Connexin-30 mRNA is up-regulated in astrocytes and expressed in apoptotic neuronal cells of rat brain following kainate-induced seizures

Glial connexins (Cxs) make an extensively interconnected functional syncytium created by a network of gap junctions between astrocytes and oligodendrocytes. Among Cxs expressed in the brain, Cx30 is expressed in grey matter astrocytes, as shown at the protein level by immunoistochemistry. In the present study we aimed to perform a detailed study of the regional distribution of Cx30 mRNA in the adult and postnatal developing rat brain, analyzing its expression by in situ hybridization, and determining its cell type localization by double labeling. Recently, it has been suggested that neuronal activity may control the level of intercellular communication between astrocytes through gap junctions channels. Thus, a second aim of the present study was to investigate the short-term effects of kainate-induced seizures on Cx30 expression. The results showed that, in basal condition, Cx30 was expressed only in grey matter astrocytes with distinct regional patterns in developing and adult brain. Kainate treatment induced strong and region-specific changes of astroglial Cx30 mRNA levels and expression of Cx30 mRNA in neuronal cells undergoing cell death, suggesting a direct or indirect involvement of this connexin in the neuronal apoptotic process.     

Reduction of connexin43 expression and dye-coupling during neuronal differentiation of human NTera2/clone D1 cells

Gap junctions are plasma membrane specializations that allow direct communication among adjoining cells. We used a human pluripotential teratocarcinoma cell line, NTera-2/clone D1 (NT2/D1), as a model to study gap junctions in CNS neurons and their neuronal precursors. These cells were differentiated following retinoic acid (RA) treatment for 4 weeks and antiproliferative agents for 3 weeks, respectively, to yield post-mitotic CNS neuronal (NT2-N) cells. The cytoplasmic RNA was isolated from NT2/D1 cells both before and during RA treatment and from differentiated neurons (NT2-N cells). These RNA samples were examined using Northern blot analysis with cDNA probes specific for connexin26, −32, and −43. Connexin26 and −32 mRNAs were absent in NT2/D1 and NT2-N cells. Connexin43 mRNA was expressed at high levels in NT2/D1 cells before RA treatment, but it decreased significantly during RA induction. There was no detectable connexin43 mRNA in NT2-N cells. Western blot analysis confirmed the expression of connexin43 protein in NT2/D1 cells before and during RA treatment. The protein profile detected in Western blot analysis indicated two bands representing different phosphorylation states of connexin43. Our immunocytochemistry results did not show connexin26 and −32 immunoreactivity in NT2/D1 and NT2-N cells. However, we detected connexin43 immunoreactivity in NT2/D1 cells with a decreasing pattern upon RA induction. Both Western blotting and immunocytochemistry confirmed the absence of connexin43 protein in NT2-N cells. NT2/D1 cells passed calcein readily to an average of 18 cells, confirming the functionality of gap junctions in these cells. The extent of dye-coupling decreased about 78% when NT2/D1 cells were RA treated for 4 weeks. NT2-N differentiated neurons did not pass dye to the adjacent cells. We conclude that both connexin43 expression and dye coupling capacity decrease during neuronal differentiation of NT2/D1 cells. J. Neurosci. Res. 49:19–31, 1997. © 1997 Wiley-Liss Inc.     

Cycloheximide prevents kainate-induced neuronal death and c-fos expression in adult rat brain

The present study was directed at evaluating the possible involvement of protein synthesis in excitotoxin-induced neuronal damage and prolonged expression of the proto-oncogene, c-fos. Kainic acid-induced seizure activity elicited varying degrees of neuronal damage and cell loss in selectively vulnerable regions of the adult rat limbic system. Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter behavioral seizure characteristics, but markedly attenuated damage to susceptible neuronal populations. A prolonged increase in c-fos mRNA was observed byin situ hybridization up to 16 h after the onset of seizures in regions exhibiting neuronal death. Pretreatment with cycloheximide did not affect the transient induction of c-fos observed in numerous structures, but significantly reduced the prolonged expression of c-fos mRNA in kainatevulnerable regions. Despite producing massive seizure activity, systemic kainic acid administration during the early postnatal period did not induce any neuronal death, and did not result in prolonged c-fos expression in any brain structures. The developmental onset of selective neuronal vulnerability coincided with that of prolonged c-fos expression in susceptible neuronal populations. In adult rats, seizure activity induced by pentylenetetrazole did not produce neuronal damage nor did it produce prolonged c-fos expression. These results not only demonstrate that kainate-induced neurotoxicity and the prolonged expression of c-fos are both prevented by cycloheximide, but also strengthen the idea that prolonged c-fos expression is a marker of neuronal death.     

Biosynthesis of DNA and RNA in neuronal and glial cells from various regions of developing rat brain

Slices of cerebral hemispheres, brain stem, and cerebellum from rats 5–30 days old were used for in vitro incorporation of [methyl-³ H] thymidine and [6-¹⁴ C] orotic acid into DNA and RNA, respectively. The rates of DNA and RNA synthesis decreased markedly during development, with the most marked decrease observed for DNA. The different brain regions showed specific patterns of decline of DNA and RNA synthesis. Following incubation of slices, the tissues were fractionated to obtain fractions enriched in neuronal cells and in glial cells. In cerebellum, the granule neurons were separated from the Purkinje neurons. The glial: neuronal ratio of DNA specific activity was different in the three regions examined: in cortex it decreased from 6 at 10 days to 3 at 20–30 days; in brain stem it was 3 throughout 10–30 days; in the cerebellum (glia:granule neuron ratio) it was also 3 at 30 days but only 0.3 at 10 days. Concerning the RNA incorporation, small differences were found between neuronal and glial cells.     

Astrocytic dye coupling in rat hippocampus: Topography,developmental onset,and modulation by protein kinase C

Previous studies have shown that astrocytes constitute a functional syncytium whereas the cytoplasmata of individual cells are connected via gap junctions. Many studies have used cultured astrocytes and have examined electrical coupling with the help of double electrode techniques. Another approach has been the immunohistochemical detection of gap junction proteins in sections of brain tissue. From the results of these experiments it is difficult to infer the extent of astrocyticcoupling in situ. To get an impression of the distribution of coupled astrocytes we took advantage of the hippocampal slice preparation which leaves the topography of neurons and astrocytes intact. We performed injections of low molecular weight dyes into single electrophysiologically identified astrocyes. As these dyes can pass through gap junctions this leads to the staining of all connected cells in a certain area, limited by the diffusional spread of the dye. The results show that there is virtually no border to astrocytic coupling between the diverse hippocampal subdivisions. This widespread coupling could already be detected at postnatal day 4, the earliest age tested. Activation of protein kinase C with phorbol esters showed that it is possible to reduce gap junctional communication by some extent. We conclude that although no compartmentalization was seen with respect to astrocytic coupling, the intercellular communication of these glial cells has the capability of being regulated for example by neuronal signals which activate the phospholipase C pathway in astrocytes. © 1994 Wiley-Liss, Inc.     

脑红蛋白在大鼠脑内表达的细胞定位

目的研究脑红蛋白(NGB)在正常大鼠脑内表达的细胞定位。方法常规方法制备SD大鼠脑组织冰冻切片。以神经元特异性烯醇化酶(NSE)和胶质纤维酸蛋白(GFAP)作为对照,分别与NGB进行免疫荧光双标记染色,共聚焦显微镜照相分析。结果免疫荧光双标和图像分析的结果表明,NGB在大鼠脑内表达的细胞定位与NSE相同,存在于神经元的胞浆中。NGB与GFAP表达的细胞不同。结论NGB在正常大鼠脑内神经元中表达,提示与脑神经元的功能活动密切相关。     

红藻氨酸诱导癫痫发作鼠脑HSP70表达与组织细胞凋亡关系的研究

目的 :探讨红藻氨酸诱导癫痫发作鼠脑 HSP70表达与组织细胞凋亡的关系。方法 :用流式细胞术及免疫印迹法分别检测红藻氨酸诱导癫痫发作鼠脑海马结构组织细胞不同时间的凋亡率及 HSP70表达量。结果 :红藻氨酸注射后 3小时 ,HSP70表达量即开始增高 ,6小时凋亡率始升高 ,至 4 8小时 ,二者同时达到高峰 (P<0 .0 1) ,此后开始下降。结论 :HSP70是调节红藻氨酸诱导癫痫发作鼠脑细胞凋亡的重要分子之一     

Effects of propofol on neuronal apoptosis and aquaporin-4 expression in a rat model of traumatic brain injury

BACKGROUND： Several studies have demonstrated that propofol exhibits protective effects in the central nervous system. OBJECTIVE： To observe the effects of propofol on neuronal apoptosis and aquaporin-4 （AQP-4） expression in a rat model of traumatic brain injury and to further investigate the mechanisms of action. DESIGN, TIME AND SETTING： The present neuronal, pathomorphological experiment was performed at the Institute of Cerebrovascular Disease, Qingdao University Medical College between April 2007 and March 2008. MATERIALS： Traumatic brain injury was induced by free falling objects in 150 healthy, male, Wistar rats. Propofol was produced by AstraZeneca, China. Rabbit anti-rat AQP-4 polyclonal antibody, SABC immunohistochemistry kit, and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling （TUNEL） kit were purchased from Wuhan Boster Bioengineering Co., Ltd., China. METHODS： All 150 rats were randomly and evenly divided into lesion-only and propofol-treated groups. One hour after traumatic brain injury, propofol-treated animals received 1% propofol （10 mg/kg） through the caudal vein, followed by a sustained perfusion of 30 mg/kg propofol per hour for 2 hours, while the lesion-only group received equal volumes of physiological saline in parallel. MAIN OUTCOME MEASURES： At 6, 12, 24, 48, and 72 hours after traumatic brain injury, morphological changes in the peritraumatic and adjacent brain areas were analyzed in all rats by hematoxylin-eosin （HE） staining. In addition, cellular apoptosis was detected by TUNEL assay and the number of AQP-4-positive cells was determined by immunohistochemistry techniques. Brain water content was calculated as the ratio of dry to wet tissue weight. RESULTS： HE staining results demonstrated that, in the lesion-only group, the peritraumatic area exhibited neuronal and glial cell necrosis and disintegration. The adjacent area displayed swollen neuronal perikarya and vascular endothelial ceils, cellular edema, and a small amount of     

Temporal changes in expression of neuronal nitric oxide synthase mRNA in the rat hippocampus associated with kainate-induced seizures

We studied the temporal changes in expression of neuronal nitric oxide (NO) synthase (nNOS) mRNA in the hippocampus of rats treated with kainic acid by use of in situ hybridization technique. Intraperitoneal injection of 10 mg kg-1 kainic acid decreased expression of nNOS mRNAs in the dentate gyrus and CA3 region of the hippocampus at 3 h and 8 h and increased it in the dentate gyrus and CA1 at one week after treatment. Although our previous study indicated that administration of kainic acid increased NO generation in the rat hippocampus, present results suggest that the injection of kainic acid results in differential regulation of nNOS mRNA and NO formation in the rat hippocampus.     

r—HuEPO对外伤性脑损伤大鼠凋亡基因表达的影响

目的探讨重组人促红细胞生成素（r—HuEPO）对外伤性脑损伤大鼠凋亡基因表达的影响。方法将48只健康成年雄性SD大鼠随机分成4组：r-HuEPO1000U／kg、3000U／kg、5000U／kg治疗组和生理盐水对照组。采用改良的Feeney氏法制作大鼠自由落体脑创伤模型,r—HuEPO干预。一周后麻醉取脑冻存：免疫组织化学法测定脑组织中NF—κB、C-myc和Fas／Fasl的阳性细胞及凋亡细胞数。结果与对照组相比,各组中NF—KB、Fas和Fasl阳性细胞及凋亡细胞数均有显著减少（P〈0．05）,尤其是5000U／kgr—HuEPO组减少最显著（P〈0．01）。结论r—HuEPO可抑制创伤性脑损伤大鼠NF—KB、Fas／Fasl的促凋亡作用,减轻迟发性神经元损伤,从而起到神经保护的作用。     

Quantitative immunohistochemical and biochemical correlates of connexin43 localization in rat brain.

We have shown by immunohistochemical methods that the gap junction protein connexin43 is heterogeneously distributed in rat brain (Yamamoto et al: J Comp Neurol 302:853, 1990). Here we have compared quantitatively the relative amount of connexin43 detected on Western blots of seven central nervous system (CNS) regions with the density of connexin43-immunoperoxidase reactivity in these regions. As has been observed on Western blots of several cell types, homogenates of these CNS regions contained two forms of connexin43, its dephospho form with an apparent mobility of approximately 41 kDa and its approximately 43 kDa phosphorylated form. While the relative quantities of connexin43 varied considerably among the brain regions, the ratio of the 43/41 kDa forms, 0.71, was relatively uniform (correlation coefficient, r = 0.92). Sections of brain processed for connexin43-immunolocalization by the peroxidase-antiperoxidase (PAP) method showed that chromogen deposition was linear with incubation time in reaction medium. Optical density of tissue connexin43-immunoreactivity in each of the seven areas plotted against the density of connexin43 bands on Western blots gave a correlation coefficient of r = 0.90. Connexin43-immunoreactivity had a similar appearance in sections processed by PAP or immunofluorescence procedures and consisted of isolated or aggregates of puncta.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic expression of Cx47 in mouse brain development and in the cuprizone model of myelin plasticity

The study shows the dynamic expression of connexin47 (Cx47) in oligodendrocytes and myelin of mice, either in myelinogenesis occurring in early development or in an experimental model of new‐myelinogenesis of adult mice. Cx47 first appeared in the embryonic mouse brain at E10.5 successively the expression increased, principally in regions populated by developing oligodendrocytes. The expression declined postnatally toward adulthood and immunoreactivity was restricted to a few specific areas, such as the corpus callosum, the striatum, the cerebellum, and the spinal cord. Since the expression of Cx47 in developing oligodendrocytes preceded those of Cx32 and Cx29, a role of Cx47 in myelinogenesis was postulated. This hypothesis was tested in a model of re‐myelination, which principally involved the corpus callosum, occurring in adult mice by treatment with cuprizone. Cx47 was upregulated during demyelination and recovered during the remyelination phase. During demyelination, Cx47 was first over‐expressed in the corpus callosum and later, when the myelin virtually disappeared in the injured areas, Cx47 was expressed in astrocytes located inside and closely around the demyelinated areas. The remyelination of injured areas occurred after stopping the administration of cuprizone and continued to complete recovery. In this period the expression of Cx47 shifted from astrocytes to newly‐formed myelin. Thus, Cx47 exhibits in this model a transient and de novo expression in astrocytes with a topographic segregation in the injured areas, only when oligodendrocytes and the myelin were most severely affected. Taken as a whole the evidence suggests that Cx47 play a key role in myelination. © 2010 Wiley‐Liss, Inc.     

Differential expression of connexin 43 in the chick tangential vestibular nucleus

The chick tangential nucleus is a major vestibular nucleus whose principal cells receive convergent inputs from primary vestibular and nonvestibular fibers and participate in the vestibular reflexes. During development, the principal cells gradually acquire the mature firing pattern in part by losing a specific potassium current around hatching (H). Here we focus on characterizing the expression of connexin 43 (Cx43), a gap junction protein found mainly between astrocytes in the mature brain. The astrocytic syncytium plays an important role in maintaining extracellular potassium ion balance in the brain. Accordingly, it is important to characterize the potential of this syncytium to communicate during the critical developmental age of hatching. Using fluorescence immunocytochemistry, we investigated whether Cx43 staining was concentrated in specific cellular compartments at H1 by applying well-known markers for astrocytes (glial fibrillary acidic protein; GFAP), oligodendrocytes (antimyelin), neurons (microtubule-associated protein 2), and synaptic terminals (synaptotagmin). GFAP-positive astrocytes and GFAP-negative nonneuronal cells around the principal cell bodies were labeled with Cx43, suggesting that Cx43 was expressed exclusively by nonneuronal cells near the neuronal elements. Next, the developmental pattern of expression of Cx43 was studied at embryonic day 16 (E16), H1, and H9. At E16, Cx43 was present weakly as random small clusters in the tangential nucleus, whereas, at H1, overall staining became localized, with increases in size, brightness, and number of immunostained clusters. Finally, at H9, Cx43 staining decreased, but cluster size and location remained unchanged. These results suggest that Cx43 is developmentally regulated with a peak at birth and is associated primarily with astrocytes and nonneuronal cells near the principal cell bodies.     

NOS抑制剂对红藻氨酸诱导癫痫发作大鼠脑海马组织细胞凋亡的影响

目的研究红藻氨酸诱导癫痫发作大鼠脑组织中一氧化氮合酶(NOS)抑制剂与海马组织细胞凋亡的关系.方法利用流式细胞术,测定红藻氨酸诱导大鼠癫痫发作及用L-精氨酸(L-Arg)的硝基衍生物N-硝基-左旋精氨酸(L-NNA)干预后的鼠脑海马组织细胞凋亡情况.结果在癫痫发作过程中,NOS抑制剂对鼠脑海马组织细胞凋亡峰有明显影响,L-NNA能增加凋亡发生率.结论在癫痫发作过程中,鼠脑海马组织存在细胞凋亡现象,NOS抑制剂对凋亡有明显影响.     

Differential expression of hippocampal connexins after acute hypoxia in the developing brain

Acute hypoxia at postnatal day (P) 10 is an accepted model of human neonatal hypoxia which results, among other consequences, in increased hippocampal excitability. Hypoxic–ischemic injury, which mimics stroke, has been shown to result in changes in connexins (Cxs), however, changes in Cxs have not been studied in the P10 hypoxia model. The aim of this study was to investigate changes in the hippocampal expression of three different connexins at consecutive developmental stages after acute hypoxia at P10 (10 min and 30 min after reoxygenation, P11, P14, P17, P29, and P45) as compared to sham manipulated pups. After acute hypoxia at P10, Cx30 protein levels were increased at 30 min after reoxygenation, at P11 and at P14, and then returned to control levels. Cx36 protein levels transiently decreased at P11 after acute hypoxia then returned to control levels. Cx43 protein levels did not change at any of the time points. Although changes in mRNA expression were observed during development for Cx30 only, acute hypoxia did not result in changes in mRNA expression of all these Cxs when compared to age matched controls suggesting that acute hypoxia induced posttranslational changes in protein expression.     

Astrocytic localization of kynurenine aminotransferase II in the rat brain visualized by immunocytochemistry

Kynurenic acid (KYNA), a metabolite of the kynurenine pathway of tryptophan degradation, is a neuroinhibitory agent present in the mammalian brain. Endogenous KYNA preferentially affects the alpha7 nicotinic acetylcholine (alpha7nACh) receptor and, possibly, the glycine co-agonist (glycineB) site of the NMDA receptor. Functionally relevant fluctuations in brain KYNA occur under both physiological and pathological conditions, affecting cholinergic and glutamatergic neurotransmission. Kynurenine aminotransferase II (KAT II), the major biosynthetic enzyme of KYNA in the rat brain, catalyzes the irreversible formation of KYNA from its immediate bioprecursor, kynurenine. We now purified rat kidney KAT II to homogeneity, generated a polyclonal rabbit anti-rat KAT II antibody, and purified the antibody using routine biochemical methods. The antibody selectively recognized KAT II by Western blot analysis and in immunotitration experiments. Used for immunocytochemistry, the antibody revealed discrete, specific staining of KAT II-positive astrocyte-like cells throughout the adult rat brain. The presence of KAT II in astrocytes was confirmed by double fluorescence immunostaining with an antibody against the astrocyte-specific marker glial fibrillary acidic protein (GFAP). No specific labeling was detected in neurons or microglia. However, KAT II-positive astrocytes were intimately associated with select neuron populations, supporting a neuromodulatory role of KYNA. Intense staining was frequently seen around brain capillaries, with astrocytic end feet contacting the capillary wall. This may explain the rapid access of blood-derived kynurenine to KAT II-containing astrocytes. The new anti-KAT II antibody should be useful in the further elucidation of the presumed role of KYNA in brain physiology and pathology.