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J Neurophysiol (November 12, 2008). doi:10.1152/jn.90338.2008
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Submitted on March 7, 2008
Revised on November 4, 2008
Accepted on November 5, 2008

Heterogenic Feedback Between Hindlimb Extensors in the Spontaneously Locomoting Premammillary Cat

Kyla Turpin Ross1* and T. Richard Nichols2

1 Georgia Institute of Technology and Emory University
2 Georgia Institute of Technology

* To whom correspondence should be addressed. E-mail: kyla.t.ross{at}gmail.com.

Electrophysiological studies in anesthetized animals have revealed that pathways carrying force information from Golgi tendon organs in antigravity muscles mediate widespread inhibition among other antigravity muscles in the feline hindlimb. More recent evidence in paralyzed or non-paralyzed decerebrate cats has shown that some inhibitory pathways are suppressed and separate excitatory pathways from Golgi tendon organ afferents are opened upon the transition from steady force production to locomotor activity. In order to obtain additional insight into the functions of these pathways during locomotion, we investigated the distribution of force dependent inhibition and excitation during spontaneous locomotion and during constant force exertion in the premammillary decerebrate cat. We used four servo-controlled stretching devices to apply controlled stretches in various combinations to the gastrocnemius muscles (G), plantaris muscle (PLAN), flexor hallucis longus muscle (FHL), and quadriceps muscles (QUADS) during treadmill stepping and the crossed-extension reflex (XER). We recorded the force responses from the same muscles and were therefore able to evaluate autogenic (intramuscular) and heterogenic (intermuscular) reflexes among this set of muscles. In previous studies utilizing the intercollicular decerebrate cat, heterogenic inhibition between QUADS, G, FHL and PLAN was bidirectional. During treadmill stepping, heterogenic feedback from QUADS onto G and G onto PLAN and FHL remained inhibitory and was force-dependent. However, heterogenic inhibition from PLAN and FHL onto G, and from G onto QUADS, was weaker than during the XER. We propose that pathways mediating heterogenic inhibition may remain inhibitory under some forms of locomotion on a level surface, but that the strengths of these pathways change to result in a proximal to distal gradient of inhibition. The potential contributions of heterogenic inhibition to interjoint coordination and limb stability are discussed.







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