EFFECT OF 5-HYDROXYTRYPTAMINE, DIMETHYLPHENYLPIPERAZINIUM AND ACETYLCHOLINE ON TRANSMISSION AND SURFACE POTENTIAL IN CAT SYMPATHETIC GANGLION

The changes in the ganglionic surface potentials produced by 5-hydroxytryptamine (5-HT), dimethylphenylpiperazinium (DMPP) and acetylcholine in doses producing a 30-75% inhibition of transmission were studied. 5-HT produced a short-lasting large initial depolarization with concomitant partial inhibition of transmission followed by a transient increase in surface potential and a third phase of late low amplitude depolarization concurrent with a secondary partial inhibition of transmission. The transient increase in surface potential evoked by 5-HT was inhibited by previous administration of ouabain. The response to DMPP was of slower onset and possessed a more pronounced transient increase in surface potential; late low amplitude depolarization was absent. Acetylcholine produced a large initial depolarization coincident with the partial inhibition of transmission. This was followed by a low amplitude depolarization during which inhibition of transmission was reversed into a facilitation. In a few of the experiments a slight transient increase in surface potential was interposed between these two phases of depolarization. The alterations in the contours of the ganglionic afterpotentials produced by 5-HT, DMPP and acetylcholine were consistent with the changes in surface potentials produced by these substances. Thus hyperpolarization following an initial large depolarization occurs after administration of a non-nicotinic ganglion-stimulating substance 5-HT. However, the transient increase in surface potential was less pronounced after 5-HT and acetylcholine than after DMPP, probably because of the presence of late depolarization after 5-HT and acetylcholine.{A table is presented}. © 1969.