The activation of 5-HT receptors in prefrontal cortex enhances dopaminergic activity

Atypical antipsychotics show preferential 5-HT 2A versus dopamine (DA) D2 receptor affinity. At clinical doses, they fully occupy cortical 5-HT2 receptors, which suggests a strong relationship with their therapeutic action. Half of the pyramidal neurones in the medial prefrontal cortex (mPFC) express 5-HT 2A receptors. Also, neurones excited through 5-HT 2A receptors project to the ventral tegmental area (VTA). We therefore hypothesized that prefrontal 5-HT 2A receptors can modulate DA transmission through excitatory mPFC-VTA inputs. In this study we used single unit recordings to examine the responses of DA neurones to local (in the mPFC) and systemic administration of the 5-HT 2A/2C agonist 1-[2,5-dimethoxy-4-iodophenyl-2-aminopropane] (DOI). Likewise, using microdialysis, we examined DA release in the mPFC and VTA (single/dual probe) in response to prefrontal and systemic drug administration. The local (in the mPFC) and systemic administration of DOI increased the firing rate and burst firing of DA neurones and DA release in the VTA and mPFC. The increase in VTA DA release was mimicked by the electrical stimulation of the mPFC. The effects of DOI were reversed by M100907 and ritanserin. These results indicate that the activity of VTA DA neurones is under the excitatory control of 5-HT 2A receptors in the mPFC. These observations may help in the understanding of the therapeutic action of atypical antipsychotics.     

Design,synthesis, and preliminary in vitro and in vivo pharmacological evaluation of 2-{4-[4-(2,5-disubstituted thiazol-4-yl)phenylethyl]piperazin-1-yl}-1,8-naphthyridine-3-carbonitriles as atypical antipsychotic agents

A series of 2-{4-[4-(2,5-disubstituted thiazolyl)phenylethyl] piperazin-1-yl}-1,8-naphthyridine-3-carbonitriles were synthesized in an effort to prepare novel atypical antipsychotic agents. The compounds were synthesized either by microwave irradiation technique or by conventional synthesis and were characterized by spectral data (IR, ¹H NMR, and MS) and the purity was ascertained by microanalysis. The D₂ and 5-HT_2A affinity of the synthesized compounds was screened in vitro by radioligand displacement assays on membrane homogenates isolated from rat striatum and rat cortex, respectively. Furthermore, all the synthesized compounds were screened for their in vivo pharmacological activity in Swiss albino mice. The D₂ antagonism studies were performed using climbing mouse assay model and 5-HT_2A antagonism studies were performed using quipazine-induced head twitches in mice. It was observed that none of the new chemical entities exhibited catalepsy and 10f is the most active among the synthesized compounds with 5-HT_2A/D₂ ratio of 1.1286 although the standard drug risperidone exhibited 5-HT_2A/D₂ ratio of 1.0989.     

5-HT(2A) and D(2) receptor blockade increases cortical DA release via 5-HT(1A) receptor activation: a possible mechanism of atypical antipsychotic-induced cortical dopamine release

Atypical antipsychotic drugs (APDs), all of which are relatively more potent as serotonin (5-HT)(2A) than dopamine D(2) antagonists, may improve negative symptoms and cognitive dysfunction in schizophrenia, in part, via increasing cortical dopamine release. 5-HT(1A) agonism has been also suggested to contribute to the ability to increase cortical dopamine release. The present study tested the hypothesis that clozapine, olanzapine, risperidone, and perhaps other atypical APDs, increase dopamine release in rat medial prefrontal cortex (mPFC) via 5-HT(1A) receptor activation, as a result of the blockade of 5-HT(2A) and D(2) receptors. M100907 (0.1 mg/kg), a 5-HT(2A) antagonist, significantly increased the ability of both S:(-)-sulpiride (10 mg/kg), a D(2) antagonist devoid of 5-HT(1A) affinity, and R:(+)-8-OH-DPAT (0.05 mg/kg), a 5-HT(1A) agonist, to increase mPFC dopamine release. These effects of M100907 were abolished by WAY100635 (0.05 mg/kg), a 5-HT(1A) antagonist, which by itself has no effect on mPFC dopamine release. WAY100635 (0.2 mg/kg) also reversed the ability of clozapine (20 mg/kg), olanzapine (1 mg/kg), risperidone (1 mg/kg), and the R:(+)-8-OH-DPAT (0.2 mg/kg) to increase mPFC dopamine release. Clozapine is a direct acting 5-HT(1A) partial agonist, whereas olanzapine and risperidone are not. These results suggest that the atypical APDs via 5-HT(2A) and D(2) receptor blockade, regardless of intrinsic 5-HT(1A) affinity, may promote the ability of 5-HT(1A) receptor stimulation to increase mPFC DA release, and provide additional evidence that coadministration of 5-HT(2A) antagonists and typical APDs, which are D(2) antagonists, may facilitate 5-HT(1A) agonist activity.     

[3H]Nemonapride and [3H]Spiperone Label Equivalent Numbers of D2 and D3 Dopamine Receptors in a Range of Tissues and Under Different Conditions

Abstract: [³H]Nemonapride and [³H]spiperone are very widely used to study dopaminergic systems in vitro and in vivo, but it has been reported that [³H]nemonapride and [³H]spiperone give markedly different B _max values for preparations of D₂ dopamine receptors from recombinant cell lines or animal tissues. We have used the two radioligands in parallel to study a range of dopamine receptors [D_2(short), D_2(long), and D₃] in different buffers. B _max values derived using either radioligand differ by an average of <20%, independent of receptor type or buffer conditions. All competition experiments show that the two ligands compete at a single site. It seems that [³H]spiperone and [³H]nemonapride do not differentiate between different forms or populations of D₂-like receptors.     

THE NEW PARADIGM OF RECOVERY FROM SCHIZOPHRENIA: CULTURAL CONUNDRUMS OF IMPROVEMENT WITHOUT CURE

This article is a qualitative investigation of the subjective experience of recovery from the perspective of persons living with schizophrenia-related disorders. An NIMH-sponsored ethnographic study of community outpatient clinics was completed for 90 persons taking second-generation antipsychotic medications. Research diagnostic criteria and clinical ratings were obtained in tandem with an anthropologically developed Subjective Experience of Medication Interview (SEMI) that elicits narrative data on everyday life and activities, medication and treatment, management of symptoms, expectations concerning recovery, and stigma. Ethnographic observations from diverse settings (clinics, public transportation, restaurants, homes) were also obtained. The primary findings are that recovery was experienced in relation to low levels of symptoms, the need to take medications to avoid hospitalization or psychotic episodes, and personal agency to struggle against the effects of illness. The majority of participants articulated their sense of illness recovery and expectation that their lives would improve. Improvement and recovery is an incremental, yet definitively discernable subjective process. Several problems were identified as part of this process surrounding cultural conflicts that generate the experience of ambivalence analyzed here as the “paradox of recovery without cure,” irreconcilable “catch-22” dilemmas involving sacrifice (e.g., one must be “fat” or be “crazy”), and substantial stigma despite improvement in illness and everyday life experience.     

大鼠局灶性脑皮质缺血/再灌注对脑神经元损伤作用及瘦素受体表达的改变

目的:研究脑缺血/再灌注(I/R)损伤后瘦素受体(OB-R)表达的变化情况.方法:雄性成年Wistar大鼠20只,随机分成4组:假手术24 h、72 h对照组及I/R 24 h、72 h实验组.线栓法制备大鼠局灶性脑皮质I/R损伤模型,在脑I/R后相应时间点分别处死大鼠,采用免疫组织化学、免疫电镜方法观察大脑皮质OB-R的表达,在光镜及电镜下观察神经元损伤改变.结果:左顶叶皮质锥体细胞、血管内皮、脉络丛发现有OB-R阳性表达;与假手术对照组相比,I/R 24 h(I/R早期)锥体细胞OB-R免疫反应阳性细胞表达减少(P＜0.05),I/R 72 h(I/R晚期)锥体细胞OB-R免疫反应阳性细胞减少更明显(P＜0.001);光镜及电镜对缺血中心区神经元的观察均显示I/R晚期的神经元损伤明显重于早期.结论:脑I/R损伤后早期神经元损害和迟发性神经元损害均伴随有OB-R的表达减少,且迟发性神经元损害表达减少更明显,因此在脑梗塞的防治中有必要对瘦素及其OB-R的作用进一步研究.     

Polypyrimidine tract-binding protein 1 regulates the alternative splicing of dopamine receptor D(2)

Dopamine receptor D(2) (DRD2) has two splicing isoforms, a long form (D2L) and short form (D2S), which have distinct functions in the dopaminergic system. However, the regulatory mechanism of the alternative splicing of DRD2 is unknown. In this study, we examined which splicing factors regulate the expression of D2L and D2S by over-expressing several RNA-binding proteins in HEK293 cells. In a cellular splicing assay, the over-expression of polypyrimidine tract-binding protein 1 (PTBP1) reduced the expression of D2S, whereas the knockdown of PTBP1 increased the expression of D2S. We also identified the regions of DRD2 that are responsive to PTBP1 using heterologous minigenes and deletion mutants. Our results indicate that PTBP1 regulates the alternative splicing of DRD2. Considering that DRD2 inhibits cAMP-dependent protein kinase A, which modulates the intracellular localization of PTBP1, PTBP1 may contribute to the autoregulation of DRD2 by regulating the expression of its isoforms.     

Inhibition of Adenylyl Cyclase Activity by a Homogeneous Population of Dopamine Receptors: Selective Blockade by Antisera Directed Against Gi1 and/or Gi2

Abstract: The 7315c pituitary tumor cell expresses a homogeneous population of dopamine receptors that are functionally similar to brain dopamine D₂ receptors. [³H]-Sulpiride binding to 7315c cell homogenates was specific and saturable, and K _i values for compounds to compete for these sites were highly correlated with values for the same compounds at D₂ receptors in brain. Dopamine maximally inhibited ∼65% of forskolin-stimulated cyclase activity in cell membranes. Some D₂ agonists had lower efficacies, suggesting that some compounds are partial agonists at this receptor. Removal of GTP from the assay buffer or pretreatment of the tissue with pertussis toxin abolished the inhibition of adenylyl cyclase by dopamine. Immunodetection of most of the known Gα subunits revealed that G_i1, G_i2, G_i3, G_o, G_q, and G_s are present in the 7315c membrane. Pretreatment with the AS antibody (which recognizes the C-terminal regions of Gα_i1 and Gα_i2) significantly attenuated the inhibition of adenylyl cyclase activity by dopamine, whereas antibodies to C-terminal regions of the other Gα subunits had no effect. These findings suggest that the dopamine D₂ receptor regulates cyclase inhibition predominantly via G_i1 and/or G_i2 and that the 7315c tumor cells provide a useful model for studying naturally expressed dopamine D₂ receptors in the absence of other dopamine receptor subtypes.     

味觉刺激后瘦素及其受体表达的变化

目的 :研究经口腔味觉刺激后 ,大鼠血清瘦素水平和脑瘦素受体表达情况。方法 :给大鼠口腔味觉刺激 ,味觉刺激物包括 3mol/L蔗糖 ,5mmol/L糖精钠 ,0 .1mol/LNaCl,0 .0 1mol/LHCl,1mmol/L奎宁H2 SO4和 0 .1mol/L谷氨酸钠 ,采用大鼠瘦素放免试剂盒测定血清瘦素水平。应用免疫组织化学ABC法对大脑切片进行染色 ,一抗为特异性羊抗瘦素受体IgG。 结果 :与对照组 (以蒸馏水代替味觉刺激物 )相比 ,仅甜味组 (包括蔗糖和糖精钠 )血清瘦素水平升高 (P <0 .0 5 )。杏仁核、下丘脑、臂旁核和孤束核等与味觉和摄食明显相关的核团均存在瘦素受体免疫反应 (LR IR)阳性细胞 ,但是阳性细胞数目在味觉刺激组和对照组间无显著性差异。结论 :给大鼠甜味觉刺激后 ,血清瘦素水平升高。并且杏仁核这个在摄食的发动和引导中起重要作用的核团存在LR IR阳性细胞。这些结果提示瘦素可能通过调节味觉感受而影响摄食 ,有必要对瘦素在味觉感受方面的作用进一步研究     

Characterization of a novel D2-like dopamine receptor with a truncated splice variant and a D1-like dopamine receptor unique to invertebrates from Caenorhabditis elegans

We have cloned two novel Caenorhabditis elegans dopamine receptors, DOP-3 and DOP-4. DOP-3 shows high sequence homology with other D2-like dopamine receptors. As a result of alternative splicing, a truncated splice variant of DOP-3, DOP-3nf, was produced. Because of the in-frame insertion of a stop codon in the third intracellular loop, DOP-3nf lacks the sixth and seventh transmembrane domains that are found in the full-length DOP-3 receptor. Reporter gene assay showed that DOP-3 attenuates forskolin-stimulated cAMP formation in response to dopamine stimulation, whereas DOP-3nf does not. When DOP-3 was coexpressed with DOP-3nf, the ability to inhibit forskolin-stimulated cAMP formation was reduced. DOP-4 shows high sequence homology with D1-like dopamine receptors unique to invertebrates, which are distinct from mammalian D1-like dopamine receptors. Reporter gene assay showed that DOP-4 stimulates cAMP accumulation in response to dopamine stimulation. These two receptors provide new opportunities to understand dopaminergic signaling at the molecular level.     

Dopamine Receptor 2 Regulates L-Type Voltage-Gated Calcium Channel in Primary Cultured Mouse Midbrain Neural Network

1. Synchronous oscillation of intracellular Ca²⁺ in the central nervous system is essential for neural development. We previously reported that endogenous dopamine was involved with synchronous Ca²⁺ oscillation of primary cultured midbrain neurons, and that regulation of dopamine in synchronous oscillation was distinctly different through dopamine receptor 1 (D1R) and 2 (D2R): the action of dopamine through D1R or D2R was facilitative or suppressive, respectively, to the Ca²⁺ influx of synchronous oscillation.2. In the present study, we confirmed that the suppressive effects of D2R were mediated by the regulation of the L-type voltage-gated Ca²⁺ channel, not by the regulation of NMDA receptor on the Ca²⁺ influx in the midbrain neural network showing synchronous oscillation.3. This evidence promotes better understanding of the regulation of neural activity by endogenous dopamine in networked neurons.     

Association of seven polymorphisms of the D2 dopamine receptor gene with brain receptor-binding characteristics

Association of alleles at the Taql A, Taql B, intron 6, Taql D, exon 7, exon 8, and promoter-141C sites of the D2 dopamine receptor gene with D2 dopamine receptor binding characteristics in the caudate nucleus of Caucasian alcoholic and nonalcoholic subjects was determined. For the Taql D, exon 7, exon 8, and promoter-141C sites there were no significant allelic differences in Bmax (number of binding sites) or Kd (binding affinity) of the D2 dopamine receptors. However, subjects having the minor alleles at the Taql A, Taql B, and intron 6 sites had significantly lower Bmax than subjects not having them. None of these three polymorphisms had any significant effect on Kd. Highly significant linkage disequilibria were observed among the Taql A, Taql B, and intron 6 polymorphic sites, but linkage disequilibria between these three sites and each of the Taql D, exon 7, exon 8, and promoter-141C sites were of lesser or of no significance. Taken together, these findings suggest that the Taql A, Taql B, and intron 6 polymorphisms, but not the Taql D, exon 7, exon 8, and promoter-141C polymorphisms, are in linkage disequilibrium with a functional allelic variant that affects D2 dopamine receptor expression.     

Adenylyl cyclase-5 activity in the nucleus accumbens regulates anxiety-related behavior

Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens (NAc), two brain areas which have been implicated in motor function, reward, and emotion. Here we demonstrate that mice lacking AC5 (AC5-/-) display strong reductions in anxiety-like behavior in several paradigms. This anxiolytic behavior in AC5-/- mice was reduced by the D(1) receptor antagonist SCH23390 and enhanced by the D(1) dopamine receptor agonist, dihydrexidine (DHX). DHX-stimulated c-fos induction in AC5-/- mice was blunted in the dorso-lateral striatum, but it was overactivated in the dorso-medial striatum and NAc. The siRNA-mediated inhibition of AC5 levels within the NAc was sufficient to produce an anxiolytic-like response. Microarray and RT-PCR analyses revealed an up-regulation of prodynorphin and down-regulation of cholecystokinin (CCK) in the NAc of AC5-/- mice. Administration of nor-binaltorphimine (a kappa opioid receptor antagonist) or CCK-8s (a CCK receptor agonist) reversed the anxiolytic-like behavior exhibited by AC5-/- mutants. Taken together, these results suggest an essential role of AC5 in the NAc for maintaining normal levels of anxiety.     

间歇性低氧对肥胖小鼠瘦素及其受体表达的影响

为探讨适度低氧环境对体重的影响及其作用机制,明确瘦素在其中的作用,用高脂饮食建立小鼠肥胖模型并观察间歇性低氧的干预效果。健康昆明小鼠随机分为4组（每组20只）,正常对照组：喂正常食物,不进行间歇性低氧训练;低氧组：喂正常食物,并进行间歇性低氧训练;肥胖组：喂高脂、高糖食物,但不进行间歇性低氧训练;低氧＋肥胖组,喂高脂、高糖食物,并进行间歇性低氧训练。40d后,测量小鼠体重,用酶联免疫吸附法测定血清瘦素水平,免疫组织化学检测肝脏瘦素受体表达,苏丹Ⅲ染色检测肝脏脂肪细胞分布和密度。结果显示,与正常对照组相比,肥胖组小鼠平均体重和平均血清瘦素水平显著升高,肝脏分布大量脂肪细胞,提示高脂模型建立成功;经过间歇性低氧训练后,低氧组和低氧＋肥胖组小鼠的平均体重及肝脏脂肪细胞分布密度和范围分别较对照组和肥胖组低,而血清瘦素水平明显增高;低氧＋肥胖组小鼠肝脏瘦素受体的表达高于肥胖组。结果提示,适度的间歇性低氧可以通过提高血清瘦素水平和增强肝脏瘦素受体表达而使体重减轻,并有效防止肝细胞脂肪变。     

An inverse correlation between the apparent rate of dopamine clearance and tonic autoinhibition in subdomains of the rat striatum: a possible role of transporter-mediated dopamine efflux

The dopaminergic terminal field in the rat striatum is compartmentalized into sub-domains that exhibit distinct dynamics of electrically evoked dopamine release. The fast striatal domains, where dopamine release is predominantly vesicular, exhibit conventional dopaminergic activity. However, vesicular dopamine release is tonically autoinhibited in the slow domains, which suggests that dopamine reaches the autoreceptors via a non-vesicular route. Hence, it appears that the domains use distinct mechanisms to regulate the basal dopamine concentration available to activate, or not, pre-synaptic autoinhibitory receptors. However, direct detection of local variations in tonic extracellular dopamine concentrations is not yet possible. So, the present study employed voltammetry to test the hypothesis that the apparent rate of dopamine clearance from the extracellular space should be domain-dependent. The apparent rate of dopamine clearance is equal to the difference in the rates of dopamine release and uptake that determine extracellular dopamine concentrations. This study confirms that the apparent rate of dopamine clearance is slower in the slow striatal domains where vesicular dopamine release is tonically autoinhibited. These findings support the view that the basal concentration in slow domains is maintained by a non-vesicular release process, possibly transporter-mediated efflux.