Painful sensations are a frequent and often chronic sequela of paraplegia and quadriplegia following partial or complete lesions of the spinal cord. Current research of mechanisms of chronic pain in these patients has suggested a related loss of inhibitory neurotransmitters and growth factors in the injured cord that may be responsible, at least in part for the onset of this condition. Efforts to restore neurotransmitter levels by pharmacological intervention has proven effective for short periods, but they are difficult to monitor and manage. We hypothesize that: 1. By exogenously modifying within the spinal cord, the levels of neurotransmitters such as serotonin (5HT), gamma-aminobutyric acid (GABA), acetylcholine (ACh), and neurotrophic factors such as brain- derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), the sequela of altered sensory perceptions associated with chronic pain after peripheral injury will be partially ameliorated and the intrinsic inhibitory neurotransmitter systems enhanced. We will test this hypothesis by transfecting the cDNA sequences encoding the synthetic enzymes and neurotrophic factors associated with restoration of the endogenous inhibitory neurotransmitter system into two immortalized raphe precursor cell lines and clones which secrete biologically active neurotrophic factors and neurotransmitters will be isolated. These novel cell lines will be transplanted int the injured spinal cord and tested for their ability to ameliorate chronic painful hypersensitivity after peripheral nerve injury. We further hypothesize that: 2. The altered biochemical environment of the spinal cord after peripheral nerve injury leads to reversible changes in the pain centers of the dorsal horn of the spinal cord. This altered biochemistry may inhibit or facilitate the long-term recovery of normal sensory responses depending on the relative secretion and release of neurotrophic factor and neurotransmitter signalling substances. We propose to immunohistochemically and biochemically define the levels of inhibitory neurotransmitter after induced peripheral nerve injury. We will further determine by in situ hybridization the altered expression of the synthetic enzymes for the inhibitory neurotransmitters after injury. We will also use behavioral measures of responses to normally non- painful and painful stimuli to relate the changes in spinal cord inhibitory biochemistry to the hypersensitivity to normally non-painful stimuli.
