Tonic activation of NMDA receptors by ambient glutamate enhances excitability of neurons

Voltage clamp recordings and noise analysis from pyramidal cells in hippocampal slices indicate that N-methyl-D-aspartate (NMDA) receptors are tonically active. On the basis of the known concentration of glutamate in the extracellular fluid, this tonic action is likely caused by the ambient glutamate level. NMDA receptors are voltage-sensitive, thus background activation of these receptors imparts a regenerative electrical property to pyramidal cells, which facilitates the coupling between dendritic excitatory synaptic input and somatic action potential discharge in these neurons.     

Harmonic oscillation as model for cortical excitability changes with attention in cats

A single shock to the prepyri-form cortex with implanted electrodes caused a damped, sinusoidal oscillation in potential. The root-mean-square amplitudes of potentials evoked by short trains of stimuli, when plotted against the frequency of stimulation, fitted the equation for forced harmonic oscillation when the cat was attentive to the stimuli     

Long-term habituation of a defensive withdrawal reflex in aplysia

A tactile stimulus to the siphon of Aplysia produces a defensive withdrawal reflex consisting of contraction of the siphon, the gill, and the mantle shelf. We studied long-term habituation of this reflex using two types of preparations, one focusing on the siphon component and the other on the gill component of the reflex. Siphon withdrawal, studied in unrestrained animals, showed marked habituation within a single ten-trial training session. Five daily training sessions produced habituaton that built up across days and lasted for at least 3 weeks. Furthermore, spaced training produced significantly longer lasting habituation than massed training. Gill withdrawal, studied in a restrained animal, also showed long-term retention of habituation. Since the neural circuitry of gill withdrawal is relatively well understood, it may be possible to study the cellular mechanisms underlying a long-term behavioral modification.     

Enzyme changes in neurons and glia during barbiturate sleep

During barbiturate sleep of rabbits, the succinoxidase activity in isolated neurons and glia from the caudal part of the reticular formation was lower than that during physiological sleep. No rhythmical, inverse enzyme changes were detected in barbiturate sleep in the neuron-glia unit, such as were found in physiological sleep.     

Bag cell control of egg laying in freely behaving aplysia

Neuroendocrine (bag cell) control of egg laying was studied in freely behaving Aplysia. Surgical lesions showed that bag cells are not necessary for egg laying, although they play a crucial role in its control, and that the pleurovisceral connectives are the afferent pathway to the bag cells. Recording in vivo showed that synchronous bag cell spikes progressively invade the network, leading to prolonged repetitive firing that initiates natural egg laying.     

Norepinephrine-containing neurons: changes in spontaneous discharge patterns during sleeping and waking

Norepinephrine-containing neurons of the locus coeruleus of the cat were recorded with microelectrodes during unrestrained sleeping and waking. The recorded neurons were subsequently defined by combined fluorescence histochemistry of catecholamines and production of microlesions at recording sites. These pontine units show homogeneous changes in discharge patterns with respect to sleep stages, firing slowly during drowsy periods and slow wave sleep and firing in rapid bursts during paradoxical sleep. These data provide a direct correlation between the activity of defined catecholamine-containing neurons and the spontaneous occurrence of sleep stages.     

Evidence for degenerative and regenerative changes in neostriatal spiny neurons in Huntington's disease

Golgi impregnations of neostriatum from deceased Huntington's disease patients and controls were examined. In all cases of Huntington's disease the morphology of dendrites of medium-sized spiny neurons was markedly altered by the appearance of recurved endings and appendages, a decrease or increase in the density of spines, and abnormalities in the size and shape of spines. Pathological changes were rarely observed in medium-sized and large aspiny neostriatal neurons. The findings provide evidence for simultaneous degeneration and growth of spiny neurons in Huntington's disease and support the view that a specific population of neostriatal neurons is selectively involved in its pathogenesis.     

Target-dependent structural changes accompanying long-term synaptic facilitation in Aplysia neurons

The mechanisms underlying structural changes that accompany learning and memory have been difficult to investigate in the intact nervous system. In order to make these changes more accessible for experimental analysis, dissociated cell culture and low-light-level video microscopy were used to examine Aplysia sensory neurons in the presence or absence of their target cells. Repeated applications of serotonin, a facilitating transmitter important in behavioral dishabituation and sensitization, produced growth of the sensory neurons that paralleled the long-term enhancement of synaptic strength. This growth required the presence of the postsynaptic motor neuron. Thus, both the structural changes and the synaptic facilitation of Aplysia sensorimotor synapses accompanying long-term behavioral sensitization can be produced in vitro by applying a single facilitating transmitter repeatedly. These structural changes depend on an interaction of the presynaptic neuron with an appropriate postsynaptic target.     

Succinylcholine and muscle excitability

Succinylcholine lowers the resting membrane potential taken with microelectrodes similarly in nerve-scarce and innervated portions of frog sartorius muscle. Twitches to electrical excitation of the nerve-scarce pelvic end of the muscle are also rapidly reduced. The results indicate that succinylcholine probably acts generally on the muscle membrance to diminish excitability.     

Rapid changes in throughput from single motor cortex neurons to muscle activity

Motor cortex output is capable of considerable reorganization, which involves modulation of excitability within the cortex. Does such reorganization also involve changes beyond the cortex, at the level of throughput from single motor cortex neurons to muscle activity? We examined such throughput during a paradigm that provided incentive for enhancing functional connectivity from motor cortex neurons to muscles. Short-latency throughput from a recorded neuron to muscle activity not present during some behavioral epochs often appeared during others. Such changes in throughput could not always be attributed to a higher neuron firing rate, to more ongoing muscle activity, or to neuronal synchronization, indicating that reorganization of motor cortex output may involve rapid changes in functional connectivity from single motor cortex neurons to alpha-motoneuron pools.     

醋酸铅对体外培养大鼠大脑皮质神经细胞形态的影响

为了观察醋酸铅对神经细胞的形态学影响,通过建立体外培养大鼠大脑皮质神经细胞模型,应用不同浓度醋酸铅(0,50,100,200,400μmol/L)与神经细胞分别培养3、6、12、24 h,倒置相差显微镜观察细胞形态变化.结果显示,醋酸铅与神经细胞共同培养12~24 h,细胞密度降低,胞体变小,突起缩短;随醋酸铅浓度递增,细胞形态较对照组差异愈加显著(P<0.05).表明染铅浓度与神经细胞形态变化存在剂量效应与时间效应关系.     

全脑缺血模型大鼠再灌后对皮层神经元L型Ca2+通道的动态观察

目的:对全脑缺血模型大鼠再灌后不同时间点L型C a2 通道的开放和关闭状态进行动态研究,以进一步揭示缺血性神经元损伤的机制。方法:参照改良的Pu lsinelli四血管闭塞法制备全脑缺血大鼠模型,缺血后的大鼠分别在再灌注2、12、24、48、72h后进行皮层神经细胞急性分离,单通道电流经EPC-9膜片钳放大器放大,用Pu lsefit Pu lse采集入计算机,用分析软件TAC进行测量。结果:再灌后2、12、24、48、72 h5个不同时间点,大鼠大脑皮层神经元L型C a2 通道平均开放时间出现两个高峰期,第1次出现在再灌2、12、24h,第2次出现在48、72 h,较第1次更高;大鼠大脑皮层神经元L型C a2 通道开放概率出现两个峰值:第1次出现在再灌后2 h(显著高于正常组),至12 h又回落至接近正常水平;第2次出现在再灌24 h。结论:在脑缺血再灌注的不同时点,缺血性损伤对L型C a2 通道的影响机制即可利用性和开放特性的影响不同。在缺血再灌后的2 h至72 h的各时段,缺血性损伤通过增加L型C a2 通道的可利用性引起神经元胞内C a2 超载;在再灌后期(48 h),缺血性损伤则通过增加L型C a2 通道的开放特性而引起神经元胞内C a2 超载。     

Effects of glucocorticoids and norepinephrine on the excitability in the hippocampus

The CA1 pyramidal neurons in the hippocampus contain a high density of adrenal corticosteroid receptors. By intracellular recording, CA1 neurons in slices from adrenalectomized rats have been found to display a markedly reduced afterhyperpolarization (that is, the hyperpolarizing phase after a brief depolarizing current pulse) when compared with their sham controls. No differences were found for other tested membrane properties. Brief exposure of hippocampal slices from adrenalectomized rats to glucocorticoid agonists, 30 to 90 minutes before recording, greatly enhanced the afterhyperpolarization. In addition, glucocorticoids attenuated the norepinephrine-induced blockade of action potential accommodation in CA1 neurons. The findings indicate that glucocorticoids can reduce transmitter-evoked excitability in the hippocampus, presumably via a receptor-mediated genomic action.     

The molecular basis of neuronal excitability

Neurons process and transmit information in the form of electrical signals. Their electrical excitability is due to the presence of voltage-sensitive ion channels in the neuronal plasma membrane. In recent years, the voltage-sensitive sodium channel of mammalian brain has become the first of these important neuronal components to be studied at the molecular level. This article describes the distribution of sodium channels among the functional compartments of the neuron and reviews work leading to the identification, purification, and characterization of this membrane glycoprotein.     

Development of excitability in embryonic muscle cell membranes in certain tunicates

During the course of development of muscle cells in certain tunicates, a sign of regenerative membrane response appears in the gastrula stage. In the early tadpole larva, the action potential consists of a spike followed by a plateau. The latter-disappears in fully differentiated cells, conceivably in association with the establishment of delayed rectification.     

Intracellular acidosis enhances the excitability of working muscle

Intracellular acidification of skeletal muscles is commonly thought to contribute to muscle fatigue. However, intracellular acidosis also acts to preserve muscle excitability when muscles become depolarized, which occurs with working muscles. Here, we show that this process may be mediated by decreased chloride permeability, which enables action potentials to still be propagated along the internal network of tubules in a muscle fiber (the T system) despite muscle depolarization. These results implicate chloride ion channels in muscle function and emphasize that intracellular acidosis of muscle has protective effects during muscle fatigue.     

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.     

Input resistance, electrical excitability, and size of ventral horn cells in cat spinal cord

Experiments on cat lumbosacral alpha motoneurones showed that, in comparison with cells possessing rapidly conducting axons, the cells with slowly conducting axons have the higher input resistance, that they need weaker stimulating currents to reach the threshold for repetitive firing, and that they need a relatively larger increment in current strength for a given increase in firing rate. Measurements of the number and diameters of dendritic trunks gave larger values for the larger cell bodies. The discussion deals with the interrelation between cell geometry, electrical properties, and the reflex action of alpha motoneurones.