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1 CRSN/Physiology, Université de Montréal, Montreal, Canada
* To whom correspondence should be addressed. E-mail: serge.rossignol{at}umontreal.ca.
In the cat, section of all cutaneous nerves of the hindfeet except the Tibial (Tib) nerve supplying the plantar surface results in a long-lasting decrease in the intensity of Tib stimulation required for a threshold response in flexor muscles as well as an increase in the amplitude of the phase-dependent responses recorded in various muscles during locomotion. Stimulating through chronically implanted nerve cuffs ensured a stable stimulation over time. The increase in reflex amplitude was well above the small increase in the amplitude of the locomotor bursts themselves that results from the denervation. Short latency responses (P1) were seen in flexor muscles especially at the knee (Semitendinosus) and ankle (Tibialis Anterior and Extensor Digitorum Longus) with stimuli applied in the swing phase and also to a lesser degree in the later part of the cycle. Longer latency responses (P2) were increased in hip, knee and ankle flexors as well as in a contralateral extensor (Vastus Lateralis) when applied in late stance. Responses evoked from stimulating the proximal end of sectioned nerves were not larger than before neurectomy. This suggests that the increased responsiveness to Tib stimulation is not simply due to an increase in motoneurone excitability, as this would have resulted in a non-specific increase of responses to stimulation of any nerve. It is concluded that the adult locomotor system is capable of central reorganization to enhance specific remaining cutaneous reflex pathways after a partial cutaneous denervation of the paw.
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