Elementary transcallosal connections of the rabbit sensomotor cortex]

Antidromic responses of two callosal neurones to a local electrical stimulation of the rabbit sensorimotor cortex may be recorded simultaneously with one microelectrode in the homotopic cortical area. In such recording conditions the relative amplitude of extracellularly recorded action potentials of the two neurones is determined primarily by the distance between these neurones and the electrode's tip. In response to the stimulation of the symmetrical area transcallosal monosynaptic excitation of the callosal neurone may occur; two callosal neurones may exite monosynaptically one and the same recorded neurone. The results suggest the existence of clusters or columns, formed jointly by the bodies and terminals of callosal neurones; a functional interconnection between symmetrical clusters or columns may exist, in particular a positive feedback.     

Electrophysiological properties of the isolated vestibulocerebellar complex of the frog in vitro

Parameters of the electrical activity of the isolated vestibulocerebellar complex of the frog were studied under in vitro conditions. In the region of the vestibular nucleus (nc. VIII), in the presence of stimulation of the stato-acoustic nerve (n. VIII), responses from efferent vestibular neurones and from unidentified (probably vestibulospinal) neurones were recorded. The latent periods of their excitatory postsynaptic potentials (EPSPs, 1.4-2.2 ms) were indicative of mono- and disynaptic connection. Inhibitory postsynaptic potentials (IPSPs) were also observed. Stimulation of the auricular lobe of the cerebellum evoked monosynaptic IPSPs, an EPSP-IPSP complex or pure EPSPs in nc. VIII, the latter probably by way of collaterals to the cerebellum. The inhibitory character of the effect of efferents from the cerebellum to the neurones of nc. VIII was demonstrated in the focal synaptic potential and in spontaneous and evoked unit activity. If n. VIII was stimulated, both focal and unit extra- and intracellular responses characteristic of activation of the Purkinje cells by mossy (MF) or climbing (CF) afferent fibres were recorded in the cerebellar cortex. The electrophysiological picture indicates that both synaptic transmission and the functional manifestations of the individual neurones are preserved in the tested preparation.     

Callosal neurons: monosynaptic connection between them and their descending projections

Antidromic and monosynaptic unit responses to the stimulation of the corpus callosum and the symmetrical cortical area as well as antidromic responses to pyramidal tract and thalamic nuclei stimulation were recorded in the sensorimotor cortex of unanaesthetized rabbits. Out of 182 callosal neurones 13 exhibited transcallosal monosynaptic responses. 8 out of 56 callosal units responded antidromically to pyramidal tract or thalamic stimulation. Thus callosal neurones may be monosynaptically excited by callosal units via the corpus callosum and by the pyramidal tract units. It was also found that a pyramidal tract neurone may send a collateral through the corpus callosum and at the same time have a transcallosal monosynaptic input. The role of monosynaptic transcallosal excitation of callosal neurones is discussed.     

The electrophysiological study of axonal branching of the C6-C7 neurones of the cat's spinal cord projecting to the lateral reticular nucleus and the cerebellum.

Ascending projections of the cervical spinal cord neurones to the lateral reticular nucleus (LRN) and the restiform body (RB) were electrophysiologically investigated in alpha-chloralose anaesthetized cats. The main purpose of the study was to demonstrate whether the some of C6/C7 segments neurones gave off collateral branches that reached both the LRN and RB. Antidromic action potentials were recorded from 50 neurones located in laminae IVVIII of the grey matter of C6/C7 segments following stimulation of the LRN and RB with tungsten electrodes. Analysis of the antidromic responses allowed to distinguish three populations of neurones according to their projection patterns, 41% cells ascended exclusively to either one of the two structures investigated (26% to LRN and 15% to RB), while in the remaining cases (59%) collateral projections ascended to both LRN and RB. The axonal conduction velocities were comprised in the range of 14-90 m/s and no differences were found when compared mean values for particular groups of neurones. In conclusion, the results obtained indicate that in a great number of C6/C7 neurones both spinoreticular and spinocerebellar projections are present. It is likely that afferent input from forelimbs may be directly of indirectly transmitted to the cerebellum through the same neurones.     

Vestibular projections in the cat temporal cortex

Boundaries of vestibular projections in the temporal cortex during stimulation of the vestibular nerve were studied in cats anesthetized with pentobarbital and chloralose or chloralose alone. The caudal boundary of the vestibular zone was shown to run along the anterior ectosylvian gyrus. A focus of evoked activity was found in the suprasylvian sulcus or 1–2 mm rostrally to it. All short-latency evoked potentials recorded during vestibular nerve stimulation in the temporal region caudally to the zone mentioned above were connected with the spread of current to auditory structures. To verify the extent of spread of the stimulating current, focal potentials were recorded in the vestibular and superior olivary groups of nuclei. Special experiments were carried out to study the topography of these potentials at the level of bulbar structures during stimulation of vestibular and auditory nerves. According to the results, there is no second vestibular area in the temporal cortex in cats. Vestibular afferentation is projected mainly into the contralateral hemisphere, and the response latency is 5.2±0.7 msec. The ipsilateral evoked potentials had a long latent period (8.4±1.3 msec), and their amplitude depended on the type of anesthesia; it was accordingly postulated that additional synaptic relays exist in this vestibulocortical pathway.     

大鼠前庭内侧核在前庭—交感反应中的作用

实验在氯醛糖和尿酯混合麻醉的大鼠上进行。在内脏大神经上记录刺激同侧前庭神经进入脑干处的交感反应。电刺激前庭神经可在同侧内脏大神经引出—明确的叠加反应,其平均潜伏期为45.8±6.98ms,时程为55.21±5.35ms。增加刺激强度,反应幅度也增加,但潜伏期不变。用前庭内侧核(NVM)的片层场电位作为指标并选择其相位倒转处作刺激点,可在同侧内脏大神经记录到潜伏期为32ms 的叠加反应,而同一动物刺激前庭神经入脑处时内脏大神经反应的潜伏期为43ms。在 NVM 头端损毁后,此前庭-交感反应明显减小,再损毁尾端 NVM 后,此反应消失。损毁 Deiters 核对前庭-交感反应无影响。这些结果表明 NVM在内脏大神经记录到的前庭-交感反应中是一重要的中继站。     

Reactions of cat motor cortex neurons to stimulation of the pyramidal tract and ventroposterolateral thalamic nuclei

Responses of neurons of motor cortex evoked by stimulations of pyramidal tract (PT) and ventroposterolateral (VPL) nucleus of thalamus were studied in cats immobilized by Myorelaxin. Antidromic spikes were found in 22.6% and in 9.9% of cortical cells when PT and VPL were stimulated, respectively. Fast- and slow-conducting PT-neurones could be differentiated according to antidromic excitation latencies. PT stimulation evoked EPSPs in 46.3% of studied neurones and VPL stimulation--in 48.2% ones. Monosynaptic EPSPs were identified in responses of fast- and slow-conducting PT-units and of neurones projecting in VPL; mechanisms and functional role of such reactions are discussed. Di- and polysynaptic IPSPs were evoked in 74.5% of units by PT stimulation and in 94.4%--by VPL stimulation. Three groups of IPSPs were classified with durations to 120, 130-280 and more than 300 ms. Duration of PT-evoked IPSPs was higher in cortical neurones from surface layers and VPL-evoked ones--in units localized in deep layers.     

The mandibular common inhibitor system

Summary The mandibular common inhibitor neurones ofHomarus gammarus receive sensory input from a wide receptive field (Table 1, Figs. 2, 3) and from their symmetrical homologue (Ferrero and Wales, 1976).The CI system receives excitatory input from mandibular proprioceptors, with the notable exception of the mandibular muscle receptor organ, and its activity increases, during mandible opening and closing, towards the extremes of movement (Fig. 1). The output of CI neurones is usually coupled except during some high frequency bursts. Unilateral sensory input usually produces a coupled output. Electrical stimulation of a wide range of mandibular nerves (Table 2) has a similar effect and entrains the CI output at lower frequencies (Figs. 4, 5).Antidromic stimulation of a CI neurone causes excitation of its homologue but to a lower level of activity and without enhanced coupling. Even when the excitatory state is raised, by concurrent stimulation of a sensory nerve, the pathway activated by antidromic stimuli does not produce coupled activity at frequencies above 20 Hz (Fig. 8).Stimulation with single pulses will frequently produce short trains of impulses from the CI neurones (Figs. 6, 7) suggesting reciprocal excitation between the neurones.A model of the system based on current knowledge is presented.     

Correlation between the amplitude of action potentials and the rate of conduction along axons of the output cells of the sensomotor cortex

Antidromic responses of neighbouring neurones in micro-areas of the sensorimotor cortex to the stimulation of fibers of the pyramidal tract as well as of the red nucleus and thalamic nuclei VPL and MGB, were studied in acute experiments on unanesthetized immobilized cats. Depending on the velocity of conduction along the axon, the neurones of all the categories were divided into fast and slow cells. When examining the two neuronal groups most differing in AP amplitude (N1 and N3), it was found that N1 neurones were mainly fast-conducting and N3 neurones-- slow-conducting. The conclusion is made that at multineuronal recording, each of the examined categories of the output neurones is characterized by positive correlation between AP amplitude and the axon conduction velocity and consequently, the size of the cell.     

The effect of a vasopressin analog on the reaction of the command neurons in the defensive behavior of the edible snail during nerve stimulation

On the level of snail command neurones of the defensive behaviour an increase was revealed of the amplitude of summary EPSP recorded in command neurones in response to nerve stimulation, an increase of probability of appearance of action potential in the reaction and, under certain conditions, a significant decrease of habituation speed at rhythmic (0.1 Hz) nerve stimulation against the background of peptide. The latter effect was found during comparison of groups of neurones--control neurones and those to which the peptide was presented before the first series of stimulation in the test, i. e. without preliminary elaboration of habituation. The decrease of the speed of habituation concerned both the amplitude of summary EPSP and the probability of action potential appearance in the reaction. All these changes against the background of vasopressin analogue may be the basis of the increase of spike reactions of command neurones of the defensive behaviour and thus the basis of the initiation or the increase of behavioural defensive reactions. The obtained effects were not protracted and took place only in the presence of the peptide in the extracellular medium.     

Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats

Sciatic nerve lesion in newborn rats is known to cause degeneration of a large number of axotomized motoneurones and spinal ganglion cells. Some of the surviving motoneurones exhibit abnormal firing properties and the projection pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following neonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birth, the tibial nerve, common peroneal nerve or sural nerve were stimulated on the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and peroneal nerve stimulation on the side of the nerve lesion were significantly smaller in amplitude representing only about 15% of the mean amplitude of VRRs on the control side. The calculated central delay of the first, presumably monosynaptic component of the VRR potential was 1.6 ms on the control side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosynaptic origin. These results suggest that neonatal sciatic nerve injury markedly alters the physiological properties and synaptic connectivity in spinal cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.     

The neurochemical basis of recurrent inhibition in the reflex arch of the defensive reaction]

Mechanisms of habituation in the network of identified neurones were investigated in isolated preparation of central nervous system in the snail Helix. It has been found that intracellularly induced spike discharge in premotor command neurones decreases synaptic responses to repeated nerve stimulation in all recorded command neurones. Application of the neuropeptide FMRFamide elicits similar changes in the network. Taking into account that the investigated command neurones contain FMRFamide, as was shown immunochemically, it is possible to assume the existence of recurrent inhibition in the network underlying avoidance reactions. This recurrent inhibition causes habituation of the network output in the cases when the repeated stimuli do not evoke sensitization via activation of serotonergic cells.     

Differential sensitivity to rotation measured on potentials evoked by electrical stimulation of the guinea-pig ear

Responses to electrical stimulation of the ear applied between round-window and vertex electrodes were recorded in awake guinea-pigs from the same electrodes or from separate vertex/mastoid subdermal needle electrodes. They were averaged during opposite phases of sinusoidal rotation or before and after constant velocity rotation. In both cases the responses were subtracted from each other and yielded differential per- or post-rotatory “electrovestibular” responses. For comparison, responses were also recorded in the same animals and conditions of electrical stimulation during silence and during presentation of a broad-band noise. The difference yielded “electroacoustic” responses. In round-window records, electrovestibular and electroacoustic responses presented typical compound nerve action potential patterns. Electrovestibular responses could be recorded for head angular velocities as low as 3° sec⁻¹ at 0.1 Hz. Response amplitude showed a logarithmic relation to head velocity. Changes in amplitude, as a function of time after rotation, were comparable to those reported for vestibular nerve fibre responses. In vertex/mastoid records, electroacoustic responses presented a sequence of peaks similar to the click-evoked auditory brain-stem responses, and electrovestibular responses presented two peaks, presumably representing contributions of central vestibular structures. Such “electrovestibulography” permits the study of an individual ear and makes available to the investigator a large range of vestibular stimulation conditions.     

Modeling the interactions between stimulation and physiologically induced APs in a mammalian nerve fiber: dependence on frequency and fiber diameter

Electrical stimulation of nerve fibers is used as a therapeutic tool to treat neurophysiological disorders. Despite efforts to model the effects of stimulation, its underlying mechanisms remain unclear. Current mechanistic models quantify the effects that the electrical field produces near the fiber but do not capture interactions between action potentials (APs) initiated by stimulus and APs initiated by underlying physiological activity. In this study, we aim to quantify the effects of stimulation frequency and fiber diameter on AP interactions involving collisions and loss of excitability. We constructed a mechanistic model of a myelinated nerve fiber receiving two inputs: the underlying physiological activity at the terminal end of the fiber, and an external stimulus applied to the middle of the fiber. We define conduction reliability as the percentage of physiological APs that make it to the somatic end of the nerve fiber. At low input frequencies, conduction reliability is greater than 95% and decreases with increasing frequency due to an increase in AP interactions. Conduction reliability is less sensitive to fiber diameter and only decreases slightly with increasing fiber diameter. Finally, both the number and type of AP interactions significantly vary with both input frequencies and fiber diameter. Modeling the interactions between APs initiated by stimulus and APs initiated by underlying physiological activity in a nerve fiber opens opportunities towards understanding mechanisms of electrical stimulation therapies.     

Characteristics of the neuronal reaction of the substantia nigra to nociceptive stimulation

The nature of neurone response of substance nigra (SN) to nociceptive stimulation of the cat's peroneal nerve has been studied. The recording of neurone SN firing rate revealed that the majority (71.0%) of the SN neurones responded to the nociceptive repetitive stimulation of the peroneal nerve. But the thresholds of nociceptive activation in SN neurones turned to be very high. As a result of it the number of SN neurones responding to repetitive peroneal stimulation was twice as many as the number of cells responding to single stimulation of the nerve. The intravenous injection of naloxone in dose 1.0 mg/kg changed both excitatory and inhibitory responses in majority (71.4%) of SN neurones responding to repetitive peroneal stimulation. Naloxone did not modify the firing rate of neurones nonresponsive to nociception.     

The role of the thalamic ventrolateral nucleus in the cortical effect on the activity of vestibular neurons

Electrocoagulation of lateral vestibular nucleus (NVL) reduces inhibitory effect of the motor and somatosensory areas and enhances the inhibitory effect of limbic, vestibular, and orbital cortical areas. Facilitating effect was enhanced by electrostimulation of the motor area and reduced by the stimulation of other cortical areas. Following the coagulation of the NVL, the ascending afferent flow to the cortex seems to be reduced. This results in diminishing of the cortical neurones tone and readjusts the descending influences upon the NVL neurones activity.     

Neuronal correlates of changes in the defensive behavior of Helix lucorum L. during ontogeny

In experiments on the isolated nervous system, responses of the same command neurones of avoidance behaviour to electrical stimulation of the intestinal nerve were compared in adult snails (Helix pomatia) and in snails 1-20 days old. Dynamics of spike reactions of the command neurones to rhythmic nerve stimulation differed in adult and newborn snails. In the neurones of young snails, no sensitization, common in the adult animals, was observed. Study of excitatory input in the command neurones during rhythmic nerve stimulation suggests independence of habituation of synaptic input amplitude and spike response sensitization, because dynamics of habituation coincided in the young and adult snails while spike response underwent sensitization only in adult animals.     

Electrophysiological Study of Spatial Distribution of Vestibulospinal Neurons in the Frog Rana ridibunda

In experiments on a perfused brain preparation of the frog Rana ridibunda, the vestibulospinal neurons were identified, based on the excitatory postsynaptic potentials (EPSP) that appeared in response to an ipsilateral stimulation of the vestibular nerve and on the antidromic activity in response to stimulation of the cervical and lumbar enlargements of the spinal cord. The cells that could be antidromically activated only by stimulation of the cervical cord were designated as C-neurons. The cells that could be antidromically activated by stimulation of the lumbar cord were designated as L-neurons. The intracellular activity was recorded in 244 neurons of the vestibular nuclear complexes, out of which 127 cells (52%) were C-neurons and 117 (48%), L-neurons. The antidromic action potentials were recorded from the cells of lateral (143 neurons, 58.6%), descending (75 neurons, 30.7%), and medial (26 neurons, 10.6%) vestibular nuclei. The axon conduction velocity was determined to amount, on average, to 10.67 m/s for C-neurons and 15.84 m/s for L-neurons. In the vestibular nuclear complex, distribution of the fast and slow C- and L-neurons was studied. This study confirmed the previously made suggestion that C- and L-neurons of the frog, as sources of vestibular fibers, are distributed separately or, more often, as small groups, which leads to a patch-like somatotopy, rather than to formation of clearly separated fields.     

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     

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2–4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di-and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs ( 60 days) with a preor postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with preor postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.Abbreviations HL hemilabyrinthectomy - VNC vestibular nuclear complex - HRP horseradish peroxidase - N. VIII eighth nerve - N. IX ninth nerve