Dynamic properties of renshaw cells: Equivalence of responses to step changes in recruitment and discharge frequency of motor axons

Abstract

In decerebrate cats, the dynamic responses of Renshaw cells to step changes in input were determined separately both for changes in the number of alpha-axons excited and for changes in the frequency at which they were stimulated. Together, these two input variables to the Renshaw cells describe the level of activity in the motor output from the spinal cord. In either case, the dynamic responses of the interneurons depend only on their static activity before and after an input step occurs, but are otherwise indistinguishable. This favors the interpretation that the two input variables are equivalent under dynamic conditions, i.e., Renshaw cells respond to total motor output.

A study and model of the role of the Renshaw cell in regulating the transient firing rate of the motoneuron

“…In each case, the resulting value msc was very near or equal to 1 (Table 1), which places the Renshaw cell's second-order linear transfer function in the critically damped state. This occurrence implies that in response to a step input, the Renshaw cell's firing rate curve would not overshoot its steadystate value, thus preventing the model from simulating the adaptation that Renshaw cells are known to exhibit in response to a step input (Ross et al 1982;Hultborn and Pierrot-Deseilligny 1979). While it is straightforward to induce adaptation, doing so degraded the accuracy of the fit to the neurophysiological data.…”

“…Notably, little or no oscillation appears when the neuron adapts. Firing rates fall anywhere from 0% to 60% in the Renshaw cell of the decerebrate cat, as evidenced in recordings by Ross et al (1982).…”

“…In the motoneuron, measured values of the minimum firing rate for the cat varied from 5-25 impulses/s (Schwindt and Crill 1989;Kernell 1983). The Renshaw cell's minimum firing rate was recorded by Hultborn and Pierrot-Deseilligny (1979) to be as low as 25 and by Ross et al (1982) to be as high as 40 impulses/s.…”

A model of the feline medial gastrocnemius motoneuron-muscle system subjected to recurrent inhibition

“…Relevant experimental studies were performed by Cleveland and coworkers (Cleveland 1980;Ross et al 1982;reviewed in Windhorst 1990). In decerebrate cats, they electrically stimulated a set of motor axons first at zero or low sustained rate and then, after 5 s, suddenly stepped up the rate to a higher sustained value.…”

“…Figure 7a replots one of the few published records. It exemplifies an RC's response to a step change in motor-axon stimulus rate from 5 pps before t ¼ 5 s to 33 pps afterwards (Ross et al 1982). The initial RC firing rate before the step is indicated by the short horizontal bar close to the ordinate and labeled ''5.''…”