We have gathered information suggesting that the spinal cord (SC) is a glucocorticoid (GC) responsive tissue. The SC contains receptors (R) for both GC and mineralocorticoids and concentrate adrenal-derived corticosterone (CORT) or exogenously given CORT in cytoplasm and nuclei. GC induce in the SC the predominantly glial enzymes glycerolphosplate dehydrogenase (GPDH) and ornithine- decarboxylase (ODC). However, comparison of the GC-R of the SC and hippocampus revealed two fundamental differences: in vivo, uptake of (3H)-CORT by nuclei was 7-8 fold higher in hippocampus than in the SC; in vitro, transformation of the GC-R to the DNA- binding form was enhanced by RNAse treatment in the hippocampus but failed to affect it in the SC, implying that translocation of the hippocampal R is improved by removal of RNA. This step may be faulty in the SC, accounting for a reduced nuclear localization and favoring cytoplasmic retention of the GC-R of possible biological significance: previous data showed that GC induction of ODC in the SC required protein synthesis but was not inhibited by actymomycin D. The present proposal intends to unravel the basis for these differences, and also apply present knowledge of GC action in the SC to an animal model of human motor neuron disease such as the wobbler mutant mouse.
Specific aims of the project are: (l) to examine the R subtypes binding (3H)-CORT and (3H)-dexamethasone (DEX) in the SC and hippocampus, considering that in the former, type II or low affinity may predominate, and type I or high affinity prevail in the hippocampus. Stereoselective markers of types I and II sites will be employed to differentiate the R; (2) to study the cause for the resistance to RNAse action of the SC, R separation and structure will be analyzed by electrophoresis and gradient ultracentrifugation before and after RNAse treatment, to disclose if the R is a ribonucleoprotein as it seems to be in the hippocampus and other GC-responsive targets; (3) based on the suggestions that GC-R in the SC may be mostly glial, whereas those in hippocampus mostly neuronal, binding to type I and II sites and the RNAse effect will be examined in gradient-separated glial and neuronal populations; (4) finally, considering that the wobbler mouse is a suitable model of multiple sclerosis, a disease benefited from GC therapy, we will determine in the SC of mutants and littermates:abundance of R subtypes, transformation of the R to the DNA-binding form, R structure, induction of enzymes (ODC, GPDH) and effect of GC during the course of the disease. These experiments may furnish information for future human biochemical studies which at the moment are totally lacking.
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