Activation of Tyrosine Hydroxylase in the Superior Cervical Ganglion by Nicotinic and Muscarinic Agonists

Both dimethylphenylpiperazinium (DMPP), a nicotinic agonist, and bethanechol, a muscarinic agonist, increase 3,4-dihydroxyphenylalanine (DOPA) synthesis in the superior cervical ganglion of the rat. DMPP causes approximately a fivefold increase in DOPA accumulation in intact ganglia whereas bethanechol causes about a two-fold increase in DOPA accumulation. These effects are additive with each other and with the increase in DOPA accumulation produced by 8-bromo cyclic AMP. The action of DMPP is dependent on extracellular Ca2+ while the actions of bethanechol and 8-bromo cyclic AMP are not dependent on extracellular Ca2+. Cholinergic agonists and cyclic nucleotides produce a stable activation of tyrosine hydroxylase (TH) in the ganglion. The activation of TH by nicotinic and muscarinic agonists can be detected after 5 min of incubation of the ganglia with these agents. The nicotinic response disappears after 30 min of incubation, whereas the muscarinic response persists for at least 30 min. The Ca2+ dependence of the TH activation produced by these agents is similar to the Ca2+ dependence of their effects on DOPA accumulation in intact ganglia. These data are consistent with the hypothesis that nicotinic agonists, muscarinic agonists, and cyclic AMP analogues increase TH activity by three distinct mechanisms. The activation of TH presumably underlies the increase in DOPA synthesis produced by these agents.