Higher-order non-linear phenomena in Renshaw cell responses to random motor axon stimulation (original) (raw)
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Neuroscience, 1989
Lumbosacral Renshaw cells were activated by random stimulation of motor axons in muscle nerves or ventral roots. The stimulus patterns had mean rates of 9.5-13 or 2&23 pulses per second. The Renshaw cell responses were evaluated by two kinds of ~ristimulus-time histograms. "Conventional" peristimulus-time histograms were calculated by averaging the cell discharge with respect to all the stimuli in a train, "Conditional" peristimulus-time histograms were determined by averaging the cell discharge with respect to the second ("test") stimulus in pairs of stimuli which were separated by varied intervals. The effects of the conditioning stimuli were evaluated after correcting for the effect of linear superposition of the conditioning and test stimuli.
Neuroscience, 1989
spinal Renshaw cells were activated by stimulating muscle nerves or ventral roots with random (pseudo-Poisson) patterns of brief electrical stimuli. This input pattern is optimal for a comparative study in both the frequency-and time-domain. The frequency-dependent variable of particular interest in this study was the coherence as a measure of the degree to which signal transmission is linear and noise-free; it was estimated via spectral analysis. Time-domain analysis consisted of calculating ~~-stimulus time histograms in order to estimate the amount of nonlinea~ty in the cell responses to pairs of stimuli. The main result was that the amount of nonlinearity measured in this way did not profoundly depress the coherence.
Experimental Brain Research, 1988
In 9 adult anaesthetized cats, 22 lumbosacral Renshaw cells recorded with NaCl-filled micropipettes were activated by random stimulation of ventral roots or peripheral nerves. The stimulus patterns had mean rates of 9.5~13 or 20–23 or 45 pulses per second and were pseudo-Poisson; short intervals below ca. 5 ms (except in two cases) were excluded. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms (PSTHs). “Conventional” PSTHs were calculated by averaging the Renshaw cell discharge with respect to all the stimuli in a train. These PSTHs showed an early excitatory response which was often followed by a longer-lasting slight reduction of the discharge probability. These two response components were positively correlated. “Conditional” PSTHs were determined by averaging the Renshaw cell discharge with respect to the second (“test” stimulus in pairs of stimuli which were separated by varied intervals, δ. The direct effect of the first “conditional” response was subtracted from the excitation following the second (“test” stimulus so as to isolate the effect caused by the second stimulus per se. After such a correction, the effect of the first “conditioning” stimulus showed pure depression, pure facilitation or mixed facilitation/depression. Analysis of such conditioning curves yielded two time constants of facilitation (ranges: ca. 4–35 ms and 93–102 ms) and two of depression (ranges: ca. 7–25 ms and 50–161 ms). It is concluded that these time constants are compatible with processes of short-term synaptic plasticity known from other synapses. Other processes such as afterhyperpolarization and mutual inhibition probably are of less importance.
In 9 adult anaesthetized cats, 22 lumbosacral Renshaw cells recorded with NaCl-filled micropipettes were activated by random stimulation of ventral roots or peripheral nerves. The stimulus patterns had mean rates of 9.5-13 or 20-23 or 45 pulses per second and were pseudo-Poisson; short intervals below ca. 5 ms (except in two cases) were excluded. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms (PSTHs). "Conventional" PSTHs were calculated by averaging the Renshaw cell discharge with respect to all the stimuli in a train. These PSTHs showed an early excitatory response which was often followed by a longer-lasting slight reduction of the discharge probability. These two response components were positively correlated. "Conditional" PSTHs were determined by averaging the Renshaw cell discharge with respect to the second ("test") stimulus in pairs of stimuli which were separated by varied intervals, 6. The direct effect of the first "conditional" response was subtracted from the excitation following the second ("test") stimulus so as to isolate the effect caused by the second stimulus per se. After such a correction, the effect of the first "conditioning" stimulus showed pure depression, pure facilitation or mixed facilitation/depression. Analysis of such conditioning curves yielded two time constants of facilitation (ranges: ca. 435 ms and 93-102 ms) and two of depression (ranges: ca. 7-25 ms and 50-161 ms). It is concluded that these time constants are compatible with processes of short-term synaptic plasticity known from other synapses. Other processes such as afterhyperpolarization and mutual inhibition probably are of less importance.
A method to estimate the effects of parallel inputs on neuronal discharge probability
Pflugers Archiv-european Journal of Physiology, 1989
We here present a method to study the interaction of parallel neural input channels regarding their effects on a neurone. In particular, the method allows to disclose the effects of oligosynaptic pathways that may exist in parallel to direct monosynaptic connections to the cell. Two (or more) inputs (nerves) are stimulated with random patterns of stimuli. The response of the cell to these patterns is evaluated by the computation of peristimulus-time histograms (PSTHs). One of the two stimulus trains is selected as the one to yield reference events for the PSTH computation. From this stimulus train are selected those stimuli as reference events which are preceded, at defined mean intervals, by stimuli in the same or a parallel channel. These “conditioning” stimuli are determined (1) separately from each single stimulus train and (2) concomitantly from the two trains as events occurring simultaneously in both. The effects exerted by these various conditioning events on the effects of the “test” pulses on the cell response yield insights into the interactions between the two (or more) inputs. These methods are demonstrated on spinal Renshaw cells activated by independent random stimulation of two muscle nerves and on dorsal horn neurones responding to cutaneous nerve stimulation.
Journal of Neurophysiology, 1998
Maltenfort, Mitchell G., C. J. Heckman, and W. Zev Rymer. Decorrelating actions of Renshaw interneurons on the firing of spinal motoneurons within a motor nucleus: a simulation study. J. Neurophysiol. 80: 309–323, 1998. A simulation of spinal motoneurons and Renshaw cells was constructed to examine possible functions of recurrent inhibition. Recurrent inhibitory feedback via Renshaw cells is known to be weak. In our model, consistent with this, motoneuron firing was only reduced by a few pulses per second. Our initial hypothesis was that Renshaw cells would suppress synchronous firings of motoneurons caused by shared, dynamic inputs. Each motoneuron received an identical pattern of noise in its input. Synchrony coefficients were defined as the average motoneuron population firing relative to the activity of selected reference motoneurons; positive coefficients resulted if the motoneuron population was particularly active at the same time the reference motoneuron was active. With or ...
Repetitive firing of Renshaw spinal interneurons
Biological Cybernetics, 1977
A model of the Renshaw spinal interneuron has been developed. The model consists of a nonhomogeneous cylinder divided into three compartments: dendrites, soma and axon initial segment (I.S). The soma and dendrites are represented as a cylindrical cable by the method of Rall (1962) ; anatomical data of Jankowska and Lindstr6m (1971) from fluorescent dye injections were used to construct the cable. The soma and I.S. membranes are assumed to have Hodgkin-Huxley-like membrane activity. In comparison with our previous model of a tonic motorneuron (Traub, 1977), the Renshaw cell has a faster membrane time constant, faster Hodgkin-Huxley rate functions, eh and flh shifted to the right on the voltage axis, and no slow potassium conductance. With appropriate input conductances, the Renshaw cell model exhibits the following features: it develops very high frequency bursts (over 1000 impulses per s) which trail off over a period of 10-20 ms ; the second spike has small amplitude and successive spikes develop progressively larger amplitudes. Comparisons are drawn with the experimental observations of Eccles et al. (1961) and Willis and Willis (1966). With this model, it is feasible to compute the steady firing rate for a large number of steady synaptic excitatory and inhibitory conductances by direct integration of the differential equations.
The Journal of physiology, 1982
1. Recordings of afferent discharges from external intercostal muscle spindles were made from in-continuity dorsal roots of anaesthetized, paralysed cats and the afferents were characterized as described in the preceding paper (Kirkwood & Sears, 1982).2. The strengths and time courses of the raised probabilities of firing of external intercostal motoneurones evoked by the synaptic actions of impulses in the afferents were measured by constructing cross-correlation histograms from the discharges of the individual afferents and the discharges of the motoneurones, which were simultaneously recorded from the cut central ends of intercostal nerve filaments. Other dorsal roots, apart from the rootlet containing the afferent fibre, were cut to prevent afferent synchronization from affecting the results.3. Cross-correlation histograms involving single efferent discharges showed narrow peaks (mean half-width 0.99 msec) at monosynaptic latencies.4. This mean half-width is slightly longer than...