Cholinergic and Peptidergic Regulation of Ganglionic Tyrosine Hydroxylase Activity

Abstract

Acetylcholine has traditionally been thought to be the sole preganglionic neurotransmitter in sympathetic ganglia. However, this view was challenged 15 years ago by Nishi and Koketsu in their studies on a frog sympathetic ganglion (10). These workers found that certain of the postsynaptic electrophysiological consequences of preganglionic nerve stimulation could not be abolished by cholinergic antagonists. More recently, Jan, Jan and Kuffler (8, 9) identified the neurotransmitter responsible for these non-cholinergic effects as being a peptide that resembles, but is not identical to, luteinizing hormone-releasing hormone. We have recently obtained evidence that a non-cholinergic transmitter is released also by preganglionic neurons in a mammalian sympathetic ganglion, the rat superior cervical ganglion, and that this neurotransmitter is different from the non-cholinergic transmitter found in frog sympathetic ganglia. Our conclusions come from studies on a postsynaptic biochemical consequence of preganglionic nerve stimulation rather than on an electrophysiological consequence. The biochemical parameter we have been investigating is the activity of the enzyme tyrosine 3-monooxygenase (tyrosine hydroxylase; TH; EC 1.14.16.2), the enzyme which catalyzes the rate-limiting step in catecholamine biosynthesis.