Brain serotonin dysfunction accounts for aggression in male mice lacking neuronal nitric oxide synthase

Association of impulsive behavior and cerebrospinal fluid/plasma oxidation and antioxidation ratio in Chinese men

OBJECTIVES

Impulsive behavior is the precursor of many psychiatric and neurological conditions. High levels of impulsive behavior will increase health risk behavior and related injuries. Impulsive behavior is produced and regulated by central and peripheral biological factors, and oxidative stress (OS) can aggravate it. However, previous studies only showed that impulsive behavior was related to the level of the peripheral OS. Therefore, this study aims to clarify the relationship between OS and impulsive behavior in the brain and peripheral blood.

METHODS

We recruited 64 Chinese men. We measured superoxide dismutase (SOD) (including copper, zinc and manganese) and nitric oxide synthase (NOS) (including total, inducible and constitutive) in cerebrospinal fluid (CSF) and plasma. The Barratt Impulsiveness Scale version 11 (BIS-11) was used to evaluate impulsive behavior. The relationship between OS and impulsive behavior was evaluated by partial correlation analysis and stepwise multiple regression analysis.

RESULTS

Partial correlation analysis showed that the ratio of total NOS-to-MnSOD and iNOS-to-MnSOD in CSF were negatively correlated with the BIS-11 motor scores (r = -0.431, p = -0.001; r = -0.434, p = -0.001). Stepwise multiple regression analysis showed that the ratio of CSF iNOS-to-MnSOD was the most influential variable on the BIS-11 motor scores(β = -0.434, t = -3.433, 95 %CI(-0.374, -0.098), p = 0.001).

CONCLUSIONS AND RELEVANCE

The imbalance of central oxidation and antioxidation is related to impulsive behavior, which broadens our understanding of the correlation between impulsive behavior and OS.

[Ketamine and suicidal behavior: Contribution of animal models of aggression-impulsivity to understanding its mechanism of action]

More than two-thirds of suicides occur during a major depressive episode. Acting out prevention measures and therapeutic options to manage the suicidal crisis are limited. The impulsive-aggressive dimensions are vulnerability factors associated with suicide in patients suffering from a characterized depressive episode: this can be a dimension involved in animals. Impulsive and aggressive rodent models can help analyze, at least in part, the neurobiology of suicide and the beneficial effects of treatments. Ketamine, a glutamatergic antagonist, by rapidly improving the symptoms of depressive episodes, would help reduce suicidal thoughts in the short term. Animal models share with humans impulsive and aggressive endophenotypes modulated by the serotonergic system (5-HTB receptor, MAO-A enzyme), neuroinflammation or the hypothalamic-pituitary-adrenal axis and stress. Significant effects of ketamine on these endophenotypes remain to be demonstrated.

Heat stress and poultry production: a comprehensive review

The impact of global warming on poultry production has gained significant attention over the years. However, our current knowledge and understanding of the mechanisms through which heat stress (HS) resulting from global warming affects the welfare, behavior, immune response, production performance, and even transgenerational effects in poultry are still incomplete. Further research is needed to delve deeper into these mechanisms to gain a comprehensive understanding. Numerous studies have investigated various biomarkers of stress in poultry, aiming to identify reliable markers that can accurately assess the physiological status and well-being of birds. However, there is a significant amount of variation and inconsistency in the results reported across different studies. This inconsistency highlights the need for more standardized methods and assays and a clearer understanding of the factors that influence these biomarkers in poultry. This review article specifically focuses on 3 main aspects: 1) the neuroendocrine and behavioral responses of poultry to HS, 2) the biomarkers of HS and 3) the impact of HS on poultry production that have been studied in poultry. By examining the neuroendocrine and behavioral changes exhibited by poultry under HS, we aim to gain insights into the physiological impact of elevated temperatures in poultry.

Pharmacological Mechanism of Ketamine in Suicidal Behavior Based on Animal Models of Aggressiveness and Impulsivity: A Narrative Review

Around 700,000 people die from suicide each year in the world. Approximately 90% of suicides have a history of mental illness, and more than two-thirds occur during a major depressive episode. Specific therapeutic options to manage the suicidal crisis are limited and measures to prevent acting out also remain limited. Drugs shown to reduce the risk of suicide (antidepressants, lithium, or clozapine) necessitate a long delay of onset. To date, no treatment is indicated for the treatment of suicidality. Ketamine, a glutamate NMDA receptor antagonist, is a fast-acting antidepressant with significant effects on suicidal ideation in the short term, while its effects on suicidal acts still need to be demonstrated. In the present article, we reviewed the literature on preclinical studies in order to identify the potential anti-suicidal pharmacological targets of ketamine. Impulsive-aggressive traits are one of the vulnerability factors common to suicide in patients with unipolar and bipolar depression. Preclinical studies in rodent models with impulsivity, aggressiveness, and anhedonia may help to analyze, at least in part, suicide neurobiology, as well as the beneficial effects of ketamine/esketamine on reducing suicidal ideations and preventing suicidal acts. The present review focuses on disruptions in the serotonergic system (5-HT_B receptor, MAO-A enzyme), neuroinflammation, and/or the HPA axis in rodent models with an impulsive/aggressive phenotype, because these traits are critical risk factors for suicide in humans. Ketamine can modulate these endophenotypes of suicide in human as well as in animal models. The main pharmacological properties of ketamine are then summarized. Finally, numerous questions arose regarding the mechanisms by which ketamine may prevent an impulsive-aggressive phenotype in rodents and suicidal ideations in humans. Animal models of anxiety/depression are important tools to better understand the pathophysiology of depressed patients, and in helping develop novel and fast antidepressant drugs with anti-suicidal properties and clinical utility.

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.

Augmented impulsive behavior in febrile seizure-induced mice

Febrile seizure (FS) is one of the most prevalent etiological events in childhood affecting 2-5% of children from 3 months to 5 years old. Debates on whether neurodevelopmental consequences rise in later life following a febrile seizure or not are still ongoing however there is limited evidence of its effect, especially in a laboratory setting. Moreover, the comparative study using both male and female animal models is sparse. To examine the effect of FS on the behavioral features of mice, both sexes of ICR mice were induced with hyperthermic seizures through exposure to an infrared heat lamp. The mice were divided into two groups, one receiving a single febrile seizure at postnatal day 11 (P11) and one receiving three FS at P11, P13, and P15. Starting at P30 the FS-induced mice were subjected to a series of behavioral tests. Mice with seizures showed no locomotor and motor coordination deficits, repetitive, and depressive-like behavior. However, the FS-induced mice showed impulsive-like behavior in both elevated plus maze and cliff avoidance tests, which is more prominent in male mice. A greater number of mice displayed impaired CAT in both males and females in the three-time FS-induced group compared to the single induction group. These results demonstrate that after induction of FS, male mice have a higher susceptibility to consequences of febrile seizure than female mice and recurrent febrile seizure has a higher chance of subsequent disorders associated with decreased anxiety and increased impulsivity. We confirmed the dysregulated expression of impulsivity-related genes such as 5-HT1A and tryptophan hydroxylase 2 from the prefrontal cortices of FS-induced mice implying that the 5-HT system would be one of the mechanisms underlying the increased impulsivity after FS. Taken together, these findings are useful in unveiling future discoveries about the effect of childhood febrile seizure and the mechanism behind it.

Activation of glucagon-like peptide-1 receptors reduces the acquisition of aggression-like behaviors in male mice

Aggression is a complex social behavior, which is provoked in the defense of limited resources including food and mates. Recent advances show that the gut-brain hormone ghrelin modulates aggressive behaviors. As the gut-brain hormone glucagon-like peptide-1 (GLP-1) reduces food intake and sexual behaviors its potential role in aggressive behaviors is likely. Therefore, we investigated a tentative link between GLP-1 and aggressive behaviors by combining preclinical and human genetic-association studies. The influence of acute or repeated injections of a GLP-1 receptor (GLP-1R) agonist, exendin-4 (Ex4), on aggressive behaviors was assessed in male mice exposed to the resident-intruder paradigm. Besides, possible mechanisms participating in the ability of Ex4 to reduce aggressive behaviors were evaluated. Associations of polymorphisms in GLP-1R genes and overt aggression in males of the CATSS cohort were assessed. In male mice, repeated, but not acute, Ex4 treatment dose-dependently reduced aggressive behaviors. Neurochemical and western blot studies further revealed that putative serotonergic and noradrenergic signaling in nucleus accumbens, specifically the shell compartment, may participate in the interaction between Ex4 and aggression. As high-fat diet (HFD) impairs the responsiveness to GLP-1 on various behaviors the possibility that HFD blunts the ability of Ex4 to reduce aggressive behaviors was explored. Indeed, the levels of aggression was similar in vehicle and Ex4 treated mice consuming HFD. In humans, there were no associations between polymorphisms of the GLP-1R genes and overt aggression. Overall, GLP-1 signaling suppresses acquisition of aggressive behaviors via central neurotransmission and additional studies exploring this link are warranted.

Absence of a significant interaction of two common NOS1 and 5-HTT polymorphisms on sensorimotor gating in humans

The neurotransmitter serotonin has been critically implicated in the pathogenesis of several mental disorders. The serotonin transporter (5-HTT) is a key regulator of serotonergic neurotransmission and its genetic variability is associated with increased risk of psychopathology. One well known polymorphic locus in the 5-HTT gene affecting its expression is a tandem repeat in the promoter region (5-HTTLPR). It has been reported that 5-HTT is functionally coupled with the neuronal nitric oxide synthase (NOS1 or nNOS), an enzyme catalyzing the production of nitric oxide (NO). We have previously demonstrated that a tandem repeat polymorphism in the promoter of NOS1 exon 1f (Ex1f-VNTR) is associated with sensorimotor gating, a marker of inhibitory processing and a well established endophenotype of several neuropsychiatric disorders. Here we investigated the combined genetic effects of NOS1 Ex1f-VNTR and 5-HTTLPR on sensorimotor gating, measured by prepulse inhibition (PPI) of the acoustic startle reflex, in 164 healthy adults. We found no evidence for the interaction between NOS1 Ex1f-VNTR and 5-HTTLPR on PPI. PPI was associated with NOS1 Ex1f-VNTR, but not 5-HTTLPR. Our data suggest that while NOS1 plays a role in sensorimotor gating, the nitrergic pathway of gating regulation does not involve the action of 5-HTT.

Transcriptome Analyses Provide Insights into the Aggressive Behavior toward Conspecific and Heterospecific in Thitarodes xiaojinensis (Lepidoptera: Hepialidae)

Simple Summary

Aggression is an evolutionarily conserved, complex behavior, essential for survival, reproduction, and the organization of social hierarchies. It is well studied in adult insects, such as flies, ants, honey bees, and crickets. However, the study of aggressive behavior in the larval stage is still lacking. T. xiaojinensis is a common species found in mountainous regions of the Tibetan Plateau, the larvae of which are highly aggressive toward conspecifics. High-throughput RNA-seq with a reference genome provides opportunities for in-depth analysis when T. xiaojinensis is aggressive toward conspecifics and heterospecifics. This study provided a set of important pathways and DEGs associated with aggressive behavior. We also constructed the weighted gene co-expression network for traits, and the central and hub genes involved in aggressive behavior were obtained. The results revealed the molecular responses when T. xiaojinensis showed aggressiveness toward conspecifics and heterospecifics. These data are important for better understanding the aggressive behavior of Lepidopteran larvae at the transcriptional level and provide a theoretical basis for the further analysis of the genetic mechanism of the insect’s aggression.

Abstract

Aggressive behavior in animals is important for survival and reproduction. It is well studied in adult insects, such as flies, ants, honey bees, and crickets. However, the larvae of Lepidopteran insects are also aggressive, studies of which are still lacking. Here, RNA-seq was used to generate a high-quality database for the aggressive behavior of Thitarodes xiaojinensis toward conspecifics and heterospecifics. Although there was similar aggressive behavior between the conspecific group and heterospecific group, significant differences were identified at the transcriptional level. When there was aggressive behavior toward conspecifics, T. xiaojinensis trended toward higher expression at the respiratory chain, while cuticle development and metabolism may have interfered. On the other hand, when there was aggressive behavior toward H. armigera, genes related to neuron and cuticle development, cellular processes, and its regulated signaling pathways were significantly upregulated, while the genes associated with oxidation-reduction and metabolism were downregulated. Weighted gene co-expression networks analysis (WGCNA) was performed, and two modules with properties correlating to the aggressive behavior of T. xiaojinensis were identified. Several hub genes were predicted and confirmed by qRT-PCR, such as CLTC, MYH, IGF2BP1, and EMC. This study provides a global view and potential key genes for the aggressive behavior of T. xiaojinensis toward conspecifics and heterospecifics. Further investigation of the hub genes would help us to better understand the aggressive behavior of insects.

Distribution of nitric oxide in the rock cavy (Kerodon rupestris) brain II: The brainstem

In a recent paper, we described the distribution of Nitric oxide (NO) in the diencephalon of the rock cavy (Kerodon rupestris). This present paper follows this work, showing the distribution of NO synthesizing neurons in the rock cavy's brainstem. For this, we used immunohistochemistry against the neuronal form of nitric oxide synthase (NOS) and NADPH diaphorase histochemistry. In contrast to the diencephalon in the rock cavy, where the NOS neurons were seen to be limited to some nuclei in the thalamus and hypothalamus, the distribution of NOS in the brainstem is widespread. Neurons immunoreactive to NOS (NOS-ir) were seen as rostral as the precommissural nuclei and as caudal as the caudal and gelatinous parts of the spinal trigeminal nucleus. Places such as the raphe nuclei, trigeminal complex, superior and inferior colliculus, oculomotor complex, periaqueductal grey matter, solitary tract nucleus, laterodorsal tegmental nucleus, pedunculopontine tegmental, and other nuclei of the reticular formation are among the locations with the most NOS-ir neurons. This distribution is similar, but with some differences, to those described for other rodents, indicating that NO also has an important role in rock cavy's physiology.

Nitric oxide interacts with monoamine oxidase to modulate aggression and anxiety-like behaviour

Nitric oxide (NO) is a gaseous neurotransmitter that has important behavioural functions in the vertebrate brain. In this study we compare the impact of decreased nitric NO signalling upon behaviour and neurobiology using both zebrafish and mouse. nitric oxide synthase mutant (nos1^-/-) zebrafish show significantly reduced aggression and an increase in anxiety-like behaviour without altered production of the stress hormone cortisol. Nos1^-/- mice also exhibit decreased aggression and are hyperactive in an open field test. Upon reduction of NO signalling, monoamine neurotransmitter metabolism is reduced as a consequence of decreased Monoamine oxidase activity. Treatment of nos1^-/- zebrafish with the 5-HT receptor 1A agonist 8-OH-DPAT rescues aggression and some aspects of anxiety-like behaviour. Taken together, the interplay between NO and 5-HT appears to be critical to control behaviour. Our cross-species approach challenges the previous notion that reduced neuronal NOS leads to increased aggression. Rather, Nos1 knock-out can also lead to decreased aggression in some situations, a finding that may have implications for future translational research.

Nitric oxide synthase genotype interacts with stressful life events to increase aggression in male subjects in a population-representative sample

Nitric oxide signalling has been implicated in impulsive and aggressive traits and behaviours in both animals and humans. In the present study, we investigated the effects of a functional variable number of tandem repeats (VNTR) polymorphism in exon 1f (ex1f) of the nitric oxide synthase 1 (NOS1) gene (NOS1 ex1f-VNTR) and stressful life events on aggressive behaviour in population representative sample of adolescents followed up from third grade to 25 years of age. We studied the younger cohort of the longitudinal Estonian Children Personality, Behaviour and Health Study (subjects in the last study wave n = 437, males n = 193; mean age 24.8 ± 0.5 years). Aggressive behaviour was rated at age 25 with the Illinois Bully Scale and Buss-Perry Aggression Questionnaire. Life history of aggression was evaluated in a structured interview. Stressful life events and family relationships were self-reported at age 15. The hypothesized risk genotype (homozygosity for the short allele) was associated with higher levels of aggression in males (statistical significance withstanding the multiple correction procedure). Exposure to stressful life events or adverse family relationships was associated with increased aggressive behaviour in subjects homozygous for either of the alleles, and these associations were mostly observed in males. However, these associations in these stratified analyses did not survive correction for multiple testing. Aggressiveness was relatively unaffected by the NOS1 ex1f-VNTR genotype in the female subjects even when taking exposure to childhood adversity into account. Our findings support the hypothesized involvement of a functional NOS1 polymorphism on aggression in a population representative sample of young adults.

Dentate nNOS accounts for stress-induced 5-HT1A receptor deficiency: Implication in anxiety behaviors

Background

Anxiety is a common disorder with high social burden worldwide. Dysfunction of serotonin‐_1A receptor (5‐HT_1A receptor) in the dentate gyrus (DG) of the hippocampus has been predominantly implicated in the anxiety behavior. However, the molecular mechanism underlying the deficiency of postsynaptic 5‐HT_1A receptor in regulating anxiety behavior remains unclear.

Methods

Using pharmacological and genetic methods, we investigated the role of detate nNOS in 5‐HT_1A receptor decline and anxiety behavior induced by chronic mild stress (CMS) in mice.

Results

Here we showed that local elevation of glucocorticoids in the DG accounted for chronic stress‐induced anxiety behavior. Neuronal nitric oxide synthase (nNOS) mediated chronic stress‐induced downregulation of 5‐HT_1A receptor in the DG through peroxynitrite anion (ONOO•) pathway but not cyclic guanosine monophosphate (cGMP) pathway. By using pharmacological tool drugs and nNOS knockout mice, we found that nNOS in the DG played a key role in chronic stress‐induced anxiety behavior.

Conclusions

These findings uncovered an important role of nNOS‐5‐HT_1A receptor pathway in the DG of the hippocampus in chronic stress‐induced anxiety. Accordingly, we developed a “dentate nNOS‐5‐HT_1A receptor closed‐loop” theory (stress‐glucocorticoids‐nNOS‐Nitric oxide‐ONOO•‐5‐HT_1A receptor ‐nNOS) of stress‐related anxiety.

Melatonin pretreatment attenuates acute methamphetamine-induced aggression in male ICR mice

Aggression is one of the symptoms of methamphetamine (MA) use and withdrawal, which can exacerbate MA addiction and relapse. Many studies have demonstrated that poor sleep is significantly associated with aggression. Melatonin has been indicated to be effective in treating sleep disorders induced by MA, and it can also protect neuronal cells against MA-induced neurotoxicity. However, the underlying effects of melatonin on MA-reduced aggression remain unclarified. This study was designed to evaluate the effects of melatonin on acute MA-induced aggressive behavior in male ICR mice and the effects on neurotransmitters related to aggression. Fifty male ICR mice were randomly assigned to control and treatment groups pretreated with MA (3 mg/kg) or melatonin (2.5, 5, 10 mg/kg) plus MA. Aggressive behaviors were observed through isolation-induced aggression in the resident-intruder model. High-performance liquid chromatography combined with electrochemical detection (HPLC-ECD) was used to anatomize the levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), and the concentrations of serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), in the hippocampus involved in behavior processing. The results showed that acute MA administration decreased latency to initial attacks and thereby increased the number and total duration of attacks. Furthermore, HVA level as well as 5-HIAA and 5-HT turnover estimated by 5-HIAA/5-HT ratios declined compared to those in the vehicle group. The medium melatonin pretreatment dose (5 mg/kg) could significantly reverse acute MA-induced aggressive behavior in the form of prolonging latency to initial attacks and thereby attenuating the number of attacks and total duration of attacks. HVA and 5-HIAA levels, 5-HT turnover estimated by 5-HIAA/5-HT ratios, and DA turnover estimated by HVA/DA ratios and (DOPAC + HVA)/DA ratios were elevated compared to those in the MA group. These results indicate that the DA and 5-HT systems are involved in the processes of MA-induced aggressive behaviors and that melatonin has the capacity to reverse MA-induced aggressive behaviors.

Ghrelin and aggressive behaviours-Evidence from preclinical and human genetic studies

Aggressive behaviour is of crucial importance in the defence for limited resources including food and mates and involves central serotonin as well as dopamine signalling. As ghrelin modulates food intake and sexual behaviour we initially investigated the hypothesis that central ghrelin signalling regulates aggressive behaviour in the resident intruder paradigm in male mice. Moreover, interaction between ghrelin signalling and serotonergic, noradrenergic as well as dopaminergic neurotransmission in aggression was investigated. The relevance of ghrelin for human aggression per se as well as for aggression induced by alcohol was evaluated in a human genetic association study comprising young men (n = 784) from the normal population assessed for anti-social behaviours. The present study demonstrates that central ghrelin infusion, but not ghrelin administered systemically, increases aggression. Moreover aggressive behaviour is decreased by pharmacological suppression of the growth hormone secretagogue receptor-1 A (GHSR-1A) by JMV2959. As indicated by the ex vivo biochemical data serotonin, rather than dopamine or noradrenaline, in amygdala may have central roles for the ability of JMV2959 to reduce aggression. This link between central serotonin, GHSR-1A and aggression is further substantiated by the behavioural data showing that JMV2959 cannot decrease aggression following depletion of central serotonin signalling. The genetic association study demonstrates that males carrying the Leu72Leu genotype of the pre-pro-ghrelin gene and displaying hazardous alcohol use are more aggressive when compared to the group carrying the Met-allele. Collectively, this contributes to the identification of central ghrelin pathway as an important modulator in the onset of aggressive behaviours in male mice.

Limited effects of early life manipulations on sex-specific gene expression and behavior in adulthood

Exposure to childhood adversity is associated with increased vulnerability to stress-related disorders in adulthood which has been replicated in rodent stress models, whereas environmental enrichment has been suggested to have beneficial effects. However, the exact neurobiological mechanisms underlying these environment influences on adult brain and behavior are not well understood. Therefore, we investigated the long-term effects of maternal separation (MS) or environmental enrichment (EE) in male and female CD1 mice. We found clear sex-specific effects, but limited influence of environmental manipulations, on adult behavior, fecal corticosterone metabolite (FCM) levels and stress- and plasticity related gene expression in discrete brain regions. In detail, adult females displayed higher locomotor activity and FCM levels compared to males and EE resulted in attenuation in both measures, but only in females. There were no sex- or postnatal manipulation-dependent differences in anxiety-related behaviors in either sex. Gene expression analyses revealed that adult males showed higher Fkbp5 mRNA levels in hippocampus, hypothalamus and raphe nuclei, and higher hippocampal Nos1 levels. Interestingly, MS elevated Nos1 levels in hippocampus but reduced Fkbp5 expression in hypothalamus of males. Finally, we also found higher Maoa expression in the hypothalamus of adult females, however no differences were observed in the expression levels of Bdnf, Crhr1, Nr3c1 and Htr1a. Our findings further contribute to sex-dependent differences in behavior, corticosterone and gene expression and reveal that the effects of postnatal manipulations on these parameters in outbred CD1 mice are limited.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

A quantitative trait locus on chromosome 1 modulates intermale aggression in mice

Aggression between male conspecifics is a complex social behavior that is likely modulated by multiple gene variants. In this study, the BXD recombinant inbred mouse strains (RIS) were used to map quantitative trait loci (QTLs) underlying behaviors associated with intermale aggression. Four hundred and fifty-seven males from 55 strains (including the parentals) were observed at an age of 13 ± 1 week in a resident-intruder test following 10 days of isolation. Attack latency was measured directly within a 10-minute time period and the test was repeated 24 hours later. The variables we analyzed were the proportion of attacking males in a given strain as well as the attack latency (on days 1 and 2, and both days combined). On day 1, 29% of males attacked, and this increased to 37% on day 2. Large strain differences were obtained for all measures of aggression, indicating substantial heritability (intraclass correlations 0.10-0.18). We identified a significant QTL on chromosome (Chr) 1 and suggestive QTLs on mouse Chrs 1 and 12 for both attack and latency variables. The significant Chr 1 locus maps to a gene-sparse region between 82 and 88.5 Mb with the C57BL/6J allele increasing aggression and explaining about 18% of the variance. The most likely candidate gene modulating this trait is Htr2b which encodes the serotonin 2B receptor and has been implicated in aggressive and impulsive behavior in mice, humans and other species.

Bi-stability in type 2 diabetes mellitus multi-organ signalling network

Type 2 diabetes mellitus (T2DM) is believed to be irreversible although no component of the pathophysiology is irreversible. We show here with a network model that the apparent irreversibility is contributed by the structure of the network of inter-organ signalling. A network model comprising all known inter-organ signals in T2DM showed bi-stability with one insulin sensitive and one insulin resistant attractor. The bi-stability was made robust by multiple positive feedback loops suggesting an evolved allostatic system rather than a homeostatic system. In the absence of the complete network, impaired insulin signalling alone failed to give a stable insulin resistant or hyperglycemic state. The model made a number of correlational predictions many of which were validated by empirical data. The current treatment practice targeting obesity, insulin resistance, beta cell function and normalization of plasma glucose failed to reverse T2DM in the model. However certain behavioural and neuro-endocrine interventions ensured a reversal. These results suggest novel prevention and treatment approaches which need to be tested empirically.

A comparative study of the effect of the dose and exposure duration of anabolic androgenic steroids on behavior, cholinergic regulation, and oxidative stress in rats

The aim of this study was to assess if the dose and exposure duration of the anabolic androgenic steroids (AAS) boldenone (BOL) and stanazolol (ST) affected memory, anxiety, and social interaction, as well as acetylcholinesterase (AChE) activity and oxidative stress in the cerebral cortex (CC) and hippocampus (HC). Male Wistar rats (90 animals) were randomly assigned to three treatment protocols: (I) 5 mg/kg BOL or ST, once a week for 4 weeks; (II) 2.5 mg/kg BOL or ST, once a week for 8 weeks; and (III) 1.25 mg/kg BOL or ST, once a week for 12 weeks. Each treatment protocol included a control group that received an olive oil injection (vehicle control) and AAS were administered intramuscularly (a total volume of 0.2 ml) once a week in all three treatment protocols. In the BOL and ST groups, a higher anxiety level was observed only for Protocol I. BOL and ST significantly affected social interaction in all protocols. Memory deficits and increased AChE activity in the CC and HC were found in the BOL groups treated according to Protocol III only. In addition, BOL and ST significantly increased oxidative stress in both the CC and HC in the groups treated according to Protocol I and III. In conclusion, our findings show that the impact of BOL and ST on memory, anxiety, and social interaction depends on the dose and exposure duration of these AAS.

Animal models to improve our understanding and treatment of suicidal behavior

Worldwide, suicide is a leading cause of death. Although a sizable proportion of deaths by suicide may be preventable, it is well documented that despite major governmental and international investments in research, education and clinical practice suicide rates have not diminished and are even increasing among several at-risk populations. Although nonhuman animals do not engage in suicidal behavior amenable to translational studies, we argue that animal model systems are necessary to investigate candidate endophenotypes of suicidal behavior and the neurobiology underlying these endophenotypes. Animal models are similarly a critical resource to help delineate treatment targets and pharmacological means to improve our ability to manage the risk of suicide. In particular, certain pathophysiological pathways to suicidal behavior, including stress and hypothalamic-pituitary-adrenal axis dysfunction, neurotransmitter system abnormalities, endocrine and neuroimmune changes, aggression, impulsivity and decision-making deficits, as well as the role of critical interactions between genetic and epigenetic factors, development and environmental risk factors can be modeled in laboratory animals. We broadly describe human biological findings, as well as protective effects of medications such as lithium, clozapine, and ketamine associated with modifying risk of engaging in suicidal behavior that are readily translatable to animal models. Endophenotypes of suicidal behavior, studied in animal models, are further useful for moving observed associations with harmful environmental factors (for example, childhood adversity, mechanical trauma aeroallergens, pathogens, inflammation triggers) from association to causation, and developing preventative strategies. Further study in animals will contribute to a more informed, comprehensive, accelerated and ultimately impactful suicide research portfolio.

The neurobiological basis of human aggression: A review on genetic and epigenetic mechanisms

Aggression is an evolutionary conserved behavior present in most species including humans. Inadequate aggression can lead to long-term detrimental personal and societal effects. Here, we differentiate between proactive and reactive forms of aggression and review the genetic determinants of it. Heritability estimates of aggression in general vary between studies due to differing assessment instruments for aggressive behavior (AB) as well as age and gender of study participants. In addition, especially non-shared environmental factors shape AB. Current hypotheses suggest that environmental effects such as early life stress or chronic psychosocial risk factors (e.g., maltreatment) and variation in genes related to neuroendocrine, dopaminergic as well as serotonergic systems increase the risk to develop AB. In this review, we summarize the current knowledge of the genetics of human aggression based on twin studies, genetic association studies, animal models, and epigenetic analyses with the aim to differentiate between mechanisms associated with proactive or reactive aggression. We hypothesize that from a genetic perspective, the aminergic systems are likely to regulate both reactive and proactive aggression, whereas the endocrine pathways seem to be more involved in regulation of reactive aggression through modulation of impulsivity. Epigenetic studies on aggression have associated non-genetic risk factors with modifications of the stress response and the immune system. Finally, we point to the urgent need for further genome-wide analyses and the integration of genetic and epigenetic information to understand individual differences in reactive and proactive AB. © 2015 Wiley Periodicals, Inc.

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

Behavioral abnormalities in mice lacking mesenchyme-specific Pten

Phosphatase and tensin homolog (Pten) is a negative regulator of cell proliferation and growth. Using a Cre-recombinase approach with Lox sequences flanking the fibroblast-specific protein 1 (Fsp1 aka S100A4; a mesenchymal marker), we probed sites of expression using a β-galactosidase Rosa26(LoxP) reporter allele; the transgene driving deletion of Pten (exons 4-5) was found throughout the brain parenchyma and pituitary, suggesting that deletion of Pten in Fsp1-positive cells may influence behavior. Because CNS-specific deletion of Pten influences social and anxiety-like behaviors and S100A4 is expressed in astrocytes, we predicted that loss of Pten in Fsp1-expressing cells would result in deficits in social interaction and increased anxiety. We further predicted that environmental enrichment would compensate for genetic deficits in these behaviors. We conducted a battery of behavioral assays on Fsp1-Cre;Pten(LoxP/LoxP) male and female homozygous knockouts (Pten(-/-)) and compared their behavior to Pten(LoxP/LoxP) (Pten(+/+)) conspecifics. Despite extensive physical differences (including reduced hippocampal size) and deficits in sensorimotor function, Pten(-/-) mice behaved remarkably similar to control mice on nearly all behavioral tasks. These results suggest that the social and anxiety-like phenotypes observed in CNS-specific Pten(-/-) mice may depend on neuronal Pten, as lack of Pten in Fsp1-expressing cells of the CNS had little effect on these behaviors.

Violent suicidal behaviour in bipolar disorder is associated with nitric oxide synthase 3 gene polymorphism

OBJECTIVE

Given the importance of nitric oxide system in oxidative stress, inflammation, neurotransmission and cerebrovascular tone regulation, we postulated its potential dysfunction in bipolar disorder (BD) and suicide. By simultaneously analysing variants of three isoforms of nitric oxide synthase (NOS) genes, we explored interindividual genetic liability to suicidal behaviour in BD.

METHOD

A total of 536 patients with BD (DSM-IV) and 160 healthy controls were genotyped for functionally relevant NOS1, NOS2 and NOS3 polymorphisms. History of suicidal behaviour and violent suicide attempt was documented for 511 patients with BD. Chi-squared test was used to perform genetic association analyses and logistic regression to test for gene-gene interactions.

RESULTS

NOS3 rs1799983 T homozygous state was associated with violent suicide attempts (26.4% vs. 10.8%, in patients and controls, P = 0.002, corrected P (Pc) = 0.004, OR: 2.96, 95% CI = 1.33-6.34), and this association was restricted to the early-onset BD subgroup (37.9% vs. 10.8%, in early-onset BD and controls, P = 0.0003, Pc = 0.0006 OR: 5.05, 95% CI: 1.95-12.45), while we found no association with BD per se and no gene-gene interactions.

CONCLUSION

Our results bring further evidence for the potential involvement of endothelial NOS gene variants in susceptibility to suicidal behaviour. Future exploration of this pathway on larger cohort of suicidal behaviour is warranted.

On the role of NOS1 ex1f-VNTR in ADHD-allelic, subgroup, and meta-analysis

Attention deficit/ hyperactivity disorder (ADHD) is a heritable neurodevelopmental disorder featuring complex genetics with common and rare variants contributing to disease risk. In a high proportion of cases, ADHD does not remit during adolescence but persists into adulthood. Several studies suggest that NOS1, encoding nitric oxide synthase I, producing the gaseous neurotransmitter NO, is a candidate gene for (adult) ADHD. We here extended our analysis by increasing the original sample, adding two further samples from Norway and Spain, and conducted subgroup and co-morbidity analysis. Our previous finding held true in the extended sample, and also meta-analysis demonstrated an association of NOS1 ex1f-VNTR short alleles with adult ADHD (aADHD). Association was restricted to females, as was the case in the discovery sample. Subgroup analysis on the single allele level suggested that the 21-repeat allele caused the association. Regarding subgroups, we found that NOS1 was associated with the hyperactive/impulsive ADHD subtype, but not to pure inattention. In terms of comorbidity, major depression, anxiety disorders, cluster C personality disorders and migraine were associated with short repeats, in particular the 21-repeat allele. Also, short allele carriers had significantly lower IQ. Finally, we again demonstrated an influence of the repeat on gene expression in human post-mortem brain samples. These data validate the role of NOS-I in hyperactive/impulsive phenotypes and call for further studies into the neurobiological underpinnings of this association. © 2015 Wiley Periodicals, Inc.

In silico Analysis and Experimental Validation of Lignan Extracts from Kadsura longipedunculata for Potential 5-HT1AR Agonists

Objectives

Kadsura longipedunculata (KL) has been widely used for the treatment of insomnia in traditional Chinese medicine. The aim of this study was to explore the mechanism of the sedative and hypnotic effects of KL.

Materials and Methods

The content of KL was evaluated by HPLC-TOF-MS, and a potential target was found and used to construct its 3D structure to screen for potential ligands among the compounds in KL by using bioinformatics analysis, including similarity ensemble approach (SEA) docking, homology modeling, molecular docking and ligand-based pharmacophore. The PCPA-induced insomnia rat model was then applied to confirm the potential targets related to the sedative effects of KL by performing the forced swimming test (FST), the tail suspension test (TST) and the measurement of target-related proteins using western blotting and immunofluorescence.

Results

Bioinformatics analysis showed that most of lignan compounds in KL were optimal ligands for the 5-HT1A receptor (5-HT1AR), and they were found to be potential targets related to sedative effects; the main lignan content of KL extracts was characterized by HPLC-TOF-MS, with 7 proposed lignans detected. Administration of KL could significantly reduce FST and TST immobility time in the PCPA-induced 5HT-depleted insomnia rat model. The expressions of proteins related to the 5-HT1AR pathway were regulated by extracts of KL in a concentration-dependent manner, indicating that extracts of KL had 5-HT1AR agonist-like effects.

Conclusion

In silico analysis and experimental validation together demonstrated that lignan extracts from KL can target 5-HT1AR in insomniac rats, which could shed light on its use as a potential 5-HT1AR agonist drug.

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.

The analysis of BDNF gene polymorphism haplotypes and impulsivity in methamphetamine abusers

An increasing number of evidence showed that genetic factors might contribute to drug abuse vulnerability. Data from genetic scans in humans suggest that brain-derived neurotrophic factor (BDNF), a member of the neurotrophic factor family, may be associated with substance abuse or dependence. To test the hypothesis that the BDNF gene polymorphism is involved in methamphetamine abuse, we compared three single nucleotide polymorphisms (SNPs, rs16917204, rs16917234, and rs2030324) of the BDNF gene in 200 methamphetamine abusers and 219 healthy individuals. We also considered the association of these polymorphisms with impulsivity in methamphetamine abusers using Barratt Impulsivity Scale-11(BIS-11) Chinese version. Individual SNP analysis showed no significant differences in genotype and allele distributions between the methamphetamine abusers and controls. Haplotype analysis of rs16917204-rs16917234-rs2030324 revealed that a major C-C-T haplotype was significantly associated a lower odds of methamphetamine abuse, even after Bonferroni correction. Within the methamphetamine-abuse group, subjects carrying the T allele of rs2030324 genotype had significantly higher motor impulsivity scores of BIS compared to those with the C/C genotype. Our findings suggest that the BDNF gene polymorphism may contribute to the impulsivity in methamphetamine abusers.

Evidence for the contribution of NOS1 gene polymorphism (rs3782206) to prefrontal function in schizophrenia patients and healthy controls

Nitric oxide (NO), a gaseous neurotransmitter, has been implicated in the pathogenesis of schizophrenia. Accordingly, several polymorphisms of the gene that codes for the main NO-producing enzyme, the nitric oxide synthase 1 (NOS1), have been found to convey a risk for schizophrenia. This study examined the role of NOS1 gene polymorphisms in cognitive functions and related neural mechanism. First, with a sample of 580 schizophrenia patients and 720 healthy controls, we found that rs3782206 genotype had main effects on the 1-back task (P=0.005), the 2-back task (P=0.049), the AY condition of the dot-pattern expectancy (DPX) task (P=0.001), and the conflict effect of the attention network (ANT) test (P<0.001 for RT differences and P=0.002 for RT ratio) and interaction effects with diagnosis on the BX condition of the DPX (P=0.009), the AY condition of the DPX (P<0.001), and the Stroop conflict effect (P=0.003 for RT differences and P=0.038 for RT ratio). Simple effect analyses further showed that the schizophrenia risk allele (T) of rs3782206 was associated with poorer performance in five measures for the patients (1-back, P=0.025; BX, P=0.017; AY, P<0.001; ANT conflict effect (RT differences), P=0.005; Stroop conflict effect (RT differences), P=0.019) and three measures for the controls ( for the 2-back task, P=0.042; for the ANT conlict effect (RT differences), P=0.013; for the ANT conflict effect (RT ratios), P=0.028). Then, with a separate sample of 78 healthy controls, we examined the association between rs3782206 and brain activation patterns during the N-back task and the Stroop task. Whole brain analyses found that the risk allele carriers showed reduced activation at the right inferior frontal gyrus (IFG) during both tasks. Finally, we examined functional connectivity seeded from the right IFG to the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex under three conditions (the N-back task, the Stroop task, and the resting state). Results showed reduced connectivity with the DLPFC for the risk allele carriers mainly in the Stroop task and the resting state. Taken together, results of this study strongly suggested a link between NOS1 gene polymorphism at rs3782206 and cognitive functions and their neural underpinnings at the IFG. These results have important implications for our understanding of the neural mechanism underlying the association between NOS1 gene polymorphism and schizophrenia.

Aberrant Monoaminergic System in Thyroid Hormone Receptor-β Deficient Mice as a Model of Attention-Deficit/Hyperactivity Disorder

BACKGROUND

Thyroid hormone receptors are divided into 2 functional types: TRα and TRβ. Thyroid hormone receptors play pivotal roles in the developing brain, and disruption of thyroid hormone receptors can produce permanent behavioral abnormality in animal models and humans.

METHODS

Here we examined behavioralchanges, regional monoamine metabolism, and expression of epigenetic modulatory proteins, including acetylated histone H3 and histone deacetylase, in the developing brain of TRα-disrupted (TRα (0/0) ) and TRβ-deficient (TRβ (-/-) ) mice. Tissue concentrations of dopamine, serotonin (5-hydroxytryptamine) and their metabolites in the mesocorticolimbic pathway were measured.

RESULTS

TRβ (-/-) mice, a model of attention-deficit/hyperactivity disorder, showed significantly high exploratory activity and reduced habituation, whereas TRα (0/0) mice showed normal exploratory activity. The biochemical profiles of dopamine and 5-hydroxytryptamine showed significantly low dopamine metabolic rates in the caudate putamen and nucleus accumbens and overall low 5-hydroxytryptamine metabolic rates in TRβ (-/-) mice, but not in TRα (0/0) mice. Furthermore, the expression of acetylated histone H3 was low in the dorsal raphe of TRβ (-/-) mice, and histone deacetylase 2/3 proteins were widely increased in the mesolimbic system.

CONCLUSIONS

These findings suggest that TRβ deficiency causes dysfunction of the monoaminergic system, accompanied by epigenetic disruption during the brain maturation process.

Involvement of nitric oxide in serotonin-induced scratching in mice

BACKGROUND

Serotonin is a pruritogenic substance in humans and animals, but the mechanisms of action through which serotonin induces itch response are not yet understood.

AIM

To examine the possible role of nitric oxide (NO) in the profile of scratching behaviour due to intradermal injection of serotonin in mice.

METHODS

Intradermal injection of serotonin (14.1-235 nmol per site) into the nape of the neck was used to elicit itch in mice. Scratching behaviour was evaluated by counting the number of bouts during 60 min after injection. To determine the possible involvement of the nitrergic system in serotonin-induced scratching, L-NG-nitroarginine methyl ester [L-NAME; a nonselective nitric oxide synthase (NOS) inhibitor], aminoguanidine [a selective inducible (i)NOS inhibitor] and L-arginine (an NO precursor) were administered intraperitoneally to control and serotonin-injected animals.

RESULTS

Intradermal serotonin caused scratching in mice with a bell-shaped dose-response correlation, and the peak effective dose was 141 nmol per site. The majority of scratching bouts in animals occurred 5-10 min after injection. Ineffective doses of L-NAME (3 mg/kg IP) and aminoguanidine (100 mg/kg IP) decreased the scratching induced by intradermal serotonin injection in animals (P < 0.001 and P < 0.001), while an subeffective dose of L-arginine (100 mg/kg IP) augmented the scratching effect of serotonin (P < 0.001).

CONCLUSIONS

We show for the first time that the scratching induced by intradermal serotonin is mediated by NOS, especially iNOS, activation. We conclude that NO may play a role in mediating itch responses. NO and NOS could be new targets for antipruritic agents.

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.

Perinatal exposure to genistein affects the normal development of anxiety and aggressive behaviors and nitric oxide system in CD1 male mice

Genistein is a phytoestrogen, particularly abundant in soybeans, that is able to bind estrogen receptors exerting both estrogenic and antiestrogenic activities. Genistein is largely present in the human diet even during pregnancy. Embryos and fetuses are therefore, commonly exposed to genistein during the development and after birth. In the present study, we used a murine model as a test end-point to investigate the effects of early exposure to genistein on adult male behavior and related neural circuits. Daily exposure of dams to genistein (100 μg/g of body weight) during late pregnancy and early lactation, produced in male offspring, when adults, significant changes in anxiety and aggressive behaviors. Moreover, we found statistically significant variations in the number of neuronal nitric-oxide synthase positive cells in the amygdala. In conclusions, these data indicate that early exposure to phytoestrogens may induce life-long effects on the differentiation of brain structures and behaviors.

Chronic exposure to a predator or its scent does not inhibit male-male competition in male mice lacking brain serotonin

Although it is well-known that defective signaling of the 5-HT system in the brain and stressful stimuli can cause psychological disorders, their combined effects on male–male aggression and sexual attractiveness remain unknown. Our research aimed at examining such effects using tryptophan hydroxylase 2 (Tph2) knockout male mice vs. a rat- or rat scent-based chronic stress model. Tph2^+/+ and Tph2^−/− male mice were placed individually into the rat home cage (rat), a cage containing soiled rat bedding (rat scent) or a cage containing fresh bedding (control) for 5 h every other day for 56 consecutive days. In Tph2^+/+ male mice, rat-exposure decreased male–male aggression and sexual attractiveness of urine odor relative to either rat scent-exposure or control; and rat scent-exposure decreased aggression rather than sexual attractiveness of urine odor compared with control. However, such dose-dependent and long-lasting behavioral inhibitory effects vanished in Tph2^−/− male mice. RT-PCR assay further revealed that putative regulatory genes, such as AR, ERα and GluR4 in the prefrontal cortex, and TrkB-Tc and 5-HTR1A in the hippocampus, were down-regulated at the mRNA level in either rat- or rat scent-exposed Tph2^+/+ male mice, but partially in the Tph2^−/− ones. Hence, we suggest that the dose-dependent and long-lasting inhibitory effects of chronic predator exposure on male–male aggression, sexual attractiveness of urine odor, and mRNA expression of central regulatory genes might be mediated through the 5-HT system in the brain of male mice.

Sex-influence of nicotine and nitric oxide on motor coordination and anxiety-related neurophysiological responses

RATIONALE

Nitric oxide (NO) is a messenger synthesized in both the neuronal and glial populations by nitric oxide synthase type 1 (NOS1). Nicotine regulates NO production in a sex-dependent manner, both molecules being involved in motor function.

OBJECTIVE

The present study evaluates sex differences in motor coordination, general movement, and anxiety-related responses resulting from both constant and continuous nicotine treatment and the genetic depletion of NOS1 activity.

METHODS

Male and female mice were analyzed with the open-field and the rotarod tests. To understand the role of NO, knockout mice for NOS1 (NOS1-/-) were analyzed. Nicotine was administered continuously at a dose of 24 mg/kg/day via osmotic mini-pumps over 14 days because the behavioral effects elicited are similar to those observed with discontinuous administration.

RESULTS

Data analyses revealed noteworthy sex differences derived from NOS1 depletion. Control NOS1-/- males exhibited an exacerbated anxiety-related response in relation to control NOS1-/- females and control wild-type (WT) males; these differences disappeared in the nicotine-administered NOS1-/- males. Additionally, nicotine administration differentially affected the horizontal movements of NOS1-/- females with respect to WT animals. NO depletion affected male but not female motor coordination improvement along the test days. However, the drug affected female motor coordination only at the end of the administration period.

CONCLUSIONS

We show for the first time that NO affects motor and anxiety behaviors in a sex-dependent manner. Moreover, the behavioral effects of constant nicotine administration are dimorphic and dependent on NO production.

Hippocampus and nitric oxide

Since it was first identified to play an important role in relaxation of blood vessels, nitric oxide has been demonstrated to regulate many biological processes, especially in the central nervous system. Of the three types of enzymes that produce nitric oxide in humans and rodents, neuronal type is found almost exclusively in the nervous system. This gaseous molecule is a nonclassical neurotransmitter, which maintains the activities of neural cells and regulates the normal functions of brain. It appears to play a role in promoting the transfer of nerve signals from one neuron to another, maintaining the synaptic strength. Meanwhile, nitric oxide is a unique regulator on neurogenesis and synaptogenesis, producing the positive or negative effects upon different signal pathways or cellular origins and locations. Based on its significant roles in neural plasticity, nitric oxide is involved in a number of central nervous diseases, such as ischemia, depression, anxiety, and Alzheimer's disease. Clarifying the profiles of nitric oxide in the brain tissues and its participation in pathophysiological processes opens a new avenue for development of new therapeutic strategies. Thus, this chapter specifies the effects of nitric oxide in the hippocampus, a key structure implicated in the modulation of mood and memories, exhibiting the trend of future research on nitric oxide.

Nitric oxide and serotonin interactions in aggression

Violence is a significant public health problem worldwide. Neurobiological research on violence and aggression attempts to elucidate the cellular and molecular pathways that increase the propensity toward this behavior. Research over the past 40 years has implicated several brain regions and neurotransmitters in aggression, mainly using rodent models. Perhaps the strongest association is the link between serotonin and aggression, which has compelling interactions with the nitric oxide system. Recently, new insights into these relationships have been added as modern techniques allow more sophisticated analyses. This chapter will discuss current developments implicating serotonin and nitric oxide in aggressive behavior. Recently developed high-resolution methods for examining the neurobiological basis of aggression will be considered, with emphasis on future directions for the field.

Female contact modulates male aggression via a sexually dimorphic GABAergic circuit in Drosophila

Intraspecific male-male aggression, which is important for sexual selection, is regulated by environment, experience and internal states through largely undefined molecular and cellular mechanisms. To understand the basic neural pathway underlying the modulation of this innate behavior, we established a behavioral assay in Drosophila melanogaster and investigated the relationship between sexual experience and aggression. In the presence of mating partners, adult male flies exhibited elevated levels of aggression, which was largely suppressed by prior exposure to females via a sexually dimorphic neural mechanism. The suppression involved the ability of male flies to detect females by contact chemosensation through the pheromone-sensing ion channel ppk29 and was mediated by male-specific GABAergic neurons acting on the GABAA receptor RDL in target cells. Silencing or activating this circuit led to dis-inhibition or elimination of sex-related aggression, respectively. We propose that the GABAergic inhibition represents a critical cellular mechanism that enables prior experience to modulate aggression.

Aggression in bipolar II disorder and its relation to the serotonin transporter

BACKGROUND

Aggression is frequently observed in patients diagnosed with bipolar disorder (BD). Previous studies found a negative association between aggression and serotoninergic function in patients with BD, as well as in healthy subjects. The objective of this study was to determine whether there is an association between aggression and the availability of the serotonin transporter (SERT) in euthymic BD II patients.

METHODS

Thirty-eight age-matched healthy controls (HCs) and 24 BD II patients were recruited. BD II patients were under stable treatment in the euthymic state. The Overt Aggression Scale (OAS) was used for the assessment of aggression. Single photon emission computed tomography with (123)I-ADAM was used for SERT imaging. A specific uptake ratio, which represents availability, was the primary measured outcome.

RESULTS

The total OAS scores, as well as the scores on all of the sub-items, were significantly higher in BD II patients than in the HCs group. There was no significant difference in SERT availability between BD II and HCs subjects in different brain regions. The Pearson's correlation between the total OAS scores and the sub-item aggression and SERT availability was significant.

LIMITATION

The OAS was used for the assessment of the past week of the patients' condition and thus did not reflect their trait status.

CONCLUSIONS

The higher total scores of OAS in euthymic BD II patients than in HCs support the idea that aggression might be a trait marker for BD. Although SERT availability in euthymic BD II patients and in HCs did not differ significantly, the correlation of SERT availability and total OAS provides the possible explanation of aggression in BD II.

Genetics of impulsive behaviour

Impulsivity, defined as the tendency to act without foresight, comprises a multitude of constructs and is associated with a variety of psychiatric disorders. Dissecting different aspects of impulsive behaviour and relating these to specific neurobiological circuits would improve our understanding of the etiology of complex behaviours for which impulsivity is key, and advance genetic studies in this behavioural domain. In this review, we will discuss the heritability of some impulsivity constructs and their possible use as endophenotypes (heritable, disease-associated intermediate phenotypes). Several functional genetic variants associated with impulsive behaviour have been identified by the candidate gene approach and re-sequencing, and whole genome strategies can be implemented for discovery of novel rare and common alleles influencing impulsivity. Via deep sequencing an uncommon HTR2B stop codon, common in one population, was discovered, with implications for understanding impulsive behaviour in both humans and rodents and for future gene discovery.