Injections of embryonic catecholamine (CA) nerve cell suspensions into the adult brain yield surviving CA cells which develop dendrites and extensive axonal arborizations and can influence the animal's behavior. Application of this technique to the adult rat spinal cord by our laboratory has resulted in the successful implantation of up to 1000 CA nerve cells into the lumbar cord. These cells produce a fiber plexus in the grey matter which appears to be of normal density when examined with Falck-Hillarp monoamine histofluorescence. The experiments proposed here are designed to determine whether or not these implanted CA neurons can influence the function of the adult spinal cord. Two types of functional tests are proposed: 1) a behavioral test of coordination and balance and 2) the hindlimb flexion reflex. The first test will assess if the implants improve the impaired motor performance that we have observed in rats whose descending CA fibers in the spinal cord have been eliminated with 6-hydroxydopamine. The second test, the hindlimb flexion reflex, is one that has been shown to be strongly affected by catecholamines and thus should be a sensitive assay for functional innervation by the implanted CA nerve cells. Two methods will be used to determine if the functional differences between control and implanted animals are due to the surviving CA cells: 1) the number of CA cells will be counted and compared to the functional results in each animal and 2) the sensitivity of the responses in the implanted animals to phenoxybenzamine, an alpha-adrenergic blocker, will be tested. Spinal cord function is drastically altered by spinal cord injury and perhaps also by the degeneration of descending systems during aging. There is the possibility that nerve cell implants will improve spinal cord function after injury or in the aged animal. The experiments proposed here are important because they will assess whether or not nerve cell implants into the adult spinal cord can influence spinal cord function and improve motor performance.
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