Static input-output relations in the spinal recurrent inhibitory pathway

Abstract

The static discharge rate of Renshaw cells (studied in deafferented, intercollicularly decerebrate cats) has a nonlinear dependence on the frequency of trains of stimulus impulses to alpha-motor axons in the ventral root. This dependence is well described by a rectangular hyperbola that approaches saturation with increasing stimulus frequency. The tendency to saturate is independent of the number of motor axons exciting a Renshaw cell. On average, the stimulus frequency at which the discharge rate reaches half its saturation value lies between 10 and 15 Hz. The effect of Renshaw cell activity -- measured as the antidromic inhibition of individual alpha-motoneurons -- reflects the forms of the static frequency characteristics. An electric circuit analog of the Renshaw cell membrane is presented which serves to explain the qualitative features of the static input-output relations; the nonlinearity is the result of synapses with linear properties acting together at the cell membrane.

Simulation system of spinal cord motor nuclei and associated nerves and muscles, in a Web-based architecture

“…For Renshaw cells, these values were adapted so that the membrane time constant could make the cell fire a burst of action potentials in response to a supra-threshold input (Hultborn and Pierrot-Deseilligny 1979). The values of parameters such as rate constants and peak conductances (for default values, see V-d conductances panel in the Configuration module of the simulator) were determined so that the AHP, the f×I relation and the generation of action potential bursts followed data from the literature (Hultborn and Pierrot-Deseilligny 1979;Cleveland et al 1981;Walmsley and Tracey 1981;Windhorst 1990;Windhorst 1996;Uchiyama et al 2003). Parameters related to the IaIn and IbIn interneuron conductances were chosen so that these interneurons would fire isolated action potentials in response to a volley coming from the sensory afferents (Jankowska 1992).…”

Inhibitory connections of ipsilateral semicircular canal afferents onto Renshaw cells in the lumbar spinal cord of the cat.

“…6. We observed total suppression of this cell's discharges when a low test activity (2 or 3 spikes/stimulus) was induced by stimulation of a very thin filament isolated from the ventral root L7 (Cleveland, Kuschmierz & Ross, 1981). Activity was first reduced with four conditioning stimuli (lateral canal nerve), and completely suppressed with twenty-two or more impulses.…”

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

“…Static I/O relations between motor-axon activation rates and RC discharge rates were first, and quantitatively most precisely, investigated by Cleveland and coworkers (Cleveland 1980;Cleveland et al 1981;reviewed in Windhorst 1990reviewed in Windhorst , 1996. In decerebrate cats, a ventral root with motor axons innervating many different muscles was electrically stimulated at different constant rates and the resulting discharge of individual responsive RCs was recorded by microelectrodes.…”

“…where c is the saturation constant and k is the semisaturation constant (Cleveland et al 1981;reviewed in Windhorst 1990reviewed in Windhorst , 1996. The experimental data obtained for each individual motor axon-RC combination were fitted by the least-squares method by a Langmuir function with appropriate parameters.…”