The Role of 5-HT1A Receptors and Neuronal Nitric Oxide Synthase in a Seizur Induced Kindling Model in Rats

Neurochemical Research - Dentate gyrus (DG) has a high density of 5-HT1A receptors. It has neural nitric oxide synthase (nNOS), which is involved in neural excitability. The purpose of this study...     

5-HT_(1A)受体参与学习记忆的分子机制研究进展

5-HT(五羟色胺)能神经元是起源最早的神经元之一,在传统的神经元形成前,成长中的轴突就可释放5-HT,并且通过5-HT的各种亚型受体来实现不同的功能。近年来,随着5-HT、5-HTRs(五羟色胺受体)的基因克隆及5-HT受体选择性激动剂和拮抗剂的研究发展,5-HT系统在学习记忆中的作用越发明确,许多研究结果表明:5-HT系统在记忆的巩固、短时程记忆(STM)及长时程记忆(LTM)中起重要作用,5-HT1A受体更是在非脊椎动物及哺乳动物的脑中都高度表达,并通过相似的信号转导途径参与学习与记忆的形成和巩固。本文将介绍5-HT1A受体、5-HT1A受体激动剂、5-HT1A受体拮抗剂及其与学习记忆的联系,重点综述5-HT1A受体参与学习记忆的信号转导途径研究进展,讨论5-HT1A受体参与学习记忆的可能性分子神经生物学机制。     

The Influence of Gender and Age on Neonatal Rat Hypothalamic 5-HT1A and 5-HT2A Receptors

1.Rat hypothalamic 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) concentrations are transiently sexually differentiated in the second week postpartum (pp), with higher levels in the female. In this report we investigate the possibility that 5-HT receptors may also exhibit sexual dimorphism in the neonatal period.2.5-HT1A and 5-HT2A receptors were quantitated by radioligand binding of [³H]ketanserin and [³H]8-OH DPAT, respectively, in hypothalamus and amygdala from male and female rats at days 8–16 pp.3.There was no sexual dimorphism or change in the density of 5-HT2A binding in hypothalamus or amygdala over days 8–16 pp. There was also no sexual dimorphism of 5-HT1A receptors.4.There was an increase in 5-HT1A receptor density in both the hypothalamus and the amygdala. In the hypothalamus, but not the amygdala, this increase was interrupted on day 14 by a decrease in 5-HT1A receptors, which we suggest may be of physiological significance in modifying the eventual pattern of adult agonistic activity.5.The results suggest that the sexual dimorphism in 5-HT turnover is predominantly presynaptic, relating to altered synthesis and/or release, and is not of sufficient magnitude or duration to produce adaptive responses in postsynaptic 5-HT1A or 5-HT2A receptors.     

Molecular Design of Novel Ligands for 5-HT1A Receptors

Abstract

Serotonin (5-HT) is a potent bioactive substance known to function through a number of different receptor types and subtypes. In our attempt to develop new agents that would interact selectively at certain 5-HT receptors, especially the 5-HT_1A subtype, 8-hydroxy-2-di-n-propylamino tetralin (8-OH-DPAT) served as a template for the design of novel agents sharing aspects of the pharmacophore of 8-OH-DPAT and 5-HT. 5-HT contains no center of asymmetry, and 8-OH-DPAT shows only very modest stereospecificity for 5-HT_1A receptors. To develop agents having enhanced potency and selectivity for the 5-HT_1A site, several ring systems offering enhanced conformational rigidity which approximate the oxygen to nitrogen interatomic distances of 8-OH-DPAT and (to a lesser extent) 5-HT were synthesized. Exemplary ring systems include the 8-alkoxy-hexahydroindeno[1,2-c]pyrrole, 5-alkoxy-hexahydro-1H-indeno-[2,1-c]pyridine, and 9-alkoxy-hexahydro-1H-benz[e]isoindole systems. These couformationally restricted molecules demonstrated moderate stereospecificity in their interaction with the 5-HT_1A binding site, which was enhanced in compounds with larger nitrogen substituents. Appropriate choice of such derivatives led to highly potent compounds selective for 5-HT_1A sites compared with their activity at other 5-HT and/or adrenergic receptors. The pharmacological profile of compounds which appear to act as agonists at 5-HT_1A receptors in the central nervous system to lower blood pressure in animal models of hypertension is presented     

Agonistic Properties of Cannabidiol at 5-HT1a Receptors

Cannabidiol (CBD) is a major, biologically active, but psycho-inactive component of cannabis. In this cell culture-based report, CBD is shown to displace the agonist, [3H]8-OH-DPAT from the cloned human 5-HT1a receptor in a concentration-dependent manner. In contrast, the major psychoactive component of cannabis, tetrahydrocannabinol (THC) does not displace agonist from the receptor in the same micromolar concentration range. In signal transduction studies, CBD acts as an agonist at the human 5-HT1a receptor as demonstrated in two related approaches. First, CBD increases [35S]GTPγS binding in this G protein coupled receptor system, as does the known agonist serotonin. Second, in this GPCR system, that is negatively coupled to cAMP production, both CBD and 5-HT decrease cAMP concentration at similar apparent levels of receptor occupancy, based upon displacement data. Preliminary comparative data is also presented from the cloned rat 5-HT2a receptor suggesting that CBD is active, but less so, relative to the human 5-HT1a receptor, in binding analyses. Overall, these studies demonstrate that CBD is a modest affinity agonist at the human 5-HT1a receptor. Additional work is required to compare CBD’s potential at other serotonin receptors and in other species. Finally, the results indicate that cannabidiol may have interesting and useful potential beyond the realm of cannabinoid receptors.     

Effect of Dopaminergic D1 Receptors on Plasticity Is Dependent of Serotoninergic 5-HT1A Receptors in L5-Pyramidal Neurons of the Prefrontal Cortex

Major depression and schizophrenia are associated with dysfunctions of serotoninergic and dopaminergic systems mainly in the prefrontal cortex (PFC). Both serotonin and dopamine are known to modulate synaptic plasticity. 5-HT_1A receptors (5-HT_1ARs) and dopaminergic type D1 receptors are highly represented on dendritic spines of layer 5 pyramidal neurons (L5PyNs) in PFC. How these receptors interact to tune plasticity is poorly understood. Here we show that D1-like receptors (D1Rs) activation requires functional 5HT_1ARs to facilitate LTP induction at the expense of LTD. Using 129/Sv and 5-HT_1AR-KO mice, we recorded post-synaptic currents evoked by electrical stimulation in layer 2/3 after activation or inhibition of D1Rs. High frequency stimulation resulted in the induction of LTP, LTD or no plasticity. The D1 agonist markedly enhanced the NMDA current in 129/Sv mice and the percentage of L5PyNs displaying LTP was enhanced whereas LTD was reduced. In 5-HT_1AR-KO mice, the D1 agonist failed to increase the NMDA current and orientated the plasticity towards L5PyNs displaying LTD, thus revealing a prominent role of 5-HT_1ARs in dopamine-induced modulation of plasticity. Our data suggest that in pathological situation where 5-HT_1ARs expression varies, dopaminergic treatment used for its ability to increase LTP could turn to be less and less effective.     

Effects of a Chronic Lithium Treatment on Cortical Serotonin Uptake Sites and 5-HT1A Receptors

The objectives of this study were to characterize the effects of a chronic lithium (Li⁺) treatment on serotonin (5-HT) uptake sites and on 5-HT_1A receptors, and to determine the eventual reversibility of the treatment. The experiments were carried out with membranes from rat cerebral cortex using 8-hydroxy-2-(propylamino)tetralin, or [³H]8-OH-DPAT, and [³H]citalopram to label 5-HT_1A receptors and 5-HT uptake sites, respectively. Endogenous levels of 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) were measured by high-performance liquid chromatography in the cingulate cortex. The saturation curves with [³H]8-OH-DPAT were always best fitted a two-site model. After a treatment with Li⁺ for 28 days, no alterations in the binding parameters of [³H]8-OH-DPAT to the high- and low-affinity binding sites could be documented. However, competition curves with 5-HT to inhibit [³H]8-OH-DPAT binding revealed a decreased proportion of sites with high affinity for the agonist, together with an increased density of sites with low affinity for 5-HT, suggesting an alteration in the coupling efficacy between 5-HT_1A receptors and their transduction systems. Saturation studies with [³H]citalopram showed an increase (>40%) in the density of 5-HT uptake sites after chronic Li⁺, suggesting a more efficient 5-HT uptake process for the treated animals, in accord with clinical observations. Although 5-HT contents in cingulate cortex remained unchanged after the treatment, 5-HIAA levels decreased (>30%), leading to a diminished (almost 50%) 5-HT turnover; and also reflecting a more efficient uptake in the treated rats, so that less 5-HT could be degraded by extracellular monoamine oxidase. All the effects revealed by [³H]8-OH-DPAT and [³H]citalopram were reversed following a recovery period of two days without Li⁺. Since symptoms of bipolar affective disorders may reappear if the chronic Li⁺ treatment is interrupted, the reversibility of the observed effects further supports the importance of central 5-HT synaptic transmission in the pathophysiology and treatment of human affective disorders.     

5-HT Receptors: Subtypes and Second Messengers

Abstract

Our knowledge about 5-HT (serotonin, 5-hydroxytryptamine) receptors has gained significantly over the recent few years. The discovery of selective ligands and the use of new techniques have led to a significant increase in the number of recognised receptors subtypes. The present status of awareness is largely related to the use of radioligand binding studies, autoradiography, second messenger analysis and more recently, molecular biological techniques. Three main families of 5-HT receptors, of which subtypes have been described, are now accepted. This heterogeneity is further substantiated by the cloning of the cDNA's of three different 5-HT receptors. This article reviews some of the recent developments which led to the characterisation of 5-HT receptor subtypes.     

Mephedrone in Adolescent Rats: Residual Memory Impairment and Acute but Not Lasting 5-HT Depletion

Mephedrone (4-methylmethcathinone, MMC) is a popular recreational drug, yet its potential harms are yet to be fully established. The current study examined the impact of single or repeated MMC exposure on various neurochemical and behavioral measures in rats. In Experiment 1 male adolescent Wistar rats received single or repeated (once a day for 10 days) injections of MMC (30 mg/kg) or the comparator drug methamphetamine (METH, 2.5 mg/kg). Both MMC and METH caused robust hyperactivity in the 1 h following injection although this effect did not tend to sensitize with repeated treatment. Striatal dopamine (DA) levels were increased 1 h following either METH or MMC while striatal and hippocampal serotonin (5-HT) levels were decreased 1 h following MMC but not METH. MMC caused greater increases in 5-HT metabolism and greater reductions in DA metabolism in rats that had been previously exposed to MMC. Autoradiographic analysis showed no signs of neuroinflammation ([¹²⁵I]CLINDE ligand used as a marker for translocator protein (TSPO) expression) with repeated exposure to either MMC or METH. In Experiment 2, rats received repeated MMC (7.5, 15 or 30 mg/kg once a day for 10 days) and were examined for residual behavioral effects following treatment. Repeated high (30 mg/kg) dose MMC produced impaired novel object recognition 5 weeks after drug treatment. However, no residual changes in 5-HT or DA tissue levels were observed at 7 weeks post-treatment. Overall these results show that MMC causes acute but not lasting changes in DA and 5-HT tissue concentrations. MMC can also cause long-term memory impairment. Future studies of cognitive function in MMC users are clearly warranted.     

丁苯酞对缺血性脑卒中大鼠记忆能力及海马5-HT1A受体和PKA信号通路活化的影响

目的:研究丁苯酞对缺血性脑卒中大鼠学习和记忆能力的影响和大鼠海马5-HT1A受体和PKA信号通路的调控作用。方法:将雄性SD大鼠随机分为假手术组、模型组和丁苯酞组(n=15)。丁苯酞组大鼠建立大脑中动脉闭塞模型,并按照每天60 mg/kg的剂量灌胃丁苯酞,假手术组和模型组灌胃等体积的玉米油,共给药2周。治疗完成后对各组大鼠进行神经功能缺损评估和Morris水迷宫测试(n=15)。通过磁共振成像(MRI)检测梗塞区域(n=15)。ELISA法检测海马组织PKA激酶活性(n=6)。使用钙检测试剂盒测定海马组织的细胞内[Ca²⁺]浓度(n=6)。Western blot检测海马组织中5-羟色胺(1A)受体(5-HT1A)、谷氨酸N-甲基-D-天冬氨酸受体1(NMDA1)和α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体1(AMPA1)的表达(n=6)。结果:与模型组相比:丁苯酞组大鼠的逃避潜伏期显著降低,而穿越平台次数显著升高(P<0.05);大鼠的神经功能缺损评分和脑梗死体积较显著降低(P<0.05);大鼠的PKA激酶活性和细胞内[Ca²⁺]浓度显著升高(P<0.05);丁苯酞组大鼠的5-HT1A蛋白相对表达量显著降低,而AMPA1和NMDA1的磷酸化水平显著升高(P<0.05)。结论:丁苯酞可改善缺血性脑卒中大鼠的学习和记忆能力,下调海马5-HT1A受体活性并激活PKA信号通路。     

Specific Involvement of Central 5-HT1A Receptors in the Mediation of Male Rat Ejaculatory Behavior

The aminotetralin 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), pharmacologically characterized as a 5-HT_1A receptor agonist, produces a pronounced decrease in ejaculation latency in the male rat. Stimulation of 5-HT receptors by a pharmacologically induced increase in the synaptic availability of 5-HT has been shown to produce the opposite effect. The 8-OH-DPAT-induced decrease in ejaculation latency is specific for this compound, and some chemically related ergot derivatives. In this paper we review the evidence in support for stimulation of serotonergic auto-receptors of the 5-HT_1A receptor subtype as a mechanism of action for effects by 8-OH-DPAT on male rat ejaculatory behavior. We also present the questions posed by the fact that quinpirole and lisuride both produce 8-OH-DPAT-like effects on male rat ejaculatory behavior. The effects by quinpirole, lisuride or 8-OH-DPAT are not sensitive to pretreatment with the DA D_2/3 receptor antagonist raclopride. Continued studies will show whether the effects of quinpirole and lisuride can be related to stimulation of 5-HT_1A receptors, or if all these compounds have as yet undefined common properties.     

A Role for Calcium-Permeable AMPA Receptors in Synaptic Plasticity and Learning

A central concept in the field of learning and memory is that NMDARs are essential for synaptic plasticity and memory formation. Surprisingly then, multiple studies have found that behavioral experience can reduce or eliminate the contribution of these receptors to learning. The cellular mechanisms that mediate learning in the absence of NMDAR activation are currently unknown. To address this issue, we examined the contribution of Ca²⁺-permeable AMPARs to learning and plasticity in the hippocampus. Mutant mice were engineered with a conditional genetic deletion of GluR2 in the CA1 region of the hippocampus (GluR2-cKO mice). Electrophysiology experiments in these animals revealed a novel form of long-term potentiation (LTP) that was independent of NMDARs and mediated by GluR2-lacking Ca²⁺-permeable AMPARs. Behavioral analyses found that GluR2-cKO mice were impaired on multiple hippocampus-dependent learning tasks that required NMDAR activation. This suggests that AMPAR-mediated LTP interferes with NMDAR-dependent plasticity. In contrast, NMDAR-independent learning was normal in knockout mice and required the activation of Ca²⁺-permeable AMPARs. These results suggest that GluR2-lacking AMPARs play a functional and previously unidentified role in learning; they appear to mediate changes in synaptic strength that occur after plasticity has been established by NMDARs.     

Involvement of 5-HT1 and 5-HT5A Receptors in Modulation of Synaptic Transmission and Intrinsic Membrane Properties of Spinal Motoneurons of the Frog (Rana ridibunda)

Journal of Evolutionary Biochemistry and Physiology - The endogenous monoamine serotonin (5-HT) is involved in the modulation of motor output in vertebrates by interacting with different types of...     

Role of Serotonin via 5-HT2B Receptors in the Reinforcing Effects of MDMA in Mice

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) reverses dopamine and serotonin transporters to produce efflux of dopamine and serotonin, respectively, in regions of the brain that have been implicated in reward. However, the role of serotonin/dopamine interactions in the behavioral effects of MDMA remains unclear. We previously showed that MDMA-induced locomotion, serotonin and dopamine release are 5-HT_2B receptor-dependent. The aim of the present study was to determine the contribution of serotonin and 5-HT_2B receptors to the reinforcing properties of MDMA.We show here that 5-HT_2B ^−/− mice do not exhibit behavioral sensitization or conditioned place preference following MDMA (10 mg/kg) injections. In addition, MDMA-induced reinstatement of conditioned place preference after extinction and locomotor sensitization development are each abolished by a 5-HT_2B receptor antagonist (RS127445) in wild type mice. Accordingly, MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in nucleus accumbens is abolished in mice lacking functional 5-HT_2B receptors. Nevertheless, high doses (30 mg/kg) of MDMA induce dopamine-dependent but serotonin and 5-HT_2B receptor-independent behavioral effects.These results underpin the importance of 5-HT_2B receptors in the reinforcing properties of MDMA and illustrate the importance of dose-dependent effects of MDMA on serotonin/dopamine interactions.     

Role of the 5-HT1A Serotonergic System in Anxiolytic-Like Effects of Silymarin

We investigated the effects of silymarin, a component of the extract from milk thistle (Silybum marianum) on the level of anxiety in rats and also the potential role of the serotonergic system in the modulatory influences of silymarin on anxiety-related behavior. The elevated plus-maze test was used for testing the above level. Oral administrations of silymarin (35, 70, 140, and 280 mg per rat) for 2 weeks induced an anxiolytic-like effect shown by specific increases in normalized values of the open arm time (OAT) and open arm entries (OAE) in the elevated plus-maze. Intraventricular infusion of a 5-HT_1A receptor agonist, 8-OH-DPAT (5, 10, and 25 ng per rat), increased the OAT and OAE, indicating that this agent also possesses an anxiolytic effect. Similar injections of a 5-HT_1A receptor antagonist, NAN190 (0.25, 0.5, and 1.0 μg per rat), intensified anxiety-related behavior. The least effective dose of intraventricularly injected 8-OH-DPAT (5 ng per rat), when co-administered with silymarin (35, 70, and 140 mg per rat, pretreatment for 2 weeks), decreased the anxiety-related behavior significantly. An effective dose of NAN190 (0.5 μg per rat) combined with silymarin in the above-mentioned dosage provided significant decreases in the OAT and OAE. These results demonstrate that the effects of silymarin on anxiety are mediated, at least partly, by 5-HT_1A receptors of serotonin.     

Role of presynaptic 5-HT1A and 5-HT3 receptors in modulation of synaptic GABA transmission in dissociated rat basolateral amygdala neurons

Serotonin (5-HT) is considered to play a significant role in anxiety-related behaviors in animals through actions on the amygdaloid complex. To evaluate this role from the point of neurotransmitter release regulation, nystatin-perforated patch recording was employed on mechanically dissociated basolateral amygdala neurons containing functional synaptic boutons. GABAAergic miniature inhibitory postsynaptic currents (mIPSCs) were pharmacologically separated. In subsets of neurons, 8-OH-DPAT (1 microM), a specific 5-HT1A agonist, continuously inhibited mIPSC frequency without effects on mIPSC amplitude. By comparison, mCPBG (1 microM), a specific 5-HT3 agonist, transiently facilitated mIPSC frequency without effects on mIPSC amplitude. Together these results suggest the presynaptic existence of both 5-HT receptor subtypes. In these neurons, application of 8-OH-DPAT and its subsequent removal still suppressed mCPBG-induced responses on mIPSCs. This suppression was not caused by a reduction of presynaptic 5-HT3 receptor affinities to mCPBG and was completely eliminated by pretreatment with N-ethylmaleimide, a pertussis toxin sensitive GTP-binding protein inhibitor. In the neurons exhibiting presynaptic modulation with mCPBG but not 8-OH-DPAT, such suppression by exposure to 8-OH-DPAT was not observed. In conclusion, activation of presynaptic 5-HT1A receptors inhibited mIPSC frequency and at the same time suppressed, via a G-protein-mediated mechanism, the transient facilitation of mIPSC frequency produced by activation of presynaptic 5-HT3 receptors.