Self-reinnervated muscles lose autogenic length feedback but intermuscular feedback can recover functional connectivity

In this study, we sought to identify sensory circuitry responsible for motor deficits or compensatory adaptations after peripheral nerve cut and repair. Self-reinnervation of the ankle extensor muscles abolishes the stretch reflex and increases ankle yielding during downslope walking, but it remains unknown whether this finding generalizes to other muscle groups and whether muscles become completely deafferented. In decerebrate cats at least 19 weeks after nerve cut and repair, we examined the influence of quadriceps muscles' self-reinnervation on autogenic length feedback, as well as intermuscular length and force feedback among the primary extensor muscles in the cat hindlimb. Effects of gastrocnemius and soleus self-reinnervation on intermuscular circuitry was also evaluated. We found that autogenic length feedback was lost after quadriceps self-reinnervation indicating loss of the stretch reflex appears to be a generalizable consequence of muscle self-reinnervation. However, intermuscular force and length feedback evoked from self-reinnervated muscles was preserved in most of the interactions evaluated with similar relative inhibitory or excitatory magnitudes. These data indicate intermuscular spinal reflex circuitry has the ability to regain functional connectivity, but the restoration is not absolute. Explanations for the recovery of intermuscular feedback are discussed based on identified mechanisms responsible for lost autogenic length feedback. Functional implications due to permanent loss of autogenic length feedback and potential for compensatory adaptations from preserved intermuscular feedback are discussed.

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