Tyrosine Hydroxylase mRNA Expression by Dopaminergic Neurons in Culture: Effect of 1 ‐Methyl‐4‐Phenylpyridinium Treatment

To enable us to study expression of tyrosine hydroxylase [TH; tyrosine 3‐monooxygenase; L‐tyrosine tetrahydropteridine: oxygen oxidoreductase (3‐hydroxylating); EC 1.14.16.2] as a measure of dopaminergic neuron function in future experiments, methods were developed to quantify TH mRNA levels in cultures of dopaminergic mesencephalic cells. The model of selective dopaminergic toxicity of 1‐methyl‐4‐phenylpyridinium (MPP⁺) was used to verify the specificity of our methods. Fetal (embryonic day 15) rat ventral mesencephalic cell cultures were treated with 15 μMMPP⁺ for 48 h, conditions previously shown to reduce the number of TH‐immunoreactive neurons, TH activity, and dopamine uptake to 5–10% of control values. This treatment decreased the number of neurons labeled by TH in situ hybridization to 9% of untreated controls and caused a strong reduction of the abundance of TH mRNA in Northern blots. Our findings establish TH mRNA expression as a parameter for future studies of toxic and trophic effects on cultured dopaminergic neurons, and they support the view that MPP⁺ destroys dopaminergic neurons.