5-hydroxytryptamine controls ACh-receptor sensitivity of bullfrog sympathetic ganglion cells

Experimental evidences showing that 5-hydroxytryptamine (5-HT) is directly interacting with nicotinic acetylcholine (ACh) receptors and thereby depresses the sensitivity of these receptors to ACh, are presented by making use of bullfrog sympathetic ganglion cells and frog skeletal muscle endplates. It was suggested that 5-HT might decrease the affinity of ACh to nicotinic receptor sites, since the mode of 5-HT action was comparable to that of D-tubocurarine action.