Effect of preganglionic nerve stimulation on sensitivity of the superior cervical ganglion to nicotinic blocking agents.

1 Periodic stimulation (every 10 min) of the cervical sympathetic nerve increased the ganglionic block by low concentrations of chlorisondamine (CHL) in the superior cervical ganglion of the cat when compared to the contralateral unstimulated side.2 Periodic stimulation of the postganglionic nerve was ineffective in increasing the block.3 Ganglionic block by low concentrations of mecamylamine had the same stimulus dependency, but ganglionic block by any dose of hexamethonium was not influenced by nerve stimulation.4 Physostigmine infused together with CHL increased the rate of onset of block produced by CHL. Atropine had no apparent effect on the development of ganglionic block by CHL.5 Repeated intra-arterial injections of 1,1-dimethyl-4-phenylpiperazinium into the circulation of the superior cervical ganglion increased the magnitude of block produced by CHL. Similar injections of methacholine had no effect on ganglionic block produced by CHL.6 The results are interpreted to indicate that activation of ganglionic nicotinic receptors increased the affinity of receptors for CHL and mecamylamine.