AMPA receptor activation induces association of G-beta protein with the alpha subunit of the sodium channel in neurons

Glutamatergic transmission is mediated by ionotropic receptors that directly gate cationic channels and metabotropic receptors that are coupled to second messenger generating systems and to ionic channels via heterotrimeric guanine-nucleotide binding- (G) proteins. This distinction cannot be made for the ionotropic receptor subclass activated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), which has been shown to be physically associated with the alpha-subunit of Gi1 protein and activates this G-protein. Here, we report that, in addition to a Ca2+ influx, AMPA induces the mobilization of Ca2+ from the mitochondrial pool by reversing the mitochondrial Na+/Ca2+ exchanger in mouse neurons in primary culture. Both processes required the activation of tetrodotoxin-sensitive Na+ channels. AMPA receptor activation modified the gating properties of the Na+ channel, independently of the AMPA current, suggesting a G-protein-mediated process. Indeed, co-immunoprecipitation experiments indicated that AMPA receptor activation induced the association of Gbeta with the alpha-subunit of the Na+ channel. These results suggest that, in addition to its ionic channel function, the AMPA receptor is coupled to Na+ channels through G-proteins and that this novel metabotropic function is involved in the control of neuronal excitability.     

Brain targeting and glomerulus formation of two olfactory neuron populations expressing related receptor types

Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily send their axons to distinct glomeruli located in the immediate vicinity in the olfactory bulb [Strotmann, J., Conzelmann, S., Beck, A., Feinstein, P., Breer, H. & Mombaerts, P. (2000) J. Neurosci., 20, 6927-6938]. In this study, the potential of transgenic mouse lines was used to explore the onset of receptor expression, the outgrowth of axons as well as the glomerulus formation for two neuron populations expressing different mOR37 subtypes. The data indicate a synchronous time course of these features for both neuron populations. From E15 until the day of birth, the axons of the two mOR37 populations terminate in a common, small area of the presumptive olfactory bulb. During a short postnatal phase, the two axon populations segregate into distinct, protoglomerular structures; some aberrant fibers can still be observed during this period.     

Notch signaling in mammary gland tumorigenesis

The Notch receptor protein and its signaling pathway have been well conserved throughout evolution and appear to be pivotal components in cell fate decisions during development. Recent studies suggest that, depending on the cellular and developmental context, Notch signaling may also affect cell proliferation and programmed cell death. Mammals have four related Notch genes. One of these, designated Notch-4, was found to be a common integration site for the mouse mammary tumor virus in mouse mammary tumors. One consequence of this type of viral integration event is the ectopic expression of the intracellular domain of Notch-4 that corresponds to a gain-of-function mutation. Expression of activated Notch-4 in mammary epithelium has profound effects on mammary gland development and tumorigenesis. In this review, we briefly summarize the structure and function of the Notch receptor, as well as the components that comprise and modify the signaling pathway. Finally we discuss the potential role of Notch in mammary gland development and tumorigenesis.     

Restoration of a normal reproductive lifespan after grafting of cryopreserved mouse ovaries

Fresh and frozen ovaries from 10 day old C57BL/6J-Gpi-1(a) mice were grafted orthotopically into ovariectomized B6CBF1 (homozygous Gpi-1(b)) recipients. The recipients were mated with B6CBF1 males. The birth and size of each litter was recorded. The electrophoretic variant of glucose phosphate isomerase was determined for each neonate. Twelve of 13 recipients of fresh ovary and 10 of 12 recipients of frozen ovary were fertile. Of these, 10 (fresh) and eight (frozen) had litters derived from the ovarian grafts only, or from the graft and native ovary. The breeding characteristics of recipients of fresh and frozen grafts were similar. The reproductive lifespan of the recipients of fresh (6.2 litters) and frozen (8.4 litters) grafts was similar to that of unoperated C57BL/6-Gpi-1(a) control females mated with B6CBF1 males (6.3 litters). Litter size was similar in recipients of grafted ovaries (fresh, 5.4 pups/litter; frozen, 6.3 pups/litter) and C57BL/6-Gpi-1(a) females (6.3 pups/litter). The results suggest that cryopreservation per se does not affect the long-term viability of ovarian tissue and provides an option for storing female germ cells. This is the first unequivocal demonstration that a normal reproductive lifespan can be restored by orthotopic grafting of frozen ovary.     

Heterogeneous distribution of AMPA glutamate receptor subunits at the photoreceptor synapses of rodent retina

In the retina the segregation of different aspects of visual information starts at the first synapse in signal transfer from the photoreceptors to the second-order neurons, via the neurotransmitter glutamate. We examined the distribution of the four AMPA glutamate receptor subunits GluR1-GluR4 at the photoreceptor synapses in mouse and rat retinae by light and immunoelectron microscopy and serial section reconstructions. On the dendrites of OFF-cone bipolar cells, which make flat, noninvaginating contacts postsynaptic at cone synaptic terminals, the subunits GluR1 and GluR2 were predominantly found. Horizontal cell processes postsynaptic at both rod and cone synaptic terminals preferentially expressed the subunits GluR2, GluR2/3 and GluR4. An intriguing finding was the presence of GluR2/3 and GluR4 subunits on dendrites of putative rod bipolar cells, which are thought to signal through the sign-inverting metabotropic glutamate receptor 6, mGluR6. Furthermore, at the rod terminals, horizontal cell processes and rod bipolar cell dendrites showed labelling for the AMPA receptor subunits at the ribbon synaptic site or perisynaptically at their site of invagination into the rod terminal. The wide distribution of AMPA receptor subunits at the photoreceptor synapses suggests that AMPA receptors play an important role in visual signal transfer from the photoreceptors to their postsynaptic partners.     

An animal model for external ear canal inflammation

OBJECTIVE: To develop an animal model for testing efficacy of anti-inflammatory drugs designed to treat external ear canal (EAC) disease. METHODS: Histological and morphometric methods were used to characterize EAC inflammation produced by topical application of tetradecanoylphorbol acetate (TPA) in mice. The effects of both single and repeated TPA applications were studied. A treatment trial was performed to evaluate the effects of a ciprofloxacin/hydrocortisone suspension on TPA-induced EAC inflammation. In 10 animals, two bilateral applications of TPA were made, spaced 24 hours apart. Immediately after the second TPA application, otic suspension was applied unilaterally four times over a 48-hour period. The contralateral EACs were left untreated to provide TPA-only controls. RESULTS: Twenty-four hours after a single TPA application, EAC skin showed polymorphonuclear (PMN) leukocyte infiltration, vascular dilation, and thickening of the dermis and epidermis. Dermal and epidermal thickening were more pronounced after two TPA applications and PMN leukocyte infiltration remained high 48 hours after a second TPA placement. After treatment with the otic suspension, PMN leukocyte counts were reduced by an average of 76% relative to EACs that received TPA only. There was also statistically significant reduction of dermal swelling and a trend toward reduced epidermal thickness. Vascular dilation was clearly reduced as well EACs that received four applications of the suspension alone showed no adverse effects compared with those that received saline. CONCLUSION: TPA-induced inflammation of the mouse EAC provides a suitable model for testing the therapeutic efficacy of anti-inflammatory agents being considered for clinical use.     

HCK基因在小鼠胚胎干细胞向心肌细胞分化过程中的表达

目的 探讨HCK基因在小鼠胚胎干细胞向心肌细胞分化过程中的表达及HCK基因在维持胚胎干细胞未分化状态中的意义.方法 培养小鼠胚胎干细胞,并诱导其向心肌细胞分化.抽提其胚胎干细胞未分化及分化第2、4、6、8天的总RNA,应用反转录聚合酶链反应(RT-PCR)方法对HCK基因mRNA的表达进行半定量分析;同时抽提胚胎干细胞未分化及分化第2、4、6、8天的总蛋白,应用Western-blot方法对HCK蛋白的表达进行半定量分析.采用SPSS 11.5软件进行统计学分析,P＜0.05为有统计学差异.结果 HCK基因mRNA在未分化的胚胎干细胞(D0)及分化的第2天(D2)均有表达,而在分化的第4天(D4)开始已不能检测到有表达,HCK基因mRNA的表达水平随小鼠胚胎干细胞的分化呈急剧下调趋势;HCK蛋白的表达与mRNA的表达相一致,在小鼠胚胎干细胞的分化进程中逐渐下调,至第4天已基本检测不出.结论 HCK基因随着小鼠胚胎干细胞向心肌分化,表达呈下调的趋势,HCK基因可能在维持胚胎干细胞未分化状态中起重要作用.     

维生素B_(12)对体外乙醇诱发小鼠胚胎畸变的影响

目的探讨维生素B12(VB12)对乙醇发育毒性的干预作用。方法采用植入后全胚胎培养技术(WEC),将GD8.5的ICR小鼠胚胎用4.0g/L乙醇处理,同时用不同浓度VB12(10-6、10-5和10-4mol/L)干预。在大鼠即刻离心血清中旋转培养48h后对小鼠胚胎生长发育和组织器官形态分化进行评分。结果应用不同浓度VB12干预后,反映胚胎生长发育和组织器官形态分化的指标得分与阳性对照组相比,均有不同程度的提高。其中,10-5mol/LVB12干预组对胚胎生长发育干预得分总和最高,颅臀长、头长、体节数与阳性对照组相比差异均有显著性(P<0.05)。10-4mol/LVB12干预组对胚胎组织器官形态分化干预得分总和最高,除尿囊、心脏、上颌突、下颌突指标外,其他与阳性对照组相比差异均有显著性(P<0.05)。结论VB12有拮抗乙醇发育毒性的作用。     

促红细胞生成素受体抗体抑制小鼠视网膜新生血管形成

目的:观察促红细胞生成素受体抗体(erythropoietin recep-tor antibody,EpoRA)对视网膜新生血管形成的抑制作用。方法:将鼠龄为7d的C57BL/6J幼鼠置于750±20mL/L氧仓中连续饲养5d,建立高氧诱导的血管增生性视网膜病变模型。幼鼠20只右眼在建模前1d予以玻璃体内注射EpoRA 2μL作为治疗眼,左眼不注射作为对照眼。在H.E.染色的组织学切片上观察并计数突破视网膜内界膜进入玻璃体的新生血管内皮细胞核数目;用ADP酶组织化学法行视网膜铺片,观察视网膜血管改变。饲养在正常条件下的幼鼠作为正常对照组;模型幼鼠8只仅在玻璃体内注射生理盐水,作为阴性对照组。结果:在组织切片上,可见突破视网膜内界膜进入玻璃体腔内的新生血管内皮细胞核,在用EpoRA注射的右眼,明显少于未经EpoRA注射的左眼(17.20±5.42个vs23.47±8.43个;P<0.01)。ADP酶组织化学法视网膜铺片中,可见视网膜新生血管的密度和异常程度,在用EpoRA注射的右眼,明显轻于未经EpoRA注射的左眼以及阴性对照组。正常对照组未见明显异常。结论:EpoRA可抑制小鼠模型中的视网膜新生血管形成。