Functional significance of the serotoninergic influence on neuronal activity of the somatosensory cortex in 12-day-old kittens

Monoamines, which participate in synaptic transmission as transmitters, also accomplish the modulation of neuronal activity. The role of serotonin (5-hydroxytryptamine--5-HT) was investigated in 8 to 14-day-old kittens by means of iontophoretic application onto neurones of the somatosensory cerebral cortex. The most typical response was the inhibition of neuronal activity. Another type of reaction was generated by inhibitory interneurones. After the microiontophoretic application of 5-HT, the tonic response of cortical neurones to the stimulation of the sciatic nerve changed into a phasic response. It is being suggested that the application of 5-HT to cortical neurones increases the excitability of inhibitory neurones. Hence, the serotoninergic regulation of neuronal activity in the somatosensory cortex may be operational from the 11th to the 12th day of postnatal life in cats.     

Reflection of the plastic properties of the simplest neuronal associations in statistical characteristics of the spike activity of their elements. Polysynaptically linked neurons

Changes of crosscorrelation histograms of trains of action potentials and mean interspike intervals of polysynaptically connected neurones were studied by means of mathematical modelling of synaptic neuronal interaction at changes of efficiency of interneuronal monosynaptic connections, at changes of neuronal excitability, and at changes of total action on them of independent disorderly afferent synaptic inflows. Increase of amplitude of the main maximum (minimum) of the normalized crosscorrelation histogram of trains of action potentials accompanied by reduction of mean interspike intervals of both neurones, was shown to be a unsignificant indication of an increase of efficiency of polysynaptic excitatory (inhibitory) connections between the neurones (due to modification of synapses or to a change of the functional state of interneurones).     

Non-spiking local interneurones mediate abdominal extension related descending control of uropod motor neurones in the crayfish terminal abdominal ganglion

The role of non-spiking local interneurones in the synaptic interactions between abdominal extension-evoking descending interneurones and uropod motor neurones in the terminal abdominal ganglion of the crayfish Procambarus clarkii (Girard) was investigated electrophysiologically. Continuous electrical stimulation of the lateral region of the 3rd-4th abdominal connective that included abdominal extension evoking interneurones excited the opener motor neurones and inhibited the closer, reductor motor neurone. Spikes from a single descending interneurone evoked consistent and short latency (0.8–0.9 ms) excitatory postsynaptic potentials (e.p.s.ps) in the opener motor neurones, and evoked rather long-latency (1.5–2.7 ms) inhibitory postsynaptic potentials (i.p.s.ps) in the reductor motor neurone. Many non-spiking interneurones also received depolarizing p.s.ps (0.8–2.5 ms in latency) that were usually faster than i.p.s.ps of the reductor motor neurone if both neurones were recorded sequentially in the same preparation. Non-spiking interneurones received convergent inputs from several descending interneurones and made inverting connection with the reductor motor neurone. Elimination of descending inputs to a particular non-spiking interneurone could reduce the inhibitory response of the reductor motor neurone. These observations strongly suggested that descending inhibitory inputs to the closer, reductor motor neurone were mediated by non-spiking interneurones. Furthermore, some non-spiking interneurones made output connections with the opener motor neurones. The disynaptic pathway through non-spiking interneurones is significant to control and modulate the opening pattern of the uropod during abdominal extension. Accepted: 27 December 1996     

Lateral giant fibre activation of exopodite motor neurones in the crayfish tailfan

The uropods of decapod crustaceans play a major role in the production of thrust during escape swimming. Here we analyse the output connections of a pair of giant interneurones, that mediate and co-ordinate swimming tail flips, on motor neurones that control the exopodite muscles of the uropods. The lateral giants make short latency output connections with phasic uropod motor neurones, including the productor, the lateral abductor and adductor exopodite motor neurones that we have identified both physiologically and anatomically. On the other hand, tonic motor neurones, including the ventral abductor and reductor exopodite motor neurones, receive no input from the lateral giants. We show that there is no simple reciprocal activation of the phasic opener (lateral abductor) and closer (adductor) motor neurones of the exopodite, but instead both phasic motor neurones are activated in parallel with the productor motor neurone during a tail flip. Our results show that the neuronal pathways activating the tonic and phasic motor neurones of the exopodite are apparently independent, with phasic motor neurones being activated during escape movements and tonic motor neurones being activated during slow postural movements.     

Cell-type specific depression of neuronal excitability in rat hippocampus by activation of ATP-sensitive potassium channels

The contribution of ATP-sensitive potassium (K(ATP)) channels to neuronal excitability was studied in different types of pyramidal cells and interneurones in hippocampal slices prepared from 9- to 15-day-old rats. The presence of functional K(ATP) channels in the neurones was detected through the sensitivity of whole-cell currents to diazoxide, a K(ATP) channel opener, and to tolbutamide, a K(ATP) channel inhibitor. The percentages of neurones with K(ATP) channels increase in the sequence: CA1 pyramidal cells (37%)相似文献   

Parallel processing of proprioceptive information in the terminal abdominal ganglion of the crayfish

The processing of proprioceptive information from the exopodite-endopodite chordotonal organ in the tailfan of the crayfish Procambarus clarkii (Girard) is described. The chordotonal organ monitors relative movements of the exopodite about the endopodite. Displacement of the chordotonal strand elicits a burst of sensory spikes in root 3 of the terminal ganglion which are followed at a short and constant latency by excitatory postsynaptic potentials in interneurones. The afferents make excitatory monosynaptic connections with spiking and nonspiking local interneurones and intersegmental interneurones. No direct connections with motor neurones were found.Individual afferents make divergent patterns of connection onto different classes of interneurone. In turn, interneurones receive convergent inputs from some, but not all, chordotonal afferents. Ascending and spiking local interneurones receive inputs from afferents with velocity thresholds from 2–400°/s, while nonspiking interneurones receive inputs only from afferents with high velocity thresholds (200–400°/s).The reflex effects of chordotonal organ stimulation upon a number of uropod motor neurones are weak. Repetitive stimulation of the chordotonal organ at 850°/s produces a small reduction in the firing frequency of the reductor motor neurone. Injecting depolarizing current into ascending or non-spiking local interneurones that receive direct chordotonal input produces a similar inhibition.     

The range of control of the afferent system of the flexor reflex]

The control processes caused by the action of electric inhibition of the nerve fibres and depolarized and hyperpolarized influences in the neurones structures of the spinal cord are discussed. Three typical bands of the amplitude control of motor apparatus in the multineuronic reflex ring are distinguished. The transmission of the action potentials in the battle control bands is carried out by the double way modulation. The first band is characterized by the most effective control with amplitude of the signal control in the limit of three thresholds. In the third band the transmission of information is possible in the inversion regime with unsteady polarity of the reflex movement. The second band unfits for the transmission of control commands.     

Parallel effects of joint receptors on motor neurones and intersegmental interneurones in the locust

Summary At the distal end of a mesothoracic tibia of the locust,Schistocerca gregaria, is a chordotonal organ which monitors the position and movement of the tarsus relative to the tibia. It contains approximately 35 receptors that variously encode different spatial and temporal parameters (position, velocity and direction of movement). Some excite intersegmental interneurones that respond phasically or tonically, with directional sensitivity to active or imposed movements of the tarsus. Some of these interneurones are also excited by intrinsic movements of the tarsal segments. Others, besides being excited by tarsal proprioceptive inputs, are also excited by exteroreceptors on the tarsus.When stimulated mechanically or electrically, chordotonal afferents evoke excitatory postsynaptic potentials with a central latency of between 0.9 and 1.4 ms simultaneously in the intersegmental interneurones and in tarsal motor neurones. The central arborizations of the afferents, the intersegmental interneurones and the tarsal motor neurones overlap in certain neuropilar regions of the mesothoracic ganglion. Other afferents cause an inhibition of the motor neurones, with a longer and non-consistent latency suggesting the involvement of other intercalated interneurones.These results indicate that proprioceptive inputs from the tarsal joint receptors are transmitted in parallel and monosynaptically to tarsal motor neurones and to the intersegmental interneurones.     

State-dependent responses of two motor systems in the crayfish,Pacifastacus leniusculus

The expression of both swimmeret and postural motor patterns in crayfish (Pacifastacus leniusculus) were affected by stimulation of a second root of a thoracic ganglion. The response of the swimmeret system depended on the state of the postural system. In most cases, the response of the swimmeret system outlasted the stimulus.Stimulation of a thoracic second root also elicited coordinated responses from the postural system, that outlasted the stimulus. In different preparations, either the flexor excitor motor neurones or the extensor excitor motor neurones were excited by this stimulation. In every case, excitation of one set of motor neurones was accompanied by inhibition of that group's functional antagonists.This stimulation seemed to coordinate the activity of both systems; when stimulation inhibited the flexor motor neurones, then the extensor motor neurones and the swimmeret system were excited. When stimulation excited the flexor motor neurones, then the extensor motor neurones and the swimmeret system were inhibited.Two classes of interneurones that responded to stimulation of a thoracic second root were encountered in the first abdominal ganglion. These interneurones could be the pathway that coordinates the response of the postural and swimmeret systems to stimulation of a thoracic second root.Abbreviations TSR thoracic second root - epsp excitatory post-synaptic potential - ipsp inhibitory post-synaptic potential - EJP excitatory jonctional potential - PS power-stroke - RS return-stroke - INT interneurone - N1 first segmental nerve - N2 second segmental nerve - N3 third segmental nerve - A1 abdominal ganglion 1     

Proprioceptive proximo-distal relationships between the quadriceps and soleus muscles in man

Electrical stimulation of femoral nerve modulates voluntary tonic activity o of ipsilateral soleus muscle. Stimulus time-locked inhibitory and facilitatory phases can be distinguished. EMG temporal analysis suggests that early perturbations are correlated with spinal effects of centripetal electrical activity. The inhibitory effects which momentarily abolish voluntary soleus activity are thought to result from quadriceps Ib fibres recruitment. While no heteronymous activity is induced at rest, femoral nerve Ia fibres activation can produce soleus muscle reflex when soleus motor nucleus excitability is increased by voluntary command. Recurrent discharge resulting from soleus reflex response enhances inhibition initially due to quadriceps Ib volley. Secondary effects of isometric quadriceps contraction (and soleus contraction when the femoral stimulus elicits a reflex in this muscle) have their own effects later. These findings suggest that proprioceptive relationships of the two muscular groups are efficient during tonic isometric voluntary command.     

Direct excitation of nonspiking local interneurones by exteroceptors underlies tactile reflexes in the locust

Summary Tactile stimulation of a leg of the locustSchistocerca gregaria can lead to specific reflex movements of that leg. At the same time nonspiking interneurones that are presynaptic to the participating motor neurones are excited or inhibited, suggesting that they are directly involved in these reflexes. The afferent pathways mediating these effects have been examined by recording from individual afferents and nonspiking interneurones.Afferent spikes fromtrichoid orcampaniform sensilla on specific regions of a leg evoke chemically-mediated EPSPs with a constant central latency of about 1.5 ms in certain nonspiking interneurones. The branches of an interneurone and the afferents from which it receives inputs overlap in the neuropil of the ganglion.No afferents have been found to evoke IPSPs directly in the nonspiking interneurones. Instead the inhibition is caused by a population of spiking local interneurones that are themselves excited directly by the afferents, and whose spikes evoke IPSPs in certain nonspiking interneurones.The tactile reflexes can involve movements about one or more joints of the leg, and these coordinated responses are explained by the participation of specific nonspiking interneurones that distribute the sensory inputs to the appropriate sets of motor neurones. For example, when hairs on the dorsal surface of a tarsus are touched, the tarsus is levated. This reflex involves nonspiking local interneurones which are excited directly by these hair afferents and which make direct excitatory connections with the single levator tarsi motor neurone.     

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     

On coupling and decoupling of spinal interneuronal networks

This review addresses the question of interrelations between spinal interneuronal networks. On the basis of electrophysiological, pharmacological, morphological and immunohistochemical analysis of interneurones mediating various reflex actions from muscle receptors and of reticulospinal neurones a considerable degree of interweaving between networks of these neurones has been established. The coupling has been found to occur at the level of several sites of these networks but the review focuses on two of these sites. The first is between dorsal horn interneurones with group II input and their target ipsilaterally and contralaterally projecting intermediate zone and commissural interneurones. The second is between commissural interneurones with input from reticulospinal neurones and their target interneurones. Several ways of both strengthening and weakening of coupling between various interneuronal networks are also briefly reviewed.     

运动过程的网络逻辑——从离子通道到动物行为

为了揭示神经网络在脊椎动物运动中所行使的内在功能,作者开发了七鳃鳗这种低等脊椎动物模型。在这套系统中,不仅可以了解到运动模式生成网络以及激活此网络的命令系统,同时还可以在运动中研究方向控制系统和变向控制系统。七鳃鳗的神经系统有较少的神经元,而且运动行为中的不同运动模式可以由分离的神经系统所引发。模式生成神经网络包括同侧的谷氨酸能中间神经元和对侧的抑制性甘氨酸能中间神经元。网络中的突触连接、细胞膜特性和神经递质都也已经被鉴定。运动是由脑干区域的网状脊髓神经元所引起,而这些神经元又是被问脑和中脑分离的一些运动命令神经元群所控制。因此,运动行为最初是由这两个“运动核心”所启动。而这两个运动核心被基底神经节调控,基底神经节即时地做出判断是否允许下游的运动程序启动。在静止情况下基底神经节的输出核团维持对下游不同运动核心的抑制作用,反之则去除抑制活化运动核心。纹状体和苍白球被认为是这个运动抉择系统的主要部件。根据“霍奇金一贺胥黎”模型神经元开发了这套网络模型,不同的细胞具有各自相应的不同亚型的钠、钾、钙离子通道和钙依赖的钾通道。每个模型神经元拥有86个不同区域模块以及其对应的生物学功能,例如频率控制、超极化等等。然后根据已有实验证据,利用突触将不同的模型神经元相连。而系统中的10000个神经元大致和生物学网络上的细胞数量相当。突触数量为760000。突触类型有AMPA、NMDA、glycine型。有了这样大规模的模型,不仅可以模拟肌节与肌节之间的神经网络,还可以模拟到由基底神经节开始的行为起始部分。此外,这些网络模拟还被用于一个神经机械学模型来模拟包含有推进和方向控制部分的真实运动。     

The effect of L-DOPA on potentials of the dorsal surface of the spinal cord evoked by the stimulation of primary afferents in newborn rat pups

In experiments on 5-30-day rat puppies, studies have been made of the effect of L-DOPA (100 mg/kg, intraperitoneally) on the activity of interneurones of the dorsal horn of the spinal cord as revealed from the parameters of potentials of the dorsal surface of the spinal cord. The specific pattern of reaction in 5-day animals is manifested in a succession of inhibitory inhibition and increase in the activity of neurones monosynaptically activated by low-threshold afferents. Both the amplitude and duration of polysynaptic components of the potentials of the dorsal surface are rather high. From the 7th day, deep and stable inhibition is observed which is accompanied by a decrease in the amplitude of all components of the potential of the dorsal surface. At later stages of ontogenesis, a decrease is observed in the inhibitory effect of L-DOPA on the activity of interneurones which monosynaptically contact with low- and especially high-threshold afferents; in contrast to earlier stages, but similar to adult animals, evident inhibition was revealed in the activity of interneurones which have polysynaptic contacts with high-threshold afferents and afferents of flexor reflex. Thus, within the first weeks of postnatal life, basic qualitative changes are observed in the pattern of the reaction of interneurones of the dorsal horn to exogenic catecholamines.     

Influence of pulmonary inflations on discharge of pontile respiratory neurons

The purpose of this study was to characterize the influence of pulmonary inflations on the discharge patterns of rostral pontile respiratory neurons. Decerebrate and paralyzed cats were ventilated with a servo-respirator which produced patterns of pulmonary inflation, assessed by tracheal pressure, which paralleled alterations in integrated activity of the phrenic nerve. Neurons with respiratory-modulated neuronal activities were recorded in the pneumotaxic region of the nucleus parabrachialis medialis and Kolliker-Fuse nucleus, as well as in the trigeminal motor nucleus. Approximately equal numbers of neurons had phasic and tonic respiratory-modulated discharge patterns. The discharge patterns of most neurons were not qualitatively altered when pulmonary inflation was prevented. However, withholding inflation did cause the recruitment of some respiratory-modulated neuronal activities. Similar findings were obtained in normocapnia and hypercapnia. Results support the concept that the discharge of neurons in the pneumotaxic region may exert phasic, as well as tonic, influences on ventilatory activity.     

The structure of the ventral nerve cord of Caenorhabditis elegans.

The nervous system of Caenorhabditis elegans is arranged as a series of fibre bundles which run along internal hypodermal ridges. Most of the sensory integration takes place in a ring of nerve fibres which is wrapped round the pharynx in the head. The body muscles in the head are innervated by motor neurones in this nerve ring while those in the lower part of the body are innervated by a set of motor neurones in a longitudinal fibre bundle which joins the nerve ring, the ventral cord. These motor neurones can be put into five classes on the basis of their morphology and synaptic input. At any one point along the cord only one member from each class has neuromuscular junctions. Members of a given class are arranged in a regular linear sequence in the cord and have non-overlapping fields of motor synaptic activity, the transition between fields of adjacent neurones being sharp and well defined. Members of a given class form gap junctions with neighbouring members of the same class but never to motor neurones of another class. Three of the motor neurone classes receive their synaptic input from a set of interneurones coming from the nerve ring. These interneurones can in turn be grouped into four classes and each of three motor neurone classes receives its synaptic input from a unique combination of interneurone classes. The possible developmental and functional significance of these observations is discussed.     

Existence of respiratory interneurons in the cervical spinal cord of the rabbit

A spinal "respiration" generator has been shown to fire phrenic motoneurones in rhythmic bursts. It is very likely driven through bulbo-spinal inspiratory neurones in intact preparations. Although no direct evidence for respiratory interneurones at the C4-C5 spinal levels has been obtained so far (except for Renshaw cells ), it is currently believed that only few inspiratory inputs to the phrenic motoneurones are transmitted monosynaptically from the medulla. We have tried here to record spinal interneuronal respiratory activities in decorticate, unanaesthetized, vagotomized and curarized rabbit preparations. Different functional categories of interneurones could be identified at the C4-C5 spinal levels: inspiratory and expiratory interneurons with various discharge patterns which rather well correspond to the functional categories of inspiratory and expiratory bulbo-spinal neurones described by Bianchi and Richter. In addition, multiunit inspiratory bursting could be followed over several 100 microns during each electrode penetration. The different categories of interneurones were encountered laterally from 700 to 1,000 microns, at depths ranging from 300 to 500 microns dorsally to the phrenic nucleus, down to the nucleus itself. These results indicate that part of the medullary inspiratory drive is channelled via spinal cord interneurones; they also suggest that an inhibition of phrenic motoneurones from the bulbo-spinal expiratory drive takes place via interneurones.     

Cholinergic transmission at mechanosensory afferents in the crayfish terminal abdominal ganglion

Electrical stimulation of mechanosensory afferents innervating hairs on the surface of the exopodite in crayfish Procambarus clarkii (Girard) elicited reciprocal activation of the antagonistic set of uropod motor neurones. The closer motor neurones were excited while the opener motor neurones were inhibited. This reciprocal pattern of activity in the uropod motor neurones was also produced by bath application of acetylcholine (ACh) and the cholinergic agonist, carbamylcholine (carbachol). The closing pattern of activity in the uropod motor neurones produced by sensory stimulation was completely eliminated by bath application of the ACh blocker, d-tubocurarine, though the spontaneous activity of the motor neurones was not affected significantly. Bath application of the acetylcholinesterase inhibitor, neostigmine, increased the amplitude and extended the time course of excitatory postsynaptic potentials (EPSPs) of ascending interneurones elicited by sensory stimulation. These results strongly suggest that synaptic transmission from mechanosensory afferents innervating hairs on the surface of the tailfan is cholinergic.Bath application of the cholinergic antagonists, dtubocurarine (vertebrate nicotinic antagonist) and atropine (muscarinic antagonist) reversibly reduced the amplitude of EPSPs in many identified ascending and spiking local interneurones during sensory stimulation. Bath application of the cholinergic agonists, nicotine (nicotinic agonist) and oxotremorine (muscarinic agonist) also reduced EPSP amplitude. Nicotine caused a rapid depolarization of membrane potential with, in some cases, spikes in the interneurones. In the presence of nicotine, interneurones showed almost no response to the sensory stimulation, probably owing to desensitization of postsynaptic receptors. On the other hand, no remarkable changes in membrane potential of interneurones were observed after oxotremorine application. These results suggest that ACh released from the mechanosensory afferents depolarizes interneurones by acting on receptors similar to vertebrate nicotinic receptors.Abbreviations ACh cetylcholine - mns motor neurones - asc int ascending interneurone     

Function of the superior colliculi of the corpora quadrigemina during creation of a local focus of increased excitability in the mesencephalic reticular formation and sensomotor cortex

In chronic experiments on waking rabbits, the foci of heightened excitability in the sensorimotor cortex and mesencephalic reticular formation affected in a similar way the background neuronal activity in the superior colliculi and that evoked by light stimuli. The effect was manifested in elimination of inhibitory pauses in the neuronal response to light stimulus and in a general increase of discharge frequency. Similarity of the cortical and reticular influences is due to their possible mediation by the same collicular interneurones participating in inhibitory pauses formation in the process of backward inhibition. Increased neuronal activity in the superior colliculi under the action of local foci in the sensorimotor cortex and mesencephalic reticular formation correlated with appearance of forelimb motor reaction to isolated light stimulus testifying to a formation of a functional connection between the visual and motor analyzers. Possible role of the superior colliculi in this process and their participation in the formation of a visually controlled reaction is discussed.