[Serotonin mediated synaptic transmission of inferior mesenteric ganglion of the guinea pig].

By means of intracellular recording technique, it was observed that: (1) Application of serotonin (5-HT) caused in a portion of the neurons of the guinea pig inferior mesenteric ganglia (IMG) a slow depolarization similar to non-cholinergic late slow excitatory postsynaptic potential (ls-EPSP). (2) Prolonged superfusion of 5-HT markedly suppressed the ls-EPSP in 5-HT sensitive neurons. (3) The ls-EPSP elicited in 5-HT sensitive neurons as well as the 5-HT depolarization could be enhanced by fluoxetine 5-HT reuptake inhibitor; In contrast, the ls-EPSP of 5-HT insensitive neurons was not appreciably changed by this drug. (4) Pretreating the guinea pigs with para-chlorophenylalanine (PCPA), a 5-HT biosynthesis inhibitor, markedly reduced the occurrence rate and amplitude of ls-EPSP. These results indicate that ls-EPSP of the guinea pig IMG is possibly mediated by several transmitters including 5-HT.