The goal of this proposal is to study the possible involvement of nerve growth factor (NGF) in lower motor neuron function, and to evaluate the role this factor may play in spinal cord motor neuron denervation- reinnervation in amyotrophic lateral sclerosis (ALS). It has recently been shown that alpha motor neurons in spinal cord express NGF receptor messenger RNA (mRNA) and protein during development and in response to peripheral nerve damage. NGF receptors appear to be essential for the initiation of the biological actions of NGF. These studies indicate that spinal cord, and possibly brain stem motor neurons have the capacity to respond to the actions of NGF. Using a radioactive NGF receptor cRNA probe with in situ hybridization histochemistry, we have obtained preliminary evidence that motor neurons in ALS postmortem spinal cord tissue express mRNA for NGF receptor. In addition, our data indicate that NGF receptor mRNA expression occurs preferentially in spinal cord segments associated with clinical symptomatology (muscle weakness, atrophy, etc.). We hypothesize that as the disease process advances, some motor neurons start to reexpress growth related proteins in an attempt to compensate for the progressive degenerative state. Interestingly, EMG evidence indicates that it is common for spinal cord motor neurons to functionally reinnervate denervated muscles, although this new growth may ultimately be lost as well. Further, one set of motor neurons in the spinal cord that do not appear to degenerate in ALS (Onufrowicz's nucleus) have recently been shown to express NGF receptors in adult experimental animals. Unlike other spinal cord motor neurons, it is possible that these neurons maintain the capacity to respond to NGF throughout adult life. We propose to study the potential expression of growth-related proteins (i.e. NGF receptor and GAP-43) in ALS spinal cord tissue. We will use in situ hybridization histochemistry, immunocytochemistry, and RNA protection assays to identify changes in the expression of NGF receptor and GAP-43. In addition, we will attempt to correlate these changes and the degree of degeneration (through the use of Nissl and silver stains) with the clinical history of each ALS patient. The experiments proposed in this application will provide a better understanding of the cellular and molecular events associated with denervation-reinnervation in ALS spinal cord, and of neuronal plasticity in the CNS.
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