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1.
This simulation study aimed at assessing linkage between the membrane properties and the effectiveness of somatopetal current
transfer from activated tonic excitatory inputs homogeneously distributed along uniform dendrites. It was shown that in the
dendrites having anN-shaped steady current-voltage membrane characteristic due to the negative slope within a certain range of potentials, distal
sites can be more effective than proximal sites in somatopetal current transfer from tonically activated excitatory synaptic
inputs. Inhomogeneous dendritic depolarization produced by these inputs should be found everywhere within a range of the negative
slope. In simulated dendrites receiving, as in rat abducens motoneurons, voltage-sensitive synaptic inputs of anN-methyl-D-aspartate (NMDA) type, such spatial effects occurred at low depolarization produced by subcritical excitation. At supercritical
excitation, depolarization increased and left the range of the negative slope, and proximal sites became much more effective
than distal ones. It is suggested that persistent inward currents (including other than of NMDA nature) can provide similar
effects. 相似文献
2.
In a two-compartment mathematical model, we studied the reason for and conditions of manifestation of electrical bistability
in a neuron composed of monostable parts. One compartment of the model simulated the dendrites; their membrane was monostable
at high depolarization and characterized by an N-shaped steady current-voltage (I–V) characteristic endowed by inward synaptic current through voltage-dependent channels sensitive to N-methyl-D-aspartate (NMDA).
Another compartment simulated the axosomatic region with a positively sloped linearizedI–V characteristic of the membrane monostable at the resting membrane potential. For the whole cell, bistability was obvious
at a subcritical intensity of NMDA activation; the reason was the current directed from the more depolarized dendritic region
into the somatic region, and the necessary condition was that the above somatopetal core current must exceed the net inward
transmembrane current (the latter was the sum of the inward synaptic and outward passive extrasynaptic currents) of the dendritic
compartment. This relation essentially depended on the size of the dendrites.
Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 98–101, March–April, 2000. 相似文献
3.
The impact of dendritic geometry on somatopetal transfer of the current generated by steady uniform activation of excitatory
synaptic conductance distributed over passive, or active (Hodgkin-Huxley type), dendrites was studied in simulated neurons.
Such tonic activation was delivered to the uniform dendrite and to the dendrites with symmetric or asymmetric branching with
various ratios of branch diameters. Transfer effectiveness of the dendrites with distributed sources was estimated by the
core current increment directly related to the total membrane current per unit path length. The effectiveness decreased with
increasing path distance from the soma along uniform branches. The primary reason for this was the asymmetry of somatopetal
vs somatofugal input core conductance met by synaptic current due to a greater leak conductance at the proximal end of the
dendrite. Under these conditions, an increasing somatopetal core current and a corresponding drop of the depolarization membrane
potential occurred. The voltage-dependent extrasynaptic conductances, if present, followed this depolarization. Consequently,
the driving potential and membrane current densities decreased with increasing path distance from the soma. All path profiles
were perturbed at bifurcations, being identical in symmetrical branches and diverging in asymmetrical ones. These perturbations
were caused by voltage gradient breaks (abrupt change in the profile slope) occurring at the branching node due to coincident
inhomogeneity of the dendritic core cross-section area and its conductance. The gradient was greater on the side of the smaller
effective cross-section. Correspondingly, the path profiles of the somatopetal current transfer effectiveness were broken
and/or diverged. The dendrites, their paths, and sites which were more effective in the current transfer from distributed
sources were also more effective in the transfer from single-site inputs. The effectiveness of the active dendrite depended
on the activation-inactivation kinetics of its voltage-gated conductances. In particular, dendrites with the same geometry
were less effective with the Hodgkin-Huxley membrane than with the passive membrane, because of the effect of the noninactivating
K+-conductance associated with the hyperpolarization equilibrium potential. Such electrogeometrical coupling may form a basis
for path-dependent input-output conversion in the dendritic neurons, as the output discharge rate is defined by the net current
delivered to the soma.
Received: 18 December 1997 / Accepted in revised form: 12 June 1998 相似文献
4.
T. L. D'yakonova 《Journal of Evolutionary Biochemistry and Physiology》2002,38(2):202-210
This work is a continuation of the study on transmitter regulation of the serotoninergic system activity in the brain of the edible snail Helix lucorum, in which serotonin and NO donors have been shown to excite serotoninergic neurons from various snail ganglia (more than 60 of them were studied) and synchronize their activity by activation of the synchronous synaptic inputs. In the current work, it has been shown that glutamate, on the contrary, has an inhibitory and desynchronizing action on the same serotonin-containing neurons by suppressing their own activity and switching off the synchronous synaptic inputs. In the same neurons, another glutamate receptor agonist, NMDA, has a pronounced excitatory effect and activates the synchronous synaptic inputs. The glutamate effects are NO-dependent: the NO donor sodium nitroprusside decreases, switches off entirely, or transforms the glutamate inhibitory effect into the excitatory one. A possible mechanism of interaction of serotonin, glutamate, and NO in regulation of the snail serotoninergic system activity is discussed. 相似文献
5.
At the cerebellar synapses between parallel fibers (PFs) and Purkinje cells (PCs), long-term depression (LTD) of the excitatory synaptic current has been assumed to be independent of the N-methyl-D-aspartate (NMDA) receptor activation because PCs lack NMDA receptors. However, we now report that LTD is suppressed by NMDA receptor antagonists that act on presynaptic NMDA receptors of the PFs. This effect is still observed when the input is restricted to a single fiber. Therefore, LTD does not require the spatial integration of multiple inputs. In contrast, it involves a temporal integration, since reliable LTD induction requires the PFs to fire two action potentials in close succession. This implies that LTD will selectively depress the response to a burst of presynaptic action potentials. 相似文献
6.
The somatopetal current transfer was studied in the mathematical models of a reconstructed brainstem motoneuron with tonically
activated excitatory synaptic inputs uniformly distributed over dendritic arborization. The soma and axon provided a constant
passive leak. The extrasynaptic dendritic membrane was either passive or active (of a Hodgkin-Huxley type). The longitudinal
membrane current density (per unit path length) was used as an estimate of the current transfer effectiveness of different
dendritic paths. Introduction of a steady uniform voltage-independent conductance per unit membrane area simulated such a
synaptic activation. This actions always produced a spatially inhomogeneous membrane depolarization decaying from the distal
dendritic tips toward the soma. The reason for such an inhomogeneity was the preponderance of somatopetal over somatofugal
input conductance at every site in the dendrites with sealed distal ends and a leaky somatic end. In active dendrites, partial
voltage-dependent extrasynaptic conductances followed this depolarization according to their activation-inactivation kinetics.
The greater the local depolarization, the greater the contribution of the non-inactivating potassium conductance to the total
membrane conductance. The contribution of the inactivated sodium conductance was one order of magnitude smaller. Correspondingly,
the effective equilibrium potential of the total transmembrane current became spatially inhomogeneous and shifted to the potassium
equilibrium potential. In the passive dendrites, the equilibrium potential remained spatially homogeneous. Inhomogeneities
of the dendritic geometry (abrupt change in the diameter and, especially, asymmetrical branching) caused characteristic perturbations
in the voltage gradient, so that the path profiles of the voltage, conductances, and currents diverged. This indicated a geometry-induced
separation of the dendritic paths in their transfer effectiveness. Active dendrites of the same geometry were less effective
than passive ones due to the effect of the potassium conductance associated with the hyperpolarizing equilibrium potential. 相似文献
7.
I. B. Kulagina 《Neurophysiology》2012,43(5):335-343
Mathematical models of abducens motoneurons with reconstructed dendritic arborizations were investigated. The two types of models differed from each other
in electrical properties of the dendrites, either passive (model group 1) or active and non-linear (model group 2). The relations
between morphology of the dendrites, their electrical transfer characteristics, and formation of impulse patterns at the cell
output were studied under conditions of tonic activation of glutamatergic (NMDA-type) excitatory synapses homogeneously distributed
over the dendrites. For reconstructed dendritic arborizations, their morphometric characteristics (size, complexity, and metrical
asymmetry) and electrical ones (somatopetal current transfer effectiveness function and sensitivity of the latter to variations
of the homogeneous membrane conductivity) were computed. Changes in the membrane potential were also studied in different
parts of the dendritic arborization during generation of various patterns of discharges of action potentials (APs) at the
neuronal output under different intensities of synaptic activation; this allowed us to reveal “spatial signatures” of the
above-mentioned temporal patterns. The output patterns and their “spatial signatures” changed in a certain manner with increase
in the intensity of synaptic activation. A simple periodical discharge of low-frequency APs with constant interspike intervals
was replaced by a complex periodical or nonperiodical (stochastic) bursting pattern, which then was replaced again by a simple
rhythmic but high-frequency discharge. Simple periodical patterns were associated with generation of synchronous oscillatory
dendritic depolarizations phase-shifted in metrically asymmetrical parts of the arborization. In the case of generation of
complex periodical or stochastic patterns, depolarization processes in asymmetrical dendritic parts were asynchronous and
differed from each other in their amplitude and duration. Such a structure-dependent repertoire of output discharge patterns
was quite compatible with that observed earlier in examined simulated neocortical pyramidal and cerebellar Purkinje neurons.
This fact is indicative of a possible similarity of the rules governing the formation of specific output patterns in neurons
with active membrane properties of the dendrites based on intrinsic mophological/functional features of the dendritic arborization
of a given neuron. 相似文献
8.
In in vitro studies on superfused slices obtained from the rat hippocampus and cortex, we found that 50 μM N-methyl-D-aspartate (NMDA)
applied to the slices in the presence of 10 μM glycine for 15 min exerts a significant damaging action to neurons of these
structures. One hour after termination of the action of NMDA, this was manifested in more than a twofold decrease in the synaptic
reactivity of pyramidal neurons of the hippocampal СА1 area and layers II/III of the cerebral cortex. The excitotoxic effect of NMDA was prevented by application of competitive
(D-2-amino-5-phosphonovaleric acid, 50 μM) and noncompetitive (ketamine, 100 μM) blockers of NMDA receptors. A blocker of
glycine-binding sites of NMDA receptors (compound ТСВ 24.15, 10 μM) weakened NMDA-induced damage to the neurons. A competitive
blocker of glutamate АМРА receptors, 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 μM), and a local anesthetic, lidocaine hydrochloride
(50 μM), did not modify the excitotoxic effect of NMDA. A blocker of voltagedependent L-type calcium channels, verapamil (20
μM), demonstrated some trend to intensification of NMDA excitotoxic action. An inhibitor of tyrosine-protein phosphatases,
sodium vanadate, when i.p. injected into rats in a dose of 15 mg/kg 6 h prior to the electrophysiological experiment, decreased
the damaging action of NMDA. Two-hour-long treatment of cerebral slices with 1 μM genistein, an inhibitor of tyrosine kinases,
weakened the neuroprotective effect of sodium vanadate. Chronic injections (14 days in daily doses of 20 mg/kg) of antidepressants
belonging to different functional classes (imipramine, fluoxetine, and pyrazidol) into rats decreased (similarly to blockers
of NMDA receptors) the excitotoxic action of NMDA receptors. Neuroprotective effects of antidepressants were weakened upon
the action of genistein. We conclude that the neuroprotective activity of antidepressants under conditions of excitotoxic
action of NMDA is mainly determined by an increase in the activity of tyrosine kinases in the cytoplasm and/or neuronal nucleus. 相似文献
9.
Sergey M. Korogod 《Biological cybernetics》1996,74(1):85-93
The relationships between somatofugal electronic voltage spread, somatopetal charge transfer and non-uniform geometry of the neuronal dendrites were studied on the basis of the linear cable theory. It is demonstrated that for the dendritic arborization of arbitrary geometry, the path distribution of the relative effectiveness of somatopetal synaptic charge transfer defined as in Barrett and Crill (1974) is identical to that of the somatofugal steady electrotonic voltage normalized to the voltage at the soma. The features of both distributions are determined by breaks in the voltage gradient (the slope of monotonic voltage decay) at the sites of local non-uniformity of the dendritic geometry, such as abrupt change in diameter and asymmetric branching. If the membrane- and cytoplasm-specific electrical parameters are assumed as uniform and the branch diameter as piece-wise uniform, then at any site of step change the square reciprocal ratio of the pre- and poststep diameters determines the ratio of the pre- and poststep electronic gradients. At branching points this ratio is modulated by partition of the core current between the daughter branches in proportion to their input conductances depending on global geometries of the daughter subtrees originating there. Thus, simply computed steady somatofugal voltages provide a physiologically meaningful estimation of the relative influence of synaptic inputs in different parts of the dendritic arborization on the output of the neuron. 相似文献
10.
Simple neural network models of the Xenopus embryo swimming CPG, based on the one originally developed by Roberts and Tunstall (1990), were used to investigate the role of the voltage-dependent N-methyl-D-aspartate (NMDA) receptor channels, in conjunction with faster non-NMDA components of synaptic excitation, in rhythm generation. The voltage-dependent NMDA current "follows" the membrane potential, leading to a postinhibitory rebound that is more efficient than one without voltage dependency and allows neurons to fire more than one action potential per cycle. Furthermore, the model demonstrated limited rhythmic activity in the absence of synaptic inhibition, supporting the hypothesis that the NMDA channels provide a basic mechanism for rhythmicity. However, the rhythmic properties induced by the NMDA current were observed only when there was moderate activation of the non-NMDA synaptic channels, suggesting a modulatory role for this component. The simulations also show that the voltage dependency of the NMDA conductance, as well as the fast non-NMDA current, stabilizes the alternation pattern versus synchrony. To verify that these effects and their implications on the mechanism of swimming and transition to other types of activity take place in the real preparation, constraints on parameter values have to be specified. A method to estimate synaptic parameters was tested with generated data. It is shown that a global analysis, based on multiple iterations of the optimization process (Foster et al., 1993), gives a better understanding of the parameter subspace describing network activity than a standard fit with a sensitivity analysis for an individual solution. 相似文献
11.
Dendritic signal integration is one of the fundamental building blocks of information processing in the brain. Dendrites are endowed with mechanisms of nonlinear summation of synaptic inputs leading to regenerative dendritic events including local sodium, NMDA and calcium spikes. The generation of these events requires distinct spatio-temporal activation patterns of synaptic inputs. We hypothesise that the recent findings on dendritic spikes and local synaptic plasticity rules suggest clustering of common inputs along a subregion of a dendritic branch. These clusters may enable dendrites to separately threshold groups of functionally similar inputs, thus allowing single neurons to act as a superposition of many separate integrate and fire units. Ultimately, these properties expand our understanding about the computational power of neuronal networks. 相似文献
12.
Matteo Farinella Daniel T. Ruedt Padraig Gleeson Frederic Lanore R. Angus Silver 《PLoS computational biology》2014,10(4)
In vivo, cortical pyramidal cells are bombarded by asynchronous synaptic input arising from ongoing network activity. However, little is known about how such ‘background’ synaptic input interacts with nonlinear dendritic mechanisms. We have modified an existing model of a layer 5 (L5) pyramidal cell to explore how dendritic integration in the apical dendritic tuft could be altered by the levels of network activity observed in vivo. Here we show that asynchronous background excitatory input increases neuronal gain and extends both temporal and spatial integration of stimulus-evoked synaptic input onto the dendritic tuft. Addition of fast and slow inhibitory synaptic conductances, with properties similar to those from dendritic targeting interneurons, that provided a ‘balanced’ background configuration, partially counteracted these effects, suggesting that inhibition can tune spatio-temporal integration in the tuft. Excitatory background input lowered the threshold for NMDA receptor-mediated dendritic spikes, extended their duration and increased the probability of additional regenerative events occurring in neighbouring branches. These effects were also observed in a passive model where all the non-synaptic voltage-gated conductances were removed. Our results show that glutamate-bound NMDA receptors arising from ongoing network activity can provide a powerful spatially distributed nonlinear dendritic conductance. This may enable L5 pyramidal cells to change their integrative properties as a function of local network activity, potentially allowing both clustered and spatially distributed synaptic inputs to be integrated over extended timescales. 相似文献
13.
Burkitt AN 《Biological cybernetics》2006,95(2):97-112
The integrate-and-fire neuron model describes the state of a neuron in terms of its membrane potential, which is determined by the synaptic inputs and the injected current that the neuron receives. When the membrane potential reaches a threshold, an action potential (spike) is generated. This review considers the model in which the synaptic input varies periodically and is described by an inhomogeneous Poisson process, with both current and conductance synapses. The focus is on the mathematical methods that allow the output spike distribution to be analyzed, including first passage time methods and the Fokker–Planck equation. Recent interest in the response of neurons to periodic input has in part arisen from the study of stochastic resonance, which is the noise-induced enhancement of the signal-to-noise ratio. Networks of integrate-and-fire neurons behave in a wide variety of ways and have been used to model a variety of neural, physiological, and psychological phenomena. The properties of the integrate-and-fire neuron model with synaptic input described as a temporally homogeneous Poisson process are reviewed in an accompanying paper (Burkitt in Biol Cybern, 2006). 相似文献
14.
Neurons display a high degree of variability and diversity in the expression and regulation of their voltage-dependent ionic channels. Under low level of synaptic background a number of physiologically distinct cell types can be identified in most brain areas that display different responses to standard forms of intracellular current stimulation. Nevertheless, it is not well understood how biophysically different neurons process synaptic inputs in natural conditions, i.e., when experiencing intense synaptic bombardment in vivo. While distinct cell types might process synaptic inputs into different patterns of action potentials representing specific “motifs” of network activity, standard methods of electrophysiology are not well suited to resolve such questions. In the current paper we performed dynamic clamp experiments with simulated synaptic inputs that were presented to three types of neurons in the juxtacapsular bed nucleus of stria terminalis (jcBNST) of the rat. Our analysis on the temporal structure of firing showed that the three types of jcBNST neurons did not produce qualitatively different spike responses under identical patterns of input. However, we observed consistent, cell type dependent variations in the fine structure of firing, at the level of single spikes. At the millisecond resolution structure of firing we found high degree of diversity across the entire spectrum of neurons irrespective of their type. Additionally, we identified a new cell type with intrinsic oscillatory properties that produced a rhythmic and regular firing under synaptic stimulation that distinguishes it from the previously described jcBNST cell types. Our findings suggest a sophisticated, cell type dependent regulation of spike dynamics of neurons when experiencing a complex synaptic background. The high degree of their dynamical diversity has implications to their cooperative dynamics and synchronization. 相似文献
15.
Baker JL Perez-Rosello T Migliore M Barrionuevo G Ascoli GA 《Journal of computational neuroscience》2011,31(1):137-158
Despite the central position of CA3 pyramidal cells in the hippocampal circuit, the experimental investigation of their synaptic
properties has been limited. Recent slice experiments from adult rats characterized AMPA and NMDA receptor unitary synaptic
responses in CA3b pyramidal cells. Here, excitatory synaptic activation is modeled to infer biophysical parameters, aid analysis
interpretation, explore mechanisms, and formulate predictions by contrasting simulated somatic recordings with experimental
data. Reconstructed CA3b pyramidal cells from the public repository NeuroMorpho.Org were used to allow for cell-specific morphological
variation. For each cell, synaptic responses were simulated for perforant pathway and associational/commissural synapses.
Means and variability for peak amplitude, time-to-peak, and half-height width in these responses were compared with equivalent
statistics from experimental recordings. Synaptic responses mediated by AMPA receptors are best fit with properties typical
of previously characterized glutamatergic receptors where perforant path synapses have conductances twice that of associational/commissural
synapses (0.9 vs. 0.5 nS) and more rapid peak times (1.0 vs. 3.3 ms). Reanalysis of passive-cell experimental traces using
the model shows no evidence of a CA1-like increase of associational/commissural AMPA receptor conductance with increasing
distance from the soma. Synaptic responses mediated by NMDA receptors are best fit with rapid kinetics, suggestive of NR2A
subunits as expected in mature animals. Predictions were made for passive-cell current clamp recordings, combined AMPA and
NMDA receptor responses, and local dendritic depolarization in response to unitary stimulations. Models of synaptic responses
in active cells suggest altered axial resistivity and the presence of synaptically activated potassium channels in spines. 相似文献
16.
Intraperitoneal injection of 1 mg/kg reserpine into rats caused the development of behavioral depression that was especially
clearly pronounced 24 h after injection. Under such conditions, induction of long-term potentiation of synaptic transmission
was suppressed, the development of long-term depression in glutamatergic synapses of pyramidal neurons of the hippocampal
CA1 area and layers II/III of the parietal cortex was facilitated, and metaplasticity threshold (θM) was shifted to the right. Such modifications of plasticity and metaplasticity of glutamatergic synapses were determined
by changes in the functional state of postsynaptic NMDA receptors, which was confirmed by a decrease in the duration of NMDA
component of field EPSPs generated in the studied neurons and by an increase in the sensitivity of this component to the action
of a nonselective blocker of NMDA receptors, ketamine. Simultaneously, the sensitivity to zinc and haloperidol, which are
selective with respect to NMDA receptors with the subunit composition NR1/NR2B, decreased. It is hypothesized that, under
conditions of depression, either replacement of a part of NR2B subunits in the structure of NMDA receptors by NR2A subunits
or biochemical inactivation of NMDA receptors containing NR2B subunit, as well as a decrease in the clearance of transmitter
in glutamatergic synapses, occur; these events determine the impairment of plastic properties of the latter contacts.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 214–221, May–June, 2007. 相似文献
17.
The output of neocortical layer 5 pyramidal cells (L5PCs) is expressed by a train of single spikes with intermittent bursts of multiple spikes at high frequencies. The bursts are the result of nonlinear dendritic properties, including Na+, Ca2+, and NMDA spikes, that interact with the ~10,000 synapses impinging on the neuron’s dendrites. Output spike bursts are thought to implement key dendritic computations, such as coincidence detection of bottom-up inputs (arriving mostly at the basal tree) and top-down inputs (arriving mostly at the apical tree). In this study we used a detailed nonlinear model of L5PC receiving excitatory and inhibitory synaptic inputs to explore the conditions for generating bursts and for modulating their properties. We established the excitatory input conditions on the basal versus the apical tree that favor burst and show that there are two distinct types of bursts. Bursts consisting of 3 or more spikes firing at < 200 Hz, which are generated by stronger excitatory input to the basal versus the apical tree, and bursts of ~2-spikes at ~250 Hz, generated by prominent apical tuft excitation. Localized and well-timed dendritic inhibition on the apical tree differentially modulates Na+, Ca2+, and NMDA spikes and, consequently, finely controls the burst output. Finally, we explored the implications of different burst classes and respective dendritic inhibition for regulating synaptic plasticity. 相似文献
18.
Glutamatergic synapses play a pivotal role in brain excitation. The synaptic response is mediated by the activity of two receptor types (AMPA and NMDA). In the present paper we propose a model of glutamatergic synaptic activity where the fast current generated by the AMPA conductance produces a local depolarization which activates the voltage- and [Mg2+]-dependent NMDA conductance. This cooperative effect is dependent on the biophysical properties of the synaptic spine which can be considered a high input resistance specialized compartment. Herein we present results of simulations where different values of the spine resistance and of the Mg2+ concentrations determine different levels of cooperativeness between AMPA and NMDA receptors in shaping the post-synaptic response. 相似文献
19.
This work considers the response to simulated synaptic inputs of an excitable membrane model. The model is essentially of the Hodgkin-Huxley type, but contains an A-current in addition to sodium and delayed-rectifier potassium channels. The results were compared with previous simulations in which the stimulus was an injected current. These two types of stimuli give somewhat different results because synaptic stimuli directly change the membrane resistance, whereas injected current does not. The results of synaptic stimulation were similar to injected current in that very low frequencies of action potentials were elicited only where the stimulus was slightly above threshold. For most of the range of synaptic inputs that produced oscillatory behavior, the A-current had little effect on oscillation frequency. With synaptic stimuli as with injected current, the model membrane's spiking behavior does not begin immediately when an excitatory stimulus is imposed on a quiescent state. The delay before spiking is closely related to the inactivation time of the A-current. The synaptic results were different from the injected current results in that when substantial inhibition was present, the ability to produce very-low-frequency spiking was absent, even just above the excitatory threshold. The higher the degree of inhibition, the narrower the range of spike frequencies that could be elicited by excitation. At very high inhibition, no degree of excitation could elicit spiking. 相似文献
20.
The activity of motoneurons during motor patterns depends on their intrinsic properties and on synaptic inputs. This study
analyzed the properties of two leech motoneurons: the excitors of dorsal longitudinal muscles (DE-3) and of dorsal and ventral
longitudinal muscles (MN-L) in basal conditions (normal and high Mg2+ saline) and during crawling. The voltage–current relationships in DE-3 and MN-L were similar. The curves exhibited the largest
slope around resting potential, showed marked inward and outward rectification, and were not affected by high Mg2+. In response to 5-s pulses, DE-3 exhibited a fast initial adaptation, a slow recovery and a very slow late adaptation. High
Mg2+ abolished the initial high frequency. The frequency–voltage relationship for the rest of the response was highly similar
in normal and in high Mg2+ saline. MN-L exhibited a minor initial adaptation and then fired steadily. High Mg2+ diminished the frequency–voltage relationship. During crawling DE-3 and MN-L fired in phase and their frequency–voltage curves
overlapped with the lower end of the curves obtained in basal conditions. The results suggest that the activity of these motoneurons
during crawling was regulated, to a large extent, by synaptic inputs. 相似文献