The 5-HT2A serotonin receptor in executive function: Implications for neuropsychiatric and neurodegenerative diseases

The Bidirectional Relationship between Weight Gain and Cognitive Function in First-Episode Schizophrenia: A Longitudinal Study in China

Patients with schizophrenia often encounter notable weight gain during their illness, heightening the risk of metabolic diseases. While previous studies have noted a correlation between obesity and cognitive impairment in schizophrenia, many were cross-sectional, posing challenges in establishing a causal relationship between weight gain and cognitive function. The aim of this longitudinal study is to examine the relationship between weight gain and cognitive function in patients with first-episode schizophrenia (FES) during the initial 6-month antipsychotic treatments. Employing linear and logistic regression analyses, the study involved 337 participants. Significantly, baseline scores in processing speed (OR = 0.834, p = 0.007), working memory and attention (OR = 0.889, p = 0.043), and executive function (OR = 0.862, p = 0.006) were associated with clinically relevant weight gain (CRW, defined as an increase in body weight > 7%) at the 6-month endpoint. On the other hand, CRW correlated with improvements in the Brief Visuospatial Memory Test (p = 0.037). These findings suggest that patients with lower baseline cognitive performance undergo more substantial weight gain. Conversely, weight gain was correlated with cognitive improvements, particularly in the domain of visual learning and memory. This suggested a potential bidirectional relationship between weight gain and cognitive function in first-episode schizophrenia patients.

Pain Comorbidities with Attention Deficit: A Narrative Review of Clinical and Preclinical Research

A negative correlation exists between attention and pain. The cognitive impairments linked to pain can significantly impede a patient's healing process and everyday tasks, particularly for individuals experiencing persistent pain. Furthermore, it has been demonstrated that diversion can effectively decrease pain levels in individuals. The focus of this review is to analyze clinical trials and fundamental investigations regarding alterations in focus and persistent discomfort. Moreover, we investigated the common neuroanatomy associated with attention and pain. Furthermore, we examined the impact of various neuromodulators on the transmission of pain and processes related to attention, while also considering the potential neural mechanisms that contribute to the co-occurrence of pain and attention deficits. Further investigation in this field will enhance our comprehension of patient symptoms and the underlying pathophysiology, ultimately resulting in more objective approaches to treatment.

Serotonergic and Adrenergic Neuroreceptor Manipulation Ameliorates Core Symptoms of ADHD through Modulating Dopaminergic Receptors in Spontaneously Hypertensive Rats

The core symptoms of attention deficit hyperactivity disorder (ADHD) are due to the hypofunction of the brain's adrenergic (NE) and dopamine (DA) systems. Drugs that enhance DA and NE neurotransmission in the brain by blocking their transporters or receptors are the current therapeutic strategies. Of late, the emerging results point out the serotonergic (5-HT) system, which indirectly modulates the DA activity in reducing the core symptoms of ADHD. On this basis, second-generation antipsychotics, which utilize 5-HT receptors, were prescribed to children with ADHD. However, it is not clear how serotonergic receptors modulate the DA activity to minimize the symptoms of ADHD. The present study investigates the efficacy of serotonergic and alpha-2 adrenergic receptor manipulation in tackling the core symptoms of ADHD and how it affects the DA neuroreceptors in the brain regions involved in ADHD. Fifteen-day-old male spontaneously hypertensive rats (SHRs) received 5-HT1A agonist (ipsapirone) or 5-HT2A antagonist (MDL 100907) (i.p.) or alpha-2 agonist (GFC) from postnatal days 15 to 42 along with age-matched Wistar Kyoto rats (WKY) (n = 8 in each group). ADHD-like behaviors were assessed using a battery of behavioral tests during postnatal days 44 to 65. After the behavioral tests, rat brains were processed to estimate the density of 5-HT1A, 5-HT2A, DA-D1, and DA-D2 neuroreceptors in the prefrontal cortex, the striatum, and the substantia nigra. All three neuroreceptor manipulations were able to minimize the core symptoms of ADHD in SHRs. The positive effect was mainly associated with the upregulation of 5-HT2A receptors in all three areas investigated, while 5-HT1A was in the prefrontal cortex and the substantia nigra. Further, the DA-D1 receptor expression was downregulated by all three neuroreceptor manipulations except for alpha-2 adrenergic receptor agonists in the striatum and 5-HT2A antagonists in the substantia nigra. The DA-D2 expression was upregulated in the striatum while downregulated in the prefrontal cortex and the substantia nigra. In this animal model study, the 5-HT1A agonist or 5-HT2A antagonist monotherapies were able to curtail the ADHD symptoms by differential expression of DA receptors in different regions of the brain.

Effects of psychedelic microdosing versus conventional ADHD medication use on emotion regulation, empathy, and ADHD symptoms in adults with severe ADHD symptoms: A naturalistic prospective comparison study

Adults with attention-deficit hyperactivity disorder (ADHD) often struggle with emotion regulation (ER), impacting their empathic skills and relationships. ADHD medication might not be as effective for ER issues as for ADHD symptoms. Microdosing (MD) psychedelics has shown promise for ADHD treatment and previous studies reported social-emotional benefits. Two online prospective studies investigated MD effects on ER and empathy in adults with severe ADHD symptoms across three assessments: baseline, two-, and four-week post-initiation. Study 1 examined adults initiating MD on their own (n = 233, n = 64, and n = 44) and found positive effects on ER (cognitive reappraisal and expressive suppression) and aspects of empathy (perspective-taking and personal distress). Study 2, including a control group and an ADHD symptom scale, compared individuals only MD (n = 180, n = 50, and n = 38) to individuals using conventional ADHD medication (n = 37, n = 27, and n = 28). After 4 weeks, ADHD symptoms were lower in the MD group. Only improvements in expressive suppression persisted after adding the control group. This study indicates the positive effects of MD psychedelics on ADHD symptoms and ER in adults with severe ADHD symptoms while lacking evidence for effects on empathy.

5-HT2A Receptor Knockout Mice Show Sex-Dependent Differences following Acute Noribogaine Administration

Noribogaine (noribo) is the primary metabolite from ibogaine, an atypical psychedelic alkaloid isolated from the root bark of the African shrub Tabernanthe iboga. The main objective of this study was to test the hypothesis that molecular, electrophysiological, and behavioral responses of noribo are mediated by the 5-HT2A receptor (5-HT2AR) in mice. In that regard, we used male and female, 5-HT2AR knockout (KO) and wild type (WT) mice injected with a single noribo dose (10 or 40 mg/kg; i.p.). After 30 min., locomotor activity was recorded followed by mRNA measurements by qPCR (immediate early genes; IEG, glutamate receptors, and 5-HT2AR levels) and electrophysiology recordings of layer V pyramidal neurons from the medial prefrontal cortex. Noribo 40 decreased locomotion in male, but not female WT. Sex and genotype differences were observed for IEG and glutamate receptor expression. Expression of 5-HT2AR mRNA increased in the mPFC of WT mice following Noribo 10 (males) or Noribo 40 (females). Patch-clamp recordings showed that Noribo 40 reduced the NMDA-mediated postsynaptic current density in mPFC pyramidal neurons only in male WT mice, but no effects were found for either KO males or females. Our results highlight that noribo produces sexually dimorphic effects while the genetic removal of 5HT2AR blunted noribo-mediated responses to NMDA synaptic transmission.

Antidepressant-like Effects of Representative Types of Food and Their Possible Mechanisms

Depression is a mental disorder characterized by low mood, lack of motivation, negative cognitive outlook, and sleep problems. Suicide may occur in severe cases, although suicidal thoughts are not seen in all cases. Globally, an estimated 350 million individuals grapple with depression, as reported by the World Health Organization. At present, drug and psychological treatments are the main treatments, but they produce insufficient responses in many patients and fail to work at all in many others. Consequently, treating depression has long been an important topic in society. Given the escalating prevalence of depression, a comprehensive strategy for managing its symptoms and impacts has garnered significant attention. In this context, nutritional psychiatry emerges as a promising avenue. Extensive research has underscored the potential benefits of a well-rounded diet rich in fruits, vegetables, fish, and meat in alleviating depressive symptoms. However, the intricate mechanisms linking dietary interventions to brain function alterations remain largely unexplored. This review delves into the intricate relationship between dietary patterns and depression, while exploring the plausible mechanisms underlying the impact of dietary interventions on depression management. As we endeavor to unveil the pathways through which nutrition influences mental well-being, a holistic perspective that encompasses multidisciplinary strategies gains prominence, potentially reshaping how we approach and address depression.

Structural studies of serotonin receptor family

Serotonin receptors, also known as 5-HT receptors, belong to the G protein-coupled receptors (GPCRs) superfamily. They mediate the effects of serotonin, a neurotransmitter that plays a key role in a wide range of functions including mood regulation, cognition and appetite. The functions of serotonin are mediated by a family of 5-HT receptors including 12 GPCRs belonging to six major families: 5-HT1, 5-HT2, 5-HT4, 5-HT5, 5-HT6 and 5-HT7. Despite their distinct characteristics and functions, these receptors' subtypes share common structural features and signaling mechanisms. Understanding the structure, functions and pharmacology of the serotonin receptor family is essential for unraveling the complexities of serotonin signaling and developing targeted therapeutics for neuropsychiatric disorders. However, developing drugs that selectively target specific receptor subtypes is challenging due to the structural similarities in their orthosteric binding sites. This review focuses on the recent advancements in the structural studies of 5-HT receptors, highlighting the key structural features of each subtype and shedding light on their potential as targets for mental health and neurological disorders (such as depression, anxiety, schizophrenia, and migraine) drugs. [BMB Reports 2023; 56(10): 527-536].

Spirocyclic Iodonium Ylides for Fluorine-18 Radiolabeling of Non-Activated Arenes: From Concept to Clinical Research

Positron emission tomography (PET) is a powerful imaging tool for drug discovery, clinical diagnosis, and monitoring of disease progression. Fluorine-18 is the most common radionuclide used for PET, but advances in radiotracer development have been limited by the historical lack of methodologies and precursors amenable to radiolabeling with fluorine-18. Radiolabeling of electron-rich (hetero)aromatic rings remains a long-standing challenge in the production of PET radiopharmaceuticals. In this personal account, we discuss the history of spirocyclic iodonium ylide precursors, from inception to applications in clinical research, for the incorporation of fluorine-18 into complex non-activated (hetero)aromatic rings.

Atypical antipsychotics attenuate MK801-induced social withdrawal and hyperlocomotion in the RHA rat model of schizophrenia-relevant features

RATIONALE

The administration of NMDA receptor (NMDAR) antagonists constitutes a widely used model that produce both positive (e.g., hyperactivity) and negative (e.g., social withdrawal) symptoms relevant for schizophrenia in rodents. These effects can be reversed with the administration of atypical (second and third generation) antipsychotics.

OBJECTIVES

In this study we combined the NMDAR-antagonist model with the Roman High-Avoidance (RHA) strain, a psychogenetically selected model of schizophrenia-relevant features. We also studied whether some atypical antipsychotic drugs (clozapine, ziprasidone, and aripiprazole) would be able to attenuate or reverse the behavioural alterations induced by MK801 and whether such effects might be dependent on the rat strain.

METHODS

MK801 dose-response study was conducted in RHA and Roman Low-Avoidance (RLA) male rats. After that, the 0.15 mg/kg MK801 dose was selected to carry out pharmacological studies versus atypical antipsychotics.

RESULTS

In the first experiment we establish that MK801 (dizocilpine), a NMDAR antagonist, produces dose-related hyperactivity and social withdrawal, which are more marked in RHA than RLA rats. The administration of the atypical antipsychotics clozapine (2.5 mg/kg) or ziprasidone (2.5 mg/kg) partially reversed or attenuated some of the social behaviour deficits and hyperactivity induced by the administration of MK801. Aripiprazole (3 mg/kg), a third-generation antipsychotic, reversed or attenuated the social preference deficit, the hyperactivity and the impairment of social latency induced by MK801.

CONCLUSIONS

These results seem to be in line with previous studies with the NMDAR-antagonist model and add face (MK801-induced social withdrawal and hyperactivity) and predictive (attenuation of MK801-induced effects by atypical antipsychotics) validity to the RHA rat strain as a model of schizophrenia-relevant features.

Shifting as an executive function separate from updating and inhibition in old age: Behavioral and genetic evidence

This study aimed to examine the organization of executive functions (EFs), specifically working memory updating, prepotent response inhibition, and mental-set shifting in old age, with a particular focus on determining whether the shifting function was behaviorally and genetically separated from the other functions. A total of 248 healthy older Chinese individuals participated, and multiple measures of executive functions were collected. Additionally, measures of fluid intelligence were included to explore the varying relationships between the three executive functions and this higher-order cognitive ability. Furthermore, genetic data were gathered and analyzed to investigate the associations between EFs and six candidate single-nucleotide polymorphisms (SNPs) mapped to dopaminergic, serotonergic, or glutamatergic genes. The results indicated that both the three-factor model and the two-factor model, which combined updating and inhibition, demonstrated a good fit. Furthermore, shifting was found to be behaviorally separated from the other two functions, and the correlation between shifting and fluid intelligence was smaller compared to the correlations between updating and inhibition with fluid intelligence. Moreover, the DRD2 SNPs showed significant associations with shifting, rather than with updating and inhibition. These findings provide evidence that shifting is distinct and separate from updating and inhibition, highlighting the diversity of EFs among older adults.

TCB-2, a 5-hydroxytryptamine 2A receptor agonist, disrupts prepulse inhibition in the ventral pallidum and nucleus accumbens

The 5-hydroxytryptamine 2A (5-HT_2A) receptor plays an important role in schizophrenia. The 5-HT_2A receptor is also involved in the regulation of prepulse inhibition (PPI) in rodents. The aim of this study was to determine whether selective 5-HT_2A receptor agonizts or antagonists may alter PPI in rats and to identify the critical brain regions in which the activity of 5-HT_2A receptors regulates PPI. The results showed that infusion of the 5-HT_2A receptor agonist TCB-2 into the lateral ventricle disrupted PPI, but the 5-HT_2A receptor antagonist M100907 had no such effect. In addition, local infusion of TCB-2 into the nucleus accumbens and ventral pallidum disrupted PPI, whereas the same manipulation in the medial prefrontal cortex, ventral hippocampus, and ventral tegmental area did not disrupt PPI. In conclusion, agonism of 5-HT_2A receptors in the ventral pallidum and nucleus accumbens can disrupt PPI. The ventral pallidum and nucleus accumbens are critical brain regions responsible for the regulation of PPI by serotonin. These findings contribute to the extensive exploration of the molecular and neural mechanisms underlying the regulatory effect of 5-HT_2A receptor activity on PPI, especially the neural circuits modulated by 5-HT_2A receptor activity.

Preferential Modulatory Action of 5-HT(2A) Receptors on the Dynamic Regulation of Basal Ganglia Circuits

In rodents, cortical information is transferred to the substantia nigra pars reticulata (SNr) through motor and medial prefrontal (mPF) basal ganglia (BG) circuits implicated in motor and cognitive/motivational behaviors, respectively. The serotonergic 5-HT_2A receptors are located in both of these neuronal networks, displaying topographical differences with a high expression in the associative/limbic territories, and a very low expression in the subthalamic nucleus. This study investigated whether the stimulation of 5-HT_2A receptors could have a specific signature on the dynamic regulation of BG circuits, preferentially modulating the mPF information processing through trans-striatal pathways. We performed in vivo single-unit extracellular recordings to assess the effect of the 5-HT_2A agonist TCB-2 on the spontaneous and cortically evoked activity of lateral and medial SNr neurons in male rats (involved in motor and mPF circuits, respectively). TCB-2 (50-200 µg/kg, i.v.) increased the basal firing rate and enhanced the cortically evoked inhibitory response of medial SNr neurons (transmission through the direct striato-nigral pathway). A prior administration of the preferential 5-HT_2A receptor antagonist MDL11939 (200 µg/kg, i.v.) did not modify any electrophysiological parameter, but occluded TCB-2-induced effects. In animals treated with the 5-HT synthesis inhibitor pCPA (4-chloro-dl-phenylalanine methyl ester hydrochloride), TCB-2 failed to induce the above-mentioned effects, thus suggesting the contribution of endogenous 5-HT. However, the mobilization of 5-HT induced by the acute administration of fluoxetine (10 mg/kg, i.p.) did not mimic the effects triggered by TCB-2. Overall, these data suggest that 5-HT_2A receptors have a preferential modulatory action on the dynamic regulation of BG circuitry.SIGNIFICANCE STATEMENT Motor and medial prefrontal (mPF) basal ganglia (BG) circuits play an important role in integrative brain functions like movement control or cognitive/motivational behavior, respectively. Although these neuronal networks express 5-HT_2A receptors, the expression is higher in associative/limbic structures than in the motor ones. We show a topographical-dependent dissociation in the effects triggered by the 5HT_2A agonist TCB-2, which specifically increases the medial substantia nigra pars reticulata neuron activity and has a preferential action on mPF information processing through the striato-nigral direct pathway. These are very likely to be 5-HT_2A receptor-mediated effects that require mobilization of the endogenous 5-HT system. These findings provide evidence about the specific signature of 5-HT_2A receptors on the dynamic regulation of BG circuits.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

A Short Synthesis of Ergot Alkaloids and Evaluation of the 5-HT1/2 Receptor Selectivity of Lysergols and Isolysergols

Key transformations in a four-step synthesis of the ergot alkaloid scaffold include a novel cesium carbonate-mediated hydrogen autotransfer alkylation to generate the C(3)-C(4) bond and an intramolecular Heck reaction that directly establishes the C(9)-C(10) alkene of methyl lysergate. An ester reduction and a streamlined experimental procedure establish a readily scalable, expedient total synthesis of all four stereoisomers of lysergol and isolysergol, including the previously unknown (-)-lysergol, for pharmacological evaluation at 5-HT_1A and 5HT_2A,B,C receptors. A bicyclic scaffold is also characterized for the first time in the intramolecular Heck coupling.

Maternal Metabolic State and Fetal Sex and Genotype Modulate Methylation of the Serotonin Receptor Type 2A Gene (HTR2A) in the Human Placenta

The serotonin receptor 2A gene (HTR2A) is a strong candidate for the fetal programming of future behavior and metabolism. Maternal obesity and gestational diabetes mellitus (GDM) have been associated with an increased risk of metabolic and psychological problems in offspring. We tested the hypothesis that maternal metabolic status affects methylation of HTR2A in the placenta. The prospective study included 199 pairs of mothers and healthy full-term newborns. Genomic DNA was extracted from feto-placental samples and analyzed for genotypes of two polymorphisms (rs6311, rs6306) and methylation of four cytosine residues (−1665, −1439, −1421, −1224) in the HTR2A promoter region. Placental HTR2A promoter methylation was higher in male than female placentas and depended on both rs6311 and rs6306 genotypes. A higher maternal pre-gestational body mass index (pBMI) and, to a lesser extent, diagnosis of GDM were associated with reduced HTR2A promoter methylation in female but not male placentas. Higher pBMI was associated with reduced methylation both directly and indirectly through increased GDM incidence. Tobacco use during pregnancy was associated with reduced HTR2A promoter methylation in male but not female placentas. The obtained results suggest that HTR2A is a sexually dimorphic epigenetic target of intrauterine exposures. The findings may contribute to a better understanding of the early developmental origins of neurobehavioral and metabolic disorders associated with altered HTR2A function.

Uncovering the Potential Mechanisms of Coptis chinensis Franch. for Serious Mental Illness by Network Pharmacology and Pharmacology-Based Analysis

Background

Serious mental illness is a disease with complex etiological factors that requires multiple interventions within a holistic disease system. With heat-clearing and detoxifying effects, Coptis chinensis Franch. is mainly used to treat serious mental illness.

Aim of the Study

To explore the underlying mechanisms and therapeutic effect by which Coptis chinensis Franch. treats serious mental illnesses at a holistic level.

Methods

A viable network pharmacology approach was adopted to obtain the potential active ingredients of Coptis chinensis Franch., and serious mental illnesses-related targets and signaling pathways. The interactions between crucial target HTR2A and constituents were verified by molecular docking, and the dynamic behaviors of binding were studied by molecular dynamics simulation. In addition, the anti-anxiety effect of Rhizoma Coptidis (the roots of Coptis chinensis Franch.) extract on lipopolysaccharide-stimulated mice was verified. The anxiety-like behavior was measured through the elevated plus-maze test, light–dark box test, and open field test. Radioimmunoassays detected the levels of interleukin-1β, tumor necrosis factor-α, interleukin-10, interleukin-4, 5-hydroxytryptamine, and dopamine in the serum, hippocampus, medial prefrontal cortex, and amygdala. Meanwhile, immunohistochemistry protocols for the assessment of neuronal loss (neuron-specific nuclear protein) and synaptic alterations (Synapsin I) were performed in the hippocampus.

Results

Based on scientific analysis of the established networks, serious mental illnesses-related targets mostly participated in the calcium signaling pathway, cyclic adenosine monophosphate signaling pathway, mitogen-activated protein kinase signaling pathway, serotonergic and dopaminergic synapse. Molecular docking and molecular dynamics simulation studies illustrated that berberine, epiberberine, palmatine, and coptisine presented favorable binding patterns with HTR2A. The in vivo experiments confirmed that Rhizoma Coptidis extract ameliorated anxiety-like behaviors by improving the survival of neurons, regulating synaptic plasticity, and inhibiting neuroinflammation.

Conclusion

These findings in the present study led to potential preventative and therapeutic strategies for serious mental illnesses with traditional Chinese medicine.

Psychedelics as Novel Therapeutics in Alzheimer's Disease: Rationale and Potential Mechanisms

Serotonin 2A receptor (5-HT_2AR) agonist "classic psychedelics" are drawing increasing interest as potential mental health treatments. Recent work suggests psychedelics can exert persisting anxiolytic and antidepressant effects lasting up to several months after a single administration. Data indicate acute subjective drug effects as important psychological factors involved in observed therapeutic benefits. Additionally, animal models have shown an important role for 5-HT_2AR agonists in modulating learning and memory function with relevance for Alzheimer's Disease (AD) and related dementias. A number of biological mechanisms of action are under investigation to elucidate 5-HT_2AR agonists' therapeutic potential, including enhanced neuroplasticity, anti-inflammatory effects, and alterations in brain functional connectivity. These diverse lines of research are reviewed here along with a discussion of AD pathophysiology and neuropsychiatric symptoms to highlight classic psychedelics as potential novel pharmacotherapies for patients with AD. Human clinical research suggests a possible role for high-dose psychedelic administration in symptomatic treatment of depressed mood and anxiety in early-stage AD. Preclinical data indicate a potential for low- or high-dose psychedelic treatment regimens to slow or reverse brain atrophy, enhance cognitive function, and slow progression of AD. In conclusion, rationale and potential approaches for preliminary research with psychedelics in patients with AD are presented, and ramifications of this line of investigation for development of novel AD treatments are discussed.

An Oppositional Tolerance Account for Potential Cognitive Deficits Caused by the Discontinuation of Antidepressant Drugs

Depression is the leading cause of disability worldwide, making antidepressant drugs the most used psychiatric drugs in the USA. Withdrawal effects and rebound symptoms frequently occur after the reduction and/or discontinuation of these drugs. Although these phenomena have been investigated with respect to the clinical symptomatology, no studies have systematically investigated the effects of withdrawal/rebound on general cognition. We present a novel framework based on the idea of allostatic adaptation, which allows to predict how different antidepressants likely impair different cognitive processes as a result of withdrawal and rebound effects. This framework relies on the assumptions that the type of cognitive impairments evoked by an antidepressant is determined by the targeted neurotransmitter systems, while the severity of deficits depends on its half-life. Our model predicts that the severity of detrimental cognitive withdrawal and rebound effects increases with a shorter half-life of the discontinued antidepressant drug. It further proposes drug-specific effects: antidepressants mainly targeting serotonin should primarily impair aversive and emotional processing, those targeting norepinephrine should impair the processing of alerting signals, those targeting dopamine should impair motivational processes and reward processing, and those targeting acetylcholine should impair spatial learning and memory. We hope that this framework will motivate further research to better understand and explain cognitive changes as a consequence of antidepressant discontinuation.

5-HT2A receptor-mediated Gαq/11 activation in psychiatric disorders: A postmortem study

OBJECTIVES

Serotonin-2A (5-HT_2A) receptors play an important role in the regulation of many brain functions that are disturbed in patients with such psychiatric diseases as mood disorders and schizophrenia. The objective of this study was to evaluate 5-HT_2A receptor-mediated signalling pathway through Gα_q/11 activation in psychiatric patients by using post-mortem brain samples.

METHODS

Functional activation of Gα_q/11 proteins coupled to 5-HT_2A receptors was determined by means of [³⁵S]GTPγS binding/immunoprecipitation assay in post-mortem prefrontal cortex of psychiatric patients diagnosed as bipolar disorder (BP), major depressive disorder (MDD), and schizophrenia, and individually matched controls. The effects of antipsychotic treatment as well as suicide were also analysed.

RESULTS

There was no significant difference in maximum percent increase (%E_max) or slope factor among the four groups. The negative logarithm of concentration eliciting the half-maximal effect (pEC₅₀) was significantly reduced in BP and schizophrenia patients as compared to controls. These alterations were attributable to antipsychotic medication. The pEC₅₀ values in 'non-suicide' group of schizophrenia, but not in 'suicide' group, were significantly reduced as compared with controls.

CONCLUSIONS

Altered 5-HT_2A receptor-mediated signalling pathway through Gα_q/11 proteins in prefrontal cortex might be apparently involved in pathophysiology and pharmacotherapy of BP and schizophrenia. In schizophrenic patients, these alterations as a result of successful treatment with antipsychotic agents may help in prevention of suicidal behaviour.

Association of 5-HTR2A -1438A/G polymorphism with anorexia nervosa and bulimia nervosa: A meta-analysis

Although a number of studies have been conducted on the association of -1438A/G polymorphism in serotonin 2A receptor (5-HTR2A) gene with anorexia nervosa (AN) and bulimia nervosa (BN), the results remained inconsistent. We thus performed a meta-analysis to clarify the effects of -1438A/G polymorphism on the risk of AN and BN. PubMed, Embase, the Cochrane Library, CNKI, Weipu and Wanfang databases were searched for eligible studies. Pooled odds ratio (OR) and 95 % confidence interval (CI) were calculated to estimate the strength of the association. Subgroup analysis was also performed by ethnicity. In total, 17 studies were included for the meta-analysis, of which 15 studies containing 2028 cases and 2725 controls were used for AN analysis and 7 studies containing 505 cases and 1129 controls for BN analysis. The results showed -1438A/G polymorphism was significantly associated with the risk of AN in four genetic models (allele model, A vs. G: OR = 1.31, 95 % CI = 1.11-1.64, P = 0.003; recessive model, AA vs. GA + GG: OR = 1.69, 95 % CI = 1.28-2.23, P = 0.000; dominant model, AA + GA vs. GG: OR = 1.35, 95 % CI = 1.02-1.79, P = 0.037; co-dominant model, AA vs. GG: OR = 1.94, 95 % CI = 1.29-2.92, P = 0.002) in Caucasians, but not in Asians. We failed to observe a significant association between -1438A/G polymorphism and the risk of BN either in overall or in Caucasian population. The present meta-analysis indicated that A allele and AA genotype of 5-HTR2A -1438A/G polymorphism may contribute to higher risk of AN, especially in Caucasians. However, this polymorphism was not associated with the susceptibility to BN.

The Relationship between Overweight/Obesity and Executive Control in College Students: The Mediating Effect of BDNF and 5-HT

The main aim of this study was to explore the association between overweight/obesity and executive control (EC) in young adults, and to further analyze the mediating effect of brain-derived neurotrophic factor (BDNF) and serotonin (5-hydroxytryptamine (5-HT)) on the relationship between overweight/obesity and EC. A total of 449 college students aged between 18 and 20 years were recruited for the study between March and December 2019. Their height and weight were then measured professionally. Subsequently, body mass index (BMI) was calculated as weight (kg) divided by the square of height (m). The EC of the participants was then estimated using the Flanker task, while their serum BDNF levels and 5-HT levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit. Finally, the multiple intermediary models in SPSS were used to analyze the mediating effect of 5-HT and BDNF between overweight/obesity and EC. The result show that the overweight/obesity of college students was positively correlated with the response of EC (p ≤ 0.005). However, it was negatively correlated with BDNF (p ≤ 0.05) and 5-HT (p ≤ 0.05). Moreover, BDNF (p ≤ 0.001) and 5-HT (p ≤ 0.001) were negatively correlated with the response of EC. The BDNF level played a partial mediating role between overweight/obesity and EC that accounted for 7.30% of the total effect value. Similarly, the 5-HT of college students played a partial mediating role between overweight/obesity and EC that accounted for 8.76% of the total effect value. Gender and age had no regulatory effect on the relationship between overweight/obesity, BDNF, 5-HT, and EC. This study provides the evidence that 5-HT and BDNF mediated the association between overweight/obesity and executive control. It is indicated that 5-HT and BDNF might be the biological pathways underpinning the link between overweight/obesity and executive control.

Medial prefrontal cortical control of reward- and aversion-based behavioral output: Bottom-up modulation

How does the brain guide our actions? This is a complex issue, where the medial prefrontal cortex (mPFC) plays a crucial role. The mPFC is essential for cognitive flexibility and decision making. These functions are related to reward- and aversion-based learning, which ultimately drive behavior. Though, cortical projections and modulatory systems that may regulate those processes in the mPFC are less understood. How does the mPFC regulate approach-avoidance behavior in the case of conflicting aversive and appetitive stimuli? This is likely dependent on the bottom-up neuromodulation of the mPFC projection neurons. In this review, we integrate behavioral-, pharmacological-, and viral-based circuit manipulation data showing the involvement of mPFC dopaminergic, noradrenergic, cholinergic, and serotoninergic inputs in reward and aversion processing. Given that an incorrect balance of reward and aversion value could be a key problem in mental diseases such as substance use disorders, we discuss outstanding questions for future research on the role of mPFC modulation in reward and aversion.

The Roles of Serotonin in Neuropsychiatric Disorders

The serotonergic system extends throughout the central nervous system (CNS) and the gastrointestinal (GI) tract. In the CNS, serotonin (5-HT, 5-hydroxytryptamine) modulates a broad spectrum of functions, including mood, cognition, anxiety, learning, memory, reward processing, and sleep. These processes are mediated through 5-HT binding to 5-HT receptors (5-HTRs), are classified into seven distinct groups. Deficits in the serotonergic system can result in various pathological conditions, particularly depression, schizophrenia, mood disorders, and autism. In this review, we outlined the complexity of serotonergic modulation of physiologic and pathologic processes. Moreover, we provided experimental and clinical evidence of 5-HT's involvement in neuropsychiatric disorders and discussed the molecular mechanisms that underlie these illnesses and contribute to the new therapies.

Dietary tryptophan depletion alters the faecal bacterial community structure of compulsive drinker rats in schedule-induced polydipsia

RATIONALE

Compulsive behaviour, present in different psychiatric disorders such as obsessive-compulsive disorder, schizophrenia and drug abuse, is associated with altered levels of serotonin (5-hydroxytryptamine, 5-HT). The gut microbiota regulates tryptophan (TRP) metabolism and may affect global 5-H synthesis in the enteric and central nervous systems, suggesting a possible involvement of gut microbiota in compulsive spectrum disorders.

OBJECTIVES

The present study investigated whether chronic TRP depletion by diet alters the faecal bacterial community profiles of compulsive versus non-compulsive rats in schedule-induced polydipsia (SIP). Peripheral plasma 5-HT and brain-derived neurotrophic factor (BDNF) levels were evaluated.

METHODS

Wistar rats were selected as High Drinkers (HD) or Low Drinkers (LD) according to their SIP behaviour and were fed for 14 days with either a TRP-free diet (T-) or a TRP-supplemented diet (T+). The faecal bacterial community structure was investigated with 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis.

RESULTS

Compulsive HD rats showed a lower bacterial diversity than LD rats, irrespectively of the diet. The TRP-depleted HD rats, the only group increasing compulsive licking in SIP, showed a reduction of bacterial evenness and a highly functionally organized community compared with the other groups, indicating that this bacterial community is more fragile to external changes due to the dominance of a low number of species. The chronic TRP depletion by diet effectively reduced peripheral plasma 5-HT levels in both HD and LD rats, while plasma BDNF levels were not altered.

CONCLUSIONS

These results highlight the possible implication of reduced microbial diversity in compulsive behaviour and the involvement of the serotonergic system in modulating the gut brain-axis in compulsive spectrum disorders.

Mania- and anxiety-like behavior and impaired maternal care in female diacylglycerol kinase eta and iota double knockout mice

Genome-wide association studies linked diacylglycerol kinase eta and iota to mood disorders, including bipolar disorder and schizophrenia, and both genes are expressed throughout the brain. Here, we generated and behaviorally characterized female mice lacking Dgkh alone, Dgki alone, and double Dgkh/Dgki-knockout (dKO) mice. We found that fewer than 30% of newborn pups raised by dKO females survived to weaning, while over 85% of pups survived to weaning when raised by wild-type (WT) females. Poor survival under the care of dKO mothers was unrelated to pup genotype. Moreover, pups from dKO dams survived when fostered by WT dams, suggesting the poor survival rate of dKO-raised litters was related to impaired maternal care by dKO dams. Nest building was similar between WT and dKO dams; however, some dKO females failed to retrieve any pups in a retrieval assay. Pups raised by dKO dams had smaller or absent milk spots and reduced weight, indicative of impaired nursing. Unlike WT females, postpartum dKO females showed erratic, panicked responses to cage disturbances. Virgin dKO females showed behavioral signs of anxiety and mania, which were not seen in mice lacking either Dgkh or Dgki alone. Our research indicates that combined deletion of Dgkh and Dgki impairs maternal behavior in the early postpartum period, and suggests female dKO mice model symptoms of mania and anxiety.

In silico toxicological analyzes of selected toxic compounds from dumpsite or contaminated soils on human health

The soil is a key component of natural ecosystems because environmental sustainability depends largely on a sustainable soil ecosystem. The objective of this study was to predict the impact of selected toxic compounds from dumpsite or contaminated soils on human health at the molecular level of biological processes. The in silico methods that were used include toxicokinetics and target gene prediction, molecular docking, and gene expressing network analysis. The result showed bisphenol A (BPA), 2,20-bis(p-chlorophenyl)-1,1-dichloroethane (DDD), 2,20-bis(p-chlorophenyl)-1,1-trichloroethane (DDT), diethylhexyl phthalate (DEHP), nonylphenol (NP) and tetrachlorodibenzodioxin (TCDD) as the active toxic compounds that can modulate biological system and are considered as potential cause of several diseases including cancer. The principal target genes include substance-P receptor (also known as Neurokinin 1 receptor), 5-hydroxytryptamine receptor, human serotonin transporter; estrogen receptor alpha; and aryl hydrocarbon receptor. These genes implicated SUZ12, STAT3, and TRIM28 as the major transcription factors while mitogen-activated protein kinases and cyclin-dependent kinases were the major kinases from the protein-protein interaction. All the six toxicants investigated showed good free binding energies (ΔG) which were below - 5.0 kcal.mol−1. These toxic compounds showed ligand efficiency greater than 0.25 kcal.mol−1. HA and would possibly cause fatal damage on human health. The order of in silico predicted toxicity of these compounds were BPA > DDD = DDT > TCDD > NP > DEHP. Our results identified potential threats, which the selected toxicants can pose to public health. More importantly, it provides basis for investigation of super bugs (microorganisms) that can remediate these toxicants in our environment. Environmental monitoring and modern wastes management system should be implemented and enforced in the affected countries in order to safeguard the health of the citizenry.

Neuromodulation of Attention

Attention is critical to high-level cognition and attention deficits are a hallmark of neurologic and neuropsychiatric disorders. Although years of research indicates that distinct neuromodulators influence attentional control, a mechanistic account that traverses levels of analysis (cells, circuits, behavior) is missing. However, such an account is critical to guide the development of next-generation pharmacotherapies aimed at forestalling or remediating the global burden associated with disorders of attention. Here, we summarize current neuroscientific understanding of how attention affects single neurons and networks of neurons. We then review key results that have informed our understanding of how neuromodulation shapes these neuron and network properties and thereby enables the appropriate allocation of attention to relevant external or internal events. Finally, we highlight areas where we believe hypotheses can be formulated and tackled experimentally in the near future, thereby critically increasing our mechanistic understanding of how attention is implemented at the cellular and network levels.

A longitudinal, epigenome-wide study of DNA methylation in anorexia nervosa: results in actively ill, partially weight-restored, long-term remitted and non-eating-disordered women

Background

This study explored state-related tendencies in DNA methylation in people with anorexia nervosa.

Methods

We measured genome-wide DNA methylation in 75 women with active anorexia nervosa (active), 31 women showing stable remission of anorexia nervosa (remitted) and 41 women with no eating disorder (NED). We also obtained post-intervention methylation data from 52 of the women from the active group.

Results

Comparisons between members of the active and NED groups showed 58 differentially methylated sites (Q < 0.01) that corresponded to genes relevant to metabolic and nutritional status (lipid and glucose metabolism), psychiatric status (serotonin receptor activity) and immune function. Methylation levels in members of the remitted group differed from those in the active group on 265 probes that also involved sites associated with genes for serotonin and insulin activity, glucose metabolism and immunity. Intriguingly, the direction of methylation effects in remitted participants tended to be opposite to those seen in active participants. The chronicity of Illness correlated (usually inversely, at Q < 0.01) with methylation levels at 64 sites that mapped onto genes regulating glutamate and serotonin activity, insulin function and epigenetic age. In contrast, body mass index increases coincided (at Q < 0.05) with generally increased methylation-level changes at 73 probes associated with lipid and glucose metabolism, immune and inflammatory processes, and olfaction.

Limitations

Sample sizes were modest for this type of inquiry, and findings may have been subject to uncontrolled effects of medication and substance use.

Conclusion

Findings point to the possibility of reversible epigenetic alterations in anorexia nervosa, and suggest that an adequate pathophysiological model would likely need to include psychiatric, metabolic and immune components.

5-HT2A receptors modulate dopamine D2-mediated maternal effects

Serotonin 5-HT_2A receptors are expressed throughout the mesolimbic and mesocortical dopamine pathways, and manipulation of this receptor system has a profound impact on dopamine functions and dopamine-mediated behaviors. It is highly likely that 5-HT_2A receptors may also modulate the D₂-mediated maternal effects. The present study investigated this issue and also explored the possible behavioral mechanisms. We tested the effects of two D₂ drugs (an agonist quinpirole: 0.5, 1.0 mg/kg, and a potent D₂ antagonist haloperidol: 0.05, 0.10 mg/kg, sc) and their combinations with two 5-HT_2A drugs (a selective 5-HT_2A agonist TCB-2: 2.5 mg/kg, and 5-HT_2A antagonist MDL100907, 1.0 mg/kg, sc) on maternal behavior in Sprague-Dawley postpartum females. Individually, TCB-2 (2.5 mg/kg, sc) and quinpirole (0.5 and 1.0 mg/kg, sc) reduced pup preference and disrupted home-cage maternal behavior. In contrast, haloperidol (0.10 mg/kg, sc) only disrupted home-cage maternal behavior, but did not suppress pup preference. MDL100907 (1.0 mg/kg, sc) by itself had no effect on either pup preference or maternal behavior. When administered in combination, pretreatment of TCB-2 did not alter quinpirole's disruption of pup preference and home-cage maternal behavior (possibly due to the floor effect), however, it did enhance haloperidol's disruption of pup retrieval in the home cage. MDL100907 had no effect both quinpirole's and haloperidol's disruption of pup preference and home-cage maternal behavior. Interestingly, haloperidol attenuated TCB-2's disruptive effect on pup preference. These findings suggest that activation of 5-HT_2A receptors tends to enhance D₂-mediated maternal disruption, whereas blockade of 5-HT_2A receptors is less effective. They also suggest that 5-HT_2A receptors may have a direct effect on maternal behavior independent of their interaction with D₂ receptors. The possible behavioral and neural mechanisms by which 5-HT_2A- and D2-mediated maternal effects and their interaction are discussed.

Structures of the 5-HT2A receptor in complex with the antipsychotics risperidone and zotepine

Many drugs target the serotonin 2A receptor (5-HT_2AR), including second-generation antipsychotics that also target the dopamine D₂ receptor (D₂R). These drugs often produce severe side effects due to non-selective binding to other aminergic receptors. Here, we report the structures of human 5-HT_2AR in complex with the second-generation antipsychotics risperidone and zotepine. These antipsychotics effectively stabilize the inactive conformation by forming direct contacts with the residues at the bottom of the ligand-binding pocket, the movements of which are important for receptor activation. 5-HT_2AR is structurally similar to 5-HT_2CR but possesses a unique side-extended cavity near the orthosteric binding site. A docking study and mutagenic studies suggest that a highly 5-HT_2AR-selective antagonist binds the side-extended cavity. The conformation of the ligand-binding pocket in 5-HT_2AR significantly differs around extracellular loops 1 and 2 from that in D₂R. These findings are beneficial for the rational design of safer antipsychotics and 5-HT_2AR-selective drugs.

Serotonin receptors and suicide, major depression, alcohol use disorder and reported early life adversity

Serotonin neurotransmitter deficits are reported in suicide, major depressive disorder (MDD) and alcohol use disorder (AUD). To compare pathophysiology in these disorders, we mapped brain serotonin transporter (SERT), 5-HT1A, and 5-HT2A receptor binding throughout prefrontal cortex and in anterior cingulate cortex postmortem. Cases and controls died suddenly minimizing agonal effects and had a postmortem interval ≤24 h to avoid compromised brain integrity. Neuropathology and toxicology confirmed absence of neuropathology and psychotropic medications. For most subjects (167 of 232), a DSM-IV Axis I diagnosis was made by psychological autopsy. Autoradiography was performed in right hemisphere coronal sections at a pre-genual level. Linear model analyses included sex and age with group and Brodmann area as interaction terms. SERT binding was lower in suicides (p = 0.004) independent of sex (females < males, p < 0.0001), however, the lower SERT binding was dependent on MDD diagnosis (p = 0.014). Higher SERT binding was associated with diagnosis of alcoholism (p = 0.012). 5-HT1A binding was greater in suicides (p < 0.001), independent of MDD (p = 0.168). Alcoholism was associated with higher 5-HT1A binding (p < 0.001) but only in suicides (p < 0.001). 5-HT2A binding was greater in suicides (p < 0.001) only when including MDD (p = 0.117) and alcoholism (p = 0.148) in the model. Reported childhood adversity was associated with higher SERT and 5-HT1A binding (p = 0.004) in nonsuicides and higher 5-HT2A binding (p < 0.001). Low SERT and more 5-HT1A and 5-HT2A binding in the neocortex in depressed suicides is dependent on Axis I diagnosis and reported childhood adversity. Findings in alcoholism differed from those in depression and suicide indicating a distinct serotonin system pathophysiology.

Behavioral mechanisms underlying the maternal disruptive effect of serotonin 5-HT2A receptor activation in Sprague-Dawley rats

Recent evidence indicates that acute activation of 5-HT_2A receptors causes a disruption of maternal behavior in rats. However, the behavioral mechanisms underlying such a disruption are not known. We addressed this issue using two behavioral approaches targeting the maternal motivational and emotional processing systems. First, we used the pup-separation technique to increase maternal motivation to see whether pup separation is capable of reducing the maternal disruptive effect of TCB-2 (a high-affinity 5-HT_2A agonist) treatment. On postpartum days 4 and 6, different groups of Sprague-Dawley dams were treated with the TCB-2 (5.0 mg/kg, sc) or vehicle and their maternal behaviors were tested after either a 4-h pup-separation or no-pup-separation condition. Although acute TCB-2 injection disrupted maternal behavior, this disruption was not attenuated by pup separation, even after we optimized the timing of separation to maximize its increase on maternal motivation. Acute TCB-2 also impaired the retrieval of food pellets, suggesting a general effect on motivated behaviors. Next, we used a pup preference test and found that dams treated with TCB-2 exhibited an even stronger preference to pups over a male conspecific than vehicle-treated dams, indicating an enhanced motivational and emotional processing of the rewarding property of pups. These findings suggest that TCB-2 has a disruptive effect on rat maternal behavior, and this disruption is not likely due to the drug's effect on mothers' motivational and emotional processing of the incentive salience of pups, although this motivational suppression account cannot be completely ruled out. Future work could explore other possible behavioral mechanisms, such as the drug's effect on executive function.

Effects of 2-bromoterguride, a dopamine D2 receptor partial agonist, on cognitive dysfunction and social aversion in rats

RATIONALE

2-Bromoterguride, a dopamine D₂ receptor partial agonist with antagonist properties at serotonin 5-HT_2A receptors and α_2C-adrenoceptors, meets the prerequisites of a putative atypical antipsychotic drug (APD). We recently showed that 2-bromoterguride is effective in tests of positive symptoms of schizophrenia in rats without inducing extrapyramidal side effects or metabolic changes.

OBJECTIVE

In continuation of our recent work, we now investigated the effect of 2-bromoterguride on apomorphine and phencyclidine (PCP)-induced disruptions of prepulse inhibition (PPI) of the acoustic startle response, a measure of sensory gating. In addition, we used subchronic PCP treatment to produce cognitive deficits and social aversion, and assessed the effect of 2-bromoterguride on the performance in the novel object recognition (NOR) task (model for studying cognitive deficit symptoms of schizophrenia) and the social interaction test (model for studying negative symptoms of schizophrenia). Finally, we extended the side effect profile of 2-bromoterguride by measuring the prolactin response to systemic administration of the drug in rats.

RESULTS

Treatment with 2-bromoterguride (0.1 and 0.3 mg/kg) reversed PPI deficits induced by apomorphine and PCP, respectively. Subchronic PCP induced impairments in object memory and social interaction behavior which were ameliorated by 2-bromoterguride but not by clozapine and aripiprazole, respectively. Prolactin concentration in blood serum was not elevated at 1, 2, or 4 h post-2-bromoterguride treatment, which further supports the safe and effective use of this drug.

CONCLUSIONS

Our data support 2-bromoterguride as a promising APD candidate due to its beneficial effect on cognitive impairments and negative symptoms of schizophrenia.

16p11.2 deletion syndrome mice perseverate with active coping response to acute stress - rescue by blocking 5-HT2A receptors

In humans a chromosomal hemideletion of the 16p11.2 region results in variable neurodevelopmental deficits including developmental delay, intellectual disability, and features of autism spectrum disorder (ASD). Serotonin is implicated in ASD but its role remains enigmatic. In this study we sought to determine if and how abnormalities in serotonin neurotransmission could contribute to the behavioral phenotype of the 16p11.2 deletion syndrome in a mouse model (Del mouse). As ASD is frequently associated with altered response to acute stress and stress may exacerbate repetitive behavior in ASD, we studied the Del mouse behavior in the context of an acute stress using the forced swim test, a paradigm well characterized with respect to serotonin. Del mice perseverated with active coping (swimming) in the forced swim test and failed to adopt passive coping strategies with time as did their wild-type littermates. Analysis of monoamine content by HPLC provided evidence for altered endogenous serotonin neurotransmission in Del mice while there was no effect of genotype on any other monoamine. Moreover, we found that Del mice were highly sensitive to the 5-HT2A antagonists M100907, which at a dose of 0.1 mg/kg normalized their level of active coping and restored the gradual shift to passive coping in the forced swim test. Supporting evidence for altered endogenous serotonin signaling was provided by observations of additional ligand effects including altered forebrain Fos expression. Taken together, these observations indicate notable changes in endogenous serotonin signaling in 16p11.2 deletion mice and support the therapeutic utility of 5-HT2A receptor antagonists.

The Association between 5HT2A T102C and Behavioral and Psychological Symptoms of Dementia in Alzheimer's Disease: A Meta-Analysis

The serotonin receptor gene (5-HT2A) has been reported to be a susceptible factor in behavioral and psychological symptoms of dementia (BPSD) in Alzheimer's disease (AD). However, previous results were conflicting. We aim to investigate the association of 5-HT2A T102C with BPSD in AD using a meta-analysis. Studies were collected using PubMed, Web of Science, the Cochrane Library databases, Chinese National Knowledge Infrastructure (CNKI), and Embase. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess associations. Nine studies with 1899 AD patients with/without BPSD were included in this meta-analysis. The 102C and CC genotypes were associated with psychosis in AD (102C: p < 0.00001, OR [95% CI] = 3.19 [2.12-4.79]; CC: p < 0.00001, OR [95% CI] = 7.24 [3.60-14.59]). The TT genotype was significantly associated with hallucinations, aberrant motor behavior, and psychosis in AD (hallucinations: p = 0.001, OR [95% CI] = 0.52 [0.36-0.77]; aberrant motor behavior: p = 0.03, OR [95% CI] = 0.58 [0.35-0.95]; and psychosis: p = 0.002, OR [95% CI] = 0.34 [0.17-0.67]). No association was observed between T102C alleles or genotypes and delusions, agitation/aggression, depression, and apathy (p > 0.05). Thus, the 5HT2A T102C might be a susceptible factor for hallucinations, aberrant motor behavior, and psychosis in AD. The potential mechanism of this polymorphism in BPSD in AD requires further exploration.

Activation of 5-HT2A receptor disrupts rat maternal behavior

Serotonin 5-HT_2A receptor is widely distributed in the central nervous system and plays an important role in sensorimotor function, emotion regulation, motivation, executive control, learning and memory. We investigated its role in rat maternal behavior, a naturalistic behavior encompassing many psychological functions that the 5-HT_2A receptor is involved in. We first showed that activation of 5-HT_2A receptor by TCB-2 (a highly selective 5-HT_2A agonist, 1, 2.5 or 5.0 mg/kg) disrupted maternal behavior dose-dependently, and this effect was reduced by pretreatment with a 5-HT_2A receptor antagonist MDL 100907, but exacerbated by pretreatment with a 5-HT_2C receptor antagonist SB242084 and a 5-HT_2C receptor agonist MK212, indicating that the maternal disruptive effect of 5-HT_2A activation is receptor-specific and can be modulated by 5-HT_2C receptor bidirectionally. We then microinjected TCB-2 into two brain regions important for the normal expression of maternal behavior: the medial prefrontal cortex (mPFC) and the medial preoptic area (mPOA) and found that only acute intra-mPFC infusion of TCB-2 suppressed pup retrieval, whereas intra-mPOA had no effect. Finally, using c-Fos immunohistochemistry, we identified that the ventral bed nucleus of stria terminalis (vBNST), the central amygdala (CeA), and the dorsal raphe (DR) were additionally involved in the maternal-disruptive effect of TCB-2. These findings suggest that the 5-HT_2A receptor in the mPFC and other maternally related regions is required for the normal expression of maternal behavior through its intrinsic action or interactions with other receptors (e.g. 5-HT_2C). Functional disruption of this neuroreceptor system might contribute to postpartum mental disorders (e.g. depression and psychosis) that impair the quality of maternal care.

Frameworking memory and serotonergic markers

The evidence for neural markers and memory is continuously being revised, and as evidence continues to accumulate, herein, we frame earlier and new evidence. Hence, in this work, the aim is to provide an appropriate conceptual framework of serotonergic markers associated with neural activity and memory. Serotonin (5-hydroxytryptamine [5-HT]) has multiple pharmacological tools, well-characterized downstream signaling in mammals’ species, and established 5-HT neural markers showing new insights about memory functions and dysfunctions, including receptors (5-HT1A/1B/1D, 5-HT2A/2B/2C, and 5-HT3-7), transporter (serotonin transporter [SERT]) and volume transmission present in brain areas involved in memory. Bidirectional influence occurs between 5-HT markers and memory/amnesia. A growing number of researchers report that memory, amnesia, or forgetting modifies neural markers. Diverse approaches support the translatability of using neural markers and cerebral functions/dysfunctions, including memory formation and amnesia. At least, 5-HT1A, 5-HT4, 5-HT6, and 5-HT7receptors and SERT seem to be useful neural markers and therapeutic targets. Hence, several mechanisms cooperate to achieve synaptic plasticity or memory, including changes in the expression of neurotransmitter receptors and transporters.

Effect of stress on human biology: Epigenetics, adaptation, inheritance, and social significance

I present a brief introduction to epigenetics, focused primarily on methylation of the genome and various regulatory RNAs, modifications of associated histones, and their importance in enabling us to adapt to real and changing environmental, developmental, and social circumstances. Following this is a more extensive overview of how it impacts our inheritance, our entire life (which changes as we age), and how we interact with others. Throughout, I emphasize the critical influence that stress, of many varieties exerts, via epigenetic means, on much of how we live and survive, mostly in the brain. I end with a short section on multigenerational transmission, drugs, and the importance of both social life and early life experiences in the development of adult diseases. There will be nothing about cancer. Although epigenetics is critical in that field, it is a whole different cobweb of complications (some involving stress).

Perinatal SSRI exposure permanently alters cerebral serotonin receptor mRNA in mice but does not impact adult behaviors

PURPOSE

Associations have been made between maternal selective serotonin reuptake inhibitor (SSRI) use during pregnancy and altered behavior in offspring, including an increased risk of autism. Given the important role serotonin plays in behavior, we hypothesized SSRI exposure in the perinatal period would alter central serotonin receptor expression and program adult behaviors in mice.

METHODS

Female mice were injected with sertraline or saline throughout pregnancy. Offspring continued to receive injections on postnatal days 1-14, a time period in mice similar to the third trimester in human pregnancy. Adult offspring underwent behavioral testing, and serotonin receptor mRNA levels were quantified.

RESULTS

Compared to controls, SSRI exposed mice did not have a reduction in social interactions, spatial learning, or exploratory behavior. As adults, sertraline exposed mice had significantly increased mRNA levels of multiple 5-HT receptors, serotonin transporter (5-HTT), and tryptophan hydroxylase isoform 2 in the cerebral cortex.

CONCLUSION

Although no behavioral phenotype was observed, SSRI exposure in the perinatal period permanently alters cerebral receptor mRNA levels. We speculate these shifts in mRNA expression provide important compensation during SSRI exposure. Further pre-clinical and clinical investigation into additional serotonin-regulated phenotypes is necessary to further assess the long-term implications of perinatal SSRI exposure.

Alteration of Monoamine Receptor Activity and Glucose Metabolism in Pediatric Patients with Anticonvulsant-Induced Cognitive Impairment

A landmark study from the Institute of Medicine reported that the assessment of cognitive difficulties in children with epilepsy is timely and imperative. Anticonvulsant-induced cognitive impairment could influence the quality of life more than seizure itself in patients. Although the monoaminergic system is involved in the regulation of cognitive process, its role in anticonvulsant-induced cognitive impairment remains unclear. Methods: To explore in vivo monoamine receptor binding activity in patients with anticonvulsant-induced cognitive impairment, each patient underwent PET imaging with both monoamine receptor binding agent ¹¹C-N-methylspiperone and glucose metabolic agent ¹⁸F-FDG. Tests of intelligence quotient (IQ), including verbal IQ (VIQ), performance IQ (PIQ), and full-scale IQ (FSIQ), were performed in each patient. Results: Compared with the patients with monotherapy, patients with polytherapy had significantly lower VIQ, PIQ, and FSIQ (P < 0.01 in each comparison), as well as significantly lower monoamine receptor activities detected in the caudate nucleus, prefrontal cortex, dorsal anterior cingulate cortex, and amygdale (P < 0.05 in each comparison). However, regarding the glucose metabolism, there was no significant difference found in patients with monotherapy or polytherapy (P > 0.05). Conclusion: Monoamine receptor PET imaging could be a promising in vivo imaging biomarker for mapping anticonvulsant-induced cognitive impairment.

Differences in 5-HT2A and mGlu2 Receptor Expression Levels and Repressive Epigenetic Modifications at the 5-HT2A Promoter Region in the Roman Low- (RLA-I) and High- (RHA-I) Avoidance Rat Strains

The serotonin 2A (5-HT_2A) and metabotropic glutamate 2 (mGlu2) receptors regulate each other and are associated with schizophrenia. The Roman high- (RHA-I) and the Roman low- (RLA-I) avoidance rat strains present well-differentiated behavioral profiles, with the RHA-I strain emerging as a putative genetic rat model of schizophrenia-related features. The RHA-I strain shows increased 5-HT_2A and decreased mGlu2 receptor binding levels in prefrontal cortex (PFC). Here, we looked for differences in gene expression and transcriptional regulation of these receptors. The striatum (STR) was included in the analysis. 5-HT_2A, 5-HT_1A, and mGlu2 mRNA and [³H]ketanserin binding levels were measured in brain homogenates. As expected, 5-HT_2A binding was significantly increased in PFC in the RHA-I rats, while no difference in binding was observed in STR. Surprisingly, 5-HT_2A gene expression was unchanged in PFC but significantly decreased in STR. mGlu2 receptor gene expression was significantly decreased in both PFC and STR. No differences were observed for the 5-HT_1A receptor. Chromatin immunoprecipitation assay revealed increased trimethylation of histone 3 at lysine 27 (H3K27me3) at the promoter region of the HTR2A gene in the STR. We further looked at the Akt/GSK3 signaling pathway, a downstream point of convergence of the serotonin and glutamate system, and found increased phosphorylation levels of GSK3β at tyrosine 216 and increased β-catenin levels in the PFC of the RHA-I rats. These results reveal region-specific regulation of the 5-HT_2A receptor in the RHA-I rats probably due to absence of mGlu2 receptor that may result in differential regulation of downstream pathways.

Involvement of serotonin 2A receptor activation in modulating medial prefrontal cortex and amygdala neuronal activation during novelty-exposure

The medial prefrontal cortex (PFC) plays a major role in executive function by exerting a top-down control onto subcortical areas. Novelty-induced frontal cortex activation is 5-HT_2A receptor (5-HT_2AR) dependent. Here, we further investigated how blockade of 5-HT_2ARs in mice exposed to a novel open-field arena affects medial PFC activation and basolateral amygdala (BLA) reactivity. We used c-Fos immunoreactivity (IR) as a marker of neuronal activation and stereological quantification for obtaining the total number of c-Fos-IR neurons as a measure of regional activation. We further examined the impact of 5-HT_2AR blockade on the striatal-projecting BLA neurons. Systemic administration of ketanserin (0.5mg/kg) prior to novel open-field exposure resulted in reduced total numbers of c-Fos-IR cells in dorsomedial PFC areas and the BLA. Moreover, there was a positive correlation between the relative time spent in the centre of the open-field and BLA c-Fos-IR in the ketanserin-treated animals. Unilateral medial PFC lesions blocked this effect, ascertaining an involvement of this frontal cortex area. On the other hand, medial PFC lesioning exacerbated the more anxiogenic-like behaviour of the ketanserin-treated animals, upholding its involvement in modulating averseness. Ketanserin did not affect the number of activated striatal-projecting BLA neurons (measured by number of Cholera Toxin b (CTb) retrograde labelled neurons also being c-Fos-IR) following CTb injection in the ventral striatum. These results support a role of 5-HT_2AR activation in modulating mPFC and BLA activation during exposure to a novel environment, which may be interrelated. Conversely, 5-HT_2AR blockade does not seem to affect the amygdala-striatal projection.

In vivo evaluation of [18F]FECIMBI-36, an agonist 5-HT2A/2C receptor PET radioligand in nonhuman primate

We recently reported the radiosynthesis and in vitro evaluation of [18F]-2-(4-bromo-2,5-dimethoxyphenyl)-N-(2-(2-fluoroethoxy)benzyl)ethanamine, ([18F]FECIMBI-36) or ([18F]1), an agonist radioligand for 5HT2A/2C receptors in postmortem samples of human brain. Herein we describe the in vivo evaluation of [18F]FECIMBI-36 in vervet/African green monkeys by PET imaging. PET images show that [18F]FECIMBI-36 penetrates the blood-brain barrier and a low retention of radioactivity is observed in monkey brain. Although the time activity curves indicate a somehow heterogeneous distribution of the radioligand in the brain, the low level of [18F]FECIMBI-36 in brain may limit the use of this tracer for quantification of 5-HT2A/2C receptors by PET.

Tryptophan depletion affects compulsive behaviour in rats: strain dependent effects and associated neuromechanisms

RATIONALE

Compulsive behaviour, present in different psychiatric disorders, such as obsessive-compulsive disorder, schizophrenia and drug abuse, is associated with altered levels of monoamines, particularly serotonin (5-hydroxytryptamine) and its receptor system.

OBJECTIVES

The present study investigated whether 5-HT manipulation, through a tryptophan (TRP) depletion by diet in Wistar and Lister Hooded rats, modulates compulsive drinking in schedule-induced polydipsia (SIP) and locomotor activity in the open-field test. The levels of dopamine, noradrenaline, serotonin and its metabolite were evaluated, as well as the 5-HT_2A and 5-HT_1A receptor binding, in different brain regions.

METHODS

Wistar rats were selected as high (HD) or low (LD) drinkers according to their SIP behaviour, while Lister hooded rats did not show SIP acquisition. Both strains were fed for 14 days with either a TRP-free diet (T-) or a TRP-supplemented diet (T+) RESULTS: The TRP depletion diet effectively reduced 5-HT levels in the frontal cortex, amygdala and hippocampus in both strains of rats. The TRP-depleted HD Wistar rats were more sensitive to 5-HT manipulation, exhibiting more licks on SIP than did the non-depleted HD Wistar rats, while the LD Wistar and the Lister Hooded rats did not exhibit differences in SIP. In contrast, the TRP-depleted Lister Hooded rats increased locomotor activity compared to the non-depleted rats, while no differences were found in the Wistar rats. Serotonin 2A receptor binding in the striatum was significantly reduced in the TRP-depleted HD Wistar rats.

CONCLUSIONS

These results suggest that alterations of the serotonergic system could be involved in compulsive behaviour in vulnerable populations.