Axonal α7 nicotinic ACh receptors modulate presynaptic NMDA receptor expression and structural plasticity of glutamatergic presynaptic boutons

In association with NMDA receptors (NMDARs), neuronal α7 nicotinic ACh receptors (nAChRs) have been implicated in neuronal plasticity as well as neurodevelopmental, neurological, and psychiatric disorders. However, the role of presynaptic NMDARs and their interaction with α7 nAChRs in these physiological and pathophysiological events remains unknown. Here we report that axonal α7 nAChRs modulate presynaptic NMDAR expression and structural plasticity of glutamatergic presynaptic boutons during early synaptic development. Chronic inactivation of α7 nAChRs markedly increased cell surface NMDAR expression as well as the number and size of glutamatergic axonal varicosities in cortical cultures. These boutons contained presynaptic NMDARs and α7 nAChRs, and recordings from outside-out pulled patches of enlarged presynaptic boutons identified functional NMDAR-mediated currents. Multiphoton imaging of presynaptic NMDAR-mediated calcium transients demonstrated significantly larger responses in these enlarged boutons, suggesting enhanced presynaptic NMDAR function that could lead to increased glutamate release. Moreover, whole-cell patch clamp showed a significant increase in synaptic charge mediated by NMDAR miniature EPSCs but no alteration in the frequency of AMPAR miniature EPSCs, suggesting the selective enhancement of postsynaptically silent synapses upon inactivation of α7 nAChRs. Taken together, these findings indicate that axonal α7 nAChRs modulate presynaptic NMDAR expression and presynaptic and postsynaptic maturation of glutamatergic synapses, and implicate presynaptic α7 nAChR/NMDAR interactions in synaptic development and plasticity.     

Distribution of Nicotinic Receptors in the Human Hippocampus and Thalamus

Neuronal nicotinic acetylcholine receptors consist of different subunits, α and β, with different subtype arrangement corresponding to distinct pharmacological and functional properties. The expression of α3, α7 and β2 mRNA in the human brain was studied by in situ hybridization and compared to [³H]nicotine, [³H]cytisine and [¹²⁵l]α-bungarotoxin binding in contiguous sections. The β2 probe showed a strong hybridization signal in the granular layer of the dentate gyrus and in the CA2/CA3 region of the hippocampus and in the insular cortex, and a signal of lower intensity in the subicular complex and entorhinal cortex. The α3 probe showed strong hybridization in the dorsomedial, lateral posterior, ventroposteromedial and reticular nuclei of the thalamus, and a weak signal in the hippocampal region and in the entorhinal, insular and cingular cortex. The amount of α7 mRNA was high at the level of the dentate granular layer and the CA2/CA3 region of the hippocampus, in the caudate nucleus and in the pulvinar and ventroposterolateral nuclei of the thalamus. [³H]Nicotine and [³H]cytisine binding appeared to be identical in anatomical distribution and relative intensity. It was high in the thalamic nuclei, the putamen and in the hippocampal formation in the subicular complex and the stratum lacunosum moleculare. The level of [¹²⁵l]α-bungarotoxin binding was particularly high in the hippocampus and in the pyramidal cells of the CA1 region, but was relatively low in the subicular complex. Our data indicate that in the human brain nicotinic receptor subtypes have discrete distributions, which are in part different from those of other species.     

The safety,effectiveness and cost‐effectiveness of cytisine in achieving six‐month continuous smoking abstinence in tuberculosis patients—protocol for a double‐blind,placebo‐controlled randomized trial

Background and aims

Tuberculosis (TB) patients who quit smoking have much better disease outcomes than those who continue to smoke. In general populations, behavioural support combined with pharmacotherapy is the most effective strategy in helping people to quit. However, there is no evidence for the effectiveness of this strategy in TB patients who smoke. We will assess the safety, effectiveness and cost‐effectiveness of cytisine—a low‐cost plant‐derived nicotine substitute—for smoking cessation in TB patients compared with placebo, over and above brief behavioural support.

Design

Two‐arm, parallel, double‐blind, placebo‐controlled, multi‐centre (30 sites in Bangladesh and Pakistan), individually randomized trial.

Setting

TB treatment centres integrated into public health care systems in Bangladesh and Pakistan.

Participants

Newly diagnosed (in the last 4 weeks) adult pulmonary TB patients who are daily smokers (with or without dual smokeless tobacco use) and are interested in quitting (n = 2388).

Measurements

The primary outcome measure is biochemically verified continuous abstinence from smoking at 6 months post‐randomization, assessed using Russell Standard criteria. The secondary outcome measures include continuous abstinence at 12 months, lapses and relapses; clinical TB outcomes; nicotine dependency and withdrawal; and adverse events.

Comments

This is the first smoking cessation trial of cytisine in low‐ and middle‐income countries evaluating both cessation and TB outcomes. If found effective, cytisine could become the most affordable cessation intervention to help TB patients who smoke.     

Partial agonists for α4β2 nicotinic receptors stimulate dopaminergic neuron firing with relatively enhanced maximal effects

BACKGROUND AND PURPOSE

Partial agonists selective for α4β2 nicotinic ACh receptors have been developed for smoking cessation as they induce weak activation of native α4β2* receptors and inhibit effect of nicotine. However, it is unclear whether at brain functions there is an existence of receptor reserve that allows weak receptor activation to induce maximum physiological effects. We assessed the extent of α4β2 partial agonist-induced increase of firing rate in dopaminergic neurons and evaluated the influence of receptor reserve.

EXPERIMENTAL APPROACH

The relative maximal effects and potencies of six nicotinic agonists were assessed on recombinant human α4β2 and α7 receptors expressed in mammalian cell lines by measuring calcium influx. Agonist-induced increase of the spontaneous firing rate of dopaminergic neurons was recorded using microelectrodes in the ventral tegmental area of rat brain slices.

KEY RESULTS

All α4β2 partial and full agonists increased the firing rate concentration-dependently. Their sensitivity to subtype-selective antagonists showed predominant activation of native α4β2* receptors. However, partial agonists with relative maximal effects as low as 33% on α4β2 receptors maximally increased the firing rate and induced additional depolarization block of firing, demonstrating that partial activation of receptors caused the maximum increase in firing rate in the presence of a receptor reserve.

CONCLUSIONS AND IMPLICATIONS

Partial α4β2 agonists induced relatively enhanced effects on the firing rate of dopaminergic neurons, and the effect was mainly attributed to the existence of native α4β2* receptor reserve. The results have implications in the understanding of physiological effects and therapeutic efficacies of α4β2 partial agonists.     

无叶假木贼的化学成分及抗菌活性研究

目的 研究无叶假木贼Anabsis aphylla的化学成分及其抗菌活性。方法 采用RP-C₁₈、Sephadex LH-20、硅胶等柱色谱进行分离纯化,根据理化性质和波谱数据鉴定化合物结构。采用MTT比色法对化合物进行抗枯草芽孢杆菌Bacillus subtilis、番茄疮痂病菌Xanthomonas vesicatoria、溶血葡萄球菌Staphylococcus haemolyticus、根癌土壤杆菌Agrobacterium tumefaciens、黄瓜角斑病菌Pseudomonas syringae pv.lachrymans活性筛选。结果 从无叶假木贼中分离了10个化合物,分别鉴定为假木贼碱(1)、N-甲基假木贼碱(2)、6-(diethylamino)-[2,3′-bipyridin]-3-ol(3)、2-(2-(pyridine-3-yl) pyridin-5-yl)-6-(pyridin-3-yl)piperidine(4)、2-(pyridine-3-yl)-5-(6-(pyridine-3-yl) pyridine-2-yl) pyridin...     

组织特异性CD/5-FC系统热化疗对裸鼠结肠癌肝转移的疗效

目的：探讨组织特异性胞嘧啶脱氨酶/5氟胞嘧啶（cytisine deaminase/5fluorocytosine,CD/5FC）系统热化疗对结肠癌肝转移裸鼠模型的治疗作用。方法：将含CEA启动子调控CD基因表达的逆转录病毒载体进行扩增、纯化、包装,并收集病毒上清。45只裸鼠经门静脉注射人结肠癌LoVo细胞,成瘤后2 d腹腔注射病毒上清（0.2 ml/次,每天1次,共5 d）。随机分为对照组、常温化疗组和热化疗组,分别经腹腔注射生理盐水、室温前药5FC和43 ℃前药5FC\[均为500 mg/（kg·d）\]进行治疗。治疗21 d后处死裸鼠, 观察肝脏转移率和转移结节数, RTPCR检测CD基因在肿瘤组织的表达,光镜及电镜下观察肿瘤病理学的变化。结果：病毒滴度为5.6×106 CFU/L。CD基因在移植瘤组织中有效表达。热化疗组的肝转移率与转移结节数均低于常温化疗组\[133% vs 40.0%,(0.20±0.56)个vs（0.80±1.01）个;均P<0.05\]。光镜下见对照组肝转移瘤组织细胞生长活跃,热化疗组较化疗组肝转移瘤细胞生长受抑制更明显。电镜下见化疗组、热化疗组肝转移瘤细胞有不同程度的凋亡改变。结论：组织特异性CD/5FC系统热化疗对裸鼠结肠癌肝转移瘤有明显的抑制作用。     

Effects of cytisine on hydroxyl radicals in vitro and MPTP-induced dopamine depletion in vivo

The potential new iron-chelator cytisine and the radical scavenger N-tert-butyl--(2-sulfophenyl) nitrone (S-PBN) were incubated in a Fenton system and hydroxyl radical formation was measured with the salicylate trapping assay. Both cytisine and S-PBN reduced hydroxyl radical formation in a concentration-dependent manner. For in vivo studies, C57BL/6 mice were injected repeatedly with cytisine (0.5 mg/kg or 2.0 mg/kg s.c.) or saline seven days before and after a single 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection (30 mg/kg s.c.). Seven days after MPTP treatment alone dopamine levels were significantly reduced to 12% of the control values (p<0.001), whereas MPTP+cytisine treatment (2 mg/kg) led to more than twofold higher dopamine levels (p<0.01) compared with MPTP alone. We have shown for the first time that cytisine attenuates hydroxyl radical formation in vitro and reduces MPTP-induced dopamine depletion. Thus, cytisine may be useful for the treatment of Parkinson's Disease where the chelation of iron ions could prevent neuronal cell death.     

Nicotinic receptor partial agonists as novel compounds for the treatment of smoking cessation

Nicotine addiction and the neurobiological mechanisms explaining nicotine reinforcement, withdrawal, and relapse involve α4β2 nicotinic acetylcholine receptors (nAChRs). This review updates readers on the preclinical and clinical pharmacology, as well as the therapeutic efficacy and safety of cytisine and varenicline, the two partial agonists of nAChRs for smoking cessation. Cytisine has been used for several decades; yet despite its surprising popularity in some parts of the world, it has been absent from almost all existing reviews of smoking cessation drugs. If safe and sufficiently efficacious, an obvious advantage would be its low cost, which could make cytisine an attractive treatment available to millions of smokers. Varenicline was recently introduced to the drug market and has been found to be more efficacious than existing treatments. Very encouraging results of early human trials and strong theoretical background for their use make the nAChRs partial agonists a promising alternative for currently available antismoking treatments.