The effects of footshock and immobilization stress on tyrosine hydroxylase phosphorylation in the rat locus coeruleus and adrenal gland.

Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, is regulated acutely by protein phosphorylation. No studies have systematically investigated the time course of TH phosphorylation in vivo in response to different stressors. We therefore determined the extent of TH phosphorylation at Ser19, Ser31, and Ser40 over a 40-min period in response to footshock or immobilization stress in the rat locus coeruleus and adrenal medulla. There were significant changes in TH phosphorylation in both tissues and the responses to the two stressors differed markedly. With each of the phosphorylation sites immobilization stress caused a much smaller, or less sustained, response than footshock stress. With immobilization stress there was a transient increase in Ser31 phosphorylation in the locus coeruleus and in the adrenal medulla, but there were no effects on Ser19 or Ser40 phosphorylation. With footshock stress there was a substantial decrease in Ser19 phosphorylation over time, a substantial increase in Ser31 phosphorylation over time, but there were no effects on Ser40 phosphorylation. Measuring TH phosphorylation at Ser19, Ser31, and Ser40 over time can therefore be used as a sensitive index to differentiate the effects of different stressors on catecholaminergic cells.