5-HT receptors and reward-related behaviour: a review

The Neurobehavioral State hypothesis

Since the early attempts to understand the brain made by Greek philosophers more than 2000 years ago, one of the main questions in neuroscience has been how the brain perceives all the stimuli in the environment and uses this information to implement a response. Recent hypotheses of the neural code rely on the existence of an ideal observer, whether on specific areas of the cerebral cortex or distributed network composed of cortical and subcortical elements. The Neurobehavioral State hypothesis stipulates that neurons are in a quasi-stable state due to the dynamic interaction of their molecular components. This increases their computational capabilities and electrophysiological behavior further than a binary active/inactive state. Together, neuronal populations across the brain learn to identify and associate internal and external stimuli with actions and emotions. Furthermore, such associations can be stored through the regulation of neuronal components as new quasi-stable states. Using this framework, behavior arises as the result of the dynamic interaction between internal and external stimuli together with previously established quasi-stable states that delineate the behavioral response. Finally, the Neurobehavioral State hypothesis is firmly grounded on present evidence of the complex dynamics within the brain, from the molecular to the network level, and avoids the need for a central observer by proposing the brain configures itself through experience-driven associations.

Striatal Serotonin Release Signals Reward Value

Serotonin modulates diverse phenotypes and functions including depressive, aggressive, impulsive, and feeding behaviors, all of which have reward-related components. To date, research has focused on understanding these effects by measuring and manipulating dorsal raphe serotonin neurons and using single-receptor approaches. These studies have led to a better understanding of the heterogeneity of serotonin actions on behavior; however, they leave open many questions about the timing and location of serotonin's actions modulating the neural circuits that drive these behaviors. Recent advances in genetically encoded fluorescent biosensors, including the GPCR activation-based sensor for serotonin (GRAB-5-HT), enable the measurement of serotonin release in mice on a timescale compatible with a single rewarding event without corelease confounds. Given substantial evidence from slice electrophysiology experiments showing that serotonin influences neural activity of the striatal circuitry, and the known role of the dorsal medial striatal (DMS) in reward-directed behavior, we focused on understanding the parameters and timing that govern serotonin release in the DMS in the context of reward consumption, external reward value, internal state, and cued reward. Overall, we found that serotonin release is associated with each of these and encodes reward anticipation, value, approach, and consumption in the DMS.

Role of serotonin neurons in the dorsal raphe nucleus in heroin self-administration and punishment

One hallmark of substance use disorder is continued drug use despite negative consequences. When drug-taking behavior is punished with aversive stimuli, i.e. footshock, rats can also be categorized into punishment-resistant or compulsive vs. punishment-sensitive or non-compulsive phenotypes. The serotonin (5-hydroxytryptamine, 5-HT) system modulates responses to both reward and punishment. The goal of the current study was to examine punishment phenotypes in heroin self-administration and to determine the role of dorsal raphe nucleus (DRN) 5-HT neurons in both basal and punished heroin self-administration. First, rats were exposed to punished heroin self-administration and neuronal excitability of DRN 5-HT neurons was compared between punishment-resistant and punishment-sensitive phenotypes using ex vivo electrophysiology. Second, DRN 5-HT neuronal activity was manipulated in vivo during basal and punished heroin self-administration using chemogenetic tools in a Tph2-iCre rat line. While rats separated into punishment-resistant and punishment-sensitive phenotypes for punished heroin self-administration, DRN 5-HT neuronal excitability did not differ between the phenotypes. While chemogenetic inhibition of DRN 5-HT neurons was without effect, chemogenetic activation of DRN 5-HT neurons increased both basal and punished heroin self-administration selectively in punishment-resistant animals. Additionally, the responsiveness to chemogenetic activation of DRN 5-HT neurons in basal self-administration and motivation for heroin in progressive ratio each predicted resistance to punishment. Therefore, our data support the role for the DRN 5-HT system in compulsive heroin self-administration.

Pathophysiological impacts of 5-MeO-MiPT on zebrafish (Danio rerio) via the Gαq/11-PLCβ signaling pathway

Novel Psychoactive Substances (NPS) derived from tryptamines has been detected in aquatic environments, leading to environmental toxicology concerns. However, the specific toxicological mechanism, underlying these NPS, remains unclear. In our previous work, we used 5-Methoxy-N-isopropyl-N-methyltryptamine (5-MeO-MiPT) as the representative drug for NPS, and found that, 5-MeO-MiPT led to obvious behavioral inhibition and oxidative stress responses in zebrafishes model. In this study, Zebrafish were injected with varying concentrations of 5-MeO-MiPT for 30 days. RNA-seq, qPCR, metabolomics, and histopathological analyses were conducted to assess gene expression and tissue integrity. This study confirms that 5-MeO-MiPT substantially influences the transcription and expression of 13 selected genes, including ucp1, pet100, grik3, and grik4, mediated by the Gαq/11-PLCβ signaling pathway. We elucidate the molecular mechanism that 5-MeO-MiPT can inhibit DAG-Ca2+/Pkc/Erk, Pkc/Pla2/PLCs and Ca2+/Camk Ⅱ/NMDA, while enhance Ca2+/Creb. Those secondary signaling pathways may be the mechanisms mediating 5-MeO-MiPT inhibiting normal behavior in zebrafish. These findings offer novel insights into the toxicological effects and addiction mechanisms of 5-MeO-MiPT. Moreover, it presents promising avenues for investigating other tryptamine-based NPS and offers a new direction for diagnosing and treating liver-brain pathway-related diseases.

The nucleus accumbens in reward and aversion processing: insights and implications

The nucleus accumbens (NAc), a central component of the brain's reward circuitry, has been implicated in a wide range of behaviors and emotional states. Emerging evidence, primarily drawing from recent rodent studies, suggests that the function of the NAc in reward and aversion processing is multifaceted. Prolonged stress or drug use induces maladaptive neuronal function in the NAc circuitry, which results in pathological conditions. This review aims to provide comprehensive and up-to-date insights on the role of the NAc in motivated behavior regulation and highlights areas that demand further in-depth analysis. It synthesizes the latest findings on how distinct NAc neuronal populations and pathways contribute to the processing of opposite valences. The review examines how a range of neuromodulators, especially monoamines, influence the NAc's control over various motivational states. Furthermore, it delves into the complex underlying mechanisms of psychiatric disorders such as addiction and depression and evaluates prospective interventions to restore NAc functionality.

Serotonin 4 receptor brain binding and oxytocin-promoted affective and social cognition in healthy women - A randomized controlled trial

Background

Oxytocin is a neuropeptide known for its prosocial properties and role in social bonding, and intervention with intranasal oxytocin is posited to modulate affective and social cognition (i.e., hot cognition). Serotonin (5-HT) neurotransmission is also involved in emotional and social behaviors and appear to work in concert with oxytocin. However, this interaction so far remains elusive in humans. Therefore, we here investigate the relation between brain 5-HT 4 receptor (5-HT4R) levels and oxytocin-modulated hot cognition.

Methods

Using a double blind, placebo-controlled, randomized crossover design, 35 healthy women received a dose of 24 IU intranasal oxytocin or placebo one month apart. The women were naturally cycling and to control for hormonal fluctuations across the menstrual cycle, intervention days were placed during the early follicular phase. Following intervention cognitive domains including affective memory, affective bias in emotion processing, moral emotions and social information preference were assessed. In a subgroup (n = 25), Positron Emission Tomography (PET) was used to image 5-HT4R brain binding at baseline with the [11C]SB207145 radiotracer.

Results

No effect of oxytocin intervention relative to placebo was observed for any of the cognitive outcomes. Likewise, regional brain 5-HT4R binding at baseline was not associated with cognitive responses to oxytocin intervention.

Conclusion

Our data suggest that intervention with intranasal oxytocin does not have an overall effect on hot cognition in healthy women and further that 5-HT4R brain architecture does not mediate cognitive effects of oxytocin in the healthy state.

Integrated metabolomics and network pharmacology to reveal the mechanism of areca nut addiction

As a chewing hobby, areca nut (Areca catechu L.) has become the most common psychoactive substance in the world, besides tobacco, alcohol and caffeinated beverages. Moreover, as a first-class carcinogen designated by International Agency for Research on Cancer, long-term chewing areca nut can result in oral mucosal diseases and even oral cancer. To clarify the potential mechanism of areca nut addiction, an integrated strategy of metabolomics and network pharmacology was adopted in this study. Network pharmacology study indicated that all the key targets related to areca nut addiction could be regulated by arecoline and pointed out the importance of G-protein coupled receptor signalling pathway. Analysis results of mice plasma metabolome and faeces metabolome intervened by arecoline suggested that the component may affect the dopamine system and 5-HT system by regulating phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, primary bile acid biosynthesis, glycerophospholipid metabolism and intestinal flora structure. Moreover, the potential importance of bile acids in formation of addictive behaviour of chewing areca nut was investigated by integrative analysis of the relationships between metabolites and intestinal flora. The study can provide scientific basis for the addiction intervention and treatment of areca nut chewers.

The Relationship Between Oxytocin and Alcohol Dependence

The hypothalamic neuropeptide oxytocin (OT) is well known for its prosocial, anxiolytic, and ameliorating effects on various psychiatric conditions, including alcohol use disorder (AUD). In this chapter, we will first introduce the basic neurophysiology of the OT system and its interaction with other neuromodulatory and neurotransmitter systems in the brain. Next, we provide an overview over the current state of research examining the effects of acute and chronic alcohol exposure on the OT system as well as the effects of OT system manipulation on alcohol-related behaviors in rodents and humans. In rodent models of AUD, OT has been repeatedly shown to reduce ethanol consumption, particularly in models of acute alcohol exposure. In humans however, the results of OT administration on alcohol-related behaviors are promising but not yet conclusive. Therefore, we further discuss several physiological and methodological limitations to the effective application of OT in the clinic and how they may be mitigated by the application of synthetic OT receptor (OTR) agonists. Finally, we discuss the potential efficacy of cutting-edge pharmacology and gene therapies designed to specifically enhance endogenous OT release and thereby rescue deficient expression of OT in the brains of patients with severe forms of AUD and other incurable mental disorders.

Sexual health and serotonin 4 receptor brain binding in unmedicated patients with depression-a NeuroPharm study

Sexual dysfunction is prominent in Major Depressive Disorder (MDD) and affects women with depression more than men. Patients with MDD relative to healthy controls have lower brain levels of the serotonin 4 receptor (5-HT₄R), which is expressed with high density in the striatum, i.e. a key hub of the reward system. Reduced sexual desire is putatively related to disturbed reward processing and may index anhedonia in MDD. Here, we aim to illuminate plausible underlying neurobiology of sexual dysfunction in unmedicated patients with MDD. We map associations between 5-HT₄R binding, as imaged with [¹¹C]SB207145 PET, in the striatum, and self-reported sexual function. We also evaluate if pre-treatment sexual desire score predicts 8-week treatment outcome in women. From the NeuroPharm study, we include 85 untreated MDD patients (71% women) who underwent eight weeks of antidepressant drug treatment. In the mixed sex group, we find no difference in 5-HT₄R binding between patients with sexual dysfunction vs normal sexual function. However, in women we find lower 5-HT₄R binding in the sexual dysfunctional group compared to women with normal sexual function (β = -0.36, 95%CI[-0.62:-0.09], p = 0.009) as well as a positive association between sexual desire and 5-HT₄R binding (β = 0.07, 95%CI [0.02:0.13], p = 0.012). Sexual desire at baseline do not predict treatment outcome (ROC curve AUC = 52%[36%:67%]) in women. Taken together, we find evidence for a positive association between sexual desire and striatal 5-HT₄R availability in women with depression. Interestingly, this raises the question if direct 5-HT₄R agonism can target reduced sexual desire or anhedonia in MDD.

Subcortical serotonin 5HT2c receptor-containing neurons sex-specifically regulate binge-like alcohol consumption, social, and arousal behaviors in mice

Binge alcohol consumption induces discrete social and arousal disturbances in human populations that promote increased drinking and accelerate the progression of Alcohol Use Disorder. Here, we show in a mouse model that binge alcohol consumption disrupts social recognition in females and potentiates sensorimotor arousal in males. These negative behavioral outcomes were associated with sex-specific adaptations in serotonergic signaling systems within the lateral habenula (LHb) and the bed nucleus of the stria terminalis (BNST), particularly those related to the receptor 5HT2c. While both BNST and LHb neurons expressing this receptor display potentiated activation following binge alcohol consumption, the primary causal mechanism underlying the effects of alcohol on social and arousal behaviors appears to be excessive activation of LHb5HT2c neurons. These findings may have valuable implications for the development of sex-specific treatments for mood and alcohol use disorders targeting the brain's serotonin system.

Exploring the underlying mechanisms of drug-induced impulse control disorders: a pharmacovigilance-pharmacodynamic study

INTRODUCTION

Impulse control disorders (e.g. pathological gambling, hypersexuality) may develop as adverse reactions to drugs. Pathogenetic hypotheses have mainly focused on D3-receptor agonism, and switching to alternatives with different pharmacologic mechanisms represents a common management strategy. Nonetheless, treatment failure is common and gaining pathophysiological insights is needed.

AIM

We aimed to identify targets potentially contributing to pathologic impulsivity.

METHOD

We performed a pharmacovigilance-pharmacodynamic study on dopamine agonists and antipsychotics using the Food and Drug Administration Adverse Event Reporting System (January 2004-December 2021). We estimated disproportionate reporting using the Bayesian information component. Using online public databases (IUPHAR, ChEMBL, PDSP, DrugBank), we calculated drug occupancies. To identify the targets potentially contributing to impulsivity, we fitted univariate regression models interpolating information components and occupancies within dopamine agonists and antipsychotics. Sensitivity analyses were performed to check for the robustness of the results.

RESULTS

Among 19 887 reports of impulsivity, 5898 recorded an antipsychotic, and 3100 a dopamine agonist. The more robust signals concerned aripiprazole (N = 3091; median information component [95% confidence interval] = 4.51[4.45-4.55]) and brexpiprazole (229; 4.00[3.78-4.16]) for antipsychotics, pergolide (105; 5.82[5.50-6.06]) and pramipexole (2009; 5.43[5.36-5.48]) for dopamine agonists. Robust, significant positive associations between drug occupancy and impulsivity reporting were found for D3 within dopamine agonists (beta = 1.52; P-value = 0.047) and 5-HT1a within antipsychotics (1.92, 0.029).

CONCLUSION

Our results supported the role of D3-receptor agonism in inducing impulsivity in dopamine receptor agonists and identified a potential role of 5-HT1a receptor agonism in antipsychotics. Investigating these receptors may drive towards a better management of drug-induced impulsivity.

Aversive motivation and cognitive control

Aversive motivation plays a prominent role in driving individuals to exert cognitive control. However, the complexity of behavioral responses attributed to aversive incentives creates significant challenges for developing a clear understanding of the neural mechanisms of this motivation-control interaction. We review the animal learning, systems neuroscience, and computational literatures to highlight the importance of experimental paradigms that incorporate both motivational context manipulations and mixed motivational components (e.g., bundling of appetitive and aversive incentives). Specifically, we postulate that to understand aversive incentive effects on cognitive control allocation, a critical contextual factor is whether such incentives are associated with negative reinforcement or punishment. We further illustrate how the inclusion of mixed motivational components in experimental paradigms enables increased precision in the measurement of aversive influences on cognitive control. A sharpened experimental and theoretical focus regarding the manipulation and assessment of distinct motivational dimensions promises to advance understanding of the neural, monoaminergic, and computational mechanisms that underlie the interaction of motivation and cognitive control.

Serotonergic regulation of the dopaminergic system: Implications for reward-related functions

Serotonin is a critical neuromodulator involved in development and behavior. Its role in reward is however still debated. Here, we first review classical studies involving electrical stimulation protocols and pharmacological approaches. Contradictory results on the serotonergic' involvement in reward emerge from these studies. These differences might be ascribable to either the diversity of cellular types within the raphe nuclei or/and the specific projection pathways of serotonergic neurons. We continue to review more recent work, using optogenetic approaches to activate serotonergic cells in the Raphe to VTA pathway. From these studies, it appears that activation of this pathway can lead to reinforcement learning mediated through the excitation of dopaminergic neurons by serotonergic neurons co-transmitting glutamate. Finally, given the importance of serotonin during development on adult emotion, the effect of abnormal early-life levels of serotonin on the dopaminergic system will also be discussed. Understanding the interaction between the serotonergic and dopaminergic systems during development and adulthood is critical to gain insight into the specific facets of neuropsychiatric disorders.

Anhedonia as a central factor in depression: Neural mechanisms revealed from preclinical to clinical evidence

Anhedonia is one of the core symptoms of major depressive disorder (MDD), which is often inadequately treated by traditional antidepressants. The modern framework of anhedonia extends the definition from impaired consummatory pleasure or interest in rewards to a broad spectrum of deficits that impact functions such as reward anticipation, approach motivation, effort expenditure, reward valuation, expectation, and reward-cue association learning. Substantial preclinical and clinical research has explored the neural basis of reward deficits in the context of depression, and has implicated mesocorticolimbic reward circuitry comprising the nucleus accumbens, ventral pallidum, ventral tegmental area, amygdala, hippocampus, anterior cingulate, insula, orbitofrontal cortex, and other prefrontal cortex regions. Dopamine modulates several reward facets including anticipation, motivation, effort, and learning. As well, serotonin, norepinephrine, opioids, glutamate, Gamma aminobutyric acid (GABA), and acetylcholine are also involved in anhedonia, and medications targeting these systems may also potentially normalize reward processing in depression. Unfortunately, whereas reward anticipation and reward outcome are extensively explored by both preclinical and clinical studies, translational gaps remain in reward motivation, effort, valuation, and learning, where clinical neuroimaging studies are in the early stages. This review aims to synthesize the neurobiological mechanisms underlying anhedonia in MDD uncovered by preclinical and clinical research. The translational difficulties in studying the neural basis of reward are also discussed.

Modulating the Neuromodulators: Dopamine, Serotonin, and the Endocannabinoid System

Dopamine (DA), serotonin (5-hydroxytryptamine, 5-HT), and endocannabinoids (ECs) are key neuromodulators involved in many aspects of motivated behavior, including reward processing, reinforcement learning, and behavioral flexibility. Among the longstanding views about possible relationships between these neuromodulators is the idea of DA and 5-HT acting as opponents. This view has been challenged by emerging evidence that 5-HT supports reward seeking via activation of DA neurons in the ventral tegmental area. Adding an extra layer of complexity to these interactions, the endocannabinoid system is uniquely placed to influence dopaminergic and serotonergic neurotransmission. In this review we discuss how these three neuromodulatory systems interact at the cellular and circuit levels. Technological advances that facilitate precise identification and control of genetically targeted neuronal populations will help to achieve a better understanding of the complex relationship between these essential systems, and the potential relevance for motivated behavior.

Identification and characterization of a novel 5-hydroxytryptamine receptor in the sea cucumber Apostichopus japonicus (Selenka)

Serotonin (5-hydroxytryptamine [5-HT]) receptors (5-HTRs) mediate neuroendocrine signaling via interactions with the ligand serotonin (5-HT). The 5-HT signaling system has been well studied in vertebrates, but rarely known in invertebrate animals, especially in the marine invertebrates. In this study, we identified and characterized a novel 5-HTR from the sea cucumber Apostichopus japonicus (Aj5-HT_4/6 ). The cloned Aj5-HT_4/6 open reading frame comprised 1290 bp and encoded 429 amino acids. Bioinformatic analysis of the receptor indicated that it was a member of the class A of the G protein-coupled receptor family. Further experiments using Aj5-HT_4/6 -transfected HEK293 cells demonstrated that treatment with 5-HT could induce rapid internalization of Aj5-HT_4/6 fused with enhanced green fluorescent protein from the cell surface into the cytoplasm and triggered a significant increase in levels of the second messenger cAMP as well as mitogen-activated protein kinase phosphorylation in a 5-HT dose-dependent manner. Quantitative real time-polymerase chain reaction demonstrated that Aj5-HT_4/6 was predominantly expressed in the muscle and respiratory tree, and its expression was significantly decreased during estivation. Taken together, these results imply that Aj5-HT_4/6 is potentially involved in the movement and metabolism of the sea cucumber.

Synergistic Effect of Several Neurotransmitters in PFC-NAc-VTA Neural Circuit for the Anti-Depression Effect of Shuganheweitang in a Chronic Unpredictable Mild Stress Model

Depression, a major worldwide mental disorder, leads to massive disability and can result in death. The PFC-NAc-VTA neuro circuit is related to emotional, neurovegetative, and cognitive functions, which emerge as a circuit-level framework for understanding reward deficits in depression. Neurotransmitters, which are widely distributed in different brain regions, are important detected targets for the evaluation of depression. Shuganheweitang (SGHWT) is a popular prescription in clinical therapy for depression. In order to investigate its possible pharmacodynamics and anti-depressive mechanism, the complex plant material was separated into different fractions. These in low and high doses, along with low and high doses of SGHWT were tested in animal behavior tests. The low and high doses of SGHWT were more effective than the various fractions, which indicate the importance of synergistic function in traditional Chinese medicine. Furthermore, amino acid (GABA, Glu) and monoamine neurotransmitters (DA, 5-HT, NA, 5-HIAA) in the PFC-NAc-VTA neuro circuit were investigated by UPLC-MS/MS. The level trend of DA and 5-HT were consistent in the PFC-NAc-VTA neuro circuit, whereas 5-HIAA was decreased in the PFC, Glu was decreased in the PFC and VTA, and NA and GABA were decreased in the NAc. The results indicate that the pathogenesis of depression is associated with dysfunction of the PFC-NAc-VTA neural circuit, mainly through the neural projection effects of neurotransmitters associated with various brain regions in the neural circuit. PCA and OPLS-DA score plots demonstrated the similarities of individuals within each group and the differences among the groups. In this study, SGHWT could regulate the concentration level of different neurotransmitters in the PFC-NAc-VTA neuro circuit to improve the depression, which benefitted from the recognition of the brain reward circuitry in mood disorders.

Oxytocin signaling in the treatment of drug addiction: Therapeutic opportunities and challenges

Drug addiction is one of the leading causes of mortality worldwide. Despite great advances were achieved in understanding the neurobiology of drug addiction, the therapeutic options are severely limited, with poor effectiveness and serious side effects. The neuropeptide oxytocin (OXT) is well known for its effects on uterine contraction, sexual/maternal behaviors, social affiliation, stress and learning/memory by interacting with the OXT receptor and other neuromodulators. Emerging evidence suggests that the acute or chronic exposure to drugs can affect the OXT system. Additionally, OXT administration can ameliorate a wide range of abused drug-induced neurobehavioral changes. Overall, OXT not only suppresses drug reward in the binge stage of drug addiction, but also reduces stress responses and social impairments during the withdrawal stage and, finally, prevents drug/cue/stress-induced reinstatement. More importantly, clinical studies have also shown that OXT can exert beneficial effects on reducing substance use disorders of a series of drugs, such as heroin, cocaine, alcohol, cannabis and nicotine. Thus, the present review focuses on the role of OXT in treating drug addiction, including the preclinical and clinical therapeutic potential of OXT and its analogs on the neurobiological perspectives of drugs, to provide a better insight of the efficacy of OXT as a clinical addiction therapeutic agent.

Basolateral Amygdala Serotonin 2C Receptor Regulates Emotional Disorder-Related Symptoms Induced by Chronic Methamphetamine Administration

Globally, methamphetamine (MA) is the second most abused drug, with psychotic symptoms being one of the most common adverse effects. Emotional disorders induced by MA abuse have been widely reported both in human and animal models; however, the mechanisms underlying such disorders have not yet been fully elucidated. In this study, a chronic MA administration mouse model was utilized to elucidate the serotonergic pathway involved in MA-induced emotional disorders. After 4 weeks of MA administration, the animals exhibited significantly increased depressive and anxious symptoms. Molecular and morphological evidence showed that chronic MA administration reduced the expression of the 5-hydroxytryptamine (5-HT) rate-limiting enzyme, tryptophan hydroxylase 2, in the dorsal raphe and the concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid in the basolateral amygdala (BLA) nuclei. Alterations in both 5-HT and 5-HT receptor levels occurred simultaneously in BLA; quantitative polymerase chain reaction, western blotting, and fluorescence analysis revealed that the expression of the 5-HT2C receptor (5-HT_2CR) increased. Neuropharmacology and virus-mediated silencing strategies confirmed that targeting 5-HT_2CR reversed the depressive and anxious behaviors induced by chronic MA administration. In the BLA, 5-HT_2CR-positive cells co-localized with GABAergic interneurons. The inactivation of 5-HT_2CR ameliorated impaired GABAergic inhibition and decreased BLA activation. Thus, herein, for the first time, we report that the abnormal regulation of 5-HT_2CR is involved in the manifestation of emotional disorder-like symptoms induced by chronic MA use. Our study suggests that 5-HT_2CR in the BLA is a promising clinical target for the treatment of MA-induced emotional disorders.

Soft Drink Consumption in Young Mexican Adults Is Associated with Higher Total Body Fat Percentage in Men but Not in Women

A high consumption of soft drinks (SDs) has been linked with the development of anthropometric and metabolic alterations. We evaluate the association between SD consumption and some anthropometric and metabolic variables. This study is an observational study, using a sample of 394 university students, of which 158 were men (40.1%) and 238 women (59.9%), between 18 and 30 years. An SD intake questionnaire provided the consumption of different SDs. The participants' weight, height, and waist and hip circumferences were collected. Metabolic biomarkers were analyzed. The average intake of caloric SDs (CSDs) was 1193.6 ± 1534.8 mL/week and 84.5 ± 115.02 mL/week for non-caloric SDs (NCSDs). Sex differences were found in the amount of SD consumption and these statistical differences were driven by those men subjects with a high total body fat percentage (TBF%). In men, correlations were found between the intake of CSDs and the body mass index, waist and hip circumferences, TBF%, and visceral fat percentage. In woman, a correlation was found with glucose and triglycerides. The prediction model revealed that the intake of CSDs predicts TBF% and low-density lipoprotein only in men. A high amount of CSD consumption in men was associated with a high TBF%, and this may be predictive of future development of metabolic abnormalities.

Reward Contributions to Serotonergic Functions

The brain serotonin systems participate in numerous aspects of reward processing, although it remains elusive how exactly serotonin signals regulate neural computation and reward-related behavior. The application of optogenetics and imaging techniques during the last decade has provided many insights. Here, we review recent progress on the organization and physiology of the dorsal raphe serotonin neurons and the relationships between their activity and behavioral functions in the context of reward processing. We also discuss several interesting theories on serotonin's function and how these theories may be reconciled by the possibility that serotonin, acting in synergy with coreleased glutamate, tracks and calculates the so-called beneficialness of the current state to guide an animal's behavior in dynamic environments.

A mechanistic account of serotonin's impact on mood

Selective serotonin reuptake inhibitors (SSRIs) constitute a first-line antidepressant intervention, though the precise cognitive and computational mechanisms that explain treatment response remain elusive. Using week-long SSRI treatment in healthy volunteer participants, we show serotonin enhances the impact of experimentally induced positive affect on learning of novel, and reconsolidation of previously learned, reward associations. Computational modelling indicated these effects are best accounted for by a boost in subjective reward perception during learning, following a positive, but not negative, mood induction. Thus, instead of influencing affect or reward sensitivity directly, SSRIs might amplify an interaction between the two, giving rise to a delayed mood response. We suggest this modulation of affect-learning dynamics may explain the evolution of a gradual mood improvement seen with these agents and provides a novel candidate mechanism for the unfolding of serotonin’s antidepressant effects over time.

The cognitive computational mechanisms underlying the antidepressant treatment response of SSRIs is not well understood. Here the authors show that SSRI treatment in healthy subjects for a week manifests as an amplification of the perception of positive outcomes when learning occurs in a positive mood setting.

Converging Relationships of Obesity and Hyperuricemia with Special Reference to Metabolic Disorders and Plausible Therapeutic Implications

BACKGROUND

Obesity and hyperuricemia mutually influence metabolic syndrome. This study discusses the metabolic relationships between obesity and hyperuricemia in terms of pathophysiology, complications, and treatments.

METHODS

We searched for preclinical or clinical studies on the pathophysiology, complications, and therapy of obesity and hyperuricemia on the PubMed database.

RESULTS

In this systemic review, we summarized our searching results on topics of pathophysiology, complications and therapeutic strategy. In pathophysiology, we firstly introduce genetic variations for obesity, hyperuricemia and their relationships by genetic studies. Secondly, we talk about the epigenetic influences on obesity and hyperuricemia. Thirdly, we describe the central metabolic regulation and the role of hyperuricemia. Then, we refer to the character of adipose tissue inflammation and oxidative stress in the obesity and hyperuricemia. In the last part of this topic, we reviewed the critical links of gut microbiota in the obesity and hyperuricemia. In the following part, we review the pathophysiology of major complications in obesity and hyperuricemia including insulin resistance and type 2 diabetes mellitus, chronic kidney disease, cardiovascular diseases, and cancers. Finally, we recapitulate the therapeutic strategies especially the novel pharmaceutic interventions for obesity and hyperuricemia, which concurrently show the mutual metabolic influences between two diseases.

CONCLUSION

The data reviewed here delineate the metabolic relationships between obesity and hyperuricemia, and provide a comprehensive overview of the therapeutic targets for the management of metabolic syndromes.

Enhancement of Aggression Induced by Isolation Rearing is Associated with a Lack of Central Serotonin

Isolation rearing (IR) enhances aggressive behavior, and the central serotonin (5-hydroxytryptamine, 5-HT) system has been linked to IR-induced aggression. However, whether the alteration of central serotonin is the cause or consequence of enhanced aggression is still unknown. In the present study, using mice deficient in central serotonin Tph2^-/- and Lmx1b^-/-, we examined the association between central serotonin and aggression with or without social isolation. We demonstrated that central serotonergic neurons are critical for the enhanced aggression after IR. 5-HT depletion in wild-type mice increased aggression. On the other hand, application of 5-HT in Lmx1b^-/- mice inhibited the enhancement of aggression under social isolation conditions. Dopamine was downregulated in Lmx1b^-/- mice. Similar to 5-HT, L-DOPA decreased aggression in Lmx1b^-/- mice. Our results link the serotoninergic system directly to aggression and this may have clinical implications for aggression-related human conditions.

Serotonergic, Dopaminergic, and Noradrenergic Modulation of Erotic Stimulus Processing in the Male Human Brain

Human sexual behavior is mediated by a complex interplay of cerebral and spinal centers, as well as hormonal, peripheral, and autonomic functions. Neuroimaging studies identified central neural signatures of human sexual responses comprising neural emotional, motivational, autonomic, and cognitive components. However, empirical evidence regarding the neuromodulation of these neural signatures of human sexual responses was scarce for decades. Pharmacological functional magnetic resonance imaging (fMRI) provides a valuable tool to examine the interaction between neuromodulator systems and functional network anatomy relevant for human sexual behavior. In addition, this approach enables the examination of potential neural mechanisms regarding treatment-related sexual dysfunction under psychopharmacological agents. In this article, we introduce common neurobiological concepts regarding cerebral sexual responses based on neuroimaging findings and we discuss challenges and findings regarding investigating the neuromodulation of neural sexual stimulus processing. In particular, we summarize findings from our research program investigating how neural correlates of sexual stimulus processing are modulated by serotonergic, dopaminergic, and noradrenergic antidepressant medication in healthy males.

Dorsal Raphe Dual Serotonin-Glutamate Neurons Drive Reward by Establishing Excitatory Synapses on VTA Mesoaccumbens Dopamine Neurons

Dorsal raphe (DR) serotonin neurons provide a major input to the ventral tegmental area (VTA). Here, we show that DR serotonin transporter (SERT) neurons establish both asymmetric and symmetric synapses on VTA dopamine neurons, but most of these synapses are asymmetric. Moreover, the DR-SERT terminals making asymmetric synapses on VTA dopamine neurons coexpress vesicular glutamate transporter 3 (VGluT3; transporter for accumulation of glutamate for its synaptic release), suggesting the excitatory nature of these synapses. VTA photoactivation of DR-SERT fibers promotes conditioned place preference, elicits excitatory currents on mesoaccumbens dopamine neurons, increases their firing, and evokes dopamine release in nucleus accumbens. These effects are blocked by VTA inactivation of glutamate and serotonin receptors, supporting the idea of glutamate release in VTA from dual DR SERT-VGluT3 inputs. Our findings suggest a path-specific input from DR serotonergic neurons to VTA that promotes reward by the release of glutamate and activation of mesoaccumbens dopamine neurons.

The abuse potential of medical psilocybin according to the 8 factors of the Controlled Substances Act

This review assesses the abuse potential of medically-administered psilocybin, following the structure of the 8 factors of the US Controlled Substances Act (CSA). Research suggests the potential safety and efficacy of psilocybin in treating cancer-related psychiatric distress and substance use disorders, setting the occasion for this review. A more extensive assessment of abuse potential according to an 8-factor analysis would eventually be required to guide appropriate schedule placement. Psilocybin, like other 5-HT2A agonist classic psychedelics, has limited reinforcing effects, supporting marginal, transient non-human self-administration. Nonetheless, mushrooms with variable psilocybin content are used illicitly, with a few lifetime use occasions being normative among users. Potential harms include dangerous behavior in unprepared, unsupervised users, and exacerbation of mental illness in those with or predisposed to psychotic disorders. However, scope of use and associated harms are low compared to prototypical abused drugs, and the medical model addresses these concerns with dose control, patient screening, preparation and follow-up, and session supervision in a medical facility. CONCLUSIONS: (1) psilocybin has an abuse potential appropriate for CSA scheduling if approved as medicine; (2) psilocybin can provide therapeutic benefits that may support the development of an approvable New Drug Application (NDA) but further studies are required which this review describes; (3) adverse effects of medical psilocybin are manageable when administered according to risk management approaches; and (4) although further study is required, this review suggests that placement in Schedule IV may be appropriate if a psilocybin-containing medicine is approved. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

An overview of energy and metabolic regulation

The physiology and behaviors related to energy balance are monitored by the nervous and humoral systems. Because of the difficulty in treating diabetes and obesity, elucidating the energy balance mechanism and identifying critical targets for treatment are important research goals. Therefore, the purpose of this article is to describe energy regulation by the central nervous system (CNS) and peripheral humoral pathway. Homeostasis and rewarding are the basis of CNS regulation. Anorexigenic or orexigenic effects reflect the activities of the POMC/CART or NPY/AgRP neurons within the hypothalamus. Neurotransmitters have roles in food intake, and responsive brain nuclei have different functions related to food intake, glucose monitoring, reward processing. Peripheral gut- or adipose-derived hormones are the major source of peripheral humoral regulation systems. Nutrients or metabolites and gut microbiota affect metabolism via a discrete pathway. We also review the role of peripheral organs, the liver, adipose tissue, and skeletal muscle in peripheral regulation. We discuss these topics and how the body regulates metabolism.

Acute tramadol enhances brain activity associated with reward anticipation in the nucleus accumbens

BACKGROUND

Tramadol is an analgesic with monoamine reuptake inhibition and μ-opioid receptor activation. Although tramadol has been widely used for treatment of various pain conditions, there is controversy over the risk of abuse potential. We examined the effects of tramadol on the reward system in humans using functional magnetic resonance imaging (fMRI) to assess the potential of tramadol for drug abuse or dependence.

METHODS

A randomized, double-blind, placebo-controlled, crossover study was conducted for 19 healthy adults under tramadol or placebo. In association with subjective mood questionnaires, monetary incentive delay (MID) task was performed to assess the neural response to reward anticipation during fMRI. Subjective mood measures and blood oxygenation level-dependent (BOLD) signal during gain and loss anticipation were compared between tramadol and placebo.

RESULTS

Tramadol significantly reduced anxiety (Z = - 2.513, p = 0.012) and enhanced vigor (Z = - 2.725, p = 0.006) compared with placebo. By Mood Rating Scale, tramadol provoked contented (Z = - 2.316, p = 0.021), relaxed (Z = - 2.236, p = 0.025), and amicable feelings (Z = - 2.015, p = 0.044) as well as increased alertness (Z = - 1.972, p = 0.049) and contentedness domains (Z = - 2.174, p = 0.030) compared with placebo. Several brain regions including nucleus accumbens (NAc) were activated during gain anticipation in the MID task under both tramadol and placebo. Tramadol increased the %BOLD signal change in NAc at +¥500 cue significantly more than the placebo (Z = - 2.295, p = 0.022).

CONCLUSION

Tramadol enhances the reward system and thereby may have abuse potential or precipitate drug abuse in human.

Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders

Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.

Antidepressive-like effect of imperatorin from Angelica dahurica in prenatally stressed offspring rats through 5-hydroxytryptamine system

Adolescence is a time of continued brain maturation, particularly in limbic and cortical regions, which undoubtedly plays a role in the physiological and emotional changes. Prenatally stressed offspring rats were used to investigate the potential antidepressive-like effects of imperatorin (IMP) extracted from the root of radix angelica. After 4 weeks of treatment of IMP, behavioral tests (sucrose-preference test, forced-swimming test, and open-field test) were measured. 5-hydroxytryptamine (5-HT) concentration in the hippocampus and frontal cortex was measured using an enzyme-linked immunosorbent assay. Serotonin transporters (5-HTT) and 5-HT1A receptor (5-HT1AR) mRNA expression in the hippocampus and frontal cortex were also determined by real-time PCR. Administration with IMP (15 and 30 mg/kg/day, intragastrically) for 28 days markedly increased the percentage of sucrose (anhedonia), decreased the immobility time, and increased the number of total crossings, center crossings, rearing, and grooming in the male prenatally stressed offspring. Meanwhile, we found that 5-HT concentration in the hippocampus and frontal cortex was significantly increased in the IMP-treated group. Subsequently, we found significantly decreased 5-HTT and increased 5-HT1AR mRNA expressions in the hippocampus and frontal cortex after IMP treatment in the prenatally stressed male offspring. IMP showed antidepressive-like effects and increased 5-HT concentration in male prenatally stressed offspring, suggesting that IMP could be of therapeutic use in preventing depressive-like behavior in adolescence.

Humans quickly learn to blink strategically in response to environmental task demands

Eye blinking is one of the most frequent human actions. The control of blinking is thought to reflect complex interactions between maintaining clear and healthy vision and influences tied to central dopaminergic functions including cognitive states, psychological factors, and medical conditions. The most imminent consequence of blinking is a temporary loss of vision. Minimizing this loss of information is a prominent explanation for changes in blink rates and temporarily suppressed blinks, but quantifying this loss is difficult, as environmental regularities are usually complex and unknown. Here we used a controlled detection experiment with parametrically generated event statistics to investigate human blinking control. Subjects were able to learn environmental regularities and adapted their blinking behavior strategically to better detect future events. Crucially, our design enabled us to develop a computational model that allows quantifying the consequence of blinking in terms of task performance. The model formalizes ideas from active perception by describing blinking in terms of optimal control in trading off intrinsic costs for blink suppression with task-related costs for missing an event under perceptual uncertainty. Remarkably, this model not only is sufficient to reproduce key characteristics of the observed blinking behavior such as blink suppression and blink compensation but also predicts without further assumptions the well-known and diverse distributions of time intervals between blinks, for which an explanation has long been elusive.

A dose-response study of separate and combined effects of the serotonin agonist 8-OH-DPAT and the dopamine agonist quinpirole on locomotor sensitization, cross-sensitization, and conditioned activity

Chronic treatment with the dopamine D2/D3 agonist, quinpirole, or the serotonin 1A agonist, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), induces behavioral sensitization. It is not known whether both drugs produce sensitization through a shared mechanism. Here, we examine whether quinpirole and 8-OH-DPAT show cross-sensitization and impact sensitization, as would be expected from shared mechanisms. Male rats (N=208) were assigned randomly to 16 groups formed by crossing four doses of quinpirole (0, 0.03125, 0.0625, or 0.125 mg/kg) with four doses of 8-OH-DPAT (0, 0.03125, 0.625, or 0.125 mg/kg). After a course of 10 drug treatments administered twice per week in locomotor activity chambers, all groups were challenged on separate tests with quinpirole (0.1 mg/kg), 8-OH-DPAT (0.1 mg/kg), or saline, and locomotor activity was evaluated. Challenge tests with quinpirole and 8-OHDPAT showed no cross-sensitization between the drugs. Chronic quinpirole (0.125 mg/kg) administration induced a sensitized quinpirole response that was attenuated dose-dependently by chronic 8-OH-DPAT cotreatment. Cotreatment with quinpirole (0.0625 mg/kg) and 8-OH-DPAT (all doses) induced quinpirole sensitization. Chronic 8-OH-DPAT (0.125 mg/kg) induced a sensitized 8-OHDPAT response that was prevented by chronic cotreatment with the lowest but not the highest dose of quinpirole. Cotreatment with 8-OHDPAT (0.0625) and quinpirole (0.125 mg/kg) induced sensitization to 8-OH-DPAT. The saline challenge test showed elevated locomotor activity in chronic quinpirole (0.125 mg/kg) and 8-OHDPAT (0.0625, 0.125 mg/kg) alone groups, and in seven of nine cotreated groups. The absence of cross-sensitization suggests separate mechanisms of sensitization to quinpirole and 8-OH-DPAT. Cotreatment effects suggest that induction of sensitization can be modulated by serotonin 1A and D2/D3 activity.

An Update on the Role of Serotonin and its Interplay with Dopamine for Reward

The specific role of serotonin and its interplay with dopamine (DA) in adaptive, reward guided behavior as well as drug dependance, still remains elusive. Recently, novel methods allowed cell type specific anatomical, functional and interventional analyses of serotonergic and dopaminergic circuits, promising significant advancement in understanding their functional roles. Furthermore, it is increasingly recognized that co-release of neurotransmitters is functionally relevant, understanding of which is required in order to interpret results of pharmacological studies and their relationship to neural recordings. Here, we review recent animal studies employing such techniques with the aim to connect their results to effects observed in human pharmacological studies and subjective effects of drugs. It appears that the additive effect of serotonin and DA conveys significant reward related information and is subjectively highly euphorizing. Neither DA nor serotonin alone have such an effect. This coincides with optogenetically targeted recordings in mice, where the dopaminergic system codes reward prediction errors (PE), and the serotonergic system mainly unsigned PE. Overall, this pattern of results indicates that joint activity between both systems carries essential reward information and invites parallel investigation of both neurotransmitter systems.

Serotonin 2B Receptors in Mesoaccumbens Dopamine Pathway Regulate Cocaine Responses

Addiction is a maladaptive pattern of behavior following repeated use of reinforcing drugs in predisposed individuals, leading to lifelong changes. Common among these changes are alterations of neurons releasing dopamine in the ventral and dorsal territories of the striatum. The serotonin 5-HT_2B receptor has been involved in various behaviors, including impulsivity, response to antidepressants, and response to psychostimulants, pointing toward putative interactions with the dopamine system. Despite these findings, it remains unknown whether 5-HT_2B receptors directly modulate dopaminergic activity and the possible mechanisms involved. To answer these questions, we investigated the contribution of 5-HT_2B receptors to cocaine-dependent behavioral responses. Male mice permanently lacking 5-HT_2B receptors, even restricted to dopamine neurons, developed heightened cocaine-induced locomotor responses. Retrograde tracing combined with single-cell mRNA amplification indicated that 5-HT_2B receptors are expressed by mesolimbic dopamine neurons. In vivo and ex vivo electrophysiological recordings showed that 5-HT_2B-receptor inactivation in dopamine neurons affects their neuronal activity and increases AMPA-mediated over NMDA-mediated excitatory synaptic currents. These changes are associated with lower ventral striatum dopamine activity and blunted cocaine self-administration. These data identify the 5-HT_2B receptor as a pharmacological intermediate and provide mechanistic insight into attenuated dopamine tone following exposure to drugs of abuse.SIGNIFICANCE STATEMENT Here we report that mice lacking 5-HT_2B receptors totally or exclusively in dopamine neurons exhibit heightened cocaine-induced locomotor responses. Despite the sensitized state of these mice, we found that associated changes include lower ventral striatum dopamine activity and lower cocaine operant self-administration. We described the selective expression of 5-HT_2B receptors in a subpopulation of dopamine neurons sending axons to the ventral striatum. Increased bursting in vivo properties of these dopamine neurons and a concomitant increase in AMPA synaptic transmission to ex vivo dopamine neurons were found in mice lacking 5-HT_2B receptors. These data support the idea that the chronic 5-HT_2B-receptor inhibition makes mice behave like animals already exposed to cocaine with higher cocaine-induced locomotion associated with changes in dopamine neuron reactivity.

Exploring a post-traumatic stress disorder paradigm in Flinders sensitive line rats to model treatment-resistant depression I: bio-behavioural validation and response to imipramine

OBJECTIVE

Co-morbid depression with post-traumatic stress disorder (PTSD) is often treatment resistant. In developing a preclinical model of treatment-resistant depression (TRD), we combined animal models of depression and PTSD to produce an animal with more severe as well as treatment-resistant depressive-like behaviours.

METHODS

Male Flinders sensitive line (FSL) rats, a genetic animal model of depression, were exposed to a stress re-stress model of PTSD [time-dependent sensitisation (TDS)] and compared with stress-naive controls. Seven days after TDS stress, depressive-like and coping behaviours as well as hippocampal and cortical noradrenaline (NA) and 5-hydroxyindoleacetic acid (5HIAA) levels were analysed. Response to sub-chronic imipramine treatment (IMI; 10 mg/kg s.c.×7 days) was subsequently studied.

RESULTS

FSL rats demonstrated bio-behavioural characteristics of depression. Exposure to TDS stress in FSL rats correlated negatively with weight gain, while demonstrating reduced swimming behaviour and increased immobility versus unstressed FSL rats. IMI significantly reversed depressive-like (immobility) behaviour and enhanced active coping behaviour (swimming and climbing) in FSL rats. The latter was significantly attenuated in FSL rats exposed to TDS versus unstressed FSL rats. IMI reversed reduced 5HIAA levels in unstressed FSL rats, whereas exposure to TDS negated this effect. Lowered NA levels in FSL rats were sustained after TDS with IMI significantly reversing this in the hippocampus.

CONCLUSION

Combining a gene-X-environment model of depression with a PTSD paradigm produces exaggerated depressive-like symptoms that display an attenuated response to antidepressant treatment. This work confirms combining FSL rats with TDS exposure as a putative animal model of TRD.

Trait Impulsivity and the Externalizing Spectrum

This article reviews evidence that trait impulsivity-expressed early in life as the hyperactive-impulsive and combined presentations of attention-deficit/hyperactivity disorder (ADHD)-is a bottom-up, subcortically mediated vulnerability to all externalizing disorders. This vulnerability arises from deficient mesolimbic dopamine responding, which imbues psychological states (irritability, discontentment) that motivate excessive approach behavior (hyperactivity, impulsivity). Through complex interactions with (a) aversive motivational states that arise from largely independent subcortical systems, (b) emotion regulatory mechanisms that arise from top-down, cortical modulation of subcortical neural function, and (c) environmental risk factors that shape and maintain emotion dysregulation, trait impulsivity confers vulnerability to increasingly severe externalizing behaviors across development. This perspective highlights the importance of identifying transdiagnostic neural vulnerabilities to psychopathology; dovetails with the hierarchical, latent structure of psychopathology; and suggests that progression along the externalizing spectrum is an ontogenic process whereby a common, multifactorially inherited trait interacts with endogenous and exogenous influences to yield increasingly intractable externalizing behaviors across development.

Identification and functional characterisation of 5-HT4 receptor in sea cucumber Apostichopus japonicus (Selenka)

Serotonin (5-HT) is an important neurotransmitter and neuromodulator that controls a variety of sensory and motor functions through 5-HT receptors (5-HTRs). The 5-HT4R subfamily is linked to Gs proteins, which activate adenylyl cyclases (ACs), and is involved in many responses in peripheral organs. In this study, the 5-HT4R from Apostichopus japonicus (Aj5-HT4R) was identified and characterised. The cloned full-length Aj5-HT4R cDNA is 1,544 bp long and contains an open reading frame 1,011 bp in length encoding 336 amino acid proteins. Bioinformatics analysis of the Aj5-HT4R protein indicated this receptor was a member of class A G protein coupled receptor (GPCR) family. Further experiments using Aj5-HT4R-transfected HEK293 cells demonstrated that treatment with 5-HT triggered a significant increase in intracellular cAMP level in a dose-dependent manner and induced a rapid internalisation of Aj5-HT4R fused with enhanced green fluorescent protein (Aj5-HT4R-EGFP) from the cell surface into the cytoplasm. In addition, the transcriptional profiles of Aj5-HT4R in aestivating A. japonicas and phosphofructokinase (AjPFK) in 5-HT administrated A. japonicus have been analysed by real-time PCR assays. Results have led to a basic understanding of Aj5-HT4R in A. japonicus, and provide a foundation for further exploration of the cell signaling and regulatory functions of this receptor.

Optimizing laboratory animal stress paradigms: The H-H* experimental design

Major advances in behavioral neuroscience have been facilitated by the development of consistent and highly reproducible experimental paradigms that have been widely adopted. In contrast, many different experimental approaches have been employed to expose laboratory mice and rats to acute versus chronic intermittent stress. An argument is advanced in this review that more consistent approaches to the design of chronic intermittent stress experiments would provide greater reproducibility of results across laboratories and greater reliability relating to various neural, endocrine, immune, genetic, and behavioral adaptations. As an example, the H-H* experimental design incorporates control, homotypic (H), and heterotypic (H*) groups and allows for comparisons across groups, where each animal is exposed to the same stressor, but that stressor has vastly different biological and behavioral effects depending upon each animal's prior stress history. Implementation of the H-H* experimental paradigm makes possible a delineation of transcriptional changes and neural, endocrine, and immune pathways that are activated in precisely defined stressor contexts.

Can We Selectively Reduce Appetite for Energy-Dense Foods? An Overview of Pharmacological Strategies for Modification of Food Preference Behavior

Excessive intake of food, especially palatable and energy-dense carbohydrates and fats, is largely responsible for the growing incidence of obesity worldwide. Although there are a number of candidate antiobesity drugs, only a few of them have been proven able to inhibit appetite for palatable foods without the concurrent reduction in regular food consumption. In this review, we discuss the interrelationships between homeostatic and hedonic food intake control mechanisms in promoting overeating with palatable foods and assess the potential usefulness of systemically administered pharmaceuticals that impinge on the endogenous cannabinoid, opioid, aminergic, cholinergic, and peptidergic systems in the modification of food preference behavior. Also, certain dietary supplements with the potency to reduce specifically palatable food intake are presented. Based on human and animal studies, we indicate the most promising therapies and agents that influence the effectiveness of appetite-modifying drugs. It should be stressed, however, that most of the data included in our review come from preclinical studies; therefore, further investigations aimed at confirming the effectiveness and safety of the aforementioned medications in the treatment of obese humans are necessary.

5-HT2A Serotonin Receptor Density in Adult Male Rats' Hippocampus after Morphine-based Conditioned Place Preference

INTRODUCTION

A close interaction exists between the brain opioid and serotonin (5-HT) neurotransmitter systems. Brain neurotransmitter 5-HT plays an important role in the regulation of reward-related processing. However, a few studies have investigated the potential role of 5-HT2A receptors in this behavior. Therefore, the aim of the present study was to assess the influence of morphine and Conditioned Place Preference (CPP) on the density of 5-HT2A receptor in neurons of rat hippocampal formation.

METHODS

Morphine (10 mg/kg, IP) was injected in male Wistar rats for 7 consecutive days (intervention group), but control rats received just normal saline (1 mL/kg, IP). We used a hotplate test of analgesia to assess induction of tolerance to analgesic effects of morphine on days 1 and 8 of injections. Later, two groups of rats were sacrificed one day after 7 days of injections, their whole brains removed, and the striatum and PFC immediately dissected. Then, the NR1 gene expression was examined with a semi-quantitative RT-PCR method.

RESULTS

Our data showed that the maximum response was obtained with 2.5 mg/kg of morphine. The density of 5-HT2A receptor in different areas of the hippocampus increased significantly at sham-morphine and CPP groups (P<0.05). On the other hand, the CPP groups had more 5-HT2A receptors than sham-morphine groups and also the sham-morphine groups had more 5-HT2A receptors than the control groups.

CONCLUSION

We concluded that the phenomenon of conditioned place preference induced by morphine can cause a significant increase in the number of serotonin 5-HT2A receptors in neurons of all areas of hippocampus.

Pattern of distribution of serotonergic fibers to the amygdala and extended amygdala in the rat

As is well recognized, serotonergic (5-HT) fibers distribute widely throughout the forebrain, including the amygdala. Although a few reports have examined the 5-HT innervation of select nuclei of the amygdala in the rat, no previous report has described overall 5-HT projections to the amygdala in the rat. Using immunostaining for the serotonin transporter, SERT, we describe the complete pattern of distribution of 5-HT fibers to the amygdala (proper) and to the extended amygdala in the rat. Based on its ontogenetic origins, the amygdala was subdivided into two major parts, pallial and subpallial components, with the pallial component further divided into superficial and deep nuclei (Olucha-Bordonau et al. 2015). SERT⁺ fibers were shown to distributed moderately to densely to the deep and cortical pallial nuclei, but, by contrast, lightly to the subpallial nuclei. Specifically, 1) of the deep pallial nuclei, the lateral, basolateral, and basomedial nuclei contained a very dense concentration of 5-HT fibers; 2) of the cortical pallial nuclei, the anterior cortical and amygdala-cortical transition zone rostrally and the posteromedial and posterolateral nuclei caudally contained a moderate concentration of 5-HT fibers; and 3) of the subpallial nuclei, the anterior nuclei and the rostral part of the medial (Me) nuclei contained a moderate concentration of 5-HT fibers, whereas caudal regions of Me as well as the central nuclei and the intercalated nuclei contained a sparse/light concentration of 5-HT fibers. With regard to the extended amygdala (primarily the bed nucleus of stria terminalis; BST), on the whole, the BST contained moderate numbers of 5-HT fibers, spread fairly uniformly throughout BST. The findings are discussed with respect to a critical serotonergic influence on the amygdala, particularly on the basal complex, and on the extended amygdala in the control of states of fear and anxiety. J. Comp. Neurol. 525:116-139, 2017. © 2016 Wiley Periodicals, Inc.

Peripheral Administration of Ethanol Results in a Correlated Increase in Dopamine and Serotonin Within the Posterior Ventral Tegmental Area

AIMS

Two critical neurotransmitter systems regulating ethanol (EtOH) reward are serotonin (5-HT) and dopamine (DA). Within the posterior ventral tegmental area (pVTA), 5-HT receptors have been shown to regulate DA neuronal activity. Increased pVTA neuronal activity has been linked to drug reinforcement. The current experiment sought to determine the effect of EtOH on 5-HT and DA levels within the pVTA.

METHODS

Wistar rats were implanted with cannula aimed at the pVTA. Neurochemical levels were determined using standard microdialysis procedures with concentric probes. Rats were randomly assigned to one of the five groups (n = 41; 7-9 per group) that were treated with 0-3.0 g/kg EtOH (intraperitoneally).

RESULTS

Ethanol produced increased extracellular DA levels in the pVTA that resembled an inverted U-shape dose-response curve with peak levels (~200% of baseline) at the 2.25 g/kg dose. The increase in DA levels was observed for an extended period of time (~100 minutes). The effects of EtOH on extracellular 5-HT levels in the pVTA also resembled an inverted U-shape dose-response curve. However, increased 5-HT levels were only observed during the initial post-injection sample. The increases in extracellular DA and 5-HT levels were significantly correlated.

CONCLUSION

The data indicate intraperitoneal EtOH administration stimulated the release of both 5-HT and DA within the pVTA, the levels of which were significantly correlated. Overall, the current findings suggest that the ability of EtOH to stimulate DA activity within the mesolimbic system may be modulated by increases in 5-HT release within the pVTA.

SHORT SUMMARY

Two critical neurotransmitter systems regulating ethanol reward are serotonin and dopamine. The current experiment determined that intraperitoneal ethanol administration increased serotonin and dopamine levels within the pVTA (levels were significantly correlated). The current findings suggest the ability of EtOH to stimulate serotonin and dopamine activity within the mesolimbic system.

Female Japanese quail with high levels of estradiol demonstrate cocaine-induced conditioned place preference

Preclinical research has indicated that females may be more sensitive to the rewarding properties of cocaine. However, the majority of this research has been done in rodent species. Environmental cues associated with human drug-taking behavior tend to be visual. Because rodents do not rely on the visual system as their primary sense modality, the use of a visually oriented species may add to our understanding of cue-elicited drug cravings and relapse. The present study examined the potential role of the steroid hormone, estradiol, in the rewarding properties of cocaine in female Japanese quail using a conditioned place preference (CPP) procedure. In the current experiment, female quail were housed on either an 8L:16D (light:dark) or 16L:8D (light:dark) cycle for 21 days to induce photoregression or photostimulation, respectively. They then received 10, 20, or 30 mg/kg cocaine, or saline during conditioning. Conditioning trials were carried out for 8 days, once per day for 30 min, for a total of 4 cocaine and 4 saline alternating conditioning trials. Results indicated that female quail housed in long-light conditions (16L:8D) had significantly higher levels of estradiol than short-cycle females. Additionally, photostimulated female quail developed a CPP to 10 and 20 mg/kg cocaine. Short-cycle females did not show cocaine-induced CPP to any dose tested. Results indicate that cocaine is dose-dependently rewarding to photostimulated female Japanese quail. Furthermore, the current findings suggest that estradiol may enhance the rewarding properties of cocaine in female quail. (PsycINFO Database Record