental periods that are sensitive to monoamine signaling and impact adult behaviors of relevance to psychiatry. Specifically, we review (1) a serotonin-sensitive period that impacts sensory system development, (2) a serotonin-sensitive period that impacts cognition, anxiety- and depression-related behaviors, and (3) a dopamine- and serotonin-sensitive period affecting aggression, impulsivity and behavioral response to psychostimulants. We discuss preclinical data to provide mechanistic insight, as well as epidemiological and clinical data to point out translational relevance. The field of translational developmental neuroscience has progressed exponentially providing solid conceptual advances and unprecedented mechanistic insight. With such knowledge at hand and important methodological innovation ongoing, the field is poised for breakthroughs elucidating the developmental origins of neuropsychiatric disorders, and thus understanding pathophysiology. Such knowledge of sensitive periods that determine the developmental trajectory of complex behaviors is a necessary step towards improving prevention and treatment approaches for neuropsychiatric disorders.

The marketing firm and consumer choice: implications of bilateral contingency for levels of analysis in organizational neuroscience

The emergence of a conception of the marketing firm (Foxall, 1999a) conceived within behavioral psychology and based on a corresponding model of consumer choice, (Foxall, 1990/2004) permits an assessment of the levels of behavioral and organizational analysis amenable to neuroscientific examination. This paper explores the ways in which the bilateral contingencies that link the marketing firm with its consumerate allow appropriate levels of organizational neuroscientific analysis to be specified. Having described the concept of the marketing firm and the model of consumer behavior on which it is based, the paper analyzes bilateral contingencies at the levels of (i) market exchange, (ii) emotional reward, and (iii) neuroeconomics. Market exchange emerges as a level of analysis that lends itself predominantly to the explanation of firm-consumerate interactions in terms of the super-personal level of reinforcing and punishing contingencies: the marketing firm can be treated as a contextual or operant system in its own right. However, the emotional reward and neuroeconomic levels of analysis should be confined to the personal level of analysis represented by individual managers on the one hand and individual consumers on the other. This also entails a level of abstraction but it is one that can be satisfactorily handled in terms of the concept of bilateral contingency.

Relationships between androgens, serotonin gene expression and innervation in male macaques

Androgen administration to castrated individuals was purported to decrease activity in the serotonin system. However, we found that androgen administration to castrated male macaques increased fenfluramine-induced serotonin release as reflected by increased prolactin secretion. In this study, we sought to define the effects of androgens and aromatase inhibition on serotonin-related gene expression in the dorsal raphe, as well as serotonergic innervation of the LC. Male Japanese macaques (Macaca fuscata) were castrated for 5-7 months and then treated for 3 months with (1) placebo, (2) testosterone (T), (3) dihydrotestosterone (DHT; non-aromatizable androgen) and ATD (steroidal aromatase inhibitor), or (4) Flutamide (FLUT; androgen antagonist) and ATD (n=5/group). This study reports the expression of serotonin-related genes: tryptophan hydroxylase 2 (TPH2), serotonin reuptake transporter (SERT) and the serotonin 1A autoreceptor (5HT1A) using digoxigenin-ISH and image analysis. To examine the production of serotonin and the serotonergic innervation of a target area underlying arousal and vigilance, we measured the serotonin axon density entering the LC with ICC and image analysis. TPH2 and SERT expression were significantly elevated in T- and DHT + ATD-treated groups over placebo- and FLUT + ATD-treated groups in the dorsal raphe (p < 0.007). There was no difference in 5HT1A expression between the groups. There was a significant decrease in the pixel area of serotonin axons and in the number of varicosities in the LC across the treatment groups with T > placebo > DHT + ATD = FLUT + ATD treatments. Comparatively, T- and DHT + ATD-treated groups had elevated TPH2 and SERT gene expression, but the DHT + ATD group had markedly suppressed serotonin axon density relative to the T-treated group. Further comparison with previously published data indicated that TPH2 and SERT expression reflected yawning and basal prolactin secretion. The serotonin axon density in the LC agreed with the area under the fenfluramine-stimulated prolactin curve, providing a morphological basis for the pharmacological results. This suggested that androgen activity increased TPH2 and SERT gene expression but, aromatase activity, and neural production of estradiol (E), may subserve axonal serotonin and determination of the compartment acted upon by fenfluramine. In summary, androgens stimulated serotonin-related gene expression, but aromatase inhibition dissociated gene expression from the serotonin innervation of the LC terminal field and fenfluramine-stimulated prolactin secretion.