Serotonin 5-HT7 receptor agents: Structure-activity relationships and potential therapeutic applications in central nervous system disorders

Neuroprotective and Neurite Outgrowth Stimulating Effects of New Low-Basicity 5-HT7 Receptor Agonists: In Vitro Study in Human Neuroblastoma SH-SY5Y Cells

There is some evidence that the serotonin receptor subtype 7 (5-HT7) could be new therapeutic target for neuroprotection. The aim of this study was to compare the neuroprotective and neurite outgrowth potential of new 5-HT7 receptor agonists (AH-494, AGH-238, AGH-194) with 5-CT (5-carboxyamidotryptamine) in human neuroblastoma SH-SY5Y cells. The results revealed that 5-HT7 mRNA expression was significantly higher in retinoic acid (RA)-differentiated cells when compared to undifferentiated ones and it was higher in cell cultured in neuroblastoma experimental medium (DMEM) compared to those placed in neuronal (NB) medium. Furthermore, the safety profile of compounds was favorable for all tested compounds at concentration used for neuroprotection evaluation (up to 1 μM), whereas at higher concentrations (above 10 μM) the one of the tested compounds, AGH-194 appeared to be cytotoxic. While we observed relatively modest protective effects of 5-CT and AH-494 in UN-SH-SY5Y cells cultured in DMEM, in UN-SH-SY5Y cells cultured in NB medium we found a significant reduction of H2O2-evoked cell damage by all tested 5-HT7 agonists. However, 5-HT7-mediated neuroprotection was not associated with inhibition of caspase-3 activity and was not observed in RA-SH-SY5Y cells exposed to H2O2. Furthermore, none of the tested 5-HT7 agonists altered the damage induced by 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium ion (MPP +) and doxorubicin (Dox) in UN- and RA-SH-SY5Y cells cultured in NB. Finally we showed a stimulating effect of AH-494 and AGH-194 on neurite outgrowth. The obtained results provide insight into neuroprotective and neurite outgrowth potential of new 5-HT7 agonists.

Modulation of neuronal morphology by antipsychotic drug: Involvement of serotonin receptor 7

Antipsychotic drugs (APDs) are the primary pharmacological treatment for schizophrenia, a complex disorder characterized by altered neuronal connectivity. Atypical or second-generation antipsychotics, such as Risperidone (RSP) and Clozapine (CZP) predominantly block dopaminergic D2 and serotonin receptor 2A (5-HT2A) neurotransmission. Both compounds also exhibit affinity for the 5-HT7R, with RSP acting as an antagonist and CZP as an inverse agonist. Our study aimed to determine whether RSP and CZP can influence neuronal morphology through a 5-HT7R-mediated mechanism. Here, we demonstrated that CZP promotes neurite outgrowth of early postnatal cortical neurons, and the 5-HT7R mediates its effect. Conversely, RSP leads to a reduction of neurite length of early postnatal cortical neurons, in a 5-HT7R-independent way. Furthermore, we found that the effects of CZP, mediated by 5-HT7R activation, require the participation of ERK and Cdk5 kinase pathways. At the same time, the modulation of neurite length by RSP does not involve these pathways. In conclusion, our findings provide valuable insights into the morphological changes induced by these two APDs in neurons and elucidate some of the associated molecular pathways. Investigating the 5-HT7R-dependent signaling pathways underlying the neuronal morphogenic effects of APDs may contribute to the identification of novel targets for the treatment of schizophrenia.

Insights into the development of 99mTc-radioligands for serotonergic receptors imaging: Synthesis, labeling, In vitro, and In vivo studies

Serotonergic (5-hydroxytryptamine; 5-HT) receptors play critical roles in neurological and psychological disorders such as schizophrenia, anxiety, depression, and Alzheimer's diseases. Therefore, it is particularly important to develop novel radioligands or modify the existing ones to identify the serotonergic receptors involved in psychiatric disorders. Among the 16 subtypes of serotonergic systems, only technetium-99m based radiopharmaceuticals have been evaluated for serotonin-1A (5-HT1A), serotonin-2A (5-HT2A), 5-HT1A/7 heterodimers and serotonin receptor neurotransmitter (SERT). This review focuses on recent efforts in the design, synthesis and evaluation of 99mTc-radioligands used for single photon emission computerized tomography (SPECT) imaging of serotonergic (5-HT) receptors. Additionally, the discussion will cover aspects such as chemical structure, in vitro/vivo stability, affinity toward serotonin receptors, blood-brain barrier permeation (BBB), and biodistribution study.

Identification of an Antagonist Targeting G Protein and β-Arrestin Signaling Pathways of 5-HT7R

In consideration of the limited number of FDA-approved drugs for autism spectrum disorder (ASD), significant efforts have been devoted to identifying novel drug candidates. Among these, 5-HT7R modulators have garnered considerable attention due to their potential in alleviating autism-like behaviors in ASD animal models. In this study, we designed and synthesized biphenyl-3-ylmethylpyrrolidines 3 and biphenyl-3-yl-dihydroimidazoles 4 as 5-HT7R modulators. Through extensive biological tests of 3 and 4 in G protein and β-arrestin signaling pathways of 5-HT7R, it was determined that 2-(2'-methoxy-[1,1'-biphenyl]-3-yl)-4,5-dihydro-1H-imidazole 4h acted as a 5-HT7R antagonist in both signaling pathways. In in vivo study with Shank3-/- transgenic (TG) mice, the self-grooming behavior test was performed with 4h, resulting in a significant reduction in the duration of self-grooming. In addition, an immunohistochemical experiment with 4h restored reduced neurogenesis in Shank3-/- TG mice, which is confirmed by the quantification of doublecortin (DCX) positive neurons, suggesting the promising therapeutic potential of 4h.

Functional Dimerization of Serotonin Receptors: Role in Health and Depressive Disorders

Understanding the neurobiological underpinnings of depressive disorder constitutes a pressing challenge in the fields of psychiatry and neurobiology. Depression represents one of the most prevalent forms of mental and behavioral disorders globally. Alterations in dimerization capacity can influence the functional characteristics of serotonin receptors and may constitute a contributing factor to the onset of depressive disorders. The objective of this review is to consolidate the current understanding of interactions within the 5-HT receptor family and between 5-HT receptors and members of other receptor families. Furthermore, it aims to elucidate the role of such complexes in depressive disorders and delineate the mechanisms through which antidepressants exert their effects.

Evaluating the effect of R-Baclofen and LP-211 on autistic behavior of the BTBR and Fmr1-KO mouse models

Introduction

Autism spectrum disorder (ASD) is a persistent neurodevelopmental condition characterized by two core behavioral symptoms: impaired social communication and interaction, as well as stereotypic, repetitive behavior. No distinct cause of ASD is known so far; however, excitatory/inhibitory imbalance and a disturbed serotoninergic transmission have been identified as prominent candidates responsible for ASD etiology.

Methods

The GABAB receptor agonist R-Baclofen and the selective agonist for the 5HT7 serotonin receptor LP-211 have been reported to correct social deficits and repetitive behaviors in mouse models of ASD. To evaluate the efficacy of these compounds in more details, we treated BTBR T+ Itpr3tf/J and B6.129P2-Fmr1tm1Cgr/J mice acutely with R-Baclofen or LP-211 and evaluated the behavior of animals in a series of tests.

Results

BTBR mice showed motor deficits, elevated anxiety, and highly repetitive behavior of self-grooming. Fmr1-KO mice exhibited decreased anxiety and hyperactivity. Additionally, Fmr1-KO mice’s ultrasonic vocalizations were impaired suggesting a reduced social interest and communication of this strain. Acute LP-211 administration did not affect the behavioral abnormalities observed in BTBR mice but improved repetitive behavior in Fmr1-KO mice and showed a trend to change anxiety of this strain. Acute R-Baclofen treatment improved repetitive behavior only in Fmr1-KO mice.

Conclusion

Our results add value to the current available data on these mouse models and the respective compounds. Yet, additional studies are needed to further test R-Baclofen and LP-211 as potential treatments for ASD therapy.

Synthesis and evaluation of 99mTc-labeled 1-(2-Pyridyl)piperazine derivatives as radioligands for 5HT7 receptors

Glioblastoma multiform (GBM) is one of the most aggressive tumors of the central nervous system in humans. GBM overexpresses serotonin-7 receptors (5-HT₇Rs); hence, this study aims to develop 5-HT₇R targeted radiotracers. Aryl piperazine derivatives can act as ligands for 5-HT₇R. Therefore, compounds 6 and 7 as 1-(3-nitropyridin-2-yl)piperazine derivatives were synthesized and radiolabeled with ^99mTcN²⁺ core. Radiolabeled 6 and 7 (^99mTcN-[6] and ^99mTcN-[7]) were prepared with high radiochemical purity (RCP > 96%). They displayed high affinity toward U-87 MG cell line 5-HT₇R. The calculated K_i for ^99mTcN-[7] was lower than that of ^99mTcN-[6] (14.85 ± 0.32 vs 22.57 ± 0.73 nM) which indicates the higher affinity of ^99mTcN-[7] toward 5-HT₇R. A molecular docking study also confirmed the binding of these radiotracers to 5-HT₇R. The biodistribution study in normal mice revealed that ^99mTcN-[7] has the highest brain accumulation at 30 min post-injection (0.54 ± 0.12 %ID/g) while the uptake of ^99mTcN-[6] is much lower (0.14 ± 0.02 %ID/g). The biodistribution study in the xenograft model confirms that the radiotracers recognize the tumor site. ^99mTcN-[6], and ^99mTcN-[7] showed the highest tumor uptake at 1-hour post-injection (5.44 ± 0.58 vs 4.94 ± 1.65 %ID/g) and tumor-to-muscle ratios were (4.61 vs. 5.61). The injection of pimozide blocks the receptors and significantly reduces the tumor-to-muscle ratios at 1-hour post-injection to 0.81 and 0.31, respectively. In correlation with in vitro study, ^99mTcN-[6] and ^99mTcN-[7] visualize the tumor site in U-87 MG glioma xenografted nude mice and display the tumor-to-muscle ratios of 7.05 and 6.03.

Exploring the Anticonvulsant Activity of Aqueous Extracts of Ficus benjamina L. Figs in Experimentally Induced Convulsions

Background. Ficus benjamina L. is an evergreen tree, native to Southeast Asia, and often known as a weeping fig. Its latex and fruit extracts are used by indigenous cultures to cure skin conditions, inflammation, vomiting, leprosy, malaria, and nasal ailments. The aqueous extract of the figs of Ficus benjamina L. has various therapeutic values, including biological activities on the central nervous system. Materials and Methods. The extract of the dried figs of Ficus benjamina L. (FBE) was prepared by defatting with petroleum ether for 16 h followed by soxhelation with 70% methanol (1 : 10 w/v) for 24 h, and standardization of the extract was carried out using HPLC with 5-HT as a standard. Electroconvulsions were induced by the maximal electroshock model, and chemoconvulsions were induced by picrotoxin. Results. The HPLC chromatogram of the Ficus benjamina L. extract showed an absorption peak with a retention time of 1.797 min, similar to that observed with standard serotonin (5-HT) solution. In the maximal electroshock model, FBE significantly reduced the duration of the tonic hind limb extensor and extensor-to-flexor ratio (E/F ratio) in a dose-dependent manner. Moreover, in the picrotoxin-induced seizure model, FBE increased the seizure latency and decreased the duration of tonic-clonic convulsions dose-dependently. We confirmed the anticonvulsant activity of the FBE extract as it attenuated both maximal electroshock and picrotoxin-induced convulsions. Conclusion. The in vivo studies revealed that the Ficus extract was found to protect the animals in electroshock-induced and picrotoxin-induced convulsions.

Identification and Pharmacological Characterization of Two Serotonin Type 7 Receptor Isoforms from Mythimna separata

Serotonin (5-hydroxytryptamine, 5-HT) is an important neuroactive molecule, as neurotransmitters regulate various biological functions in vertebrates and invertebrates by binding and activating specific 5-HT receptors. The pharmacology and tissue distribution of 5-HT receptors have been investigated in several model insects, and these receptors are recognized as potential insecticide targets. However, little is known about the pharmacological characterization of the 5-HT receptors in important agricultural pests. In this study, we investigated the sequence, pharmacology, and tissue distribution of 5-HT7 receptors from oriental armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae), an important migratory and polyphagous pest species. We found that the 5-HT7 receptor gene encodes two molecularly distinct transcripts, Msep5-HT7L and Msep5-HT7S, by the mechanism of alternative splicing in M. separata. Msep5-HT7S differs from Msep5-HT7L based on the deletion of 95 amino acids within the third intracellular loop. Two Msep5-HT7 receptor isoforms were activated by 5-HT and synthetic agonists α-methylserotonin, 8-hydroxy-DPAT, and 5-methoxytryptamine, resulting in increased intracellular cAMP levels in a dose-dependent manner, although these agonists showed much poorer potency and efficacy than 5-HT. The maximum efficacy of 5-HT compared to the two 5-HT isoforms was equivalent, but 5-HT exhibited 2.63-fold higher potency against the Msep5-HT7S than the Msep5-HT7L receptor. These two isoforms were also blocked by the non-selective antagonist methiothepin and the selective antagonists WAY-100635, ketanserin, SB-258719, and SB-269970. Moreover, two distinct mRNA transcripts were expressed preferentially in the brain and chemosensory organs of M. separata adults, as determined by qPCR assay. This study is the first comprehensive characterization of two splicing isoforms of 5-HT7 receptors in M. separata, and the first to demonstrate that alternative splicing is also the mechanism for producing multiple 5-HT7 isoforms in insects. Pharmacological and gene expression profiles offer important information that could facilitate further exploration of their function in the central nervous system and peripheral chemosensory organs, and may even contribute to the development of new selective pesticides.

5-HT7 Receptors Regulate Excitatory-Inhibitory Balance in Mouse Spinal Cord Dorsal Horn

Serotonergic receptors of the 5-HT₇ type (5-HT₇Rs) are widely expressed in the central nervous system (CNS), where they modulate several functions, such as pain. Behavioral experiments in vivo have shown both anti- and pro-nociceptive actions of 5-HT₇Rs, although an analgesic effect seems to be prevalent. In the spinal cord dorsal horn, the mechanisms involved in 5-HT₇R-mediated synaptic modulation are still poorly understood, especially those regarding the control of synaptic inhibition. The present study investigated the modulation exerted by 5-HT₇Rs on dorsal horn excitatory and inhibitory synaptic circuits, by performing patch-clamp recordings from lamina II neurons in mouse spinal cord slices. Our results show that applying the selective 5-HT₇ agonist LP-211 facilitates glutamatergic release by enhancing the frequency of spontaneous postsynaptic currents (sEPSCs) and increasing the peak amplitude of excitatory postsynaptic currents (EPSCs) evoked by dorsal root stimulation. The effects on sEPSCs were still observed in the presence of the 5-HT_1A antagonist WAY-100635, while the 5-HT₇ antagonist SB-269970 blocked them. LP-211 was also able to increase the release of gamma-aminobutyric acid (GABA) and glycine, as shown by the increase of spontaneous inhibitory currents (sIPSC) frequency and evoked inhibitory postsynaptic currents (IPSC) amplitude. LP-211 was proved to be more effective in potentiating synaptic inhibition as compared to excitation: consistently, 5-HT₇R activation significantly enhanced the excitability of tonic firing neurons, mainly corresponding to inhibitory interneurons. Our data bring new insights into the mechanisms of synaptic modulation mediated by 5-HT₇Rs in the dorsal horn. Stronger impact on synaptic inhibition supports the hypothesis that these receptors may play an anti-nociceptive role in the spinal cord of naïve animals.

A new paradigm shift in antidepressant therapy? From dual-action to multitarget-directed ligands

Major Depressive Disorder is a chronic, recurring, and potentially fatal disease affecting up to 20% of the global population. Since the monoamine hypothesis was proposed more than 60 years ago, only a few relevant advances have been achieved, with very little disease course changing, from a pharmacological perspective. Moreover, since negative efficacy studies with novel molecules are frequent, many pharmaceutical companies have put new studies on hold. Fortunately, relevant clinical studies are currently being performed, and extensive striving is being developed by universities, research centers, and other public and private institutions. Depression is no longer considered a simple disease but a multifactorial one. New research fields are emerging in what could be a paradigm shift: the multitarget approach beyond monoamines. In this review, we summarize the present and the past of antidepressant drug discovery, with the aim to shed some light on the current state of the art in clinical and preclinical advances to face this increasingly devastating disease.

Imperatorin Influences Depressive-like Behaviors: A Preclinical Study on Behavioral and Neurochemical Sex Differences

Imperatorin, a naturally derived furanocoumarin, exerts promising neuropharmacological properties. Therefore, it might be applicable in the treatment of brain diseases such as depression. In the present project, we aimed to investigate the sex-dependent effects of imperatorin (1, 5, and 10 mg/kg) on behavior and neurochemistry associated with antidepressant effects. The depressive-like behaviors of male and female Swiss mice were investigated in a forced swim test (FST). Subsequently, High-Performance Liquid Chromatography (HPLC) was used to evaluate the level of serotonin, its metabolite, 5-HIAA, and noradrenaline, in mouse brains. The study revealed that only males responded to imperatorin (1 and 5 mg/kg) treatment and caused an antidepressant effect, such as with respect to depressive-like behaviors, lowering immobility time and increasing immobility latency. The HPLC analysis demonstrated that serotonin levels in the prefrontal cortex of females decreased with the middle dose of imperatorin (5 mg/kg), while in the male prefrontal cortex, the lower dose (1 mg/kg) boosted serotonin levels. There were no evident changes observed with respect to noradrenaline and serotonin metabolite levels in the male hippocampus. To conclude, we propose that imperatorin has antidepressant potential, seemingly only in males, influencing brain serotonin level, but the direct mechanism of action requires further investigation.

The role of 5-HT7R in the memory impairment of mice induced by long-term isoflurane anesthesia

General anesthesia is widely utilized in the clinic for surgical and diagnostic procedures. However, growing evidence suggests that anesthetic exposure may affect cognitive function negatively. Unfortunately, little is known about the underlying mechanisms and efficient prevention and therapeutic strategies for the anesthesia-induced cognitive dysfunction. 5-HT₇R, a serotonin receptor family member, is functionally associated with learning and memory. It has recently become a potential therapeutic target in various neurological diseases as its ligands have a wide range of neuropharmacological effects. However, it remains unknown the role of 5-HT₇R in the long-term isoflurane anesthesia-induced memory impairment and whether prior activation or blockade of 5-HT₇R before anesthesia has modulating effects on this memory impairment. In this study, 5-HT₇R selective agonist LP-211 and 5-HT₇R selective antagonist SB-269970 were pretreated intraperitoneally to mice before anesthesia; their effects on the cognitive performance of mice were assessed using fear conditioning test and novel object recognition test. Furthermore, the transcriptional level of 5-HT₇R in the hippocampus was detected using qRT-PCR, and proteomics was conducted to probe the underlying mechanisms. As a result, long-term exposure to isoflurane anesthesia caused memory impairment and an increase in hippocampal 5-HT₇R mRNA expression, which could be attenuated by SB-269970 pretreatment but not LP-211pretreatment. According to the proteomics results, the antiamnestic effect of SB-269970 pretreatment was probably attributed to its action on the gene expression of Slc6a11, Itpka, Arf3, Srcin1, and Epb41l2, and synapse organization in the hippocampus. In conclusion, 5-HT₇R is involved in the memory impairment induced by long-term isoflurane anesthesia, and the prior blockade of 5-HT₇R with SB-269970 protects the memory impairment. This finding may help to improve the understanding of the long-term isoflurane anesthesia-induced memory impairment and to construct potential preventive and therapeutic strategies for the adverse effects after long-term isoflurane exposure.

Regulatory T cells in ischemic stroke

Recent evidence shows that when ischemic stroke (IS) occurs, the BBB would be destructed, thereby promoting the immune cells to migrate into the brain, suggesting that the immune responses can play a vital role in the pathology of IS. As an essential subpopulation of immunosuppressive T cells, regulatory T (Treg) cells are involved in maintaining immune homeostasis and suppressing immune responses in the pathophysiological conditions of IS. During the past decades, the regulatory role of Treg cells has attracted the interest of numerous researchers. However, whether they are beneficial or detrimental to the outcomes of IS remains controversial. Moreover, Treg cells exert distinctive effects in the different stages of IS. Therefore, it is urgent to elucidate how Treg cells modulate the immune responses induced by IS. In this review, we describe how Treg cells fluctuate and play a role in the regulation of immune responses after IS in both experimental animals and humans, and summarize their biological functions and mechanisms in both CNS and periphery. We also discuss how Treg cells participate in poststroke inflammation and immunodepression and the potential of Treg cells as a novel therapeutic approach.

5-HT Receptors and Temperature Homeostasis

The present review summarizes the data concerning the influence of serotonin (5-HT) receptors on body temperature in warm-blooded animals and on processes associated with its maintenance. This review includes the most important part of investigations from the first studies to the latest ones. The established results on the pharmacological activation of 5-HT1A, 5-HT3, 5-HT7 and 5-HT2 receptor types are discussed. Such activation of the first 3 type of receptors causes a decrease in body temperature, whereas the 5-HT2 activation causes its increase. Physiological mechanisms leading to changes in body temperature as a result of 5-HT receptors' activation are discussed. In case of 5-HT1A receptor, they include an inhibition of shivering and non-shivering thermogenesis, as well simultaneous increase of peripheral blood flow, i.e., the processes of heat production and heat loss. The physiological processes mediated by 5-HT2 receptor are opposite to those of the 5-HT1A receptor. Mechanisms of 5-HT3 and 5-HT7 receptor participation in these processes are yet to be studied in more detail. Some facts indicating that in natural conditions, without pharmacological impact, these 5-HT receptors are important links in the system of temperature homeostasis, are also discussed.

5-HT7 receptors in Alzheimer's disease

Even though the involvement of serotonin (5-hydroxytryptamine; 5-HT) and its receptors in Alzheimer's disease (AD) is widely accepted, data on the expression and the role of 5-HT₇ receptors in AD is relatively limited. Therefore, the objective of the present work was to study the expression of serotonergic 5-HT₇ receptors in postmortem samples of AD brains and correlate it with neurotransmitter levels, cognition and behavior. The study population consisted of clinically well-characterized and neuropathologically confirmed AD patients (n = 42) and age-matched control subjects (n = 18). Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) and high-performance liquid chromatography were performed on Brodmann area (BA) 7, BA10, BA22, BA24, hippocampus, amygdala, thalamus and cerebellum to measure mRNA levels of 5-HT₇ receptors (HTR7), as well as the concentrations of various monoamine neurotransmitters and their metabolites. Decreased levels of HTR7 mRNA were observed in BA10. A significant association was observed between HTR7 levels in BA10 and BEHAVE-AD cluster B (hallucinations) (rs(28) = 0.444, P < 0.05). In addition, a negative correlation was observed between HTR7 levels in BA10 and both MHPG concentrations in this brain region (rs(45) = -0.311; P < 0.05), and DOPAC levels in the amygdala (rs(42) = -0.311; P < 0.05). Quite surprisingly, no association was found between HTR7 levels and cognitive status. Altogether, this study supports the notion of the involvement of 5-HT₇ receptors in psychotic symptoms in AD, suggesting the interest of testing antagonist acting at this receptor to specifically treat psychotic symptoms in this illness.

Unusual Quadrupedal Locomotion in Rat during Recovery from Lumbar Spinal Blockade of 5-HT7 Receptors

Coordination of four-limb movements during quadrupedal locomotion is controlled by supraspinal monoaminergic descending pathways, among which serotoninergic ones play a crucial role. Here we investigated the locomotor pattern during recovery from blockade of 5-HT₇ or 5-HT_2A receptors after intrathecal application of SB269970 or cyproheptadine in adult rats with chronic intrathecal cannula implanted in the lumbar spinal cord. The interlimb coordination was investigated based on electromyographic activity recorded from selected fore- and hindlimb muscles during rat locomotion on a treadmill. In the time of recovery after hindlimb transient paralysis, we noticed a presence of an unusual pattern of quadrupedal locomotion characterized by a doubling of forelimb stepping in relation to unaffected hindlimb stepping (2FL-1HL) after blockade of 5-HT₇ receptors but not after blockade of 5-HT_2A receptors. The 2FL-1HL pattern, although transient, was observed as a stable form of fore-hindlimb coupling during quadrupedal locomotion. We suggest that modulation of the 5-HT₇ receptors on interneurons located in lamina VII with ascending projections to the forelimb spinal network can be responsible for the 2FL-1HL locomotor pattern. In support, our immunohistochemical analysis of the lumbar spinal cord demonstrated the presence of the 5-HT₇ immunoreactive cells in the lamina VII, which were rarely 5-HT_2A immunoreactive.

Modulation of Serotonin Receptors in Neurodevelopmental Disorders: Focus on 5-HT7 Receptor

Since neurodevelopmental disorders (NDDs) influence more than 3% of children worldwide, there has been intense investigation to understand the etiology of disorders and develop treatments. Although there are drugs such as aripiprazole, risperidone, and lurasidone, these medications are not cures for the disorders and can only help people feel better or alleviate their symptoms. Thus, it is required to discover therapeutic targets in order to find the ultimate treatments of neurodevelopmental disorders. It is suggested that abnormal neuronal morphology in the neurodevelopment process is a main cause of NDDs, in which the serotonergic system is emerging as playing a crucial role. From this point of view, we noticed the correlation between serotonin receptor subtype 7 (5-HT₇R) and NDDs including autism spectrum disorder (ASD), fragile X syndrome (FXS), and Rett syndrome (RTT). 5-HT₇R modulators improved altered behaviors in animal models and also affected neuronal morphology via the 5-HT₇R/G₁₂ signaling pathway. Through the investigation of recent studies, it is suggested that 5-HT₇R could be a potential therapeutic target for the treatment of NDDs.

Discovery of G Protein-Biased Ligands against 5-HT7R

There has been significant attention concerning the biased agonism of G protein-coupled receptors (GPCRs), and it has resulted in various pharmacological benefits. 5-HT₇R belongs to a GPCR, and it is a promising pharmaceutical target for the treatment of neurodevelopmental and neuropsychiatric disorders. Based on our previous research, we synthesized a series of 6-chloro-2'-methoxy biphenyl derivatives 1, 2, and 3 with a variety of amine scaffolds. These compounds were evaluated for their binding affinities to 5-HTR subtypes and their functional selectivity toward the Gs protein and the β-arrestin signaling pathways of 5-HT₇R. Among them, 2-(6-chloro-2'-methoxy-[1,1'-biphenyl]-3-yl)-N-ethylethan-1-amine, 2b, was found to be a G-protein-biased ligand of 5-HT₇R. In an in vivo study with Shank3 transgenic mice, the self-grooming behavior test was performed with 2b, which increased the duration of self-grooming. The experiments further suggested that 5-HT₇R is associated with autism spectrum disorders (ASDs) and could be a therapeutic target for the treatment of stereotypy in ASDs.

Synthesis and Biological Evaluation of 99mTc-Labeled Phenylpiperazine Derivatives as Selective Serotonin-7 Receptor Ligands for Brain Tumor Imaging

With a poor prognosis, glioblastoma multiforme is the most aggressive tumor of the central nervous system in humans. The aim of this study was to develop novel tracers for the tumor targeting and imaging of overexpressed serotonin-7 receptors (5-HT₇Rs) in U-87 MG glioma xenografted nude mice. Two phenylpiperazine derivatives named as PHH and MPHH were designed, and the corresponding radiotracers ^99mTc-PHH and ^99mTc-MPHH were synthesized in high radiochemical purity (>95%). ^99mTc-MPHH showed a higher affinity to 5-HT₇Rs on U-87 MG cells compared to ^99mTc-PHH. In biodistribution studies, the radiocomplexes showed good brain uptake at 15 min combined with good radioactivity retention in the brain for 240 min. Regional rabbit brain studies indicated a higher radioactivity concentration in the hippocampus and diencephalon than in the cerebellum. Compared to ^99mTc-MPHH, the ^99mTc-PHH exhibited a significantly increased tumor uptake at 15 and 60 min, but the rapid blood clearance of ^99mTc-MPHH led to enhanced tumor-to-muscle ratios at 240 min. A significant reduction in tumor uptake 60 min after an injection of pimozide (5-HT₇ receptor antagonist) confirms the tumor uptake was receptor-mediated specifically. The tumor-to-contralateral muscle tissue ratio of ^99mTc-PHH and ^99mTc-MPHH in nude mice with U-87 MG xenograft was measured (5.25 and 4.65) at 60 min as well as (6.25 and 6.76) at 240 min, respectively.

Discovery of Nonracemic Amisulpride to Maximize Benefit/Risk of 5-HT7 and D2 Receptor Antagonism for the Treatment of Mood Disorders

In contrast to the dose‐occupancy relationship in the treatment of schizophrenia, the minimal effective level of dopamine receptor 2 (D2R) blockade for antipsychotics in the treatment of bipolar depression is unknown. Lower doses aimed at reducing extrapyramidal side effects must be balanced against the need to retain the therapeutic benefit of D2R blockade on emergent cycling, mixed, manic, anxiety, and/or psychotic symptoms. Dose‐reductions intended to lower D2R blockade, however, could also decrease concomitant serotonin receptor antagonism and its potential benefit on depressive symptoms. Here, we uncoupled the potential antidepressant activity in amisulpride, driven by 5‐HT7 receptor (5‐HT7R) antagonism, from the D2R‐mediated antipsychotic activity by discovering that each enantiomer favors a different receptor. Aramisulpride was more potent at 5‐HT7R relative to esamisulpride (Ki 47 vs. 1,900 nM, respectively), whereas esamisulpride was more potent at D2R (4.0 vs. 140 nM). We hypothesized that a nonracemic ratio might achieve greater 5‐HT7R‐mediated antidepressant effects at a lower level of D2R blockade. The dose‐occupancy relationship of esamisulpride at D2R was determined by positron emission tomography (PET) imaging in human volunteers. Separately the dose‐relationship of aramisulpride was established in humans using suppression of rapid eye movement (REM) sleep as a marker of 5‐HT7R antagonism. These results led to the discovery of an 85:15 ratio of aramisulpride to esamisulpride (SEP‐4199) that maximizes the potential for antidepressant benefit of aramisulpride via 5‐HT7R and reduces esamisulpride to minimize D2R‐related extrapyramidal side effects while still retaining D2R‐mediated effects predicted to provide benefit in bipolar depression. The antidepressant efficacy of SEP‐4199 was recently confirmed in a proof‐of‐concept trial for the treatment of bipolar depression (NCT03543410).

Discovery and SAR studies of 2-alkyl-3-phenyl-2,4,5,6,7,8-hexahydropyrazolo[3,4-d]azepines as 5-HT7/2 inhibitors leading to the identification of a clinical candidate

We report here the synthesis and characterization of a dual 5-HT₇ / 5-HT₂ receptor antagonist 3-(4-Fluoro-phenyl)-2-isopropyl-2,4,5,6,7,8-hexahydro-1,2,6-triaza-azulene (4j). 4j is a high affinity 5-HT₇ and 5-HT_2A receptor ligand having a pK_i = 8.1 at both receptors. It behaves as an antagonist in an in vitro functional assay for 5-HT_2A and as an inverse agonist in an in vitro functional assay for 5-HT₇. In a validated in vivo model for central 5-HT₇ activity in rats, blockade of 5-carboxamidotryptamine (5-CT) induced hypothermia, 4j shows efficacy at low doses (ED₅₀ = 0.05 mg/kg, p.o., 1 h) and maximal efficacy was observed at 0.3 mg/kg p.o. with a corresponding plasma concentration of ~27 ng/ml. In a validated in vivo model for central 5-HT_2A activity, blockade of 2,5-dimethoxy-4-iodoamphetamine (DOI) induced head-twitches in mice, 4j shows efficacy at low doses with an ED₅₀ = 0.3 mg/kg p.o. Ex vivo receptor binding studies demonstrate that 4j occupied 5-HT_2A receptor binding sites in the frontal cortex of the rat brain with an ED₅₀ in good agreement with the ED₅₀ value for central functional effect mediated by 5-HT_2A receptor (ED₅₀ = 0.8 mg/kg, p.o., 1 h).

Investigation of the Role of Stimulation and Blockade of 5-HT7 Receptors in Ketamine Anesthesia

Although several pieces of evidence have indicated the ability of the serotonin-7 receptor (5-HTR₇) to modulate N-methyl-_D-aspartate receptor (NMDAR) activation, the possible impact on ketamine anesthesia has not been examined directly. The purpose of the present study is thus to investigate the possible role of the 5-HTR₇ in ketamine anesthesia using a 5-HTR₇ agonist and/or antagonist. The influence of a 5-HTR₇ agonist/antagonist on ketamine anesthesia for behavioral impact was assessed by testing potential anesthetic parameters. Its functional impact was assessed by mRNA expression with real-time PCR and immunostaining in the hippocampus and prefrontal cortex of mice. Two different doses of ketamine-high and low-were administered to induce anesthesia. In the high-dose ketamine-applied group in particular, the administration of both the 5-HTR₇ agonist and antagonist intensified the anesthetic effect of ketamine. The reflection of the change in anesthesia parameters to 5-HTR₇ expression was observed as an increase in the hippocampus and a decrease in the prefrontal cortex in the anesthetized groups by stimulation of 5-HTR₇. It is noteworthy that the results of NMDAR expressions are parallel to the results of the 5-HTR₇ expressions of both the hippocampus and the prefrontal cortex. The 5-HTR₇ may play a role in ketamine anesthesia. It may act through NMDAR in ketamine anesthesia, depending on the parallelism between both receptors.

The Contribution of Serotonergic Receptors and Nitric Oxide Systems in the Analgesic Effect of Acetaminophen: An Overview of the Last Decade

Acetaminophen is a widely used analgesic and antipyretic agent. It is also available in over the counter formulations, which has increased its wide use. There have been many studies to date that have aimed to evaluate the mechanism of the analgesic action of acetaminophen. Additional to the inhibition of the cyclooxygenase pathway in the central nervous system, the involvement of opioidergic, cannabinoidergic, dopaminergic, cholinergic, and nitrergic systems as well as the contribution of descending pain inhibitory systems like the bulbospinal serotonergic pathway has been proposed as possible mechanisms of the analgesic action of acetaminophen. In this review, we aimed to collect the data from studies revealing the contribution of the central serotonergic system and the role of central nervous system-located serotonergic receptor subtypes in the analgesic effect of acetaminophen. While doing this, we mainly focused on the research that has been performed in the last ten years and tried to link the previous data with the lately added results. In addition to serotonergic system involvement, we also reviewed the role of nitric oxide in the analgesic action of acetaminophen, especially with the new findings reported over the last decade.

Pharmacological Treatment of Anxiety Disorders: The Role of the HPA Axis

Stress in general, and early life stress in particular, has been associated with the development of anxiety and mood disorders. The molecular, biological and psychological links between stress exposure and the pathogenesis of anxiety and mood disorders have been extensively studied, resulting in the search of novel psychopharmacological strategies aimed at targets of the hypothalamic-pituitary-adrenal (HPA) axis. Hyperactivity of the HPA axis has been observed in certain subgroups of patients with anxiety and mood disorders. In addition, the effects of different anti-anxiety agents on various components of the HPA axis has been investigated, including benzodiazepines, tricyclic antidepressants (TCAs), and selective serotonin reuptake inhibitors (SSRIs). For example, benzodiazepines, including clonazepam and alprazolam, have been demonstrated to reduce the activity of corticotrophin releasing factor (CRF) neurons in the hypothalamus. TCAs and SSRIs are also effective anti-anxiety agents and these may act, in part, by modulating the HPA axis. In this regard, the SSRI escitalopram inhibits CRF release in the central nucleus of the amygdala, while increasing glucocorticoid receptor (GRs) density in the hippocampus and hypothalamus. The molecular effects of these anti-anxiety agents in the regulation of the HPA axis, taken together with their clinical efficacy, may provide further understanding about the role of the HPA axis in the pathophysiology of mood and anxiety disorders, paving the way for the development of novel therapeutic strategies.

Privileged scaffold-based design to identify a novel drug-like 5-HT7 receptor-preferring agonist to target Fragile X syndrome

Recent preclinical studies have shown that activation of the serotonin 5-HT₇ receptor has the potential to treat neurodevelopmental disorders such as Fragile X syndrome, a rare disease characterized by autistic features. With the aim to provide the scientific community with diversified drug-like 5-HT₇ receptor-preferring agonists, we designed a set of new long-chain arylpiperazines by exploiting structural fragments present in clinically approved drugs or in preclinical candidates (privileged scaffolds). The new compounds were synthesized, tested for their affinity at 5-HT₇ and 5-HT_1A receptors, and screened for their in vitro stability to microsomal degradation and toxicity. Selected compounds were characterized as 5-HT₇ receptor-preferring ligands, endowed with high metabolic stability and low toxicity. Compound 7g emerged as a drug-like 5-HT₇ receptor-preferring agonist capable to rescue synaptic plasticity and attenuate stereotyped behavior in a mouse model of Fragile X syndrome.

Contribution of 5-HT2 Receptors to the Control of the Spinal Locomotor System in Intact Rats

Applying serotonergic (5-HT) agonists or grafting of fetal serotonergic cells into the spinal cord improves locomotion after spinal cord injury. Little is known about the role of 5-HT receptors in the control of voluntary locomotion, so we administered inverse agonists of 5-HT₂ (Cyproheptadine; Cypr), 5-HT_2A neutral antagonist (Volinanserin; Volin), 5-HT_2C neutral antagonist (SB 242084), and 5-HT_2B/2C inverse agonist (SB 206553) receptors intrathecally in intact rats and monitored their effects on unrestrained locomotion. An intrathecal cannula was introduced at the low thoracic level and pushed caudally until the tip reached the L2/L3 or L5/L6 spinal segments. Locomotor performance was evaluated using EMG activity of hindlimb muscles during locomotion on a 2 m long runway. Motoneuron excitability was estimated using EMG recordings during dorsi- and plantar flexion at the ankle. Locomotion was dramatically impaired after the blockage of 5-HT_2A receptors. The effect of Cypr was more pronounced than that of Volin since in the L5/L6 rats Cypr (but not Volin) induced significant alteration of the strength of interlimb coordination followed by total paralysis. These agents significantly decreased locomotor EMG amplitude and abolished or substantially decreased stretch reflexes. Blocking 5-HT_2B/2C receptors had no effect either on locomotion or reflexes. We suggest that in intact rats serotonin controls timing and amplitude of muscle activity by acting on 5-HT_2A receptors on both CPG interneurons and motoneurons, while 5-HT_2B/2C receptors are not involved in control of the locomotor pattern in lumbar spinal cord.

5-HT7 Receptor Contributes to Proliferation, Migration and Invasion in NSCLC Cells

Introduction

Because only a small portion of NSCLC (non-small-cell lung cancer) patients benefit from molecular targeted therapy or immunotherapy and do not develop therapeutic resistance, continued research on new targets is warranted. Serotonin has recently emerged as a growth factor for tumor cells, and its receptors may be potential therapeutic targets. The mechanism related to the behavior of the 5-HT₇ receptor in NSCLC remains unknown.

Methods

Both gene expression analysis and immunohistochemical analysis were conducted to evaluate 5-HT₇ receptor expression in NSCLC tissues. The correlation between 5-HT₇ receptor expression and clinicopathological features was also examined. Cell proliferation was measured using a CCK8 (Cell Counting Kit-8) assay and colony formation, migration and invasion were evaluated by the Transwell assay. siRNA transfection and stimulation with the selective agonist LP211 were used to identify the involvement of molecules in proliferation, migration and invasion. Quantitative real-time chain reaction (qRT-PCR) and Western blotting were used to quantifiy mRNA and protein levels, respectively. Pathway inhibitors facilitated the exploration of possible signaling pathways regulated by the 5-HT₇ receptor in migration and invasion.

Results

The 5-HT₇ receptor was overexpressed in NSCLC tumor tissues compared with adjacent normal lung tissues. High 5-HT₇ receptor expression levels were correlated with lymph node metastasis (P=0.007) and advanced TNM stage (P=0.000) in NSCLC patients. The 5-HT₇ receptor positively regulated cell proliferation, migration and invasion in NSCLC cells. The stimulatory effect of the 5-HT₇ receptor on A549 cell migration and invasion may occur through the P38 pathway. In H1299 cells, the 5-HT₇ receptor might positively regulate Src to promote cell migration and invasion.

Conclusion

Our findings suggest that the 5-HT₇ receptor, which mediates NSCLC progression, may be a potential therapeutic target.

Role of the Serotonin Receptor 7 in Brain Plasticity: From Development to Disease

Our knowledge on the plastic functions of the serotonin (5-HT) receptor subtype 7 (5-HT7R) in the brain physiology and pathology have advanced considerably in recent years. A wealth of data show that 5-HT7R is a key player in the establishment and remodeling of neuronal cytoarchitecture during development and in the mature brain, and its dysfunction is linked to neuropsychiatric and neurodevelopmental diseases. The involvement of this receptor in synaptic plasticity is further demonstrated by data showing that its activation allows the rescue of long-term potentiation (LTP) and long-term depression (LTD) deficits in various animal models of neurodevelopmental diseases. In addition, it is becoming clear that the 5-HT7R is involved in inflammatory intestinal diseases, modulates the function of immune cells, and is likely to play a role in the gut-brain axis. In this review, we will mainly focus on recent findings on this receptor’s role in the structural and synaptic plasticity of the mammalian brain, although we will also illustrate novel aspects highlighted in gastrointestinal (GI) tract and immune system.

The Role of Descending Pain Modulation in Chronic Primary Pain: Potential Application of Drugs Targeting Serotonergic System

Chronic primary pain (CPP) is a group of diseases with long-term pain and functional disorders but without structural or specific tissue pathologies. CPP is becoming a serious health problem in clinical practice due to the unknown cause of intractable pain and high cost of health care yet has not been satisfactorily addressed. During the past decades, a significant role for the descending pain modulation and alterations due to specific diseases of CPP has been emphasized. It has been widely established that central sensitization and alterations in neuroplasticity induced by the enhancement of descending pain facilitation and/or the impairment of descending pain inhibition can explain many chronic pain states including CPP. The descending serotonergic neurons in the raphe nuclei target receptors along the descending pain circuits and exert either pro- or antinociceptive effects in different pain conditions. In this review, we summarize the possible underlying descending pain regulation mechanisms in CPP and the role of serotonin, thus providing evidence for potential application of analgesic medications based on the serotonergic system in CPP patients.

Towards selective CNS PET imaging of the 5-HT7 receptor system: Past, present and future

Since its discovery in 1993, the serotonin receptor subtype 7 (5-HT₇) has attracted significant attention as a potential drug target; due to its elucidated roles in conditions such as insomnia, schizophrenia, and more. Therefore, it is unsurprising that there has been relatively early efforts undertaken to develop a positron emission tomography (PET) imaging agent for said receptor system. PET can be clinically used to probe receptor systems in vivo, permitting information such as a drug's occupancy against this system to be investigated. This review focuses on the efforts towards the development of a 5-HT₇R selective PET CNS tracer over the last 20 years, critically reflecting on applied strategies and commonly employed chemical frameworks and suggests future considerations that are needed to successfully develop a PET tracer for this clinically relevant target. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Prior Activation of 5-HT7 Receptors Modulates the Conditioned Place Preference With Methylphenidate

The serotonin receptor subtype 7 (5-HT7R) is clearly involved in behavioral functions such as learning/memory, mood regulation and circadian rhythm. Recent discoveries proposed modulatory physiological roles for serotonergic systems in reward-guided behavior. However, the interplay between serotonin (5-HT) and dopamine (DA) in reward-related behavioral adaptations needs to be further assessed. TP-22 is a recently developed arylpiperazine-based 5-HT7R agonist, which is also showing high affinity and selectivity towards D1 receptors. Here, we report that TP-22 displays D1 receptor antagonist activity. Moreover, we describe the first in vivo tests with TP-22: first, a pilot experiment (assessing dosage and timing of action) identified the 0.25 mg/kg i.v. dosage for locomotor stimulation of rats. Then, a conditioned place preference (CPP) test with the DA-releasing psychostimulant drug, methylphenidate (MPH), involved three rat groups: prior i.v. administration of TP-22 (0.25 mg/kg), or vehicle (VEH), 90 min before MPH (5 mg/kg), was intended for modulation of conditioning to the white chamber (saline associated to the black chamber); control group (SAL) was conditioned with saline in both chambers. Prior TP-22 further increased the stimulant effect of MPH on locomotor activity. During the place-conditioning test, drug-free activity of TP-22+MPH subjects remained steadily elevated, while VEH+MPH subjects showed a decline. Finally, after a priming injection of TP-22 in MPH-free conditions, rats showed a high preference for the MPH-associated white chamber, which conversely had vanished in VEH-primed MPH-conditioned subjects. Overall, the interaction between MPH and pre-treatment with TP-22 seems to improve both locomotor stimulation and the conditioning of motivational drives to environmental cues. Together with recent studies, a main modulatory role of 5-HT7R for the processing of rewards can be suggested. In the present study, TP-22 proved to be a useful psychoactive tool to better elucidate the role of 5-HT7R and its interplay with DA in reward-related behavior.

New dual ligands for the D2 and 5-HT1A receptors from the group of 1,8-naphthyl derivatives of LCAP

More than 300 million people are suffering from depression, one of the civilization diseases in the 21st century. Serotonin 5-HT_1AR and dopamine D₂R play an important role in the treatment and pathogenesis of depression. Moreover, in recent years, the efficacy of dual 5-HT_1A/D₂ receptors ligands has been demonstrated in the fight against depression. In this work the new bulky arylpiperazine derivatives (LCAP) were synthesized in microwave radiation field. The affinities for the selected serotonin (5-HT_1A,5-HT_2A,5-HT₆,5-HT₇) and dopamine (D₂) receptors have been evaluated in vitro. Compounds 5.3a, 5.4, 5.1c, 5.3d, 5.2a are promising dual 5-HT_1AR/D₂R ligands. The SAR analysis were additionally supported with molecular docking studies.

Fear memory-induced alterations in the mRNA expression of G proteins in the mouse brain and the impact of immediate posttraining treatment with morphine

Disturbances in fear-evoked signal transduction in the hippocampus (HP), the nuclei of the amygdala (AMY), and the prefrontal cortex (PFC) underlie anxiety-related disorders. However, the molecular mechanisms underlying these effects remain elusive. Heterotrimeric G proteins (GPs) are divided into the following four families based on the intracellular activity of their alpha subunit (Gα): Gα(s) proteins stimulate cyclic AMP (cAMP) generation, Gα(i/o) proteins inhibit the cAMP pathway, Gα(q/11) proteins increase the intracellular Ca⁺⁺ concentration and the inositol trisphosphate level, and Gα(12/13) proteins activate monomeric GP-Rho. In the present study, we assessed the effects of a fear memory procedure on the mRNA expression of the Gα subunits of all four GP families in the HP, AMY and PFC. C57BL/6 J mice were subjected to a fear conditioning (FC) procedure followed by a contextual or cued fear memory test (CTX-R and CS-R, respectively). Morphine (MOR, 1 mg/kg/ip) was injected immediately after FC to prevent the fear consolidation process. Real-time quantitative PCR was used to measure the mRNA expression levels of Gα subunits at 1 h after FC, 24 h after FC, and 1 h after the CTX-R or CS-R. In the HP, the mRNA levels of Gα(s), Gα(12) and Gα(11) were higher at 1 h after training. Gα(s) levels were slightly lower when consolidation was stabilized and after the CS-R. The mRNA levels of Gα(12) were increased at 1 h after FC, returned to control levels at 24 h after FC and increased again with the CTX-R. The increase in the Gα(11) level persisted at 24 h after FC and after CTX-R. In the AMY, no specific changes were induced by FC. In the PFC, CTX-R was accompanied by a decrease in Gα(i/o) mRNA levels; however, only Gα(i2) downregulation was prevented by MOR treatment. Hence, the FC-evoked changes in Gα mRNA expression were observed mainly in the HP and connected primarily to contextual learning. These results suggest that the activation of signaling pathways by Gα(s) and Gα(12) is required to begin the fear memory consolidation process in the HP, while signal transduction via Gα(11) is implicated in the maintenance of fear consolidation. In the PFC, the downregulation of Gα(i2) appears to be related to the contextual learning of fear.

Enantioseparation of 5-chloro-2-{2-[3,4-dihydroisoquinoline-2(1H)-yl]ethyl}-2-methyl-2,3-dihydro-1H-inden-1-one (SYA 40247), a high-affinity 5-HT7 receptor ligand, by HPLC-PDA using amylose tris-(3, 5- dimethylphenylcarbamate) as a chiral stationary phase

In previous structure-activity relationship studies to identify new and selective 5-HT₇ receptor (5-HT₇ R) ligands, we identified the chiral compound, 5-chloro-2-{2-[3,4-dihydroisoquinoline-2(1H)-yl]ethyl}-2-methyl-2,3-dihydro-1H-inden-1-one (SYA 40247), with high-affinity binding to the 5-HT₇ R. Thus, it was of interest to separate the enantiomers in order to evaluate their affinity at the 5-HT₇ R. To achieve this separation, a normal-phase analytical method using HPLC-PDA and a 4.6 × 250 mm Chiralpak AD-H column was developed. Optimized isocratic conditions of 1.00 mL/min 95:5:0.1 v/v/v hexane-ethanol-diethylamine and a 254 nm analysis wavelength yielded a 6.07 min baseline separation. The method was scaled up to a 10 × 250 mm Chiralpak AD-H column, allowing 3 mg of racemate to be separated with a single injection, and 6 mg for an overlapping double injection in the same run. The separated enantiomers were reinjected into the analytical HPLC system, peak identities confirmed by retention time and PDA UV spectra, and the enantiomeric purities determined to be 100% for peak 1 and 100% for peak 2. A Jasco P-1020 polarimeter was used to determine the specific rotation [α] of the enantiomers of peaks 1 and 2, which were -86.2 and +93.3 (deg mL)/(g dm) respectively. No racemization was observed, and the enantiomeric purity remained at 100% for each peak.

The microRNA-29a Modulates Serotonin 5-HT7 Receptor Expression and Its Effects on Hippocampal Neuronal Morphology

miRNAs are master regulators of gene expression in diverse biological processes, including the modulation of neuronal cytoarchitecture. The identification of their physiological target genes remains one of the outstanding challenges. Recently, it has been demonstrated that the activation of serotonin receptor 7 (5-HT7R) plays a key role in regulating the neuronal structure, synaptogenesis, and synaptic plasticity during embryonic and early postnatal development of the central nervous system (CNS). In order to identify putative miRNAs targeting the 3'UTR of 5-HT7R mouse transcript, we used a computational prediction tool and detected the miR-29 family members as the only candidates. Thus, since miR-29a is more expressed than other members in the brain, we investigated its possible involvement in the regulation of neuronal morphology mediated by 5-HT7R. By luciferase assay, we show that miR-29a can act as a post-transcriptional regulator of 5-HT7R mRNA. Indeed, it downregulates 5-HT7R gene expression in cultured hippocampal neurons, while the expression of other serotonin receptors is not affected. From a functional point of view, miR-29a overexpression in hippocampal primary cultures impairs the 5HT7R-dependent neurite elongation and remodeling through the inhibition of the ERK intracellular signaling pathway. In vivo, the upregulation of miR-29a in the developing hippocampus parallels with the downregulation of 5-HT7R expression, supporting the hypothesis that this miRNA is a physiological modulator of 5-HT7R expression in the CNS.

Stimulating DDX3 expression by serotonin 5-HT receptor 7 through phosphorylation of p53 via the AC-PKA-ERK signaling pathway

DDX3 is a host viral factor that can inhibit the hepatitis B virus-induced innate immune responses. In this study, the 20 bioactive compounds have screened the effects on DDX3 and we found that 5-HT upregulated DDX3 promoter activity via the 5-HT₇ receptor on liver hepatocellular cells (HepG2 cells) by using a luciferase assay, reverse transcription-polymerase chain reaction analysis, and Western blot analysis. Furthermore, we are trying to elucidate the pathways involved in the stimulating effect of 5-HT on DDX3 expression to induce innate immune responses against hepatitis B virus infection. A knockdown of the 5-HT₇ receptor by transfection si-5-HT₇ receptors or si-control into HepG2 cells treated by 5-HT (or 5-HT plus agonist) confirmed the role of the 5-HT₇ receptor in DDX3 expression. The IFN-β-Luc expression and level of hepatitis B virus surface Antigen (HBsAg) showed that DDX3 mediated by the 5-HT₇ agonist (AS-19) increased IFN-β expression and inhibited HBV replication. Luciferase assays showed the involvement of 5-HT₇ receptors in DDX3 expression via cAMP/AC/PKA pathways by using protein kinase A (PKA) and adenylyl cyclase inhibitor (MDL 12330A). AS-19 mediated DDX3 promoter activated PKA extracellular signal-regulated kinase ERK signaling the p53 phosphorylation (-1080/-1070) resulted in upregulation of DDX3 promoter transactivation via the 5-HT₇ receptors agonist. Overall, 5-HT₇ was found to be a new potential target to inhibit hepatitis B infection by activating AC/PKA/ERK pathways by phosphorylating p53 via the 5-HT₇ agonist response by mediating DDX3 expression.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT₇, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT₇ plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT₇ activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT₇ in normal physiology and the therapeutic potential of this interesting drug target.

Search for a 5-CT alternative. In vitro and in vivo evaluation of novel pharmacological tools: 3-(1-alkyl-1H-imidazol-5-yl)-1H-indole-5-carboxamides, low-basicity 5-HT7 receptor agonists

Close structural analogues of 5-carboxamidotryptamine (5-CT) based on the newly discovered indole-imidazole scaffold were synthesized and evaluated to search for a 5-HT7 receptor agonist of higher selectivity. In vitro drug-likeness studies and in vivo pharmacological evaluation of potent and selective low-basicity 5-HT7 receptor agonists, previously published 7 (3-(1-ethyl-1H-imidazol-5-yl)-1H-indole-5-carboxamide, AH-494) and 13 (3-(1-methyl-1H-imidazol-5-yl)-1H-indole-5-carboxamide), have supported their usefulness as pharmacological tools. Comprehensive in vitro comparison studies between 7, 13 and the commonly used 5-CT showed their very similar ADMET properties. Compound 7 at 1 mg kg-1 reversed MK-801-induced disruption in novel object recognition in mice and alleviated stress-induced hyperthermia (SIH) at high doses. Taking into account both in vitro and in vivo data, 7 and 13 may be considered as alternatives to 5-CT as pharmacological tools with important additional benefit associated with their low-basicity: high selectivity over 5-HT1AR.

Review: 5-HT1, 5-HT2, 5-HT3 and 5-HT7 Receptors and their Role in the Modulation of Pain Response in the Central Nervous System

BACKGROUND

The aim of this review was to identify the mechanisms by which serotonin receptors involved at the central level are able to modulate the nociceptive response. Pain is a defense mechanism of the body that entails physiological, anatomical, neurochemical, and psychological changes, and is defined as an unpleasant sensory and emotional experience with potential risk of tissue damage, comprising the leading cause of appointments with Physicians worldwide. Treatment for this symptom has generated several neuropharmacological lines of research, due to the different types of pain and the various drugs employed to treat this condition. Serotonin [5- HydroxyTryptamine (5-HT)] is a neurotransmitter with seven families (5-HT1-5-HT7) and approximately 15 receptor subtypes. Serotonin modulates neuronal activity; however, this neurotransmitter is related with a number of physiological processes, such as cardiovascular function, gastric motility, renal function, etc. On the other hand, several researches reported that serotonin modulates nociceptive response through 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the Central Nervous System (CNS).

METHOD

In this review, a search was conducted on PubMed, ProQuest, EBSCO, and the Science Citation Index for studies evaluating the effects of 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the CNS on the modulation of different types of pain.

CONCLUSION

We concluded that 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the CNS modulate the pain, but this depends on the distribution of the receptors, dose of agonists or antagonists, administration route, pain type and duration in order to inhibit, excite, or even maintain the nociceptive response.

Prefrontal cortex executive processes affected by stress in health and disease

Prefrontal cortical executive functions comprise a number of cognitive capabilities necessary for goal directed behavior and adaptation to a changing environment. Executive dysfunction that leads to maladaptive behavior and is a symptom of psychiatric pathology can be instigated or exacerbated by stress. In this review we survey research addressing the impact of stress on executive function, with specific focus on working memory, attention, response inhibition, and cognitive flexibility. We then consider the neurochemical pathways underlying these cognitive capabilities and, where known, how stress alters them. Finally, we review work exploring potential pharmacological and non-pharmacological approaches that can ameliorate deficits in executive function. Both preclinical and clinical literature indicates that chronic stress negatively affects executive function. Although some of the circuitry and neurochemical processes underlying executive function have been characterized, a great deal is still unknown regarding how stress affects these processes. Additional work focusing on this question is needed in order to make progress on developing interventions that ameliorate executive dysfunction.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

The effect of chronic stimulation of serotonin receptor type 7 on recognition, passive avoidance memory, hippocampal long-term potentiation, and neuronal apoptosis in the amyloid β protein treated rat

RATIONALE

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory impairment, neuronal death, and synaptic loss in the hippocampus. Long-term potentiation (LTP), a type of synaptic plasticity, occurs during learning and memory. Serotonin receptor type 7 (5-HTR7) activation is suggested as a possible therapeutic target for AD.

OBJECTIVE

The aim of the present study was to examine the effects of chronic treatment with the 5-HTR7 agonist, AS19, on cognitive function, memory, hippocampal plasticity, amyloid beta (Aβ) plaque accumulation, and apoptosis in an adult rat model of AD.

METHODS

AD was induced in rats using Aβ (single 1 μg/μL intracerebroventricular (icv) injection during surgery). The following experimental groups were included: control, sham-operated, Aβ + saline (1 μL icv for 30 days), and Aβ + AS19 (1 μg/μL icv for 30 days) groups. The animals were tested for cognition and memory performance using the novel object recognition and passive avoidance tests, respectively. Next, anesthetized rats were placed in a stereotaxic apparatus for electrode implantation, and field potentials were recorded in the hippocampal dentate gyrus. Lastly, brains were removed and Aβ plaques and neuronal apoptosis were evaluated using Congo red staining and TUNEL assay, respectively.

RESULTS

Administration of AS19 in the Aβ rats increased the discrimination index of the novel object recognition test. Furthermore, AS19 treatment decreased time spent in the dark compartment during the passive avoidance test. AS19 also enhanced both the population spike (PS) amplitude and the field excitatory postsynaptic potential (fEPSP) slope evoked potentials of the LTP components. Aβ plaques and neuronal apoptosis were decreased in the AS19-treated Aβ rats.

CONCLUSIONS

These results indicate that chronic treatment with a 5-HTR7 agonist can prevent Aβ-related impairments in cognition and memory performance by alleviating Aβ plaque accumulation and neuronal apoptosis, hence improving neuronal plasticity. AS19 may be useful as a therapeutic agent for AD.