Expression of tyrosine hydroxylase in the striatum of atipamezole-treated rats.

The effect of atipamezole, an alpha-2-adrenergic antagonist, was examined on the expression of tyrosine hydroxylase, the rate-limiting enzyme of synthesis of catecholamines such as dopamine, in the rat striatum. It has been reported that the alpha-2-adrenergic pathways can modulate the levodopa- and apomorphine-induced dopaminergic turning behavior in the rat model of Parkinson's disease. It is also known that catecholamines have a feed back inhibition of TH activity. Since atipamezole can increase the levodopa-induced turning behavior, a potential feed back effect on the TH enzyme was estimated by measuring the TH protein. In the present study, the atipamezole and/or levodopa treatments did not clearly affect on the amount of TH in the rat striata when measured by Western blot. However, it is possible that the sensitivity of the method limits the detection of changes, and therefore further studies are needed to examine the potential of atipamezole and/or levodopa effects on the regulation of TH enzyme, e.g., by measuring the phosphorylation status, activity and mRNA expression of TH enzyme.