5-HT antagonists and blockade of neuronal (5-HT) receptors on ganglion cells.

Potential changes in superior cervical ganglion cells evoked by 5-HT or the nicotinic agonist, dimethyl-phenyl piperazinium (DMPP), were recorded using the sucrose-gap method and a number of putative 5-HT antagonists tested for potency and selectivity. Selective blockade of 5-HT responses was produced by 5-HT itself and, in increasing order of potency, by cocaine, metoclopramide and quipazine. A non-selective blockade was observed with bufotenine and d-tubocurarine. Substances which had no effect on 5-HT responses included methysergide and other compounds related to LSD, cinanserin, cyproheptadine, phenylbiguanide and morphine. The results provide further information about the 5-HT receptor on sympathetic ganglion cells and support the view that this receptor is distinct from neuronal receptors in the myenteric plexus and on cholinergic nerve terminals.