5-HT1A Receptor Subtype Research Articles

Chemical manipulations on the 1,4-dioxane ring of 5-HT1A receptor agonists lead to antagonists endowed with antitumor activity in prostate cancer cells

A series of derivatives obtained by moving the aromatic moiety on the 1,4-dioxane ring of compounds 1–3 from position 6 to position 2 or 3 was prepared and evaluated for the affinity for 5-HT1A receptor (5-HT1AR) and α1-adrenoceptor (α1-AR) subtypes. Moreover, the flexible 2-ethanolamine linker of the most interesting compounds was replaced by the more conformationally constrained piperazine ring. In vitro functional studies performed on derivatives showing the highest affinities for 5-HT1AR highlighted that the shifting of the diphenyl moiety of derivatives 2 and 13 from position 6 to position 3 of the 1,4-dioxane nucleus, affording 11 and 16, respectively, modulated the 5-HT1AR functional profile from agonism to antagonism. Docking simulations, performed on the human 5-HT1AR, further rationalized the biological results, delving into the features which modulate the shift between agonist and antagonist activity. Interestingly, compound 11, endowed with mixed 5-HT1AR/α1d-AR antagonist profile, showed antiproliferative and cytotoxic effects on both PC-3 and DU-145 prostate cancer cell lines higher than those of the α1d-AR antagonist 2 and the 5-HT1AR antagonist 16. The experiments performed in the presence of the endogenous agonists norepinephrine and serotonin confirmed the involvement of both receptor systems in the antitumor activity of 11.

Glial Activation and Expression of the Serotonin Transporter in Chronic Fatigue Syndrome.

Fatigue is commonly reported in a variety of illnesses and has major impact on quality of life. Chronic fatigue syndrome (CFS) is a debilitating syndrome of unknown etiology. The clinical symptoms include problems in neuroendocrine, autonomic, and immune systems. It is becoming clear that the brain is the central regulator of CFS. For example, neuroinflammation, especially induced by activation of microglia and astrocytes, may play a prominent role in the development of CFS, though little is known about molecular mechanisms. Many possible causes of CFS have been proposed. However, in this mini-review, we summarize evidence for a role for microglia and astrocytes in the onset and the maintenance of immunologically induced CFS. In a model using virus mimicking synthetic double-stranded RNA, infection causes sequential signaling such as increased blood brain barrier (BBB) permeability, microglia/macrophage activation through Toll-like receptor 3 (TLR3) signaling, secretion of IL-1β, upregulation of the serotonin transporter (5-HTT) in astrocytes, reducing extracellular serotonin (5-HT) levels and hence reduced activation of 5-HT1A receptor subtype. Hopefully, drug discovery targeting these pathways may be effective for CFS therapy.

Diverse serotonin actions of vilazodone reduce l-3,4-dihidroxyphenylalanine-induced dyskinesia in hemi-parkinsonian rats.

The serotonergic system is a well-established modulator of l-dopa-induced dyskinesia. To date, targeting serotonin transporters or serotonin receptor subtype 1A (5-HT1A ) reduces l-dopa-induced dyskinesia in animal models; however, these strategies have failed to translate clinically. Ideally, a compound acting at both known antidyskinetic sites could optimize serotonin-mediated approaches. Vilazodone is a selective serotonin reuptake inhibitor and a partial 5-HT1A agonist approved by the U.S. Food and Drug Administration, situating Vilazodone in a unique position to reduce l-dopa-induced dyskinesia without compromising l-dopa-mediated motor improvements. The goal of the present study was to characterize Vilazodone's effects on l-dopa-induced behaviors, neurochemistry and gene expression in unilateral 6-hydroxydopamine-lesioned hemi-parkinsonian rats. In experiments 1 and 2, l-dopa-naïve and l-dopa-primed animals were coadministered Vilazodone and l-dopa daily for 3 weeks to model subchronic use, and behavioral, neurochemical, and messenger RNA (mRNA) expression changes were measured. In experiment 3, dyskinetic behavior was assessed following 5-HT1A or serotonin receptor subtype 1B blockade prior to Vilazodone-l-dopa coadministration. Vilazodone significantly suppressed developing and established l-dopa-induced dyskinesia without compromising the promotor effects of l-dopa therapy. In the dopamine-depleted striatum, Vilazodone-l-dopa cotreatment increased dopamine content, suggesting a normalization of dopamine kinetics in dyskinetic brain, and reduced l-dopa-induced c-Fos and preprodynorphin mRNA overexpression, indicative of attenuated dopamine D1 receptor-mediated direct pathway overactivity. Only 5-HT1A antagonism partially attenuated Vilazodone's antidyskinetic efficacy, suggesting both serotonin transporter-dependent effects and 5-HT1A receptors in Vilazodone's actions. Our findings show Vilazodone has a serotonin-dependent effect on rodent l-dopa-induced dyskinesia and implicate the potential for repositioning Vilazodone against l-dopa-induced dyskinesia development and expression in Parkinson's disease patients. © 2018 International Parkinson and Movement Disorder Society.

Long-Term Effects of Iloperidone on Cerebral Serotonin and Adrenoceptor Subtypes

The atypical antipsychotic drug iloperidone has high affinity for a wide range of neurotransmitter receptors, including serotonin and adrenoceptors. We examined the long-term effects of multiple doses of iloperidone (0.5, 1.5, or 5mg/kg) on serotonin (5-HT) 5-HT1A, 5-HT2A receptor subtypes, and adrenoceptors α1 and α2 subtypes. Rats received daily intraperitoneal injections of different doses of iloperiodone or vehicle for 4weeks. Receptor autoradiography quantified the levels of 5-HT and adrenoceptors in medial prefrontal cortex (MPC), dorsolateral frontal cortex (DFC), caudate putamen (CPu), nucleus accumbens (NAc), and hippocampal CA1 (HIP-CA1) and CA3 (HIP-CA3) regions. Four weeks of iloperidone treatment significantly and dose-dependently increased 5-HT1A and decreased 5-HT2A receptors in the MPC and DFC. Higher doses of iloperidone (1.5 and 5mg/kg) increased 5-HT1A and decreased 5-HT2A receptors in HIP-CA1 and HIP-CA3 regions. In addition, repeated iloperidone treatment produced significant increases in α1- and α2-adrenoceptors in MPC, DFC, HIP-CA1, and HIP-CA3 regions. No changes in 5-HT and adrenoceptors were observed in other brain regions examined. These results suggest that long-term iloperidone treatment exerts region- and dose-specific effects on forebrain 5-HT and adrenoceptors, which may contribute to its therapeutic benefits in improving positive and negative symptoms of schizophrenia as well as maintaining a benign safety profile.

Classics in Neuroimaging: The Serotonergic 2A Receptor System-from Discovery to Modern Molecular Imaging.

Already in 1953, Woolley and Shaw speculated that serotonin could be involved in a range of central nervous system (CNS) disorders. Lysergic acid diethylamide (LSD) displayed an important role in this respect. It was used not only to antagonize biological effects of serotonin and to study the system itself, but also to identify serotonergic subtype receptors. The 5-HT2A receptor was discovered in the 1970s and identified as the responsible receptor mediating psychedelic effects of LSD. The development of positron emission tomography (PET) allowed to study this receptor system in vivo. Parameters such as abundance of 5-HT2A neuroreceptors or receptor occupancy can be determined using PET. As such, the development of 5-HT2A receptor tracers started immediately after the introduction of PET in the mid-1970s. In this Viewpoint, we provide a historical overview from the discovery of serotonin to the identification of the 5-HT2A receptor subtype and the subsequent development of 5-HT2A receptor subtype specific PET tracers over the last four decades. We emphasize the interplay between pharmacology, medicinal chemistry, radiochemistry, and nuclear medicine that is important while developing a PET tracer. Moreover, we highlight selected examples applying 5-HT2A receptor PET tracers within neurological diseases and drug occupancy studies.

5-HT2A receptor is the predominant receptor mediating contraction of the isolated porcine distal ureter to 5-HT in young and old animals

Isolated ureteral strips develop spontaneous phasic contractile activity which is enhanced by 5-hydroytryptamine (5-HT). The aim of this study was to identify the receptor subtype mediating these responses and to determine whether responses to 5-HT change with age. The frequency of contractions and the overall contractile activity (measured as the area under the curve, AUC) were recorded in strips of porcine distal ureter isolated from young (3 months) and old (2 years) pigs. Responses to 5-HT were examined in the absence and presence of selective 5-HT receptor subtype antagonists. Tissues from the younger animals elicited larger contractile responses to 5-HT (5885 ± 335g−1 s) than tissues from the older animals (2787 ± 317g−1 s, P < 0.001). The 5-HT2A receptor antagonist ketanserin (10–100nM) elicited rightward shifts of 5-HT concentration-response curves, antagonising AUC and frequency responses with high affinity in tissues from both age groups (pKD values 8.4–8.8). The slopes of the corresponding Schild plots were not significantly different from unity, suggesting a competitive antagonism at a single receptor, except for frequency responses to 5-HT in the older animals. Antagonists selective for other 5-HT receptor subtypes: methiothepin (non-selective), RS-10221 (5-HT2C), ondansetron (5-HT3), GR-113808 (5-HT4), SB699551 (5-HT5), SB399885 (5-HT6), SB269970 (5-HT7)) had no effect on 5-HT-induced responses. The results suggest that the 5-HT2A receptor subtype is the predominant receptor mediating 5-HT responses in ureteral tissues, being the sole mediator of responses in tissues from young animals, but with another receptor subtype also playing a minor role in the older animals.

Contribution of 5-HT2A receptors on diaphragmatic recovery after chronic cervical spinal cord injury

Unilateral C2 spinal cord hemisection (C2Hx) interrupts bulbospinal respiratory pathways innervating ipsilateral phrenic motoneurons, resulting in cessation of ipsilateral diaphragm motor output. Plasticity within the spinal neural circuitry controlling the diaphragm can induce partial recovery of phrenic bursting which correlates with the time-dependent return of spinal serotonin (5-HT) immunoreactivity in the vicinity of phrenic motoneurons. The 5-HT2A receptor subtype is present on phrenic motoneurons and its expression is up-regulated after cervical spinal cord injury; however the functional role of these receptors following injury has not been clearly defined. The present study evaluated the functional role of 5-HT2A receptors by testing the hypothesis that pharmacologic blockade would attenuate diaphragm activity in rats with chronic cervical spinal cord injury. Bilateral diaphragm electromyography (EMG) was performed in vagal-intact and spontaneously breathing rats before and after intravenous administration of the 5-HT2A receptor antagonist Ketanserin (1mg/kg). Intravenous ketanserin significantly attenuated ipsilateral diaphragm EMG activity in C2Hx animals but had no impact on diaphragm output in uninjured animals. We conclude that 5-HT2A receptor activation contributes to the recovery of ipsilateral phrenic motor output after chronic cervical spinal cord injury.

Utilization of an Active Site Mutant Receptor for the Identification of Potent and Selective Atypical 5-HT2C Receptor Agonists.

Agonism of the 5-HT2C receptor represents one of the most well-studied and clinically proven mechanisms for pharmacological weight reduction. Selectivity over the closely related 5-HT2A and 5-HT2B receptors is critical as their activation has been shown to lead to undesirable side effects and major safety concerns. In this communication, we report the development of a new screening paradigm that utilizes an active site mutant D134A (D3.32) 5-HT2C receptor to identify atypical agonist structures. We additionally report the discovery and optimization of a novel class of nonbasic heterocyclic amide agonists of 5-HT2C. SAR investigations around the screening hits provided a diverse set of potent agonists at 5-HT2C with high selectivity over the related 5-HT2A and 5-HT2B receptor subtypes. Further optimization through replacement of the amide with a variety of five- and six-membered heterocycles led to the identification of 6-(1-ethyl-3-(quinolin-8-yl)-1H-pyrazol-5-yl)pyridazin-3-amine (69). Oral administration of 69 to rats reduced food intake in an ad libitum feeding model, which could be completely reversed by a selective 5-HT2C antagonist.

The Effect of Serotonin-Targeting Antidepressants on Neurogenesis and Neuronal Maturation of the Hippocampus Mediated via 5-HT1A and 5-HT4 Receptors.

Antidepressant drugs such as selective serotonin reuptake inhibitors (SSRIs) specifically increase serotonin (5-HT) levels in the synaptic cleft and are widely used to treat mood and anxiety disorders. There are 14 established subtypes of 5-HT receptors in rodents, each of which has regionally different expression patterns. Many preclinical studies have suggested that the hippocampus, which contains abundant 5-HT1A and 5-HT4 receptor subtypes in the dentate gyrus (DG), is critically involved in the mechanisms of action of antidepressants. This review article will analyze studies demonstrating regulation of hippocampal functions and hippocampus-dependent behaviors by SSRIs and similar serotonergic agents. Multiple studies indicate that 5-HT1A and 5-HT4 receptor signaling in the DG contributes to SSRI-mediated promotion of neurogenesis and increased neurotrophic factors expression. Chronic SSRI treatment causes functions and phenotypes of mature granule cells (GCs) to revert to immature-like phenotypes defined as a “dematured” state in the DG, and to increase monoamine reactivity at the dentate-to-CA3 synapses, via 5-HT4 receptor signaling. Behavioral studies demonstrate that the 5-HT1A receptors on mature GCs are critical for expression of antidepressant effects in the forced swim test and in novelty suppressed feeding; such studies also note that 5-HT4 receptors mediate neurogenesis-dependent antidepressant activity in, for example, novelty-suppressed feeding. Despite their limitations, the collective results of these studies describe a potential new mechanism of action, in which 5-HT1A and 5-HT4 receptor signaling, either independently or cooperatively, modulates the function of the hippocampal DG at multiple levels, any of which could play a critical role in the antidepressant actions of 5-HT-enhancing drugs.

Growing Evidence for Heterogeneous Synaptic Localization of 5-HT2A Receptors.

The serotonin 2A (5-HT2A) receptor subtype continues to attract attention as a target for numerous psychoactive drugs including psychedelic hallucinogens, antidepressants, anxiolytics, and atypical antipsychotics. 5-HT2A receptors are a principal G protein-coupled receptor subtype mediating the excitatory effects of serotonin. Nonetheless, pre- vs postsynaptic localization of 5HT2A receptors, relative to glutamatergic synapses, has remained controversial. Here, we discuss recent findings highlighting the existence and roles of presynaptic 5-HT2A receptors in regulating glutamatergic transmission and cognition.

Editorial: Serotonin and Memory.

Several neurotransmission systems have been involved in function and dysfunctional memory (e.g., Myhrer, 2003; Decker and McGaugh, 2004; Reis et al., 2009; Cassel, 2010; Rodriguez et al., 2012; Komal and Nashmi, 2015), including serotonin (5-hydroxytryptamine, 5-HT), which accounts with multiple neural markers (receptors, transporter; e.g., Hannon and Hoyer, 2008; Saulin et al., 2012; Seyedabadi et al., 2014; McCorvy and Roth, 2015). Indeed, the 5-HT system can be manipulated in multiple ways with pharmacological tools and possesses well characterized downstream signaling in mammals' species (e.g., Marin et al., 2012; McCorvy and Roth, 2015). Emergent evidence indicates that this monoamine system might be a therapeutic target and neural marker regarding function and dysfunctional memory. This issue presents recent advances including the role of 5-HT2A and 5-HT1A receptors in the medial prefrontal cortex during recognition memory (Morici et al.). Hippocampal 5-HT1A receptors and spatial and memory is revised by Glikmann-Johnston et al. Ochoa et al. report that post-training serotonergic depletions of the basolateral amygdala did not disrupt discrimination, retention or reversal learning; suggesting that this serotonergic activity is not required for formation and flexible adjustment of new stimulus-reward associations when the strategy to efficiently solve the task has already been learned. Hernandez-Perez et al. report that serotonin reduction in the supramammillary nucleus alters place learning and concomitant hippocampal, septal, and supramammillar theta activity in spatial memory. Zhang and Stackman review progress in the 5-HT2A receptor distribution, signaling, polymerization, and allosteric modulation; as well as functions in learning and memory, hallucination and spatial cognition, and mental disorders. Pereira et al. show us that 5-HT6 receptor agonism facilitates emotional learning and involves prefrontal cortex and hippocampal signaling. Serotonergic transporter function is reported by Sivamaruthi et al. demonstrating that cronobacter sakazakii infection alters serotonin transporter and improved fear memory retention. Stiedl et al. discuss the role of the serotonin receptor subtypes 5-HT1A and 5-HT7 and their interaction in emotional learning and memory; including the role of these receptors and their interplay at the molecular, neurochemical, and behavioral level. The potential involvement of serotonergic neural markers with respect to memory is reviewed by Meneses. Special mention and thanks to the expert work of the referees, who made professional and careful reviews that improved the papers in this topic.

Hippocampal 5-HT1A Receptor and Spatial Learning and Memory.

Spatial cognition is fundamental for survival in the topographically complex environments inhabited by humans and other animals. The hippocampus, which has a central role in spatial cognition, is characterized by high concentration of serotonin (5-hydroxytryptamine; 5-HT) receptor binding sites, particularly of the 1A receptor (5-HT1A) subtype. This review highlights converging evidence for the role of hippocampal 5-HT1A receptors in spatial learning and memory. We consider studies showing that activation or blockade of the 5-HT1A receptors using agonists or antagonists, respectively, lead to changes in spatial learning and memory. For example, pharmacological manipulation to induce 5-HT release, or to block 5-HT uptake, have indicated that increased extracellular 5-HT concentrations maintain or improve memory performance. In contrast, reduced levels of 5-HT have been shown to impair spatial memory. Furthermore, the lack of 5-HT1A receptor subtype in single gene knockout mice is specifically associated with spatial memory impairments. These findings, along with evidence from recent cognitive imaging studies using positron emission tomography (PET) with 5-HT1A receptor ligands, and studies of individual genetic variance in 5-HT1A receptor availability, strongly suggests that 5-HT, mediated by the 5-HT1A receptor subtype, plays a key role in spatial learning and memory.

Mirtazapine in Paroxetine Induced Hyper-prolactinemic Galactorrhoea.

TO THE EDITOR Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat a gamut of depression-anxiety-spectrum disorders. Paroxetine is preferred in cases with co-existent anxiety because of its sedating properties. One problematic side-effect of all SSRIs is galactorrhea, secondary to raised prolactin levels, which might compromise treatment of index symptoms and impose additional morbidity. A 48-years old, postmenopausal housewife, with nil contributory family/past medical/past psychiatric or substance related history; hysterectomy with bilateral salpingo-oophorectomy (for fibroid-uterus) one year ago; presented to us with chief complaints of low mood, feeling anxious, restlessness, and with decreased sleep for one year. She reported feeling sad for most of last year, with an inability to feel good in social company, family gatherings or while doing previously-pleasurable activities. She reported feeling anxious and restless for no particular reason; reduced interest in household activities and a feeling of fatigue while doing minor works, leading to gradual neglect of these. There was subjective reduction in body weight, and feeling of heaviness and generalized bodyache during this time. Her sleep time had also reduced significantly, from 6-8 hours to 3-4 hours, with difficulty in falling asleep and frequent awakenings. There was also a reduction in her libido for last one year. She was not on any hormone-replacement therapy. On mental status examination patient was looking of her age, dressed appropriately to her socioeconomic status, but had reduced eye contact. Her motor activity was reduced, speech was coherent and relevant but with reduced productivity; with depressed affect, intact abstract and judgment abilities. She reported feelings of hopelessness and helplessness. There was nil active suicidality, and Hamilton Depression Rating Scale (HAM-D) and Hamilton Anxiety Rating Scale (HAM-A) scores were 13/51 and 16/56 respectively. General physical and systemic examinations were within normal limit, and brain magnetic resonance imaging was unremarkable. She was prescribed paroxetine extended-release 12.5 mg at night, and advised thyroid profile. After 20 days of treatment, thyroid profile was normal. Though depressive and anxiety symptoms had improved (HAM-D, 10; HAM-A, 11), she had a fresh complain of galactorrhea for past 6 days. Prolactin level was found to be 41.31 g/L. Paroxetine was discontinued, and we shifted her to mirtazapine 7.5 mg at night, hiked to 15 mg after 7 days. In 15 days, her galactorrhea improved, and stopped over next fortnight. Her prolactin level reduced to 20.53 g/L, while HAM-D and HAM-A had improved to 8 each. All SSRIs are known to cause hyperprolactenemia, but the exact mechanism is not known. Serotonin is one of the modulators affecting prolactin release in neurohypophysis; mediated directly or indirectly via stimulation of post-synaptic 5-HT1A, 5-HT2A, and 5-HT2C receptor subtypes from excess serotonin levels at the synapses. Mirtazapine has a markedly different receptor profile, as it blocks presynaptic alpha-2 adrenergic receptors and inhibits, rather than stimulating, postsynaptic serotonin 5-HT2 and 5-HT3 receptors. Therefore, mirtazapine is theoretically not expected to raise prolactin levels, and thus is unlikely to cause galactorrhea. Hence, mirtazapine may be a safe option for those unable to tolerate SSRI-associated galactorrhea, but nevertheless requiring antidepressant treatment for their symptoms.

The role of serotonergic system in cardiovascular diseases development in children

The role of the serotonin system as a link in the pathogenesis of atherosclerosis and arterial hypertension is widely discussed during the recent decades. Serotonin and histamine are part of humoral system of physiological processes regulators and modulators which under pathological conditions are transformed into factors contributing to the disease development. The membrane serotonin transporter has been identified on neurons, platelets, myocardium and smooth muscle cells. The higher is the activity of membrane transporter, the higher is the platelet serotonin concentration, its release into the blood plasma increases thus implementing its negative effects on platelets and wall of the vessels. 5-HT1A, 5-HT2 and 5-HT3 receptor subtypes play a key role in the central mechanisms of regulation of cardiovascular activities while peripheral effects of serotonin on the vascular system are mediated by 5-HT1, 5-HT2, 5-HT3, 5-HT4 and 5-HT7 receptor subtypes. Activation of 5-HT1A receptors causes inhibition of central sympathetic influences and further bradycardia, while 5-HT2 receptors activation - arousal of the sympathetic division, blood pressure elevation, and tachycardia. With the development of anaerobic processes serotonin via 5-HT2 receptors triggers apoptosis of cardiomyocytes leading to the development and progression of heart failure. Participation of 5HT2B receptors in the regulation of heart development during embryogenesis was shown on the mutant mice: cardiomyopathy with ventricular mass loss due to reduction of cardiomyocytes number and size was revealed. The involvement of 5-HT4 receptors in the development of sinus tachycardia and atrial fibrillation; in turn, the use of 5-HT4 receptor antagonists proved to be effective in the treatment of this kind of arrhythmias. Therefore, the study of the serotonergic system role in the development of cardiovascular diseases will allow to open new links in the pathogenesis of arterial hypertension in childhood.

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-HT1AR 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-HT1AR and 5-HT7R as well as their interplay at the molecular, neurochemical and behavioral level. Activation of postsynaptic 5-HT1ARs impairs emotional memory through attenuation of neuronal activity, whereas presynaptic 5-HT1AR activation reduces 5-HT release and exerts pro-cognitive effects on PA retention. Antagonism of the 5-HT1AR facilitates memory retention possibly via 5-HT7R activation and evidence is provided that 5HT7R can facilitate emotional memory upon reduced 5-HT1AR 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-HT1ARs 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.

Ketanserin, a serotonin 2A receptor antagonist, alleviates ischemia-related biliary fibrosis following donation after cardiac death liver transplantation in rats.

Biliary fibrosis is a major complication after donation after cardiac death (DCD) liver transplantation. In this process, the roles of serotonin [5-hydroxytryptamine (5-HT)] and the 5-HT2A receptor subtype are still unknown. In this study, we analyzed markers of portal fibroblast (PF)/myofibroblast (MF) transdifferentiation such as transforming growth factor β1 (TGF-β1), phosphorylated smad2/3, α-smooth muscle actin (α-SMA), collagen I, and collagen III in a primary culture system of PFs after the administration of 5-HT or 5-HT plus ketanserin (a selective 5-HT2A receptor antagonist). A rat DCD transplant model was established with 30 minutes of warm ischemia and 4 hours of cold ischemia during organ procurement. Recipients were intraperitoneally injected with ketanserin (1 mg·kg(-1)·day(-1)) or normal saline. Grafts without in situ warm ischemia instead of minimal cold storage (30 minutes) served as controls. The serum biochemistry, the liver contents of 5-HT and hydroxyproline (HYP), and the expression of fibrosis-related genes (including TGF-β1, matrix metalloproteinase 2, procollagen α1, and α-SMA messenger RNA) were determined. The extent of biliary fibrosis was also assessed histopathologically. The results indicated that ketanserin inhibited 5-HT-activated TGF-β1-smad2/3 signaling in vitro and thereby depressed the MF conversion of PFs. Rats receiving DCD livers showed increased liver contents of 5-HT and HYP, impaired biliary function, up-regulation of fibrosis-related genes, and aggravated biliary fibrosis. However, these phenomena were alleviated by treatment with ketanserin. We concluded that the profibrotic activity of 5-HT occurred through the activation of TGF-β1 signaling and the 5-HT2A receptor. Thus, these data suggest that the 5-HT2A receptor may be a potential therapeutic target for ischemia-related biliary fibrosis after DCD liver transplantation.

Synthesis and evaluation of fluoro substituted pyridinylcarboxamides and their phenylazo analogues for potential dopamine D3 receptor PET imaging

A series of fluoro substituted pyridinylcarboxamides and their phenylazo analogues with high affinity and selectivity for the dopamine D3 receptor was synthesized by the use of 6-fluoropyridine-3-carbonyl chloride (1) and fluorophenylazocarboxylic ester (2). Several of these compounds (9a–e and 10a–h) have been evaluated in vitro, among which 9b, 10a, 10c and 10d proved to have at least single-digit nanomolar affinity for D3. They also exhibit considerable selectivity over the other dopamine receptor subtypes and noteworthy selectivity over the structurally related serotonin receptor subtypes 5-HT1A and 5-HT2, offering potential radiotracers for positron emission tomography.

5-Hydroxytryptamine1A receptor-activation hyperpolarizes pyramidal cells and suppresses hippocampal gamma oscillations via Kir3 channel activation.

Rhythmic cortical neuronal oscillations in the gamma frequency band (30-80 Hz, gamma oscillations) have been associated with cognitive processes such as sensory perception and integration, attention, learning, and memory. Gamma oscillations are disrupted in disorders for which cognitive deficits are hallmark symptoms such as schizophrenia and Alzheimer's disease.In vitro, various neurotransmitters have been found to modulate gamma oscillations. Serotonin(5-HT) has long been known to be important for both behavioural and cognitive functions such as learning and memory. Multiple 5-HT receptor subtypes are expressed in the CA3 region of the hippocampus and high doses of 5-HT reduce the power of induced gamma oscillations.Hypothesizing that 5-HT may have cell- and receptor subtype-specific modulatory effects, we investigated the receptor subtypes, cell types and cellular mechanisms engaged by 5-HT in the modulation of gamma oscillations in mice and rats. We found that 5-HT decreases the power of kainate-induced hippocampal gamma oscillations in both species via the 5-HT1A receptor subtype. Whole-cell patch clamp recordings demonstrated that this decrease was caused by a hyperpolarization of CA3 pyramidal cells and a reduction of their firing frequency, but not by alteration of inhibitory neurotransmission. Finally, our results show that the effect on pyramidal cells is mediated via the G protein-coupled receptor inwardly rectifying potassium channel Kir3.Our findings suggest this novel cellular mechanism as a potential target for therapies that are aimed at alleviating cognitive decline by helping the brain to maintain or re-establish normal gamma oscillation levels in neuropsychiatric and neurodegenerative disorders.

Serotonin activates cell survival and apoptotic death responses in cultured epithelial thyroid cells.

Anatomic and physiological interactions between central serotonergic system and thyroid gland are well established. However, the effects of locally available serotonin on the thyroid functions are poorly known. Here, we first demonstrate the expression of serotonin transporter SERT and 5-HT2A receptor subtype in rat thyroid epithelial cell line FRT both at mRNA and protein levels. In order to investigate the molecular mechanisms of serotonin action, FRT cells were exposed to increasing concentrations of the amine. Low concentrations of serotonin (up to 5μM) enhanced FRT cell growth, and ERK1/2 and SMAD2/3 phosphorylation. Cell exposure to the selective 5-HT2A receptor agonist DOI recapitulated the effects of 5-HT on ERK1/2 phosphorylation. By contrast, administration of M100907, a specific 5-HT2A receptor inhibitor, prevented 5-HT induced ERK1/2 activation. On the other hand, high doses of serotonin (50μM up to 1mM) activated a caspase-3 mediated apoptosis of cells. Overall, our findings demonstrate that low levels of serotonin, interacting with 5-HT2A receptor, are able to activate proliferative signals in the thyroid epithelial cells, while high levels of serotonin cause pro-apoptotic responses, thus suggesting an active role of the amine in the thyroid functions and disorders.

Neuronal localization of the 5-HT2 receptor family in the amygdaloid complex.

The amygdaloid complex (or amygdala), a heterogeneous structure located in the medial portion of the temporal lobe, is composed of deep, superficial, and “remaining” nuclei. This structure is involved in the generation of emotional behavior, in the formation of emotional memories and in the modulation of the consolidation of explicit memories for emotionally arousing events. The serotoninergic fibers originating in the dorsal and medial raphe nuclei are critically involved in amygdalar functions. Serotonin (5-hydroxytryptamine, 5-HT) regulates amygdalar activity through the activation of the 5-HT2 receptor family, which includes three receptor subtypes: 5-HT2A, 5-HT2B, and 5-HT2C. The distribution and the functional activity of the 5-HT2 receptor family has been studied more extensively than that of the 5-HT2A receptor subtypes, especially in the deep nuclei. In these nuclei, the 5-HT2A receptor is expressed on both pyramidal and non-pyramidal neurons, and could play a critical role in the formation of emotional memories. However, the exact role of the 5-HT2A receptor subtypes, as well as that of the 5-HT2B and 5-HT2C receptor subtypes, in the modulation of the amygdalar microcircuits requires additional study. The present review reports data concerning the distribution and the functional roles of the 5-HT2 receptor family in the amygdala.