The use of a tyrosine-hydroxylase cDNA probe to study the neurotransmitter plasticity of rat sympathetic neurons in culture.

We have compared quantitatively the effects of muscle-conditioned medium (CM) and elevated K+ concentration (40 mM) on the enzymatic activity of tyrosine hydroxylase (TH) and on TH-mRNA levels in primary cultures of rat sympathetic neurons. Northern blot analysis of RNA from cultured neurons with a 32P-labeled rat TH-cDNA probe was performed. The probe hybridized strongly with a single RNA species of 1.9 kb, similar in size to the TH-mRNA from PC12 pheochromocytoma cells. In agreement with earlier data both CM and a partially purified factor from CM increased choline acetyltransferase activity up to 200-fold and depressed TH activity by 2- to 7-fold in cultured sympathetic neurons. These effects were accompanied by a decrease in TH-mRNA level, which correlated with the decrease in TH activity. On the other hand, a culture medium supplemented with 40 mM KCl caused a 1.5- to 5-fold increase in TH activity, which was accompanied by an increase in TH-mRNA level of the same order of magnitude. As a working hypothesis, we suggest that CM and neuronal depolarization control the transcription of the TH gene in an antagonistic manner.