Effects of the potential 5-HT7 receptor agonist AS 19 in an autoshaping learning task

Therapeutic Potential and Limitation of Serotonin Type 7 Receptor Modulation

Although a number of mood-stabilising atypical antipsychotics and antidepressants modulate serotonin type 7 receptor (5-HT7), the detailed contributions of 5-HT7 function to clinical efficacy and pathophysiology have not been fully understood. The mood-stabilising antipsychotic agent, lurasidone, and the serotonin partial agonist reuptake inhibitor, vortioxetine, exhibit higher binding affinity to 5-HT7 than other conventional antipsychotics and antidepressants. To date, the initially expected rapid onset of antidepressant effects-in comparison with conventional antidepressants or mood-stabilising antipsychotics-due to 5-HT7 inhibition has not been observed with lurasidone and vortioxetine; however, several clinical studies suggest that 5-HT7 inhibition likely contributes to quality of life of patients with schizophrenia and mood disorders via the improvement of cognition. Furthermore, recent preclinical studies reported that 5-HT7 inhibition might mitigate antipsychotic-induced weight gain and metabolic complication by blocking other monoamine receptors. Further preclinical studies for the development of 5-HT7 modulation against neurodevelopmental disorders and neurodegenerative diseases have been ongoing. To date, various findings from various preclinical studies indicate the possibility that 5-HT7 modifications can provide two independent strategies. The first is that 5-HT7 inhibition ameliorates the dysfunction of inter-neuronal transmission in mature networks. The other is that activation of 5-HT7 can improve transmission dysfunction due to microstructure abnormality in the neurotransmission network-which could be unaffected by conventional therapeutic agents-via modulating intracellular signalling during the neurodevelopmental stage or via loss of neural networks with aging. This review attempts to describe the current and novel clinical applications of 5-HT7 modulation based on preclinical findings.

2-Phenethylamines in Medicinal Chemistry: A Review

A concise review covering updated presence and role of 2-phenethylamines in medicinal chemistry is presented. Open-chain, flexible alicyclic amine derivatives of this motif are enumerated in key therapeutic targets, listing medicinal chemistry hits and appealing screening compounds. Latest reports in discovering new bioactive 2-phenethylamines by research groups are covered too.

Therapeutic Effect of Erythropoietin on Alzheimer's Disease by Activating the Serotonin Pathway

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by memory impairment in patients. Erythropoietin (EPO) has been reported to stimulate neurogenesis. This study was conducted to determine the regenerative effects of EPO in an AD model and to assess its underlying mechanism. Recombinant human EPO was intraperitoneally administered to AD mice induced by intracerebroventricular Aβ oligomer injection. Behavioral assessments with novel object recognition test and passive avoidance task showed improvement in memory function of the EPO-treated AD mice compared to that of the saline-treated AD mice (p < 0.0001). An in vivo protein assay for the hippocampus and cortex tissue indicated that EPO treatment modulated neurotransmitters, including dopamine, serotonin, and adrenaline. EPO treatment also restored the activity of serotonin receptors, including 5-HT4R, 5-HT7R, and 5-HT1aR (p < 0.01), at mRNA levels. Furthermore, EPO seemed to exert an anti-inflammatory influence by downregulating TLR4 at mRNA and protein levels (p < 0.05). Finally, an immunohistochemical assay revealed increments of Nestin(+) and NeuN(+) neuronal cells in the CA3 region in the EPO-treated AD mice compared to those in the saline-treated AD mice. The conclusion is that EPO administration might be therapeutic for AD by activating the serotonergic pathway, anti-inflammatory action, and neurogenic characteristics.

Central nervous system effects of 5-HT7 receptors: a potential target for neurodegenerative diseases

5-HT₇ receptors (5-HT₇R) are the most recently identified among the family of serotonin receptors. Their role in health and disease, particularly as mediators of, and druggable targets for, neurodegenerative diseases, is incompletely understood. Unlike other serotonin receptors, for which abundant preclinical and clinical data evaluating their effect on neurodegenerative conditions exist, the available information on the role of the 5-HT₇R receptor is limited. In this review, we describe the signaling pathways and cellular mechanisms implicated in the activation of the 5-HT₇R; also, we analyze different mechanisms of neurodegeneration and the potential therapeutic implications of pharmacological interventions for 5-HT₇R signaling.

Participation of Hippocampal 5-HT5A, 5-HT6 and 5-HT7 Serotonin Receptors on the Consolidation of Social Recognition Memory

Social recognition is the ability of animals to identify and recognize a conspecific. The consolidation of social stimuli in long-term memory is crucial for the establishment and maintenance of social groups, reproduction and species survival. Despite its importance, little is known about the circuitry and molecular mechanisms involved in the social recognition memory (SRM). Serotonin (5-hydroxytryptamine, 5-HT) is acknowledged as a major neuromodulator, which plays a key role in learning and memory. Focusing on the more recently described 5-HT receptors, we investigated in the CA1 region of the dorsal hippocampus the participation of 5-HT_5A, 5-HT₆ and 5-HT₇ receptors in the consolidation of SRM. Male Wistar rats cannulated in CA1 were subjected to a social discrimination task. In the sample phase the animals were exposed to a juvenile conspecific for 1 h. Immediately after, they received different pharmacological treatments. Twenty-four hours later, they were submitted to a 5 min retention test in the presence of the previously presented juvenile (familiar) and a novel juvenile. The animals that received infusions of 5-HT_5A receptor antagonist SB-699551 (10 µg/µL), 5-HT₆ receptor agonist WAY-208466 (0.63 µg/µL) or 5-HT₇ receptor agonist AS-19 (5 µg/µL) intra-CA1 were unable to recognize the familiar juvenile. This effect was blocked by the coinfusion of WAY-208466 plus 5-HT₆ receptor antagonist SB-271046 (10 µg/µL) or AS-19 plus 5-HT₇ receptor antagonist SB-269970 (5 µg/µL). The present study helps to clarify the neurobiological functions of the 5-HT receptors more recently described and extends our knowledge about mechanisms underlying the SRM.

Serotonin modulation of hippocampal functions: From anatomy to neurotherapeutics

The hippocampal region receives a dense serotoninergic innervation originating from both medial and dorsal raphe nuclei. This innervation regulates hippocampal activity through the activation of distinct receptor families that are expressed in excitatory and inhibitory neurons, terminals of several afferent neurotransmitter systems, and glial cells. Preclinical and clinical studies indicate that hippocampal dysfunctions are involved in learning and memory deficits, dementia, Alzheimer's disease, epilepsy and mood disorders such as anxiety, depression and post-traumatic syndrome disorder, whereas the hippocampus participates also in the therapeutic mechanisms of numerous medicines. Not surprisingly, several drugs acting via 5-HT mechanisms are efficacious to some extent in some diseases and the link between 5-HT and the hippocampus although clear remains difficult to untangle. For this reason, we review reported data concerning the distribution and the functional roles of the 5-HT receptors in the hippocampal region in health and disease. The impact of the 5-HT systems on the hippocampal function is such that the research of new 5-HT mechanisms and drugs is still very active. It concerns notably drugs acting at the 5-HT_1A,_2A,_2C,_4,6 receptor subtypes, in addition to the already existing drugs including the selective serotonin reuptake inhibitors.

Alterations and interactions of subcortical modulatory systems in Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is not fully understood. Here we summarize current knowledge on the involvement of the serotonergic, noradrenergic, dopaminergic, cholinergic, and opioid systems in AD, emphasizing the importance of interactions between the serotonergic and the other subcortical modulatory systems during the progression of AD. In physiological conditions, all neurotransmitter systems function in concert and are interdependent at both the neuroanatomical and molecular levels. Through their early involvement in AD, cognitive and behavioral abilities that rely on their interactions also become disrupted. Considering that serotonin (5HT) regulates the release of noradrenaline (NA), dopamine (DA) and acetylcholine (ACh), any alteration in 5HT levels leads to disturbance of NA, DA, and ACh homeostasis in the brain. One of the earliest pathological changes during the prodromal phase of AD is a decrease of serotonergic transmission throughout the brain, with serotonergic receptors being also affected. Additionally, serotonergic and noradrenergic as well as serotonergic and dopaminergic nuclei are reciprocally interconnected. As the serotonergic dorsal raphe nucleus (DRN) is affected by pathological changes early in AD, and the noradrenergic locus coeruleus (LC) and dopaminergic ventral tegmental area (VTA) exhibit AD-related pathological changes, their connectivity also becomes altered in AD. Such disrupted interactions among neurotransmitter systems in AD can be used in the development of multi-target drugs. Some of the potential AD therapeutics (such as ASS234, RS67333, tropisetron) target multiple neurotransmitter systems to achieve the best possible improvement of cognitive and behavioral deficits observed in AD. Here, we review how serotonergic system interacts with other subcortical modulatory systems (noradrenergic, dopaminergic, cholinergic, and opioid systems) during AD.

Utilizing Designed Receptors Exclusively Activated by Designer Drug Chemogenetic Tools to Identify Beneficial G Protein-Coupled Receptor Signaling for Fibrosis

Fibrosis or accumulation of extracellular matrix is an evolutionarily conserved mechanism adopted by an organism as a response to chronic injury. Excessive fibrosis, however, leads to disruption of organ homeostasis and is a common feature of many chronic diseases. G protein-coupled receptors (GPCRs) are important cell signaling mediators and represent molecular targets for many Food and Drug Administration-approved drugs. To identify new targets for fibrosis, we used a synthetic GPCR system named designed receptors exclusively activated by designer drugs (DREADDs) to probe signaling pathways essential for fibrotic response. We found that upon expression in human lung fibroblasts, activation of Gq- and Gs-DREADDs abrogated the induction of TGFβ-induced fibrosis marker genes. Genome-wide transcriptome analysis identified dysregulation of multiple GPCRs in lung fibroblasts treated with TGFβ To investigate endogenous GPCR modulating TGFβ signaling, we selected 13 GPCRs that signal through Gq or Gs and activated them by using specific agonists. We examined the impact of each agonist and how activation of endogenous GPCR affects TGFβ signaling. Among the agonists examined, prostaglandin receptor agonists demonstrated the strongest inhibitory effect on fibrosis. Together, we have demonstrated that the DREADDs system is a valuable tool to identify beneficial GPCR signaling for fibrosis. This study in fibroblasts has served as a proof of concept and allowed us to further develop in vivo models for fibrosis GPCR discovery. SIGNIFICANCE STATEMENT: Fibrosis is the hallmark of many end-stage cardiometabolic diseases, and there is an unmet medical need to discover new antifibrotic therapies, reduce disease progression, and bring clinically meaningful efficacy to patients. Our work utilizes designed receptors exclusively activated by designer drug chemogenetic tools to identify beneficial GPCR signaling for fibrosis, providing new insights into GPCR drug discovery.

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

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

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.

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.

Unraveling the genes implicated in Alzheimer's disease

Alzheimer's disease (AD) is a heterogeneous neurodegenerative disorder and it is the most common form of dementia in the elderly. Early onset AD is caused by mutations in three genes: Amyloid-β precursor protein, presenilin 1 (PSEN1) and PSEN2. Late onset AD (LOAD) is complex and apolipoprotein E is the only unanimously accepted genetic risk factor for its development. Various genes implicated in AD have been identified using advanced genetic technologies, however, there are many additional genes that remain unidentified. The present review highlights the genetics of early and LOAD and summarizes the genes involved in different signaling pathways. This may provide insight into neurodegenerative disease research and will facilitate the development of effective strategies to combat AD.

Serotonin 5-HT6 Receptor Antagonists in Alzheimer's Disease: Therapeutic Rationale and Current Development Status

Alzheimer's disease (AD) is the most common cause of dementia in elderly people. Because of the lack of effective treatments for this illness, research focused on identifying compounds that restore cognition and functional impairments in patients with AD is a very active field. Since its discovery in 1993, the serotonin 5-HT₆ receptor has received increasing attention, and a growing number of studies supported 5-HT₆ receptor antagonism as a target for improving cognitive dysfunction in AD. This article reviews the rationale behind investigations into the targeting of 5-HT₆ receptors as a symptomatic treatment for cognitive and/or behavioral symptoms of AD. In addition to describing the available clinical evidence, this article also describes the purported biochemical and neurochemical mechanisms of action by which 5-HT₆ receptor antagonists could influence cognition, and the preclinical data supporting this therapeutic approach to AD. A large number of publications describing the development of ligands for this receptor have come to light and preclinical data indicate the procognitive efficacy of 5-HT₆ receptor antagonists. Subsequently, the number of patents protecting 5-HT₆ chemical entities has continuously grown. Some of these compounds have successfully undergone phase I clinical studies and have been further evaluated in clinical phase II trials with variable success. Phase II studies have also revealed the potential of combining 5-HT₆ receptor antagonism and cholinesterase inhibition. Two of these antagonists, idalopirdine and RVT-101, have been further developed into ongoing phase III clinical trials. Overall, 5-HT₆ receptor antagonists can reasonably be regarded as potential drug candidates for the treatment of AD.

Liver 5-HT7 receptors: A novel regulator target of fibrosis and inflammation-induced chronic liver injury in vivo and in vitro

BACKGROUND AND AIM

Hepatocellular cancer (HCC) is the sixth most common cancer and liver fibrosis is strongly associated with HCC. Treatment options are limited, and preventive strategies should be developed. An important step in the beginning of liver fibrosis is a strong inflammatory response. 5-HT7 is the last recognized member of the serotonin receptor family and is expressed in both central nerve system and peripheral system and have a lot of functions like learning, memory, smooth muscular relaxation, in the control of circadian rhythms and thermoregulation, pain and migraine, schizophrenia, anxiety, cognitive disturbances, and even inflammation.

METHODS

We therefore examined the biochemical, histopathological and molecular effects of the 5-HT7 receptor agonist and antagonist on inflammatory liver fibrogenesis in animal models of progressive cirrhosis: a mouse model induced by carbon tetrachloride (CCl4) and in Hep3b cells.

RESULTS

5-HT7 expression was observed in the liver in vivo and in vitro in CCl4-induced damage. 5-HT7 receptor agonist but not the antagonist reduced liver markers in mice and in Hep3b cells in carbon tetrachloride (CCl4) induced damage. 5-HT7 agonist, but not antagonist, protected liver tissue from oxidative stress in fibrosis. 5-HT7 agonist but not antagonist induces anti-inflammatory, anti-fibrinotic and anti-cytokine features in liver fibrosis in vivo and in vitro.

CONCLUSIONS

5-HT7 receptors have modulatory function and are an up-and-coming pharmacological target in the inflammatory fibrotic process. 5-HT7 receptor agonist LP-44 showed significant hepatoprotective effects against liver fibrosis, and LP-44 might become a useful therapeutic target for chronic liver inflammation and fibrosis.

Improvement of ketamine-induced social withdrawal in rats: the role of 5-HT7 receptors

Social withdrawal, one of the core negative symptoms of schizophrenia, can be modelled in the social interaction (SI) test in rats using N-methyl-D-aspartate receptor glutamate receptor antagonists. We have recently shown that amisulpride, an antipsychotic with a high affinity for serotonin 5-HT7 receptors, reversed ketamine-induced SI deficits in rats. The aim of the present study was to further elucidate the potential involvement of 5-HT7 receptors in the prosocial action of amisulpride. Acute administration of amisulpride (3 mg/kg) and SB-269970 (1 mg/kg), a 5-HT7 receptor antagonist, reversed ketamine-induced social withdrawal, whereas sulpiride (20 or 30 mg/kg) and haloperidol (0.2 mg/kg) were ineffective. The 5-HT7 receptor agonist AS19 (10 mg/kg) abolished the prosocial efficacy of amisulpride (3 mg/kg). The coadministration of an inactive dose of SB-269970 (0.2 mg/kg) showed the prosocial effects of inactive doses of amisulpride (1 mg/kg) and sulpiride (20 mg/kg). The anxiolytic chlordiazepoxide (2.5 mg/kg) and the antidepressant fluoxetine (2.5 mg/kg) were ineffective in reversing ketamine-induced SI deficits. The present study suggests that the antagonism of 5-HT7 receptors may contribute towards the mechanisms underlying the prosocial action of amisulpride. These results may have therapeutic implications for the treatment of negative symptoms in schizophrenia and other disorders characterized by social withdrawal.

An Algorithm to Identify Target-Selective Ligands - A Case Study of 5-HT7/5-HT1A Receptor Selectivity

A computational procedure to search for selective ligands for structurally related protein targets was developed and verified for serotonergic 5-HT7/5-HT1A receptor ligands. Starting from a set of compounds with annotated activity at both targets (grouped into four classes according to their activity: selective toward each target, not-selective and not-selective but active) and with an additional set of decoys (prepared using DUD methodology), the SVM (Support Vector Machines) models were constructed using a selective subset as positive examples and four remaining classes as negative training examples. Based on these four component models, the consensus classifier was then constructed using a data fusion approach. The combination of two approaches of data representation (molecular fingerprints vs. structural interaction fingerprints), different training set sizes and selection of the best SVM component models for consensus model generation, were evaluated to determine the optimal settings for the developed algorithm. The results showed that consensus models with molecular fingerprints, a larger training set and the selection of component models based on MCC maximization provided the best predictive performance.

The serotonergic system and cognitive function

Symptoms of cognitive dysfunction like memory loss, poor concentration, impaired learning and executive functions are characteristic features of both schizophrenia and Alzheimer’s disease (AD). The neurobiological mechanisms underlying cognition in healthy subjects and neuropsychiatric patients are not completely understood. Studies have focused on serotonin (5-hydroxytryptamine, 5-HT) as one of the possible cognitionrelated biomarkers. The aim of this review is to provide a summary of the current literature on the role of the serotonergic (5-HTergic) system in cognitive function, particularly in AD and schizophrenia.

The role of the 5-HTergic system in cognition is modulated by the activity and function of 5-HT receptors (5-HTR) classified into seven groups, which differ in structure, action, and localization. Many 5-HTR are located in the regions linked to various cognitive processes. Preclinical studies using animal models of learning and memory, as well as clinical in vivo (neuroimaging) and in vitro (post-mortem) studies in humans have shown that alterations in 5-HTR activity influence cognitive performance.

The current evidence implies that reduced 5-HT neurotransmission negatively influences cognitive functions and that normalization of 5-HT activity may have beneficial effects, suggesting that 5-HT and 5-HTR represent important pharmacological targets for cognition enhancement and restoration of impaired cognitive performance in neuropsychiatric disorders.

Hippocampal 5-HT7 receptors signal phosphorylation of the GluA1 subunit to facilitate AMPA receptor mediated-neurotransmission in vitro and in vivo

BACKGROUND AND PURPOSE

The 5-HT7 receptor is a GPCR that is the target of a broad range of antidepressant and antipsychotic drugs. Various studies have demonstrated an ability of the 5-HT7 receptor to modulate glutamatergic neurotransmission and cognitive processes although the potential impact upon AMPA receptors has not been investigated directly. The purposes of the present study were to investigate a direct modulation of the GluA1 AMPA receptor subunit and determine how this might influence AMPA receptor function.

EXPERIMENTAL APPROACH

The influence of pharmacological manipulation of the 5-HT7 receptor system upon phosphorylation of GluA1 subunits was assessed by Western blotting of fractionated proteins from hippocampal neurones in culture (or proteins resident at the neurone surface) and the functional impact assessed by electrophysiological recordings in rat hippocampus in vitro and in vivo.

KEY RESULTS

5-HT7 receptor activation increased cAMP and relative pCREB levels in cultures of rat hippocampal neurones along with an increase in phosphorylation (Ser845) of the GluA1 AMPA receptor subunit evident in whole neurone extracts and within the neurone surface compartment. Electrophysiological recordings in rat hippocampus demonstrated a 5-HT7 receptor-mediated increase in AMPA receptor-mediated neurotransmission in vitro and in vivo.

CONCLUSIONS AND IMPLICATIONS

The 5-HT7 receptor-mediated phosphorylation of the GluA1 AMPA receptor provides a molecular mechanism consistent with the 5-HT7 receptor-mediated increase in AMPA receptor-mediated neurotransmission.

Synthesis and Structure-Activity Relationship Analysis of 5-HT₇ Receptor Antagonists: Piperazin-1-yl Substituted Unfused Heterobiaryls

A series of piperazin-1-yl substituted unfused heterobiaryls was synthesized as ligands of the 5-HT₇ receptors. The goal of this project was to elucidate the structural features that affect the 5-HT₇ binding affinity of this class of compounds represented by the model ligand 4-(3-furyl)-2-(4-methylpiperazin-1-yl)pyrimidine (2). The SAR studies included systematical structural changes of the pyrimidine core moiety in 2 to quinazoline, pyridine and benzene, changes of the 3-furyl group to other heteroaryl substituents, the presence of various analogs of the 4-methylpiperazin-1-yl group, as well as additional substitutions at positions 5 and 6 of the pyrimidine. Substitution of position 6 of the pyrimidine in the model ligand with an alkyl group results in a substantial increase of the binding affinity (note a change in position numbers due to the nomenclature rules). It was also demonstrated that 4-(3-furyl) moiety is crucial for the 5-HT₇ binding affinity of the substituted pyrimidines, although, the pyrimidine core can be replaced with a pyridine ring without a dramatic loss of the binding affinity. The selected ethylpyrimidine (12) and butylpyrimidine (13) analogs of high 5-HT₇ binding affinity showed antagonistic properties in cAMP functional test and varied selectivity profile-compound 12 can be regarded as a dual 5-HT₇/5-HT2AR ligand, and 13 as a multi-receptor (5-HT₇, 5-HT2A, 5-HT₆ and D₂) agent.

Serotonin (5-HT)1A receptor agonism and 5-HT7 receptor antagonism ameliorate the subchronic phencyclidine-induced deficit in executive functioning in mice

RATIONALE

Reversal learning (RL), a type of executive function, dependent on prefrontal cortical function, is impaired in rodents by subchronic (sc) treatment with the N-methyl-D-aspartate receptor antagonist, phencyclidine (PCP), a widely studied model of cognitive impairment in schizophrenia (CIS).

OBJECTIVE

The principal objective of this study was to determine the ability of serotonin (5-HT)1A partial agonism and 5-HT7 receptor antagonism to improve RL in scPCP-treated mice.

METHODS

Male C57BL/6J mice were trained on an operant RL (ORL) task, then received PCP, 10 mg/kg, or saline, bid, for 7 days, followed by a 7-day washout period.

RESULTS

scPCP significantly diminished the percent correct responding, increased total incorrect trials, and total incorrect responses, in the reversal phase performance of the ORL task. Pre-treatment with the selective 5-HT1A partial agonist, tandospirone, or the selective 5-HT7 antagonist, SB269970, but not the 5-HT7 agonist, AS 19, reversed the scPCP-induced deficit in RL. Pre-treatment with atypical antipsychotic drug lurasidone, which is a 5-HT1A partial agonist and 5-HT7 antagonist, as well as a 5-HT2A and dopamine (D)2 antagonist, also reversed RL deficit in the scPCP-treated mice. Furthermore, the selective 5-HT1A antagonist, WAY100635, blocked the ability of lurasidone to reverse the scPCP-induced RL deficit.

CONCLUSIONS

These results indicate that 5-HT7 antagonism and 5-HT1A partial agonism contribute to restoration of RL in scPCP-treated mice. It is suggested that these two mechanisms are effective in restoring RL by decreasing excessive GABAergic inhibition of cortical pyramidal neurons following withdrawal of scPCP treatment.

The role of the serotonin receptor subtypes 5-HT1A and 5-HT7 and its interaction in emotional learning and memory

Serotonin [5-hydroxytryptamine (5-HT)] is a multifunctional neurotransmitter innervating cortical and limbic areas involved in cognition and emotional regulation. Dysregulation of serotonergic transmission is associated with emotional and cognitive deficits in psychiatric patients and animal models. Drugs targeting the 5-HT system are widely used to treat mood disorders and anxiety-like behaviors. Among the fourteen 5-HT receptor (5-HTR) subtypes, the 5-HT_1AR and 5-HT₇R are associated with the development of anxiety, depression and cognitive function linked to mechanisms of emotional learning and memory. In rodents fear conditioning and passive avoidance (PA) are associative learning paradigms to study emotional memory. This review assesses the role of 5-HT_1AR and 5-HT₇R as well as their interplay at the molecular, neurochemical and behavioral level. Activation of postsynaptic 5-HT_1ARs impairs emotional memory through attenuation of neuronal activity, whereas presynaptic 5-HT_1AR activation reduces 5-HT release and exerts pro-cognitive effects on PA retention. Antagonism of the 5-HT_1AR facilitates memory retention possibly via 5-HT₇R activation and evidence is provided that 5HT₇R can facilitate emotional memory upon reduced 5-HT_1AR transmission. These findings highlight the differential role of these 5-HTRs in cognitive/emotional domains of behavior. Moreover, the results indicate that tonic and phasic 5-HT release can exert different and potentially opposing effects on emotional memory, depending on the states of 5-HT_1ARs and 5-HT₇Rs and their interaction. Consequently, individual differences due to genetic and/or epigenetic mechanisms play an essential role for the responsiveness to drug treatment, e.g., by SSRIs which increase intrasynaptic 5-HT levels thereby activating multiple pre- and postsynaptic 5-HTR subtypes.

Serotonin, neural markers, and memory

Diverse neuropsychiatric disorders present dysfunctional memory and no effective treatment exits for them; likely as result of the absence of neural markers associated to memory. Neurotransmitter systems and signaling pathways have been implicated in memory and dysfunctional memory; however, their role is poorly understood. Hence, neural markers and cerebral functions and dysfunctions are revised. To our knowledge no previous systematic works have been published addressing these issues. The interactions among behavioral tasks, control groups and molecular changes and/or pharmacological effects are mentioned. Neurotransmitter receptors and signaling pathways, during normal and abnormally functioning memory with an emphasis on the behavioral aspects of memory are revised. With focus on serotonin, since as it is a well characterized neurotransmitter, with multiple pharmacological tools, and well characterized downstream signaling in mammals' species. 5-HT_1A, 5-HT₄, 5-HT₅, 5-HT₆, and 5-HT₇ receptors as well as SERT (serotonin transporter) seem to be useful neural markers and/or therapeutic targets. Certainly, if the mentioned evidence is replicated, then the translatability from preclinical and clinical studies to neural changes might be confirmed. Hypothesis and theories might provide appropriate limits and perspectives of evidence.

Effects of the selective 5-HT7 receptor antagonist SB-269970 on premature responding in the five-choice serial reaction time test in rats

The antagonists of serotonin 5-HT7 receptors have been demonstrated to ameliorate cognitive impairments in pharmacological animal models of schizophrenia that involve blockade of N-methyl-D-aspartate receptors (NMDARs). The administration of NMDAR antagonists evokes a broad range of cognitive deficits, including a loss of impulse control. The involvement of 5-HT7 receptors in the modulation of impulsivity has been recently suggested but has not been studied in great detail. The aim of the present study was to examine the effect of a selective 5-HT7 receptor antagonist SB-269970 on a measure of impulsive action, i.e., premature responding on the five-choice serial reaction time task (5-CSRTT) in rats. The antagonist of 5-HT2A receptor M100,907 was used as a positive control. The efficacies of both compounds were assessed in conditions of increased impulsivity that were produced by the administration of the NMDAR antagonist MK-801 or/and non-drug stimuli, i.e., using variable inter-trial intervals (vITIs). To examine the general ability of SB-269970 to counteract the MK-801-induced impairments, a discrete paired-trial delayed alternation task in a T-maze was employed. MK-801 significantly increased the number of premature responses in 5-CSRTT, and this effect was abolished by the administration of M100,907 (0.5 mg/kg) and SB-269970 (1 mg/kg). In addition, M100,907, but not SB-269970, reduced premature responding in the prolonged ITI trials. Both M100,907 and SB-269970 attenuated MK-801-induced working memory impairment in a T-maze. The present study demonstrated the efficacy of SB-269970 against MK-801-induced premature responding in the 5-CSRTT. This anti-impulsive action may offer additional benefits to the cognitive-enhancing effects of pharmacological blockade of 5-HT7 receptors.

Novel agonists for serotonin 5-HT7 receptors reverse metabotropic glutamate receptor-mediated long-term depression in the hippocampus of wild-type and Fmr1 KO mice, a model of Fragile X Syndrome

Serotonin 5-HT₇ receptors are expressed in the hippocampus and modulate the excitability of hippocampal neurons. We have previously shown that 5-HT₇ receptors modulate glutamate-mediated hippocampal synaptic transmission and long-term synaptic plasticity. In particular, we have shown that activation of 5-HT₇ receptors reversed metabotropic glutamate receptor-mediated long-term depression (mGluR-LTD) in wild-type (wt) and in Fmr1 KO mice, a mouse model of Fragile X Syndrome in which mGluR-LTD is abnormally enhanced, suggesting that 5-HT₇ receptor agonists might be envisaged as a novel therapeutic strategy for Fragile X Syndrome. In this perspective, we have characterized the basic in vitro pharmacokinetic properties of novel molecules with high binding affinity and selectivity for 5-HT₇ receptors and we have tested their effects on synaptic plasticity using patch clamp on acute hippocampal slices. Here we show that LP-211, a high affinity selective agonist of 5-HT₇ receptors, reverses mGluR-LTD in wt and Fmr1 KO mice, correcting a synaptic malfunction in the mouse model of Fragile X Syndrome. Among novel putative agonists of 5-HT₇ receptors, the compound BA-10 displayed improved affinity and selectivity for 5-HT₇ receptors and improved in vitro pharmacokinetic properties with respect to LP-211. BA-10 significantly reversed mGluR-LTD in the CA3-CA1 synapse in wt and Fmr1KO mice, indicating that BA-10 behaved as a highly effective agonist of 5-HT₇ receptors and reduced exaggerated mGluR-LTD in a mouse model of Fragile X Syndrome. On the other side, the compounds RA-7 and PM-20, respectively arising from in vivo metabolism of LP-211 and BA-10, had no effect on mGluR-LTD thus did not behave as agonists of 5-HT₇ receptors in our conditions. The present results provide information about the structure-activity relationship of novel 5-HT₇ receptor agonists and indicate that LP-211 and BA-10 might be used as novel pharmacological tools for the therapy of Fragile X Syndrome.

Targeting the Serotonin 5-HT7 Receptor in the Search for Treatments for CNS Disorders: Rationale and Progress to Date

The 5-HT7 (5-hydroxytryptamine 7, serotonin 7) receptor is one of the most recently identified members of the serotonin receptor family. Pharmacological tools, including selective antagonists and, more recently, agonists, along with 5-HT7 receptor (5-HT7R) knock-out mice have revealed the involvement of this receptor in central nervous system processes. Its well-established role in controlling body temperature and regulating sleep and circadian rhythms has implicated this receptor in mood disorders. Thus, the 5-HT7R has gained much attention as a possible target for the treatment of depression. Although preclinical data support the antidepressant-like actions of 5-HT7R antagonists, their clinical efficacy has not been yet established. Other evidence has implicated the 5-HT7R in learning and memory. Preclinical findings suggest that blockade of this receptor may be beneficial against schizophrenia-like cognitive deficits. Other possible indications include nociception, epilepsy, migraine, autism spectrum disorders, and Rett Syndrome. However, the question is whether the beneficial effects may be achieved by activation or blockade of 5-HT7Rs. Hence, this review briefly summarises the recent findings on the role of 5-HT7Rs and their ligands in CNS disorders.

Persistent modification of forebrain networks and metabolism in rats following adolescent exposure to a 5-HT7 receptor agonist

RATIONALE

The serotonin 7 receptor (5-HT7-R) is part of a neuro-transmission system with a proposed role in neural plasticity and in mood, cognitive or sleep regulation.

OBJECTIVES

We investigated long-term consequences of sub-chronic treatment, during adolescence (43-45 to 47-49 days old) in rats, with a novel 5-HT7-R agonist (LP-211, 0 or 0.250 mg/kg/day).

METHODS

We evaluated behavioural changes as well as forebrain structural/functional modifications by in vivo magnetic resonance (MR) in a 4.7 T system, followed by ex vivo histology.

RESULTS

Adult rats pre-treated during adolescence showed reduced anxiety-related behaviour, in terms of reduced avoidance in the light/dark test and a less fragmented pattern of exploration in the novel object recognition test. Diffusion tensor imaging (DTI) revealed decreased mean diffusivity (MD) in the amygdala, increased fractional anisotropy (FA) in the hippocampus (Hip) and reduced axial (D||) together with increased radial (D⊥) diffusivity in the nucleus accumbens (NAcc). An increased neural dendritic arborization was confirmed in the NAcc by ex vivo histology. Seed-based functional MR imaging (fMRI) identified increased strength of connectivity within and between "limbic" and "cortical" loops, with affected cross-correlations between amygdala, NAcc and Hip. The latter displayed enhanced connections through the dorsal striatum (dStr) to dorso-lateral prefrontal cortex (dl-PFC) and cerebellum. Functional connection also increased between amygdala and limbic elements such as NAcc, orbito-frontal cortex (OFC) and hypothalamus. MR spectroscopy (1H-MRS) indicated that adolescent LP-211 exposure increased glutamate and total creatine in the adult Hip.

CONCLUSIONS

Persistent MR-detectable modifications indicate a rearrangement within forebrain networks, accounting for long-lasting behavioural changes as a function of developmental 5-HT7-R stimulation.

Effect of 5-HT7 receptor blockade on liver regeneration after 60-70% partial hepatectomy

Background

Serotonin exhibits a vast repertoire of actions including cell proliferation and differentiation. The effect of serotonin, as an incomplete mitogen, on liver regeneration has recently been unveiled and is mediated through 5-HT₂ receptor. The aim of the present study was to investigate the effect of 5-HT₇ receptor blockade on liver regeneration after partial hepatectomy.

Methods

Male Wistar rats were subjected to 60-70% partial hepatectomy. 5-HT₇ receptor blockade was applied by intraperitoneal administration of SB-269970 hydrochloride two hours prior to and sixteen hours after partial hepatectomy and by intraperitoneal administration of SB-258719 sixteen hours after partial hepatectomy. Animals were sacrificed at different time points until 72 h after partial hepatectomy. Liver regeneration was evaluated by [³H]-thymidine incorporation into hepatic DNA, the mitotic index in hematoxylin-eosin (HE) sections and by immunochemical detection of Ki67 nuclear antigen. Reversion of 5-HT₇ blockade was performed by intraperitoneal administration of AS-19. Serum and liver tissue lipids were also quantified.

Results

Liver regeneration peaked at 24 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and at 32 h (mitotic index in HE sections) in the control group of rats. 5-HT₇ receptor blockade had no effect on liver regeneration when applied 2 h prior to partial hepatectomy. Liver regeneration was greatly attenuated when blockade of 5-HT₇ receptor was applied (by SB-258719 and SB-269970) at 16 h after partial hepatectomy and peaked at 32 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and 40 h (mitotic index in HE sections) after partial hepatectomy. AS-19 administration totally reversed the observed attenuation of liver regeneration.

Conclusions

In conclusion, 5-HT₇ receptor is a novel type of serotonin receptor implicated in hepatocyte proliferation.

5-HT7 receptors as modulators of neuronal excitability, synaptic transmission and plasticity: physiological role and possible implications in autism spectrum disorders

Serotonin type 7 receptors (5-HT7) are expressed in several brain areas, regulate brain development, synaptic transmission and plasticity, and therefore are involved in various brain functions such as learning and memory. A number of studies suggest that 5-HT7 receptors could be potential pharmacotherapeutic target for cognitive disorders. Several abnormalities of serotonergic system have been described in patients with autism spectrum disorder (ASD), including abnormal activity of 5-HT transporter, altered blood and brain 5-HT levels, reduced 5-HT synthesis and altered expression of 5-HT receptors in the brain. A specific role for 5-HT7 receptors in ASD has not yet been demonstrated but some evidence implicates their possible involvement. We have recently shown that 5-HT7 receptor activation rescues hippocampal synaptic plasticity in a mouse model of Fragile X Syndrome, a monogenic cause of autism. Several other studies have shown that 5-HT7 receptors modulate behavioral flexibility, exploratory behavior, mood disorders and epilepsy, which include core and co-morbid symptoms of ASD. These findings further suggest an involvement of 5-HT7 receptors in ASD. Here, we review the physiological roles of 5-HT7 receptors and their implications in Fragile X Syndrome and other ASD.

The role of serotonin in memory: interactions with neurotransmitters and downstream signaling

Serotonin, or 5-hydroxytryptamine (5-HT), is found to be involved in many physiological or pathophysiological processes including cognitive function. Seven distinct receptors (5-HT1-7), each with several subpopulations, have been identified for serotonin, which are different in terms of localization and downstream signaling. Because of the development of selective agonists and antagonists for these receptors as well as transgenic animal models of cognitive disorders, our understanding of the role of serotonergic transmission in learning and memory has improved in recent years. A large body of evidence indicates the interplay between serotonergic transmission and other neurotransmitters including acetylcholine, dopamine, γ-aminobutyric acid (GABA) and glutamate, in the neurobiological control of learning and memory. In addition, there has been an alteration in the density of serotonergic receptors in aging and Alzheimer's disease, and serotonin modulators are found to alter the process of amyloidogenesis and exert cognitive-enhancing properties. Here, we discuss the serotonin-induced modulation of various systems involved in mnesic function including cholinergic, dopaminergic, GABAergic, glutamatergic transmissions as well as amyloidogenesis and intracellular pathways.

Serotonin modulation of macrophage polarization: inflammation and beyond

Macrophages display a ample plethora of effector functions whose acquisition is promoted by the surrounding cytokine and cellular environment. Depending on the stimulus, macrophages become specialized ("polarized") for either pathogen elimination, tissue repair and wound healing or immunosuppression. This "polarization" versatility allows macrophages to critically contribute to tissue homeostasis, as they promote initiation and resolution of inflammatory responses. As a consequence, deregulation of the tissue macrophage polarization balance is an etiological agent of chronic inflammation, autoimmune diseases, cancer and even obesity and insulin resistance. In the present review we describe current concepts on the molecular basis and the patho-physiological implications of macrophage polarization, and describe its modulation by serotonin (5-HT), a neurotransmitter that regulates inflammation and tissue repair via a large set of receptors (5-HTR1-7). 5-HT modulates the phenotypic and functional polarization of macrophages, and contributes to the maintenance of an anti-inflammatory state mainly via 5-HTR2B and 5-HTR7, whose activation has a great impact on macrophage gene expression profile. The identification of 5-HTR2B and 5-HTR7 as functionally-relevant polarization markers suggests their therapeutic value in inflammatory pathologies as well as their potential involvement in linking the immune and nervous systems.

Modulation of 5-HT7 receptor: effect on object recognition performances in mice

OBJECTIVE

Recent data suggest that 5-HT7 receptors (5-HT7R) are involved in memory processes and, particularly, those related to novelty-induced arousal, even though this remains so far speculative and controversial. In order to assess the role of 5-HT7R in episodic-like memory, mice were administered 5-carboxamidotryptamine (5-CT, a 5-HT1A/1B/1D/7R agonist) and/or SB-269970 (a selective 5-HT7R antagonist) immediately after the acquisition session of the novel object recognition test.

MATERIALS AND METHODS

The object recognition test was performed in order to assess the effects of modulation of 5-HT7R during consolidation phase on episodic-like memory performances in mice. A protocol including 3 days of familiarisation to the apparatus has been realised in order to decrease the effect of novelty-induced arousal.

RESULTS

With a 2-h delay, SB-269970 (3 and 10 mg/kg, administered subcutaneously) impaired the discrimination of the novel object. With a 4-h delay, while control mice were not able to discriminate the novel object, mice treated with 5-CT (1 mg/kg) showed a significant discrimination. This promnesic effect with a long delay is effectively mediated by 5-HT7R activation since it was blocked by SB-269970 (10 mg/kg), but not by WAY-100135 (10 mg/kg) or by GR-127935 (10 mg/kg).

CONCLUSION

These data suggest that 5-HT7R tonically modulates cognitive processes involved in consolidation performances in object recognition. Therefore, 5-HT7R could be a promising target to treat memory dysfunctions (especially episodically related deficits) related to normal or pathological ageing.

Serotonergic modulation of neuronal activity in the nucleus accumbens following repeated methamphetamine administration in rats

Electrophysiological studies were performed to determine whether serotonergic modulation in the nucleus accumbens (NAcc) was affected after repeated methamphetamine (MAP) administration. NAcc slices (400 μm) from Wistar rats administered MAP (5 mg/kg) or saline once daily for 5 days were prepared 1, 5, or 10 days after the final injection. Population spikes (PS) induced by local stimulation of NAcc were recorded. PS inhibition by serotonin was significantly attenuated in the MAP group at 5 days but did not differ at 1 or 10 days. We next analyzed the effects of serotonin receptor subtype (5-HT1A,2,3,4,6,7)-selective agonists of PS. Differences between saline and MAP groups in 5-HT1A,2,3,4,6 receptor agonist-induced changes of PS were small or not significant. Interestingly, 5-HT7 receptor agonists significantly enhanced PS in the MAP group. Changes in the secondary messenger system related to 5-HT7 receptors were also investigated. Adenylate cyclase activator-induced PS enhancements were significantly larger in the MAP group. However, dibutyryl-cAMP-induced PS enhancement was not significantly different. In conclusion, 5-HT-induced inhibition of PS in NAcc was attenuated 5 days after repeated MAP treatment: the change in the effect of 5-HT was probably due to enhancement of the excitatory modulation via the 5-HT7 receptor with adenylate cyclase signal transduction systems.

The serotonin 5-HT7 receptors: two decades of research

Like most neurotransmitters, serotonin possesses a simple structure. However, the pharmacological consequences are more complex and diverse. Serotonin is involved in numerous functions in the human body including the control of appetite, sleep, memory and learning, temperature regulation, mood, behavior, cardiovascular function, muscle contraction, endocrine regulation, and depression. Low levels of serotonin may be associated with several disorders, namely increase in aggressive and angry behaviors, clinical depression, Parkinson's disease, obsessive-compulsive disorder, eating disorders, migraine, irritable bowel syndrome, tinnitus, and bipolar disease. These effects are mediated via different serotonin (5-HT) receptors. In this review, we will focus on the last discovered member of this serotonin receptor family, the 5-HT7 receptor. This receptor belongs to the G protein-coupled receptor superfamily and was cloned two decades ago. Later, different splice variants were described but no major functional differences have been described so far. All 5-HT7 receptor variants are coupled to Gαs proteins and stimulate cAMP formation. Recently, several interacting proteins have been reported, which can influence receptor signaling and trafficking.

Spinal 5-HT7 receptors and protein kinase A constrain intermittent hypoxia-induced phrenic long-term facilitation

Phrenic long-term facilitation (pLTF) is a form of serotonin-dependent respiratory plasticity induced by acute intermittent hypoxia (AIH). pLTF requires spinal Gq protein-coupled serotonin-2 receptor (5-HT2) activation, new synthesis of brain-derived neurotrophic factor (BDNF) and activation of its high-affinity receptor, TrkB. Intrathecal injections of selective agonists for Gs protein-coupled receptors (adenosine 2A and serotonin-7; 5-HT7) also induce long-lasting phrenic motor facilitation via TrkB "trans-activation." Since serotonin released near phrenic motor neurons may activate multiple serotonin receptor subtypes, we tested the hypothesis that 5-HT7 receptor activation contributes to AIH-induced pLTF. A selective 5-HT7 receptor antagonist (SB-269970, 5mM, 12 μl) was administered intrathecally at C4 to anesthetized, vagotomized and ventilated rats prior to AIH (3, 5-min episodes, 11% O2). Contrary to predictions, pLTF was greater in SB-269970 treated versus control rats (80 ± 11% versus 45 ± 6% 60 min post-AIH; p<0.05). Hypoglossal LTF was unaffected by spinal 5-HT7 receptor inhibition, suggesting that drug effects were localized to the spinal cord. Since 5-HT7 receptors are coupled to protein kinase A (PKA), we tested the hypothesis that PKA inhibits AIH-induced pLTF. Similar to 5-HT7 receptor inhibition, spinal PKA inhibition (KT-5720, 100 μM, 15 μl) enhanced pLTF (99 ± 15% 60 min post-AIH; p<0.05). Conversely, PKA activation (8-br-cAMP, 100 μM, 15 μl) blunted pLTF versus control rats (16 ± 5% versus 45 ± 6% 60 min post-AIH; p<0.05). These findings suggest a novel mechanism whereby spinal Gs protein-coupled 5-HT7 receptors constrain AIH-induced pLTF via PKA activity.

Acute 5-HT7 receptor activation increases NMDA-evoked currents and differentially alters NMDA receptor subunit phosphorylation and trafficking in hippocampal neurons

Background

N-methyl-D-aspartate (NMDA) receptors are regulated by several G protein-coupled receptors (GPCRs) as well as receptor tyrosine kinases. Serotonin (5-HT) type 7 receptors are expressed throughout the brain including the thalamus and hippocampus. Long-term (2–24 h) activation of 5-HT7 receptors promotes the expression of neuroprotective growth factor receptors, including the platelet-derived growth factor (PDGF) β receptors which can protect neurons against NMDA-induced neurotoxicity.

Results

In contrast to long-term activation of 5-HT7 receptors, acute (5 min) treatment of isolated hippocampal neurons with the 5-HT7 receptor agonist 5-carboxamidotryptamine (5-CT) enhances NMDA-evoked peak currents and this increase in peak currents is blocked by the 5-HT7 receptor antagonist, SB 269970. In hippocampal slices, acute 5-HT7 receptor activation increases NR1 NMDA receptor subunit phosphorylation and differentially alters the phosphorylation state of the NR2B and NR2A subunits. NMDA receptor subunit cell surface expression is also differentially altered by 5-HT7 receptor agonists: NR2B cell surface expression is decreased whereas NR1 and NR2A surface expression are not significantly altered.

Conclusions

In contrast to the negative regulatory effects of long-term activation of 5-HT7 receptors on NMDA receptor signaling, acute activation of 5-HT7 receptors promotes NMDA receptor activity. These findings highlight the potential for temporally differential regulation of NMDA receptors by the 5-HT7 receptor.

Only repeated administration of the serotonergic agonist 8-OH-DPAT improves place learning of rats subjected to fimbria-fornix transection

Serotonergic agonists may act neuroprotectively against brain injury. This study addressed the therapeutic potential of 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT), a selective 5-HT1A/7 receptor agonist, after mechanical brain injury, and evaluated its effects in terms of acquisition of an allocentric place learning task in a water maze. Rats were divided into 6 experimental groups, three of which were subjected to bilateral transection of fimbria-fornix (FF), while three groups were given control surgery (Sham). After surgery, within both the lesioned, and sham-operated animals, respectively, one group was administered a single dose of saline, one group was given a single dose (0.5 mg/kg/b.w.) of 8-OH-DPAT, and one group was treated with daily administration of 8-OH-DPAT (0.5 mg/kg/b.w.) for eight days. The acquisition of the water maze based place learning task started on the 8th day post-surgery and continued for 20 days. The results show that the lesioned group subjected to repeated administration of 8-OH-DPAT demonstrated a significantly improved acquisition of the place learning task compared to the vehicle injected lesion group. In contrast, the lesioned group treated with a single administration displayed impaired performance compared to the baseline lesion group. There were no significant effects of the 8-OH-DPAT administration in the sham control groups. We conclude that only the repeated stimulation of the 5-HT1A/7 system was associated with beneficial, recovery enhancing effects.

Amisulpride promotes cognitive flexibility in rats: the role of 5-HT7 receptors

The antagonism of 5-HT7 receptors may contribute to the antidepressant and procognitive actions of the atypical antipsychotic drug, amisulpride. It has been previously demonstrated that the selective 5-HT7 receptor antagonist reversed restraint stress-induced cognitive impairments in a rat model of frontal-dependent attentional set-shifting task (ASST). Therefore, the first aim of the present study was to assess the effectiveness of amisulpride against stress-evoked cognitive inflexibility. The second goal was to elucidate whether the pro-cognitive effect of amisulpride could be due to the compound's action at 5-HT7 receptors. Rats repeatedly exposed (1 h daily for 7 days) to restraint stress demonstrated impaired performance on the extra-dimensional (ED) set-shifting stage of the ASST. Amisulpride (3 mg/kg) given to stressed rats 30 min before testing reversed this restraint-induced cognitive inflexibility and improved ED performance of the unstressed control group. The 5-HT7 receptor agonist, AS19 (10 mg/kg), abolished the pro-cognitive efficacy of amisulpride (3 mg/kg). The present study suggests that the antagonism of 5-HT7 receptors may contribute to the mechanisms underlining the pro-cognitive action of amisulpride. These results may have therapeutic implications in frontal-like deficits associated with stress-related disorders.

Lurasidone: An Atypical Antipsychotic for Schizophrenia

OBJECTIVE:

To provide a clinical overview of the antipsychotic lurasidone.

DATA SOURCES:

Articles were identified by searching the MEDLINE, PubMed, Cochrane Library, and EBSCO databases (through February 2012) using the key word lurasidone. The manufacturer provided information on unpublished Phase 2 and 3 trials. The Clinicaltrials.gov database was reviewed for the status of ongoing and upcoming trials.

STUDY SELECTION AND DATA EXTRACTION:

All clinical trials lasting longer than 3 weeks and published in the English language were selected for review. Additional documentation, including the product dossier, package insert, and poster presentations supplied by the publisher, was also evaluated.

DATA SYNTHESIS:

Lurasidone hydrochloride is an atypical antipsychotic that is approved for the treatment of schizophrenia. It is under investigation for treatment of bipolar I disorder. It should be administered with food, is pregnancy category B, is contraindicated for coadministration with strong CYP3A4 inducers and inhibitors, and requires dose adjustments with certain medications and in renal and hepatic impairment. Like other atypical antipsychotics, lurasidone possesses dopamine D2 and serotonin 5-HT2A antagonism but exhibits little affinity for histamine H1, α1-adrenergic, or cholinergic M1 receptors. Additionally, it is a potent 5-HT7 antagonist, which may impact depression and cognition. Phase 3 trial results revealed that 40-80 mg administered once daily resulted in statistically significant improvements in schizophrenia symptomatology compared with placebo. Lurasidone's rate of metabolic adverse events is low relative to other atypical antipsychotics; however, this is offset by dose-dependent increases in somnolence, akathisia, and parkinsonism.

CONCLUSIONS:

Lurasidone has shown efficacy when compared to placebo in acute schizophrenia. Full characterization of the adverse effect profile and cognitive and affective benefits requires publication of trials with longer durations.