Acidic Fibroblast Growth Factor and Catecholamines Synergistically Up‐Regulate Tyrosine Hydroxylase Activity in Developing and Damaged Dopamine Neurons in Culture

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Abstract
Our previous studies indicate that, in certain non-catecholamine (CA) neurons, expression of the gene for the CA biosynthetic enzyme tyrosine hydroxylase (TH) can be initiated by the obligatory interaction of acidic fibroblast growth factor (aFGF) and a CA activator. In this study, we sought to determine whether these same differentiation factors also play a role in regulating existing TH expression in CA neurons. Thus, the effects of exogenous aFGF and CAs on TH were studied in developing or toxin-damaged dopamine (DA) neurons from the embryonic day 15 rat ventral midbrain, where it was likely to be at physiologically low levels. Cultures were incubated with various concentrations of aFGF, DA, or aFGF and DA. Some cultures were first damaged with 2.5 microM 1-methyl-4-phenylpyridinium. In developing DA neurons, an 80% increase in TH activity was found only after co-treatment with aFGF (100 ng/ml) and DA (1 microM) or other monoamines. Likewise, in damaged DA neurons, aFGF and DA reversed the 50% loss in TH activity caused by toxin. This was observed within 4 h of treatment and was not associated with changes in the number or appearance of DA neurons, suggesting a biochemical rather than a trophic effect. Pretreatment with protein or RNA synthesis inhibitors eliminated the increase. In PC12 cells, where TH is highly expressed, activity was unaltered by treatment. We conclude that the aFGF and CAs may be involved in not only the initiation but also the regulation of TH.

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