大眼鳜垂体的组织学和组织化学研究

[目的]探讨大眼鳜垂体的组织学结构。[方法]以大眼鳜成鱼为试验材料,通过显微镜观察对其垂体的组织学、组织化学进行研究。[结果]大眼鳜垂体由神经垂体和腺垂体两部分组成,腺垂体分为前外侧部、中外侧部和中间部。神经垂体十分发达,尤其是后腺垂体神经部,占垂体后部大部分区域;腺垂体可分辨出7种分泌细胞类型,即前外侧部的催乳激素细胞和促肾上腺皮质激素细胞,中外侧部的生长激素细胞、促性腺激素细胞和促甲状腺激素细胞,中间部的促黑色素细胞刺激激素细胞和PAS阳性细胞;中间部后方腹面边缘微血管十分发达。[结论]该研究为进一步弄清大眼鳜的繁殖机理提供了科学依据。     

Regulation of dendritic protein synthesis by miniature synaptic events

We examined dendritic protein synthesis after a prolonged blockade of action potentials alone and after a blockade of both action potentials and miniature excitatory synaptic events (minis). Relative to controls, dendrites exposed to a prolonged blockade of action potentials showed diminished protein synthesis. Dendrites in which both action potentials and minis were blocked showed enhanced protein synthesis, suggesting that minis inhibit dendritic translation. When minis were acutely blocked or stimulated, an immediate increase or decrease, respectively, in dendritic translation was observed. Taken together, these results reveal a role for miniature synaptic events in the acute regulation of dendritic protein synthesis in neurons.     

Transmembrane action potentials from smooth muscle in turtle arteries and veins

Transmembrane potential and active tension were measured in isolated segments of turtle aorta and inferior vena cava. Changes in tension were associated with action potentials, but the potentials had a different pattern in the two tissues. When the frequency of the action potentials increased, the contractions summated, resulting in a steadily maintained contraction.     

DDT: interaction with nerve membrane conductance changes

The falling phase of action potentials of lobster giant axons is prolonged by DDT; finally a plateau phase is produced like cardiac action potentials. In axons poisoned with DDT, peak transient (sodium) currents associated with step depolarizations are turned off very slowly, and steady-state (potassium) currents are markedly suppressed. These two changes would cause the prolongation of action potentials and are considered the major ionic mechanisms of DDT action.     

Combined analog and action potential coding in hippocampal mossy fibers

In the mammalian cortex, it is generally assumed that the output information of neurons is encoded in the number and the timing of action potentials. Here, we show, by using direct patchclamp recordings from presynaptic hippocampal mossy fiber boutons, that axons transmit analog signals in addition to action potentials. Excitatory presynaptic potentials result from subthreshold dendritic synaptic inputs, which propagate several hundreds of micrometers along the axon and modulate action potential-evoked transmitter release at the mossy fiber-CA3 synapse. This combined analog and action potential coding represents an additional mechanism for information transmission in a major hippocampal pathway.     

Neuroscience. Noise makes sense in neuronal computing

The united efforts of assemblies of neurons in the brain's primary visual cortex translate incoming visual signals into action potentials. These action potentials encode, for example, the contrast and orientation of different parts of the image. Some neurons are sensitive to one particular orientation, other are sensitive to other orientations, but all neurons respond equally well to the image contrast. In a Perspective, Volgushev and Eysel explain the finding (Anderson et al.) that neurons are able to maintain this sensitivity to the orientation of a stimulus regardless of the contrast by adding noise to the membrane potential, such that action potentials can also be generated in response to weak signals at low contrast.     

Dendritic spikes and their inhibition in alligator Purkinje cells

Alligator Purkinje cells generate action potentials in the peripheral dendritic tree, after synaptic depolarization via superficial parallel fibers. These action potentials are inhibited at the dendrite level by preceding parallel-fiber volleys at close intervals. We conclude that this inhibition is produced by the activation of the inhibitory interneurons of the molecular layer, the stellate cells, which establish synaptic contacts with the dendrites of the Purkinje cells.     

A new laser scanning system for measuring action potential propagation in the heart

A rapid laser scanning system was developed to map the spread of excitation in amphibian and mammalian hearts stained with fluorescent dye. Isochronic maps of conduction were constructed by timing the upstroke of the optical action potential; 128 sites could be scanned in 4 milliseconds. The accuracy of this technique was verified by recording simultaneously from 16 unipolar electrodes placed in different areas of the heart. Conducted action potentials in normal frog heart propagated at 0.1 meter per second. Propagation of action potentials was also monitored in ischemic cat heart, in which both driven and arrhythmic action potential upstrokes could be tracked. The results suggest that this system is capable of scanning the normal and abnormal spread of electrical activity in the heart.     

Differential shunting of EPSPs by action potentials

Neurons encode information and communicate via action potentials, which are generated following the summation of synaptic events. It is commonly assumed that action potentials reset the membrane potential completely, allowing another round of synaptic integration to begin. We show here that the conductances underlying the action potential act instead as a variable reset of synaptic integration. The strength of this reset is cell type-specific and depends on the kinetics, location, and timing of the synaptic input. As a consequence, distal synapses, as well as inputs mediated by N-methyl-d-aspartate receptor activation, can contribute disproportionately to synaptic integration during action potential firing.     

Xenopus oocytes injected with rat uterine RNA express very slowly activating potassium currents

Under the influence of estrogen, uterine smooth muscle becomes highly excitable, generating spontaneous and prolonged bursts of action potentials. In a study of the mechanisms by which this transition in excitability occurs, polyadenylated RNA from the uteri of estrogen-treated rats was injected into Xenopus oocytes. The injected oocytes expressed a novel voltage-dependent potassium current. This current was not observed in oocytes injected with RNA from several other excitable tissues, including rat brain and uterine smooth muscle from ovariectomized rats not treated with estrogen. The activation of this current on depolarization was exceptionally slow, particularly for depolarizations from relatively negative membrane potentials. Such a slowly activating channel may play an important role in the slow, repetitive bursts of action potentials in the myometrium.     

Effects of tetrodotoxin on excitability of squid giant axons in sodium-free media

The effect of tetrodotoxin on excitability of internally perfused squid giant axons immersed in various sodium-free media was examined. Action potentials were found to be suppressed by this substance, with or without sodium ion in the external medium. Tetrodotoxin showed a strong suppressive effect upon action potentials produced in media containing salts of only divalent cations (CaCl(2), CaBr(2), SrCl(2), or BaCl(2)). Our findings concerning the action of tetrodotoxin do not support the separate-channel hypothesis for excitable membranes.     

Voltage-dependent calcium channels in glial cells

The electrophysiological properties of glial cells were examined in primary culture in the presence of tetraethylammonium and Ba2+, a treatment that reduces K+ permeability of the membrane and enhances currents through voltage-dependent Ca2+ channels. Under these conditions, glial cells showed both spontaneous action potentials and action potentials evoked by the injections of current. These responses appear to represent entry of Ba2+ through Ca2+ channels because they were resistant to tetrodotoxin but were blocked by Mn2+ or Cd2+.     

Suppression of neurite elongation and growth cone motility by electrical activity

Electrical activity may regulate a number of neuronal functions in addition to its role in transmitting signals along nerve cells. The hypothesis that electrical activity affects neurite elongation in sprouting neurons was tested by stimulating individual snail neurons isolated in cell culture. The findings demonstrated that growth cone advance, and thus neurite elongation, is reversibly stopped during periods when action potentials are experimentally evoked. A decrease in filopodial number and growth cone area was also observed. Thus, action potentials can mediate the cessation of neurite outgrowth and thereby may influence structure and connectivity within the nervous system.     

Hemodynamic signals correlate tightly with synchronized gamma oscillations

Functional imaging methods monitor neural activity by measuring hemodynamic signals. These are more closely related to local field potentials (LFPs) than to action potentials. We simultaneously recorded electrical and hemodynamic responses in the cat visual cortex. Increasing stimulus strength enhanced spiking activity, high-frequency LFP oscillations, and hemodynamic responses. With constant stimulus intensity, the hemodynamic response fluctuated; these fluctuations were only loosely related to action potential frequency but tightly correlated to the power of LFP oscillations in the gamma range. These oscillations increase with the synchrony of synaptic events, which suggests a close correlation between hemodynamic responses and neuronal synchronization.     

促性腺激素释放激素在不同品种母牛垂体中的免疫组化定位

为了掌握促性腺激素释放激素（GnRH）及其受体在不同品种母牛垂体中的变化规律,采用免疫组化SP染色法分别对广西沼泽型水牛、摩拉杂交水牛、荷斯坦奶牛、广西本地黄牛垂体中GnRH的分布表达进行对比研究。结果表明,不同品种母牛垂体中均发现有呈棕黄色或黄褐色的GnRH阳性物质存在,经Image-Pro Plus 6.0软件统计发现,摩拉杂交母水牛的GnRH免疫阳性细胞较其他3个品种的大（P〈0.05）,而平均光密度值介于荷斯坦母奶牛和广西本地母黄牛之间（P〉0.05）。在神经垂体中仅发现GnRH免疫阳性纤维,而未发现GnRH免疫阳性细胞;在腺垂体远侧部的细胞均呈GnRH免疫反应阳性,阳性物质主要分布在腺垂体远侧部嫌色细胞和嗜色细胞胞质内。说明GnRH对腺垂体激素分泌的调节可能是直接通过神经调节,而神经垂体可能只是GnRH调节过程的通路。     

Decremental Conduction over "Giant" Afferent Processes in an Arthropod

Four "giant" mechanoreceptive cells form part of a stretch receptor organ at the base of the uropod in the sand crab, Emerita (Crustacea, Anomura). Injection of the fluorescent dye Procion Yellow revealed that these sensory cells are monopolar with somata located in the central nervous system. No such cells have previously been described in arthropods. These neurons are also unusual in that they do not generate propagated action potentials; rather, they mediate stretch reflexes by transmission of graded, decremental potentials.     

Internally perfused axons: effects of two different anions on ionic conductance

Voltage-clamizped giant axons of squid, internally perfused with potassiumt chloride solutions, showed reduced initial transient memnbrane conductance to voltage and increased overall (leakage) conductance. Unclamtped axons showed reduced action and resting potentials. Ionic conductances and memtbrane potentials were maintained or restored by perfusion with potassiuwn fluoride solutions. As much as 90 percent of internal fluoride could be replaced with chloride without alterationt of normal properties of membrane.     

Identified sources and targets of slow inhibition in the neocortex

There are two types of inhibitory postsynaptic potentials in the cerebral cortex. Fast inhibition is mediated by ionotropic gamma-aminobutyric acid type A (GABA(A)) receptors, and slow inhibition is due to metabotropic GABA(B) receptors. Several neuron classes elicit inhibitory postsynaptic potentials through GABA(A) receptors, but possible distinct sources of slow inhibition remain unknown. We identified a class of GABAergic interneurons, the neurogliaform cells, that, in contrast to other GABA-releasing cells, elicited combined GABA(A) and GABA(B) receptor-mediated responses with single action potentials and that predominantly targeted the dendritic spines of pyramidal neurons. Slow inhibition evoked by a distinct interneuron in spatially restricted postsynaptic compartments could locally and selectively modulate cortical excitability.     

Diphasic postsynaptic potential: a chemical synapse capable of mediating conjoint excitation and inhibition

Two identified interneurons in each buccal ganglion of Aplysia can mediate conjoined excitation and inhibition to a single follower cell. A single presynaptic action potential in one of these interneurons produces a diphasic, depolarizing-hyperpolarizing synaptic potential apparently as a result of a single transmitter acting on two types of postsynaptic receptors in the follower cell. These receptors produce synaptic potentials with differing reversal potentials, ionic conductances, time courses, rates of decrement with repetition, pharmacological properties, and functional consequences. The excitatory receptor controls a sodium conductance, the inhibitory receptor controls a chloride conductance. Both components of the synaptic potentials can be produced by iontophoretic application of acetylcholine on the cell body of the follower cell, and each component is differentially sensitive to different cholinergic blocking agents.     

苦参碱对低钾致兔左心室流出道细胞电生理异常保护作用及其机制

目的探讨苦参碱对低钾致兔左心室流出道细胞电生理异常保护作用及其机制.方法应用常规玻璃微电极细胞内记录技术,观察正常灌流液、低钾灌流液、低钾＋苦参碱（50μmol/L）灌流液对兔左心室流出道慢反应自律细胞最大舒张电位（MDP）,动作电位0相幅值（APA）,50%复极化时间（APD50）,90%复极化时间（APD90）,4...