杀虫环对黑胸大蠊神经突触传递的阻遏作用

用电生理糖间隙法研究杀虫环对黑胸大蠊神经突触传递的作用,并以α-银环蛇毒素作比较。结果证明:1)杀虫环阈浓度1×10^-5M即显著地抑制兴奋性突触后电位(EPSP)。作用开始使之阈值递增,此时只有增加刺激强度方可诱出EPSP。2)(虫非)蠊第Ⅵ腹神经节是胆碱能的。已知突触后阻遏剂如α-银环蛇毒素的作用是N型乙酰胆碱受体(n-AchR)的专一性配基,与杀虫环阻遏神经突触的传递颇为相似,二者均不影响突触后神经元的静息电位和动作电位的传导;而杀虫环对非胆磁能的神经肌肉接头则无影响。3)自发突触后电位随杀虫环处理时间的不同而变化。开始自发释放电位的振幅、频率逐渐增加,继之产生持续期较长的阵发性高频发放,以后又逐渐消失。     

马氏钳蝎毒昆虫类神经毒素的分离、纯化及性质研究

经Sephadex G-50,sp-Sephadex C-25二步柱层析法,从山东马氏钳蝎(Bu-thus martensii Karch)粗毒中分离出四种对美洲(虫非)蠊有强直麻痹反应的毒性蛋白组份。其中二个组分在SDS聚丙烯酰胺电泳和等电聚焦电泳上均呈现单一区带,命名为BmK IT-Ⅰ,BmK IT-Ⅱ其pI分别为8.2和8.4,分子量分别为8400和7560。同时还分析了二个组份的氨基酸组成。经DABITC/PITC双偶合法测定了BmKIT-Ⅰ和BmK IT-Ⅱ的N端部份氨基酸排列顺序,它们分别为H_2NVal.Arg.Asp.Ala……H_2NVal.Arg.Asp.Gly……。 电生理学研究表明,纯化的BmK IT-I(1×10~(-5)g/ml)对(虫非)蠊腹Ⅵ神经节的突触传递有阻断作用,阻断后用生理溶液洗,则突触传递可恢复。从同一蝎毒粗毒中分离纯化的哺乳动物类神经毒素BmKⅢ在浓度高出100倍(1×10~(-3)g/ml)时也可以阻断(虫非)蠊腹Ⅵ神经节的突触传递,但用生理溶液冲洗没有观察到恢复。     

皮质醇对离体牛蛙交感神经节B细胞胆碱能突触传递的快速作用

在离体灌流的牛蛙交感神经节标本上,电刺激节前纤维,细胞内记录Ｂ细胞的电活动,观察给予皮质醇对Ｂ细胞突触传递作用。主要结果有：（１）电刺激节前纤维,细胞内记录１７０个Ｂ细胞的动作电位,给予皮质醇后０．５￣３ｍｉｎ内,５２个Ｂ细胞的突触传递发生脱漏甚至完全阻断,有明显的量效关系。甾体激素胞内受体阻断剂ＲＵ３８４８６可部分阻断这种作用。（２）蛋白合成抑制剂放线菌酮不能阻断皮质醇的快速阻断作用。（３）阿托     

四种鬼臼毒素类似物对美洲大蠊腹神经索动作电位的作用

为了解鬼臼毒素对昆虫神经系统的影响,采用胞外记录电生理方法观察了4种鬼臼毒素类似物对美洲大蠊Periplaneta americana 中枢神经自发放动作电位的影响。结果显示: 在0.1 mmol/L的浓度下,4种物质对美洲大蠊中枢神经自发放动作电位的作用不同。脱氧鬼臼毒素可完全抑制美洲大蠊中枢神经自发放动作电位的产生,其抑制作用可逆;β-阿朴苦鬼臼毒素对美洲大蠊中枢神经自发放动作电位的作用是先兴奋后抑制;鬼臼毒素对美洲大蠊中枢神经自发放动作电位有抑制作用,其抑制作用不完全;4′-去甲鬼臼毒素对大蠊中枢神经自发放动作电位无影响。结果提示,4种鬼臼毒素类似物对昆虫中枢神经自发放动作电位的影响方式与其结构官能团密切相关。     

杀虫环对昆虫血淋巴糖和游离氨基酸的影响

 用毛细管色谱和离子交换色谱法分析了黑胸大蠊雄性成虫血淋巴糖和游离氨基酸的组分、合量及杀虫环对它们的影响,并与电生理记录的EPSP电位比较,表明:1.黑胸大蠊血淋巴有五种糖,海藻糖、葡萄糖含量最多。2×10~(-5)mol/L杀虫环作用于虫体5分钟后,五种糖含量迅速增加;30分钟后下降23～47％。2.血淋巴中含有16种游离氨基酸及大量的NH_3。杀虫环可降低14种氨基酸的含量,尤其对生糖氨基酸(丙、异亮、酪、脯)的影响显著。3.2×10~(-5)mol/L杀虫环作用5分钟可增加中枢第Ⅵ腹神经节自发电位的释放频率和振幅,6～7分钟后迅速减少并消失,此时诱发EPSP电位振幅下降。18～20分钟突触传递被阻断。此过程恰巧与血淋巴糖代谢的加快而减缓的过程一致。     

5—羟色胺抑制离体脊髓运动神经元的突触传递

应用新生大鼠脊髓切片运动神经元(MN)细胞内记录技术,发现5-羟色胺(5-HT)10～100μmol/L灌流可浓度依从地抑制背、腹根刺激在MN诱发的兴奋性突触后电位(EPSP)和抑制性突触后电位,但可增大外源性谷氨酸引起的MN去极化。5-HT对背根性EPSP的抑制无刺激频率依赖性,可为5-HT_(1A)受体激动剂8-OH-DPAT模拟,但不受士的宁、酮色林及MDL 72222的影响。结果表明5-HT可直接激活初级传入纤维末梢5-HT_(1A)受体而抑制MN的突触传递。     

辛硫磷与氯氰菊酯混配对美洲大蠊的增效机理研究

利用电生理和生化方法 ,以美洲大蠊为材料 ,研究辛硫磷与氯氰菊酯混用的增效机理。实验结果表明 :辛硫磷与 3种氯氰菊酯混配 ,EPSP的开始兴奋时间和阻断时间均低于各单剂。促进了突触间隙乙酰胆碱的积累。生化分析结果表明 ,混剂增效的原因之一是提高了对靶标酶———AchE的抑制。     

豚鼠肠系膜下神经节细胞电活动与结肠运动的关系

在豚鼠肠系膜下神经节(IMG)及其支配的结肠段联合标本上,对IMG细胞内电位与肠段纵肌或环肌舒缩活动进行了同步记录。实验结果表明:(1)肠段预置张力为零时,约50％IMG细胞有自发的快兴奋性突触后电位(EPSP)活动,切断结肠神经或以筒箭毒(50μmol/L)灌流IMG后消失;(2)筒箭毒或低钙高镁溶液阻断神经节传递时,环肌节律性收缩幅度增大,节律变慢,但对纵肌节律性收缩无明显影响,(3)串刺激节前神经,在IMG细胞引起一串快EPSP或动作电位并常跟随迟慢的EPSP,同时,纵肌在0.1-0.2s潜伏期后出现迅速的、时程基本与动作电位串一致的舒张波,后者在筒箭毒灌流IMG后消失,而环肌运动可见舒张、舒张波延长或收缩波增大。结果提示:IMG不仅中继经典的胆碱能传出功能,还参与以胆碱能传递为中介的肠-肠反射,该反射活动的传出效应主要在于抑制环肌收缩。     

硝苯吡啶对腹腔神经节突触传递的阻断作用

本文应用细胞内记录技术,观察了钙通道阻滞剂硝苯吡啶（nifedipine)对离体豚鼠腹腔神经节突触传递的影响,硝苯吡啶（0.1-10umol/L)不影响所检细胞的静息膜电位,膜电阻及细胞内刺激引起的动作电位,但能显著阻断N-型胆碱能的突触传递,并且这种作用可被低钙模拟、高钙拮抗,硝苯吡啶（10umol/L)也不影响突触后膜对乙酰胆碱（ACh)的敏感性;但在高钾克氏液中,能减少微小兴奋性突触后电位（mEPSPs)的频率;在低钙和高镁克氏液中,能减少量子含量,而对量子大小无影响。结果表明,治疗量的硝苯吡啶(0.1umol/L)通过阻滞突触前膜钙内流及ACh的量子性释放,产生突触阻断作用。这可能是硝苯吡啶降压机理的一个组成部分。     

呲虫啉、杀虫双对美洲蜚蠊中枢神经的电生理影响

本文运用美洲蜚蠊(Periplaneta americana)第V1腹神经节突触后电位细胞外记录方法研究了吡虫啉、杀虫双对中枢神经活动的影响。结果显示：1.73x10^-7mol/L吡虫啉和 1.38XlO^-5Stool/L杀虫双处理后初期均能引起自发性突触后电位发放增强,随后导致突触传递阻断。而吡虫啉较杀虫双阻断传递快,且用Ringer生理溶液冲洗不易恢复,表明吡虫啉较杀虫双激动剂活性更强。以3.37×10^-5mol/L甲胺磷预处理中枢神经样品后,再进行杀虫双处理,则突触后电位的发放频率和幅值有明显增强,产生连续超幅排放(overshooting)现象,相反,甲胺磷预处理对随后进行吡虫啉处理无明显影响。这些结果说明,吡虫啉、杀虫双和乙酰胆碱受体发生相互作用过程存在差异。     

Effects of AF64A on cholinergic neurotransmission in the sixth abdominal ganglion of the cockroach

1. The effects of ethylcholine mustard aziridinium ion (AF64A) on the cholinergic neurotransmission in the sixth abdominal ganglion of the cockroach were studied electrophysiologically and morphologically. 2. The pre- and post-synaptic compound action potentials (CAPs) elicited via electrical stimulation of the presynaptic fibers were recorded extracellularly. 3. The amplitude of both CAPs was depressed by AF64A (50-400 microM) in a concentration- and time-dependent manner. 4. At a high concentration, they were abolished but 100 microM of carbachol still evoked the postsynaptic event. 5. Electron microscopic observation of AF64A-treated ganglia showed that nerve terminals containing small lucent vesicles could not be observed but those containing dense core or large granular vesicles changed only slightly in shape. 6. These results suggest that AF64A is selectively neurotoxic for the presynaptic cholinergic neurons in the sixth abdominal ganglion of the cockroach.     

Effects of the venom of Philanthus triangulum F. (Hym. sphecidae) and β- and δ-philanthotoxin on axonal excitability and synaptic transmission in the cockroach CNS

This paper provides answers to the questions which of the toxins present in the venom of the wasp Philanthus triangulum may be responsible for the previously reported blockage of transmission through the sixth abdominal ganglion of the cockroach, and whether this may occur by block of synaptic transmission or by affecting axonal exitability. In current clamp experiments the crude venom induces a slight depolarization of the membrane of the giant axon from the sixth abdominal ganglion of the cockroach and a small and irreversible decrease in the amplitude of the action potential. These marginal effects are not seen with relatively high concentrations of the philanthotoxins β-PTX and δ-PTX. It appears that neither the crude venom nor the toxins significantly affect the excitability of the cockroach giant axon. At a concentration of 20 μg ml^?1 δ-PTX causes a slowly reversible block of synaptic transmission from the cercal nerve XI to a giant interneuron without any change in resting membrane potential, whereas β-PTX is inactive. Iontophoretically evoked acetylcholine potentials of the giant neuron are more sensitive to δ-PTX than excitatory postsynaptic potentials. This suggests that the toxin acts on the postsynaptic membrane.     

Long-term potentiation in the neurons of the edible snail

A brief high-frequency stimulation of the anal nerve of the isolated nerve ring of snail Helix induced a pronounced increase in the amplitude of EPSPs, evoked in identified neurons of left parietal and visceral ganglions by low frequency (once in 5 min) stimulation of the same nerve. The amplitude of EPSP returned to the control level 30-120 min after tetanization. We called this effect long-term potentiation. A brief application of serotonin (10 microM) in the majority of neurons also induced lasting either 15-30 min or more than 2 hours facilitation of EPSP, evoked by anal nerve stimulation. Intracellular cAMP injections, being without effect on EPSP amplitude in many neurons, in certain neurons caused an increase in EPSP amplitude, lasting up to 30 min. It is suggested that the 3 factors shown to increase synaptic efficiency in molluscan neurons may have common mechanisms of action.     

Actions of amantadine at synaptic and extrasynaptic cholinergic receptors in the central nervous system of the cockroach Periplaneta americana

The effects of amantadine were investigated on cercal afferent, giant interneurone synapses and on the cell body membrane of the fast coxal depressor motoneurone (D_f), in the cockroach Periplaneta americana. Bath-applied amantadine at concentrations above 2.0 × 10^?5 M significantly reduced the amplitude of unitary and compound epsps recorded by sucrose-gap methods from cercal afferent, giant interneurone synapses in the desheathed sixth abdominal ganglion. Complete block of synaptic transmission was achieved at 1.0 × 10^?3 M amantadine. Synaptic blockade, which was not accompanied by changes in resting potential, was almost fully reversed by washing the ganglion in normal saline. From the dose-dependence of the synaptic blocking action, a Hill coefficient of 0.94 was estimated, indicating that there is no co-operativity in the binding of amantadine to its site of action.Bath-application of amantadine (5.0 × 10^?5 M) resulted in a parallel shift to the right of the dose-response curve for the depolarizing postsynaptic actions of acetylcholine. Nevertheless, even at a concentration of 2.0 × 10^?3 M, amantadine failed to protect the synaptic acetylcholine receptor/ion channel complex from the blocking action of α-bungarotoxin (5.0 × 10^?7 M). In addition, the block by amantadine of the acetylcholine-induced current recorded from the cell body membrane of the fast coxal depressor motoneurone (D_f), was strongly dependent on membrane potential in the range ? 120mV to ? 70mV. An action of amantadine at the open acetylcholine receptor/ion channel complex is proposed.     

A presynaptic locus of the action of Met-enkephalin demonstrated in mouse spinal cord cultures

Monosynaptic excitatory post-synaptic potentials (EPSPs) evoked in spinal cord (SC) neurons by stimulation of dorsal root ganglion (DRG) neurons in cell cultures were reduced by perfusion application of the opiate peptide, Met-enkephalin (2-4 microM). In about 2/3 of cases examined, EPSPs evoked by stimulation of spinal cord cells were also reduced by Met-enkephalin. The effects were antagonized by concomitant perfusion with naloxone (1-2 microM) and recovered when perfusion with Met-enkephalin was stopped. Statistical analysis of synaptic responses indicated that the reduction of EPSP amplitude was due, at least to a major extent, to a decrease in presynaptic transmitter release.     

Presynaptic inhibition in the cercal-afferent giant-interneurone synapses of the cockroach, Periplaneta americana L.

The occurrence of presynaptic control of synaptic transmission in the cercal-afferent giant-interneurone system of the cockroach was investigated. Reduction in amplitude (up to 50%, lasting about 200–250 ms) of the compound evoked EPSP followed repetitive (300 to 500 Hz) supra-threshold stimulation of cercal nerves XI. A similar but weaker depressive effect was detected on the unitary EPSP resulting from stimulation of an ipsilateral cercal mechanoreceptor.This inhibition is attributed to multisynaptic inhibitory pathways impinging upon presynaptic excitatory neurones. The involvement of chloride ions is suggested by the observation that both picrotoxin and chloride-deficient salines abolished the inhibitory phenomenon. Presynaptic mannitolgap recording from cercal nerve XI revealed a chloride-dependent hyperpolarization in response to repetitive conditioning stimulation. The time course of this response was similar to that of presynaptic inhibition. Bath-application of GABA (20 mM) produced a chloride-dependent hyperpolarization followed by a depolarization of the intraganglionic part of the cerca-afferents. GABA-induced hyperpolarization and electrically-induced presynaptic hyperpolarization were both reversed in low chloride saline (166 mM chloride). It is proposed that presynaptic modulation of acetyl-choline release occurs at the cercal-afferent giant-interneurone synapses. The role played by GABA is duscussed.     

Monosynaptic excitory postsynaptic potentials in thoracic motoneurons under reticulospinal influences

We studied synaptic processes in motoneurons of thoracic segments (T_IX-T_XI) evoked by stimulation of the medial area of the giant-cell reticular nucleus in decerebrated cats. Monosynaptic EPSP were recorded in the majority of investigated motoneurons upon activation of the most rapidly conducting reticulospinal fibers. In some cells, such monosynaptic EPSP were accompanied by late EPSP or IPSP. Amplitude of monosynaptic EPSP attained 5 mV, but this value usually was insufficient for development of an action potential. Upon summation of single monosynaptic EPSP, the membrane potential reached the critical level and an action potential arose in the motoneuron. The efficiency of summary processes evoked by stimulation of the reticular formation exceeded the intensity of synaptic processes that arise in thoracic motoneurons on stimulating the nucleus of Deiters. Functional characteristics of reticular and vestibular monosynaptic EPSP are discussed in the work.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 243–252, November–December, 1969.     

The organization of exteroceptive information from the uropod to ascending interneurones of the crayfish

The organization of exteroceptive inputs to identified ascending interneurones of the crayfish, Procambarus clarkii (Girard), has been analyzed by stimulation of hairs on the uropod and simultaneous intracellular recordings from ascending interneurones. The spikes of single afferent neurones which innervated hairs on the distal ventral surface of the exopodite were consistently followed by a depolarizing synaptic potential in many identified ascending interneurones with a constant and short central delay of 0.7–1.5 ms. The amplitude of the potentials depended on the membrane potential of the ascending interneurones. Each afferent neurone made divergent outputs onto several ascending interneurones and each ascending interneurone received convergent inputs from several afferent neurones. Certain ascending interneurones made inhibitory or excitatory connections with other ascending interneurones. These central interactions were always one-way, and the spikes from one ascending interneurone consistently evoked excitatory or inhibitory post-synaptic potentials in other interneurones which followed with a constant and short latency of 0.7–1.0 ms. The inhibitory postsynaptic potential was reversed by injection of steady hyperpolarizing current.Abbreviations EPSP excitatory post-synaptic potential - IPSP inhibitory post-synaptic potential     

Organization of Synaptic Inputs to Rubro-Spinal Neurons in the Cat: Interaction of the Effects of Stimulation of the Cerebellar Nucl. Interpositus and Thalamic Nucl. Ventrolateralis

We studied the interaction of synaptic effects in efferent (rubro-spinal) neurons (RSN) of the red nucleus (NR) of the cat brain using intracellular recording and different variants of stimulation of the cerebellar nucl. interpositus (NI) and nucl. ventrolateralis (VL) of the thalamus. Combined simultaneous or consequent stimulation of the above two inputs allowed us to use collision of the impulses in pre-synaptic pathways for estimation of the peculiarities of summation of post-synaptic potentials; it was taken into consideration that cerebello-rubral fibers are collaterals of the cerebello-thalamic axons. In the case of relatively low intensities of stimulation of the VL and NI, EPSP evoked by these stimulations in RSN could demonstrate linear summation, which is indicative of the absence of common fibers excited by stimulation of both the thalamic and cerebellar structures and of the absence of interaction of synaptic effects on the membrane of the postsynaptic unit (an RSN). With increased stimulation intensity and definite time relations between the stimuli applied to the above structures, the second EPSP evoked by the two stimuli was significantly suppressed; this resulted from a decrease of the afferent drive coming to the NR due to collision of afferent impulses in presynaptic pathways. When an interstimulus interval was increased, the second EPSP could be facilitated (probably due to generation of repetitive impulses in common presynaptic fibers). Our experiments show that the statement concerning the nature of cerebello-rubral inputs (all these inputs are formed by collaterals of the cerebello-(interposito)-thalamic pathways) should be considered with reservation.     

Propofol suppresses synaptic responsiveness of somatosensory relay neurons to excitatory input by potentiating GABAA receptor chloride channels

Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in humans is associated with inhibition of thalamic activity evoked by somatosensory stimuli. However, the cellular mechanisms underlying the effects of propofol in thalamic circuits are largely unknown. We investigated the influence of propofol on synaptic responsiveness of thalamocortical relay neurons in the ventrobasal complex (VB) to excitatory input in mouse brain slices, using both current- and voltage-clamp recording techniques. Excitatory responses including EPSP temporal summation and action potential firing were evoked in VB neurons by electrical stimulation of corticothalamic fibers or pharmacological activation of glutamate receptors. Propofol (0.6 – 3 μM) suppressed temporal summation and spike firing in a concentration-dependent manner. The thalamocortical suppression was accompanied by a marked decrease in both EPSP amplitude and input resistance, indicating that a shunting mechanism was involved. The propofol-mediated thalamocortical suppression could be blocked by a GABA_A receptor antagonist or chloride channel blocker, suggesting that postsynaptic GABA_A receptors in VB neurons were involved in the shunting inhibition. GABA_A receptor-mediated inhibitory postsynaptic currents (IPSCs) were evoked in VB neurons by electrical stimulation of the reticular thalamic nucleus. Propofol markedly increased amplitude, decay time, and charge transfer of GABA_A IPSCs. The results demonstrated that shunting inhibition of thalamic somatosensory relay neurons by propofol at clinically relevant concentrations is primarily mediated through the potentiation of the GABA_A receptor chloride channel-mediated conductance, and such inhibition may contribute to the impaired thalamic responses to sensory stimuli seen during propofol-induced anesthesia.