Distribution of 5-ht(1E) receptors in the mammalian brain and cerebral vasculature: an immunohistochemical and pharmacological study

Development of 2-Aminotetralin-Type Serotonin 5-HT1 Agonists: Molecular Determinants for Selective Binding and Signaling at 5-HT1A, 5-HT1B, 5-HT1D, and 5-HT1F Receptors

The serotonin (5-hydroxytryptamine, 5-HT) 5-HT1 G-protein coupled receptor subtypes (5-HT1A/1B/1D/1E/1F) share a high sequence homology, confounding development of subtype-specific ligands. This study used a 5-HT1 structure-based ligand design approach to develop subtype-selective ligands using a 5-substituted-2-aminotetralin (5-SAT) chemotype, leveraging results from pharmacological, molecular modeling, and mutagenesis studies to delineate molecular determinants for 5-SAT binding and function at 5-HT1 subtypes. 5-SATs demonstrated high affinity (Ki ≤ 25 nM) and at least 50-fold stereoselective preference ([2S] > [2R]) at 5-HT1A, 5-HT1B, and 5-HT1D receptors but essentially nil affinity (Ki > 1 μM) at 5-HT1F receptors. The 5-SATs tested were agonists with varying degrees of potency and efficacy, depending on chemotype substitution and 5-HT1 receptor subtype. Models were built from the 5-HT1A (cryo-EM), 5-HT1B (crystal), and 5-HT1D (cryo-EM) structures, and 5-SATs underwent docking studies with up to 1 μs molecular dynamics simulations. 5-SAT interactions observed at positions 3.33, 5.38, 5.42, 5.43, and 7.39 of 5-HT1 subtypes were confirmed with point mutation experiments. Additional 5-SATs were designed and synthesized to exploit experimental and computational results, yielding a new full efficacy 5-HT1A agonist with 100-fold selectivity over 5-HT1B/1D receptors. The results presented lay the foundation for the development of additional 5-HT1 subtype selective ligands for drug discovery purposes.

The discovery, structure, and function of 5-HTR1E serotonin receptor

Serotonin (5-hydroxytryptamine, 5-HT) is a unique neurotransmitter which can regulate various biological processes by activating thirteen different receptors. These serotonin receptors are divided into seven different classes based on their structure and functions. Since these receptors co-express in various tissue and cell types and share the same ligand (5-HT), it has been a challenge for the researchers to define specific pathway and separate physiological role for each of these serotonin receptors. Though the evidence of operational diversity of these receptors is continuously emerging, much work remains to be done. 5-HTR1E is a member of 5-HT1 receptor family which belongs to G-protein coupled receptors (GPCRs). Even after three decades since its discovery, 5-HTR1E remains the least explored serotonin receptor. Very high similarity with another family member (5-HTR1F) and its non-existence in mice or rats makes 5-HTR1E a difficult target to study. Despite these challenges, recent findings on the role of 5-HTR1E in neuroprotection and diseases such as cancer, have excited many researchers to explore this receptor in detail. Here, we provide the first review of 5-HTR1E, since its discovery in 1989 to 2023. We highlight the structural and functional characteristics of this important serotonin receptor in detail and propose future directions in developing 5-HTR1E as a drug target. Video Abstract.

Characterization of serotonin-5-HTR1E signaling pathways and its role in cell survival

5-Hydroxytryptamine receptor 1E (5-HTR1E) is reported to activate cyclic AMP (cAMP) and extracellular-signal related kinases (ERK) pathways via its ligands and binding partners, but the detailed mechanism underlying the serotonin-induced 5-HTR1E signaling is still not known. In the present study, we determined the cellular regulators of ERK and cAMP signaling pathways in response to serotonin-induced 5-HTR1E activation in 5-HTR1E overexpressing HEK293 cells. We found that Pertussis Toxin (PTX) treatment completely reversed the effect of serotonin-5-HTR1E mediated signaling on cAMP and ERK pathways, confirming the involvement of a Gαi-linked cascade. We also observed that Gβγ and Gq were not associated with 5-HTR1E activation, while blocking protein kinase A (PKA) inhibited ERK signaling only, and had no effect on cAMP. Additionally, serotonin-stimulated ERK1/2 phosphorylation was similar in 5-HTR1E overexpressing, β-arrestin-deficient HEK293 cells and is solely dependent on G protein signaling. siRNA mediated gene knockdown studies in SH-SY5Y cells revealed that the inhibition of 5-HTR1E reduced the expression of cMyc, Cyclin D1, Cyclin E and BCL2 genes which are related to cell cycle regulation and survival. MTT assays showed that 5-HTR1E knockdown in SHSY-5Y and U118 cells inhibited cell survival significantly. In addition to the signaling mechanism, we also performed RNA-seq analysis in 5-HTR1E overexpressing HEK293 cells and found that 5-HTR1E can regulate the expression of Receptor activity modifying protein 1 (RAMP1), Nuclear receptor 1 (NR4A1) and other Cyclin genes. These findings indicate that serotonin interaction with 5-HTR1E receptor simultaneously activates cAMP and ERK pathway in HEK293 cells and its expression is important for cell survival.

Characterization of serotonin-5-HTR1E signaling pathways and its role in cell survival

5-Hydroxy tryptamine receptor 1E (5-HTR1E) is reported to activate cAMP and ERK pathways via its ligands and binding partners, but the detailed mechanism underlying the serotonin induced 5-HTR1E signaling is still not known. In the present study, we determined the cellular regulators of ERK and cAMP signaling pathways in response to serotonin induced 5-HTR1E activation in 5-HTR1E overexpressing HEK293 cells. We found that Pertussis Toxin (PTX) treatment completely reversed the effect of serotonin-5-HTR1E mediated signaling on cAMP and ERK pathways, confirming the involvement of a Gαi-linked cascade. We also observed that Gβγ and Gq were not associated with 5-HTR1E activation, while blocking PKA inhibited ERK signaling only, and had no effect on cAMP. Additionally, serotonin-stimulated ERK1/2 phosphorylation was similar in 5-HTR1E overexpressing, β-arrestin-deficient HEK293 cells and is solely dependent on G protein signaling. siRNA mediated gene knockout studies in SH-SY5Y cells revealed that the inhibition of 5-HTR1E reduced the expression of cMyc, Cyclin D1, Cyclin E and BCL2 genes which are related to cell cycle regulation and survival. MTT assays showed that 5-HTR1E knockdown in SHSY-5Y and U118 cells inhibited cell survival significantly. In addition to the signaling mechanism, we also performed RNA-seq analysis in 5-HTR1E overexpressing HEK293 cells and found that 5-HTR1E can regulate the expression of Receptor activity modifying protein 1 ( RAMP1 ), Nuclear receptor 1 ( NR4A1 ) and other Cyclin genes. These findings indicate that serotonin interaction with 5-HTR1E receptor simultaneously activates cAMP and ERK pathway in HEK293 cells and its expression is important for cell survival.

Serotonin receptors in epilepsy: novel treatment targets?

Despite the availability of over 30 antiseizure medications (ASMs), there is no “one size fits it all,” so there is a continuing search for novel ASMs. There are divergent data demonstrating that modulation of distinct serotonin (5‐hydroxytryptamine, 5‐HT) receptors subtypes could be beneficial in the treatment of epilepsy and its comorbidities, whereas only a few ASM, such as fenfluramine (FA), act via 5‐HT. There are 14 different 5‐HT receptor subtypes, and most epilepsy studies focus on one or a few of these subtypes, using different animal models and different ligands. We reviewed the available evidence of each 5‐HT receptor subtype using MEDLINE up to July 2021. Our search included medical subject heading (MeSH) and free terms of each “5‐HT subtype” separately and its relation to “epilepsy or seizures.” Most research underlines the antiseizure activity of 5‐HT_{1A,1D,2A,2C,3} agonism and 5‐HT₆ antagonism. Consistently, FA, which has recently been approved for the treatment of seizures in Dravet syndrome, is an agonist of 5‐HT_1D,2A,2C receptors. Even though each study focused on a distinct seizure/epilepsy type and generalization of different findings could lead to false interpretations, we believe that the available preclinical and clinical studies emphasize the role of serotonergic modulation, especially stimulation, as a promising avenue in epilepsy treatment.

Serotonergic Neurons in the Chick Brainstem Express Various Serotonin Receptor Subfamily Genes

Serotonin (5-hydroxytryptamine, 5-HT) is a phylogenetically conserved modulatory neurotransmitter. In mammals, 5-HT plays an important role in the regulation of many mental states and the processing of emotions in the central nervous system. Serotonergic neurons in the central nervous system, including the dorsal raphe (DR) and median raphe (MR) nuclei, are spatially clustered in the brainstem and provide ascending innervation to the entire forebrain and midbrain. Both between and within the DR and MR, these serotonergic neurons have different cellular characteristics, developmental origin, connectivity, physiology, and related behavioral functions. Recently, an understanding of the heterogeneity of the DR and MR serotonergic neurons has been developed at the molecular level. In birds, emotion-related behavior is suggested to be modulated by the 5-HT system. However, correspondence between the raphe nuclei of birds and mammals, as well as the cellular heterogeneity in the serotonergic neurons of birds are poorly understood. To further understand the heterogeneity of serotonergic neurons in birds, we performed a molecular dissection of the chick brainstem using in situ hybridization. In this study, we prepared RNA probes for chick orthologs of the following serotonin receptor genes: 5-HTR1A, 5-HTR1B, 5-HTR1D, 5-HTR1E, 5-HTR1F, 5-HTR2A, 5-HTR2B, 5-HTR2C, 5-HTR3A, 5-HTR4, 5-HTR5A, and 5-HTR7. We showed that the expression pattern of 5-HT receptors in the serotonin neurons of chick DR and MR may vary, suggesting heterogeneity among and within the serotonin neurons of the DR and MR in the chick brainstem. Our findings regarding the molecular properties of serotonergic neurons in the bird raphe system will facilitate a good understanding of the correspondence between bird and mammalian raphes.

Novel interaction between neurotrophic factor-α1/carboxypeptidase E and serotonin receptor, 5-HTR1E, protects human neurons against oxidative/neuroexcitotoxic stress via β-arrestin/ERK signaling

Protecting neurons from death during oxidative and neuroexcitotoxic stress is key for preventing cognitive dysfunction. We uncovered a novel neuroprotective mechanism involving interaction between neurotrophic factor-α1 (NF-α1/carboxypeptidase E, CPE) and human 5-HTR1E, a G protein-coupled serotonin receptor with no previously known neurological function. Co-immunoprecipitation and pull-down assays confirmed interaction between NFα1/CPE and 5-HTR1E and 125I NF-α1/CPE-binding studies demonstrated saturable, high-affinity binding to 5-HTR1E in stably transfected HEK293 cells (Kd = 13.82 nM). Treatment of 5-HTR1E stable cells with NF-α1/CPE increased pERK 1/2 and pCREB levels which prevented a decrease in pro-survival protein, BCL2, during H2O2-induced oxidative stress. Cell survival assay in β-arrestin Knockout HEK293 cells showed that the NF-α1/CPE-5-HTR1E-mediated protection against oxidative stress was β-arrestin-dependent. Molecular dynamics studies revealed that NF-α1/CPE interacts with 5-HTR1E via 3 salt bridges, stabilized by several hydrogen bonds, independent of the serotonin pocket. Furthermore, after phosphorylating the C-terminal tail and intracellular loop 3 (ICL3) of NF-α1/CPE-5-HTR1E, it recruited β-arrestin1 by forming numerous salt bridges and hydrogen bonds to ICL2 and ICL3, leading to activation of β-arrestin1. Immunofluorescence studies showed 5-HTR1E and NF-α1/CPE are highly expressed and co-localized on cell surface of human hippocampal neurons. Importantly, knock-down of 5-HTR1E in human primary neurons diminished the NF-α1/CPE-mediated protection of these neurons against oxidative stress and glutamate neurotoxicity-induced cell death. Thus, NF-α1/CPE uniquely interacts with serotonin receptor 5-HTR1E to activate the β-arrestin/ERK/CREB/BCL2 pathway to mediate stress-induced neuroprotection.

Molecular Cloning and Functional Characterization of Three 5-HT Receptor Genes (HTR1B, HTR1E, and HTR1F) in Chickens

The serotonin (5-hydroxytryptamine, 5-HT) signaling system is involved in a variety of physiological functions, including the control of cognition, reward, learning, memory, and vasoconstriction in vertebrates. Contrary to the extensive studies in the mammalian system, little is known about the molecular characteristics of the avian serotonin signaling network. In this study, we cloned and characterized the full-length cDNA of three serotonin receptor genes (HTR1B, HTR1E and HTR1F) in chicken pituitaries. Synteny analyses indicated that HTR1B, HTR1E and HTR1F were highly conserved across vertebrates. Cell-based luciferase reporter assays showed that the three chicken HTRs were functional, capable of binding their natural ligands (5-HT) or selective agonists (CP94253, BRL54443, and LY344864) and inhibiting intracellular cAMP production in a dose-dependent manner. Moreover, activation of these receptors could stimulate the MAPK/ERK signaling cascade. Quantitative real-time PCR analyses revealed that HTR1B, HTR1E and HTR1F were primarily expressed in various brain regions and the pituitary. In cultured chicken pituitary cells, we found that LY344864 could significantly inhibit the secretion of PRL stimulated by vasoactive intestinal peptide (VIP) or forskolin, revealing that HTR1F might be involved in the release of prolactin in chicken. Our findings provide insights into the molecular mechanism and facilitate a better understanding of the serotonergic modulation via HTR1B, HTR1E and HTR1F in avian species.

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.

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

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

Sex and the serotonergic underpinnings of depression and migraine

Most psychiatric disorders demonstrate sex differences in their prevalence and symptomatology, and in their response to treatment. These differences are particularly pronounced in mood disorders. Differences in sex hormone levels are among the most overt distinctions between males and females and are thus an intuitive underpinning for these clinical observations. In fact, treatment with estrogen and testosterone was shown to exert antidepressant effects, which underscores this link. Changes to monoaminergic signaling in general, and serotonergic transmission in particular, are understood as central components of depressive pathophysiology. Thus, modulation of the serotonin system may serve as a mechanism via which sex hormones exert their clinical effects in mental health disorders. Over the past 20 years, various experimental approaches have been applied to identify modes of influence of sex and sex hormones on the serotonin system. This chapter provides an overview of different molecular components of the serotonin system, followed by a review of studies performed in animals and in humans with the purpose of elucidating sex hormone effects. Particular emphasis will be placed on studies performed with positron emission tomography, a method that allows for human in vivo molecular imaging and, therefore, assessment of effects in a clinically representative context. The studies addressed in this chapter provide a wealth of information on the interaction between sex, sex hormones, and serotonin in the brain. In general, they offer evidence for the concept that the influence of sex hormones on various components of the serotonin system may serve as an underpinning for the clinical effects these hormones demonstrate.

Serotonergic modulation across sensory modalities

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

Species Classification for Neuroscience Literature Based on Span of Interest Using Sequence-to-Sequence Learning Model

Large-scale neuroscience literature call for effective methods to mine the knowledge from species perspective to link the brain and neuroscience communities, neurorobotics, computing devices, and AI research communities. Structured knowledge can motivate researchers to better understand the functionality and structure of the brain and link the related resources and components. However, the abstracts of massive scientific works do not explicitly mention the species. Therefore, in addition to dictionary-based methods, we need to mine species using cognitive computing models that are more like the human reading process, and these methods can take advantage of the rich information in the literature. We also enable the model to automatically distinguish whether the mentioned species is the main research subject. Distinguishing the two situations can generate value at different levels of knowledge management. We propose SpecExplorer project which is used to explore the knowledge associations of different species for brain and neuroscience. This project frees humans from the tedious task of classifying neuroscience literature by species. Species classification task belongs to the multi-label classification which is more complex than the single-label classification due to the correlation between labels. To resolve this problem, we present the sequence-to-sequence classification framework to adaptively assign multiple species to the literature. To model the structure information of documents, we propose the hierarchical attentive decoding (HAD) to extract span of interest (SOI) for predicting each species. We create three datasets from PubMed and PMC corpora. We present two versions of annotation criteria (mention-based annotation and semantic-based annotation) for species research. Experiments demonstrate that our approach achieves improvements in the final results. Finally, we perform species-based analysis of brain diseases, brain cognitive functions, and proteins related to the hippocampus and provide potential research directions for certain species.

Therapeutic potential of serotonin 4 receptor for chronic depression and its associated comorbidity in the gut

The latest estimates from world health organization suggest that more than 450 million people are suffering from depression and other psychiatric conditions. Of these, 50-60% have been reported to have progression of gut diseases. In the last two decades, researchers introduced incipient physiological roles for serotonin (5-HT) receptors (5-HTRs), suggesting their importance as a potential pharmacological target in various psychiatric and gut diseases. A growing body of evidence suggests that 5-HT systems affect the brain-gut axis in depressive patients, which leads to gut comorbidity. Recently, preclinical trials of 5-HT4R agonists and antagonists were promising as antipsychotic and prokinetic agents. In the current review, we address the possible pharmacological role and contribution of 5-HT4R in the pathophysiology of chronic depression and associated gut abnormalities. Physiologically, during depression episodes, centers of the sympathetic and parasympathetic nervous system couple together with neuroendocrine systems to alter the function of hypothalamic-pituitary-adrenal (HPA) axis and enteric nervous system (ENS), which in turn leads to onset of gastrointestinal tract (GIT) disorders. Consecutively, the ENS governs a broad spectrum of physiological activities of gut, such as visceral pain and motility. During the stages of emotional stress, hyperactivity of the HPA axis alters the ENS response to physiological and noxious stimuli. Consecutively, stress-induced flare, swelling, hyperalgesia and altered reflexes in gut eventually lead to GIT disorders. In summary, the current review provides prospective information about the role and mechanism of 5-HT4R-based therapeutics for the treatment of depressive disorder and possible consequences for the gut via brain-gut axis interactions. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Microdosing psychedelics: More questions than answers? An overview and suggestions for future research

BACKGROUND

In the past few years, the issue of 'microdosing' psychedelics has been openly discussed in the public arena where claims have been made about their positive effect on mood state and cognitive processes such as concentration. However, there are very few scientific studies that have specifically addressed this issue, and there is no agreed scientific consensus on what microdosing is.

AIM

This critique paper is designed to address questions that need to be answered by future scientific studies and to offer guidelines for these studies.

APPROACH

Owing to its proximity for a possible approval in clinical use and short-lasting pharmacokinetics, our focus is predominantly on psilocybin. Psilocybin is allegedly, next to lysergic acid diethylamide (LSD), one of the two most frequently used psychedelics to microdose. Where relevant and available, data for other psychedelic drugs are also mentioned.

CONCLUSION

It is concluded that while most anecdotal reports focus on the positive experiences with microdosing, future research should also focus on potential risks of (multiple) administrations of a psychedelic in low doses. To that end, (pre)clinical studies including biological (e.g. heart rate, receptor turnover and occupancy) as well as cognitive (e.g. memory, attention) parameters have to be conducted and will shed light on the potential negative consequences microdosing could have.

The morphological and functional characteristics of the pineal gland

Introduction

The pineal gland is a photo-neuro-endocrine organ situated inside the brain, that secretes serotonin, melatonin and N,N-dymethyltriptamine. This narrative review will address the latest information gathered on this function of the gland as well as the unknown roles it may have. The different histological and pathological findings of the pineal gland have demonstrated a role in clinical manifestations of numerous endocrine, neurological and psychiatric pathologies.

Materials

For this narrative review we used the NCBI website database PubMed. The search terms were “Pineal Gland” AND/OR “histology, melatonin, DMT, pathology”. Total number of articles included were 86.

Results

We have reviewed physiological information of melatonin and DMT, anatomical, histological and histopathological information on the pineal gland and its role in endocrine, neurological and psychiatric pathology.

Conclusion

The role of melatonin in immunity and its potential therapeutic effects show promising potential for further research. DMT seems to have a role in psychiatric pathology and potential therapeutic effects. Proper tumoral screening and diagnostic protocol are required.

Serotonergic Modulation of Olfaction in Rodents and Insects

Recent advances in genetic tools and optical imaging technology have allowed rodent and Drosophila researchers to explore the relationship between serotonergic modulation and olfactory processing at a mechanistic level previously unfeasible. Here, I review the basic organization of olfactory and serotonergic systems in both rodents and Drosophila and draw comparisons where similarities exist. I discuss circuit level models that explain many of serotonin's effects on olfactory responses in the olfactory system's inputs and outputs. Finally, I discuss models of integration within wide-field centrifugal neurons to emphasize the importance of studying serotonergic neurons directly to build more realistic models of olfactory and modulatory interactions.

A pilot study on the impact of dopamine, serotonin, and brain-derived neurotrophic factor genotype on long-term functional outcomes after subarachnoid hemorrhage

Objectives:

Many that survive an aneurysmal subarachnoid hemorrhage experience lasting physical disability, which might be improved by medications with effects on the dopaminergic, serotonergic, and brain-derived neurotrophic factor neurotransmitter systems. But it is not clear which patients are most likely to benefit from these therapies. The purpose of this pilot study was to explore the relationship of genetic polymorphisms in these pathways with 12-month functional outcomes after aneurysmal subarachnoid hemorrhage.

Methods:

Subjects were recruited at the time of admission as a part of a larger parent study. Genotypes were generated using the Affymetrix genome-wide human single-nucleotide polymorphism array 6.0. Those within dopaminergic, serotonergic, and brain-derived neurotrophic factor pathways were analyzed for associations with functional outcomes at 12 months post aneurysmal subarachnoid hemorrhage using the Glasgow Outcome Scale and the Modified Rankin Scale.

Results:

The 154 subjects were 55.8 ± 11.3 years old and 74% female; they had Fisher scores of 2.95 ± 0.67, Hunt/Hess scores of 2.66 ± 1.13, and admission Glasgow Coma Scale scores of 12.52 ± 3.79. Single-nucleotide polymorphisms in the serotonin receptor genes 1B and 1E and dopamine receptor D2 were associated with greater disability (odds ratio: 3.88–3.25, confidence interval: 1.01–14.77), while single-nucleotide polymorphisms in the serotonin receptor genes 2A and 2C and dopamine receptor D5 conferred a risk of poor recovery (odds ratio: 3.31–2.32, confidence interval: 1.00–10.80). Single-nucleotide polymorphisms within the same serotonin genes, and within the dopamine receptor gene D2, were associated with greater recovery after aneurysmal subarachnoid hemorrhage (odds ratio: 0.17–0.34, confidence interval: 0.05–0.89).

Conclusions:

These data demonstrate that there may be an association between genetic factors and functional outcomes post stroke.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

Approaches for probing allosteric interactions at 7 transmembrane spanning receptors

In recent years, allosteric modulation of 7 transmembrane spanning receptors (7TMRs) has become a highly productive and exciting field of receptor pharmacology and drug discovery efforts. Positive and negative allosteric modulators (PAMs and NAMs, respectively) present a number of pharmacological and therapeutic advantages over conventional orthosteric ligands, including improved receptor-subtype selectivity, a lower propensity to induce receptor desensitization, the preservation of endogenous temporal and spatial activation of receptors, greater chemical flexibility for optimization of drug metabolism and pharmacokinetic parameters, and saturability of effect at target receptors, thus improving safety concerns and risk of overdose. Additionally, the relatively new concept of allosteric modulator-mediated receptor signal bias opens up a number of intriguing possibilities for PAMs, NAMs, and allosteric agonists, including the potential to selectively activate therapeutically beneficial signaling cascades, which could yield a superior tissue selectivity and side effect profile of allosteric modulators. However, there are a number of considerations and caveats that must be addressed when screening for and characterizing the properties of 7TMR allosteric modulators. Mode of pharmacology, methodology used to monitor receptor activity, detection of appropriate downstream analytes, selection of orthosteric probe, and assay time-course must all be considered when implementing any high-throughput screening campaign or when characterizing the properties of active compounds. Yet compared to conventional agonist/antagonist drug discovery programs, these elements of assay design are often a great deal more complicated when working with 7TMRs allosteric modulators. Moreover, for classical pharmacological methodologies and analyses, like radioligand binding and the assessment of compound affinity, the properties of allosteric modulators yield data that are more nuanced than orthosteric ligand-receptor interactions. In this review, we discuss the current methodologies being used to identify and characterize allosteric modulators, lending insight into the approaches that have been most successful in accurately and robustly identifying hit compounds. New label-free technologies capable of detecting phenotypic cellular changes in response to receptor activation are powerful tools well suited for assessing subtle or potentially masked cellular responses to allosteric modulation of 7TMRs. Allosteric modulator-induced receptor signal bias and the assay systems available to probe the various downstream signaling outcomes of receptor activation are also discussed.