Increased ganglionic tyrosine hydroxylase and dopamine-beta-hydroxylase activities following preganglionic nerve stimulation: role of nicotine receptors.

The activity of the enzyme tyrosine hydroxylase (TH) can be increased in the rat superior cervical ganglion by stimulating the preganglionic cervical sympathetic trunk. Since nicotinic, muscarinic and alpha adrenergic receptors have been implicated in ganglionic transmission, the role of each of these receptors in the trans-synaptic regulation of TH activity has been studied. Chlorisondamine, administered at a dose which completely blocks ganglion transmission, blocked the increase in TH activity. Atropine and dihydroergotamine, injected at doses which block peripheral muscarinic and alpha adrenergic receptors, respectively, did not significantly affect the increase in enzyme activity. Thus, of these three receptor systems, only nicotinic receptors seem to play a major role in the increase in TH activity produced by preganglionic nerve stimulation. Simultaneous measurements of tyrosine hydroxylase, dopa decarboxylase and dopamine-beta-hydroxylase activities indicate that both TH and dopamine-beta-hydroxylase activities increase after stimulation of the cervical sympathetic trunk, although dopa decarboxylase activity is unchanged. The time courses of the increase in TH and dopamine-beta-hydroxylase activities were similar, both reaching maximum values 3 days after the end of a 90-min period of nerve stimulation.