TYROSINE HYDROXYLASE PHOSPHORYLATION AND SCHIZOPHRENIA

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The long-term objectives of the proposed research are to determine whether alterations in the levels and/or phosphorylation of tyrosine hydroxylase in the brain may be involved the etiology and/or pathogenesis of schizophrenia. In normal animals, activation of dopaminergic neurons results in the secretion of dopamine and a compensatory replenishment of dopamine stores. This replenishment of dopamine stores results from an increase in dopamine biosynthesis, the underlying basis of which is an increase in the catalytic activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine biosynthesis. One mechanism to increase the activity of tyrosine hydroxylase, described in other catecholamine-containing neurons, is the stimulation-dependent phosphorylation of tyrosine hydroxylase. Abberations in the dopaminergic systems in brain have been previously linked to schizophrenia; however, the exact relationship is as yet unknown. It is the premise of this grant application that alterations either in tyrosine hydroxylase or the protein kinase systems that attend tyrosine hydroxylase may be involved in schizophrenia. The specific objectives of the proposed research are 1.) to describe the regulation of tyrosine hydroxylase phosphorylation in dopaminergic nerve terminals in brain, 2.) to determine protein kinases systems that are involved in this regulation by using peptide mapping, and 3.) to assess the effects of acute and chronic drug treatments that have been shown to be effective in treating schizophrenia in a clinical setting. Specifically, the ability of treatments that cause the release of dopamine from rat, corpus striatum synaptosomes will be evaluated for their ability to increase the phosphorylation of tyrosine hydroxylase. The site-specificity of this phosphorylation will then be used to infer the protein kinase systems involved in this effect. Lastly, acute and chronic treatment of rats with haloperidol, clozapine, lithium chloride, or carbamazepine will be evaluated for their effects upon tyrosine hydroxylase levels, secretagogue- dependent phosphorylation of tyrosine hydroxylase, and the site- specificity of tyrosine hydroxylase phosphorylation.