Developmental effects of serotonin 1A autoreceptors on anxiety and social behavior

Sex-specific and developmental effects of early life adversity on stress reactivity are rescued by postnatal knockdown of 5-HT1A autoreceptors

Early Life Adversity (ELA) predisposes to stress hypersensitivity in adulthood, but neurobiological mechanisms that protect from the enduring effects of ELA are poorly understood. Serotonin 1A (5HT1A) autoreceptors in the raphé nuclei regulate adult stress vulnerability, but whether 5HT1A could be targeted to prevent ELA effects on susceptibility to future stressors is unknown. Here, we exposed mice with postnatal knockdown of 5HT1A autoreceptors to the limited bedding and nesting model of ELA from postnatal day (P)3-10 and tested behavioral, neuroendocrine, neurogenic, and neuroinflammatory responses to an acute swim stress in male and female mice in adolescence (P35) and in adulthood (P56). In females, ELA decreased raphé 5HT neuron activity in adulthood and increased passive coping with the acute swim stress, corticosterone levels, neuronal activity, and corticotropin-releasing factor (CRF) levels in the paraventricular nucleus (PVN) of the hypothalamus. ELA also reduced neurogenesis in the ventral dentate gyrus (vDG) of the hippocampus, an important mediator of individual differences in stress susceptibility, and increased microglia activation in the PVN and vDG. These effects of ELA were specific to females and manifested predominantly in adulthood, but not earlier on in adolescence. Postnatal knockdown of 5HT1A autoreceptors prevented these effects of ELA on 5HT neuron activity, stress reactivity, neurogenesis, and neuroinflammation in adult female mice. Our findings demonstrate that ELA induces long-lasting and sex-specific impairments in the serotonin system, stress reactivity, and vDG function, and identify 5HT1A autoreceptors as potential targets to prevent these enduring effects of ELA.

Sex-specific and Developmental Effects of Early Life Adversity on Stress Reactivity are Rescued by Postnatal Knockdown of 5-HT 1A Autoreceptors

Early Life Adversity (ELA) predisposes to stress hypersensitivity in adulthood, but neurobiological mechanisms that protect from the enduring effects of ELA are poorly understood. Serotonin 1A (5HT 1A ) autoreceptors in the raphé nuclei regulate adult stress vulnerability, but whether 5HT 1A could be targeted to prevent ELA effects on susceptibility to future stressors is unknown. Here, we exposed mice with postnatal knockdown of 5HT 1A autoreceptors to the limited bedding and nesting model of ELA from postnatal day (P)3-10 and tested behavioral, neuroendocrine, neurogenic, and neuroinflammatory responses to an acute swim stress in male and female mice in adolescence (P35) and in adulthood (P56). In females, ELA decreased raphé 5HT neuron activity in adulthood and increased passive coping with the acute swim stress, corticosterone levels, neuronal activity, and corticotropin-releasing factor (CRF) levels in the paraventricular nucleus (PVN) of the hypothalamus. ELA also reduced neurogenesis in the ventral dentate gyrus (vDG) of the hippocampus, an important mediator of individual differences in stress susceptibility, and increased microglia activation in the PVN and vDG. These effects of ELA were specific to females and manifested predominantly in adulthood, but not earlier on in adolescence. Postnatal knockdown of 5HT 1A autoreceptors prevented these effects of ELA on 5HT neuron activity, stress reactivity, neurogenesis, and neuroinflammation in adult female mice. Our findings demonstrate that ELA induces long-lasting and sex-specific impairments in the serotonin system, stress reactivity, and vDG function, and identify 5HT 1A autoreceptors as potential targets to prevent these enduring effects of ELA.

Astrocytic 5-HT1A receptor mediates age-dependent hippocampal LTD and fear memory extinction in male mice

NMDA receptor-dependent long-term depression (LTD) in the hippocampus is a well-known form of synaptic plasticity that has been linked to different cognitive functions. Although the underlying mechanisms remain unclear, this form of LTD cannot be induced by low-frequency stimulation (LFS) in adult mice. In this study, we found that LFS-induced LTD was not easily induced in adult animals and was age dependent. Interestingly, the level of the 5-HT1A receptor was correspondingly increased and exhibited an inverse correlation with the magnitude of LFS-LTD during development. Knockout or pharmacological inhibition of the 5-HT1A receptor reversed impaired LFS-LTD in adult mice (P60), while activation or inhibition of this receptor disturbed or enhanced LFS-LTD in adolescent mice (P21), respectively. Furthermore, the astrocytic 5-HT1A receptor in the hippocampus predominantly mediated age-dependent LFS-LTD through enhancing GABAergic neurotransmission. Finally, fear memory extinction differed among the above conditions. These observations enrich our knowledge of LTD at the cellular level and suggest a therapeutic approach for LTD-related psychiatric disorders.

High-fat diet, microbiome-gut-brain axis signaling, and anxiety-like behavior in male rats

Obesity, associated with the intake of a high-fat diet (HFD), and anxiety are common among those living in modern urban societies. Recent studies suggest a role of microbiome-gut-brain axis signaling, including a role for brain serotonergic systems in the relationship between HFD and anxiety. Evidence suggests the gut microbiome and the serotonergic brain system together may play an important role in this response. Here we conducted a nine-week HFD protocol in male rats, followed by an analysis of the gut microbiome diversity and community composition, brainstem serotonergic gene expression (tph2, htr1a, and slc6a4), and anxiety-related defensive behavioral responses. We show that HFD intake decreased alpha diversity and altered the community composition of the gut microbiome in association with obesity, increased brainstem tph2, htr1a and slc6a4 mRNA expression, including in the caudal part of the dorsomedial dorsal raphe nucleus (cDRD), a subregion previously associated with stress- and anxiety-related behavioral responses, and, finally, increased anxiety-related defensive behavioral responses. The HFD increased the Firmicutes/Bacteroidetes ratio relative to control diet, as well as higher relative abundances of Blautia, and decreases in Prevotella. We found that tph2, htr1a and slc6a4 mRNA expression were increased in subregions of the dorsal raphe nucleus in the HFD, relative to control diet. Specific bacterial taxa were associated with increased serotonergic gene expression in the cDRD. Thus, we propose that HFD-induced obesity is associated with altered microbiome-gut-serotonergic brain axis signaling, leading to increased anxiety-related defensive behavioral responses in rats.

5-HT1A Receptors on Dentate Gyrus Granule Cells Confer Stress Resilience

BACKGROUND

Hyperactivity of granule cells in the ventral dentate gyrus (vDG) promotes vulnerability to chronic stress. However, which receptors in the vDG could be targeted to inhibit this hyperactivity and confer stress resilience is not known. The serotonin 1A receptor (5-HT1AR) is a Gi protein-coupled inhibitory receptor that has been implicated in stress adaptation, anxiety, depression, and antidepressant responses. 5-HT1ARs are highly expressed in the DG, but their potential to promote stress resilience by regulating granule cell activity has never been examined.

METHODS

We exposed male and female mice expressing 5-HT1ARs only in DG granule cells to 10 days of chronic social defeat stress (CSDS) and treated them with the 5-HT1AR agonist 8-OH-DPAT every day 30 minutes before each defeat throughout the CSDS paradigm. We then used whole-cell current clamp recordings, immunohistochemistry for the immediate early gene cFos, corticosterone immunoassays, and behavioral testing to determine how activating 5-HT1ARs on granule cells affects DG activity, neuroendocrine stress responses, and avoidance behavior.

RESULTS

We found that activating 5-HT1ARs hyperpolarized DG granule cells and reduced cFos+ granule cells in the vDG following CSDS, indicating that 5-HT1AR activation rescued stress-induced vDG hyperactivity. Moreover, 5-HT1AR activation dampened corticosterone responses to CSDS and prevented the development of stress-induced avoidance in the social interaction test and in the open field test.

CONCLUSIONS

Our findings show that activating 5-HT1ARs on DG granule cells can prevent stress-induced neuronal hyperactivity of the vDG and confer resilience to chronic stress.

The brain serotonin system in autism

Autism spectrum disorders (ASDs) are among the most common neurodevelopmental diseases. These disorders are characterized by lack of social interaction, by repetitive behavior, and often anxiety and learning disabilities. The brain serotonin (5-HT) system is known to be crucially implicated in a wide range of physiological functions and in the control of different kinds of normal and pathological behavior. A growing number of studies indicate the involvement of the brain 5-HT system in the mechanisms underlying both ASD development and ASD-related behavioral disorders. There are some review papers describing the role of separate key players of the 5-HT system in an ASD and/or autistic-like behavior. In this review, we summarize existing data on the participation of all members of the brain 5-HT system, namely, 5-HT transporter, tryptophan hydroxylase 2, MAOA, and 5-HT receptors, in autism in human and various animal models. Additionally, we describe the most recent studies involving modern techniques for in vivo regulation of gene expression that are aimed at identifying exact roles of 5-HT receptors, MAOA, and 5-HT transporter in the mechanisms underlying autistic-like behavior. Altogether, results of multiple research articles show that the brain 5-HT system intimately partakes in the control of some types of ASD-related behavior, and that specific changes in a function of a certain 5-HT receptor, transporter, and/or enzyme may normalize this aberrant behavior. These data give hope that some of clinically used 5-HT-related drugs have potential for ASD treatment.

An Overview about New Methods in Management of Gag Reflex during Dental Treatment: A Systematic Review

Statement of the Problem

Management of gag reflex is a challenging process during many dental treatments. Various studies have been carried out to evaluate different pharmacological and non-pharmacological techniques to control gagging.

Purpose

The aim of this study is to review the available evidence on methods proposed for managing the gag reflex.

Materials and Method

This systematic review adheres to the preferred reporting items for systematic review and meta-analysis (PRISMA) guidelines. A comprehensive search was conducted in English and Persian based on articles published from 2015 to 2022 (February) in PubMed, Scopus, Science Direct, Web of Science, Google Scholar, ISC and SID. All studies were first screened based on their title and abstract. The quality assessment of articles was carried out by two independent authors. Then, risk of bias evaluation was conducted according to Cochrane parameters.

Results

In total, 1704 studies were identified via search. After reviewing title and abstract, 16 studies found eligible based on inclusion and exclusion criteria. Following quality and risk of bias assessment, 9 studies included in the systematic review.

Conclusion

Based on the finding of this review, distraction techniques, nitrous oxide, and low-level laser therapy were found effective in management of gag reflex. The dentist should consider gag reflex management based on the type of dental treatment, gag severity, patient's age, and available capabilities.

Vagus nerve-dependent effects of fluoxetine on anxiety- and depression-like behaviors in mice

The vagus nerve is a major pathway in the body that is responsible for regulating the activity of the parasympathetic nervous system, which plays an important role in mood disorders including anxiety and depression. Fluoxetine, also known as Prozac, is widely used to treat depression. Nevertheless, there are few studies on the vagus nerve-mediated action of fluoxetine. In this study, we aimed to investigate the vagus nerve-dependent actions of fluoxetine in mice with restraint stress-induced or antibiotics-induced anxiety- and depression-like behaviors. Compared to sham operation, vagotomy alone did not exhibit significant effects on behavioral changes and serotonin-related biomarkers in mice not exposed to stress, antibiotics, or fluoxetine. Oral administration of fluoxetine significantly alleviated anxiety- and depression-like behaviors. However, celiac vagotomy significantly attenuated the anti-depressive effects of fluoxetine. The vagotomy also inhibited the effect of fluoxetine to attenuate restraint stress- or cefaclor-induced reduction in serotonin levels and Htr1a mRNA expression in the hippocampus. These findings suggest that the vagus nerve may regulate the efficacy of fluoxetine for depression.

Serotonergic circuit dysregulation underlying autism-related phenotypes in BTBR mouse model of autism

The inbred mouse strain, BTBR T⁺Itpr3^tf/J (BTBR), possesses neuronal and circuit abnormalities that underlie atypical behavioral profiles resembling the major symptoms of human autism spectrum disorder (ASD). Forebrain serotonin (5-HT) transmission has been implicated in ASD-related behavioral alterations. In this study, we assessed 5-HT signals and the functional responsiveness in BTBR mice compared to standard C57BL/6J (B6) control mice to elucidate how 5-HT alterations contribute to behavioral abnormalities in BTBR mice. A lower number of 5-HT neurons in the median raphe, but not in the dorsal raphe, was observed in male and female BTBR mice. Acute systemic injection of buspirone, a 5-HT1A receptor agonist, induced c-Fos in several brain regions in both B6 and BTBR mice; however, blunted c-Fos induction in BTBR mice was documented in the cingulate cortex, basolateral amygdala (BLA), and ventral hippocampus (Hipp). Decreased c-Fos responses in these regions are associated with a lack of buspirone effects on anxiety-like behavior in BTBR mice. Analysis of mRNA expression following acute buspirone injection indicated that 5HTR1a gene downregulation (or upregulation) occurred in the BLA and Hipp of B6 mice, respectively, but not BTBR mice. The mRNA expression of factors associated with neurogenesis or the pro-inflammatory state was not consistently altered by acute buspirone injection. Therefore, 5-HT responsivity via 5-HT1A receptors in the BLA and Hipp are linked to anxiety-like behavior, in which circuits are disrupted in BTBR mice. Other distinct 5-HT circuits from the BLA and Hipp that regulate social behavior are restricted but preserved in BTBR mice.

Investigating the genetic basis of vertebrate dispersal combining RNA-seq, RAD-seq and quantitative genetics

Although animal dispersal is known to play key roles in ecological and evolutionary processes such as colonization, population extinction and local adaptation, little is known about its genetic basis, particularly in vertebrates. Untapping the genetic basis of dispersal should deepen our understanding of how dispersal behaviour evolves, the molecular mechanisms that regulate it and link it to other phenotypic aspects in order to form the so-called dispersal syndromes. Here, we comprehensively combined quantitative genetics, genome-wide sequencing and transcriptome sequencing to investigate the genetic basis of natal dispersal in a known ecological and evolutionary model of vertebrate dispersal: the common lizard, Zootoca vivipara. Our study supports the heritability of dispersal in semi-natural populations, with less variation attributable to maternal and natal environment effects. In addition, we found an association between natal dispersal and both variation in the carbonic anhydrase (CA10) gene, and in the expression of several genes (TGFB2, SLC6A4, NOS1) involved in central nervous system functioning. These findings suggest that neurotransmitters (serotonin and nitric oxide) are involved in the regulation of dispersal and shaping dispersal syndromes. Several genes from the circadian clock (CRY2, KCTD21) were also differentially expressed between disperser and resident lizards, supporting that the circadian rhythm, known to be involved in long-distance migration in other taxa, might affect dispersal as well. Since neuronal and circadian pathways are relatively well conserved across vertebrates, our results are likely to be generalisable, and we therefore encourage future studies to further investigate the role of these pathways in shaping dispersal in vertebrates.

On the role of serotonin 5-HT1A receptor in autistic-like behavior: сross talk of 5-HT and BDNF systems

Autism spectrum disorders (ASDs) are some of the most common neurodevelopmental disorders; however, the mechanisms underlying ASDs are still poorly understood. Serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) are known as key players in brain and behavioral plasticity and interact with each other. 5-HT_1A receptor is a principal regulator of the brain 5-HT system, which modulates normal and pathological behavior. Here we investigated effects of adeno-associated-virus-based 5-HT_1A receptor overexpression in the hippocampus of BTBR mice (which are a model of autism) on various types of behavior and on the expression of 5-HT₇ receptor, proBDNF, mature BDNF, and BDNF receptors (TrkB and p75^NTR). The 5-HT_1A receptor overexpression in BTBR mice reduced stereotyped behavior in the marble-burying test and extended the time spent in the center in the open field test. Meanwhile, this overexpression failed to affect social behavior in the three-chambered test, immobility time in the tail suspension test, locomotor activity in the open field test, and associative learning within the "operant wall" paradigm. The 5-HT_1A receptor overexpression in the hippocampus raised hippocampal 5-HT₇ receptor mRNA and protein levels. Additionally, the 5-HT_1A receptor overexpression lowered both mRNA and protein levels of TrkB receptor but failed to affect proBDNF, mature BDNF, and p75^NTR receptor expression in the hippocampus of BTBR mice. Thus, obtained results suggest the involvement of the 5-HT and BDNF systems' interaction mediated by 5-HT_1A and TrkB receptors in the mechanisms underlying autistic-like behavior in BTBR mice.

Identification of l-Tryptophan by down-field 1 H MRS: A precursor for brain NAD+ and serotonin syntheses

PURPOSE

To explore the presence of new resonances beyond 9.4 ppm from the human brain, down-field proton MRS was performed in vivo in the human brain on 6 healthy volunteers at 7 T.

METHODS

To maximize the SNR, a large voxel was placed within the brain to cover the maximal area in such a way that sinus cavities were avoided. A spectrally selective 90° E-BURP pulse with an excitation bandwidth of 2 ppm was used to probe the spectral chemical shift range between 9.1 and 10.5 ppm. The E-BURP pulse was integrated with PRESS spatial localization to obtain non-water-suppressed proton MR spectra from the desired spectral region.

RESULTS

In the down-field proton MRS obtained from all of the volunteers scanned, we identified a new peak consistently resonating at 10.1 ppm. Protons associated with this resonance are in cross-relaxation with the bulk water, as demonstrated by the water saturation and deuterium exchange experiments.

CONCLUSION

Based on the chemical shift, this new peak was identified as the indole (-NH) proton of l-tryptophan (l-TRP) and was further confirmed from phantom experiments on l-TRP. These promising preliminary results potentially pave the way to investigate the role of cerebral metabolism of l-TRP in healthy and disease conditions.

Locus coeruleus catecholamines link neuroticism and vulnerability to tau pathology in aging

Higher neuroticism is a risk factor for Alzheimer's disease (AD), and is implicated in disordered stress responses. The locus coeruleus (LC)-catecholamine system is activated during perceived threat and is a centerpiece of developing models of the pathophysiology of AD, as it is the first brain region to develop abnormal tau. We examined relationships among the "Big 5" personality traits, LC catecholamine synthesis capacity measured with [18F]Fluoro-m-tyrosine PET, and tau burden measured with [18F]Flortaucipir PET in cognitively normal older adults (n = 47). β-amyloid (Aβ) status was determined using [11C]Pittsburgh compound B PET (n = 14 Aβ positive). Lower LC catecholamine synthesis capacity was associated with higher neuroticism, more depressive symptoms as measured by the Geriatric Depression Scale, and higher amygdala tau-PET binding. Exploratory analyses with other personality traits revealed that low trait conscientiousness was also related to both lower LC catecholamine synthesis capacity, and more depressive symptoms. A significant indirect path linked both high neuroticism and low conscientiousness to greater amygdala tau burden via their mutual association with low LC catecholamine synthesis capacity. Together, these findings reveal LC catecholamine synthesis capacity to be a promising marker of affective health and pathology burden in aging, and identifies candidate neurobiological mechanisms for the effect of personality on increased vulnerability to dementia.

Early life adversity shapes neural circuit function during sensitive postnatal developmental periods

Early life adversity (ELA) is a major risk factor for mental illness, but the neurobiological mechanisms by which ELA increases the risk for future psychopathology are still poorly understood. Brain development is particularly malleable during prenatal and early postnatal life, when complex neural circuits are being formed and refined through an interplay of excitatory and inhibitory neural input, synaptogenesis, synaptic pruning, myelination, and neurogenesis. Adversity that influences these processes during sensitive periods of development can thus have long-lasting and pervasive effects on neural circuit maturation. In this review, we will discuss clinical and preclinical evidence for the impact of ELA on neural circuit formation with a focus on the early postnatal period, and how long-lasting impairments in these circuits can affect future behavior. We provide converging evidence from human and animal studies on how ELA alters the functional development of brain regions, neural circuits, and neurotransmitter systems that are crucial for cognition and affective behavior, including the hippocampus, the hypothalamus-pituitary-adrenal (HPA) axis, neural networks of fear responses and cognition, and the serotonin (5-HT) system. We also discuss how gene-by-environment (GxE) interactions can determine individual differences in susceptibility and resilience to ELA, as well as molecular pathways by which ELA regulates neural circuit development, for which we emphasize epigenetic mechanisms. Understanding the molecular and neurobiological mechanisms underlying ELA effects on brain function and psychopathology during early postnatal sensitive periods may have great potential to advance strategies to better treat or prevent psychiatric disorders that have their origin early in life.

Serotonin Receptor and Transporter Endocytosis Is an Important Factor in the Cellular Basis of Depression and Anxiety

Depression and anxiety are common, debilitating psychiatric conditions affecting millions of people throughout the world. Current treatments revolve around selective serotonin reuptake inhibitors (SSRIs), yet these drugs are only moderately effective at relieving depression. Moreover, up to 30% of sufferers are SSRI non-responders. Endocytosis, the process by which plasma membrane and extracellular constituents are internalized into the cell, plays a central role in the regulation of serotonin (5-hydroxytryptophan, 5-HT) signaling, SSRI function and depression and anxiety pathogenesis. Despite their therapeutic potential, surprisingly little is known about the endocytosis of the serotonin receptors (5-HT receptors) or the serotonin transporter (SERT). A subset of 5-HT receptors are endocytosed by clathrin-mediated endocytosis following serotonin binding, while for the majority of 5-HT receptors the endocytic regulation is not known. SERT internalizes serotonin from the extracellular space into the cell to limit the availability of serotonin for receptor binding and signaling. Endocytosis of SERT reduces serotonin uptake, facilitating serotonin signaling. SSRIs predominantly inhibit SERT, preventing serotonin uptake to enhance 5-HT receptor signaling, while hallucinogenic compounds directly activate specific 5-HT receptors, altering their interaction with endocytic adaptor proteins to induce alternate signaling outcomes. Further, multiple polymorphisms and transcriptional/proteomic alterations have been linked to depression, anxiety, and SSRI non-response. In this review, we detail the endocytic regulation of 5-HT receptors and SERT and outline how SSRIs and hallucinogenic compounds modulate serotonin signaling through endocytosis. Finally, we will examine the deregulated proteomes in depression and anxiety and link these with 5-HT receptor and SERT endocytosis. Ultimately, in attempting to integrate the current studies on the cellular biology of depression and anxiety, we propose that endocytosis is an important factor in the cellular basis of depression and anxiety. We will highlight how a thorough understanding 5-HT receptor and SERT endocytosis is integral to understanding the biological basis of depression and anxiety, and to facilitate the development of a next generation of specific, efficacious antidepressant treatments.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Somatosensorimotor and Odor Modification, Along with Serotonergic Processes Underlying the Social Deficits in BTBR T+ Itpr3tf/J and BALB/cJ Mouse Models of Autism

Autism is a complex spectrum of disorders characterized by core behavioral deficits in social communicative behavior, which are also required for comprehensive analysis of preclinical mouse models. As animal models of the core behavioral deficits in autism, two inbred mouse strains, BTBR T+ Itpr3tf/J (BTBR) and BALB/cJ (BALB), were compared with the standard social strain, C57BL/6J (B6), regarding a variety of behavioral factors underlying social communicative interactions, including olfactory and tactile sensory processes, social recognition abilities and behavioral expression strategies. Although both female BTBR and BALB mice can express social recognition and approach behavior depending on the stimuli they encounter, the available sensory modalities, along with modulation of the serotonergic system, differ between the two strains. BALB mice have deficits in using volatile olfactory cues and tactile information in a social context; they fail to exhibit a social approach to volatile cues and seek nonvolatile cues by exhibiting substantial sniff/contact behavior when allowed direct contact with social opponents. Systemic injection of the serotonin (5-HT1A) agonist buspirone has little effect on these social deficits, suggesting a congenitally degraded serotonergic system in BALB mice. In contrast, BTBR mice exhibit impaired body coordination and social motivation-modified olfactory signals, which are relevant to a reduced social approach. A systemic injection of the 5-HT1A agonist restored these social deficits in BTBR mice, indicating that a downregulated serotonergic system is involved in the social deficits exhibited by BTBR mice.

Molecular and neurocircuitry mechanisms of social avoidance

Humans and animals live in social relationships shaped by actions of approach and avoidance. Both are crucial for normal physical and mental development, survival, and well-being. Active withdrawal from social interaction is often induced by the perception of threat or unpleasant social experience and relies on adaptive mechanisms within neuronal networks associated with social behavior. In case of confrontation with overly strong or persistent stressors and/or dispositions of the affected individual, maladaptive processes in the neuronal circuitries and its associated transmitters and modulators lead to pathological social avoidance. This review focuses on active, fear-driven social avoidance, affected circuits within the mesocorticolimbic system and associated regions and a selection of molecular modulators that promise translational potential. A comprehensive review of human research in this field is followed by a reflection on animal studies that offer a broader and often more detailed range of analytical methodologies. Finally, we take a critical look at challenges that could be addressed in future translational research on fear-driven social avoidance.

Dietary Exposure to Excess Saturated Fat During Early Life Alters Hippocampal Gene Expression and Increases Risk for Behavioral Disorders in Adulthood

Purpose

Maternal and postnatal diets result in long-term changes in offspring brain and behavior; however, the key mediators of these developmental changes are not well-defined. In this study, we investigated the impact of maternal and post-weaning high-fat diets on gene expression of key components mediating hippocampal synaptic efficacy. In addition, we evaluated the risk for impaired stress-coping and anxiety-like behaviors in adult offspring exposed to obesogenic diets during early life.

Methods

Dams were fed a control (C) or high-fat (HF) diet prior to mating, pregnancy, and lactation. Male offspring from control chow and high-fat fed dams were weaned to control chow or HF diets. The forced swim test (FST) and the elevated-plus maze (EPM) were used to detect stress-coping and anxiety-like behavior, respectively. Real-time RT-PCR and ELISA were used to analyze hippocampal expression of genes mediating synaptic function.

Results

Animals fed a HF diet post-weaning spent more time immobile in the FST. Swimming time was reduced in response to both maternal and post-weaning HF diets. Both maternal and post-weaning HF diets contributed to anxiety-like behavior in animals exposed to the EPM. Maternal and post-weaning HF diets were associated with a significant decrease in mRNA and protein expression for hippocampal GDNF, MAP2, SNAP25, and synaptophysin. Hippocampal mRNA expression of key serotonergic and glutamatergic receptors also exhibited differential responses to maternal and post-weaning HF diets. Hippocampal serotonergic receptor 5HT1A mRNA was reduced in response to both the maternal and post-weaning diet, whereas, 5HT2A receptor mRNA expression was increased in response to the maternal HF diet. The glutamate AMPA receptor subunit, GluA1, mRNA expression was significantly reduced in response to both diets, whereas no change was detected in GluA2 subunit mRNA expression.

Conclusion

These data demonstrate that the expression of genes mediating synaptic function are differentially affected by maternal and post-weaning high-fat diets. The post-weaning high-fat diet clearly disturbs both behavior and gene expression. In addition, although the transition to control diet at weaning partially compensates for the adverse effects of the maternal HF diet, the negative consequence of the maternal HF diet is exacerbated by continuing the high-fat diet post-weaning. We present evidence to support the claim that these dietary influences increase the risk for anxiety and impaired stress-coping abilities in adulthood.

Serotonergic modulation across sensory modalities

The serotonergic system has been widely studied across animal taxa and different functional networks. This modulatory system is therefore well positioned to compare the consequences of neuromodulation for sensory processing across species and modalities at multiple levels of sensory organization. Serotonergic neurons that innervate sensory networks often bidirectionally exchange information with these networks but also receive input representative of motor events or motivational state. This convergence of information supports serotonin's capacity for contextualizing sensory information according to the animal's physiological state and external events. At the level of sensory circuitry, serotonin can have variable effects due to differential projections across specific sensory subregions, as well as differential serotonin receptor type expression within those subregions. Functionally, this infrastructure may gate or filter sensory inputs to emphasize specific stimulus features or select among different streams of information. The near-ubiquitous presence of serotonin and other neuromodulators within sensory regions, coupled with their strong effects on stimulus representation, suggests that these signaling pathways should be considered integral components of sensory systems.

Effects of chronic exposure to selenomethionine on social learning outcomes in zebrafish (Danio rerio): serotonergic dysregulation and oxidative stress in the brain

For many species, social learning is crucial for fitness-related activities, but human-induced environmental changes can impair such learning processes. For instance, mining can release the element, selenium (Se), that is vital for physiological functions but also has toxicological properties at elevated concentrations. In this study, we investigated the effects of chronic exposure to Se on social learning outcomes and potential underlying molecular mechanisms in adult zebrafish. After exposure to different levels of dietary selenomethionine (control, 3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days, we examined the ability of observer fish to follow demonstrators (experienced individuals) in escaping an oncoming trawl. Social learning outcomes were then assessed in the absence of demonstrators. Our results indicated that fish in the highest exposure group (34.1 μg/g) displayed significantly slower escape responses compared to fish in the control and lower exposure groups (3.6 and 12.8 μg Se/g). This impaired behavior was associated with higher oxidative stress and dysregulation in genes that are key in the serotonergic pathway, indicating that oxidative stress and alteration in the serotonergic system lead to impairment of social learning.

Inter-individual and inter-strain differences in cognitive and social abilities of Dark Agouti and Wistar Han rats

Healthy animals displaying extreme behaviours that resemble human psychiatric symptoms are relevant models to study the natural psychobiological processes of maladapted behaviours. Using a Rat Gambling Task, healthy individuals spontaneously making poor decisions (PDMs) were found to co-express a combination of other cognitive and reward-based characteristics similar to symptoms observed in human patients with impulse-control disorders. The main goals of this study were to 1) confirm the existence of PDMs and their unique behavioural phenotypes in Dark Agouti (DA) and Wistar Han (WH) rats, 2) to extend the behavioural profile of the PDMs to probability-based decision-making and social behaviours and 3) to extract key discriminative traits between DA and WH strains, relevant for biomedical research. We have compared cognitive abilities, natural behaviours and physiological responses in DA and WH rats at the strain and at the individual level. Here we found that the naturally occurring PDM's profile was consistent between both rat lines. Then, although the PDM individuals did not take more risks in probability discounting task, they seemed to be of higher social ranks. Finally and despite their similarities in performance, WH and DA lines differed in degree of reward sensitivity, impulsivity, locomotor activity and open space-occupation. The reproducibility and conservation of the complex phenotypes of PDMs and GDMs (good decision makers) in these two genetically different strains support their translational potential. Both strains, present large phenotypic variation in behaviours pertinent for the study of the underlying mechanisms of poor decision making and associated disorders.

[Modern concepts of pathogenetic therapy of anxiety disorders]

The high prevalence of anxiety disorders around the world leads to a high interest in the study of anxiety. At the moment, a lot of knowledge about the pathogenesis and therapy of anxiety disorders has been accumulated, which is well covered in modern domestic and world medical literature. It is known that many areas of the brain are involved in the modulation of anxiety, among which the amygdala is considered the key in the modulation of anxiety and fear. A large body of evidence supports the involvement of different neurotransmitter systems in the processes of anxiogenesis-anxiolysis (GABA, monoamines, glutamate, neuropeptides, neurosteroids). This article provides an analysis of methods of pharmacological impact on each of these systems, which serve to optimize the already known strategies of anxiolytic therapy.

Toward an animal model of borderline personality disorder

BACKGROUND

Borderline personality disorder (BPD) is a pervasive psychiatric disorder characterized by emotion dysregulation, impulsivity, impaired self-perceptions, and interpersonal relationships and currently affects 1-3% of the US population as reported by Torgersen et al. (Arch Gen Psychiatry 58:590-596, Torgersen et al. 2001), Lenzenweger et al. (Biol Psychiatry 62:553-564, Lenzenweger et al. 2007), and Tomko et al. (J Personal Disord 28:734-750, Tomko et al. 2014). One major obstacle to our understanding of the neural underpinnings of BPD is a lack of valid animal models that translate the key known features of the disorder to a system that is amenable to study.

OBJECTIVE

To summarize the etiology, major symptoms, and symptom triggers of BPD and then propose a blueprint for building an animal model of BPD by choosing key components of the disorder that can be implemented in rodents.

RESULTS

We identify the role of early life stress and subsequent mild stress in adulthood as contributing etiological factors and the potential use of altered communication between frontal cortices and the amygdala in extinction and habituation, increased impulsivity, dysregulation of the hypothalamic pituitary axis (HPA), and increased neuroinflammation as biological markers of BPD. Building upon these features of BPD, we propose a two-hit animal model that uses maternal abandonment to alter maturation of the HPA axis and mild secondary adult stress to evoke behavioral symptoms such as increased impulsivity and impaired extinction, habituation, and social interactions.

CONCLUSION

Through exploration of the etiology, symptom presentation, and altered neurological function, we propose an animal model of BPD. We believe that a number of existing animal paradigms that model other mental health disorders should be combined in a unique way to reflect the etiology, symptom presentation, and altered neurological function that is evident in BPD. These model, when compared with available human data, will inform research and treatment in humans for better understanding of systems from the micro-molecular level to more global physiology underlying BPD.

Functional Interrogation of a Depression-Related Serotonergic Single Nucleotide Polymorphism, rs6295, Using a Humanized Mouse Model

The serotonin 1A receptor (5-HT1A) system has been extensively implicated in modulating mood and behavior. Notably, 5-HT1A levels in humans display remarkable variation, and differences in receptor levels have been linked with a variety of psychiatric disorders. Further, reduction of receptor levels by 30-50% in mice suggests that changes in receptor levels that model existing human variation are sufficient to drive behavioral alterations. As a result, genetic mechanisms that modulate human 5-HT1A levels may be important for explaining individual differences in mood and behavior, representing a potential source of psychiatric disease risk. One common genetic variant implicated in differential 5-HT1A levels is the G/C single nucleotide polymorphism (SNP) rs6295, located upstream of the human 5-HT1A gene. This SNP differentially binds the transcription factor, NUDR/Deaf1, leading to cell-type specific effects on transcription in vitro. To investigate the direct effects of this SNP in the heterogeneous cellular context of the brain, we generated humanized transgenic mice using a design that maximized the local transcriptional landscape of the human HTR1A gene while also controlling for effects of genomic insertion location. We integrated a 180 kb human bacteria artificial chromosome (BAC) transgene containing G- and C-alleles of rs6295 flanked by FRT or loxP sites. Subsequent deletion of each allele by Cre- or Flp-recombinase resulted in rs6295G and C alleles in the same genomic location. These alleles were bred onto a 5-HT1A null mouse such that the human BAC was the sole source of 5-HT1A in these mice. We generated three separate lines, two of which had detectable human 5-HT1A levels in the brain, although none displayed expression in the raphe. Of these, one line exhibited rs6295-dependent differences in 5-HT1A levels and differences in behavior, even though the overall levels were considerably lower than native expression levels. The line-dependent effect of rs6295 on protein levels and behavior may depend upon differences in background genetic factors or different insertion sites across each line. This work confirms that relatively subtle differences in 5-HT1A levels can contribute to differences in behavior and highlights the challenges of modeling human noncoding genetic variation in mice.

Genetic approaches to the investigation of serotonergic neuron functions in animals

The serotonergic system is one of the most important neurotransmitter systems that take part in the regulation of vital CNS functions. The understanding of its mechanisms will help scientists create new therapeutic approaches to the treatment of mental and neurodegenerative diseases and find out how this neurotransmitter system interacts with other parts of the brain and regulates their activity. Since the serotonergic system anatomy and functionality are heterogeneous and complex, the best tools for studying them are based on manipulation of individual types of neurons without affecting neurons of other neurotransmitter systems. The selective cell control is possible due to the genetic determinism of their functions. Proteins that determine the uniqueness of the cell type are expressed under the regulation of cell-specific promoters. By using promoters that are specific for genes of the serotonin system, one can control the expression of a gene of interest in serotonergic neurons. Here we review approaches based on such promoters. The genetic models to be discussed in the article have already shed the light on the role of the serotonergic system in modulating behavior and processing sensory information. In particular, genetic knockouts of serotonin genes sert, pet1, and tph2 promoted the determination of their contribution to the development and functioning of the brain. In addition, the review describes inducible models that allow gene expression to be controlled at various developmental stages. Finally, the application of these genetic approaches in optogenetics and chemogenetics provided a new resource for studying the functions, discharge activity, and signal transduction of serotonergic neurons. Nevertheless, the advantages and limitations of the discussed genetic approaches should be taken into consideration in the course of creating models of pathological conditions and developing pharmacological treatments for their correction.

Genetic, epigenetic and posttranscriptional mechanisms for treatment of major depression: the 5-HT1A receptor gene as a paradigm

Major depression and anxiety are highly prevalent and involve chronic dysregulation of serotonin, but they remain poorly understood. Here, we review novel transcriptional (genetic, epigenetic) and posttranscriptional (microRNA, alternative splicing) mechanisms implicated in mental illness, focusing on a key serotonin-related regulator, the serotonin 1A (5-HT1A) receptor. Functional single-nucleotide polymorphisms and stress-induced DNA methylation of the 5-HT1A promoter converge to differentially alter pre- and postsynaptic 5-HT1A receptor expression associated with major depression and reduced therapeutic response to serotonergic antidepressants. Major depression is also associated with altered levels of splice factors and microRNA, posttranscriptional mechanisms that regulate RNA stability. The human 5-HT1A 3′-untranslated region is alternatively spliced, removing microRNA sites and increasing 5-HT1A expression, which is reduced in major depression and may be genotype-dependent. Thus, the 5-HT1A receptor gene illustrates the convergence of genetic, epigenetic and posttranscriptional mechanisms in gene expression, neurodevelopment and neuroplasticity, and major depression. Understanding gene regulatory mechanisms could enhance the detection, categorization and personalized treatment of major depression.

Overcoming Resistance to Selective Serotonin Reuptake Inhibitors: Targeting Serotonin, Serotonin-1A Receptors and Adult Neuroplasticity

Major depressive disorder (MDD) is the most prevalent mental illness contributing to global disease burden. Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are the first-line treatment for MDD, but are only fully effective in 30% of patients and require weeks before improvement may be seen. About 30% of SSRI-resistant patients may respond to augmentation or switching to another antidepressant, often selected by trial and error. Hence a better understanding of the causes of SSRI resistance is needed to provide models for optimizing treatment. Since SSRIs enhance 5-HT, in this review we discuss new findings on the circuitry, development and function of the 5-HT system in modulating behavior, and on how 5-HT neuronal activity is regulated. We focus on the 5-HT1A autoreceptor, which controls 5-HT activity, and the 5-HT1A heteroreceptor that mediates 5-HT actions. A series of mice models now implicate increased levels of 5-HT1A autoreceptors in SSRI resistance, and the requirement of hippocampal 5-HT1A heteroreceptor for neurogenic and behavioral response to SSRIs. We also present clinical data that show promise for identifying biomarkers of 5-HT activity, 5-HT1A regulation and regional changes in brain activity in MDD patients that may provide biomarkers for tailored interventions to overcome or bypass resistance to SSRI treatment. We identify a series of potential strategies including inhibiting 5-HT auto-inhibition, stimulating 5-HT1A heteroreceptors, other monoamine systems, or cortical stimulation to overcome SSRI resistance.

Long-Term Behavioral Effects of Post-weaning Social Isolation in Males and Females

Adolescence is a developmental period associated with vast neural and behavioral changes which are accompanied by altered sensitivity to stimuli, both stressful and rewarding. Perturbations, especially stressful stimuli, during this period have been shown to alter behavior in adulthood. Social isolation rearing is one such perturbation. This review highlights the long-term behavioral consequences of adolescent social isolation rearing in rodents with a specific focus on anxiety- and addiction-related behaviors. Sex-specific effects are discussed where data are available. We then consider changes in monoaminergic neurotransmission as one possible mechanism for the behavioral effects described. This research on both normative and perturbed adolescent development is crucial to understanding and treating the increased vulnerability to psychiatric disorders seen in humans during this life stage.

Serotonergic system, cognition, and BPSD in Alzheimer's disease

Behavioral and Psychological Symptoms of Dementia (BPSD), present in almost 90% of patients with Alzheimer's Disease (AD), cause extensive impairment leading to reduced independence and inability to complete activities of daily living. Though BPSD includes a wide range of symptoms, such as agitation, aggression, disinhibition, anxiety, depression, apathy, delusions, and hallucinations. Certain BPSD in AD co-present and can be clustered into distinct domains based on their frequency of co-occurrence. As these BPSD are so pervasive in any stages of AD, the disease may be better characterized as a disorder of heterogeneous degenerative symptoms across a number of symptom domains, with the most prominent domain comprising memory and cognitive deficits. Importantly, there are no FDA-approved drugs to treat these BPSD, and new approaches must be considered to develop effective treatments for AD patients. The biogenic monoamine 5-hydroxytryptamine (5-HT), or serotonin, works as both a neurotransmitter and neuromodulator, which has been tied to cognitive decline and multiple BPSD domains. This review summarizes the evidence for specific serotonergic system alterations across some of the well-studied cognitive, behavioral, and psychiatric domains. Though differences in overall serotonergic transmission occur in AD, circuit-specific alterations in individual 5-HT receptors (5-HTRs) are likely linked to the heterogeneous presentation of BPSD in AD.

Loss of Adult 5-HT1A Autoreceptors Results in a Paradoxical Anxiogenic Response to Antidepressant Treatment

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are first-line antidepressants but require several weeks to elicit their actions. Chronic SSRI treatment induces desensitization of 5-HT1A autoreceptors to enhance 5-HT neurotransmission. Mice (both sexes) with gene deletion of 5-HT1A autoreceptors in adult 5-HT neurons (1AcKO) were tested for response to SSRIs. Tamoxifen-induced recombination in adult 1AcKO mice specifically reduced 5-HT1A autoreceptor levels. The 1AcKO mice showed a loss of 5-HT1A autoreceptor-mediated hypothermia and electrophysiological responses, but no changes in anxiety- or depression-like behavior. Subchronic fluoxetine (FLX) treatment induced an unexpected anxiogenic effect in 1AcKO mice in the novelty suppressed feeding and elevated plus maze tests, as did escitalopram in the novelty suppressed feeding test. No effect was seen in wild-type (WT) mice. Subchronic FLX increased 5-HT metabolism in prefrontal cortex, hippocampus, and raphe of 1AcKO but not WT mice, suggesting hyperactivation of 5-HT release. To detect chronic cellular activation, FosB⁺ cells were quantified. FosB⁺ cells were reduced in entorhinal cortex and hippocampus (CA2/3) and increased in dorsal raphe 5-HT cells of 1AcKO mice, suggesting increased raphe activation. In WT but not 1AcKO mice, FLX reduced FosB⁺ cells in the median raphe, hippocampus, entorhinal cortex, and median septum, which receive rich 5-HT projections. Thus, in the absence of 5-HT1A autoreceptors, SSRIs induce a paradoxical anxiogenic response. This may involve imbalance in activation of dorsal and median raphe to regulate septohippocampal or fimbria-fornix pathways. These results suggest that markedly reduced 5-HT1A autoreceptors may provide a marker for aberrant response to SSRI treatment.SIGNIFICANCE STATEMENT Serotonin-selective reuptake inhibitors (SSRIs) are effective in treating anxiety and depression in humans and mouse models. However, in some cases, SSRIs can increase anxiety, but the mechanisms involved are unclear. Here we show that, rather than enhancing SSRI benefits, adulthood knockout (KO) of the 5-HT1A autoreceptor, a critical negative regulator of 5-HT activity, results in an SSRI-induced anxiety effect that appears to involve a hyperactivation of the 5-HT system in certain brain areas. Thus, subjects with very low levels of 5-HT1A autoreceptors, such as during childhood or adolescence, may be at risk for an SSRI-induced anxiety response.

Loss of MeCP2 in adult 5-HT neurons induces 5-HT1A autoreceptors, with opposite sex-dependent anxiety and depression phenotypes

The 5-HT1A autoreceptor mediates feedback inhibition of serotonin (5-HT) neurons, and is implicated in major depression. The human 5-HT1A gene (HTR1A) rs6295 risk allele prevents Deaf1 binding to HTR1A, resulting in increased 5-HT1A autoreceptor transcription. Since chronic stress alters HTR1A methylation and expression, we addressed whether recruitment of methyl-binding protein MeCP2 may alter Deaf1 regulation at the HTR1A locus. We show that MeCP2 enhances Deaf1 binding to its HTR1A site and co-immunoprecipitates with Deaf1 in cells and brain tissue. Chromatin immunoprecipitation assays showed Deaf1-dependent recruitment of MeCP2 to the mouse HTR1A promoter, and MeCP2 modulated human and mouse HTR1A gene transcription in a Deaf1-dependent fashion, enhancing Deaf1-induced repression at the Deaf1 site. To address the role of MeCP2 in HTR1A regulation in vivo, mice with conditional knockout of MeCP2 in adult 5-HT neurons (MeCP2 cKO) were generated. These mice exhibited increased 5-HT1A autoreceptor levels and function, consistent with MeCP2 enhancement of Deaf1 repression in 5-HT neurons. Interestingly, female MeCP2-cKO mice displayed reduced anxiety, while males showed increased anxiety and reduced depression-like behaviors. These data uncover a novel role for MeCP2 in 5-HT neurons to repress HTR1A expression and drive adult anxiety- and depression-like behaviors in a sex-specific manner.

Synthesis and biological evaluation of a series of multi-target N-substituted cyclic imide derivatives with potential antipsychotic effect

In the present study, a series of multi-target N-substituted cyclic imide derivatives which possessed potent dopamine D₂, serotonin 5-HT_1A and 5-HT_2A receptors properties were synthesized and evaluated as potential antipsychotics. Among these compounds, (3aR,4R,7S,7aS)-2-(4-(4-(benzo[b]thiophen-4-yl)piperazin-1-yl)butyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione hydrochloride (3d) held a promising pharmacological profile. 3d not only showed potent and balanced in vitro activities on D₂/5-HT_1A/5-HT_2A receptors, but also endowed with low to moderate activities on 5-HT_2C, H₁, α_1A, M₃ receptors and hERG channel, suggesting a low liability to induce side effects such as weight gain, orthostatic hypotension and QT prolongation. In animal behavioral studies, 3d reduced phencyclidine-induced hyperlocomotion with a high threshold for catalepsy induction. Compound 3d was selected as a potential antipsychotic candidate for further development.

Treatment resistant depression: A multi-scale, systems biology approach

An estimated 50% of depressed patients are inadequately treated by available interventions. Even with an eventual recovery, many patients require a trial and error approach, as there are no reliable guidelines to match patients to optimal treatments and many patients develop treatment resistance over time. This situation derives from the heterogeneity of depression and the lack of biomarkers for stratification by distinct depression subtypes. There is thus a dire need for novel therapies. To address these known challenges, we propose a multi-scale framework for fundamental research on depression, aimed at identifying the brain circuits that are dysfunctional in several animal models of depression as well the changes in gene expression that are associated with these models. When combined with human genetic and imaging studies, our preclinical studies are starting to identify candidate circuits and molecules that are altered both in models of disease and in patient populations. Targeting these circuits and mechanisms can lead to novel generations of antidepressants tailored to specific patient populations with distinctive types of molecular and circuit dysfunction.

Effectiveness of Intellectual Distraction on Gagging and Anxiety Management in Children: A Prospective Clinical Study

Objectives:

The aim of the present prospective study is to determine the effect of an intellectual colored game (ICG) on the severity of gag reflex (GR) and anxiety in children during dental alginate impression.

Materials and Methods:

Forty-one children, aging between 5 and 11 years, having a GR varying from normal to moderate had upper alginate impressions. The children's anxiety was evaluated with a facial image scale (FIS) before (T0) and after first failed impression (T1), then, after playing an intellectual colored game (ICG) at T2, while taking an upper alginate impression.

Results:

42.9 % of the children had a gag reflex of stage 2 and 31.0 % a facial scale of 3. Initial GR was not significantly associated with the final success of the impression (P =0.260) whereas final impression success was strongly associated with FIS (P <0.001). There was a statistically significant reduction in median GR score from T0 to T2 (P < 0.001) and FIS dropped significantly at T2 with ICG (P < 0.001).

Conclusion:

This study highlights the clinical performance of the intellectual distraction approach in GR management

Extracellular regulated protein kinaseis critical for the role of 5-HT1a receptor in modulating nNOS expression and anxiety-related behaviors

Our previous study found that serotonin 1A receptor (5-HT1aR) is an endogenous suppressor of nNOS expression in the hippocampus, which accounts for anxiolytic effect of fluoxetine. However, the precise molecular mechanism remains unknown. By using 8-OH-DPAT, a selective 5-HT1aR agonist, NAN-190, a selective 5-HT1aR antagonist, and U0126, an Extracellular Regulated Protein Kinases (ERK) phosphorylation inhibitor, we investigated the role of ERK in 5-HT1aR-nNOS pathway. Western blots analysis demonstrated that 5-HT1aR activation up-regulated the level of phosphorylated ERK (P-ERK) beginning at 5 min and down-regulated the expression of nNOS beginning at 20 min. Meanwhile, blockage of 5-HT1aR resulted in a decrease in P-ERK beginning at 20 min and caused an increase in nNOS expression beginning at 6 h. Although U0126 itself did not alter nNOS expression and activity, NO level, and anxiety-related behaviors, the treatment totally reversed 8-OH-DPAT-induced reduction in nNOS expression and function, and anxiolytic effect. Besides, our data showed that ERK phosphorylation was essential for 5-HT1aR activation-induced cAMP responsive element binding protein (CREB) phosphorylation, hippocampal neurogenesis and synaptogenesis of newborn neuron. Our study suggests a crucial role of ERK phosphorylation in the regulation of nNOS expression by 5-HT1aR, which is helpful for understanding the mechanism of 5-HT1aR-based anxiolytic treatment.

Serotonin Signaling through Prefrontal Cortex 5-HT1A Receptors during Adolescence Can Determine Baseline Mood-Related Behaviors

Lifelong homeostatic setpoints for mood-related behaviors emerge during adolescence. Serotonin (5-HT) plays an important role in refining the formation of brain circuits during sensitive developmental periods. In rodents, the role of 5-HT_1A receptors in general and autoreceptors in particular has been characterized in anxiety. However, less is known about the role of 5-HT_1A receptors in depression-related behavior. Here, we show that whole-life suppression of heteroreceptor expression results in a broad depression-like behavioral phenotype accompanied by physiological and cellular changes within medial prefrontal cortex-dorsal raphe proper (mPFC-DRN) circuitry. These changes include increased basal 5-HT in a mPFC that is hyporesponsive to stress and decreased basal 5-HT levels and firing rates in a DRN hyperactivated by the same stressor. Remarkably, loss of heteroreceptors in the PFC at adolescence is sufficient to recapitulate this depression-like behavioral syndrome. Our results suggest that targeting mPFC 5-HT_1A heteroreceptors during adolescence in humans may have lifelong ramifications for depression and its treatment.

Abrogated Freud-1/Cc2d1a Repression of 5-HT1A Autoreceptors Induces Fluoxetine-Resistant Anxiety/Depression-Like Behavior

Freud-1/Cc2d1a represses the gene transcription of serotonin-1A (5-HT1A) autoreceptors, which negatively regulate 5-HT tone. To test the role of Freud-1 in vivo, we generated mice with adulthood conditional knock-out of Freud-1 in 5-HT neurons (cF1ko). In cF1ko mice, 5-HT1A autoreceptor protein, binding and hypothermia response were increased, with reduced 5-HT content and neuronal activity in the dorsal raphe. The cF1ko mice displayed increased anxiety- and depression-like behavior that was resistant to chronic antidepressant (fluoxetine) treatment. Using conditional Freud-1/5-HT1A double knock-out (cF1/1A dko) to disrupt both Freud-1 and 5-HT1A genes in 5-HT neurons, no increase in anxiety- or depression-like behavior was seen upon knock-out of Freud-1 on the 5-HT1A autoreceptor-negative background; rather, a reduction in depression-like behavior emerged. These studies implicate transcriptional dysregulation of 5-HT1A autoreceptors by the repressor Freud-1 in anxiety and depression and provide a clinically relevant genetic model of antidepressant resistance. Targeting specific transcription factors, such as Freud-1, to restore transcriptional balance may augment response to antidepressant treatment.SIGNIFICANCE STATEMENT Altered regulation of the 5-HT1A autoreceptor has been implicated in human anxiety, major depression, suicide, and resistance to antidepressants. This study uniquely identifies a single transcription factor, Freud-1, as crucial for 5-HT1A autoreceptor expression in vivo Disruption of Freud-1 in serotonin neurons in mice links upregulation of 5-HT1A autoreceptors to anxiety/depression-like behavior and provides a new model of antidepressant resistance. Treatment strategies to reestablish transcriptional regulation of 5-HT1A autoreceptors could provide a more robust and sustained antidepressant response.

Regulatory Mechanisms Controlling Maturation of Serotonin Neuron Identity and Function

The brain serotonin (5-hydroxytryptamine; 5-HT) system has been extensively studied for its role in normal physiology and behavior, as well as, neuropsychiatric disorders. The broad influence of 5-HT on brain function, is in part due to the vast connectivity pattern of 5-HT-producing neurons throughout the CNS. 5-HT neurons are born and terminally specified midway through embryogenesis, then enter a protracted period of maturation, where they functionally integrate into CNS circuitry and then are maintained throughout life. The transcriptional regulatory networks controlling progenitor cell generation and terminal specification of 5-HT neurons are relatively well-understood, yet the factors controlling 5-HT neuron maturation are only recently coming to light. In this review, we first provide an update on the regulatory network controlling 5-HT neuron development, then delve deeper into the properties and regulatory strategies governing 5-HT neuron maturation. In particular, we discuss the role of the 5-HT neuron terminal selector transcription factor (TF) Pet-1 as a key regulator of 5-HT neuron maturation. Pet-1 was originally shown to positively regulate genes needed for 5-HT synthesis, reuptake and vesicular transport, hence 5-HT neuron-type transmitter identity. It has now been shown to regulate, both positively and negatively, many other categories of genes in 5-HT neurons including ion channels, GPCRs, transporters, neuropeptides, and other transcription factors. Its function as a terminal selector results in the maturation of 5-HT neuron excitability, firing characteristics, and synaptic modulation by several neurotransmitters. Furthermore, there is a temporal requirement for Pet-1 in the control of postmitotic gene expression trajectories thus indicating a direct role in 5-HT neuron maturation. Proper regulation of the maturation of cellular identity is critical for normal neuronal functioning and perturbations in the gene regulatory networks controlling these processes may result in long-lasting changes in brain function in adulthood. Further study of 5-HT neuron gene regulatory networks is likely to provide additional insight into how neurons acquire their mature identities and how terminal selector-type TFs function in postmitotic vertebrate neurons.

Refining the Role of 5-HT in Postnatal Development of Brain Circuits

Changing serotonin (5-hydroxytryptamine, 5-HT) brain levels during critical periods in development has long-lasting effects on brain function, particularly on later anxiety/depression-related behaviors in adulthood. A large part of the known developmental effects of 5-HT occur during critical periods of postnatal life, when activity-dependent mechanisms remodel neural circuits. This was first demonstrated for the maturation of sensory brain maps in the barrel cortex and the visual system. More recently this has been extended to the 5-HT raphe circuits themselves and to limbic circuits. Recent studies overviewed here used new genetic models in mice and rats and combined physiological and structural approaches to provide new insights on the cellular and molecular mechanisms controlled by 5-HT during late stages of neural circuit maturation in the raphe projections, the somatosensory cortex and the visual system. Similar mechanisms appear to be also involved in the maturation of limbic circuits such as prefrontal circuits. The latter are of particular relevance to understand the impact of transient 5-HT dysfunction during postnatal life on psychiatric illnesses and emotional disorders in adult life.

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.

Serotonin receptors in depression: from A to B

The role of serotonin in major depressive disorder (MDD) is the focus of accumulating clinical and preclinical research. The results of these studies reflect the complexity of serotonin signaling through many receptors, in a large number of brain regions, and throughout the lifespan. The role of the serotonin transporter in MDD has been highlighted in gene by environment association studies as well as its role as a critical player in the mechanism of the most effective antidepressant treatments – selective serotonin reuptake inhibitors. While the majority of the 15 known receptors for serotonin have been implicated in depression or depressive-like behavior, the serotonin 1A (5-HT _1A) and 1B (5-HT _1B) receptors are among the most studied. Human brain imaging and genetic studies point to the involvement of 5-HT _1A and 5-HT _1B receptors in MDD and the response to antidepressant treatment. In rodents, the availability of tissue-specific and inducible knockout mouse lines has made possible the identification of the involvement of 5-HT _1A and 5-HT _1B receptors throughout development and in a cell-type specific manner. This, and other preclinical pharmacology work, shows that autoreceptor and heteroreceptor populations of these receptors have divergent roles in modulating depression-related behavior as well as responses to antidepressants and also have different functions during early postnatal development compared to during adulthood.

A Lack of Serotonin 1B Autoreceptors Results in Decreased Anxiety and Depression-Related Behaviors

The effects of serotonin (5-HT) on anxiety and depression are mediated by a number of 5-HT receptors, including autoreceptors that act to inhibit 5-HT release. While the majority of anxiety and depression-related research has focused on the 5-HT_1A receptor, the 5-HT_1B receptor has a lesser known role in modulating emotional behavior. 5-HT_1B receptors are inhibitory GPCRs located on the presynaptic terminal of both serotonin and non-serotonin neurons, where they act to inhibit neurotransmitter release. The autoreceptor population located on the axon terminals of 5-HT neurons is a difficult population to study due to their diffuse localization throughout the brain that overlaps with 5-HT_1B heteroreceptors (receptors located on non-serotonergic neurons). In order to study the contribution of 5-HT_1B autoreceptors to anxiety and depression-related behaviors, we developed a genetic mouse model that allows for selective ablation of 5-HT_1B autoreceptors. Mice lacking 5-HT_1B autoreceptors displayed the expected increases in extracellular serotonin levels in the ventral hippocampus following administration of a selective serotonin reuptake inhibitor. In behavioral studies, they displayed decreased anxiety-like behavior in the open field and antidepressant-like effects in the forced swim and sucrose preference tests. These results suggest that strategies aimed at blocking 5-HT_1B autoreceptors may be useful for the treatment of anxiety and depression.