The principal objectives of this proposal are to elucidate the properties of axonal lipid metabolism and relate the metabolism to neuronal function. Our program is based on a dual approach: biochemical studies to detect and characterize properties of lipid metabolism at the tissue level, and complementary quantitative EM autoradiography to locate sites of synthesis and redeposition of lipids. During the current granting period we have applied these approaches to characterize axonal lipid metabolism in three model systems: (1) rodent sciatic nerves (normal and diabetic), (2) frog nerves; olfactory (nonmyelinated), optic (DNS myelin) and sciatic (PNS myelin) and (3) squid nervous system including the giant axon (axoplasm) and giant synapse. The major objective of the current proposal is to exploit the information gained from these studies toward establishing the relationships between axonal lipid metabolism and neural activity. By further characterizing changes in inositol lipid metabolism with nerve conduction impairment (experimental diabetic neuropathy) and physiological perturbation (i.e. high frequency electrical stimulation and/or potassium depolarization), we will clarify relationships between nerve function and local lipid metabolism under in vivo conditions. By studying the lipid enzymes from axoplasm (squid giant axons) and axolemma (frog olfactory nerve) in a comparative way, we can begin to understand how activities of the key axonal enzymes might be regulated in vivo. We are extending our studies to the expression of mRNAs for neuronal sodium channels and Na+,K+-ATPase, proteins which physiologically mediate nerve conduction. These studies will be a basis for determining modulatory influences of local lipid metabolism. Also, these studies will provide a framework for our applying molecular biological approaches to understanding the regulation of axon-based lipid enzymes as cDNA probes for them become available.
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