The long-term goals of this project are to understand spinal reflex mechanisms that regulate the mechanical properties of muscle and interjoint coordination. Most studies of the mechanical actions of spinal reflexes have focused on autogenic, or stretch, reflexes. A muscle, however, also receives powerful reflex inputs from other muscles in the joint and limb (Heterogenic reflexes). Although the synaptic connectivity of heterogenic reflexes has been studied extensively, the mechanical actions of these pathways have received little attention. The decerebrate preparation will be used to evaluate the organization of autogenic and heterogenic reflexes of knee and ankle musculature under a variety of states of activation. Measurement of heterogenic actions between two muscles will be achieved by applying mechanical inputs independently to the freed tendons and measuring the force responses. A functional and quantitative map of reflexes appropriate for modellingg will be obtained. The rules by which autogenic and heterogenic inputs are integrated in the spinal cord, receptor mechanisms and pharmacology of heterogenic pathways, and the effect of stimulating supraspinal strutures on the organization of spinal pathways will also be studied. The predictions from these measurements will be tested by applying perturbations to the intact, instrumented limbs of decerebrate animals with intact muscle attachments and feedback from cutaneous and joint receptors. Malfunction of heterogenic reflexes may be an important component of motor disorders such as spasticity. Knowledge about heterogenic reflex organization is needed to understand these motor disorders and to suggest improved diagnostic methods.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Orthopedics and Musculoskeletal Study Section (ORTH)
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Emory University
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Honeycutt, Claire F; Nichols, T Richard (2014) The mechanical actions of muscles predict the direction of muscle activation during postural perturbations in the cat hindlimb. J Neurophysiol 111:900-7
Livingston, Beven P; Nichols, T Richard (2014) Effects of reinnervation of the triceps brachii on joint kinematics and electromyographic patterns of the feline forelimb during level and upslope walking. Cells Tissues Organs 199:405-22
Nichols, T Richard; Gottschall, Jinger S; Tuthill, Christopher (2014) The regulation of limb stiffness in the context of locomotor tasks. Adv Exp Med Biol 826:41-54
Livingston, Beven P; Nichols, T Richard (2014) Effects of reinnervation of the biarticular shoulder-elbow muscles on joint kinematics and electromyographic patterns of the feline forelimb during downslope walking. Cells Tissues Organs 199:423-40
Honeycutt, Claire F; Nardelli, Paul; Cope, Timothy C et al. (2012) Muscle spindle responses to horizontal support surface perturbation in the anesthetized cat: insights into the role of autogenic feedback in whole body postural control. J Neurophysiol 108:1253-61
Gottschall, Jinger S; Nichols, T Richard (2011) Neuromuscular strategies for the transitions between level and hill surfaces during walking. Philos Trans R Soc Lond B Biol Sci 366:1565-79
Honeycutt, Claire F; Nichols, T Richard (2010) The decerebrate cat generates the essential features of the force constraint strategy. J Neurophysiol 103:3266-73
Honeycutt, Claire F; Nichols, T Richard (2010) Disruption of cutaneous feedback alters magnitude but not direction of muscle responses to postural perturbations in the decerebrate cat. Exp Brain Res 203:765-71
Nichols, Richard; Ross, Kyla T (2009) The implications of force feedback for the lambda model. Adv Exp Med Biol 629:663-79
Ross, Kyla T; Nichols, T Richard (2009) Heterogenic feedback between hindlimb extensors in the spontaneously locomoting premammillary cat. J Neurophysiol 101:184-97

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