The mammalian spinal cord contains neuronal circuits that can generate rhythmic flexion and extension movements - the spinal central pattern generator (CPG) for locomotion. Although the CPG determines the basic pattern of muscular activity, sensory feedback is necessary for adjusting motoneuron recruitment and for determining the timing of switching between the stance and swing phases. Stimulation of afferents transmitting information on length and contraction force of extensor muscles is able to "reset" the rhythm e.g. initiate a new stance phase. Specific spinal neurons involved in this resetting reflex pathway must also receive information from the CPG to coordinate sensory feedback and the centrally generated rhythmic activity during locomotion.
The goal of this project is to characterize spinal neurons involved in resetting reflex pathways from extensor afferents. Candidate cells are best characterized by input from extensor group I afferents and activity during resetting to extension. Previous studies have reported the location of putative resetting neurons and recorded their firing profiles extra-cellularly during locomotor-like activity. Intracellular recordings will now be used to determine the synaptic connectivity and activity of candidate reset ting neurons during fictive locomotion (i.e. motor activity under paralysis) in decerebrate cats.
Anatomical reconstructions of stained neurons will be used to determine axonal trajectories and immunohistochemistry will be applied to assess the neurotrans mitters expressed in these neurons. It is of great importance to identify spinal neurons taking part in rhythm generation and to describe their intrinsic properties since other cells involved in generating patterned movements may share many characteristic s of CPG neurons. Understanding the spinal neuronal circuitry responsible for generating rhythmic motor activity will improve strategies for restoration of spinal cord function after traumatic injury.
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