PHYSIOLOGICAL CORRELATES OF COLLATERAL SPROUTING

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The long term objectives of this research are to understand the bases of recovery of function in the spinal cord following partial devervation. The relationship of latent synapses to recovery of function will be studied by comparing response to cutaneous and nerve stimulation in normal and deafferented animals. The role of collateral sprouting in mediating increased responses to high threshold stimuli following lesions will be assessed by HRP labelling of individual high-threshold afferents in normal and partially deafferented animals. The hypothesis that some loss and recovery of function following lesions can be accounted for by a transient failure of synaptic transmission will be tested by recording electrical properties of dorsal horn neurons related to excitability. Analysis will be carried out using populations of nerve cells whose properties have been well characterized in normal animals, namely, the cells of origin of the spinocervical tract, and high-threshold A-delta mechanoreceptive afferent fibers. The methods to be used include intra- and extracellular electrophysiological recording from spinocervical tract neurons following acute and chronic dorsal root and peripheral nerve lesions in cats. Responses to both mechanical stimulation of the skin and electrical stimulation of nerves will be evaluated. The effects of acute injury will be compared with those of reversible conduction block of nerves and dorsal roots. These studies are related to the health goals of preventing disability following peripheral nerve or spinal injury, and rehabilitating individuals with chronic spinal cord or peripheral nerve lesions.