Bovine cumulus-oocyte disconnection in vitro

Summary Cumulus-oocyte complexes were obtained from cows by aspiration of small (1–6 mm in diameter) antral follicles after slaughter. Complexes with a compact multilayered cumulus investment were cultured and processed for transmission electron microscopy after different periods of culture including a 0 h control group. In 0 h control oocytes the cumulus cells had numerous projections which penetrated the zona pellucida and established gap junctions with the oolemma. A partial loss of these junctions was noticed as an early event of oocyte maturation occurring within the first 3 h of culture. A low frequency of gap junctions was maintained until 12–18 h of culture where the junctional contact was completely disrupted. This decrease in intercellular communication was parallelled by resumption of oocyte meiosis.     

Visual fixation offsets affect both the initiation and the kinematic features of saccades

It is well known that the removal of a fixation point prior to the presentation of a peripheral target dramatically reduces saccadic reaction time (SRT). This effect has become known as the “gap effect”. The present study examined several detailed kinematic variables to determine whether the removal of the fixation point also affects the manner in which saccades are produced. The findings indicate that saccades that were initiated after the removal of the fixation point had higher average velocities and reached greater peak velocities, accelerations, and decelerations than did saccades produced in the presence of the fixation point. The results suggest that the removal of the fixation point may affect the force-time curves of saccades in addition to affecting the time needed to initiate the saccades. Received: 21 February 1997 / Accepted: 24 July 1997     

Effects of horizontal cell network architecture on signal spread in the turtle outer retina. experiments and simulations

In thePseudemys turtle retina five functionally distinct, electrically coupled networks of horizontal cells distribute signals in the outer plexiform layer. These networks differ significantly in their architecture, as determined by intracellular labeling with Neurobiotin after physiological recording and identification. The density of H1 horizontal cells is highest, ranging around 1800 cells/mm² at approximately 2.3 mm eccentricity. H1 horizontal cell somata are connected via 6–10 thin, short dendrites. The H1 horizontal cell axon terminal network is composed of thick axon terminals, forming a three-dimensional, sheath-like structure. Networks of coupled H2 and H3 horizontal cells have cell densities of around 210 cells/mm² and 350 cells/mm² respectively, at the same eccentricity of 2.3 mm. Cell bodies are connected with 6–12 long, thin dendrites. Here we report for the first time H4 horizontal cell networks. Cell density is approximately 970 cells/mm² at 2 mm eccentricity, and cell bodies are connected with 6–10 thin, short dendrites. General properties of passive voltage spread were compared for three of these horizontal cell networks using NeuronC. Realistic network architectures were obtained by digitizing the intracellularly labeled networks, respectively. One network obtained from coupled H1 horizontal cell bodies, one from coupled H1 horizontal cell axon terminals, and one from H2 horizontal cells were simulated. These three realistic networks were compared with an artificial, electrically coupled regular triangular network. Passive signal spread in these networks strongly depended on the exact network architecture using otherwise identical parameters. Changes in coupling strength affected signal spread in these networks differently. As in the experimental situation, changes in synaptic conductance influenced signal spread. Some principal effects of extensively coupled horizontal cells on photoreceptor signal processing were simulated with one type of photoreceptor connected by telodendria, synapsing onto an underlying triangular network and receiving feedback synapses. Under certain conditions, spatial information is coded in single photoreceptors. This was also the case in the experimental situation. In the simulation, spatial filter adjustment for optimal spatial coding in photoreceptors can be achieved by changing coupling strength in the horizontal cell network.     

d-宁烯、丹参及姜黄素衍生物对ras基因产物膜结合和细胞间隙信息传导的影响

目的旨在寻找新型抗肿瘤药物,进一步研究d-宁烯、丹参及姜黄素衍生物的抗肿瘤机理。采用分子生物学方法及划痕标记染料示踪技术,研究了4种人实体瘤起源的细胞系的细胞间隙信息传导(GJIC)、H-ras癌基因表达以及ras癌基因产物(P21^ras蛋白)表达状态,并观察了4种天然产物对它们的影响。结果表明,细胞内染料传输功能的丧失与ras基因突变率呈正相关;单萜化合物d-宁烯和酚类化合物丹参衍生物的抗肿瘤作用可能与抑制P21^ras蛋白膜结合和增强细胞间隙信息传导功能有关。提示Ras癌基因产物P21^ras蛋白膜结合的抑制与细胞间隙信息传导功能的增强有直接关系。     

连接蛋白拟似肽对海人酸致痫大鼠脑电活动的影响

目的观察针对连接蛋白43(CX43)合成的特异性的缝隙连接阻断剂-连接蛋白拟似肽对海人酸致痫大鼠脑电活动的影响。方法建立18只大鼠癫痫动物模型,分连接蛋白拟似肽组、甘珀酸组和对照组(每组6只),在在体上分别局部给予连接蛋白似似肽、甘珀酸和生理盐水,用脑电图仪观测用药前后每组大鼠皮层脑电活动的变化情况。结果连接蛋白拟似肽组及甘珀酸组给药后癫痫的发作次数明显比给药前发作次数减少,癫痫波的平均振幅也明显变小,给药前后比较有显著性差异(P<0.01),生理盐水组给药前后癫痫的发作次数及平均振幅几乎没有变化。连接蛋白拟似肽组给药前后癫痫的发作次数和波幅的变化值与甘珀酸组给药前后癫痫的发作次数和波幅的变化值相比无显著性差异。结论针对CX43合成的连接蛋白拟似肽可以特异性地抑制癫痫的发作。     

工频磁场对星形胶质细胞间隙连接通讯功能的影响

目的　探讨工频磁场 (PFMF)是否有促癌或协同促癌作用。方法　利用荧光光漂白后再恢复法观察漂白细胞荧光强度的恢复以判断经间隙连接的细胞间通讯 ,以相对荧光强度恢复速率(CFIRR)作为对细胞间隙连接通讯 (GJIC)作用的评价指标 ,研究不同磁场强度单独作用或协同佛波酯(TPA)对星形胶质细胞GJIC功能的影响。结果　 3ng/mlTPA作用 1h时CFIRR的中位数 (Md)值为4 .53 % /min ,空白对照组为 9.74% /min ,两组的差异有显著性 (H =1 2 .0 84,P <0 .0 0 5)。 0 .8或 1 .6mT磁场作用 2 4h时CFIRR的Md 分别 8.2 5、6 .68% /min ,与空白对照组比较 ,差异无显著性 (H =32 .61 7,P >0 .0 5)。 0 .8或 1 .6mT磁场作用 2 3h ,再与TPA共同作用 1h时CFIRR的Md 分别为 3 .32、2 .85% /min ,与TPA组比较 ,差异无显著性 (H =2 .589,P >0 .0 5)。结论　 0～ 1 .6mT的 50Hz磁场单独作用不能抑制星形胶质细胞GJIC功能 ;协同TPA ,不能增强TPA对星形胶质细胞GJIC的抑制作用 ;但是磁场对星形胶质细胞GJIC的抑制作用随着磁场强度增强呈递增趋势     

Dopamine receptor agonists alter gap prestimulus modulation

An innocuous sensory event (a prestimulus) that briefly precedes a startle-eliciting stimulus (SES) will reduce the amplitude of the subsequently elicited reflex. In three experiments brief silent periods in otherwise continuous noise (gaps) were used as prestimuli to investigate the effects of the D₁ dopamine receptor agonist (±)-SKF-38393 (SKF) and the dopamine D₂ receptor group agonist (−)-quinpirole hydrochloride on gap inhibition of the rat’s acoustic startle reflex. Gap durations of 4 and 50 ms were analyzed. Quinpirole (0–1.6 mg/kg) had a biphasic effect on gap inhibition. Lower doses increased gap inhibition, an effect that peaked at the 0.4 mg/kg dose. For higher doses, inhibition returned to control levels for the 4-ms long gap, but remained elevated for the 50-ms long gap. SKF had no effect on gap inhibition, and haloperidol (0.2 mg/kg) reversed the quinpirole-induced increase of gap inhibition. These data implicate the D₂ dopamine receptor group in gap inhibition of startle modulation. The results are discussed in terms of the effects of catecholamine agonists on attention. Received: 25 July 1995/Final version: 28 April 1997     

Does Fluid Flow Across the Intestinal Mucosa Affect Quantitative Oral Drug Absorption? Is It Time for a Reevaluation?

Purpose. Hydrophilic and charged solutes have a lower membrane permeability which is due to a lower partition into the lipid membrane (low solubility in the membrane phase) and/or a slower transcellular diffusion coefficient. They are therefore anticipated to be absorbed through the paracellular route, which is a consequence of diffusion and a convective volume flow through the water-filled intercellular space. Methods. Two approaches have been used to investigate the mechanisms underlying the paracellular drug transport across the intestinal mucosa: (a) including water transport by exposing the apical side of the epithelium with a hypotonic solution, and (b) stimulated paracellular transport by widening of tight junction and increased water absorption as a consequence of the sodium-coupled transport of nutrients. Results. Among the first studies that recognized this fluid flux dependent transmucosal transport of drugs, was one published by Oschenfahrt & Winne in 1973 and the one by Kitazawa et al. in 1975. During the last two decades the importance of this paracellular route for drug delivery have been explored in vitro and in situ. Conclusions. The limits concerning molecular weight, shape, ionization and the effect of physiological stimulants, such as luminal concentrations of nutrients, osmolality and motility, are currently under investigation. However, recently published in vivo human data by ourselves and others indicate that the promising results obtained in vitro and in situ for various hydrophilic compounds might not be valid in quantitative aspects in humans, especially not for drugs with a molecular weight over 200.     

Immunofluorescent labeling of tight junctions in the rat brain and spinal cord

Tight junctions may play an important role in maintaining the integrity of the blood-brain barrier. These junctions can be individually visualized using electron microscopy but no current technique is able to provide a more global picture of the presence and density of tight junctions in central nervous system tissue. We used an antibody that recognizes a high molecular weight protein (ZO-1) associated with tight junctions, to identify these specialized junctions within the rat brain and spinal cord. Immunofluorescent labeling showed a network of tight junctions between cells in the brain vasculature, leptomeninges and choroid plexus, and between tanycytes lining the floor of the third ventricle and the central canal of the spinal cord. Anti-ZO-1 labeled the majority of cells associated with the blood-brain barrier and may prove a useful marker, possibly in conjunction with functional dye studies, in evaluating the anatomical and functional integrity of the blood-brain barrier.