The objectives of this proposal center around an improved understanding of the spinal nicotinic acetylcholine receptors in the spinal cord of normal and nerve-injured rats. A further understanding of spinal nicotinic systems will result in novel, specific pharmacological targets for the treatment of neuropathic pain. The spinal nicotinic system has been largely ignored because the intrathecal administration of nicotinic agonists generally produces more pronociception than antinociception. Recently, data from our laboratory and others, has shown that the pharmacology of nicotinic agonists in the presence of chronic, neuropathic pain is altered. In nerve-injured mice and rats, intrathecal nicotinic agonists produce only antinociception. Data from our laboratory has shown that several nicotinic acetylcholine receptor subunits are upregulated following spinal nerve ligation. Spinal interneurons upregulate their expression of the alpha3 and the alpha7 subunits while primary afferents increase their expression of the alpha5 subunit. Previously, we have also found that the alpha5 subunit contributes to mechanical allodynia in neuropathic rats. However, the contributions of the alpha3 and alpha7 subunits are still unknown. This proposal outlines both anatomical and functional experiments to determine the contribution of these upregulated subunits to the maintenance of mechanical allodynia following nerve injury. We will use immunocytochemistry to identify the spinal structures that upregulate these two nicotinic subunits. We will use the anatomical data obtained from these studies to further investigate the function of these upregulated subunits in the spinal cord of neuropathic rats. The functionality of these subunits will be investigated using in vitro release experiments. Selective nicotinic agonists and antagonists will be used to elicit the release of GABA in the isolated spinal cord slice and in synaptosomes. Finally, the behavioral implications of nicotinic subunit upregulation will be determined with the intrathecal administration of selective nicotinic agonists and antagonists in normal and spinal nerve-ligated rats. The results of these studies will further define spinal nicotinic anatomy and functioning in the nerve-injured animal thereby, providing unique potential targets for the pharmacological treatment of neuropathic pain.
