The effects of recurrent inhibitory feedback in shaping discharge patterns of motoneurones excited by phasic muscle stretches

摘要

The spinal motoneurone-Renshaw cell circuitry, which constitutes an intricate negative feedback system, was investigated with respect to its significance for the shaping of motoneurone firing patterns excited by strong phasic inputs. Discharge patterns of single motoneurones were compared before and after opening of the recurrent inhibitory pathways by Renshaw cell blocking agents. Serial correlograms computed from motoneurone interspike intervals which were modulated by sinusoidal muscle stretch replicated the input periodicity, but were not changed in any consistent manner after Renshaw cell blockage. Longterm regularity and periodicity of motoneurone firing, i.e. the overall response characteristics, do not appear to be significantly determined by Renshaw cells under these conditions. The modulation of motoneurone interspike intervals was assessed by computing power spectra for corresponding instantaneous frequencies. The harmonic contents (2ndand 3rdharmonic of the driving frequency) of these spectra tended to decrease after Renshaw cell depression. The distortion of signal transmission in a single motoneurone channel is thus stronger with, than without, the recurrent inhibitory feedback. The implication of these findings for signal transmission from the spinal cord to the muscle is discussed.