Effects of synaptic and antidromic stimulation on tyrosine hydroxylase activity in the rat superior cervical ganglion.

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Abstract
The effects of orthodromic and antidromic stimulation of the rat superior cervical ganglion on the specific activity of the enzyme tyrosine hydroxylase were studied. Orthodromic stimulation of the ganglion via the cervical sympathetic trunk produced an increase in the activity of tyrosine hydroxylase when measured 3 days later; no change was caused in the protein content of the ganglion. This increase in the specific activity of tyrosine hydroxylase was blocked by administration of the nicotinic antagonist, hexamethonium. Antidromic stimulation of the superior cervical ganglion by stimulating the internal carotid nerve, the external carotid nerve or both nerves simultaneously produced no change in the specific activity of tyrosine hydroxylase. Parallel increases in tyrosine hydroxylase activity and protein content per ganglion were seen when the internal carotid nerve was stimulated but similar changes were seen in sham-stimulated animals. These non-specific changes were apparently produced by the trauma involved in the extensive dissection necessary to position electrodes on this nerve trunk. An increased frequency of firing in post-ganglionic neurones is not a sufficient stimulus to elevate the specific activity of tyrosine hydroxylase. Some other aspect of nicotinic receptor stimulation apparently is required.