Plasticity of the extensor group I pathway controlling the stance to swing transition in the cat.
1. This study examines whether the efficacy of polysynaptic group I excitatory pathways to extensor motoneurons are modified after axotomy of a synergistic nerve. Previously, it has been shown that stimulation of extensor nerves at group I strength can extend the stance phase and delay swing. Stimulation of the lateral gastrocnemius and soleus (LG/S) nerve prolongs stance for the duration of the stimulus train, whereas stimulation of the medial gastrocnemius (MG) nerve moderately increases stance. Our hypothesis was that after axotomy of the LG/S nerve the efficacy of the MG group I input would increase. 2. This idea was tested in 10 adult cats that had their left LG/S nerves axotomized for 3-28 days. On the experimental day the cats were decerebrated and the left (experimental) and right (control) LG/S and MG nerves were stimulated during late stance as the animals were walking on a motorized treadmill. A significant increase in the efficacy of the left MG nerve occurred 5 days after axotomy of the LG/S nerve when compared with the control response. By contrast, the previously cut LG/S nerve showed a reduction in efficacy after 3 days compared with the control limb. 3. Functionally, this plasticity may be an important mechanism by which the strength of the group I pathway is calibrated to different loads on the extensor muscles.
Whelan
P J
PJ
Department of Physiology, University of Alberta, Edmonton, Canada.
Hiebert
G W
GW
Pearson
K G
KG
D000818:Animals; D001369:Axons / Q000502:physiology; D002415:Cats; D004576:Electromyography; D005260:Female; D006614:Hindlimb / Q000294:innervation; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009121:Muscle Denervation; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D011187:Posture / Q000502:physiology*; D012018:Reflex / Q000502:physiology